source: src/AST/TypeEnvironment.cpp@ 331eacbe

//
// 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.
//
// TypeEnvironment.cpp --
//
// Author           : Aaron B. Moss
// Created On       : Wed May 29 11:00:00 2019
// Last Modified By : Peter A. Buhr
// Last Modified On : Wed Dec 11 21:49:13 2019
// Update Count     : 4
//

#include "TypeEnvironment.hpp"

#include <algorithm>  // for copy
#include <cassert>
#include <iterator>   // for ostream_iterator
#include <iostream>
#include <string>
#include <utility>    // for move
#include <vector>

#include "Decl.hpp"
#include "Node.hpp"
#include "Pass.hpp"
#include "Print.hpp"
#include "Type.hpp"
#include "Common/Indenter.h"
#include "ResolvExpr/typeops.h"    // for occurs
#include "ResolvExpr/WidenMode.h"
#include "ResolvExpr/Unify.h"      // for unifyInexact
#include "Tuples/Tuples.h"         // for isTtype

using ResolvExpr::WidenMode;

namespace ast {

void print( std::ostream & out, const AssertionSet & assns, Indenter indent ) {
        for ( const auto & i : assns ) {
                print( out, i.first, indent );
                out << ( i.second.isUsed ? " (used)" : " (not used)" );
        }
}

void print( std::ostream & out, const OpenVarSet & open, Indenter indent ) {
        out << indent;
        bool first = true;
        for ( const auto & i : open ) {
                if ( first ) { first = false; } else { out << ' '; }
                out << i.first << "(" << i.second << ")";
        }
}

void print( std::ostream & out, const EqvClass & clz, Indenter indent ) {
        out << "( ";
        std::copy( clz.vars.begin(), clz.vars.end(), std::ostream_iterator< std::string >( out, " " ) );
        out << ")";
        
        if ( clz.bound ) {
                out << " -> ";
                print( out, clz.bound, indent+1 );
        }

        if ( ! clz.allowWidening ) {
                out << " (no widening)";
        }

        out << std::endl;
}

const EqvClass * TypeEnvironment::lookup( const std::string & var ) const {
        for ( ClassList::const_iterator i = env.begin(); i != env.end(); ++i ) {
                if ( i->vars.find( var ) != i->vars.end() ) return &*i;
        }
        return nullptr;
}

namespace {
        /// Removes any class from env that intersects eqvClass
        void filterOverlappingClasses( std::list<EqvClass> & env, const EqvClass & eqvClass ) {
                auto i = env.begin();
                while ( i != env.end() ) {
                        auto next = i; ++next;  // save next node in case of erasure

                        for ( const auto & v : eqvClass.vars ) {
                                if ( i->vars.count( v ) ) {
                                        env.erase( i );  // remove overlapping class
                                        break;           // done with this class
                                }
                        }
                        
                        i = next;  // go to next node even if this removed
                }
        }
}

void TypeEnvironment::add( const ParameterizedType::ForallList & tyDecls ) {
        for ( const TypeDecl * tyDecl : tyDecls ) {
                env.emplace_back( tyDecl );
        }
}

void TypeEnvironment::add( const TypeSubstitution & sub ) {
        for ( const auto p : sub ) {
                add( EqvClass{ p.first, p.second } );
        }
}

void TypeEnvironment::writeToSubstitution( TypeSubstitution & sub ) const {
        for ( const auto & clz : env ) {
                std::string clzRep;
                for ( const auto & var : clz.vars ) {
                        if ( clz.bound ) {
                                sub.add( var, clz.bound );
                        } else if ( clzRep.empty() ) {
                                clzRep = var;
                        } else {
                                sub.add( var, new TypeInstType{ clzRep, clz.data.kind } );
                        }
                }
        }
        sub.normalize();
}

void TypeEnvironment::simpleCombine( const TypeEnvironment & o ) {
        env.insert( env.end(), o.env.begin(), o.env.end() );
}

namespace {
        /// Implements occurs check by traversing type
        struct Occurs : public ast::WithVisitorRef<Occurs> {
                bool result;
                std::set< std::string > vars;
                const TypeEnvironment & tenv;

                Occurs( const std::string & var, const TypeEnvironment & env )
                : result( false ), vars(), tenv( env ) {
                        if ( const EqvClass * clz = tenv.lookup( var ) ) {
                                vars = clz->vars;
                        } else {
                                vars.emplace( var );
                        }
                }

                void previsit( const TypeInstType * typeInst ) {
                        if ( vars.count( typeInst->name ) ) {
                                result = true;
                        } else if ( const EqvClass * clz = tenv.lookup( typeInst->name ) ) {
                                if ( clz->bound ) {
                                        clz->bound->accept( *visitor );
                                }
                        }
                }
        };

        /// true if `var` occurs in `ty` under `env`
        bool occurs( const Type * ty, const std::string & var, const TypeEnvironment & env ) {
                Pass<Occurs> occur{ var, env };
                maybe_accept( ty, occur );
                return occur.pass.result;
        }
}

bool TypeEnvironment::combine( 
                const TypeEnvironment & o, OpenVarSet & open, const SymbolTable & symtab ) {
        // short-circuit easy cases
        if ( o.empty() ) return true;
        if ( empty() ) {
                simpleCombine( o );
                return true;
        }

        // merge classes
        for ( const EqvClass & c : o.env ) {
                // index of typeclass in local environment bound to c
                auto rt = env.end();

                // look for first existing bound variable
                auto vt = c.vars.begin();
                for ( ; vt != c.vars.end(); ++vt ) {
                        rt = internal_lookup( *vt );
                        if ( rt != env.end() ) break;
                }

                if ( rt != env.end() ) {  // c needs to be merged into *rt
                        EqvClass & r = *rt;
                        // merge bindings
                        if ( ! mergeBound( r, c, open, symtab ) ) return false;
                        // merge previous unbound variables into this class, checking occurs if needed
                        if ( r.bound ) for ( const auto & u : c.vars ) {
                                if ( occurs( r.bound, u, *this ) ) return false;
                                r.vars.emplace( u );
                        } else { r.vars.insert( c.vars.begin(), vt ); }
                        // merge subsequent variables into this class (skipping *vt, already there)
                        while ( ++vt != c.vars.end() ) {
                                auto st = internal_lookup( *vt );
                                if ( st == env.end() ) {
                                        // unbound, safe to add if occurs 
                                        if ( r.bound && occurs( r.bound, *vt, *this ) ) return false;
                                        r.vars.emplace( *vt );
                                } else if ( st != rt ) {
                                        // bound, but not to the same class
                                        if ( ! mergeClasses( rt, st, open, symtab ) ) return false;
                                }       // ignore bound into the same class
                        }
                } else {  // no variables in c bound; just copy up
                        env.emplace_back( c );
                }
        }

        // merged all classes
        return true;
}

void TypeEnvironment::extractOpenVars( OpenVarSet & open ) const {
        for ( const auto & clz : env ) {
                for ( const auto & var : clz.vars ) {
                        open[ var ] = clz.data;
                }
        }
}

void TypeEnvironment::addActual( const TypeEnvironment & actualEnv, OpenVarSet & open ) {
        for ( const auto & clz : actualEnv ) {
                EqvClass c = clz;
                c.allowWidening = false;
                for ( const auto & var : c.vars ) {
                        open[ var ] = c.data;
                }
                env.emplace_back( std::move(c) );
        }
}

/// true if a type is a function type
bool isFtype( const Type * type ) {
        if ( dynamic_cast< const FunctionType * >( type ) ) {
                return true;
        } else if ( auto typeInst = dynamic_cast< const TypeInstType * >( type ) ) {
                return typeInst->kind == TypeDecl::Ftype;
        } else return false;
}

namespace {
        /// true if the given type can be bound to the given type variable
        bool tyVarCompatible( const TypeDecl::Data & data, const Type * type ) {
                switch ( data.kind ) {
                  case TypeDecl::Dtype:
                        // to bind to an object type variable, the type must not be a function type.
                        // if the type variable is specified to be a complete type then the incoming
                        // type must also be complete
                        // xxx - should this also check that type is not a tuple type and that it's not a ttype?
                        return ! isFtype( type ) && ( ! data.isComplete || type->isComplete() );
                  case TypeDecl::Ftype:
                        return isFtype( type );
                  case TypeDecl::Ttype:
                        // ttype unifies with any tuple type
                        return dynamic_cast< const TupleType * >( type ) || Tuples::isTtype( type );
                  default:
                        assertf(false, "Unhandled tyvar kind: %d", data.kind);
                        return false;
                }
        }
}

bool TypeEnvironment::bindVar( 
                const TypeInstType * typeInst, const Type * bindTo, const TypeDecl::Data & data, 
                AssertionSet & need, AssertionSet & have, const OpenVarSet & open, WidenMode widen, 
                const SymbolTable & symtab 
) {
        // remove references from bound type, so that type variables can only bind to value types
        ptr<Type> target = bindTo->stripReferences();
        auto tyvar = open.find( typeInst->name );
        assert( tyvar != open.end() );
        if ( ! tyVarCompatible( tyvar->second, target ) ) return false;
        if ( occurs( target, typeInst->name, *this ) ) return false;

        auto it = internal_lookup( typeInst->name );
        if ( it != env.end() ) {
                if ( it->bound ) {
                        // attempt to unify equivalence class type with type to bind to.
                        // equivalence class type has stripped qualifiers which must be restored
                        ptr<Type> common;
                        ptr<Type> newType = it->bound;
                        reset_qualifiers( newType, typeInst->qualifiers );
                        if ( unifyInexact( 
                                        newType, target, *this, need, have, open, 
                                        widen & WidenMode{ it->allowWidening, true }, symtab, common ) ) {
                                if ( common ) {
                                        it->bound = std::move(common);
                                        reset_qualifiers( it->bound );
                                }
                        } else return false;
                } else {
                        it->bound = std::move(target);
                        reset_qualifiers( it->bound );
                        it->allowWidening = widen.first && widen.second;
                }
        } else {
                env.emplace_back( 
                        typeInst->name, target, widen.first && widen.second, data );
        }
        return true;
}

bool TypeEnvironment::bindVarToVar( 
                const TypeInstType * var1, const TypeInstType * var2, TypeDecl::Data && data, 
                AssertionSet & need, AssertionSet & have, const OpenVarSet & open, 
                WidenMode widen, const SymbolTable & symtab 
) {
        auto c1 = internal_lookup( var1->name );
        auto c2 = internal_lookup( var2->name );
        
        // exit early if variables already bound together
        if ( c1 != env.end() && c1 == c2 ) {
                c1->allowWidening &= widen;
                return true;
        }

        bool widen1 = false, widen2 = false;
        const Type * type1 = nullptr, * type2 = nullptr;

        // check for existing bindings, perform occurs check
        if ( c1 != env.end() ) {
                if ( c1->bound ) {
                        if ( occurs( c1->bound, var2->name, *this ) ) return false;
                        type1 = c1->bound;
                }
                widen1 = widen.first && c1->allowWidening;
        }
        if ( c2 != env.end() ) {
                if ( c2->bound ) {
                        if ( occurs( c2->bound, var1->name, *this ) ) return false;
                        type2 = c2->bound;
                }
                widen2 = widen.second && c2->allowWidening;
        }

        if ( type1 && type2 ) {
                // both classes bound, merge if bound types can be unified
                ptr<Type> newType1{ type1 }, newType2{ type2 };
                WidenMode newWidenMode{ widen1, widen2 };
                ptr<Type> common;

                if ( unifyInexact(
                                newType1, newType2, *this, need, have, open, newWidenMode, symtab, common ) ) {
                        c1->vars.insert( c2->vars.begin(), c2->vars.end() );
                        c1->allowWidening = widen1 && widen2;
                        if ( common ) {
                                c1->bound = std::move(common);
                                reset_qualifiers( c1->bound );
                        }
                        c1->data.isComplete |= data.isComplete;
                        env.erase( c2 );
                } else return false;
        } else if ( c1 != env.end() && c2 != env.end() ) {
                // both classes exist, at least one unbound, merge unconditionally
                if ( type1 ) {
                        c1->vars.insert( c2->vars.begin(), c2->vars.end() );
                        c1->allowWidening = widen1;
                        c1->data.isComplete |= data.isComplete;
                        env.erase( c2 );
                } else {
                        c2->vars.insert( c1->vars.begin(), c1->vars.end() );
                        c2->allowWidening = widen2;
                        c2->data.isComplete |= data.isComplete;
                        env.erase( c1 );
                }
        } else if ( c1 != env.end() ) {
                // var2 unbound, add to env[c1]
                c1->vars.emplace( var2->name );
                c1->allowWidening = widen1;
                c1->data.isComplete |= data.isComplete;
        } else if ( c2 != env.end() ) {
                // var1 unbound, add to env[c2]
                c2->vars.emplace( var1->name );
                c2->allowWidening = widen2;
                c2->data.isComplete |= data.isComplete;
        } else {
                // neither var bound, create new class
                env.emplace_back( var1->name, var2->name, widen1 && widen2, data );
        }

        return true;
}

void TypeEnvironment::forbidWidening() {
        for ( EqvClass& c : env ) c.allowWidening = false;
}

void TypeEnvironment::add( EqvClass && eqvClass ) {
        filterOverlappingClasses( env, eqvClass );
        env.emplace_back( std::move(eqvClass) );
}

bool TypeEnvironment::mergeBound( 
                EqvClass & to, const EqvClass & from, OpenVarSet & open, const SymbolTable & symtab ) {
        if ( from.bound ) {
                if ( to.bound ) {
                        // attempt to unify bound types
                        ptr<Type> toType{ to.bound }, fromType{ from.bound };
                        WidenMode widen{ to.allowWidening, from.allowWidening };
                        ptr<Type> common;
                        AssertionSet need, have;

                        if ( unifyInexact( 
                                        toType, fromType, *this, need, have, open, widen, symtab, common ) ) {
                                // unifies, set common type if necessary
                                if ( common ) {
                                        to.bound = std::move(common);
                                        reset_qualifiers( to.bound );
                                }
                        } else return false; // cannot unify
                } else {
                        to.bound = from.bound;
                }
        }

        // unify widening if matches
        to.allowWidening &= from.allowWidening;
        return true;
}

bool TypeEnvironment::mergeClasses( 
        ClassList::iterator to, ClassList::iterator from, OpenVarSet & open, const SymbolTable & symtab
) {
        EqvClass & r = *to, & s = *from;

        // ensure bounds match
        if ( ! mergeBound( r, s, open, symtab ) ) return false;

        // check safely bindable
        if ( r.bound ) {
                for ( const auto & v : s.vars ) if ( occurs( r.bound, v, *this ) ) return false;
        }

        // merge classes
        r.vars.insert( s.vars.begin(), s.vars.end() );
        r.allowWidening &= s.allowWidening;
        env.erase( from );

        return true;
}

TypeEnvironment::ClassList::iterator TypeEnvironment::internal_lookup( const std::string & var ) {
        for ( ClassList::iterator i = env.begin(); i != env.end(); ++i ) {
                if ( i->vars.count( var ) ) return i;
        }
        return env.end();
}

void print( std::ostream & out, const TypeEnvironment & env, Indenter indent ) {
        for ( const auto & clz : env ) {
                print( out, clz, indent );
        }
}

std::ostream & operator<<( std::ostream & out, const TypeEnvironment & env ) {
        print( out, env );
        return out;
}

}

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