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src/InitTweak/FixInitNew.cpp (modified) (2 diffs)

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src/InitTweak/FixInitNew.cpp

-              r4852232
+              r000d68f
 namespace InitTweak {
 namespace {
+// Shallow copy the pointer list for return.
+std::vector<ast::ptr<ast::TypeDecl>> getGenericParams( const ast::Type * t ) {
+        if ( auto inst = dynamic_cast<const ast::StructInstType *>( t ) ) {
+                return inst->base->params;
+        }
+        if ( auto inst = dynamic_cast<const ast::UnionInstType *>( t ) ) {
+                return inst->base->params;
+        }
+        return {};
+}
+/// Given type T, generate type of default ctor/dtor, i.e. function type void (*) (T &).
+ast::FunctionDecl * genDefaultFunc(
+                const CodeLocation loc,
+                const std::string fname,
+                const ast::Type * paramType,
+                bool maybePolymorphic = true) {
+        std::vector<ast::ptr<ast::TypeDecl>> typeParams;
+        if ( maybePolymorphic ) typeParams = getGenericParams( paramType );
+        auto dstParam = new ast::ObjectDecl( loc,
+                "_dst",
+                new ast::ReferenceType( paramType ),
+                nullptr,
+                {},
+                ast::Linkage::Cforall
+        );
+        return new ast::FunctionDecl( loc,
+                fname,
+                std::move(typeParams),
+                {dstParam},
+                {},
+                new ast::CompoundStmt(loc),
+                {},
+                ast::Linkage::Cforall
+        );
+}
+struct SelfAssignChecker {
+        void previsit( const ast::ApplicationExpr * appExpr );
+};
+struct StmtExprResult {
+        const ast::StmtExpr * previsit( const ast::StmtExpr * stmtExpr );
+};
+/// wrap function application expressions as ImplicitCopyCtorExpr nodes so that it is easy to identify which
+/// function calls need their parameters to be copy constructed
+struct InsertImplicitCalls : public ast::WithShortCircuiting {
+        const ast::Expr * postvisit( const ast::ApplicationExpr * appExpr );
+        // only handles each UniqueExpr once
+        // if order of visit does not change, this should be safe
+        void previsit (const ast::UniqueExpr *);
+        std::unordered_set<decltype(ast::UniqueExpr::id)> visitedIds;
+};
+/// generate temporary ObjectDecls for each argument and return value of each ImplicitCopyCtorExpr,
+/// generate/resolve copy construction expressions for each, and generate/resolve destructors for both
+/// arguments and return value temporaries
+struct ResolveCopyCtors final : public ast::WithGuards, public ast::WithStmtsToAdd<>, public ast::WithSymbolTable, public ast::WithShortCircuiting, public ast::WithVisitorRef<ResolveCopyCtors>, public ast::WithConstTranslationUnit {
+        const ast::Expr * postvisit( const ast::ImplicitCopyCtorExpr * impCpCtorExpr );
+        const ast::StmtExpr * previsit( const ast::StmtExpr * stmtExpr );
+        const ast::UniqueExpr * previsit( const ast::UniqueExpr * unqExpr );
+        /// handles distant mutations of environment manually.
+        /// WithConstTypeSubstitution cannot remember where the environment is from
+        /// MUST be called at start of overload previsit
+        void previsit( const ast::Expr * expr);
+        /// MUST be called at return of overload postvisit
+        const ast::Expr * postvisit(const ast::Expr * expr);
+        /// create and resolve ctor/dtor expression: fname(var, [cpArg])
+        const ast::Expr * makeCtorDtor( const std::string & fname, const ast::ObjectDecl * var, const ast::Expr * cpArg = nullptr );
+        /// true if type does not need to be copy constructed to ensure correctness
+        bool skipCopyConstruct( const ast::Type * type );
+        ast::ptr< ast::Expr > copyConstructArg( const ast::Expr * arg, const ast::ImplicitCopyCtorExpr * impCpCtorExpr, const ast::Type * formal );
+        ast::Expr * destructRet( const ast::ObjectDecl * ret, const ast::Expr * arg );
+private:
+        /// hack to implement WithTypeSubstitution while conforming to mutation safety.
+        ast::TypeSubstitution * env         = nullptr;
+        bool                    envModified = false;
+};
+/// collects constructed object decls - used as a base class
+struct ObjDeclCollector : public ast::WithGuards, public ast::WithShortCircuiting {
+        // use ordered data structure to maintain ordering for set_difference and for consistent error messages
+        typedef std::list< const ast::ObjectDecl * > ObjectSet;
+        void previsit( const ast::CompoundStmt *compoundStmt );
+        void previsit( const ast::DeclStmt *stmt );
+        // don't go into other functions
+        void previsit( const ast::FunctionDecl * ) { visit_children = false; }
+protected:
+        ObjectSet curVars;
+};
+// debug
+template<typename ObjectSet>
+struct PrintSet {
+        PrintSet( const ObjectSet & objs ) : objs( objs ) {}
+        const ObjectSet & objs;
+};
+template<typename ObjectSet>
+PrintSet<ObjectSet> printSet( const ObjectSet & objs ) { return PrintSet<ObjectSet>( objs ); }
+template<typename ObjectSet>
+std::ostream & operator<<( std::ostream & out, const PrintSet<ObjectSet> & set) {
+        out << "{ ";
+        for ( auto & obj : set.objs ) {
+                out << obj->name << ", " ;
+        } // for
+        out << " }";
+        return out;
+}
+struct LabelFinder final : public ObjDeclCollector {
+        typedef std::map< std::string, ObjectSet > LabelMap;
+        // map of Label -> live variables at that label
+        LabelMap vars;
+        typedef ObjDeclCollector Parent;
+        using Parent::previsit;
+        void previsit( const ast::Stmt * stmt );
+        void previsit( const ast::CompoundStmt *compoundStmt );
+        void previsit( const ast::DeclStmt *stmt );
+};
+/// insert destructor calls at the appropriate places.  must happen before CtorInit nodes are removed
+/// (currently by FixInit)
+struct InsertDtors final : public ObjDeclCollector, public ast::WithStmtsToAdd<> {
+        typedef std::list< ObjectDecl * > OrderedDecls;
+        typedef std::list< OrderedDecls > OrderedDeclsStack;
+        InsertDtors( ast::Pass<LabelFinder> & finder ) : finder( finder ), labelVars( finder.core.vars ) {}
+        typedef ObjDeclCollector Parent;
+        using Parent::previsit;
+        void previsit( const ast::FunctionDecl * funcDecl );
+        void previsit( const ast::BranchStmt * stmt );
+private:
+        void handleGoto( const ast::BranchStmt * stmt );
+        ast::Pass<LabelFinder> & finder;
+        LabelFinder::LabelMap & labelVars;
+        OrderedDeclsStack reverseDeclOrder;
+};
+/// expand each object declaration to use its constructor after it is declared.
+struct FixInit : public ast::WithStmtsToAdd<> {
+        static void fixInitializers( ast::TranslationUnit &translationUnit );
+        const ast::DeclWithType * postvisit( const ast::ObjectDecl *objDecl );
+        std::list< ast::ptr< ast::Decl > > staticDtorDecls;
+};
+/// generate default/copy ctor and dtor calls for user-defined struct ctor/dtors
+/// for any member that is missing a corresponding ctor/dtor call.
+/// error if a member is used before constructed
+struct GenStructMemberCalls final : public ast::WithGuards, public ast::WithShortCircuiting, public ast::WithSymbolTable, public ast::WithVisitorRef<GenStructMemberCalls>, public ast::WithConstTranslationUnit {
+        void previsit( const ast::FunctionDecl * funcDecl );
+        const ast::DeclWithType * postvisit( const ast::FunctionDecl * funcDecl );
+        void previsit( const ast::MemberExpr * memberExpr );
+        void previsit( const ast::ApplicationExpr * appExpr );
+        /// Note: this post mutate used to be in a separate visitor. If this pass breaks, one place to examine is whether it is
+        /// okay for this part of the recursion to occur alongside the rest.
+        const ast::Expr * postvisit( const ast::UntypedExpr * expr );
+        SemanticErrorException errors;
+private:
+        template< typename... Params >
+        void emit( CodeLocation, const Params &... params );
+        ast::FunctionDecl * function = nullptr;
+        std::set< const ast::DeclWithType * > unhandled;
+        std::map< const ast::DeclWithType *, CodeLocation > usedUninit;
+        const ast::ObjectDecl * thisParam = nullptr;
+        bool isCtor = false; // true if current function is a constructor
+        const ast::StructDecl * structDecl = nullptr;
+};
+/// expands ConstructorExpr nodes into comma expressions, using a temporary for the first argument
+struct FixCtorExprs final : public ast::WithDeclsToAdd<>, public ast::WithSymbolTable, public ast::WithShortCircuiting, public ast::WithConstTranslationUnit {
+        const ast::Expr * postvisit( const ast::ConstructorExpr * ctorExpr );
+};
+/// add CompoundStmts around top-level expressions so that temporaries are destroyed in the correct places.
+struct SplitExpressions : public ast::WithShortCircuiting {
+        ast::Stmt * postvisit( const ast::ExprStmt * stmt );
+        void previsit( const ast::TupleAssignExpr * expr );
+};
+/// find and return the destructor used in `input`. If `input` is not a simple destructor call, generate a thunk
+/// that wraps the destructor, insert it into `stmtsToAdd` and return the new function declaration
+const ast::DeclWithType * getDtorFunc( const ast::ObjectDecl * objDecl, const ast::Stmt * input, std::list< ast::ptr<ast::Stmt> > & stmtsToAdd ) {
+        const CodeLocation loc = input->location;
+        // unwrap implicit statement wrapper
+        // Statement * dtor = input;
+        assert( input );
+        // std::list< const ast::Expr * > matches;
+        auto matches = collectCtorDtorCalls( input );
+        if ( dynamic_cast< const ast::ExprStmt * >( input ) ) {
+                // only one destructor call in the expression
+                if ( matches.size() == 1 ) {
+                        auto func = getFunction( matches.front() );
+                        assertf( func, "getFunction failed to find function in %s", toString( matches.front() ).c_str() );
+                        // cleanup argument must be a function, not an object (including function pointer)
+                        if ( auto dtorFunc = dynamic_cast< const ast::FunctionDecl * > ( func ) ) {
+                                if ( dtorFunc->type->forall.empty() ) {
+                                        // simple case where the destructor is a monomorphic function call - can simply
+                                        // use that function as the cleanup function.
+                                        return func;
+                                }
+                        }
+                }
+        }
+        // otherwise the cleanup is more complicated - need to build a single argument cleanup function that
+        // wraps the more complicated code.
+        static UniqueName dtorNamer( "__cleanup_dtor" );
+        std::string name = dtorNamer.newName();
+        ast::FunctionDecl * dtorFunc = genDefaultFunc( loc, name, objDecl->type->stripReferences(), false );
+        stmtsToAdd.push_back( new ast::DeclStmt(loc, dtorFunc ) );
+        // the original code contains uses of objDecl - replace them with the newly generated 'this' parameter.
+        const ast::ObjectDecl * thisParam = getParamThis( dtorFunc );
+        const ast::Expr * replacement = new ast::VariableExpr( loc, thisParam );
+        auto base = replacement->result->stripReferences();
+        if ( dynamic_cast< const ast::ArrayType * >( base ) || dynamic_cast< const ast::TupleType * > ( base ) ) {
+                // need to cast away reference for array types, since the destructor is generated without the reference type,
+                // and for tuple types since tuple indexing does not work directly on a reference
+                replacement = new ast::CastExpr( replacement, base );
+        }
+        auto dtor = ast::DeclReplacer::replace( input, ast::DeclReplacer::ExprMap{ std::make_pair( objDecl, replacement ) } );
+        auto mutStmts = dtorFunc->stmts.get_and_mutate();
+        mutStmts->push_back(strict_dynamic_cast<const ast::Stmt *>( dtor ));
+        dtorFunc->stmts = mutStmts;
+        return dtorFunc;
+}
+void FixInit::fixInitializers( ast::TranslationUnit & translationUnit ) {
+        ast::Pass<FixInit> fixer;
+        // can't use mutateAll, because need to insert declarations at top-level
+        // can't use DeclMutator, because sometimes need to insert IfStmt, etc.
+        SemanticErrorException errors;
+        for ( auto i = translationUnit.decls.begin(); i != translationUnit.decls.end(); ++i ) {
+                try {
+                        // maybeAccept( *i, fixer ); translationUnit should never contain null
+                        *i = (*i)->accept(fixer);
+                        translationUnit.decls.splice( i, fixer.core.staticDtorDecls );
+                } catch( SemanticErrorException &e ) {
+                        errors.append( e );
+                } // try
+        } // for
+        if ( ! errors.isEmpty() ) {
+                throw errors;
+        } // if
+}
+const ast::StmtExpr * StmtExprResult::previsit( const ast::StmtExpr * stmtExpr ) {
+        // we might loose the result expression here so add a pointer to trace back
+        assert( stmtExpr->result );
+        const ast::Type * result = stmtExpr->result;
+        if ( ! result->isVoid() ) {
+                auto mutExpr = mutate(stmtExpr);
+                const ast::CompoundStmt * body = mutExpr->stmts;
+                assert( ! body->kids.empty() );
+                mutExpr->resultExpr = body->kids.back().strict_as<ast::ExprStmt>();
+                return mutExpr;
+        }
+        return stmtExpr;
+}
+ast::Stmt * SplitExpressions::postvisit( const ast::ExprStmt * stmt ) {
+        // wrap each top-level ExprStmt in a block so that destructors for argument and return temporaries are destroyed
+        // in the correct places
+        ast::CompoundStmt * ret = new ast::CompoundStmt( stmt->location, { stmt } );
+        return ret;
+}
+void SplitExpressions::previsit( const ast::TupleAssignExpr * ) {
+        // don't do this within TupleAssignExpr, since it is already broken up into multiple expressions
+        visit_children = false;
+}
+// Relatively simple structural comparison for expressions, needed to determine
+// if two expressions are "the same" (used to determine if self assignment occurs)
+struct StructuralChecker {
+        // Strip all casts and then dynamic_cast.
+        template<typename T>
+        static const T * cast( const ast::Expr * expr ) {
+                // this might be too permissive. It's possible that only particular casts are relevant.
+                while ( auto cast = dynamic_cast< const ast::CastExpr * >( expr ) ) {
+                        expr = cast->arg;
+                }
+                return dynamic_cast< const T * >( expr );
+        }
+        void previsit( const ast::Expr * ) {
+                // anything else does not qualify
+                result = false;
+        }
+        // ignore casts
+        void previsit( const ast::CastExpr * ) {}
+        void previsit( const ast::MemberExpr * memExpr ) {
+                if ( auto otherMember = cast< ast::MemberExpr >( other ) ) {
+                        if ( otherMember->member == memExpr->member ) {
+                                other = otherMember->aggregate;
+                                return;
+                        }
+                }
+                result = false;
+        }
+        void previsit( const ast::VariableExpr * varExpr ) {
+                if ( auto otherVar = cast< ast::VariableExpr >( other ) ) {
+                        if ( otherVar->var == varExpr->var ) {
+                                return;
+                        }
+                }
+                result = false;
+        }
+        void previsit( const ast::AddressExpr * ) {
+                if ( auto addrExpr = cast< ast::AddressExpr >( other ) ) {
+                        other = addrExpr->arg;
+                        return;
+                }
+                result = false;
+        }
+        const ast::Expr * other;
+        bool result = true;
+        StructuralChecker( const ast::Expr * other ) : other(other) {}
+};
+bool structurallySimilar( const ast::Expr * e1, const ast::Expr * e2 ) {
+        return ast::Pass<StructuralChecker>::read( e1, e2 );
+}
+void SelfAssignChecker::previsit( const ast::ApplicationExpr * appExpr ) {
+        auto function = getFunction( appExpr );
+        // Doesn't use isAssignment, because ?+=?, etc. should not count as self-assignment.
+        if ( function->name == "?=?" && appExpr->args.size() == 2
+                        // Check for structural similarity (same variable use, ignore casts, etc.
+                        // (but does not look too deeply, anything looking like a function is off limits).
+                        && structurallySimilar( appExpr->args.front(), appExpr->args.back() ) ) {
+                SemanticWarning( appExpr->location, Warning::SelfAssignment, toCString( appExpr->args.front() ) );
+        }
+}
+const ast::Expr * InsertImplicitCalls::postvisit( const ast::ApplicationExpr * appExpr ) {
+        if ( auto function = appExpr->func.as<ast::VariableExpr>() ) {
+                if ( function->var->linkage.is_builtin ) {
+                        // optimization: don't need to copy construct in order to call intrinsic functions
+                        return appExpr;
+                } else if ( auto funcDecl = function->var.as<ast::DeclWithType>() ) {
+                        auto ftype = dynamic_cast< const ast::FunctionType * >( GenPoly::getFunctionType( funcDecl->get_type() ) );
+                        assertf( ftype, "Function call without function type: %s", toString( funcDecl ).c_str() );
+                        if ( CodeGen::isConstructor( funcDecl->name ) && ftype->params.size() == 2 ) {
+                                auto t1 = getPointerBase( ftype->params.front() );
+                                auto t2 = ftype->params.back();
+                                assert( t1 );
+                                if ( ResolvExpr::typesCompatible( t1, t2 ) ) {
+                                        // optimization: don't need to copy construct in order to call a copy constructor
+                                        return appExpr;
+                                } // if
+                        } else if ( CodeGen::isDestructor( funcDecl->name ) ) {
+                                // correctness: never copy construct arguments to a destructor
+                                return appExpr;
+                        } // if
+                } // if
+        } // if
+        CP_CTOR_PRINT( std::cerr << "InsertImplicitCalls: adding a wrapper " << appExpr << std::endl; )
+        // wrap each function call so that it is easy to identify nodes that have to be copy constructed
+        ast::ptr<ast::TypeSubstitution> tmp = appExpr->env;
+        auto mutExpr = mutate(appExpr);
+        mutExpr->env = nullptr;
+        auto expr = new ast::ImplicitCopyCtorExpr( appExpr->location, mutExpr );
+        // Move the type substitution to the new top-level. The substitution
+        // is needed to obtain the type of temporary variables so that copy
+        // constructor calls can be resolved.
+        expr->env = tmp;
+        return expr;
+}
+void ResolveCopyCtors::previsit(const ast::Expr * expr) {
+        if ( nullptr == expr->env ) {
+                return;
+        }
+        GuardValue( env ) = expr->env->clone();
+        GuardValue( envModified ) = false;
+}
+const ast::Expr * ResolveCopyCtors::postvisit(const ast::Expr * expr) {
+        // No local environment, skip.
+        if ( nullptr == expr->env ) {
+                return expr;
+        // Environment was modified, mutate and replace.
+        } else if ( envModified ) {
+                auto mutExpr = mutate(expr);
+                mutExpr->env = env;
+                return mutExpr;
+        // Environment was not mutated, delete the shallow copy before guard.
+        } else {
+                delete env;
+                return expr;
+        }
+}
+bool ResolveCopyCtors::skipCopyConstruct( const ast::Type * type ) { return ! isConstructable( type ); }
+const ast::Expr * ResolveCopyCtors::makeCtorDtor( const std::string & fname, const ast::ObjectDecl * var, const ast::Expr * cpArg ) {
+        assert( var );
+        assert( var->isManaged() );
+        assert( !cpArg || cpArg->isManaged() );
+        // arrays are not copy constructed, so this should always be an ExprStmt
+        ast::ptr< ast::Stmt > stmt = genCtorDtor(var->location, fname, var, cpArg );
+        assertf( stmt, "ResolveCopyCtors: genCtorDtor returned nullptr: %s / %s / %s", fname.c_str(), toString( var ).c_str(), toString( cpArg ).c_str() );
+        auto exprStmt = stmt.strict_as<ast::ImplicitCtorDtorStmt>()->callStmt.strict_as<ast::ExprStmt>();
+        ast::ptr<ast::Expr> untyped = exprStmt->expr; // take ownership of expr
+        // resolve copy constructor
+        // should only be one alternative for copy ctor and dtor expressions, since all arguments are fixed
+        // (VariableExpr and already resolved expression)
+        CP_CTOR_PRINT( std::cerr << "ResolvingCtorDtor " << untyped << std::endl; )
+        ast::ptr<ast::Expr> resolved = ResolvExpr::findVoidExpression(untyped, { symtab, transUnit().global } );
+        assert( resolved );
+        if ( resolved->env ) {
+                // Extract useful information and discard new environments. Keeping them causes problems in PolyMutator passes.
+                env->add( *resolved->env );
+                envModified = true;
+                auto mut = mutate(resolved.get());
+                assertf(mut == resolved.get(), "newly resolved expression must be unique");
+                mut->env = nullptr;
+        } // if
+        if ( auto assign = resolved.as<ast::TupleAssignExpr>() ) {
+                // fix newly generated StmtExpr
+                previsit( assign->stmtExpr );
+        }
+        return resolved.release();
+}
+ast::ptr<ast::Expr> ResolveCopyCtors::copyConstructArg(
+        const ast::Expr * arg, const ast::ImplicitCopyCtorExpr * impCpCtorExpr, const ast::Type * formal )
+{
+        static UniqueName tempNamer("_tmp_cp");
+        const CodeLocation loc = impCpCtorExpr->location;
+        // CP_CTOR_PRINT( std::cerr << "Type Substitution: " << *env << std::endl; )
+        assert( arg->result );
+        ast::ptr<ast::Type> result = arg->result;
+        if ( skipCopyConstruct( result ) ) return arg; // skip certain non-copyable types
+        // type may involve type variables, so apply type substitution to get temporary variable's actual type,
+        // since result type may not be substituted (e.g., if the type does not appear in the parameter list)
+        // Use applyFree so that types bound in function pointers are not substituted, e.g. in forall(dtype T) void (*)(T).
+        // xxx - this originally mutates arg->result in place. is it correct?
+        assert( env );
+        result = env->applyFree( result.get() ).node;
+        auto mutResult = result.get_and_mutate();
+        mutResult->set_const(false);
+        auto mutArg = mutate(arg);
+        mutArg->result = mutResult;
+        ast::ptr<ast::Expr> guard = mutArg;
+        ast::ptr<ast::ObjectDecl> tmp = new ast::ObjectDecl(loc, "__tmp", mutResult, nullptr );
+        // create and resolve copy constructor
+        CP_CTOR_PRINT( std::cerr << "makeCtorDtor for an argument" << std::endl; )
+        auto cpCtor = makeCtorDtor( "?{}", tmp, mutArg );
+        if ( auto appExpr = dynamic_cast< const ast::ApplicationExpr * >( cpCtor ) ) {
+                // if the chosen constructor is intrinsic, the copy is unnecessary, so
+                // don't create the temporary and don't call the copy constructor
+                auto function = appExpr->func.strict_as<ast::VariableExpr>();
+                if ( function->var->linkage == ast::Linkage::Intrinsic ) {
+                        // arguments that need to be boxed need a temporary regardless of whether the copy constructor is intrinsic,
+                        // so that the object isn't changed inside of the polymorphic function
+                        if ( ! GenPoly::needsBoxing( formal, result, impCpCtorExpr->callExpr, env ) ) {
+                                // xxx - should arg->result be mutated? see comment above.
+                                return guard;
+                        }
+                }
+        }
+        // set a unique name for the temporary once it's certain the call is necessary
+        auto mut = tmp.get_and_mutate();
+        assertf (mut == tmp, "newly created ObjectDecl must be unique");
+        mut->name = tempNamer.newName();
+        // replace argument to function call with temporary
+        stmtsToAddBefore.push_back( new ast::DeclStmt(loc, tmp ) );
+        arg = cpCtor;
+        return destructRet( tmp, arg );
+        // impCpCtorExpr->dtors.push_front( makeCtorDtor( "^?{}", tmp ) );
+}
+ast::Expr * ResolveCopyCtors::destructRet( const ast::ObjectDecl * ret, const ast::Expr * arg ) {
+        auto global = transUnit().global;
+        // TODO: refactor code for generating cleanup attribute, since it's common and reused in ~3-4 places
+        // check for existing cleanup attribute before adding another(?)
+        // need to add __Destructor for _tmp_cp variables as well
+        assertf( global.dtorStruct, "Destructor generation requires __Destructor definition." );
+        assertf( global.dtorStruct->members.size() == 2, "__Destructor definition does not have expected fields." );
+        assertf( global.dtorDestroy, "Destructor generation requires __destroy_Destructor." );
+        const CodeLocation loc = ret->location;
+        // generate a __Destructor for ret that calls the destructor
+        auto res = makeCtorDtor( "^?{}", ret );
+        auto dtor = mutate(res);
+        // if the chosen destructor is intrinsic, elide the generated dtor handler
+        if ( arg && isIntrinsicCallExpr( dtor ) ) {
+                return new ast::CommaExpr(loc, arg, new ast::VariableExpr(loc, ret ) );
+        }
+        if ( ! dtor->env ) dtor->env = maybeClone( env );
+        auto dtorFunc = getDtorFunc( ret, new ast::ExprStmt(loc, dtor ), stmtsToAddBefore );
+        auto dtorStructType = new ast::StructInstType( global.dtorStruct );
+        // what does this do???
+        dtorStructType->params.push_back( new ast::TypeExpr(loc, new ast::VoidType() ) );
+        // cast destructor pointer to void (*)(void *), to silence GCC incompatible pointer warnings
+        auto dtorFtype = new ast::FunctionType();
+        dtorFtype->params.push_back( new ast::PointerType(new ast::VoidType( ) ) );
+        auto dtorType = new ast::PointerType( dtorFtype );
+        static UniqueName namer( "_ret_dtor" );
+        auto retDtor = new ast::ObjectDecl(loc, namer.newName(), dtorStructType, new ast::ListInit(loc, { new ast::SingleInit(loc, ast::ConstantExpr::null(loc) ), new ast::SingleInit(loc, new ast::CastExpr( new ast::VariableExpr(loc, dtorFunc ), dtorType ) ) } ) );
+        retDtor->attributes.push_back( new ast::Attribute( "cleanup", { new ast::VariableExpr(loc, global.dtorDestroy ) } ) );
+        stmtsToAddBefore.push_back( new ast::DeclStmt(loc, retDtor ) );
+        if ( arg ) {
+                auto member = new ast::MemberExpr(loc, global.dtorStruct->members.front().strict_as<ast::DeclWithType>(), new ast::VariableExpr(loc, retDtor ) );
+                auto object = new ast::CastExpr( new ast::AddressExpr( new ast::VariableExpr(loc, ret ) ), new ast::PointerType(new ast::VoidType() ) );
+                ast::Expr * assign = createBitwiseAssignment( member, object );
+                return new ast::CommaExpr(loc, new ast::CommaExpr(loc, arg, assign ), new ast::VariableExpr(loc, ret ) );
+        }
+        return nullptr;
+        // impCpCtorExpr->get_dtors().push_front( makeCtorDtor( "^?{}", ret ) );
+}
+const ast::Expr * ResolveCopyCtors::postvisit( const ast::ImplicitCopyCtorExpr *impCpCtorExpr ) {
+        CP_CTOR_PRINT( std::cerr << "ResolveCopyCtors: " << impCpCtorExpr << std::endl; )
+        ast::ApplicationExpr * appExpr = mutate(impCpCtorExpr->callExpr.get());
+        const ast::ObjectDecl * returnDecl = nullptr;
+        const CodeLocation loc = appExpr->location;
+        // take each argument and attempt to copy construct it.
+        auto ftype = GenPoly::getFunctionType( appExpr->func->result );
+        assert( ftype );
+        auto & params = ftype->params;
+        auto iter = params.begin();
+        for ( auto & arg : appExpr->args ) {
+                const ast::Type * formal = nullptr;
+                if ( iter != params.end() ) { // does not copy construct C-style variadic arguments
+                        // DeclarationWithType * param = *iter++;
+                        formal = *iter++;
+                }
+                arg = copyConstructArg( arg, impCpCtorExpr, formal );
+        } // for
+        // each return value from the call needs to be connected with an ObjectDecl at the call site, which is
+        // initialized with the return value and is destructed later
+        // xxx - handle named return values?
+        const ast::Type * result = appExpr->result;
+        if ( ! result->isVoid() ) {
+                static UniqueName retNamer("_tmp_cp_ret");
+                auto subResult = env->apply( result ).node;
+                auto ret = new ast::ObjectDecl(loc, retNamer.newName(), subResult, nullptr );
+                auto mutType = mutate(ret->type.get());
+                mutType->set_const( false );
+                ret->type = mutType;
+                returnDecl = ret;
+                stmtsToAddBefore.push_back( new ast::DeclStmt(loc, ret ) );
+                CP_CTOR_PRINT( std::cerr << "makeCtorDtor for a return" << std::endl; )
+        } // for
+        CP_CTOR_PRINT( std::cerr << "after Resolving: " << impCpCtorExpr << std::endl; )
+        // ------------------------------------------------------
+        CP_CTOR_PRINT( std::cerr << "Coming out the back..." << impCpCtorExpr << std::endl; )
+        // detach fields from wrapper node so that it can be deleted without deleting too much
+        // xxx - actual env might be somewhere else, need to keep invariant
+        // deletion of wrapper should be handled by pass template now
+        // impCpCtorExpr->callExpr = nullptr;
+        assert (appExpr->env == nullptr);
+        appExpr->env = impCpCtorExpr->env;
+        // std::swap( impCpCtorExpr->env, appExpr->env );
+        // assert( impCpCtorExpr->env == nullptr );
+        // delete impCpCtorExpr;
+        if ( returnDecl ) {
+                ast::Expr * assign = createBitwiseAssignment( new ast::VariableExpr(loc, returnDecl ), appExpr );
+                if ( ! dynamic_cast< const ast::ReferenceType * >( result ) ) {
+                        // destructing reference returns is bad because it can cause multiple destructor calls to the same object - the returned object is not a temporary
+                        assign = destructRet( returnDecl, assign );
+                        assert(assign);
+                } else {
+                        assign = new ast::CommaExpr(loc, assign, new ast::VariableExpr(loc, returnDecl ) );
+                }
+                // move env from appExpr to retExpr
+                // std::swap( assign->env, appExpr->env );
+                assign->env = appExpr->env;
+                // actual env is handled by common routine that replaces WithTypeSubstitution
+                return postvisit((const ast::Expr *)assign);
+        } else {
+                return postvisit((const ast::Expr *)appExpr);
+        } // if
+}
+const ast::StmtExpr * ResolveCopyCtors::previsit( const ast::StmtExpr * _stmtExpr ) {
+        // function call temporaries should be placed at statement-level, rather than nested inside of a new statement expression,
+        // since temporaries can be shared across sub-expressions, e.g.
+        //   [A, A] f();       // decl
+        //   g([A] x, [A] y);  // decl
+        //   g(f());           // call
+        // f is executed once, so the return temporary is shared across the tuple constructors for x and y.
+        // Explicitly mutating children instead of mutating the inner compound statement forces the temporaries to be added
+        // to the outer context, rather than inside of the statement expression.
+        // call the common routine that replaces WithTypeSubstitution
+        previsit((const ast::Expr *) _stmtExpr);
+        visit_children = false;
+        const CodeLocation loc = _stmtExpr->location;
+        assert( env );
+        symtab.enterScope();
+        // visit all statements
+        auto stmtExpr = mutate(_stmtExpr);
+        auto mutStmts = mutate(stmtExpr->stmts.get());
+        auto & stmts = mutStmts->kids;
+        for ( auto & stmt : stmts ) {
+                stmt = stmt->accept( *visitor );
+        } // for
+        stmtExpr->stmts = mutStmts;
+        symtab.leaveScope();
+        assert( stmtExpr->result );
+        // const ast::Type * result = stmtExpr->result;
+        if ( ! stmtExpr->result->isVoid() ) {
+                static UniqueName retNamer("_tmp_stmtexpr_ret");
+                // result = result->clone();
+                auto result = env->apply( stmtExpr->result.get() ).node;
+                if ( ! InitTweak::isConstructable( result ) ) {
+                        // delete result;
+                        return stmtExpr;
+                }
+                auto mutResult = result.get_and_mutate();
+                mutResult->set_const(false);
+                // create variable that will hold the result of the stmt expr
+                auto ret = new ast::ObjectDecl(loc, retNamer.newName(), mutResult, nullptr );
+                stmtsToAddBefore.push_back( new ast::DeclStmt(loc, ret ) );
+                assertf(
+                        stmtExpr->resultExpr,
+                        "Statement-Expression should have a resulting expression at %s:%d",
+                        stmtExpr->location.filename.c_str(),
+                        stmtExpr->location.first_line
+        // Shallow copy the pointer list for return.
+        std::vector<ast::ptr<ast::TypeDecl>> getGenericParams( const ast::Type * t ) {
+                if ( auto inst = dynamic_cast<const ast::StructInstType *>( t ) ) {
+                        return inst->base->params;
+                }
+                if ( auto inst = dynamic_cast<const ast::UnionInstType *>( t ) ) {
+                        return inst->base->params;
+                }
+                return {};
+        }
+        /// Given type T, generate type of default ctor/dtor, i.e. function type void (*) (T &).
+        ast::FunctionDecl * genDefaultFunc(
+                        const CodeLocation loc,
+                        const std::string fname,
+                        const ast::Type * paramType,
+                        bool maybePolymorphic = true) {
+                std::vector<ast::ptr<ast::TypeDecl>> typeParams;
+                if ( maybePolymorphic ) typeParams = getGenericParams( paramType );
+                auto dstParam = new ast::ObjectDecl( loc,
+                        "_dst",
+                        new ast::ReferenceType( paramType ),
+                        nullptr,
+                        {},
+                        ast::Linkage::Cforall
                 );
+                const ast::ExprStmt * last = stmtExpr->resultExpr;
+                // xxx - if this is non-unique, need to copy while making resultExpr ref
+                assertf(last->unique(), "attempt to modify weakly shared statement");
+                auto mutLast = mutate(last);
+                // above assertion means in-place mutation is OK
+                try {
+                        mutLast->expr = makeCtorDtor( "?{}", ret, mutLast->expr );
+                } catch(...) {
+                        std::cerr << "*CFA internal error: ";
+                        std::cerr << "can't resolve implicit constructor";
+                        std::cerr << " at " << stmtExpr->location.filename;
+                        std::cerr << ":" << stmtExpr->location.first_line << std::endl;
+                        abort();
+                }
+                // add destructors after current statement
+                stmtsToAddAfter.push_back( new ast::ExprStmt(loc, makeCtorDtor( "^?{}", ret ) ) );
+                // must have a non-empty body, otherwise it wouldn't have a result
+                assert( ! stmts.empty() );
+                // if there is a return decl, add a use as the last statement; will not have return decl on non-constructable returns
+                stmts.push_back( new ast::ExprStmt(loc, new ast::VariableExpr(loc, ret ) ) );
+        } // if
+        assert( stmtExpr->returnDecls.empty() );
+        assert( stmtExpr->dtors.empty() );
+        return stmtExpr;
+}
+// to prevent warnings ('_unq0' may be used uninitialized in this function),
+// insert an appropriate zero initializer for UniqueExpr temporaries.
+ast::Init * makeInit( const ast::Type * t, CodeLocation const & loc ) {
+        if ( auto inst = dynamic_cast< const ast::StructInstType * >( t ) ) {
+                // initizer for empty struct must be empty
+                if ( inst->base->members.empty() ) {
+                        return new ast::ListInit( loc, {} );
+                }
+        } else if ( auto inst = dynamic_cast< const ast::UnionInstType * >( t ) ) {
+                // initizer for empty union must be empty
+                if ( inst->base->members.empty() ) {
+                        return new ast::ListInit( loc, {} );
+                }
+        }
+        return new ast::ListInit( loc, {
+                new ast::SingleInit( loc, ast::ConstantExpr::from_int( loc, 0 ) )
+        } );
+}
+const ast::UniqueExpr * ResolveCopyCtors::previsit( const ast::UniqueExpr * unqExpr ) {
+        visit_children = false;
+        // xxx - hack to prevent double-handling of unique exprs, otherwise too many temporary variables and destructors are generated
+        static std::unordered_map< int, const ast::UniqueExpr * > unqMap;
+        auto mutExpr = mutate(unqExpr);
+        if ( ! unqMap.count( unqExpr->id ) ) {
+                // resolve expr and find its
+                auto impCpCtorExpr = mutExpr->expr.as<ast::ImplicitCopyCtorExpr>();
+                // PassVisitor<ResolveCopyCtors> fixer;
+                mutExpr->expr = mutExpr->expr->accept( *visitor );
+                // it should never be necessary to wrap a void-returning expression in a UniqueExpr - if this assumption changes, this needs to be rethought
+                assert( unqExpr->result );
+                if ( impCpCtorExpr ) {
+                        auto comma = unqExpr->expr.strict_as<ast::CommaExpr>();
+                        auto var = comma->arg2.strict_as<ast::VariableExpr>();
+                        // note the variable used as the result from the call
+                        mutExpr->var = var;
+                } else {
+                        // expr isn't a call expr, so create a new temporary variable to use to hold the value of the unique expression
+                        mutExpr->object = new ast::ObjectDecl( mutExpr->location, toString("_unq", mutExpr->id), mutExpr->result, makeInit( mutExpr->result, mutExpr->location ) );
+                        mutExpr->var = new ast::VariableExpr( mutExpr->location, mutExpr->object );
+                }
+                unqMap[mutExpr->id] = mutExpr;
+        } else {
+                // take data from other UniqueExpr to ensure consistency
+                // delete unqExpr->get_expr();
+                mutExpr->expr = unqMap[mutExpr->id]->expr;
+                // delete unqExpr->result;
+                mutExpr->result = mutExpr->expr->result;
+        }
+        return mutExpr;
+}
+const ast::DeclWithType * FixInit::postvisit( const ast::ObjectDecl *_objDecl ) {
+        const CodeLocation loc = _objDecl->location;
+        // since this removes the init field from objDecl, it must occur after children are mutated (i.e. postvisit)
+        if ( ast::ptr<ast::ConstructorInit> ctorInit = _objDecl->init.as<ast::ConstructorInit>() ) {
+                auto objDecl = mutate(_objDecl);
+                // could this be non-unique?
+                if (objDecl != _objDecl) {
+                        std::cerr << "FixInit: non-unique object decl " << objDecl->location << objDecl->name << std::endl;
+                }
+                // a decision should have been made by the resolver, so ctor and init are not both non-NULL
+                assert( ! ctorInit->ctor || ! ctorInit->init );
+                if ( const ast::Stmt * ctor = ctorInit->ctor ) {
+                        if ( objDecl->storage.is_static ) {
+                                addDataSectionAttribute(objDecl);
+                                // originally wanted to take advantage of gcc nested functions, but
+                                // we get memory errors with this approach. To remedy this, the static
+                                // variable is hoisted when the destructor needs to be called.
+                                //
+                                // generate:
+                                // static T __objName_static_varN;
+                                // void __objName_dtor_atexitN() {
+                                //   __dtor__...;
+                                // }
+                                // int f(...) {
+                                //   ...
+                                //   static bool __objName_uninitialized = true;
+                                //   if (__objName_uninitialized) {
+                                //     __ctor(__objName);
+                                //     __objName_uninitialized = false;
+                                //     atexit(__objName_dtor_atexitN);
+                                //   }
+                                //   ...
+                                // }
+                                static UniqueName dtorCallerNamer( "_dtor_atexit" );
+                                // static bool __objName_uninitialized = true
+                                auto boolType = new ast::BasicType( ast::BasicType::Kind::Bool );
+                                auto boolInitExpr = new ast::SingleInit(loc, ast::ConstantExpr::from_int(loc, 1 ) );
+                                auto isUninitializedVar = new ast::ObjectDecl(loc, objDecl->mangleName + "_uninitialized", boolType, boolInitExpr, ast::Storage::Static, ast::Linkage::Cforall);
+                                isUninitializedVar->fixUniqueId();
+                                // __objName_uninitialized = false;
+                                auto setTrue = new ast::UntypedExpr(loc, new ast::NameExpr(loc, "?=?" ) );
+                                setTrue->args.push_back( new ast::VariableExpr(loc, isUninitializedVar ) );
+                                setTrue->args.push_back( ast::ConstantExpr::from_int(loc, 0 ) );
+                                // generate body of if
+                                auto initStmts = new ast::CompoundStmt(loc);
+                                auto & body = initStmts->kids;
+                                body.push_back( ctor );
+                                body.push_back( new ast::ExprStmt(loc, setTrue ) );
+                                // put it all together
+                                auto ifStmt = new ast::IfStmt(loc, new ast::VariableExpr(loc, isUninitializedVar ), initStmts, 0 );
+                                stmtsToAddAfter.push_back( new ast::DeclStmt(loc, isUninitializedVar ) );
+                                stmtsToAddAfter.push_back( ifStmt );
+                                const ast::Stmt * dtor = ctorInit->dtor;
+                                // these should be automatically managed once reassigned
+                                // objDecl->set_init( nullptr );
+                                // ctorInit->set_ctor( nullptr );
+                                // ctorInit->set_dtor( nullptr );
+                                if ( dtor ) {
+                                        // if the object has a non-trivial destructor, have to
+                                        // hoist it and the object into the global space and
+                                        // call the destructor function with atexit.
+                                        // Statement * dtorStmt = dtor->clone();
+                                        // void __objName_dtor_atexitN(...) {...}
+                                        ast::FunctionDecl * dtorCaller = new ast::FunctionDecl(loc, objDecl->mangleName + dtorCallerNamer.newName(), {}, {}, {}, new ast::CompoundStmt(loc, {dtor}), ast::Storage::Static, ast::Linkage::C );
+                                        dtorCaller->fixUniqueId();
+                                        // dtorCaller->stmts->push_back( dtor );
+                                        // atexit(dtor_atexit);
+                                        auto callAtexit = new ast::UntypedExpr(loc, new ast::NameExpr(loc, "atexit" ) );
+                                        callAtexit->args.push_back( new ast::VariableExpr(loc, dtorCaller ) );
+                                        body.push_back( new ast::ExprStmt(loc, callAtexit ) );
+                                        // hoist variable and dtor caller decls to list of decls that will be added into global scope
+                                        staticDtorDecls.push_back( objDecl );
+                                        staticDtorDecls.push_back( dtorCaller );
+                                        // need to rename object uniquely since it now appears
+                                        // at global scope and there could be multiple function-scoped
+                                        // static variables with the same name in different functions.
+                                        // Note: it isn't sufficient to modify only the mangleName, because
+                                        // then subsequent Indexer passes can choke on seeing the object's name
+                                        // if another object has the same name and type. An unfortunate side-effect
+                                        // of renaming the object is that subsequent NameExprs may fail to resolve,
+                                        // but there shouldn't be any remaining past this point.
+                                        static UniqueName staticNamer( "_static_var" );
+                                        objDecl->name = objDecl->name + staticNamer.newName();
+                                        objDecl->mangleName = Mangle::mangle( objDecl );
+                                        objDecl->init = nullptr;
+                                        // xxx - temporary hack: need to return a declaration, but want to hoist the current object out of this scope
+                                        // create a new object which is never used
+                                        static UniqueName dummyNamer( "_dummy" );
+                                        auto dummy = new ast::ObjectDecl(loc, dummyNamer.newName(), new ast::PointerType(new ast::VoidType()), nullptr, ast::Storage::Static, ast::Linkage::Cforall, 0, { new ast::Attribute("unused") } );
+                                        // delete ctorInit;
+                                        return dummy;
+                                } else {
+                                        objDecl->init = nullptr;
+                                        return objDecl;
+                                }
+                        } else {
+                                auto implicit = strict_dynamic_cast< const ast::ImplicitCtorDtorStmt * > ( ctor );
+                                auto ctorStmt = implicit->callStmt.as<ast::ExprStmt>();
+                                const ast::ApplicationExpr * ctorCall = nullptr;
+                                if ( ctorStmt && (ctorCall = isIntrinsicCallExpr( ctorStmt->expr )) && ctorCall->args.size() == 2 ) {
+                                        // clean up intrinsic copy constructor calls by making them into SingleInits
+                                        const ast::Expr * ctorArg = ctorCall->args.back();
+                                        // ctorCall should be gone afterwards
+                                        auto mutArg = mutate(ctorArg);
+                                        mutArg->env = ctorCall->env;
+                                        // std::swap( ctorArg->env, ctorCall->env );
+                                        objDecl->init = new ast::SingleInit(loc, mutArg );
+                                        // ctorCall->args.pop_back();
+                                } else {
+                                        stmtsToAddAfter.push_back( ctor );
+                                        objDecl->init = nullptr;
+                                        // ctorInit->ctor = nullptr;
+                                }
+                                const ast::Stmt * dtor = ctorInit->dtor;
+                                if ( dtor ) {
+                                        auto implicit = strict_dynamic_cast< const ast::ImplicitCtorDtorStmt * >( dtor );
+                                        const ast::Stmt * dtorStmt = implicit->callStmt;
+                                        // don't need to call intrinsic dtor, because it does nothing, but
+                                        // non-intrinsic dtors must be called
+                                        if ( ! isIntrinsicSingleArgCallStmt( dtorStmt ) ) {
+                                                // set dtor location to the object's location for error messages
+                                                auto dtorFunc = getDtorFunc( objDecl, dtorStmt, stmtsToAddBefore );
+                                                objDecl->attributes.push_back( new ast::Attribute( "cleanup", { new ast::VariableExpr(loc, dtorFunc ) } ) );
+                                                // ctorInit->dtor = nullptr;
+                                        } // if
+                                }
+                        } // if
+                } else if ( const ast::Init * init = ctorInit->init ) {
+                        objDecl->init = init;
+                        // ctorInit->init = nullptr;
+                } else {
+                        // no constructor and no initializer, which is okay
+                        objDecl->init = nullptr;
+                } // if
+                // delete ctorInit;
+                return objDecl;
+        } // if
+        return _objDecl;
+}
+void ObjDeclCollector::previsit( const ast::CompoundStmt * ) {
+        GuardValue( curVars );
+}
+void ObjDeclCollector::previsit( const ast::DeclStmt * stmt ) {
+        // keep track of all variables currently in scope
+        if ( auto objDecl = stmt->decl.as<ast::ObjectDecl>() ) {
+                curVars.push_back( objDecl );
+        } // if
+}
+void LabelFinder::previsit( const ast::Stmt * stmt ) {
+        // for each label, remember the variables in scope at that label.
+        for ( auto l : stmt->labels ) {
+                vars[l] = curVars;
+        } // for
+}
+void LabelFinder::previsit( const ast::CompoundStmt * stmt ) {
+        previsit( (const ast::Stmt *) stmt );
+        Parent::previsit( stmt );
+}
+void LabelFinder::previsit( const ast::DeclStmt * stmt ) {
+        previsit( (const ast::Stmt *)stmt );
+        Parent::previsit( stmt );
+}
+void InsertDtors::previsit( const ast::FunctionDecl * funcDecl ) {
+        // each function needs to have its own set of labels
+        GuardValue( labelVars );
+        labelVars.clear();
+        // LabelFinder does not recurse into FunctionDecl, so need to visit
+        // its children manually.
+        if (funcDecl->type) funcDecl->type->accept(finder);
+        // maybeAccept( funcDecl->type, finder );
+        if (funcDecl->stmts) funcDecl->stmts->accept(finder) ;
+        // all labels for this function have been collected, insert destructors as appropriate via implicit recursion.
+}
+// Handle break/continue/goto in the same manner as C++.  Basic idea: any objects that are in scope at the
+// BranchStmt but not at the labelled (target) statement must be destructed.  If there are any objects in scope
+// at the target location but not at the BranchStmt then those objects would be uninitialized so notify the user
+// of the error.  See C++ Reference 6.6 Jump Statements for details.
+void InsertDtors::handleGoto( const ast::BranchStmt * stmt ) {
+        // can't do anything for computed goto
+        if ( stmt->computedTarget ) return;
+        assertf( stmt->target.name != "", "BranchStmt missing a label: %s", toString( stmt ).c_str() );
+        // S_L = lvars = set of objects in scope at label definition
+        // S_G = curVars = set of objects in scope at goto statement
+        ObjectSet & lvars = labelVars[ stmt->target ];
+        DTOR_PRINT(
+                std::cerr << "at goto label: " << stmt->target.name << std::endl;
+                std::cerr << "S_G = " << printSet( curVars ) << std::endl;
+                std::cerr << "S_L = " << printSet( lvars ) << std::endl;
+        )
+        // std::set_difference requires that the inputs be sorted.
+        lvars.sort();
+        curVars.sort();
+        ObjectSet diff;
+        // S_L-S_G results in set of objects whose construction is skipped - it's an error if this set is non-empty
+        std::set_difference( lvars.begin(), lvars.end(), curVars.begin(), curVars.end(), std::inserter( diff, diff.begin() ) );
+        DTOR_PRINT(
+                std::cerr << "S_L-S_G = " << printSet( diff ) << std::endl;
+        )
+        if ( ! diff.empty() ) {
+                SemanticError( stmt, std::string("jump to label '") + stmt->target.name + "' crosses initialization of " + (*diff.begin())->name + " " );
+        } // if
+}
+void InsertDtors::previsit( const ast::BranchStmt * stmt ) {
+        switch( stmt->kind ) {
+        case ast::BranchStmt::Continue:
+        case ast::BranchStmt::Break:
+                // could optimize the break/continue case, because the S_L-S_G check is unnecessary (this set should
+                // always be empty), but it serves as a small sanity check.
+        case ast::BranchStmt::Goto:
+                handleGoto( stmt );
+                break;
+        default:
+                assert( false );
+        } // switch
+}
+bool checkWarnings( const ast::FunctionDecl * funcDecl ) {
+        // only check for warnings if the current function is a user-defined
+        // constructor or destructor
+        if ( ! funcDecl ) return false;
+        if ( ! funcDecl->stmts ) return false;
+        return CodeGen::isCtorDtor( funcDecl->name ) && ! funcDecl->linkage.is_overrideable;
+}
+void GenStructMemberCalls::previsit( const ast::FunctionDecl * funcDecl ) {
+        GuardValue( function );
+        GuardValue( unhandled );
+        GuardValue( usedUninit );
+        GuardValue( thisParam );
+        GuardValue( isCtor );
+        GuardValue( structDecl );
+        errors = SemanticErrorException();  // clear previous errors
+        // need to start with fresh sets
+        unhandled.clear();
+        usedUninit.clear();
+        function = mutate(funcDecl);
+        // could this be non-unique?
+        if (function != funcDecl) {
+                std::cerr << "GenStructMemberCalls: non-unique FunctionDecl " << funcDecl->location << funcDecl->name << std::endl;
+        }
+        isCtor = CodeGen::isConstructor( function->name );
+        if ( checkWarnings( function ) ) {
+                // const ast::FunctionType * type = function->type;
+                // assert( ! type->params.empty() );
+                thisParam = function->params.front().strict_as<ast::ObjectDecl>();
+                auto thisType = getPointerBase( thisParam->get_type() );
+                auto structType = dynamic_cast< const ast::StructInstType * >( thisType );
+                if ( structType ) {
+                        structDecl = structType->base;
+                        for ( auto & member : structDecl->members ) {
+                                if ( auto field = member.as<ast::ObjectDecl>() ) {
+                                        // record all of the struct type's members that need to be constructed or
+                                        // destructed by the end of the function
+                                        unhandled.insert( field );
+                                }
+                        }
+                }
+        }
+}
+const ast::DeclWithType * GenStructMemberCalls::postvisit( const ast::FunctionDecl * funcDecl ) {
+        // remove the unhandled objects from usedUninit, because a call is inserted
+        // to handle them - only objects that are later constructed are used uninitialized.
+        std::map< const ast::DeclWithType *, CodeLocation > diff;
+        // need the comparator since usedUninit and unhandled have different types
+        struct comp_t {
+                typedef decltype(usedUninit)::value_type usedUninit_t;
+                typedef decltype(unhandled)::value_type unhandled_t;
+                bool operator()(usedUninit_t x, unhandled_t y) { return x.first < y; }
+                bool operator()(unhandled_t x, usedUninit_t y) { return x < y.first; }
+        } comp;
+        std::set_difference( usedUninit.begin(), usedUninit.end(), unhandled.begin(), unhandled.end(), std::inserter( diff, diff.begin() ), comp );
+        for ( auto p : diff ) {
+                auto member = p.first;
+                auto loc = p.second;
+                // xxx - make error message better by also tracking the location that the object is constructed at?
+                emit( loc, "in ", function->name, ", field ", member->name, " used before being constructed" );
+        }
+        const CodeLocation loc = funcDecl->location;
+        if ( ! unhandled.empty() ) {
+                auto mutStmts = function->stmts.get_and_mutate();
+                // need to explicitly re-add function parameters to the indexer in order to resolve copy constructors
+                auto guard = makeFuncGuard( [this]() { symtab.enterScope(); }, [this]() { symtab.leaveScope(); } );
+                symtab.addFunction( function );
+                auto global = transUnit().global;
+                // need to iterate through members in reverse in order for
+                // ctor/dtor statements to come out in the right order
+                for ( auto & member : reverseIterate( structDecl->members ) ) {
+                        auto field = member.as<ast::ObjectDecl>();
+                        // skip non-DWT members
+                        if ( ! field ) continue;
+                        // skip non-constructable members
+                        if ( ! tryConstruct( field ) ) continue;
+                        // skip handled members
+                        if ( ! unhandled.count( field ) ) continue;
+                        // insert and resolve default/copy constructor call for each field that's unhandled
+                        // std::list< const ast::Stmt * > stmt;
+                        ast::Expr * arg2 = nullptr;
+                        if ( function->name == "?{}" && isCopyFunction( function ) ) {
+                                // if copy ctor, need to pass second-param-of-this-function.field
+                                // std::list< DeclarationWithType * > & params = function->get_functionType()->get_parameters();
+                                assert( function->params.size() == 2 );
+                                arg2 = new ast::MemberExpr(funcDecl->location, field, new ast::VariableExpr(funcDecl->location, function->params.back() ) );
+                        }
+                        InitExpander_new srcParam( arg2 );
+                        // cast away reference type and construct field.
+                        ast::Expr * thisExpr = new ast::CastExpr(funcDecl->location, new ast::VariableExpr(funcDecl->location, thisParam ), thisParam->get_type()->stripReferences());
+                        ast::Expr * memberDest = new ast::MemberExpr(funcDecl->location, field, thisExpr );
+                        ast::ptr<ast::Stmt> callStmt = SymTab::genImplicitCall( srcParam, memberDest, loc, function->name, field, static_cast<SymTab::LoopDirection>(isCtor) );
+                        if ( callStmt ) {
+                                // auto & callStmt = stmt.front();
+                                try {
+                                        callStmt = callStmt->accept( *visitor );
+                                        if ( isCtor ) {
+                                                mutStmts->push_front( callStmt );
+                                        } else { // TODO: don't generate destructor function/object for intrinsic calls
+                                                // destructor statements should be added at the end
+                                                // function->get_statements()->push_back( callStmt );
+                                                // Optimization: do not need to call intrinsic destructors on members
+                                                if ( isIntrinsicSingleArgCallStmt( callStmt ) ) continue;
+                                                // __Destructor _dtor0 = { (void *)&b.a1, (void (*)(void *)_destroy_A };
+                                                std::list< ast::ptr<ast::Stmt> > stmtsToAdd;
+                                                static UniqueName memberDtorNamer = { "__memberDtor" };
+                                                assertf( global.dtorStruct, "builtin __Destructor not found." );
+                                                assertf( global.dtorDestroy, "builtin __destroy_Destructor not found." );
+                                                ast::Expr * thisExpr = new ast::CastExpr( new ast::AddressExpr( new ast::VariableExpr(loc, thisParam ) ), new ast::PointerType( new ast::VoidType(), ast::CV::Qualifiers() ) );
+                                                ast::Expr * dtorExpr = new ast::VariableExpr(loc, getDtorFunc( thisParam, callStmt, stmtsToAdd ) );
+                                                // cast destructor pointer to void (*)(void *), to silence GCC incompatible pointer warnings
+                                                auto dtorFtype = new ast::FunctionType();
+                                                dtorFtype->params.emplace_back( new ast::PointerType( new ast::VoidType() ) );
+                                                auto dtorType = new ast::PointerType( dtorFtype );
+                                                auto destructor = new ast::ObjectDecl(loc, memberDtorNamer.newName(), new ast::StructInstType( global.dtorStruct ), new ast::ListInit(loc, { new ast::SingleInit(loc, thisExpr ), new ast::SingleInit(loc, new ast::CastExpr( dtorExpr, dtorType ) ) } ) );
+                                                destructor->attributes.push_back( new ast::Attribute( "cleanup", { new ast::VariableExpr( loc, global.dtorDestroy ) } ) );
+                                                mutStmts->push_front( new ast::DeclStmt(loc, destructor ) );
+                                                mutStmts->kids.splice( mutStmts->kids.begin(), stmtsToAdd );
+                                        }
+                                } catch ( SemanticErrorException & error ) {
+                                        emit( funcDecl->location, "in ", function->name , ", field ", field->name, " not explicitly ", isCtor ? "constructed" : "destructed",  " and no ", isCtor ? "default constructor" : "destructor", " found" );
+                                }
+                        }
+                }
+                function->stmts = mutStmts;
+        }
+        if (! errors.isEmpty()) {
+                throw errors;
+        }
+        // return funcDecl;
+        return function;
+}
+/// true if expr is effectively just the 'this' parameter
+bool isThisExpression( const ast::Expr * expr, const ast::DeclWithType * thisParam ) {
+        // TODO: there are more complicated ways to pass 'this' to a constructor, e.g. &*, *&, etc.
+        if ( auto varExpr = dynamic_cast< const ast::VariableExpr * >( expr ) ) {
+                return varExpr->var == thisParam;
+        } else if ( auto castExpr = dynamic_cast< const ast::CastExpr * > ( expr ) ) {
+                return isThisExpression( castExpr->arg, thisParam );
+        }
+        return false;
+}
+/// returns a MemberExpr if expr is effectively just member access on the 'this' parameter, else nullptr
+const ast::MemberExpr * isThisMemberExpr( const ast::Expr * expr, const ast::DeclWithType * thisParam ) {
+        if ( auto memberExpr = dynamic_cast< const ast::MemberExpr * >( expr ) ) {
+                if ( isThisExpression( memberExpr->aggregate, thisParam ) ) {
+                        return memberExpr;
+                }
+        } else if ( auto castExpr = dynamic_cast< const ast::CastExpr * >( expr ) ) {
+                return isThisMemberExpr( castExpr->arg, thisParam );
+        }
+        return nullptr;
+}
+void GenStructMemberCalls::previsit( const ast::ApplicationExpr * appExpr ) {
+        if ( ! checkWarnings( function ) ) {
+                visit_children = false;
+                return;
+        }
+        std::string fname = getFunctionName( appExpr );
+        if ( fname == function->name ) {
+                // call to same kind of function
+                const ast::Expr * firstParam = appExpr->args.front();
+                if ( isThisExpression( firstParam, thisParam ) ) {
+                        // if calling another constructor on thisParam, assume that function handles
+                        // all members - if it doesn't a warning will appear in that function.
+                        unhandled.clear();
+                } else if ( auto memberExpr = isThisMemberExpr( firstParam, thisParam ) ) {
+                        // if first parameter is a member expression on the this parameter,
+                        // then remove the member from unhandled set.
+                        if ( isThisExpression( memberExpr->aggregate, thisParam ) ) {
+                                unhandled.erase( memberExpr->member );
+                        }
+                }
+        }
+}
+void GenStructMemberCalls::previsit( const ast::MemberExpr * memberExpr ) {
+        if ( ! checkWarnings( function ) || ! isCtor ) {
+                visit_children = false;
+                return;
+        }
+        if ( isThisExpression( memberExpr->aggregate, thisParam ) ) {
+                if ( unhandled.count( memberExpr->member ) ) {
+                        // emit a warning because a member was used before it was constructed
+                        usedUninit.insert( { memberExpr->member, memberExpr->location } );
+                }
+        }
+}
+template< typename... Params >
+void GenStructMemberCalls::emit( CodeLocation loc, const Params &... params ) {
+        SemanticErrorException err( loc, toString( params... ) );
+        errors.append( err );
+}
+const ast::Expr * GenStructMemberCalls::postvisit( const ast::UntypedExpr * untypedExpr ) {
+        // xxx - functions returning ast::ptr seems wrong...
+        auto res = ResolvExpr::findVoidExpression( untypedExpr, { symtab, transUnit().global } );
+        return res.release();
+}
+void InsertImplicitCalls::previsit(const ast::UniqueExpr * unqExpr) {
+        if (visitedIds.count(unqExpr->id)) visit_children = false;
+        else visitedIds.insert(unqExpr->id);
+}
+const ast::Expr * FixCtorExprs::postvisit( const ast::ConstructorExpr * ctorExpr ) {
+        const CodeLocation loc = ctorExpr->location;
+        static UniqueName tempNamer( "_tmp_ctor_expr" );
+        // xxx - is the size check necessary?
+        assert( ctorExpr->result && ctorExpr->result->size() == 1 );
+        // xxx - this can be TupleAssignExpr now. Need to properly handle this case.
+        // take possession of expr and env
+        ast::ptr<ast::ApplicationExpr> callExpr = ctorExpr->callExpr.strict_as<ast::ApplicationExpr>();
+        ast::ptr<ast::TypeSubstitution> env = ctorExpr->env;
+        // ctorExpr->set_callExpr( nullptr );
+        // ctorExpr->set_env( nullptr );
+        // xxx - ideally we would reuse the temporary generated from the copy constructor passes from within firstArg if it exists and not generate a temporary if it's unnecessary.
+        auto tmp = new ast::ObjectDecl(loc, tempNamer.newName(), callExpr->args.front()->result );
+        declsToAddBefore.push_back( tmp );
+        // build assignment and replace constructor's first argument with new temporary
+        auto mutCallExpr = callExpr.get_and_mutate();
+        const ast::Expr * firstArg = callExpr->args.front();
+        ast::Expr * assign = new ast::UntypedExpr(loc, new ast::NameExpr(loc, "?=?" ), { new ast::AddressExpr(loc, new ast::VariableExpr(loc, tmp ) ), new ast::AddressExpr( firstArg ) } );
+        firstArg = new ast::VariableExpr(loc, tmp );
+        mutCallExpr->args.front() = firstArg;
+        // resolve assignment and dispose of new env
+        auto resolved = ResolvExpr::findVoidExpression( assign, { symtab, transUnit().global } );
+        auto mut = resolved.get_and_mutate();
+        assertf(resolved.get() == mut, "newly resolved expression must be unique");
+        mut->env = nullptr;
+        // for constructor expr:
+        //   T x;
+        //   x{};
+        // results in:
+        //   T x;
+        //   T & tmp;
+        //   &tmp = &x, ?{}(tmp), tmp
+        ast::CommaExpr * commaExpr = new ast::CommaExpr(loc, resolved, new ast::CommaExpr(loc, mutCallExpr, new ast::VariableExpr(loc, tmp ) ) );
+        commaExpr->env = env;
+        return commaExpr;
+}
+                return new ast::FunctionDecl( loc,
+                        fname,
+                        std::move(typeParams),
+                        {dstParam},
+                        {},
+                        new ast::CompoundStmt(loc),
+                        {},
+                        ast::Linkage::Cforall
+                );
+        }
+        struct SelfAssignChecker {
+                void previsit( const ast::ApplicationExpr * appExpr );
+        };
+        struct StmtExprResult {
+                const ast::StmtExpr * previsit( const ast::StmtExpr * stmtExpr );
+        };
+        /// wrap function application expressions as ImplicitCopyCtorExpr nodes so that it is easy to identify which
+        /// function calls need their parameters to be copy constructed
+        struct InsertImplicitCalls : public ast::WithShortCircuiting {
+                const ast::Expr * postvisit( const ast::ApplicationExpr * appExpr );
+                // only handles each UniqueExpr once
+                // if order of visit does not change, this should be safe
+                void previsit (const ast::UniqueExpr *);
+                std::unordered_set<decltype(ast::UniqueExpr::id)> visitedIds;
+        };
+        /// generate temporary ObjectDecls for each argument and return value of each ImplicitCopyCtorExpr,
+        /// generate/resolve copy construction expressions for each, and generate/resolve destructors for both
+        /// arguments and return value temporaries
+        struct ResolveCopyCtors final : public ast::WithGuards, public ast::WithStmtsToAdd<>, public ast::WithSymbolTable, public ast::WithShortCircuiting, public ast::WithVisitorRef<ResolveCopyCtors>, public ast::WithConstTranslationUnit {
+                const ast::Expr * postvisit( const ast::ImplicitCopyCtorExpr * impCpCtorExpr );
+                const ast::StmtExpr * previsit( const ast::StmtExpr * stmtExpr );
+                const ast::UniqueExpr * previsit( const ast::UniqueExpr * unqExpr );
+                /// handles distant mutations of environment manually.
+                /// WithConstTypeSubstitution cannot remember where the environment is from
+                /// MUST be called at start of overload previsit
+                void previsit( const ast::Expr * expr);
+                /// MUST be called at return of overload postvisit
+                const ast::Expr * postvisit(const ast::Expr * expr);
+                /// create and resolve ctor/dtor expression: fname(var, [cpArg])
+                const ast::Expr * makeCtorDtor( const std::string & fname, const ast::ObjectDecl * var, const ast::Expr * cpArg = nullptr );
+                /// true if type does not need to be copy constructed to ensure correctness
+                bool skipCopyConstruct( const ast::Type * type );
+                ast::ptr< ast::Expr > copyConstructArg( const ast::Expr * arg, const ast::ImplicitCopyCtorExpr * impCpCtorExpr, const ast::Type * formal );
+                ast::Expr * destructRet( const ast::ObjectDecl * ret, const ast::Expr * arg );
+        private:
+                /// hack to implement WithTypeSubstitution while conforming to mutation safety.
+                ast::TypeSubstitution * env         = nullptr;
+                bool                    envModified = false;
+        };
+        /// collects constructed object decls - used as a base class
+        struct ObjDeclCollector : public ast::WithGuards, public ast::WithShortCircuiting {
+                // use ordered data structure to maintain ordering for set_difference and for consistent error messages
+                typedef std::list< const ast::ObjectDecl * > ObjectSet;
+                void previsit( const ast::CompoundStmt *compoundStmt );
+                void previsit( const ast::DeclStmt *stmt );
+                // don't go into other functions
+                void previsit( const ast::FunctionDecl * ) { visit_children = false; }
+        protected:
+                ObjectSet curVars;
+        };
+        // debug
+        template<typename ObjectSet>
+        struct PrintSet {
+                PrintSet( const ObjectSet & objs ) : objs( objs ) {}
+                const ObjectSet & objs;
+        };
+        template<typename ObjectSet>
+        PrintSet<ObjectSet> printSet( const ObjectSet & objs ) { return PrintSet<ObjectSet>( objs ); }
+        template<typename ObjectSet>
+        std::ostream & operator<<( std::ostream & out, const PrintSet<ObjectSet> & set) {
+                out << "{ ";
+                for ( auto & obj : set.objs ) {
+                        out << obj->name << ", " ;
+                } // for
+                out << " }";
+                return out;
+        }
+        struct LabelFinder final : public ObjDeclCollector {
+                typedef std::map< std::string, ObjectSet > LabelMap;
+                // map of Label -> live variables at that label
+                LabelMap vars;
+                typedef ObjDeclCollector Parent;
+                using Parent::previsit;
+                void previsit( const ast::Stmt * stmt );
+                void previsit( const ast::CompoundStmt *compoundStmt );
+                void previsit( const ast::DeclStmt *stmt );
+        };
+        /// insert destructor calls at the appropriate places.  must happen before CtorInit nodes are removed
+        /// (currently by FixInit)
+        struct InsertDtors final : public ObjDeclCollector, public ast::WithStmtsToAdd<> {
+                typedef std::list< ObjectDecl * > OrderedDecls;
+                typedef std::list< OrderedDecls > OrderedDeclsStack;
+                InsertDtors( ast::Pass<LabelFinder> & finder ) : finder( finder ), labelVars( finder.core.vars ) {}
+                typedef ObjDeclCollector Parent;
+                using Parent::previsit;
+                void previsit( const ast::FunctionDecl * funcDecl );
+                void previsit( const ast::BranchStmt * stmt );
+        private:
+                void handleGoto( const ast::BranchStmt * stmt );
+                ast::Pass<LabelFinder> & finder;
+                LabelFinder::LabelMap & labelVars;
+                OrderedDeclsStack reverseDeclOrder;
+        };
+        /// expand each object declaration to use its constructor after it is declared.
+        struct FixInit : public ast::WithStmtsToAdd<> {
+                static void fixInitializers( ast::TranslationUnit &translationUnit );
+                const ast::DeclWithType * postvisit( const ast::ObjectDecl *objDecl );
+                std::list< ast::ptr< ast::Decl > > staticDtorDecls;
+        };
+        /// generate default/copy ctor and dtor calls for user-defined struct ctor/dtors
+        /// for any member that is missing a corresponding ctor/dtor call.
+        /// error if a member is used before constructed
+        struct GenStructMemberCalls final : public ast::WithGuards, public ast::WithShortCircuiting, public ast::WithSymbolTable, public ast::WithVisitorRef<GenStructMemberCalls>, public ast::WithConstTranslationUnit {
+                void previsit( const ast::FunctionDecl * funcDecl );
+                const ast::DeclWithType * postvisit( const ast::FunctionDecl * funcDecl );
+                void previsit( const ast::MemberExpr * memberExpr );
+                void previsit( const ast::ApplicationExpr * appExpr );
+                /// Note: this post mutate used to be in a separate visitor. If this pass breaks, one place to examine is whether it is
+                /// okay for this part of the recursion to occur alongside the rest.
+                const ast::Expr * postvisit( const ast::UntypedExpr * expr );
+                SemanticErrorException errors;
+        private:
+                template< typename... Params >
+                void emit( CodeLocation, const Params &... params );
+                ast::FunctionDecl * function = nullptr;
+                std::set< const ast::DeclWithType * > unhandled;
+                std::map< const ast::DeclWithType *, CodeLocation > usedUninit;
+                const ast::ObjectDecl * thisParam = nullptr;
+                bool isCtor = false; // true if current function is a constructor
+                const ast::StructDecl * structDecl = nullptr;
+        };
+        /// expands ConstructorExpr nodes into comma expressions, using a temporary for the first argument
+        struct FixCtorExprs final : public ast::WithDeclsToAdd<>, public ast::WithSymbolTable, public ast::WithShortCircuiting, public ast::WithConstTranslationUnit {
+                const ast::Expr * postvisit( const ast::ConstructorExpr * ctorExpr );
+        };
+        /// add CompoundStmts around top-level expressions so that temporaries are destroyed in the correct places.
+        struct SplitExpressions : public ast::WithShortCircuiting {
+                ast::Stmt * postvisit( const ast::ExprStmt * stmt );
+                void previsit( const ast::TupleAssignExpr * expr );
+        };
 } // namespace
 …
+}
+namespace {
+        /// find and return the destructor used in `input`. If `input` is not a simple destructor call, generate a thunk
+        /// that wraps the destructor, insert it into `stmtsToAdd` and return the new function declaration
+        const ast::DeclWithType * getDtorFunc( const ast::ObjectDecl * objDecl, const ast::Stmt * input, std::list< ast::ptr<ast::Stmt> > & stmtsToAdd ) {
+                const CodeLocation loc = input->location;
+                // unwrap implicit statement wrapper
+                // Statement * dtor = input;
+                assert( input );
+                // std::list< const ast::Expr * > matches;
+                auto matches = collectCtorDtorCalls( input );
+                if ( dynamic_cast< const ast::ExprStmt * >( input ) ) {
+                        // only one destructor call in the expression
+                        if ( matches.size() == 1 ) {
+                                auto func = getFunction( matches.front() );
+                                assertf( func, "getFunction failed to find function in %s", toString( matches.front() ).c_str() );
+                                // cleanup argument must be a function, not an object (including function pointer)
+                                if ( auto dtorFunc = dynamic_cast< const ast::FunctionDecl * > ( func ) ) {
+                                        if ( dtorFunc->type->forall.empty() ) {
+                                                // simple case where the destructor is a monomorphic function call - can simply
+                                                // use that function as the cleanup function.
+                                                return func;
+                                        }
+                                }
+                        }
+                }
+                // otherwise the cleanup is more complicated - need to build a single argument cleanup function that
+                // wraps the more complicated code.
+                static UniqueName dtorNamer( "__cleanup_dtor" );
+                std::string name = dtorNamer.newName();
+                ast::FunctionDecl * dtorFunc = genDefaultFunc( loc, name, objDecl->type->stripReferences(), false );
+                stmtsToAdd.push_back( new ast::DeclStmt(loc, dtorFunc ) );
+                // the original code contains uses of objDecl - replace them with the newly generated 'this' parameter.
+                const ast::ObjectDecl * thisParam = getParamThis( dtorFunc );
+                const ast::Expr * replacement = new ast::VariableExpr( loc, thisParam );
+                auto base = replacement->result->stripReferences();
+                if ( dynamic_cast< const ast::ArrayType * >( base ) || dynamic_cast< const ast::TupleType * > ( base ) ) {
+                        // need to cast away reference for array types, since the destructor is generated without the reference type,
+                        // and for tuple types since tuple indexing does not work directly on a reference
+                        replacement = new ast::CastExpr( replacement, base );
+                }
+                auto dtor = ast::DeclReplacer::replace( input, ast::DeclReplacer::ExprMap{ std::make_pair( objDecl, replacement ) } );
+                auto mutStmts = dtorFunc->stmts.get_and_mutate();
+                mutStmts->push_back(strict_dynamic_cast<const ast::Stmt *>( dtor ));
+                dtorFunc->stmts = mutStmts;
+                return dtorFunc;
+        }
+        void FixInit::fixInitializers( ast::TranslationUnit & translationUnit ) {
+                ast::Pass<FixInit> fixer;
+                // can't use mutateAll, because need to insert declarations at top-level
+                // can't use DeclMutator, because sometimes need to insert IfStmt, etc.
+                SemanticErrorException errors;
+                for ( auto i = translationUnit.decls.begin(); i != translationUnit.decls.end(); ++i ) {
+                        try {
+                                // maybeAccept( *i, fixer ); translationUnit should never contain null
+                                *i = (*i)->accept(fixer);
+                                translationUnit.decls.splice( i, fixer.core.staticDtorDecls );
+                        } catch( SemanticErrorException &e ) {
+                                errors.append( e );
+                        } // try
+                } // for
+                if ( ! errors.isEmpty() ) {
+                        throw errors;
+                } // if
+        }
+        const ast::StmtExpr * StmtExprResult::previsit( const ast::StmtExpr * stmtExpr ) {
+                // we might loose the result expression here so add a pointer to trace back
+                assert( stmtExpr->result );
+                const ast::Type * result = stmtExpr->result;
+                if ( ! result->isVoid() ) {
+                        auto mutExpr = mutate(stmtExpr);
+                        const ast::CompoundStmt * body = mutExpr->stmts;
+                        assert( ! body->kids.empty() );
+                        mutExpr->resultExpr = body->kids.back().strict_as<ast::ExprStmt>();
+                        return mutExpr;
+                }
+                return stmtExpr;
+        }
+        ast::Stmt * SplitExpressions::postvisit( const ast::ExprStmt * stmt ) {
+                // wrap each top-level ExprStmt in a block so that destructors for argument and return temporaries are destroyed
+                // in the correct places
+                ast::CompoundStmt * ret = new ast::CompoundStmt( stmt->location, { stmt } );
+                return ret;
+        }
+        void SplitExpressions::previsit( const ast::TupleAssignExpr * ) {
+                // don't do this within TupleAssignExpr, since it is already broken up into multiple expressions
+                visit_children = false;
+        }
+        // Relatively simple structural comparison for expressions, needed to determine
+        // if two expressions are "the same" (used to determine if self assignment occurs)
+        struct StructuralChecker {
+                // Strip all casts and then dynamic_cast.
+                template<typename T>
+                static const T * cast( const ast::Expr * expr ) {
+                        // this might be too permissive. It's possible that only particular casts are relevant.
+                        while ( auto cast = dynamic_cast< const ast::CastExpr * >( expr ) ) {
+                                expr = cast->arg;
+                        }
+                        return dynamic_cast< const T * >( expr );
+                }
+                void previsit( const ast::Expr * ) {
+                        // anything else does not qualify
+                        result = false;
+                }
+                // ignore casts
+                void previsit( const ast::CastExpr * ) {}
+                void previsit( const ast::MemberExpr * memExpr ) {
+                        if ( auto otherMember = cast< ast::MemberExpr >( other ) ) {
+                                if ( otherMember->member == memExpr->member ) {
+                                        other = otherMember->aggregate;
+                                        return;
+                                }
+                        }
+                        result = false;
+                }
+                void previsit( const ast::VariableExpr * varExpr ) {
+                        if ( auto otherVar = cast< ast::VariableExpr >( other ) ) {
+                                if ( otherVar->var == varExpr->var ) {
+                                        return;
+                                }
+                        }
+                        result = false;
+                }
+                void previsit( const ast::AddressExpr * ) {
+                        if ( auto addrExpr = cast< ast::AddressExpr >( other ) ) {
+                                other = addrExpr->arg;
+                                return;
+                        }
+                        result = false;
+                }
+                const ast::Expr * other;
+                bool result = true;
+                StructuralChecker( const ast::Expr * other ) : other(other) {}
+        };
+        bool structurallySimilar( const ast::Expr * e1, const ast::Expr * e2 ) {
+                return ast::Pass<StructuralChecker>::read( e1, e2 );
+        }
+        void SelfAssignChecker::previsit( const ast::ApplicationExpr * appExpr ) {
+                auto function = getFunction( appExpr );
+                // Doesn't use isAssignment, because ?+=?, etc. should not count as self-assignment.
+                if ( function->name == "?=?" && appExpr->args.size() == 2
+                                // Check for structural similarity (same variable use, ignore casts, etc.
+                                // (but does not look too deeply, anything looking like a function is off limits).
+                                && structurallySimilar( appExpr->args.front(), appExpr->args.back() ) ) {
+                        SemanticWarning( appExpr->location, Warning::SelfAssignment, toCString( appExpr->args.front() ) );
+                }
+        }
+        const ast::Expr * InsertImplicitCalls::postvisit( const ast::ApplicationExpr * appExpr ) {
+                if ( auto function = appExpr->func.as<ast::VariableExpr>() ) {
+                        if ( function->var->linkage.is_builtin ) {
+                                // optimization: don't need to copy construct in order to call intrinsic functions
+                                return appExpr;
+                        } else if ( auto funcDecl = function->var.as<ast::DeclWithType>() ) {
+                                auto ftype = dynamic_cast< const ast::FunctionType * >( GenPoly::getFunctionType( funcDecl->get_type() ) );
+                                assertf( ftype, "Function call without function type: %s", toString( funcDecl ).c_str() );
+                                if ( CodeGen::isConstructor( funcDecl->name ) && ftype->params.size() == 2 ) {
+                                        auto t1 = getPointerBase( ftype->params.front() );
+                                        auto t2 = ftype->params.back();
+                                        assert( t1 );
+                                        if ( ResolvExpr::typesCompatible( t1, t2 ) ) {
+                                                // optimization: don't need to copy construct in order to call a copy constructor
+                                                return appExpr;
+                                        } // if
+                                } else if ( CodeGen::isDestructor( funcDecl->name ) ) {
+                                        // correctness: never copy construct arguments to a destructor
+                                        return appExpr;
+                                } // if
+                        } // if
+                } // if
+                CP_CTOR_PRINT( std::cerr << "InsertImplicitCalls: adding a wrapper " << appExpr << std::endl; )
+                // wrap each function call so that it is easy to identify nodes that have to be copy constructed
+                ast::ptr<ast::TypeSubstitution> tmp = appExpr->env;
+                auto mutExpr = mutate(appExpr);
+                mutExpr->env = nullptr;
+                auto expr = new ast::ImplicitCopyCtorExpr( appExpr->location, mutExpr );
+                // Move the type substitution to the new top-level. The substitution
+                // is needed to obtain the type of temporary variables so that copy
+                // constructor calls can be resolved.
+                expr->env = tmp;
+                return expr;
+        }
+        void ResolveCopyCtors::previsit(const ast::Expr * expr) {
+                if ( nullptr == expr->env ) {
+                        return;
+                }
+                GuardValue( env ) = expr->env->clone();
+                GuardValue( envModified ) = false;
+        }
+        const ast::Expr * ResolveCopyCtors::postvisit(const ast::Expr * expr) {
+                // No local environment, skip.
+                if ( nullptr == expr->env ) {
+                        return expr;
+                // Environment was modified, mutate and replace.
+                } else if ( envModified ) {
+                        auto mutExpr = mutate(expr);
+                        mutExpr->env = env;
+                        return mutExpr;
+                // Environment was not mutated, delete the shallow copy before guard.
+                } else {
+                        delete env;
+                        return expr;
+                }
+        }
+        bool ResolveCopyCtors::skipCopyConstruct( const ast::Type * type ) { return ! isConstructable( type ); }
+        const ast::Expr * ResolveCopyCtors::makeCtorDtor( const std::string & fname, const ast::ObjectDecl * var, const ast::Expr * cpArg ) {
+                assert( var );
+                assert( var->isManaged() );
+                assert( !cpArg || cpArg->isManaged() );
+                // arrays are not copy constructed, so this should always be an ExprStmt
+                ast::ptr< ast::Stmt > stmt = genCtorDtor(var->location, fname, var, cpArg );
+                assertf( stmt, "ResolveCopyCtors: genCtorDtor returned nullptr: %s / %s / %s", fname.c_str(), toString( var ).c_str(), toString( cpArg ).c_str() );
+                auto exprStmt = stmt.strict_as<ast::ImplicitCtorDtorStmt>()->callStmt.strict_as<ast::ExprStmt>();
+                ast::ptr<ast::Expr> untyped = exprStmt->expr; // take ownership of expr
+                // resolve copy constructor
+                // should only be one alternative for copy ctor and dtor expressions, since all arguments are fixed
+                // (VariableExpr and already resolved expression)
+                CP_CTOR_PRINT( std::cerr << "ResolvingCtorDtor " << untyped << std::endl; )
+                ast::ptr<ast::Expr> resolved = ResolvExpr::findVoidExpression(untyped, { symtab, transUnit().global } );
+                assert( resolved );
+                if ( resolved->env ) {
+                        // Extract useful information and discard new environments. Keeping them causes problems in PolyMutator passes.
+                        env->add( *resolved->env );
+                        envModified = true;
+                        auto mut = mutate(resolved.get());
+                        assertf(mut == resolved.get(), "newly resolved expression must be unique");
+                        mut->env = nullptr;
+                } // if
+                if ( auto assign = resolved.as<ast::TupleAssignExpr>() ) {
+                        // fix newly generated StmtExpr
+                        previsit( assign->stmtExpr );
+                }
+                return resolved.release();
+        }
+        ast::ptr<ast::Expr> ResolveCopyCtors::copyConstructArg(
+                const ast::Expr * arg, const ast::ImplicitCopyCtorExpr * impCpCtorExpr, const ast::Type * formal )
+        {
+                static UniqueName tempNamer("_tmp_cp");
+                const CodeLocation loc = impCpCtorExpr->location;
+                // CP_CTOR_PRINT( std::cerr << "Type Substitution: " << *env << std::endl; )
+                assert( arg->result );
+                ast::ptr<ast::Type> result = arg->result;
+                if ( skipCopyConstruct( result ) ) return arg; // skip certain non-copyable types
+                // type may involve type variables, so apply type substitution to get temporary variable's actual type,
+                // since result type may not be substituted (e.g., if the type does not appear in the parameter list)
+                // Use applyFree so that types bound in function pointers are not substituted, e.g. in forall(dtype T) void (*)(T).
+                // xxx - this originally mutates arg->result in place. is it correct?
+                assert( env );
+                result = env->applyFree( result.get() ).node;
+                auto mutResult = result.get_and_mutate();
+                mutResult->set_const(false);
+                auto mutArg = mutate(arg);
+                mutArg->result = mutResult;
+                ast::ptr<ast::Expr> guard = mutArg;
+                ast::ptr<ast::ObjectDecl> tmp = new ast::ObjectDecl(loc, "__tmp", mutResult, nullptr );
+                // create and resolve copy constructor
+                CP_CTOR_PRINT( std::cerr << "makeCtorDtor for an argument" << std::endl; )
+                auto cpCtor = makeCtorDtor( "?{}", tmp, mutArg );
+                if ( auto appExpr = dynamic_cast< const ast::ApplicationExpr * >( cpCtor ) ) {
+                        // if the chosen constructor is intrinsic, the copy is unnecessary, so
+                        // don't create the temporary and don't call the copy constructor
+                        auto function = appExpr->func.strict_as<ast::VariableExpr>();
+                        if ( function->var->linkage == ast::Linkage::Intrinsic ) {
+                                // arguments that need to be boxed need a temporary regardless of whether the copy constructor is intrinsic,
+                                // so that the object isn't changed inside of the polymorphic function
+                                if ( ! GenPoly::needsBoxing( formal, result, impCpCtorExpr->callExpr, env ) ) {
+                                        // xxx - should arg->result be mutated? see comment above.
+                                        return guard;
+                                }
+                        }
+                }
+                // set a unique name for the temporary once it's certain the call is necessary
+                auto mut = tmp.get_and_mutate();
+                assertf (mut == tmp, "newly created ObjectDecl must be unique");
+                mut->name = tempNamer.newName();
+                // replace argument to function call with temporary
+                stmtsToAddBefore.push_back( new ast::DeclStmt(loc, tmp ) );
+                arg = cpCtor;
+                return destructRet( tmp, arg );
+                // impCpCtorExpr->dtors.push_front( makeCtorDtor( "^?{}", tmp ) );
+        }
+        ast::Expr * ResolveCopyCtors::destructRet( const ast::ObjectDecl * ret, const ast::Expr * arg ) {
+                auto global = transUnit().global;
+                // TODO: refactor code for generating cleanup attribute, since it's common and reused in ~3-4 places
+                // check for existing cleanup attribute before adding another(?)
+                // need to add __Destructor for _tmp_cp variables as well
+                assertf( global.dtorStruct, "Destructor generation requires __Destructor definition." );
+                assertf( global.dtorStruct->members.size() == 2, "__Destructor definition does not have expected fields." );
+                assertf( global.dtorDestroy, "Destructor generation requires __destroy_Destructor." );
+                const CodeLocation loc = ret->location;
+                // generate a __Destructor for ret that calls the destructor
+                auto res = makeCtorDtor( "^?{}", ret );
+                auto dtor = mutate(res);
+                // if the chosen destructor is intrinsic, elide the generated dtor handler
+                if ( arg && isIntrinsicCallExpr( dtor ) ) {
+                        return new ast::CommaExpr(loc, arg, new ast::VariableExpr(loc, ret ) );
+                }
+                if ( ! dtor->env ) dtor->env = maybeClone( env );
+                auto dtorFunc = getDtorFunc( ret, new ast::ExprStmt(loc, dtor ), stmtsToAddBefore );
+                auto dtorStructType = new ast::StructInstType( global.dtorStruct );
+                // what does this do???
+                dtorStructType->params.push_back( new ast::TypeExpr(loc, new ast::VoidType() ) );
+                // cast destructor pointer to void (*)(void *), to silence GCC incompatible pointer warnings
+                auto dtorFtype = new ast::FunctionType();
+                dtorFtype->params.push_back( new ast::PointerType(new ast::VoidType( ) ) );
+                auto dtorType = new ast::PointerType( dtorFtype );
+                static UniqueName namer( "_ret_dtor" );
+                auto retDtor = new ast::ObjectDecl(loc, namer.newName(), dtorStructType, new ast::ListInit(loc, { new ast::SingleInit(loc, ast::ConstantExpr::null(loc) ), new ast::SingleInit(loc, new ast::CastExpr( new ast::VariableExpr(loc, dtorFunc ), dtorType ) ) } ) );
+                retDtor->attributes.push_back( new ast::Attribute( "cleanup", { new ast::VariableExpr(loc, global.dtorDestroy ) } ) );
+                stmtsToAddBefore.push_back( new ast::DeclStmt(loc, retDtor ) );
+                if ( arg ) {
+                        auto member = new ast::MemberExpr(loc, global.dtorStruct->members.front().strict_as<ast::DeclWithType>(), new ast::VariableExpr(loc, retDtor ) );
+                        auto object = new ast::CastExpr( new ast::AddressExpr( new ast::VariableExpr(loc, ret ) ), new ast::PointerType(new ast::VoidType() ) );
+                        ast::Expr * assign = createBitwiseAssignment( member, object );
+                        return new ast::CommaExpr(loc, new ast::CommaExpr(loc, arg, assign ), new ast::VariableExpr(loc, ret ) );
+                }
+                return nullptr;
+                // impCpCtorExpr->get_dtors().push_front( makeCtorDtor( "^?{}", ret ) );
+        }
+        const ast::Expr * ResolveCopyCtors::postvisit( const ast::ImplicitCopyCtorExpr *impCpCtorExpr ) {
+                CP_CTOR_PRINT( std::cerr << "ResolveCopyCtors: " << impCpCtorExpr << std::endl; )
+                ast::ApplicationExpr * appExpr = mutate(impCpCtorExpr->callExpr.get());
+                const ast::ObjectDecl * returnDecl = nullptr;
+                const CodeLocation loc = appExpr->location;
+                // take each argument and attempt to copy construct it.
+                auto ftype = GenPoly::getFunctionType( appExpr->func->result );
+                assert( ftype );
+                auto & params = ftype->params;
+                auto iter = params.begin();
+                for ( auto & arg : appExpr->args ) {
+                        const ast::Type * formal = nullptr;
+                        if ( iter != params.end() ) { // does not copy construct C-style variadic arguments
+                                // DeclarationWithType * param = *iter++;
+                                formal = *iter++;
+                        }
+                        arg = copyConstructArg( arg, impCpCtorExpr, formal );
+                } // for
+                // each return value from the call needs to be connected with an ObjectDecl at the call site, which is
+                // initialized with the return value and is destructed later
+                // xxx - handle named return values?
+                const ast::Type * result = appExpr->result;
+                if ( ! result->isVoid() ) {
+                        static UniqueName retNamer("_tmp_cp_ret");
+                        auto subResult = env->apply( result ).node;
+                        auto ret = new ast::ObjectDecl(loc, retNamer.newName(), subResult, nullptr );
+                        auto mutType = mutate(ret->type.get());
+                        mutType->set_const( false );
+                        ret->type = mutType;
+                        returnDecl = ret;
+                        stmtsToAddBefore.push_back( new ast::DeclStmt(loc, ret ) );
+                        CP_CTOR_PRINT( std::cerr << "makeCtorDtor for a return" << std::endl; )
+                } // for
+                CP_CTOR_PRINT( std::cerr << "after Resolving: " << impCpCtorExpr << std::endl; )
+                // ------------------------------------------------------
+                CP_CTOR_PRINT( std::cerr << "Coming out the back..." << impCpCtorExpr << std::endl; )
+                // detach fields from wrapper node so that it can be deleted without deleting too much
+                // xxx - actual env might be somewhere else, need to keep invariant
+                // deletion of wrapper should be handled by pass template now
+                // impCpCtorExpr->callExpr = nullptr;
+                assert (appExpr->env == nullptr);
+                appExpr->env = impCpCtorExpr->env;
+                // std::swap( impCpCtorExpr->env, appExpr->env );
+                // assert( impCpCtorExpr->env == nullptr );
+                // delete impCpCtorExpr;
+                if ( returnDecl ) {
+                        ast::Expr * assign = createBitwiseAssignment( new ast::VariableExpr(loc, returnDecl ), appExpr );
+                        if ( ! dynamic_cast< const ast::ReferenceType * >( result ) ) {
+                                // destructing reference returns is bad because it can cause multiple destructor calls to the same object - the returned object is not a temporary
+                                assign = destructRet( returnDecl, assign );
+                                assert(assign);
+                        } else {
+                                assign = new ast::CommaExpr(loc, assign, new ast::VariableExpr(loc, returnDecl ) );
+                        }
+                        // move env from appExpr to retExpr
+                        // std::swap( assign->env, appExpr->env );
+                        assign->env = appExpr->env;
+                        // actual env is handled by common routine that replaces WithTypeSubstitution
+                        return postvisit((const ast::Expr *)assign);
+                } else {
+                        return postvisit((const ast::Expr *)appExpr);
+                } // if
+        }
+        const ast::StmtExpr * ResolveCopyCtors::previsit( const ast::StmtExpr * _stmtExpr ) {
+                // function call temporaries should be placed at statement-level, rather than nested inside of a new statement expression,
+                // since temporaries can be shared across sub-expressions, e.g.
+                //   [A, A] f();       // decl
+                //   g([A] x, [A] y);  // decl
+                //   g(f());           // call
+                // f is executed once, so the return temporary is shared across the tuple constructors for x and y.
+                // Explicitly mutating children instead of mutating the inner compound statement forces the temporaries to be added
+                // to the outer context, rather than inside of the statement expression.
+                // call the common routine that replaces WithTypeSubstitution
+                previsit((const ast::Expr *) _stmtExpr);
+                visit_children = false;
+                const CodeLocation loc = _stmtExpr->location;
+                assert( env );
+                symtab.enterScope();
+                // visit all statements
+                auto stmtExpr = mutate(_stmtExpr);
+                auto mutStmts = mutate(stmtExpr->stmts.get());
+                auto & stmts = mutStmts->kids;
+                for ( auto & stmt : stmts ) {
+                        stmt = stmt->accept( *visitor );
+                } // for
+                stmtExpr->stmts = mutStmts;
+                symtab.leaveScope();
+                assert( stmtExpr->result );
+                // const ast::Type * result = stmtExpr->result;
+                if ( ! stmtExpr->result->isVoid() ) {
+                        static UniqueName retNamer("_tmp_stmtexpr_ret");
+                        // result = result->clone();
+                        auto result = env->apply( stmtExpr->result.get() ).node;
+                        if ( ! InitTweak::isConstructable( result ) ) {
+                                // delete result;
+                                return stmtExpr;
+                        }
+                        auto mutResult = result.get_and_mutate();
+                        mutResult->set_const(false);
+                        // create variable that will hold the result of the stmt expr
+                        auto ret = new ast::ObjectDecl(loc, retNamer.newName(), mutResult, nullptr );
+                        stmtsToAddBefore.push_back( new ast::DeclStmt(loc, ret ) );
+                        assertf(
+                                stmtExpr->resultExpr,
+                                "Statement-Expression should have a resulting expression at %s:%d",
+                                stmtExpr->location.filename.c_str(),
+                                stmtExpr->location.first_line
+                        );
+                        const ast::ExprStmt * last = stmtExpr->resultExpr;
+                        // xxx - if this is non-unique, need to copy while making resultExpr ref
+                        assertf(last->unique(), "attempt to modify weakly shared statement");
+                        auto mutLast = mutate(last);
+                        // above assertion means in-place mutation is OK
+                        try {
+                                mutLast->expr = makeCtorDtor( "?{}", ret, mutLast->expr );
+                        } catch(...) {
+                                std::cerr << "*CFA internal error: ";
+                                std::cerr << "can't resolve implicit constructor";
+                                std::cerr << " at " << stmtExpr->location.filename;
+                                std::cerr << ":" << stmtExpr->location.first_line << std::endl;
+                                abort();
+                        }
+                        // add destructors after current statement
+                        stmtsToAddAfter.push_back( new ast::ExprStmt(loc, makeCtorDtor( "^?{}", ret ) ) );
+                        // must have a non-empty body, otherwise it wouldn't have a result
+                        assert( ! stmts.empty() );
+                        // if there is a return decl, add a use as the last statement; will not have return decl on non-constructable returns
+                        stmts.push_back( new ast::ExprStmt(loc, new ast::VariableExpr(loc, ret ) ) );
+                } // if
+                assert( stmtExpr->returnDecls.empty() );
+                assert( stmtExpr->dtors.empty() );
+                return stmtExpr;
+        }
+        // to prevent warnings ('_unq0' may be used uninitialized in this function),
+        // insert an appropriate zero initializer for UniqueExpr temporaries.
+        ast::Init * makeInit( const ast::Type * t, CodeLocation const & loc ) {
+                if ( auto inst = dynamic_cast< const ast::StructInstType * >( t ) ) {
+                        // initizer for empty struct must be empty
+                        if ( inst->base->members.empty() ) {
+                                return new ast::ListInit( loc, {} );
+                        }
+                } else if ( auto inst = dynamic_cast< const ast::UnionInstType * >( t ) ) {
+                        // initizer for empty union must be empty
+                        if ( inst->base->members.empty() ) {
+                                return new ast::ListInit( loc, {} );
+                        }
+                }
+                return new ast::ListInit( loc, {
+                        new ast::SingleInit( loc, ast::ConstantExpr::from_int( loc, 0 ) )
+                } );
+        }
+        const ast::UniqueExpr * ResolveCopyCtors::previsit( const ast::UniqueExpr * unqExpr ) {
+                visit_children = false;
+                // xxx - hack to prevent double-handling of unique exprs, otherwise too many temporary variables and destructors are generated
+                static std::unordered_map< int, const ast::UniqueExpr * > unqMap;
+                auto mutExpr = mutate(unqExpr);
+                if ( ! unqMap.count( unqExpr->id ) ) {
+                        // resolve expr and find its
+                        auto impCpCtorExpr = mutExpr->expr.as<ast::ImplicitCopyCtorExpr>();
+                        // PassVisitor<ResolveCopyCtors> fixer;
+                        mutExpr->expr = mutExpr->expr->accept( *visitor );
+                        // it should never be necessary to wrap a void-returning expression in a UniqueExpr - if this assumption changes, this needs to be rethought
+                        assert( unqExpr->result );
+                        if ( impCpCtorExpr ) {
+                                auto comma = unqExpr->expr.strict_as<ast::CommaExpr>();
+                                auto var = comma->arg2.strict_as<ast::VariableExpr>();
+                                // note the variable used as the result from the call
+                                mutExpr->var = var;
+                        } else {
+                                // expr isn't a call expr, so create a new temporary variable to use to hold the value of the unique expression
+                                mutExpr->object = new ast::ObjectDecl( mutExpr->location, toString("_unq", mutExpr->id), mutExpr->result, makeInit( mutExpr->result, mutExpr->location ) );
+                                mutExpr->var = new ast::VariableExpr( mutExpr->location, mutExpr->object );
+                        }
+                        unqMap[mutExpr->id] = mutExpr;
+                } else {
+                        // take data from other UniqueExpr to ensure consistency
+                        // delete unqExpr->get_expr();
+                        mutExpr->expr = unqMap[mutExpr->id]->expr;
+                        // delete unqExpr->result;
+                        mutExpr->result = mutExpr->expr->result;
+                }
+                return mutExpr;
+        }
+        const ast::DeclWithType * FixInit::postvisit( const ast::ObjectDecl *_objDecl ) {
+                const CodeLocation loc = _objDecl->location;
+                // since this removes the init field from objDecl, it must occur after children are mutated (i.e. postvisit)
+                if ( ast::ptr<ast::ConstructorInit> ctorInit = _objDecl->init.as<ast::ConstructorInit>() ) {
+                        auto objDecl = mutate(_objDecl);
+                        // could this be non-unique?
+                        if (objDecl != _objDecl) {
+                                std::cerr << "FixInit: non-unique object decl " << objDecl->location << objDecl->name << std::endl;
+                        }
+                        // a decision should have been made by the resolver, so ctor and init are not both non-NULL
+                        assert( ! ctorInit->ctor || ! ctorInit->init );
+                        if ( const ast::Stmt * ctor = ctorInit->ctor ) {
+                                if ( objDecl->storage.is_static ) {
+                                        addDataSectionAttribute(objDecl);
+                                        // originally wanted to take advantage of gcc nested functions, but
+                                        // we get memory errors with this approach. To remedy this, the static
+                                        // variable is hoisted when the destructor needs to be called.
+                                        //
+                                        // generate:
+                                        // static T __objName_static_varN;
+                                        // void __objName_dtor_atexitN() {
+                                        //   __dtor__...;
+                                        // }
+                                        // int f(...) {
+                                        //   ...
+                                        //   static bool __objName_uninitialized = true;
+                                        //   if (__objName_uninitialized) {
+                                        //     __ctor(__objName);
+                                        //     __objName_uninitialized = false;
+                                        //     atexit(__objName_dtor_atexitN);
+                                        //   }
+                                        //   ...
+                                        // }
+                                        static UniqueName dtorCallerNamer( "_dtor_atexit" );
+                                        // static bool __objName_uninitialized = true
+                                        auto boolType = new ast::BasicType( ast::BasicType::Kind::Bool );
+                                        auto boolInitExpr = new ast::SingleInit(loc, ast::ConstantExpr::from_int(loc, 1 ) );
+                                        auto isUninitializedVar = new ast::ObjectDecl(loc, objDecl->mangleName + "_uninitialized", boolType, boolInitExpr, ast::Storage::Static, ast::Linkage::Cforall);
+                                        isUninitializedVar->fixUniqueId();
+                                        // __objName_uninitialized = false;
+                                        auto setTrue = new ast::UntypedExpr(loc, new ast::NameExpr(loc, "?=?" ) );
+                                        setTrue->args.push_back( new ast::VariableExpr(loc, isUninitializedVar ) );
+                                        setTrue->args.push_back( ast::ConstantExpr::from_int(loc, 0 ) );
+                                        // generate body of if
+                                        auto initStmts = new ast::CompoundStmt(loc);
+                                        auto & body = initStmts->kids;
+                                        body.push_back( ctor );
+                                        body.push_back( new ast::ExprStmt(loc, setTrue ) );
+                                        // put it all together
+                                        auto ifStmt = new ast::IfStmt(loc, new ast::VariableExpr(loc, isUninitializedVar ), initStmts, 0 );
+                                        stmtsToAddAfter.push_back( new ast::DeclStmt(loc, isUninitializedVar ) );
+                                        stmtsToAddAfter.push_back( ifStmt );
+                                        const ast::Stmt * dtor = ctorInit->dtor;
+                                        // these should be automatically managed once reassigned
+                                        // objDecl->set_init( nullptr );
+                                        // ctorInit->set_ctor( nullptr );
+                                        // ctorInit->set_dtor( nullptr );
+                                        if ( dtor ) {
+                                                // if the object has a non-trivial destructor, have to
+                                                // hoist it and the object into the global space and
+                                                // call the destructor function with atexit.
+                                                // Statement * dtorStmt = dtor->clone();
+                                                // void __objName_dtor_atexitN(...) {...}
+                                                ast::FunctionDecl * dtorCaller = new ast::FunctionDecl(loc, objDecl->mangleName + dtorCallerNamer.newName(), {}, {}, {}, new ast::CompoundStmt(loc, {dtor}), ast::Storage::Static, ast::Linkage::C );
+                                                dtorCaller->fixUniqueId();
+                                                // dtorCaller->stmts->push_back( dtor );
+                                                // atexit(dtor_atexit);
+                                                auto callAtexit = new ast::UntypedExpr(loc, new ast::NameExpr(loc, "atexit" ) );
+                                                callAtexit->args.push_back( new ast::VariableExpr(loc, dtorCaller ) );
+                                                body.push_back( new ast::ExprStmt(loc, callAtexit ) );
+                                                // hoist variable and dtor caller decls to list of decls that will be added into global scope
+                                                staticDtorDecls.push_back( objDecl );
+                                                staticDtorDecls.push_back( dtorCaller );
+                                                // need to rename object uniquely since it now appears
+                                                // at global scope and there could be multiple function-scoped
+                                                // static variables with the same name in different functions.
+                                                // Note: it isn't sufficient to modify only the mangleName, because
+                                                // then subsequent Indexer passes can choke on seeing the object's name
+                                                // if another object has the same name and type. An unfortunate side-effect
+                                                // of renaming the object is that subsequent NameExprs may fail to resolve,
+                                                // but there shouldn't be any remaining past this point.
+                                                static UniqueName staticNamer( "_static_var" );
+                                                objDecl->name = objDecl->name + staticNamer.newName();
+                                                objDecl->mangleName = Mangle::mangle( objDecl );
+                                                objDecl->init = nullptr;
+                                                // xxx - temporary hack: need to return a declaration, but want to hoist the current object out of this scope
+                                                // create a new object which is never used
+                                                static UniqueName dummyNamer( "_dummy" );
+                                                auto dummy = new ast::ObjectDecl(loc, dummyNamer.newName(), new ast::PointerType(new ast::VoidType()), nullptr, ast::Storage::Static, ast::Linkage::Cforall, 0, { new ast::Attribute("unused") } );
+                                                // delete ctorInit;
+                                                return dummy;
+                                        } else {
+                                                objDecl->init = nullptr;
+                                                return objDecl;
+                                        }
+                                } else {
+                                        auto implicit = strict_dynamic_cast< const ast::ImplicitCtorDtorStmt * > ( ctor );
+                                        auto ctorStmt = implicit->callStmt.as<ast::ExprStmt>();
+                                        const ast::ApplicationExpr * ctorCall = nullptr;
+                                        if ( ctorStmt && (ctorCall = isIntrinsicCallExpr( ctorStmt->expr )) && ctorCall->args.size() == 2 ) {
+                                                // clean up intrinsic copy constructor calls by making them into SingleInits
+                                                const ast::Expr * ctorArg = ctorCall->args.back();
+                                                // ctorCall should be gone afterwards
+                                                auto mutArg = mutate(ctorArg);
+                                                mutArg->env = ctorCall->env;
+                                                // std::swap( ctorArg->env, ctorCall->env );
+                                                objDecl->init = new ast::SingleInit(loc, mutArg );
+                                                // ctorCall->args.pop_back();
+                                        } else {
+                                                stmtsToAddAfter.push_back( ctor );
+                                                objDecl->init = nullptr;
+                                                // ctorInit->ctor = nullptr;
+                                        }
+                                        const ast::Stmt * dtor = ctorInit->dtor;
+                                        if ( dtor ) {
+                                                auto implicit = strict_dynamic_cast< const ast::ImplicitCtorDtorStmt * >( dtor );
+                                                const ast::Stmt * dtorStmt = implicit->callStmt;
+                                                // don't need to call intrinsic dtor, because it does nothing, but
+                                                // non-intrinsic dtors must be called
+                                                if ( ! isIntrinsicSingleArgCallStmt( dtorStmt ) ) {
+                                                        // set dtor location to the object's location for error messages
+                                                        auto dtorFunc = getDtorFunc( objDecl, dtorStmt, stmtsToAddBefore );
+                                                        objDecl->attributes.push_back( new ast::Attribute( "cleanup", { new ast::VariableExpr(loc, dtorFunc ) } ) );
+                                                        // ctorInit->dtor = nullptr;
+                                                } // if
+                                        }
+                                } // if
+                        } else if ( const ast::Init * init = ctorInit->init ) {
+                                objDecl->init = init;
+                                // ctorInit->init = nullptr;
+                        } else {
+                                // no constructor and no initializer, which is okay
+                                objDecl->init = nullptr;
+                        } // if
+                        // delete ctorInit;
+                        return objDecl;
+                } // if
+                return _objDecl;
+        }
+        void ObjDeclCollector::previsit( const ast::CompoundStmt * ) {
+                GuardValue( curVars );
+        }
+        void ObjDeclCollector::previsit( const ast::DeclStmt * stmt ) {
+                // keep track of all variables currently in scope
+                if ( auto objDecl = stmt->decl.as<ast::ObjectDecl>() ) {
+                        curVars.push_back( objDecl );
+                } // if
+        }
+        void LabelFinder::previsit( const ast::Stmt * stmt ) {
+                // for each label, remember the variables in scope at that label.
+                for ( auto l : stmt->labels ) {
+                        vars[l] = curVars;
+                } // for
+        }
+        void LabelFinder::previsit( const ast::CompoundStmt * stmt ) {
+                previsit( (const ast::Stmt *) stmt );
+                Parent::previsit( stmt );
+        }
+        void LabelFinder::previsit( const ast::DeclStmt * stmt ) {
+                previsit( (const ast::Stmt *)stmt );
+                Parent::previsit( stmt );
+        }
+        void InsertDtors::previsit( const ast::FunctionDecl * funcDecl ) {
+                // each function needs to have its own set of labels
+                GuardValue( labelVars );
+                labelVars.clear();
+                // LabelFinder does not recurse into FunctionDecl, so need to visit
+                // its children manually.
+                if (funcDecl->type) funcDecl->type->accept(finder);
+                // maybeAccept( funcDecl->type, finder );
+                if (funcDecl->stmts) funcDecl->stmts->accept(finder) ;
+                // all labels for this function have been collected, insert destructors as appropriate via implicit recursion.
+        }
+        // Handle break/continue/goto in the same manner as C++.  Basic idea: any objects that are in scope at the
+        // BranchStmt but not at the labelled (target) statement must be destructed.  If there are any objects in scope
+        // at the target location but not at the BranchStmt then those objects would be uninitialized so notify the user
+        // of the error.  See C++ Reference 6.6 Jump Statements for details.
+        void InsertDtors::handleGoto( const ast::BranchStmt * stmt ) {
+                // can't do anything for computed goto
+                if ( stmt->computedTarget ) return;
+                assertf( stmt->target.name != "", "BranchStmt missing a label: %s", toString( stmt ).c_str() );
+                // S_L = lvars = set of objects in scope at label definition
+                // S_G = curVars = set of objects in scope at goto statement
+                ObjectSet & lvars = labelVars[ stmt->target ];
+                DTOR_PRINT(
+                        std::cerr << "at goto label: " << stmt->target.name << std::endl;
+                        std::cerr << "S_G = " << printSet( curVars ) << std::endl;
+                        std::cerr << "S_L = " << printSet( lvars ) << std::endl;
+                )
+                // std::set_difference requires that the inputs be sorted.
+                lvars.sort();
+                curVars.sort();
+                ObjectSet diff;
+                // S_L-S_G results in set of objects whose construction is skipped - it's an error if this set is non-empty
+                std::set_difference( lvars.begin(), lvars.end(), curVars.begin(), curVars.end(), std::inserter( diff, diff.begin() ) );
+                DTOR_PRINT(
+                        std::cerr << "S_L-S_G = " << printSet( diff ) << std::endl;
+                )
+                if ( ! diff.empty() ) {
+                        SemanticError( stmt, std::string("jump to label '") + stmt->target.name + "' crosses initialization of " + (*diff.begin())->name + " " );
+                } // if
+        }
+        void InsertDtors::previsit( const ast::BranchStmt * stmt ) {
+                switch( stmt->kind ) {
+                case ast::BranchStmt::Continue:
+                case ast::BranchStmt::Break:
+                        // could optimize the break/continue case, because the S_L-S_G check is unnecessary (this set should
+                        // always be empty), but it serves as a small sanity check.
+                case ast::BranchStmt::Goto:
+                        handleGoto( stmt );
+                        break;
+                default:
+                        assert( false );
+                } // switch
+        }
+        bool checkWarnings( const ast::FunctionDecl * funcDecl ) {
+                // only check for warnings if the current function is a user-defined
+                // constructor or destructor
+                if ( ! funcDecl ) return false;
+                if ( ! funcDecl->stmts ) return false;
+                return CodeGen::isCtorDtor( funcDecl->name ) && ! funcDecl->linkage.is_overrideable;
+        }
+        void GenStructMemberCalls::previsit( const ast::FunctionDecl * funcDecl ) {
+                GuardValue( function );
+                GuardValue( unhandled );
+                GuardValue( usedUninit );
+                GuardValue( thisParam );
+                GuardValue( isCtor );
+                GuardValue( structDecl );
+                errors = SemanticErrorException();  // clear previous errors
+                // need to start with fresh sets
+                unhandled.clear();
+                usedUninit.clear();
+                function = mutate(funcDecl);
+                // could this be non-unique?
+                if (function != funcDecl) {
+                        std::cerr << "GenStructMemberCalls: non-unique FunctionDecl " << funcDecl->location << funcDecl->name << std::endl;
+                }
+                isCtor = CodeGen::isConstructor( function->name );
+                if ( checkWarnings( function ) ) {
+                        // const ast::FunctionType * type = function->type;
+                        // assert( ! type->params.empty() );
+                        thisParam = function->params.front().strict_as<ast::ObjectDecl>();
+                        auto thisType = getPointerBase( thisParam->get_type() );
+                        auto structType = dynamic_cast< const ast::StructInstType * >( thisType );
+                        if ( structType ) {
+                                structDecl = structType->base;
+                                for ( auto & member : structDecl->members ) {
+                                        if ( auto field = member.as<ast::ObjectDecl>() ) {
+                                                // record all of the struct type's members that need to be constructed or
+                                                // destructed by the end of the function
+                                                unhandled.insert( field );
+                                        }
+                                }
+                        }
+                }
+        }
+        const ast::DeclWithType * GenStructMemberCalls::postvisit( const ast::FunctionDecl * funcDecl ) {
+                // remove the unhandled objects from usedUninit, because a call is inserted
+                // to handle them - only objects that are later constructed are used uninitialized.
+                std::map< const ast::DeclWithType *, CodeLocation > diff;
+                // need the comparator since usedUninit and unhandled have different types
+                struct comp_t {
+                        typedef decltype(usedUninit)::value_type usedUninit_t;
+                        typedef decltype(unhandled)::value_type unhandled_t;
+                        bool operator()(usedUninit_t x, unhandled_t y) { return x.first < y; }
+                        bool operator()(unhandled_t x, usedUninit_t y) { return x < y.first; }
+                } comp;
+                std::set_difference( usedUninit.begin(), usedUninit.end(), unhandled.begin(), unhandled.end(), std::inserter( diff, diff.begin() ), comp );
+                for ( auto p : diff ) {
+                        auto member = p.first;
+                        auto loc = p.second;
+                        // xxx - make error message better by also tracking the location that the object is constructed at?
+                        emit( loc, "in ", function->name, ", field ", member->name, " used before being constructed" );
+                }
+                const CodeLocation loc = funcDecl->location;
+                if ( ! unhandled.empty() ) {
+                        auto mutStmts = function->stmts.get_and_mutate();
+                        // need to explicitly re-add function parameters to the indexer in order to resolve copy constructors
+                        auto guard = makeFuncGuard( [this]() { symtab.enterScope(); }, [this]() { symtab.leaveScope(); } );
+                        symtab.addFunction( function );
+                        auto global = transUnit().global;
+                        // need to iterate through members in reverse in order for
+                        // ctor/dtor statements to come out in the right order
+                        for ( auto & member : reverseIterate( structDecl->members ) ) {
+                                auto field = member.as<ast::ObjectDecl>();
+                                // skip non-DWT members
+                                if ( ! field ) continue;
+                                // skip non-constructable members
+                                if ( ! tryConstruct( field ) ) continue;
+                                // skip handled members
+                                if ( ! unhandled.count( field ) ) continue;
+                                // insert and resolve default/copy constructor call for each field that's unhandled
+                                // std::list< const ast::Stmt * > stmt;
+                                ast::Expr * arg2 = nullptr;
+                                if ( function->name == "?{}" && isCopyFunction( function ) ) {
+                                        // if copy ctor, need to pass second-param-of-this-function.field
+                                        // std::list< DeclarationWithType * > & params = function->get_functionType()->get_parameters();
+                                        assert( function->params.size() == 2 );
+                                        arg2 = new ast::MemberExpr(funcDecl->location, field, new ast::VariableExpr(funcDecl->location, function->params.back() ) );
+                                }
+                                InitExpander_new srcParam( arg2 );
+                                // cast away reference type and construct field.
+                                ast::Expr * thisExpr = new ast::CastExpr(funcDecl->location, new ast::VariableExpr(funcDecl->location, thisParam ), thisParam->get_type()->stripReferences());
+                                ast::Expr * memberDest = new ast::MemberExpr(funcDecl->location, field, thisExpr );
+                                ast::ptr<ast::Stmt> callStmt = SymTab::genImplicitCall( srcParam, memberDest, loc, function->name, field, static_cast<SymTab::LoopDirection>(isCtor) );
+                                if ( callStmt ) {
+                                        // auto & callStmt = stmt.front();
+                                        try {
+                                                callStmt = callStmt->accept( *visitor );
+                                                if ( isCtor ) {
+                                                        mutStmts->push_front( callStmt );
+                                                } else { // TODO: don't generate destructor function/object for intrinsic calls
+                                                        // destructor statements should be added at the end
+                                                        // function->get_statements()->push_back( callStmt );
+                                                        // Optimization: do not need to call intrinsic destructors on members
+                                                        if ( isIntrinsicSingleArgCallStmt( callStmt ) ) continue;
+                                                        // __Destructor _dtor0 = { (void *)&b.a1, (void (*)(void *)_destroy_A };
+                                                        std::list< ast::ptr<ast::Stmt> > stmtsToAdd;
+                                                        static UniqueName memberDtorNamer = { "__memberDtor" };
+                                                        assertf( global.dtorStruct, "builtin __Destructor not found." );
+                                                        assertf( global.dtorDestroy, "builtin __destroy_Destructor not found." );
+                                                        ast::Expr * thisExpr = new ast::CastExpr( new ast::AddressExpr( new ast::VariableExpr(loc, thisParam ) ), new ast::PointerType( new ast::VoidType(), ast::CV::Qualifiers() ) );
+                                                        ast::Expr * dtorExpr = new ast::VariableExpr(loc, getDtorFunc( thisParam, callStmt, stmtsToAdd ) );
+                                                        // cast destructor pointer to void (*)(void *), to silence GCC incompatible pointer warnings
+                                                        auto dtorFtype = new ast::FunctionType();
+                                                        dtorFtype->params.emplace_back( new ast::PointerType( new ast::VoidType() ) );
+                                                        auto dtorType = new ast::PointerType( dtorFtype );
+                                                        auto destructor = new ast::ObjectDecl(loc, memberDtorNamer.newName(), new ast::StructInstType( global.dtorStruct ), new ast::ListInit(loc, { new ast::SingleInit(loc, thisExpr ), new ast::SingleInit(loc, new ast::CastExpr( dtorExpr, dtorType ) ) } ) );
+                                                        destructor->attributes.push_back( new ast::Attribute( "cleanup", { new ast::VariableExpr( loc, global.dtorDestroy ) } ) );
+                                                        mutStmts->push_front( new ast::DeclStmt(loc, destructor ) );
+                                                        mutStmts->kids.splice( mutStmts->kids.begin(), stmtsToAdd );
+                                                }
+                                        } catch ( SemanticErrorException & error ) {
+                                                emit( funcDecl->location, "in ", function->name , ", field ", field->name, " not explicitly ", isCtor ? "constructed" : "destructed",  " and no ", isCtor ? "default constructor" : "destructor", " found" );
+                                        }
+                                }
+                        }
+                        function->stmts = mutStmts;
+                }
+                if (! errors.isEmpty()) {
+                        throw errors;
+                }
+                // return funcDecl;
+                return function;
+        }
+        /// true if expr is effectively just the 'this' parameter
+        bool isThisExpression( const ast::Expr * expr, const ast::DeclWithType * thisParam ) {
+                // TODO: there are more complicated ways to pass 'this' to a constructor, e.g. &*, *&, etc.
+                if ( auto varExpr = dynamic_cast< const ast::VariableExpr * >( expr ) ) {
+                        return varExpr->var == thisParam;
+                } else if ( auto castExpr = dynamic_cast< const ast::CastExpr * > ( expr ) ) {
+                        return isThisExpression( castExpr->arg, thisParam );
+                }
+                return false;
+        }
+        /// returns a MemberExpr if expr is effectively just member access on the 'this' parameter, else nullptr
+        const ast::MemberExpr * isThisMemberExpr( const ast::Expr * expr, const ast::DeclWithType * thisParam ) {
+                if ( auto memberExpr = dynamic_cast< const ast::MemberExpr * >( expr ) ) {
+                        if ( isThisExpression( memberExpr->aggregate, thisParam ) ) {
+                                return memberExpr;
+                        }
+                } else if ( auto castExpr = dynamic_cast< const ast::CastExpr * >( expr ) ) {
+                        return isThisMemberExpr( castExpr->arg, thisParam );
+                }
+                return nullptr;
+        }
+        void GenStructMemberCalls::previsit( const ast::ApplicationExpr * appExpr ) {
+                if ( ! checkWarnings( function ) ) {
+                        visit_children = false;
+                        return;
+                }
+                std::string fname = getFunctionName( appExpr );
+                if ( fname == function->name ) {
+                        // call to same kind of function
+                        const ast::Expr * firstParam = appExpr->args.front();
+                        if ( isThisExpression( firstParam, thisParam ) ) {
+                                // if calling another constructor on thisParam, assume that function handles
+                                // all members - if it doesn't a warning will appear in that function.
+                                unhandled.clear();
+                        } else if ( auto memberExpr = isThisMemberExpr( firstParam, thisParam ) ) {
+                                // if first parameter is a member expression on the this parameter,
+                                // then remove the member from unhandled set.
+                                if ( isThisExpression( memberExpr->aggregate, thisParam ) ) {
+                                        unhandled.erase( memberExpr->member );
+                                }
+                        }
+                }
+        }
+        void GenStructMemberCalls::previsit( const ast::MemberExpr * memberExpr ) {
+                if ( ! checkWarnings( function ) || ! isCtor ) {
+                        visit_children = false;
+                        return;
+                }
+                if ( isThisExpression( memberExpr->aggregate, thisParam ) ) {
+                        if ( unhandled.count( memberExpr->member ) ) {
+                                // emit a warning because a member was used before it was constructed
+                                usedUninit.insert( { memberExpr->member, memberExpr->location } );
+                        }
+                }
+        }
+        template< typename... Params >
+        void GenStructMemberCalls::emit( CodeLocation loc, const Params &... params ) {
+                SemanticErrorException err( loc, toString( params... ) );
+                errors.append( err );
+        }
+        const ast::Expr * GenStructMemberCalls::postvisit( const ast::UntypedExpr * untypedExpr ) {
+                // xxx - functions returning ast::ptr seems wrong...
+                auto res = ResolvExpr::findVoidExpression( untypedExpr, { symtab, transUnit().global } );
+                return res.release();
+        }
+        void InsertImplicitCalls::previsit(const ast::UniqueExpr * unqExpr) {
+                if (visitedIds.count(unqExpr->id)) visit_children = false;
+                else visitedIds.insert(unqExpr->id);
+        }
+        const ast::Expr * FixCtorExprs::postvisit( const ast::ConstructorExpr * ctorExpr ) {
+                const CodeLocation loc = ctorExpr->location;
+                static UniqueName tempNamer( "_tmp_ctor_expr" );
+                // xxx - is the size check necessary?
+                assert( ctorExpr->result && ctorExpr->result->size() == 1 );
+                // xxx - this can be TupleAssignExpr now. Need to properly handle this case.
+                // take possession of expr and env
+                ast::ptr<ast::ApplicationExpr> callExpr = ctorExpr->callExpr.strict_as<ast::ApplicationExpr>();
+                ast::ptr<ast::TypeSubstitution> env = ctorExpr->env;
+                // ctorExpr->set_callExpr( nullptr );
+                // ctorExpr->set_env( nullptr );
+                // xxx - ideally we would reuse the temporary generated from the copy constructor passes from within firstArg if it exists and not generate a temporary if it's unnecessary.
+                auto tmp = new ast::ObjectDecl(loc, tempNamer.newName(), callExpr->args.front()->result );
+                declsToAddBefore.push_back( tmp );
+                // build assignment and replace constructor's first argument with new temporary
+                auto mutCallExpr = callExpr.get_and_mutate();
+                const ast::Expr * firstArg = callExpr->args.front();
+                ast::Expr * assign = new ast::UntypedExpr(loc, new ast::NameExpr(loc, "?=?" ), { new ast::AddressExpr(loc, new ast::VariableExpr(loc, tmp ) ), new ast::AddressExpr( firstArg ) } );
+                firstArg = new ast::VariableExpr(loc, tmp );
+                mutCallExpr->args.front() = firstArg;
+                // resolve assignment and dispose of new env
+                auto resolved = ResolvExpr::findVoidExpression( assign, { symtab, transUnit().global } );
+                auto mut = resolved.get_and_mutate();
+                assertf(resolved.get() == mut, "newly resolved expression must be unique");
+                mut->env = nullptr;
+                // for constructor expr:
+                //   T x;
+                //   x{};
+                // results in:
+                //   T x;
+                //   T & tmp;
+                //   &tmp = &x, ?{}(tmp), tmp
+                ast::CommaExpr * commaExpr = new ast::CommaExpr(loc, resolved, new ast::CommaExpr(loc, mutCallExpr, new ast::VariableExpr(loc, tmp ) ) );
+                commaExpr->env = env;
+                return commaExpr;
+        }
+} // namespace
 } // namespace InitTweak

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src/InitTweak/FixInitNew.cpp

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