1	//===--- SemaExceptionSpec.cpp - C++ Exception Specifications ---*- C++ -*-===//
2	//
3	// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4	// See https://llvm.org/LICENSE.txt for license information.
5	// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6	//
7	//===----------------------------------------------------------------------===//
8	//
9	// This file provides Sema routines for C++ exception specification testing.
10	//
11	//===----------------------------------------------------------------------===//
12
13	#include "clang/Sema/SemaInternal.h"
14	#include "clang/AST/ASTMutationListener.h"
15	#include "clang/AST/CXXInheritance.h"
16	#include "clang/AST/Expr.h"
17	#include "clang/AST/ExprCXX.h"
18	#include "clang/AST/StmtObjC.h"
19	#include "clang/AST/TypeLoc.h"
20	#include "clang/Basic/Diagnostic.h"
21	#include "clang/Basic/SourceManager.h"
22	#include "llvm/ADT/SmallPtrSet.h"
23	#include "llvm/ADT/SmallString.h"
24	#include <optional>
25
26	namespace clang {
27
28	static const FunctionProtoType *GetUnderlyingFunction(QualType T)
29	{
30	if (const PointerType *PtrTy = T->getAs<PointerType>())
31	T = PtrTy->getPointeeType();
32	else if (const ReferenceType *RefTy = T->getAs<ReferenceType>())
33	T = RefTy->getPointeeType();
34	else if (const MemberPointerType *MPTy = T->getAs<MemberPointerType>())
35	T = MPTy->getPointeeType();
36	return T->getAs<FunctionProtoType>();
37	}
38
39	/// HACK: 2014-11-14 libstdc++ had a bug where it shadows std::swap with a
40	/// member swap function then tries to call std::swap unqualified from the
41	/// exception specification of that function. This function detects whether
42	/// we're in such a case and turns off delay-parsing of exception
43	/// specifications. Libstdc++ 6.1 (released 2016-04-27) appears to have
44	/// resolved it as side-effect of commit ddb63209a8d (2015-06-05).
45	bool Sema::isLibstdcxxEagerExceptionSpecHack(const Declarator &D) {
46	auto *RD = dyn_cast<CXXRecordDecl>(Val: CurContext);
47
48	// All the problem cases are member functions named "swap" within class
49	// templates declared directly within namespace std or std::__debug or
50	// std::__profile.
51	if (!RD || !RD->getIdentifier() || !RD->getDescribedClassTemplate() ||
52	!D.getIdentifier() || !D.getIdentifier()->isStr(Str: "swap"))
53	return false;
54
55	auto *ND = dyn_cast<NamespaceDecl>(RD->getDeclContext());
56	if (!ND)
57	return false;
58
59	bool IsInStd = ND->isStdNamespace();
60	if (!IsInStd) {
61	// This isn't a direct member of namespace std, but it might still be
62	// libstdc++'s std::__debug::array or std::__profile::array.
63	IdentifierInfo *II = ND->getIdentifier();
64	if (!II || !(II->isStr(Str: "__debug") || II->isStr(Str: "__profile")) ||
65	!ND->isInStdNamespace())
66	return false;
67	}
68
69	// Only apply this hack within a system header.
70	if (!Context.getSourceManager().isInSystemHeader(Loc: D.getBeginLoc()))
71	return false;
72
73	return llvm::StringSwitch<bool>(RD->getIdentifier()->getName())
74	.Case(S: "array", Value: true)
75	.Case(S: "pair", Value: IsInStd)
76	.Case(S: "priority_queue", Value: IsInStd)
77	.Case(S: "stack", Value: IsInStd)
78	.Case(S: "queue", Value: IsInStd)
79	.Default(Value: false);
80	}
81
82	ExprResult Sema::ActOnNoexceptSpec(Expr *NoexceptExpr,
83	ExceptionSpecificationType &EST) {
84
85	if (NoexceptExpr->isTypeDependent() ||
86	NoexceptExpr->containsUnexpandedParameterPack()) {
87	EST = EST_DependentNoexcept;
88	return NoexceptExpr;
89	}
90
91	llvm::APSInt Result;
92	ExprResult Converted = CheckConvertedConstantExpression(
93	NoexceptExpr, Context.BoolTy, Result, CCEK_Noexcept);
94
95	if (Converted.isInvalid()) {
96	EST = EST_NoexceptFalse;
97	// Fill in an expression of 'false' as a fixup.
98	auto *BoolExpr = new (Context)
99	CXXBoolLiteralExpr(false, Context.BoolTy, NoexceptExpr->getBeginLoc());
100	llvm::APSInt Value{1};
101	Value = 0;
102	return ConstantExpr::Create(Context, BoolExpr, APValue{Value});
103	}
104
105	if (Converted.get()->isValueDependent()) {
106	EST = EST_DependentNoexcept;
107	return Converted;
108	}
109
110	if (!Converted.isInvalid())
111	EST = !Result ? EST_NoexceptFalse : EST_NoexceptTrue;
112	return Converted;
113	}
114
115	/// CheckSpecifiedExceptionType - Check if the given type is valid in an
116	/// exception specification. Incomplete types, or pointers to incomplete types
117	/// other than void are not allowed.
118	///
119	/// \param[in,out] T The exception type. This will be decayed to a pointer type
120	/// when the input is an array or a function type.
121	bool Sema::CheckSpecifiedExceptionType(QualType &T, SourceRange Range) {
122	// C++11 [except.spec]p2:
123	// A type cv T, "array of T", or "function returning T" denoted
124	// in an exception-specification is adjusted to type T, "pointer to T", or
125	// "pointer to function returning T", respectively.
126	//
127	// We also apply this rule in C++98.
128	if (T->isArrayType())
129	T = Context.getArrayDecayedType(T);
130	else if (T->isFunctionType())
131	T = Context.getPointerType(T);
132
133	int Kind = 0;
134	QualType PointeeT = T;
135	if (const PointerType *PT = T->getAs<PointerType>()) {
136	PointeeT = PT->getPointeeType();
137	Kind = 1;
138
139	// cv void* is explicitly permitted, despite being a pointer to an
140	// incomplete type.
141	if (PointeeT->isVoidType())
142	return false;
143	} else if (const ReferenceType *RT = T->getAs<ReferenceType>()) {
144	PointeeT = RT->getPointeeType();
145	Kind = 2;
146
147	if (RT->isRValueReferenceType()) {
148	// C++11 [except.spec]p2:
149	// A type denoted in an exception-specification shall not denote [...]
150	// an rvalue reference type.
151	Diag(Range.getBegin(), diag::err_rref_in_exception_spec)
152	<< T << Range;
153	return true;
154	}
155	}
156
157	// C++11 [except.spec]p2:
158	// A type denoted in an exception-specification shall not denote an
159	// incomplete type other than a class currently being defined [...].
160	// A type denoted in an exception-specification shall not denote a
161	// pointer or reference to an incomplete type, other than (cv) void* or a
162	// pointer or reference to a class currently being defined.
163	// In Microsoft mode, downgrade this to a warning.
164	unsigned DiagID = diag::err_incomplete_in_exception_spec;
165	bool ReturnValueOnError = true;
166	if (getLangOpts().MSVCCompat) {
167	DiagID = diag::ext_incomplete_in_exception_spec;
168	ReturnValueOnError = false;
169	}
170	if (!(PointeeT->isRecordType() &&
171	PointeeT->castAs<RecordType>()->isBeingDefined()) &&
172	RequireCompleteType(Loc: Range.getBegin(), T: PointeeT, DiagID, Args: Kind, Args: Range))
173	return ReturnValueOnError;
174
175	// WebAssembly reference types can't be used in exception specifications.
176	if (PointeeT.isWebAssemblyReferenceType()) {
177	Diag(Range.getBegin(), diag::err_wasm_reftype_exception_spec);
178	return true;
179	}
180
181	// The MSVC compatibility mode doesn't extend to sizeless types,
182	// so diagnose them separately.
183	if (PointeeT->isSizelessType() && Kind != 1) {
184	Diag(Range.getBegin(), diag::err_sizeless_in_exception_spec)
185	<< (Kind == 2 ? 1 : 0) << PointeeT << Range;
186	return true;
187	}
188
189	return false;
190	}
191
192	/// CheckDistantExceptionSpec - Check if the given type is a pointer or pointer
193	/// to member to a function with an exception specification. This means that
194	/// it is invalid to add another level of indirection.
195	bool Sema::CheckDistantExceptionSpec(QualType T) {
196	// C++17 removes this rule in favor of putting exception specifications into
197	// the type system.
198	if (getLangOpts().CPlusPlus17)
199	return false;
200
201	if (const PointerType *PT = T->getAs<PointerType>())
202	T = PT->getPointeeType();
203	else if (const MemberPointerType *PT = T->getAs<MemberPointerType>())
204	T = PT->getPointeeType();
205	else
206	return false;
207
208	const FunctionProtoType *FnT = T->getAs<FunctionProtoType>();
209	if (!FnT)
210	return false;
211
212	return FnT->hasExceptionSpec();
213	}
214
215	const FunctionProtoType *
216	Sema::ResolveExceptionSpec(SourceLocation Loc, const FunctionProtoType *FPT) {
217	if (FPT->getExceptionSpecType() == EST_Unparsed) {
218	Diag(Loc, diag::err_exception_spec_not_parsed);
219	return nullptr;
220	}
221
222	if (!isUnresolvedExceptionSpec(ESpecType: FPT->getExceptionSpecType()))
223	return FPT;
224
225	FunctionDecl *SourceDecl = FPT->getExceptionSpecDecl();
226	const FunctionProtoType *SourceFPT =
227	SourceDecl->getType()->castAs<FunctionProtoType>();
228
229	// If the exception specification has already been resolved, just return it.
230	if (!isUnresolvedExceptionSpec(ESpecType: SourceFPT->getExceptionSpecType()))
231	return SourceFPT;
232
233	// Compute or instantiate the exception specification now.
234	if (SourceFPT->getExceptionSpecType() == EST_Unevaluated)
235	EvaluateImplicitExceptionSpec(Loc, FD: SourceDecl);
236	else
237	InstantiateExceptionSpec(PointOfInstantiation: Loc, Function: SourceDecl);
238
239	const FunctionProtoType *Proto =
240	SourceDecl->getType()->castAs<FunctionProtoType>();
241	if (Proto->getExceptionSpecType() == clang::EST_Unparsed) {
242	Diag(Loc, diag::err_exception_spec_not_parsed);
243	Proto = nullptr;
244	}
245	return Proto;
246	}
247
248	void
249	Sema::UpdateExceptionSpec(FunctionDecl *FD,
250	const FunctionProtoType::ExceptionSpecInfo &ESI) {
251	// If we've fully resolved the exception specification, notify listeners.
252	if (!isUnresolvedExceptionSpec(ESpecType: ESI.Type))
253	if (auto *Listener = getASTMutationListener())
254	Listener->ResolvedExceptionSpec(FD);
255
256	for (FunctionDecl *Redecl : FD->redecls())
257	Context.adjustExceptionSpec(Redecl, ESI);
258	}
259
260	static bool exceptionSpecNotKnownYet(const FunctionDecl *FD) {
261	auto *MD = dyn_cast<CXXMethodDecl>(Val: FD);
262	if (!MD)
263	return false;
264
265	auto EST = MD->getType()->castAs<FunctionProtoType>()->getExceptionSpecType();
266	return EST == EST_Unparsed ||
267	(EST == EST_Unevaluated && MD->getParent()->isBeingDefined());
268	}
269
270	static bool CheckEquivalentExceptionSpecImpl(
271	Sema &S, const PartialDiagnostic &DiagID, const PartialDiagnostic &NoteID,
272	const FunctionProtoType *Old, SourceLocation OldLoc,
273	const FunctionProtoType *New, SourceLocation NewLoc,
274	bool *MissingExceptionSpecification = nullptr,
275	bool *MissingEmptyExceptionSpecification = nullptr,
276	bool AllowNoexceptAllMatchWithNoSpec = false, bool IsOperatorNew = false);
277
278	/// Determine whether a function has an implicitly-generated exception
279	/// specification.
280	static bool hasImplicitExceptionSpec(FunctionDecl *Decl) {
281	if (!isa<CXXDestructorDecl>(Val: Decl) &&
282	Decl->getDeclName().getCXXOverloadedOperator() != OO_Delete &&
283	Decl->getDeclName().getCXXOverloadedOperator() != OO_Array_Delete)
284	return false;
285
286	// For a function that the user didn't declare:
287	// - if this is a destructor, its exception specification is implicit.
288	// - if this is 'operator delete' or 'operator delete[]', the exception
289	// specification is as-if an explicit exception specification was given
290	// (per [basic.stc.dynamic]p2).
291	if (!Decl->getTypeSourceInfo())
292	return isa<CXXDestructorDecl>(Val: Decl);
293
294	auto *Ty = Decl->getTypeSourceInfo()->getType()->castAs<FunctionProtoType>();
295	return !Ty->hasExceptionSpec();
296	}
297
298	bool Sema::CheckEquivalentExceptionSpec(FunctionDecl *Old, FunctionDecl *New) {
299	// Just completely ignore this under -fno-exceptions prior to C++17.
300	// In C++17 onwards, the exception specification is part of the type and
301	// we will diagnose mismatches anyway, so it's better to check for them here.
302	if (!getLangOpts().CXXExceptions && !getLangOpts().CPlusPlus17)
303	return false;
304
305	OverloadedOperatorKind OO = New->getDeclName().getCXXOverloadedOperator();
306	bool IsOperatorNew = OO == OO_New || OO == OO_Array_New;
307	bool MissingExceptionSpecification = false;
308	bool MissingEmptyExceptionSpecification = false;
309
310	unsigned DiagID = diag::err_mismatched_exception_spec;
311	bool ReturnValueOnError = true;
312	if (getLangOpts().MSVCCompat) {
313	DiagID = diag::ext_mismatched_exception_spec;
314	ReturnValueOnError = false;
315	}
316
317	// If we're befriending a member function of a class that's currently being
318	// defined, we might not be able to work out its exception specification yet.
319	// If not, defer the check until later.
320	if (exceptionSpecNotKnownYet(FD: Old) || exceptionSpecNotKnownYet(FD: New)) {
321	DelayedEquivalentExceptionSpecChecks.push_back(Elt: {New, Old});
322	return false;
323	}
324
325	// Check the types as written: they must match before any exception
326	// specification adjustment is applied.
327	if (!CheckEquivalentExceptionSpecImpl(
328	*this, PDiag(DiagID), PDiag(diag::note_previous_declaration),
329	Old->getType()->getAs<FunctionProtoType>(), Old->getLocation(),
330	New->getType()->getAs<FunctionProtoType>(), New->getLocation(),
331	&MissingExceptionSpecification, &MissingEmptyExceptionSpecification,
332	/*AllowNoexceptAllMatchWithNoSpec=*/true, IsOperatorNew)) {
333	// C++11 [except.spec]p4 [DR1492]:
334	// If a declaration of a function has an implicit
335	// exception-specification, other declarations of the function shall
336	// not specify an exception-specification.
337	if (getLangOpts().CPlusPlus11 && getLangOpts().CXXExceptions &&
338	hasImplicitExceptionSpec(Decl: Old) != hasImplicitExceptionSpec(Decl: New)) {
339	Diag(New->getLocation(), diag::ext_implicit_exception_spec_mismatch)
340	<< hasImplicitExceptionSpec(Old);
341	if (Old->getLocation().isValid())
342	Diag(Old->getLocation(), diag::note_previous_declaration);
343	}
344	return false;
345	}
346
347	// The failure was something other than an missing exception
348	// specification; return an error, except in MS mode where this is a warning.
349	if (!MissingExceptionSpecification)
350	return ReturnValueOnError;
351
352	const auto *NewProto = New->getType()->castAs<FunctionProtoType>();
353
354	// The new function declaration is only missing an empty exception
355	// specification "throw()". If the throw() specification came from a
356	// function in a system header that has C linkage, just add an empty
357	// exception specification to the "new" declaration. Note that C library
358	// implementations are permitted to add these nothrow exception
359	// specifications.
360	//
361	// Likewise if the old function is a builtin.
362	if (MissingEmptyExceptionSpecification &&
363	(Old->getLocation().isInvalid() ||
364	Context.getSourceManager().isInSystemHeader(Loc: Old->getLocation()) ||
365	Old->getBuiltinID()) &&
366	Old->isExternC()) {
367	New->setType(Context.getFunctionType(
368	ResultTy: NewProto->getReturnType(), Args: NewProto->getParamTypes(),
369	EPI: NewProto->getExtProtoInfo().withExceptionSpec(EST_DynamicNone)));
370	return false;
371	}
372
373	const auto *OldProto = Old->getType()->castAs<FunctionProtoType>();
374
375	FunctionProtoType::ExceptionSpecInfo ESI = OldProto->getExceptionSpecType();
376	if (ESI.Type == EST_Dynamic) {
377	// FIXME: What if the exceptions are described in terms of the old
378	// prototype's parameters?
379	ESI.Exceptions = OldProto->exceptions();
380	}
381
382	if (ESI.Type == EST_NoexceptFalse)
383	ESI.Type = EST_None;
384	if (ESI.Type == EST_NoexceptTrue)
385	ESI.Type = EST_BasicNoexcept;
386
387	// For dependent noexcept, we can't just take the expression from the old
388	// prototype. It likely contains references to the old prototype's parameters.
389	if (ESI.Type == EST_DependentNoexcept) {
390	New->setInvalidDecl();
391	} else {
392	// Update the type of the function with the appropriate exception
393	// specification.
394	New->setType(Context.getFunctionType(
395	ResultTy: NewProto->getReturnType(), Args: NewProto->getParamTypes(),
396	EPI: NewProto->getExtProtoInfo().withExceptionSpec(ESI)));
397	}
398
399	if (getLangOpts().MSVCCompat && isDynamicExceptionSpec(ESpecType: ESI.Type)) {
400	DiagID = diag::ext_missing_exception_specification;
401	ReturnValueOnError = false;
402	} else if (New->isReplaceableGlobalAllocationFunction() &&
403	ESI.Type != EST_DependentNoexcept) {
404	// Allow missing exception specifications in redeclarations as an extension,
405	// when declaring a replaceable global allocation function.
406	DiagID = diag::ext_missing_exception_specification;
407	ReturnValueOnError = false;
408	} else if (ESI.Type == EST_NoThrow) {
409	// Don't emit any warning for missing 'nothrow' in MSVC.
410	if (getLangOpts().MSVCCompat) {
411	return false;
412	}
413	// Allow missing attribute 'nothrow' in redeclarations, since this is a very
414	// common omission.
415	DiagID = diag::ext_missing_exception_specification;
416	ReturnValueOnError = false;
417	} else {
418	DiagID = diag::err_missing_exception_specification;
419	ReturnValueOnError = true;
420	}
421
422	// Warn about the lack of exception specification.
423	SmallString<128> ExceptionSpecString;
424	llvm::raw_svector_ostream OS(ExceptionSpecString);
425	switch (OldProto->getExceptionSpecType()) {
426	case EST_DynamicNone:
427	OS << "throw()";
428	break;
429
430	case EST_Dynamic: {
431	OS << "throw(";
432	bool OnFirstException = true;
433	for (const auto &E : OldProto->exceptions()) {
434	if (OnFirstException)
435	OnFirstException = false;
436	else
437	OS << ", ";
438
439	OS << E.getAsString(getPrintingPolicy());
440	}
441	OS << ")";
442	break;
443	}
444
445	case EST_BasicNoexcept:
446	OS << "noexcept";
447	break;
448
449	case EST_DependentNoexcept:
450	case EST_NoexceptFalse:
451	case EST_NoexceptTrue:
452	OS << "noexcept(";
453	assert(OldProto->getNoexceptExpr() != nullptr && "Expected non-null Expr");
454	OldProto->getNoexceptExpr()->printPretty(OS, nullptr, getPrintingPolicy());
455	OS << ")";
456	break;
457	case EST_NoThrow:
458	OS <<"__attribute__((nothrow))";
459	break;
460	case EST_None:
461	case EST_MSAny:
462	case EST_Unevaluated:
463	case EST_Uninstantiated:
464	case EST_Unparsed:
465	llvm_unreachable("This spec type is compatible with none.");
466	}
467
468	SourceLocation FixItLoc;
469	if (TypeSourceInfo *TSInfo = New->getTypeSourceInfo()) {
470	TypeLoc TL = TSInfo->getTypeLoc().IgnoreParens();
471	// FIXME: Preserve enough information so that we can produce a correct fixit
472	// location when there is a trailing return type.
473	if (auto FTLoc = TL.getAs<FunctionProtoTypeLoc>())
474	if (!FTLoc.getTypePtr()->hasTrailingReturn())
475	FixItLoc = getLocForEndOfToken(Loc: FTLoc.getLocalRangeEnd());
476	}
477
478	if (FixItLoc.isInvalid())
479	Diag(New->getLocation(), DiagID)
480	<< New << OS.str();
481	else {
482	Diag(New->getLocation(), DiagID)
483	<< New << OS.str()
484	<< FixItHint::CreateInsertion(InsertionLoc: FixItLoc, Code: " " + OS.str().str());
485	}
486
487	if (Old->getLocation().isValid())
488	Diag(Old->getLocation(), diag::note_previous_declaration);
489
490	return ReturnValueOnError;
491	}
492
493	/// CheckEquivalentExceptionSpec - Check if the two types have equivalent
494	/// exception specifications. Exception specifications are equivalent if
495	/// they allow exactly the same set of exception types. It does not matter how
496	/// that is achieved. See C++ [except.spec]p2.
497	bool Sema::CheckEquivalentExceptionSpec(
498	const FunctionProtoType *Old, SourceLocation OldLoc,
499	const FunctionProtoType *New, SourceLocation NewLoc) {
500	if (!getLangOpts().CXXExceptions)
501	return false;
502
503	unsigned DiagID = diag::err_mismatched_exception_spec;
504	if (getLangOpts().MSVCCompat)
505	DiagID = diag::ext_mismatched_exception_spec;
506	bool Result = CheckEquivalentExceptionSpecImpl(
507	*this, PDiag(DiagID), PDiag(diag::note_previous_declaration),
508	Old, OldLoc, New, NewLoc);
509
510	// In Microsoft mode, mismatching exception specifications just cause a warning.
511	if (getLangOpts().MSVCCompat)
512	return false;
513	return Result;
514	}
515
516	/// CheckEquivalentExceptionSpec - Check if the two types have compatible
517	/// exception specifications. See C++ [except.spec]p3.
518	///
519	/// \return \c false if the exception specifications match, \c true if there is
520	/// a problem. If \c true is returned, either a diagnostic has already been
521	/// produced or \c *MissingExceptionSpecification is set to \c true.
522	static bool CheckEquivalentExceptionSpecImpl(
523	Sema &S, const PartialDiagnostic &DiagID, const PartialDiagnostic &NoteID,
524	const FunctionProtoType *Old, SourceLocation OldLoc,
525	const FunctionProtoType *New, SourceLocation NewLoc,
526	bool *MissingExceptionSpecification,
527	bool *MissingEmptyExceptionSpecification,
528	bool AllowNoexceptAllMatchWithNoSpec, bool IsOperatorNew) {
529	if (MissingExceptionSpecification)
530	*MissingExceptionSpecification = false;
531
532	if (MissingEmptyExceptionSpecification)
533	*MissingEmptyExceptionSpecification = false;
534
535	Old = S.ResolveExceptionSpec(Loc: NewLoc, FPT: Old);
536	if (!Old)
537	return false;
538	New = S.ResolveExceptionSpec(Loc: NewLoc, FPT: New);
539	if (!New)
540	return false;
541
542	// C++0x [except.spec]p3: Two exception-specifications are compatible if:
543	// - both are non-throwing, regardless of their form,
544	// - both have the form noexcept(constant-expression) and the constant-
545	// expressions are equivalent,
546	// - both are dynamic-exception-specifications that have the same set of
547	// adjusted types.
548	//
549	// C++0x [except.spec]p12: An exception-specification is non-throwing if it is
550	// of the form throw(), noexcept, or noexcept(constant-expression) where the
551	// constant-expression yields true.
552	//
553	// C++0x [except.spec]p4: If any declaration of a function has an exception-
554	// specifier that is not a noexcept-specification allowing all exceptions,
555	// all declarations [...] of that function shall have a compatible
556	// exception-specification.
557	//
558	// That last point basically means that noexcept(false) matches no spec.
559	// It's considered when AllowNoexceptAllMatchWithNoSpec is true.
560
561	ExceptionSpecificationType OldEST = Old->getExceptionSpecType();
562	ExceptionSpecificationType NewEST = New->getExceptionSpecType();
563
564	assert(!isUnresolvedExceptionSpec(OldEST) &&
565	!isUnresolvedExceptionSpec(NewEST) &&
566	"Shouldn't see unknown exception specifications here");
567
568	CanThrowResult OldCanThrow = Old->canThrow();
569	CanThrowResult NewCanThrow = New->canThrow();
570
571	// Any non-throwing specifications are compatible.
572	if (OldCanThrow == CT_Cannot && NewCanThrow == CT_Cannot)
573	return false;
574
575	// Any throws-anything specifications are usually compatible.
576	if (OldCanThrow == CT_Can && OldEST != EST_Dynamic &&
577	NewCanThrow == CT_Can && NewEST != EST_Dynamic) {
578	// The exception is that the absence of an exception specification only
579	// matches noexcept(false) for functions, as described above.
580	if (!AllowNoexceptAllMatchWithNoSpec &&
581	((OldEST == EST_None && NewEST == EST_NoexceptFalse) ||
582	(OldEST == EST_NoexceptFalse && NewEST == EST_None))) {
583	// This is the disallowed case.
584	} else {
585	return false;
586	}
587	}
588
589	// C++14 [except.spec]p3:
590	// Two exception-specifications are compatible if [...] both have the form
591	// noexcept(constant-expression) and the constant-expressions are equivalent
592	if (OldEST == EST_DependentNoexcept && NewEST == EST_DependentNoexcept) {
593	llvm::FoldingSetNodeID OldFSN, NewFSN;
594	Old->getNoexceptExpr()->Profile(OldFSN, S.Context, true);
595	New->getNoexceptExpr()->Profile(NewFSN, S.Context, true);
596	if (OldFSN == NewFSN)
597	return false;
598	}
599
600	// Dynamic exception specifications with the same set of adjusted types
601	// are compatible.
602	if (OldEST == EST_Dynamic && NewEST == EST_Dynamic) {
603	bool Success = true;
604	// Both have a dynamic exception spec. Collect the first set, then compare
605	// to the second.
606	llvm::SmallPtrSet<CanQualType, 8> OldTypes, NewTypes;
607	for (const auto &I : Old->exceptions())
608	OldTypes.insert(Ptr: S.Context.getCanonicalType(T: I).getUnqualifiedType());
609
610	for (const auto &I : New->exceptions()) {
611	CanQualType TypePtr = S.Context.getCanonicalType(T: I).getUnqualifiedType();
612	if (OldTypes.count(Ptr: TypePtr))
613	NewTypes.insert(Ptr: TypePtr);
614	else {
615	Success = false;
616	break;
617	}
618	}
619
620	if (Success && OldTypes.size() == NewTypes.size())
621	return false;
622	}
623
624	// As a special compatibility feature, under C++0x we accept no spec and
625	// throw(std::bad_alloc) as equivalent for operator new and operator new[].
626	// This is because the implicit declaration changed, but old code would break.
627	if (S.getLangOpts().CPlusPlus11 && IsOperatorNew) {
628	const FunctionProtoType *WithExceptions = nullptr;
629	if (OldEST == EST_None && NewEST == EST_Dynamic)
630	WithExceptions = New;
631	else if (OldEST == EST_Dynamic && NewEST == EST_None)
632	WithExceptions = Old;
633	if (WithExceptions && WithExceptions->getNumExceptions() == 1) {
634	// One has no spec, the other throw(something). If that something is
635	// std::bad_alloc, all conditions are met.
636	QualType Exception = *WithExceptions->exception_begin();
637	if (CXXRecordDecl *ExRecord = Exception->getAsCXXRecordDecl()) {
638	IdentifierInfo* Name = ExRecord->getIdentifier();
639	if (Name && Name->getName() == "bad_alloc") {
640	// It's called bad_alloc, but is it in std?
641	if (ExRecord->isInStdNamespace()) {
642	return false;
643	}
644	}
645	}
646	}
647	}
648
649	// If the caller wants to handle the case that the new function is
650	// incompatible due to a missing exception specification, let it.
651	if (MissingExceptionSpecification && OldEST != EST_None &&
652	NewEST == EST_None) {
653	// The old type has an exception specification of some sort, but
654	// the new type does not.
655	*MissingExceptionSpecification = true;
656
657	if (MissingEmptyExceptionSpecification && OldCanThrow == CT_Cannot) {
658	// The old type has a throw() or noexcept(true) exception specification
659	// and the new type has no exception specification, and the caller asked
660	// to handle this itself.
661	*MissingEmptyExceptionSpecification = true;
662	}
663
664	return true;
665	}
666
667	S.Diag(NewLoc, DiagID);
668	if (NoteID.getDiagID() != 0 && OldLoc.isValid())
669	S.Diag(OldLoc, NoteID);
670	return true;
671	}
672
673	bool Sema::CheckEquivalentExceptionSpec(const PartialDiagnostic &DiagID,
674	const PartialDiagnostic &NoteID,
675	const FunctionProtoType *Old,
676	SourceLocation OldLoc,
677	const FunctionProtoType *New,
678	SourceLocation NewLoc) {
679	if (!getLangOpts().CXXExceptions)
680	return false;
681	return CheckEquivalentExceptionSpecImpl(S&: *this, DiagID, NoteID, Old, OldLoc,
682	New, NewLoc);
683	}
684
685	bool Sema::handlerCanCatch(QualType HandlerType, QualType ExceptionType) {
686	// [except.handle]p3:
687	// A handler is a match for an exception object of type E if:
688
689	// HandlerType must be ExceptionType or derived from it, or pointer or
690	// reference to such types.
691	const ReferenceType *RefTy = HandlerType->getAs<ReferenceType>();
692	if (RefTy)
693	HandlerType = RefTy->getPointeeType();
694
695	// -- the handler is of type cv T or cv T& and E and T are the same type
696	if (Context.hasSameUnqualifiedType(T1: ExceptionType, T2: HandlerType))
697	return true;
698
699	// FIXME: ObjC pointer types?
700	if (HandlerType->isPointerType() || HandlerType->isMemberPointerType()) {
701	if (RefTy && (!HandlerType.isConstQualified() ||
702	HandlerType.isVolatileQualified()))
703	return false;
704
705	// -- the handler is of type cv T or const T& where T is a pointer or
706	// pointer to member type and E is std::nullptr_t
707	if (ExceptionType->isNullPtrType())
708	return true;
709
710	// -- the handler is of type cv T or const T& where T is a pointer or
711	// pointer to member type and E is a pointer or pointer to member type
712	// that can be converted to T by one or more of
713	// -- a qualification conversion
714	// -- a function pointer conversion
715	bool LifetimeConv;
716	QualType Result;
717	// FIXME: Should we treat the exception as catchable if a lifetime
718	// conversion is required?
719	if (IsQualificationConversion(FromType: ExceptionType, ToType: HandlerType, CStyle: false,
720	ObjCLifetimeConversion&: LifetimeConv) ||
721	IsFunctionConversion(FromType: ExceptionType, ToType: HandlerType, ResultTy&: Result))
722	return true;
723
724	// -- a standard pointer conversion [...]
725	if (!ExceptionType->isPointerType() || !HandlerType->isPointerType())
726	return false;
727
728	// Handle the "qualification conversion" portion.
729	Qualifiers EQuals, HQuals;
730	ExceptionType = Context.getUnqualifiedArrayType(
731	T: ExceptionType->getPointeeType(), Quals&: EQuals);
732	HandlerType = Context.getUnqualifiedArrayType(
733	T: HandlerType->getPointeeType(), Quals&: HQuals);
734	if (!HQuals.compatiblyIncludes(other: EQuals))
735	return false;
736
737	if (HandlerType->isVoidType() && ExceptionType->isObjectType())
738	return true;
739
740	// The only remaining case is a derived-to-base conversion.
741	}
742
743	// -- the handler is of type cg T or cv T& and T is an unambiguous public
744	// base class of E
745	if (!ExceptionType->isRecordType() || !HandlerType->isRecordType())
746	return false;
747	CXXBasePaths Paths(/*FindAmbiguities=*/true, /*RecordPaths=*/true,
748	/*DetectVirtual=*/false);
749	if (!IsDerivedFrom(Loc: SourceLocation(), Derived: ExceptionType, Base: HandlerType, Paths) ||
750	Paths.isAmbiguous(BaseType: Context.getCanonicalType(T: HandlerType)))
751	return false;
752
753	// Do this check from a context without privileges.
754	switch (CheckBaseClassAccess(AccessLoc: SourceLocation(), Base: HandlerType, Derived: ExceptionType,
755	Path: Paths.front(),
756	/*Diagnostic*/ DiagID: 0,
757	/*ForceCheck*/ true,
758	/*ForceUnprivileged*/ true)) {
759	case AR_accessible: return true;
760	case AR_inaccessible: return false;
761	case AR_dependent:
762	llvm_unreachable("access check dependent for unprivileged context");
763	case AR_delayed:
764	llvm_unreachable("access check delayed in non-declaration");
765	}
766	llvm_unreachable("unexpected access check result");
767	}
768
769	/// CheckExceptionSpecSubset - Check whether the second function type's
770	/// exception specification is a subset (or equivalent) of the first function
771	/// type. This is used by override and pointer assignment checks.
772	bool Sema::CheckExceptionSpecSubset(
773	const PartialDiagnostic &DiagID, const PartialDiagnostic &NestedDiagID,
774	const PartialDiagnostic &NoteID, const PartialDiagnostic &NoThrowDiagID,
775	const FunctionProtoType *Superset, bool SkipSupersetFirstParameter,
776	SourceLocation SuperLoc, const FunctionProtoType *Subset,
777	bool SkipSubsetFirstParameter, SourceLocation SubLoc) {
778
779	// Just auto-succeed under -fno-exceptions.
780	if (!getLangOpts().CXXExceptions)
781	return false;
782
783	// FIXME: As usual, we could be more specific in our error messages, but
784	// that better waits until we've got types with source locations.
785
786	if (!SubLoc.isValid())
787	SubLoc = SuperLoc;
788
789	// Resolve the exception specifications, if needed.
790	Superset = ResolveExceptionSpec(Loc: SuperLoc, FPT: Superset);
791	if (!Superset)
792	return false;
793	Subset = ResolveExceptionSpec(Loc: SubLoc, FPT: Subset);
794	if (!Subset)
795	return false;
796
797	ExceptionSpecificationType SuperEST = Superset->getExceptionSpecType();
798	ExceptionSpecificationType SubEST = Subset->getExceptionSpecType();
799	assert(!isUnresolvedExceptionSpec(SuperEST) &&
800	!isUnresolvedExceptionSpec(SubEST) &&
801	"Shouldn't see unknown exception specifications here");
802
803	// If there are dependent noexcept specs, assume everything is fine. Unlike
804	// with the equivalency check, this is safe in this case, because we don't
805	// want to merge declarations. Checks after instantiation will catch any
806	// omissions we make here.
807	if (SuperEST == EST_DependentNoexcept || SubEST == EST_DependentNoexcept)
808	return false;
809
810	CanThrowResult SuperCanThrow = Superset->canThrow();
811	CanThrowResult SubCanThrow = Subset->canThrow();
812
813	// If the superset contains everything or the subset contains nothing, we're
814	// done.
815	if ((SuperCanThrow == CT_Can && SuperEST != EST_Dynamic) ||
816	SubCanThrow == CT_Cannot)
817	return CheckParamExceptionSpec(NestedDiagID, NoteID, Target: Superset,
818	SkipTargetFirstParameter: SkipSupersetFirstParameter, TargetLoc: SuperLoc, Source: Subset,
819	SkipSourceFirstParameter: SkipSubsetFirstParameter, SourceLoc: SubLoc);
820
821	// Allow __declspec(nothrow) to be missing on redeclaration as an extension in
822	// some cases.
823	if (NoThrowDiagID.getDiagID() != 0 && SubCanThrow == CT_Can &&
824	SuperCanThrow == CT_Cannot && SuperEST == EST_NoThrow) {
825	Diag(SubLoc, NoThrowDiagID);
826	if (NoteID.getDiagID() != 0)
827	Diag(SuperLoc, NoteID);
828	return true;
829	}
830
831	// If the subset contains everything or the superset contains nothing, we've
832	// failed.
833	if ((SubCanThrow == CT_Can && SubEST != EST_Dynamic) ||
834	SuperCanThrow == CT_Cannot) {
835	Diag(SubLoc, DiagID);
836	if (NoteID.getDiagID() != 0)
837	Diag(SuperLoc, NoteID);
838	return true;
839	}
840
841	assert(SuperEST == EST_Dynamic && SubEST == EST_Dynamic &&
842	"Exception spec subset: non-dynamic case slipped through.");
843
844	// Neither contains everything or nothing. Do a proper comparison.
845	for (QualType SubI : Subset->exceptions()) {
846	if (const ReferenceType *RefTy = SubI->getAs<ReferenceType>())
847	SubI = RefTy->getPointeeType();
848
849	// Make sure it's in the superset.
850	bool Contained = false;
851	for (QualType SuperI : Superset->exceptions()) {
852	// [except.spec]p5:
853	// the target entity shall allow at least the exceptions allowed by the
854	// source
855	//
856	// We interpret this as meaning that a handler for some target type would
857	// catch an exception of each source type.
858	if (handlerCanCatch(HandlerType: SuperI, ExceptionType: SubI)) {
859	Contained = true;
860	break;
861	}
862	}
863	if (!Contained) {
864	Diag(SubLoc, DiagID);
865	if (NoteID.getDiagID() != 0)
866	Diag(SuperLoc, NoteID);
867	return true;
868	}
869	}
870	// We've run half the gauntlet.
871	return CheckParamExceptionSpec(NestedDiagID, NoteID, Target: Superset,
872	SkipTargetFirstParameter: SkipSupersetFirstParameter, TargetLoc: SuperLoc, Source: Subset,
873	SkipSourceFirstParameter: SkipSupersetFirstParameter, SourceLoc: SubLoc);
874	}
875
876	static bool
877	CheckSpecForTypesEquivalent(Sema &S, const PartialDiagnostic &DiagID,
878	const PartialDiagnostic &NoteID, QualType Target,
879	SourceLocation TargetLoc, QualType Source,
880	SourceLocation SourceLoc) {
881	const FunctionProtoType *TFunc = GetUnderlyingFunction(T: Target);
882	if (!TFunc)
883	return false;
884	const FunctionProtoType *SFunc = GetUnderlyingFunction(T: Source);
885	if (!SFunc)
886	return false;
887
888	return S.CheckEquivalentExceptionSpec(DiagID, NoteID, Old: TFunc, OldLoc: TargetLoc,
889	New: SFunc, NewLoc: SourceLoc);
890	}
891
892	/// CheckParamExceptionSpec - Check if the parameter and return types of the
893	/// two functions have equivalent exception specs. This is part of the
894	/// assignment and override compatibility check. We do not check the parameters
895	/// of parameter function pointers recursively, as no sane programmer would
896	/// even be able to write such a function type.
897	bool Sema::CheckParamExceptionSpec(
898	const PartialDiagnostic &DiagID, const PartialDiagnostic &NoteID,
899	const FunctionProtoType *Target, bool SkipTargetFirstParameter,
900	SourceLocation TargetLoc, const FunctionProtoType *Source,
901	bool SkipSourceFirstParameter, SourceLocation SourceLoc) {
902	auto RetDiag = DiagID;
903	RetDiag << 0;
904	if (CheckSpecForTypesEquivalent(
905	*this, RetDiag, PDiag(),
906	Target->getReturnType(), TargetLoc, Source->getReturnType(),
907	SourceLoc))
908	return true;
909
910	// We shouldn't even be testing this unless the arguments are otherwise
911	// compatible.
912	assert((Target->getNumParams() - (unsigned)SkipTargetFirstParameter) ==
913	(Source->getNumParams() - (unsigned)SkipSourceFirstParameter) &&
914	"Functions have different argument counts.");
915	for (unsigned i = 0, E = Target->getNumParams(); i != E; ++i) {
916	auto ParamDiag = DiagID;
917	ParamDiag << 1;
918	if (CheckSpecForTypesEquivalent(
919	S&: *this, DiagID: ParamDiag, NoteID: PDiag(),
920	Target: Target->getParamType(i: i + (SkipTargetFirstParameter ? 1 : 0)),
921	TargetLoc, Source: Source->getParamType(i: SkipSourceFirstParameter ? 1 : 0),
922	SourceLoc))
923	return true;
924	}
925	return false;
926	}
927
928	bool Sema::CheckExceptionSpecCompatibility(Expr *From, QualType ToType) {
929	// First we check for applicability.
930	// Target type must be a function, function pointer or function reference.
931	const FunctionProtoType *ToFunc = GetUnderlyingFunction(T: ToType);
932	if (!ToFunc || ToFunc->hasDependentExceptionSpec())
933	return false;
934
935	// SourceType must be a function or function pointer.
936	const FunctionProtoType *FromFunc = GetUnderlyingFunction(T: From->getType());
937	if (!FromFunc || FromFunc->hasDependentExceptionSpec())
938	return false;
939
940	unsigned DiagID = diag::err_incompatible_exception_specs;
941	unsigned NestedDiagID = diag::err_deep_exception_specs_differ;
942	// This is not an error in C++17 onwards, unless the noexceptness doesn't
943	// match, but in that case we have a full-on type mismatch, not just a
944	// type sugar mismatch.
945	if (getLangOpts().CPlusPlus17) {
946	DiagID = diag::warn_incompatible_exception_specs;
947	NestedDiagID = diag::warn_deep_exception_specs_differ;
948	}
949
950	// Now we've got the correct types on both sides, check their compatibility.
951	// This means that the source of the conversion can only throw a subset of
952	// the exceptions of the target, and any exception specs on arguments or
953	// return types must be equivalent.
954	//
955	// FIXME: If there is a nested dependent exception specification, we should
956	// not be checking it here. This is fine:
957	// template<typename T> void f() {
958	// void (*p)(void (*) throw(T));
959	// void (*q)(void (*) throw(int)) = p;
960	// }
961	// ... because it might be instantiated with T=int.
962	return CheckExceptionSpecSubset(DiagID: PDiag(DiagID), NestedDiagID: PDiag(DiagID: NestedDiagID), NoteID: PDiag(),
963	NoThrowDiagID: PDiag(), Superset: ToFunc, SkipSupersetFirstParameter: 0,
964	SuperLoc: From->getSourceRange().getBegin(), Subset: FromFunc,
965	SkipSubsetFirstParameter: 0, SubLoc: SourceLocation()) &&
966	!getLangOpts().CPlusPlus17;
967	}
968
969	bool Sema::CheckOverridingFunctionExceptionSpec(const CXXMethodDecl *New,
970	const CXXMethodDecl *Old) {
971	// If the new exception specification hasn't been parsed yet, skip the check.
972	// We'll get called again once it's been parsed.
973	if (New->getType()->castAs<FunctionProtoType>()->getExceptionSpecType() ==
974	EST_Unparsed)
975	return false;
976
977	// Don't check uninstantiated template destructors at all. We can only
978	// synthesize correct specs after the template is instantiated.
979	if (isa<CXXDestructorDecl>(Val: New) && New->getParent()->isDependentType())
980	return false;
981
982	// If the old exception specification hasn't been parsed yet, or the new
983	// exception specification can't be computed yet, remember that we need to
984	// perform this check when we get to the end of the outermost
985	// lexically-surrounding class.
986	if (exceptionSpecNotKnownYet(Old) || exceptionSpecNotKnownYet(New)) {
987	DelayedOverridingExceptionSpecChecks.push_back(Elt: {New, Old});
988	return false;
989	}
990
991	unsigned DiagID = diag::err_override_exception_spec;
992	if (getLangOpts().MSVCCompat)
993	DiagID = diag::ext_override_exception_spec;
994	return CheckExceptionSpecSubset(
995	PDiag(DiagID), PDiag(diag::err_deep_exception_specs_differ),
996	PDiag(diag::note_overridden_virtual_function),
997	PDiag(diag::ext_override_exception_spec),
998	Old->getType()->castAs<FunctionProtoType>(),
999	Old->hasCXXExplicitFunctionObjectParameter(), Old->getLocation(),
1000	New->getType()->castAs<FunctionProtoType>(),
1001	New->hasCXXExplicitFunctionObjectParameter(), New->getLocation());
1002	}
1003
1004	static CanThrowResult canSubStmtsThrow(Sema &Self, const Stmt *S) {
1005	CanThrowResult R = CT_Cannot;
1006	for (const Stmt *SubStmt : S->children()) {
1007	if (!SubStmt)
1008	continue;
1009	R = mergeCanThrow(CT1: R, CT2: Self.canThrow(E: SubStmt));
1010	if (R == CT_Can)
1011	break;
1012	}
1013	return R;
1014	}
1015
1016	CanThrowResult Sema::canCalleeThrow(Sema &S, const Expr *E, const Decl *D,
1017	SourceLocation Loc) {
1018	// As an extension, we assume that __attribute__((nothrow)) functions don't
1019	// throw.
1020	if (isa_and_nonnull<FunctionDecl>(D) && D->hasAttr<NoThrowAttr>())
1021	return CT_Cannot;
1022
1023	QualType T;
1024
1025	// In C++1z, just look at the function type of the callee.
1026	if (S.getLangOpts().CPlusPlus17 && isa_and_nonnull<CallExpr>(Val: E)) {
1027	E = cast<CallExpr>(Val: E)->getCallee();
1028	T = E->getType();
1029	if (T->isSpecificPlaceholderType(K: BuiltinType::BoundMember)) {
1030	// Sadly we don't preserve the actual type as part of the "bound member"
1031	// placeholder, so we need to reconstruct it.
1032	E = E->IgnoreParenImpCasts();
1033
1034	// Could be a call to a pointer-to-member or a plain member access.
1035	if (auto *Op = dyn_cast<BinaryOperator>(Val: E)) {
1036	assert(Op->getOpcode() == BO_PtrMemD || Op->getOpcode() == BO_PtrMemI);
1037	T = Op->getRHS()->getType()
1038	->castAs<MemberPointerType>()->getPointeeType();
1039	} else {
1040	T = cast<MemberExpr>(Val: E)->getMemberDecl()->getType();
1041	}
1042	}
1043	} else if (const ValueDecl *VD = dyn_cast_or_null<ValueDecl>(Val: D))
1044	T = VD->getType();
1045	else
1046	// If we have no clue what we're calling, assume the worst.
1047	return CT_Can;
1048
1049	const FunctionProtoType *FT;
1050	if ((FT = T->getAs<FunctionProtoType>())) {
1051	} else if (const PointerType *PT = T->getAs<PointerType>())
1052	FT = PT->getPointeeType()->getAs<FunctionProtoType>();
1053	else if (const ReferenceType *RT = T->getAs<ReferenceType>())
1054	FT = RT->getPointeeType()->getAs<FunctionProtoType>();
1055	else if (const MemberPointerType *MT = T->getAs<MemberPointerType>())
1056	FT = MT->getPointeeType()->getAs<FunctionProtoType>();
1057	else if (const BlockPointerType *BT = T->getAs<BlockPointerType>())
1058	FT = BT->getPointeeType()->getAs<FunctionProtoType>();
1059
1060	if (!FT)
1061	return CT_Can;
1062
1063	if (Loc.isValid() || (Loc.isInvalid() && E))
1064	FT = S.ResolveExceptionSpec(Loc: Loc.isInvalid() ? E->getBeginLoc() : Loc, FPT: FT);
1065	if (!FT)
1066	return CT_Can;
1067
1068	return FT->canThrow();
1069	}
1070
1071	static CanThrowResult canVarDeclThrow(Sema &Self, const VarDecl *VD) {
1072	CanThrowResult CT = CT_Cannot;
1073
1074	// Initialization might throw.
1075	if (!VD->isUsableInConstantExpressions(C: Self.Context))
1076	if (const Expr *Init = VD->getInit())
1077	CT = mergeCanThrow(CT1: CT, CT2: Self.canThrow(Init));
1078
1079	// Destructor might throw.
1080	if (VD->needsDestruction(Ctx: Self.Context) == QualType::DK_cxx_destructor) {
1081	if (auto *RD =
1082	VD->getType()->getBaseElementTypeUnsafe()->getAsCXXRecordDecl()) {
1083	if (auto *Dtor = RD->getDestructor()) {
1084	CT = mergeCanThrow(
1085	CT, Sema::canCalleeThrow(S&: Self, E: nullptr, D: Dtor, Loc: VD->getLocation()));
1086	}
1087	}
1088	}
1089
1090	// If this is a decomposition declaration, bindings might throw.
1091	if (auto *DD = dyn_cast<DecompositionDecl>(Val: VD))
1092	for (auto *B : DD->bindings())
1093	if (auto *HD = B->getHoldingVar())
1094	CT = mergeCanThrow(CT1: CT, CT2: canVarDeclThrow(Self, VD: HD));
1095
1096	return CT;
1097	}
1098
1099	static CanThrowResult canDynamicCastThrow(const CXXDynamicCastExpr *DC) {
1100	if (DC->isTypeDependent())
1101	return CT_Dependent;
1102
1103	if (!DC->getTypeAsWritten()->isReferenceType())
1104	return CT_Cannot;
1105
1106	if (DC->getSubExpr()->isTypeDependent())
1107	return CT_Dependent;
1108
1109	return DC->getCastKind() == clang::CK_Dynamic? CT_Can : CT_Cannot;
1110	}
1111
1112	static CanThrowResult canTypeidThrow(Sema &S, const CXXTypeidExpr *DC) {
1113	if (DC->isTypeOperand())
1114	return CT_Cannot;
1115
1116	Expr *Op = DC->getExprOperand();
1117	if (Op->isTypeDependent())
1118	return CT_Dependent;
1119
1120	const RecordType *RT = Op->getType()->getAs<RecordType>();
1121	if (!RT)
1122	return CT_Cannot;
1123
1124	if (!cast<CXXRecordDecl>(Val: RT->getDecl())->isPolymorphic())
1125	return CT_Cannot;
1126
1127	if (Op->Classify(Ctx&: S.Context).isPRValue())
1128	return CT_Cannot;
1129
1130	return CT_Can;
1131	}
1132
1133	CanThrowResult Sema::canThrow(const Stmt *S) {
1134	// C++ [expr.unary.noexcept]p3:
1135	// [Can throw] if in a potentially-evaluated context the expression would
1136	// contain:
1137	switch (S->getStmtClass()) {
1138	case Expr::ConstantExprClass:
1139	return canThrow(S: cast<ConstantExpr>(Val: S)->getSubExpr());
1140
1141	case Expr::CXXThrowExprClass:
1142	// - a potentially evaluated throw-expression
1143	return CT_Can;
1144
1145	case Expr::CXXDynamicCastExprClass: {
1146	// - a potentially evaluated dynamic_cast expression dynamic_cast<T>(v),
1147	// where T is a reference type, that requires a run-time check
1148	auto *CE = cast<CXXDynamicCastExpr>(Val: S);
1149	// FIXME: Properly determine whether a variably-modified type can throw.
1150	if (CE->getType()->isVariablyModifiedType())
1151	return CT_Can;
1152	CanThrowResult CT = canDynamicCastThrow(DC: CE);
1153	if (CT == CT_Can)
1154	return CT;
1155	return mergeCanThrow(CT1: CT, CT2: canSubStmtsThrow(*this, CE));
1156	}
1157
1158	case Expr::CXXTypeidExprClass:
1159	// - a potentially evaluated typeid expression applied to a glvalue
1160	// expression whose type is a polymorphic class type
1161	return canTypeidThrow(S&: *this, DC: cast<CXXTypeidExpr>(Val: S));
1162
1163	// - a potentially evaluated call to a function, member function, function
1164	// pointer, or member function pointer that does not have a non-throwing
1165	// exception-specification
1166	case Expr::CallExprClass:
1167	case Expr::CXXMemberCallExprClass:
1168	case Expr::CXXOperatorCallExprClass:
1169	case Expr::UserDefinedLiteralClass: {
1170	const CallExpr *CE = cast<CallExpr>(Val: S);
1171	CanThrowResult CT;
1172	if (CE->isTypeDependent())
1173	CT = CT_Dependent;
1174	else if (isa<CXXPseudoDestructorExpr>(Val: CE->getCallee()->IgnoreParens()))
1175	CT = CT_Cannot;
1176	else
1177	CT = canCalleeThrow(*this, CE, CE->getCalleeDecl());
1178	if (CT == CT_Can)
1179	return CT;
1180	return mergeCanThrow(CT1: CT, CT2: canSubStmtsThrow(*this, CE));
1181	}
1182
1183	case Expr::CXXConstructExprClass:
1184	case Expr::CXXTemporaryObjectExprClass: {
1185	auto *CE = cast<CXXConstructExpr>(Val: S);
1186	// FIXME: Properly determine whether a variably-modified type can throw.
1187	if (CE->getType()->isVariablyModifiedType())
1188	return CT_Can;
1189	CanThrowResult CT = canCalleeThrow(*this, CE, CE->getConstructor());
1190	if (CT == CT_Can)
1191	return CT;
1192	return mergeCanThrow(CT1: CT, CT2: canSubStmtsThrow(*this, CE));
1193	}
1194
1195	case Expr::CXXInheritedCtorInitExprClass: {
1196	auto *ICIE = cast<CXXInheritedCtorInitExpr>(Val: S);
1197	return canCalleeThrow(*this, ICIE, ICIE->getConstructor());
1198	}
1199
1200	case Expr::LambdaExprClass: {
1201	const LambdaExpr *Lambda = cast<LambdaExpr>(Val: S);
1202	CanThrowResult CT = CT_Cannot;
1203	for (LambdaExpr::const_capture_init_iterator
1204	Cap = Lambda->capture_init_begin(),
1205	CapEnd = Lambda->capture_init_end();
1206	Cap != CapEnd; ++Cap)
1207	CT = mergeCanThrow(CT1: CT, CT2: canThrow(*Cap));
1208	return CT;
1209	}
1210
1211	case Expr::CXXNewExprClass: {
1212	auto *NE = cast<CXXNewExpr>(Val: S);
1213	CanThrowResult CT;
1214	if (NE->isTypeDependent())
1215	CT = CT_Dependent;
1216	else
1217	CT = canCalleeThrow(*this, NE, NE->getOperatorNew());
1218	if (CT == CT_Can)
1219	return CT;
1220	return mergeCanThrow(CT1: CT, CT2: canSubStmtsThrow(*this, NE));
1221	}
1222
1223	case Expr::CXXDeleteExprClass: {
1224	auto *DE = cast<CXXDeleteExpr>(Val: S);
1225	CanThrowResult CT;
1226	QualType DTy = DE->getDestroyedType();
1227	if (DTy.isNull() || DTy->isDependentType()) {
1228	CT = CT_Dependent;
1229	} else {
1230	CT = canCalleeThrow(*this, DE, DE->getOperatorDelete());
1231	if (const RecordType *RT = DTy->getAs<RecordType>()) {
1232	const CXXRecordDecl *RD = cast<CXXRecordDecl>(Val: RT->getDecl());
1233	const CXXDestructorDecl *DD = RD->getDestructor();
1234	if (DD)
1235	CT = mergeCanThrow(CT, canCalleeThrow(*this, DE, DD));
1236	}
1237	if (CT == CT_Can)
1238	return CT;
1239	}
1240	return mergeCanThrow(CT1: CT, CT2: canSubStmtsThrow(*this, DE));
1241	}
1242
1243	case Expr::CXXBindTemporaryExprClass: {
1244	auto *BTE = cast<CXXBindTemporaryExpr>(Val: S);
1245	// The bound temporary has to be destroyed again, which might throw.
1246	CanThrowResult CT =
1247	canCalleeThrow(*this, BTE, BTE->getTemporary()->getDestructor());
1248	if (CT == CT_Can)
1249	return CT;
1250	return mergeCanThrow(CT1: CT, CT2: canSubStmtsThrow(*this, BTE));
1251	}
1252
1253	case Expr::PseudoObjectExprClass: {
1254	auto *POE = cast<PseudoObjectExpr>(Val: S);
1255	CanThrowResult CT = CT_Cannot;
1256	for (const Expr *E : POE->semantics()) {
1257	CT = mergeCanThrow(CT1: CT, CT2: canThrow(E));
1258	if (CT == CT_Can)
1259	break;
1260	}
1261	return CT;
1262	}
1263
1264	// ObjC message sends are like function calls, but never have exception
1265	// specs.
1266	case Expr::ObjCMessageExprClass:
1267	case Expr::ObjCPropertyRefExprClass:
1268	case Expr::ObjCSubscriptRefExprClass:
1269	return CT_Can;
1270
1271	// All the ObjC literals that are implemented as calls are
1272	// potentially throwing unless we decide to close off that
1273	// possibility.
1274	case Expr::ObjCArrayLiteralClass:
1275	case Expr::ObjCDictionaryLiteralClass:
1276	case Expr::ObjCBoxedExprClass:
1277	return CT_Can;
1278
1279	// Many other things have subexpressions, so we have to test those.
1280	// Some are simple:
1281	case Expr::CoawaitExprClass:
1282	case Expr::ConditionalOperatorClass:
1283	case Expr::CoyieldExprClass:
1284	case Expr::CXXRewrittenBinaryOperatorClass:
1285	case Expr::CXXStdInitializerListExprClass:
1286	case Expr::DesignatedInitExprClass:
1287	case Expr::DesignatedInitUpdateExprClass:
1288	case Expr::ExprWithCleanupsClass:
1289	case Expr::ExtVectorElementExprClass:
1290	case Expr::InitListExprClass:
1291	case Expr::ArrayInitLoopExprClass:
1292	case Expr::MemberExprClass:
1293	case Expr::ObjCIsaExprClass:
1294	case Expr::ObjCIvarRefExprClass:
1295	case Expr::ParenExprClass:
1296	case Expr::ParenListExprClass:
1297	case Expr::ShuffleVectorExprClass:
1298	case Expr::StmtExprClass:
1299	case Expr::ConvertVectorExprClass:
1300	case Expr::VAArgExprClass:
1301	case Expr::CXXParenListInitExprClass:
1302	return canSubStmtsThrow(Self&: *this, S);
1303
1304	case Expr::CompoundLiteralExprClass:
1305	case Expr::CXXConstCastExprClass:
1306	case Expr::CXXAddrspaceCastExprClass:
1307	case Expr::CXXReinterpretCastExprClass:
1308	case Expr::BuiltinBitCastExprClass:
1309	// FIXME: Properly determine whether a variably-modified type can throw.
1310	if (cast<Expr>(Val: S)->getType()->isVariablyModifiedType())
1311	return CT_Can;
1312	return canSubStmtsThrow(Self&: *this, S);
1313
1314	// Some might be dependent for other reasons.
1315	case Expr::ArraySubscriptExprClass:
1316	case Expr::MatrixSubscriptExprClass:
1317	case Expr::OMPArraySectionExprClass:
1318	case Expr::OMPArrayShapingExprClass:
1319	case Expr::OMPIteratorExprClass:
1320	case Expr::BinaryOperatorClass:
1321	case Expr::DependentCoawaitExprClass:
1322	case Expr::CompoundAssignOperatorClass:
1323	case Expr::CStyleCastExprClass:
1324	case Expr::CXXStaticCastExprClass:
1325	case Expr::CXXFunctionalCastExprClass:
1326	case Expr::ImplicitCastExprClass:
1327	case Expr::MaterializeTemporaryExprClass:
1328	case Expr::UnaryOperatorClass: {
1329	// FIXME: Properly determine whether a variably-modified type can throw.
1330	if (auto *CE = dyn_cast<CastExpr>(Val: S))
1331	if (CE->getType()->isVariablyModifiedType())
1332	return CT_Can;
1333	CanThrowResult CT =
1334	cast<Expr>(Val: S)->isTypeDependent() ? CT_Dependent : CT_Cannot;
1335	return mergeCanThrow(CT1: CT, CT2: canSubStmtsThrow(Self&: *this, S));
1336	}
1337
1338	case Expr::CXXDefaultArgExprClass:
1339	return canThrow(cast<CXXDefaultArgExpr>(Val: S)->getExpr());
1340
1341	case Expr::CXXDefaultInitExprClass:
1342	return canThrow(cast<CXXDefaultInitExpr>(Val: S)->getExpr());
1343
1344	case Expr::ChooseExprClass: {
1345	auto *CE = cast<ChooseExpr>(Val: S);
1346	if (CE->isTypeDependent() || CE->isValueDependent())
1347	return CT_Dependent;
1348	return canThrow(CE->getChosenSubExpr());
1349	}
1350
1351	case Expr::GenericSelectionExprClass:
1352	if (cast<GenericSelectionExpr>(Val: S)->isResultDependent())
1353	return CT_Dependent;
1354	return canThrow(cast<GenericSelectionExpr>(Val: S)->getResultExpr());
1355
1356	// Some expressions are always dependent.
1357	case Expr::CXXDependentScopeMemberExprClass:
1358	case Expr::CXXUnresolvedConstructExprClass:
1359	case Expr::DependentScopeDeclRefExprClass:
1360	case Expr::CXXFoldExprClass:
1361	case Expr::RecoveryExprClass:
1362	return CT_Dependent;
1363
1364	case Expr::AsTypeExprClass:
1365	case Expr::BinaryConditionalOperatorClass:
1366	case Expr::BlockExprClass:
1367	case Expr::CUDAKernelCallExprClass:
1368	case Expr::DeclRefExprClass:
1369	case Expr::ObjCBridgedCastExprClass:
1370	case Expr::ObjCIndirectCopyRestoreExprClass:
1371	case Expr::ObjCProtocolExprClass:
1372	case Expr::ObjCSelectorExprClass:
1373	case Expr::ObjCAvailabilityCheckExprClass:
1374	case Expr::OffsetOfExprClass:
1375	case Expr::PackExpansionExprClass:
1376	case Expr::SubstNonTypeTemplateParmExprClass:
1377	case Expr::SubstNonTypeTemplateParmPackExprClass:
1378	case Expr::FunctionParmPackExprClass:
1379	case Expr::UnaryExprOrTypeTraitExprClass:
1380	case Expr::UnresolvedLookupExprClass:
1381	case Expr::UnresolvedMemberExprClass:
1382	case Expr::TypoExprClass:
1383	// FIXME: Many of the above can throw.
1384	return CT_Cannot;
1385
1386	case Expr::AddrLabelExprClass:
1387	case Expr::ArrayTypeTraitExprClass:
1388	case Expr::AtomicExprClass:
1389	case Expr::TypeTraitExprClass:
1390	case Expr::CXXBoolLiteralExprClass:
1391	case Expr::CXXNoexceptExprClass:
1392	case Expr::CXXNullPtrLiteralExprClass:
1393	case Expr::CXXPseudoDestructorExprClass:
1394	case Expr::CXXScalarValueInitExprClass:
1395	case Expr::CXXThisExprClass:
1396	case Expr::CXXUuidofExprClass:
1397	case Expr::CharacterLiteralClass:
1398	case Expr::ExpressionTraitExprClass:
1399	case Expr::FloatingLiteralClass:
1400	case Expr::GNUNullExprClass:
1401	case Expr::ImaginaryLiteralClass:
1402	case Expr::ImplicitValueInitExprClass:
1403	case Expr::IntegerLiteralClass:
1404	case Expr::FixedPointLiteralClass:
1405	case Expr::ArrayInitIndexExprClass:
1406	case Expr::NoInitExprClass:
1407	case Expr::ObjCEncodeExprClass:
1408	case Expr::ObjCStringLiteralClass:
1409	case Expr::ObjCBoolLiteralExprClass:
1410	case Expr::OpaqueValueExprClass:
1411	case Expr::PredefinedExprClass:
1412	case Expr::SizeOfPackExprClass:
1413	case Expr::PackIndexingExprClass:
1414	case Expr::StringLiteralClass:
1415	case Expr::SourceLocExprClass:
1416	case Expr::ConceptSpecializationExprClass:
1417	case Expr::RequiresExprClass:
1418	// These expressions can never throw.
1419	return CT_Cannot;
1420
1421	case Expr::MSPropertyRefExprClass:
1422	case Expr::MSPropertySubscriptExprClass:
1423	llvm_unreachable("Invalid class for expression");
1424
1425	// Most statements can throw if any substatement can throw.
1426	case Stmt::OpenACCComputeConstructClass:
1427	case Stmt::AttributedStmtClass:
1428	case Stmt::BreakStmtClass:
1429	case Stmt::CapturedStmtClass:
1430	case Stmt::CaseStmtClass:
1431	case Stmt::CompoundStmtClass:
1432	case Stmt::ContinueStmtClass:
1433	case Stmt::CoreturnStmtClass:
1434	case Stmt::CoroutineBodyStmtClass:
1435	case Stmt::CXXCatchStmtClass:
1436	case Stmt::CXXForRangeStmtClass:
1437	case Stmt::DefaultStmtClass:
1438	case Stmt::DoStmtClass:
1439	case Stmt::ForStmtClass:
1440	case Stmt::GCCAsmStmtClass:
1441	case Stmt::GotoStmtClass:
1442	case Stmt::IndirectGotoStmtClass:
1443	case Stmt::LabelStmtClass:
1444	case Stmt::MSAsmStmtClass:
1445	case Stmt::MSDependentExistsStmtClass:
1446	case Stmt::NullStmtClass:
1447	case Stmt::ObjCAtCatchStmtClass:
1448	case Stmt::ObjCAtFinallyStmtClass:
1449	case Stmt::ObjCAtSynchronizedStmtClass:
1450	case Stmt::ObjCAutoreleasePoolStmtClass:
1451	case Stmt::ObjCForCollectionStmtClass:
1452	case Stmt::OMPAtomicDirectiveClass:
1453	case Stmt::OMPBarrierDirectiveClass:
1454	case Stmt::OMPCancelDirectiveClass:
1455	case Stmt::OMPCancellationPointDirectiveClass:
1456	case Stmt::OMPCriticalDirectiveClass:
1457	case Stmt::OMPDistributeDirectiveClass:
1458	case Stmt::OMPDistributeParallelForDirectiveClass:
1459	case Stmt::OMPDistributeParallelForSimdDirectiveClass:
1460	case Stmt::OMPDistributeSimdDirectiveClass:
1461	case Stmt::OMPFlushDirectiveClass:
1462	case Stmt::OMPDepobjDirectiveClass:
1463	case Stmt::OMPScanDirectiveClass:
1464	case Stmt::OMPForDirectiveClass:
1465	case Stmt::OMPForSimdDirectiveClass:
1466	case Stmt::OMPMasterDirectiveClass:
1467	case Stmt::OMPMasterTaskLoopDirectiveClass:
1468	case Stmt::OMPMaskedTaskLoopDirectiveClass:
1469	case Stmt::OMPMasterTaskLoopSimdDirectiveClass:
1470	case Stmt::OMPMaskedTaskLoopSimdDirectiveClass:
1471	case Stmt::OMPOrderedDirectiveClass:
1472	case Stmt::OMPCanonicalLoopClass:
1473	case Stmt::OMPParallelDirectiveClass:
1474	case Stmt::OMPParallelForDirectiveClass:
1475	case Stmt::OMPParallelForSimdDirectiveClass:
1476	case Stmt::OMPParallelMasterDirectiveClass:
1477	case Stmt::OMPParallelMaskedDirectiveClass:
1478	case Stmt::OMPParallelMasterTaskLoopDirectiveClass:
1479	case Stmt::OMPParallelMaskedTaskLoopDirectiveClass:
1480	case Stmt::OMPParallelMasterTaskLoopSimdDirectiveClass:
1481	case Stmt::OMPParallelMaskedTaskLoopSimdDirectiveClass:
1482	case Stmt::OMPParallelSectionsDirectiveClass:
1483	case Stmt::OMPSectionDirectiveClass:
1484	case Stmt::OMPSectionsDirectiveClass:
1485	case Stmt::OMPSimdDirectiveClass:
1486	case Stmt::OMPTileDirectiveClass:
1487	case Stmt::OMPUnrollDirectiveClass:
1488	case Stmt::OMPSingleDirectiveClass:
1489	case Stmt::OMPTargetDataDirectiveClass:
1490	case Stmt::OMPTargetDirectiveClass:
1491	case Stmt::OMPTargetEnterDataDirectiveClass:
1492	case Stmt::OMPTargetExitDataDirectiveClass:
1493	case Stmt::OMPTargetParallelDirectiveClass:
1494	case Stmt::OMPTargetParallelForDirectiveClass:
1495	case Stmt::OMPTargetParallelForSimdDirectiveClass:
1496	case Stmt::OMPTargetSimdDirectiveClass:
1497	case Stmt::OMPTargetTeamsDirectiveClass:
1498	case Stmt::OMPTargetTeamsDistributeDirectiveClass:
1499	case Stmt::OMPTargetTeamsDistributeParallelForDirectiveClass:
1500	case Stmt::OMPTargetTeamsDistributeParallelForSimdDirectiveClass:
1501	case Stmt::OMPTargetTeamsDistributeSimdDirectiveClass:
1502	case Stmt::OMPTargetUpdateDirectiveClass:
1503	case Stmt::OMPScopeDirectiveClass:
1504	case Stmt::OMPTaskDirectiveClass:
1505	case Stmt::OMPTaskgroupDirectiveClass:
1506	case Stmt::OMPTaskLoopDirectiveClass:
1507	case Stmt::OMPTaskLoopSimdDirectiveClass:
1508	case Stmt::OMPTaskwaitDirectiveClass:
1509	case Stmt::OMPTaskyieldDirectiveClass:
1510	case Stmt::OMPErrorDirectiveClass:
1511	case Stmt::OMPTeamsDirectiveClass:
1512	case Stmt::OMPTeamsDistributeDirectiveClass:
1513	case Stmt::OMPTeamsDistributeParallelForDirectiveClass:
1514	case Stmt::OMPTeamsDistributeParallelForSimdDirectiveClass:
1515	case Stmt::OMPTeamsDistributeSimdDirectiveClass:
1516	case Stmt::OMPInteropDirectiveClass:
1517	case Stmt::OMPDispatchDirectiveClass:
1518	case Stmt::OMPMaskedDirectiveClass:
1519	case Stmt::OMPMetaDirectiveClass:
1520	case Stmt::OMPGenericLoopDirectiveClass:
1521	case Stmt::OMPTeamsGenericLoopDirectiveClass:
1522	case Stmt::OMPTargetTeamsGenericLoopDirectiveClass:
1523	case Stmt::OMPParallelGenericLoopDirectiveClass:
1524	case Stmt::OMPTargetParallelGenericLoopDirectiveClass:
1525	case Stmt::ReturnStmtClass:
1526	case Stmt::SEHExceptStmtClass:
1527	case Stmt::SEHFinallyStmtClass:
1528	case Stmt::SEHLeaveStmtClass:
1529	case Stmt::SEHTryStmtClass:
1530	case Stmt::SwitchStmtClass:
1531	case Stmt::WhileStmtClass:
1532	return canSubStmtsThrow(Self&: *this, S);
1533
1534	case Stmt::DeclStmtClass: {
1535	CanThrowResult CT = CT_Cannot;
1536	for (const Decl *D : cast<DeclStmt>(Val: S)->decls()) {
1537	if (auto *VD = dyn_cast<VarDecl>(Val: D))
1538	CT = mergeCanThrow(CT1: CT, CT2: canVarDeclThrow(Self&: *this, VD));
1539
1540	// FIXME: Properly determine whether a variably-modified type can throw.
1541	if (auto *TND = dyn_cast<TypedefNameDecl>(Val: D))
1542	if (TND->getUnderlyingType()->isVariablyModifiedType())
1543	return CT_Can;
1544	if (auto *VD = dyn_cast<ValueDecl>(Val: D))
1545	if (VD->getType()->isVariablyModifiedType())
1546	return CT_Can;
1547	}
1548	return CT;
1549	}
1550
1551	case Stmt::IfStmtClass: {
1552	auto *IS = cast<IfStmt>(Val: S);
1553	CanThrowResult CT = CT_Cannot;
1554	if (const Stmt *Init = IS->getInit())
1555	CT = mergeCanThrow(CT1: CT, CT2: canThrow(S: Init));
1556	if (const Stmt *CondDS = IS->getConditionVariableDeclStmt())
1557	CT = mergeCanThrow(CT1: CT, CT2: canThrow(S: CondDS));
1558	CT = mergeCanThrow(CT1: CT, CT2: canThrow(IS->getCond()));
1559
1560	// For 'if constexpr', consider only the non-discarded case.
1561	// FIXME: We should add a DiscardedStmt marker to the AST.
1562	if (std::optional<const Stmt *> Case = IS->getNondiscardedCase(Ctx: Context))
1563	return *Case ? mergeCanThrow(CT1: CT, CT2: canThrow(S: *Case)) : CT;
1564
1565	CanThrowResult Then = canThrow(S: IS->getThen());
1566	CanThrowResult Else = IS->getElse() ? canThrow(S: IS->getElse()) : CT_Cannot;
1567	if (Then == Else)
1568	return mergeCanThrow(CT1: CT, CT2: Then);
1569
1570	// For a dependent 'if constexpr', the result is dependent if it depends on
1571	// the value of the condition.
1572	return mergeCanThrow(CT1: CT, CT2: IS->isConstexpr() ? CT_Dependent
1573	: mergeCanThrow(CT1: Then, CT2: Else));
1574	}
1575
1576	case Stmt::CXXTryStmtClass: {
1577	auto *TS = cast<CXXTryStmt>(Val: S);
1578	// try /*...*/ catch (...) { H } can throw only if H can throw.
1579	// Any other try-catch can throw if any substatement can throw.
1580	const CXXCatchStmt *FinalHandler = TS->getHandler(i: TS->getNumHandlers() - 1);
1581	if (!FinalHandler->getExceptionDecl())
1582	return canThrow(S: FinalHandler->getHandlerBlock());
1583	return canSubStmtsThrow(Self&: *this, S);
1584	}
1585
1586	case Stmt::ObjCAtThrowStmtClass:
1587	return CT_Can;
1588
1589	case Stmt::ObjCAtTryStmtClass: {
1590	auto *TS = cast<ObjCAtTryStmt>(Val: S);
1591
1592	// @catch(...) need not be last in Objective-C. Walk backwards until we
1593	// see one or hit the @try.
1594	CanThrowResult CT = CT_Cannot;
1595	if (const Stmt *Finally = TS->getFinallyStmt())
1596	CT = mergeCanThrow(CT1: CT, CT2: canThrow(S: Finally));
1597	for (unsigned I = TS->getNumCatchStmts(); I != 0; --I) {
1598	const ObjCAtCatchStmt *Catch = TS->getCatchStmt(I: I - 1);
1599	CT = mergeCanThrow(CT1: CT, CT2: canThrow(S: Catch));
1600	// If we reach a @catch(...), no earlier exceptions can escape.
1601	if (Catch->hasEllipsis())
1602	return CT;
1603	}
1604
1605	// Didn't find an @catch(...). Exceptions from the @try body can escape.
1606	return mergeCanThrow(CT1: CT, CT2: canThrow(S: TS->getTryBody()));
1607	}
1608
1609	case Stmt::SYCLUniqueStableNameExprClass:
1610	return CT_Cannot;
1611	case Stmt::NoStmtClass:
1612	llvm_unreachable("Invalid class for statement");
1613	}
1614	llvm_unreachable("Bogus StmtClass");
1615	}
1616
1617	} // end namespace clang
1618