source: src/InitTweak/FixInit.cpp @ 508cff0

#include "FixInit.hpp"

#include <stddef.h>                    // for NULL
#include <algorithm>                   // for set_difference, copy_if
#include <cassert>                     // for assert, strict_dynamic_cast
#include <iostream>                    // for operator<<, ostream, basic_ost...
#include <iterator>                    // for insert_iterator, back_inserter
#include <list>                        // for _List_iterator, list, list<>::...
#include <map>                         // for _Rb_tree_iterator, _Rb_tree_co...
#include <memory>                      // for allocator_traits<>::value_type
#include <set>                         // for set, set<>::value_type
#include <unordered_map>               // for unordered_map, unordered_map<>...
#include <unordered_set>               // for unordered_set
#include <utility>                     // for pair

#include "AST/DeclReplacer.hpp"
#include "AST/Expr.hpp"
#include "AST/Inspect.hpp"             // for getFunction, getPointerBase, g...
#include "AST/Node.hpp"
#include "AST/Pass.hpp"
#include "AST/Print.hpp"
#include "AST/SymbolTable.hpp"
#include "AST/Type.hpp"
#include "CodeGen/OperatorTable.hpp"   // for isConstructor, isCtorDtor, isD...
#include "Common/SemanticError.hpp"    // for SemanticError
#include "Common/ToString.hpp"         // for toCString
#include "Common/UniqueName.hpp"       // for UniqueName
#include "FixGlobalInit.hpp"           // for fixGlobalInit
#include "GenInit.hpp"                 // for genCtorDtor
#include "GenPoly/GenPoly.hpp"         // for getFunctionType
#include "ResolvExpr/Resolver.hpp"     // for findVoidExpression
#include "ResolvExpr/Unify.hpp"        // for typesCompatible
#include "SymTab/GenImplicitCall.hpp"  // for genImplicitCall

bool ctordtorp = false; // print all debug
bool ctorp = false; // print ctor debug
bool cpctorp = false; // print copy ctor debug
bool dtorp = false; // print dtor debug
#define PRINT( text ) if ( ctordtorp ) { text }
#define CP_CTOR_PRINT( text ) if ( ctordtorp || cpctorp ) { text }
#define DTOR_PRINT( text ) if ( ctordtorp || dtorp ) { text }

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;
        } else 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<> {
        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;
};

/// 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;
        assert( input );
        auto matches = collectCtorDtorCalls( input );

        // The simple case requires a direct call and only one destructor call.
        if ( dynamic_cast< const ast::ExprStmt * >( input ) && 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 {
                        *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 ) {
        assert( stmtExpr->result );
        if ( stmtExpr->result->isVoid() ) return stmtExpr;

        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;
}

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
        return new ast::CompoundStmt( stmt->location, { stmt } );
}

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 );
}

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 ( nullptr == dtor->env && nullptr != env ) {
                dtor->env = ast::shallowCopy( 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;
}

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;
                // Do not copy construct C-style variadic arguments.
                if ( iter != params.end() ) {
                        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

        assert (appExpr->env == nullptr);
        appExpr->env = impCpCtorExpr->env;

        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
                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 );
        if ( stmtExpr->result->isVoid() ) {
                assert( stmtExpr->returnDecls.empty() );
                assert( stmtExpr->dtors.empty() );

                return stmtExpr;
        }

        static UniqueName retNamer("_tmp_stmtexpr_ret");

        auto result = env->apply( stmtExpr->result.get() ).node;
        if ( ! InitTweak::isConstructable( 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.c_str();
                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 ) ) );

        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 ) ) {
                auto impCpCtorExpr = mutExpr->expr.as<ast::ImplicitCopyCtorExpr>();
                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
                mutExpr->expr = unqMap[mutExpr->id]->expr;
                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)
        ast::ptr<ast::ConstructorInit> ctorInit = _objDecl->init.as<ast::ConstructorInit>();

        if ( nullptr == ctorInit ) return _objDecl;

        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::BasicKind::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;
                        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.

                                // 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();

                                // 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 SymbolTable 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") } );
                                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;
                                objDecl->init = new ast::SingleInit(loc, mutArg );
                        } else {
                                stmtsToAddAfter.push_back( ctor );
                                objDecl->init = 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 ) } ) );
                                } // if
                        }
                } // if
        } else if ( const ast::Init * init = ctorInit->init ) {
                objDecl->init = init;
        } else {
                // no constructor and no initializer, which is okay
                objDecl->init = nullptr;
        } // 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);
        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->location, "jump to label \"%s\" crosses initialization of \"%s\".",
                                           stmt->target.name.c_str(), (*diff.begin())->name.c_str() );
        } // 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
}

/// Should we check for warnings? (The function is user-defined constrctor or destructor.)
bool checkWarnings( const ast::FunctionDecl * funcDecl ) {
        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 );

        // Remaining code is only for warnings.
        if ( ! checkWarnings( function ) ) return;
        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
                        ast::Expr * arg2 = nullptr;
                        if ( function->name == "?{}" && isCopyFunction( function ) ) {
                                // if copy ctor, need to pass second-param-of-this-function.field
                                assert( function->params.size() == 2 );
                                arg2 = new ast::MemberExpr(funcDecl->location, field, new ast::VariableExpr(funcDecl->location, function->params.back() ) );
                        }
                        InitExpander 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 );
                        const ast::Stmt * callStmt = SymTab::genImplicitCall( srcParam, memberDest, loc, function->name, field, static_cast<SymTab::LoopDirection>(isCtor) );

                        if ( callStmt ) {
                                try {
                                        callStmt = callStmt->accept( *visitor );
                                        if ( isCtor ) {
                                                mutStmts->push_front( callStmt );
                                        } else { // TODO: don't generate destructor function/object for intrinsic calls

                                                // 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 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 ) return;

        // 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;

        // 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

void fix( ast::TranslationUnit & translationUnit, bool inLibrary ) {
        ast::Pass<SelfAssignChecker>::run( translationUnit );

        // fixes StmtExpr to properly link to their resulting expression
        ast::Pass<StmtExprResult>::run( translationUnit );

        // fixes ConstructorInit for global variables. should happen before fixInitializers.
        InitTweak::fixGlobalInit( translationUnit, inLibrary );

        // must happen before ResolveCopyCtors because temporaries have to be inserted into the correct scope
        ast::Pass<SplitExpressions>::run( translationUnit );

        ast::Pass<InsertImplicitCalls>::run( translationUnit );

        // Needs to happen before ResolveCopyCtors, because argument/return temporaries should not be considered in
        // error checking branch statements
        {
                ast::Pass<LabelFinder> finder;
                ast::Pass<InsertDtors>::run( translationUnit, finder );
        }

        ast::Pass<ResolveCopyCtors>::run( translationUnit );
        FixInit::fixInitializers( translationUnit );
        ast::Pass<GenStructMemberCalls>::run( translationUnit );

        // Needs to happen after GenStructMemberCalls, since otherwise member constructors exprs
        // don't have the correct form, and a member can be constructed more than once.
        ast::Pass<FixCtorExprs>::run( translationUnit );
}

} // namespace InitTweak

// Local Variables: //
// tab-width: 4 //
// mode: c++ //
// compile-command: "make install" //
// End: //