CompilerMSL elide unused builtins from entry function input and output structs.

Add Compiler::has_active_builtin() function.
Update test reference shaders that included unused builtins.

reference/shaders-msl/flatten/basic.flatten.vert

@@ -18,7 +18,6 @@ struct main0_out
 {
     float3 vNormal [[user(locn0)]];
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant UBO& _16 [[buffer(0)]])

reference/shaders-msl/flatten/multiindex.flatten.vert

@@ -16,7 +16,6 @@ struct main0_in
 struct main0_out
 {
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant UBO& _20 [[buffer(0)]])

reference/shaders-msl/flatten/push-constant.flatten.vert

@@ -20,7 +20,6 @@ struct main0_out
 {
     float2 vRot [[user(locn0)]];
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant PushMe& registers [[buffer(0)]])

reference/shaders-msl/flatten/struct.flatten.vert

@@ -26,7 +26,6 @@ struct main0_out
 {
     float4 vColor [[user(locn0)]];
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant UBO& _18 [[buffer(0)]])

reference/shaders-msl/flatten/swizzle.flatten.vert

@@ -30,7 +30,6 @@ struct main0_out
     float4 oB [[user(locn4)]];
     float4 oA [[user(locn5)]];
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(constant UBO& _22 [[buffer(0)]])

reference/shaders-msl/legacy/vert/transpose.legacy.vert

@@ -18,7 +18,6 @@ struct main0_in
 struct main0_out
 {
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant Buffer& _13 [[buffer(0)]])

reference/shaders-msl/vert/basic.vert

@@ -18,7 +18,6 @@ struct main0_out
 {
     float3 vNormal [[user(locn0)]];
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant UBO& _16 [[buffer(0)]])

reference/shaders-msl/vert/copy.flatten.vert

@@ -26,7 +26,6 @@ struct main0_out
 {
     float4 vColor [[user(locn0)]];
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant UBO& _21 [[buffer(0)]])

reference/shaders-msl/vert/dynamic.flatten.vert

@@ -26,7 +26,6 @@ struct main0_out
 {
     float4 vColor [[user(locn0)]];
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant UBO& _21 [[buffer(0)]])

reference/shaders-msl/vert/functions.vert

@@ -27,7 +27,6 @@ struct main0_out
     int2 vMSB [[user(locn3)]];
     int2 vLSB [[user(locn4)]];
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 // Implementation of the GLSL radians() function

reference/shaders-msl/vert/out_block.vert

@@ -18,8 +18,6 @@ struct main0_out
 {
     float4 VertexOut_color [[user(locn0)]];
     float4 gl_Position [[position]];
-    float gl_PointSize;
-    float gl_ClipDistance [[clip_distance]] [1];
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant Transform& block [[buffer(0)]])

reference/shaders-msl/vert/pointsize.vert

@@ -20,7 +20,6 @@ struct main0_out
     float4 color [[user(locn0)]];
     float4 gl_Position [[position]];
     float gl_PointSize [[point_size]];
-    float gl_ClipDistance [[clip_distance]] [1];
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant params& _19 [[buffer(0)]])

reference/shaders-msl/vert/texture_buffer.vert

@@ -6,7 +6,6 @@ using namespace metal;
 struct main0_out
 {
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(texture2d<float> uSamp [[texture(0)]], texture2d<float> uSampo [[texture(1)]])

reference/shaders-msl/vert/ubo.alignment.vert

@@ -24,7 +24,6 @@ struct main0_out
     float3 vNormal [[user(locn1)]];
     float3 vColor [[user(locn2)]];
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant UBO& _18 [[buffer(0)]])

reference/shaders-msl/vert/ubo.vert

@@ -18,7 +18,6 @@ struct main0_out
 {
     float3 vNormal [[user(locn0)]];
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(main0_in in [[stage_in]], constant UBO& _16 [[buffer(0)]])

reference/shaders-msl/vulkan/vert/vulkan-vertex.vk.vert

@@ -6,7 +6,6 @@ using namespace metal;
 struct main0_out
 {
     float4 gl_Position [[position]];
-    float gl_PointSize;
 };
 
 vertex main0_out main0(uint gl_VertexIndex [[vertex_id]], uint gl_InstanceIndex [[instance_id]])

spirv_cross.cpp

@@ -3409,6 +3409,25 @@ void Compiler::update_active_builtins()
 	traverse_all_reachable_opcodes(get<SPIRFunction>(entry_point), handler);
 }
 
+// Returns whether this shader uses a builtin of the storage class
+bool Compiler::has_active_builtin(BuiltIn builtin, StorageClass storage)
+{
+	uint64_t flags;
+	switch (storage)
+	{
+	case StorageClassInput:
+		flags = active_input_builtins;
+		break;
+	case StorageClassOutput:
+		flags = active_output_builtins;
+		break;
+
+	default:
+		return false;
+	}
+	return flags & (1ull << builtin);
+}
+
 void Compiler::analyze_sampler_comparison_states()
 {
 	CombinedImageSamplerUsageHandler handler(*this);

spirv_cross.hpp

@@ -640,6 +640,7 @@ protected:
 	uint64_t active_output_builtins = 0;
 	// Traverses all reachable opcodes and sets active_builtins to a bitmask of all builtin variables which are accessed in the shader.
 	void update_active_builtins();
+	bool has_active_builtin(spv::BuiltIn builtin, spv::StorageClass storage);
 
 	void analyze_parameter_preservation(
 	    SPIRFunction &entry, const CFG &cfg,

spirv_msl.cpp

@@ -406,12 +406,14 @@ uint32_t CompilerMSL::add_interface_block(StorageClass storage)
 			uint32_t mbr_idx = 0;
 			for (auto &mbr_type_id : type.member_types)
 			{
+				BuiltIn builtin;
+				bool is_builtin = is_member_builtin(type, mbr_idx, &builtin);
+
 				auto &mbr_type = get<SPIRType>(mbr_type_id);
 				if (is_matrix(mbr_type))
-				{
 					exclude_member_from_stage_in(type, mbr_idx);
-				}
-				else
+
+				else if (!is_builtin || has_active_builtin(builtin, storage))
 				{
 					// Add a reference to the member to the interface struct.
 					uint32_t ib_mbr_idx = uint32_t(ib_type.member_types.size());
@@ -434,8 +436,7 @@ uint32_t CompilerMSL::add_interface_block(StorageClass storage)
 					}
 
 					// Mark the member as builtin if needed
-					BuiltIn builtin;
-					if (is_member_builtin(type, mbr_idx, &builtin))
+					if (is_builtin)
 					{
 						set_member_decoration(ib_type_id, ib_mbr_idx, DecorationBuiltIn, builtin);
 						if (builtin == BuiltInPosition)
@@ -451,11 +452,13 @@ uint32_t CompilerMSL::add_interface_block(StorageClass storage)
 		         type.basetype == SPIRType::Float || type.basetype == SPIRType::Double ||
 		         type.basetype == SPIRType::Boolean)
 		{
+			bool is_builtin = is_builtin_variable(*p_var);
+			BuiltIn builtin = BuiltIn(get_decoration(p_var->self, DecorationBuiltIn));
+
 			if (is_matrix(type))
-			{
 				exclude_from_stage_in(*p_var);
-			}
-			else
+
+			else if (!is_builtin || has_active_builtin(builtin, storage))
 			{
 				// Add a reference to the variable type to the interface struct.
 				uint32_t ib_mbr_idx = uint32_t(ib_type.member_types.size());
@@ -478,9 +481,8 @@ uint32_t CompilerMSL::add_interface_block(StorageClass storage)
 				}
 
 				// Mark the member as builtin if needed
-				if (is_builtin_variable(*p_var))
+				if (is_builtin)
 				{
-					uint32_t builtin = get_decoration(p_var->self, DecorationBuiltIn);
 					set_member_decoration(ib_type_id, ib_mbr_idx, DecorationBuiltIn, builtin);
 					if (builtin == BuiltInPosition)
 						qual_pos_var_name = qual_var_name;
@@ -1959,14 +1961,12 @@ string CompilerMSL::member_attribute_qualifier(const SPIRType &type, uint32_t in
 		{
 			switch (builtin)
 			{
-			case BuiltInPointSize: // Must output only if really rendering points
-				// SPIR-V might declare PointSize as a builtin even though it's not really used.
-				// In some cases PointSize builtin may be written without Point topology.
-				// This is not an issue on GL/Vulkan, but it is on Metal, so we also have some way to forcefully disable
-				// this builtin.
-				return (active_output_builtins & (1ull << BuiltInPointSize)) && options.enable_point_size_builtin ?
-				           (string(" [[") + builtin_qualifier(builtin) + "]]") :
-				           "";
+			case BuiltInPointSize:
+				// Only mark the PointSize builtin if really rendering points.
+				// Some shaders may include a PointSize builtin even when used to render
+				// non-point topologies, and Metal will reject this builtin when compiling
+				// the shader into a render pipeline that uses a non-point topology.
+				return options.enable_point_size_builtin ? (string(" [[") + builtin_qualifier(builtin) + "]]") : "";
 
 			case BuiltInPosition:
 			case BuiltInLayer: