[mlir][ArmSME] Fix crash on empty vector.mask in arm-sme-vector-legalization

[MacDue]

Fixes #118449

[llvmbot]

@llvm/pr-subscribers-mlir

@llvm/pr-subscribers-mlir-sme

Author: Benjamin Maxwell (MacDue)

Changes

Fixes #118449

---

Full diff: https://github.com/llvm/llvm-project/pull/118613.diff

2 Files Affected:

• (modified) mlir/lib/Dialect/ArmSME/Transforms/VectorLegalization.cpp (+2-2)
• (modified) mlir/test/Dialect/ArmSME/vector-legalization.mlir (+8)

diff --git a/mlir/lib/Dialect/ArmSME/Transforms/VectorLegalization.cpp b/mlir/lib/Dialect/ArmSME/Transforms/VectorLegalization.cpp
index e908a536e6fb27..61767f3b21c9c3 100644
--- a/mlir/lib/Dialect/ArmSME/Transforms/VectorLegalization.cpp
+++ b/mlir/lib/Dialect/ArmSME/Transforms/VectorLegalization.cpp
@@ -265,8 +265,8 @@ struct LegalizeMaskedVectorOuterProductOpsByDecomposition
   LogicalResult
   matchAndRewrite(vector::MaskOp maskOp, OpAdaptor adaptor,
                   OneToNPatternRewriter &rewriter) const override {
-    if (auto outerProductOp =
-            llvm::dyn_cast<vector::OuterProductOp>(maskOp.getMaskableOp())) {
+    if (auto outerProductOp = llvm::dyn_cast_or_null<vector::OuterProductOp>(
+            maskOp.getMaskableOp())) {
       LegalizeVectorOuterProductOpsByDecomposition pattern(*getTypeConverter(),
                                                            getContext());
       return static_cast<RewritePattern &>(pattern).matchAndRewrite(
diff --git a/mlir/test/Dialect/ArmSME/vector-legalization.mlir b/mlir/test/Dialect/ArmSME/vector-legalization.mlir
index 458906a1879829..2f33007720258b 100644
--- a/mlir/test/Dialect/ArmSME/vector-legalization.mlir
+++ b/mlir/test/Dialect/ArmSME/vector-legalization.mlir
@@ -646,3 +646,11 @@ func.func @negative_transpose_store_scalable_via_za__bad_source_shape(%vec: vect
   vector.transfer_write %tr, %dest[%i, %j] {in_bounds = [true, true]} : vector<[7]x2xf32>,  memref<?x?xf32>
   return
 }
+
+// -----
+
+// From: https://github.com/llvm/llvm-project/issues/118449 (check we don't crash).
+func.func @vector_mask_empty(%m0: vector<16x2xi1>, %arg1: vector<16x16xf32>) -> vector<16x16xf32> {
+  %0 = vector.mask %m0 { vector.yield %arg1 : vector<16x16xf32> } : vector<16x2xi1> -> vector<16x16xf32>
+  return %0 : vector<16x16xf32>
+}

[banach-space]

Thanks for the fix Ben and for paying attention to GitHub issues 🙏🏻

Makes sense, but I'd appreciate some clarification in comments and code. In particular, "crash on empty vector.mask" -> "crash on vector.mask masking an empty block"? That wasn't immediately obvious to me.

[banach-space]

LGTM, thanks!