MSL: Fix regression in image gather handling.

It was not always possible to get backing variable for a late-combined
image sampler.

reference/shaders-msl-no-opt/asm/frag/image-gather.asm.frag

@@ -0,0 +1,22 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+struct main0_out
+{
+    float4 out_var_SV_Target0 [[color(0)]];
+};
+
+struct main0_in
+{
+    float2 in_var_TEXCOORD0 [[user(locn0)]];
+};
+
+fragment main0_out main0(main0_in in [[stage_in]], texture2d<float> g_texture [[texture(0)]], sampler g_sampler [[sampler(0)]], sampler g_comp [[sampler(1)]])
+{
+    main0_out out = {};
+    out.out_var_SV_Target0 = g_texture.gather(g_sampler, in.in_var_TEXCOORD0, int2(0), component::x) * g_texture.gather(g_sampler, in.in_var_TEXCOORD0, int2(0), component::y);
+    return out;
+}
+

reference/shaders-msl-no-opt/frag/image-gather.frag

@@ -0,0 +1,24 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+struct main0_out
+{
+    float4 FragColor [[color(0)]];
+};
+
+struct main0_in
+{
+    float3 vUV [[user(locn0)]];
+};
+
+fragment main0_out main0(main0_in in [[stage_in]], texture2d<float> uSamp [[texture(0)]], depth2d<float> uSampShadow [[texture(1)]], sampler uSampSmplr [[sampler(0)]], sampler uSampShadowSmplr [[sampler(1)]])
+{
+    main0_out out = {};
+    out.FragColor = uSamp.gather(uSampSmplr, in.vUV.xy, int2(0), component::x);
+    out.FragColor += uSamp.gather(uSampSmplr, in.vUV.xy, int2(0), component::y);
+    out.FragColor += uSampShadow.gather_compare(uSampShadowSmplr, in.vUV.xy, in.vUV.z);
+    return out;
+}
+

reference/shaders-no-opt/frag/image-gather.frag

@@ -0,0 +1,15 @@
+#version 450
+
+layout(binding = 0) uniform sampler2D uSamp;
+layout(binding = 1) uniform sampler2DShadow uSampShadow;
+
+layout(location = 0) out vec4 FragColor;
+layout(location = 0) in vec3 vUV;
+
+void main()
+{
+    FragColor = textureGather(uSamp, vUV.xy, 0);
+    FragColor += textureGather(uSamp, vUV.xy, 1);
+    FragColor += textureGather(uSampShadow, vUV.xy, vUV.z);
+}
+

shaders-msl-no-opt/asm/frag/image-gather.asm.frag

@@ -0,0 +1,74 @@
+; SPIR-V
+; Version: 1.3
+; Generator: Google spiregg; 0
+; Bound: 36
+; Schema: 0
+               OpCapability Shader
+               OpExtension "SPV_GOOGLE_hlsl_functionality1"
+               OpExtension "SPV_GOOGLE_user_type"
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %psMain "main" %gl_FragCoord %in_var_TEXCOORD0 %out_var_SV_Target0
+               OpExecutionMode %psMain OriginUpperLeft
+               OpSource HLSL 500
+               OpName %type_2d_image "type.2d.image"
+               OpName %g_texture "g_texture"
+               OpName %type_sampler "type.sampler"
+               OpName %g_sampler "g_sampler"
+               OpName %g_comp "g_comp"
+               OpName %in_var_TEXCOORD0 "in.var.TEXCOORD0"
+               OpName %out_var_SV_Target0 "out.var.SV_Target0"
+               OpName %psMain "psMain"
+               OpName %type_sampled_image "type.sampled.image"
+               OpDecorate %gl_FragCoord BuiltIn FragCoord
+               OpDecorateString %gl_FragCoord UserSemantic "SV_Position"
+               OpDecorateString %in_var_TEXCOORD0 UserSemantic "TEXCOORD0"
+               OpDecorateString %out_var_SV_Target0 UserSemantic "SV_Target0"
+               OpDecorate %in_var_TEXCOORD0 Location 0
+               OpDecorate %out_var_SV_Target0 Location 0
+               OpDecorate %g_texture DescriptorSet 0
+               OpDecorate %g_texture Binding 0
+               OpDecorate %g_sampler DescriptorSet 0
+               OpDecorate %g_sampler Binding 0
+               OpDecorate %g_comp DescriptorSet 0
+               OpDecorate %g_comp Binding 1
+               OpDecorateString %g_texture UserTypeGOOGLE "texture2d"
+      %float = OpTypeFloat 32
+  %float_0_5 = OpConstant %float 0.5
+        %int = OpTypeInt 32 1
+      %int_0 = OpConstant %int 0
+      %int_1 = OpConstant %int 1
+      %v2int = OpTypeVector %int 2
+         %16 = OpConstantComposite %v2int %int_0 %int_0
+%type_2d_image = OpTypeImage %float 2D 2 0 0 1 Unknown
+%_ptr_UniformConstant_type_2d_image = OpTypePointer UniformConstant %type_2d_image
+%type_sampler = OpTypeSampler
+%_ptr_UniformConstant_type_sampler = OpTypePointer UniformConstant %type_sampler
+    %v4float = OpTypeVector %float 4
+%_ptr_Input_v4float = OpTypePointer Input %v4float
+    %v2float = OpTypeVector %float 2
+%_ptr_Input_v2float = OpTypePointer Input %v2float
+%_ptr_Output_v4float = OpTypePointer Output %v4float
+       %void = OpTypeVoid
+         %25 = OpTypeFunction %void
+%type_sampled_image = OpTypeSampledImage %type_2d_image
+%g_texture = OpVariable %_ptr_UniformConstant_type_2d_image UniformConstant
+  %g_sampler = OpVariable %_ptr_UniformConstant_type_sampler UniformConstant
+     %g_comp = OpVariable %_ptr_UniformConstant_type_sampler UniformConstant
+%gl_FragCoord = OpVariable %_ptr_Input_v4float Input
+%in_var_TEXCOORD0 = OpVariable %_ptr_Input_v2float Input
+%out_var_SV_Target0 = OpVariable %_ptr_Output_v4float Output
+     %psMain = OpFunction %void None %25
+         %26 = OpLabel
+         %27 = OpLoad %v2float %in_var_TEXCOORD0
+         %28 = OpLoad %type_2d_image %g_texture
+         %29 = OpLoad %type_sampler %g_comp
+         %30 = OpSampledImage %type_sampled_image %28 %29
+         %32 = OpLoad %type_sampler %g_sampler
+         %33 = OpSampledImage %type_sampled_image %28 %32
+         %31 = OpImageGather %v4float %33 %27 %int_1 ConstOffset %16
+         %34 = OpImageGather %v4float %33 %27 %int_0 ConstOffset %16
+         %35 = OpFMul %v4float %34 %31
+               OpStore %out_var_SV_Target0 %35
+               OpReturn
+               OpFunctionEnd
+

shaders-msl-no-opt/frag/image-gather.frag

@@ -0,0 +1,14 @@
+#version 450
+
+layout(location = 0) out vec4 FragColor;
+
+layout(set = 0, binding = 0) uniform sampler2D uSamp;
+layout(set = 0, binding = 1) uniform sampler2DShadow uSampShadow;
+layout(location = 0) in vec3 vUV;
+
+void main()
+{
+	FragColor = textureGather(uSamp, vUV.xy, 0);
+	FragColor += textureGather(uSamp, vUV.xy, 1);
+	FragColor += textureGather(uSampShadow, vUV.xy, vUV.z);
+}

shaders-no-opt/frag/image-gather.frag

@@ -0,0 +1,14 @@
+#version 450
+
+layout(location = 0) out vec4 FragColor;
+
+layout(set = 0, binding = 0) uniform sampler2D uSamp;
+layout(set = 0, binding = 1) uniform sampler2DShadow uSampShadow;
+layout(location = 0) in vec3 vUV;
+
+void main()
+{
+	FragColor = textureGather(uSamp, vUV.xy, 0);
+	FragColor += textureGather(uSamp, vUV.xy, 1);
+	FragColor += textureGather(uSampShadow, vUV.xy, vUV.z);
+}

spirv_msl.cpp

@@ -8804,9 +8804,19 @@ string CompilerMSL::to_function_args(const TextureFunctionArguments &args, bool
 		{
 			forward = forward && should_forward(args.component);
 
-			if (const auto *var = maybe_get_backing_variable(img))
-				if (!image_is_comparison(get<SPIRType>(var->basetype), var->self))
-					farg_str += ", " + to_component_argument(args.component);
+			uint32_t image_var = 0;
+			if (const auto *combined = maybe_get<SPIRCombinedImageSampler>(img))
+			{
+				if (const auto *img_var = maybe_get_backing_variable(combined->image))
+					image_var = img_var->self;
+			}
+			else if (const auto *var = maybe_get_backing_variable(img))
+			{
+				image_var = var->self;
+			}
+
+			if (image_var == 0 || !image_is_comparison(expression_type(image_var), image_var))
+				farg_str += ", " + to_component_argument(args.component);
 		}
 	}