source: src/InitTweak/FixInit.cc @ caab997

//
// 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 Jun 21 17:35:05 2017
// Update Count     : 74
//
#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/Visitor.h"           // for acceptAll, maybeAccept

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 {
                typedef std::unordered_map< int, int > UnqCount;

                struct InsertImplicitCalls : public WithTypeSubstitution {
                        /// 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 WithIndexer, public WithShortCircuiting, public WithTypeSubstitution {
                        /// 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, UnqCount & unqCount );

                        ResolveCopyCtors( UnqCount & unqCount ) : unqCount( unqCount ) {}

                        void postvisit( ImplicitCopyCtorExpr * impCpCtorExpr );
                        void postvisit( StmtExpr * stmtExpr );
                        void previsit( UniqueExpr * unqExpr );
                        void postvisit( 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 );

                        UnqCount & unqCount; // count the number of times each unique expr ID appears
                        std::unordered_set< int > vars;
                };

                /// 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( ObjectDecl * objDecl );
                        void previsit( FunctionDecl * funcDecl );

                        void previsit( CompoundStmt * compoundStmt );
                        void postvisit( CompoundStmt * compoundStmt );
                        void previsit( ReturnStmt * returnStmt );
                        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;
                };

                class FixCopyCtors final : public WithStmtsToAdd, public WithShortCircuiting, public WithVisitorRef<FixCopyCtors> {
                  public:
                        FixCopyCtors( UnqCount & unqCount ) : unqCount( unqCount ){}
                        /// expand ImplicitCopyCtorExpr nodes into the temporary declarations, copy constructors, call expression,
                        /// and destructors
                        static void fixCopyCtors( std::list< Declaration * > &translationUnit, UnqCount & unqCount );

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

                        UnqCount & unqCount;
                };

                struct GenStructMemberCalls final : public WithGuards, public WithShortCircuiting, public WithIndexer {
                        /// 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 previsit( FunctionDecl * funcDecl );
                        void postvisit( FunctionDecl * funcDecl );

                        void previsit( MemberExpr * memberExpr );
                        void previsit( ApplicationExpr * appExpr );

                        SemanticError 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;
                };

                // very simple resolver-like mutator class - used to
                // resolve UntypedExprs that are found within newly
                // generated constructor/destructor calls
                class MutatingResolver final : public Mutator {
                  public:
                        MutatingResolver( SymTab::Indexer & indexer ) : indexer( indexer ) {}

                        using Mutator::mutate;
                        virtual DeclarationWithType* mutate( ObjectDecl *objectDecl ) override;
                        virtual Expression* mutate( UntypedExpr *untypedExpr ) override;

                  private:
                        SymTab::Indexer & indexer;
                };

                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 );
                };
        } // namespace

        void fix( std::list< Declaration * > & translationUnit, const std::string & filename, bool inLibrary ) {
                // fixes ConstructorInit for global variables. should happen before fixInitializers.
                InitTweak::fixGlobalInit( translationUnit, filename, inLibrary );

                UnqCount unqCount;

                InsertImplicitCalls::insert( translationUnit );
                ResolveCopyCtors::resolveImplicitCalls( translationUnit, unqCount );
                InsertDtors::insert( translationUnit );
                FixInit::fixInitializers( translationUnit );

                // FixCopyCtors must happen after FixInit, so that destructors are placed correctly
                FixCopyCtors::fixCopyCtors( translationUnit, unqCount );

                GenStructMemberCalls::generate( translationUnit );

                // xxx - ctor expansion currently has to be after FixCopyCtors, because there is currently a
                // hack in the way untyped assignments are generated, where the first argument cannot have
                // its address taken because of the way codegeneration handles UntypedExpr vs. ApplicationExpr.
                // Thus such assignment exprs must never pushed through expression resolution (and thus should
                // not go through the FixCopyCtors pass), otherwise they will fail -- guaranteed.
                // Also needs to happen after GenStructMemberCalls, since otherwise member constructors exprs
                // don't look right, and a member can be constructed more than once.
                FixCtorExprs::fix( translationUnit );
        }

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

                void ResolveCopyCtors::resolveImplicitCalls( std::list< Declaration * > & translationUnit, UnqCount & unqCount ) {
                        PassVisitor<ResolveCopyCtors> resolver( unqCount );
                        acceptAll( 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.
                        SemanticError errors;
                        for ( std::list< Declaration * >::iterator i = translationUnit.begin(); i != translationUnit.end(); ++i ) {
                                try {
                                        maybeMutate( *i, fixer );
                                        translationUnit.splice( i, fixer.pass.staticDtorDecls );
                                } catch( SemanticError &e ) {
                                        e.set_location( (*i)->location );
                                        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 FixCopyCtors::fixCopyCtors( std::list< Declaration * > & translationUnit, UnqCount & unqCount ) {
                        PassVisitor<FixCopyCtors> fixer( unqCount );
                        mutateAll( translationUnit, fixer );
                }

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

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

                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->get_env() ) {
                                // Extract useful information and discard new environments. Keeping them causes problems in PolyMutator passes.
                                env->add( *resolved->get_env() );
                                delete resolved->get_env();
                                resolved->set_env( nullptr );
                        } // if
                        delete stmt;
                        if ( TupleAssignExpr * assign = dynamic_cast< TupleAssignExpr * >( resolved ) ) {
                                // fix newly generated StmtExpr
                                postvisit( 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;
                                }
                        }

                        // 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
                        arg = new CommaExpr( cpCtor, new VariableExpr( tmp ) );
                        impCpCtorExpr->tempDecls.push_back( tmp );
                        impCpCtorExpr->dtors.push_front( makeCtorDtor( "^?{}", tmp ) );
                }

                void ResolveCopyCtors::destructRet( ObjectDecl * ret, ImplicitCopyCtorExpr * impCpCtorExpr ) {
                        impCpCtorExpr->get_dtors().push_front( makeCtorDtor( "^?{}", ret ) );
                }

                void ResolveCopyCtors::postvisit( ImplicitCopyCtorExpr *impCpCtorExpr ) {
                        CP_CTOR_PRINT( std::cerr << "ResolveCopyCtors: " << impCpCtorExpr << std::endl; )

                        ApplicationExpr * appExpr = impCpCtorExpr->callExpr;

                        // 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() ) {
                                        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 );
                                impCpCtorExpr->returnDecls.push_back( ret );
                                CP_CTOR_PRINT( std::cerr << "makeCtorDtor for a return" << std::endl; )
                                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( ret, impCpCtorExpr );
                                }
                        } // for
                        CP_CTOR_PRINT( std::cerr << "after Resolving: " << impCpCtorExpr << std::endl; )
                }

                void ResolveCopyCtors::postvisit( StmtExpr * stmtExpr ) {
                        assert( env );
                        assert( stmtExpr->get_result() );
                        Type * result = stmtExpr->get_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 );
                                stmtExpr->returnDecls.push_front( ret );

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

                                stmtExpr->dtors.push_front( makeCtorDtor( "^?{}", ret ) );
                        } // if
                }

                void ResolveCopyCtors::previsit( UniqueExpr * unqExpr ) {
                        unqCount[ unqExpr->get_id() ]++;  // count the number of unique expressions for each ID
                        if ( vars.count( unqExpr->get_id() ) ) {
                                // xxx - hack to prevent double-handling of unique exprs, otherwise too many temporary variables and destructors are generated
                                visit_children = false;
                        }
                }

                // 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::postvisit( UniqueExpr * unqExpr ) {
                        if ( vars.count( unqExpr->get_id() ) ) {
                                // xxx - hack to prevent double-handling of unique exprs, otherwise too many temporary variables and destructors are generated
                                return;
                        }

                        // 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->get_result() );
                        if ( ImplicitCopyCtorExpr * impCpCtorExpr = dynamic_cast<ImplicitCopyCtorExpr*>( unqExpr->get_expr() ) ) {
                                // note the variable used as the result from the call
                                assert( impCpCtorExpr->get_result() && impCpCtorExpr->get_returnDecls().size() == 1 );
                                unqExpr->set_var( new VariableExpr( impCpCtorExpr->get_returnDecls().front() ) );
                        } else {
                                // expr isn't a call expr, so create a new temporary variable to use to hold the value of the unique expression
                                unqExpr->set_object( ObjectDecl::newObject( toString("_unq", unqExpr->get_id()), unqExpr->get_result()->clone(), makeInit( unqExpr->get_result() ) ) );
                                unqExpr->set_var( new VariableExpr( unqExpr->get_object() ) );
                        }
                        vars.insert( unqExpr->get_id() );
                }

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

                        std::list< ObjectDecl * > & tempDecls = impCpCtorExpr->get_tempDecls();
                        std::list< ObjectDecl * > & returnDecls = impCpCtorExpr->get_returnDecls();
                        std::list< Expression * > & dtors = impCpCtorExpr->get_dtors();

                        // add all temporary declarations and their constructors
                        for ( ObjectDecl * obj : tempDecls ) {
                                stmtsToAddBefore.push_back( new DeclStmt( obj ) );
                        } // for
                        for ( ObjectDecl * obj : returnDecls ) {
                                stmtsToAddBefore.push_back( new DeclStmt( obj ) );
                        } // for

                        // add destructors after current statement
                        for ( Expression * dtor : dtors ) {
                                stmtsToAddAfter.push_back( new ExprStmt( dtor ) );
                        } // for

                        ObjectDecl * returnDecl = returnDecls.empty() ? nullptr : returnDecls.front();
                        Expression * callExpr = impCpCtorExpr->get_callExpr();

                        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
                        dtors.clear();
                        tempDecls.clear();
                        returnDecls.clear();
                        impCpCtorExpr->set_callExpr( nullptr );
                        std::swap( impCpCtorExpr->env, callExpr->env );
                        assert( impCpCtorExpr->env == nullptr );
                        delete impCpCtorExpr;

                        if ( returnDecl ) {
                                ApplicationExpr * assign = createBitwiseAssignment( new VariableExpr( returnDecl ), callExpr );
                                Expression * retExpr = new CommaExpr( assign, new VariableExpr( returnDecl ) );
                                // move env from callExpr to retExpr
                                std::swap( retExpr->env, callExpr->env );
                                return retExpr;
                        } else {
                                return callExpr;
                        } // if
                }

                void FixCopyCtors::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 statment forces the temporaries to be added
                        // to the outer context, rather than inside of the statement expression.
                        visit_children = false;
                        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() ) {
                                for ( ObjectDecl * obj : stmtExpr->returnDecls ) {
                                        stmtsToAddBefore.push_back( new DeclStmt( obj ) );
                                } // for
                                // add destructors after current statement
                                for ( Expression * dtor : stmtExpr->dtors ) {
                                        stmtsToAddAfter.push_back( new ExprStmt( dtor ) );
                                } // for
                                // must have a non-empty body, otherwise it wouldn't have a result
                                assert( ! stmts.empty() );
                                assertf( ! stmtExpr->returnDecls.empty() || stmtExpr->dtors.empty(), "StmtExpr returns non-void, but no return decls: %s", toString( stmtExpr ).c_str() );
                                // if there is a return decl, add a use as the last statement; will not have return decl on non-constructable returns
                                if ( ! stmtExpr->returnDecls.empty() ) {
                                        stmts.push_back( new ExprStmt( new VariableExpr( stmtExpr->returnDecls.front() ) ) );
                                }
                                stmtExpr->returnDecls.clear();
                                stmtExpr->dtors.clear();
                        }
                        assert( stmtExpr->returnDecls.empty() );
                        assert( stmtExpr->dtors.empty() );
                }

                void FixCopyCtors::premutate( UniqueExpr * unqExpr ) {
                        visit_children = false;
                        unqCount[ unqExpr->get_id() ]--;
                        static std::unordered_map< int, std::list< Statement * > > dtors;
                        static std::unordered_map< int, UniqueExpr * > unqMap;
                        // has to be done to clean up ImplicitCopyCtorExpr nodes, even when this node was skipped in previous passes
                        if ( unqMap.count( unqExpr->get_id() ) ) {
                                // take data from other UniqueExpr to ensure consistency
                                delete unqExpr->get_expr();
                                unqExpr->set_expr( unqMap[unqExpr->get_id()]->get_expr()->clone() );
                                delete unqExpr->get_result();
                                unqExpr->set_result( maybeClone( unqExpr->get_expr()->get_result() ) );
                                if ( unqCount[ unqExpr->get_id() ] == 0 ) {  // insert destructor after the last use of the unique expression
                                        stmtsToAddAfter.splice( stmtsToAddAfter.end(), dtors[ unqExpr->get_id() ] );
                                }
                                return;
                        }
                        PassVisitor<FixCopyCtors> fixer( unqCount );
                        unqExpr->set_expr( unqExpr->get_expr()->acceptMutator( fixer ) ); // stmtexprs contained should not be separately fixed, so this must occur after the lookup
                        stmtsToAddBefore.splice( stmtsToAddBefore.end(), fixer.pass.stmtsToAddBefore );
                        unqMap[unqExpr->get_id()] = unqExpr;
                        if ( unqCount[ unqExpr->get_id() ] == 0 ) {  // insert destructor after the last use of the unique expression
                                stmtsToAddAfter.splice( stmtsToAddAfter.end(), dtors[ unqExpr->get_id() ] );
                        } else { // remember dtors for last instance of unique expr
                                dtors[ unqExpr->get_id() ] = fixer.pass.stmtsToAddAfter;
                        }
                        return;
                }

                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;
                                                }
                                        } // 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 );
                }


                template<typename Iterator, typename OutputIterator>
                void insertDtors( Iterator begin, Iterator end, OutputIterator out ) {
                        for ( Iterator it = begin ; it != end ; ++it ) {
                                // extract destructor statement from the object decl and insert it into the output. Note that this is
                                // only called on lists of non-static objects with implicit non-intrinsic dtors, so if the user manually
                                // calls an intrinsic dtor then the call must (and will) still be generated since the argument may
                                // contain side effects.
                                ObjectDecl * objDecl = *it;
                                ConstructorInit * ctorInit = dynamic_cast< ConstructorInit * >( objDecl->get_init() );
                                assert( ctorInit && ctorInit->get_dtor() );
                                *out++ = ctorInit->get_dtor()->clone();
                        } // for
                }

                void InsertDtors::previsit( ObjectDecl * objDecl ) {
                        // remember non-static destructed objects so that their destructors can be inserted later
                        if ( ! objDecl->get_storageClasses().is_static ) {
                                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() );
                                        Statement * dtor = ctorInit->get_dtor();
                                        // don't need to call intrinsic dtor, because it does nothing, but
                                        // non-intrinsic dtors must be called
                                        if ( dtor && ! isIntrinsicSingleArgCallStmt( dtor ) ) {
                                                // set dtor location to the object's location for error messages
                                                ctorInit->dtor->location = objDecl->location;
                                                reverseDeclOrder.front().push_front( objDecl );
                                        } // if
                                } // if
                        } // if
                }

                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.
                }

                void InsertDtors::previsit( CompoundStmt * compoundStmt ) {
                        // visit statements - this will also populate reverseDeclOrder list.  don't want to dump all destructors
                        // when block is left, just the destructors associated with variables defined in this block, so push a new
                        // list to the top of the stack so that we can differentiate scopes
                        reverseDeclOrder.push_front( OrderedDecls() );
                        Parent::previsit( compoundStmt );
                }

                void InsertDtors::postvisit( CompoundStmt * compoundStmt ) {
                        // add destructors for the current scope that we're exiting, unless the last statement is a return, which
                        // causes unreachable code warnings
                        std::list< Statement * > & statements = compoundStmt->get_kids();
                        if ( ! statements.empty() && ! dynamic_cast< ReturnStmt * >( statements.back() ) ) {
                                insertDtors( reverseDeclOrder.front().begin(), reverseDeclOrder.front().end(), back_inserter( statements ) );
                        }
                        reverseDeclOrder.pop_front();
                }

                void InsertDtors::previsit( ReturnStmt * ) {
                        // return exits all scopes, so dump destructors for all scopes
                        for ( OrderedDecls & od : reverseDeclOrder ) {
                                insertDtors( od.begin(), od.end(), back_inserter( stmtsToAddBefore ) );
                        } // for
                }

                // 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() ) {
                                throw SemanticError( std::string("jump to label '") + stmt->get_target().get_name() + "' crosses initialization of " + (*diff.begin())->get_name() + " ", stmt );
                        } // if
                        // S_G-S_L results in set of objects that must be destructed
                        diff.clear();
                        std::set_difference( curVars.begin(), curVars.end(), lvars.begin(), lvars.end(), std::inserter( diff, diff.end() ) );
                        DTOR_PRINT(
                                std::cerr << "S_G-S_L = " << printSet( diff ) << std::endl;
                        )
                        if ( ! diff.empty() ) {
                                // create an auxilliary set for fast lookup -- can't make diff a set, because diff ordering should be consistent for error messages.
                                std::unordered_set<ObjectDecl *> needsDestructor( diff.begin(), diff.end() );

                                // go through decl ordered list of objectdecl. for each element that occurs in diff, output destructor
                                OrderedDecls ordered;
                                for ( OrderedDecls & rdo : reverseDeclOrder ) {
                                        // add elements from reverseDeclOrder into ordered if they occur in diff - it is key that this happens in reverse declaration order.
                                        copy_if( rdo.begin(), rdo.end(), back_inserter( ordered ), [&]( ObjectDecl * objDecl ) { return needsDestructor.count( objDecl ); } );
                                } // for
                                insertDtors( ordered.begin(), ordered.end(), back_inserter( stmtsToAddBefore ) );
                        } // 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::previsit( FunctionDecl * funcDecl ) {
                        GuardValue( function );
                        GuardValue( unhandled );
                        GuardValue( usedUninit );
                        GuardValue( thisParam );
                        GuardValue( isCtor );
                        GuardValue( structDecl );
                        errors = SemanticError();  // 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 );
                                                }
                                        }
                                }
                        }
                }

                void GenStructMemberCalls::postvisit( 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();

                                                MutatingResolver resolver( indexer );
                                                try {
                                                        callStmt->acceptMutator( resolver );
                                                        if ( isCtor ) {
                                                                function->get_statements()->push_front( callStmt );
                                                        } else {
                                                                // destructor statements should be added at the end
                                                                function->get_statements()->push_back( callStmt );
                                                        }
                                                } catch ( SemanticError & 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;
                        }
                }

                /// 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::previsit( ApplicationExpr * appExpr ) {
                        if ( ! checkWarnings( function ) ) {
                                visit_children = false;
                                return;
                        }

                        std::string fname = getFunctionName( appExpr );
                        if ( fname == function->get_name() ) {
                                // call to same kind of function
                                Expression * firstParam = appExpr->get_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->get_aggregate(), thisParam ) ) {
                                                unhandled.erase( memberExpr->get_member() );
                                        }
                                }
                        }
                }

                void GenStructMemberCalls::previsit( 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 ) {
                        SemanticError err( toString( params... ) );
                        err.set_location( loc );
                        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... );
                }

                DeclarationWithType * MutatingResolver::mutate( ObjectDecl * objectDecl ) {
                        // add object to the indexer assumes that there will be no name collisions
                        // in generated code. If this changes, add mutate methods for entities with
                        // scope and call {enter,leave}Scope explicitly.
                        indexer.addId( objectDecl );
                        return objectDecl;
                }

                Expression * MutatingResolver::mutate( 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: //