trace: improve error handling and error messages. (#9630)

This PR refactors the `trace` operation implementation by improving its
error message, and returning a status type value.

**Key Changes:**

- Make `tensor_methods::trace` return `StatusOr<XLATensorPtr>`
- Improve error messages and error handling
    - Renamed `CheckMMInputIsMatrix` to `CheckInputIsMatrix`
- Added a new parameter for specifying the operation name, so as to
build a better error message

Author: ysiraichi

test/test_ops_error_message.py

@@ -222,6 +222,19 @@ def test():
         expect="""roll(): expected `dims` [0] (size=1) to match the size of `shifts` [2, 2] (size=2)."""
     )
 
+  def test_trace_raises_error_on_non_matrix_input(self):
+    device = torch_xla.device()
+    a = torch.rand(2, 2, 2, device=device)
+
+    def test():
+      torch.trace(a)
+
+    self.assertExpectedRaisesInline(
+        exc_type=RuntimeError,
+        callable=test,
+        expect="""trace(): expected the input tensor f32[2,2,2] to be a matrix (i.e. a 2D tensor)."""
+    )
+
 
 if __name__ == "__main__":
   unittest.main()

torch_xla/csrc/aten_xla_type.cpp

@@ -3875,8 +3875,11 @@ std::tuple<at::Tensor, at::Tensor> XLANativeFunctions::topk(
 
 at::Tensor XLANativeFunctions::trace(const at::Tensor& self) {
   TORCH_LAZY_FN_COUNTER_TIMED_TRACING("xla::");
-  XLA_ASSIGN_OR_THROW(XLATensorPtr xla_self, bridge::GetXlaTensor(self));
-  return bridge::AtenFromXlaTensor(tensor_methods::trace(xla_self));
+  XLA_ASSIGN_OR_THROW(absl_nonnull XLATensorPtr xla_self,
+                      bridge::GetXlaTensor(self));
+  XLA_ASSIGN_OR_THROW(absl_nonnull XLATensorPtr output,
+                      tensor_methods::trace(xla_self));
+  return bridge::AtenFromXlaTensor(std::move(output));
 }
 
 at::Tensor XLANativeFunctions::transpose_copy(const at::Tensor& self,

torch_xla/csrc/tensor_methods.cpp

@@ -511,13 +511,16 @@ absl::Status CheckGatherSizesAreCompatible(const XLATensorPtr& input,
   return absl::OkStatus();
 }
 
-absl::Status CheckMMInputIsMatrix(const XLATensorPtr& mat,
-                                  const std::string_view arg) {
-  xla::Shape shape = mat->shape();
+absl::Status CheckInputIsMatrix(const XLATensorPtr& tensor,
+                                const std::string_view op,
+                                const std::string_view arg = "") {
+  xla::Shape shape = tensor->shape();
   if (shape.dimensions().size() != 2) {
-    return XLA_ERROR_WITH_LOCATION(absl::InvalidArgumentError(
-        absl::StrCat("mm(): expected the ", arg, " input tensor ",
-                     shape.ToString(), " to be a matrix (i.e. a 2D tensor).")));
+    const std::string arg_with_trailing_space =
+        arg.empty() ? std::string("") : absl::StrCat(arg, " ");
+    return XLA_ERROR_WITH_LOCATION(absl::InvalidArgumentError(absl::StrCat(
+        op, "(): expected the ", arg_with_trailing_space, "input tensor ",
+        shape.ToString(), " to be a matrix (i.e. a 2D tensor).")));
   }
   return absl::OkStatus();
 }
@@ -2452,8 +2455,8 @@ XLATensorPtr mish(const XLATensorPtr& input) {
 
 absl::StatusOr<XLATensorPtr> mm(const XLATensorPtr& input,
                                 const XLATensorPtr& weight) {
-  XLA_RETURN_IF_ERROR(CheckMMInputIsMatrix(input, "first"));
-  XLA_RETURN_IF_ERROR(CheckMMInputIsMatrix(weight, "second"));
+  XLA_RETURN_IF_ERROR(CheckInputIsMatrix(input, "mm", "first"));
+  XLA_RETURN_IF_ERROR(CheckInputIsMatrix(weight, "mm", "second"));
   XLA_RETURN_IF_ERROR(CheckMMMatrixSizesAreCompatible(input, weight));
   return input->CreateFrom(Dot(input->GetIrValue(), weight->GetIrValue()));
 }
@@ -3648,13 +3651,11 @@ std::tuple<XLATensorPtr, XLATensorPtr> topk(const XLATensorPtr& input,
   return std::make_tuple(t1, t2);
 }
 
-XLATensorPtr trace(const XLATensorPtr& input) {
-  auto input_shape_ref = input->shape();
-  XLA_CHECK_EQ((*input_shape_ref).dimensions_size(), 2)
-      << "invalid argument for trace: expected a matrix";
-  torch::lazy::NodePtr eye = Identity((*input_shape_ref).dimensions(0),
-                                      (*input_shape_ref).dimensions(1),
-                                      (*input_shape_ref).element_type());
+absl::StatusOr<absl_nonnull XLATensorPtr> trace(const XLATensorPtr& input) {
+  XLA_RETURN_IF_ERROR(CheckInputIsMatrix(input, "trace"));
+  xla::Shape shape = input->shape();
+  torch::lazy::NodePtr eye =
+      Identity(shape.dimensions(0), shape.dimensions(1), shape.element_type());
   return sum(input->CreateFrom(eye * input->GetIrValue()), {0, 1}, false,
              input->dtype());
 }

torch_xla/csrc/tensor_methods.h

@@ -973,7 +973,7 @@ std::tuple<XLATensorPtr, XLATensorPtr> topk(const XLATensorPtr& input,
                                             bool stable);
 
 // Returns the sum of the elements of the diagonal of the input 2-D matrix.
-XLATensorPtr trace(const XLATensorPtr& input);
+absl::StatusOr<absl_nonnull XLATensorPtr> trace(const XLATensorPtr& input);
 
 // Swap given dimensions of the input.
 XLATensorPtr transpose(const XLATensorPtr& input, int64_t dim0, int64_t dim1);