source: src/Virtual/ExpandCasts.cc @ 9bbbc8e

//
// 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 May 26 14:37:00 2020
// Update Count     : 2
//

#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 "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 {

        /* 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.
         */

        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_name( std::string const & name ) {
                return (name.substr( name.size() - 7 ) == "_vtable" );
        }

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

        class VirtualCastCore {
        std::map<std::string, ObjectDecl *> 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() ) ) {
                        vtable_instances[objectDecl->get_name()] = objectDecl;
                }
        }

        // Better error locations for generated casts.
        static CodeLocation castLocation( 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();
                }
        }

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

                assert( vcast_decl );
                assert( pvt_decl );

                // Get the base type of the pointer/reference.
                Type * base;
                Type * result_type = castExpr->result;
                if ( PointerType * target = dynamic_cast<PointerType *>( result_type ) ) {
                        base = target->base;
                } else if ( ReferenceType * target = dynamic_cast<ReferenceType *>( result_type ) ) {
                        base = target->base;
                } else {
                        SemanticError( castLocation( castExpr ),
                                "Virtual cast type must be a pointer or reference type." );
                }

                StructInstType * target_struct = dynamic_cast<StructInstType *>( base );
                if ( nullptr == target_struct ) {
                        SemanticError( castLocation( castExpr ),
                                "Virtual cast type must refer to a structure type." );
                }
                StructDecl * target_decl = target_struct->get_baseStruct();

                std::map<std::string, ObjectDecl *>::iterator found =
                        vtable_instances.find( get_vtable_inst_name( target_decl->get_name() ) );
                if ( vtable_instances.end() == found ) {
                        SemanticError( castLocation( castExpr ),
                                "Virtual cast type does not have a virtual table instance." );
                }
                ObjectDecl * table = found->second;

                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;
                return result;
        }

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