webnn: Switch to runtime flag to disable Core ML backend

This enables testing the TFLite backend on macOS without rebuilding
Chrome.

Bug: 394119734
Change-Id: I31a0715a46c27a13f1046f618c69b72d9f4d98fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6240633
Auto-Submit: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Will Harris <wfh@chromium.org>
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1417095}

chrome/browser/about_flags.cc

@@ -8329,6 +8329,12 @@ const FeatureEntry kFeatureEntries[] = {
      FEATURE_VALUE_TYPE(
          webnn::mojom::features::kExperimentalWebMachineLearningNeuralNetwork)},
 
+#if BUILDFLAG(IS_MAC)
+    {"webnn-coreml", flag_descriptions::kWebNNCoreMLName,
+     flag_descriptions::kWebNNCoreMLDescription, kOsMac,
+     FEATURE_VALUE_TYPE(webnn::mojom::features::kWebNNCoreML)},
+#endif  // BUILDFLAG(IS_MAC)
+
 #if BUILDFLAG(IS_WIN)
     {"webnn-directml", flag_descriptions::kWebNNDirectMLName,
      flag_descriptions::kWebNNDirectMLDescription, kOsWin,

chrome/browser/flag-metadata.json

@@ -9281,6 +9281,11 @@
     "owners": [ "mhochk@microsoft.com", "ericwilligers@google.com", "hatalat@microsoft.com" ],
     "expiry_milestone": 135
   },
+  {
+    "name": "webnn-coreml",
+    "owners": [ "reillyg@chromium.org", "phillis@chromium.org" ],
+    "expiry_milestone": 146
+  },
   {
     "name": "webnn-directml",
     "owners": [ "reillyg@chromium.org", "rafael.cintron@microsoft.com" ],

chrome/browser/flag_descriptions.cc

@@ -2459,6 +2459,12 @@ const char kExperimentalWebMachineLearningNeuralNetworkDescription[] =
     "Enables additional, experimental features in Web Machine Learning Neural "
     "Network (WebNN) API. Requires the \"WebNN API\" flag to be enabled.";
 
+const char kWebNNCoreMLName[] = "Core ML backend for WebNN";
+const char kWebNNCoreMLDescription[] =
+    "Enables using Core ML for GPU and "
+    "NPU inference with the WebNN API. Disabling this flag enables a "
+    "fallback to TFLite.";
+
 const char kWebNNDirectMLName[] = "DirectML backend for WebNN";
 const char kWebNNDirectMLDescription[] =
     "Enables using DirectML for GPU and "

chrome/browser/flag_descriptions.h

@@ -1417,6 +1417,9 @@ extern const char kWebMachineLearningNeuralNetworkDescription[];
 extern const char kExperimentalWebMachineLearningNeuralNetworkName[];
 extern const char kExperimentalWebMachineLearningNeuralNetworkDescription[];
 
+extern const char kWebNNCoreMLName[];
+extern const char kWebNNCoreMLDescription[];
+
 extern const char kWebNNDirectMLName[];
 extern const char kWebNNDirectMLDescription[];
 

services/webnn/BUILD.gn

@@ -12,7 +12,6 @@ import("//third_party/tflite/features.gni")
 buildflag_header("buildflags") {
   header = "buildflags.h"
   flags = [
-    "WEBNN_USE_COREML=$webnn_use_coreml",
     "WEBNN_USE_TFLITE=$webnn_use_tflite",
     "WEBNN_ENABLE_TFLITE_PROFILER=$webnn_enable_tflite_profiler",
   ]
@@ -91,8 +90,7 @@ component("webnn_service") {
     libs = [ "dxgi.lib" ]
   }
 
-  if (webnn_use_coreml) {
-    assert(is_mac)
+  if (is_mac) {
     sources += [
       "coreml/buffer_content_coreml.h",
       "coreml/buffer_content_coreml.mm",
@@ -147,15 +145,13 @@ component("webnn_service") {
     }
 
     if (enable_ml_internal) {
-      deps += [
-        "//services/on_device_model/ml",
-      ]
+      deps += [ "//services/on_device_model/ml" ]
 
       defines += [ "ENABLE_ML_INTERNAL" ]
     }
   }
 
-  if (webnn_use_coreml || webnn_use_tflite) {
+  if (is_mac || webnn_use_tflite) {
     sources += [
       "queueable_resource_state.h",
       "queueable_resource_state_base.cc",
@@ -191,7 +187,7 @@ source_set("tests") {
     ]
   }
 
-  if (webnn_use_coreml || webnn_use_tflite || is_win) {
+  if (webnn_use_tflite || is_mac || is_win) {
     sources += [
       "webnn_graph_impl_backend_test.cc",
       "webnn_tensor_impl_backend_test.cc",

services/webnn/features.gni

@@ -5,11 +5,8 @@
 import("//build/config/features.gni")
 
 declare_args() {
-  # Enable the Core ML backend by default on macOS. This flag allows it to be
-  # disabled for testing.
-  webnn_use_coreml = is_mac
-
-  webnn_use_tflite = is_android || is_chromeos || is_linux || is_win
+  # TFLite is used as a fallback option on macOS and Windows.
+  webnn_use_tflite = is_android || is_chromeos || is_linux || is_mac || is_win
 
   # Enable logging of TFLite profiling information on MLGraph destruction.
   webnn_enable_tflite_profiler = false

services/webnn/public/mojom/features.mojom

@@ -17,7 +17,15 @@ feature kExperimentalWebMachineLearningNeuralNetwork {
   const bool default_state = false;
 };
 
+// Enables the Core ML backend for WebNN.
+[EnableIf=is_mac]
+feature kWebNNCoreML {
+  const string name = "WebNNCoreML";
+  const bool default_state = true;
+};
+
 // Enables the DirectML backend for WebNN.
+[EnableIf=is_win]
 feature kWebNNDirectML {
   const string name = "WebNNDirectML";
   const bool default_state = true;

services/webnn/webnn_context_provider_impl.cc

@@ -30,7 +30,7 @@
 #include "services/webnn/dml/utils.h"
 #endif
 
-#if BUILDFLAG(WEBNN_USE_COREML)
+#if BUILDFLAG(IS_MAC)
 #include "services/webnn/coreml/context_impl_coreml.h"
 #endif
 
@@ -288,14 +288,14 @@ void WebNNContextProviderImpl::CreateWebNNContext(
   }
 #endif  // BUILDFLAG(IS_WIN)
 
-#if BUILDFLAG(WEBNN_USE_COREML)
-  // TODO: crbug.com/325612086 - Consider using supporting older Macs either
-  // with TFLite or a more restrictive implementation on CoreML.
+#if BUILDFLAG(IS_MAC)
   if (__builtin_available(macOS 14, *)) {
-    context_impl = new coreml::ContextImplCoreml(std::move(receiver), this,
-                                                 std::move(options));
+    if (base::FeatureList::IsEnabled(mojom::features::kWebNNCoreML)) {
+      context_impl = new coreml::ContextImplCoreml(std::move(receiver), this,
+                                                   std::move(options));
+    }
   }
-#endif  // BUILDFLAG(WEBNN_USE_COREML)
+#endif  // BUILDFLAG(IS_MAC)
 
 #if BUILDFLAG(WEBNN_USE_TFLITE)
   if (!context_impl) {

services/webnn/webnn_graph_impl_backend_test.cc

@@ -264,14 +264,14 @@ struct OperandInfo {
   OperandDataType type;
   std::vector<uint32_t> dimensions;
   std::vector<T> values;
-#if BUILDFLAG(WEBNN_USE_COREML)
+#if BUILDFLAG(IS_MAC)
   OperandInfo<int32_t> ToInt32() {
     return OperandInfo<int32_t>{
         .type = OperandDataType::kInt32,
         .dimensions = dimensions,
         .values = std::vector<int32_t>(values.begin(), values.end())};
   }
-#endif  // BUILDFLAG(WEBNN_USE_COREML)
+#endif  // BUILDFLAG(IS_MAC)
 };
 
 void VerifyIsEqual(base::span<const float> actual,
@@ -376,7 +376,7 @@ void WebNNGraphImplBackendTest::SetUp() {
 }
 #endif  // #if BUILDFLAG(IS_WIN)
 
-#if BUILDFLAG(WEBNN_USE_COREML)
+#if BUILDFLAG(IS_MAC)
 class WebNNGraphImplBackendTest : public testing::Test {
  public:
   WebNNGraphImplBackendTest()
@@ -420,11 +420,10 @@ void WebNNGraphImplBackendTest::SetUp() {
 
   SetUpBase();
 }
-#endif  // BUILDFLAG(WEBNN_USE_COREML)
+#endif  // BUILDFLAG(IS_MAC)
 
 // TODO(crbug.com/325612086): Parameterize these tests for different backends.
-#if BUILDFLAG(WEBNN_USE_TFLITE) && !BUILDFLAG(WEBNN_USE_COREML) && \
-    !BUILDFLAG(IS_WIN)
+#if BUILDFLAG(WEBNN_USE_TFLITE) && !BUILDFLAG(IS_MAC) && !BUILDFLAG(IS_WIN)
 class WebNNGraphImplBackendTest : public testing::Test {
  public:
   WebNNGraphImplBackendTest()
@@ -1055,32 +1054,32 @@ struct ElementWiseBinaryTester {
     uint64_t rhs_operand_id =
         builder.BuildInput("rhs", rhs.dimensions, rhs.type);
     auto graph_output_type = output.type;
-#if BUILDFLAG(WEBNN_USE_COREML)
+#if BUILDFLAG(IS_MAC)
     if (output.type == OperandDataType::kUint8) {
       // macOS only supports FP16,FP32,DOUBLE,INT32 as outputs of graph.
       // For testing, we cast the output of the element-wise logical
       // operators to Int32 and set the graph output to Int32.
       graph_output_type = OperandDataType::kInt32;
     }
-#endif  // BUILDFLAG(WEBNN_USE_COREML)
+#endif  // BUILDFLAG(IS_MAC)
     uint64_t output_operand_id =
         builder.BuildOutput("output", output.dimensions, graph_output_type);
     uint64_t element_wise_binary_output_operand_id = output_operand_id;
-#if BUILDFLAG(WEBNN_USE_COREML)
+#if BUILDFLAG(IS_MAC)
     if (output.type == OperandDataType::kUint8) {
       element_wise_binary_output_operand_id = builder.BuildIntermediateOperand(
           output.dimensions, OperandDataType::kUint8);
     }
-#endif  // BUILDFLAG(WEBNN_USE_COREML)
+#endif  // BUILDFLAG(IS_MAC)
     builder.BuildElementWiseBinary(kind, lhs_operand_id, rhs_operand_id,
                                    element_wise_binary_output_operand_id);
-#if BUILDFLAG(WEBNN_USE_COREML)
+#if BUILDFLAG(IS_MAC)
     if (output.type == OperandDataType::kUint8) {
       builder.BuildElementWiseUnary(mojom::ElementWiseUnary::Kind::kCast,
                                     element_wise_binary_output_operand_id,
                                     output_operand_id);
     }
-#endif  // BUILDFLAG(WEBNN_USE_COREML)
+#endif  // BUILDFLAG(IS_MAC)
 
     base::flat_map<std::string, base::span<const I>> named_inputs;
     named_inputs.insert({"lhs", lhs.values});
@@ -1089,12 +1088,12 @@ struct ElementWiseBinaryTester {
         BuildAndCompute<O>(std::move(remote), builder.TakeGraphInfo(),
                            std::move(named_inputs));
 
-#if BUILDFLAG(WEBNN_USE_COREML)
+#if BUILDFLAG(IS_MAC)
     if (output.type == OperandDataType::kUint8) {
       VerifyIsEqual(named_outputs["output"], output.ToInt32());
       return;
     }
-#endif  // BUILDFLAG(WEBNN_USE_COREML)
+#endif  // BUILDFLAG(IS_MAC)
 
     VerifyIsEqual(named_outputs["output"], output);
   }

tools/metrics/histograms/enums.xml

@@ -10790,6 +10790,7 @@ from previous Chrome versions.
   <int value="-1321640296"
       label="AutofillDownstreamCvcPromptUseGooglePayLogo:enabled"/>
   <int value="-1321212159" label="MediaAppAnnotation:enabled"/>
+  <int value="-1320724945" label="WebNNCoreML:disabled"/>
   <int value="-1319688939" label="ignore-gpu-blacklist"/>
   <int value="-1318914924" label="OverflowIconsForMediaControls:enabled"/>
   <int value="-1317782739" label="OmniboxAsyncViewInflation:enabled"/>
@@ -19062,6 +19063,7 @@ from previous Chrome versions.
   <int value="1927259098" label="TranslateLanguageByULP:enabled"/>
   <int value="1927374573" label="EnterpriseRealtimeExtensionRequest:enabled"/>
   <int value="1927572319" label="OmniboxShortcutExpanding:enabled"/>
+  <int value="1928193837" label="WebNNCoreML:enabled"/>
   <int value="1928641476" label="enable-builtin-hls:disabled"/>
   <int value="1928944156" label="ReadLaterNewBadgePromo:disabled"/>
   <int value="1929174284" label="ChromeManagementPageAndroid:disabled"/>