source: src/Virtual/ExpandCasts.cc@ 4cf617e

//
// 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 : Tue Jul 22 10:04:00 2020
// Update Count     : 3
//

#include "ExpandCasts.h"

#include <cassert>                 // for assert, assertf
#include <iterator>                // for back_inserter, inserter
#include <map>                     // for map, _Rb_tree_iterator, map<>::ite...
#include <string>                  // for string, allocator, operator==, ope...
#include <utility>                 // for pair

#include "Common/PassVisitor.h"    // for PassVisitor
#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 {

        // Indented until the new ast code gets added.

        /// Maps virtual table types the instance for that type.
        class VirtualTableMap final {
                std::unordered_map<std::string, ObjectDecl *> vtable_instances;
        public:
                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;
                }
        };

        /* Currently virtual depends on the rather brittle name matching between
         * a (strict/explicate) virtual type, its vtable type and the vtable
         * instance.
         * A stronger implementation, would probably keep track of those triads
         * and use that information to create better error messages.
         */

        namespace {

        std::string get_vtable_name( std::string const & name ) {
                return name + "_vtable";
        }

        std::string get_vtable_inst_name( std::string const & name ) {
                return std::string("_") + get_vtable_name( name ) + "_instance";
        }

        std::string get_vtable_name_root( std::string const & name ) {
                return name.substr(0, name.size() - 7 );
        }

        std::string get_vtable_inst_name_root( std::string const & name ) {
                return get_vtable_name_root( name.substr(1, name.size() - 10 ) );
        }

        bool is_vtable_inst_name( std::string const & name ) {
                return 17 < name.size() &&
                        name == get_vtable_inst_name( get_vtable_inst_name_root( name ) );
        }

        } // namespace

        class VirtualCastCore {
                VirtualTableMap vtable_instances;
                FunctionDecl *vcast_decl;
                StructDecl *pvt_decl;

                Type * pointer_to_pvt(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 type;
                }

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

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

                Expression * postmutate( VirtualCastExpr * castExpr );
        };

        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_vtable_inst_name( objectDecl->get_name() ) ) {
                        if ( ObjectDecl * existing = vtable_instances.insert( objectDecl ) ) {
                                std::string msg = "Repeated instance of virtual table, original found at: ";
                                msg += existing->location.filename;
                                msg += ":" + toString( existing->location.first_line );
                                SemanticError( objectDecl->location, msg );
                        }
                }
        }

        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 virtual table type used in a virtual cast.
        Type * getVirtualTableType( const VirtualCastExpr * castExpr ) {
                const Type * objectType;
                if ( auto target = dynamic_cast<const PointerType *>( castExpr->result ) ) {
                        objectType = target->base;
                } else if ( auto target = dynamic_cast<const ReferenceType *>( castExpr->result ) ) {
                        objectType = target->base;
                } else {
                        castError( castExpr, "Virtual cast type must be a pointer or reference type." );
                }
                assert( objectType );

                const StructInstType * structType = dynamic_cast<const StructInstType *>( objectType );
                if ( nullptr == structType ) {
                        castError( castExpr, "Virtual cast type must refer to a structure type." );
                }
                const StructDecl * structDecl = structType->baseStruct;
                assert( structDecl );

                const ObjectDecl * fieldDecl = nullptr;
                if ( 0 < structDecl->members.size() ) {
                        const Declaration * memberDecl = structDecl->members.front();
                        assert( memberDecl );
                        fieldDecl = dynamic_cast<const ObjectDecl *>( memberDecl );
                        if ( fieldDecl && fieldDecl->name != "virtual_table" ) {
                                fieldDecl = nullptr;
                        }
                }
                if ( nullptr == fieldDecl ) {
                        castError( castExpr, "Virtual cast type must have a leading virtual_table field." );
                }
                const PointerType * fieldType = dynamic_cast<const PointerType *>( fieldDecl->type );
                if ( nullptr == fieldType ) {
                        castError( castExpr, "Virtual cast type virtual_table field is not a pointer." );
                }
                assert( fieldType->base );
                auto virtualStructType = dynamic_cast<const StructInstType *>( fieldType->base );
                assert( virtualStructType );

                // Here is the type, but if it is polymorphic it will have lost information.
                // (Always a clone so that it may always be deleted.)
                StructInstType * virtualType = virtualStructType->clone();
                if ( ! structType->parameters.empty() ) {
                        deleteAll( virtualType->parameters );
                        virtualType->parameters.clear();
                        cloneAll( structType->parameters, virtualType->parameters );
                }
                return virtualType;
        }

        } // namespace

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

                assert( vcast_decl );
                assert( pvt_decl );

                const Type * vtable_type = getVirtualTableType( castExpr );
                ObjectDecl * table = vtable_instances.lookup( vtable_type );
                if ( nullptr == table ) {
                        SemanticError( castLocation( castExpr ),
                                "Could not find virtual table instance." );
                }

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

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

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