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Author: Keenuts

clang/lib/Sema/SemaHLSL.cpp

@@ -771,8 +771,9 @@ void SemaHLSL::ActOnTopLevelFunction(FunctionDecl *FD) {
   }
 }
 
-static bool isPipelineBuiltin(const ASTContext &AstContext, FunctionDecl *FD,
-                              HLSLAppliedSemanticAttr *Semantic) {
+static bool isVkPipelineBuiltin(const ASTContext &AstContext, FunctionDecl *FD,
+                                HLSLAppliedSemanticAttr *Semantic,
+                                bool IsInput) {
   if (AstContext.getTargetInfo().getTriple().getOS() != llvm::Triple::Vulkan)
     return false;
 
@@ -781,8 +782,13 @@ static bool isPipelineBuiltin(const ASTContext &AstContext, FunctionDecl *FD,
   llvm::Triple::EnvironmentType ST = ShaderAttr->getType();
   auto SemanticName = Semantic->getSemanticName().upper();
 
-  if (ST == llvm::Triple::Pixel && SemanticName == "SV_POSITION")
-    return true;
+  // The SV_Position semantic is lowered to:
+  //  - Position built-in for vertex output.
+  //  - FragCoord built-in for fragment input.
+  if (SemanticName == "SV_POSITION") {
+    return (ST == llvm::Triple::Vertex && !IsInput) ||
+           (ST == llvm::Triple::Pixel && IsInput);
+  }
 
   return false;
 }
@@ -816,7 +822,7 @@ bool SemaHLSL::determineActiveSemanticOnScalar(FunctionDecl *FD,
 
   unsigned Location = ActiveSemantic.Index.value_or(0);
 
-  if (!isPipelineBuiltin(getASTContext(), FD, A)) {
+  if (!isVkPipelineBuiltin(getASTContext(), FD, A, IsInput)) {
     bool HasVkLocation = false;
     if (auto *A = D->getAttr<HLSLVkLocationAttr>()) {
       HasVkLocation = true;

clang/test/CodeGenHLSL/semantics/semantic.explicit-mix-builtin.vs.hlsl

@@ -0,0 +1,31 @@
+// RUN: %clang_cc1 -triple spirv-linux-vulkan-vertex -x hlsl -emit-llvm -finclude-default-header -disable-llvm-passes -o - %s | FileCheck %s
+
+// This is almost the same as semantic.explicit-mix-builtin.hlsl, except this
+// time we build a vertex shader. This means the SV_Position semantic output
+// is also a BuiltIn, This means we can mix implicit and explicit location
+// assignment.
+struct S1 {
+  float4 position : SV_Position;
+  [[vk::location(3)]] float4 color : A;
+};
+
+// CHECK: @SV_Position0 = external hidden thread_local addrspace(7) externally_initialized constant <4 x float>, !spirv.Decorations ![[#MD_0:]]
+// CHECK: @SV_Position = external hidden thread_local addrspace(8) global <4 x float>, !spirv.Decorations ![[#MD_2:]]
+// CHECK: @A0 = external hidden thread_local addrspace(8) global <4 x float>, !spirv.Decorations ![[#MD_0]]
+
+[shader("vertex")]
+S1 main1(float4 position : SV_Position) {
+  S1 output;
+  output.position = position;
+  output.color = position;
+  return output;
+}
+
+// CHECK: ![[#MD_0]] = !{![[#MD_1:]]}
+// CHECK: ![[#MD_1]] = !{i32 30, i32 0}
+//                            |       `-> Location index
+//                            `-> SPIR-V decoration 'Location'
+// CHECK: ![[#MD_2]] = !{![[#MD_3:]]}
+// CHECK: ![[#MD_3]] = !{i32 11, i32 0}
+//                            |       `-> BuiltIn 'Position'
+//                            `-> SPIR-V decoration 'BuiltIn'