Fix mismatched argument order in TFL->TOSA gather op.

TFL_GatherOp takes in params then indices while the Tosa_GatherOp accepts indices then params. This updates the compiler conversion to swap arguments and adds a test.

PiperOrigin-RevId: 357822827
Change-Id: I538c4ef83367ca7532eef49592019e29accbbc72

tensorflow/compiler/mlir/tosa/tests/tfl-to-tosa-pipeline.mlir

@@ -81,6 +81,13 @@ func @test_add(%arg0: tensor<13x21x1xf32>, %arg1: tensor<13x21x3xf32>) -> tensor
   return %0 : tensor<13x21x3xf32>
 }
 
+// CHECK-LABEL: test_gather
+// CHECK: tosa.gather
+func @test_gather(%arg0: tensor<100x25xf32>, %arg1: tensor<1x20xi32>) -> tensor<20x25x3xf32> {
+  %0 = "tfl.gather"(%arg0, %arg1) {axis = 0 : i32} : (tensor<100x25xf32>, tensor<1x20xi32>) -> tensor<20x25x3xf32>
+  return %0 : tensor<20x25x3xf32>
+}
+
 // -----
 
 // CHECK-LABEL: test_sub

tensorflow/compiler/mlir/tosa/transforms/tfl_legalize_patterns.td

@@ -49,6 +49,6 @@ def : Pat<(TFL_PowOp $l, $r), (Tosa_PowOp $l, $r)>;
 def : Pat<(TFL_GatherOp $params,
                         $indices,
                         $axis),
-          (Tosa_GatherOp $params,
+          (Tosa_GatherOp $indices,
-                           $indices,
+                           $params,
                            $axis)>;