source: src/SymTab/Validate.cc@ ea89e36

//
// 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 : Andrew Beach
// Last Modified On : Fri Nov 12 11:00:00 2021
// Update Count     : 364
//

// 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 <unordered_map>               // for unordered_map
#include <utility>                     // for pair

#include "AST/Chain.hpp"
#include "AST/Decl.hpp"
#include "AST/Node.hpp"
#include "AST/Pass.hpp"
#include "AST/SymbolTable.hpp"
#include "AST/Type.hpp"
#include "AST/TypeSubstitution.hpp"
#include "CodeGen/CodeGenerator.h"     // for genName
#include "CodeGen/OperatorTable.h"     // for isCtorDtor, isCtorDtorAssign
#include "ControlStruct/Mutate.h"      // for ForExprMutator
#include "Common/CodeLocation.h"       // for CodeLocation
#include "Common/Stats.h"              // for Stats::Heap
#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 "CompilationState.h"          // skip some passes in new-ast build
#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 "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/LinkageSpec.h"       // for C
#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
#include "Validate/FindSpecialDecls.h" // for FindSpecialDecls

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 {
                FixQualifiedTypes() : WithIndexer(false) {}
                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_old {
                void previsit( EnumDecl * aggregateDecl );
                void previsit( FunctionType * func );
        };

        /// Associates forward declarations of aggregates with their definitions
        struct LinkReferenceToTypes_old final : public WithIndexer, public WithGuards, public WithVisitorRef<LinkReferenceToTypes_old>, public WithShortCircuiting {
                LinkReferenceToTypes_old( 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;
        };

        /// Does early resolution on the expressions that give enumeration constants their values
        struct ResolveEnumInitializers final : public WithIndexer, public WithGuards, public WithVisitorRef<ResolveEnumInitializers>, public WithShortCircuiting {
                ResolveEnumInitializers( const Indexer * indexer );
                void postvisit( EnumDecl * enumDecl );

          private:
                const Indexer * local_indexer;

        };

        /// Replaces array and function types in forall lists by appropriate pointer type and assigns each Object and Function declaration a unique ID.
        struct ForallPointerDecay_old 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 );
        };

        /// desugar declarations and uses of dimension paramaters like [N],
        /// from type-system managed values, to tunnneling via ordinary types,
        /// as char[-] in and sizeof(-) out
        struct TranslateDimensionGenericParameters : public WithIndexer, public WithGuards {
                static void translateDimensions( std::list< Declaration * > &translationUnit );
                TranslateDimensionGenericParameters();

                bool nextVisitedNodeIsChildOfSUIT = false; // SUIT = Struct or Union -Inst Type
                bool visitingChildOfSUIT = false;
                void changeState_ChildOfSUIT( bool newVal );
                void premutate( StructInstType * sit );
                void premutate( UnionInstType * uit );
                void premutate( BaseSyntaxNode * node );

                TypeDecl * postmutate( TypeDecl * td );
                Expression * postmutate( DimensionExpr * de );
                Expression * postmutate( Expression * e );
        };

        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 InitializerLength {
                /// 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 );
        };

        struct ArrayLength : public WithIndexer {
                static void computeLength( std::list< Declaration * > & translationUnit );

                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 );
        };

        void validate_A( std::list< Declaration * > & translationUnit ) {
                PassVisitor<EnumAndPointerDecay_old> epc;
                PassVisitor<HoistTypeDecls> hoistDecls;
                {
                        Stats::Heap::newPass("validate-A");
                        Stats::Time::BlockGuard guard("validate-A");
                        VerifyCtorDtorAssign::verify( translationUnit );  // must happen before autogen, because autogen examines existing ctor/dtors
                        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_old because it is an indexer and needs correct types for mangling
                }
        }

        void validate_B( std::list< Declaration * > & translationUnit ) {
                PassVisitor<LinkReferenceToTypes_old> lrt( nullptr );
                PassVisitor<FixQualifiedTypes> fixQual;
                {
                        Stats::Heap::newPass("validate-B");
                        Stats::Time::BlockGuard guard("validate-B");
                        acceptAll( translationUnit, lrt ); // must happen before autogen, because sized flag needs to propagate to generated functions
                        mutateAll( translationUnit, fixQual ); // must happen after LinkReferenceToTypes_old, because aggregate members are accessed
                        HoistStruct::hoistStruct( translationUnit );
                        EliminateTypedef::eliminateTypedef( translationUnit );
                }
        }

        void validate_C( std::list< Declaration * > & translationUnit ) {
                PassVisitor<ValidateGenericParameters> genericParams;
                PassVisitor<ResolveEnumInitializers> rei( nullptr );
                {
                        Stats::Heap::newPass("validate-C");
                        Stats::Time::BlockGuard guard("validate-C");
                        Stats::Time::TimeBlock("Validate Generic Parameters", [&]() {
                                acceptAll( translationUnit, genericParams );  // check as early as possible - can't happen before LinkReferenceToTypes_old; observed failing when attempted before eliminateTypedef
                        });
                        Stats::Time::TimeBlock("Translate Dimensions", [&]() {
                                TranslateDimensionGenericParameters::translateDimensions( translationUnit );
                        });
                        Stats::Time::TimeBlock("Resolve Enum Initializers", [&]() {
                                acceptAll( translationUnit, rei ); // must happen after translateDimensions because rei needs identifier lookup, which needs name mangling
                        });
                        Stats::Time::TimeBlock("Check Function Returns", [&]() {
                                ReturnChecker::checkFunctionReturns( translationUnit );
                        });
                        Stats::Time::TimeBlock("Fix Return Statements", [&]() {
                                InitTweak::fixReturnStatements( translationUnit ); // must happen before autogen
                        });
                }
        }

        void validate_D( std::list< Declaration * > & translationUnit ) {
                PassVisitor<ForallPointerDecay_old> fpd;
                {
                        Stats::Heap::newPass("validate-D");
                        Stats::Time::BlockGuard guard("validate-D");
                        Stats::Time::TimeBlock("Apply Concurrent Keywords", [&]() {
                                Concurrency::applyKeywords( translationUnit );
                        });
                        Stats::Time::TimeBlock("Forall Pointer Decay", [&]() {
                                acceptAll( translationUnit, fpd ); // must happen before autogenerateRoutines, after Concurrency::applyKeywords because uniqueIds must be set on declaration before resolution
                        });
                        Stats::Time::TimeBlock("Hoist Control Declarations", [&]() {
                                ControlStruct::hoistControlDecls( translationUnit );  // hoist initialization out of for statements; must happen before autogenerateRoutines
                        });
                        Stats::Time::TimeBlock("Generate Autogen routines", [&]() {
                                autogenerateRoutines( translationUnit ); // moved up, used to be below compoundLiteral - currently needs EnumAndPointerDecay_old
                        });
                }
        }

        void validate_E( std::list< Declaration * > & translationUnit ) {
                PassVisitor<CompoundLiteral> compoundliteral;
                {
                        Stats::Heap::newPass("validate-E");
                        Stats::Time::BlockGuard guard("validate-E");
                        Stats::Time::TimeBlock("Implement Mutex Func", [&]() {
                                Concurrency::implementMutexFuncs( translationUnit );
                        });
                        Stats::Time::TimeBlock("Implement Thread Start", [&]() {
                                Concurrency::implementThreadStarter( translationUnit );
                        });
                        Stats::Time::TimeBlock("Compound Literal", [&]() {
                                mutateAll( translationUnit, compoundliteral );
                        });
                        if (!useNewAST) {
                                Stats::Time::TimeBlock("Resolve With Expressions", [&]() {
                                        ResolvExpr::resolveWithExprs( translationUnit ); // must happen before FixObjectType because user-code is resolved and may contain with variables
                                });
                        }
                }
        }

        void validate_F( std::list< Declaration * > & translationUnit ) {
                PassVisitor<LabelAddressFixer> labelAddrFixer;
                {
                        Stats::Heap::newPass("validate-F");
                        Stats::Time::BlockGuard guard("validate-F");
                        if (!useNewAST) {
                                Stats::Time::TimeCall("Fix Object Type",
                                        FixObjectType::fix, translationUnit);
                        }
                        Stats::Time::TimeCall("Initializer Length",
                                InitializerLength::computeLength, translationUnit);
                        if (!useNewAST) {
                                Stats::Time::TimeCall("Array Length",
                                        ArrayLength::computeLength, translationUnit);
                        }
                        Stats::Time::TimeCall("Find Special Declarations",
                                Validate::findSpecialDecls, translationUnit);
                        Stats::Time::TimeCall("Fix Label Address",
                                mutateAll<LabelAddressFixer>, translationUnit, labelAddrFixer);
                        if (!useNewAST) {
                                Stats::Time::TimeCall("Handle Attributes",
                                        Validate::handleAttributes, translationUnit);
                        }
                }
        }

        void decayForallPointers( std::list< Declaration * > & translationUnit ) {
                PassVisitor<ForallPointerDecay_old> fpd;
                acceptAll( translationUnit, fpd );
        }

        void validate( std::list< Declaration * > &translationUnit, __attribute__((unused)) bool doDebug ) {
                validate_A( translationUnit );
                validate_B( translationUnit );
                validate_C( translationUnit );
                validate_D( translationUnit );
                validate_E( translationUnit );
                validate_F( translationUnit );
        }

        void validateType( Type * type, const Indexer * indexer ) {
                PassVisitor<EnumAndPointerDecay_old> epc;
                PassVisitor<LinkReferenceToTypes_old> lrt( indexer );
                PassVisitor<ForallPointerDecay_old> 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 ( 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();
                                                        TypeSubstitution sub = parent->genericSubstitution();
                                                        sub.apply(ret);
                                                        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_old::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_old::previsit( FunctionType * func ) {
                // Fix up parameters and return types
                fixFunctionList( func->parameters, func->isVarArgs, func );
                fixFunctionList( func->returnVals, false, func );
        }

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

        void LinkReferenceToTypes_old::postvisit( EnumInstType * enumInst ) {
                const 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 = const_cast<EnumDecl *>(st); // Just linking in the node
                } // if
                if ( ! st || ! st->body ) {
                        // use of forward declaration
                        forwardEnums[ enumInst->name ].push_back( enumInst );
                } // if
        }

        void LinkReferenceToTypes_old::postvisit( StructInstType * structInst ) {
                const 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 = const_cast<StructDecl *>(st); // Just linking in the node
                } // if
                if ( ! st || ! st->body ) {
                        // use of forward declaration
                        forwardStructs[ structInst->name ].push_back( structInst );
                } // if
        }

        void LinkReferenceToTypes_old::postvisit( UnionInstType * unionInst ) {
                const 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 = const_cast<UnionDecl *>(un); // Just linking in the node
                } // if
                if ( ! un || ! un->body ) {
                        // use of forward declaration
                        forwardUnions[ unionInst->name ].push_back( unionInst );
                } // if
        }

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

        void LinkReferenceToTypes_old::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_old::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_old::postvisit( TraitInstType * traitInst ) {
                // handle other traits
                const 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 = const_cast<TraitDecl *>(traitDecl); // Just linking in the node

                // 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_old::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
                } // if
        }

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

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

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

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

        void ResolveEnumInitializers::postvisit( EnumDecl * enumDecl ) {
                if ( enumDecl->body ) {
                        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
        }

        /// 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_old::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_old::previsit( FunctionDecl * func ) {
                func->fixUniqueId();
        }

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

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

        void ForallPointerDecay_old::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
                        Validate::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.
                        Validate::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;
        }

        static bool isNonParameterAttribute( Attribute * attr ) {
                static const std::vector<std::string> bad_names = {
                        "aligned", "__aligned__",
                };
                for ( auto name : bad_names ) {
                        if ( name == attr->name ) {
                                return true;
                        }
                }
                return false;
        }

        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();
                        // GCC ignores certain attributes if they arrive by typedef, this mimics that.
                        if ( inFunctionType ) {
                                ret->attributes.remove_if( isNonParameterAttribute );
                        }
                        ret->attributes.splice( ret->attributes.end(), typeInst->attributes );
                        // 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, AggregateDecl::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 );
                mutateAll( aggr->attributes, * 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->location, "Constructors, destructors, and assignment functions require at least one parameter." );
                        }
                        ReferenceType * refType = dynamic_cast< ReferenceType * >( params.front()->get_type() );
                        if ( ! refType ) {
                                SemanticError( funcDecl->location, "First parameter of a constructor, destructor, or assignment function must be a reference." );
                        }
                        if ( CodeGen::isCtorDtor( funcDecl->get_name() ) && returnVals.size() != 0 ) {
                                if(!returnVals.front()->get_type()->isVoid()) {
                                        SemanticError( funcDecl->location, "Constructors and destructors cannot have explicit return values." );
                                }
                        }
                }
        }

        // Test for special name on a generic parameter.  Special treatment for the
        // special name is a bootstrapping hack.  In most cases, the worlds of T's
        // and of N's don't overlap (normal treamtemt).  The foundations in
        // array.hfa use tagging for both types and dimensions.  Tagging treats
        // its subject parameter even more opaquely than T&, which assumes it is
        // possible to have a pointer/reference to such an object.  Tagging only
        // seeks to identify the type-system resident at compile time.  Both N's
        // and T's can make tags.  The tag definition uses the special name, which
        // is treated as "an N or a T."  This feature is not inteded to be used
        // outside of the definition and immediate uses of a tag.
        static inline bool isReservedTysysIdOnlyName( const std::string & name ) {
                // name's prefix was __CFA_tysys_id_only, before it got wrapped in __..._generic
                int foundAt = name.find("__CFA_tysys_id_only");
                if (foundAt == 0) return true;
                if (foundAt == 2 && name[0] == '_' && name[1] == '_') return true;
                return false;
        }

        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();
                        auto argIter = args.begin();
                        for ( ; paramIter != params->end(); ++paramIter, ++argIter ) {
                                if ( argIter != args.end() ) {
                                        TypeExpr * expr = dynamic_cast< TypeExpr * >( * argIter );
                                        if ( expr ) {
                                                sub.add( (* paramIter)->get_name(), expr->get_type()->clone() );
                                        }
                                } else {
                                        Type * defaultType = (* paramIter)->get_init();
                                        if ( defaultType ) {
                                                args.push_back( new TypeExpr( defaultType->clone() ) );
                                                sub.add( (* paramIter)->get_name(), defaultType->clone() );
                                                argIter = std::prev(args.end());
                                        } else {
                                                SemanticError( inst, "Too few type arguments in generic type " );
                                        }
                                }
                                assert( argIter != args.end() );
                                bool typeParamDeclared = (*paramIter)->kind != TypeDecl::Kind::Dimension;
                                bool typeArgGiven;
                                if ( isReservedTysysIdOnlyName( (*paramIter)->name ) ) {
                                        // coerce a match when declaration is reserved name, which means "either"
                                        typeArgGiven = typeParamDeclared;
                                } else {
                                        typeArgGiven = dynamic_cast< TypeExpr * >( * argIter );
                                }
                                if ( ! typeParamDeclared &&   typeArgGiven ) SemanticError( inst, "Type argument given for value parameter: " );
                                if (   typeParamDeclared && ! typeArgGiven ) SemanticError( inst, "Expression argument given for type parameter: " );
                        }

                        sub.apply( inst );
                        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 TranslateDimensionGenericParameters::translateDimensions( std::list< Declaration * > &translationUnit ) {
                PassVisitor<TranslateDimensionGenericParameters> translator;
                mutateAll( translationUnit, translator );
        }

        TranslateDimensionGenericParameters::TranslateDimensionGenericParameters() : WithIndexer( false ) {}

        // Declaration of type variable:           forall( [N] )          ->  forall( N & | sized( N ) )
        TypeDecl * TranslateDimensionGenericParameters::postmutate( TypeDecl * td ) {
                if ( td->kind == TypeDecl::Dimension ) {
                        td->kind = TypeDecl::Dtype;
                        if ( ! isReservedTysysIdOnlyName( td->name ) ) {
                                td->sized = true;
                        }
                }
                return td;
        }

        // Situational awareness:
        // array( float, [[currentExpr]]     )  has  visitingChildOfSUIT == true
        // array( float, [[currentExpr]] - 1 )  has  visitingChildOfSUIT == false
        // size_t x =    [[currentExpr]]        has  visitingChildOfSUIT == false
        void TranslateDimensionGenericParameters::changeState_ChildOfSUIT( bool newVal ) {
                GuardValue( nextVisitedNodeIsChildOfSUIT );
                GuardValue( visitingChildOfSUIT );
                visitingChildOfSUIT = nextVisitedNodeIsChildOfSUIT;
                nextVisitedNodeIsChildOfSUIT = newVal;
        }
        void TranslateDimensionGenericParameters::premutate( StructInstType * sit ) {
                (void) sit;
                changeState_ChildOfSUIT(true);
        }
        void TranslateDimensionGenericParameters::premutate( UnionInstType * uit ) {
                (void) uit;
                changeState_ChildOfSUIT(true);
        }
        void TranslateDimensionGenericParameters::premutate( BaseSyntaxNode * node ) {
                (void) node;
                changeState_ChildOfSUIT(false);
        }

        // Passing values as dimension arguments:  array( float,     7 )  -> array( float, char[             7 ] )
        // Consuming dimension parameters:         size_t x =    N - 1 ;  -> size_t x =          sizeof(N) - 1   ;
        // Intertwined reality:                    array( float, N     )  -> array( float,              N        )
        //                                         array( float, N - 1 )  -> array( float, char[ sizeof(N) - 1 ] )
        // Intertwined case 1 is not just an optimization.
        // Avoiding char[sizeof(-)] is necessary to enable the call of f to bind the value of N, in:
        //   forall([N]) void f( array(float, N) & );
        //   array(float, 7) a;
        //   f(a);

        Expression * TranslateDimensionGenericParameters::postmutate( DimensionExpr * de ) {
                // Expression de is an occurrence of N in LHS of above examples.
                // Look up the name that de references.
                // If we are in a struct body, then this reference can be to an entry of the stuct's forall list.
                // Whether or not we are in a struct body, this reference can be to an entry of a containing function's forall list.
                // If we are in a struct body, then the stuct's forall declarations are innermost (functions don't occur in structs).
                // Thus, a potential struct's declaration is highest priority.
                // A struct's forall declarations are already renamed with _generic_ suffix.  Try that name variant first.

                std::string useName = "__" + de->name + "_generic_";
                TypeDecl * namedParamDecl = const_cast<TypeDecl *>( strict_dynamic_cast<const TypeDecl *, nullptr >( indexer.lookupType( useName ) ) );

                if ( ! namedParamDecl ) {
                        useName = de->name;
                        namedParamDecl = const_cast<TypeDecl *>( strict_dynamic_cast<const TypeDecl *, nullptr >( indexer.lookupType( useName ) ) );
                }

                // Expect to find it always.  A misspelled name would have been parsed as an identifier.
                assert( namedParamDecl && "Type-system-managed value name not found in symbol table" );

                delete de;

                TypeInstType * refToDecl = new TypeInstType( 0, useName, namedParamDecl );

                if ( visitingChildOfSUIT ) {
                        // As in postmutate( Expression * ), topmost expression needs a TypeExpr wrapper
                        // But avoid ArrayType-Sizeof
                        return new TypeExpr( refToDecl );
                } else {
                        // the N occurrence is being used directly as a runtime value,
                        // if we are in a type instantiation, then the N is within a bigger value computation
                        return new SizeofExpr( refToDecl );
                }
        }

        Expression * TranslateDimensionGenericParameters::postmutate( Expression * e ) {
                if ( visitingChildOfSUIT ) {
                        // e is an expression used as an argument to instantiate a type
                        if (! dynamic_cast< TypeExpr * >( e ) ) {
                                // e is a value expression
                                // but not a DimensionExpr, which has a distinct postmutate
                                Type * typeExprContent = new ArrayType( 0, new BasicType( 0, BasicType::Char ), e, true, false );
                                TypeExpr * result = new TypeExpr( typeExprContent );
                                return result;
                        }
                }
                return e;
        }

        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 );
                objDecl->set_type( new_type );
        }

        void FixObjectType::previsit( FunctionDecl * funcDecl ) {
                Type * new_type = ResolvExpr::resolveTypeof( funcDecl->type, indexer );
                funcDecl->set_type( new_type );
        }

        void FixObjectType::previsit( TypeDecl * typeDecl ) {
                if ( typeDecl->get_base() ) {
                        Type * new_type = ResolvExpr::resolveTypeof( typeDecl->get_base(), indexer );
                        typeDecl->set_base( new_type );
                } // if
        }

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

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

        void InitializerLength::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, Validate::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;
        }

namespace {
        /// Replaces enum types by int, and function/array types in function parameter and return
        /// lists by appropriate pointers
        /*
        struct EnumAndPointerDecay_new {
                const ast::EnumDecl * previsit( const ast::EnumDecl * enumDecl ) {
                        // set the type of each member of the enumeration to be EnumConstant
                        for ( unsigned i = 0; i < enumDecl->members.size(); ++i ) {
                                // build new version of object with EnumConstant
                                ast::ptr< ast::ObjectDecl > obj =
                                        enumDecl->members[i].strict_as< ast::ObjectDecl >();
                                obj.get_and_mutate()->type =
                                        new ast::EnumInstType{ enumDecl->name, ast::CV::Const };

                                // set into decl
                                ast::EnumDecl * mut = mutate( enumDecl );
                                mut->members[i] = obj.get();
                                enumDecl = mut;
                        }
                        return enumDecl;
                }

                static const ast::FunctionType * fixFunctionList(
                        const ast::FunctionType * func,
                        std::vector< ast::ptr< ast::DeclWithType > > ast::FunctionType::* field,
                        ast::ArgumentFlag isVarArgs = ast::FixedArgs
                ) {
                        const auto & dwts = func->* field;
                        unsigned nvals = dwts.size();
                        bool hasVoid = false;
                        for ( unsigned i = 0; i < nvals; ++i ) {
                                func = ast::mutate_field_index( func, field, i, fixFunction( dwts[i], hasVoid ) );
                        }

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

                        // one void is the only thing in the list, remove it
                        if ( hasVoid ) {
                                func = ast::mutate_field(
                                        func, field, std::vector< ast::ptr< ast::DeclWithType > >{} );
                        }

                        return func;
                }

                const ast::FunctionType * previsit( const ast::FunctionType * func ) {
                        func = fixFunctionList( func, &ast::FunctionType::params, func->isVarArgs );
                        return fixFunctionList( func, &ast::FunctionType::returns );
                }
        };

        /// expand assertions from a trait instance, performing appropriate type variable substitutions
        void expandAssertions(
                const ast::TraitInstType * inst, std::vector< ast::ptr< ast::DeclWithType > > & out
        ) {
                assertf( inst->base, "Trait instance not linked to base trait: %s", toCString( inst ) );

                // build list of trait members, substituting trait decl parameters for instance parameters
                ast::TypeSubstitution sub{
                        inst->base->params.begin(), inst->base->params.end(), inst->params.begin() };
                // deliberately take ast::ptr by-value to ensure this does not mutate inst->base
                for ( ast::ptr< ast::Decl > decl : inst->base->members ) {
                        auto member = decl.strict_as< ast::DeclWithType >();
                        sub.apply( member );
                        out.emplace_back( member );
                }
        }

        /// Associates forward declarations of aggregates with their definitions
        class LinkReferenceToTypes_new final
        : public ast::WithSymbolTable, public ast::WithGuards, public
          ast::WithVisitorRef<LinkReferenceToTypes_new>, public ast::WithShortCircuiting {

                // these maps of uses of forward declarations of types need to have the actual type
                // declaration switched in * after * they have been traversed. To enable this in the
                // ast::Pass framework, any node that needs to be so mutated has mutate() called on it
                // before it is placed in the map, properly updating its parents in the usual traversal,
                // then can have the actual mutation applied later
                using ForwardEnumsType = std::unordered_multimap< std::string, ast::EnumInstType * >;
                using ForwardStructsType = std::unordered_multimap< std::string, ast::StructInstType * >;
                using ForwardUnionsType = std::unordered_multimap< std::string, ast::UnionInstType * >;

                const CodeLocation & location;
                const ast::SymbolTable * localSymtab;

                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;

        public:
                /// contstruct using running symbol table
                LinkReferenceToTypes_new( const CodeLocation & loc )
                : location( loc ), localSymtab( &symtab ) {}

                /// construct using provided symbol table
                LinkReferenceToTypes_new( const CodeLocation & loc, const ast::SymbolTable & syms )
                : location( loc ), localSymtab( &syms ) {}

                const ast::Type * postvisit( const ast::TypeInstType * typeInst ) {
                        // ensure generic parameter instances are renamed like the base type
                        if ( inGeneric && typeInst->base ) {
                                typeInst = ast::mutate_field(
                                        typeInst, &ast::TypeInstType::name, typeInst->base->name );
                        }

                        if (
                                auto typeDecl = dynamic_cast< const ast::TypeDecl * >(
                                        localSymtab->lookupType( typeInst->name ) )
                        ) {
                                typeInst = ast::mutate_field( typeInst, &ast::TypeInstType::kind, typeDecl->kind );
                        }

                        return typeInst;
                }

                const ast::Type * postvisit( const ast::EnumInstType * inst ) {
                        const ast::EnumDecl * decl = localSymtab->lookupEnum( inst->name );
                        // not a semantic error if the enum is not found, just an implicit forward declaration
                        if ( decl ) {
                                inst = ast::mutate_field( inst, &ast::EnumInstType::base, decl );
                        }
                        if ( ! decl || ! decl->body ) {
                                // forward declaration
                                auto mut = mutate( inst );
                                forwardEnums.emplace( inst->name, mut );
                                inst = mut;
                        }
                        return inst;
                }

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

                const ast::StructInstType * postvisit( const ast::StructInstType * inst ) {
                        const ast::StructDecl * decl = localSymtab->lookupStruct( inst->name );
                        // not a semantic error if the struct is not found, just an implicit forward declaration
                        if ( decl ) {
                                inst = ast::mutate_field( inst, &ast::StructInstType::base, decl );
                        }
                        if ( ! decl || ! decl->body ) {
                                // forward declaration
                                auto mut = mutate( inst );
                                forwardStructs.emplace( inst->name, mut );
                                inst = mut;
                        }
                        checkGenericParameters( inst );
                        return inst;
                }

                const ast::UnionInstType * postvisit( const ast::UnionInstType * inst ) {
                        const ast::UnionDecl * decl = localSymtab->lookupUnion( inst->name );
                        // not a semantic error if the struct is not found, just an implicit forward declaration
                        if ( decl ) {
                                inst = ast::mutate_field( inst, &ast::UnionInstType::base, decl );
                        }
                        if ( ! decl || ! decl->body ) {
                                // forward declaration
                                auto mut = mutate( inst );
                                forwardUnions.emplace( inst->name, mut );
                                inst = mut;
                        }
                        checkGenericParameters( inst );
                        return inst;
                }

                const ast::Type * postvisit( const ast::TraitInstType * traitInst ) {
                        // handle other traits
                        const ast::TraitDecl * traitDecl = localSymtab->lookupTrait( traitInst->name );
                        if ( ! traitDecl )       {
                                SemanticError( location, "use of undeclared trait " + traitInst->name );
                        }
                        if ( traitDecl->params.size() != traitInst->params.size() ) {
                                SemanticError( location, traitInst, "incorrect number of trait parameters: " );
                        }
                        traitInst = ast::mutate_field( traitInst, &ast::TraitInstType::base, traitDecl );

                        // need to carry over the "sized" status of each decl in the instance
                        for ( unsigned i = 0; i < traitDecl->params.size(); ++i ) {
                                auto expr = traitInst->params[i].as< ast::TypeExpr >();
                                if ( ! expr ) {
                                        SemanticError(
                                                traitInst->params[i].get(), "Expression parameters for trait instances "
                                                "are currently unsupported: " );
                                }

                                if ( auto inst = expr->type.as< ast::TypeInstType >() ) {
                                        if ( traitDecl->params[i]->sized && ! inst->base->sized ) {
                                                // traitInst = ast::mutate_field_index(
                                                //      traitInst, &ast::TraitInstType::params, i,
                                                //      ...
                                                // );
                                                ast::TraitInstType * mut = ast::mutate( traitInst );
                                                ast::chain_mutate( mut->params[i] )
                                                        ( &ast::TypeExpr::type )
                                                                ( &ast::TypeInstType::base )->sized = true;
                                                traitInst = mut;
                                        }
                                }
                        }

                        return traitInst;
                }

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

                const ast::Type * postvisit( const ast::QualifiedType * qualType ) {
                        // linking only makes sense for the "oldest ancestor" of the qualified type
                        return ast::mutate_field(
                                qualType, &ast::QualifiedType::parent, qualType->parent->accept( * visitor ) );
                }

                const ast::Decl * postvisit( const ast::EnumDecl * enumDecl ) {
                        // visit enum members first so that the types of self-referencing members are updated
                        // properly
                        if ( ! enumDecl->body ) return enumDecl;

                        // update forward declarations to point here
                        auto fwds = forwardEnums.equal_range( enumDecl->name );
                        if ( fwds.first != fwds.second ) {
                                auto inst = fwds.first;
                                do {
                                        // forward decl is stored * mutably * in map, can thus be updated
                                        inst->second->base = enumDecl;
                                } while ( ++inst != fwds.second );
                                forwardEnums.erase( fwds.first, fwds.second );
                        }

                        // ensure that enumerator initializers are properly set
                        for ( unsigned i = 0; i < enumDecl->members.size(); ++i ) {
                                auto field = enumDecl->members[i].strict_as< ast::ObjectDecl >();
                                if ( field->init ) {
                                        // need to resolve enumerator initializers early so that other passes that
                                        // determine if an expression is constexpr have appropriate information
                                        auto init = field->init.strict_as< ast::SingleInit >();

                                        enumDecl = ast::mutate_field_index(
                                                enumDecl, &ast::EnumDecl::members, i,
                                                ast::mutate_field( field, &ast::ObjectDecl::init,
                                                        ast::mutate_field( init, &ast::SingleInit::value,
                                                                ResolvExpr::findSingleExpression(
                                                                        init->value, new ast::BasicType{ ast::BasicType::SignedInt },
                                                                        symtab ) ) ) );
                                }
                        }

                        return enumDecl;
                }

                /// rename generic type parameters uniquely so that they do not conflict with user defined
                /// function forall parameters, e.g. the T in Box and the T in f, below
                ///   forall(otype T)
                ///   struct Box {
                ///     T x;
                ///   };
                ///   forall(otype T)
                ///   void f(Box(T) b) {
                ///     ...
                ///   }
                template< typename AggrDecl >
                const AggrDecl * renameGenericParams( const AggrDecl * aggr ) {
                        GuardValue( inGeneric );
                        inGeneric = ! aggr->params.empty();

                        for ( unsigned i = 0; i < aggr->params.size(); ++i ) {
                                const ast::TypeDecl * td = aggr->params[i];

                                aggr = ast::mutate_field_index(
                                        aggr, &AggrDecl::params, i,
                                        ast::mutate_field( td, &ast::TypeDecl::name, "__" + td->name + "_generic_" ) );
                        }
                        return aggr;
                }

                const ast::StructDecl * previsit( const ast::StructDecl * structDecl ) {
                        return renameGenericParams( structDecl );
                }

                void postvisit( const ast::StructDecl * structDecl ) {
                        // visit struct members first so that the types of self-referencing members are
                        // updated properly
                        if ( ! structDecl->body ) return;

                        // update forward declarations to point here
                        auto fwds = forwardStructs.equal_range( structDecl->name );
                        if ( fwds.first != fwds.second ) {
                                auto inst = fwds.first;
                                do {
                                        // forward decl is stored * mutably * in map, can thus be updated
                                        inst->second->base = structDecl;
                                } while ( ++inst != fwds.second );
                                forwardStructs.erase( fwds.first, fwds.second );
                        }
                }

                const ast::UnionDecl * previsit( const ast::UnionDecl * unionDecl ) {
                        return renameGenericParams( unionDecl );
                }

                void postvisit( const ast::UnionDecl * unionDecl ) {
                        // visit union members first so that the types of self-referencing members are updated
                        // properly
                        if ( ! unionDecl->body ) return;

                        // update forward declarations to point here
                        auto fwds = forwardUnions.equal_range( unionDecl->name );
                        if ( fwds.first != fwds.second ) {
                                auto inst = fwds.first;
                                do {
                                        // forward decl is stored * mutably * in map, can thus be updated
                                        inst->second->base = unionDecl;
                                } while ( ++inst != fwds.second );
                                forwardUnions.erase( fwds.first, fwds.second );
                        }
                }

                const ast::Decl * postvisit( const ast::TraitDecl * traitDecl ) {
                        // set the "sized" status for the special "sized" trait
                        if ( traitDecl->name == "sized" ) {
                                assertf( traitDecl->params.size() == 1, "Built-in trait 'sized' has incorrect "
                                        "number of parameters: %zd", traitDecl->params.size() );

                                traitDecl = ast::mutate_field_index(
                                        traitDecl, &ast::TraitDecl::params, 0,
                                        ast::mutate_field(
                                                traitDecl->params.front().get(), &ast::TypeDecl::sized, true ) );
                        }

                        // move assertions from type parameters into the body of the trait
                        std::vector< ast::ptr< ast::DeclWithType > > added;
                        for ( const ast::TypeDecl * td : traitDecl->params ) {
                                for ( const ast::DeclWithType * assn : td->assertions ) {
                                        auto inst = dynamic_cast< const ast::TraitInstType * >( assn->get_type() );
                                        if ( inst ) {
                                                expandAssertions( inst, added );
                                        } else {
                                                added.emplace_back( assn );
                                        }
                                }
                        }
                        if ( ! added.empty() ) {
                                auto mut = mutate( traitDecl );
                                for ( const ast::DeclWithType * decl : added ) {
                                        mut->members.emplace_back( decl );
                                }
                                traitDecl = mut;
                        }

                        return traitDecl;
                }
        };

        /// Replaces array and function types in forall lists by appropriate pointer type and assigns
        /// each object and function declaration a unique ID
        class ForallPointerDecay_new {
                const CodeLocation & location;
        public:
                ForallPointerDecay_new( const CodeLocation & loc ) : location( loc ) {}

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

                        // ensure object has unique ID
                        if ( obj->uniqueId ) return obj;
                        auto mut = mutate( obj );
                        mut->fixUniqueId();
                        return mut;
                }

                const ast::FunctionDecl * previsit( const ast::FunctionDecl * func ) {
                        // ensure function has unique ID
                        if ( func->uniqueId ) return func;
                        auto mut = mutate( func );
                        mut->fixUniqueId();
                        return mut;
                }

                /// Fix up assertions -- flattens assertion lists, removing all trait instances
                template< typename node_t, typename parent_t >
                static const node_t * forallFixer(
                        const CodeLocation & loc, const node_t * node,
                        ast::FunctionType::ForallList parent_t::* forallField
                ) {
                        for ( unsigned i = 0; i < (node->* forallField).size(); ++i ) {
                                const ast::TypeDecl * type = (node->* forallField)[i];
                                if ( type->assertions.empty() ) continue;

                                std::vector< ast::ptr< ast::DeclWithType > > asserts;
                                asserts.reserve( type->assertions.size() );

                                // expand trait instances into their members
                                for ( const ast::DeclWithType * assn : type->assertions ) {
                                        auto traitInst =
                                                dynamic_cast< const ast::TraitInstType * >( assn->get_type() );
                                        if ( traitInst ) {
                                                // expand trait instance to all its members
                                                expandAssertions( traitInst, asserts );
                                        } else {
                                                // pass other assertions through
                                                asserts.emplace_back( assn );
                                        }
                                }

                                // apply FixFunction to every assertion to check for invalid void type
                                for ( ast::ptr< ast::DeclWithType > & assn : asserts ) {
                                        bool isVoid = false;
                                        assn = fixFunction( assn, isVoid );
                                        if ( isVoid ) {
                                                SemanticError( loc, node, "invalid type void in assertion of function " );
                                        }
                                }

                                // place mutated assertion list in node
                                auto mut = mutate( type );
                                mut->assertions = move( asserts );
                                node = ast::mutate_field_index( node, forallField, i, mut );
                        }
                        return node;
                }

                const ast::FunctionType * previsit( const ast::FunctionType * ftype ) {
                        return forallFixer( location, ftype, &ast::FunctionType::forall );
                }

                const ast::StructDecl * previsit( const ast::StructDecl * aggrDecl ) {
                        return forallFixer( aggrDecl->location, aggrDecl, &ast::StructDecl::params );
                }

                const ast::UnionDecl * previsit( const ast::UnionDecl * aggrDecl ) {
                        return forallFixer( aggrDecl->location, aggrDecl, &ast::UnionDecl::params );
                }
        };
        */
} // anonymous namespace

/*
const ast::Type * validateType(
                const CodeLocation & loc, const ast::Type * type, const ast::SymbolTable & symtab ) {
        // ast::Pass< EnumAndPointerDecay_new > epc;
        ast::Pass< LinkReferenceToTypes_new > lrt{ loc, symtab };
        ast::Pass< ForallPointerDecay_new > fpd{ loc };

        return type->accept( lrt )->accept( fpd );
}
*/

} // namespace SymTab

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