source: src/Tuples/TupleAssignment.cc @ 91fb850

//
// 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.
//
// TupleAssignment.cc --
//
// Author           : Rodolfo G. Esteves
// Created On       : Mon May 18 07:44:20 2015
// Last Modified By : Peter A. Buhr
// Last Modified On : Fri Dec 13 23:45:33 2019
// Update Count     : 9
//

#include <algorithm>                       // for transform
#include <cassert>                         // for assert
#include <iterator>                        // for back_insert_iterator, back...
#include <list>                            // for _List_const_iterator, _Lis...
#include <memory>                          // for unique_ptr, allocator_trai...
#include <string>                          // for string
#include <vector>

#include "AST/Decl.hpp"
#include "AST/Init.hpp"
#include "AST/Pass.hpp"
#include "AST/Stmt.hpp"
#include "AST/TypeEnvironment.hpp"
#include "CodeGen/OperatorTable.h"
#include "Common/PassVisitor.h"
#include "Common/UniqueName.h"             // for UniqueName
#include "Common/utility.h"                // for splice, zipWith
#include "Explode.h"                       // for explode
#include "InitTweak/GenInit.h"             // for genCtorInit
#include "InitTweak/InitTweak.h"           // for getPointerBase, isAssignment
#include "ResolvExpr/Alternative.h"        // for AltList, Alternative
#include "ResolvExpr/AlternativeFinder.h"  // for AlternativeFinder, simpleC...
#include "ResolvExpr/Cost.h"               // for Cost
#include "ResolvExpr/Resolver.h"           // for resolveCtorInit
#include "ResolvExpr/TypeEnvironment.h"    // for TypeEnvironment
#include "ResolvExpr/typeops.h"            // for combos
#include "SynTree/LinkageSpec.h"           // for Cforall
#include "SynTree/Declaration.h"           // for ObjectDecl
#include "SynTree/Expression.h"            // for Expression, CastExpr, Name...
#include "SynTree/Initializer.h"           // for ConstructorInit, SingleInit
#include "SynTree/Statement.h"             // for ExprStmt
#include "SynTree/Type.h"                  // for Type, Type::Qualifiers
#include "SynTree/TypeSubstitution.h"      // for TypeSubstitution
#include "SynTree/Visitor.h"               // for Visitor

#if 0
#define PRINT(x) x
#else
#define PRINT(x)
#endif

namespace Tuples {
        class TupleAssignSpotter_old {
          public:
                // dispatcher for Tuple (multiple and mass) assignment operations
                TupleAssignSpotter_old( ResolvExpr::AlternativeFinder & );
                void spot( UntypedExpr * expr, std::vector<ResolvExpr::AlternativeFinder> &args );

          private:
                void match();

                struct Matcher {
                  public:
                        Matcher( TupleAssignSpotter_old &spotter, const ResolvExpr::AltList& lhs,
                                const ResolvExpr::AltList& rhs );
                        virtual ~Matcher() {}

                        virtual void match( std::list< Expression * > &out ) = 0;
                        ObjectDecl * newObject( UniqueName & namer, Expression * expr );

                        void combineState( const ResolvExpr::Alternative& alt ) {
                                compositeEnv.simpleCombine( alt.env );
                                ResolvExpr::mergeOpenVars( openVars, alt.openVars );
                                cloneAll( alt.need, need );
                        }

                        void combineState( const ResolvExpr::AltList& alts ) {
                                for ( const ResolvExpr::Alternative& alt : alts ) { combineState( alt ); }
                        }

                        ResolvExpr::AltList lhs, rhs;
                        TupleAssignSpotter_old &spotter;
                        ResolvExpr::Cost baseCost;
                        std::list< ObjectDecl * > tmpDecls;
                        ResolvExpr::TypeEnvironment compositeEnv;
                        ResolvExpr::OpenVarSet openVars;
                        ResolvExpr::AssertionSet need;
                };

                struct MassAssignMatcher : public Matcher {
                  public:
                        MassAssignMatcher( TupleAssignSpotter_old &spotter, const ResolvExpr::AltList& lhs,
                                const ResolvExpr::AltList& rhs ) : Matcher(spotter, lhs, rhs) {}
                        virtual void match( std::list< Expression * > &out );
                };

                struct MultipleAssignMatcher : public Matcher {
                  public:
                        MultipleAssignMatcher( TupleAssignSpotter_old &spotter, const ResolvExpr::AltList& lhs,
                                const ResolvExpr::AltList& rhs ) : Matcher(spotter, lhs, rhs) {}
                        virtual void match( std::list< Expression * > &out );
                };

                ResolvExpr::AlternativeFinder &currentFinder;
                std::string fname;
                std::unique_ptr< Matcher > matcher;
        };

        /// true if expr is an expression of tuple type
        bool isTuple( Expression *expr ) {
                if ( ! expr ) return false;
                assert( expr->result );
                return dynamic_cast< TupleType * >( expr->get_result()->stripReferences() );
        }

        template< typename AltIter >
        bool isMultAssign( AltIter begin, AltIter end ) {
                // multiple assignment if more than one alternative in the range or if
                // the alternative is a tuple
                if ( begin == end ) return false;
                if ( isTuple( begin->expr ) ) return true;
                return ++begin != end;
        }

        bool refToTuple( Expression *expr ) {
                assert( expr->get_result() );
                // also check for function returning tuple of reference types
                if ( CastExpr * castExpr = dynamic_cast< CastExpr * >( expr ) ) {
                        return refToTuple( castExpr->get_arg() );
                } else {
                        return isTuple( expr );
                }
                return false;
        }

        void handleTupleAssignment( ResolvExpr::AlternativeFinder & currentFinder, UntypedExpr * expr,
                                std::vector<ResolvExpr::AlternativeFinder> &args ) {
                TupleAssignSpotter_old spotter( currentFinder );
                spotter.spot( expr, args );
        }

        TupleAssignSpotter_old::TupleAssignSpotter_old( ResolvExpr::AlternativeFinder &f )
                : currentFinder(f) {}

        void TupleAssignSpotter_old::spot( UntypedExpr * expr,
                        std::vector<ResolvExpr::AlternativeFinder> &args ) {
                if (  NameExpr *op = dynamic_cast< NameExpr * >(expr->get_function()) ) {
                        if ( CodeGen::isCtorDtorAssign( op->get_name() ) ) {
                                fname = op->get_name();

                                // AlternativeFinder will naturally handle this case case, if it's legal
                                if ( args.size() == 0 ) return;

                                // if an assignment only takes 1 argument, that's odd, but maybe someone wrote
                                // the function, in which case AlternativeFinder will handle it normally
                                if ( args.size() == 1 && CodeGen::isAssignment( fname ) ) return;

                                // look over all possible left-hand-sides
                                for ( ResolvExpr::Alternative& lhsAlt : args[0] ) {
                                        // skip non-tuple LHS
                                        if ( ! refToTuple(lhsAlt.expr) ) continue;

                                        // explode is aware of casts - ensure every LHS expression is sent into explode
                                        // with a reference cast
                                        // xxx - this seems to change the alternatives before the normal
                                        //  AlternativeFinder flow; maybe this is desired?
                                        if ( ! dynamic_cast<CastExpr*>( lhsAlt.expr ) ) {
                                                lhsAlt.expr = new CastExpr( lhsAlt.expr,
                                                                new ReferenceType( Type::Qualifiers(),
                                                                        lhsAlt.expr->result->clone() ) );
                                        }

                                        // explode the LHS so that each field of a tuple-valued-expr is assigned
                                        ResolvExpr::AltList lhs;
                                        explode( lhsAlt, currentFinder.get_indexer(), back_inserter(lhs), true );
                                        for ( ResolvExpr::Alternative& alt : lhs ) {
                                                // each LHS value must be a reference - some come in with a cast expression,
                                                // if not just cast to reference here
                                                if ( ! dynamic_cast<ReferenceType*>( alt.expr->get_result() ) ) {
                                                        alt.expr = new CastExpr( alt.expr,
                                                                new ReferenceType( Type::Qualifiers(),
                                                                        alt.expr->get_result()->clone() ) );
                                                }
                                        }

                                        if ( args.size() == 1 ) {
                                                // mass default-initialization/destruction
                                                ResolvExpr::AltList rhs{};
                                                matcher.reset( new MassAssignMatcher( *this, lhs, rhs ) );
                                                match();
                                        } else if ( args.size() > 2 ) {
                                                // expand all possible RHS possibilities
                                                // TODO build iterative version of this instead of using combos
                                                std::vector< ResolvExpr::AltList > rhsAlts;
                                                combos( std::next(args.begin(), 1), args.end(),
                                                        std::back_inserter( rhsAlts ) );
                                                for ( const ResolvExpr::AltList& rhsAlt : rhsAlts ) {
                                                        // multiple assignment
                                                        ResolvExpr::AltList rhs;
                                                        explode( rhsAlt, currentFinder.get_indexer(),
                                                                std::back_inserter(rhs), true );
                                                        matcher.reset( new MultipleAssignMatcher( *this, lhs, rhs ) );
                                                        match();
                                                }
                                        } else {
                                                for ( const ResolvExpr::Alternative& rhsAlt : args[1] ) {
                                                        ResolvExpr::AltList rhs;
                                                        if ( isTuple(rhsAlt.expr) ) {
                                                                // multiple assignment
                                                                explode( rhsAlt, currentFinder.get_indexer(),
                                                                        std::back_inserter(rhs), true );
                                                                matcher.reset( new MultipleAssignMatcher( *this, lhs, rhs ) );
                                                        } else {
                                                                // mass assignment
                                                                rhs.push_back( rhsAlt );
                                                                matcher.reset( new MassAssignMatcher( *this, lhs, rhs ) );
                                                        }
                                                        match();
                                                }
                                        }
                                }
                        }
                }
        }

        void TupleAssignSpotter_old::match() {
                assert ( matcher != 0 );

                std::list< Expression * > new_assigns;
                matcher->match( new_assigns );

                if ( ! matcher->lhs.empty() || ! matcher->rhs.empty() ) {
                        // if both lhs and rhs are empty then this is the empty tuple case, wherein it's okay for new_assigns to be empty.
                        // if not the empty tuple case, return early so that no new alternatives are generated.
                        if ( new_assigns.empty() ) return;
                }
                ResolvExpr::AltList current;
                // now resolve new assignments
                for ( std::list< Expression * >::iterator i = new_assigns.begin();
                                i != new_assigns.end(); ++i ) {
                        PRINT(
                                std::cerr << "== resolving tuple assign ==" << std::endl;
                                std::cerr << *i << std::endl;
                        )

                        ResolvExpr::AlternativeFinder finder{ currentFinder.get_indexer(),
                                matcher->compositeEnv };

                        try {
                                finder.findWithAdjustment(*i);
                        } catch (...) {
                                return; // no match should not mean failure, it just means this particular tuple assignment isn't valid
                        }
                        // prune expressions that don't coincide with
                        ResolvExpr::AltList alts = finder.get_alternatives();
                        assert( alts.size() == 1 );
                        assert( alts.front().expr != 0 );
                        current.push_back( alts.front() );
                }

                // extract expressions from the assignment alternatives to produce a list of assignments
                // that together form a single alternative
                std::list< Expression *> solved_assigns;
                for ( ResolvExpr::Alternative & alt : current ) {
                        solved_assigns.push_back( alt.expr->clone() );
                        matcher->combineState( alt );
                }

                // xxx -- was push_front
                currentFinder.get_alternatives().push_back( ResolvExpr::Alternative{
                        new TupleAssignExpr{ solved_assigns, matcher->tmpDecls }, matcher->compositeEnv,
                        matcher->openVars,
                        ResolvExpr::AssertionList( matcher->need.begin(), matcher->need.end() ),
                        ResolvExpr::sumCost( current ) + matcher->baseCost } );
        }

        TupleAssignSpotter_old::Matcher::Matcher( TupleAssignSpotter_old &spotter,
                const ResolvExpr::AltList &lhs, const ResolvExpr::AltList &rhs )
        : lhs(lhs), rhs(rhs), spotter(spotter),
          baseCost( ResolvExpr::sumCost( lhs ) + ResolvExpr::sumCost( rhs ) ) {
                combineState( lhs );
                combineState( rhs );
        }

        UntypedExpr * createFunc( const std::string &fname, ObjectDecl *left, ObjectDecl *right ) {
                assert( left );
                std::list< Expression * > args;
                args.push_back( new VariableExpr( left ) );
                // args.push_back( new AddressExpr( new VariableExpr( left ) ) );
                if ( right ) args.push_back( new VariableExpr( right ) );
                if ( left->type->referenceDepth() > 1 && CodeGen::isConstructor( fname ) ) {
                        args.front() = new AddressExpr( args.front() );
                        if ( right ) args.back() = new AddressExpr( args.back() );
                        return new UntypedExpr( new NameExpr( "?=?" ), args );
                } else {
                        return new UntypedExpr( new NameExpr( fname ), args );
                }
        }

        // removes environments from subexpressions within statement exprs, which could throw off later passes like those in Box which rely on PolyMutator, and adds the bindings to the compositeEnv
        // xxx - maybe this should happen in alternative finder for every StmtExpr?
        struct EnvRemover {
                void previsit( ExprStmt * stmt ) {
                        assert( compositeEnv );
                        if ( stmt->expr->env ) {
                                compositeEnv->add( *stmt->expr->env );
                                delete stmt->expr->env;
                                stmt->expr->env = nullptr;
                        }
                }

                ResolvExpr::TypeEnvironment * compositeEnv = nullptr;
        };

        ObjectDecl * TupleAssignSpotter_old::Matcher::newObject( UniqueName & namer, Expression * expr ) {
                assert( expr->result && ! expr->get_result()->isVoid() );
                ObjectDecl * ret = new ObjectDecl( namer.newName(), Type::StorageClasses(), LinkageSpec::Cforall, nullptr, expr->result->clone(), new SingleInit( expr->clone() ) );
                // if expression type is a reference, don't need to construct anything, a simple initializer is sufficient.
                if ( ! dynamic_cast< ReferenceType * >( expr->result ) ) {
                        ConstructorInit * ctorInit = InitTweak::genCtorInit( ret );
                        ret->init = ctorInit;
                        ResolvExpr::resolveCtorInit( ctorInit, spotter.currentFinder.get_indexer() ); // resolve ctor/dtors for the new object
                        PassVisitor<EnvRemover> rm; // remove environments from subexpressions of StmtExprs
                        rm.pass.compositeEnv = &compositeEnv;
                        ctorInit->accept( rm );
                }
                PRINT( std::cerr << "new object: " << ret << std::endl; )
                return ret;
        }

        void TupleAssignSpotter_old::MassAssignMatcher::match( std::list< Expression * > &out ) {
                static UniqueName lhsNamer( "__massassign_L" );
                static UniqueName rhsNamer( "__massassign_R" );
                // empty tuple case falls into this matcher, hence the second part of the assert
                assert( (! lhs.empty() && rhs.size() <= 1) || (lhs.empty() && rhs.empty()) );

                // xxx - may need to split this up into multiple declarations, because potential conversion to references
                //  probably should not reference local variable - see MultipleAssignMatcher::match
                ObjectDecl * rtmp = rhs.size() == 1 ? newObject( rhsNamer, rhs.front().expr ) : nullptr;
                for ( ResolvExpr::Alternative & lhsAlt : lhs ) {
                        // create a temporary object for each value in the lhs and create a call involving the rhs
                        ObjectDecl * ltmp = newObject( lhsNamer, lhsAlt.expr );
                        out.push_back( createFunc( spotter.fname, ltmp, rtmp ) );
                        tmpDecls.push_back( ltmp );
                }
                if ( rtmp ) tmpDecls.push_back( rtmp );
        }

        void TupleAssignSpotter_old::MultipleAssignMatcher::match( std::list< Expression * > &out ) {
                static UniqueName lhsNamer( "__multassign_L" );
                static UniqueName rhsNamer( "__multassign_R" );

                if ( lhs.size() == rhs.size() ) {
                        // produce a new temporary object for each value in the lhs and rhs and pairwise create the calls
                        std::list< ObjectDecl * > ltmp;
                        std::list< ObjectDecl * > rtmp;
                        for ( auto p : group_iterate( lhs, rhs ) ) {
                                ResolvExpr::Alternative & lhsAlt = std::get<0>(p);
                                ResolvExpr::Alternative & rhsAlt = std::get<1>(p);
                                // convert RHS to LHS type minus one reference -- important for the case where LHS is && and RHS is lvalue, etc.
                                ReferenceType * lhsType = strict_dynamic_cast<ReferenceType *>( lhsAlt.expr->result );
                                rhsAlt.expr = new CastExpr( rhsAlt.expr, lhsType->base->clone() );
                                ObjectDecl * lobj = newObject( lhsNamer, lhsAlt.expr );
                                ObjectDecl * robj = newObject( rhsNamer, rhsAlt.expr );
                                out.push_back( createFunc(spotter.fname, lobj, robj) );
                                ltmp.push_back( lobj );
                                rtmp.push_back( robj );

                                // resolve the cast expression so that rhsAlt return type is bound by the cast type as needed, and transfer the resulting environment
                                ResolvExpr::AlternativeFinder finder{ spotter.currentFinder.get_indexer(), compositeEnv };
                                finder.findWithAdjustment( rhsAlt.expr );
                                assert( finder.get_alternatives().size() == 1 );
                                compositeEnv = std::move( finder.get_alternatives().front().env );
                        }
                        tmpDecls.splice( tmpDecls.end(), ltmp );
                        tmpDecls.splice( tmpDecls.end(), rtmp );
                }
        }

namespace {
        /// true if `expr` is of tuple type
        bool isTuple( const ast::Expr * expr ) {
                if ( ! expr ) return false;
                assert( expr->result );
                return dynamic_cast< const ast::TupleType * >( expr->result->stripReferences() );
        }

        /// true if `expr` is of tuple type or a reference to one
        bool refToTuple( const ast::Expr * expr ) {
                assert( expr->result );
                // check for function returning tuple of reference types
                if ( auto castExpr = dynamic_cast< const ast::CastExpr * >( expr ) ) {
                        return refToTuple( castExpr->arg );
                } else {
                        return isTuple( expr );
                }
        }

        /// Dispatcher for tuple (multiple and mass) assignment operations
        class TupleAssignSpotter_new final {
                /// Actually finds tuple assignment operations, by subclass
                struct Matcher {
                        ResolvExpr::CandidateList lhs, rhs;
                        TupleAssignSpotter_new & spotter;
                        CodeLocation location;
                        ResolvExpr::Cost baseCost;
                        std::vector< ast::ptr< ast::ObjectDecl > > tmpDecls;
                        ast::TypeEnvironment env;
                        ast::OpenVarSet open;
                        ast::AssertionSet need;

                        void combineState( const ResolvExpr::Candidate & cand ) {
                                env.simpleCombine( cand.env );
                                ast::mergeOpenVars( open, cand.open );
                                need.insert( cand.need.begin(), cand.need.end() );
                        }

                        Matcher(
                                TupleAssignSpotter_new & s, const CodeLocation & loc,
                                const ResolvExpr::CandidateList & l, const ResolvExpr::CandidateList & r )
                        : lhs( l ), rhs( r ), spotter( s ), location( loc ),
                          baseCost( ResolvExpr::sumCost( lhs ) + ResolvExpr::sumCost( rhs ) ), tmpDecls(),
                          env(), open(), need() {
                                for ( auto & cand : lhs ) combineState( *cand );
                                for ( auto & cand : rhs ) combineState( *cand );
                        }
                        virtual ~Matcher() = default;

                        virtual std::vector< ast::ptr< ast::Expr > > match() = 0;

                        /// removes environments from subexpressions within statement expressions, which could
                        /// throw off later passes like those in Box which rely on PolyMutator, and adds the
                        /// bindings to the env
                        struct EnvRemover {
                                /// environment to hoist ExprStmt environments to
                                ast::TypeEnvironment & tenv;

                                EnvRemover( ast::TypeEnvironment & e ) : tenv( e ) {}

                                const ast::ExprStmt * previsit( const ast::ExprStmt * stmt ) {
                                        if ( stmt->expr->env ) {
                                                tenv.add( *stmt->expr->env );
                                                ast::ExprStmt * mut = mutate( stmt );
                                                mut->expr.get_and_mutate()->env = nullptr;
                                                return mut;
                                        }
                                        return stmt;
                                }
                        };

                        ast::ObjectDecl * newObject( UniqueName & namer, const ast::Expr * expr ) {
                                assert( expr->result && ! expr->result->isVoid() );

                                ast::ObjectDecl * ret = new ast::ObjectDecl{
                                        location, namer.newName(), expr->result, new ast::SingleInit{ location, expr },
                                        ast::Storage::Classes{}, ast::Linkage::Cforall };

                                // if expression type is a reference, just need an initializer, otherwise construct
                                if ( ! expr->result.as< ast::ReferenceType >() ) {
                                        // resolve ctor/dtor for the new object
                                        ast::ptr< ast::Init > ctorInit = ResolvExpr::resolveCtorInit(
                                                        InitTweak::genCtorInit( location, ret ), spotter.crntFinder.localSyms );
                                        // remove environments from subexpressions of stmtExpr
                                        ast::Pass< EnvRemover > rm{ env };
                                        ret->init = ctorInit->accept( rm );
                                }

                                PRINT( std::cerr << "new object: " << ret << std::endl; )
                                return ret;
                        }

                        ast::UntypedExpr * createFunc(
                                const std::string & fname, const ast::ObjectDecl * left,
                                const ast::ObjectDecl * right
                        ) {
                                assert( left );
                                std::vector< ast::ptr< ast::Expr > > args;
                                args.emplace_back( new ast::VariableExpr{ location, left } );
                                if ( right ) { args.emplace_back( new ast::VariableExpr{ location, right } ); }

                                if ( left->type->referenceDepth() > 1 && CodeGen::isConstructor( fname ) ) {
                                        args.front() = new ast::AddressExpr{ location, args.front() };
                                        if ( right ) { args.back() = new ast::AddressExpr{ location, args.back() }; }
                                        return new ast::UntypedExpr{
                                                location, new ast::NameExpr{ location, "?=?" }, std::move(args) };
                                } else {
                                        return new ast::UntypedExpr{
                                                location, new ast::NameExpr{ location, fname }, std::move(args) };
                                }
                        }
                };

                /// Finds mass-assignment operations
                struct MassAssignMatcher final : public Matcher {
                        MassAssignMatcher(
                                TupleAssignSpotter_new & s, const CodeLocation & loc,
                                const ResolvExpr::CandidateList & l, const ResolvExpr::CandidateList & r )
                        : Matcher( s, loc, l, r ) {}

                        std::vector< ast::ptr< ast::Expr > > match() override {
                                // temporary workaround for new and old ast to coexist and avoid name collision
                                static UniqueName lhsNamer( "__massassign_Ln" );
                                static UniqueName rhsNamer( "__massassign_Rn" );
                                // empty tuple case falls into this matcher
                                assert( lhs.empty() ? rhs.empty() : rhs.size() <= 1 );

                                ast::ptr< ast::ObjectDecl > rtmp =
                                        rhs.size() == 1 ? newObject( rhsNamer, rhs.front()->expr ) : nullptr;

                                std::vector< ast::ptr< ast::Expr > > out;
                                for ( ResolvExpr::CandidateRef & lhsCand : lhs ) {
                                        // create a temporary object for each value in the LHS and create a call
                                        // involving the RHS
                                        ast::ptr< ast::ObjectDecl > ltmp = newObject( lhsNamer, lhsCand->expr );
                                        out.emplace_back( createFunc( spotter.fname, ltmp, rtmp ) );
                                        tmpDecls.emplace_back( std::move( ltmp ) );
                                }
                                if ( rtmp ) tmpDecls.emplace_back( std::move( rtmp ) );

                                return out;
                        }
                };

                /// Finds multiple-assignment operations
                struct MultipleAssignMatcher final : public Matcher {
                        MultipleAssignMatcher(
                                TupleAssignSpotter_new & s, const CodeLocation & loc,
                                const ResolvExpr::CandidateList & l, const ResolvExpr::CandidateList & r )
                        : Matcher( s, loc, l, r ) {}

                        std::vector< ast::ptr< ast::Expr > > match() override {
                                // temporary workaround for new and old ast to coexist and avoid name collision
                                static UniqueName lhsNamer( "__multassign_Ln" );
                                static UniqueName rhsNamer( "__multassign_Rn" );

                                if ( lhs.size() != rhs.size() ) return {};

                                // produce a new temporary object for each value in the LHS and RHS and pairwise
                                // create the calls
                                std::vector< ast::ptr< ast::ObjectDecl > > ltmp, rtmp;

                                std::vector< ast::ptr< ast::Expr > > out;
                                for ( unsigned i = 0; i < lhs.size(); ++i ) {
                                        ResolvExpr::CandidateRef & lhsCand = lhs[i];
                                        ResolvExpr::CandidateRef & rhsCand = rhs[i];

                                        // convert RHS to LHS type minus one reference -- important for case where LHS
                                        // is && and RHS is lvalue
                                        auto lhsType = lhsCand->expr->result.strict_as< ast::ReferenceType >();
                                        rhsCand->expr = new ast::CastExpr{ rhsCand->expr, lhsType->base };
                                        ast::ptr< ast::ObjectDecl > lobj = newObject( lhsNamer, lhsCand->expr );
                                        ast::ptr< ast::ObjectDecl > robj = newObject( rhsNamer, rhsCand->expr );
                                        out.emplace_back( createFunc( spotter.fname, lobj, robj ) );
                                        ltmp.emplace_back( std::move( lobj ) );
                                        rtmp.emplace_back( std::move( robj ) );

                                        // resolve the cast expression so that rhsCand return type is bound by the cast
                                        // type as needed, and transfer the resulting environment
                                        ResolvExpr::CandidateFinder finder{ spotter.crntFinder.localSyms, env };
                                        finder.find( rhsCand->expr, ResolvExpr::ResolvMode::withAdjustment() );
                                        assert( finder.candidates.size() == 1 );
                                        env = std::move( finder.candidates.front()->env );
                                }

                                splice( tmpDecls, ltmp );
                                splice( tmpDecls, rtmp );

                                return out;
                        }
                };

                ResolvExpr::CandidateFinder & crntFinder;
                std::string fname;
                std::unique_ptr< Matcher > matcher;

        public:
                TupleAssignSpotter_new( ResolvExpr::CandidateFinder & f )
                : crntFinder( f ), fname(), matcher() {}

                // find left- and right-hand-sides for mass or multiple assignment
                void spot(
                        const ast::UntypedExpr * expr, std::vector< ResolvExpr::CandidateFinder > & args
                ) {
                        if ( auto op = expr->func.as< ast::NameExpr >() ) {
                                // skip non-assignment functions
                                if ( ! CodeGen::isCtorDtorAssign( op->name ) ) return;
                                fname = op->name;

                                // handled by CandidateFinder if applicable (both odd cases)
                                if ( args.empty() || ( args.size() == 1 && CodeGen::isAssignment( fname ) ) ) {
                                        return;
                                }

                                // look over all possible left-hand-side
                                for ( ResolvExpr::CandidateRef & lhsCand : args[0] ) {
                                        // skip non-tuple LHS
                                        if ( ! refToTuple( lhsCand->expr ) ) continue;

                                        // explode is aware of casts - ensure every LHS is sent into explode with a
                                        // reference cast
                                        if ( ! lhsCand->expr.as< ast::CastExpr >() ) {
                                                lhsCand->expr = new ast::CastExpr{
                                                        lhsCand->expr, new ast::ReferenceType{ lhsCand->expr->result } };
                                        }

                                        // explode the LHS so that each field of a tuple-valued expr is assigned
                                        ResolvExpr::CandidateList lhs;
                                        explode( *lhsCand, crntFinder.localSyms, back_inserter(lhs), true );
                                        for ( ResolvExpr::CandidateRef & cand : lhs ) {
                                                // each LHS value must be a reference - some come in with a cast, if not
                                                // just cast to reference here
                                                if ( ! cand->expr->result.as< ast::ReferenceType >() ) {
                                                        cand->expr = new ast::CastExpr{
                                                                cand->expr, new ast::ReferenceType{ cand->expr->result } };
                                                }
                                        }

                                        if ( args.size() == 1 ) {
                                                // mass default-initialization/destruction
                                                ResolvExpr::CandidateList rhs{};
                                                matcher.reset( new MassAssignMatcher{ *this, expr->location, lhs, rhs } );
                                                match();
                                        } else if ( args.size() == 2 ) {
                                                for ( const ResolvExpr::CandidateRef & rhsCand : args[1] ) {
                                                        ResolvExpr::CandidateList rhs;
                                                        if ( isTuple( rhsCand->expr ) ) {
                                                                // multiple assignment
                                                                explode( *rhsCand, crntFinder.localSyms, back_inserter(rhs), true );
                                                                matcher.reset(
                                                                        new MultipleAssignMatcher{ *this, expr->location, lhs, rhs } );
                                                        } else {
                                                                // mass assignment
                                                                rhs.emplace_back( rhsCand );
                                                                matcher.reset(
                                                                        new MassAssignMatcher{ *this, expr->location, lhs, rhs } );
                                                        }
                                                        match();
                                                }
                                        } else {
                                                // expand all possible RHS possibilities
                                                std::vector< ResolvExpr::CandidateList > rhsCands;
                                                combos(
                                                        std::next( args.begin(), 1 ), args.end(), back_inserter( rhsCands ) );
                                                for ( const ResolvExpr::CandidateList & rhsCand : rhsCands ) {
                                                        // multiple assignment
                                                        ResolvExpr::CandidateList rhs;
                                                        explode( rhsCand, crntFinder.localSyms, back_inserter(rhs), true );
                                                        matcher.reset(
                                                                new MultipleAssignMatcher{ *this, expr->location, lhs, rhs } );
                                                        match();
                                                }
                                        }
                                }
                        }
                }

                void match() {
                        assert( matcher );

                        std::vector< ast::ptr< ast::Expr > > newAssigns = matcher->match();

                        if ( ! ( matcher->lhs.empty() && matcher->rhs.empty() ) ) {
                                // if both LHS and RHS are empty than this is the empty tuple case, wherein it's
                                // okay for newAssigns to be empty. Otherwise, return early so that no new
                                // candidates are generated
                                if ( newAssigns.empty() ) return;
                        }

                        ResolvExpr::CandidateList crnt;
                        // now resolve new assignments
                        for ( const ast::Expr * expr : newAssigns ) {
                                PRINT(
                                        std::cerr << "== resolving tuple assign ==" << std::endl;
                                        std::cerr << expr << std::endl;
                                )

                                ResolvExpr::CandidateFinder finder{ crntFinder.localSyms, matcher->env };

                                try {
                                        finder.find( expr, ResolvExpr::ResolvMode::withAdjustment() );
                                } catch (...) {
                                        // no match is not failure, just that this tuple assignment is invalid
                                        return;
                                }

                                ResolvExpr::CandidateList & cands = finder.candidates;
                                assert( cands.size() == 1 );
                                assert( cands.front()->expr );
                                crnt.emplace_back( std::move( cands.front() ) );
                        }

                        // extract expressions from the assignment candidates to produce a list of assignments
                        // that together form a sigle candidate
                        std::vector< ast::ptr< ast::Expr > > solved;
                        for ( ResolvExpr::CandidateRef & cand : crnt ) {
                                solved.emplace_back( cand->expr );
                                matcher->combineState( *cand );
                        }

                        crntFinder.candidates.emplace_back( std::make_shared< ResolvExpr::Candidate >(
                                new ast::TupleAssignExpr{
                                        matcher->location, std::move( solved ), std::move( matcher->tmpDecls ) },
                                std::move( matcher->env ), std::move( matcher->open ), std::move( matcher->need ),
                                ResolvExpr::sumCost( crnt ) + matcher->baseCost ) );
                }
        };
} // anonymous namespace

void handleTupleAssignment(
        ResolvExpr::CandidateFinder & finder, const ast::UntypedExpr * assign,
        std::vector< ResolvExpr::CandidateFinder > & args
) {
        TupleAssignSpotter_new spotter{ finder };
        spotter.spot( assign, args );
}

} // namespace Tuples

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