[clang] [llvm] [HLSL] Mark `GroupMemoryBarrierWithGroupSync` as `convergent` (PR #160175)

[Finn Plummer via llvm-commits]

https://github.com/inbelic created https://github.com/llvm/llvm-project/pull/160175

`GroupMemoryBarrierWithGroupSync` is required to be marked as convergent so that it can't generate duplicate calls or be moved to identical control flow.

Without it, we generate undefined behaviour during optimization. For instance: https://godbolt.org/z/9j3vsq1h3.

Testing that the convergent attribute is added is sufficient. There already exists testing, [here](https://github.com/inbelic/llvm-project/blob/main/llvm/test/Transforms/SimplifyCFG/attr-convergent.ll), that it will not be moved as described in the above link.

>From 29a68514d624f773d55c5b843aafc11c5353bf43 Mon Sep 17 00:00:00 2001
From: Finn Plummer <mail at inbelic.dev>
Date: Mon, 22 Sep 2025 09:58:11 -0700
Subject: [PATCH 1/2] mark groupmembarrierwithgroupsync as convergent

---
 clang/lib/Headers/hlsl/hlsl_alias_intrinsics.h | 2 +-
 llvm/include/llvm/IR/IntrinsicsDirectX.td      | 3 ++-
 llvm/include/llvm/IR/IntrinsicsSPIRV.td        | 3 ++-
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/clang/lib/Headers/hlsl/hlsl_alias_intrinsics.h b/clang/lib/Headers/hlsl/hlsl_alias_intrinsics.h
index 21a9c30d9f445..cd1ffc8c23298 100644
--- a/clang/lib/Headers/hlsl/hlsl_alias_intrinsics.h
+++ b/clang/lib/Headers/hlsl/hlsl_alias_intrinsics.h
@@ -2805,7 +2805,7 @@ float4 radians(float4);
 /// call.
 
 _HLSL_BUILTIN_ALIAS(__builtin_hlsl_group_memory_barrier_with_group_sync)
-void GroupMemoryBarrierWithGroupSync(void);
+__attribute__((convergent)) void GroupMemoryBarrierWithGroupSync(void);
 
 } // namespace hlsl
 #endif //_HLSL_HLSL_ALIAS_INTRINSICS_H_
diff --git a/llvm/include/llvm/IR/IntrinsicsDirectX.td b/llvm/include/llvm/IR/IntrinsicsDirectX.td
index 5d76c3f8df89d..e60e07801455f 100644
--- a/llvm/include/llvm/IR/IntrinsicsDirectX.td
+++ b/llvm/include/llvm/IR/IntrinsicsDirectX.td
@@ -160,5 +160,6 @@ def int_dx_firstbituhigh : DefaultAttrsIntrinsic<[LLVMScalarOrSameVectorWidth<0,
 def int_dx_firstbitshigh : DefaultAttrsIntrinsic<[LLVMScalarOrSameVectorWidth<0, llvm_i32_ty>], [llvm_anyint_ty], [IntrNoMem]>;
 def int_dx_firstbitlow : DefaultAttrsIntrinsic<[LLVMScalarOrSameVectorWidth<0, llvm_i32_ty>], [llvm_anyint_ty], [IntrNoMem]>;
 
-def int_dx_group_memory_barrier_with_group_sync : DefaultAttrsIntrinsic<[], [], []>;
+def int_dx_group_memory_barrier_with_group_sync
+    : DefaultAttrsIntrinsic<[], [], [IntrConvergent]>;
 }
diff --git a/llvm/include/llvm/IR/IntrinsicsSPIRV.td b/llvm/include/llvm/IR/IntrinsicsSPIRV.td
index bc026fa33c769..0b0c2b137e55b 100644
--- a/llvm/include/llvm/IR/IntrinsicsSPIRV.td
+++ b/llvm/include/llvm/IR/IntrinsicsSPIRV.td
@@ -127,7 +127,8 @@ def int_spv_rsqrt : DefaultAttrsIntrinsic<[LLVMMatchType<0>], [llvm_anyfloat_ty]
       : DefaultAttrsIntrinsic<[llvm_i32_ty], [], [IntrConvergent]>;
   def int_spv_sign : DefaultAttrsIntrinsic<[LLVMScalarOrSameVectorWidth<0, llvm_i32_ty>], [llvm_any_ty], [IntrNoMem]>;
   def int_spv_radians : DefaultAttrsIntrinsic<[LLVMMatchType<0>], [llvm_anyfloat_ty], [IntrNoMem]>;
-  def int_spv_group_memory_barrier_with_group_sync : DefaultAttrsIntrinsic<[], [], []>;
+  def int_spv_group_memory_barrier_with_group_sync
+      : DefaultAttrsIntrinsic<[], [], [IntrConvergent]>;
   def int_spv_discard : DefaultAttrsIntrinsic<[], [], []>;
   def int_spv_uclamp : DefaultAttrsIntrinsic<[llvm_anyint_ty], [LLVMMatchType<0>, LLVMMatchType<0>, LLVMMatchType<0>], [IntrNoMem]>;
   def int_spv_sclamp : DefaultAttrsIntrinsic<[llvm_anyint_ty], [LLVMMatchType<0>, LLVMMatchType<0>, LLVMMatchType<0>], [IntrNoMem]>;

>From 905d8f4966a08f6bcd61e67a86f08e7106e01fdb Mon Sep 17 00:00:00 2001
From: Finn Plummer <mail at inbelic.dev>
Date: Mon, 22 Sep 2025 11:36:34 -0700
Subject: [PATCH 2/2] update testcase

---
 .../CodeGenHLSL/builtins/GroupMemoryBarrierWithGroupSync.hlsl   | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/test/CodeGenHLSL/builtins/GroupMemoryBarrierWithGroupSync.hlsl b/clang/test/CodeGenHLSL/builtins/GroupMemoryBarrierWithGroupSync.hlsl
index 114230d38ba54..e709ed3616f0d 100644
--- a/clang/test/CodeGenHLSL/builtins/GroupMemoryBarrierWithGroupSync.hlsl
+++ b/clang/test/CodeGenHLSL/builtins/GroupMemoryBarrierWithGroupSync.hlsl
@@ -17,4 +17,4 @@ void test_GroupMemoryBarrierWithGroupSync() {
 
 // CHECK: declare void @llvm.[[TARGET]].group.memory.barrier.with.group.sync() #[[ATTRS:[0-9]+]]
 // CHECK-NOT: attributes #[[ATTRS]] = {{.+}}memory(none){{.+}}
-// CHECK: attributes #[[ATTRS]] = {
+// CHECK: attributes #[[ATTRS]] = {{.+}}convergent{{.+}}