[Mlir-commits] [mlir] 0c91f5b - [mlir][vector] Disallow vector broadcast along scalable dim (#212197)

[llvmlistbot at llvm.org]

Author: Bryth
Date: 2026-08-06T13:16:55+02:00
New Revision: 0c91f5b25492e552f2f24f4d56750c3948dd6e90

URL: https://github.com/llvm/llvm-project/commit/0c91f5b25492e552f2f24f4d56750c3948dd6e90
DIFF: https://github.com/llvm/llvm-project/commit/0c91f5b25492e552f2f24f4d56750c3948dd6e90.diff

LOG: [mlir][vector] Disallow vector broadcast along scalable dim (#212197)

Broadcasts from vectors to higher rank vectors get lowered recursively
by iterating over leading dimensions to create "size(dimension)" insert
ops. This cannot be done for scalable dimensions whose size is unknown.
This PR prevents such transforms from occurring by stopping if the
leading dimension is scalable.

Added: 
    

Modified: 
    mlir/lib/Dialect/Vector/Transforms/LowerVectorBroadcast.cpp
    mlir/test/Dialect/Vector/vector-broadcast-lowering-transforms.mlir

Removed: 
    


################################################################################
diff  --git a/mlir/lib/Dialect/Vector/Transforms/LowerVectorBroadcast.cpp b/mlir/lib/Dialect/Vector/Transforms/LowerVectorBroadcast.cpp
index a78c31367ee28..ceeb258805c6a 100644
--- a/mlir/lib/Dialect/Vector/Transforms/LowerVectorBroadcast.cpp
+++ b/mlir/lib/Dialect/Vector/Transforms/LowerVectorBroadcast.cpp
@@ -73,6 +73,10 @@ class BroadcastOpLowering : public OpRewritePattern<vector::BroadcastOp> {
     //   %x = [%b,%b,%b,%b] : n-D
     if (srcRank < dstRank) {
       // Duplication.
+      if (dstType.getScalableDims()[0])
+        return rewriter.notifyMatchFailure(
+            op, "Vector broadcasting over a scalable dimension is not "
+                "currently supported");
       VectorType resType = VectorType::Builder(dstType).dropDim(0);
       Value bcst =
           vector::BroadcastOp::create(rewriter, loc, resType, op.getSource());

diff  --git a/mlir/test/Dialect/Vector/vector-broadcast-lowering-transforms.mlir b/mlir/test/Dialect/Vector/vector-broadcast-lowering-transforms.mlir
index 5b193c5e25ca0..c2922cdbe55aa 100644
--- a/mlir/test/Dialect/Vector/vector-broadcast-lowering-transforms.mlir
+++ b/mlir/test/Dialect/Vector/vector-broadcast-lowering-transforms.mlir
@@ -209,6 +209,33 @@ func.func @broadcast_scalable_duplication(%arg0: vector<[32]xf32>) -> vector<1x[
   return %res : vector<1x[32]xf32>
 }
 
+// TODO: Add support for scalable vectors
+
+// CHECK-LABEL: @broadcast_vec2d_from_vec1d_scalable_leading
+// CHECK-SAME:  %[[A:.*]]: vector<2xf32>)
+// CHECK: vector.broadcast %[[A]] : vector<2xf32> to vector<[4]x2xf32>
+
+func.func @broadcast_vec2d_from_vec1d_scalable_leading(%arg0: vector<2xf32>) -> vector<[4]x2xf32> {
+  %0 = vector.broadcast %arg0 : vector<2xf32> to vector<[4]x2xf32>
+  return %0 : vector<[4]x2xf32>
+}
+
+// TODO: Add support for scalable vectors
+
+// CHECK-LABEL: @broadcast_vec2d_from_vec1d_scalable_inner
+// CHECK-SAME:  %[[A:.*]]: vector<2xf32>)
+// CHECK:       %[[T0:.*]] = ub.poison : vector<3x[4]x2xf32>
+// CHECK:       %[[T1:.*]] = vector.broadcast %[[A]] : vector<2xf32> to vector<[4]x2xf32>
+// CHECK:       %[[T2:.*]] = vector.insert %[[T1]], %[[T0]] [0] : vector<[4]x2xf32> into vector<3x[4]x2xf32>
+// CHECK:       %[[T3:.*]] = vector.insert %[[T1]], %[[T2]] [1] : vector<[4]x2xf32> into vector<3x[4]x2xf32>
+// CHECK:       %[[T4:.*]] = vector.insert %[[T1]], %[[T3]] [2] : vector<[4]x2xf32> into vector<3x[4]x2xf32>
+// CHECK:       return %[[T4]] : vector<3x[4]x2xf32>
+
+func.func @broadcast_vec2d_from_vec1d_scalable_inner(%arg0: vector<2xf32>) -> vector<3x[4]x2xf32> {
+  %0 = vector.broadcast %arg0 : vector<2xf32> to vector<3x[4]x2xf32>
+  return %0 : vector<3x[4]x2xf32>
+}
+
 module attributes {transform.with_named_sequence} {
   transform.named_sequence @__transform_main(%module_op: !transform.any_op {transform.readonly}) {
     %f = transform.structured.match ops{["func.func"]} in %module_op