Fix const var init with NRVO (#3803)

Author: tex3d

tools/clang/lib/CodeGen/CGDecl.cpp

@@ -142,7 +142,9 @@ void CodeGenFunction::EmitVarDecl(const VarDecl &D) {
   }
   // HLSL Change Begin - treat local constant as static.
   // Global variable will be generated instead of alloca.
-  if (D.getType().isConstQualified() && D.isLocalVarDecl()) {
+  if (D.getType().isConstQualified() &&
+      (D.isLocalVarDecl() && D.getKind() != Decl::ParmVar &&
+       !D.isNRVOVariable())) {
     // Only create global when has constant init.
     if (!isTrivialInitializer(D.getInit()) && CGM.EmitConstantInit(D, this)) {
       llvm::GlobalValue::LinkageTypes Linkage =

tools/clang/test/HLSLFileCheck/hlsl/functions/misc/const-pos-out.hlsl

@@ -0,0 +1,16 @@
+// RUN: %dxc -E main -T vs_6_0 %s | FileCheck %s
+
+// Make sure NRVO works with constant initializer for return value
+// CHECK: call void @dx.op.storeOutput.f32(i32 5, i32 0, i32 0, i8 0, float 2.500000e-01)
+// CHECK: call void @dx.op.storeOutput.f32(i32 5, i32 0, i32 0, i8 1, float 5.000000e-01)
+// CHECK: call void @dx.op.storeOutput.f32(i32 5, i32 0, i32 0, i8 2, float 7.500000e-01)
+// CHECK: call void @dx.op.storeOutput.f32(i32 5, i32 0, i32 0, i8 3, float 1.000000e+00)
+
+struct VSOUT {
+  float4 pos : SV_Position;
+};
+
+VSOUT main() {
+  const VSOUT Out = {float4(0.25, 0.5, 0.75, 1.0)};
+  return Out;
+}