Make DxilSignatureElement::m_SemanticName canonical for system values (microsoft#5889)

When DxilModule metadata is serialized, semantic strings for system values are canonicalized. If these strings are used anywhere, this can lead to a difference in behavior between an original DxilModule that has not undergone serialization and one that has been deserialized. This change canonicalizes the string as soon as a DxilSignatureElement is created, thereby removing the possibility of accidentally relying on the non-canonical string for a system value.

Author: tex3d

lib/DXIL/DxilSignatureElement.cpp

@@ -51,6 +51,9 @@ void DxilSignatureElement::Initialize(llvm::StringRef Name,
  m_SemanticStartIndex = IndexVector[0];
  // Find semantic in the table.
  m_pSemantic = Semantic::GetByName(m_SemanticName, m_sigPointKind);
+ // Replace semantic name with canonical name if it's a system value.
+ if (!m_pSemantic->IsInvalid() && !m_pSemantic->IsArbitrary())
+ m_SemanticName = m_pSemantic->GetName();
  SetCompType(ElementType);
  m_InterpMode = InterpMode;
  m_SemanticIndex = IndexVector;

tools/clang/unittests/HLSL/DxilModuleTest.cpp

@@ -71,6 +71,8 @@ class DxilModuleTest : public ::testing::Test {
 
  TEST_METHOD(PayloadQualifier)
 
+ TEST_METHOD(CanonicalSystemValueSemantic)
+
  void VerifyValidatorVersionFails(LPCWSTR shaderModel,
  const std::vector<LPCWSTR> &arguments,
  const std::vector<LPCSTR> &expectedErrors);
@@ -598,4 +600,24 @@ TEST_F(DxilModuleTest, PayloadQualifier) {
  DXIL::PayloadAccessShaderStage::Anyhit));
  }
  }
-}
+}
+
+TEST_F(DxilModuleTest, CanonicalSystemValueSemantic) {
+ // Verify that the semantic name is canonicalized.
+
+ // This is difficult to do from a FileCheck test because system value
+ // semantics get canonicallized during the metadata emit. However, having a
+ // non-canonical semantic name at earlier stages can lead to inconsistency
+ // between the strings used earlier and the final canonicalized version. This
+ // makes sure the string gets canonicalized when the signature elsement is
+ // created.
+
+ std::unique_ptr<hlsl::DxilSignatureElement> newElt =
+ std::make_unique<hlsl::DxilSignatureElement>(
+ hlsl::DXIL::SigPointKind::VSOut);
+ newElt->Initialize("sV_pOsItIoN", hlsl::CompType::getF32(),
+ hlsl::InterpolationMode(
+ hlsl::DXIL::InterpolationMode::LinearNoperspective),
+ 1, 4, 0, 0, 0, {0});
+ VERIFY_ARE_EQUAL_STR("SV_Position", newElt->GetSemanticName().data());
+}