source: src/InitTweak/GenInit.cc @ 2a84d994

//
// 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.
//
// GenInit.cc -- Generate initializers, and other stuff.
//
// Author           : Rob Schluntz
// Created On       : Mon May 18 07:44:20 2015
// Last Modified By : Andrew Beach
// Last Modified On : Mon Oct 25 13:53:00 2021
// Update Count     : 186
//
#include "GenInit.h"

#include <stddef.h>                    // for NULL
#include <algorithm>                   // for any_of
#include <cassert>                     // for assert, strict_dynamic_cast, assertf
#include <deque>
#include <iterator>                    // for back_inserter, inserter, back_inse...
#include <list>                        // for _List_iterator, list

#include "AST/Decl.hpp"
#include "AST/Init.hpp"
#include "AST/Pass.hpp"
#include "AST/Node.hpp"
#include "AST/Stmt.hpp"
#include "CompilationState.h"
#include "CodeGen/OperatorTable.h"
#include "Common/PassVisitor.h"        // for PassVisitor, WithGuards, WithShort...
#include "Common/SemanticError.h"      // for SemanticError
#include "Common/ToString.hpp"         // for toCString
#include "Common/UniqueName.h"         // for UniqueName
#include "Common/utility.h"            // for ValueGuard, maybeClone
#include "GenPoly/GenPoly.h"           // for getFunctionType, isPolyType
#include "GenPoly/ScopedSet.h"         // for ScopedSet, ScopedSet<>::const_iter...
#include "InitTweak.h"                 // for isConstExpr, InitExpander, checkIn...
#include "ResolvExpr/Resolver.h"
#include "SymTab/Autogen.h"            // for genImplicitCall
#include "SymTab/Mangler.h"            // for Mangler
#include "SynTree/LinkageSpec.h"       // for isOverridable, C
#include "SynTree/Declaration.h"       // for ObjectDecl, DeclarationWithType
#include "SynTree/Expression.h"        // for VariableExpr, UntypedExpr, Address...
#include "SynTree/Initializer.h"       // for ConstructorInit, SingleInit, Initi...
#include "SynTree/Label.h"             // for Label
#include "SynTree/Mutator.h"           // for mutateAll
#include "SynTree/Statement.h"         // for CompoundStmt, ImplicitCtorDtorStmt
#include "SynTree/Type.h"              // for Type, ArrayType, Type::Qualifiers
#include "SynTree/Visitor.h"           // for acceptAll, maybeAccept
#include "Tuples/Tuples.h"             // for maybeImpure
#include "Validate/FindSpecialDecls.h" // for SizeType

namespace InitTweak {
        namespace {
                const std::list<Label> noLabels;
                const std::list<Expression *> noDesignators;
        }

        struct ReturnFixer : public WithStmtsToAdd, public WithGuards {
                /// consistently allocates a temporary variable for the return value
                /// of a function so that anything which the resolver decides can be constructed
                /// into the return type of a function can be returned.
                static void makeReturnTemp( std::list< Declaration * > &translationUnit );

                void premutate( FunctionDecl *functionDecl );
                void premutate( ReturnStmt * returnStmt );

          protected:
                FunctionType * ftype = nullptr;
                std::string funcName;
        };

        struct CtorDtor : public WithGuards, public WithShortCircuiting, public WithVisitorRef<CtorDtor>  {
                /// create constructor and destructor statements for object declarations.
                /// the actual call statements will be added in after the resolver has run
                /// so that the initializer expression is only removed if a constructor is found
                /// and the same destructor call is inserted in all of the appropriate locations.
                static void generateCtorDtor( std::list< Declaration * > &translationUnit );

                void previsit( ObjectDecl * );
                void previsit( FunctionDecl *functionDecl );

                // should not traverse into any of these declarations to find objects
                // that need to be constructed or destructed
                void previsit( StructDecl *aggregateDecl );
                void previsit( AggregateDecl * ) { visit_children = false; }
                void previsit( NamedTypeDecl * ) { visit_children = false; }
                void previsit( FunctionType * ) { visit_children = false; }

                void previsit( CompoundStmt * compoundStmt );

          private:
                // set of mangled type names for which a constructor or destructor exists in the current scope.
                // these types require a ConstructorInit node to be generated, anything else is a POD type and thus
                // should not have a ConstructorInit generated.

                ManagedTypes managedTypes;
                bool inFunction = false;
        };

        struct HoistArrayDimension final : public WithDeclsToAdd, public WithShortCircuiting, public WithGuards, public WithIndexer {
                /// hoist dimension from array types in object declaration so that it uses a single
                /// const variable of type size_t, so that side effecting array dimensions are only
                /// computed once.
                static void hoistArrayDimension( std::list< Declaration * > & translationUnit );

                void premutate( ObjectDecl * objectDecl );
                DeclarationWithType * postmutate( ObjectDecl * objectDecl );
                void premutate( FunctionDecl *functionDecl );
                // should not traverse into any of these declarations to find objects
                // that need to be constructed or destructed
                void premutate( AggregateDecl * ) { visit_children = false; }
                void premutate( NamedTypeDecl * ) { visit_children = false; }
                void premutate( FunctionType * ) { visit_children = false; }

                // need this so that enumerators are added to the indexer, due to premutate(AggregateDecl *)
                void premutate( EnumDecl * ) {}

                void hoist( Type * type );

                Type::StorageClasses storageClasses;
                bool inFunction = false;
        };

        struct HoistArrayDimension_NoResolve final : public WithDeclsToAdd, public WithShortCircuiting, public WithGuards {
                /// hoist dimension from array types in object declaration so that it uses a single
                /// const variable of type size_t, so that side effecting array dimensions are only
                /// computed once.
                static void hoistArrayDimension( std::list< Declaration * > & translationUnit );

                void premutate( ObjectDecl * objectDecl );
                DeclarationWithType * postmutate( ObjectDecl * objectDecl );
                void premutate( FunctionDecl *functionDecl );
                // should not traverse into any of these declarations to find objects
                // that need to be constructed or destructed
                void premutate( AggregateDecl * ) { visit_children = false; }
                void premutate( NamedTypeDecl * ) { visit_children = false; }
                void premutate( FunctionType * ) { visit_children = false; }

                void hoist( Type * type );

                Type::StorageClasses storageClasses;
                bool inFunction = false;
        };

        void genInit( std::list< Declaration * > & translationUnit ) {
                if (!useNewAST) {
                        HoistArrayDimension::hoistArrayDimension( translationUnit );
                }
                else {
                        HoistArrayDimension_NoResolve::hoistArrayDimension( translationUnit );
                }
                fixReturnStatements( translationUnit );

                if (!useNewAST) {
                        CtorDtor::generateCtorDtor( translationUnit );
                }
        }

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

        void ReturnFixer::premutate( ReturnStmt *returnStmt ) {
                std::list< DeclarationWithType * > & returnVals = ftype->get_returnVals();
                assert( returnVals.size() == 0 || returnVals.size() == 1 );
                // hands off if the function returns a reference - we don't want to allocate a temporary if a variable's address
                // is being returned
                if ( returnStmt->expr && returnVals.size() == 1 && isConstructable( returnVals.front()->get_type() ) ) {
                        // explicitly construct the return value using the return expression and the retVal object
                        assertf( returnVals.front()->name != "", "Function %s has unnamed return value\n", funcName.c_str() );

                        ObjectDecl * retVal = strict_dynamic_cast< ObjectDecl * >( returnVals.front() );
                        if ( VariableExpr * varExpr = dynamic_cast< VariableExpr * >( returnStmt->expr ) ) {
                                // return statement has already been mutated - don't need to do it again
                                if ( varExpr->var == retVal ) return;
                        }
                        Statement * stmt = genCtorDtor( "?{}", retVal, returnStmt->expr );
                        assertf( stmt, "ReturnFixer: genCtorDtor returned nullptr: %s / %s", toString( retVal ).c_str(), toString( returnStmt->expr ).c_str() );
                        stmtsToAddBefore.push_back( stmt );

                        // return the retVal object
                        returnStmt->expr = new VariableExpr( returnVals.front() );
                } // if
        }

        void ReturnFixer::premutate( FunctionDecl *functionDecl ) {
                GuardValue( ftype );
                GuardValue( funcName );

                ftype = functionDecl->type;
                funcName = functionDecl->name;
        }

        // precompute array dimension expression, because constructor generation may duplicate it,
        // which would be incorrect if it is a side-effecting computation.
        void HoistArrayDimension::hoistArrayDimension( std::list< Declaration * > & translationUnit ) {
                PassVisitor<HoistArrayDimension> hoister;
                mutateAll( translationUnit, hoister );
        }

        void HoistArrayDimension::premutate( ObjectDecl * objectDecl ) {
                GuardValue( storageClasses );
                storageClasses = objectDecl->get_storageClasses();
        }

        DeclarationWithType * HoistArrayDimension::postmutate( ObjectDecl * objectDecl ) {
                hoist( objectDecl->get_type() );
                return objectDecl;
        }

        void HoistArrayDimension::hoist( Type * type ) {
                // if in function, generate const size_t var
                static UniqueName dimensionName( "_array_dim" );

                // C doesn't allow variable sized arrays at global scope or for static variables, so don't hoist dimension.
                if ( ! inFunction ) return;
                if ( storageClasses.is_static ) return;

                if ( ArrayType * arrayType = dynamic_cast< ArrayType * >( type ) ) {
                        if ( ! arrayType->get_dimension() ) return; // xxx - recursive call to hoist?

                        // need to resolve array dimensions in order to accurately determine if constexpr
                        ResolvExpr::findSingleExpression( arrayType->dimension, Validate::SizeType->clone(), indexer );
                        // array is variable-length when the dimension is not constexpr
                        arrayType->isVarLen = ! isConstExpr( arrayType->dimension );
                        // don't need to hoist dimension if it's definitely pure - only need to if there's potential for side effects.
                        // xxx - hoisting has no side effects anyways, so don't skip since we delay resolve
                        // still try to detect constant expressions
                        if ( ! Tuples::maybeImpure( arrayType->dimension ) ) return;

                        ObjectDecl * arrayDimension = new ObjectDecl( dimensionName.newName(), storageClasses, LinkageSpec::C, 0, Validate::SizeType->clone(), new SingleInit( arrayType->get_dimension() ) );
                        arrayDimension->get_type()->set_const( true );

                        arrayType->set_dimension( new VariableExpr( arrayDimension ) );
                        declsToAddBefore.push_back( arrayDimension );

                        hoist( arrayType->get_base() );
                        return;
                }
        }

        void HoistArrayDimension::premutate( FunctionDecl * ) {
                GuardValue( inFunction );
                inFunction = true;
        }

        // precompute array dimension expression, because constructor generation may duplicate it,
        // which would be incorrect if it is a side-effecting computation.
        void HoistArrayDimension_NoResolve::hoistArrayDimension( std::list< Declaration * > & translationUnit ) {
                PassVisitor<HoistArrayDimension_NoResolve> hoister;
                mutateAll( translationUnit, hoister );
        }

        void HoistArrayDimension_NoResolve::premutate( ObjectDecl * objectDecl ) {
                GuardValue( storageClasses );
                storageClasses = objectDecl->get_storageClasses();
        }

        DeclarationWithType * HoistArrayDimension_NoResolve::postmutate( ObjectDecl * objectDecl ) {
                hoist( objectDecl->get_type() );
                return objectDecl;
        }

        void HoistArrayDimension_NoResolve::hoist( Type * type ) {
                // if in function, generate const size_t var
                static UniqueName dimensionName( "_array_dim" );

                // C doesn't allow variable sized arrays at global scope or for static variables, so don't hoist dimension.
                if ( ! inFunction ) return;
                if ( storageClasses.is_static ) return;

                if ( ArrayType * arrayType = dynamic_cast< ArrayType * >( type ) ) {
                        if ( ! arrayType->get_dimension() ) return; // xxx - recursive call to hoist?
                        // don't need to hoist dimension if it's definitely pure - only need to if there's potential for side effects.
                        // xxx - hoisting has no side effects anyways, so don't skip since we delay resolve
                        // still try to detect constant expressions
                        if ( ! Tuples::maybeImpure( arrayType->dimension ) ) return;

                        ObjectDecl * arrayDimension = new ObjectDecl( dimensionName.newName(), storageClasses, LinkageSpec::C, 0, Validate::SizeType->clone(), new SingleInit( arrayType->get_dimension() ) );
                        arrayDimension->get_type()->set_const( true );

                        arrayType->set_dimension( new VariableExpr( arrayDimension ) );
                        declsToAddBefore.push_back( arrayDimension );

                        hoist( arrayType->get_base() );
                        return;
                }
        }

        void HoistArrayDimension_NoResolve::premutate( FunctionDecl * ) {
                GuardValue( inFunction );
                inFunction = true;
        }

namespace {

#       warning Remove the _New suffix after the conversion is complete.
        struct HoistArrayDimension_NoResolve_New final :
                        public ast::WithDeclsToAdd<>, public ast::WithShortCircuiting,
                        public ast::WithGuards, public ast::WithConstTranslationUnit,
                        public ast::WithVisitorRef<HoistArrayDimension_NoResolve_New> {
                void previsit( const ast::ObjectDecl * decl );
                const ast::DeclWithType * postvisit( const ast::ObjectDecl * decl );
                // Do not look for objects inside there declarations (and type).
                void previsit( const ast::AggregateDecl * ) { visit_children = false; }
                void previsit( const ast::NamedTypeDecl * ) { visit_children = false; }
                void previsit( const ast::FunctionType * ) { visit_children = false; }

                const ast::Type * hoist( const ast::Type * type );

                ast::Storage::Classes storageClasses;
        };

        void HoistArrayDimension_NoResolve_New::previsit(
                        const ast::ObjectDecl * decl ) {
                GuardValue( storageClasses ) = decl->storage;
        }

        const ast::DeclWithType * HoistArrayDimension_NoResolve_New::postvisit(
                        const ast::ObjectDecl * objectDecl ) {
                return mutate_field( objectDecl, &ast::ObjectDecl::type,
                                hoist( objectDecl->type ) );
        }

        const ast::Type * HoistArrayDimension_NoResolve_New::hoist(
                        const ast::Type * type ) {
                static UniqueName dimensionName( "_array_dim" );

                if ( !isInFunction() || storageClasses.is_static ) {
                        return type;
                }

                if ( auto arrayType = dynamic_cast< const ast::ArrayType * >( type ) ) {
                        if ( nullptr == arrayType->dimension ) {
                                return type;
                        }

                        if ( !Tuples::maybeImpure( arrayType->dimension ) ) {
                                return type;
                        }

                        ast::ptr<ast::Type> dimType = transUnit().global.sizeType;
                        assert( dimType );
                        add_qualifiers( dimType, ast::CV::Qualifiers( ast::CV::Const ) );

                        ast::ObjectDecl * arrayDimension = new ast::ObjectDecl(
                                arrayType->dimension->location,
                                dimensionName.newName(),
                                dimType,
                                new ast::SingleInit(
                                        arrayType->dimension->location,
                                        arrayType->dimension
                                )
                        );

                        ast::ArrayType * mutType = ast::mutate( arrayType );
                        mutType->dimension = new ast::VariableExpr(
                                        arrayDimension->location, arrayDimension );
                        declsToAddBefore.push_back( arrayDimension );

                        mutType->base = hoist( mutType->base );
                        return mutType;
                }
                return type;
        }

        struct ReturnFixer_New final :
                        public ast::WithStmtsToAdd<>, ast::WithGuards, ast::WithShortCircuiting {
                void previsit( const ast::FunctionDecl * decl );
                const ast::ReturnStmt * previsit( const ast::ReturnStmt * stmt );
        private:
                const ast::FunctionDecl * funcDecl = nullptr;
        };

        void ReturnFixer_New::previsit( const ast::FunctionDecl * decl ) {
                if (decl->linkage == ast::Linkage::Intrinsic) visit_children = false;
                GuardValue( funcDecl ) = decl;
        }

        const ast::ReturnStmt * ReturnFixer_New::previsit(
                        const ast::ReturnStmt * stmt ) {
                auto & returns = funcDecl->returns;
                assert( returns.size() < 2 );
                // Hands off if the function returns a reference.
                // Don't allocate a temporary if the address is returned.
                if ( stmt->expr && 1 == returns.size() ) {
                        ast::ptr<ast::DeclWithType> retDecl = returns.front();
                        if ( isConstructable( retDecl->get_type() ) ) {
                                // Explicitly construct the return value using the return
                                // expression and the retVal object.
                                assertf( "" != retDecl->name,
                                        "Function %s has unnamed return value.\n",
                                        funcDecl->name.c_str() );

                                auto retVal = retDecl.strict_as<ast::ObjectDecl>();
                                if ( auto varExpr = stmt->expr.as<ast::VariableExpr>() ) {
                                        // Check if the return statement is already set up.
                                        if ( varExpr->var == retVal ) return stmt;
                                }
                                ast::ptr<ast::Stmt> ctorStmt = genCtorDtor(
                                        retVal->location, "?{}", retVal, stmt->expr );
                                assertf( ctorStmt,
                                        "ReturnFixer: genCtorDtor returned nullptr: %s / %s",
                                        toString( retVal ).c_str(),
                                        toString( stmt->expr ).c_str() );
                                stmtsToAddBefore.push_back( ctorStmt );

                                // Return the retVal object.
                                ast::ReturnStmt * mutStmt = ast::mutate( stmt );
                                mutStmt->expr = new ast::VariableExpr(
                                        stmt->location, retDecl );
                                return mutStmt;
                        }
                }
                return stmt;
        }

} // namespace

        void genInit( ast::TranslationUnit & transUnit ) {
                ast::Pass<HoistArrayDimension_NoResolve_New>::run( transUnit );
                ast::Pass<ReturnFixer_New>::run( transUnit );
        }

        void fixReturnStatements( ast::TranslationUnit & transUnit ) {
                ast::Pass<ReturnFixer_New>::run( transUnit );
        }

        void CtorDtor::generateCtorDtor( std::list< Declaration * > & translationUnit ) {
                PassVisitor<CtorDtor> ctordtor;
                acceptAll( translationUnit, ctordtor );
        }

        bool ManagedTypes::isManaged( Type * type ) const {
                // references are never constructed
                if ( dynamic_cast< ReferenceType * >( type ) ) return false;
                // need to clear and reset qualifiers when determining if a type is managed
                ValueGuard< Type::Qualifiers > qualifiers( type->get_qualifiers() );
                type->get_qualifiers() = Type::Qualifiers();
                if ( TupleType * tupleType = dynamic_cast< TupleType * > ( type ) ) {
                        // tuple is also managed if any of its components are managed
                        if ( std::any_of( tupleType->types.begin(), tupleType->types.end(), [&](Type * type) { return isManaged( type ); }) ) {
                                return true;
                        }
                }
                // a type is managed if it appears in the map of known managed types, or if it contains any polymorphism (is a type variable or generic type containing a type variable)
                return managedTypes.find( SymTab::Mangler::mangleConcrete( type ) ) != managedTypes.end() || GenPoly::isPolyType( type );
        }

        bool ManagedTypes::isManaged( ObjectDecl * objDecl ) const {
                Type * type = objDecl->get_type();
                while ( ArrayType * at = dynamic_cast< ArrayType * >( type ) ) {
                        // must always construct VLAs with an initializer, since this is an error in C
                        if ( at->isVarLen && objDecl->init ) return true;
                        type = at->get_base();
                }
                return isManaged( type );
        }

        // why is this not just on FunctionDecl?
        void ManagedTypes::handleDWT( DeclarationWithType * dwt ) {
                // if this function is a user-defined constructor or destructor, mark down the type as "managed"
                if ( ! LinkageSpec::isOverridable( dwt->get_linkage() ) && CodeGen::isCtorDtor( dwt->get_name() ) ) {
                        std::list< DeclarationWithType * > & params = GenPoly::getFunctionType( dwt->get_type() )->get_parameters();
                        assert( ! params.empty() );
                        Type * type = InitTweak::getPointerBase( params.front()->get_type() );
                        assert( type );
                        managedTypes.insert( SymTab::Mangler::mangleConcrete( type ) );
                }
        }

        void ManagedTypes::handleStruct( StructDecl * aggregateDecl ) {
                // don't construct members, but need to take note if there is a managed member,
                // because that means that this type is also managed
                for ( Declaration * member : aggregateDecl->get_members() ) {
                        if ( ObjectDecl * field = dynamic_cast< ObjectDecl * >( member ) ) {
                                if ( isManaged( field ) ) {
                                        // generic parameters should not play a role in determining whether a generic type is constructed - construct all generic types, so that
                                        // polymorphic constructors make generic types managed types
                                        StructInstType inst( Type::Qualifiers(), aggregateDecl );
                                        managedTypes.insert( SymTab::Mangler::mangleConcrete( &inst ) );
                                        break;
                                }
                        }
                }
        }

        void ManagedTypes::beginScope() { managedTypes.beginScope(); }
        void ManagedTypes::endScope() { managedTypes.endScope(); }

        bool ManagedTypes_new::isManaged( const ast::Type * type ) const {
                // references are never constructed
                if ( dynamic_cast< const ast::ReferenceType * >( type ) ) return false;
                if ( auto tupleType = dynamic_cast< const ast::TupleType * > ( type ) ) {
                        // tuple is also managed if any of its components are managed
                        for (auto & component : tupleType->types) {
                                if (isManaged(component)) return true;
                        }
                }
                // need to clear and reset qualifiers when determining if a type is managed
                // ValueGuard< Type::Qualifiers > qualifiers( type->get_qualifiers() );
                auto tmp = shallowCopy(type);
                tmp->qualifiers = {};
                // delete tmp at return
                ast::ptr<ast::Type> guard = tmp;
                // a type is managed if it appears in the map of known managed types, or if it contains any polymorphism (is a type variable or generic type containing a type variable)
                return managedTypes.find( Mangle::mangle( tmp, {Mangle::NoOverrideable | Mangle::NoGenericParams | Mangle::Type} ) ) != managedTypes.end() || GenPoly::isPolyType( tmp );
        }

        bool ManagedTypes_new::isManaged( const ast::ObjectDecl * objDecl ) const {
                const ast::Type * type = objDecl->type;
                while ( auto at = dynamic_cast< const ast::ArrayType * >( type ) ) {
                        // must always construct VLAs with an initializer, since this is an error in C
                        if ( at->isVarLen && objDecl->init ) return true;
                        type = at->base;
                }
                return isManaged( type );
        }

        void ManagedTypes_new::handleDWT( const ast::DeclWithType * dwt ) {
                // if this function is a user-defined constructor or destructor, mark down the type as "managed"
                if ( ! dwt->linkage.is_overrideable && CodeGen::isCtorDtor( dwt->name ) ) {
                        auto & params = GenPoly::getFunctionType( dwt->get_type())->params;
                        assert( ! params.empty() );
                        // Type * type = InitTweak::getPointerBase( params.front() );
                        // assert( type );
                        managedTypes.insert( Mangle::mangle( params.front(), {Mangle::NoOverrideable | Mangle::NoGenericParams | Mangle::Type} ) );
                }
        }

        void ManagedTypes_new::handleStruct( const ast::StructDecl * aggregateDecl ) {
                // don't construct members, but need to take note if there is a managed member,
                // because that means that this type is also managed
                for ( auto & member : aggregateDecl->members ) {
                        if ( auto field = member.as<ast::ObjectDecl>() ) {
                                if ( isManaged( field ) ) {
                                        // generic parameters should not play a role in determining whether a generic type is constructed - construct all generic types, so that
                                        // polymorphic constructors make generic types managed types
                                        ast::StructInstType inst( aggregateDecl );
                                        managedTypes.insert( Mangle::mangle( &inst, {Mangle::NoOverrideable | Mangle::NoGenericParams | Mangle::Type} ) );
                                        break;
                                }
                        }
                }
        }

        void ManagedTypes_new::beginScope() { managedTypes.beginScope(); }
        void ManagedTypes_new::endScope() { managedTypes.endScope(); }

        ImplicitCtorDtorStmt * genCtorDtor( const std::string & fname, ObjectDecl * objDecl, Expression * arg ) {
                // call into genImplicitCall from Autogen.h to generate calls to ctor/dtor
                assertf( objDecl, "genCtorDtor passed null objDecl" );
                std::list< Statement * > stmts;
                InitExpander_old srcParam( maybeClone( arg ) );
                SymTab::genImplicitCall( srcParam, new VariableExpr( objDecl ), fname, back_inserter( stmts ), objDecl );
                assert( stmts.size() <= 1 );
                return stmts.size() == 1 ? strict_dynamic_cast< ImplicitCtorDtorStmt * >( stmts.front() ) : nullptr;

        }

        ast::ptr<ast::Stmt> genCtorDtor (const CodeLocation & loc, const std::string & fname, const ast::ObjectDecl * objDecl, const ast::Expr * arg) {
                assertf(objDecl, "genCtorDtor passed null objDecl");
                InitExpander_new srcParam(arg);
                return SymTab::genImplicitCall(srcParam, new ast::VariableExpr(loc, objDecl), loc, fname, objDecl);
        }

        ConstructorInit * genCtorInit( ObjectDecl * objDecl ) {
                // call into genImplicitCall from Autogen.h to generate calls to ctor/dtor
                // for each constructable object
                std::list< Statement * > ctor;
                std::list< Statement * > dtor;

                InitExpander_old srcParam( objDecl->get_init() );
                InitExpander_old nullParam( (Initializer *)NULL );
                SymTab::genImplicitCall( srcParam, new VariableExpr( objDecl ), "?{}", back_inserter( ctor ), objDecl );
                SymTab::genImplicitCall( nullParam, new VariableExpr( objDecl ), "^?{}", front_inserter( dtor ), objDecl, false );

                // Currently genImplicitCall produces a single Statement - a CompoundStmt
                // which  wraps everything that needs to happen. As such, it's technically
                // possible to use a Statement ** in the above calls, but this is inherently
                // unsafe, so instead we take the slightly less efficient route, but will be
                // immediately informed if somehow the above assumption is broken. In this case,
                // we could always wrap the list of statements at this point with a CompoundStmt,
                // but it seems reasonable at the moment for this to be done by genImplicitCall
                // itself. It is possible that genImplicitCall produces no statements (e.g. if
                // an array type does not have a dimension). In this case, it's fine to ignore
                // the object for the purposes of construction.
                assert( ctor.size() == dtor.size() && ctor.size() <= 1 );
                if ( ctor.size() == 1 ) {
                        // need to remember init expression, in case no ctors exist
                        // if ctor does exist, want to use ctor expression instead of init
                        // push this decision to the resolver
                        assert( dynamic_cast< ImplicitCtorDtorStmt * > ( ctor.front() ) && dynamic_cast< ImplicitCtorDtorStmt * > ( dtor.front() ) );
                        return new ConstructorInit( ctor.front(), dtor.front(), objDecl->get_init() );
                }
                return nullptr;
        }

        void CtorDtor::previsit( ObjectDecl * objDecl ) {
                managedTypes.handleDWT( objDecl );
                // hands off if @=, extern, builtin, etc.
                // even if unmanaged, try to construct global or static if initializer is not constexpr, since this is not legal C
                if ( tryConstruct( objDecl ) && ( managedTypes.isManaged( objDecl ) || ((! inFunction || objDecl->get_storageClasses().is_static ) && ! isConstExpr( objDecl->get_init() ) ) ) ) {
                        // constructed objects cannot be designated
                        if ( isDesignated( objDecl->get_init() ) ) SemanticError( objDecl, "Cannot include designations in the initializer for a managed Object. If this is really what you want, then initialize with @=.\n" );
                        // constructed objects should not have initializers nested too deeply
                        if ( ! checkInitDepth( objDecl ) ) SemanticError( objDecl, "Managed object's initializer is too deep " );

                        objDecl->set_init( genCtorInit( objDecl ) );
                }
        }

        void CtorDtor::previsit( FunctionDecl *functionDecl ) {
                visit_children = false;  // do not try and construct parameters or forall parameters
                GuardValue( inFunction );
                inFunction = true;

                managedTypes.handleDWT( functionDecl );

                GuardScope( managedTypes );
                // go through assertions and recursively add seen ctor/dtors
                for ( auto & tyDecl : functionDecl->get_functionType()->get_forall() ) {
                        for ( DeclarationWithType *& assertion : tyDecl->get_assertions() ) {
                                managedTypes.handleDWT( assertion );
                        }
                }

                maybeAccept( functionDecl->get_statements(), *visitor );
        }

        void CtorDtor::previsit( StructDecl *aggregateDecl ) {
                visit_children = false; // do not try to construct and destruct aggregate members

                managedTypes.handleStruct( aggregateDecl );
        }

        void CtorDtor::previsit( CompoundStmt * ) {
                GuardScope( managedTypes );
        }

ast::ConstructorInit * genCtorInit( const CodeLocation & loc, const ast::ObjectDecl * objDecl ) {
        // call into genImplicitCall from Autogen.h to generate calls to ctor/dtor for each
        // constructable object
        InitExpander_new srcParam{ objDecl->init }, nullParam{ (const ast::Init *)nullptr };
        ast::ptr< ast::Expr > dstParam = new ast::VariableExpr(loc, objDecl);

        ast::ptr< ast::Stmt > ctor = SymTab::genImplicitCall(
                srcParam, dstParam, loc, "?{}", objDecl );
        ast::ptr< ast::Stmt > dtor = SymTab::genImplicitCall(
                nullParam, dstParam, loc, "^?{}", objDecl,
                SymTab::LoopBackward );

        // check that either both ctor and dtor are present, or neither
        assert( (bool)ctor == (bool)dtor );

        if ( ctor ) {
                // need to remember init expression, in case no ctors exist. If ctor does exist, want to
                // use ctor expression instead of init.
                ctor.strict_as< ast::ImplicitCtorDtorStmt >();
                dtor.strict_as< ast::ImplicitCtorDtorStmt >();

                return new ast::ConstructorInit{ loc, ctor, dtor, objDecl->init };
        }

        return nullptr;
}

} // namespace InitTweak

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