[Mlir-commits] [mlir] [mlir][vector] Prevent folding non memref-type gather into maskedload (PR #135371)

[Sagar Kulkarni]

https://github.com/sagarkulkarni19 created https://github.com/llvm/llvm-project/pull/135371

This patch fixes an issue in the FoldContiguousGather pattern which was incorrectly folding vector.gather operations with contiguous indices into vector.maskedload operations regardless of the base operand type.

While vector.gather operations can work on both tensor and memref types, vector.maskedload operations are only valid for memref types. The pattern was incorrectly lowering a tensor-based gather into a masked-load, which is invalid.

This fix adds a type check to ensure the pattern only applies to memref-based gather operations.

>From 1e501156729070452c57e70e7a8a769fb7aa2050 Mon Sep 17 00:00:00 2001
From: Sagar Kulkarni <sagar at rain.ai>
Date: Fri, 11 Apr 2025 09:48:40 -0400
Subject: [PATCH] [mlir][vector] Prevent folding non memref-type gather into
 maskedload

This patch fixes an issue in the FoldContiguousGather pattern which was
incorrectly folding vector.gather operations with contiguous indices into
vector.maskedload operations regardless of the base operand type.

While vector.gather operations can work on both tensor and memref types,
vector.maskedload operations are only valid for memref types. The pattern
was incorrectly lowering a tensor-based gather into a masked-load, which
is invalid.

This fix adds a type check to ensure the pattern only applies to memref-based
gather operations.
---
 mlir/lib/Dialect/Vector/IR/VectorOps.cpp   |  3 +++
 mlir/test/Dialect/Vector/canonicalize.mlir | 12 ++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
index 98d98f067de14..8955438b57343 100644
--- a/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
+++ b/mlir/lib/Dialect/Vector/IR/VectorOps.cpp
@@ -5340,6 +5340,9 @@ class FoldContiguousGather final : public OpRewritePattern<GatherOp> {
   using OpRewritePattern::OpRewritePattern;
   LogicalResult matchAndRewrite(GatherOp op,
                                 PatternRewriter &rewriter) const override {
+    if (!op.getBase().getType().isa<MemRefType>())
+      return failure();
+
     if (failed(isZeroBasedContiguousSeq(op.getIndexVec())))
       return failure();
 
diff --git a/mlir/test/Dialect/Vector/canonicalize.mlir b/mlir/test/Dialect/Vector/canonicalize.mlir
index b7db8ec834be7..7d9223696712d 100644
--- a/mlir/test/Dialect/Vector/canonicalize.mlir
+++ b/mlir/test/Dialect/Vector/canonicalize.mlir
@@ -3149,6 +3149,18 @@ func.func @contiguous_gather_step(%base: memref<?xf32>,
 
 // -----
 
+// CHECK-LABEL: @dont_fold_tensor_type_contiguous_gather
+func.func @dont_fold_tensor_type_contiguous_gather(%base: tensor<8xf32>, %mask: vector<4xi1>, %pass_thru: vector<4xf32>) -> vector<4xf32> {
+  %c0 = arith.constant 0 : index
+  %indices = arith.constant dense<[0, 1, 2, 3]> : vector<4xindex>
+  // CHECK: vector.gather
+  // CHECK-NOT: vector.maskedload
+  %0 = vector.gather %base[%c0][%indices], %mask, %pass_thru : tensor<8xf32>, vector<4xindex>, vector<4xi1>, vector<4xf32> into vector<4xf32>
+  return %0 : vector<4xf32>
+}
+
+// -----
+
 // CHECK-LABEL: @gather_broadcast(
 // TODO: Broadcast is not supported yet
 //       CHECK:   %[[R:.*]] = vector.gather