1 //===--- SemaCoroutines.cpp - Semantic Analysis for Coroutines ------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 //  This file implements semantic analysis for C++ Coroutines.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "clang/Sema/SemaInternal.h"
15 #include "clang/AST/Decl.h"
16 #include "clang/AST/ExprCXX.h"
17 #include "clang/AST/StmtCXX.h"
18 #include "clang/Lex/Preprocessor.h"
19 #include "clang/Sema/Initialization.h"
20 #include "clang/Sema/Overload.h"
21 using namespace clang;
22 using namespace sema;
23 
24 /// Look up the std::coroutine_traits<...>::promise_type for the given
25 /// function type.
26 static QualType lookupPromiseType(Sema &S, const FunctionProtoType *FnType,
27                                   SourceLocation Loc) {
28   // FIXME: Cache std::coroutine_traits once we've found it.
29   NamespaceDecl *StdExp = S.lookupStdExperimentalNamespace();
30   if (!StdExp) {
31     S.Diag(Loc, diag::err_implied_std_coroutine_traits_not_found);
32     return QualType();
33   }
34 
35   LookupResult Result(S, &S.PP.getIdentifierTable().get("coroutine_traits"),
36                       Loc, Sema::LookupOrdinaryName);
37   if (!S.LookupQualifiedName(Result, StdExp)) {
38     S.Diag(Loc, diag::err_implied_std_coroutine_traits_not_found);
39     return QualType();
40   }
41 
42   ClassTemplateDecl *CoroTraits = Result.getAsSingle<ClassTemplateDecl>();
43   if (!CoroTraits) {
44     Result.suppressDiagnostics();
45     // We found something weird. Complain about the first thing we found.
46     NamedDecl *Found = *Result.begin();
47     S.Diag(Found->getLocation(), diag::err_malformed_std_coroutine_traits);
48     return QualType();
49   }
50 
51   // Form template argument list for coroutine_traits<R, P1, P2, ...>.
52   TemplateArgumentListInfo Args(Loc, Loc);
53   Args.addArgument(TemplateArgumentLoc(
54       TemplateArgument(FnType->getReturnType()),
55       S.Context.getTrivialTypeSourceInfo(FnType->getReturnType(), Loc)));
56   // FIXME: If the function is a non-static member function, add the type
57   // of the implicit object parameter before the formal parameters.
58   for (QualType T : FnType->getParamTypes())
59     Args.addArgument(TemplateArgumentLoc(
60         TemplateArgument(T), S.Context.getTrivialTypeSourceInfo(T, Loc)));
61 
62   // Build the template-id.
63   QualType CoroTrait =
64       S.CheckTemplateIdType(TemplateName(CoroTraits), Loc, Args);
65   if (CoroTrait.isNull())
66     return QualType();
67   if (S.RequireCompleteType(Loc, CoroTrait,
68                             diag::err_coroutine_traits_missing_specialization))
69     return QualType();
70 
71   CXXRecordDecl *RD = CoroTrait->getAsCXXRecordDecl();
72   assert(RD && "specialization of class template is not a class?");
73 
74   // Look up the ::promise_type member.
75   LookupResult R(S, &S.PP.getIdentifierTable().get("promise_type"), Loc,
76                  Sema::LookupOrdinaryName);
77   S.LookupQualifiedName(R, RD);
78   auto *Promise = R.getAsSingle<TypeDecl>();
79   if (!Promise) {
80     S.Diag(Loc, diag::err_implied_std_coroutine_traits_promise_type_not_found)
81         << RD;
82     return QualType();
83   }
84 
85   // The promise type is required to be a class type.
86   QualType PromiseType = S.Context.getTypeDeclType(Promise);
87   if (!PromiseType->getAsCXXRecordDecl()) {
88     // Use the fully-qualified name of the type.
89     auto *NNS = NestedNameSpecifier::Create(S.Context, nullptr, StdExp);
90     NNS = NestedNameSpecifier::Create(S.Context, NNS, false,
91                                       CoroTrait.getTypePtr());
92     PromiseType = S.Context.getElaboratedType(ETK_None, NNS, PromiseType);
93 
94     S.Diag(Loc, diag::err_implied_std_coroutine_traits_promise_type_not_class)
95         << PromiseType;
96     return QualType();
97   }
98 
99   return PromiseType;
100 }
101 
102 static bool isValidCoroutineContext(Sema &S, SourceLocation Loc,
103                                     StringRef Keyword) {
104   // 'co_await' and 'co_yield' are not permitted in unevaluated operands.
105   if (S.isUnevaluatedContext()) {
106     S.Diag(Loc, diag::err_coroutine_unevaluated_context) << Keyword;
107     return false;
108   }
109 
110   // Any other usage must be within a function.
111   auto *FD = dyn_cast<FunctionDecl>(S.CurContext);
112   if (!FD) {
113     S.Diag(Loc, isa<ObjCMethodDecl>(S.CurContext)
114                     ? diag::err_coroutine_objc_method
115                     : diag::err_coroutine_outside_function) << Keyword;
116     return false;
117   }
118 
119   // An enumeration for mapping the diagnostic type to the correct diagnostic
120   // selection index.
121   enum InvalidFuncDiag {
122     DiagCtor = 0,
123     DiagDtor,
124     DiagCopyAssign,
125     DiagMoveAssign,
126     DiagMain,
127     DiagConstexpr,
128     DiagAutoRet,
129     DiagVarargs,
130   };
131   bool Diagnosed = false;
132   auto DiagInvalid = [&](InvalidFuncDiag ID) {
133     S.Diag(Loc, diag::err_coroutine_invalid_func_context) << ID << Keyword;
134     Diagnosed = true;
135     return false;
136   };
137 
138   // Diagnose when a constructor, destructor, copy/move assignment operator,
139   // or the function 'main' are declared as a coroutine.
140   auto *MD = dyn_cast<CXXMethodDecl>(FD);
141   if (MD && isa<CXXConstructorDecl>(MD))
142     return DiagInvalid(DiagCtor);
143   else if (MD && isa<CXXDestructorDecl>(MD))
144     return DiagInvalid(DiagDtor);
145   else if (MD && MD->isCopyAssignmentOperator())
146     return DiagInvalid(DiagCopyAssign);
147   else if (MD && MD->isMoveAssignmentOperator())
148     return DiagInvalid(DiagMoveAssign);
149   else if (FD->isMain())
150     return DiagInvalid(DiagMain);
151 
152   // Emit a diagnostics for each of the following conditions which is not met.
153   if (FD->isConstexpr())
154     DiagInvalid(DiagConstexpr);
155   if (FD->getReturnType()->isUndeducedType())
156     DiagInvalid(DiagAutoRet);
157   if (FD->isVariadic())
158     DiagInvalid(DiagVarargs);
159 
160   return !Diagnosed;
161 }
162 
163 /// Check that this is a context in which a coroutine suspension can appear.
164 static FunctionScopeInfo *checkCoroutineContext(Sema &S, SourceLocation Loc,
165                                                 StringRef Keyword) {
166   if (!isValidCoroutineContext(S, Loc, Keyword))
167     return nullptr;
168 
169   assert(isa<FunctionDecl>(S.CurContext) && "not in a function scope");
170   auto *FD = cast<FunctionDecl>(S.CurContext);
171   auto *ScopeInfo = S.getCurFunction();
172   assert(ScopeInfo && "missing function scope for function");
173 
174   // If we don't have a promise variable, build one now.
175   if (!ScopeInfo->CoroutinePromise) {
176     QualType T = FD->getType()->isDependentType()
177                      ? S.Context.DependentTy
178                      : lookupPromiseType(
179                            S, FD->getType()->castAs<FunctionProtoType>(), Loc);
180     if (T.isNull())
181       return nullptr;
182 
183     // Create and default-initialize the promise.
184     ScopeInfo->CoroutinePromise =
185         VarDecl::Create(S.Context, FD, FD->getLocation(), FD->getLocation(),
186                         &S.PP.getIdentifierTable().get("__promise"), T,
187                         S.Context.getTrivialTypeSourceInfo(T, Loc), SC_None);
188     S.CheckVariableDeclarationType(ScopeInfo->CoroutinePromise);
189     if (!ScopeInfo->CoroutinePromise->isInvalidDecl())
190       S.ActOnUninitializedDecl(ScopeInfo->CoroutinePromise);
191   }
192 
193   return ScopeInfo;
194 }
195 
196 static Expr *buildBuiltinCall(Sema &S, SourceLocation Loc, Builtin::ID Id,
197                               MutableArrayRef<Expr *> CallArgs) {
198   StringRef Name = S.Context.BuiltinInfo.getName(Id);
199   LookupResult R(S, &S.Context.Idents.get(Name), Loc, Sema::LookupOrdinaryName);
200   S.LookupName(R, S.TUScope, /*AllowBuiltinCreation=*/true);
201 
202   auto *BuiltInDecl = R.getAsSingle<FunctionDecl>();
203   assert(BuiltInDecl && "failed to find builtin declaration");
204 
205   ExprResult DeclRef =
206       S.BuildDeclRefExpr(BuiltInDecl, BuiltInDecl->getType(), VK_LValue, Loc);
207   assert(DeclRef.isUsable() && "Builtin reference cannot fail");
208 
209   ExprResult Call =
210       S.ActOnCallExpr(/*Scope=*/nullptr, DeclRef.get(), Loc, CallArgs, Loc);
211 
212   assert(!Call.isInvalid() && "Call to builtin cannot fail!");
213   return Call.get();
214 }
215 
216 /// Build a call to 'operator co_await' if there is a suitable operator for
217 /// the given expression.
218 static ExprResult buildOperatorCoawaitCall(Sema &SemaRef, Scope *S,
219                                            SourceLocation Loc, Expr *E) {
220   UnresolvedSet<16> Functions;
221   SemaRef.LookupOverloadedOperatorName(OO_Coawait, S, E->getType(), QualType(),
222                                        Functions);
223   return SemaRef.CreateOverloadedUnaryOp(Loc, UO_Coawait, Functions, E);
224 }
225 
226 struct ReadySuspendResumeResult {
227   bool IsInvalid;
228   Expr *Results[3];
229 };
230 
231 static ExprResult buildMemberCall(Sema &S, Expr *Base, SourceLocation Loc,
232                                   StringRef Name,
233                                   MutableArrayRef<Expr *> Args) {
234   DeclarationNameInfo NameInfo(&S.PP.getIdentifierTable().get(Name), Loc);
235 
236   // FIXME: Fix BuildMemberReferenceExpr to take a const CXXScopeSpec&.
237   CXXScopeSpec SS;
238   ExprResult Result = S.BuildMemberReferenceExpr(
239       Base, Base->getType(), Loc, /*IsPtr=*/false, SS,
240       SourceLocation(), nullptr, NameInfo, /*TemplateArgs=*/nullptr,
241       /*Scope=*/nullptr);
242   if (Result.isInvalid())
243     return ExprError();
244 
245   return S.ActOnCallExpr(nullptr, Result.get(), Loc, Args, Loc, nullptr);
246 }
247 
248 /// Build calls to await_ready, await_suspend, and await_resume for a co_await
249 /// expression.
250 static ReadySuspendResumeResult buildCoawaitCalls(Sema &S, SourceLocation Loc,
251                                                   Expr *E) {
252   // Assume invalid until we see otherwise.
253   ReadySuspendResumeResult Calls = {true, {}};
254 
255   const StringRef Funcs[] = {"await_ready", "await_suspend", "await_resume"};
256   for (size_t I = 0, N = llvm::array_lengthof(Funcs); I != N; ++I) {
257     Expr *Operand = new (S.Context) OpaqueValueExpr(
258       Loc, E->getType(), VK_LValue, E->getObjectKind(), E);
259 
260     // FIXME: Pass coroutine handle to await_suspend.
261     ExprResult Result = buildMemberCall(S, Operand, Loc, Funcs[I], None);
262     if (Result.isInvalid())
263       return Calls;
264     Calls.Results[I] = Result.get();
265   }
266 
267   Calls.IsInvalid = false;
268   return Calls;
269 }
270 
271 ExprResult Sema::ActOnCoawaitExpr(Scope *S, SourceLocation Loc, Expr *E) {
272   auto *Coroutine = checkCoroutineContext(*this, Loc, "co_await");
273   if (!Coroutine) {
274     CorrectDelayedTyposInExpr(E);
275     return ExprError();
276   }
277   if (E->getType()->isPlaceholderType()) {
278     ExprResult R = CheckPlaceholderExpr(E);
279     if (R.isInvalid()) return ExprError();
280     E = R.get();
281   }
282 
283   ExprResult Awaitable = buildOperatorCoawaitCall(*this, S, Loc, E);
284   if (Awaitable.isInvalid())
285     return ExprError();
286 
287   return BuildCoawaitExpr(Loc, Awaitable.get());
288 }
289 ExprResult Sema::BuildCoawaitExpr(SourceLocation Loc, Expr *E) {
290   auto *Coroutine = checkCoroutineContext(*this, Loc, "co_await");
291   if (!Coroutine)
292     return ExprError();
293 
294   if (E->getType()->isPlaceholderType()) {
295     ExprResult R = CheckPlaceholderExpr(E);
296     if (R.isInvalid()) return ExprError();
297     E = R.get();
298   }
299 
300   if (E->getType()->isDependentType()) {
301     Expr *Res = new (Context) CoawaitExpr(Loc, Context.DependentTy, E);
302     Coroutine->CoroutineStmts.push_back(Res);
303     return Res;
304   }
305 
306   // If the expression is a temporary, materialize it as an lvalue so that we
307   // can use it multiple times.
308   if (E->getValueKind() == VK_RValue)
309     E = CreateMaterializeTemporaryExpr(E->getType(), E, true);
310 
311   // Build the await_ready, await_suspend, await_resume calls.
312   ReadySuspendResumeResult RSS = buildCoawaitCalls(*this, Loc, E);
313   if (RSS.IsInvalid)
314     return ExprError();
315 
316   Expr *Res = new (Context) CoawaitExpr(Loc, E, RSS.Results[0], RSS.Results[1],
317                                         RSS.Results[2]);
318   Coroutine->CoroutineStmts.push_back(Res);
319   return Res;
320 }
321 
322 static ExprResult buildPromiseCall(Sema &S, FunctionScopeInfo *Coroutine,
323                                    SourceLocation Loc, StringRef Name,
324                                    MutableArrayRef<Expr *> Args) {
325   assert(Coroutine->CoroutinePromise && "no promise for coroutine");
326 
327   // Form a reference to the promise.
328   auto *Promise = Coroutine->CoroutinePromise;
329   ExprResult PromiseRef = S.BuildDeclRefExpr(
330       Promise, Promise->getType().getNonReferenceType(), VK_LValue, Loc);
331   if (PromiseRef.isInvalid())
332     return ExprError();
333 
334   // Call 'yield_value', passing in E.
335   return buildMemberCall(S, PromiseRef.get(), Loc, Name, Args);
336 }
337 
338 ExprResult Sema::ActOnCoyieldExpr(Scope *S, SourceLocation Loc, Expr *E) {
339   auto *Coroutine = checkCoroutineContext(*this, Loc, "co_yield");
340   if (!Coroutine) {
341     CorrectDelayedTyposInExpr(E);
342     return ExprError();
343   }
344 
345   // Build yield_value call.
346   ExprResult Awaitable =
347       buildPromiseCall(*this, Coroutine, Loc, "yield_value", E);
348   if (Awaitable.isInvalid())
349     return ExprError();
350 
351   // Build 'operator co_await' call.
352   Awaitable = buildOperatorCoawaitCall(*this, S, Loc, Awaitable.get());
353   if (Awaitable.isInvalid())
354     return ExprError();
355 
356   return BuildCoyieldExpr(Loc, Awaitable.get());
357 }
358 ExprResult Sema::BuildCoyieldExpr(SourceLocation Loc, Expr *E) {
359   auto *Coroutine = checkCoroutineContext(*this, Loc, "co_yield");
360   if (!Coroutine)
361     return ExprError();
362 
363   if (E->getType()->isPlaceholderType()) {
364     ExprResult R = CheckPlaceholderExpr(E);
365     if (R.isInvalid()) return ExprError();
366     E = R.get();
367   }
368 
369   if (E->getType()->isDependentType()) {
370     Expr *Res = new (Context) CoyieldExpr(Loc, Context.DependentTy, E);
371     Coroutine->CoroutineStmts.push_back(Res);
372     return Res;
373   }
374 
375   // If the expression is a temporary, materialize it as an lvalue so that we
376   // can use it multiple times.
377   if (E->getValueKind() == VK_RValue)
378     E = CreateMaterializeTemporaryExpr(E->getType(), E, true);
379 
380   // Build the await_ready, await_suspend, await_resume calls.
381   ReadySuspendResumeResult RSS = buildCoawaitCalls(*this, Loc, E);
382   if (RSS.IsInvalid)
383     return ExprError();
384 
385   Expr *Res = new (Context) CoyieldExpr(Loc, E, RSS.Results[0], RSS.Results[1],
386                                         RSS.Results[2]);
387   Coroutine->CoroutineStmts.push_back(Res);
388   return Res;
389 }
390 
391 StmtResult Sema::ActOnCoreturnStmt(SourceLocation Loc, Expr *E) {
392   auto *Coroutine = checkCoroutineContext(*this, Loc, "co_return");
393   if (!Coroutine) {
394     CorrectDelayedTyposInExpr(E);
395     return StmtError();
396   }
397   return BuildCoreturnStmt(Loc, E);
398 }
399 
400 StmtResult Sema::BuildCoreturnStmt(SourceLocation Loc, Expr *E) {
401   auto *Coroutine = checkCoroutineContext(*this, Loc, "co_return");
402   if (!Coroutine)
403     return StmtError();
404 
405   if (E && E->getType()->isPlaceholderType() &&
406       !E->getType()->isSpecificPlaceholderType(BuiltinType::Overload)) {
407     ExprResult R = CheckPlaceholderExpr(E);
408     if (R.isInvalid()) return StmtError();
409     E = R.get();
410   }
411 
412   // FIXME: If the operand is a reference to a variable that's about to go out
413   // of scope, we should treat the operand as an xvalue for this overload
414   // resolution.
415   ExprResult PC;
416   if (E && (isa<InitListExpr>(E) || !E->getType()->isVoidType())) {
417     PC = buildPromiseCall(*this, Coroutine, Loc, "return_value", E);
418   } else {
419     E = MakeFullDiscardedValueExpr(E).get();
420     PC = buildPromiseCall(*this, Coroutine, Loc, "return_void", None);
421   }
422   if (PC.isInvalid())
423     return StmtError();
424 
425   Expr *PCE = ActOnFinishFullExpr(PC.get()).get();
426 
427   Stmt *Res = new (Context) CoreturnStmt(Loc, E, PCE);
428   Coroutine->CoroutineStmts.push_back(Res);
429   return Res;
430 }
431 
432 static ExprResult buildStdCurrentExceptionCall(Sema &S, SourceLocation Loc) {
433   NamespaceDecl *Std = S.getStdNamespace();
434   if (!Std) {
435     S.Diag(Loc, diag::err_implied_std_current_exception_not_found);
436     return ExprError();
437   }
438   LookupResult Result(S, &S.PP.getIdentifierTable().get("current_exception"),
439                       Loc, Sema::LookupOrdinaryName);
440   if (!S.LookupQualifiedName(Result, Std)) {
441     S.Diag(Loc, diag::err_implied_std_current_exception_not_found);
442     return ExprError();
443   }
444 
445   // FIXME The STL is free to provide more than one overload.
446   FunctionDecl *FD = Result.getAsSingle<FunctionDecl>();
447   if (!FD) {
448     S.Diag(Loc, diag::err_malformed_std_current_exception);
449     return ExprError();
450   }
451   ExprResult Res = S.BuildDeclRefExpr(FD, FD->getType(), VK_LValue, Loc);
452   Res = S.ActOnCallExpr(/*Scope*/ nullptr, Res.get(), Loc, None, Loc);
453   if (Res.isInvalid()) {
454     S.Diag(Loc, diag::err_malformed_std_current_exception);
455     return ExprError();
456   }
457   return Res;
458 }
459 
460 // Find an appropriate delete for the promise.
461 static FunctionDecl *findDeleteForPromise(Sema &S, SourceLocation Loc,
462                                           QualType PromiseType) {
463   FunctionDecl *OperatorDelete = nullptr;
464 
465   DeclarationName DeleteName =
466       S.Context.DeclarationNames.getCXXOperatorName(OO_Delete);
467 
468   auto *PointeeRD = PromiseType->getAsCXXRecordDecl();
469   assert(PointeeRD && "PromiseType must be a CxxRecordDecl type");
470 
471   if (S.FindDeallocationFunction(Loc, PointeeRD, DeleteName, OperatorDelete))
472     return nullptr;
473 
474   if (!OperatorDelete) {
475     // Look for a global declaration.
476     const bool CanProvideSize = S.isCompleteType(Loc, PromiseType);
477     const bool Overaligned = false;
478     OperatorDelete = S.FindUsualDeallocationFunction(Loc, CanProvideSize,
479                                                      Overaligned, DeleteName);
480   }
481   S.MarkFunctionReferenced(Loc, OperatorDelete);
482   return OperatorDelete;
483 }
484 
485 // Builds allocation and deallocation for the coroutine. Returns false on
486 // failure.
487 static bool buildAllocationAndDeallocation(Sema &S, SourceLocation Loc,
488                                            FunctionScopeInfo *Fn,
489                                            Expr *&Allocation,
490                                            Stmt *&Deallocation) {
491   TypeSourceInfo *TInfo = Fn->CoroutinePromise->getTypeSourceInfo();
492   QualType PromiseType = TInfo->getType();
493   if (PromiseType->isDependentType())
494     return true;
495 
496   if (S.RequireCompleteType(Loc, PromiseType, diag::err_incomplete_type))
497     return false;
498 
499   // FIXME: Add support for get_return_object_on_allocation failure.
500   // FIXME: Add support for stateful allocators.
501 
502   FunctionDecl *OperatorNew = nullptr;
503   FunctionDecl *OperatorDelete = nullptr;
504   FunctionDecl *UnusedResult = nullptr;
505   bool PassAlignment = false;
506 
507   S.FindAllocationFunctions(Loc, SourceRange(),
508                             /*UseGlobal*/ false, PromiseType,
509                             /*isArray*/ false, PassAlignment,
510                             /*PlacementArgs*/ None, OperatorNew, UnusedResult);
511 
512   OperatorDelete = findDeleteForPromise(S, Loc, PromiseType);
513 
514   if (!OperatorDelete || !OperatorNew)
515     return false;
516 
517   Expr *FramePtr =
518       buildBuiltinCall(S, Loc, Builtin::BI__builtin_coro_frame, {});
519 
520   Expr *FrameSize =
521       buildBuiltinCall(S, Loc, Builtin::BI__builtin_coro_size, {});
522 
523   // Make new call.
524 
525   ExprResult NewRef =
526       S.BuildDeclRefExpr(OperatorNew, OperatorNew->getType(), VK_LValue, Loc);
527   if (NewRef.isInvalid())
528     return false;
529 
530   ExprResult NewExpr =
531       S.ActOnCallExpr(S.getCurScope(), NewRef.get(), Loc, FrameSize, Loc);
532   if (NewExpr.isInvalid())
533     return false;
534 
535   Allocation = NewExpr.get();
536 
537   // Make delete call.
538 
539   QualType OpDeleteQualType = OperatorDelete->getType();
540 
541   ExprResult DeleteRef =
542       S.BuildDeclRefExpr(OperatorDelete, OpDeleteQualType, VK_LValue, Loc);
543   if (DeleteRef.isInvalid())
544     return false;
545 
546   Expr *CoroFree =
547       buildBuiltinCall(S, Loc, Builtin::BI__builtin_coro_free, {FramePtr});
548 
549   SmallVector<Expr *, 2> DeleteArgs{CoroFree};
550 
551   // Check if we need to pass the size.
552   const auto *OpDeleteType =
553       OpDeleteQualType.getTypePtr()->getAs<FunctionProtoType>();
554   if (OpDeleteType->getNumParams() > 1)
555     DeleteArgs.push_back(FrameSize);
556 
557   ExprResult DeleteExpr =
558       S.ActOnCallExpr(S.getCurScope(), DeleteRef.get(), Loc, DeleteArgs, Loc);
559   if (DeleteExpr.isInvalid())
560     return false;
561 
562   Deallocation = DeleteExpr.get();
563 
564   return true;
565 }
566 
567 void Sema::CheckCompletedCoroutineBody(FunctionDecl *FD, Stmt *&Body) {
568   FunctionScopeInfo *Fn = getCurFunction();
569   assert(Fn && !Fn->CoroutineStmts.empty() && "not a coroutine");
570 
571   // Coroutines [stmt.return]p1:
572   //   A return statement shall not appear in a coroutine.
573   if (Fn->FirstReturnLoc.isValid()) {
574     Diag(Fn->FirstReturnLoc, diag::err_return_in_coroutine);
575     auto *First = Fn->CoroutineStmts[0];
576     Diag(First->getLocStart(), diag::note_declared_coroutine_here)
577         << (isa<CoawaitExpr>(First) ? 0 :
578             isa<CoyieldExpr>(First) ? 1 : 2);
579   }
580 
581   SourceLocation Loc = FD->getLocation();
582 
583   // Form a declaration statement for the promise declaration, so that AST
584   // visitors can more easily find it.
585   StmtResult PromiseStmt =
586       ActOnDeclStmt(ConvertDeclToDeclGroup(Fn->CoroutinePromise), Loc, Loc);
587   if (PromiseStmt.isInvalid())
588     return FD->setInvalidDecl();
589 
590   // Form and check implicit 'co_await p.initial_suspend();' statement.
591   ExprResult InitialSuspend =
592       buildPromiseCall(*this, Fn, Loc, "initial_suspend", None);
593   // FIXME: Support operator co_await here.
594   if (!InitialSuspend.isInvalid())
595     InitialSuspend = BuildCoawaitExpr(Loc, InitialSuspend.get());
596   InitialSuspend = ActOnFinishFullExpr(InitialSuspend.get());
597   if (InitialSuspend.isInvalid())
598     return FD->setInvalidDecl();
599 
600   // Form and check implicit 'co_await p.final_suspend();' statement.
601   ExprResult FinalSuspend =
602       buildPromiseCall(*this, Fn, Loc, "final_suspend", None);
603   // FIXME: Support operator co_await here.
604   if (!FinalSuspend.isInvalid())
605     FinalSuspend = BuildCoawaitExpr(Loc, FinalSuspend.get());
606   FinalSuspend = ActOnFinishFullExpr(FinalSuspend.get());
607   if (FinalSuspend.isInvalid())
608     return FD->setInvalidDecl();
609 
610   // Form and check allocation and deallocation calls.
611   Expr *Allocation = nullptr;
612   Stmt *Deallocation = nullptr;
613   if (!buildAllocationAndDeallocation(*this, Loc, Fn, Allocation, Deallocation))
614     return FD->setInvalidDecl();
615 
616   // control flowing off the end of the coroutine.
617   // Also try to form 'p.set_exception(std::current_exception());' to handle
618   // uncaught exceptions.
619   ExprResult SetException;
620   StmtResult Fallthrough;
621   if (Fn->CoroutinePromise &&
622       !Fn->CoroutinePromise->getType()->isDependentType()) {
623     CXXRecordDecl *RD = Fn->CoroutinePromise->getType()->getAsCXXRecordDecl();
624     assert(RD && "Type should have already been checked");
625     // [dcl.fct.def.coroutine]/4
626     // The unqualified-ids 'return_void' and 'return_value' are looked up in
627     // the scope of class P. If both are found, the program is ill-formed.
628     DeclarationName RVoidDN = PP.getIdentifierInfo("return_void");
629     LookupResult RVoidResult(*this, RVoidDN, Loc, Sema::LookupMemberName);
630     const bool HasRVoid = LookupQualifiedName(RVoidResult, RD);
631 
632     DeclarationName RValueDN = PP.getIdentifierInfo("return_value");
633     LookupResult RValueResult(*this, RValueDN, Loc, Sema::LookupMemberName);
634     const bool HasRValue = LookupQualifiedName(RValueResult, RD);
635 
636     if (HasRVoid && HasRValue) {
637       // FIXME Improve this diagnostic
638       Diag(FD->getLocation(), diag::err_coroutine_promise_return_ill_formed)
639           << RD;
640       return FD->setInvalidDecl();
641     } else if (HasRVoid) {
642       // If the unqualified-id return_void is found, flowing off the end of a
643       // coroutine is equivalent to a co_return with no operand. Otherwise,
644       // flowing off the end of a coroutine results in undefined behavior.
645       Fallthrough = BuildCoreturnStmt(FD->getLocation(), nullptr);
646       Fallthrough = ActOnFinishFullStmt(Fallthrough.get());
647       if (Fallthrough.isInvalid())
648         return FD->setInvalidDecl();
649     }
650 
651     // [dcl.fct.def.coroutine]/3
652     // The unqualified-id set_exception is found in the scope of P by class
653     // member access lookup (3.4.5).
654     DeclarationName SetExDN = PP.getIdentifierInfo("set_exception");
655     LookupResult SetExResult(*this, SetExDN, Loc, Sema::LookupMemberName);
656     if (LookupQualifiedName(SetExResult, RD)) {
657       // Form the call 'p.set_exception(std::current_exception())'
658       SetException = buildStdCurrentExceptionCall(*this, Loc);
659       if (SetException.isInvalid())
660         return FD->setInvalidDecl();
661       Expr *E = SetException.get();
662       SetException = buildPromiseCall(*this, Fn, Loc, "set_exception", E);
663       SetException = ActOnFinishFullExpr(SetException.get(), Loc);
664       if (SetException.isInvalid())
665         return FD->setInvalidDecl();
666     }
667   }
668 
669   // Build implicit 'p.get_return_object()' expression and form initialization
670   // of return type from it.
671   ExprResult ReturnObject =
672       buildPromiseCall(*this, Fn, Loc, "get_return_object", None);
673   if (ReturnObject.isInvalid())
674     return FD->setInvalidDecl();
675   QualType RetType = FD->getReturnType();
676   if (!RetType->isDependentType()) {
677     InitializedEntity Entity =
678         InitializedEntity::InitializeResult(Loc, RetType, false);
679     ReturnObject = PerformMoveOrCopyInitialization(Entity, nullptr, RetType,
680                                                    ReturnObject.get());
681     if (ReturnObject.isInvalid())
682       return FD->setInvalidDecl();
683   }
684   ReturnObject = ActOnFinishFullExpr(ReturnObject.get(), Loc);
685   if (ReturnObject.isInvalid())
686     return FD->setInvalidDecl();
687 
688   // FIXME: Perform move-initialization of parameters into frame-local copies.
689   SmallVector<Expr*, 16> ParamMoves;
690 
691   // Build body for the coroutine wrapper statement.
692   Body = new (Context) CoroutineBodyStmt(
693       Body, PromiseStmt.get(), InitialSuspend.get(), FinalSuspend.get(),
694       SetException.get(), Fallthrough.get(), Allocation, Deallocation,
695       ReturnObject.get(), ParamMoves);
696 }
697