[mlir][vector] Fix vector.broadcast lowering for scalable vectors

[banach-space]

This patch makes sure that the following case is lowered correctly
("duplication"):

  func.func @broadcast_scalable_duplication(%arg0: vector<[32]xf32>) -> vector<1x[32]xf32> {
    %res = vector.broadcast %arg0 : vector<[32]xf32> to vector<1x[32]xf32>
    return %res : vector<1x[32]xf32>
  }

[llvmbot]

@llvm/pr-subscribers-mlir
@llvm/pr-subscribers-mlir-vector

@llvm/pr-subscribers-mlir-core

Changes

This patch makes sure that the following case is lowered correctly ("duplication"): ``` func.func @broadcast_scalable_duplication(%arg0: vector<[32]xf32>) -> vector<1x[32]xf32> { %res = vector.broadcast %arg0 : vector<[32]xf32> to vector<1x[32]xf32> return %res : vector<1x[32]xf32> } ```

--
Full diff: https://github.com/llvm/llvm-project/pull/66344.diff

2 Files Affected:

• (modified) mlir/lib/Dialect/Vector/Transforms/LowerVectorBroadcast.cpp (+2-1)
• (modified) mlir/test/Dialect/Vector/vector-broadcast-lowering-transforms.mlir (+11)

diff --git a/mlir/lib/Dialect/Vector/Transforms/LowerVectorBroadcast.cpp b/mlir/lib/Dialect/Vector/Transforms/LowerVectorBroadcast.cpp
index 7c606e0c35f0899..2937b2d08b06979 100644
--- a/mlir/lib/Dialect/Vector/Transforms/LowerVectorBroadcast.cpp
+++ b/mlir/lib/Dialect/Vector/Transforms/LowerVectorBroadcast.cpp
@@ -85,7 +85,8 @@ class BroadcastOpLowering : public OpRewritePattern<vector::BroadcastOp> {
     if (srcRank < dstRank) {
       // Duplication.
       VectorType resType =
-          VectorType::get(dstType.getShape().drop_front(), eltType);
+          VectorType::get(dstType.getShape().drop_front(), eltType,
+                          dstType.getScalableDims().drop_front());
       Value bcst =
           rewriter.create<vector::BroadcastOp>(loc, resType, op.getSource());
       Value result = rewriter.create<arith::ConstantOp>(
diff --git a/mlir/test/Dialect/Vector/vector-broadcast-lowering-transforms.mlir b/mlir/test/Dialect/Vector/vector-broadcast-lowering-transforms.mlir
index 2d3c88d751192aa..386102cf5b4d225 100644
--- a/mlir/test/Dialect/Vector/vector-broadcast-lowering-transforms.mlir
+++ b/mlir/test/Dialect/Vector/vector-broadcast-lowering-transforms.mlir
@@ -162,6 +162,17 @@ func.func @broadcast_stretch_in_middle(%arg0: vector<4x1x2xf32>) -> vector<4x3x2
   return %0 : vector<4x3x2xf32>
 }
 
+// CHECK-LABEL:   func.func @broadcast_scalable_duplication
+// CHECK-SAME:      %[[ARG0:.*]]: vector<[32]xf32>)
+// CHECK:           %[[CST:.*]] = arith.constant dense<0.000000e+00> : vector<1x[32]xf32>
+// CHECK:           %[[RES:.*]] = vector.insert %[[ARG0]], %[[CST]] [0] : vector<[32]xf32> into vector<1x[32]xf32>
+// CHECK:           return %[[RES]] : vector<1x[32]xf32>
+
+func.func @broadcast_scalable_duplication(%arg0: vector<[32]xf32>) -> vector<1x[32]xf32> {
+  %res = vector.broadcast %arg0 : vector<[32]xf32> to vector<1x[32]xf32>
+  return %res : vector<1x[32]xf32>
+}
+
 transform.sequence failures(propagate) {
 ^bb1(%module_op: !transform.any_op):
   %f = transform.structured.match ops{["func.func"]} in %module_op 

[c-rhodes]

One small suggestion but otherwise LGTM, cheers