[clang] [llvm] [coroutine] Implement llvm.coro.await.suspend intrinsic (PR #79712)

[Akira Hatanaka via cfe-commits]

================
@@ -338,6 +409,69 @@ static QualType getCoroutineSuspendExprReturnType(const ASTContext &Ctx,
 }
 #endif
 
+llvm::Function *
+CodeGenFunction::generateAwaitSuspendWrapper(Twine const &CoroName,
+                                             Twine const &SuspendPointName,
+                                             CoroutineSuspendExpr const &S) {
+  std::string FuncName = "__await_suspend_wrapper_";
+  FuncName += CoroName.str();
+  FuncName += '_';
+  FuncName += SuspendPointName.str();
+
+  ASTContext &C = getContext();
+
+  FunctionArgList args;
+
+  ImplicitParamDecl AwaiterDecl(C, C.VoidPtrTy, ImplicitParamKind::Other);
+  ImplicitParamDecl FrameDecl(C, C.VoidPtrTy, ImplicitParamKind::Other);
+  QualType ReturnTy = S.getSuspendExpr()->getType();
+
+  args.push_back(&AwaiterDecl);
+  args.push_back(&FrameDecl);
+
+  const CGFunctionInfo &FI =
+      CGM.getTypes().arrangeBuiltinFunctionDeclaration(ReturnTy, args);
+
+  llvm::FunctionType *LTy = CGM.getTypes().GetFunctionType(FI);
+
+  llvm::Function *Fn = llvm::Function::Create(
+      LTy, llvm::GlobalValue::PrivateLinkage, FuncName, &CGM.getModule());
+
+  Fn->addParamAttr(0, llvm::Attribute::AttrKind::NonNull);
+  Fn->addParamAttr(0, llvm::Attribute::AttrKind::NoUndef);
+
+  Fn->addParamAttr(1, llvm::Attribute::AttrKind::NoUndef);
+
+  Fn->setMustProgress();
+  Fn->addFnAttr(llvm::Attribute::AttrKind::AlwaysInline);
+
+  StartFunction(GlobalDecl(), ReturnTy, Fn, FI, args);
+
+  // FIXME: add TBAA metadata to the loads
+  llvm::Value *AwaiterPtr = Builder.CreateLoad(GetAddrOfLocalVar(&AwaiterDecl));
+  auto AwaiterLValue =
+      MakeNaturalAlignAddrLValue(AwaiterPtr, AwaiterDecl.getType());
----------------
ahatanak wrote:

I wonder whether the type passed to `MakeNaturalAlignAddrLValue` is correct. `AwaiterDecl.getType()` is `void *`, but shouldn't `S.getOpaqueValue()` be passed?

I think this was causing a libc++ test to crash when ubsan was enabled (see https://github.com/llvm/llvm-project/pull/86898).

`S.getOpaqueValue()` and `AwaiterLValue` are passed to `OpaqueValueMappingData::bind`. clang  mis-compiles when the lvalue has a larger alignment than the type of `S.getOpaqueValue()`.

https://github.com/llvm/llvm-project/pull/79712/files#diff-da3676b91275038b801aabe1e10b6fdedfbe50b679eac152080c2a26fbd8ec7dR458

https://github.com/llvm/llvm-project/pull/79712