Guard macOS or iOS specific code in #if guards

This is necessary because @available(macOS 10.N, *) is taken on all iOS
versions but there is no way to say the branch is just not taken on any
iOS version. The proper way to deal with this is to add additional #if
guards to just not compile the code on iOS / macOS.

BUG=dawn:225

Change-Id: I76ec01f933364e9b47b5dda1198359f2ab4d1188
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/11900
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>

src/dawn_native/metal/BackendMTL.mm

@@ -28,7 +28,6 @@ namespace dawn_native { namespace metal {
 
     namespace {
 
-#if defined(DAWN_PLATFORM_MACOS)
         struct PCIIDs {
             uint32_t vendorId;
             uint32_t deviceId;
@@ -39,6 +38,7 @@ namespace dawn_native { namespace metal {
             uint32_t vendorId;
         };
 
+#if defined(DAWN_PLATFORM_MACOS)
         const Vendor kVendors[] = {{"AMD", kVendorID_AMD},
                                    {"Radeon", kVendorID_AMD},
                                    {"Intel", kVendorID_Intel},
@@ -158,7 +158,8 @@ namespace dawn_native { namespace metal {
 #elif defined(DAWN_PLATFORM_IOS)
         MaybeError GetDevicePCIInfo(id<MTLDevice> device, PCIIDs* ids) {
             DAWN_UNUSED(device);
-            *ids = PCIIDs(0, 0);
+            *ids = PCIIDs{0, 0};
+            return {};
         }
 
         bool IsMetalSupported() {
@@ -183,11 +184,17 @@ namespace dawn_native { namespace metal {
                 mPCIInfo.deviceId = ids.deviceId;
             };
 
+#if defined(DAWN_PLATFORM_IOS)
+            mDeviceType = DeviceType::IntegratedGPU;
+#elif defined(DAWN_PLATFORM_MACOS)
             if ([device isLowPower]) {
                 mDeviceType = DeviceType::IntegratedGPU;
             } else {
                 mDeviceType = DeviceType::DiscreteGPU;
             }
+#else
+#    error "Unsupported Apple platform."
+#endif
 
             InitializeSupportedExtensions();
         }
@@ -201,9 +208,11 @@ namespace dawn_native { namespace metal {
             return {new Device(this, mDevice, descriptor)};
         }
         void InitializeSupportedExtensions() {
+#if defined(DAWN_PLATFORM_MACOS)
             if ([mDevice supportsFeatureSet:MTLFeatureSet_macOS_GPUFamily1_v1]) {
                 mSupportedExtensions.EnableExtension(Extension::TextureCompressionBC);
             }
+#endif
         }
 
         id<MTLDevice> mDevice = nil;
@@ -221,6 +230,7 @@ namespace dawn_native { namespace metal {
         std::vector<std::unique_ptr<AdapterBase>> adapters;
 
         if (@available(macOS 10.11, *)) {
+#if defined(DAWN_PLATFORM_MACOS)
             NSArray<id<MTLDevice>>* devices = MTLCopyAllDevices();
 
             for (id<MTLDevice> device in devices) {
@@ -228,10 +238,13 @@ namespace dawn_native { namespace metal {
             }
 
             [devices release];
+#endif
         } else if (@available(iOS 8.0, *)) {
+#if defined(DAWN_PLATFORM_IOS)
             // iOS only has a single device so MTLCopyAllDevices doesn't exist there.
             adapters.push_back(
                 std::make_unique<Adapter>(GetInstance(), MTLCreateSystemDefaultDevice()));
+#endif
         } else {
             UNREACHABLE();
         }

src/dawn_native/metal/DeviceMTL.mm

@@ -76,11 +76,13 @@ namespace dawn_native { namespace metal {
     }
 
     void Device::InitTogglesFromDriver() {
+#if defined(DAWN_PLATFORM_MACOS)
         if (@available(macOS 10.12, *)) {
             bool emulateStoreAndMSAAResolve =
                 ![mMtlDevice supportsFeatureSet:MTLFeatureSet_macOS_GPUFamily1_v2];
             SetToggle(Toggle::EmulateStoreAndMSAAResolve, emulateStoreAndMSAAResolve);
         }
+#endif
 
         // TODO(jiawei.shao@intel.com): check iOS feature sets
 

src/dawn_native/metal/TextureMTL.mm

@@ -214,6 +214,7 @@ namespace dawn_native { namespace metal {
             case dawn::TextureFormat::Depth24PlusStencil8:
                 return MTLPixelFormatDepth32Float_Stencil8;
 
+#if defined(DAWN_PLATFORM_MACOS)
             case dawn::TextureFormat::BC1RGBAUnorm:
                 return MTLPixelFormatBC1_RGBA;
             case dawn::TextureFormat::BC1RGBAUnormSrgb:
@@ -242,6 +243,7 @@ namespace dawn_native { namespace metal {
                 return MTLPixelFormatBC7_RGBAUnorm;
             case dawn::TextureFormat::BC7RGBAUnormSrgb:
                 return MTLPixelFormatBC7_RGBAUnorm_sRGB;
+#endif
 
             default:
                 UNREACHABLE();