Support compiling MSL with position invariance if indicated in SPIRV shader.

Add SPIRVToMSLConversionResults::isPositionInvariant to query
position invariance from SPIR-V.
MVKDevice::getMTLCompileOptions() takes into consideration need to preserve invariance.
MVKShaderModule compile MSL to preserve invariance if required by shader.

Docs/Whats_New.md

@@ -21,6 +21,7 @@ Released TBD
 - Advertise support for `shaderInt64` feature.
 - Support fast math on MSL compiler via `MVKConfiguration::fastMathEnabled` configuration 
   setting and `MVK_CONFIG_FAST_MATH_ENABLED` environment variable (enabled by default).
+- Support compiling MSL with position invariance if indicated in SPIRV shader.
 - `vkGetMoltenVKConfigurationMVK()` and `vkSetMoltenVKConfigurationMVK()` functions
   can now be used with a `VkInstance` from another Vulkan layer, or with a `VK_NULL_HANDLE VkInstance`.
 - `MVKConfiguration` extended to cover all MoltenVK environment variables.

MoltenVK/MoltenVK/GPUObjects/MVKDevice.h

@@ -650,10 +650,12 @@ public:
 
 	/**
 	 * Returns an autoreleased options object to be used when compiling MSL shaders.
-	 * The useFastMath parameteris and-combined with MVKConfiguration::fastMathEnabled
+	 * The useFastMath parameter is and-combined with MVKConfiguration::fastMathEnabled
 	 * to determine whether to enable fast math optimizations in the compiled shader.
+	 * The preserveInvariance parameter indicates that the shader requires the position
+	 * output invariance across invocations (typically for the position output).
 	 */
-	MTLCompileOptions* getMTLCompileOptions(bool useFastMath = true);
+	MTLCompileOptions* getMTLCompileOptions(bool useFastMath = true, bool preserveInvariance = false);
 
 	/** Returns the Metal vertex buffer index to use for the specified vertex attribute binding number.  */
 	uint32_t getMetalBufferIndexForVertexAttributeBinding(uint32_t binding);

MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm

@@ -3639,10 +3639,13 @@ id<MTLSamplerState> MVKDevice::getDefaultMTLSamplerState() {
 	return _defaultMTLSamplerState;
 }
 
-MTLCompileOptions* MVKDevice::getMTLCompileOptions(bool useFastMath) {
+MTLCompileOptions* MVKDevice::getMTLCompileOptions(bool useFastMath, bool preserveInvariance) {
 	MTLCompileOptions* mtlCompOpt = [MTLCompileOptions new];
 	mtlCompOpt.languageVersion = _pMetalFeatures->mslVersionEnum;
 	mtlCompOpt.fastMathEnabled = useFastMath && mvkGetMVKConfiguration()->fastMathEnabled;
+	if ([mtlCompOpt respondsToSelector: @selector(setPreserveInvariance:)]) {
+		[mtlCompOpt setPreserveInvariance: preserveInvariance];
+	}
 	return [mtlCompOpt autorelease];
 }
 

MoltenVK/MoltenVK/GPUObjects/MVKPipeline.mm

@@ -2114,6 +2114,7 @@ namespace mvk {
 	void serialize(Archive & archive, SPIRVToMSLConversionResults& scr) {
 		archive(scr.entryPoint,
 				scr.isRasterizationDisabled,
+				scr.isPositionInvariant,
 				scr.needsSwizzleBuffer,
 				scr.needsOutputBuffer,
 				scr.needsPatchOutputBuffer,

MoltenVK/MoltenVK/GPUObjects/MVKShaderModule.h

@@ -254,7 +254,8 @@ public:
 	 * If the Metal library compiler does not return within MVKConfiguration::metalCompileTimeout
 	 * nanoseconds, an error will be generated and logged, and nil will be returned.
 	 */
-	id<MTLLibrary> newMTLLibrary(NSString* mslSourceCode, bool useFastMath);
+	id<MTLLibrary> newMTLLibrary(NSString* mslSourceCode,
+								 const SPIRVToMSLConversionResults& shaderConversionResults);
 
 
 #pragma mark Construction

MoltenVK/MoltenVK/GPUObjects/MVKShaderModule.mm

@@ -136,7 +136,7 @@ MVKShaderLibrary::MVKShaderLibrary(MVKVulkanAPIDeviceObject* owner,
 	MVKShaderLibraryCompiler* slc = new MVKShaderLibraryCompiler(_owner);
 
 	NSString* nsSrc = [[NSString alloc] initWithUTF8String: mslSourceCode.c_str()];					// temp retained
-	_mtlLibrary = slc->newMTLLibrary(nsSrc, shaderConversionResults.entryPoint.supportsFastMath);	// retained
+	_mtlLibrary = slc->newMTLLibrary(nsSrc, shaderConversionResults);	// retained
 	[nsSrc release];	// release temp string
 
 	slc->destroy();
@@ -415,12 +415,14 @@ MVKShaderModule::~MVKShaderModule() {
 #pragma mark -
 #pragma mark MVKShaderLibraryCompiler
 
-id<MTLLibrary> MVKShaderLibraryCompiler::newMTLLibrary(NSString* mslSourceCode, bool useFastMath) {
+id<MTLLibrary> MVKShaderLibraryCompiler::newMTLLibrary(NSString* mslSourceCode,
+													   const SPIRVToMSLConversionResults& shaderConversionResults) {
 	unique_lock<mutex> lock(_completionLock);
 
 	compile(lock, ^{
 		[_owner->getMTLDevice() newLibraryWithSource: mslSourceCode
-											 options: _owner->getDevice()->getMTLCompileOptions(useFastMath)
+											 options: _owner->getDevice()->getMTLCompileOptions(shaderConversionResults.entryPoint.supportsFastMath,
+																								shaderConversionResults.isPositionInvariant)
 								   completionHandler: ^(id<MTLLibrary> mtlLib, NSError* error) {
 									   bool isLate = compileComplete(mtlLib, error);
 									   if (isLate) { destroy(); }

MoltenVKShaderConverter/MoltenVKShaderConverter/SPIRVToMSLConverter.cpp

@@ -298,6 +298,7 @@ MVK_PUBLIC_SYMBOL bool SPIRVToMSLConverter::convert(SPIRVToMSLConversionConfigur
 	// and mark which vertex attributes and resource bindings are used by the shader
 	populateEntryPoint(pMSLCompiler, context.options);
 	_shaderConversionResults.isRasterizationDisabled = pMSLCompiler && pMSLCompiler->get_is_rasterization_disabled();
+	_shaderConversionResults.isPositionInvariant = pMSLCompiler && pMSLCompiler->is_position_invariant();
 	_shaderConversionResults.needsSwizzleBuffer = pMSLCompiler && pMSLCompiler->needs_swizzle_buffer();
 	_shaderConversionResults.needsOutputBuffer = pMSLCompiler && pMSLCompiler->needs_output_buffer();
 	_shaderConversionResults.needsPatchOutputBuffer = pMSLCompiler && pMSLCompiler->needs_patch_output_buffer();
@@ -306,8 +307,6 @@ MVK_PUBLIC_SYMBOL bool SPIRVToMSLConverter::convert(SPIRVToMSLConversionConfigur
 	_shaderConversionResults.needsDispatchBaseBuffer = pMSLCompiler && pMSLCompiler->needs_dispatch_base_buffer();
 	_shaderConversionResults.needsViewRangeBuffer = pMSLCompiler && pMSLCompiler->needs_view_mask_buffer();
 
-
-
 	for (auto& ctxSI : context.shaderInputs) {
 		ctxSI.isUsedByShader = pMSLCompiler->is_msl_shader_input_used(ctxSI.shaderInput.location);
 	}

MoltenVKShaderConverter/MoltenVKShaderConverter/SPIRVToMSLConverter.h

@@ -204,6 +204,7 @@ namespace mvk {
 	typedef struct SPIRVToMSLConversionResults {
 		SPIRVEntryPoint entryPoint;
 		bool isRasterizationDisabled = false;
+		bool isPositionInvariant = false;
 		bool needsSwizzleBuffer = false;
 		bool needsOutputBuffer = false;
 		bool needsPatchOutputBuffer = false;