#include "FixInit.h"

#include <stddef.h>                    // for NULL
#include <algorithm>                   // for set_difference, copy_if
#include <cassert>                     // for assert, strict_dynamic_cast
#include <iostream>                    // for operator<<, ostream, basic_ost...
#include <iterator>                    // for insert_iterator, back_inserter
#include <list>                        // for _List_iterator, list, list<>::...
#include <map>                         // for _Rb_tree_iterator, _Rb_tree_co...
#include <memory>                      // for allocator_traits<>::value_type
#include <set>                         // for set, set<>::value_type
#include <unordered_map>               // for unordered_map, unordered_map<>...
#include <unordered_set>               // for unordered_set
#include <utility>                     // for pair

#include "AST/DeclReplacer.hpp"
#include "AST/Expr.hpp"
#include "AST/Inspect.hpp"             // for getFunction, getPointerBase, g...
#include "AST/Node.hpp"
#include "AST/Pass.hpp"
#include "AST/Print.hpp"
#include "AST/SymbolTable.hpp"
#include "AST/Type.hpp"
#include "CodeGen/OperatorTable.h"     // for isConstructor, isCtorDtor, isD...
#include "Common/SemanticError.h"      // for SemanticError
#include "Common/ToString.hpp"         // for toCString
#include "Common/UniqueName.h"         // for UniqueName
#include "FixGlobalInit.h"             // for fixGlobalInit
#include "GenInit.h"                   // for genCtorDtor
#include "GenPoly/GenPoly.h"           // for getFunctionType
#include "ResolvExpr/Resolver.h"       // for findVoidExpression
#include "ResolvExpr/Unify.h"          // for typesCompatible
#include "SymTab/GenImplicitCall.hpp"  // for genImplicitCall

extern bool ctordtorp; // print all debug
extern bool ctorp; // print ctor debug
extern bool cpctorp; // print copy ctor debug
extern bool dtorp; // print dtor debug
#define PRINT( text ) if ( ctordtorp ) { text }
#define CP_CTOR_PRINT( text ) if ( ctordtorp || cpctorp ) { text }
#define DTOR_PRINT( text ) if ( ctordtorp || dtorp ) { text }

namespace InitTweak {

namespace {

// Shallow copy the pointer list for return.
std::vector<ast::ptr<ast::TypeDecl>> getGenericParams( const ast::Type * t ) {
	if ( auto inst = dynamic_cast<const ast::StructInstType *>( t ) ) {
		return inst->base->params;
	}
	if ( auto inst = dynamic_cast<const ast::UnionInstType *>( t ) ) {
		return inst->base->params;
	}
	return {};
}

/// Given type T, generate type of default ctor/dtor, i.e. function type void (*) (T &).
ast::FunctionDecl * genDefaultFunc(
		const CodeLocation loc,
		const std::string fname,
		const ast::Type * paramType,
		bool maybePolymorphic = true) {
	std::vector<ast::ptr<ast::TypeDecl>> typeParams;
	if ( maybePolymorphic ) typeParams = getGenericParams( paramType );
	auto dstParam = new ast::ObjectDecl( loc,
		"_dst",
		new ast::ReferenceType( paramType ),
		nullptr,
		{},
		ast::Linkage::Cforall
	);
	return new ast::FunctionDecl( loc,
		fname,
		std::move(typeParams),
		{dstParam},
		{},
		new ast::CompoundStmt(loc),
		{},
		ast::Linkage::Cforall
	);
}

struct SelfAssignChecker {
	void previsit( const ast::ApplicationExpr * appExpr );
};

struct StmtExprResult {
	const ast::StmtExpr * previsit( const ast::StmtExpr * stmtExpr );
};

/// wrap function application expressions as ImplicitCopyCtorExpr nodes so that it is easy to identify which
/// function calls need their parameters to be copy constructed
struct InsertImplicitCalls : public ast::WithShortCircuiting {
	const ast::Expr * postvisit( const ast::ApplicationExpr * appExpr );

	// only handles each UniqueExpr once
	// if order of visit does not change, this should be safe
	void previsit (const ast::UniqueExpr *);

	std::unordered_set<decltype(ast::UniqueExpr::id)> visitedIds;
};

/// generate temporary ObjectDecls for each argument and return value of each ImplicitCopyCtorExpr,
/// generate/resolve copy construction expressions for each, and generate/resolve destructors for both
/// arguments and return value temporaries
struct ResolveCopyCtors final : public ast::WithGuards, public ast::WithStmtsToAdd<>, public ast::WithSymbolTable, public ast::WithShortCircuiting, public ast::WithVisitorRef<ResolveCopyCtors>, public ast::WithConstTranslationUnit {
	const ast::Expr * postvisit( const ast::ImplicitCopyCtorExpr * impCpCtorExpr );
	const ast::StmtExpr * previsit( const ast::StmtExpr * stmtExpr );
	const ast::UniqueExpr * previsit( const ast::UniqueExpr * unqExpr );

	/// handles distant mutations of environment manually.
	/// WithConstTypeSubstitution cannot remember where the environment is from

	/// MUST be called at start of overload previsit
	void previsit( const ast::Expr * expr);
	/// MUST be called at return of overload postvisit
	const ast::Expr * postvisit(const ast::Expr * expr);

	/// create and resolve ctor/dtor expression: fname(var, [cpArg])
	const ast::Expr * makeCtorDtor( const std::string & fname, const ast::ObjectDecl * var, const ast::Expr * cpArg = nullptr );
	/// true if type does not need to be copy constructed to ensure correctness
	bool skipCopyConstruct( const ast::Type * type );
	ast::ptr< ast::Expr > copyConstructArg( const ast::Expr * arg, const ast::ImplicitCopyCtorExpr * impCpCtorExpr, const ast::Type * formal );
	ast::Expr * destructRet( const ast::ObjectDecl * ret, const ast::Expr * arg );
private:
	/// hack to implement WithTypeSubstitution while conforming to mutation safety.
	ast::TypeSubstitution * env         = nullptr;
	bool                    envModified = false;
};

/// collects constructed object decls - used as a base class
struct ObjDeclCollector : public ast::WithGuards, public ast::WithShortCircuiting {
	// use ordered data structure to maintain ordering for set_difference and for consistent error messages
	typedef std::list< const ast::ObjectDecl * > ObjectSet;
	void previsit( const ast::CompoundStmt *compoundStmt );
	void previsit( const ast::DeclStmt *stmt );

	// don't go into other functions
	void previsit( const ast::FunctionDecl * ) { visit_children = false; }

protected:
	ObjectSet curVars;
};

// debug
template<typename ObjectSet>
struct PrintSet {
	PrintSet( const ObjectSet & objs ) : objs( objs ) {}
	const ObjectSet & objs;
};
template<typename ObjectSet>
PrintSet<ObjectSet> printSet( const ObjectSet & objs ) { return PrintSet<ObjectSet>( objs ); }
template<typename ObjectSet>
std::ostream & operator<<( std::ostream & out, const PrintSet<ObjectSet> & set) {
	out << "{ ";
	for ( auto & obj : set.objs ) {
		out << obj->name << ", " ;
	} // for
	out << " }";
	return out;
}

struct LabelFinder final : public ObjDeclCollector {
	typedef std::map< std::string, ObjectSet > LabelMap;
	// map of Label -> live variables at that label
	LabelMap vars;

	typedef ObjDeclCollector Parent;
	using Parent::previsit;
	void previsit( const ast::Stmt * stmt );

	void previsit( const ast::CompoundStmt *compoundStmt );
	void previsit( const ast::DeclStmt *stmt );
};

/// insert destructor calls at the appropriate places.  must happen before CtorInit nodes are removed
/// (currently by FixInit)
struct InsertDtors final : public ObjDeclCollector, public ast::WithStmtsToAdd<> {
	typedef std::list< ObjectDecl * > OrderedDecls;
	typedef std::list< OrderedDecls > OrderedDeclsStack;

	InsertDtors( ast::Pass<LabelFinder> & finder ) : finder( finder ), labelVars( finder.core.vars ) {}

	typedef ObjDeclCollector Parent;
	using Parent::previsit;

	void previsit( const ast::FunctionDecl * funcDecl );

	void previsit( const ast::BranchStmt * stmt );
private:
	void handleGoto( const ast::BranchStmt * stmt );

	ast::Pass<LabelFinder> & finder;
	LabelFinder::LabelMap & labelVars;
	OrderedDeclsStack reverseDeclOrder;
};

/// expand each object declaration to use its constructor after it is declared.
struct FixInit : public ast::WithStmtsToAdd<> {
	static void fixInitializers( ast::TranslationUnit &translationUnit );

	const ast::DeclWithType * postvisit( const ast::ObjectDecl *objDecl );

	std::list< ast::ptr< ast::Decl > > staticDtorDecls;
};

/// generate default/copy ctor and dtor calls for user-defined struct ctor/dtors
/// for any member that is missing a corresponding ctor/dtor call.
/// error if a member is used before constructed
struct GenStructMemberCalls final : public ast::WithGuards, public ast::WithShortCircuiting, public ast::WithSymbolTable, public ast::WithVisitorRef<GenStructMemberCalls>, public ast::WithConstTranslationUnit {
	void previsit( const ast::FunctionDecl * funcDecl );
	const ast::DeclWithType * postvisit( const ast::FunctionDecl * funcDecl );

	void previsit( const ast::MemberExpr * memberExpr );
	void previsit( const ast::ApplicationExpr * appExpr );

	/// Note: this post mutate used to be in a separate visitor. If this pass breaks, one place to examine is whether it is
	/// okay for this part of the recursion to occur alongside the rest.
	const ast::Expr * postvisit( const ast::UntypedExpr * expr );

	SemanticErrorException errors;
private:
	template< typename... Params >
	void emit( CodeLocation, const Params &... params );

	ast::FunctionDecl * function = nullptr;
	std::set< const ast::DeclWithType * > unhandled;
	std::map< const ast::DeclWithType *, CodeLocation > usedUninit;
	const ast::ObjectDecl * thisParam = nullptr;
	bool isCtor = false; // true if current function is a constructor
	const ast::StructDecl * structDecl = nullptr;
};

/// expands ConstructorExpr nodes into comma expressions, using a temporary for the first argument
struct FixCtorExprs final : public ast::WithDeclsToAdd<>, public ast::WithSymbolTable, public ast::WithShortCircuiting, public ast::WithConstTranslationUnit {
	const ast::Expr * postvisit( const ast::ConstructorExpr * ctorExpr );
};

/// add CompoundStmts around top-level expressions so that temporaries are destroyed in the correct places.
struct SplitExpressions : public ast::WithShortCircuiting {
	ast::Stmt * postvisit( const ast::ExprStmt * stmt );
	void previsit( const ast::TupleAssignExpr * expr );
};

/// find and return the destructor used in `input`. If `input` is not a simple destructor call, generate a thunk
/// that wraps the destructor, insert it into `stmtsToAdd` and return the new function declaration
const ast::DeclWithType * getDtorFunc( const ast::ObjectDecl * objDecl, const ast::Stmt * input, std::list< ast::ptr<ast::Stmt> > & stmtsToAdd ) {
	const CodeLocation loc = input->location;
	// unwrap implicit statement wrapper
	// Statement * dtor = input;
	assert( input );
	// std::list< const ast::Expr * > matches;
	auto matches = collectCtorDtorCalls( input );

	if ( dynamic_cast< const ast::ExprStmt * >( input ) ) {
		// only one destructor call in the expression
		if ( matches.size() == 1 ) {
			auto func = getFunction( matches.front() );
			assertf( func, "getFunction failed to find function in %s", toString( matches.front() ).c_str() );

			// cleanup argument must be a function, not an object (including function pointer)
			if ( auto dtorFunc = dynamic_cast< const ast::FunctionDecl * > ( func ) ) {
				if ( dtorFunc->type->forall.empty() ) {
					// simple case where the destructor is a monomorphic function call - can simply
					// use that function as the cleanup function.
					return func;
				}
			}
		}
	}

	// otherwise the cleanup is more complicated - need to build a single argument cleanup function that
	// wraps the more complicated code.
	static UniqueName dtorNamer( "__cleanup_dtor" );
	std::string name = dtorNamer.newName();
	ast::FunctionDecl * dtorFunc = genDefaultFunc( loc, name, objDecl->type->stripReferences(), false );
	stmtsToAdd.push_back( new ast::DeclStmt(loc, dtorFunc ) );

	// the original code contains uses of objDecl - replace them with the newly generated 'this' parameter.
	const ast::ObjectDecl * thisParam = getParamThis( dtorFunc );
	const ast::Expr * replacement = new ast::VariableExpr( loc, thisParam );

	auto base = replacement->result->stripReferences();
	if ( dynamic_cast< const ast::ArrayType * >( base ) || dynamic_cast< const ast::TupleType * > ( base ) ) {
		// need to cast away reference for array types, since the destructor is generated without the reference type,
		// and for tuple types since tuple indexing does not work directly on a reference
		replacement = new ast::CastExpr( replacement, base );
	}
	auto dtor = ast::DeclReplacer::replace( input, ast::DeclReplacer::ExprMap{ std::make_pair( objDecl, replacement ) } );
	auto mutStmts = dtorFunc->stmts.get_and_mutate();
	mutStmts->push_back(strict_dynamic_cast<const ast::Stmt *>( dtor ));
	dtorFunc->stmts = mutStmts;

	return dtorFunc;
}

void FixInit::fixInitializers( ast::TranslationUnit & translationUnit ) {
	ast::Pass<FixInit> fixer;

	// can't use mutateAll, because need to insert declarations at top-level
	// can't use DeclMutator, because sometimes need to insert IfStmt, etc.
	SemanticErrorException errors;
	for ( auto i = translationUnit.decls.begin(); i != translationUnit.decls.end(); ++i ) {
		try {
			// maybeAccept( *i, fixer ); translationUnit should never contain null
			*i = (*i)->accept(fixer);
			translationUnit.decls.splice( i, fixer.core.staticDtorDecls );
		} catch( SemanticErrorException &e ) {
			errors.append( e );
		} // try
	} // for
	if ( ! errors.isEmpty() ) {
		throw errors;
	} // if
}

const ast::StmtExpr * StmtExprResult::previsit( const ast::StmtExpr * stmtExpr ) {
	// we might loose the result expression here so add a pointer to trace back
	assert( stmtExpr->result );
	const ast::Type * result = stmtExpr->result;
	if ( ! result->isVoid() ) {
		auto mutExpr = mutate(stmtExpr);
		const ast::CompoundStmt * body = mutExpr->stmts;
		assert( ! body->kids.empty() );
		mutExpr->resultExpr = body->kids.back().strict_as<ast::ExprStmt>();
		return mutExpr;
	}
	return stmtExpr;
}

ast::Stmt * SplitExpressions::postvisit( const ast::ExprStmt * stmt ) {
	// wrap each top-level ExprStmt in a block so that destructors for argument and return temporaries are destroyed
	// in the correct places
	ast::CompoundStmt * ret = new ast::CompoundStmt( stmt->location, { stmt } );
	return ret;
}

void SplitExpressions::previsit( const ast::TupleAssignExpr * ) {
	// don't do this within TupleAssignExpr, since it is already broken up into multiple expressions
	visit_children = false;
}

// Relatively simple structural comparison for expressions, needed to determine
// if two expressions are "the same" (used to determine if self assignment occurs)
struct StructuralChecker {
	// Strip all casts and then dynamic_cast.
	template<typename T>
	static const T * cast( const ast::Expr * expr ) {
		// this might be too permissive. It's possible that only particular casts are relevant.
		while ( auto cast = dynamic_cast< const ast::CastExpr * >( expr ) ) {
			expr = cast->arg;
		}
		return dynamic_cast< const T * >( expr );
	}

	void previsit( const ast::Expr * ) {
		// anything else does not qualify
		result = false;
	}

	// ignore casts
	void previsit( const ast::CastExpr * ) {}

	void previsit( const ast::MemberExpr * memExpr ) {
		if ( auto otherMember = cast< ast::MemberExpr >( other ) ) {
			if ( otherMember->member == memExpr->member ) {
				other = otherMember->aggregate;
				return;
			}
		}
		result = false;
	}

	void previsit( const ast::VariableExpr * varExpr ) {
		if ( auto otherVar = cast< ast::VariableExpr >( other ) ) {
			if ( otherVar->var == varExpr->var ) {
				return;
			}
		}
		result = false;
	}

	void previsit( const ast::AddressExpr * ) {
		if ( auto addrExpr = cast< ast::AddressExpr >( other ) ) {
			other = addrExpr->arg;
			return;
		}
		result = false;
	}

	const ast::Expr * other;
	bool result = true;
	StructuralChecker( const ast::Expr * other ) : other(other) {}
};

bool structurallySimilar( const ast::Expr * e1, const ast::Expr * e2 ) {
	return ast::Pass<StructuralChecker>::read( e1, e2 );
}

void SelfAssignChecker::previsit( const ast::ApplicationExpr * appExpr ) {
	auto function = getFunction( appExpr );
	// Doesn't use isAssignment, because ?+=?, etc. should not count as self-assignment.
	if ( function->name == "?=?" && appExpr->args.size() == 2
			// Check for structural similarity (same variable use, ignore casts, etc.
			// (but does not look too deeply, anything looking like a function is off limits).
			&& structurallySimilar( appExpr->args.front(), appExpr->args.back() ) ) {
		SemanticWarning( appExpr->location, Warning::SelfAssignment, toCString( appExpr->args.front() ) );
	}
}

const ast::Expr * InsertImplicitCalls::postvisit( const ast::ApplicationExpr * appExpr ) {
	if ( auto function = appExpr->func.as<ast::VariableExpr>() ) {
		if ( function->var->linkage.is_builtin ) {
			// optimization: don't need to copy construct in order to call intrinsic functions
			return appExpr;
		} else if ( auto funcDecl = function->var.as<ast::DeclWithType>() ) {
			auto ftype = dynamic_cast< const ast::FunctionType * >( GenPoly::getFunctionType( funcDecl->get_type() ) );
			assertf( ftype, "Function call without function type: %s", toString( funcDecl ).c_str() );
			if ( CodeGen::isConstructor( funcDecl->name ) && ftype->params.size() == 2 ) {
				auto t1 = getPointerBase( ftype->params.front() );
				auto t2 = ftype->params.back();
				assert( t1 );

				if ( ResolvExpr::typesCompatible( t1, t2 ) ) {
					// optimization: don't need to copy construct in order to call a copy constructor
					return appExpr;
				} // if
			} else if ( CodeGen::isDestructor( funcDecl->name ) ) {
				// correctness: never copy construct arguments to a destructor
				return appExpr;
			} // if
		} // if
	} // if
	CP_CTOR_PRINT( std::cerr << "InsertImplicitCalls: adding a wrapper " << appExpr << std::endl; )

	// wrap each function call so that it is easy to identify nodes that have to be copy constructed
	ast::ptr<ast::TypeSubstitution> tmp = appExpr->env;
	auto mutExpr = mutate(appExpr);
	mutExpr->env = nullptr;

	auto expr = new ast::ImplicitCopyCtorExpr( appExpr->location, mutExpr );
	// Move the type substitution to the new top-level. The substitution
	// is needed to obtain the type of temporary variables so that copy
	// constructor calls can be resolved.
	expr->env = tmp;
	return expr;
}

void ResolveCopyCtors::previsit(const ast::Expr * expr) {
	if ( nullptr == expr->env ) {
		return;
	}
	GuardValue( env ) = expr->env->clone();
	GuardValue( envModified ) = false;
}

const ast::Expr * ResolveCopyCtors::postvisit(const ast::Expr * expr) {
	// No local environment, skip.
	if ( nullptr == expr->env ) {
		return expr;
	// Environment was modified, mutate and replace.
	} else if ( envModified ) {
		auto mutExpr = mutate(expr);
		mutExpr->env = env;
		return mutExpr;
	// Environment was not mutated, delete the shallow copy before guard.
	} else {
		delete env;
		return expr;
	}
}

bool ResolveCopyCtors::skipCopyConstruct( const ast::Type * type ) { return ! isConstructable( type ); }

const ast::Expr * ResolveCopyCtors::makeCtorDtor( const std::string & fname, const ast::ObjectDecl * var, const ast::Expr * cpArg ) {
	assert( var );
	assert( var->isManaged() );
	assert( !cpArg || cpArg->isManaged() );
	// arrays are not copy constructed, so this should always be an ExprStmt
	ast::ptr< ast::Stmt > stmt = genCtorDtor(var->location, fname, var, cpArg );
	assertf( stmt, "ResolveCopyCtors: genCtorDtor returned nullptr: %s / %s / %s", fname.c_str(), toString( var ).c_str(), toString( cpArg ).c_str() );
	auto exprStmt = stmt.strict_as<ast::ImplicitCtorDtorStmt>()->callStmt.strict_as<ast::ExprStmt>();
	ast::ptr<ast::Expr> untyped = exprStmt->expr; // take ownership of expr

	// resolve copy constructor
	// should only be one alternative for copy ctor and dtor expressions, since all arguments are fixed
	// (VariableExpr and already resolved expression)
	CP_CTOR_PRINT( std::cerr << "ResolvingCtorDtor " << untyped << std::endl; )
	ast::ptr<ast::Expr> resolved = ResolvExpr::findVoidExpression(untyped, { symtab, transUnit().global } );
	assert( resolved );
	if ( resolved->env ) {
		// Extract useful information and discard new environments. Keeping them causes problems in PolyMutator passes.
		env->add( *resolved->env );
		envModified = true;
		auto mut = mutate(resolved.get());
		assertf(mut == resolved.get(), "newly resolved expression must be unique");
		mut->env = nullptr;
	} // if
	if ( auto assign = resolved.as<ast::TupleAssignExpr>() ) {
		// fix newly generated StmtExpr
		previsit( assign->stmtExpr );
	}
	return resolved.release();
}

ast::ptr<ast::Expr> ResolveCopyCtors::copyConstructArg(
	const ast::Expr * arg, const ast::ImplicitCopyCtorExpr * impCpCtorExpr, const ast::Type * formal )
{
	static UniqueName tempNamer("_tmp_cp");
	const CodeLocation loc = impCpCtorExpr->location;
	// CP_CTOR_PRINT( std::cerr << "Type Substitution: " << *env << std::endl; )
	assert( arg->result );
	ast::ptr<ast::Type> result = arg->result;
	if ( skipCopyConstruct( result ) ) return arg; // skip certain non-copyable types

	// type may involve type variables, so apply type substitution to get temporary variable's actual type,
	// since result type may not be substituted (e.g., if the type does not appear in the parameter list)
	// Use applyFree so that types bound in function pointers are not substituted, e.g. in forall(dtype T) void (*)(T).

	// xxx - this originally mutates arg->result in place. is it correct?
	assert( env );
	result = env->applyFree( result.get() ).node;
	auto mutResult = result.get_and_mutate();
	mutResult->set_const(false);

	auto mutArg = mutate(arg);
	mutArg->result = mutResult;

	ast::ptr<ast::Expr> guard = mutArg;

	ast::ptr<ast::ObjectDecl> tmp = new ast::ObjectDecl(loc, "__tmp", mutResult, nullptr );

	// create and resolve copy constructor
	CP_CTOR_PRINT( std::cerr << "makeCtorDtor for an argument" << std::endl; )
	auto cpCtor = makeCtorDtor( "?{}", tmp, mutArg );

	if ( auto appExpr = dynamic_cast< const ast::ApplicationExpr * >( cpCtor ) ) {
		// if the chosen constructor is intrinsic, the copy is unnecessary, so
		// don't create the temporary and don't call the copy constructor
		auto function = appExpr->func.strict_as<ast::VariableExpr>();
		if ( function->var->linkage == ast::Linkage::Intrinsic ) {
			// arguments that need to be boxed need a temporary regardless of whether the copy constructor is intrinsic,
			// so that the object isn't changed inside of the polymorphic function
			if ( ! GenPoly::needsBoxing( formal, result, impCpCtorExpr->callExpr, env ) ) {
				// xxx - should arg->result be mutated? see comment above.
				return guard;
			}
		}
	}

	// set a unique name for the temporary once it's certain the call is necessary
	auto mut = tmp.get_and_mutate();
	assertf (mut == tmp, "newly created ObjectDecl must be unique");
	mut->name = tempNamer.newName();

	// replace argument to function call with temporary
	stmtsToAddBefore.push_back( new ast::DeclStmt(loc, tmp ) );
	arg = cpCtor;
	return destructRet( tmp, arg );

	// impCpCtorExpr->dtors.push_front( makeCtorDtor( "^?{}", tmp ) );
}

ast::Expr * ResolveCopyCtors::destructRet( const ast::ObjectDecl * ret, const ast::Expr * arg ) {
	auto global = transUnit().global;
	// TODO: refactor code for generating cleanup attribute, since it's common and reused in ~3-4 places
	// check for existing cleanup attribute before adding another(?)
	// need to add __Destructor for _tmp_cp variables as well

	assertf( global.dtorStruct, "Destructor generation requires __Destructor definition." );
	assertf( global.dtorStruct->members.size() == 2, "__Destructor definition does not have expected fields." );
	assertf( global.dtorDestroy, "Destructor generation requires __destroy_Destructor." );

	const CodeLocation loc = ret->location;

	// generate a __Destructor for ret that calls the destructor
	auto res = makeCtorDtor( "^?{}", ret );
	auto dtor = mutate(res);

	// if the chosen destructor is intrinsic, elide the generated dtor handler
	if ( arg && isIntrinsicCallExpr( dtor ) ) {
		return new ast::CommaExpr(loc, arg, new ast::VariableExpr(loc, ret ) );
	}

	if ( ! dtor->env ) dtor->env = maybeClone( env );
	auto dtorFunc = getDtorFunc( ret, new ast::ExprStmt(loc, dtor ), stmtsToAddBefore );

	auto dtorStructType = new ast::StructInstType( global.dtorStruct );

	// what does this do???
	dtorStructType->params.push_back( new ast::TypeExpr(loc, new ast::VoidType() ) );

	// cast destructor pointer to void (*)(void *), to silence GCC incompatible pointer warnings
	auto dtorFtype = new ast::FunctionType();
	dtorFtype->params.push_back( new ast::PointerType(new ast::VoidType( ) ) );
	auto dtorType = new ast::PointerType( dtorFtype );

	static UniqueName namer( "_ret_dtor" );
	auto retDtor = new ast::ObjectDecl(loc, namer.newName(), dtorStructType, new ast::ListInit(loc, { new ast::SingleInit(loc, ast::ConstantExpr::null(loc) ), new ast::SingleInit(loc, new ast::CastExpr( new ast::VariableExpr(loc, dtorFunc ), dtorType ) ) } ) );
	retDtor->attributes.push_back( new ast::Attribute( "cleanup", { new ast::VariableExpr(loc, global.dtorDestroy ) } ) );
	stmtsToAddBefore.push_back( new ast::DeclStmt(loc, retDtor ) );

	if ( arg ) {
		auto member = new ast::MemberExpr(loc, global.dtorStruct->members.front().strict_as<ast::DeclWithType>(), new ast::VariableExpr(loc, retDtor ) );
		auto object = new ast::CastExpr( new ast::AddressExpr( new ast::VariableExpr(loc, ret ) ), new ast::PointerType(new ast::VoidType() ) );
		ast::Expr * assign = createBitwiseAssignment( member, object );
		return new ast::CommaExpr(loc, new ast::CommaExpr(loc, arg, assign ), new ast::VariableExpr(loc, ret ) );
	}
	return nullptr;
	// impCpCtorExpr->get_dtors().push_front( makeCtorDtor( "^?{}", ret ) );
}

const ast::Expr * ResolveCopyCtors::postvisit( const ast::ImplicitCopyCtorExpr *impCpCtorExpr ) {
	CP_CTOR_PRINT( std::cerr << "ResolveCopyCtors: " << impCpCtorExpr << std::endl; )

	ast::ApplicationExpr * appExpr = mutate(impCpCtorExpr->callExpr.get());
	const ast::ObjectDecl * returnDecl = nullptr;
	const CodeLocation loc = appExpr->location;

	// take each argument and attempt to copy construct it.
	auto ftype = GenPoly::getFunctionType( appExpr->func->result );
	assert( ftype );
	auto & params = ftype->params;
	auto iter = params.begin();
	for ( auto & arg : appExpr->args ) {
		const ast::Type * formal = nullptr;
		if ( iter != params.end() ) { // does not copy construct C-style variadic arguments
			// DeclarationWithType * param = *iter++;
			formal = *iter++;
		}

		arg = copyConstructArg( arg, impCpCtorExpr, formal );
	} // for

	// each return value from the call needs to be connected with an ObjectDecl at the call site, which is
	// initialized with the return value and is destructed later
	// xxx - handle named return values?
	const ast::Type * result = appExpr->result;
	if ( ! result->isVoid() ) {
		static UniqueName retNamer("_tmp_cp_ret");
		auto subResult = env->apply( result ).node;
		auto ret = new ast::ObjectDecl(loc, retNamer.newName(), subResult, nullptr );
		auto mutType = mutate(ret->type.get());
		mutType->set_const( false );
		ret->type = mutType;
		returnDecl = ret;
		stmtsToAddBefore.push_back( new ast::DeclStmt(loc, ret ) );
		CP_CTOR_PRINT( std::cerr << "makeCtorDtor for a return" << std::endl; )
	} // for
	CP_CTOR_PRINT( std::cerr << "after Resolving: " << impCpCtorExpr << std::endl; )
	// ------------------------------------------------------

	CP_CTOR_PRINT( std::cerr << "Coming out the back..." << impCpCtorExpr << std::endl; )

	// detach fields from wrapper node so that it can be deleted without deleting too much

	// xxx - actual env might be somewhere else, need to keep invariant

	// deletion of wrapper should be handled by pass template now

	// impCpCtorExpr->callExpr = nullptr;
	assert (appExpr->env == nullptr);
	appExpr->env = impCpCtorExpr->env;
	// std::swap( impCpCtorExpr->env, appExpr->env );
	// assert( impCpCtorExpr->env == nullptr );
	// delete impCpCtorExpr;

	if ( returnDecl ) {
		ast::Expr * assign = createBitwiseAssignment( new ast::VariableExpr(loc, returnDecl ), appExpr );
		if ( ! dynamic_cast< const ast::ReferenceType * >( result ) ) {
			// destructing reference returns is bad because it can cause multiple destructor calls to the same object - the returned object is not a temporary
			assign = destructRet( returnDecl, assign );
			assert(assign);
		} else {
			assign = new ast::CommaExpr(loc, assign, new ast::VariableExpr(loc, returnDecl ) );
		}
		// move env from appExpr to retExpr
		// std::swap( assign->env, appExpr->env );
		assign->env = appExpr->env;
		// actual env is handled by common routine that replaces WithTypeSubstitution
		return postvisit((const ast::Expr *)assign);
	} else {
		return postvisit((const ast::Expr *)appExpr);
	} // if
}

const ast::StmtExpr * ResolveCopyCtors::previsit( const ast::StmtExpr * _stmtExpr ) {
	// function call temporaries should be placed at statement-level, rather than nested inside of a new statement expression,
	// since temporaries can be shared across sub-expressions, e.g.
	//   [A, A] f();       // decl
	//   g([A] x, [A] y);  // decl
	//   g(f());           // call
	// f is executed once, so the return temporary is shared across the tuple constructors for x and y.
	// Explicitly mutating children instead of mutating the inner compound statement forces the temporaries to be added
	// to the outer context, rather than inside of the statement expression.

	// call the common routine that replaces WithTypeSubstitution
	previsit((const ast::Expr *) _stmtExpr);

	visit_children = false;
	const CodeLocation loc = _stmtExpr->location;

	assert( env );

	symtab.enterScope();
	// visit all statements
	auto stmtExpr = mutate(_stmtExpr);
	auto mutStmts = mutate(stmtExpr->stmts.get());

	auto & stmts = mutStmts->kids;
	for ( auto & stmt : stmts ) {
		stmt = stmt->accept( *visitor );
	} // for
	stmtExpr->stmts = mutStmts;
	symtab.leaveScope();

	assert( stmtExpr->result );
	// const ast::Type * result = stmtExpr->result;
	if ( ! stmtExpr->result->isVoid() ) {
		static UniqueName retNamer("_tmp_stmtexpr_ret");

		// result = result->clone();
		auto result = env->apply( stmtExpr->result.get() ).node;
		if ( ! InitTweak::isConstructable( result ) ) {
			// delete result;
			return stmtExpr;
		}
		auto mutResult = result.get_and_mutate();
		mutResult->set_const(false);

		// create variable that will hold the result of the stmt expr
		auto ret = new ast::ObjectDecl(loc, retNamer.newName(), mutResult, nullptr );
		stmtsToAddBefore.push_back( new ast::DeclStmt(loc, ret ) );

		assertf(
			stmtExpr->resultExpr,
			"Statement-Expression should have a resulting expression at %s:%d",
			stmtExpr->location.filename.c_str(),
			stmtExpr->location.first_line
		);

		const ast::ExprStmt * last = stmtExpr->resultExpr;
		// xxx - if this is non-unique, need to copy while making resultExpr ref
		assertf(last->unique(), "attempt to modify weakly shared statement");
		auto mutLast = mutate(last);
		// above assertion means in-place mutation is OK
		try {
			mutLast->expr = makeCtorDtor( "?{}", ret, mutLast->expr );
		} catch(...) {
			std::cerr << "*CFA internal error: ";
			std::cerr << "can't resolve implicit constructor";
			std::cerr << " at " << stmtExpr->location.filename;
			std::cerr << ":" << stmtExpr->location.first_line << std::endl;

			abort();
		}

		// add destructors after current statement
		stmtsToAddAfter.push_back( new ast::ExprStmt(loc, makeCtorDtor( "^?{}", ret ) ) );

		// must have a non-empty body, otherwise it wouldn't have a result
		assert( ! stmts.empty() );

		// if there is a return decl, add a use as the last statement; will not have return decl on non-constructable returns
		stmts.push_back( new ast::ExprStmt(loc, new ast::VariableExpr(loc, ret ) ) );
	} // if

	assert( stmtExpr->returnDecls.empty() );
	assert( stmtExpr->dtors.empty() );

	return stmtExpr;
}

// to prevent warnings ('_unq0' may be used uninitialized in this function),
// insert an appropriate zero initializer for UniqueExpr temporaries.
ast::Init * makeInit( const ast::Type * t, CodeLocation const & loc ) {
	if ( auto inst = dynamic_cast< const ast::StructInstType * >( t ) ) {
		// initizer for empty struct must be empty
		if ( inst->base->members.empty() ) {
			return new ast::ListInit( loc, {} );
		}
	} else if ( auto inst = dynamic_cast< const ast::UnionInstType * >( t ) ) {
		// initizer for empty union must be empty
		if ( inst->base->members.empty() ) {
			return new ast::ListInit( loc, {} );
		}
	}

	return new ast::ListInit( loc, {
		new ast::SingleInit( loc, ast::ConstantExpr::from_int( loc, 0 ) )
	} );
}

const ast::UniqueExpr * ResolveCopyCtors::previsit( const ast::UniqueExpr * unqExpr ) {
	visit_children = false;
	// xxx - hack to prevent double-handling of unique exprs, otherwise too many temporary variables and destructors are generated
	static std::unordered_map< int, const ast::UniqueExpr * > unqMap;
	auto mutExpr = mutate(unqExpr);
	if ( ! unqMap.count( unqExpr->id ) ) {
		// resolve expr and find its

		auto impCpCtorExpr = mutExpr->expr.as<ast::ImplicitCopyCtorExpr>();
		// PassVisitor<ResolveCopyCtors> fixer;

		mutExpr->expr = mutExpr->expr->accept( *visitor );
		// it should never be necessary to wrap a void-returning expression in a UniqueExpr - if this assumption changes, this needs to be rethought
		assert( unqExpr->result );
		if ( impCpCtorExpr ) {
			auto comma = unqExpr->expr.strict_as<ast::CommaExpr>();
			auto var = comma->arg2.strict_as<ast::VariableExpr>();
			// note the variable used as the result from the call
			mutExpr->var = var;
		} else {
			// expr isn't a call expr, so create a new temporary variable to use to hold the value of the unique expression
			mutExpr->object = new ast::ObjectDecl( mutExpr->location, toString("_unq", mutExpr->id), mutExpr->result, makeInit( mutExpr->result, mutExpr->location ) );
			mutExpr->var = new ast::VariableExpr( mutExpr->location, mutExpr->object );
		}

		unqMap[mutExpr->id] = mutExpr;
	} else {
		// take data from other UniqueExpr to ensure consistency
		// delete unqExpr->get_expr();
		mutExpr->expr = unqMap[mutExpr->id]->expr;
		// delete unqExpr->result;
		mutExpr->result = mutExpr->expr->result;
	}
	return mutExpr;
}

const ast::DeclWithType * FixInit::postvisit( const ast::ObjectDecl *_objDecl ) {
	const CodeLocation loc = _objDecl->location;

	// since this removes the init field from objDecl, it must occur after children are mutated (i.e. postvisit)
	if ( ast::ptr<ast::ConstructorInit> ctorInit = _objDecl->init.as<ast::ConstructorInit>() ) {
		auto objDecl = mutate(_objDecl);

		// could this be non-unique?
		if (objDecl != _objDecl) {
			std::cerr << "FixInit: non-unique object decl " << objDecl->location << objDecl->name << std::endl;
		}
		// a decision should have been made by the resolver, so ctor and init are not both non-NULL
		assert( ! ctorInit->ctor || ! ctorInit->init );
		if ( const ast::Stmt * ctor = ctorInit->ctor ) {
			if ( objDecl->storage.is_static ) {
				addDataSectionAttribute(objDecl);
				// originally wanted to take advantage of gcc nested functions, but
				// we get memory errors with this approach. To remedy this, the static
				// variable is hoisted when the destructor needs to be called.
				//
				// generate:
				// static T __objName_static_varN;
				// void __objName_dtor_atexitN() {
				//   __dtor__...;
				// }
				// int f(...) {
				//   ...
				//   static bool __objName_uninitialized = true;
				//   if (__objName_uninitialized) {
				//     __ctor(__objName);
				//     __objName_uninitialized = false;
				//     atexit(__objName_dtor_atexitN);
				//   }
				//   ...
				// }

				static UniqueName dtorCallerNamer( "_dtor_atexit" );

				// static bool __objName_uninitialized = true
				auto boolType = new ast::BasicType( ast::BasicType::Kind::Bool );
				auto boolInitExpr = new ast::SingleInit(loc, ast::ConstantExpr::from_int(loc, 1 ) );
				auto isUninitializedVar = new ast::ObjectDecl(loc, objDecl->mangleName + "_uninitialized", boolType, boolInitExpr, ast::Storage::Static, ast::Linkage::Cforall);
				isUninitializedVar->fixUniqueId();

				// __objName_uninitialized = false;
				auto setTrue = new ast::UntypedExpr(loc, new ast::NameExpr(loc, "?=?" ) );
				setTrue->args.push_back( new ast::VariableExpr(loc, isUninitializedVar ) );
				setTrue->args.push_back( ast::ConstantExpr::from_int(loc, 0 ) );

				// generate body of if
				auto initStmts = new ast::CompoundStmt(loc);
				auto & body = initStmts->kids;
				body.push_back( ctor );
				body.push_back( new ast::ExprStmt(loc, setTrue ) );

				// put it all together
				auto ifStmt = new ast::IfStmt(loc, new ast::VariableExpr(loc, isUninitializedVar ), initStmts, 0 );
				stmtsToAddAfter.push_back( new ast::DeclStmt(loc, isUninitializedVar ) );
				stmtsToAddAfter.push_back( ifStmt );

				const ast::Stmt * dtor = ctorInit->dtor;

				// these should be automatically managed once reassigned
				// objDecl->set_init( nullptr );
				// ctorInit->set_ctor( nullptr );
				// ctorInit->set_dtor( nullptr );
				if ( dtor ) {
					// if the object has a non-trivial destructor, have to
					// hoist it and the object into the global space and
					// call the destructor function with atexit.

					// Statement * dtorStmt = dtor->clone();

					// void __objName_dtor_atexitN(...) {...}
					ast::FunctionDecl * dtorCaller = new ast::FunctionDecl(loc, objDecl->mangleName + dtorCallerNamer.newName(), {}, {}, {}, new ast::CompoundStmt(loc, {dtor}), ast::Storage::Static, ast::Linkage::C );
					dtorCaller->fixUniqueId();
					// dtorCaller->stmts->push_back( dtor );

					// atexit(dtor_atexit);
					auto callAtexit = new ast::UntypedExpr(loc, new ast::NameExpr(loc, "atexit" ) );
					callAtexit->args.push_back( new ast::VariableExpr(loc, dtorCaller ) );

					body.push_back( new ast::ExprStmt(loc, callAtexit ) );

					// hoist variable and dtor caller decls to list of decls that will be added into global scope
					staticDtorDecls.push_back( objDecl );
					staticDtorDecls.push_back( dtorCaller );

					// need to rename object uniquely since it now appears
					// at global scope and there could be multiple function-scoped
					// static variables with the same name in different functions.
					// Note: it isn't sufficient to modify only the mangleName, because
					// then subsequent Indexer passes can choke on seeing the object's name
					// if another object has the same name and type. An unfortunate side-effect
					// of renaming the object is that subsequent NameExprs may fail to resolve,
					// but there shouldn't be any remaining past this point.
					static UniqueName staticNamer( "_static_var" );
					objDecl->name = objDecl->name + staticNamer.newName();
					objDecl->mangleName = Mangle::mangle( objDecl );
					objDecl->init = nullptr;

					// xxx - temporary hack: need to return a declaration, but want to hoist the current object out of this scope
					// create a new object which is never used
					static UniqueName dummyNamer( "_dummy" );
					auto dummy = new ast::ObjectDecl(loc, dummyNamer.newName(), new ast::PointerType(new ast::VoidType()), nullptr, ast::Storage::Static, ast::Linkage::Cforall, 0, { new ast::Attribute("unused") } );
					// delete ctorInit;
					return dummy;
				} else {
					objDecl->init = nullptr;
					return objDecl;
				}
			} else {
				auto implicit = strict_dynamic_cast< const ast::ImplicitCtorDtorStmt * > ( ctor );
				auto ctorStmt = implicit->callStmt.as<ast::ExprStmt>();
				const ast::ApplicationExpr * ctorCall = nullptr;
				if ( ctorStmt && (ctorCall = isIntrinsicCallExpr( ctorStmt->expr )) && ctorCall->args.size() == 2 ) {
					// clean up intrinsic copy constructor calls by making them into SingleInits
					const ast::Expr * ctorArg = ctorCall->args.back();
					// ctorCall should be gone afterwards
					auto mutArg = mutate(ctorArg);
					mutArg->env = ctorCall->env;
					// std::swap( ctorArg->env, ctorCall->env );
					objDecl->init = new ast::SingleInit(loc, mutArg );

					// ctorCall->args.pop_back();
				} else {
					stmtsToAddAfter.push_back( ctor );
					objDecl->init = nullptr;
					// ctorInit->ctor = nullptr;
				}

				const ast::Stmt * dtor = ctorInit->dtor;
				if ( dtor ) {
					auto implicit = strict_dynamic_cast< const ast::ImplicitCtorDtorStmt * >( dtor );
					const ast::Stmt * dtorStmt = implicit->callStmt;

					// don't need to call intrinsic dtor, because it does nothing, but
					// non-intrinsic dtors must be called
					if ( ! isIntrinsicSingleArgCallStmt( dtorStmt ) ) {
						// set dtor location to the object's location for error messages
						auto dtorFunc = getDtorFunc( objDecl, dtorStmt, stmtsToAddBefore );
						objDecl->attributes.push_back( new ast::Attribute( "cleanup", { new ast::VariableExpr(loc, dtorFunc ) } ) );
						// ctorInit->dtor = nullptr;
					} // if
				}
			} // if
		} else if ( const ast::Init * init = ctorInit->init ) {
			objDecl->init = init;
			// ctorInit->init = nullptr;
		} else {
			// no constructor and no initializer, which is okay
			objDecl->init = nullptr;
		} // if
		// delete ctorInit;
		return objDecl;
	} // if
	return _objDecl;
}

void ObjDeclCollector::previsit( const ast::CompoundStmt * ) {
	GuardValue( curVars );
}

void ObjDeclCollector::previsit( const ast::DeclStmt * stmt ) {
	// keep track of all variables currently in scope
	if ( auto objDecl = stmt->decl.as<ast::ObjectDecl>() ) {
		curVars.push_back( objDecl );
	} // if
}

void LabelFinder::previsit( const ast::Stmt * stmt ) {
	// for each label, remember the variables in scope at that label.
	for ( auto l : stmt->labels ) {
		vars[l] = curVars;
	} // for
}

void LabelFinder::previsit( const ast::CompoundStmt * stmt ) {
	previsit( (const ast::Stmt *) stmt );
	Parent::previsit( stmt );
}

void LabelFinder::previsit( const ast::DeclStmt * stmt ) {
	previsit( (const ast::Stmt *)stmt );
	Parent::previsit( stmt );
}

void InsertDtors::previsit( const ast::FunctionDecl * funcDecl ) {
	// each function needs to have its own set of labels
	GuardValue( labelVars );
	labelVars.clear();
	// LabelFinder does not recurse into FunctionDecl, so need to visit
	// its children manually.
	if (funcDecl->type) funcDecl->type->accept(finder);
	// maybeAccept( funcDecl->type, finder );
	if (funcDecl->stmts) funcDecl->stmts->accept(finder) ;

	// all labels for this function have been collected, insert destructors as appropriate via implicit recursion.
}

// Handle break/continue/goto in the same manner as C++.  Basic idea: any objects that are in scope at the
// BranchStmt but not at the labelled (target) statement must be destructed.  If there are any objects in scope
// at the target location but not at the BranchStmt then those objects would be uninitialized so notify the user
// of the error.  See C++ Reference 6.6 Jump Statements for details.
void InsertDtors::handleGoto( const ast::BranchStmt * stmt ) {
	// can't do anything for computed goto
	if ( stmt->computedTarget ) return;

	assertf( stmt->target.name != "", "BranchStmt missing a label: %s", toString( stmt ).c_str() );
	// S_L = lvars = set of objects in scope at label definition
	// S_G = curVars = set of objects in scope at goto statement
	ObjectSet & lvars = labelVars[ stmt->target ];

	DTOR_PRINT(
		std::cerr << "at goto label: " << stmt->target.name << std::endl;
		std::cerr << "S_G = " << printSet( curVars ) << std::endl;
		std::cerr << "S_L = " << printSet( lvars ) << std::endl;
	)


	// std::set_difference requires that the inputs be sorted.
	lvars.sort();
	curVars.sort();

	ObjectSet diff;
	// S_L-S_G results in set of objects whose construction is skipped - it's an error if this set is non-empty
	std::set_difference( lvars.begin(), lvars.end(), curVars.begin(), curVars.end(), std::inserter( diff, diff.begin() ) );
	DTOR_PRINT(
		std::cerr << "S_L-S_G = " << printSet( diff ) << std::endl;
	)
	if ( ! diff.empty() ) {
		SemanticError( stmt, std::string("jump to label '") + stmt->target.name + "' crosses initialization of " + (*diff.begin())->name + " " );
	} // if
}

void InsertDtors::previsit( const ast::BranchStmt * stmt ) {
	switch( stmt->kind ) {
	case ast::BranchStmt::Continue:
	case ast::BranchStmt::Break:
		// could optimize the break/continue case, because the S_L-S_G check is unnecessary (this set should
		// always be empty), but it serves as a small sanity check.
	case ast::BranchStmt::Goto:
		handleGoto( stmt );
		break;
	default:
		assert( false );
	} // switch
}

bool checkWarnings( const ast::FunctionDecl * funcDecl ) {
	// only check for warnings if the current function is a user-defined
	// constructor or destructor
	if ( ! funcDecl ) return false;
	if ( ! funcDecl->stmts ) return false;
	return CodeGen::isCtorDtor( funcDecl->name ) && ! funcDecl->linkage.is_overrideable;
}

void GenStructMemberCalls::previsit( const ast::FunctionDecl * funcDecl ) {
	GuardValue( function );
	GuardValue( unhandled );
	GuardValue( usedUninit );
	GuardValue( thisParam );
	GuardValue( isCtor );
	GuardValue( structDecl );
	errors = SemanticErrorException();  // clear previous errors

	// need to start with fresh sets
	unhandled.clear();
	usedUninit.clear();

	function = mutate(funcDecl);
	// could this be non-unique?
	if (function != funcDecl) {
		std::cerr << "GenStructMemberCalls: non-unique FunctionDecl " << funcDecl->location << funcDecl->name << std::endl;
	}

	isCtor = CodeGen::isConstructor( function->name );
	if ( checkWarnings( function ) ) {
		// const ast::FunctionType * type = function->type;
		// assert( ! type->params.empty() );
		thisParam = function->params.front().strict_as<ast::ObjectDecl>();
		auto thisType = getPointerBase( thisParam->get_type() );
		auto structType = dynamic_cast< const ast::StructInstType * >( thisType );
		if ( structType ) {
			structDecl = structType->base;
			for ( auto & member : structDecl->members ) {
				if ( auto field = member.as<ast::ObjectDecl>() ) {
					// record all of the struct type's members that need to be constructed or
					// destructed by the end of the function
					unhandled.insert( field );
				}
			}
		}
	}
}

const ast::DeclWithType * GenStructMemberCalls::postvisit( const ast::FunctionDecl * funcDecl ) {
	// remove the unhandled objects from usedUninit, because a call is inserted
	// to handle them - only objects that are later constructed are used uninitialized.
	std::map< const ast::DeclWithType *, CodeLocation > diff;
	// need the comparator since usedUninit and unhandled have different types
	struct comp_t {
		typedef decltype(usedUninit)::value_type usedUninit_t;
		typedef decltype(unhandled)::value_type unhandled_t;
		bool operator()(usedUninit_t x, unhandled_t y) { return x.first < y; }
		bool operator()(unhandled_t x, usedUninit_t y) { return x < y.first; }
	} comp;
	std::set_difference( usedUninit.begin(), usedUninit.end(), unhandled.begin(), unhandled.end(), std::inserter( diff, diff.begin() ), comp );
	for ( auto p : diff ) {
		auto member = p.first;
		auto loc = p.second;
		// xxx - make error message better by also tracking the location that the object is constructed at?
		emit( loc, "in ", function->name, ", field ", member->name, " used before being constructed" );
	}

	const CodeLocation loc = funcDecl->location;

	if ( ! unhandled.empty() ) {
		auto mutStmts = function->stmts.get_and_mutate();
		// need to explicitly re-add function parameters to the indexer in order to resolve copy constructors
		auto guard = makeFuncGuard( [this]() { symtab.enterScope(); }, [this]() { symtab.leaveScope(); } );
		symtab.addFunction( function );
		auto global = transUnit().global;

		// need to iterate through members in reverse in order for
		// ctor/dtor statements to come out in the right order
		for ( auto & member : reverseIterate( structDecl->members ) ) {
			auto field = member.as<ast::ObjectDecl>();
			// skip non-DWT members
			if ( ! field ) continue;
			// skip non-constructable members
			if ( ! tryConstruct( field ) ) continue;
			// skip handled members
			if ( ! unhandled.count( field ) ) continue;

			// insert and resolve default/copy constructor call for each field that's unhandled
			// std::list< const ast::Stmt * > stmt;
			ast::Expr * arg2 = nullptr;
			if ( function->name == "?{}" && isCopyFunction( function ) ) {
				// if copy ctor, need to pass second-param-of-this-function.field
				// std::list< DeclarationWithType * > & params = function->get_functionType()->get_parameters();
				assert( function->params.size() == 2 );
				arg2 = new ast::MemberExpr(funcDecl->location, field, new ast::VariableExpr(funcDecl->location, function->params.back() ) );
			}
			InitExpander_new srcParam( arg2 );
			// cast away reference type and construct field.
			ast::Expr * thisExpr = new ast::CastExpr(funcDecl->location, new ast::VariableExpr(funcDecl->location, thisParam ), thisParam->get_type()->stripReferences());
			ast::Expr * memberDest = new ast::MemberExpr(funcDecl->location, field, thisExpr );
			ast::ptr<ast::Stmt> callStmt = SymTab::genImplicitCall( srcParam, memberDest, loc, function->name, field, static_cast<SymTab::LoopDirection>(isCtor) );

			if ( callStmt ) {
				// auto & callStmt = stmt.front();

				try {
					callStmt = callStmt->accept( *visitor );
					if ( isCtor ) {
						mutStmts->push_front( callStmt );
					} else { // TODO: don't generate destructor function/object for intrinsic calls
						// destructor statements should be added at the end
						// function->get_statements()->push_back( callStmt );

						// Optimization: do not need to call intrinsic destructors on members
						if ( isIntrinsicSingleArgCallStmt( callStmt ) ) continue;

						// __Destructor _dtor0 = { (void *)&b.a1, (void (*)(void *)_destroy_A };
						std::list< ast::ptr<ast::Stmt> > stmtsToAdd;

						static UniqueName memberDtorNamer = { "__memberDtor" };
						assertf( global.dtorStruct, "builtin __Destructor not found." );
						assertf( global.dtorDestroy, "builtin __destroy_Destructor not found." );

						ast::Expr * thisExpr = new ast::CastExpr( new ast::AddressExpr( new ast::VariableExpr(loc, thisParam ) ), new ast::PointerType( new ast::VoidType(), ast::CV::Qualifiers() ) );
						ast::Expr * dtorExpr = new ast::VariableExpr(loc, getDtorFunc( thisParam, callStmt, stmtsToAdd ) );

						// cast destructor pointer to void (*)(void *), to silence GCC incompatible pointer warnings
						auto dtorFtype = new ast::FunctionType();
						dtorFtype->params.emplace_back( new ast::PointerType( new ast::VoidType() ) );
						auto dtorType = new ast::PointerType( dtorFtype );

						auto destructor = new ast::ObjectDecl(loc, memberDtorNamer.newName(), new ast::StructInstType( global.dtorStruct ), new ast::ListInit(loc, { new ast::SingleInit(loc, thisExpr ), new ast::SingleInit(loc, new ast::CastExpr( dtorExpr, dtorType ) ) } ) );
						destructor->attributes.push_back( new ast::Attribute( "cleanup", { new ast::VariableExpr( loc, global.dtorDestroy ) } ) );
						mutStmts->push_front( new ast::DeclStmt(loc, destructor ) );
						mutStmts->kids.splice( mutStmts->kids.begin(), stmtsToAdd );
					}
				} catch ( SemanticErrorException & error ) {
					emit( funcDecl->location, "in ", function->name , ", field ", field->name, " not explicitly ", isCtor ? "constructed" : "destructed",  " and no ", isCtor ? "default constructor" : "destructor", " found" );
				}
			}
		}
		function->stmts = mutStmts;
	}
	if (! errors.isEmpty()) {
		throw errors;
	}
	// return funcDecl;
	return function;
}

/// true if expr is effectively just the 'this' parameter
bool isThisExpression( const ast::Expr * expr, const ast::DeclWithType * thisParam ) {
	// TODO: there are more complicated ways to pass 'this' to a constructor, e.g. &*, *&, etc.
	if ( auto varExpr = dynamic_cast< const ast::VariableExpr * >( expr ) ) {
		return varExpr->var == thisParam;
	} else if ( auto castExpr = dynamic_cast< const ast::CastExpr * > ( expr ) ) {
		return isThisExpression( castExpr->arg, thisParam );
	}
	return false;
}

/// returns a MemberExpr if expr is effectively just member access on the 'this' parameter, else nullptr
const ast::MemberExpr * isThisMemberExpr( const ast::Expr * expr, const ast::DeclWithType * thisParam ) {
	if ( auto memberExpr = dynamic_cast< const ast::MemberExpr * >( expr ) ) {
		if ( isThisExpression( memberExpr->aggregate, thisParam ) ) {
			return memberExpr;
		}
	} else if ( auto castExpr = dynamic_cast< const ast::CastExpr * >( expr ) ) {
		return isThisMemberExpr( castExpr->arg, thisParam );
	}
	return nullptr;
}

void GenStructMemberCalls::previsit( const ast::ApplicationExpr * appExpr ) {
	if ( ! checkWarnings( function ) ) {
		visit_children = false;
		return;
	}

	std::string fname = getFunctionName( appExpr );
	if ( fname == function->name ) {
		// call to same kind of function
		const ast::Expr * firstParam = appExpr->args.front();

		if ( isThisExpression( firstParam, thisParam ) ) {
			// if calling another constructor on thisParam, assume that function handles
			// all members - if it doesn't a warning will appear in that function.
			unhandled.clear();
		} else if ( auto memberExpr = isThisMemberExpr( firstParam, thisParam ) ) {
			// if first parameter is a member expression on the this parameter,
			// then remove the member from unhandled set.
			if ( isThisExpression( memberExpr->aggregate, thisParam ) ) {
				unhandled.erase( memberExpr->member );
			}
		}
	}
}

void GenStructMemberCalls::previsit( const ast::MemberExpr * memberExpr ) {
	if ( ! checkWarnings( function ) || ! isCtor ) {
		visit_children = false;
		return;
	}

	if ( isThisExpression( memberExpr->aggregate, thisParam ) ) {
		if ( unhandled.count( memberExpr->member ) ) {
			// emit a warning because a member was used before it was constructed
			usedUninit.insert( { memberExpr->member, memberExpr->location } );
		}
	}
}

template< typename... Params >
void GenStructMemberCalls::emit( CodeLocation loc, const Params &... params ) {
	SemanticErrorException err( loc, toString( params... ) );
	errors.append( err );
}

const ast::Expr * GenStructMemberCalls::postvisit( const ast::UntypedExpr * untypedExpr ) {
	// xxx - functions returning ast::ptr seems wrong...
	auto res = ResolvExpr::findVoidExpression( untypedExpr, { symtab, transUnit().global } );
	return res.release();
}

void InsertImplicitCalls::previsit(const ast::UniqueExpr * unqExpr) {
	if (visitedIds.count(unqExpr->id)) visit_children = false;
	else visitedIds.insert(unqExpr->id);
}

const ast::Expr * FixCtorExprs::postvisit( const ast::ConstructorExpr * ctorExpr ) {
	const CodeLocation loc = ctorExpr->location;
	static UniqueName tempNamer( "_tmp_ctor_expr" );
	// xxx - is the size check necessary?
	assert( ctorExpr->result && ctorExpr->result->size() == 1 );

	// xxx - this can be TupleAssignExpr now. Need to properly handle this case.
	// take possession of expr and env
	ast::ptr<ast::ApplicationExpr> callExpr = ctorExpr->callExpr.strict_as<ast::ApplicationExpr>();
	ast::ptr<ast::TypeSubstitution> env = ctorExpr->env;
	// ctorExpr->set_callExpr( nullptr );
	// ctorExpr->set_env( nullptr );

	// xxx - ideally we would reuse the temporary generated from the copy constructor passes from within firstArg if it exists and not generate a temporary if it's unnecessary.
	auto tmp = new ast::ObjectDecl(loc, tempNamer.newName(), callExpr->args.front()->result );
	declsToAddBefore.push_back( tmp );

	// build assignment and replace constructor's first argument with new temporary
	auto mutCallExpr = callExpr.get_and_mutate();
	const ast::Expr * firstArg = callExpr->args.front();
	ast::Expr * assign = new ast::UntypedExpr(loc, new ast::NameExpr(loc, "?=?" ), { new ast::AddressExpr(loc, new ast::VariableExpr(loc, tmp ) ), new ast::AddressExpr( firstArg ) } );
	firstArg = new ast::VariableExpr(loc, tmp );
	mutCallExpr->args.front() = firstArg;

	// resolve assignment and dispose of new env
	auto resolved = ResolvExpr::findVoidExpression( assign, { symtab, transUnit().global } );
	auto mut = resolved.get_and_mutate();
	assertf(resolved.get() == mut, "newly resolved expression must be unique");
	mut->env = nullptr;

	// for constructor expr:
	//   T x;
	//   x{};
	// results in:
	//   T x;
	//   T & tmp;
	//   &tmp = &x, ?{}(tmp), tmp
	ast::CommaExpr * commaExpr = new ast::CommaExpr(loc, resolved, new ast::CommaExpr(loc, mutCallExpr, new ast::VariableExpr(loc, tmp ) ) );
	commaExpr->env = env;
	return commaExpr;
}

} // namespace

void fix( ast::TranslationUnit & translationUnit, bool inLibrary ) {
	ast::Pass<SelfAssignChecker>::run( translationUnit );

	// fixes StmtExpr to properly link to their resulting expression
	ast::Pass<StmtExprResult>::run( translationUnit );

	// fixes ConstructorInit for global variables. should happen before fixInitializers.
	InitTweak::fixGlobalInit( translationUnit, inLibrary );

	// must happen before ResolveCopyCtors because temporaries have to be inserted into the correct scope
	ast::Pass<SplitExpressions>::run( translationUnit );

	ast::Pass<InsertImplicitCalls>::run( translationUnit );

	// Needs to happen before ResolveCopyCtors, because argument/return temporaries should not be considered in
	// error checking branch statements
	{
		ast::Pass<LabelFinder> finder;
		ast::Pass<InsertDtors>::run( translationUnit, finder );
	}

	ast::Pass<ResolveCopyCtors>::run( translationUnit );
	FixInit::fixInitializers( translationUnit );
	ast::Pass<GenStructMemberCalls>::run( translationUnit );

	// Needs to happen after GenStructMemberCalls, since otherwise member constructors exprs
	// don't have the correct form, and a member can be constructed more than once.
	ast::Pass<FixCtorExprs>::run( translationUnit );
}

} // namespace InitTweak

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