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

[Victor Campos via llvm-commits]

https://github.com/vhscampos created https://github.com/llvm/llvm-project/pull/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.

>From d93f02021b0380b8b1b3432327b05b556dae9bfe Mon Sep 17 00:00:00 2001
From: Victor Campos <victor.campos at arm.com>
Date: Fri, 4 Apr 2025 17:45:43 +0100
Subject: [PATCH] [Coroutines] Create C++ noop coroutine with default function
 attributes

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.
---
 llvm/lib/Transforms/Coroutines/CoroEarly.cpp  |  7 +++---
 .../Transforms/Coroutines/coro-noop-pacbti.ll | 23 +++++++++++++++++++
 2 files changed, 27 insertions(+), 3 deletions(-)
 create mode 100644 llvm/test/Transforms/Coroutines/coro-noop-pacbti.ll

diff --git a/llvm/lib/Transforms/Coroutines/CoroEarly.cpp b/llvm/lib/Transforms/Coroutines/CoroEarly.cpp
index 5375448d2d2e2..fd0c5e2e240c2 100644
--- a/llvm/lib/Transforms/Coroutines/CoroEarly.cpp
+++ b/llvm/lib/Transforms/Coroutines/CoroEarly.cpp
@@ -130,9 +130,10 @@ 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);
diff --git a/llvm/test/Transforms/Coroutines/coro-noop-pacbti.ll b/llvm/test/Transforms/Coroutines/coro-noop-pacbti.ll
new file mode 100644
index 0000000000000..4f302a6acc649
--- /dev/null
+++ b/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}