[Mlir-commits] [mlir] [mlir][gpu] Add `gpu.subgroup_uniform` op (PR #157743)

[Fabian Mora]

================
@@ -3255,4 +3255,37 @@ def GPU_SubgroupBroadcastOp : GPU_Op<"subgroup_broadcast",
   let hasVerifier = 1;
 }
 
+def GPU_SubgroupUniformOp : GPU_Op<"subgroup_uniform",
+    [Pure, AllTypesMatch<["result", "src"]>,
+    DeclareOpInterfaceMethods<InferIntRangeInterface, ["inferResultRanges"]>] #
+    ElementwiseMappable.traits>,
+  Arguments<(ins AnyType:$src)> {
+  let summary = "Assumes value is unform across the lanes in subgroup";
+  let description = [{
+    The "subgroup_uniform" op assumes that the value is uniform across all lanes
+    in a subgroup. This means that all active lanes in the subgroup are expected
+    to have the same value.
+
+    This op can be used to inform the compiler that a value is uniform across
+    the subgroup, enabling optimizations. The result is poison if the value
+    is not actually uniform.
+
+    This op is functionally no-op as no valid program should change its
+    semantics if this op is removed. Backends can choose to ignore it or do
+    some optimizations (e.g. put value into scalar registers).
+
+    This op can be freely speculated across structured control flow as parent
+    active mask is always superset of current mask and if can hoist input
----------------
fabianmcg wrote:

```suggestion
    active mask is always a superset of the current mask, and if it is possible to the hoist input
```

https://github.com/llvm/llvm-project/pull/157743