source: src/ResolvExpr/TypeEnvironment.h @ 1a59641

//
// 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.h --
//
// Author           : Aaron B. Moss
// Created On       : Sun May 17 12:24:58 2015
// Last Modified By : Aaron B. Moss
// Last Modified On : Fri Jun 29 16:00:00 2018
// Update Count     : 5
//

#pragma once

#include <iostream>                        // for ostream
#include <iterator>
#include <list>                            // for list, list<>::iterator, list<>...
#include <map>                             // for map, map<>::value_compare
#include <set>                             // for set
#include <string>                          // for string
#include <utility>                         // for pair
#include <vector>                          // for vector

#include "WidenMode.h"                 // for WidenMode

#include "Common/InternedString.h"         // for interned_string
#include "Common/PersistentDisjointSet.h"  // for PersistentDisjointSet
#include "Common/PersistentMap.h"          // for PersistentMap
#include "SynTree/Declaration.h"           // for TypeDecl::Data, DeclarationWit...
#include "SynTree/SynTree.h"               // for UniqueId
#include "SynTree/Type.h"                  // for Type, TypeInstType, Type::ForallList
#include "SynTree/TypeSubstitution.h"      // for TypeSubstitution

template< typename Pass > class PassVisitor;
class GcTracer;
namespace SymTab { class Indexer; }

namespace ResolvExpr {
        // adding this comparison operator significantly improves assertion resolution run time for
        // some cases. The current resolution algorithm's speed partially depends on the order of
        // assertions. Assertions which have fewer possible matches should appear before
        // assertions which have more possible matches. This seems to imply that this could
        // be further improved by providing an indexer as an additional argument and ordering based
        // on the number of matches of the same kind (object, function) for the names of the
        // declarations.
        //
        // I've seen a TU go from 54 minutes to 1 minute 34 seconds with the addition of this 
        // comparator.
        //
        // Note: since this compares pointers for position, minor changes in the source file that affect
        // memory layout can alter compilation time in unpredictable ways. For example, the placement
        // of a line directive can reorder type pointers with respect to each other so that assertions
        // are seen in different orders, causing a potentially different number of unification calls 
        // when resolving assertions. I've seen a TU go from 36 seconds to 27 seconds by reordering 
        // line directives alone, so it would be nice to fix this comparison so that assertions compare 
        // more consistently. I've tried to modify this to compare on mangle name instead of type as 
        // the second comparator, but this causes some assertions to never be recorded. More 
        // investigation is needed.
        struct AssertCompare {
                bool operator()( DeclarationWithType * d1, DeclarationWithType * d2 ) const {
                        int cmp = d1->get_name().compare( d2->get_name() );
                        return cmp < 0 ||
                                ( cmp == 0 && d1->get_type() < d2->get_type() );
                }
        };
        struct AssertionSetValue {
                bool isUsed;
                // chain of Unique IDs of the assertion declarations. The first ID in the chain is the ID 
                // of an assertion on the current type, with each successive ID being the ID of an 
                // assertion pulled in by the previous ID. The last ID in the chain is the ID of the 
                // assertion that pulled in the current assertion.
                std::list< UniqueId > idChain;
        };
        typedef std::map< DeclarationWithType*, AssertionSetValue, AssertCompare > AssertionSet;
        typedef std::map< std::string, TypeDecl::Data > OpenVarSet;

        /// merges one set of open vars into another
        static inline void mergeOpenVars( OpenVarSet& dst, const OpenVarSet& src ) {
                for ( const auto& entry : src ) { dst[ entry.first ] = entry.second; }
        }

        void printAssertionSet( const AssertionSet &, std::ostream &, int indent = 0 );
        void printOpenVarSet( const OpenVarSet &, std::ostream &, int indent = 0 );

        /// A data structure for holding all the necessary information for a type binding
        struct BoundType {
                Type* type;
                bool allowWidening;
                TypeDecl::Data data;

                BoundType() = default;
                BoundType( TypeDecl* td ) : type{nullptr}, allowWidening{true}, data{td} {}
                BoundType( Type* ty, bool aw, const TypeDecl::Data& td )
                        : type{ty}, allowWidening{aw}, data{td} {}
                BoundType( const BoundType& o )
                        : type{maybeClone(o.type)}, allowWidening{o.allowWidening}, data{o.data} {}
                BoundType( BoundType&& o ) = default;
                BoundType& operator= (const BoundType& o) {
                        if ( this == &o ) return *this;
                        type = maybeClone( o.type );
                        allowWidening = o.allowWidening;
                        data = o.data;
                        return *this;
                }
                BoundType& operator= (BoundType&& o) = default;
        };

        class TypeEnvironment;

        /// A reference to an equivalence class that may be used to constitute one from its environment
        class ClassRef {
                friend TypeEnvironment;

                const TypeEnvironment* env;  ///< Containing environment
                interned_string root;        ///< Name of root type

        public:
                ClassRef() : env(nullptr), root(nullptr) {}
                ClassRef( const TypeEnvironment* env, interned_string root ) : env(env), root(root) {}

                /// Gets the root of the reference equivalence class;
                interned_string get_root() const { return root; }

                /// Ensures that root is still the representative element of this typeclass;
                /// undefined behaviour if called without referenced typeclass; returns new root
                inline interned_string update_root();

                /// Gets the type variables of the referenced equivalence class, empty list for none
                template<typename T = std::vector<interned_string>>
                inline T get_vars() const;

                /// Gets the bound type information of the referenced equivalence class, default if none
                inline BoundType get_bound() const;

                // Check that there is a referenced typeclass
                explicit operator bool() const { return env != nullptr; }

                bool operator== (const ClassRef& o) const { return env == o.env && root == o.root; }
                bool operator!= (const ClassRef& o) const { return !(*this == o); }
        };

        //#define EXPENSIVE_ENV_VALIDATION
        #ifdef EXPENSIVE_ENV_VALIDATION
        class ValidateGuard;
        #endif

        class TypeEnvironment {
                friend ClassRef;
                friend GcTracer;
                
                /// Backing storage for equivalence classes
                using Classes = PersistentDisjointSet<interned_string>;
                /// Type bindings included in this environment (from class root)
                using Bindings = PersistentMap<interned_string, BoundType>;

                /// Sets of equivalent type variables, stored by name
                Classes* classes;
                /// Bindings from roots of equivalence classes to type binding information. 
                /// All roots have a binding so that the list of classes can be reconstituted, though these 
                /// may be null.
                Bindings* bindings;

                #ifdef EXPENSIVE_ENV_VALIDATION
                /// for debugging
                friend ValidateGuard;
                const char* last_fn = "<none>";
                #endif

                /// Merges the classes rooted at root1 and root2, returning a pair containing the root and 
                /// child of the bound class. Does not check for validity of merge.
                std::pair<interned_string, interned_string> mergeClasses( 
                        interned_string root1, interned_string root2 );

        public:
                class iterator : public std::iterator<
                                std::forward_iterator_tag, 
                                ClassRef, 
                                std::iterator_traits<Bindings::iterator>::difference_type,
                                ClassRef,
                                ClassRef> {
                        friend TypeEnvironment;
                        
                        const TypeEnvironment* env;
                        Bindings::iterator it;

                        iterator(const TypeEnvironment* e, Bindings::iterator&& i) : env(e), it(std::move(i)) {}

                        ClassRef ref() const { return { env, it->first }; }
                public:
                        iterator() = default;

                        reference operator* () { return ref(); }
                        pointer operator-> () { return ref(); }

                        iterator& operator++ () { ++it; return *this; }
                        iterator operator++ (int) { iterator tmp = *this; ++(*this); return tmp; }

                        bool operator== (const iterator& o) const { return env == o.env && it == o.it; }
                        bool operator!= (const iterator& o) const { return !(*this == o); }
                };

                /// Finds a reference to the class containing `var`, invalid if none such.
                /// returned root variable will be valid regardless
                ClassRef lookup( interned_string var ) const;

                /// Binds a type variable to a type; returns false if fails
                bool bindVar( TypeInstType* typeInst, Type* bindTo, const TypeDecl::Data& data, 
                        AssertionSet& need, AssertionSet& have, const OpenVarSet& openVars, 
                        WidenMode widenMode, const SymTab::Indexer& indexer );
                
                /// Binds two type variables together; returns false if fails
                bool bindVarToVar( TypeInstType* var1, TypeInstType* var2, const TypeDecl::Data& data, 
                        AssertionSet& need, AssertionSet& have, const OpenVarSet& openVars, 
                        WidenMode widenMode, const SymTab::Indexer& indexer );

        public:
                TypeEnvironment() : classes{ new Classes{} }, bindings{ new Bindings{} } {}

                void add( const Type::ForallList &tyDecls );
                void add( const TypeSubstitution & sub );
                template< typename SynTreeClass > int apply( SynTreeClass *&type ) const;
                template< typename SynTreeClass > int applyFree( SynTreeClass *&type ) const;
                void makeSubstitution( TypeSubstitution &result ) const;
                bool isEmpty() const { return classes->empty(); }
                void print( std::ostream &os, Indenter indent = {} ) const;
        
                /// Combines two environments without checking invariants.
                /// Caller should ensure environments do not share type variables.
                void simpleCombine( const TypeEnvironment &second );

                /// Combines two environments, checking compatibility. Both environments must be versioned 
                /// from the same initial environment.
                /// Returns false if unsuccessful, but does NOT roll back partial changes
                bool combine( const TypeEnvironment& o, OpenVarSet& openVars, 
                        const SymTab::Indexer& indexer );
        
                void extractOpenVars( OpenVarSet &openVars ) const;
                TypeEnvironment *clone() const { return new TypeEnvironment( *this ); }

                /// Iteratively adds the environment of a new actual (with allowWidening = false),
                /// and extracts open variables.
                void addActual( const TypeEnvironment& actualEnv, OpenVarSet& openVars );

                /// Disallows widening for all bindings in the environment
                void forbidWidening();

                iterator begin() const { return { this, bindings->begin() }; }
                iterator end() const { return { this, bindings->end() }; }
        };

        interned_string ClassRef::update_root() { return root = env->classes->find( root ); }

        template<typename T>
        T ClassRef::get_vars() const {
                T vars;
                env->classes->for_class( root, [&vars]( interned_string var ) {
                        vars.insert( vars.end(), var );
                } );
                return vars;
        }

        BoundType ClassRef::get_bound() const {
                return env->bindings->get_or_default( root, BoundType{} );
        }

        template< typename SynTreeClass >
        int TypeEnvironment::apply( SynTreeClass *&type ) const {
                TypeSubstitution sub;
                makeSubstitution( sub );
                return sub.apply( type );
        }

        template< typename SynTreeClass >
        int TypeEnvironment::applyFree( SynTreeClass *&type ) const {
                TypeSubstitution sub;
                makeSubstitution( sub );
                return sub.applyFree( type );
        }

        std::ostream & operator<<( std::ostream & out, const TypeEnvironment & env );

        PassVisitor<GcTracer> & operator<<( PassVisitor<GcTracer> & gc, const TypeEnvironment & env );
} // namespace ResolvExpr

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