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

[Chuanqi Xu via cfe-commits]

================
@@ -338,6 +386,85 @@ static QualType getCoroutineSuspendExprReturnType(const ASTContext &Ctx,
 }
 #endif
 
+llvm::Function *CodeGenFunction::generateAwaitSuspendHelper(
+    Twine const &CoroName, Twine const &SuspendPointName,
+    CoroutineSuspendExpr const &S, bool CanThrow) {
+  std::string FuncName = "__await_suspend_helper_";
+  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();
+
+  if (ReturnTy->isBooleanType()) {
+    ReturnTy = C.BoolTy;
+  } else if (ReturnTy->isVoidPointerType()) {
+    ReturnTy = C.VoidPtrTy;
+  } else {
+    ReturnTy = C.VoidTy;
+  }
+
+  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);
+
+  if (!CanThrow) {
+    Fn->addFnAttr(llvm::Attribute::AttrKind::NoUnwind);
+  }
----------------
ChuanqiXu9 wrote:

We don't need this. If I remember correctly, LLVM can add it automatically as long as the await_suspend is marked noexcept.

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