[Coroutines] Create C++ noop coroutine with default function attributes (#134878)

This change makes the C++ noop coroutine to be built with attributes
based on the module flags. Among other things, this adds function
attributes related to the Pointer Authentication and Branch Target
Enforcement module flags, which are set by command-line options.

Before this patch, C++ programs built with either PAC-RET or BTI that
had the noop coroutine emitted could have a runtime error because this
function wasn't compatible with the rest of the program.

Author: vhscampos

llvm/lib/Transforms/Coroutines/CoroEarly.cpp

@@ -131,9 +131,10 @@ void Lowerer::lowerCoroNoop(IntrinsicInst *II) {
         StructType::create({FnPtrTy, FnPtrTy}, "NoopCoro.Frame");
 
     // Create a Noop function that does nothing.
-    Function *NoopFn =
-        Function::Create(FnTy, GlobalValue::LinkageTypes::PrivateLinkage,
-                         "__NoopCoro_ResumeDestroy", &M);
+    Function *NoopFn = Function::createWithDefaultAttr(
+        FnTy, GlobalValue::LinkageTypes::PrivateLinkage,
+        M.getDataLayout().getProgramAddressSpace(), "__NoopCoro_ResumeDestroy",
+        &M);
     NoopFn->setCallingConv(CallingConv::Fast);
     buildDebugInfoForNoopResumeDestroyFunc(NoopFn);
     auto *Entry = BasicBlock::Create(C, "entry", NoopFn);

llvm/test/Transforms/Coroutines/coro-noop-pacbti.ll

@@ -0,0 +1,23 @@
+
+; RUN: opt < %s -S -passes=coro-early | FileCheck %s
+
+; CHECK:      define private fastcc void @__NoopCoro_ResumeDestroy(ptr %0) #1 {
+; CHECK-NEXT: entry:
+; CHECK-NEXT:   ret void
+; CHECK-NEXT: }
+
+; CHECK:      attributes #1 = { "branch-target-enforcement" "sign-return-address"="all" "sign-return-address-key"="a_key" }
+
+define ptr @noop() {
+entry:
+  %n = call ptr @llvm.coro.noop()
+  ret ptr %n
+}
+
+declare ptr @llvm.coro.noop()
+
+!llvm.module.flags = !{!0, !1, !2}
+
+!0 = !{i32 8, !"branch-target-enforcement", i32 1}
+!1 = !{i32 8, !"sign-return-address", i32 1}
+!2 = !{i32 8, !"sign-return-address-all", i32 1}