source: src/Virtual/ExpandCasts.cc @ 8edbe40

//
// 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.
//
// ExpandCasts.cc --
//
// Author           : Andrew Beach
// Created On       : Mon Jul 24 13:59:00 2017
// Last Modified By : Andrew Beach
// Last Modified On : Fri Jul 31 10:29:00 2020
// Update Count     : 4
//

#include "ExpandCasts.h"

#include <cassert>                 // for assert, assertf
#include <iterator>                // for back_inserter, inserter
#include <string>                  // for string, allocator, operator==, ope...

#include "Common/PassVisitor.h"    // for PassVisitor
#include "Common/ScopedMap.h"      // for ScopedMap
#include "Common/SemanticError.h"  // for SemanticError
#include "SymTab/Mangler.h"        // for mangleType
#include "SynTree/Declaration.h"   // for ObjectDecl, StructDecl, FunctionDecl
#include "SynTree/Expression.h"    // for VirtualCastExpr, CastExpr, Address...
#include "SynTree/Mutator.h"       // for mutateAll
#include "SynTree/Type.h"          // for Type, PointerType, StructInstType
#include "SynTree/Visitor.h"       // for acceptAll

namespace Virtual {

static bool is_prefix( const std::string & prefix, const std::string& entire ) {
        size_t const p_size = prefix.size();
        return (p_size < entire.size() && prefix == entire.substr(0, p_size));
}

static bool is_type_id_object( const ObjectDecl * objectDecl ) {
        const std::string & objectName = objectDecl->name;
        return is_prefix( "__cfatid_", objectName );
}

        // Indented until the new ast code gets added.

        /// Maps virtual table types the instance for that type.
        class VirtualTableMap final {
                ScopedMap<std::string, ObjectDecl *> vtable_instances;
        public:
                void enterScope() {
                        vtable_instances.beginScope();
                }
                void leaveScope() {
                        vtable_instances.endScope();
                }

                ObjectDecl * insert( ObjectDecl * vtableDecl ) {
                        std::string const & mangledName = SymTab::Mangler::mangleType( vtableDecl->type );
                        ObjectDecl *& value = vtable_instances[ mangledName ];
                        if ( value ) {
                                if ( vtableDecl->storageClasses.is_extern ) {
                                        return nullptr;
                                } else if ( ! value->storageClasses.is_extern ) {
                                        return value;
                                }
                        }
                        value = vtableDecl;
                        return nullptr;
                }

                ObjectDecl * lookup( const Type * vtableType ) {
                        std::string const & mangledName = SymTab::Mangler::mangleType( vtableType );
                        const auto it = vtable_instances.find( mangledName );
                        return ( vtable_instances.end() == it ) ? nullptr : it->second;
                }
        };

        class VirtualCastCore {
                CastExpr * cast_to_type_id( Expression * expr, int level_of_indirection ) {
                        Type * type = new StructInstType(
                                Type::Qualifiers( Type::Const ), pvt_decl );
                        for (int i = 0 ; i < level_of_indirection ; ++i) {
                                type = new PointerType( noQualifiers, type );
                        }
                        return new CastExpr( expr, type );
                }

        public:
                VirtualCastCore() :
                        indexer(), vcast_decl( nullptr ), pvt_decl( nullptr )
                {}

                void premutate( FunctionDecl * functionDecl );
                void premutate( StructDecl * structDecl );
                void premutate( ObjectDecl * objectDecl );

                Expression * postmutate( VirtualCastExpr * castExpr );

                VirtualTableMap indexer;
        private:
                FunctionDecl *vcast_decl;
                StructDecl *pvt_decl;
        };

        void VirtualCastCore::premutate( FunctionDecl * functionDecl ) {
                if ( (! vcast_decl) &&
                     functionDecl->get_name() == "__cfa__virtual_cast" ) {
                        vcast_decl = functionDecl;
                }
        }

        void VirtualCastCore::premutate( StructDecl * structDecl ) {
                if ( pvt_decl || ! structDecl->has_body() ) {
                        return;
                } else if ( structDecl->get_name() == "__cfa__parent_vtable" ) {
                        pvt_decl = structDecl;
                }
        }

        void VirtualCastCore::premutate( ObjectDecl * objectDecl ) {
                if ( is_type_id_object( objectDecl ) ) {
                        // Multiple definitions should be fine because of linkonce.
                        indexer.insert( objectDecl );
                }
        }

        namespace {

        /// Better error locations for generated casts.
        CodeLocation castLocation( const VirtualCastExpr * castExpr ) {
                if ( castExpr->location.isSet() ) {
                        return castExpr->location;
                } else if ( castExpr->arg->location.isSet() ) {
                        return castExpr->arg->location;
                } else if ( castExpr->result->location.isSet() ) {
                        return castExpr->result->location;
                } else {
                        return CodeLocation();
                }
        }

        [[noreturn]] void castError( const VirtualCastExpr * castExpr, std::string const & message ) {
                SemanticError( castLocation( castExpr ), message );
        }

        /// Get the base type from a pointer or reference.
        const Type * getBaseType( const Type * type ) {
                if ( auto target = dynamic_cast<const PointerType *>( type ) ) {
                        return target->base;
                } else if ( auto target = dynamic_cast<const ReferenceType *>( type ) ) {
                        return target->base;
                } else {
                        return nullptr;
                }
        }

        /* Attempt to follow the "head" field of the structure to get the...
         * Returns nullptr on error, otherwise owner must free returned node.
         */
        StructInstType * followHeadPointerType(
                        const StructInstType * oldType,
                        const std::string& fieldName,
                        const CodeLocation& errorLocation ) {

                // First section of the function is all about trying to fill this variable in.
                StructInstType * newType = nullptr;
                {
                        const StructDecl * oldDecl = oldType->baseStruct;
                        assert( oldDecl );

                        // Helper function for throwing semantic errors.
                        auto throwError = [&fieldName, &errorLocation, &oldDecl](const std::string& message) {
                                const std::string& context = "While following head pointer of " +
                                        oldDecl->name + " named '" + fieldName + "': ";
                                SemanticError( errorLocation, context + message );
                        };

                        if ( oldDecl->members.empty() ) {
                                throwError( "Type has no fields." );
                        }
                        const Declaration * memberDecl = oldDecl->members.front();
                        assert( memberDecl );
                        const ObjectDecl * fieldDecl = dynamic_cast<const ObjectDecl *>( memberDecl );
                        assert( fieldDecl );
                        if ( fieldName != fieldDecl->name ) {
                                throwError( "Head field did not have expected name." );
                        }

                        const Type * fieldType = fieldDecl->type;
                        if ( nullptr == fieldType ) {
                                throwError( "Could not get head field." );
                        }
                        const PointerType * ptrType = dynamic_cast<const PointerType *>( fieldType );
                        if ( nullptr == ptrType ) {
                                throwError( "First field is not a pointer type." );
                        }
                        assert( ptrType->base );
                        newType = dynamic_cast<StructInstType *>( ptrType->base );
                        if ( nullptr == newType ) {
                                throwError( "First field does not point to a structure type." );
                        }
                }

                // Now we can look into copying it.
                newType = newType->clone();
                if ( ! oldType->parameters.empty() ) {
                        deleteAll( newType->parameters );
                        newType->parameters.clear();
                        cloneAll( oldType->parameters, newType->parameters );
                }
                return newType;
        }

        /// Get the type-id type from a virtual type.
        StructInstType * getTypeIdType( const Type * type, const CodeLocation& errorLocation ) {
                const StructInstType * typeInst = dynamic_cast<const StructInstType *>( type );
                if ( nullptr == typeInst ) {
                        return nullptr;
                }
                StructInstType * tableInst =
                        followHeadPointerType( typeInst, "virtual_table", errorLocation );
                if ( nullptr == tableInst ) {
                        return nullptr;
                }
                StructInstType * typeIdInst =
                        followHeadPointerType( tableInst, "__cfavir_typeid", errorLocation );
                delete tableInst;
                return typeIdInst;
        }

        } // namespace

        Expression * VirtualCastCore::postmutate( VirtualCastExpr * castExpr ) {
                assertf( castExpr->result, "Virtual Cast target not found before expansion." );

                assert( vcast_decl );
                assert( pvt_decl );

                const Type * base_type = getBaseType( castExpr->result );
                if ( nullptr == base_type ) {
                        castError( castExpr, "Virtual cast target must be a pointer or reference type." );
                }
                const Type * type_id_type = getTypeIdType( base_type, castLocation( castExpr ) );
                if ( nullptr == type_id_type ) {
                        castError( castExpr, "Ill formed virtual cast target type." );
                }
                ObjectDecl * type_id = indexer.lookup( type_id_type );
                delete type_id_type;
                if ( nullptr == type_id ) {
                        castError( castExpr, "Virtual cast does not target a virtual type." );
                }

                Expression * result = new CastExpr(
                        new ApplicationExpr( VariableExpr::functionPointer( vcast_decl ), {
                                cast_to_type_id( new AddressExpr( new VariableExpr( type_id ) ), 1 ),
                                cast_to_type_id( castExpr->get_arg(), 2 ),
                        } ),
                        castExpr->get_result()->clone()
                );

                castExpr->set_arg( nullptr );
                castExpr->set_result( nullptr );
                delete castExpr;
                return result;
        }

        void expandCasts( std::list< Declaration * > & translationUnit ) {
                PassVisitor<VirtualCastCore> translator;
                mutateAll( translationUnit, translator );
        }
}