source: translator/ResolvExpr/AlternativeFinder.cc @ 8c17ab0

/*
 * This file is part of the Cforall project
 *
 * $Id: AlternativeFinder.cc,v 1.36 2005/08/29 20:14:15 rcbilson Exp $
 *
 */

#include <list>
#include <iterator>
#include <algorithm>
#include <functional>
#include <cassert>

#include "AlternativeFinder.h"
#include "Alternative.h"
#include "Cost.h"
#include "typeops.h"
#include "Unify.h"
#include "RenameVars.h"
#include "SynTree/Type.h"
#include "SynTree/Declaration.h"
#include "SynTree/Expression.h"
#include "SynTree/Initializer.h"
#include "SynTree/Visitor.h"
#include "SymTab/Indexer.h"
#include "SymTab/Mangler.h"
#include "SynTree/TypeSubstitution.h"
#include "SymTab/Validate.h"
#include "Designators/Processor.h"
#include "Tuples/TupleAssignment.h"
#include "Tuples/NameMatcher.h"
#include "utility.h"


//#define DEBUG_COST

namespace ResolvExpr {

Expression *
resolveInVoidContext( Expression *expr, const SymTab::Indexer &indexer, TypeEnvironment &env )
{
  CastExpr *castToVoid = new CastExpr( expr );

  AlternativeFinder finder( indexer, env );
  finder.findWithAdjustment( castToVoid );

  // it's a property of the language that a cast expression has either 1 or 0 interpretations;
  // if it has 0 interpretations, an exception has already been thrown.
  assert( finder.get_alternatives().size() == 1 );
  CastExpr *newExpr = dynamic_cast< CastExpr* >( finder.get_alternatives().front().expr );
  assert( newExpr );
  env = finder.get_alternatives().front().env;
  return newExpr->get_arg()->clone();
}

namespace {

  void
  printAlts( const AltList &list, std::ostream &os, int indent = 0 )
  {
    for( AltList::const_iterator i = list.begin(); i != list.end(); ++i ) {
      i->print( os, indent );
      os << std::endl;
    }
  }

  void
  makeExprList( const AltList &in, std::list< Expression* > &out )
  {
    for( AltList::const_iterator i = in.begin(); i != in.end(); ++i ) {
      out.push_back( i->expr->clone() );
    }
  }

  Cost
  sumCost( const AltList &in )
  {
    Cost total;
    for( AltList::const_iterator i = in.begin(); i != in.end(); ++i ) {
      total += i->cost;
    }
    return total;
  }

  struct PruneStruct
  {
    bool isAmbiguous;
    AltList::iterator candidate;
    PruneStruct() {}
    PruneStruct( AltList::iterator candidate ): isAmbiguous( false ), candidate( candidate ) {}
  };

  template< typename InputIterator, typename OutputIterator >
  void
  pruneAlternatives( InputIterator begin, InputIterator end, OutputIterator out, const SymTab::Indexer &indexer )
  {
    // select the alternatives that have the minimum conversion cost for a particular set of result types
    std::map< std::string, PruneStruct > selected;
    for( AltList::iterator candidate = begin; candidate != end; ++candidate ) {
      PruneStruct current( candidate );
      std::string mangleName;
      for( std::list< Type* >::const_iterator retType = candidate->expr->get_results().begin(); retType != candidate->expr->get_results().end(); ++retType ) {
        Type *newType = (*retType)->clone();
        candidate->env.apply( newType );
        mangleName += SymTab::Mangler::mangle( newType );
        delete newType;
      }
      std::map< std::string, PruneStruct >::iterator mapPlace = selected.find( mangleName );
      if( mapPlace != selected.end() ) {
        if( candidate->cost < mapPlace->second.candidate->cost ) {
///           std::cout << "cost " << candidate->cost << " beats " << target->second.cost << std::endl;
          selected[ mangleName ] = current;
        } else if( candidate->cost == mapPlace->second.candidate->cost ) {
///           std::cout << "marking ambiguous" << std::endl;
          mapPlace->second.isAmbiguous = true;
        }
      } else {
        selected[ mangleName ] = current;
      }
    }

///     std::cout << "there are " << selected.size() << " alternatives before elimination" << std::endl;

    // accept the alternatives that were unambiguous
    for( std::map< std::string, PruneStruct >::iterator target = selected.begin(); target != selected.end(); ++target) {
      if( !target->second.isAmbiguous ) {
        Alternative &alt = *target->second.candidate;
        for( std::list< Type* >::iterator result = alt.expr->get_results().begin(); result != alt.expr->get_results().end(); ++result ) {
          alt.env.applyFree( *result );
        }
        *out++ = alt;
      }
    }

  }

  template< typename InputIterator, typename OutputIterator >
  void
  findMinCost( InputIterator begin, InputIterator end, OutputIterator out )
  {
    AltList alternatives;

    // select the alternatives that have the minimum parameter cost
    Cost minCost = Cost::infinity;
    for( AltList::iterator i = begin; i != end; ++i ) {
      if( i->cost < minCost ) {
        minCost = i->cost;
        i->cost = i->cvtCost;
        alternatives.clear();
        alternatives.push_back( *i );
      } else if( i->cost == minCost ) {
        i->cost = i->cvtCost;
        alternatives.push_back( *i );
      }
    }
    std::copy( alternatives.begin(), alternatives.end(), out );
  }

  template< typename InputIterator >
  void
  simpleCombineEnvironments( InputIterator begin, InputIterator end, TypeEnvironment &result )
  {
    while( begin != end ) {
      result.simpleCombine( (*begin++).env );
    }
  }

  void
  renameTypes( Expression *expr )
  {
    for( std::list< Type* >::iterator i = expr->get_results().begin(); i != expr->get_results().end(); ++i ) {
      (*i)->accept( global_renamer );
    }
  }
}

template< typename InputIterator, typename OutputIterator >
void
AlternativeFinder::findSubExprs( InputIterator begin, InputIterator end, OutputIterator out )
{
  while( begin != end ) {
    AlternativeFinder finder( indexer, env );
    finder.findWithAdjustment( *begin );
    // XXX  either this
    //Designators::fixDesignations( finder, (*begin++)->get_argName() );
    // or XXX this
    begin++;
///     std::cout << "findSubExprs" << std::endl;
///     printAlts( finder.alternatives, std::cout );
    *out++ = finder;
  }
}

AlternativeFinder::AlternativeFinder( const SymTab::Indexer &indexer, const TypeEnvironment &env )
  : indexer( indexer ), env( env )
{
}

void
AlternativeFinder::find( Expression *expr, bool adjust )
{
  expr->accept( *this );
  if( alternatives.empty() ) {
    throw SemanticError( "No reasonable alternatives for expression ", expr );
  }
  for( AltList::iterator i = alternatives.begin(); i != alternatives.end(); ++i ) {
    if( adjust ) {
      adjustExprTypeList( i->expr->get_results().begin(), i->expr->get_results().end(), i->env, indexer );
    }
  }
///   std::cout << "alternatives before prune:" << std::endl;
///   printAlts( alternatives, std::cout );
  AltList::iterator oldBegin = alternatives.begin();
  pruneAlternatives( alternatives.begin(), alternatives.end(), front_inserter( alternatives ), indexer );
  if( alternatives.begin() == oldBegin ) {
    std::ostrstream stream;
    stream << "Can't choose between alternatives for expression ";
    expr->print( stream );
    stream << "Alternatives are:";
    AltList winners;
    findMinCost( alternatives.begin(), alternatives.end(), back_inserter( winners ) );
    printAlts( winners, stream, 8 );
    throw SemanticError( std::string( stream.str(), stream.pcount() ) );
  }
  alternatives.erase( oldBegin, alternatives.end() );
///   std::cout << "there are " << alternatives.size() << " alternatives after elimination" << std::endl;
}

void
AlternativeFinder::findWithAdjustment( Expression *expr )
{
  find( expr, true );
}

template< typename StructOrUnionType >
void
AlternativeFinder::addAggMembers( StructOrUnionType *aggInst, Expression *expr, const Cost &newCost, const std::string &name )
{
  std::list< Declaration* > members;
  aggInst->lookup( name, members );
  for( std::list< Declaration* >::const_iterator i = members.begin(); i != members.end(); ++i ) {
    if( DeclarationWithType *dwt = dynamic_cast< DeclarationWithType* >( *i ) ) {
      alternatives.push_back( Alternative( new MemberExpr( dwt->clone(), expr->clone() ), env, newCost ) );
      renameTypes( alternatives.back().expr );
    } else {
      assert( false );
    }
  }
}

void
AlternativeFinder::visit(ApplicationExpr *applicationExpr)
{
  alternatives.push_back( Alternative( applicationExpr->clone(), env, Cost::zero ) );
}

Cost
computeConversionCost( Alternative &alt, const SymTab::Indexer &indexer )
{
  ApplicationExpr *appExpr = dynamic_cast< ApplicationExpr* >( alt.expr );
  assert( appExpr );
  PointerType *pointer = dynamic_cast< PointerType* >( appExpr->get_function()->get_results().front() );
  assert( pointer );
  FunctionType *function = dynamic_cast< FunctionType* >( pointer->get_base() );
  assert( function );

  Cost convCost( 0, 0, 0 );
  std::list< DeclarationWithType* >& formals = function->get_parameters();
  std::list< DeclarationWithType* >::iterator formal = formals.begin();
  std::list< Expression* >& actuals = appExpr->get_args();
  for( std::list< Expression* >::iterator actualExpr = actuals.begin(); actualExpr != actuals.end(); ++actualExpr ) {
///     std::cout << "actual expression:" << std::endl;
///     (*actualExpr)->print( std::cout, 8 );
///     std::cout << "--- results are" << std::endl;
///     printAll( (*actualExpr)->get_results(), std::cout, 8 );
    std::list< DeclarationWithType* >::iterator startFormal = formal;
    Cost actualCost;
    for( std::list< Type* >::iterator actual = (*actualExpr)->get_results().begin(); actual != (*actualExpr)->get_results().end(); ++actual ) {
      if( formal == formals.end() ) {
        if( function->get_isVarArgs() ) {
          convCost += Cost( 1, 0, 0 );
          break;
        } else {
          return Cost::infinity;
        }
      }
///       std::cout << std::endl << "converting ";
///       (*actual)->print( std::cout, 8 );
///       std::cout << std::endl << " to ";
///       (*formal)->get_type()->print( std::cout, 8 );
      Cost newCost = conversionCost( *actual, (*formal)->get_type(), indexer, alt.env );
///       std::cout << std::endl << "cost is" << newCost << std::endl;

      if( newCost == Cost::infinity ) {
        return newCost;
      }
      convCost += newCost;
      actualCost += newCost;

      convCost += Cost( 0, polyCost( (*formal)->get_type(), alt.env, indexer ) + polyCost( *actual, alt.env, indexer), 0 );

      formal++;
    }
    if( actualCost != Cost( 0, 0, 0 ) ) {
      std::list< DeclarationWithType* >::iterator startFormalPlusOne = startFormal;
      startFormalPlusOne++;
      if( formal == startFormalPlusOne ) {
        // not a tuple type
        Type *newType = (*startFormal)->get_type()->clone();
        alt.env.apply( newType );
        *actualExpr = new CastExpr( *actualExpr, newType );
      } else {
        TupleType *newType = new TupleType( Type::Qualifiers() );
        for( std::list< DeclarationWithType* >::iterator i = startFormal; i != formal; ++i ) {
          newType->get_types().push_back( (*i)->get_type()->clone() );
        }
        alt.env.apply( newType );
        *actualExpr = new CastExpr( *actualExpr, newType );
      }
    }

  }
  if( formal != formals.end() ) {
    return Cost::infinity;
  }

  for( InferredParams::const_iterator assert = appExpr->get_inferParams().begin(); assert != appExpr->get_inferParams().end(); ++assert ) {
///     std::cout << std::endl << "converting ";
///     assert->second.actualType->print( std::cout, 8 );
///     std::cout << std::endl << " to ";
///     assert->second.formalType->print( std::cout, 8 );
    Cost newCost = conversionCost( assert->second.actualType, assert->second.formalType, indexer, alt.env );
///     std::cout << std::endl << "cost of conversion is " << newCost << std::endl;
    if( newCost == Cost::infinity ) {
      return newCost;
    }
    convCost += newCost;

    convCost += Cost( 0, polyCost( assert->second.formalType, alt.env, indexer ) + polyCost( assert->second.actualType, alt.env, indexer), 0 );
  }

  return convCost;
}

void
makeUnifiableVars( Type *type, OpenVarSet &unifiableVars, AssertionSet &needAssertions )
{
  for( std::list< TypeDecl* >::const_iterator tyvar = type->get_forall().begin(); tyvar != type->get_forall().end(); ++tyvar ) {
    unifiableVars[ (*tyvar)->get_name() ] = (*tyvar)->get_kind();
    for( std::list< DeclarationWithType* >::iterator assert = (*tyvar)->get_assertions().begin(); assert != (*tyvar)->get_assertions().end(); ++assert ) {
      needAssertions[ *assert ] = true;
    }
///     needAssertions.insert( needAssertions.end(), (*tyvar)->get_assertions().begin(), (*tyvar)->get_assertions().end() );
  }
}

bool
AlternativeFinder::instantiateFunction( std::list< DeclarationWithType* >& formals, /*const*/ AltList &actuals, bool isVarArgs, OpenVarSet& openVars, TypeEnvironment &resultEnv, AssertionSet &resultNeed, AssertionSet &resultHave )
{
  std::list< TypeEnvironment > toBeDone;
  simpleCombineEnvironments( actuals.begin(), actuals.end(), resultEnv );
  // make sure we don't widen any existing bindings
  for( TypeEnvironment::iterator i = resultEnv.begin(); i != resultEnv.end(); ++i ) {
    i->allowWidening  = false;
  }
  resultEnv.extractOpenVars( openVars );

  /*
  Tuples::NameMatcher matcher( formals );
  try {
    matcher.match( actuals );
  } catch ( Tuples::NoMatch &e ) {
    std::cerr << "Alternative doesn't match: " << e.message << std::endl;
  }
  */
  std::list< DeclarationWithType* >::iterator formal = formals.begin();
  for( AltList::const_iterator actualExpr = actuals.begin(); actualExpr != actuals.end(); ++actualExpr ) {
    for( std::list< Type* >::iterator actual = actualExpr->expr->get_results().begin(); actual != actualExpr->expr->get_results().end(); ++actual ) {
      if( formal == formals.end() ) {
        return isVarArgs;
      }
///       std::cerr << "formal type is ";
///       (*formal)->get_type()->print( std::cerr );
///       std::cerr << std::endl << "actual type is ";
///       (*actual)->print( std::cerr );
///       std::cerr << std::endl;
      if( !unify( (*formal)->get_type(), *actual, resultEnv, resultNeed, resultHave, openVars, indexer ) ) {
        return false;
      }
      formal++;
    }
  }
  // Handling of default values
  while( formal != formals.end() ) {
    if( ObjectDecl *od = dynamic_cast<ObjectDecl *>( *formal ) )
      if( SingleInit *si = dynamic_cast<SingleInit *>( od->get_init() ))
        // so far, only constant expressions are accepted as default values
        if ( ConstantExpr *cnstexpr = dynamic_cast<ConstantExpr *>(si->get_value()) )
          if ( Constant *cnst = dynamic_cast<Constant *>( cnstexpr->get_constant() ) )
            if( unify( (*formal)->get_type(), cnst->get_type(), resultEnv, resultNeed, resultHave, openVars, indexer ) ) {
              // XXX Don't know if this is right
              actuals.push_back( Alternative( cnstexpr->clone(), env, Cost::zero ) );
              formal++;
              if (formal == formals.end()) break;
            }
    return false;
  }
  return true;
}

static const int recursionLimit = 10;

void
addToIndexer( AssertionSet &assertSet, SymTab::Indexer &indexer )
{
  for( AssertionSet::iterator i = assertSet.begin(); i != assertSet.end(); ++i ) {
    if( i->second == true ) {
      i->first->accept( indexer );
    }
  }
}

template< typename ForwardIterator, typename OutputIterator >
void
inferRecursive( ForwardIterator begin, ForwardIterator end, const Alternative &newAlt, OpenVarSet &openVars, const SymTab::Indexer &decls, const AssertionSet &newNeed, int level, const SymTab::Indexer &indexer, OutputIterator out )
{
  if( begin == end ) {
    if( newNeed.empty() ) {
      *out++ = newAlt;
      return;
    } else if( level >= recursionLimit ) {
      throw SemanticError( "Too many recursive assertions" );
    } else {
      AssertionSet newerNeed;
///       std::cerr << "recursing with new set:" << std::endl;
///       printAssertionSet( newNeed, std::cerr, 8 );
      inferRecursive( newNeed.begin(), newNeed.end(), newAlt, openVars, decls, newerNeed, level+1, indexer, out );
      return;
    }
  }

  ForwardIterator cur = begin++;
  if( !cur->second ) {
    inferRecursive( begin, end, newAlt, openVars, decls, newNeed, level, indexer, out );
  }
  DeclarationWithType *curDecl = cur->first;
///   std::cerr << "inferRecursive: assertion is ";
///   curDecl->print( std::cerr );
///   std::cerr << std::endl;
  std::list< DeclarationWithType* > candidates;
  decls.lookupId( curDecl->get_name(), candidates );
///   if( candidates.empty() ) { std::cout << "no candidates!" << std::endl; }
  for( std::list< DeclarationWithType* >::const_iterator candidate = candidates.begin(); candidate != candidates.end(); ++candidate ) {
///     std::cout << "inferRecursive: candidate is ";
///     (*candidate)->print( std::cout );
///     std::cout << std::endl;
    AssertionSet newHave, newerNeed( newNeed );
    TypeEnvironment newEnv( newAlt.env );
    OpenVarSet newOpenVars( openVars );
    Type *adjType = (*candidate)->get_type()->clone();
    adjustExprType( adjType, newEnv, indexer );
    adjType->accept( global_renamer );
///     std::cerr << "unifying ";
///     curDecl->get_type()->print( std::cerr );
///     std::cerr << " with ";
///     adjType->print( std::cerr );
///     std::cerr << std::endl;
    if( unify( curDecl->get_type(), adjType, newEnv, newerNeed, newHave, newOpenVars, indexer ) ) {
///       std::cerr << "success!" << std::endl;
      SymTab::Indexer newDecls( decls );
      addToIndexer( newHave, newDecls );
      Alternative newerAlt( newAlt );
      newerAlt.env = newEnv;
      assert( (*candidate)->get_uniqueId() );
      Expression *varExpr = new VariableExpr( static_cast< DeclarationWithType* >( Declaration::declFromId( (*candidate)->get_uniqueId() ) ) );
      deleteAll( varExpr->get_results() );
      varExpr->get_results().clear();
      varExpr->get_results().push_front( adjType->clone() );
///       std::cout << "satisfying assertion " << curDecl->get_uniqueId() << " ";
///       curDecl->print( std::cout );
///       std::cout << " with declaration " << (*candidate)->get_uniqueId() << " ";
///       (*candidate)->print( std::cout );
///       std::cout << std::endl;
      ApplicationExpr *appExpr = static_cast< ApplicationExpr* >( newerAlt.expr );
      // XXX: this is a memory leak, but adjType can't be deleted because it might contain assertions
      appExpr->get_inferParams()[ curDecl->get_uniqueId() ] = ParamEntry( (*candidate)->get_uniqueId(), adjType->clone(), curDecl->get_type()->clone(), varExpr );
      inferRecursive( begin, end, newerAlt, newOpenVars, newDecls, newerNeed, level, indexer, out );
    } else {
      delete adjType;
    }
  }
}

template< typename OutputIterator >
void
AlternativeFinder::inferParameters( const AssertionSet &need, AssertionSet &have, const Alternative &newAlt, OpenVarSet &openVars, OutputIterator out )
{
///   std::cout << "inferParameters: assertions needed are" << std::endl;
///   printAll( need, std::cout, 8 );
  SymTab::Indexer decls( indexer );
///   std::cout << "============= original indexer" << std::endl;
///   indexer.print( std::cout );
///   std::cout << "============= new indexer" << std::endl;
///   decls.print( std::cout );
  addToIndexer( have, decls );
  AssertionSet newNeed;
  inferRecursive( need.begin(), need.end(), newAlt, openVars, decls, newNeed, 0, indexer, out );
///   std::cout << "declaration 14 is ";
///   Declaration::declFromId
///    *out++ = newAlt;
}

template< typename OutputIterator >
void
AlternativeFinder::makeFunctionAlternatives( const Alternative &func, FunctionType *funcType, AltList &actualAlt, OutputIterator out )
{
  OpenVarSet openVars;
  AssertionSet resultNeed, resultHave;
  TypeEnvironment resultEnv;
  makeUnifiableVars( funcType, openVars, resultNeed );
  if( instantiateFunction( funcType->get_parameters(), actualAlt, funcType->get_isVarArgs(), openVars, resultEnv, resultNeed, resultHave ) ) {
    ApplicationExpr *appExpr = new ApplicationExpr( func.expr->clone() );
    Alternative newAlt( appExpr, resultEnv, sumCost( actualAlt ) );
    makeExprList( actualAlt, appExpr->get_args() );
///     std::cout << "need assertions:" << std::endl;
///     printAssertionSet( resultNeed, std::cout, 8 );
    inferParameters( resultNeed, resultHave, newAlt, openVars, out );
  }
}

void
AlternativeFinder::visit(UntypedExpr *untypedExpr)
{
  bool doneInit = false;
  AlternativeFinder funcOpFinder( indexer, env );

  AlternativeFinder funcFinder( indexer, env );
  {
    NameExpr *fname;
    if ( (fname = dynamic_cast<NameExpr *>(untypedExpr->get_function()))
         && ( fname->get_name() == std::string("LabAddress")) ) {
        alternatives.push_back( Alternative(untypedExpr, env, Cost()) );
        return;
      }
  }

  funcFinder.findWithAdjustment( untypedExpr->get_function() );
  std::list< AlternativeFinder > argAlternatives;
  findSubExprs( untypedExpr->begin_args(), untypedExpr->end_args(), back_inserter( argAlternatives ) );

  std::list< AltList > possibilities;
  combos( argAlternatives.begin(), argAlternatives.end(), back_inserter( possibilities ) );

  Tuples::TupleAssignSpotter tassign(this);
  if ( tassign.isTupleAssignment(untypedExpr, possibilities) ) {
    // take care of possible tuple assignments, or discard expression
    return;
  } // else ...

  AltList candidates;

  for( AltList::const_iterator func = funcFinder.alternatives.begin(); func != funcFinder.alternatives.end(); ++func ) {
///     std::cout << "working on alternative: " << std::endl;
///     func->print( std::cout, 8 );
    // check if the type is pointer to function
    PointerType *pointer;
    if( func->expr->get_results().size() == 1 && ( pointer = dynamic_cast< PointerType* >( func->expr->get_results().front() ) ) ) {
      if( FunctionType *function = dynamic_cast< FunctionType* >( pointer->get_base() ) ) {
        for( std::list< AltList >::iterator actualAlt = possibilities.begin(); actualAlt != possibilities.end(); ++actualAlt ) {
          // XXX
          //Designators::check_alternative( function, *actualAlt );
          makeFunctionAlternatives( *func, function, *actualAlt, std::back_inserter( candidates ) );
        }
      } else if( TypeInstType *typeInst = dynamic_cast< TypeInstType* >( pointer->get_base() ) ) {
        EqvClass eqvClass;
        if( func->env.lookup( typeInst->get_name(), eqvClass ) && eqvClass.type ) {
          if( FunctionType *function = dynamic_cast< FunctionType* >( eqvClass.type ) ) {
            for( std::list< AltList >::iterator actualAlt = possibilities.begin(); actualAlt != possibilities.end(); ++actualAlt ) {
              makeFunctionAlternatives( *func, function, *actualAlt, std::back_inserter( candidates ) );
            }
          }
        }
      }
    } else {
      // seek a function operator that's compatible
      if( !doneInit ) {
        doneInit = true;
        NameExpr *opExpr = new NameExpr( "?()" );
        try {
          funcOpFinder.findWithAdjustment( opExpr );
        } catch( SemanticError &e ) {
          // it's ok if there aren't any defined function ops
        }
///         std::cout << "known function ops:" << std::endl;
///         printAlts( funcOpFinder.alternatives, std::cout, 8 );
      }

      for( AltList::const_iterator funcOp = funcOpFinder.alternatives.begin(); funcOp != funcOpFinder.alternatives.end(); ++funcOp ) {
        // check if the type is pointer to function
        PointerType *pointer;
        if( funcOp->expr->get_results().size() == 1
                && ( pointer = dynamic_cast< PointerType* >( funcOp->expr->get_results().front() ) ) ) {
          if ( FunctionType *function = dynamic_cast< FunctionType* >( pointer->get_base() ) ) {
            for( std::list< AltList >::iterator actualAlt = possibilities.begin(); actualAlt != possibilities.end(); ++actualAlt ) {
              AltList currentAlt;
              currentAlt.push_back( *func );
              currentAlt.insert( currentAlt.end(), actualAlt->begin(), actualAlt->end() );
              makeFunctionAlternatives( *funcOp, function, currentAlt, std::back_inserter( candidates ) );
            }
          }
        }
      }
    }
  }

  for( AltList::iterator withFunc = candidates.begin(); withFunc != candidates.end(); ++withFunc ) {
    Cost cvtCost = computeConversionCost( *withFunc, indexer );

#ifdef DEBUG_COST
    ApplicationExpr *appExpr = dynamic_cast< ApplicationExpr* >( withFunc->expr );
    assert( appExpr );
    PointerType *pointer = dynamic_cast< PointerType* >( appExpr->get_function()->get_results().front() );
    assert( pointer );
    FunctionType *function = dynamic_cast< FunctionType* >( pointer->get_base() );
    assert( function );
    std::cout << "Case +++++++++++++" << std::endl;
    std::cout << "formals are:" << std::endl;
    printAll( function->get_parameters(), std::cout, 8 );
    std::cout << "actuals are:" << std::endl;
    printAll( appExpr->get_args(), std::cout, 8 );
    std::cout << "bindings are:" << std::endl;
    withFunc->env.print( std::cout, 8 );
    std::cout << "cost of conversion is:" << cvtCost << std::endl;
#endif

    if( cvtCost != Cost::infinity ) {
      withFunc->cvtCost = cvtCost;
      alternatives.push_back( *withFunc );
    }
  }
  candidates.clear();
  candidates.splice( candidates.end(), alternatives );

  findMinCost( candidates.begin(), candidates.end(), std::back_inserter( alternatives ) );
}

bool
isLvalue( Expression *expr ) {
  for( std::list< Type* >::const_iterator i = expr->get_results().begin(); i != expr->get_results().end(); ++i ) {
    if( !(*i)->get_isLvalue() ) return false;
  }
  return true;
}

void
AlternativeFinder::visit(AddressExpr *addressExpr)
{
  AlternativeFinder finder( indexer, env );
  finder.find( addressExpr->get_arg() );
  for( std::list< Alternative >::iterator i = finder.alternatives.begin(); i != finder.alternatives.end(); ++i ) {
    if( isLvalue( i->expr ) ) {
      alternatives.push_back( Alternative( new AddressExpr( i->expr->clone() ), i->env, i->cost ) );
    }
  }
}

void
AlternativeFinder::visit(CastExpr *castExpr)
{
  for( std::list< Type* >::iterator i = castExpr->get_results().begin(); i != castExpr->get_results().end(); ++i ) {
    SymTab::validateType( *i, &indexer );
    adjustExprType( *i, env, indexer );
  }

  AlternativeFinder finder( indexer, env );
  finder.findWithAdjustment( castExpr->get_arg() );

  AltList candidates;
  for( std::list< Alternative >::iterator i = finder.alternatives.begin(); i != finder.alternatives.end(); ++i ) {
    AssertionSet needAssertions, haveAssertions;
    OpenVarSet openVars;

    // It's possible that a cast can throw away some values in a multiply-valued expression.
    // (An example is a cast-to-void, which casts from one value to zero.)
    // Figure out the prefix of the subexpression results that are cast directly.
    // The candidate is invalid if it has fewer results than there are types to cast to.
    int discardedValues = (*i).expr->get_results().size() - castExpr->get_results().size();
    if( discardedValues < 0 ) continue;
    std::list< Type* >::iterator candidate_end = (*i).expr->get_results().begin();
    std::advance( candidate_end, castExpr->get_results().size() );
    if( !unifyList( (*i).expr->get_results().begin(), candidate_end,
        castExpr->get_results().begin(), castExpr->get_results().end(), i->env, needAssertions, haveAssertions, openVars, indexer ) ) continue;
    Cost thisCost = castCostList( (*i).expr->get_results().begin(), candidate_end,
        castExpr->get_results().begin(), castExpr->get_results().end(), indexer, i->env );
    if( thisCost != Cost::infinity ) {
      // count one safe conversion for each value that is thrown away
      thisCost += Cost( 0, 0, discardedValues );
      CastExpr *newExpr = castExpr->clone();
      newExpr->set_arg( i->expr->clone() );
      candidates.push_back( Alternative( newExpr, i->env, i->cost, thisCost ) );
    }
  }

  // findMinCost selects the alternatives with the lowest "cost" members, but has the side effect
  // of copying the cvtCost member to the cost member (since the old cost is now irrelevant).
  // Thus, calling findMinCost twice selects first based on argument cost, then on conversion cost.
  AltList minArgCost;
  findMinCost( candidates.begin(), candidates.end(), std::back_inserter( minArgCost ) );
  findMinCost( minArgCost.begin(), minArgCost.end(), std::back_inserter( alternatives ) );
}

void
AlternativeFinder::visit(UntypedMemberExpr *memberExpr)
{
  AlternativeFinder funcFinder( indexer, env );
  funcFinder.findWithAdjustment( memberExpr->get_aggregate() );

  for( AltList::const_iterator agg = funcFinder.alternatives.begin(); agg != funcFinder.alternatives.end(); ++agg ) {
    if( agg->expr->get_results().size() == 1 ) {
      if( StructInstType *structInst = dynamic_cast< StructInstType* >( agg->expr->get_results().front() ) ) {
        addAggMembers( structInst, agg->expr, agg->cost, memberExpr->get_member() );
      } else if( UnionInstType *unionInst = dynamic_cast< UnionInstType* >( agg->expr->get_results().front() ) ) {
        addAggMembers( unionInst, agg->expr, agg->cost, memberExpr->get_member() );
      }
    }
  }
}

void
AlternativeFinder::visit(MemberExpr *memberExpr)
{
  alternatives.push_back( Alternative( memberExpr->clone(), env, Cost::zero ) );
}

void
AlternativeFinder::visit(NameExpr *nameExpr)
{
  std::list< DeclarationWithType* > declList;
  indexer.lookupId( nameExpr->get_name(), declList );
///     std::cerr << "nameExpr is " << nameExpr->get_name() << std::endl;
  for( std::list< DeclarationWithType* >::iterator i = declList.begin(); i != declList.end(); ++i ) {
    VariableExpr newExpr( *i, nameExpr->get_argName() );
    alternatives.push_back( Alternative( newExpr.clone(), env, Cost() ) );
///     std::cerr << "decl is ";
///     (*i)->print( std::cerr );
///     std::cerr << std::endl;
///     std::cerr << "newExpr is ";
///     newExpr.print( std::cerr );
///     std::cerr << std::endl;
    renameTypes( alternatives.back().expr );
    if( StructInstType *structInst = dynamic_cast< StructInstType* >( (*i)->get_type() ) ) {
      addAggMembers( structInst, &newExpr, Cost( 0, 0, 1 ), "" );
    } else if( UnionInstType *unionInst = dynamic_cast< UnionInstType* >( (*i)->get_type() ) ) {
      addAggMembers( unionInst, &newExpr, Cost( 0, 0, 1 ), "" );
    }
  }
}

void
AlternativeFinder::visit(VariableExpr *variableExpr)
{
  alternatives.push_back( Alternative( variableExpr->clone(), env, Cost::zero ) );
}

void
AlternativeFinder::visit(ConstantExpr *constantExpr)
{
  alternatives.push_back( Alternative( constantExpr->clone(), env, Cost::zero ) );
}

void
AlternativeFinder::visit(SizeofExpr *sizeofExpr)
{
  if( sizeofExpr->get_isType() ) {
    alternatives.push_back( Alternative( sizeofExpr->clone(), env, Cost::zero ) );
  } else {
    AlternativeFinder finder( indexer, env );
    finder.find( sizeofExpr->get_expr() );
    if( finder.alternatives.size() != 1 ) {
      throw SemanticError( "Ambiguous expression in sizeof operand: ", sizeofExpr->get_expr() );
    }
    Alternative &choice = finder.alternatives.front();
    alternatives.push_back( Alternative( new SizeofExpr( choice.expr->clone() ), choice.env, Cost::zero ) );
  }
}

void
AlternativeFinder::resolveAttr( DeclarationWithType *funcDecl, FunctionType *function, Type *argType, const TypeEnvironment &env )
{
  // assume no polymorphism
  // assume no implicit conversions
  assert( function->get_parameters().size() == 1 );
///   std::cout << "resolvAttr: funcDecl is ";
///   funcDecl->print( std::cout );
///   std::cout << " argType is ";
///   argType->print( std::cout );
///   std::cout << std::endl;
  if( typesCompatibleIgnoreQualifiers( argType, function->get_parameters().front()->get_type(), indexer, env ) ) {
    alternatives.push_back( Alternative( new AttrExpr( new VariableExpr( funcDecl ), argType->clone() ), env, Cost::zero ) );
    for( std::list< DeclarationWithType* >::iterator i = function->get_returnVals().begin(); i != function->get_returnVals().end(); ++i ) {
      alternatives.back().expr->get_results().push_back( (*i)->get_type()->clone() );
    }
  }
}

void
AlternativeFinder::visit(AttrExpr *attrExpr)
{
  // assume no 'pointer-to-attribute'
  NameExpr *nameExpr = dynamic_cast< NameExpr* >( attrExpr->get_attr() );
  assert( nameExpr );
  std::list< DeclarationWithType* > attrList;
  indexer.lookupId( nameExpr->get_name(), attrList );
  if( attrExpr->get_isType() || attrExpr->get_expr() ) {
    for( std::list< DeclarationWithType* >::iterator i = attrList.begin(); i != attrList.end(); ++i ) {
      // check if the type is function
      if( FunctionType *function = dynamic_cast< FunctionType* >( (*i)->get_type() ) ) {
        // assume exactly one parameter
        if( function->get_parameters().size() == 1 ) {
          if( attrExpr->get_isType() ) {
            resolveAttr( *i, function, attrExpr->get_type(), env );
          } else {
            AlternativeFinder finder( indexer, env );
            finder.find( attrExpr->get_expr() );
            for( AltList::iterator choice = finder.alternatives.begin(); choice != finder.alternatives.end(); ++choice ) {
              if( choice->expr->get_results().size() == 1 ) {
                resolveAttr(*i, function, choice->expr->get_results().front(), choice->env );
              }
            }
          }
        }
      }
    }
  } else {
    for( std::list< DeclarationWithType* >::iterator i = attrList.begin(); i != attrList.end(); ++i ) {
      VariableExpr newExpr( *i );
      alternatives.push_back( Alternative( newExpr.clone(), env, Cost() ) );
      renameTypes( alternatives.back().expr );
    }
  }
}

void
AlternativeFinder::visit(LogicalExpr *logicalExpr)
{
  AlternativeFinder firstFinder( indexer, env );
  firstFinder.findWithAdjustment( logicalExpr->get_arg1() );
  for( AltList::const_iterator first = firstFinder.alternatives.begin(); first != firstFinder.alternatives.end(); ++first ) {
    AlternativeFinder secondFinder( indexer, first->env );
    secondFinder.findWithAdjustment( logicalExpr->get_arg2() );
    for( AltList::const_iterator second = secondFinder.alternatives.begin(); second != secondFinder.alternatives.end(); ++second ) {
      LogicalExpr *newExpr = new LogicalExpr( first->expr->clone(), second->expr->clone(), logicalExpr->get_isAnd() );
      alternatives.push_back( Alternative( newExpr, second->env, first->cost + second->cost ) );
    }
  }
}

void
AlternativeFinder::visit(ConditionalExpr *conditionalExpr)
{
  AlternativeFinder firstFinder( indexer, env );
  firstFinder.findWithAdjustment( conditionalExpr->get_arg1() );
  for( AltList::const_iterator first = firstFinder.alternatives.begin(); first != firstFinder.alternatives.end(); ++first ) {
    AlternativeFinder secondFinder( indexer, first->env );
    secondFinder.findWithAdjustment( conditionalExpr->get_arg2() );
    for( AltList::const_iterator second = secondFinder.alternatives.begin(); second != secondFinder.alternatives.end(); ++second ) {
      AlternativeFinder thirdFinder( indexer, second->env );
      thirdFinder.findWithAdjustment( conditionalExpr->get_arg3() );
      for( AltList::const_iterator third = thirdFinder.alternatives.begin(); third != thirdFinder.alternatives.end(); ++third ) {
        OpenVarSet openVars;
        AssertionSet needAssertions, haveAssertions;
        Alternative newAlt( 0, third->env, first->cost + second->cost + third->cost );
        std::list< Type* > commonTypes;
        if( unifyList( second->expr->get_results().begin(), second->expr->get_results().end(), third->expr->get_results().begin(), third->expr->get_results().end(), newAlt.env, needAssertions, haveAssertions, openVars, indexer, commonTypes ) ) {
          ConditionalExpr *newExpr = new ConditionalExpr( first->expr->clone(), second->expr->clone(), third->expr->clone() );
          std::list< Type* >::const_iterator original = second->expr->get_results().begin();
          std::list< Type* >::const_iterator commonType = commonTypes.begin();
          for( ; original != second->expr->get_results().end() && commonType != commonTypes.end(); ++original, ++commonType ) {
            if( *commonType ) {
              newExpr->get_results().push_back( *commonType );
            } else {
              newExpr->get_results().push_back( (*original)->clone() );
            }
          }
          newAlt.expr = newExpr;
          inferParameters( needAssertions, haveAssertions, newAlt, openVars, back_inserter( alternatives ) );
        }
      }
    }
  }
}

void
AlternativeFinder::visit(CommaExpr *commaExpr)
{
  TypeEnvironment newEnv( env );
  Expression *newFirstArg = resolveInVoidContext( commaExpr->get_arg1(), indexer, newEnv );
  AlternativeFinder secondFinder( indexer, newEnv );
  secondFinder.findWithAdjustment( commaExpr->get_arg2() );
  for( AltList::const_iterator alt = secondFinder.alternatives.begin(); alt != secondFinder.alternatives.end(); ++alt ) {
    alternatives.push_back( Alternative( new CommaExpr( newFirstArg->clone(), alt->expr->clone() ), alt->env, alt->cost ) );
  }
  delete newFirstArg;
}

void
AlternativeFinder::visit(TupleExpr *tupleExpr)
{
  std::list< AlternativeFinder > subExprAlternatives;
  findSubExprs( tupleExpr->get_exprs().begin(), tupleExpr->get_exprs().end(), back_inserter( subExprAlternatives ) );
  std::list< AltList > possibilities;
  combos( subExprAlternatives.begin(), subExprAlternatives.end(), back_inserter( possibilities ) );
  for( std::list< AltList >::const_iterator i = possibilities.begin(); i != possibilities.end(); ++i ) {
    TupleExpr *newExpr = new TupleExpr;
    makeExprList( *i, newExpr->get_exprs() );
    for( std::list< Expression* >::const_iterator resultExpr = newExpr->get_exprs().begin(); resultExpr != newExpr->get_exprs().end(); ++resultExpr ) {
      for( std::list< Type* >::const_iterator resultType = (*resultExpr)->get_results().begin(); resultType != (*resultExpr)->get_results().end(); ++resultType ) {
        newExpr->get_results().push_back( (*resultType)->clone() );
      }
    }

    TypeEnvironment compositeEnv;
    simpleCombineEnvironments( i->begin(), i->end(), compositeEnv );
    alternatives.push_back( Alternative( newExpr, compositeEnv, sumCost( *i ) ) );
  }
}

} // namespace ResolvExpr