source: src/InitTweak/InitTweak.cc @ 3648d98

#include <algorithm>               // for find, all_of
#include <cassert>                 // for assertf, assert, strict_dynamic_cast
#include <iostream>                // for ostream, cerr, endl
#include <iterator>                // for back_insert_iterator, back_inserter
#include <memory>                  // for __shared_ptr

#include "AST/Type.hpp"
#include "Common/PassVisitor.h"
#include "Common/SemanticError.h"  // for SemanticError
#include "Common/UniqueName.h"     // for UniqueName
#include "Common/utility.h"        // for toString, deleteAll, maybeClone
#include "GenPoly/GenPoly.h"       // for getFunctionType
#include "InitTweak.h"
#include "Parser/LinkageSpec.h"    // for Spec, isBuiltin, Intrinsic
#include "ResolvExpr/typeops.h"    // for typesCompatibleIgnoreQualifiers
#include "SymTab/Autogen.h"
#include "SymTab/Indexer.h"        // for Indexer
#include "SynTree/Attribute.h"     // for Attribute
#include "SynTree/Constant.h"      // for Constant
#include "SynTree/Declaration.h"   // for ObjectDecl, DeclarationWithType
#include "SynTree/Expression.h"    // for Expression, UntypedExpr, Applicati...
#include "SynTree/Initializer.h"   // for Initializer, ListInit, Designation
#include "SynTree/Label.h"         // for Label
#include "SynTree/Statement.h"     // for CompoundStmt, ExprStmt, BranchStmt
#include "SynTree/Type.h"          // for FunctionType, ArrayType, PointerType
#include "SynTree/Visitor.h"       // for Visitor, maybeAccept
#include "Tuples/Tuples.h"         // for Tuples::isTtype

class UntypedValofExpr;

namespace InitTweak {
        namespace {
                struct HasDesignations : public WithShortCircuiting {
                        bool hasDesignations = false;

                        void previsit( BaseSyntaxNode * ) {
                                // short circuit if we already know there are designations
                                if ( hasDesignations ) visit_children = false;
                        }

                        void previsit( Designation * des ) {
                                // short circuit if we already know there are designations
                                if ( hasDesignations ) visit_children = false;
                                else if ( ! des->get_designators().empty() ) {
                                        hasDesignations = true;
                                        visit_children = false;
                                }
                        }
                };

                struct InitDepthChecker : public WithGuards {
                        bool depthOkay = true;
                        Type * type;
                        int curDepth = 0, maxDepth = 0;
                        InitDepthChecker( Type * type ) : type( type ) {
                                Type * t = type;
                                while ( ArrayType * at = dynamic_cast< ArrayType * >( t ) ) {
                                        maxDepth++;
                                        t = at->get_base();
                                }
                                maxDepth++;
                        }
                        void previsit( ListInit * ) {
                                curDepth++;
                                GuardAction( [this]() { curDepth--; } );
                                if ( curDepth > maxDepth ) depthOkay = false;
                        }
                };

                struct InitFlattener : public WithShortCircuiting {
                        void previsit( SingleInit * singleInit ) {
                                visit_children = false;
                                argList.push_back( singleInit->value->clone() );
                        }
                        std::list< Expression * > argList;
                };

        }

        std::list< Expression * > makeInitList( Initializer * init ) {
                PassVisitor<InitFlattener> flattener;
                maybeAccept( init, flattener );
                return flattener.pass.argList;
        }

        bool isDesignated( Initializer * init ) {
                PassVisitor<HasDesignations> finder;
                maybeAccept( init, finder );
                return finder.pass.hasDesignations;
        }

        bool checkInitDepth( ObjectDecl * objDecl ) {
                PassVisitor<InitDepthChecker> checker( objDecl->type );
                maybeAccept( objDecl->init, checker );
                return checker.pass.depthOkay;
        }

        class InitExpander::ExpanderImpl {
        public:
                virtual ~ExpanderImpl() = default;
                virtual std::list< Expression * > next( std::list< Expression * > & indices ) = 0;
                virtual Statement * buildListInit( UntypedExpr * callExpr, std::list< Expression * > & indices ) = 0;
        };

        class InitImpl : public InitExpander::ExpanderImpl {
        public:
                InitImpl( Initializer * init ) : init( init ) {}
                virtual ~InitImpl() = default;

                virtual std::list< Expression * > next( __attribute((unused)) std::list< Expression * > & indices ) {
                        // this is wrong, but just a placeholder for now
                        // if ( ! flattened ) flatten( indices );
                        // return ! inits.empty() ? makeInitList( inits.front() ) : std::list< Expression * >();
                        return makeInitList( init );
                }

                virtual Statement * buildListInit( UntypedExpr * callExpr, std::list< Expression * > & indices );
        private:
                Initializer * init;
        };

        class ExprImpl : public InitExpander::ExpanderImpl {
        public:
                ExprImpl( Expression * expr ) : arg( expr ) {}
                virtual ~ExprImpl() { delete arg; }

                virtual std::list< Expression * > next( std::list< Expression * > & indices ) {
                        std::list< Expression * > ret;
                        Expression * expr = maybeClone( arg );
                        if ( expr ) {
                                for ( std::list< Expression * >::reverse_iterator it = indices.rbegin(); it != indices.rend(); ++it ) {
                                        // go through indices and layer on subscript exprs ?[?]
                                        ++it;
                                        UntypedExpr * subscriptExpr = new UntypedExpr( new NameExpr( "?[?]") );
                                        subscriptExpr->get_args().push_back( expr );
                                        subscriptExpr->get_args().push_back( (*it)->clone() );
                                        expr = subscriptExpr;
                                }
                                ret.push_back( expr );
                        }
                        return ret;
                }

                virtual Statement * buildListInit( UntypedExpr * callExpr, std::list< Expression * > & indices );
        private:
                Expression * arg;
        };

        InitExpander::InitExpander( Initializer * init ) : expander( new InitImpl( init ) ) {}

        InitExpander::InitExpander( Expression * expr ) : expander( new ExprImpl( expr ) ) {}

        std::list< Expression * > InitExpander::operator*() {
                return cur;
        }

        InitExpander & InitExpander::operator++() {
                cur = expander->next( indices );
                return *this;
        }

        // use array indices list to build switch statement
        void InitExpander::addArrayIndex( Expression * index, Expression * dimension ) {
                indices.push_back( index );
                indices.push_back( dimension );
        }

        void InitExpander::clearArrayIndices() {
                deleteAll( indices );
                indices.clear();
        }

        bool InitExpander::addReference() {
                bool added = false;
                for ( Expression *& expr : cur ) {
                        expr = new AddressExpr( expr );
                        added = true;
                }
                return added;
        }

        namespace {
                /// given index i, dimension d, initializer init, and callExpr f, generates
                ///   if (i < d) f(..., init)
                ///   ++i;
                /// so that only elements within the range of the array are constructed
                template< typename OutIterator >
                void buildCallExpr( UntypedExpr * callExpr, Expression * index, Expression * dimension, Initializer * init, OutIterator out ) {
                        UntypedExpr * cond = new UntypedExpr( new NameExpr( "?<?") );
                        cond->get_args().push_back( index->clone() );
                        cond->get_args().push_back( dimension->clone() );

                        std::list< Expression * > args = makeInitList( init );
                        callExpr->get_args().splice( callExpr->get_args().end(), args );

                        *out++ = new IfStmt( cond, new ExprStmt( callExpr ), nullptr );

                        UntypedExpr * increment = new UntypedExpr( new NameExpr( "++?" ) );
                        increment->get_args().push_back( index->clone() );
                        *out++ = new ExprStmt( increment );
                }

                template< typename OutIterator >
                void build( UntypedExpr * callExpr, InitExpander::IndexList::iterator idx, InitExpander::IndexList::iterator idxEnd, Initializer * init, OutIterator out ) {
                        if ( idx == idxEnd ) return;
                        Expression * index = *idx++;
                        assert( idx != idxEnd );
                        Expression * dimension = *idx++;

                        // xxx - may want to eventually issue a warning here if we can detect
                        // that the number of elements exceeds to dimension of the array
                        if ( idx == idxEnd ) {
                                if ( ListInit * listInit = dynamic_cast< ListInit * >( init ) ) {
                                        for ( Initializer * init : *listInit ) {
                                                buildCallExpr( callExpr->clone(), index, dimension, init, out );
                                        }
                                } else {
                                        buildCallExpr( callExpr->clone(), index, dimension, init, out );
                                }
                        } else {
                                std::list< Statement * > branches;

                                unsigned long cond = 0;
                                ListInit * listInit = dynamic_cast< ListInit * >( init );
                                if ( ! listInit ) {
                                        // xxx - this shouldn't be an error, but need a way to
                                        // terminate without creating output, so should catch this error
                                        SemanticError( init->location, "unbalanced list initializers" );
                                }

                                static UniqueName targetLabel( "L__autogen__" );
                                Label switchLabel( targetLabel.newName(), 0, std::list< Attribute * >{ new Attribute("unused") } );
                                for ( Initializer * init : *listInit ) {
                                        Expression * condition;
                                        // check for designations
                                        // if ( init-> ) {
                                                condition = new ConstantExpr( Constant::from_ulong( cond ) );
                                                ++cond;
                                        // } else {
                                        //      condition = // ... take designation
                                        //      cond = // ... take designation+1
                                        // }
                                        std::list< Statement * > stmts;
                                        build( callExpr, idx, idxEnd, init, back_inserter( stmts ) );
                                        stmts.push_back( new BranchStmt( switchLabel, BranchStmt::Break ) );
                                        CaseStmt * caseStmt = new CaseStmt( condition, stmts );
                                        branches.push_back( caseStmt );
                                }
                                *out++ = new SwitchStmt( index->clone(), branches );
                                *out++ = new NullStmt( { switchLabel } );
                        }
                }
        }

        // if array came with an initializer list: initialize each element
        // may have more initializers than elements in the array - need to check at each index that
        // we haven't exceeded size.
        // may have fewer initializers than elements in the array - need to default construct
        // remaining elements.
        // To accomplish this, generate switch statement, consuming all of expander's elements
        Statement * InitImpl::buildListInit( UntypedExpr * dst, std::list< Expression * > & indices ) {
                if ( ! init ) return nullptr;
                CompoundStmt * block = new CompoundStmt();
                build( dst, indices.begin(), indices.end(), init, back_inserter( block->get_kids() ) );
                if ( block->get_kids().empty() ) {
                        delete block;
                        return nullptr;
                } else {
                        init = nullptr; // init was consumed in creating the list init
                        return block;
                }
        }

        Statement * ExprImpl::buildListInit( UntypedExpr *, std::list< Expression * > & ) {
                return nullptr;
        }

        Statement * InitExpander::buildListInit( UntypedExpr * dst ) {
                return expander->buildListInit( dst, indices );
        }

        Type * getTypeofThis( FunctionType * ftype ) {
                assertf( ftype, "getTypeofThis: nullptr ftype" );
                ObjectDecl * thisParam = getParamThis( ftype );
                ReferenceType * refType = strict_dynamic_cast< ReferenceType * >( thisParam->type );
                return refType->base;
        }

        ObjectDecl * getParamThis( FunctionType * ftype ) {
                assertf( ftype, "getParamThis: nullptr ftype" );
                auto & params = ftype->parameters;
                assertf( ! params.empty(), "getParamThis: ftype with 0 parameters: %s", toString( ftype ).c_str() );
                return strict_dynamic_cast< ObjectDecl * >( params.front() );
        }

        bool tryConstruct( DeclarationWithType * dwt ) {
                ObjectDecl * objDecl = dynamic_cast< ObjectDecl * >( dwt );
                if ( ! objDecl ) return false;
                return (objDecl->get_init() == nullptr ||
                                ( objDecl->get_init() != nullptr && objDecl->get_init()->get_maybeConstructed() ))
                        && ! objDecl->get_storageClasses().is_extern
                        && isConstructable( objDecl->type );
        }

        bool isConstructable( Type * type ) {
                return ! dynamic_cast< VarArgsType * >( type ) && ! dynamic_cast< ReferenceType * >( type ) && ! dynamic_cast< FunctionType * >( type ) && ! Tuples::isTtype( type );
        }

        struct CallFinder {
                CallFinder( const std::list< std::string > & names ) : names( names ) {}

                void postvisit( ApplicationExpr * appExpr ) {
                        handleCallExpr( appExpr );
                }

                void postvisit( UntypedExpr * untypedExpr ) {
                        handleCallExpr( untypedExpr );
                }

                std::list< Expression * > * matches;
        private:
                const std::list< std::string > names;

                template< typename CallExpr >
                void handleCallExpr( CallExpr * expr ) {
                        std::string fname = getFunctionName( expr );
                        if ( std::find( names.begin(), names.end(), fname ) != names.end() ) {
                                matches->push_back( expr );
                        }
                }
        };

        void collectCtorDtorCalls( Statement * stmt, std::list< Expression * > & matches ) {
                static PassVisitor<CallFinder> finder( std::list< std::string >{ "?{}", "^?{}" } );
                finder.pass.matches = &matches;
                maybeAccept( stmt, finder );
        }

        Expression * getCtorDtorCall( Statement * stmt ) {
                std::list< Expression * > matches;
                collectCtorDtorCalls( stmt, matches );
                assert( matches.size() <= 1 );
                return matches.size() == 1 ? matches.front() : nullptr;
        }

        namespace {
                DeclarationWithType * getCalledFunction( Expression * expr );

                template<typename CallExpr>
                DeclarationWithType * handleDerefCalledFunction( CallExpr * expr ) {
                        // (*f)(x) => should get "f"
                        std::string name = getFunctionName( expr );
                        assertf( name == "*?", "Unexpected untyped expression: %s", name.c_str() );
                        assertf( ! expr->get_args().empty(), "Cannot get called function from dereference with no arguments" );
                        return getCalledFunction( expr->get_args().front() );
                }

                DeclarationWithType * getCalledFunction( Expression * expr ) {
                        assert( expr );
                        if ( VariableExpr * varExpr = dynamic_cast< VariableExpr * >( expr ) ) {
                                return varExpr->var;
                        } else if ( MemberExpr * memberExpr = dynamic_cast< MemberExpr * >( expr ) ) {
                                return memberExpr->member;
                        } else if ( CastExpr * castExpr = dynamic_cast< CastExpr * >( expr ) ) {
                                return getCalledFunction( castExpr->arg );
                        } else if ( UntypedExpr * untypedExpr = dynamic_cast< UntypedExpr * >( expr ) ) {
                                return handleDerefCalledFunction( untypedExpr );
                        } else if ( ApplicationExpr * appExpr = dynamic_cast< ApplicationExpr * > ( expr ) ) {
                                return handleDerefCalledFunction( appExpr );
                        } else if ( AddressExpr * addrExpr = dynamic_cast< AddressExpr * >( expr ) ) {
                                return getCalledFunction( addrExpr->arg );
                        } else if ( CommaExpr * commaExpr = dynamic_cast< CommaExpr * >( expr ) ) {
                                return getCalledFunction( commaExpr->arg2 );
                        }
                        return nullptr;
                }
        }

        DeclarationWithType * getFunction( Expression * expr ) {
                if ( ApplicationExpr * appExpr = dynamic_cast< ApplicationExpr * >( expr ) ) {
                        return getCalledFunction( appExpr->get_function() );
                } else if ( UntypedExpr * untyped = dynamic_cast< UntypedExpr * > ( expr ) ) {
                        return getCalledFunction( untyped->get_function() );
                }
                assertf( false, "getFunction received unknown expression: %s", toString( expr ).c_str() );
        }

        ApplicationExpr * isIntrinsicCallExpr( Expression * expr ) {
                ApplicationExpr * appExpr = dynamic_cast< ApplicationExpr * >( expr );
                if ( ! appExpr ) return nullptr;
                DeclarationWithType * function = getCalledFunction( appExpr->get_function() );
                assertf( function, "getCalledFunction returned nullptr: %s", toString( appExpr->get_function() ).c_str() );
                // check for Intrinsic only - don't want to remove all overridable ctor/dtors because autogenerated ctor/dtor
                // will call all member dtors, and some members may have a user defined dtor.
                return function->get_linkage() == LinkageSpec::Intrinsic ? appExpr : nullptr;
        }

        namespace {
                template <typename Predicate>
                bool allofCtorDtor( Statement * stmt, const Predicate & pred ) {
                        std::list< Expression * > callExprs;
                        collectCtorDtorCalls( stmt, callExprs );
                        // if ( callExprs.empty() ) return false; // xxx - do I still need this check?
                        return std::all_of( callExprs.begin(), callExprs.end(), pred);
                }
        }

        bool isIntrinsicSingleArgCallStmt( Statement * stmt ) {
                return allofCtorDtor( stmt, []( Expression * callExpr ){
                        if ( ApplicationExpr * appExpr = isIntrinsicCallExpr( callExpr ) ) {
                                FunctionType *funcType = GenPoly::getFunctionType( appExpr->function->result );
                                assert( funcType );
                                return funcType->get_parameters().size() == 1;
                        }
                        return false;
                });
        }

        bool isIntrinsicCallStmt( Statement * stmt ) {
                return allofCtorDtor( stmt, []( Expression * callExpr ) {
                        return isIntrinsicCallExpr( callExpr );
                });
        }

        namespace {
                template<typename CallExpr>
                Expression *& callArg( CallExpr * callExpr, unsigned int pos ) {
                        if ( pos >= callExpr->get_args().size() ) assertf( false, "getCallArg for argument that doesn't exist: (%u); %s.", pos, toString( callExpr ).c_str() );
                        for ( Expression *& arg : callExpr->get_args() ) {
                                if ( pos == 0 ) return arg;
                                pos--;
                        }
                        assert( false );
                }
        }

        Expression *& getCallArg( Expression * callExpr, unsigned int pos ) {
                if ( ApplicationExpr * appExpr = dynamic_cast< ApplicationExpr * >( callExpr ) ) {
                        return callArg( appExpr, pos );
                } else if ( UntypedExpr * untypedExpr = dynamic_cast< UntypedExpr * >( callExpr ) ) {
                        return callArg( untypedExpr, pos );
                } else if ( TupleAssignExpr * tupleExpr = dynamic_cast< TupleAssignExpr * > ( callExpr ) ) {
                        std::list< Statement * > & stmts = tupleExpr->get_stmtExpr()->get_statements()->get_kids();
                        assertf( ! stmts.empty(), "TupleAssignExpr somehow has no statements." );
                        ExprStmt * stmt = strict_dynamic_cast< ExprStmt * >( stmts.back() );
                        TupleExpr * tuple = strict_dynamic_cast< TupleExpr * >( stmt->get_expr() );
                        assertf( ! tuple->get_exprs().empty(), "TupleAssignExpr somehow has empty tuple expr." );
                        return getCallArg( tuple->get_exprs().front(), pos );
                } else if ( ImplicitCopyCtorExpr * copyCtor = dynamic_cast< ImplicitCopyCtorExpr * >( callExpr ) ) {
                        return getCallArg( copyCtor->callExpr, pos );
                } else {
                        assertf( false, "Unexpected expression type passed to getCallArg: %s", toString( callExpr ).c_str() );
                }
        }

        namespace {
                std::string funcName( Expression * func );

                template<typename CallExpr>
                std::string handleDerefName( CallExpr * expr ) {
                        // (*f)(x) => should get name "f"
                        std::string name = getFunctionName( expr );
                        assertf( name == "*?", "Unexpected untyped expression: %s", name.c_str() );
                        assertf( ! expr->get_args().empty(), "Cannot get function name from dereference with no arguments" );
                        return funcName( expr->get_args().front() );
                }

                std::string funcName( Expression * func ) {
                        if ( NameExpr * nameExpr = dynamic_cast< NameExpr * >( func ) ) {
                                return nameExpr->get_name();
                        } else if ( VariableExpr * varExpr = dynamic_cast< VariableExpr * >( func ) ) {
                                return varExpr->get_var()->get_name();
                        }       else if ( CastExpr * castExpr = dynamic_cast< CastExpr * >( func ) ) {
                                return funcName( castExpr->get_arg() );
                        } else if ( MemberExpr * memberExpr = dynamic_cast< MemberExpr * >( func ) ) {
                                return memberExpr->get_member()->get_name();
                        } else if ( UntypedMemberExpr * memberExpr = dynamic_cast< UntypedMemberExpr * > ( func ) ) {
                                return funcName( memberExpr->get_member() );
                        } else if ( UntypedExpr * untypedExpr = dynamic_cast< UntypedExpr * >( func ) ) {
                                return handleDerefName( untypedExpr );
                        } else if ( ApplicationExpr * appExpr = dynamic_cast< ApplicationExpr * >( func ) ) {
                                return handleDerefName( appExpr );
                        } else if ( ConstructorExpr * ctorExpr = dynamic_cast< ConstructorExpr * >( func ) ) {
                                return funcName( getCallArg( ctorExpr->get_callExpr(), 0 ) );
                        } else {
                                assertf( false, "Unexpected expression type being called as a function in call expression: %s", toString( func ).c_str() );
                        }
                }
        }

        std::string getFunctionName( Expression * expr ) {
                // there's some unforunate overlap here with getCalledFunction. Ideally this would be able to use getCalledFunction and
                // return the name of the DeclarationWithType, but this needs to work for NameExpr and UntypedMemberExpr, where getCalledFunction
                // can't possibly do anything reasonable.
                if ( ApplicationExpr * appExpr = dynamic_cast< ApplicationExpr * >( expr ) ) {
                        return funcName( appExpr->get_function() );
                } else if ( UntypedExpr * untypedExpr = dynamic_cast< UntypedExpr * > ( expr ) ) {
                        return funcName( untypedExpr->get_function() );
                } else {
                        std::cerr << expr << std::endl;
                        assertf( false, "Unexpected expression type passed to getFunctionName" );
                }
        }

        Type * getPointerBase( Type * type ) {
                if ( PointerType * ptrType = dynamic_cast< PointerType * >( type ) ) {
                        return ptrType->get_base();
                } else if ( ArrayType * arrayType = dynamic_cast< ArrayType * >( type ) ) {
                        return arrayType->get_base();
                } else if ( ReferenceType * refType = dynamic_cast< ReferenceType * >( type ) ) {
                        return refType->get_base();
                } else {
                        return nullptr;
                }
        }
        const ast::Type* getPointerBase( const ast::Type* t ) {
                assert(!"needs to build Type.cpp before inclusion");
                // if ( const ast::PointerType* p = dynamic_cast< const ast::PointerType* >( t ) ) {
                //      return p->base;
                // } else if ( const ast::ArrayType* a = dynamic_cast< const ast::ArrayType* >( t ) ) {
                //      return a->base;
                // } else if ( const ast::ReferenceType* r = dynamic_cast< const ast::ReferenceType* >( t ) ) {
                //      return r->base;
                // } else return nullptr;
        }

        Type * isPointerType( Type * type ) {
                if ( getPointerBase( type ) ) return type;
                else return nullptr;
        }

        ApplicationExpr * createBitwiseAssignment( Expression * dst, Expression * src ) {
                static FunctionDecl * assign = nullptr;
                if ( ! assign ) {
                        // temporary? Generate a fake assignment operator to represent bitwise assignments.
                        // This operator could easily exist as a real function, but it's tricky because nothing should resolve to this function.
                        TypeDecl * td = new TypeDecl( "T", noStorageClasses, nullptr, TypeDecl::Dtype, true );
                        assign = new FunctionDecl( "?=?", noStorageClasses, LinkageSpec::Intrinsic, SymTab::genAssignType( new TypeInstType( noQualifiers, td->name, td ) ), nullptr );
                }
                if ( dynamic_cast< ReferenceType * >( dst->result ) ) {
                        for (int depth = dst->result->referenceDepth(); depth > 0; depth--) {
                                dst = new AddressExpr( dst );
                        }
                } else {
                        dst = new CastExpr( dst, new ReferenceType( noQualifiers, dst->result->clone() ) );
                }
                if ( dynamic_cast< ReferenceType * >( src->result ) ) {
                        for (int depth = src->result->referenceDepth(); depth > 0; depth--) {
                                src = new AddressExpr( src );
                        }
                        // src = new CastExpr( src, new ReferenceType( noQualifiers, src->result->stripReferences()->clone() ) );
                }
                return new ApplicationExpr( VariableExpr::functionPointer( assign ), { dst, src } );
        }

        struct ConstExprChecker : public WithShortCircuiting {
                // most expressions are not const expr
                void previsit( Expression * ) { isConstExpr = false; visit_children = false; }

                void previsit( AddressExpr *addressExpr ) {
                        visit_children = false;

                        // address of a variable or member expression is constexpr
                        Expression * arg = addressExpr->get_arg();
                        if ( ! dynamic_cast< NameExpr * >( arg) && ! dynamic_cast< VariableExpr * >( arg ) && ! dynamic_cast< MemberExpr * >( arg ) && ! dynamic_cast< UntypedMemberExpr * >( arg ) ) isConstExpr = false;
                }

                // these expressions may be const expr, depending on their children
                void previsit( SizeofExpr * ) {}
                void previsit( AlignofExpr * ) {}
                void previsit( UntypedOffsetofExpr * ) {}
                void previsit( OffsetofExpr * ) {}
                void previsit( OffsetPackExpr * ) {}
                void previsit( AttrExpr * ) {}
                void previsit( CommaExpr * ) {}
                void previsit( LogicalExpr * ) {}
                void previsit( ConditionalExpr * ) {}
                void previsit( CastExpr * ) {}
                void previsit( ConstantExpr * ) {}

                void previsit( VariableExpr * varExpr ) {
                        visit_children = false;

                        if ( EnumInstType * inst = dynamic_cast< EnumInstType * >( varExpr->result ) ) {
                                long long int value;
                                if ( inst->baseEnum->valueOf( varExpr->var, value ) ) {
                                        // enumerators are const expr
                                        return;
                                }
                        }
                        isConstExpr = false;
                }

                bool isConstExpr = true;
        };

        bool isConstExpr( Expression * expr ) {
                if ( expr ) {
                        PassVisitor<ConstExprChecker> checker;
                        expr->accept( checker );
                        return checker.pass.isConstExpr;
                }
                return true;
        }

        bool isConstExpr( Initializer * init ) {
                if ( init ) {
                        PassVisitor<ConstExprChecker> checker;
                        init->accept( checker );
                        return checker.pass.isConstExpr;
                } // if
                // for all intents and purposes, no initializer means const expr
                return true;
        }

        bool isConstructor( const std::string & str ) { return str == "?{}"; }
        bool isDestructor( const std::string & str ) { return str == "^?{}"; }
        bool isAssignment( const std::string & str ) { return str == "?=?"; }
        bool isCtorDtor( const std::string & str ) { return isConstructor( str ) || isDestructor( str ); }
        bool isCtorDtorAssign( const std::string & str ) { return isCtorDtor( str ) || isAssignment( str ); }

        FunctionDecl * isCopyFunction( Declaration * decl, const std::string & fname ) {
                FunctionDecl * function = dynamic_cast< FunctionDecl * >( decl );
                if ( ! function ) return nullptr;
                if ( function->name != fname ) return nullptr;
                FunctionType * ftype = function->type;
                if ( ftype->parameters.size() != 2 ) return nullptr;

                Type * t1 = getPointerBase( ftype->get_parameters().front()->get_type() );
                Type * t2 = ftype->parameters.back()->get_type();
                assert( t1 );

                if ( ResolvExpr::typesCompatibleIgnoreQualifiers( t1, t2, SymTab::Indexer() ) ) {
                        return function;
                } else {
                        return nullptr;
                }
        }

        FunctionDecl * isAssignment( Declaration * decl ) {
                return isCopyFunction( decl, "?=?" );
        }
        FunctionDecl * isDestructor( Declaration * decl ) {
                if ( isDestructor( decl->get_name() ) ) {
                        return dynamic_cast< FunctionDecl * >( decl );
                }
                return nullptr;
        }
        FunctionDecl * isDefaultConstructor( Declaration * decl ) {
                if ( isConstructor( decl->name ) ) {
                        if ( FunctionDecl * func = dynamic_cast< FunctionDecl * >( decl ) ) {
                                if ( func->type->parameters.size() == 1 ) {
                                        return func;
                                }
                        }
                }
                return nullptr;
        }
        FunctionDecl * isCopyConstructor( Declaration * decl ) {
                return isCopyFunction( decl, "?{}" );
        }
}