MSL: Support SPV_EXT_demote_to_helper_invocation for MSL 2.3.

MSL 2.3 has everything needed to support this extension on all
platforms. The existing `discard_fragment()` function was given demote
semantics, similar to Direct3D, and the `simd_is_helper_thread()`
function was finally added to iOS.

I've left the old test alone. Should I remove it in favor of these?

reference/opt/shaders-msl/vulkan/frag/demote-to-helper-forwarding.asm.vk.nocompat.msl23.frag

@@ -0,0 +1,22 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+struct main0_out
+{
+    float4 FragColor [[color(0)]];
+};
+
+fragment main0_out main0()
+{
+    main0_out out = {};
+    bool _15 = simd_is_helper_thread();
+    discard_fragment();
+    if (!_15)
+    {
+        out.FragColor = float4(1.0, 0.0, 0.0, 1.0);
+    }
+    return out;
+}
+

reference/opt/shaders-msl/vulkan/frag/demote-to-helper.vk.nocompat.msl23.frag

@@ -0,0 +1,11 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+fragment void main0()
+{
+    discard_fragment();
+    bool _9 = simd_is_helper_thread();
+}
+

reference/opt/shaders-msl/vulkan/frag/demote-to-helper.vk.nocompat.msl23.ios.frag

@@ -0,0 +1,11 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+fragment void main0()
+{
+    discard_fragment();
+    bool _9 = simd_is_helper_thread();
+}
+

reference/shaders-msl/vulkan/frag/demote-to-helper-forwarding.asm.vk.nocompat.msl23.frag

@@ -0,0 +1,22 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+struct main0_out
+{
+    float4 FragColor [[color(0)]];
+};
+
+fragment main0_out main0()
+{
+    main0_out out = {};
+    bool _15 = simd_is_helper_thread();
+    discard_fragment();
+    if (!_15)
+    {
+        out.FragColor = float4(1.0, 0.0, 0.0, 1.0);
+    }
+    return out;
+}
+

reference/shaders-msl/vulkan/frag/demote-to-helper.vk.nocompat.msl23.frag

@@ -0,0 +1,12 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+fragment void main0()
+{
+    discard_fragment();
+    bool _9 = simd_is_helper_thread();
+    bool helper = _9;
+}
+

reference/shaders-msl/vulkan/frag/demote-to-helper.vk.nocompat.msl23.ios.frag

@@ -0,0 +1,12 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+fragment void main0()
+{
+    discard_fragment();
+    bool _9 = simd_is_helper_thread();
+    bool helper = _9;
+}
+

shaders-msl/vulkan/frag/demote-to-helper-forwarding.asm.vk.nocompat.msl23.frag

@@ -0,0 +1,41 @@
+; SPIR-V
+; Version: 1.3
+; Generator: Khronos Glslang Reference Front End; 7
+; Bound: 19
+; Schema: 0
+               OpCapability Shader
+               OpCapability DemoteToHelperInvocationEXT
+               OpExtension "SPV_EXT_demote_to_helper_invocation"
+          %1 = OpExtInstImport "GLSL.std.450"
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %main "main" %FragColor
+               OpExecutionMode %main OriginUpperLeft
+               OpSource GLSL 450
+               OpSourceExtension "GL_EXT_demote_to_helper_invocation"
+               OpName %main "main"
+               OpName %FragColor "FragColor"
+               OpDecorate %FragColor Location 0
+       %void = OpTypeVoid
+          %3 = OpTypeFunction %void
+       %bool = OpTypeBool
+%_ptr_Function_bool = OpTypePointer Function %bool
+      %float = OpTypeFloat 32
+    %v4float = OpTypeVector %float 4
+%_ptr_Output_v4float = OpTypePointer Output %v4float
+  %FragColor = OpVariable %_ptr_Output_v4float Output
+    %float_1 = OpConstant %float 1
+    %float_0 = OpConstant %float 0
+         %19 = OpConstantComposite %v4float %float_1 %float_0 %float_0 %float_1
+       %main = OpFunction %void None %3
+          %5 = OpLabel
+          %9 = OpIsHelperInvocationEXT %bool
+               OpDemoteToHelperInvocationEXT
+         %10 = OpLogicalNot %bool %9
+               OpSelectionMerge %12 None
+               OpBranchConditional %10 %11 %12
+         %11 = OpLabel
+               OpStore %FragColor %19
+               OpBranch %12
+         %12 = OpLabel
+               OpReturn
+               OpFunctionEnd

shaders-msl/vulkan/frag/demote-to-helper.vk.nocompat.msl23.frag

@@ -0,0 +1,8 @@
+#version 450
+#extension GL_EXT_demote_to_helper_invocation : require
+
+void main()
+{
+	demote;
+	bool helper = helperInvocationEXT();
+}

shaders-msl/vulkan/frag/demote-to-helper.vk.nocompat.msl23.ios.frag

@@ -0,0 +1,8 @@
+#version 450
+#extension GL_EXT_demote_to_helper_invocation : require
+
+void main()
+{
+	demote;
+	bool helper = helperInvocationEXT();
+}

spirv_msl.cpp

@@ -1120,7 +1120,7 @@ string CompilerMSL::compile()
 	backend.basic_int16_type = "short";
 	backend.basic_uint16_type = "ushort";
 	backend.discard_literal = "discard_fragment()";
-	backend.demote_literal = "unsupported-demote";
+	backend.demote_literal = "discard_fragment()";
 	backend.boolean_mix_function = "select";
 	backend.swizzle_is_function = false;
 	backend.shared_is_implied = false;
@@ -7117,11 +7117,18 @@ void CompilerMSL::emit_instruction(const Instruction &instruction)
 		break;
 	}
 
+	// SPV_EXT_demote_to_helper_invocation
+	case OpDemoteToHelperInvocationEXT:
+		if (!msl_options.supports_msl_version(2, 3))
+			SPIRV_CROSS_THROW("discard_fragment() does not formally have demote semantics until MSL 2.3.");
+		CompilerGLSL::emit_instruction(instruction);
+		break;
+
 	case OpIsHelperInvocationEXT:
-		if (msl_options.is_ios())
+		if (msl_options.is_ios() && !msl_options.supports_msl_version(2, 3))
-			SPIRV_CROSS_THROW("simd_is_helper_thread() is only supported on macOS.");
+			SPIRV_CROSS_THROW("simd_is_helper_thread() requires MSL 2.3 on iOS.");
 		else if (msl_options.is_macos() && !msl_options.supports_msl_version(2, 1))
-			SPIRV_CROSS_THROW("simd_is_helper_thread() requires version 2.1 on macOS.");
+			SPIRV_CROSS_THROW("simd_is_helper_thread() requires MSL 2.1 on macOS.");
 		emit_op(ops[0], ops[1], "simd_is_helper_thread()", false);
 		break;
 

test_shaders.py

@@ -107,17 +107,17 @@ def print_msl_compiler_version():
     except subprocess.CalledProcessError:
         pass
 
-def msl_compiler_supports_22():
+def msl_compiler_supports_version(version):
     try:
-        subprocess.check_call(['xcrun', '--sdk', 'macosx', 'metal', '-x', 'metal', '-std=macos-metal2.2', '-'],
+        subprocess.check_call(['xcrun', '--sdk', 'macosx', 'metal', '-x', 'metal', '-std=macos-metal' + version, '-'],
                 stdin = subprocess.DEVNULL, stdout = subprocess.DEVNULL, stderr = subprocess.DEVNULL)
-        print('Current SDK supports MSL 2.2. Enabling validation for MSL 2.2 shaders.')
+        print('Current SDK supports MSL {0}. Enabling validation for MSL {0} shaders.'.format(version))
         return True
     except OSError as e:
-        print('Failed to check if MSL 2.2 is not supported. It probably is not.')
+        print('Failed to check if MSL {} is not supported. It probably is not.'.format(version))
         return False
     except subprocess.CalledProcessError:
-        print('Current SDK does NOT support MSL 2.2. Disabling validation for MSL 2.2 shaders.')
+        print('Current SDK does NOT support MSL {0}. Disabling validation for MSL {0} shaders.'.format(version))
         return False
 
 def path_to_msl_standard(shader):
@@ -128,6 +128,8 @@ def path_to_msl_standard(shader):
             return '-std=ios-metal2.1'
         elif '.msl22.' in shader:
             return '-std=ios-metal2.2'
+        elif '.msl23.' in shader:
+            return '-std=ios-metal2.3'
         elif '.msl11.' in shader:
             return '-std=ios-metal1.1'
         elif '.msl10.' in shader:
@@ -141,6 +143,8 @@ def path_to_msl_standard(shader):
             return '-std=macos-metal2.1'
         elif '.msl22.' in shader:
             return '-std=macos-metal2.2'
+        elif '.msl23.' in shader:
+            return '-std=macos-metal2.3'
         elif '.msl11.' in shader:
             return '-std=macos-metal1.1'
         else:
@@ -153,6 +157,8 @@ def path_to_msl_standard_cli(shader):
         return '20100'
     elif '.msl22.' in shader:
         return '20200'
+    elif '.msl23.' in shader:
+        return '20300'
     elif '.msl11.' in shader:
         return '10100'
     else:
@@ -712,7 +718,8 @@ def test_shader_msl(stats, shader, args, paths):
 #    print('SPRIV shader: ' + spirv)
 
     shader_is_msl22 = 'msl22' in joined_path
-    skip_validation = shader_is_msl22 and (not args.msl22)
+    shader_is_msl23 = 'msl23' in joined_path
+    skip_validation = (shader_is_msl22 and (not args.msl22)) or (shader_is_msl23 and (not args.msl23))
     if '.invalid.' in joined_path:
         skip_validation = True
 
@@ -860,9 +867,11 @@ def main():
         args.parallel = False
 
     args.msl22 = False
+    args.msl23 = False
     if args.msl:
         print_msl_compiler_version()
-        args.msl22 = msl_compiler_supports_22()
+        args.msl22 = msl_compiler_supports_version('2.2')
+        args.msl23 = msl_compiler_supports_version('2.3')
 
     backend = 'glsl'
     if (args.msl or args.metal):