[mlir][linalg] Add a test for linalg.matmul --> vector.outerproduct

Representing matmuls as a sum of outer products is central to various
matrix extensions (e.g. Arm's SME). This test demonstrates how to use
Linalg's vectoriser and Vector's lowerings to represent `linalg.matmul`
as a chain of `vector.outerproduct` Ops.

Differential Revision: https://reviews.llvm.org/D150457

Author: banach-space

mlir/test/Dialect/Linalg/transform-op-matmul-to-outerproduct.mlir

@@ -0,0 +1,36 @@
+// RUN: mlir-opt %s -test-transform-dialect-interpreter -split-input-file | FileCheck %s
+
+func.func @outerproduct_matmul(%A: memref<3x3xf32>, %B: memref<3x3xf32>, %C: memref<3x3xf32>) {
+  linalg.matmul ins(%A, %B: memref<3x3xf32>, memref<3x3xf32>)
+            outs(%C: memref<3x3xf32>)
+  return
+}
+
+// CHECK-LABEL:   func.func @outerproduct_matmul(
+// CHECK-SAME:      %[[VAL_0:.*]]: memref<3x3xf32>, %[[VAL_1:.*]]: memref<3x3xf32>, %[[VAL_2:.*]]: memref<3x3xf32>) {
+// CHECK:           %[[VAL_3:.*]] = arith.constant 0 : index
+// CHECK:           %[[VAL_4:.*]] = arith.constant 0.000000e+00 : f32
+// CHECK:           %[[VAL_5:.*]] = vector.transfer_read %[[VAL_0]]{{\[}}%[[VAL_3]], %[[VAL_3]]], %[[VAL_4]] {in_bounds = [true, true]} : memref<3x3xf32>, vector<3x3xf32>
+// CHECK:           %[[VAL_6:.*]] = vector.transfer_read %[[VAL_1]]{{\[}}%[[VAL_3]], %[[VAL_3]]], %[[VAL_4]] {in_bounds = [true, true]} : memref<3x3xf32>, vector<3x3xf32>
+// CHECK:           %[[VAL_7:.*]] = vector.transfer_read %[[VAL_2]]{{\[}}%[[VAL_3]], %[[VAL_3]]], %[[VAL_4]] {in_bounds = [true, true]} : memref<3x3xf32>, vector<3x3xf32>
+// CHECK:           %[[VAL_8:.*]] = vector.transpose %[[VAL_5]], [1, 0] : vector<3x3xf32> to vector<3x3xf32>
+// CHECK:           %[[VAL_9:.*]] = vector.extract %[[VAL_8]][0] : vector<3x3xf32>
+// CHECK:           %[[VAL_10:.*]] = vector.extract %[[VAL_6]][0] : vector<3x3xf32>
+// CHECK:           %[[VAL_11:.*]] = vector.outerproduct %[[VAL_9]], %[[VAL_10]], %[[VAL_7]] {kind = #vector.kind<add>} : vector<3xf32>, vector<3xf32>
+// CHECK:           %[[VAL_12:.*]] = vector.extract %[[VAL_8]][1] : vector<3x3xf32>
+// CHECK:           %[[VAL_13:.*]] = vector.extract %[[VAL_6]][1] : vector<3x3xf32>
+// CHECK:           %[[VAL_14:.*]] = vector.outerproduct %[[VAL_12]], %[[VAL_13]], %[[VAL_11]] {kind = #vector.kind<add>} : vector<3xf32>, vector<3xf32>
+// CHECK:           %[[VAL_15:.*]] = vector.extract %[[VAL_8]][2] : vector<3x3xf32>
+// CHECK:           %[[VAL_16:.*]] = vector.extract %[[VAL_6]][2] : vector<3x3xf32>
+// CHECK:           %[[VAL_17:.*]] = vector.outerproduct %[[VAL_15]], %[[VAL_16]], %[[VAL_14]] {kind = #vector.kind<add>} : vector<3xf32>, vector<3xf32>
+// CHECK:           vector.transfer_write %[[VAL_17]], %[[VAL_2]]{{\[}}%[[VAL_3]], %[[VAL_3]]] {in_bounds = [true, true]} : vector<3x3xf32>, memref<3x3xf32>
+// CHECK:           return
+// CHECK:         }
+
+transform.sequence failures(propagate) {
+^bb1(%arg1: !pdl.operation):
+  %0 = transform.structured.match ops{["linalg.matmul"]} in %arg1 : (!pdl.operation) -> !pdl.operation
+  %1 = get_closest_isolated_parent %0 : (!pdl.operation) -> !pdl.operation
+  %2 = transform.structured.vectorize %1
+  transform.vector.lower_contraction %2 lowering_strategy = "outerproduct" : (!pdl.operation) -> !pdl.operation
+}