xref: /freebsd/contrib/llvm-project/clang/lib/Sema/SemaCoroutine.cpp (revision 3a9a9c0ca44ec535dcf73fe8462bee458e54814b)
1 //===-- SemaCoroutine.cpp - Semantic Analysis for Coroutines --------------===//
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 implements semantic analysis for C++ Coroutines.
10 //
11 //  This file contains references to sections of the Coroutines TS, which
12 //  can be found at http://wg21.link/coroutines.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "CoroutineStmtBuilder.h"
17 #include "clang/AST/ASTLambda.h"
18 #include "clang/AST/Decl.h"
19 #include "clang/AST/ExprCXX.h"
20 #include "clang/AST/StmtCXX.h"
21 #include "clang/Basic/Builtins.h"
22 #include "clang/Lex/Preprocessor.h"
23 #include "clang/Sema/Initialization.h"
24 #include "clang/Sema/Overload.h"
25 #include "clang/Sema/ScopeInfo.h"
26 #include "clang/Sema/SemaInternal.h"
27 #include "llvm/ADT/SmallSet.h"
28 
29 using namespace clang;
30 using namespace sema;
31 
32 static LookupResult lookupMember(Sema &S, const char *Name, CXXRecordDecl *RD,
33                                  SourceLocation Loc, bool &Res) {
34   DeclarationName DN = S.PP.getIdentifierInfo(Name);
35   LookupResult LR(S, DN, Loc, Sema::LookupMemberName);
36   // Suppress diagnostics when a private member is selected. The same warnings
37   // will be produced again when building the call.
38   LR.suppressDiagnostics();
39   Res = S.LookupQualifiedName(LR, RD);
40   return LR;
41 }
42 
43 static bool lookupMember(Sema &S, const char *Name, CXXRecordDecl *RD,
44                          SourceLocation Loc) {
45   bool Res;
46   lookupMember(S, Name, RD, Loc, Res);
47   return Res;
48 }
49 
50 /// Look up the std::coroutine_traits<...>::promise_type for the given
51 /// function type.
52 static QualType lookupPromiseType(Sema &S, const FunctionDecl *FD,
53                                   SourceLocation KwLoc) {
54   const FunctionProtoType *FnType = FD->getType()->castAs<FunctionProtoType>();
55   const SourceLocation FuncLoc = FD->getLocation();
56 
57   NamespaceDecl *CoroNamespace = nullptr;
58   ClassTemplateDecl *CoroTraits =
59       S.lookupCoroutineTraits(KwLoc, FuncLoc, CoroNamespace);
60   if (!CoroTraits) {
61     return QualType();
62   }
63 
64   // Form template argument list for coroutine_traits<R, P1, P2, ...> according
65   // to [dcl.fct.def.coroutine]3
66   TemplateArgumentListInfo Args(KwLoc, KwLoc);
67   auto AddArg = [&](QualType T) {
68     Args.addArgument(TemplateArgumentLoc(
69         TemplateArgument(T), S.Context.getTrivialTypeSourceInfo(T, KwLoc)));
70   };
71   AddArg(FnType->getReturnType());
72   // If the function is a non-static member function, add the type
73   // of the implicit object parameter before the formal parameters.
74   if (auto *MD = dyn_cast<CXXMethodDecl>(FD)) {
75     if (MD->isInstance()) {
76       // [over.match.funcs]4
77       // For non-static member functions, the type of the implicit object
78       // parameter is
79       //  -- "lvalue reference to cv X" for functions declared without a
80       //      ref-qualifier or with the & ref-qualifier
81       //  -- "rvalue reference to cv X" for functions declared with the &&
82       //      ref-qualifier
83       QualType T = MD->getThisType()->castAs<PointerType>()->getPointeeType();
84       T = FnType->getRefQualifier() == RQ_RValue
85               ? S.Context.getRValueReferenceType(T)
86               : S.Context.getLValueReferenceType(T, /*SpelledAsLValue*/ true);
87       AddArg(T);
88     }
89   }
90   for (QualType T : FnType->getParamTypes())
91     AddArg(T);
92 
93   // Build the template-id.
94   QualType CoroTrait =
95       S.CheckTemplateIdType(TemplateName(CoroTraits), KwLoc, Args);
96   if (CoroTrait.isNull())
97     return QualType();
98   if (S.RequireCompleteType(KwLoc, CoroTrait,
99                             diag::err_coroutine_type_missing_specialization))
100     return QualType();
101 
102   auto *RD = CoroTrait->getAsCXXRecordDecl();
103   assert(RD && "specialization of class template is not a class?");
104 
105   // Look up the ::promise_type member.
106   LookupResult R(S, &S.PP.getIdentifierTable().get("promise_type"), KwLoc,
107                  Sema::LookupOrdinaryName);
108   S.LookupQualifiedName(R, RD);
109   auto *Promise = R.getAsSingle<TypeDecl>();
110   if (!Promise) {
111     S.Diag(FuncLoc,
112            diag::err_implied_std_coroutine_traits_promise_type_not_found)
113         << RD;
114     return QualType();
115   }
116   // The promise type is required to be a class type.
117   QualType PromiseType = S.Context.getTypeDeclType(Promise);
118 
119   auto buildElaboratedType = [&]() {
120     auto *NNS = NestedNameSpecifier::Create(S.Context, nullptr, CoroNamespace);
121     NNS = NestedNameSpecifier::Create(S.Context, NNS, false,
122                                       CoroTrait.getTypePtr());
123     return S.Context.getElaboratedType(ETK_None, NNS, PromiseType);
124   };
125 
126   if (!PromiseType->getAsCXXRecordDecl()) {
127     S.Diag(FuncLoc,
128            diag::err_implied_std_coroutine_traits_promise_type_not_class)
129         << buildElaboratedType();
130     return QualType();
131   }
132   if (S.RequireCompleteType(FuncLoc, buildElaboratedType(),
133                             diag::err_coroutine_promise_type_incomplete))
134     return QualType();
135 
136   return PromiseType;
137 }
138 
139 /// Look up the std::coroutine_handle<PromiseType>.
140 static QualType lookupCoroutineHandleType(Sema &S, QualType PromiseType,
141                                           SourceLocation Loc) {
142   if (PromiseType.isNull())
143     return QualType();
144 
145   NamespaceDecl *CoroNamespace = S.getCachedCoroNamespace();
146   assert(CoroNamespace && "Should already be diagnosed");
147 
148   LookupResult Result(S, &S.PP.getIdentifierTable().get("coroutine_handle"),
149                       Loc, Sema::LookupOrdinaryName);
150   if (!S.LookupQualifiedName(Result, CoroNamespace)) {
151     S.Diag(Loc, diag::err_implied_coroutine_type_not_found)
152         << "std::coroutine_handle";
153     return QualType();
154   }
155 
156   ClassTemplateDecl *CoroHandle = Result.getAsSingle<ClassTemplateDecl>();
157   if (!CoroHandle) {
158     Result.suppressDiagnostics();
159     // We found something weird. Complain about the first thing we found.
160     NamedDecl *Found = *Result.begin();
161     S.Diag(Found->getLocation(), diag::err_malformed_std_coroutine_handle);
162     return QualType();
163   }
164 
165   // Form template argument list for coroutine_handle<Promise>.
166   TemplateArgumentListInfo Args(Loc, Loc);
167   Args.addArgument(TemplateArgumentLoc(
168       TemplateArgument(PromiseType),
169       S.Context.getTrivialTypeSourceInfo(PromiseType, Loc)));
170 
171   // Build the template-id.
172   QualType CoroHandleType =
173       S.CheckTemplateIdType(TemplateName(CoroHandle), Loc, Args);
174   if (CoroHandleType.isNull())
175     return QualType();
176   if (S.RequireCompleteType(Loc, CoroHandleType,
177                             diag::err_coroutine_type_missing_specialization))
178     return QualType();
179 
180   return CoroHandleType;
181 }
182 
183 static bool isValidCoroutineContext(Sema &S, SourceLocation Loc,
184                                     StringRef Keyword) {
185   // [expr.await]p2 dictates that 'co_await' and 'co_yield' must be used within
186   // a function body.
187   // FIXME: This also covers [expr.await]p2: "An await-expression shall not
188   // appear in a default argument." But the diagnostic QoI here could be
189   // improved to inform the user that default arguments specifically are not
190   // allowed.
191   auto *FD = dyn_cast<FunctionDecl>(S.CurContext);
192   if (!FD) {
193     S.Diag(Loc, isa<ObjCMethodDecl>(S.CurContext)
194                     ? diag::err_coroutine_objc_method
195                     : diag::err_coroutine_outside_function) << Keyword;
196     return false;
197   }
198 
199   // An enumeration for mapping the diagnostic type to the correct diagnostic
200   // selection index.
201   enum InvalidFuncDiag {
202     DiagCtor = 0,
203     DiagDtor,
204     DiagMain,
205     DiagConstexpr,
206     DiagAutoRet,
207     DiagVarargs,
208     DiagConsteval,
209   };
210   bool Diagnosed = false;
211   auto DiagInvalid = [&](InvalidFuncDiag ID) {
212     S.Diag(Loc, diag::err_coroutine_invalid_func_context) << ID << Keyword;
213     Diagnosed = true;
214     return false;
215   };
216 
217   // Diagnose when a constructor, destructor
218   // or the function 'main' are declared as a coroutine.
219   auto *MD = dyn_cast<CXXMethodDecl>(FD);
220   // [class.ctor]p11: "A constructor shall not be a coroutine."
221   if (MD && isa<CXXConstructorDecl>(MD))
222     return DiagInvalid(DiagCtor);
223   // [class.dtor]p17: "A destructor shall not be a coroutine."
224   else if (MD && isa<CXXDestructorDecl>(MD))
225     return DiagInvalid(DiagDtor);
226   // [basic.start.main]p3: "The function main shall not be a coroutine."
227   else if (FD->isMain())
228     return DiagInvalid(DiagMain);
229 
230   // Emit a diagnostics for each of the following conditions which is not met.
231   // [expr.const]p2: "An expression e is a core constant expression unless the
232   // evaluation of e [...] would evaluate one of the following expressions:
233   // [...] an await-expression [...] a yield-expression."
234   if (FD->isConstexpr())
235     DiagInvalid(FD->isConsteval() ? DiagConsteval : DiagConstexpr);
236   // [dcl.spec.auto]p15: "A function declared with a return type that uses a
237   // placeholder type shall not be a coroutine."
238   if (FD->getReturnType()->isUndeducedType())
239     DiagInvalid(DiagAutoRet);
240   // [dcl.fct.def.coroutine]p1
241   // The parameter-declaration-clause of the coroutine shall not terminate with
242   // an ellipsis that is not part of a parameter-declaration.
243   if (FD->isVariadic())
244     DiagInvalid(DiagVarargs);
245 
246   return !Diagnosed;
247 }
248 
249 static ExprResult buildOperatorCoawaitLookupExpr(Sema &SemaRef, Scope *S,
250                                                  SourceLocation Loc) {
251   DeclarationName OpName =
252       SemaRef.Context.DeclarationNames.getCXXOperatorName(OO_Coawait);
253   LookupResult Operators(SemaRef, OpName, SourceLocation(),
254                          Sema::LookupOperatorName);
255   SemaRef.LookupName(Operators, S);
256 
257   assert(!Operators.isAmbiguous() && "Operator lookup cannot be ambiguous");
258   const auto &Functions = Operators.asUnresolvedSet();
259   bool IsOverloaded =
260       Functions.size() > 1 ||
261       (Functions.size() == 1 && isa<FunctionTemplateDecl>(*Functions.begin()));
262   Expr *CoawaitOp = UnresolvedLookupExpr::Create(
263       SemaRef.Context, /*NamingClass*/ nullptr, NestedNameSpecifierLoc(),
264       DeclarationNameInfo(OpName, Loc), /*RequiresADL*/ true, IsOverloaded,
265       Functions.begin(), Functions.end());
266   assert(CoawaitOp);
267   return CoawaitOp;
268 }
269 
270 /// Build a call to 'operator co_await' if there is a suitable operator for
271 /// the given expression.
272 static ExprResult buildOperatorCoawaitCall(Sema &SemaRef, SourceLocation Loc,
273                                            Expr *E,
274                                            UnresolvedLookupExpr *Lookup) {
275   UnresolvedSet<16> Functions;
276   Functions.append(Lookup->decls_begin(), Lookup->decls_end());
277   return SemaRef.CreateOverloadedUnaryOp(Loc, UO_Coawait, Functions, E);
278 }
279 
280 static ExprResult buildOperatorCoawaitCall(Sema &SemaRef, Scope *S,
281                                            SourceLocation Loc, Expr *E) {
282   ExprResult R = buildOperatorCoawaitLookupExpr(SemaRef, S, Loc);
283   if (R.isInvalid())
284     return ExprError();
285   return buildOperatorCoawaitCall(SemaRef, Loc, E,
286                                   cast<UnresolvedLookupExpr>(R.get()));
287 }
288 
289 static ExprResult buildCoroutineHandle(Sema &S, QualType PromiseType,
290                                        SourceLocation Loc) {
291   QualType CoroHandleType = lookupCoroutineHandleType(S, PromiseType, Loc);
292   if (CoroHandleType.isNull())
293     return ExprError();
294 
295   DeclContext *LookupCtx = S.computeDeclContext(CoroHandleType);
296   LookupResult Found(S, &S.PP.getIdentifierTable().get("from_address"), Loc,
297                      Sema::LookupOrdinaryName);
298   if (!S.LookupQualifiedName(Found, LookupCtx)) {
299     S.Diag(Loc, diag::err_coroutine_handle_missing_member)
300         << "from_address";
301     return ExprError();
302   }
303 
304   Expr *FramePtr =
305       S.BuildBuiltinCallExpr(Loc, Builtin::BI__builtin_coro_frame, {});
306 
307   CXXScopeSpec SS;
308   ExprResult FromAddr =
309       S.BuildDeclarationNameExpr(SS, Found, /*NeedsADL=*/false);
310   if (FromAddr.isInvalid())
311     return ExprError();
312 
313   return S.BuildCallExpr(nullptr, FromAddr.get(), Loc, FramePtr, Loc);
314 }
315 
316 struct ReadySuspendResumeResult {
317   enum AwaitCallType { ACT_Ready, ACT_Suspend, ACT_Resume };
318   Expr *Results[3];
319   OpaqueValueExpr *OpaqueValue;
320   bool IsInvalid;
321 };
322 
323 static ExprResult buildMemberCall(Sema &S, Expr *Base, SourceLocation Loc,
324                                   StringRef Name, MultiExprArg Args) {
325   DeclarationNameInfo NameInfo(&S.PP.getIdentifierTable().get(Name), Loc);
326 
327   // FIXME: Fix BuildMemberReferenceExpr to take a const CXXScopeSpec&.
328   CXXScopeSpec SS;
329   ExprResult Result = S.BuildMemberReferenceExpr(
330       Base, Base->getType(), Loc, /*IsPtr=*/false, SS,
331       SourceLocation(), nullptr, NameInfo, /*TemplateArgs=*/nullptr,
332       /*Scope=*/nullptr);
333   if (Result.isInvalid())
334     return ExprError();
335 
336   // We meant exactly what we asked for. No need for typo correction.
337   if (auto *TE = dyn_cast<TypoExpr>(Result.get())) {
338     S.clearDelayedTypo(TE);
339     S.Diag(Loc, diag::err_no_member)
340         << NameInfo.getName() << Base->getType()->getAsCXXRecordDecl()
341         << Base->getSourceRange();
342     return ExprError();
343   }
344 
345   return S.BuildCallExpr(nullptr, Result.get(), Loc, Args, Loc, nullptr);
346 }
347 
348 // See if return type is coroutine-handle and if so, invoke builtin coro-resume
349 // on its address. This is to enable experimental support for coroutine-handle
350 // returning await_suspend that results in a guaranteed tail call to the target
351 // coroutine.
352 static Expr *maybeTailCall(Sema &S, QualType RetType, Expr *E,
353                            SourceLocation Loc) {
354   if (RetType->isReferenceType())
355     return nullptr;
356   Type const *T = RetType.getTypePtr();
357   if (!T->isClassType() && !T->isStructureType())
358     return nullptr;
359 
360   // FIXME: Add convertability check to coroutine_handle<>. Possibly via
361   // EvaluateBinaryTypeTrait(BTT_IsConvertible, ...) which is at the moment
362   // a private function in SemaExprCXX.cpp
363 
364   ExprResult AddressExpr = buildMemberCall(S, E, Loc, "address", None);
365   if (AddressExpr.isInvalid())
366     return nullptr;
367 
368   Expr *JustAddress = AddressExpr.get();
369 
370   // Check that the type of AddressExpr is void*
371   if (!JustAddress->getType().getTypePtr()->isVoidPointerType())
372     S.Diag(cast<CallExpr>(JustAddress)->getCalleeDecl()->getLocation(),
373            diag::warn_coroutine_handle_address_invalid_return_type)
374         << JustAddress->getType();
375 
376   // Clean up temporary objects so that they don't live across suspension points
377   // unnecessarily. We choose to clean up before the call to
378   // __builtin_coro_resume so that the cleanup code are not inserted in-between
379   // the resume call and return instruction, which would interfere with the
380   // musttail call contract.
381   JustAddress = S.MaybeCreateExprWithCleanups(JustAddress);
382   return S.BuildBuiltinCallExpr(Loc, Builtin::BI__builtin_coro_resume,
383                                 JustAddress);
384 }
385 
386 /// Build calls to await_ready, await_suspend, and await_resume for a co_await
387 /// expression.
388 /// The generated AST tries to clean up temporary objects as early as
389 /// possible so that they don't live across suspension points if possible.
390 /// Having temporary objects living across suspension points unnecessarily can
391 /// lead to large frame size, and also lead to memory corruptions if the
392 /// coroutine frame is destroyed after coming back from suspension. This is done
393 /// by wrapping both the await_ready call and the await_suspend call with
394 /// ExprWithCleanups. In the end of this function, we also need to explicitly
395 /// set cleanup state so that the CoawaitExpr is also wrapped with an
396 /// ExprWithCleanups to clean up the awaiter associated with the co_await
397 /// expression.
398 static ReadySuspendResumeResult buildCoawaitCalls(Sema &S, VarDecl *CoroPromise,
399                                                   SourceLocation Loc, Expr *E) {
400   OpaqueValueExpr *Operand = new (S.Context)
401       OpaqueValueExpr(Loc, E->getType(), VK_LValue, E->getObjectKind(), E);
402 
403   // Assume valid until we see otherwise.
404   // Further operations are responsible for setting IsInalid to true.
405   ReadySuspendResumeResult Calls = {{}, Operand, /*IsInvalid=*/false};
406 
407   using ACT = ReadySuspendResumeResult::AwaitCallType;
408 
409   auto BuildSubExpr = [&](ACT CallType, StringRef Func,
410                           MultiExprArg Arg) -> Expr * {
411     ExprResult Result = buildMemberCall(S, Operand, Loc, Func, Arg);
412     if (Result.isInvalid()) {
413       Calls.IsInvalid = true;
414       return nullptr;
415     }
416     Calls.Results[CallType] = Result.get();
417     return Result.get();
418   };
419 
420   CallExpr *AwaitReady =
421       cast_or_null<CallExpr>(BuildSubExpr(ACT::ACT_Ready, "await_ready", None));
422   if (!AwaitReady)
423     return Calls;
424   if (!AwaitReady->getType()->isDependentType()) {
425     // [expr.await]p3 [...]
426     // — await-ready is the expression e.await_ready(), contextually converted
427     // to bool.
428     ExprResult Conv = S.PerformContextuallyConvertToBool(AwaitReady);
429     if (Conv.isInvalid()) {
430       S.Diag(AwaitReady->getDirectCallee()->getBeginLoc(),
431              diag::note_await_ready_no_bool_conversion);
432       S.Diag(Loc, diag::note_coroutine_promise_call_implicitly_required)
433           << AwaitReady->getDirectCallee() << E->getSourceRange();
434       Calls.IsInvalid = true;
435     } else
436       Calls.Results[ACT::ACT_Ready] = S.MaybeCreateExprWithCleanups(Conv.get());
437   }
438 
439   ExprResult CoroHandleRes =
440       buildCoroutineHandle(S, CoroPromise->getType(), Loc);
441   if (CoroHandleRes.isInvalid()) {
442     Calls.IsInvalid = true;
443     return Calls;
444   }
445   Expr *CoroHandle = CoroHandleRes.get();
446   CallExpr *AwaitSuspend = cast_or_null<CallExpr>(
447       BuildSubExpr(ACT::ACT_Suspend, "await_suspend", CoroHandle));
448   if (!AwaitSuspend)
449     return Calls;
450   if (!AwaitSuspend->getType()->isDependentType()) {
451     // [expr.await]p3 [...]
452     //   - await-suspend is the expression e.await_suspend(h), which shall be
453     //     a prvalue of type void, bool, or std::coroutine_handle<Z> for some
454     //     type Z.
455     QualType RetType = AwaitSuspend->getCallReturnType(S.Context);
456 
457     // Experimental support for coroutine_handle returning await_suspend.
458     if (Expr *TailCallSuspend =
459             maybeTailCall(S, RetType, AwaitSuspend, Loc))
460       // Note that we don't wrap the expression with ExprWithCleanups here
461       // because that might interfere with tailcall contract (e.g. inserting
462       // clean up instructions in-between tailcall and return). Instead
463       // ExprWithCleanups is wrapped within maybeTailCall() prior to the resume
464       // call.
465       Calls.Results[ACT::ACT_Suspend] = TailCallSuspend;
466     else {
467       // non-class prvalues always have cv-unqualified types
468       if (RetType->isReferenceType() ||
469           (!RetType->isBooleanType() && !RetType->isVoidType())) {
470         S.Diag(AwaitSuspend->getCalleeDecl()->getLocation(),
471                diag::err_await_suspend_invalid_return_type)
472             << RetType;
473         S.Diag(Loc, diag::note_coroutine_promise_call_implicitly_required)
474             << AwaitSuspend->getDirectCallee();
475         Calls.IsInvalid = true;
476       } else
477         Calls.Results[ACT::ACT_Suspend] =
478             S.MaybeCreateExprWithCleanups(AwaitSuspend);
479     }
480   }
481 
482   BuildSubExpr(ACT::ACT_Resume, "await_resume", None);
483 
484   // Make sure the awaiter object gets a chance to be cleaned up.
485   S.Cleanup.setExprNeedsCleanups(true);
486 
487   return Calls;
488 }
489 
490 static ExprResult buildPromiseCall(Sema &S, VarDecl *Promise,
491                                    SourceLocation Loc, StringRef Name,
492                                    MultiExprArg Args) {
493 
494   // Form a reference to the promise.
495   ExprResult PromiseRef = S.BuildDeclRefExpr(
496       Promise, Promise->getType().getNonReferenceType(), VK_LValue, Loc);
497   if (PromiseRef.isInvalid())
498     return ExprError();
499 
500   return buildMemberCall(S, PromiseRef.get(), Loc, Name, Args);
501 }
502 
503 VarDecl *Sema::buildCoroutinePromise(SourceLocation Loc) {
504   assert(isa<FunctionDecl>(CurContext) && "not in a function scope");
505   auto *FD = cast<FunctionDecl>(CurContext);
506   bool IsThisDependentType = [&] {
507     if (auto *MD = dyn_cast_or_null<CXXMethodDecl>(FD))
508       return MD->isInstance() && MD->getThisType()->isDependentType();
509     else
510       return false;
511   }();
512 
513   QualType T = FD->getType()->isDependentType() || IsThisDependentType
514                    ? Context.DependentTy
515                    : lookupPromiseType(*this, FD, Loc);
516   if (T.isNull())
517     return nullptr;
518 
519   auto *VD = VarDecl::Create(Context, FD, FD->getLocation(), FD->getLocation(),
520                              &PP.getIdentifierTable().get("__promise"), T,
521                              Context.getTrivialTypeSourceInfo(T, Loc), SC_None);
522   VD->setImplicit();
523   CheckVariableDeclarationType(VD);
524   if (VD->isInvalidDecl())
525     return nullptr;
526 
527   auto *ScopeInfo = getCurFunction();
528 
529   // Build a list of arguments, based on the coroutine function's arguments,
530   // that if present will be passed to the promise type's constructor.
531   llvm::SmallVector<Expr *, 4> CtorArgExprs;
532 
533   // Add implicit object parameter.
534   if (auto *MD = dyn_cast<CXXMethodDecl>(FD)) {
535     if (MD->isInstance() && !isLambdaCallOperator(MD)) {
536       ExprResult ThisExpr = ActOnCXXThis(Loc);
537       if (ThisExpr.isInvalid())
538         return nullptr;
539       ThisExpr = CreateBuiltinUnaryOp(Loc, UO_Deref, ThisExpr.get());
540       if (ThisExpr.isInvalid())
541         return nullptr;
542       CtorArgExprs.push_back(ThisExpr.get());
543     }
544   }
545 
546   // Add the coroutine function's parameters.
547   auto &Moves = ScopeInfo->CoroutineParameterMoves;
548   for (auto *PD : FD->parameters()) {
549     if (PD->getType()->isDependentType())
550       continue;
551 
552     auto RefExpr = ExprEmpty();
553     auto Move = Moves.find(PD);
554     assert(Move != Moves.end() &&
555            "Coroutine function parameter not inserted into move map");
556     // If a reference to the function parameter exists in the coroutine
557     // frame, use that reference.
558     auto *MoveDecl =
559         cast<VarDecl>(cast<DeclStmt>(Move->second)->getSingleDecl());
560     RefExpr =
561         BuildDeclRefExpr(MoveDecl, MoveDecl->getType().getNonReferenceType(),
562                          ExprValueKind::VK_LValue, FD->getLocation());
563     if (RefExpr.isInvalid())
564       return nullptr;
565     CtorArgExprs.push_back(RefExpr.get());
566   }
567 
568   // If we have a non-zero number of constructor arguments, try to use them.
569   // Otherwise, fall back to the promise type's default constructor.
570   if (!CtorArgExprs.empty()) {
571     // Create an initialization sequence for the promise type using the
572     // constructor arguments, wrapped in a parenthesized list expression.
573     Expr *PLE = ParenListExpr::Create(Context, FD->getLocation(),
574                                       CtorArgExprs, FD->getLocation());
575     InitializedEntity Entity = InitializedEntity::InitializeVariable(VD);
576     InitializationKind Kind = InitializationKind::CreateForInit(
577         VD->getLocation(), /*DirectInit=*/true, PLE);
578     InitializationSequence InitSeq(*this, Entity, Kind, CtorArgExprs,
579                                    /*TopLevelOfInitList=*/false,
580                                    /*TreatUnavailableAsInvalid=*/false);
581 
582     // [dcl.fct.def.coroutine]5.7
583     // promise-constructor-arguments is determined as follows: overload
584     // resolution is performed on a promise constructor call created by
585     // assembling an argument list  q_1 ... q_n . If a viable constructor is
586     // found ([over.match.viable]), then promise-constructor-arguments is ( q_1
587     // , ...,  q_n ), otherwise promise-constructor-arguments is empty.
588     if (InitSeq) {
589       ExprResult Result = InitSeq.Perform(*this, Entity, Kind, CtorArgExprs);
590       if (Result.isInvalid()) {
591         VD->setInvalidDecl();
592       } else if (Result.get()) {
593         VD->setInit(MaybeCreateExprWithCleanups(Result.get()));
594         VD->setInitStyle(VarDecl::CallInit);
595         CheckCompleteVariableDeclaration(VD);
596       }
597     } else
598       ActOnUninitializedDecl(VD);
599   } else
600     ActOnUninitializedDecl(VD);
601 
602   FD->addDecl(VD);
603   return VD;
604 }
605 
606 /// Check that this is a context in which a coroutine suspension can appear.
607 static FunctionScopeInfo *checkCoroutineContext(Sema &S, SourceLocation Loc,
608                                                 StringRef Keyword,
609                                                 bool IsImplicit = false) {
610   if (!isValidCoroutineContext(S, Loc, Keyword))
611     return nullptr;
612 
613   assert(isa<FunctionDecl>(S.CurContext) && "not in a function scope");
614 
615   auto *ScopeInfo = S.getCurFunction();
616   assert(ScopeInfo && "missing function scope for function");
617 
618   if (ScopeInfo->FirstCoroutineStmtLoc.isInvalid() && !IsImplicit)
619     ScopeInfo->setFirstCoroutineStmt(Loc, Keyword);
620 
621   if (ScopeInfo->CoroutinePromise)
622     return ScopeInfo;
623 
624   if (!S.buildCoroutineParameterMoves(Loc))
625     return nullptr;
626 
627   ScopeInfo->CoroutinePromise = S.buildCoroutinePromise(Loc);
628   if (!ScopeInfo->CoroutinePromise)
629     return nullptr;
630 
631   return ScopeInfo;
632 }
633 
634 /// Recursively check \p E and all its children to see if any call target
635 /// (including constructor call) is declared noexcept. Also any value returned
636 /// from the call has a noexcept destructor.
637 static void checkNoThrow(Sema &S, const Stmt *E,
638                          llvm::SmallPtrSetImpl<const Decl *> &ThrowingDecls) {
639   auto checkDeclNoexcept = [&](const Decl *D, bool IsDtor = false) {
640     // In the case of dtor, the call to dtor is implicit and hence we should
641     // pass nullptr to canCalleeThrow.
642     if (Sema::canCalleeThrow(S, IsDtor ? nullptr : cast<Expr>(E), D)) {
643       if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
644         // co_await promise.final_suspend() could end up calling
645         // __builtin_coro_resume for symmetric transfer if await_suspend()
646         // returns a handle. In that case, even __builtin_coro_resume is not
647         // declared as noexcept and may throw, it does not throw _into_ the
648         // coroutine that just suspended, but rather throws back out from
649         // whoever called coroutine_handle::resume(), hence we claim that
650         // logically it does not throw.
651         if (FD->getBuiltinID() == Builtin::BI__builtin_coro_resume)
652           return;
653       }
654       if (ThrowingDecls.empty()) {
655         // [dcl.fct.def.coroutine]p15
656         //   The expression co_await promise.final_suspend() shall not be
657         //   potentially-throwing ([except.spec]).
658         //
659         // First time seeing an error, emit the error message.
660         S.Diag(cast<FunctionDecl>(S.CurContext)->getLocation(),
661                diag::err_coroutine_promise_final_suspend_requires_nothrow);
662       }
663       ThrowingDecls.insert(D);
664     }
665   };
666 
667   if (auto *CE = dyn_cast<CXXConstructExpr>(E)) {
668     CXXConstructorDecl *Ctor = CE->getConstructor();
669     checkDeclNoexcept(Ctor);
670     // Check the corresponding destructor of the constructor.
671     checkDeclNoexcept(Ctor->getParent()->getDestructor(), /*IsDtor=*/true);
672   } else if (auto *CE = dyn_cast<CallExpr>(E)) {
673     if (CE->isTypeDependent())
674       return;
675 
676     checkDeclNoexcept(CE->getCalleeDecl());
677     QualType ReturnType = CE->getCallReturnType(S.getASTContext());
678     // Check the destructor of the call return type, if any.
679     if (ReturnType.isDestructedType() ==
680         QualType::DestructionKind::DK_cxx_destructor) {
681       const auto *T =
682           cast<RecordType>(ReturnType.getCanonicalType().getTypePtr());
683       checkDeclNoexcept(dyn_cast<CXXRecordDecl>(T->getDecl())->getDestructor(),
684                         /*IsDtor=*/true);
685     }
686   } else
687     for (const auto *Child : E->children()) {
688       if (!Child)
689         continue;
690       checkNoThrow(S, Child, ThrowingDecls);
691     }
692 }
693 
694 bool Sema::checkFinalSuspendNoThrow(const Stmt *FinalSuspend) {
695   llvm::SmallPtrSet<const Decl *, 4> ThrowingDecls;
696   // We first collect all declarations that should not throw but not declared
697   // with noexcept. We then sort them based on the location before printing.
698   // This is to avoid emitting the same note multiple times on the same
699   // declaration, and also provide a deterministic order for the messages.
700   checkNoThrow(*this, FinalSuspend, ThrowingDecls);
701   auto SortedDecls = llvm::SmallVector<const Decl *, 4>{ThrowingDecls.begin(),
702                                                         ThrowingDecls.end()};
703   sort(SortedDecls, [](const Decl *A, const Decl *B) {
704     return A->getEndLoc() < B->getEndLoc();
705   });
706   for (const auto *D : SortedDecls) {
707     Diag(D->getEndLoc(), diag::note_coroutine_function_declare_noexcept);
708   }
709   return ThrowingDecls.empty();
710 }
711 
712 bool Sema::ActOnCoroutineBodyStart(Scope *SC, SourceLocation KWLoc,
713                                    StringRef Keyword) {
714   if (!checkCoroutineContext(*this, KWLoc, Keyword))
715     return false;
716   auto *ScopeInfo = getCurFunction();
717   assert(ScopeInfo->CoroutinePromise);
718 
719   // If we have existing coroutine statements then we have already built
720   // the initial and final suspend points.
721   if (!ScopeInfo->NeedsCoroutineSuspends)
722     return true;
723 
724   ScopeInfo->setNeedsCoroutineSuspends(false);
725 
726   auto *Fn = cast<FunctionDecl>(CurContext);
727   SourceLocation Loc = Fn->getLocation();
728   // Build the initial suspend point
729   auto buildSuspends = [&](StringRef Name) mutable -> StmtResult {
730     ExprResult Suspend =
731         buildPromiseCall(*this, ScopeInfo->CoroutinePromise, Loc, Name, None);
732     if (Suspend.isInvalid())
733       return StmtError();
734     Suspend = buildOperatorCoawaitCall(*this, SC, Loc, Suspend.get());
735     if (Suspend.isInvalid())
736       return StmtError();
737     Suspend = BuildResolvedCoawaitExpr(Loc, Suspend.get(),
738                                        /*IsImplicit*/ true);
739     Suspend = ActOnFinishFullExpr(Suspend.get(), /*DiscardedValue*/ false);
740     if (Suspend.isInvalid()) {
741       Diag(Loc, diag::note_coroutine_promise_suspend_implicitly_required)
742           << ((Name == "initial_suspend") ? 0 : 1);
743       Diag(KWLoc, diag::note_declared_coroutine_here) << Keyword;
744       return StmtError();
745     }
746     return cast<Stmt>(Suspend.get());
747   };
748 
749   StmtResult InitSuspend = buildSuspends("initial_suspend");
750   if (InitSuspend.isInvalid())
751     return true;
752 
753   StmtResult FinalSuspend = buildSuspends("final_suspend");
754   if (FinalSuspend.isInvalid() || !checkFinalSuspendNoThrow(FinalSuspend.get()))
755     return true;
756 
757   ScopeInfo->setCoroutineSuspends(InitSuspend.get(), FinalSuspend.get());
758 
759   return true;
760 }
761 
762 // Recursively walks up the scope hierarchy until either a 'catch' or a function
763 // scope is found, whichever comes first.
764 static bool isWithinCatchScope(Scope *S) {
765   // 'co_await' and 'co_yield' keywords are disallowed within catch blocks, but
766   // lambdas that use 'co_await' are allowed. The loop below ends when a
767   // function scope is found in order to ensure the following behavior:
768   //
769   // void foo() {      // <- function scope
770   //   try {           //
771   //     co_await x;   // <- 'co_await' is OK within a function scope
772   //   } catch {       // <- catch scope
773   //     co_await x;   // <- 'co_await' is not OK within a catch scope
774   //     []() {        // <- function scope
775   //       co_await x; // <- 'co_await' is OK within a function scope
776   //     }();
777   //   }
778   // }
779   while (S && !(S->getFlags() & Scope::FnScope)) {
780     if (S->getFlags() & Scope::CatchScope)
781       return true;
782     S = S->getParent();
783   }
784   return false;
785 }
786 
787 // [expr.await]p2, emphasis added: "An await-expression shall appear only in
788 // a *potentially evaluated* expression within the compound-statement of a
789 // function-body *outside of a handler* [...] A context within a function
790 // where an await-expression can appear is called a suspension context of the
791 // function."
792 static void checkSuspensionContext(Sema &S, SourceLocation Loc,
793                                    StringRef Keyword) {
794   // First emphasis of [expr.await]p2: must be a potentially evaluated context.
795   // That is, 'co_await' and 'co_yield' cannot appear in subexpressions of
796   // \c sizeof.
797   if (S.isUnevaluatedContext())
798     S.Diag(Loc, diag::err_coroutine_unevaluated_context) << Keyword;
799 
800   // Second emphasis of [expr.await]p2: must be outside of an exception handler.
801   if (isWithinCatchScope(S.getCurScope()))
802     S.Diag(Loc, diag::err_coroutine_within_handler) << Keyword;
803 }
804 
805 ExprResult Sema::ActOnCoawaitExpr(Scope *S, SourceLocation Loc, Expr *E) {
806   if (!ActOnCoroutineBodyStart(S, Loc, "co_await")) {
807     CorrectDelayedTyposInExpr(E);
808     return ExprError();
809   }
810 
811   checkSuspensionContext(*this, Loc, "co_await");
812 
813   if (E->hasPlaceholderType()) {
814     ExprResult R = CheckPlaceholderExpr(E);
815     if (R.isInvalid()) return ExprError();
816     E = R.get();
817   }
818   ExprResult Lookup = buildOperatorCoawaitLookupExpr(*this, S, Loc);
819   if (Lookup.isInvalid())
820     return ExprError();
821   return BuildUnresolvedCoawaitExpr(Loc, E,
822                                    cast<UnresolvedLookupExpr>(Lookup.get()));
823 }
824 
825 ExprResult Sema::BuildUnresolvedCoawaitExpr(SourceLocation Loc, Expr *E,
826                                             UnresolvedLookupExpr *Lookup) {
827   auto *FSI = checkCoroutineContext(*this, Loc, "co_await");
828   if (!FSI)
829     return ExprError();
830 
831   if (E->hasPlaceholderType()) {
832     ExprResult R = CheckPlaceholderExpr(E);
833     if (R.isInvalid())
834       return ExprError();
835     E = R.get();
836   }
837 
838   auto *Promise = FSI->CoroutinePromise;
839   if (Promise->getType()->isDependentType()) {
840     Expr *Res =
841         new (Context) DependentCoawaitExpr(Loc, Context.DependentTy, E, Lookup);
842     return Res;
843   }
844 
845   auto *RD = Promise->getType()->getAsCXXRecordDecl();
846   if (lookupMember(*this, "await_transform", RD, Loc)) {
847     ExprResult R = buildPromiseCall(*this, Promise, Loc, "await_transform", E);
848     if (R.isInvalid()) {
849       Diag(Loc,
850            diag::note_coroutine_promise_implicit_await_transform_required_here)
851           << E->getSourceRange();
852       return ExprError();
853     }
854     E = R.get();
855   }
856   ExprResult Awaitable = buildOperatorCoawaitCall(*this, Loc, E, Lookup);
857   if (Awaitable.isInvalid())
858     return ExprError();
859 
860   return BuildResolvedCoawaitExpr(Loc, Awaitable.get());
861 }
862 
863 ExprResult Sema::BuildResolvedCoawaitExpr(SourceLocation Loc, Expr *E,
864                                   bool IsImplicit) {
865   auto *Coroutine = checkCoroutineContext(*this, Loc, "co_await", IsImplicit);
866   if (!Coroutine)
867     return ExprError();
868 
869   if (E->hasPlaceholderType()) {
870     ExprResult R = CheckPlaceholderExpr(E);
871     if (R.isInvalid()) return ExprError();
872     E = R.get();
873   }
874 
875   if (E->getType()->isDependentType()) {
876     Expr *Res = new (Context)
877         CoawaitExpr(Loc, Context.DependentTy, E, IsImplicit);
878     return Res;
879   }
880 
881   // If the expression is a temporary, materialize it as an lvalue so that we
882   // can use it multiple times.
883   if (E->isPRValue())
884     E = CreateMaterializeTemporaryExpr(E->getType(), E, true);
885 
886   // The location of the `co_await` token cannot be used when constructing
887   // the member call expressions since it's before the location of `Expr`, which
888   // is used as the start of the member call expression.
889   SourceLocation CallLoc = E->getExprLoc();
890 
891   // Build the await_ready, await_suspend, await_resume calls.
892   ReadySuspendResumeResult RSS = buildCoawaitCalls(
893       *this, Coroutine->CoroutinePromise, CallLoc, E);
894   if (RSS.IsInvalid)
895     return ExprError();
896 
897   Expr *Res =
898       new (Context) CoawaitExpr(Loc, E, RSS.Results[0], RSS.Results[1],
899                                 RSS.Results[2], RSS.OpaqueValue, IsImplicit);
900 
901   return Res;
902 }
903 
904 ExprResult Sema::ActOnCoyieldExpr(Scope *S, SourceLocation Loc, Expr *E) {
905   if (!ActOnCoroutineBodyStart(S, Loc, "co_yield")) {
906     CorrectDelayedTyposInExpr(E);
907     return ExprError();
908   }
909 
910   checkSuspensionContext(*this, Loc, "co_yield");
911 
912   // Build yield_value call.
913   ExprResult Awaitable = buildPromiseCall(
914       *this, getCurFunction()->CoroutinePromise, Loc, "yield_value", E);
915   if (Awaitable.isInvalid())
916     return ExprError();
917 
918   // Build 'operator co_await' call.
919   Awaitable = buildOperatorCoawaitCall(*this, S, Loc, Awaitable.get());
920   if (Awaitable.isInvalid())
921     return ExprError();
922 
923   return BuildCoyieldExpr(Loc, Awaitable.get());
924 }
925 ExprResult Sema::BuildCoyieldExpr(SourceLocation Loc, Expr *E) {
926   auto *Coroutine = checkCoroutineContext(*this, Loc, "co_yield");
927   if (!Coroutine)
928     return ExprError();
929 
930   if (E->hasPlaceholderType()) {
931     ExprResult R = CheckPlaceholderExpr(E);
932     if (R.isInvalid()) return ExprError();
933     E = R.get();
934   }
935 
936   if (E->getType()->isDependentType()) {
937     Expr *Res = new (Context) CoyieldExpr(Loc, Context.DependentTy, E);
938     return Res;
939   }
940 
941   // If the expression is a temporary, materialize it as an lvalue so that we
942   // can use it multiple times.
943   if (E->isPRValue())
944     E = CreateMaterializeTemporaryExpr(E->getType(), E, true);
945 
946   // Build the await_ready, await_suspend, await_resume calls.
947   ReadySuspendResumeResult RSS = buildCoawaitCalls(
948       *this, Coroutine->CoroutinePromise, Loc, E);
949   if (RSS.IsInvalid)
950     return ExprError();
951 
952   Expr *Res =
953       new (Context) CoyieldExpr(Loc, E, RSS.Results[0], RSS.Results[1],
954                                 RSS.Results[2], RSS.OpaqueValue);
955 
956   return Res;
957 }
958 
959 StmtResult Sema::ActOnCoreturnStmt(Scope *S, SourceLocation Loc, Expr *E) {
960   if (!ActOnCoroutineBodyStart(S, Loc, "co_return")) {
961     CorrectDelayedTyposInExpr(E);
962     return StmtError();
963   }
964   return BuildCoreturnStmt(Loc, E);
965 }
966 
967 StmtResult Sema::BuildCoreturnStmt(SourceLocation Loc, Expr *E,
968                                    bool IsImplicit) {
969   auto *FSI = checkCoroutineContext(*this, Loc, "co_return", IsImplicit);
970   if (!FSI)
971     return StmtError();
972 
973   if (E && E->hasPlaceholderType() &&
974       !E->hasPlaceholderType(BuiltinType::Overload)) {
975     ExprResult R = CheckPlaceholderExpr(E);
976     if (R.isInvalid()) return StmtError();
977     E = R.get();
978   }
979 
980   VarDecl *Promise = FSI->CoroutinePromise;
981   ExprResult PC;
982   if (E && (isa<InitListExpr>(E) || !E->getType()->isVoidType())) {
983     getNamedReturnInfo(E, SimplerImplicitMoveMode::ForceOn);
984     PC = buildPromiseCall(*this, Promise, Loc, "return_value", E);
985   } else {
986     E = MakeFullDiscardedValueExpr(E).get();
987     PC = buildPromiseCall(*this, Promise, Loc, "return_void", None);
988   }
989   if (PC.isInvalid())
990     return StmtError();
991 
992   Expr *PCE = ActOnFinishFullExpr(PC.get(), /*DiscardedValue*/ false).get();
993 
994   Stmt *Res = new (Context) CoreturnStmt(Loc, E, PCE, IsImplicit);
995   return Res;
996 }
997 
998 /// Look up the std::nothrow object.
999 static Expr *buildStdNoThrowDeclRef(Sema &S, SourceLocation Loc) {
1000   NamespaceDecl *Std = S.getStdNamespace();
1001   assert(Std && "Should already be diagnosed");
1002 
1003   LookupResult Result(S, &S.PP.getIdentifierTable().get("nothrow"), Loc,
1004                       Sema::LookupOrdinaryName);
1005   if (!S.LookupQualifiedName(Result, Std)) {
1006     // <coroutine> is not requred to include <new>, so we couldn't omit
1007     // the check here.
1008     S.Diag(Loc, diag::err_implicit_coroutine_std_nothrow_type_not_found);
1009     return nullptr;
1010   }
1011 
1012   auto *VD = Result.getAsSingle<VarDecl>();
1013   if (!VD) {
1014     Result.suppressDiagnostics();
1015     // We found something weird. Complain about the first thing we found.
1016     NamedDecl *Found = *Result.begin();
1017     S.Diag(Found->getLocation(), diag::err_malformed_std_nothrow);
1018     return nullptr;
1019   }
1020 
1021   ExprResult DR = S.BuildDeclRefExpr(VD, VD->getType(), VK_LValue, Loc);
1022   if (DR.isInvalid())
1023     return nullptr;
1024 
1025   return DR.get();
1026 }
1027 
1028 // Find an appropriate delete for the promise.
1029 static FunctionDecl *findDeleteForPromise(Sema &S, SourceLocation Loc,
1030                                           QualType PromiseType) {
1031   FunctionDecl *OperatorDelete = nullptr;
1032 
1033   DeclarationName DeleteName =
1034       S.Context.DeclarationNames.getCXXOperatorName(OO_Delete);
1035 
1036   auto *PointeeRD = PromiseType->getAsCXXRecordDecl();
1037   assert(PointeeRD && "PromiseType must be a CxxRecordDecl type");
1038 
1039   // [dcl.fct.def.coroutine]p12
1040   // The deallocation function's name is looked up by searching for it in the
1041   // scope of the promise type. If nothing is found, a search is performed in
1042   // the global scope.
1043   if (S.FindDeallocationFunction(Loc, PointeeRD, DeleteName, OperatorDelete))
1044     return nullptr;
1045 
1046   // FIXME: We didn't implement following selection:
1047   // [dcl.fct.def.coroutine]p12
1048   //   If both a usual deallocation function with only a pointer parameter and a
1049   //   usual deallocation function with both a pointer parameter and a size
1050   //   parameter are found, then the selected deallocation function shall be the
1051   //   one with two parameters. Otherwise, the selected deallocation function
1052   //   shall be the function with one parameter.
1053 
1054   if (!OperatorDelete) {
1055     // Look for a global declaration.
1056     const bool CanProvideSize = S.isCompleteType(Loc, PromiseType);
1057     const bool Overaligned = false;
1058     OperatorDelete = S.FindUsualDeallocationFunction(Loc, CanProvideSize,
1059                                                      Overaligned, DeleteName);
1060   }
1061   S.MarkFunctionReferenced(Loc, OperatorDelete);
1062   return OperatorDelete;
1063 }
1064 
1065 
1066 void Sema::CheckCompletedCoroutineBody(FunctionDecl *FD, Stmt *&Body) {
1067   FunctionScopeInfo *Fn = getCurFunction();
1068   assert(Fn && Fn->isCoroutine() && "not a coroutine");
1069   if (!Body) {
1070     assert(FD->isInvalidDecl() &&
1071            "a null body is only allowed for invalid declarations");
1072     return;
1073   }
1074   // We have a function that uses coroutine keywords, but we failed to build
1075   // the promise type.
1076   if (!Fn->CoroutinePromise)
1077     return FD->setInvalidDecl();
1078 
1079   if (isa<CoroutineBodyStmt>(Body)) {
1080     // Nothing todo. the body is already a transformed coroutine body statement.
1081     return;
1082   }
1083 
1084   // [stmt.return.coroutine]p1:
1085   //   A coroutine shall not enclose a return statement ([stmt.return]).
1086   if (Fn->FirstReturnLoc.isValid()) {
1087     assert(Fn->FirstCoroutineStmtLoc.isValid() &&
1088                    "first coroutine location not set");
1089     Diag(Fn->FirstReturnLoc, diag::err_return_in_coroutine);
1090     Diag(Fn->FirstCoroutineStmtLoc, diag::note_declared_coroutine_here)
1091             << Fn->getFirstCoroutineStmtKeyword();
1092   }
1093   CoroutineStmtBuilder Builder(*this, *FD, *Fn, Body);
1094   if (Builder.isInvalid() || !Builder.buildStatements())
1095     return FD->setInvalidDecl();
1096 
1097   // Build body for the coroutine wrapper statement.
1098   Body = CoroutineBodyStmt::Create(Context, Builder);
1099 }
1100 
1101 CoroutineStmtBuilder::CoroutineStmtBuilder(Sema &S, FunctionDecl &FD,
1102                                            sema::FunctionScopeInfo &Fn,
1103                                            Stmt *Body)
1104     : S(S), FD(FD), Fn(Fn), Loc(FD.getLocation()),
1105       IsPromiseDependentType(
1106           !Fn.CoroutinePromise ||
1107           Fn.CoroutinePromise->getType()->isDependentType()) {
1108   this->Body = Body;
1109 
1110   for (auto KV : Fn.CoroutineParameterMoves)
1111     this->ParamMovesVector.push_back(KV.second);
1112   this->ParamMoves = this->ParamMovesVector;
1113 
1114   if (!IsPromiseDependentType) {
1115     PromiseRecordDecl = Fn.CoroutinePromise->getType()->getAsCXXRecordDecl();
1116     assert(PromiseRecordDecl && "Type should have already been checked");
1117   }
1118   this->IsValid = makePromiseStmt() && makeInitialAndFinalSuspend();
1119 }
1120 
1121 bool CoroutineStmtBuilder::buildStatements() {
1122   assert(this->IsValid && "coroutine already invalid");
1123   this->IsValid = makeReturnObject();
1124   if (this->IsValid && !IsPromiseDependentType)
1125     buildDependentStatements();
1126   return this->IsValid;
1127 }
1128 
1129 bool CoroutineStmtBuilder::buildDependentStatements() {
1130   assert(this->IsValid && "coroutine already invalid");
1131   assert(!this->IsPromiseDependentType &&
1132          "coroutine cannot have a dependent promise type");
1133   this->IsValid = makeOnException() && makeOnFallthrough() &&
1134                   makeGroDeclAndReturnStmt() && makeReturnOnAllocFailure() &&
1135                   makeNewAndDeleteExpr();
1136   return this->IsValid;
1137 }
1138 
1139 bool CoroutineStmtBuilder::makePromiseStmt() {
1140   // Form a declaration statement for the promise declaration, so that AST
1141   // visitors can more easily find it.
1142   StmtResult PromiseStmt =
1143       S.ActOnDeclStmt(S.ConvertDeclToDeclGroup(Fn.CoroutinePromise), Loc, Loc);
1144   if (PromiseStmt.isInvalid())
1145     return false;
1146 
1147   this->Promise = PromiseStmt.get();
1148   return true;
1149 }
1150 
1151 bool CoroutineStmtBuilder::makeInitialAndFinalSuspend() {
1152   if (Fn.hasInvalidCoroutineSuspends())
1153     return false;
1154   this->InitialSuspend = cast<Expr>(Fn.CoroutineSuspends.first);
1155   this->FinalSuspend = cast<Expr>(Fn.CoroutineSuspends.second);
1156   return true;
1157 }
1158 
1159 static bool diagReturnOnAllocFailure(Sema &S, Expr *E,
1160                                      CXXRecordDecl *PromiseRecordDecl,
1161                                      FunctionScopeInfo &Fn) {
1162   auto Loc = E->getExprLoc();
1163   if (auto *DeclRef = dyn_cast_or_null<DeclRefExpr>(E)) {
1164     auto *Decl = DeclRef->getDecl();
1165     if (CXXMethodDecl *Method = dyn_cast_or_null<CXXMethodDecl>(Decl)) {
1166       if (Method->isStatic())
1167         return true;
1168       else
1169         Loc = Decl->getLocation();
1170     }
1171   }
1172 
1173   S.Diag(
1174       Loc,
1175       diag::err_coroutine_promise_get_return_object_on_allocation_failure)
1176       << PromiseRecordDecl;
1177   S.Diag(Fn.FirstCoroutineStmtLoc, diag::note_declared_coroutine_here)
1178       << Fn.getFirstCoroutineStmtKeyword();
1179   return false;
1180 }
1181 
1182 bool CoroutineStmtBuilder::makeReturnOnAllocFailure() {
1183   assert(!IsPromiseDependentType &&
1184          "cannot make statement while the promise type is dependent");
1185 
1186   // [dcl.fct.def.coroutine]p10
1187   //   If a search for the name get_return_object_on_allocation_failure in
1188   // the scope of the promise type ([class.member.lookup]) finds any
1189   // declarations, then the result of a call to an allocation function used to
1190   // obtain storage for the coroutine state is assumed to return nullptr if it
1191   // fails to obtain storage, ... If the allocation function returns nullptr,
1192   // ... and the return value is obtained by a call to
1193   // T::get_return_object_on_allocation_failure(), where T is the
1194   // promise type.
1195   DeclarationName DN =
1196       S.PP.getIdentifierInfo("get_return_object_on_allocation_failure");
1197   LookupResult Found(S, DN, Loc, Sema::LookupMemberName);
1198   if (!S.LookupQualifiedName(Found, PromiseRecordDecl))
1199     return true;
1200 
1201   CXXScopeSpec SS;
1202   ExprResult DeclNameExpr =
1203       S.BuildDeclarationNameExpr(SS, Found, /*NeedsADL=*/false);
1204   if (DeclNameExpr.isInvalid())
1205     return false;
1206 
1207   if (!diagReturnOnAllocFailure(S, DeclNameExpr.get(), PromiseRecordDecl, Fn))
1208     return false;
1209 
1210   ExprResult ReturnObjectOnAllocationFailure =
1211       S.BuildCallExpr(nullptr, DeclNameExpr.get(), Loc, {}, Loc);
1212   if (ReturnObjectOnAllocationFailure.isInvalid())
1213     return false;
1214 
1215   StmtResult ReturnStmt =
1216       S.BuildReturnStmt(Loc, ReturnObjectOnAllocationFailure.get());
1217   if (ReturnStmt.isInvalid()) {
1218     S.Diag(Found.getFoundDecl()->getLocation(), diag::note_member_declared_here)
1219         << DN;
1220     S.Diag(Fn.FirstCoroutineStmtLoc, diag::note_declared_coroutine_here)
1221         << Fn.getFirstCoroutineStmtKeyword();
1222     return false;
1223   }
1224 
1225   this->ReturnStmtOnAllocFailure = ReturnStmt.get();
1226   return true;
1227 }
1228 
1229 bool CoroutineStmtBuilder::makeNewAndDeleteExpr() {
1230   // Form and check allocation and deallocation calls.
1231   assert(!IsPromiseDependentType &&
1232          "cannot make statement while the promise type is dependent");
1233   QualType PromiseType = Fn.CoroutinePromise->getType();
1234 
1235   if (S.RequireCompleteType(Loc, PromiseType, diag::err_incomplete_type))
1236     return false;
1237 
1238   const bool RequiresNoThrowAlloc = ReturnStmtOnAllocFailure != nullptr;
1239 
1240   // According to [dcl.fct.def.coroutine]p9, Lookup allocation functions using a
1241   // parameter list composed of the requested size of the coroutine state being
1242   // allocated, followed by the coroutine function's arguments. If a matching
1243   // allocation function exists, use it. Otherwise, use an allocation function
1244   // that just takes the requested size.
1245 
1246   FunctionDecl *OperatorNew = nullptr;
1247   FunctionDecl *OperatorDelete = nullptr;
1248   FunctionDecl *UnusedResult = nullptr;
1249   bool PassAlignment = false;
1250   SmallVector<Expr *, 1> PlacementArgs;
1251 
1252   // [dcl.fct.def.coroutine]p9
1253   //   An implementation may need to allocate additional storage for a
1254   //   coroutine.
1255   // This storage is known as the coroutine state and is obtained by calling a
1256   // non-array allocation function ([basic.stc.dynamic.allocation]). The
1257   // allocation function's name is looked up by searching for it in the scope of
1258   // the promise type.
1259   // - If any declarations are found, overload resolution is performed on a
1260   // function call created by assembling an argument list. The first argument is
1261   // the amount of space requested, and has type std::size_t. The
1262   // lvalues p1 ... pn are the succeeding arguments.
1263   //
1264   // ...where "p1 ... pn" are defined earlier as:
1265   //
1266   // [dcl.fct.def.coroutine]p3
1267   //   The promise type of a coroutine is `std::coroutine_traits<R, P1, ...,
1268   //   Pn>`
1269   // , where R is the return type of the function, and `P1, ..., Pn` are the
1270   // sequence of types of the non-object function parameters, preceded by the
1271   // type of the object parameter ([dcl.fct]) if the coroutine is a non-static
1272   // member function. [dcl.fct.def.coroutine]p4 In the following, p_i is an
1273   // lvalue of type P_i, where p1 denotes the object parameter and p_i+1 denotes
1274   // the i-th non-object function parameter for a non-static member function,
1275   // and p_i denotes the i-th function parameter otherwise. For a non-static
1276   // member function, q_1 is an lvalue that denotes *this; any other q_i is an
1277   // lvalue that denotes the parameter copy corresponding to p_i.
1278   if (auto *MD = dyn_cast<CXXMethodDecl>(&FD)) {
1279     if (MD->isInstance() && !isLambdaCallOperator(MD)) {
1280       ExprResult ThisExpr = S.ActOnCXXThis(Loc);
1281       if (ThisExpr.isInvalid())
1282         return false;
1283       ThisExpr = S.CreateBuiltinUnaryOp(Loc, UO_Deref, ThisExpr.get());
1284       if (ThisExpr.isInvalid())
1285         return false;
1286       PlacementArgs.push_back(ThisExpr.get());
1287     }
1288   }
1289   for (auto *PD : FD.parameters()) {
1290     if (PD->getType()->isDependentType())
1291       continue;
1292 
1293     // Build a reference to the parameter.
1294     auto PDLoc = PD->getLocation();
1295     ExprResult PDRefExpr =
1296         S.BuildDeclRefExpr(PD, PD->getOriginalType().getNonReferenceType(),
1297                            ExprValueKind::VK_LValue, PDLoc);
1298     if (PDRefExpr.isInvalid())
1299       return false;
1300 
1301     PlacementArgs.push_back(PDRefExpr.get());
1302   }
1303   S.FindAllocationFunctions(Loc, SourceRange(), /*NewScope*/ Sema::AFS_Class,
1304                             /*DeleteScope*/ Sema::AFS_Both, PromiseType,
1305                             /*isArray*/ false, PassAlignment, PlacementArgs,
1306                             OperatorNew, UnusedResult, /*Diagnose*/ false);
1307 
1308   // [dcl.fct.def.coroutine]p9
1309   //   If no viable function is found ([over.match.viable]), overload resolution
1310   // is performed again on a function call created by passing just the amount of
1311   // space required as an argument of type std::size_t.
1312   if (!OperatorNew && !PlacementArgs.empty()) {
1313     PlacementArgs.clear();
1314     S.FindAllocationFunctions(Loc, SourceRange(), /*NewScope*/ Sema::AFS_Class,
1315                               /*DeleteScope*/ Sema::AFS_Both, PromiseType,
1316                               /*isArray*/ false, PassAlignment, PlacementArgs,
1317                               OperatorNew, UnusedResult, /*Diagnose*/ false);
1318   }
1319 
1320   // [dcl.fct.def.coroutine]p9
1321   //   The allocation function's name is looked up by searching for it in the
1322   // scope of the promise type.
1323   // - If any declarations are found, ...
1324   // - Otherwise, a search is performed in the global scope.
1325   if (!OperatorNew) {
1326     S.FindAllocationFunctions(Loc, SourceRange(), /*NewScope*/ Sema::AFS_Global,
1327                               /*DeleteScope*/ Sema::AFS_Both, PromiseType,
1328                               /*isArray*/ false, PassAlignment, PlacementArgs,
1329                               OperatorNew, UnusedResult);
1330   }
1331 
1332   bool IsGlobalOverload =
1333       OperatorNew && !isa<CXXRecordDecl>(OperatorNew->getDeclContext());
1334   // If we didn't find a class-local new declaration and non-throwing new
1335   // was is required then we need to lookup the non-throwing global operator
1336   // instead.
1337   if (RequiresNoThrowAlloc && (!OperatorNew || IsGlobalOverload)) {
1338     auto *StdNoThrow = buildStdNoThrowDeclRef(S, Loc);
1339     if (!StdNoThrow)
1340       return false;
1341     PlacementArgs = {StdNoThrow};
1342     OperatorNew = nullptr;
1343     S.FindAllocationFunctions(Loc, SourceRange(), /*NewScope*/ Sema::AFS_Both,
1344                               /*DeleteScope*/ Sema::AFS_Both, PromiseType,
1345                               /*isArray*/ false, PassAlignment, PlacementArgs,
1346                               OperatorNew, UnusedResult);
1347   }
1348 
1349   if (!OperatorNew)
1350     return false;
1351 
1352   if (RequiresNoThrowAlloc) {
1353     const auto *FT = OperatorNew->getType()->castAs<FunctionProtoType>();
1354     if (!FT->isNothrow(/*ResultIfDependent*/ false)) {
1355       S.Diag(OperatorNew->getLocation(),
1356              diag::err_coroutine_promise_new_requires_nothrow)
1357           << OperatorNew;
1358       S.Diag(Loc, diag::note_coroutine_promise_call_implicitly_required)
1359           << OperatorNew;
1360       return false;
1361     }
1362   }
1363 
1364   if ((OperatorDelete = findDeleteForPromise(S, Loc, PromiseType)) == nullptr) {
1365     // FIXME: We should add an error here. According to:
1366     // [dcl.fct.def.coroutine]p12
1367     //   If no usual deallocation function is found, the program is ill-formed.
1368     return false;
1369   }
1370 
1371   Expr *FramePtr =
1372       S.BuildBuiltinCallExpr(Loc, Builtin::BI__builtin_coro_frame, {});
1373 
1374   Expr *FrameSize =
1375       S.BuildBuiltinCallExpr(Loc, Builtin::BI__builtin_coro_size, {});
1376 
1377   // Make new call.
1378 
1379   ExprResult NewRef =
1380       S.BuildDeclRefExpr(OperatorNew, OperatorNew->getType(), VK_LValue, Loc);
1381   if (NewRef.isInvalid())
1382     return false;
1383 
1384   SmallVector<Expr *, 2> NewArgs(1, FrameSize);
1385   for (auto Arg : PlacementArgs)
1386     NewArgs.push_back(Arg);
1387 
1388   ExprResult NewExpr =
1389       S.BuildCallExpr(S.getCurScope(), NewRef.get(), Loc, NewArgs, Loc);
1390   NewExpr = S.ActOnFinishFullExpr(NewExpr.get(), /*DiscardedValue*/ false);
1391   if (NewExpr.isInvalid())
1392     return false;
1393 
1394   // Make delete call.
1395 
1396   QualType OpDeleteQualType = OperatorDelete->getType();
1397 
1398   ExprResult DeleteRef =
1399       S.BuildDeclRefExpr(OperatorDelete, OpDeleteQualType, VK_LValue, Loc);
1400   if (DeleteRef.isInvalid())
1401     return false;
1402 
1403   Expr *CoroFree =
1404       S.BuildBuiltinCallExpr(Loc, Builtin::BI__builtin_coro_free, {FramePtr});
1405 
1406   SmallVector<Expr *, 2> DeleteArgs{CoroFree};
1407 
1408   // [dcl.fct.def.coroutine]p12
1409   //   The selected deallocation function shall be called with the address of
1410   //   the block of storage to be reclaimed as its first argument. If a
1411   //   deallocation function with a parameter of type std::size_t is
1412   //   used, the size of the block is passed as the corresponding argument.
1413   const auto *OpDeleteType =
1414       OpDeleteQualType.getTypePtr()->castAs<FunctionProtoType>();
1415   if (OpDeleteType->getNumParams() > 1)
1416     DeleteArgs.push_back(FrameSize);
1417 
1418   ExprResult DeleteExpr =
1419       S.BuildCallExpr(S.getCurScope(), DeleteRef.get(), Loc, DeleteArgs, Loc);
1420   DeleteExpr =
1421       S.ActOnFinishFullExpr(DeleteExpr.get(), /*DiscardedValue*/ false);
1422   if (DeleteExpr.isInvalid())
1423     return false;
1424 
1425   this->Allocate = NewExpr.get();
1426   this->Deallocate = DeleteExpr.get();
1427 
1428   return true;
1429 }
1430 
1431 bool CoroutineStmtBuilder::makeOnFallthrough() {
1432   assert(!IsPromiseDependentType &&
1433          "cannot make statement while the promise type is dependent");
1434 
1435   // [dcl.fct.def.coroutine]/p6
1436   // If searches for the names return_void and return_value in the scope of
1437   // the promise type each find any declarations, the program is ill-formed.
1438   // [Note 1: If return_void is found, flowing off the end of a coroutine is
1439   // equivalent to a co_return with no operand. Otherwise, flowing off the end
1440   // of a coroutine results in undefined behavior ([stmt.return.coroutine]). —
1441   // end note]
1442   bool HasRVoid, HasRValue;
1443   LookupResult LRVoid =
1444       lookupMember(S, "return_void", PromiseRecordDecl, Loc, HasRVoid);
1445   LookupResult LRValue =
1446       lookupMember(S, "return_value", PromiseRecordDecl, Loc, HasRValue);
1447 
1448   StmtResult Fallthrough;
1449   if (HasRVoid && HasRValue) {
1450     // FIXME Improve this diagnostic
1451     S.Diag(FD.getLocation(),
1452            diag::err_coroutine_promise_incompatible_return_functions)
1453         << PromiseRecordDecl;
1454     S.Diag(LRVoid.getRepresentativeDecl()->getLocation(),
1455            diag::note_member_first_declared_here)
1456         << LRVoid.getLookupName();
1457     S.Diag(LRValue.getRepresentativeDecl()->getLocation(),
1458            diag::note_member_first_declared_here)
1459         << LRValue.getLookupName();
1460     return false;
1461   } else if (!HasRVoid && !HasRValue) {
1462     // We need to set 'Fallthrough'. Otherwise the other analysis part might
1463     // think the coroutine has defined a return_value method. So it might emit
1464     // **false** positive warning. e.g.,
1465     //
1466     //    promise_without_return_func foo() {
1467     //        co_await something();
1468     //    }
1469     //
1470     // Then AnalysisBasedWarning would emit a warning about `foo()` lacking a
1471     // co_return statements, which isn't correct.
1472     Fallthrough = S.ActOnNullStmt(PromiseRecordDecl->getLocation());
1473     if (Fallthrough.isInvalid())
1474       return false;
1475   } else if (HasRVoid) {
1476     Fallthrough = S.BuildCoreturnStmt(FD.getLocation(), nullptr,
1477                                       /*IsImplicit*/false);
1478     Fallthrough = S.ActOnFinishFullStmt(Fallthrough.get());
1479     if (Fallthrough.isInvalid())
1480       return false;
1481   }
1482 
1483   this->OnFallthrough = Fallthrough.get();
1484   return true;
1485 }
1486 
1487 bool CoroutineStmtBuilder::makeOnException() {
1488   // Try to form 'p.unhandled_exception();'
1489   assert(!IsPromiseDependentType &&
1490          "cannot make statement while the promise type is dependent");
1491 
1492   const bool RequireUnhandledException = S.getLangOpts().CXXExceptions;
1493 
1494   if (!lookupMember(S, "unhandled_exception", PromiseRecordDecl, Loc)) {
1495     auto DiagID =
1496         RequireUnhandledException
1497             ? diag::err_coroutine_promise_unhandled_exception_required
1498             : diag::
1499                   warn_coroutine_promise_unhandled_exception_required_with_exceptions;
1500     S.Diag(Loc, DiagID) << PromiseRecordDecl;
1501     S.Diag(PromiseRecordDecl->getLocation(), diag::note_defined_here)
1502         << PromiseRecordDecl;
1503     return !RequireUnhandledException;
1504   }
1505 
1506   // If exceptions are disabled, don't try to build OnException.
1507   if (!S.getLangOpts().CXXExceptions)
1508     return true;
1509 
1510   ExprResult UnhandledException = buildPromiseCall(S, Fn.CoroutinePromise, Loc,
1511                                                    "unhandled_exception", None);
1512   UnhandledException = S.ActOnFinishFullExpr(UnhandledException.get(), Loc,
1513                                              /*DiscardedValue*/ false);
1514   if (UnhandledException.isInvalid())
1515     return false;
1516 
1517   // Since the body of the coroutine will be wrapped in try-catch, it will
1518   // be incompatible with SEH __try if present in a function.
1519   if (!S.getLangOpts().Borland && Fn.FirstSEHTryLoc.isValid()) {
1520     S.Diag(Fn.FirstSEHTryLoc, diag::err_seh_in_a_coroutine_with_cxx_exceptions);
1521     S.Diag(Fn.FirstCoroutineStmtLoc, diag::note_declared_coroutine_here)
1522         << Fn.getFirstCoroutineStmtKeyword();
1523     return false;
1524   }
1525 
1526   this->OnException = UnhandledException.get();
1527   return true;
1528 }
1529 
1530 bool CoroutineStmtBuilder::makeReturnObject() {
1531   // [dcl.fct.def.coroutine]p7
1532   // The expression promise.get_return_object() is used to initialize the
1533   // returned reference or prvalue result object of a call to a coroutine.
1534   ExprResult ReturnObject =
1535       buildPromiseCall(S, Fn.CoroutinePromise, Loc, "get_return_object", None);
1536   if (ReturnObject.isInvalid())
1537     return false;
1538 
1539   this->ReturnValue = ReturnObject.get();
1540   return true;
1541 }
1542 
1543 static void noteMemberDeclaredHere(Sema &S, Expr *E, FunctionScopeInfo &Fn) {
1544   if (auto *MbrRef = dyn_cast<CXXMemberCallExpr>(E)) {
1545     auto *MethodDecl = MbrRef->getMethodDecl();
1546     S.Diag(MethodDecl->getLocation(), diag::note_member_declared_here)
1547         << MethodDecl;
1548   }
1549   S.Diag(Fn.FirstCoroutineStmtLoc, diag::note_declared_coroutine_here)
1550       << Fn.getFirstCoroutineStmtKeyword();
1551 }
1552 
1553 bool CoroutineStmtBuilder::makeGroDeclAndReturnStmt() {
1554   assert(!IsPromiseDependentType &&
1555          "cannot make statement while the promise type is dependent");
1556   assert(this->ReturnValue && "ReturnValue must be already formed");
1557 
1558   QualType const GroType = this->ReturnValue->getType();
1559   assert(!GroType->isDependentType() &&
1560          "get_return_object type must no longer be dependent");
1561 
1562   QualType const FnRetType = FD.getReturnType();
1563   assert(!FnRetType->isDependentType() &&
1564          "get_return_object type must no longer be dependent");
1565 
1566   if (FnRetType->isVoidType()) {
1567     ExprResult Res =
1568         S.ActOnFinishFullExpr(this->ReturnValue, Loc, /*DiscardedValue*/ false);
1569     if (Res.isInvalid())
1570       return false;
1571 
1572     this->ResultDecl = Res.get();
1573     return true;
1574   }
1575 
1576   if (GroType->isVoidType()) {
1577     // Trigger a nice error message.
1578     InitializedEntity Entity =
1579         InitializedEntity::InitializeResult(Loc, FnRetType);
1580     S.PerformCopyInitialization(Entity, SourceLocation(), ReturnValue);
1581     noteMemberDeclaredHere(S, ReturnValue, Fn);
1582     return false;
1583   }
1584 
1585   auto *GroDecl = VarDecl::Create(
1586       S.Context, &FD, FD.getLocation(), FD.getLocation(),
1587       &S.PP.getIdentifierTable().get("__coro_gro"), GroType,
1588       S.Context.getTrivialTypeSourceInfo(GroType, Loc), SC_None);
1589   GroDecl->setImplicit();
1590 
1591   S.CheckVariableDeclarationType(GroDecl);
1592   if (GroDecl->isInvalidDecl())
1593     return false;
1594 
1595   InitializedEntity Entity = InitializedEntity::InitializeVariable(GroDecl);
1596   ExprResult Res =
1597       S.PerformCopyInitialization(Entity, SourceLocation(), ReturnValue);
1598   if (Res.isInvalid())
1599     return false;
1600 
1601   Res = S.ActOnFinishFullExpr(Res.get(), /*DiscardedValue*/ false);
1602   if (Res.isInvalid())
1603     return false;
1604 
1605   S.AddInitializerToDecl(GroDecl, Res.get(),
1606                          /*DirectInit=*/false);
1607 
1608   S.FinalizeDeclaration(GroDecl);
1609 
1610   // Form a declaration statement for the return declaration, so that AST
1611   // visitors can more easily find it.
1612   StmtResult GroDeclStmt =
1613       S.ActOnDeclStmt(S.ConvertDeclToDeclGroup(GroDecl), Loc, Loc);
1614   if (GroDeclStmt.isInvalid())
1615     return false;
1616 
1617   this->ResultDecl = GroDeclStmt.get();
1618 
1619   ExprResult declRef = S.BuildDeclRefExpr(GroDecl, GroType, VK_LValue, Loc);
1620   if (declRef.isInvalid())
1621     return false;
1622 
1623   StmtResult ReturnStmt = S.BuildReturnStmt(Loc, declRef.get());
1624   if (ReturnStmt.isInvalid()) {
1625     noteMemberDeclaredHere(S, ReturnValue, Fn);
1626     return false;
1627   }
1628   if (cast<clang::ReturnStmt>(ReturnStmt.get())->getNRVOCandidate() == GroDecl)
1629     GroDecl->setNRVOVariable(true);
1630 
1631   this->ReturnStmt = ReturnStmt.get();
1632   return true;
1633 }
1634 
1635 // Create a static_cast\<T&&>(expr).
1636 static Expr *castForMoving(Sema &S, Expr *E, QualType T = QualType()) {
1637   if (T.isNull())
1638     T = E->getType();
1639   QualType TargetType = S.BuildReferenceType(
1640       T, /*SpelledAsLValue*/ false, SourceLocation(), DeclarationName());
1641   SourceLocation ExprLoc = E->getBeginLoc();
1642   TypeSourceInfo *TargetLoc =
1643       S.Context.getTrivialTypeSourceInfo(TargetType, ExprLoc);
1644 
1645   return S
1646       .BuildCXXNamedCast(ExprLoc, tok::kw_static_cast, TargetLoc, E,
1647                          SourceRange(ExprLoc, ExprLoc), E->getSourceRange())
1648       .get();
1649 }
1650 
1651 /// Build a variable declaration for move parameter.
1652 static VarDecl *buildVarDecl(Sema &S, SourceLocation Loc, QualType Type,
1653                              IdentifierInfo *II) {
1654   TypeSourceInfo *TInfo = S.Context.getTrivialTypeSourceInfo(Type, Loc);
1655   VarDecl *Decl = VarDecl::Create(S.Context, S.CurContext, Loc, Loc, II, Type,
1656                                   TInfo, SC_None);
1657   Decl->setImplicit();
1658   return Decl;
1659 }
1660 
1661 // Build statements that move coroutine function parameters to the coroutine
1662 // frame, and store them on the function scope info.
1663 bool Sema::buildCoroutineParameterMoves(SourceLocation Loc) {
1664   assert(isa<FunctionDecl>(CurContext) && "not in a function scope");
1665   auto *FD = cast<FunctionDecl>(CurContext);
1666 
1667   auto *ScopeInfo = getCurFunction();
1668   if (!ScopeInfo->CoroutineParameterMoves.empty())
1669     return false;
1670 
1671   // [dcl.fct.def.coroutine]p13
1672   //   When a coroutine is invoked, after initializing its parameters
1673   //   ([expr.call]), a copy is created for each coroutine parameter. For a
1674   //   parameter of type cv T, the copy is a variable of type cv T with
1675   //   automatic storage duration that is direct-initialized from an xvalue of
1676   //   type T referring to the parameter.
1677   for (auto *PD : FD->parameters()) {
1678     if (PD->getType()->isDependentType())
1679       continue;
1680 
1681     ExprResult PDRefExpr =
1682         BuildDeclRefExpr(PD, PD->getType().getNonReferenceType(),
1683                          ExprValueKind::VK_LValue, Loc); // FIXME: scope?
1684     if (PDRefExpr.isInvalid())
1685       return false;
1686 
1687     Expr *CExpr = nullptr;
1688     if (PD->getType()->getAsCXXRecordDecl() ||
1689         PD->getType()->isRValueReferenceType())
1690       CExpr = castForMoving(*this, PDRefExpr.get());
1691     else
1692       CExpr = PDRefExpr.get();
1693     // [dcl.fct.def.coroutine]p13
1694     //   The initialization and destruction of each parameter copy occurs in the
1695     //   context of the called coroutine.
1696     auto D = buildVarDecl(*this, Loc, PD->getType(), PD->getIdentifier());
1697     AddInitializerToDecl(D, CExpr, /*DirectInit=*/true);
1698 
1699     // Convert decl to a statement.
1700     StmtResult Stmt = ActOnDeclStmt(ConvertDeclToDeclGroup(D), Loc, Loc);
1701     if (Stmt.isInvalid())
1702       return false;
1703 
1704     ScopeInfo->CoroutineParameterMoves.insert(std::make_pair(PD, Stmt.get()));
1705   }
1706   return true;
1707 }
1708 
1709 StmtResult Sema::BuildCoroutineBodyStmt(CoroutineBodyStmt::CtorArgs Args) {
1710   CoroutineBodyStmt *Res = CoroutineBodyStmt::Create(Context, Args);
1711   if (!Res)
1712     return StmtError();
1713   return Res;
1714 }
1715 
1716 ClassTemplateDecl *Sema::lookupCoroutineTraits(SourceLocation KwLoc,
1717                                                SourceLocation FuncLoc,
1718                                                NamespaceDecl *&Namespace) {
1719   if (!StdCoroutineTraitsCache) {
1720     // Because coroutines moved from std::experimental in the TS to std in
1721     // C++20, we look in both places to give users time to transition their
1722     // TS-specific code to C++20.  Diagnostics are given when the TS usage is
1723     // discovered.
1724     // TODO: Become stricter when <experimental/coroutine> is removed.
1725 
1726     auto const &TraitIdent = PP.getIdentifierTable().get("coroutine_traits");
1727 
1728     NamespaceDecl *StdSpace = getStdNamespace();
1729     LookupResult ResStd(*this, &TraitIdent, FuncLoc, LookupOrdinaryName);
1730     bool InStd = StdSpace && LookupQualifiedName(ResStd, StdSpace);
1731 
1732     NamespaceDecl *ExpSpace = lookupStdExperimentalNamespace();
1733     LookupResult ResExp(*this, &TraitIdent, FuncLoc, LookupOrdinaryName);
1734     bool InExp = ExpSpace && LookupQualifiedName(ResExp, ExpSpace);
1735 
1736     if (!InStd && !InExp) {
1737       // The goggles, they found nothing!
1738       Diag(KwLoc, diag::err_implied_coroutine_type_not_found)
1739           << "std::coroutine_traits";
1740       return nullptr;
1741     }
1742 
1743     // Prefer ::std to std::experimental.
1744     auto &Result = InStd ? ResStd : ResExp;
1745     CoroTraitsNamespaceCache = InStd ? StdSpace : ExpSpace;
1746 
1747     // coroutine_traits is required to be a class template.
1748     StdCoroutineTraitsCache = Result.getAsSingle<ClassTemplateDecl>();
1749     if (!StdCoroutineTraitsCache) {
1750       Result.suppressDiagnostics();
1751       NamedDecl *Found = *Result.begin();
1752       Diag(Found->getLocation(), diag::err_malformed_std_coroutine_traits);
1753       return nullptr;
1754     }
1755 
1756     if (InExp) {
1757       // Found in std::experimental
1758       Diag(KwLoc, diag::warn_deprecated_coroutine_namespace)
1759           << "coroutine_traits";
1760       ResExp.suppressDiagnostics();
1761       auto *Found = *ResExp.begin();
1762       Diag(Found->getLocation(), diag::note_entity_declared_at) << Found;
1763 
1764       if (InStd &&
1765           StdCoroutineTraitsCache != ResExp.getAsSingle<ClassTemplateDecl>()) {
1766         // Also found something different in std
1767         Diag(KwLoc,
1768              diag::err_mixed_use_std_and_experimental_namespace_for_coroutine);
1769         Diag(StdCoroutineTraitsCache->getLocation(),
1770              diag::note_entity_declared_at)
1771             << StdCoroutineTraitsCache;
1772 
1773         return nullptr;
1774       }
1775     }
1776   }
1777   Namespace = CoroTraitsNamespaceCache;
1778   return StdCoroutineTraitsCache;
1779 }
1780