[dawn] MacOS use relaxed math where possible
Fast math has potential downsides due to its treatment of inf/nan. We
can use relaxed math as a pragma in MacOSx 15+ versions.
Bug: 425650181
Change-Id: I30794e90928f8841879f528e2598aaf885af22b7
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/249035
Commit-Queue: Peter McNeeley <petermcneeley@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>
Reviewed-by: James Price <jrprice@google.com>
diff --git a/src/dawn/native/metal/ShaderModuleMTL.mm b/src/dawn/native/metal/ShaderModuleMTL.mm
index d5af501..1f9dc46 100644
--- a/src/dawn/native/metal/ShaderModuleMTL.mm
+++ b/src/dawn/native/metal/ShaderModuleMTL.mm
@@ -65,6 +65,7 @@
X(uint32_t, maxSubgroupSize) \
X(std::string, entryPointName) \
X(bool, usesSubgroupMatrix) \
+ X(bool, useStrictMath) \
X(bool, disableSymbolRenaming) \
X(tint::msl::writer::Options, tintOptions) \
X(UnsafeUnserializedValue<dawn::platform::Platform*>, platform)
@@ -221,7 +222,8 @@
ShaderModule::MetalFunctionData* out,
uint32_t sampleMask,
const RenderPipeline* renderPipeline,
- const BindingInfoArray& moduleBindingInfo) {
+ const BindingInfoArray& moduleBindingInfo,
+ bool useStrictMath) {
std::ostringstream errorStream;
errorStream << "Tint MSL failure:\n";
@@ -278,6 +280,7 @@
req.disableSymbolRenaming = device->IsToggleEnabled(Toggle::DisableSymbolRenaming);
req.usesSubgroupMatrix = programmableStage.metadata->usesSubgroupMatrix;
req.platform = UnsafeUnserializedValue(device->GetPlatform());
+ req.useStrictMath = useStrictMath;
req.tintOptions.strip_all_names = !req.disableSymbolRenaming;
req.tintOptions.remapped_entry_point_name = device->GetIsolatedEntryPointName();
@@ -374,17 +377,28 @@
r.adapterSupportedLimits.UnsafeGetValue()));
}
+ auto msl = std::move(result->msl);
+ // Metal supports math_mode as both compiler option and as a pragma. We add the
+ // math_mode here as a string conditional on OSx version as the compiler option only
+ // exists for MacOS after 15. See the Metal 4 spec for more information.
+ // Note: this math_mode takes precedence over global flags provide to the compiler
+ // (including the deprecated fastMathEnabled compiler option).
+ std::string math_mode_heading;
+ if (@available(macOS 15.0, iOS 18.0, *)) {
+ math_mode_heading = "\n#pragma METAL fp math_mode(";
+ math_mode_heading += r.useStrictMath ? "safe" : "relaxed";
+ math_mode_heading += +")\n";
+ }
// Metal uses Clang to compile the shader as C++14. Disable everything in the -Wall
// category. -Wunused-variable in particular comes up a lot in generated code, and
// some (old?) Metal drivers accidentally treat it as a MTLLibraryErrorCompileError
// instead of a warning.
- auto msl = std::move(result->msl);
msl = R"(
#ifdef __clang__
#pragma clang diagnostic ignored "-Wall"
#endif
)" +
- msl;
+ math_mode_heading + msl;
return MslCompilation{{
std::move(msl),
@@ -430,7 +444,8 @@
CacheResult<MslCompilation> mslCompilation;
DAWN_TRY_ASSIGN(mslCompilation,
TranslateToMSL(GetDevice(), programmableStage, stage, layout, out, sampleMask,
- renderPipeline, GetEntryPoint(entryPointName).bindings));
+ renderPipeline, GetEntryPoint(entryPointName).bindings,
+ GetStrictMath().value_or(false)));
out->needsStorageBufferLength = mslCompilation->needsStorageBufferLength;
out->workgroupAllocations = std::move(mslCompilation->workgroupAllocations);
@@ -446,7 +461,11 @@
(*compileOptions).preserveInvariance = true;
}
- (*compileOptions).fastMathEnabled = !GetStrictMath().value_or(false);
+ // If possible we will use relaxed math as a pragma in the source rather than this fast math
+ // global compiler option. See crbug.com/425650181
+ if (!@available(macOS 15.0, iOS 18.0, *)) {
+ (*compileOptions).fastMathEnabled = !GetStrictMath().value_or(false);
+ }
auto mtlDevice = ToBackend(GetDevice())->GetMTLDevice();
NSError* error = nullptr;
diff --git a/src/tint/lang/msl/validate/validate_metal.mm b/src/tint/lang/msl/validate/validate_metal.mm
index d548da8..b458509 100644
--- a/src/tint/lang/msl/validate/validate_metal.mm
+++ b/src/tint/lang/msl/validate/validate_metal.mm
@@ -33,7 +33,7 @@
namespace tint::msl::validate {
-Result ValidateUsingMetal(const std::string& src, MslVersion version) {
+Result ValidateUsingMetal(const std::string& src_original, MslVersion version) {
Result result;
NSError* error = nil;
@@ -45,10 +45,18 @@
return result;
}
- NSString* source = [NSString stringWithCString:src.c_str() encoding:NSUTF8StringEncoding];
-
+ std::string src_modified = src_original;
MTLCompileOptions* compileOptions = [MTLCompileOptions new];
- compileOptions.fastMathEnabled = true;
+ if (@available(macOS 15.0, iOS 18.0, *)) {
+ // Use relaxed math where possible.
+ // See crbug.com/425650181
+ std::string("\n#pragma METAL fp math_mode(relaxed)\n") + src_original;
+ } else {
+ compileOptions.fastMathEnabled = true;
+ }
+ NSString* source = [NSString stringWithCString:src_modified.c_str()
+ encoding:NSUTF8StringEncoding];
+
switch (version) {
case MslVersion::kMsl_2_3:
compileOptions.languageVersion = MTLLanguageVersion2_3;
