Fix spirv builtin for `SV_ShadingRate`. (#3730)

3 files changed, 20 insertions, 1 deletions

diff --git a/source/slang/slang-emit-glsl.cpp b/source/slang/slang-emit-glsl.cpp
index 55f6d140c..d37a6840b 100644
--- a/source/slang/slang-emit-glsl.cpp
+++ b/source/slang/slang-emit-glsl.cpp
@@ -928,6 +928,14 @@ void GLSLSourceEmitter::_maybeEmitGLSLBuiltin(IRGlobalParam* var, UnownedStringS
             m_writer->emit(";\n\n");
         }
     }
+    else if (name == "gl_ShadingRateEXT")
+    {
+        _requireGLSLExtension(toSlice("GL_EXT_fragment_shading_rate"));
+    }
+    else if (name == "gl_PrimitiveShadingRateEXT")
+    {
+        _requireGLSLExtension(toSlice("GL_EXT_fragment_shading_rate_primitive"));
+    }
 }
 
 void GLSLSourceEmitter::_requireBaseType(BaseType baseType)
diff --git a/source/slang/slang-emit-spirv.cpp b/source/slang/slang-emit-spirv.cpp
index 1a661920a..2f318c464 100644
--- a/source/slang/slang-emit-spirv.cpp
+++ b/source/slang/slang-emit-spirv.cpp
@@ -3663,7 +3663,11 @@ struct SPIRVEmitContext
                 {
                     requireSPIRVCapability(SpvCapabilityFragmentShadingRateKHR);
                     ensureExtensionDeclaration(UnownedStringSlice("SPV_KHR_fragment_shading_rate"));
-                    return getBuiltinGlobalVar(inst->getFullType(), SpvBuiltInPrimitiveShadingRateKHR);
+                    auto importDecor = inst->findDecoration<IRImportDecoration>();
+                    if (importDecor && importDecor->getMangledName() == "gl_PrimitiveShadingRateEXT")
+                        return getBuiltinGlobalVar(inst->getFullType(), SpvBuiltInPrimitiveShadingRateKHR);
+                    else
+                        return getBuiltinGlobalVar(inst->getFullType(), SpvBuiltInShadingRateKHR);
                 }
                 SLANG_UNREACHABLE("Unimplemented system value in spirv emit.");
             }
diff --git a/tests/spirv/shading-rate.slang b/tests/spirv/shading-rate.slang
new file mode 100644
index 000000000..638ed7548
--- /dev/null
+++ b/tests/spirv/shading-rate.slang
@@ -0,0 +1,7 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv -entry main -emit-spirv-directly
+
+// CHECK: BuiltIn ShadingRateKHR
+[shader("fragment")]
+uint main(uint shading_rate : SV_ShadingRate) : SV_Target {
+    return shading_rate;
+}