source: src/InitTweak/FixInit.cc @ ebc0a85

//
// Cforall Version 1.0.0 Copyright (C) 2015 University of Waterloo
//
// The contents of this file are covered under the licence agreement in the
// file "LICENCE" distributed with Cforall.
//
// FixInit.cc --
//
// Author           : Rob Schluntz
// Created On       : Wed Jan 13 16:29:30 2016
// Last Modified By : Peter A. Buhr
// Last Modified On : Wed Feb 13 18:15:56 2019
// Update Count     : 76
//
#include "FixInit.h"

#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 "CodeGen/GenType.h"           // for genPrettyType
#include "CodeGen/OperatorTable.h"
#include "Common/PassVisitor.h"        // for PassVisitor, WithStmtsToAdd
#include "Common/SemanticError.h"      // for SemanticError
#include "Common/UniqueName.h"         // for UniqueName
#include "Common/utility.h"            // for CodeLocation, ValueGuard, toSt...
#include "FixGlobalInit.h"             // for fixGlobalInit
#include "GenInit.h"                   // for genCtorDtor
#include "GenPoly/GenPoly.h"           // for getFunctionType
#include "InitTweak.h"                 // for getFunctionName, getCallArg
#include "Parser/LinkageSpec.h"        // for C, Spec, Cforall, isBuiltin
#include "ResolvExpr/Resolver.h"       // for findVoidExpression
#include "ResolvExpr/typeops.h"        // for typesCompatible
#include "SymTab/Autogen.h"            // for genImplicitCall
#include "SymTab/Indexer.h"            // for Indexer
#include "SymTab/Mangler.h"            // for Mangler
#include "SynTree/Attribute.h"         // for Attribute
#include "SynTree/Constant.h"          // for Constant
#include "SynTree/Declaration.h"       // for ObjectDecl, FunctionDecl, Decl...
#include "SynTree/Expression.h"        // for UniqueExpr, VariableExpr, Unty...
#include "SynTree/Initializer.h"       // for ConstructorInit, SingleInit
#include "SynTree/Label.h"             // for Label, operator<
#include "SynTree/Mutator.h"           // for mutateAll, Mutator, maybeMutate
#include "SynTree/Statement.h"         // for ExprStmt, CompoundStmt, Branch...
#include "SynTree/Type.h"              // for Type, Type::StorageClasses
#include "SynTree/TypeSubstitution.h"  // for TypeSubstitution, operator<<
#include "SynTree/DeclReplacer.h"      // for DeclReplacer
#include "SynTree/Visitor.h"           // for acceptAll, maybeAccept
#include "Validate/FindSpecialDecls.h" // for dtorStmt, dtorStructDestroy

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 {
                struct SelfAssignChecker {
                        void previsit( ApplicationExpr * appExpr );
                };

                struct InsertImplicitCalls : public WithConstTypeSubstitution {
                        /// wrap function application expressions as ImplicitCopyCtorExpr nodes so that it is easy to identify which
                        /// function calls need their parameters to be copy constructed
                        static void insert( std::list< Declaration * > & translationUnit );

                        Expression * postmutate( ApplicationExpr * appExpr );
                };

                struct ResolveCopyCtors final : public WithStmtsToAdd, public WithIndexer, public WithShortCircuiting, public WithTypeSubstitution, public WithVisitorRef<ResolveCopyCtors> {
                        /// 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
                        static void resolveImplicitCalls( std::list< Declaration * > & translationUnit );

                        Expression * postmutate( ImplicitCopyCtorExpr * impCpCtorExpr );
                        void premutate( StmtExpr * stmtExpr );
                        void premutate( UniqueExpr * unqExpr );

                        /// create and resolve ctor/dtor expression: fname(var, [cpArg])
                        Expression * makeCtorDtor( const std::string & fname, ObjectDecl * var, Expression * cpArg = NULL );
                        /// true if type does not need to be copy constructed to ensure correctness
                        bool skipCopyConstruct( Type * type );
                        void copyConstructArg( Expression *& arg, ImplicitCopyCtorExpr * impCpCtorExpr, Type * formal );
                        void destructRet( ObjectDecl * ret, ImplicitCopyCtorExpr * impCpCtorExpr, Expression *& arg );
                };

                /// collects constructed object decls - used as a base class
                struct ObjDeclCollector : public WithGuards, public WithShortCircuiting {
                        // use ordered data structure to maintain ordering for set_difference and for consistent error messages
                        typedef std::list< ObjectDecl * > ObjectSet;
                        void previsit( CompoundStmt *compoundStmt );
                        void previsit( DeclStmt *stmt );

                        // don't go into other functions
                        void previsit( 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 ( ObjectDecl * obj : set.objs ) {
                                out << obj->get_name() << ", " ;
                        } // for
                        out << " }";
                        return out;
                }

                struct LabelFinder final : public ObjDeclCollector {
                        typedef std::map< Label, ObjectSet > LabelMap;
                        // map of Label -> live variables at that label
                        LabelMap vars;

                        typedef ObjDeclCollector Parent;
                        using Parent::previsit;
                        void previsit( Statement * stmt );

                        void previsit( CompoundStmt *compoundStmt );
                        void previsit( DeclStmt *stmt );
                };

                struct InsertDtors final : public ObjDeclCollector, public WithStmtsToAdd {
                        /// insert destructor calls at the appropriate places.  must happen before CtorInit nodes are removed
                        /// (currently by FixInit)
                        static void insert( std::list< Declaration * > & translationUnit );

                        typedef std::list< ObjectDecl * > OrderedDecls;
                        typedef std::list< OrderedDecls > OrderedDeclsStack;

                        InsertDtors( PassVisitor<LabelFinder> & finder ) : finder( finder ), labelVars( finder.pass.vars ) {}

                        typedef ObjDeclCollector Parent;
                        using Parent::previsit;

                        void previsit( FunctionDecl * funcDecl );

                        void previsit( BranchStmt * stmt );
                private:
                        void handleGoto( BranchStmt * stmt );

                        PassVisitor<LabelFinder> & finder;
                        LabelFinder::LabelMap & labelVars;
                        OrderedDeclsStack reverseDeclOrder;
                };

                class FixInit : public WithStmtsToAdd {
                  public:
                        /// expand each object declaration to use its constructor after it is declared.
                        static void fixInitializers( std::list< Declaration * > &translationUnit );

                        DeclarationWithType * postmutate( ObjectDecl *objDecl );

                        std::list< Declaration * > staticDtorDecls;
                };

                struct GenStructMemberCalls final : public WithGuards, public WithShortCircuiting, public WithIndexer, public WithVisitorRef<GenStructMemberCalls> {
                        /// 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
                        static void generate( std::list< Declaration * > & translationUnit );

                        void premutate( FunctionDecl * funcDecl );
                        DeclarationWithType * postmutate( FunctionDecl * funcDecl );

                        void premutate( MemberExpr * memberExpr );
                        void premutate( 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.
                        Expression * postmutate( UntypedExpr * expr );

                        SemanticErrorException errors;
                  private:
                        template< typename... Params >
                        void emit( CodeLocation, const Params &... params );

                        FunctionDecl * function = nullptr;
                        std::set< DeclarationWithType * > unhandled;
                        std::map< DeclarationWithType *, CodeLocation > usedUninit;
                        ObjectDecl * thisParam = nullptr;
                        bool isCtor = false; // true if current function is a constructor
                        StructDecl * structDecl = nullptr;
                };

                struct FixCtorExprs final : public WithDeclsToAdd, public WithIndexer {
                        /// expands ConstructorExpr nodes into comma expressions, using a temporary for the first argument
                        static void fix( std::list< Declaration * > & translationUnit );

                        Expression * postmutate( ConstructorExpr * ctorExpr );
                };

                struct SplitExpressions : public WithShortCircuiting, public WithTypeSubstitution, public WithStmtsToAdd {
                        /// add CompoundStmts around top-level expressions so that temporaries are destroyed in the correct places.
                        static void split( std::list< Declaration * > &translationUnit );

                        Statement * postmutate( ExprStmt * stmt );
                        void premutate( TupleAssignExpr * expr );
                };
        } // namespace

        void fix( std::list< Declaration * > & translationUnit, bool inLibrary ) {
                PassVisitor<SelfAssignChecker> checker;
                acceptAll( translationUnit, checker );

                // 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
                SplitExpressions::split( translationUnit );

                InsertImplicitCalls::insert( translationUnit );

                // Needs to happen before ResolveCopyCtors, because argument/return temporaries should not be considered in
                // error checking branch statements
                InsertDtors::insert( translationUnit );

                ResolveCopyCtors::resolveImplicitCalls( translationUnit );
                FixInit::fixInitializers( translationUnit );
                GenStructMemberCalls::generate( 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.
                FixCtorExprs::fix( translationUnit );
        }

        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
                DeclarationWithType * getDtorFunc( ObjectDecl * objDecl, Statement * input, std::list< Statement * > & stmtsToAdd ) {
                        // unwrap implicit statement wrapper
                        Statement * dtor = input;
                        if ( ImplicitCtorDtorStmt * implicit = dynamic_cast< ImplicitCtorDtorStmt * >( input ) ) {
                                // dtor = implicit->callStmt;
                                // implicit->callStmt = nullptr;
                        }
                        assert( dtor );
                        std::list< Expression * > matches;
                        collectCtorDtorCalls( dtor, matches );

                        if ( dynamic_cast< ExprStmt * >( dtor ) ) {
                                // only one destructor call in the expression
                                if ( matches.size() == 1 ) {
                                        DeclarationWithType * 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 ( FunctionDecl * dtorFunc = dynamic_cast< 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.
                                                        delete dtor;
                                                        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" );
                        FunctionDecl * dtorFunc = FunctionDecl::newFunction( dtorNamer.newName(), SymTab::genDefaultType( objDecl->type->stripReferences(), false ), new CompoundStmt() );
                        stmtsToAdd.push_back( new DeclStmt( dtorFunc ) );

                        // the original code contains uses of objDecl - replace them with the newly generated 'this' parameter.
                        ObjectDecl * thisParam = getParamThis( dtorFunc->type );
                        Expression * replacement = new VariableExpr( thisParam );

                        Type * base = replacement->result->stripReferences();
                        if ( dynamic_cast< ArrayType * >( base ) || dynamic_cast< 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 CastExpr( replacement, base->clone() );
                        }
                        DeclReplacer::replace( dtor, { std::make_pair( objDecl, replacement ) } );
                        dtorFunc->statements->push_back( strict_dynamic_cast<Statement *>( dtor ) );

                        return dtorFunc;
                }

                void SplitExpressions::split( std::list< Declaration * > & translationUnit ) {
                        PassVisitor<SplitExpressions> splitter;
                        mutateAll( translationUnit, splitter );
                }

                void InsertImplicitCalls::insert( std::list< Declaration * > & translationUnit ) {
                        PassVisitor<InsertImplicitCalls> inserter;
                        mutateAll( translationUnit, inserter );
                }

                void ResolveCopyCtors::resolveImplicitCalls( std::list< Declaration * > & translationUnit ) {
                        PassVisitor<ResolveCopyCtors> resolver;
                        mutateAll( translationUnit, resolver );
                }

                void FixInit::fixInitializers( std::list< Declaration * > & translationUnit ) {
                        PassVisitor<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 ( std::list< Declaration * >::iterator i = translationUnit.begin(); i != translationUnit.end(); ++i ) {
                                try {
                                        maybeMutate( *i, fixer );
                                        translationUnit.splice( i, fixer.pass.staticDtorDecls );
                                } catch( SemanticErrorException &e ) {
                                        errors.append( e );
                                } // try
                        } // for
                        if ( ! errors.isEmpty() ) {
                                throw errors;
                        } // if
                }

                void InsertDtors::insert( std::list< Declaration * > & translationUnit ) {
                        PassVisitor<LabelFinder> finder;
                        PassVisitor<InsertDtors> inserter( finder );
                        acceptAll( translationUnit, inserter );
                }

                void GenStructMemberCalls::generate( std::list< Declaration * > & translationUnit ) {
                        PassVisitor<GenStructMemberCalls> warner;
                        mutateAll( translationUnit, warner );
                }

                void FixCtorExprs::fix( std::list< Declaration * > & translationUnit ) {
                        PassVisitor<FixCtorExprs> fixer;
                        mutateAll( translationUnit, fixer );
                }

                Statement * SplitExpressions::postmutate( ExprStmt * stmt ) {
                        // wrap each top-level ExprStmt in a block so that destructors for argument and return temporaries are destroyed
                        // in the correct places
                        CompoundStmt * ret = new CompoundStmt( { stmt } );
                        return ret;
                }

                void SplitExpressions::premutate( 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 {
                        Expression * stripCasts( Expression * expr ) {
                                // this might be too permissive. It's possible that only particular casts are relevant.
                                while ( CastExpr * cast = dynamic_cast< CastExpr * >( expr ) ) {
                                        expr = cast->arg;
                                }
                                return expr;
                        }

                        void previsit( Expression * ) {
                                // anything else does not qualify
                                isSimilar = false;
                        }

                        template<typename T>
                        T * cast( Expression * node ) {
                                // all expressions need to ignore casts, so this bit has been factored out
                                return dynamic_cast< T * >( stripCasts( node ) );
                        }

                        // ignore casts
                        void previsit( CastExpr * ) {}

                        void previsit( MemberExpr * memExpr ) {
                                if ( MemberExpr * otherMember = cast< MemberExpr >( other ) ) {
                                        if ( otherMember->member == memExpr->member ) {
                                                other = otherMember->aggregate;
                                                return;
                                        }
                                }
                                isSimilar = false;
                        }

                        void previsit( VariableExpr * varExpr ) {
                                if ( VariableExpr * otherVar = cast< VariableExpr >( other ) ) {
                                        if ( otherVar->var == varExpr->var ) {
                                                return;
                                        }
                                }
                                isSimilar = false;
                        }

                        void previsit( AddressExpr * ) {
                                if ( AddressExpr * addrExpr = cast< AddressExpr >( other ) ) {
                                        other = addrExpr->arg;
                                        return;
                                }
                                isSimilar = false;
                        }

                        Expression * other = nullptr;
                        bool isSimilar = true;
                };

                bool structurallySimilar( Expression * e1, Expression * e2 ) {
                        PassVisitor<StructuralChecker> checker;
                        checker.pass.other = e2;
                        e1->accept( checker );
                        return checker.pass.isSimilar;
                }

                void SelfAssignChecker::previsit( ApplicationExpr * appExpr ) {
                        DeclarationWithType * function = getFunction( appExpr );
                        if ( function->name == "?=?" ) { // doesn't use isAssignment, because ?+=?, etc. should not count as self-assignment
                                if ( 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)
                                        if ( structurallySimilar( appExpr->args.front(), appExpr->args.back() ) ) {
                                                SemanticWarning( appExpr->location, Warning::SelfAssignment, toCString( appExpr->args.front() ) );
                                        }
                                }
                        }
                }

                Expression * InsertImplicitCalls::postmutate( ApplicationExpr * appExpr ) {
                        if ( VariableExpr * function = dynamic_cast< VariableExpr * > ( appExpr->get_function() ) ) {
                                if ( function->var->linkage.is_builtin ) {
                                        // optimization: don't need to copy construct in order to call intrinsic functions
                                        return appExpr;
                                } else if ( DeclarationWithType * funcDecl = dynamic_cast< DeclarationWithType * > ( function->get_var() ) ) {
                                        FunctionType * ftype = dynamic_cast< FunctionType * >( GenPoly::getFunctionType( funcDecl->get_type() ) );
                                        assertf( ftype, "Function call without function type: %s", toString( funcDecl ).c_str() );
                                        if ( CodeGen::isConstructor( funcDecl->get_name() ) && ftype->parameters.size() == 2 ) {
                                                Type * t1 = getPointerBase( ftype->parameters.front()->get_type() );
                                                Type * t2 = ftype->parameters.back()->get_type();
                                                assert( t1 );

                                                if ( ResolvExpr::typesCompatible( t1, t2, SymTab::Indexer() ) ) {
                                                        // optimization: don't need to copy construct in order to call a copy constructor
                                                        return appExpr;
                                                } // if
                                        } else if ( CodeGen::isDestructor( funcDecl->get_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
                        ImplicitCopyCtorExpr * expr = new ImplicitCopyCtorExpr( appExpr );
                        // Move the type substitution to the new top-level, if it is attached to the appExpr.
                        // Ensure it is not deleted with the ImplicitCopyCtorExpr by removing it before deletion.
                        // The substitution is needed to obtain the type of temporary variables so that copy constructor
                        // calls can be resolved.
                        assert( env );
                        std::swap( expr->env, appExpr->env );
                        return expr;
                }

                bool ResolveCopyCtors::skipCopyConstruct( Type * type ) { return ! isConstructable( type ); }

                Expression * ResolveCopyCtors::makeCtorDtor( const std::string & fname, ObjectDecl * var, Expression * cpArg ) {
                        assert( var );
                        // arrays are not copy constructed, so this should always be an ExprStmt
                        ImplicitCtorDtorStmt * stmt = genCtorDtor( fname, var, cpArg );
                        assertf( stmt, "ResolveCopyCtors: genCtorDtor returned nullptr: %s / %s / %s", fname.c_str(), toString( var ).c_str(), toString( cpArg ).c_str() );
                        ExprStmt * exprStmt = strict_dynamic_cast< ExprStmt * >( stmt->callStmt );
                        Expression * resolved = exprStmt->expr;
                        exprStmt->expr = nullptr; // 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 " << resolved << std::endl; )
                        ResolvExpr::findVoidExpression( resolved, indexer );
                        assert( resolved );
                        if ( resolved->env ) {
                                // Extract useful information and discard new environments. Keeping them causes problems in PolyMutator passes.
                                env->add( *resolved->env );
                                delete resolved->env;
                                resolved->env = nullptr;
                        } // if
                        delete stmt;
                        if ( TupleAssignExpr * assign = dynamic_cast< TupleAssignExpr * >( resolved ) ) {
                                // fix newly generated StmtExpr
                                premutate( assign->stmtExpr );
                        }
                        return resolved;
                }

                void ResolveCopyCtors::copyConstructArg( Expression *& arg, ImplicitCopyCtorExpr * impCpCtorExpr, Type * formal ) {
                        static UniqueName tempNamer("_tmp_cp");
                        assert( env );
                        CP_CTOR_PRINT( std::cerr << "Type Substitution: " << *env << std::endl; )
                        assert( arg->result );
                        Type * result = arg->result;
                        if ( skipCopyConstruct( result ) ) return; // 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).
                        env->applyFree( result );
                        ObjectDecl * tmp = ObjectDecl::newObject( "__tmp", result, nullptr );
                        tmp->get_type()->set_const( false );

                        // create and resolve copy constructor
                        CP_CTOR_PRINT( std::cerr << "makeCtorDtor for an argument" << std::endl; )
                        Expression * cpCtor = makeCtorDtor( "?{}", tmp, arg );

                        if ( ApplicationExpr * appExpr = dynamic_cast< 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
                                VariableExpr * function = strict_dynamic_cast< VariableExpr * >( appExpr->function );
                                if ( function->var->linkage == LinkageSpec::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 ) ) return;
                                        // xxx - leaking tmp
                                }
                        }

                        // set a unique name for the temporary once it's certain the call is necessary
                        tmp->name = tempNamer.newName();

                        // replace argument to function call with temporary
                        stmtsToAddBefore.push_back( new DeclStmt( tmp ) );
                        arg = cpCtor;
                        destructRet( tmp, impCpCtorExpr, arg );

                        // impCpCtorExpr->dtors.push_front( makeCtorDtor( "^?{}", tmp ) );
                }

                void ResolveCopyCtors::destructRet( ObjectDecl * ret, ImplicitCopyCtorExpr * /*impCpCtorExpr*/, Expression *& arg ) {
                        // 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( Validate::dtorStruct && Validate::dtorStruct->members.size() == 2, "Destructor generation requires __Destructor definition." );
                        assertf( Validate::dtorStructDestroy, "Destructor generation requires __destroy_Destructor." );

                        // generate a __Destructor for ret that calls the destructor
                        Expression * dtor = makeCtorDtor( "^?{}", ret );

                        // if the chosen destructor is intrinsic, elide the generated dtor handler
                        if ( arg && isIntrinsicCallExpr( dtor ) ) {
                                arg = new CommaExpr( arg, new VariableExpr( ret ) );
                                return;
                        }

                        if ( ! dtor->env ) dtor->env = maybeClone( env );
                        DeclarationWithType * dtorFunc = getDtorFunc( ret, new ExprStmt( dtor ), stmtsToAddBefore );

                        StructInstType * dtorStructType = new StructInstType( Type::Qualifiers(), Validate::dtorStruct );
                        dtorStructType->parameters.push_back( new TypeExpr( new VoidType( Type::Qualifiers() ) ) );

                        // cast destructor pointer to void (*)(void *), to silence GCC incompatible pointer warnings
                        FunctionType * dtorFtype = new FunctionType( Type::Qualifiers(), false );
                        dtorFtype->parameters.push_back( ObjectDecl::newObject( "", new PointerType( Type::Qualifiers(), new VoidType( Type::Qualifiers() ) ), nullptr ) );
                        Type * dtorType = new PointerType( Type::Qualifiers(), dtorFtype );

                        static UniqueName namer( "_ret_dtor" );
                        ObjectDecl * retDtor = ObjectDecl::newObject( namer.newName(), dtorStructType, new ListInit( { new SingleInit( new ConstantExpr( Constant::null() ) ), new SingleInit( new CastExpr( new VariableExpr( dtorFunc ), dtorType ) ) } ) );
                        retDtor->attributes.push_back( new Attribute( "cleanup", { new VariableExpr( Validate::dtorStructDestroy ) } ) );
                        stmtsToAddBefore.push_back( new DeclStmt( retDtor ) );

                        if ( arg ) {
                                Expression * member = new MemberExpr( strict_dynamic_cast<DeclarationWithType *>( Validate::dtorStruct->members.front() ), new VariableExpr( retDtor ) );
                                Expression * object = new CastExpr( new AddressExpr( new VariableExpr( ret ) ), new PointerType( Type::Qualifiers(), new VoidType( Type::Qualifiers() ) ) );
                                Expression * assign = createBitwiseAssignment( member, object );
                                arg = new CommaExpr( new CommaExpr( arg, assign ), new VariableExpr( ret ) );
                        }

                        // impCpCtorExpr->get_dtors().push_front( makeCtorDtor( "^?{}", ret ) );
                }

                Expression * ResolveCopyCtors::postmutate( ImplicitCopyCtorExpr *impCpCtorExpr ) {
                        CP_CTOR_PRINT( std::cerr << "ResolveCopyCtors: " << impCpCtorExpr << std::endl; )

                        ApplicationExpr * appExpr = impCpCtorExpr->callExpr;
                        ObjectDecl * returnDecl = nullptr;

                        // take each argument and attempt to copy construct it.
                        FunctionType * ftype = GenPoly::getFunctionType( appExpr->function->result );
                        assert( ftype );
                        auto & params = ftype->parameters;
                        auto iter = params.begin();
                        for ( Expression * & arg : appExpr->args ) {
                                Type * formal = nullptr;
                                if ( iter != params.end() ) { // does not copy construct C-style variadic arguments
                                        DeclarationWithType * param = *iter++;
                                        formal = param->get_type();
                                }

                                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?
                        Type * result = appExpr->result;
                        if ( ! result->isVoid() ) {
                                static UniqueName retNamer("_tmp_cp_ret");
                                result = result->clone();
                                env->apply( result );
                                ObjectDecl * ret = ObjectDecl::newObject( retNamer.newName(), result, nullptr );
                                ret->type->set_const( false );
                                returnDecl = ret;
                                stmtsToAddBefore.push_back( new DeclStmt( 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
                        impCpCtorExpr->callExpr = nullptr;
                        std::swap( impCpCtorExpr->env, appExpr->env );
                        assert( impCpCtorExpr->env == nullptr );
                        delete impCpCtorExpr;

                        if ( returnDecl ) {
                                Expression * assign = createBitwiseAssignment( new VariableExpr( returnDecl ), appExpr );
                                if ( ! dynamic_cast< 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
                                        destructRet( returnDecl, impCpCtorExpr, assign );
                                } else {
                                        assign = new CommaExpr( assign, new VariableExpr( returnDecl ) );
                                }
                                // move env from appExpr to retExpr
                                std::swap( assign->env, appExpr->env );
                                return assign;
                        } else {
                                return appExpr;
                        } // if
                }

                void ResolveCopyCtors::premutate( 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();
                        //   g([A] x, [A] y);
                        //   g(f());
                        // 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.
                        visit_children = false;

                        assert( env );

                        // visit all statements
                        std::list< Statement * > & stmts = stmtExpr->statements->get_kids();
                        for ( Statement *& stmt : stmts ) {
                                stmt = stmt->acceptMutator( *visitor );
                        } // for

                        assert( stmtExpr->result );
                        Type * result = stmtExpr->result;
                        if ( ! result->isVoid() ) {
                                static UniqueName retNamer("_tmp_stmtexpr_ret");

                                result = result->clone();
                                env->apply( result );
                                if ( ! InitTweak::isConstructable( result ) ) {
                                        delete result;
                                        return;
                                }

                                // create variable that will hold the result of the stmt expr
                                ObjectDecl * ret = ObjectDecl::newObject( retNamer.newName(), result, nullptr );
                                ret->type->set_const( false );
                                stmtsToAddBefore.push_back( new DeclStmt( ret ) );

                                // must have a non-empty body, otherwise it wouldn't have a result
                                CompoundStmt * body = stmtExpr->statements;
                                assert( ! body->kids.empty() );
                                // must be an ExprStmt, otherwise it wouldn't have a result
                                ExprStmt * last = strict_dynamic_cast< ExprStmt * >( body->kids.back() );
                                last->expr = makeCtorDtor( "?{}", ret, last->expr );

                                // add destructors after current statement
                                stmtsToAddAfter.push_back( new ExprStmt( 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 ExprStmt( new VariableExpr( ret ) ) );
                        } // if

                        assert( stmtExpr->returnDecls.empty() );
                        assert( stmtExpr->dtors.empty() );
                }

                // to prevent warnings (‘_unq0’ may be used uninitialized in this function),
                // insert an appropriate zero initializer for UniqueExpr temporaries.
                Initializer * makeInit( Type * t ) {
                        if ( StructInstType * inst = dynamic_cast< StructInstType * >( t ) ) {
                                // initizer for empty struct must be empty
                                if ( inst->baseStruct->members.empty() ) return new ListInit({});
                        } else if ( UnionInstType * inst = dynamic_cast< UnionInstType * >( t ) ) {
                                // initizer for empty union must be empty
                                if ( inst->baseUnion->members.empty() ) return new ListInit({});
                        }

                        return new ListInit( { new SingleInit( new ConstantExpr( Constant::from_int( 0 ) ) ) } );
                }

                void ResolveCopyCtors::premutate( 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, UniqueExpr * > unqMap;
                        if ( ! unqMap.count( unqExpr->get_id() ) ) {
                                // resolve expr and find its

                                ImplicitCopyCtorExpr * impCpCtorExpr = dynamic_cast< ImplicitCopyCtorExpr * >( unqExpr->expr );
                                // PassVisitor<ResolveCopyCtors> fixer;
                                unqExpr->expr = unqExpr->expr->acceptMutator( *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 ) {
                                        CommaExpr * comma = strict_dynamic_cast< CommaExpr * >( unqExpr->expr );
                                        VariableExpr * var = strict_dynamic_cast<VariableExpr *>( comma->arg2 );
                                        // note the variable used as the result from the call
                                        unqExpr->var = var->clone();
                                } else {
                                        // expr isn't a call expr, so create a new temporary variable to use to hold the value of the unique expression
                                        unqExpr->object = ObjectDecl::newObject( toString("_unq", unqExpr->get_id()), unqExpr->result->clone(), makeInit( unqExpr->result ) );
                                        unqExpr->var = new VariableExpr( unqExpr->object );
                                }

                                // stmtsToAddBefore.splice( stmtsToAddBefore.end(), fixer.pass.stmtsToAddBefore );
                                // stmtsToAddAfter.splice( stmtsToAddAfter.end(), fixer.pass.stmtsToAddAfter );
                                unqMap[unqExpr->get_id()] = unqExpr;
                        } else {
                                // take data from other UniqueExpr to ensure consistency
                                delete unqExpr->get_expr();
                                unqExpr->expr = unqMap[unqExpr->get_id()]->expr->clone();
                                delete unqExpr->result;
                                unqExpr->result = maybeClone( unqExpr->expr->result );
                        }
                }

                DeclarationWithType * FixInit::postmutate( ObjectDecl *objDecl ) {
                        // since this removes the init field from objDecl, it must occur after children are mutated (i.e. postmutate)
                        if ( ConstructorInit * ctorInit = dynamic_cast< ConstructorInit * >( objDecl->get_init() ) ) {
                                // a decision should have been made by the resolver, so ctor and init are not both non-NULL
                                assert( ! ctorInit->get_ctor() || ! ctorInit->get_init() );
                                if ( Statement * ctor = ctorInit->get_ctor() ) {
                                        if ( objDecl->get_storageClasses().is_static ) {
                                                // 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
                                                BasicType * boolType = new BasicType( Type::Qualifiers(), BasicType::Bool );
                                                SingleInit * boolInitExpr = new SingleInit( new ConstantExpr( Constant::from_int( 1 ) ) );
                                                ObjectDecl * isUninitializedVar = new ObjectDecl( objDecl->get_mangleName() + "_uninitialized", Type::StorageClasses( Type::Static ), LinkageSpec::Cforall, 0, boolType, boolInitExpr );
                                                isUninitializedVar->fixUniqueId();

                                                // __objName_uninitialized = false;
                                                UntypedExpr * setTrue = new UntypedExpr( new NameExpr( "?=?" ) );
                                                setTrue->get_args().push_back( new VariableExpr( isUninitializedVar ) );
                                                setTrue->get_args().push_back( new ConstantExpr( Constant::from_int( 0 ) ) );

                                                // generate body of if
                                                CompoundStmt * initStmts = new CompoundStmt();
                                                std::list< Statement * > & body = initStmts->get_kids();
                                                body.push_back( ctor );
                                                body.push_back( new ExprStmt( setTrue ) );

                                                // put it all together
                                                IfStmt * ifStmt = new IfStmt( new VariableExpr( isUninitializedVar ), initStmts, 0 );
                                                stmtsToAddAfter.push_back( new DeclStmt( isUninitializedVar ) );
                                                stmtsToAddAfter.push_back( ifStmt );

                                                Statement * dtor = ctorInit->get_dtor();
                                                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(...) {...}
                                                        FunctionDecl * dtorCaller = new FunctionDecl( objDecl->get_mangleName() + dtorCallerNamer.newName(), Type::StorageClasses( Type::Static ), LinkageSpec::C, new FunctionType( Type::Qualifiers(), false ), new CompoundStmt() );
                                                        dtorCaller->fixUniqueId();
                                                        dtorCaller->get_statements()->push_back( dtorStmt );

                                                        // atexit(dtor_atexit);
                                                        UntypedExpr * callAtexit = new UntypedExpr( new NameExpr( "atexit" ) );
                                                        callAtexit->get_args().push_back( new VariableExpr( dtorCaller ) );

                                                        body.push_back( new ExprStmt( 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->set_name( objDecl->get_name() + staticNamer.newName() );
                                                        objDecl->set_mangleName( SymTab::Mangler::mangle( objDecl ) );

                                                        // 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" );
                                                        ObjectDecl * dummy = new ObjectDecl( dummyNamer.newName(), Type::StorageClasses( Type::Static ), LinkageSpec::Cforall, 0, new PointerType( Type::Qualifiers(), new VoidType( Type::Qualifiers() ) ), 0, std::list< Attribute * >{ new Attribute("unused") } );
                                                        delete ctorInit;
                                                        return dummy;
                                                }
                                        } else {
                                                ImplicitCtorDtorStmt * implicit = strict_dynamic_cast< ImplicitCtorDtorStmt * > ( ctor );
                                                ExprStmt * ctorStmt = dynamic_cast< ExprStmt * >( implicit->callStmt );
                                                ApplicationExpr * ctorCall = nullptr;
                                                if ( ctorStmt && (ctorCall = isIntrinsicCallExpr( ctorStmt->expr )) && ctorCall->get_args().size() == 2 ) {
                                                        // clean up intrinsic copy constructor calls by making them into SingleInits
                                                        Expression * ctorArg = ctorCall->args.back();
                                                        std::swap( ctorArg->env, ctorCall->env );
                                                        objDecl->init = new SingleInit( ctorArg );

                                                        ctorCall->args.pop_back();
                                                } else {
                                                        stmtsToAddAfter.push_back( ctor );
                                                        objDecl->init = nullptr;
                                                        ctorInit->ctor = nullptr;
                                                }

                                                Statement * dtor = ctorInit->dtor;
                                                if ( dtor ) {
                                                        ImplicitCtorDtorStmt * implicit = strict_dynamic_cast< ImplicitCtorDtorStmt * >( dtor );
                                                        Statement * 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
                                                                DeclarationWithType * dtorFunc = getDtorFunc( objDecl, dtorStmt, stmtsToAddBefore );
                                                                objDecl->attributes.push_back( new Attribute( "cleanup", { new VariableExpr( dtorFunc ) } ) );
                                                                ctorInit->dtor = nullptr;
                                                        } // if
                                                }
                                        } // if
                                } else if ( Initializer * init = ctorInit->init ) {
                                        objDecl->init = init;
                                        ctorInit->init = nullptr;
                                } else {
                                        // no constructor and no initializer, which is okay
                                        objDecl->init = nullptr;
                                } // if
                                delete ctorInit;
                        } // if
                        return objDecl;
                }

                void ObjDeclCollector::previsit( CompoundStmt * ) {
                        GuardValue( curVars );
                }

                void ObjDeclCollector::previsit( DeclStmt * stmt ) {
                        // keep track of all variables currently in scope
                        if ( ObjectDecl * objDecl = dynamic_cast< ObjectDecl * > ( stmt->get_decl() ) ) {
                                curVars.push_back( objDecl );
                        } // if
                }

                void LabelFinder::previsit( Statement * stmt ) {
                        // for each label, remember the variables in scope at that label.
                        for ( Label l : stmt->get_labels() ) {
                                vars[l] = curVars;
                        } // for
                }

                void LabelFinder::previsit( CompoundStmt * stmt ) {
                        previsit( (Statement *)stmt );
                        Parent::previsit( stmt );
                }

                void LabelFinder::previsit( DeclStmt * stmt ) {
                        previsit( (Statement *)stmt );
                        Parent::previsit( stmt );
                }


                void InsertDtors::previsit( 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.
                        maybeAccept( funcDecl->type, finder );
                        maybeAccept( funcDecl->statements, 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( BranchStmt * stmt ) {
                        // can't do anything for computed goto
                        if ( stmt->computedTarget ) return;

                        assertf( stmt->get_target() != "", "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->get_target() ];

                        DTOR_PRINT(
                                std::cerr << "at goto label: " << stmt->get_target().get_name() << std::endl;
                                std::cerr << "S_G = " << printSet( curVars ) << std::endl;
                                std::cerr << "S_L = " << printSet( lvars ) << std::endl;
                        )

                        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->get_target().get_name() + "' crosses initialization of " + (*diff.begin())->get_name() + " " );
                        } // if
                }

                void InsertDtors::previsit( BranchStmt * stmt ) {
                        switch( stmt->get_type() ) {
                          case BranchStmt::Continue:
                          case 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 BranchStmt::Goto:
                                handleGoto( stmt );
                                break;
                          default:
                                assert( false );
                        } // switch
                }

                bool checkWarnings( FunctionDecl * funcDecl ) {
                        // only check for warnings if the current function is a user-defined
                        // constructor or destructor
                        if ( ! funcDecl ) return false;
                        if ( ! funcDecl->get_statements() ) return false;
                        return CodeGen::isCtorDtor( funcDecl->get_name() ) && ! LinkageSpec::isOverridable( funcDecl->get_linkage() );
                }

                void GenStructMemberCalls::premutate( 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 = funcDecl;
                        isCtor = CodeGen::isConstructor( function->get_name() );
                        if ( checkWarnings( function ) ) {
                                FunctionType * type = function->get_functionType();
                                assert( ! type->get_parameters().empty() );
                                thisParam = strict_dynamic_cast< ObjectDecl * >( type->get_parameters().front() );
                                Type * thisType = getPointerBase( thisParam->get_type() );
                                StructInstType * structType = dynamic_cast< StructInstType * >( thisType );
                                if ( structType ) {
                                        structDecl = structType->get_baseStruct();
                                        for ( Declaration * member : structDecl->get_members() ) {
                                                if ( ObjectDecl * field = dynamic_cast< ObjectDecl * >( member ) ) {
                                                        // record all of the struct type's members that need to be constructed or
                                                        // destructed by the end of the function
                                                        unhandled.insert( field );
                                                }
                                        }
                                }
                        }
                }

                DeclarationWithType * GenStructMemberCalls::postmutate( 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< DeclarationWithType *, 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 ) {
                                DeclarationWithType * member = p.first;
                                CodeLocation loc = p.second;
                                // xxx - make error message better by also tracking the location that the object is constructed at?
                                emit( loc, "in ", CodeGen::genPrettyType( function->get_functionType(), function->get_name() ), ", field ", member->get_name(), " used before being constructed" );
                        }

                        if ( ! unhandled.empty() ) {
                                // need to explicitly re-add function parameters to the indexer in order to resolve copy constructors
                                auto guard = makeFuncGuard( [this]() { indexer.enterScope(); }, [this]() { indexer.leaveScope(); } );
                                indexer.addFunctionType( function->type );

                                // need to iterate through members in reverse in order for
                                // ctor/dtor statements to come out in the right order
                                for ( Declaration * member : reverseIterate( structDecl->get_members() ) ) {
                                        DeclarationWithType * field = dynamic_cast< DeclarationWithType * >( member );
                                        // 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< Statement * > stmt;
                                        Expression * arg2 = nullptr;
                                        if ( isCopyConstructor( function ) ) {
                                                // if copy ctor, need to pass second-param-of-this-function.field
                                                std::list< DeclarationWithType * > & params = function->get_functionType()->get_parameters();
                                                assert( params.size() == 2 );
                                                arg2 = new MemberExpr( field, new VariableExpr( params.back() ) );
                                        }
                                        InitExpander srcParam( arg2 );
                                        // cast away reference type and construct field.
                                        Expression * thisExpr = new CastExpr( new VariableExpr( thisParam ), thisParam->get_type()->stripReferences()->clone() );
                                        Expression * memberDest = new MemberExpr( field, thisExpr );
                                        SymTab::genImplicitCall( srcParam, memberDest, function->get_name(), back_inserter( stmt ), field, isCtor );

                                        assert( stmt.size() <= 1 );
                                        if ( stmt.size() == 1 ) {
                                                Statement * callStmt = stmt.front();

                                                try {
                                                        callStmt->acceptMutator( *visitor );
                                                        if ( isCtor ) {
                                                                function->statements->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< Statement * > stmtsToAdd;

                                                                static UniqueName memberDtorNamer = { "__memberDtor" };
                                                                assertf( Validate::dtorStruct, "builtin __Destructor not found." );
                                                                assertf( Validate::dtorStructDestroy, "builtin __destroy_Destructor not found." );

                                                                Expression * thisExpr = new CastExpr( new AddressExpr( new VariableExpr( thisParam ) ), new PointerType( Type::Qualifiers(), new VoidType( Type::Qualifiers() ) ) );
                                                                Expression * dtorExpr = new VariableExpr( getDtorFunc( thisParam, callStmt, stmtsToAdd ) );

                                                                // cast destructor pointer to void (*)(void *), to silence GCC incompatible pointer warnings
                                                                FunctionType * dtorFtype = new FunctionType( Type::Qualifiers(), false );
                                                                dtorFtype->parameters.push_back( ObjectDecl::newObject( "", new PointerType( Type::Qualifiers(), new VoidType( Type::Qualifiers() ) ), nullptr ) );
                                                                Type * dtorType = new PointerType( Type::Qualifiers(), dtorFtype );

                                                                ObjectDecl * destructor = ObjectDecl::newObject( memberDtorNamer.newName(), new StructInstType( Type::Qualifiers(), Validate::dtorStruct ), new ListInit( { new SingleInit( thisExpr ), new SingleInit( new CastExpr( dtorExpr, dtorType ) ) } ) );
                                                                function->statements->push_front( new DeclStmt( destructor ) );
                                                                destructor->attributes.push_back( new Attribute( "cleanup", { new VariableExpr( Validate::dtorStructDestroy ) } ) );

                                                                function->statements->kids.splice( function->statements->kids.begin(), stmtsToAdd );
                                                        }
                                                } catch ( SemanticErrorException & error ) {
                                                        emit( funcDecl->location, "in ", CodeGen::genPrettyType( function->get_functionType(), function->get_name() ), ", field ", field->get_name(), " not explicitly ", isCtor ? "constructed" : "destructed",  " and no ", isCtor ? "default constructor" : "destructor", " found" );
                                                }
                                        }
                                }
                        }
                        if (! errors.isEmpty()) {
                                throw errors;
                        }
                        return funcDecl;
                }

                /// true if expr is effectively just the 'this' parameter
                bool isThisExpression( Expression * expr, DeclarationWithType * thisParam ) {
                        // TODO: there are more complicated ways to pass 'this' to a constructor, e.g. &*, *&, etc.
                        if ( VariableExpr * varExpr = dynamic_cast< VariableExpr * >( expr ) ) {
                                return varExpr->get_var() == thisParam;
                        } else if ( CastExpr * castExpr = dynamic_cast< CastExpr * > ( expr ) ) {
                                return isThisExpression( castExpr->get_arg(), thisParam );
                        }
                        return false;
                }

                /// returns a MemberExpr if expr is effectively just member access on the 'this' parameter, else nullptr
                MemberExpr * isThisMemberExpr( Expression * expr, DeclarationWithType * thisParam ) {
                        if ( MemberExpr * memberExpr = dynamic_cast< MemberExpr * >( expr ) ) {
                                if ( isThisExpression( memberExpr->get_aggregate(), thisParam ) ) {
                                        return memberExpr;
                                }
                        } else if ( CastExpr * castExpr = dynamic_cast< CastExpr * >( expr ) ) {
                                return isThisMemberExpr( castExpr->get_arg(), thisParam );
                        }
                        return nullptr;
                }

                void GenStructMemberCalls::premutate( ApplicationExpr * appExpr ) {
                        if ( ! checkWarnings( function ) ) {
                                visit_children = false;
                                return;
                        }

                        std::string fname = getFunctionName( appExpr );
                        if ( fname == function->name ) {
                                // call to same kind of function
                                Expression * 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 ( MemberExpr * 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::premutate( MemberExpr * memberExpr ) {
                        if ( ! checkWarnings( function ) || ! isCtor ) {
                                visit_children = false;
                                return;
                        }

                        if ( isThisExpression( memberExpr->get_aggregate(), thisParam ) ) {
                                if ( unhandled.count( memberExpr->get_member() ) ) {
                                        // emit a warning because a member was used before it was constructed
                                        usedUninit.insert( { memberExpr->get_member(), memberExpr->location } );
                                }
                        }
                }

                template< typename Visitor, typename... Params >
                void error( Visitor & v, CodeLocation loc, const Params &... params ) {
                        SemanticErrorException err( loc, toString( params... ) );
                        v.errors.append( err );
                }

                template< typename... Params >
                void GenStructMemberCalls::emit( CodeLocation loc, const Params &... params ) {
                        // toggle warnings vs. errors here.
                        // warn( params... );
                        error( *this, loc, params... );
                }

                Expression * GenStructMemberCalls::postmutate( UntypedExpr * untypedExpr ) {
                        Expression * newExpr = untypedExpr;
                        ResolvExpr::findVoidExpression( newExpr, indexer );
                        return newExpr;
                }

                Expression * FixCtorExprs::postmutate( ConstructorExpr * ctorExpr ) {
                        static UniqueName tempNamer( "_tmp_ctor_expr" );
                        // xxx - is the size check necessary?
                        assert( ctorExpr->result && ctorExpr->get_result()->size() == 1 );

                        // xxx - this can be TupleAssignExpr now. Need to properly handle this case.
                        ApplicationExpr * callExpr = strict_dynamic_cast< ApplicationExpr * > ( ctorExpr->get_callExpr() );
                        TypeSubstitution * env = ctorExpr->get_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.
                        ObjectDecl * tmp = ObjectDecl::newObject( tempNamer.newName(), callExpr->args.front()->result->clone(), nullptr );
                        declsToAddBefore.push_back( tmp );
                        delete ctorExpr;

                        // build assignment and replace constructor's first argument with new temporary
                        Expression *& firstArg = callExpr->get_args().front();
                        Expression * assign = new UntypedExpr( new NameExpr( "?=?" ), { new AddressExpr( new VariableExpr( tmp ) ), new AddressExpr( firstArg ) } );
                        firstArg = new VariableExpr( tmp );

                        // resolve assignment and dispose of new env
                        ResolvExpr::findVoidExpression( assign, indexer );
                        delete assign->env;
                        assign->env = nullptr;

                        // for constructor expr:
                        //   T x;
                        //   x{};
                        // results in:
                        //   T x;
                        //   T & tmp;
                        //   &tmp = &x, ?{}(tmp), tmp
                        CommaExpr * commaExpr = new CommaExpr( assign, new CommaExpr( callExpr, new VariableExpr( tmp ) ) );
                        commaExpr->set_env( env );
                        return commaExpr;
                }
        } // namespace
} // namespace InitTweak

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