source: src/GenPoly/Lvalue.cc @ 453b586

//
// 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.
//
// Lvalue.cc --
//
// Author           : Richard C. Bilson
// Created On       : Mon May 18 07:44:20 2015
// Last Modified By : Peter A. Buhr
// Last Modified On : Fri Mar 17 09:11:18 2017
// Update Count     : 5
//

#include <cassert>                       // for strict_dynamic_cast
#include <string>                        // for string

#include "Common/PassVisitor.h"
#include "GenPoly.h"                     // for isPolyType
#include "Lvalue.h"

#include "Parser/LinkageSpec.h"          // for Spec, isBuiltin, Intrinsic
#include "ResolvExpr/TypeEnvironment.h"  // for AssertionSet, OpenVarSet
#include "ResolvExpr/Unify.h"            // for unify
#include "ResolvExpr/typeops.h"
#include "SymTab/Autogen.h"
#include "SymTab/Indexer.h"              // for Indexer
#include "SynTree/Declaration.h"         // for Declaration, FunctionDecl
#include "SynTree/Expression.h"          // for Expression, ConditionalExpr
#include "SynTree/Mutator.h"             // for mutateAll, Mutator
#include "SynTree/Statement.h"           // for ReturnStmt, Statement (ptr o...
#include "SynTree/Type.h"                // for PointerType, Type, FunctionType
#include "SynTree/Visitor.h"             // for Visitor, acceptAll

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

namespace GenPoly {
        namespace {
                // TODO: fold this into the general createDeref function??
                Expression * mkDeref( Expression * arg ) {
                        if ( SymTab::dereferenceOperator ) {
                                VariableExpr * deref = new VariableExpr( SymTab::dereferenceOperator );
                                deref->result = new PointerType( Type::Qualifiers(), deref->result );
                                Type * base = InitTweak::getPointerBase( arg->result );
                                assertf( base, "expected pointer type in dereference (type was %s)", toString( arg->result ).c_str() );
                                ApplicationExpr * ret = new ApplicationExpr( deref, { arg } );
                                delete ret->result;
                                ret->result = base->clone();
                                ret->result->set_lvalue( true );
                                return ret;
                        } else {
                                return UntypedExpr::createDeref( arg );
                        }
                }

                struct ReferenceConversions final : public WithStmtsToAdd {
                        Expression * postmutate( CastExpr * castExpr );
                        Expression * postmutate( AddressExpr * addrExpr );
                };

                /// Intrinsic functions that take reference parameters don't REALLY take reference parameters -- their reference arguments must always be implicitly dereferenced.
                struct FixIntrinsicArgs final {
                        Expression * postmutate( ApplicationExpr * appExpr );
                };

                struct FixIntrinsicResult final : public WithGuards {
                        Expression * postmutate( ApplicationExpr * appExpr );
                        void premutate( FunctionDecl * funcDecl );
                        bool inIntrinsic = false;
                };

                /// Replace reference types with pointer types
                struct ReferenceTypeElimination final {
                        Type * postmutate( ReferenceType * refType );
                };

                /// GCC-like Generalized Lvalues (which have since been removed from GCC)
                /// https://gcc.gnu.org/onlinedocs/gcc-3.4.6/gcc/Lvalues.html#Lvalues
                /// Replaces &(a,b) with (a, &b), &(a ? b : c) with (a ? &b : &c)
                struct GeneralizedLvalue final : public WithVisitorRef<GeneralizedLvalue> {
                        Expression * postmutate( AddressExpr * addressExpr );
                        Expression * postmutate( MemberExpr * memExpr );

                        template<typename Func>
                        Expression * applyTransformation( Expression * expr, Expression * arg, Func mkExpr );
                };

                /// Removes redundant &*/*& pattern that this pass can generate
                struct CollapseAddrDeref final {
                        Expression * postmutate( AddressExpr * addressExpr );
                        Expression * postmutate( ApplicationExpr * appExpr );
                };

                struct AddrRef final : public WithGuards {
                        void premutate( AddressExpr * addrExpr );
                        Expression * postmutate( AddressExpr * addrExpr );
                        void premutate( Expression * expr );

                        bool first = true;
                        bool current = false;
                        int refDepth = 0;
                };
        } // namespace

        static bool referencesEliminated = false;
        // used by UntypedExpr::createDeref to determine whether result type of dereference should be ReferenceType or value type.
        bool referencesPermissable() {
                return ! referencesEliminated;
        }

        void convertLvalue( std::list< Declaration* > & translationUnit ) {
                PassVisitor<ReferenceConversions> refCvt;
                PassVisitor<ReferenceTypeElimination> elim;
                PassVisitor<GeneralizedLvalue> genLval;
                PassVisitor<FixIntrinsicArgs> fixer;
                PassVisitor<CollapseAddrDeref> collapser;
                PassVisitor<AddrRef> addrRef;
                PassVisitor<FixIntrinsicResult> intrinsicResults;
                mutateAll( translationUnit, intrinsicResults );
                mutateAll( translationUnit, addrRef );
                mutateAll( translationUnit, refCvt );
                mutateAll( translationUnit, fixer );
                mutateAll( translationUnit, collapser );
                mutateAll( translationUnit, genLval );
                mutateAll( translationUnit, elim );  // last because other passes need reference types to work

                // from this point forward, no other pass should create reference types.
                referencesEliminated = true;
        }

        Expression * generalizedLvalue( Expression * expr ) {
                PassVisitor<GeneralizedLvalue> genLval;
                return expr->acceptMutator( genLval );
        }

        namespace {
                // true for intrinsic function calls that return a reference
                bool isIntrinsicReference( Expression * expr ) {
                        if ( UntypedExpr * untyped = dynamic_cast< UntypedExpr * >( expr ) ) {
                                std::string fname = InitTweak::getFunctionName( untyped );
                                // known intrinsic-reference prelude functions
                                return fname == "*?" || fname == "?[?]";
                        } else if ( ApplicationExpr * appExpr = dynamic_cast< ApplicationExpr * > ( expr ) ) {
                                if ( DeclarationWithType * func = InitTweak::getFunction( appExpr ) ) {
                                        // use type of return variable rather than expr result type, since it may have been changed to a pointer type
                                        FunctionType * ftype = GenPoly::getFunctionType( func->get_type() );
                                        Type * ret = ftype->returnVals.empty() ? nullptr : ftype->returnVals.front()->get_type();
                                        return func->linkage == LinkageSpec::Intrinsic && dynamic_cast<ReferenceType *>( ret );
                                }
                        }
                        return false;
                }

                Expression * FixIntrinsicResult::postmutate( ApplicationExpr * appExpr ) {
                        if ( isIntrinsicReference( appExpr ) ) {
                                // eliminate reference types from intrinsic applications - now they return lvalues
                                Type * result = appExpr->result;
                                appExpr->result = result->stripReferences()->clone();
                                appExpr->result->set_lvalue( true );
                                if ( ! inIntrinsic ) {
                                        // when not in an intrinsic function, add a cast to
                                        // don't add cast when in an intrinsic function, since they already have the cast
                                        Expression * ret = new CastExpr( appExpr, result );
                                        std::swap( ret->env, appExpr->env );
                                        return ret;
                                }
                                delete result;
                        }
                        return appExpr;
                }

                void FixIntrinsicResult::premutate( FunctionDecl * funcDecl ) {
                        GuardValue( inIntrinsic );
                        inIntrinsic =  funcDecl->linkage == LinkageSpec::Intrinsic;
                }

                Expression * FixIntrinsicArgs::postmutate( ApplicationExpr * appExpr ) {
                        // intrinsic functions don't really take reference-typed parameters, so they require an implicit dereference on their arguments.
                        if ( DeclarationWithType * function = InitTweak::getFunction( appExpr ) ) {
                                FunctionType * ftype = GenPoly::getFunctionType( function->get_type() );
                                assertf( ftype, "Function declaration does not have function type." );
                                // can be of differing lengths only when function is variadic
                                assertf( ftype->parameters.size() == appExpr->args.size() || ftype->isVarArgs, "ApplicationExpr args do not match formal parameter type." );


                                unsigned int i = 0;
                                const unsigned int end = ftype->parameters.size();
                                for ( auto p : unsafe_group_iterate( appExpr->args, ftype->parameters ) ) {
                                        if (i == end) break;
                                        Expression *& arg = std::get<0>( p );
                                        Type * formal = std::get<1>( p )->get_type();
                                        PRINT(
                                                std::cerr << "pair<0>: " << arg << std::endl;
                                                std::cerr << "pair<1>: " << formal << std::endl;
                                        )
                                        if ( dynamic_cast<ReferenceType*>( formal ) ) {
                                                if ( isIntrinsicReference( arg ) ) { // do not combine conditions, because that changes the meaning of the else if
                                                        if ( function->get_linkage() != LinkageSpec::Intrinsic ) { // intrinsic functions that turn pointers into references
                                                                // if argument is dereference or array subscript, the result isn't REALLY a reference, so it's not necessary to fix the argument
                                                                PRINT(
                                                                        std::cerr << "===is intrinsic arg in non-intrinsic call - adding address" << std::endl;
                                                                )
                                                                arg = new AddressExpr( arg );
                                                        }
                                                } else if ( function->get_linkage() == LinkageSpec::Intrinsic ) {
                                                        // std::cerr << "===adding deref to arg" << std::endl;
                                                        // if the parameter is a reference, add a dereference to the reference-typed argument.
                                                        Type * baseType = InitTweak::getPointerBase( arg->result );
                                                        assertf( baseType, "parameter is reference, arg must be pointer or reference: %s", toString( arg->result ).c_str() );
                                                        PointerType * ptrType = new PointerType( Type::Qualifiers(), baseType->clone() );
                                                        delete arg->result;
                                                        arg->set_result( ptrType );
                                                        arg = mkDeref( arg );
                                                }
                                        }
                                        ++i;
                                }
                        }
                        return appExpr;
                }

                // idea: &&&E: get outer &, inner &
                // at inner &, record depth D of reference type
                // at outer &, add D derefs.
                void AddrRef::premutate( Expression * ) {
                        GuardValue( current );
                        GuardValue( first );
                        current = false;
                        first = true;
                }

                void AddrRef::premutate( AddressExpr * ) {
                        GuardValue( current );
                        GuardValue( first );
                        current = first;
                        first = false;
                        if ( current ) {
                                GuardValue( refDepth );
                                refDepth = 0;
                        }
                }

                Expression * AddrRef::postmutate( AddressExpr * addrExpr ) {
                        if ( refDepth == 0 ) {
                                if ( ! isIntrinsicReference( addrExpr->arg ) ) {
                                        // try to avoid ?[?]
                                        refDepth = addrExpr->arg->result->referenceDepth();
                                }
                        }
                        if ( current ) {
                                Expression * ret = addrExpr;
                                while ( refDepth ) {
                                        ret = mkDeref( ret );
                                        refDepth--;
                                }
                                return ret;
                        }
                        return addrExpr;
                }

                Expression * ReferenceConversions::postmutate( AddressExpr * addrExpr ) {
                        // Inner expression may have been lvalue to reference conversion, which becomes an address expression.
                        // In this case, remove the outer address expression and return the argument.
                        // TODO: It's possible that this might catch too much and require a more sophisticated check.
                        return addrExpr;
                }

                Expression * ReferenceConversions::postmutate( CastExpr * castExpr ) {
                        // xxx - is it possible to convert directly between reference types with a different base? E.g.,
                        //   int x;
                        //   (double&)x;
                        // At the moment, I am working off of the assumption that this is illegal, thus the cast becomes redundant
                        // after this pass, so trash the cast altogether. If that changes, care must be taken to insert the correct
                        // pointer casts in the right places.

                        // need to reorganize this so that depth difference is the determining factor in what code is run, rather than whether something is reference type or not.

                        Type * destType = castExpr->result;
                        Type * srcType = castExpr->arg->result;
                        int depth1 = destType->referenceDepth();
                        int depth2 = srcType->referenceDepth();
                        int diff = depth1 - depth2;

                        if ( diff > 0 && ! srcType->get_lvalue() ) {
                                // rvalue to reference conversion -- introduce temporary
                                // know that reference depth of cast argument is 0, need to introduce n temporaries for reference depth of n, e.g.
                                //   (int &&&)3;
                                // becomes
                                //   int __ref_tmp_0 = 3;
                                //   int & __ref_tmp_1 = _&_ref_tmp_0;
                                //   int && __ref_tmp_2 = &__ref_tmp_1;
                                //   &__ref_tmp_2;
                                // the last & comes from the remaining reference conversion code
                                SemanticWarning( castExpr->arg->location, Warning::RvalueToReferenceConversion, toCString( castExpr->arg ) );

                                static UniqueName tempNamer( "__ref_tmp_" );
                                ObjectDecl * temp = ObjectDecl::newObject( tempNamer.newName(), castExpr->arg->result->clone(), new SingleInit( castExpr->arg ) );
                                PRINT( std::cerr << "made temp: " << temp << std::endl; )
                                stmtsToAddBefore.push_back( new DeclStmt( temp ) );
                                for ( int i = 0; i < depth1-1; i++ ) {
                                        ObjectDecl * newTemp = ObjectDecl::newObject( tempNamer.newName(), new ReferenceType( Type::Qualifiers(), temp->type->clone() ), new SingleInit( new AddressExpr( new VariableExpr( temp ) ) ) );
                                        PRINT( std::cerr << "made temp" << i << ": " << newTemp << std::endl; )
                                        stmtsToAddBefore.push_back( new DeclStmt( newTemp ) );
                                        temp = newTemp;
                                }
                                // update diff so that remaining code works out correctly
                                castExpr->arg = new VariableExpr( temp );
                                PRINT( std::cerr << "update cast to: " << castExpr << std::endl; )
                                srcType = castExpr->arg->result;
                                depth2 = srcType->referenceDepth();
                                diff = depth1 - depth2;
                                assert( diff == 1 );
                        }

                        PRINT (
                                if ( depth1 || depth2 ) {
                                        std::cerr << "destType: " << destType << " / srcType: " << srcType << std::endl;
                                        std::cerr << "depth: " << depth1 << " / " << depth2 << std::endl;
                                }
                        )
                        if ( diff > 0 ) {
                                // conversion to type with more depth (e.g. int & -> int &&): add address-of for each level of difference
                                Expression * ret = castExpr->arg;
                                for ( int i = 0; i < diff; ++i ) {
                                        ret = new AddressExpr( ret );
                                }
                                if ( srcType->get_lvalue() && srcType->get_qualifiers() != strict_dynamic_cast<ReferenceType *>( destType )->base->get_qualifiers() ) {
                                        // must keep cast if cast-to type is different from the actual type
                                        castExpr->arg = ret;
                                        return castExpr;
                                }
                                ret->env = castExpr->env;
                                delete ret->result;
                                ret->result = castExpr->result;
                                castExpr->env = nullptr;
                                castExpr->arg = nullptr;
                                castExpr->result = nullptr;
                                delete castExpr;
                                return ret;
                        } else if ( diff < 0 ) {
                                // conversion to type with less depth (e.g. int && -> int &): add dereferences for each level of difference
                                diff = -diff; // care only about magnitude now
                                Expression * ret = castExpr->arg;
                                for ( int i = 0; i < diff; ++i ) {
                                        ret = mkDeref( ret );
                                }
                                if ( ! ResolvExpr::typesCompatibleIgnoreQualifiers( destType->stripReferences(), srcType->stripReferences(), SymTab::Indexer() ) ) {
                                        // must keep cast if types are different
                                        castExpr->arg = ret;
                                        return castExpr;
                                }
                                ret->env = castExpr->env;
                                delete ret->result;
                                ret->result = castExpr->result;
                                ret->result->set_lvalue( true ); // ensure result is lvalue
                                castExpr->env = nullptr;
                                castExpr->arg = nullptr;
                                castExpr->result = nullptr;
                                delete castExpr;
                                return ret;
                        } else {
                                assert( diff == 0 );
                                // conversion between references of the same depth
                                return castExpr;
                        }

                        // // conversion to reference type
                        // if ( ReferenceType * refType = dynamic_cast< ReferenceType * >( castExpr->result ) ) {
                        //      (void)refType;
                        //      if ( ReferenceType * otherRef = dynamic_cast< ReferenceType * >( castExpr->arg->result ) ) {
                        //              // nothing to do if casting from reference to reference.
                        //              (void)otherRef;
                        //              PRINT( std::cerr << "convert reference to reference -- nop" << std::endl; )
                        //              if ( isIntrinsicReference( castExpr->arg ) ) {
                        //                      Expression * callExpr = castExpr->arg;
                        //                      PRINT(
                        //                              std::cerr << "but arg is deref -- &" << std::endl;
                        //                              std::cerr << callExpr << std::endl;
                        //                      )
                        //                      callExpr = new AddressExpr( callExpr ); // this doesn't work properly for multiple casts
                        //                      delete callExpr->result;
                        //                      callExpr->set_result( refType->clone() );
                        //                      // move environment out to new top-level
                        //                      callExpr->env = castExpr->env;
                        //                      castExpr->arg = nullptr;
                        //                      castExpr->env = nullptr;
                        //                      delete castExpr;
                        //                      return callExpr;
                        //              }
                        //              int depth1 = refType->referenceDepth();
                        //              int depth2 = otherRef->referenceDepth();
                        //              int diff = depth1-depth2;
                        //              if ( diff == 0 ) {
                        //                      // conversion between references of the same depth
                        //                      assertf( depth1 == depth2, "non-intrinsic reference with cast of reference to reference not yet supported: %d %d %s", depth1, depth2, toString( castExpr ).c_str() );
                        //                      PRINT( std::cerr << castExpr << std::endl; )
                        //                      return castExpr;
                        //              } else if ( diff < 0 ) {
                        //                      // conversion from reference to reference with less depth (e.g. int && -> int &): add dereferences
                        //                      Expression * ret = castExpr->arg;
                        //                      for ( int i = 0; i < diff; ++i ) {
                        //                              ret = mkDeref( ret );
                        //                      }
                        //                      ret->env = castExpr->env;
                        //                      delete ret->result;
                        //                      ret->result = castExpr->result;
                        //                      ret->result->set_lvalue( true ); // ensure result is lvalue
                        //                      castExpr->env = nullptr;
                        //                      castExpr->arg = nullptr;
                        //                      castExpr->result = nullptr;
                        //                      delete castExpr;
                        //                      return ret;
                        //              } else if ( diff > 0 ) {
                        //                      // conversion from reference to reference with more depth (e.g. int & -> int &&): add address-of
                        //                      Expression * ret = castExpr->arg;
                        //                      for ( int i = 0; i < diff; ++i ) {
                        //                              ret = new AddressExpr( ret );
                        //                      }
                        //                      ret->env = castExpr->env;
                        //                      delete ret->result;
                        //                      ret->result = castExpr->result;
                        //                      castExpr->env = nullptr;
                        //                      castExpr->arg = nullptr;
                        //                      castExpr->result = nullptr;
                        //                      delete castExpr;
                        //                      return ret;
                        //              }

                        //              assertf( depth1 == depth2, "non-intrinsic reference with cast of reference to reference not yet supported: %d %d %s", depth1, depth2, toString( castExpr ).c_str() );
                        //              PRINT( std::cerr << castExpr << std::endl; )
                        //              return castExpr;
                        //      } else if ( castExpr->arg->result->get_lvalue() ) {
                        //              // conversion from lvalue to reference
                        //              // xxx - keep cast, but turn into pointer cast??
                        //              // xxx - memory
                        //              PRINT(
                        //                      std::cerr << "convert lvalue to reference -- &" << std::endl;
                        //                      std::cerr << castExpr->arg << std::endl;
                        //              )
                        //              AddressExpr * ret = new AddressExpr( castExpr->arg );
                        //              if ( refType->base->get_qualifiers() != castExpr->arg->result->get_qualifiers() ) {
                        //                      // must keep cast if cast-to type is different from the actual type
                        //                      castExpr->arg = ret;
                        //                      return castExpr;
                        //              }
                        //              ret->env = castExpr->env;
                        //              delete ret->result;
                        //              ret->result = castExpr->result;
                        //              castExpr->env = nullptr;
                        //              castExpr->arg = nullptr;
                        //              castExpr->result = nullptr;
                        //              delete castExpr;
                        //              return ret;
                        //      } else {
                        //              // rvalue to reference conversion -- introduce temporary
                        //              // know that reference depth of cast argument is 0, need to introduce n temporaries for reference depth of n, e.g.
                        //              //   (int &&&)3;
                        //              // becomes
                        //              //   int __ref_tmp_0 = 3;
                        //              //   int & __ref_tmp_1 = _&_ref_tmp_0;
                        //              //   int && __ref_tmp_2 = &__ref_tmp_1;
                        //              //   &__ref_tmp_2;

                        //              static UniqueName tempNamer( "__ref_tmp_" );
                        //              ObjectDecl * temp = ObjectDecl::newObject( tempNamer.newName(), castExpr->arg->result->clone(), new SingleInit( castExpr->arg ) );
                        //              stmtsToAddBefore.push_back( new DeclStmt( temp ) );
                        //              auto depth = castExpr->result->referenceDepth();
                        //              for ( int i = 0; i < depth-1; i++ ) {
                        //                      ObjectDecl * newTemp = ObjectDecl::newObject( tempNamer.newName(), new ReferenceType( Type::Qualifiers(), temp->type->clone() ), new SingleInit( new AddressExpr( new VariableExpr( temp ) ) ) );
                        //                      stmtsToAddBefore.push_back( new DeclStmt( newTemp ) );
                        //                      temp = newTemp;
                        //              }
                        //              Expression * ret = new AddressExpr( new VariableExpr( temp ) );
                        //              // for ( int i = 0; i < depth; ++i ) {
                        //              //      ret = mkDeref( ret );
                        //              // }
                        //              ret->result = castExpr->result;
                        //              ret->result->set_lvalue( true ); // ensure result is lvalue
                        //              ret->env = castExpr->env;
                        //              castExpr->arg = nullptr;
                        //              castExpr->env = nullptr;
                        //              castExpr->result = nullptr;
                        //              delete castExpr;
                        //              return ret;
                        //      }
                        // } else if ( ReferenceType * refType = dynamic_cast< ReferenceType * >( castExpr->arg->result ) ) {
                        //      (void)refType;
                        //      // conversion from reference to rvalue
                        //      PRINT(
                        //              std::cerr << "convert reference to rvalue -- *" << std::endl;
                        //              std::cerr << "was = " << castExpr << std::endl;
                        //      )
                        //      Expression * ret = castExpr->arg;
                        //      TypeSubstitution * env = castExpr->env;
                        //      castExpr->set_env( nullptr );
                        //      if ( ! isIntrinsicReference( ret ) ) {
                        //              // dereference if not already dereferenced
                        //              ret = mkDeref( ret );
                        //      }
                        //      if ( ResolvExpr::typesCompatibleIgnoreQualifiers( castExpr->result, castExpr->arg->result->stripReferences(), SymTab::Indexer() ) ) {
                        //              // can remove cast if types are compatible, changing expression type to value type
                        //              ret->result = castExpr->result->clone();
                        //              ret->result->set_lvalue( true );  // ensure result is lvalue
                        //              castExpr->arg = nullptr;
                        //              delete castExpr;
                        //      } else {
                        //              // must keep cast if types are different
                        //              castExpr->arg = ret;
                        //              ret = castExpr;
                        //      }
                        //      ret->set_env( env );
                        //      PRINT( std::cerr << "now: " << ret << std::endl; )
                        //      return ret;
                        // }
                        // return castExpr;
                }

                Type * ReferenceTypeElimination::postmutate( ReferenceType * refType ) {
                        Type * base = refType->base;
                        Type::Qualifiers qualifiers = refType->get_qualifiers();
                        refType->base = nullptr;
                        delete refType;
                        return new PointerType( qualifiers, base );
                }

                template<typename Func>
                Expression * GeneralizedLvalue::applyTransformation( Expression * expr, Expression * arg, Func mkExpr ) {
                        if ( CommaExpr * commaExpr = dynamic_cast< CommaExpr * >( arg ) ) {
                                Expression * arg1 = commaExpr->arg1->clone();
                                Expression * arg2 = commaExpr->arg2->clone();
                                Expression * ret = new CommaExpr( arg1, mkExpr( arg2 )->acceptMutator( *visitor ) );
                                ret->env = expr->env;
                                expr->env = nullptr;
                                delete expr;
                                return ret;
                        } else if ( ConditionalExpr * condExpr = dynamic_cast< ConditionalExpr * >( arg ) ) {
                                Expression * arg1 = condExpr->arg1->clone();
                                Expression * arg2 = condExpr->arg2->clone();
                                Expression * arg3 = condExpr->arg3->clone();
                                ConditionalExpr * ret = new ConditionalExpr( arg1, mkExpr( arg2 )->acceptMutator( *visitor ), mkExpr( arg3 )->acceptMutator( *visitor ) );
                                ret->env = expr->env;
                                expr->env = nullptr;
                                delete expr;

                                // conditional expr type may not be either of the argument types, need to unify
                                using namespace ResolvExpr;
                                Type* commonType = nullptr;
                                TypeEnvironment newEnv;
                                AssertionSet needAssertions, haveAssertions;
                                OpenVarSet openVars;
                                unify( ret->arg2->result, ret->arg3->result, newEnv, needAssertions, haveAssertions, openVars, SymTab::Indexer(), commonType );
                                ret->result = commonType ? commonType : ret->arg2->result->clone();
                                return ret;
                        }
                        return expr;
                }

                Expression * GeneralizedLvalue::postmutate( MemberExpr * memExpr ) {
                        return applyTransformation( memExpr, memExpr->aggregate, [=]( Expression * aggr ) { return new MemberExpr( memExpr->member, aggr ); } );
                }

                Expression * GeneralizedLvalue::postmutate( AddressExpr * addrExpr ) {
                        return applyTransformation( addrExpr, addrExpr->arg, []( Expression * arg ) { return new AddressExpr( arg ); } );
                }

                Expression * CollapseAddrDeref::postmutate( AddressExpr * addrExpr ) {
                        Expression * arg = addrExpr->arg;
                        if ( isIntrinsicReference( arg ) ) {
                                std::string fname = InitTweak::getFunctionName( arg );
                                if ( fname == "*?" ) {
                                        Expression *& arg0 = InitTweak::getCallArg( arg, 0 );
                                        Expression * ret = arg0;
                                        ret->set_env( addrExpr->env );
                                        arg0 = nullptr;
                                        addrExpr->env = nullptr;
                                        delete addrExpr;
                                        return ret;
                                }
                        } else if ( CastExpr * castExpr = dynamic_cast< CastExpr * > ( arg ) ) {
                                // need to move cast to pointer type out a level since address of pointer
                                // is not valid C code (can be introduced in prior passes, e.g., InstantiateGeneric)
                                if ( InitTweak::getPointerBase( castExpr->result ) ) {
                                        addrExpr->arg = castExpr->arg;
                                        castExpr->arg = addrExpr;
                                        castExpr->result = new PointerType( Type::Qualifiers(), castExpr->result );
                                        return castExpr;
                                }
                        }
                        return addrExpr;
                }

                Expression * CollapseAddrDeref::postmutate( ApplicationExpr * appExpr ) {
                        if ( isIntrinsicReference( appExpr ) ) {
                                std::string fname = InitTweak::getFunctionName( appExpr );
                                if ( fname == "*?" ) {
                                        Expression * arg = InitTweak::getCallArg( appExpr, 0 );
                                        // xxx - this isn't right, because it can remove casts that should be there...
                                        // while ( CastExpr * castExpr = dynamic_cast< CastExpr * >( arg ) ) {
                                        //      arg = castExpr->get_arg();
                                        // }
                                        if ( AddressExpr * addrExpr = dynamic_cast< AddressExpr * >( arg ) ) {
                                                Expression * ret = addrExpr->arg;
                                                ret->env = appExpr->env;
                                                addrExpr->arg = nullptr;
                                                appExpr->env = nullptr;
                                                delete appExpr;
                                                return ret;
                                        }
                                }
                        }
                        return appExpr;
                }
        } // namespace
} // namespace GenPoly

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// mode: c++ //
// compile-command: "make install" //
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