source: src/AST/TypeSubstitution.cpp @ 96ac72c

//
// 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.
//
// TypeSubstitution.cc --
//
// Author           : Richard C. Bilson
// Created On       : Mon May 18 07:44:20 2015
// Last Modified By : Andrew Beach
// Last Modified On : Mon Jun  3 13:26:00 2017
// Update Count     : 5
//

#include "Type.hpp"   // for TypeInstType, Type, StructInstType, UnionInstType
#include "TypeSubstitution.hpp"

namespace ast {

TypeSubstitution::TypeSubstitution() {
}

TypeSubstitution::TypeSubstitution( const TypeSubstitution &other ) : Node() {
        initialize( other, *this );
}

TypeSubstitution::~TypeSubstitution() {}

TypeSubstitution &TypeSubstitution::operator=( const TypeSubstitution &other ) {
        if ( this == &other ) return *this;
        initialize( other, *this );
        return *this;
}

void TypeSubstitution::initialize( const TypeSubstitution &src, TypeSubstitution &dest ) {
        dest.typeEnv.clear();
        dest.varEnv.clear();
        dest.add( src );
}

void TypeSubstitution::add( const TypeSubstitution &other ) {
        for ( TypeEnvType::const_iterator i = other.typeEnv.begin(); i != other.typeEnv.end(); ++i ) {
                typeEnv[ i->first ] = i->second;
        } // for
        for ( VarEnvType::const_iterator i = other.varEnv.begin(); i != other.varEnv.end(); ++i ) {
                varEnv[ i->first ] = i->second;
        } // for
}

void TypeSubstitution::add( std::string formalType, const Type *actualType ) {
        typeEnv[ formalType ] = actualType;
}

void TypeSubstitution::addVar( std::string formalExpr, const Expr *actualExpr ) {
        varEnv[ formalExpr ] = actualExpr;
}

void TypeSubstitution::remove( std::string formalType ) {
        TypeEnvType::iterator i = typeEnv.find( formalType );
        if ( i != typeEnv.end() ) {
                typeEnv.erase( formalType );
        } // if
}

const Type *TypeSubstitution::lookup( std::string formalType ) const {
        TypeEnvType::const_iterator i = typeEnv.find( formalType );

        // break on not in substitution set
        if ( i == typeEnv.end() ) return 0;

        // attempt to transitively follow TypeInstType links.
        while ( const TypeInstType *actualType = i->second.as<TypeInstType>()) {
                const std::string& typeName = actualType->name;

                // break cycles in the transitive follow
                if ( formalType == typeName ) break;

                // Look for the type this maps to, returning previous mapping if none-such
                i = typeEnv.find( typeName );
                if ( i == typeEnv.end() ) return actualType;
        }

        // return type from substitution set
        return i->second;
}

bool TypeSubstitution::empty() const {
        return typeEnv.empty() && varEnv.empty();
}

namespace {
        struct EnvTrimmer {
                const TypeSubstitution * env;
                TypeSubstitution * newEnv;
                EnvTrimmer( const TypeSubstitution * env, TypeSubstitution * newEnv ) : env( env ), newEnv( newEnv ){}
                void previsit( TypeDecl * tyDecl ) {
                        // transfer known bindings for seen type variables
                        if ( const Type * t = env->lookup( tyDecl->name ) ) {
                                newEnv->add( tyDecl->name, t );
                        }
                }
        };
} // namespace

/// reduce environment to just the parts that are referenced in a given expression
TypeSubstitution * TypeSubstitution::newFromExpr( const Expr * expr, const TypeSubstitution * env ) {
        if ( env ) {
                TypeSubstitution * newEnv = new TypeSubstitution();
                Pass<EnvTrimmer> trimmer( env, newEnv );
                expr->accept( trimmer );
                return newEnv;
        }
        return nullptr;
}

void TypeSubstitution::normalize() {
        Pass<Substituter> sub( *this, true );
        do {
                sub.pass.subCount = 0;
                sub.pass.freeOnly = true;
                for ( TypeEnvType::iterator i = typeEnv.begin(); i != typeEnv.end(); ++i ) {
                        i->second = i->second->accept( sub );
                }
        } while ( sub.pass.subCount );
}

const Type * TypeSubstitution::Substituter::postvisit( const TypeInstType *inst ) {
        BoundVarsType::const_iterator bound = boundVars.find( inst->name );
        if ( bound != boundVars.end() ) return inst;

        TypeEnvType::const_iterator i = sub.typeEnv.find( inst->name );
        if ( i == sub.typeEnv.end() ) {
                return inst;
        } else {
                // cut off infinite loop for the case where a type is bound to itself.
                // Note: this does not prevent cycles in the general case, so it may be necessary to do something more sophisticated here.
                // TODO: investigate preventing type variables from being bound to themselves in the first place.
                if ( const TypeInstType * replacement = i->second.as<TypeInstType>() ) {
                        if ( inst->name == replacement->name ) {
                                return inst;
                        }
                }
                // std::cerr << "found " << inst->name << ", replacing with " << i->second << std::endl;
                subCount++;
                ptr<Type> newType = i->second; // force clone if needed
                add_qualifiers( newType, inst->qualifiers );
                // Note: need to recursively apply substitution to the new type because normalize does not 
                // substitute bound vars, but bound vars must be substituted when not in freeOnly mode.
                newType = newType->accept( *visitor );
                return newType.release();
        } // if
}

const Expr * TypeSubstitution::Substituter::postvisit( const NameExpr * nameExpr ) {
        VarEnvType::const_iterator i = sub.varEnv.find( nameExpr->name );
        if ( i == sub.varEnv.end() ) {
                return nameExpr;
        } else {
                subCount++;
                delete nameExpr;
                return i->second;
        } // if
}

void TypeSubstitution::Substituter::previsit( const ParameterizedType * ptype ) {
        GuardValue( boundVars );
        // bind type variables from forall-qualifiers
        if ( freeOnly ) {
                for ( const TypeDecl * tyvar : ptype->forall ) {
                                boundVars.insert( tyvar->name );
                } // for
        } // if
}

void TypeSubstitution::Substituter::handleAggregateType( const ReferenceToType * type ) {
        GuardValue( boundVars );
        // bind type variables from forall-qualifiers
        if ( freeOnly ) {
                for ( const TypeDecl * tyvar : type->forall ) {
                        boundVars.insert( tyvar->name );
                } // for
                // bind type variables from generic type instantiations
                if ( auto decl = type->aggr() ) {
                        if ( ! type->params.empty() ) {
                                for ( const TypeDecl * tyvar : decl->params ) {
                                        boundVars.insert( tyvar->name );
                                } // for
                        } // if
                }
        } // if
}

void TypeSubstitution::Substituter::previsit( const StructInstType * aggregateUseType ) {
        handleAggregateType( aggregateUseType );
}

void TypeSubstitution::Substituter::previsit( const UnionInstType *aggregateUseType ) {
        handleAggregateType( aggregateUseType );
}

} // namespace ast

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