[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.

Author: sagar-rain

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();
 

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