source: src/AST/TypeSubstitution.cpp@ 185cd94

//
// 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.cpp --
//
// Author           : Richard C. Bilson
// Created On       : Mon May 18 07:44:20 2015
// Last Modified By : Andrew Beach
// Last Modified On : Thr May 25 11:24:00 2023
// Update Count     : 6
//

#include "TypeSubstitution.hpp"

#include "Type.hpp"   // for TypeInstType, Type, StructInstType, UnionInstType
#include "Pass.hpp"   // for Pass, PureVisitor, WithGuards, WithVisitorRef

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.typeMap.clear();
        dest.add( src );
}

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

void TypeSubstitution::add( const TypeInstType * formalType, const Type *actualType ) {
        typeMap[ *formalType ] = actualType;
}

void TypeSubstitution::add( const TypeEnvKey & key, const Type * actualType) {
        typeMap[ key ] = actualType;
}

void TypeSubstitution::remove( const TypeInstType * formalType ) {
        TypeMap::iterator i = typeMap.find( *formalType );
        if ( i != typeMap.end() ) {
                typeMap.erase( *formalType );
        } // if
}

const Type *TypeSubstitution::lookup(
                const TypeEnvKey & formalType ) const {
        TypeMap::const_iterator i = typeMap.find( formalType );

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

        // attempt to transitively follow TypeInstType links.
        while ( const TypeInstType *actualType = i->second.as<TypeInstType>()) {
                // break cycles in the transitive follow
                if ( formalType == *actualType ) break;

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

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

const Type *TypeSubstitution::lookup( const TypeInstType * formalType ) const {
        return lookup( ast::TypeEnvKey( *formalType ) );
}

bool TypeSubstitution::empty() const {
        return typeMap.empty();
}

namespace {
        struct EnvTrimmer {
                const TypeSubstitution * env;
                TypeSubstitution * newEnv;
                EnvTrimmer( const TypeSubstitution * env, TypeSubstitution * newEnv ) : env( env ), newEnv( newEnv ){}
                void previsit( const FunctionType * ftype ) {
                        // transfer known bindings for seen type variables
                        for (auto & formal : ftype->forall) {
                                if ( const Type * t = env->lookup( formal ) ) {
                                        newEnv->add( formal, 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;
}

// definitition must happen after PassVisitor is included so that WithGuards can be used
struct TypeSubstitution::Substituter : public WithGuards, public WithVisitorRef<Substituter>, public PureVisitor {
        //static size_t traceId;

        Substituter( const TypeSubstitution & sub, bool freeOnly ) : sub( sub ), freeOnly( freeOnly ) {}

        const Type * postvisit( const TypeInstType * aggregateUseType );

        /// Records type variable bindings from forall-statements
        void previsit( const FunctionType * type );
        /// Records type variable bindings from forall-statements and instantiations of generic types
        // void handleAggregateType( const BaseInstType * type );

        // void previsit( const StructInstType * aggregateUseType );
        // void previsit( const UnionInstType * aggregateUseType );

        const TypeSubstitution & sub;
        int subCount = 0;
        bool freeOnly;
        typedef std::unordered_set< TypeEnvKey > BoundVarsType;
        BoundVarsType boundVars;
};

// size_t TypeSubstitution::Substituter::traceId = Stats::Heap::new_stacktrace_id("TypeSubstitution");

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

TypeSubstitution::ApplyResult<Node> TypeSubstitution::applyBase(
                const Node * input, bool isFree ) const {
        assert( input );
        Pass<Substituter> sub( *this, isFree );
        const Node * output = input->accept( sub );
        return { output, sub.core.subCount };
}

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

        TypeMap::const_iterator i = sub.typeMap.find( *inst );
        if ( i == sub.typeMap.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 == *replacement ) {
                                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
}

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

/*
void TypeSubstitution::Substituter::handleAggregateType( const BaseInstType * type ) {
        GuardValue( boundVars );
        // bind type variables from forall-qualifiers
        if ( freeOnly ) {
                // 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 );
                                } // 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" //
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