[ExecuTorch][Vulkan] Tests for et_vk.fused_ce

Pull Request resolved: #20942

Vulkan op-test golden for `et_vk.fused_ce` (ATen transcription of the CPU-eager loss/dlogits reference). 3 cases: all-valid, a masked label (`label<0`), and vocab >> workers (strided per-row reduce). Wires `fused_ce_test` in `targets.bzl` + `CMakeLists.txt`.
ghstack-source-id: 405059109
@exported-using-ghexport

Differential Revision: [D111761774](https://our.internmc.facebook.com/intern/diff/D111761774/)

Author: JCNTH

backends/vulkan/test/op_tests/CMakeLists.txt

@@ -122,6 +122,9 @@ if(TARGET vulkan_backend AND LIB_TORCH)
   vulkan_op_test(
     linear_dW_test ${CMAKE_CURRENT_SOURCE_DIR}/linear_dW_test.cpp test_utils
   )
+  vulkan_op_test(
+    fused_ce_test ${CMAKE_CURRENT_SOURCE_DIR}/fused_ce_test.cpp test_utils
+  )
 
   # Only build generated op tests if a path to tags.yaml and
   # native_functions.yaml is provided. These files are required for codegen.

backends/vulkan/test/op_tests/fused_ce_test.cpp

@@ -0,0 +1,145 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <gtest/gtest.h>
+
+#include <ATen/ATen.h>
+
+#include <executorch/backends/vulkan/runtime/api/api.h>
+#include <executorch/backends/vulkan/runtime/graph/ComputeGraph.h>
+#include <executorch/backends/vulkan/runtime/graph/ops/OperatorRegistry.h>
+
+#include "test_utils.h"
+
+#include <iostream>
+#include <vector>
+
+//
+// Reference implementation: transcription of the CPU-eager fused_ce_impl
+// (backends/vulkan/custom_ops_lib.py), computed with ATen (library golden).
+//
+
+std::pair<at::Tensor, at::Tensor> fused_ce_reference(
+    const at::Tensor& logits,
+    const at::Tensor& labels,
+    double n_valid) {
+  at::Tensor mask = labels.ge(0);
+  at::Tensor safe = labels.clamp_min(0).to(at::kLong);
+  at::Tensor lse = at::logsumexp(logits, -1);
+  at::Tensor picked = logits.gather(-1, safe.unsqueeze(-1)).squeeze(-1);
+  at::Tensor loss =
+      at::where(mask, (lse - picked) / n_valid, at::zeros_like(lse)).sum();
+  at::Tensor softmax = at::softmax(logits, -1);
+  at::Tensor onehot = at::one_hot(safe, logits.size(-1)).to(logits.dtype());
+  at::Tensor dlogits = at::where(
+      mask.unsqueeze(-1),
+      (softmax - onehot) / n_valid,
+      at::zeros_like(softmax));
+  return {loss, dlogits};
+}
+
+void test_vulkan_fused_ce(
+    const int n_rows,
+    const int vocab,
+    const std::vector<int32_t>& labels_data,
+    const double n_valid) {
+  at::manual_seed(0);
+
+  at::Tensor logits =
+      at::rand({n_rows, vocab}, at::device(at::kCPU).dtype(at::kFloat)) * 4.0 -
+      2.0;
+  at::Tensor labels =
+      at::from_blob(
+          const_cast<int32_t*>(labels_data.data()), {n_rows}, at::kInt)
+          .clone();
+
+  auto ref = fused_ce_reference(logits, labels, n_valid);
+  at::Tensor ref_loss = ref.first;
+  at::Tensor ref_dlogits = ref.second;
+
+  using namespace vkcompute;
+
+  GraphConfig config;
+  ComputeGraph graph(config);
+
+  IOValueRef r_logits = graph.add_input_tensor(
+      logits.sizes().vec(), vkapi::kFloat, utils::kBuffer);
+  IOValueRef r_labels =
+      graph.add_input_tensor(labels.sizes().vec(), vkapi::kInt, utils::kBuffer);
+
+  const ValueRef r_n_valid = graph.add_scalar<double>(n_valid);
+
+  const ValueRef r_loss = graph.add_tensor({}, vkapi::kFloat, utils::kBuffer);
+  const ValueRef r_dlogits =
+      graph.add_tensor({n_rows, vocab}, vkapi::kFloat, utils::kBuffer);
+  const ValueRef r_out = graph.add_value_list({r_loss, r_dlogits});
+
+  VK_GET_OP_FN("et_vk.fused_ce.default")
+  (graph, {r_logits.value, r_labels.value, r_n_valid, r_out});
+
+  ValueRef staging_loss = graph.set_output_tensor(r_loss);
+  ValueRef staging_dlogits = graph.set_output_tensor(r_dlogits);
+
+  graph.prepare();
+  graph.prepack();
+  graph.propagate_resize();
+
+  graph.maybe_cast_and_copy_into_staging(
+      r_logits.staging, logits.const_data_ptr(), logits.numel(), vkapi::kFloat);
+  graph.maybe_cast_and_copy_into_staging(
+      r_labels.staging, labels.const_data_ptr(), labels.numel(), vkapi::kInt);
+
+  graph.execute();
+
+  at::Tensor vk_loss = at::zeros({}, at::device(at::kCPU).dtype(at::kFloat));
+  graph.maybe_cast_and_copy_from_staging(
+      staging_loss, vk_loss.mutable_data_ptr(), 1, vkapi::kFloat);
+
+  at::Tensor vk_dlogits =
+      at::zeros({n_rows, vocab}, at::device(at::kCPU).dtype(at::kFloat));
+  graph.maybe_cast_and_copy_from_staging(
+      staging_dlogits,
+      vk_dlogits.mutable_data_ptr(),
+      vk_dlogits.numel(),
+      vkapi::kFloat);
+
+  const double atol = 1e-4;
+  const double rtol = 1e-4;
+
+  const bool loss_ok = at::allclose(ref_loss, vk_loss, rtol, atol);
+  const bool dlogits_ok = at::allclose(ref_dlogits, vk_dlogits, rtol, atol);
+
+  if (!loss_ok || !dlogits_ok) {
+    std::cout << "fused_ce mismatch: n_rows=" << n_rows << " vocab=" << vocab
+              << " n_valid=" << n_valid << std::endl;
+    std::cout << "loss ref=" << ref_loss.item<float>()
+              << " vk=" << vk_loss.item<float>() << std::endl;
+    std::cout << "max dlogits diff="
+              << at::max(at::abs(ref_dlogits - vk_dlogits)).item<float>()
+              << std::endl;
+  }
+  ASSERT_TRUE(loss_ok);
+  ASSERT_TRUE(dlogits_ok);
+}
+
+TEST(VulkanFusedCeTest, all_valid_small) {
+  test_vulkan_fused_ce(
+      /*n_rows=*/4, /*vocab=*/8, /*labels=*/{0, 3, 7, 1}, /*n_valid=*/4.0);
+}
+
+TEST(VulkanFusedCeTest, masked_label) {
+  // One masked row (label < 0): contributes 0 to loss and 0 gradient.
+  test_vulkan_fused_ce(
+      /*n_rows=*/4, /*vocab=*/8, /*labels=*/{2, -1, 5, 0}, /*n_valid=*/3.0);
+}
+
+TEST(VulkanFusedCeTest, large_vocab_strided_reduce) {
+  // vocab >> NWORKERS exercises the strided per-row reduction.
+  test_vulkan_fused_ce(
+      /*n_rows=*/3, /*vocab=*/200, /*labels=*/{17, -1, 199}, /*n_valid=*/2.0);
+}

backends/vulkan/test/op_tests/targets.bzl

@@ -192,6 +192,12 @@ def define_common_targets(is_fbcode = False):
             ":test_utils",
         ]
     )
+    define_test_targets(
+        "fused_ce_test",
+        extra_deps = [
+            ":test_utils",
+        ]
+    )
     define_test_targets(
         "rms_norm_test",
         extra_deps = [