[mlir][vector] fold transpose(poison) -> poison (#135675)

Following on from #133988

---------

Signed-off-by: James Newling <[email protected]>

Author: newling

mlir/lib/Dialect/Vector/IR/VectorOps.cpp

@@ -6009,6 +6009,10 @@ OpFoldResult vector::TransposeOp::fold(FoldAdaptor adaptor) {
     if (attr.isSplat())
       return attr.reshape(getResultVectorType());
 
+  // Eliminate poison transpose ops.
+  if (llvm::dyn_cast_if_present<ub::PoisonAttr>(adaptor.getVector()))
+    return ub::PoisonAttr::get(getContext());
+
   // Eliminate identity transpose ops. This happens when the dimensions of the
   // input vector remain in their original order after the transpose operation.
   ArrayRef<int64_t> perm = getPermutation();

mlir/test/Dialect/Vector/canonicalize.mlir

@@ -2240,6 +2240,17 @@ func.func @transpose_splat2(%arg : f32) -> vector<3x4xf32> {
 
 // -----
 
+// CHECK-LABEL: transpose_poison
+//       CHECK:  %[[POISON:.*]] = ub.poison : vector<4x6xi8>
+//       CHECK:  return %[[POISON]] : vector<4x6xi8>
+func.func @transpose_poison() -> vector<4x6xi8> {
+  %poison = ub.poison : vector<6x4xi8>
+  %transpose = vector.transpose %poison, [1, 0] : vector<6x4xi8> to vector<4x6xi8>
+  return %transpose : vector<4x6xi8>
+}
+
+// -----
+
 // CHECK-LABEL: func.func @insert_1d_constant
 //   CHECK-DAG: %[[ACST:.*]] = arith.constant dense<[9, 1, 2]> : vector<3xi32>
 //   CHECK-DAG: %[[BCST:.*]] = arith.constant dense<[0, 9, 2]> : vector<3xi32>