source: src/SymTab/Validate.cc @ a715b5c

//
// 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.
//
// Validate.cc --
//
// Author           : Richard C. Bilson
// Created On       : Sun May 17 21:50:04 2015
// Last Modified By : Peter A. Buhr
// Last Modified On : Mon Aug 28 13:47:23 2017
// Update Count     : 359
//

// The "validate" phase of translation is used to take a syntax tree and convert it into a standard form that aims to be
// as regular in structure as possible.  Some assumptions can be made regarding the state of the tree after this pass is
// complete, including:
//
// - No nested structure or union definitions; any in the input are "hoisted" to the level of the containing struct or
//   union.
//
// - All enumeration constants have type EnumInstType.
//
// - The type "void" never occurs in lists of function parameter or return types.  A function
//   taking no arguments has no argument types.
//
// - No context instances exist; they are all replaced by the set of declarations signified by the context, instantiated
//   by the particular set of type arguments.
//
// - Every declaration is assigned a unique id.
//
// - No typedef declarations or instances exist; the actual type is substituted for each instance.
//
// - Each type, struct, and union definition is followed by an appropriate assignment operator.
//
// - Each use of a struct or union is connected to a complete definition of that struct or union, even if that
//   definition occurs later in the input.

#include "Validate.h"

#include <cassert>                     // for assertf, assert
#include <cstddef>                     // for size_t
#include <list>                        // for list
#include <string>                      // for string
#include <utility>                     // for pair

#include "CodeGen/CodeGenerator.h"     // for genName
#include "CodeGen/OperatorTable.h"     // for isCtorDtor, isCtorDtorAssign
#include "ControlStruct/Mutate.h"      // for ForExprMutator
#include "Common/PassVisitor.h"        // for PassVisitor, WithDeclsToAdd
#include "Common/ScopedMap.h"          // for ScopedMap
#include "Common/SemanticError.h"      // for SemanticError
#include "Common/UniqueName.h"         // for UniqueName
#include "Common/utility.h"            // for operator+, cloneAll, deleteAll
#include "Concurrency/Keywords.h"      // for applyKeywords
#include "FixFunction.h"               // for FixFunction
#include "Indexer.h"                   // for Indexer
#include "InitTweak/GenInit.h"         // for fixReturnStatements
#include "InitTweak/InitTweak.h"       // for isCtorDtorAssign
#include "Parser/LinkageSpec.h"        // for C
#include "ResolvExpr/typeops.h"        // for typesCompatible
#include "ResolvExpr/Resolver.h"       // for findSingleExpression
#include "ResolvExpr/ResolveTypeof.h"  // for resolveTypeof
#include "SymTab/Autogen.h"            // for SizeType
#include "SynTree/Attribute.h"         // for noAttributes, Attribute
#include "SynTree/Constant.h"          // for Constant
#include "SynTree/Declaration.h"       // for ObjectDecl, DeclarationWithType
#include "SynTree/Expression.h"        // for CompoundLiteralExpr, Expressio...
#include "SynTree/Initializer.h"       // for ListInit, Initializer
#include "SynTree/Label.h"             // for operator==, Label
#include "SynTree/Mutator.h"           // for Mutator
#include "SynTree/Type.h"              // for Type, TypeInstType, EnumInstType
#include "SynTree/TypeSubstitution.h"  // for TypeSubstitution
#include "SynTree/Visitor.h"           // for Visitor
#include "Validate/HandleAttributes.h" // for handleAttributes

class CompoundStmt;
class ReturnStmt;
class SwitchStmt;

#define debugPrint( x ) if ( doDebug ) x

namespace SymTab {
        /// hoists declarations that are difficult to hoist while parsing
        struct HoistTypeDecls final : public WithDeclsToAdd {
                void previsit( SizeofExpr * );
                void previsit( AlignofExpr * );
                void previsit( UntypedOffsetofExpr * );
                void previsit( CompoundLiteralExpr * );
                void handleType( Type * );
        };

        struct FixQualifiedTypes final : public WithIndexer {
                Type * postmutate( QualifiedType * );
        };

        struct HoistStruct final : public WithDeclsToAdd, public WithGuards {
                /// Flattens nested struct types
                static void hoistStruct( std::list< Declaration * > &translationUnit );

                void previsit( StructDecl * aggregateDecl );
                void previsit( UnionDecl * aggregateDecl );
                void previsit( StaticAssertDecl * assertDecl );
                void previsit( StructInstType * type );
                void previsit( UnionInstType * type );
                void previsit( EnumInstType * type );

          private:
                template< typename AggDecl > void handleAggregate( AggDecl *aggregateDecl );

                AggregateDecl * parentAggr = nullptr;
        };

        /// Fix return types so that every function returns exactly one value
        struct ReturnTypeFixer {
                static void fix( std::list< Declaration * > &translationUnit );

                void postvisit( FunctionDecl * functionDecl );
                void postvisit( FunctionType * ftype );
        };

        /// Replaces enum types by int, and function or array types in function parameter and return lists by appropriate pointers.
        struct EnumAndPointerDecay {
                void previsit( EnumDecl *aggregateDecl );
                void previsit( FunctionType *func );
        };

        /// Associates forward declarations of aggregates with their definitions
        struct LinkReferenceToTypes final : public WithIndexer, public WithGuards, public WithVisitorRef<LinkReferenceToTypes>, public WithShortCircuiting {
                LinkReferenceToTypes( const Indexer *indexer );
                void postvisit( TypeInstType *typeInst );

                void postvisit( EnumInstType *enumInst );
                void postvisit( StructInstType *structInst );
                void postvisit( UnionInstType *unionInst );
                void postvisit( TraitInstType *traitInst );
                void previsit( QualifiedType * qualType );
                void postvisit( QualifiedType * qualType );

                void postvisit( EnumDecl *enumDecl );
                void postvisit( StructDecl *structDecl );
                void postvisit( UnionDecl *unionDecl );
                void postvisit( TraitDecl * traitDecl );

                void previsit( StructDecl *structDecl );
                void previsit( UnionDecl *unionDecl );

                void renameGenericParams( std::list< TypeDecl * > & params );

          private:
                const Indexer *local_indexer;

                typedef std::map< std::string, std::list< EnumInstType * > > ForwardEnumsType;
                typedef std::map< std::string, std::list< StructInstType * > > ForwardStructsType;
                typedef std::map< std::string, std::list< UnionInstType * > > ForwardUnionsType;
                ForwardEnumsType forwardEnums;
                ForwardStructsType forwardStructs;
                ForwardUnionsType forwardUnions;
                /// true if currently in a generic type body, so that type parameter instances can be renamed appropriately
                bool inGeneric = false;
        };

        /// Replaces array and function types in forall lists by appropriate pointer type and assigns each Object and Function declaration a unique ID.
        struct ForallPointerDecay final {
                void previsit( ObjectDecl * object );
                void previsit( FunctionDecl * func );
                void previsit( FunctionType * ftype );
                void previsit( StructDecl * aggrDecl );
                void previsit( UnionDecl * aggrDecl );
        };

        struct ReturnChecker : public WithGuards {
                /// Checks that return statements return nothing if their return type is void
                /// and return something if the return type is non-void.
                static void checkFunctionReturns( std::list< Declaration * > & translationUnit );

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

                typedef std::list< DeclarationWithType * > ReturnVals;
                ReturnVals returnVals;
        };

        struct ReplaceTypedef final : public WithVisitorRef<ReplaceTypedef>, public WithGuards, public WithShortCircuiting, public WithDeclsToAdd {
                ReplaceTypedef() : scopeLevel( 0 ) {}
                /// Replaces typedefs by forward declarations
                static void replaceTypedef( std::list< Declaration * > &translationUnit );

                void premutate( QualifiedType * );
                Type * postmutate( QualifiedType * qualType );
                Type * postmutate( TypeInstType * aggregateUseType );
                Declaration * postmutate( TypedefDecl * typeDecl );
                void premutate( TypeDecl * typeDecl );
                void premutate( FunctionDecl * funcDecl );
                void premutate( ObjectDecl * objDecl );
                DeclarationWithType * postmutate( ObjectDecl * objDecl );

                void premutate( CastExpr * castExpr );

                void premutate( CompoundStmt * compoundStmt );

                void premutate( StructDecl * structDecl );
                void premutate( UnionDecl * unionDecl );
                void premutate( EnumDecl * enumDecl );
                void premutate( TraitDecl * );

                void premutate( FunctionType * ftype );

          private:
                template<typename AggDecl>
                void addImplicitTypedef( AggDecl * aggDecl );
                template< typename AggDecl >
                void handleAggregate( AggDecl * aggr );

                typedef std::unique_ptr<TypedefDecl> TypedefDeclPtr;
                typedef ScopedMap< std::string, std::pair< TypedefDeclPtr, int > > TypedefMap;
                typedef ScopedMap< std::string, TypeDecl * > TypeDeclMap;
                TypedefMap typedefNames;
                TypeDeclMap typedeclNames;
                int scopeLevel;
                bool inFunctionType = false;
        };

        struct EliminateTypedef {
                /// removes TypedefDecls from the AST
                static void eliminateTypedef( std::list< Declaration * > &translationUnit );

                template<typename AggDecl>
                void handleAggregate( AggDecl *aggregateDecl );

                void previsit( StructDecl * aggregateDecl );
                void previsit( UnionDecl * aggregateDecl );
                void previsit( CompoundStmt * compoundStmt );
        };

        struct VerifyCtorDtorAssign {
                /// ensure that constructors, destructors, and assignment have at least one
                /// parameter, the first of which must be a pointer, and that ctor/dtors have no
                /// return values.
                static void verify( std::list< Declaration * > &translationUnit );

                void previsit( FunctionDecl *funcDecl );
        };

        /// ensure that generic types have the correct number of type arguments
        struct ValidateGenericParameters {
                void previsit( StructInstType * inst );
                void previsit( UnionInstType * inst );
        };

        struct FixObjectType : public WithIndexer {
                /// resolves typeof type in object, function, and type declarations
                static void fix( std::list< Declaration * > & translationUnit );

                void previsit( ObjectDecl * );
                void previsit( FunctionDecl * );
                void previsit( TypeDecl * );
        };

        struct ArrayLength : public WithIndexer {
                /// for array types without an explicit length, compute the length and store it so that it
                /// is known to the rest of the phases. For example,
                ///   int x[] = { 1, 2, 3 };
                ///   int y[][2] = { { 1, 2, 3 }, { 1, 2, 3 } };
                /// here x and y are known at compile-time to have length 3, so change this into
                ///   int x[3] = { 1, 2, 3 };
                ///   int y[3][2] = { { 1, 2, 3 }, { 1, 2, 3 } };
                static void computeLength( std::list< Declaration * > & translationUnit );

                void previsit( ObjectDecl * objDecl );
                void previsit( ArrayType * arrayType );
        };

        struct CompoundLiteral final : public WithDeclsToAdd, public WithVisitorRef<CompoundLiteral> {
                Type::StorageClasses storageClasses;

                void premutate( ObjectDecl *objectDecl );
                Expression * postmutate( CompoundLiteralExpr *compLitExpr );
        };

        struct LabelAddressFixer final : public WithGuards {
                std::set< Label > labels;

                void premutate( FunctionDecl * funcDecl );
                Expression * postmutate( AddressExpr * addrExpr );
        };

        FunctionDecl * dereferenceOperator = nullptr;
        struct FindSpecialDeclarations final {
                void previsit( FunctionDecl * funcDecl );
        };

        void validate( std::list< Declaration * > &translationUnit, __attribute__((unused)) bool doDebug ) {
                PassVisitor<EnumAndPointerDecay> epc;
                PassVisitor<LinkReferenceToTypes> lrt( nullptr );
                PassVisitor<ForallPointerDecay> fpd;
                PassVisitor<CompoundLiteral> compoundliteral;
                PassVisitor<ValidateGenericParameters> genericParams;
                PassVisitor<FindSpecialDeclarations> finder;
                PassVisitor<LabelAddressFixer> labelAddrFixer;
                PassVisitor<HoistTypeDecls> hoistDecls;
                PassVisitor<FixQualifiedTypes> fixQual;

                acceptAll( translationUnit, hoistDecls );
                ReplaceTypedef::replaceTypedef( translationUnit );
                ReturnTypeFixer::fix( translationUnit ); // must happen before autogen
                acceptAll( translationUnit, epc ); // must happen before VerifyCtorDtorAssign, because void return objects should not exist; before LinkReferenceToTypes because it is an indexer and needs correct types for mangling
                acceptAll( translationUnit, lrt ); // must happen before autogen, because sized flag needs to propagate to generated functions
                mutateAll( translationUnit, fixQual ); // must happen after LinkReferenceToTypes, because aggregate members are accessed
                HoistStruct::hoistStruct( translationUnit ); // must happen after EliminateTypedef, so that aggregate typedefs occur in the correct order
                EliminateTypedef::eliminateTypedef( translationUnit ); //
                acceptAll( translationUnit, genericParams );  // check as early as possible - can't happen before LinkReferenceToTypes
                VerifyCtorDtorAssign::verify( translationUnit );  // must happen before autogen, because autogen examines existing ctor/dtors
                ReturnChecker::checkFunctionReturns( translationUnit );
                InitTweak::fixReturnStatements( translationUnit ); // must happen before autogen
                Concurrency::applyKeywords( translationUnit );
                acceptAll( translationUnit, fpd ); // must happen before autogenerateRoutines, after Concurrency::applyKeywords because uniqueIds must be set on declaration before resolution
                ControlStruct::hoistControlDecls( translationUnit );  // hoist initialization out of for statements; must happen before autogenerateRoutines
                autogenerateRoutines( translationUnit ); // moved up, used to be below compoundLiteral - currently needs EnumAndPointerDecay
                Concurrency::implementMutexFuncs( translationUnit );
                Concurrency::implementThreadStarter( translationUnit );
                mutateAll( translationUnit, compoundliteral );
                ResolvExpr::resolveWithExprs( translationUnit ); // must happen before FixObjectType because user-code is resolved and may contain with variables
                FixObjectType::fix( translationUnit );
                ArrayLength::computeLength( translationUnit );
                acceptAll( translationUnit, finder ); // xxx - remove this pass soon
                mutateAll( translationUnit, labelAddrFixer );
                Validate::handleAttributes( translationUnit );
        }

        void validateType( Type *type, const Indexer *indexer ) {
                PassVisitor<EnumAndPointerDecay> epc;
                PassVisitor<LinkReferenceToTypes> lrt( indexer );
                PassVisitor<ForallPointerDecay> fpd;
                type->accept( epc );
                type->accept( lrt );
                type->accept( fpd );
        }


        void HoistTypeDecls::handleType( Type * type ) {
                // some type declarations are buried in expressions and not easy to hoist during parsing; hoist them here
                AggregateDecl * aggr = nullptr;
                if ( StructInstType * inst = dynamic_cast< StructInstType * >( type ) ) {
                        aggr = inst->baseStruct;
                } else if ( UnionInstType * inst = dynamic_cast< UnionInstType * >( type ) ) {
                        aggr = inst->baseUnion;
                } else if ( EnumInstType * inst = dynamic_cast< EnumInstType * >( type ) ) {
                        aggr = inst->baseEnum;
                }
                if ( aggr && aggr->body ) {
                        declsToAddBefore.push_front( aggr );
                }
        }

        void HoistTypeDecls::previsit( SizeofExpr * expr ) {
                handleType( expr->type );
        }

        void HoistTypeDecls::previsit( AlignofExpr * expr ) {
                handleType( expr->type );
        }

        void HoistTypeDecls::previsit( UntypedOffsetofExpr * expr ) {
                handleType( expr->type );
        }

        void HoistTypeDecls::previsit( CompoundLiteralExpr * expr ) {
                handleType( expr->result );
        }


        Type * FixQualifiedTypes::postmutate( QualifiedType * qualType ) {
                Type * parent = qualType->parent;
                Type * child = qualType->child;
                if ( dynamic_cast< GlobalScopeType * >( qualType->parent ) ) {
                        // .T => lookup T at global scope
                        if ( TypeInstType * inst = dynamic_cast< TypeInstType * >( child ) ) {
                                auto td = indexer.globalLookupType( inst->name );
                                if ( ! td ) {
                                        SemanticError( qualType->location, toString("Use of undefined global type ", inst->name) );
                                }
                                auto base = td->base;
                                assert( base );
                                Type * ret = base->clone();
                                ret->get_qualifiers() = qualType->get_qualifiers();
                                return ret;
                        } else {
                                // .T => T is not a type name
                                assertf( false, "unhandled global qualified child type: %s", toCString(child) );
                        }
                } else {
                        // S.T => S must be an aggregate type, find the declaration for T in S.
                        AggregateDecl * aggr = nullptr;
                        if ( StructInstType * inst = dynamic_cast< StructInstType * >( parent ) ) {
                                aggr = inst->baseStruct;
                        } else if ( UnionInstType * inst = dynamic_cast< UnionInstType * > ( parent ) ) {
                                aggr = inst->baseUnion;
                        } else {
                                SemanticError( qualType->location, toString("Qualified type requires an aggregate on the left, but has: ", parent) );
                        }
                        assert( aggr ); // TODO: need to handle forward declarations
                        for ( Declaration * member : aggr->members ) {
                                if ( StructInstType * inst = dynamic_cast< StructInstType * >( child ) ) {
                                        if ( StructDecl * aggr = dynamic_cast< StructDecl * >( member ) ) {
                                                if ( aggr->name == inst->name ) {
                                                        // TODO: is this case, and other non-TypeInstType cases, necessary?
                                                        return new StructInstType( qualType->get_qualifiers(), aggr );
                                                }
                                        }
                                } else if ( UnionInstType * inst = dynamic_cast< UnionInstType * >( child ) ) {
                                        if ( UnionDecl * aggr = dynamic_cast< UnionDecl * > ( member ) ) {
                                                if ( aggr->name == inst->name ) {
                                                        return new UnionInstType( qualType->get_qualifiers(), aggr );
                                                }
                                        }
                                } else if ( EnumInstType * inst = dynamic_cast< EnumInstType * >( child ) ) {
                                        if ( EnumDecl * aggr = dynamic_cast< EnumDecl * > ( member ) ) {
                                                if ( aggr->name == inst->name ) {
                                                        return new EnumInstType( qualType->get_qualifiers(), aggr );
                                                }
                                        }
                                } else if ( TypeInstType * inst = dynamic_cast< TypeInstType * >( child ) ) {
                                        // name on the right is a typedef
                                        if ( NamedTypeDecl * aggr = dynamic_cast< NamedTypeDecl * > ( member ) ) {
                                                if ( aggr->name == inst->name ) {
                                                        assert( aggr->base );
                                                        Type * ret = aggr->base->clone();
                                                        ret->get_qualifiers() = qualType->get_qualifiers();
                                                        return ret;
                                                }
                                        }
                                } else {
                                        // S.T - S is not an aggregate => error
                                        assertf( false, "unhandled qualified child type: %s", toCString(qualType) );
                                }
                        }
                        // failed to find a satisfying definition of type
                        SemanticError( qualType->location, toString("Undefined type in qualified type: ", qualType) );
                }

                // ... may want to link canonical SUE definition to each forward decl so that it becomes easier to lookup?
        }


        void HoistStruct::hoistStruct( std::list< Declaration * > &translationUnit ) {
                PassVisitor<HoistStruct> hoister;
                acceptAll( translationUnit, hoister );
        }

        bool shouldHoist( Declaration *decl ) {
                return dynamic_cast< StructDecl * >( decl ) || dynamic_cast< UnionDecl * >( decl ) || dynamic_cast< StaticAssertDecl * >( decl );
        }

        namespace {
                void qualifiedName( AggregateDecl * aggr, std::ostringstream & ss ) {
                        if ( aggr->parent ) qualifiedName( aggr->parent, ss );
                        ss << "__" << aggr->name;
                }

                // mangle nested type names using entire parent chain
                std::string qualifiedName( AggregateDecl * aggr ) {
                        std::ostringstream ss;
                        qualifiedName( aggr, ss );
                        return ss.str();
                }
        }

        template< typename AggDecl >
        void HoistStruct::handleAggregate( AggDecl *aggregateDecl ) {
                if ( parentAggr ) {
                        aggregateDecl->parent = parentAggr;
                        aggregateDecl->name = qualifiedName( aggregateDecl );
                        // Add elements in stack order corresponding to nesting structure.
                        declsToAddBefore.push_front( aggregateDecl );
                } else {
                        GuardValue( parentAggr );
                        parentAggr = aggregateDecl;
                } // if
                // Always remove the hoisted aggregate from the inner structure.
                GuardAction( [aggregateDecl]() { filter( aggregateDecl->members, shouldHoist, false ); } );
        }

        void HoistStruct::previsit( StaticAssertDecl * assertDecl ) {
                if ( parentAggr ) {
                        declsToAddBefore.push_back( assertDecl );
                }
        }

        void HoistStruct::previsit( StructDecl * aggregateDecl ) {
                handleAggregate( aggregateDecl );
        }

        void HoistStruct::previsit( UnionDecl * aggregateDecl ) {
                handleAggregate( aggregateDecl );
        }

        void HoistStruct::previsit( StructInstType * type ) {
                // need to reset type name after expanding to qualified name
                assert( type->baseStruct );
                type->name = type->baseStruct->name;
        }

        void HoistStruct::previsit( UnionInstType * type ) {
                assert( type->baseUnion );
                type->name = type->baseUnion->name;
        }

        void HoistStruct::previsit( EnumInstType * type ) {
                assert( type->baseEnum );
                type->name = type->baseEnum->name;
        }


        bool isTypedef( Declaration *decl ) {
                return dynamic_cast< TypedefDecl * >( decl );
        }

        void EliminateTypedef::eliminateTypedef( std::list< Declaration * > &translationUnit ) {
                PassVisitor<EliminateTypedef> eliminator;
                acceptAll( translationUnit, eliminator );
                filter( translationUnit, isTypedef, true );
        }

        template< typename AggDecl >
        void EliminateTypedef::handleAggregate( AggDecl *aggregateDecl ) {
                filter( aggregateDecl->members, isTypedef, true );
        }

        void EliminateTypedef::previsit( StructDecl * aggregateDecl ) {
                handleAggregate( aggregateDecl );
        }

        void EliminateTypedef::previsit( UnionDecl * aggregateDecl ) {
                handleAggregate( aggregateDecl );
        }

        void EliminateTypedef::previsit( CompoundStmt * compoundStmt ) {
                // remove and delete decl stmts
                filter( compoundStmt->kids, [](Statement * stmt) {
                        if ( DeclStmt *declStmt = dynamic_cast< DeclStmt * >( stmt ) ) {
                                if ( dynamic_cast< TypedefDecl * >( declStmt->decl ) ) {
                                        return true;
                                } // if
                        } // if
                        return false;
                }, true);
        }

        void EnumAndPointerDecay::previsit( EnumDecl *enumDecl ) {
                // Set the type of each member of the enumeration to be EnumConstant
                for ( std::list< Declaration * >::iterator i = enumDecl->members.begin(); i != enumDecl->members.end(); ++i ) {
                        ObjectDecl * obj = dynamic_cast< ObjectDecl * >( *i );
                        assert( obj );
                        obj->set_type( new EnumInstType( Type::Qualifiers( Type::Const ), enumDecl->name ) );
                } // for
        }

        namespace {
                template< typename DWTList >
                void fixFunctionList( DWTList & dwts, bool isVarArgs, FunctionType * func ) {
                        auto nvals = dwts.size();
                        bool containsVoid = false;
                        for ( auto & dwt : dwts ) {
                                // fix each DWT and record whether a void was found
                                containsVoid |= fixFunction( dwt );
                        }

                        // the only case in which "void" is valid is where it is the only one in the list
                        if ( containsVoid && ( nvals > 1 || isVarArgs ) ) {
                                SemanticError( func, "invalid type void in function type " );
                        }

                        // one void is the only thing in the list; remove it.
                        if ( containsVoid ) {
                                delete dwts.front();
                                dwts.clear();
                        }
                }
        }

        void EnumAndPointerDecay::previsit( FunctionType *func ) {
                // Fix up parameters and return types
                fixFunctionList( func->parameters, func->isVarArgs, func );
                fixFunctionList( func->returnVals, false, func );
        }

        LinkReferenceToTypes::LinkReferenceToTypes( const Indexer *other_indexer ) {
                if ( other_indexer ) {
                        local_indexer = other_indexer;
                } else {
                        local_indexer = &indexer;
                } // if
        }

        void LinkReferenceToTypes::postvisit( EnumInstType *enumInst ) {
                EnumDecl *st = local_indexer->lookupEnum( enumInst->name );
                // it's not a semantic error if the enum is not found, just an implicit forward declaration
                if ( st ) {
                        enumInst->baseEnum = st;
                } // if
                if ( ! st || ! st->body ) {
                        // use of forward declaration
                        forwardEnums[ enumInst->name ].push_back( enumInst );
                } // if
        }

        void checkGenericParameters( ReferenceToType * inst ) {
                for ( Expression * param : inst->parameters ) {
                        if ( ! dynamic_cast< TypeExpr * >( param ) ) {
                                SemanticError( inst, "Expression parameters for generic types are currently unsupported: " );
                        }
                }
        }

        void LinkReferenceToTypes::postvisit( StructInstType *structInst ) {
                StructDecl *st = local_indexer->lookupStruct( structInst->name );
                // it's not a semantic error if the struct is not found, just an implicit forward declaration
                if ( st ) {
                        structInst->baseStruct = st;
                } // if
                if ( ! st || ! st->body ) {
                        // use of forward declaration
                        forwardStructs[ structInst->name ].push_back( structInst );
                } // if
                checkGenericParameters( structInst );
        }

        void LinkReferenceToTypes::postvisit( UnionInstType *unionInst ) {
                UnionDecl *un = local_indexer->lookupUnion( unionInst->name );
                // it's not a semantic error if the union is not found, just an implicit forward declaration
                if ( un ) {
                        unionInst->baseUnion = un;
                } // if
                if ( ! un || ! un->body ) {
                        // use of forward declaration
                        forwardUnions[ unionInst->name ].push_back( unionInst );
                } // if
                checkGenericParameters( unionInst );
        }

        void LinkReferenceToTypes::previsit( QualifiedType * ) {
                visit_children = false;
        }

        void LinkReferenceToTypes::postvisit( QualifiedType * qualType ) {
                // linking only makes sense for the 'oldest ancestor' of the qualified type
                qualType->parent->accept( *visitor );
        }

        template< typename Decl >
        void normalizeAssertions( std::list< Decl * > & assertions ) {
                // ensure no duplicate trait members after the clone
                auto pred = [](Decl * d1, Decl * d2) {
                        // only care if they're equal
                        DeclarationWithType * dwt1 = dynamic_cast<DeclarationWithType *>( d1 );
                        DeclarationWithType * dwt2 = dynamic_cast<DeclarationWithType *>( d2 );
                        if ( dwt1 && dwt2 ) {
                                if ( dwt1->name == dwt2->name && ResolvExpr::typesCompatible( dwt1->get_type(), dwt2->get_type(), SymTab::Indexer() ) ) {
                                        // std::cerr << "=========== equal:" << std::endl;
                                        // std::cerr << "d1: " << d1 << std::endl;
                                        // std::cerr << "d2: " << d2 << std::endl;
                                        return false;
                                }
                        }
                        return d1 < d2;
                };
                std::set<Decl *, decltype(pred)> unique_members( assertions.begin(), assertions.end(), pred );
                // if ( unique_members.size() != assertions.size() ) {
                //      std::cerr << "============different" << std::endl;
                //      std::cerr << unique_members.size() << " " << assertions.size() << std::endl;
                // }

                std::list< Decl * > order;
                order.splice( order.end(), assertions );
                std::copy_if( order.begin(), order.end(), back_inserter( assertions ), [&]( Decl * decl ) {
                        return unique_members.count( decl );
                });
        }

        // expand assertions from trait instance, performing the appropriate type variable substitutions
        template< typename Iterator >
        void expandAssertions( TraitInstType * inst, Iterator out ) {
                assertf( inst->baseTrait, "Trait instance not linked to base trait: %s", toCString( inst ) );
                std::list< DeclarationWithType * > asserts;
                for ( Declaration * decl : inst->baseTrait->members ) {
                        asserts.push_back( strict_dynamic_cast<DeclarationWithType *>( decl->clone() ) );
                }
                // substitute trait decl parameters for instance parameters
                applySubstitution( inst->baseTrait->parameters.begin(), inst->baseTrait->parameters.end(), inst->parameters.begin(), asserts.begin(), asserts.end(), out );
        }

        void LinkReferenceToTypes::postvisit( TraitDecl * traitDecl ) {
                if ( traitDecl->name == "sized" ) {
                        // "sized" is a special trait - flick the sized status on for the type variable
                        assertf( traitDecl->parameters.size() == 1, "Built-in trait 'sized' has incorrect number of parameters: %zd", traitDecl->parameters.size() );
                        TypeDecl * td = traitDecl->parameters.front();
                        td->set_sized( true );
                }

                // move assertions from type parameters into the body of the trait
                for ( TypeDecl * td : traitDecl->parameters ) {
                        for ( DeclarationWithType * assert : td->assertions ) {
                                if ( TraitInstType * inst = dynamic_cast< TraitInstType * >( assert->get_type() ) ) {
                                        expandAssertions( inst, back_inserter( traitDecl->members ) );
                                } else {
                                        traitDecl->members.push_back( assert->clone() );
                                }
                        }
                        deleteAll( td->assertions );
                        td->assertions.clear();
                } // for
        }

        void LinkReferenceToTypes::postvisit( TraitInstType * traitInst ) {
                // handle other traits
                TraitDecl *traitDecl = local_indexer->lookupTrait( traitInst->name );
                if ( ! traitDecl ) {
                        SemanticError( traitInst->location, "use of undeclared trait " + traitInst->name );
                } // if
                if ( traitDecl->parameters.size() != traitInst->parameters.size() ) {
                        SemanticError( traitInst, "incorrect number of trait parameters: " );
                } // if
                traitInst->baseTrait = traitDecl;

                // need to carry over the 'sized' status of each decl in the instance
                for ( auto p : group_iterate( traitDecl->parameters, traitInst->parameters ) ) {
                        TypeExpr * expr = dynamic_cast< TypeExpr * >( std::get<1>(p) );
                        if ( ! expr ) {
                                SemanticError( std::get<1>(p), "Expression parameters for trait instances are currently unsupported: " );
                        }
                        if ( TypeInstType * inst = dynamic_cast< TypeInstType * >( expr->get_type() ) ) {
                                TypeDecl * formalDecl = std::get<0>(p);
                                TypeDecl * instDecl = inst->baseType;
                                if ( formalDecl->get_sized() ) instDecl->set_sized( true );
                        }
                }
                // normalizeAssertions( traitInst->members );
        }

        void LinkReferenceToTypes::postvisit( EnumDecl *enumDecl ) {
                // visit enum members first so that the types of self-referencing members are updated properly
                if ( enumDecl->body ) {
                        ForwardEnumsType::iterator fwds = forwardEnums.find( enumDecl->name );
                        if ( fwds != forwardEnums.end() ) {
                                for ( std::list< EnumInstType * >::iterator inst = fwds->second.begin(); inst != fwds->second.end(); ++inst ) {
                                        (*inst)->baseEnum = enumDecl;
                                } // for
                                forwardEnums.erase( fwds );
                        } // if

                        for ( Declaration * member : enumDecl->members ) {
                                ObjectDecl * field = strict_dynamic_cast<ObjectDecl *>( member );
                                if ( field->init ) {
                                        // need to resolve enumerator initializers early so that other passes that determine if an expression is constexpr have the appropriate information.
                                        SingleInit * init = strict_dynamic_cast<SingleInit *>( field->init );
                                        ResolvExpr::findSingleExpression( init->value, new BasicType( Type::Qualifiers(), BasicType::SignedInt ), indexer );
                                }
                        }
                } // if
        }

        void LinkReferenceToTypes::renameGenericParams( std::list< TypeDecl * > & params ) {
                // rename generic type parameters uniquely so that they do not conflict with user-defined function forall parameters, e.g.
                //   forall(otype T)
                //   struct Box {
                //     T x;
                //   };
                //   forall(otype T)
                //   void f(Box(T) b) {
                //     ...
                //   }
                // The T in Box and the T in f are different, so internally the naming must reflect that.
                GuardValue( inGeneric );
                inGeneric = ! params.empty();
                for ( TypeDecl * td : params ) {
                        td->name = "__" + td->name + "_generic_";
                }
        }

        void LinkReferenceToTypes::previsit( StructDecl * structDecl ) {
                renameGenericParams( structDecl->parameters );
        }

        void LinkReferenceToTypes::previsit( UnionDecl * unionDecl ) {
                renameGenericParams( unionDecl->parameters );
        }

        void LinkReferenceToTypes::postvisit( StructDecl *structDecl ) {
                // visit struct members first so that the types of self-referencing members are updated properly
                // xxx - need to ensure that type parameters match up between forward declarations and definition (most importantly, number of type parameters and their defaults)
                if ( structDecl->body ) {
                        ForwardStructsType::iterator fwds = forwardStructs.find( structDecl->name );
                        if ( fwds != forwardStructs.end() ) {
                                for ( std::list< StructInstType * >::iterator inst = fwds->second.begin(); inst != fwds->second.end(); ++inst ) {
                                        (*inst)->baseStruct = structDecl;
                                } // for
                                forwardStructs.erase( fwds );
                        } // if
                } // if
        }

        void LinkReferenceToTypes::postvisit( UnionDecl *unionDecl ) {
                if ( unionDecl->body ) {
                        ForwardUnionsType::iterator fwds = forwardUnions.find( unionDecl->name );
                        if ( fwds != forwardUnions.end() ) {
                                for ( std::list< UnionInstType * >::iterator inst = fwds->second.begin(); inst != fwds->second.end(); ++inst ) {
                                        (*inst)->baseUnion = unionDecl;
                                } // for
                                forwardUnions.erase( fwds );
                        } // if
                } // if
        }

        void LinkReferenceToTypes::postvisit( TypeInstType *typeInst ) {
                // ensure generic parameter instances are renamed like the base type
                if ( inGeneric && typeInst->baseType ) typeInst->name = typeInst->baseType->name;
                if ( NamedTypeDecl *namedTypeDecl = local_indexer->lookupType( typeInst->name ) ) {
                        if ( TypeDecl *typeDecl = dynamic_cast< TypeDecl * >( namedTypeDecl ) ) {
                                typeInst->set_isFtype( typeDecl->get_kind() == TypeDecl::Ftype );
                        } // if
                } // if
        }

        /// Fix up assertions - flattens assertion lists, removing all trait instances
        void forallFixer( std::list< TypeDecl * > & forall, BaseSyntaxNode * node ) {
                for ( TypeDecl * type : forall ) {
                        std::list< DeclarationWithType * > asserts;
                        asserts.splice( asserts.end(), type->assertions );
                        // expand trait instances into their members
                        for ( DeclarationWithType * assertion : asserts ) {
                                if ( TraitInstType *traitInst = dynamic_cast< TraitInstType * >( assertion->get_type() ) ) {
                                        // expand trait instance into all of its members
                                        expandAssertions( traitInst, back_inserter( type->assertions ) );
                                        delete traitInst;
                                } else {
                                        // pass other assertions through
                                        type->assertions.push_back( assertion );
                                } // if
                        } // for
                        // apply FixFunction to every assertion to check for invalid void type
                        for ( DeclarationWithType *& assertion : type->assertions ) {
                                bool isVoid = fixFunction( assertion );
                                if ( isVoid ) {
                                        SemanticError( node, "invalid type void in assertion of function " );
                                } // if
                        } // for
                        // normalizeAssertions( type->assertions );
                } // for
        }

        void ForallPointerDecay::previsit( ObjectDecl *object ) {
                // ensure that operator names only apply to functions or function pointers
                if ( CodeGen::isOperator( object->name ) && ! dynamic_cast< FunctionType * >( object->type->stripDeclarator() ) ) {
                        SemanticError( object->location, toCString( "operator ", object->name.c_str(), " is not a function or function pointer." )  );
                }
                object->fixUniqueId();
        }

        void ForallPointerDecay::previsit( FunctionDecl *func ) {
                func->fixUniqueId();
        }

        void ForallPointerDecay::previsit( FunctionType * ftype ) {
                forallFixer( ftype->forall, ftype );
        }

        void ForallPointerDecay::previsit( StructDecl * aggrDecl ) {
                forallFixer( aggrDecl->parameters, aggrDecl );
        }

        void ForallPointerDecay::previsit( UnionDecl * aggrDecl ) {
                forallFixer( aggrDecl->parameters, aggrDecl );
        }

        void ReturnChecker::checkFunctionReturns( std::list< Declaration * > & translationUnit ) {
                PassVisitor<ReturnChecker> checker;
                acceptAll( translationUnit, checker );
        }

        void ReturnChecker::previsit( FunctionDecl * functionDecl ) {
                GuardValue( returnVals );
                returnVals = functionDecl->get_functionType()->get_returnVals();
        }

        void ReturnChecker::previsit( ReturnStmt * returnStmt ) {
                // Previously this also checked for the existence of an expr paired with no return values on
                // the  function return type. This is incorrect, since you can have an expression attached to
                // a return statement in a void-returning function in C. The expression is treated as if it
                // were cast to void.
                if ( ! returnStmt->get_expr() && returnVals.size() != 0 ) {
                        SemanticError( returnStmt, "Non-void function returns no values: " );
                }
        }


        void ReplaceTypedef::replaceTypedef( std::list< Declaration * > &translationUnit ) {
                PassVisitor<ReplaceTypedef> eliminator;
                mutateAll( translationUnit, eliminator );
                if ( eliminator.pass.typedefNames.count( "size_t" ) ) {
                        // grab and remember declaration of size_t
                        SizeType = eliminator.pass.typedefNames["size_t"].first->base->clone();
                } else {
                        // xxx - missing global typedef for size_t - default to long unsigned int, even though that may be wrong
                        // eventually should have a warning for this case.
                        SizeType = new BasicType( Type::Qualifiers(), BasicType::LongUnsignedInt );
                }
        }

        void ReplaceTypedef::premutate( QualifiedType * ) {
                visit_children = false;
        }

        Type * ReplaceTypedef::postmutate( QualifiedType * qualType ) {
                // replacing typedefs only makes sense for the 'oldest ancestor' of the qualified type
                qualType->parent = qualType->parent->acceptMutator( *visitor );
                return qualType;
        }

        Type * ReplaceTypedef::postmutate( TypeInstType * typeInst ) {
                // instances of typedef types will come here. If it is an instance
                // of a typdef type, link the instance to its actual type.
                TypedefMap::const_iterator def = typedefNames.find( typeInst->name );
                if ( def != typedefNames.end() ) {
                        Type *ret = def->second.first->base->clone();
                        ret->location = typeInst->location;
                        ret->get_qualifiers() |= typeInst->get_qualifiers();
                        // attributes are not carried over from typedef to function parameters/return values
                        if ( ! inFunctionType ) {
                                ret->attributes.splice( ret->attributes.end(), typeInst->attributes );
                        } else {
                                deleteAll( ret->attributes );
                                ret->attributes.clear();
                        }
                        // place instance parameters on the typedef'd type
                        if ( ! typeInst->parameters.empty() ) {
                                ReferenceToType *rtt = dynamic_cast<ReferenceToType*>(ret);
                                if ( ! rtt ) {
                                        SemanticError( typeInst->location, "Cannot apply type parameters to base type of " + typeInst->name );
                                }
                                rtt->parameters.clear();
                                cloneAll( typeInst->parameters, rtt->parameters );
                                mutateAll( rtt->parameters, *visitor );  // recursively fix typedefs on parameters
                        } // if
                        delete typeInst;
                        return ret;
                } else {
                        TypeDeclMap::const_iterator base = typedeclNames.find( typeInst->name );
                        if ( base == typedeclNames.end() ) {
                                SemanticError( typeInst->location, toString("Use of undefined type ", typeInst->name) );
                        }
                        typeInst->set_baseType( base->second );
                        return typeInst;
                } // if
                assert( false );
        }

        struct VarLenChecker : WithShortCircuiting {
                void previsit( FunctionType * ) { visit_children = false; }
                void previsit( ArrayType * at ) {
                        isVarLen |= at->isVarLen;
                }
                bool isVarLen = false;
        };

        bool isVariableLength( Type * t ) {
                PassVisitor<VarLenChecker> varLenChecker;
                maybeAccept( t, varLenChecker );
                return varLenChecker.pass.isVarLen;
        }

        Declaration * ReplaceTypedef::postmutate( TypedefDecl * tyDecl ) {
                if ( typedefNames.count( tyDecl->name ) == 1 && typedefNames[ tyDecl->name ].second == scopeLevel ) {
                        // typedef to the same name from the same scope
                        // must be from the same type

                        Type * t1 = tyDecl->base;
                        Type * t2 = typedefNames[ tyDecl->name ].first->base;
                        if ( ! ResolvExpr::typesCompatible( t1, t2, Indexer() ) ) {
                                SemanticError( tyDecl->location, "Cannot redefine typedef: " + tyDecl->name );
                        }
                        // Cannot redefine VLA typedefs. Note: this is slightly incorrect, because our notion of VLAs
                        // at this point in the translator is imprecise. In particular, this will disallow redefining typedefs
                        // with arrays whose dimension is an enumerator or a cast of a constant/enumerator. The effort required
                        // to fix this corner case likely outweighs the utility of allowing it.
                        if ( isVariableLength( t1 ) || isVariableLength( t2 ) ) {
                                SemanticError( tyDecl->location, "Cannot redefine typedef: " + tyDecl->name );
                        }
                } else {
                        typedefNames[ tyDecl->name ] = std::make_pair( TypedefDeclPtr( tyDecl ), scopeLevel );
                } // if

                // When a typedef is a forward declaration:
                //    typedef struct screen SCREEN;
                // the declaration portion must be retained:
                //    struct screen;
                // because the expansion of the typedef is:
                //    void rtn( SCREEN *p ) => void rtn( struct screen *p )
                // hence the type-name "screen" must be defined.
                // Note, qualifiers on the typedef are superfluous for the forward declaration.

                Type *designatorType = tyDecl->base->stripDeclarator();
                if ( StructInstType *aggDecl = dynamic_cast< StructInstType * >( designatorType ) ) {
                        declsToAddBefore.push_back( new StructDecl( aggDecl->name, DeclarationNode::Struct, noAttributes, tyDecl->linkage ) );
                } else if ( UnionInstType *aggDecl = dynamic_cast< UnionInstType * >( designatorType ) ) {
                        declsToAddBefore.push_back( new UnionDecl( aggDecl->name, noAttributes, tyDecl->linkage ) );
                } else if ( EnumInstType *enumDecl = dynamic_cast< EnumInstType * >( designatorType ) ) {
                        declsToAddBefore.push_back( new EnumDecl( enumDecl->name, noAttributes, tyDecl->linkage ) );
                } // if
                return tyDecl->clone();
        }

        void ReplaceTypedef::premutate( TypeDecl * typeDecl ) {
                TypedefMap::iterator i = typedefNames.find( typeDecl->name );
                if ( i != typedefNames.end() ) {
                        typedefNames.erase( i ) ;
                } // if

                typedeclNames.insert( typeDecl->name, typeDecl );
        }

        void ReplaceTypedef::premutate( FunctionDecl * ) {
                GuardScope( typedefNames );
                GuardScope( typedeclNames );
        }

        void ReplaceTypedef::premutate( ObjectDecl * ) {
                GuardScope( typedefNames );
                GuardScope( typedeclNames );
        }

        DeclarationWithType * ReplaceTypedef::postmutate( ObjectDecl * objDecl ) {
                if ( FunctionType *funtype = dynamic_cast<FunctionType *>( objDecl->type ) ) { // function type?
                        // replace the current object declaration with a function declaration
                        FunctionDecl * newDecl = new FunctionDecl( objDecl->name, objDecl->get_storageClasses(), objDecl->linkage, funtype, 0, objDecl->attributes, objDecl->get_funcSpec() );
                        objDecl->attributes.clear();
                        objDecl->set_type( nullptr );
                        delete objDecl;
                        return newDecl;
                } // if
                return objDecl;
        }

        void ReplaceTypedef::premutate( CastExpr * ) {
                GuardScope( typedefNames );
                GuardScope( typedeclNames );
        }

        void ReplaceTypedef::premutate( CompoundStmt * ) {
                GuardScope( typedefNames );
                GuardScope( typedeclNames );
                scopeLevel += 1;
                GuardAction( [this](){ scopeLevel -= 1; } );
        }

        template<typename AggDecl>
        void ReplaceTypedef::addImplicitTypedef( AggDecl * aggDecl ) {
                if ( typedefNames.count( aggDecl->get_name() ) == 0 ) {
                        Type *type = nullptr;
                        if ( StructDecl * newDeclStructDecl = dynamic_cast< StructDecl * >( aggDecl ) ) {
                                type = new StructInstType( Type::Qualifiers(), newDeclStructDecl->get_name() );
                        } else if ( UnionDecl * newDeclUnionDecl = dynamic_cast< UnionDecl * >( aggDecl ) ) {
                                type = new UnionInstType( Type::Qualifiers(), newDeclUnionDecl->get_name() );
                        } else if ( EnumDecl * newDeclEnumDecl = dynamic_cast< EnumDecl * >( aggDecl )  ) {
                                type = new EnumInstType( Type::Qualifiers(), newDeclEnumDecl->get_name() );
                        } // if
                        TypedefDeclPtr tyDecl( new TypedefDecl( aggDecl->get_name(), aggDecl->location, Type::StorageClasses(), type, aggDecl->get_linkage() ) );
                        typedefNames[ aggDecl->get_name() ] = std::make_pair( std::move( tyDecl ), scopeLevel );
                        // add the implicit typedef to the AST
                        declsToAddBefore.push_back( new TypedefDecl( aggDecl->get_name(), aggDecl->location, Type::StorageClasses(), type->clone(), aggDecl->get_linkage() ) );
                } // if
        }

        template< typename AggDecl >
        void ReplaceTypedef::handleAggregate( AggDecl * aggr ) {
                SemanticErrorException errors;

                ValueGuard< std::list<Declaration * > > oldBeforeDecls( declsToAddBefore );
                ValueGuard< std::list<Declaration * > > oldAfterDecls ( declsToAddAfter  );
                declsToAddBefore.clear();
                declsToAddAfter.clear();

                GuardScope( typedefNames );
                GuardScope( typedeclNames );
                mutateAll( aggr->parameters, *visitor );

                // unroll mutateAll for aggr->members so that implicit typedefs for nested types are added to the aggregate body.
                for ( std::list< Declaration * >::iterator i = aggr->members.begin(); i != aggr->members.end(); ++i ) {
                        if ( !declsToAddAfter.empty() ) { aggr->members.splice( i, declsToAddAfter ); }

                        try {
                                *i = maybeMutate( *i, *visitor );
                        } catch ( SemanticErrorException &e ) {
                                errors.append( e );
                        }

                        if ( !declsToAddBefore.empty() ) { aggr->members.splice( i, declsToAddBefore ); }
                }

                if ( !declsToAddAfter.empty() ) { aggr->members.splice( aggr->members.end(), declsToAddAfter ); }
                if ( !errors.isEmpty() ) { throw errors; }
        }

        void ReplaceTypedef::premutate( StructDecl * structDecl ) {
                visit_children = false;
                addImplicitTypedef( structDecl );
                handleAggregate( structDecl );
        }

        void ReplaceTypedef::premutate( UnionDecl * unionDecl ) {
                visit_children = false;
                addImplicitTypedef( unionDecl );
                handleAggregate( unionDecl );
        }

        void ReplaceTypedef::premutate( EnumDecl * enumDecl ) {
                addImplicitTypedef( enumDecl );
        }

        void ReplaceTypedef::premutate( FunctionType * ) {
                GuardValue( inFunctionType );
                inFunctionType = true;
        }

        void ReplaceTypedef::premutate( TraitDecl * ) {
                GuardScope( typedefNames );
                GuardScope( typedeclNames);
        }

        void VerifyCtorDtorAssign::verify( std::list< Declaration * > & translationUnit ) {
                PassVisitor<VerifyCtorDtorAssign> verifier;
                acceptAll( translationUnit, verifier );
        }

        void VerifyCtorDtorAssign::previsit( FunctionDecl * funcDecl ) {
                FunctionType * funcType = funcDecl->get_functionType();
                std::list< DeclarationWithType * > &returnVals = funcType->get_returnVals();
                std::list< DeclarationWithType * > &params = funcType->get_parameters();

                if ( CodeGen::isCtorDtorAssign( funcDecl->get_name() ) ) { // TODO: also check /=, etc.
                        if ( params.size() == 0 ) {
                                SemanticError( funcDecl, "Constructors, destructors, and assignment functions require at least one parameter " );
                        }
                        ReferenceType * refType = dynamic_cast< ReferenceType * >( params.front()->get_type() );
                        if ( ! refType ) {
                                SemanticError( funcDecl, "First parameter of a constructor, destructor, or assignment function must be a reference " );
                        }
                        if ( CodeGen::isCtorDtor( funcDecl->get_name() ) && returnVals.size() != 0 ) {
                                SemanticError( funcDecl, "Constructors and destructors cannot have explicit return values " );
                        }
                }
        }

        template< typename Aggr >
        void validateGeneric( Aggr * inst ) {
                std::list< TypeDecl * > * params = inst->get_baseParameters();
                if ( params ) {
                        std::list< Expression * > & args = inst->get_parameters();

                        // insert defaults arguments when a type argument is missing (currently only supports missing arguments at the end of the list).
                        // A substitution is used to ensure that defaults are replaced correctly, e.g.,
                        //   forall(otype T, otype alloc = heap_allocator(T)) struct vector;
                        //   vector(int) v;
                        // after insertion of default values becomes
                        //   vector(int, heap_allocator(T))
                        // and the substitution is built with T=int so that after substitution, the result is
                        //   vector(int, heap_allocator(int))
                        TypeSubstitution sub;
                        auto paramIter = params->begin();
                        for ( size_t i = 0; paramIter != params->end(); ++paramIter, ++i ) {
                                if ( i < args.size() ) {
                                        TypeExpr * expr = strict_dynamic_cast< TypeExpr * >( *std::next( args.begin(), i ) );
                                        sub.add( (*paramIter)->get_name(), expr->get_type()->clone() );
                                } else if ( i == args.size() ) {
                                        Type * defaultType = (*paramIter)->get_init();
                                        if ( defaultType ) {
                                                args.push_back( new TypeExpr( defaultType->clone() ) );
                                                sub.add( (*paramIter)->get_name(), defaultType->clone() );
                                        }
                                }
                        }

                        sub.apply( inst );
                        if ( args.size() < params->size() ) SemanticError( inst, "Too few type arguments in generic type " );
                        if ( args.size() > params->size() ) SemanticError( inst, "Too many type arguments in generic type " );
                }
        }

        void ValidateGenericParameters::previsit( StructInstType * inst ) {
                validateGeneric( inst );
        }

        void ValidateGenericParameters::previsit( UnionInstType * inst ) {
                validateGeneric( inst );
        }

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

        Expression *CompoundLiteral::postmutate( CompoundLiteralExpr *compLitExpr ) {
                // transform [storage_class] ... (struct S){ 3, ... };
                // into [storage_class] struct S temp =  { 3, ... };
                static UniqueName indexName( "_compLit" );

                ObjectDecl *tempvar = new ObjectDecl( indexName.newName(), storageClasses, LinkageSpec::C, nullptr, compLitExpr->get_result(), compLitExpr->get_initializer() );
                compLitExpr->set_result( nullptr );
                compLitExpr->set_initializer( nullptr );
                delete compLitExpr;
                declsToAddBefore.push_back( tempvar );                                  // add modified temporary to current block
                return new VariableExpr( tempvar );
        }

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

        void ReturnTypeFixer::postvisit( FunctionDecl * functionDecl ) {
                FunctionType * ftype = functionDecl->get_functionType();
                std::list< DeclarationWithType * > & retVals = ftype->get_returnVals();
                assertf( retVals.size() == 0 || retVals.size() == 1, "Function %s has too many return values: %zu", functionDecl->get_name().c_str(), retVals.size() );
                if ( retVals.size() == 1 ) {
                        // ensure all function return values have a name - use the name of the function to disambiguate (this also provides a nice bit of help for debugging).
                        // ensure other return values have a name.
                        DeclarationWithType * ret = retVals.front();
                        if ( ret->get_name() == "" ) {
                                ret->set_name( toString( "_retval_", CodeGen::genName( functionDecl ) ) );
                        }
                        ret->get_attributes().push_back( new Attribute( "unused" ) );
                }
        }

        void ReturnTypeFixer::postvisit( FunctionType * ftype ) {
                // xxx - need to handle named return values - this information needs to be saved somehow
                // so that resolution has access to the names.
                // Note that this pass needs to happen early so that other passes which look for tuple types
                // find them in all of the right places, including function return types.
                std::list< DeclarationWithType * > & retVals = ftype->get_returnVals();
                if ( retVals.size() > 1 ) {
                        // generate a single return parameter which is the tuple of all of the return values
                        TupleType * tupleType = strict_dynamic_cast< TupleType * >( ResolvExpr::extractResultType( ftype ) );
                        // ensure return value is not destructed by explicitly creating an empty ListInit node wherein maybeConstruct is false.
                        ObjectDecl * newRet = new ObjectDecl( "", Type::StorageClasses(), LinkageSpec::Cforall, 0, tupleType, new ListInit( std::list<Initializer*>(), noDesignators, false ) );
                        deleteAll( retVals );
                        retVals.clear();
                        retVals.push_back( newRet );
                }
        }

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

        void FixObjectType::previsit( ObjectDecl * objDecl ) {
                Type *new_type = ResolvExpr::resolveTypeof( objDecl->get_type(), indexer );
                new_type->get_qualifiers() -= Type::Lvalue; // even if typeof is lvalue, variable can never have lvalue-qualified type
                objDecl->set_type( new_type );
        }

        void FixObjectType::previsit( FunctionDecl * funcDecl ) {
                Type *new_type = ResolvExpr::resolveTypeof( funcDecl->type, indexer );
                new_type->get_qualifiers() -= Type::Lvalue; // even if typeof is lvalue, variable can never have lvalue-qualified type
                funcDecl->set_type( new_type );
        }

        void FixObjectType::previsit( TypeDecl *typeDecl ) {
                if ( typeDecl->get_base() ) {
                        Type *new_type = ResolvExpr::resolveTypeof( typeDecl->get_base(), indexer );
                        new_type->get_qualifiers() -= Type::Lvalue; // even if typeof is lvalue, variable can never have lvalue-qualified type
                        typeDecl->set_base( new_type );
                } // if
        }

        void ArrayLength::computeLength( std::list< Declaration * > & translationUnit ) {
                PassVisitor<ArrayLength> len;
                acceptAll( translationUnit, len );
        }

        void ArrayLength::previsit( ObjectDecl * objDecl ) {
                if ( ArrayType * at = dynamic_cast< ArrayType * >( objDecl->type ) ) {
                        if ( at->dimension ) return;
                        if ( ListInit * init = dynamic_cast< ListInit * >( objDecl->init ) ) {
                                at->dimension = new ConstantExpr( Constant::from_ulong( init->initializers.size() ) );
                        }
                }
        }

        void ArrayLength::previsit( ArrayType * type ) {
                if ( type->dimension ) {
                        // need to resolve array dimensions early so that constructor code can correctly determine
                        // if a type is a VLA (and hence whether its elements need to be constructed)
                        ResolvExpr::findSingleExpression( type->dimension, SymTab::SizeType->clone(), indexer );

                        // must re-evaluate whether a type is a VLA, now that more information is available
                        // (e.g. the dimension may have been an enumerator, which was unknown prior to this step)
                        type->isVarLen = ! InitTweak::isConstExpr( type->dimension );
                }
        }

        struct LabelFinder {
                std::set< Label > & labels;
                LabelFinder( std::set< Label > & labels ) : labels( labels ) {}
                void previsit( Statement * stmt ) {
                        for ( Label & l : stmt->labels ) {
                                labels.insert( l );
                        }
                }
        };

        void LabelAddressFixer::premutate( FunctionDecl * funcDecl ) {
                GuardValue( labels );
                PassVisitor<LabelFinder> finder( labels );
                funcDecl->accept( finder );
        }

        Expression * LabelAddressFixer::postmutate( AddressExpr * addrExpr ) {
                // convert &&label into label address
                if ( AddressExpr * inner = dynamic_cast< AddressExpr * >( addrExpr->arg ) ) {
                        if ( NameExpr * nameExpr = dynamic_cast< NameExpr * >( inner->arg ) ) {
                                if ( labels.count( nameExpr->name ) ) {
                                        Label name = nameExpr->name;
                                        delete addrExpr;
                                        return new LabelAddressExpr( name );
                                }
                        }
                }
                return addrExpr;
        }

        void FindSpecialDeclarations::previsit( FunctionDecl * funcDecl ) {
                if ( ! dereferenceOperator ) {
                        // find and remember the intrinsic dereference operator for object pointers
                        if ( funcDecl->name == "*?" && funcDecl->linkage == LinkageSpec::Intrinsic ) {
                                FunctionType * ftype = funcDecl->type;
                                if ( ftype->parameters.size() == 1 ) {
                                        PointerType * ptrType = strict_dynamic_cast<PointerType *>( ftype->parameters.front()->get_type() );
                                        if ( ptrType->base->get_qualifiers() == Type::Qualifiers() ) {
                                                TypeInstType * inst = dynamic_cast<TypeInstType *>( ptrType->base );
                                                if ( inst && ! inst->get_isFtype() ) {
                                                        dereferenceOperator = funcDecl;
                                                }
                                        }
                                }
                        }
                }
        }
} // namespace SymTab

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