[Metal] Support SV_TargetN. (shader-slang#4390)

* [Metal] Support SV_TargetN.

* Fix.

Author: csyonghe

source/slang/slang-ir-metal-legalize.cpp

@@ -5,6 +5,7 @@
 #include "slang-ir-util.h"
 #include "slang-ir-clone.h"
 #include "slang-ir-specialize-address-space.h"
+#include "slang-parameter-binding.h"
 #include "slang-ir-legalize-varying-params.h"
 
 namespace Slang
@@ -237,13 +238,15 @@ namespace Slang
         return builder.getVectorType(builder.getBasicType(BaseType::UInt), builder.getIntValue(builder.getIntType(), 3));
     }
 
-    MetalSystemValueInfo getSystemValueInfo(IRBuilder& builder, String semanticName, UInt attrIndex)
+    MetalSystemValueInfo getSystemValueInfo(IRBuilder& builder, String inSemanticName)
     {
-        SLANG_UNUSED(attrIndex);
+        inSemanticName = inSemanticName.toLower();
 
-        MetalSystemValueInfo result = {};
+        UnownedStringSlice semanticName;
+        UnownedStringSlice semanticIndex;
+        splitNameAndIndex(inSemanticName.getUnownedSlice(), semanticName, semanticIndex);
 
-        semanticName = semanticName.toLower();
+        MetalSystemValueInfo result = {};
 
         if (semanticName == "sv_position")
         {
@@ -374,9 +377,12 @@ namespace Slang
             result.requiredType = builder.getBasicType(BaseType::UInt);
             result.altRequiredType = builder.getBasicType(BaseType::UInt16);
         }
-        else if (semanticName == "sv_target")
+        else if (semanticName.startsWith("sv_target"))
         {
-            result.metalSystemValueName = (StringBuilder() << "color(" << String(attrIndex) << ")").produceString();
+            
+            result.metalSystemValueName = (StringBuilder() << "color("
+                << (semanticIndex.getLength() != 0 ? semanticIndex : toSlice("0"))
+                << ")").produceString();
         }
         else
         {
@@ -404,7 +410,7 @@ namespace Slang
             {
                 if (semanticDecor->getSemanticName().startsWithCaseInsensitive(toSlice("sv_")))
                 {
-                    auto sysValInfo = getSystemValueInfo(builder, semanticDecor->getSemanticName(), semanticDecor->getSemanticIndex());
+                    auto sysValInfo = getSystemValueInfo(builder, semanticDecor->getSemanticName());
                     if (sysValInfo.isUnsupported || sysValInfo.isSpecial)
                     {
                         reportUnsupportedSystemAttribute(sink, field, semanticDecor->getSemanticName());
@@ -670,9 +676,8 @@ namespace Slang
 
             auto param = workItem.param;
             auto semanticName = workItem.attrName;
-            auto sysAttrIndex = workItem.attrIndex;
 
-            auto info = getSystemValueInfo(builder, semanticName, sysAttrIndex);
+            auto info = getSystemValueInfo(builder, semanticName);
             if (info.isSpecial)
             {
                 if (semanticName == "sv_innercoverage")

source/slang/slang-parameter-binding.cpp

@@ -480,9 +480,7 @@ static bool isDigit(char c)
     return (c >= '0') && (c <= '9');
 }
 
-/// Given a string that specifies a name and index (e.g., `COLOR0`),
-/// split it into slices for the name part and the index part.
-static void splitNameAndIndex(
+void splitNameAndIndex(
     UnownedStringSlice const&       text,
     UnownedStringSlice& outName,
     UnownedStringSlice& outDigits)

source/slang/slang-parameter-binding.h

@@ -29,6 +29,14 @@ void generateParameterBindings(
     TargetRequest*  targetReq,
     DiagnosticSink* sink);
 
+/// Given a string that specifies a name and index (e.g., `COLOR0`),
+/// split it into slices for the name part and the index part.
+/// 
+void splitNameAndIndex(
+    UnownedStringSlice const& text,
+    UnownedStringSlice& outName,
+    UnownedStringSlice& outDigits);
+
 }
 
 #endif 

tests/metal/sv_target.slang

@@ -0,0 +1,20 @@
+//TEST:SIMPLE(filecheck=CHECK): -target metal
+//TEST:SIMPLE(filecheck=CHECK-ASM): -target metallib
+
+struct Output
+{
+  float4 Diffuse  : SV_Target0;
+  float4 Normal   : SV_Target1;
+  float4 Material : SV_Target2;
+}
+
+// CHECK-ASM: define {{.*}} @fragMain
+// CHECK: color(0)
+// CHECK: color(1)
+// CHECK: color(2)
+
+[shader("fragment")]
+Output fragMain()
+{
+    return { float4(1), float4(2), float4(3) };
+}