source: src/Virtual/ExpandCasts.cc @ 6a0b043

//
// 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 : Thu Aug 11 12:06:00 2022
// Update Count     : 5
//

#include "ExpandCasts.h"

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

#include "AST/Copy.hpp"
#include "AST/Decl.hpp"
#include "AST/Expr.hpp"
#include "AST/Pass.hpp"
#include "Common/ScopedMap.h"      // for ScopedMap
#include "Common/SemanticError.h"  // for SemanticError
#include "SymTab/Mangler.h"        // for mangleType

namespace Virtual {

namespace {

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));
}

bool is_type_id_object( const ast::ObjectDecl * decl ) {
        return is_prefix( "__cfatid_", decl->name );
}

        // Indented until the new ast code gets added.

        /// Maps virtual table types the instance for that type.

/// Better error locations for generated casts.
// TODO: Does the improved distribution of code locations make this unneeded?
CodeLocation castLocation( const ast::VirtualCastExpr * castExpr ) {
        if ( castExpr->location.isSet() ) {
                return castExpr->location;
        } else if ( castExpr->arg->location.isSet() ) {
                return castExpr->arg->location;
        } else {
                return CodeLocation();
        }
}

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

class TypeIdTable final {
        ScopedMap<std::string, ast::ObjectDecl const *> instances;
public:
        void enterScope() { instances.beginScope(); }
        void leaveScope() { instances.endScope(); }

        // Attempt to insert an instance into the map. If there is a conflict,
        // returns the previous declaration for error messages.
        ast::ObjectDecl const * insert( ast::ObjectDecl const * typeIdDecl ) {
                std::string mangledName = Mangle::mangleType( typeIdDecl->type );
                ast::ObjectDecl const *& value = instances[ mangledName ];
                if ( value ) {
                        if ( typeIdDecl->storage.is_extern ) {
                                return nullptr;
                        } else if ( !value->storage.is_extern ) {
                                return value;
                        }
                }
                value = typeIdDecl;
                return nullptr;
        }

        ast::ObjectDecl const * lookup( ast::Type const * typeIdType ) {
                std::string mangledName = Mangle::mangleType( typeIdType );
                auto const it = instances.find( mangledName );
                return ( instances.end() == it ) ? nullptr : it->second;
        }
};

struct ExpandCastsCore final {
        void previsit( ast::FunctionDecl const * decl );
        void previsit( ast::StructDecl const * decl );
        void previsit( ast::ObjectDecl const * decl );
        ast::Expr const * postvisit( ast::VirtualCastExpr const * expr );

        ast::CastExpr const * cast_to_type_id(
                ast::Expr const * expr, unsigned int level_of_indirection );

        ast::FunctionDecl const * vcast_decl = nullptr;
        ast::StructDecl const * info_decl = nullptr;

        TypeIdTable symtab;
};

void ExpandCastsCore::previsit( ast::FunctionDecl const * decl ) {
        if ( !vcast_decl && "__cfavir_virtual_cast" == decl->name ) {
                vcast_decl = decl;
        }
}

void ExpandCastsCore::previsit( ast::StructDecl const * decl ) {
        if ( !info_decl && decl->body && "__cfavir_type_info" == decl->name ) {
                info_decl = decl;
        }
}

void ExpandCastsCore::previsit( ast::ObjectDecl const * decl ) {
        if ( is_type_id_object( decl ) ) {
                // Multiple definitions should be fine because of linkonce.
                symtab.insert( decl );
        }
}

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

/// Copy newType, but give the copy the params of the oldType.
ast::StructInstType * polyCopy(
                ast::StructInstType const * oldType,
                ast::StructInstType const * newType ) {
        assert( oldType->params.size() == newType->params.size() );
        ast::StructInstType * retType = ast::deepCopy( newType );
        if ( ! oldType->params.empty() ) {
                retType->params.clear();
                for ( auto oldParams : oldType->params ) {
                        retType->params.push_back( ast::deepCopy( oldParams ) );
                }
        }
        return retType;
}

/// Follow the "head" field of the structure to get the type that is pointed
/// to by that field.
ast::StructInstType const * followHeadPointerType(
                CodeLocation const & errorLocation,
                ast::StructInstType const * oldType,
                std::string const & fieldName ) {
        ast::StructDecl const * oldDecl = oldType->base;
        assert( oldDecl );

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

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

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

        return polyCopy( oldType, newType );
}

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

ast::Expr const * ExpandCastsCore::postvisit(
                ast::VirtualCastExpr const * expr ) {
        assertf( expr->result, "Virtual cast target not found before expansion." );

        assert( vcast_decl );
        assert( info_decl );

        ast::Type const * base_type = getBaseType( expr->result );
        if ( nullptr == base_type ) {
                castError( expr, "Virtual cast target must be a pointer or reference type." );
        }
        ast::StructInstType const * type_id_type =
                        getTypeIdType( castLocation( expr ), base_type );
        if ( nullptr == type_id_type ) {
                castError( expr, "Ill formed virtual cast target type." );
        }
        ast::ObjectDecl const * type_id = symtab.lookup( type_id_type );
        if ( nullptr == type_id ) {
                // I'm trying to give a different error for polymorpic types as
                // different things can go wrong there.
                if ( type_id_type->params.empty() ) {
                        castError( expr, "Virtual cast does not target a virtual type." );
                } else {
                        castError( expr, "Virtual cast does not target a type with a "
                                "type id (possible missing virtual table)." );
                }
        }

        return new ast::CastExpr( expr->location,
                new ast::ApplicationExpr( expr->location,
                        ast::VariableExpr::functionPointer( expr->location, vcast_decl ),
                        {
                                cast_to_type_id(
                                        new ast::AddressExpr( expr->location,
                                                new ast::VariableExpr( expr->location, type_id ) ),
                                        1 ),
                                cast_to_type_id( expr->arg, 2 ),
                        }
                ),
                ast::deepCopy( expr->result )
        );
}

ast::CastExpr const * ExpandCastsCore::cast_to_type_id(
                ast::Expr const * expr, unsigned int level_of_indirection ) {
        assert( info_decl );
        ast::Type * type = new ast::StructInstType( info_decl, ast::CV::Const );
        for ( unsigned int i = 0 ; i < level_of_indirection ; ++i ) {
                type = new ast::PointerType( type );
        }
        return new ast::CastExpr( expr->location, expr, type );
}

} // namespace

void expandCasts( ast::TranslationUnit & translationUnit ) {
        ast::Pass<ExpandCastsCore>::run( translationUnit );
}

} // namespace Virtual