[Mlir-commits] [mlir] [mlir][vector] Fix fold result for empty vector.mask with no results (PR #180345)

[Longsheng Mou]

https://github.com/CoTinker created https://github.com/llvm/llvm-project/pull/180345

This PR fixes `foldEmptyMaskOp` to return `failure` when folding an empty vector.mask whose terminatorhas no operands. Previously this case returned success without producing any folded results, which violates the folding contract. Fixes #177825.

>From bc90fa29026277aa6a93a4c1150db60b5dfd1bd8 Mon Sep 17 00:00:00 2001
From: Longsheng Mou <longshengmou at gmail.com>
Date: Sat, 7 Feb 2026 20:36:43 +0800
Subject: [PATCH] [mlir][vector] Fix fold result for empty vector.mask with no
 results

This PR fixes `foldEmptyMaskOp` to return `failure` when folding an empty vector.mask whose terminatorhas no operands. Previously this case returned success without producing any folded results, which violates the folding contract.
---
 mlir/lib/Dialect/Vector/IR/VectorOps.cpp              |  2 +-
 mlir/test/Conversion/ArithToEmitC/arith-to-emitc.mlir | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
index 613adeb5eeaaf..089f41142dfd5 100644
--- a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
+++ b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
@@ -7614,7 +7614,7 @@ static LogicalResult foldEmptyMaskOp(MaskOp maskOp, MaskOp::FoldAdaptor adaptor,
   auto terminator = cast<vector::YieldOp>(block->front());
   if (terminator.getNumOperands() == 0) {
     // `vector.mask` has no results, just remove the `vector.mask`.
-    return success();
+    return failure();
   }
 
   // `vector.mask` has results, propagate the results.
diff --git a/mlir/test/Conversion/ArithToEmitC/arith-to-emitc.mlir b/mlir/test/Conversion/ArithToEmitC/arith-to-emitc.mlir
index 319dfc31ab637..5655c76d37faf 100644
--- a/mlir/test/Conversion/ArithToEmitC/arith-to-emitc.mlir
+++ b/mlir/test/Conversion/ArithToEmitC/arith-to-emitc.mlir
@@ -772,3 +772,14 @@ func.func @arith_truncf(%arg0: f64) -> f16 {
 
   return %truncd1 : f16
 }
+
+// -----
+
+// Ensure that vector.mask with an empty mask does not cause issues.
+
+// CHECK-LABEL: empty_vector_mask
+func.func @empty_vector_mask(%mask : vector<8xi1>) {
+  // CHECK: vector.mask
+  vector.mask %mask { vector.yield } : vector<8xi1>
+  return
+}