[HLSL][RootSignature] Add parsing of flags to RootParam

inbelic · inbelic · commit ab3904222ef1 · 2025-05-15T21:57:40.000Z
- defines RootDescriptorFlags in-memory representation
- defines parseRootDescriptorFlags to be DXC compatible. This is why we
support multiple `|` flags even validation will assert that only one
flag is set...
- add unit tests to demonstrate functionality
diff --git a/clang/include/clang/Parse/ParseHLSLRootSignature.h b/clang/include/clang/Parse/ParseHLSLRootSignature.h
@@ -93,6 +93,7 @@ class RootSignatureParser {
     std::optional<llvm::hlsl::rootsig::Register> Reg;
     std::optional<uint32_t> Space;
     std::optional<llvm::hlsl::rootsig::ShaderVisibility> Visibility;
+    std::optional<llvm::hlsl::rootsig::RootDescriptorFlags> Flags;
   };
   std::optional<ParsedRootParamParams>
   parseRootParamParams(RootSignatureToken::Kind RegType);
@@ -113,6 +114,8 @@ class RootSignatureParser {
 
   /// Parsing methods of various enums
   std::optional<llvm::hlsl::rootsig::ShaderVisibility> parseShaderVisibility();
+  std::optional<llvm::hlsl::rootsig::RootDescriptorFlags>
+  parseRootDescriptorFlags();
   std::optional<llvm::hlsl::rootsig::DescriptorRangeFlags>
   parseDescriptorRangeFlags();
 
diff --git a/clang/lib/Parse/ParseHLSLRootSignature.cpp b/clang/lib/Parse/ParseHLSLRootSignature.cpp
@@ -193,6 +193,7 @@ std::optional<RootParam> RootSignatureParser::parseRootParam() {
     ExpectedReg = TokenKind::uReg;
     break;
   }
+  Param.setDefaultFlags();
 
   auto Params = parseRootParamParams(ExpectedReg);
   if (!Params.has_value())
@@ -214,6 +215,9 @@ std::optional<RootParam> RootSignatureParser::parseRootParam() {
   if (Params->Visibility.has_value())
     Param.Visibility = Params->Visibility.value();
 
+  if (Params->Flags.has_value())
+    Param.Flags = Params->Flags.value();
+
   if (consumeExpectedToken(TokenKind::pu_r_paren,
                            diag::err_hlsl_unexpected_end_of_params,
                            /*param of=*/TokenKind::kw_RootConstants))
@@ -475,6 +479,23 @@ RootSignatureParser::parseRootParamParams(TokenKind RegType) {
         return std::nullopt;
       Params.Visibility = Visibility;
     }
+
+    // `flags` `=` ROOT_DESCRIPTOR_FLAGS
+    if (tryConsumeExpectedToken(TokenKind::kw_flags)) {
+      if (Params.Flags.has_value()) {
+        getDiags().Report(CurToken.TokLoc, diag::err_hlsl_rootsig_repeat_param)
+            << CurToken.TokKind;
+        return std::nullopt;
+      }
+
+      if (consumeExpectedToken(TokenKind::pu_equal))
+        return std::nullopt;
+
+      auto Flags = parseRootDescriptorFlags();
+      if (!Flags.has_value())
+        return std::nullopt;
+      Params.Flags = Flags;
+    }
   } while (tryConsumeExpectedToken(TokenKind::pu_comma));
 
   return Params;
@@ -654,6 +675,45 @@ RootSignatureParser::parseShaderVisibility() {
   return std::nullopt;
 }
 
+std::optional<llvm::hlsl::rootsig::RootDescriptorFlags>
+RootSignatureParser::parseRootDescriptorFlags() {
+  assert(CurToken.TokKind == TokenKind::pu_equal &&
+         "Expects to only be invoked starting at given keyword");
+
+  // Handle the edge-case of '0' to specify no flags set
+  if (tryConsumeExpectedToken(TokenKind::int_literal)) {
+    if (!verifyZeroFlag()) {
+      getDiags().Report(CurToken.TokLoc, diag::err_hlsl_rootsig_non_zero_flag);
+      return std::nullopt;
+    }
+    return RootDescriptorFlags::None;
+  }
+
+  TokenKind Expected[] = {
+#define ROOT_DESCRIPTOR_FLAG_ENUM(NAME, LIT) TokenKind::en_##NAME,
+#include "clang/Lex/HLSLRootSignatureTokenKinds.def"
+  };
+
+  std::optional<RootDescriptorFlags> Flags;
+
+  do {
+    if (tryConsumeExpectedToken(Expected)) {
+      switch (CurToken.TokKind) {
+#define ROOT_DESCRIPTOR_FLAG_ENUM(NAME, LIT)                                   \
+  case TokenKind::en_##NAME:                                                   \
+    Flags =                                                                    \
+        maybeOrFlag<RootDescriptorFlags>(Flags, RootDescriptorFlags::NAME);    \
+    break;
+#include "clang/Lex/HLSLRootSignatureTokenKinds.def"
+      default:
+        llvm_unreachable("Switch for consumed enum token was not provided");
+      }
+    }
+  } while (tryConsumeExpectedToken(TokenKind::pu_or));
+
+  return Flags;
+}
+
 std::optional<llvm::hlsl::rootsig::DescriptorRangeFlags>
 RootSignatureParser::parseDescriptorRangeFlags() {
   assert(CurToken.TokKind == TokenKind::pu_equal &&
diff --git a/clang/unittests/Parse/ParseHLSLRootSignatureTest.cpp b/clang/unittests/Parse/ParseHLSLRootSignatureTest.cpp
@@ -347,8 +347,11 @@ TEST_F(ParseHLSLRootSignatureTest, ValidParseRootFlagsTest) {
 TEST_F(ParseHLSLRootSignatureTest, ValidParseRootParamsTest) {
   const llvm::StringLiteral Source = R"cc(
     CBV(b0),
-    SRV(space = 4, t42, visibility = SHADER_VISIBILITY_GEOMETRY),
-    UAV(visibility = SHADER_VISIBILITY_HULL, u34893247)
+    SRV(space = 4, t42, visibility = SHADER_VISIBILITY_GEOMETRY,
+      flags = DATA_VOLATILE | DATA_STATIC | DATA_STATIC_WHILE_SET_AT_EXECUTE
+    ),
+    UAV(visibility = SHADER_VISIBILITY_HULL, u34893247),
+    CBV(b0, flags = 0),
   )cc";
 
   TrivialModuleLoader ModLoader;
@@ -364,14 +367,16 @@ TEST_F(ParseHLSLRootSignatureTest, ValidParseRootParamsTest) {
 
   ASSERT_FALSE(Parser.parse());
 
-  ASSERT_EQ(Elements.size(), 3u);
+  ASSERT_EQ(Elements.size(), 4u);
 
   RootElement Elem = Elements[0];
   ASSERT_TRUE(std::holds_alternative<RootParam>(Elem));
   ASSERT_EQ(std::get<RootParam>(Elem).Reg.ViewType, RegisterType::BReg);
   ASSERT_EQ(std::get<RootParam>(Elem).Reg.Number, 0u);
   ASSERT_EQ(std::get<RootParam>(Elem).Space, 0u);
   ASSERT_EQ(std::get<RootParam>(Elem).Visibility, ShaderVisibility::All);
+  ASSERT_EQ(std::get<RootParam>(Elem).Flags,
+            RootDescriptorFlags::DataStaticWhileSetAtExecute);
 
   Elem = Elements[1];
   ASSERT_TRUE(std::holds_alternative<RootParam>(Elem));
@@ -380,6 +385,7 @@ TEST_F(ParseHLSLRootSignatureTest, ValidParseRootParamsTest) {
   ASSERT_EQ(std::get<RootParam>(Elem).Reg.Number, 42u);
   ASSERT_EQ(std::get<RootParam>(Elem).Space, 4u);
   ASSERT_EQ(std::get<RootParam>(Elem).Visibility, ShaderVisibility::Geometry);
+  ASSERT_EQ(std::get<RootParam>(Elem).Flags, RootDescriptorFlags::ValidFlags);
 
   Elem = Elements[2];
   ASSERT_TRUE(std::holds_alternative<RootParam>(Elem));
@@ -388,6 +394,14 @@ TEST_F(ParseHLSLRootSignatureTest, ValidParseRootParamsTest) {
   ASSERT_EQ(std::get<RootParam>(Elem).Reg.Number, 34893247u);
   ASSERT_EQ(std::get<RootParam>(Elem).Space, 0u);
   ASSERT_EQ(std::get<RootParam>(Elem).Visibility, ShaderVisibility::Hull);
+  ASSERT_EQ(std::get<RootParam>(Elem).Flags, RootDescriptorFlags::DataVolatile);
+
+  Elem = Elements[3];
+  ASSERT_EQ(std::get<RootParam>(Elem).Reg.ViewType, RegisterType::BReg);
+  ASSERT_EQ(std::get<RootParam>(Elem).Reg.Number, 0u);
+  ASSERT_EQ(std::get<RootParam>(Elem).Space, 0u);
+  ASSERT_EQ(std::get<RootParam>(Elem).Visibility, ShaderVisibility::All);
+  ASSERT_EQ(std::get<RootParam>(Elem).Flags, RootDescriptorFlags::None);
 
   ASSERT_TRUE(Consumer->isSatisfied());
 }
diff --git a/llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h b/llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h
@@ -46,6 +46,14 @@ enum class RootFlags : uint32_t {
   ValidFlags = 0x00000fff
 };
 
+enum class RootDescriptorFlags : unsigned {
+  None = 0,
+  DataVolatile = 0x2,
+  DataStaticWhileSetAtExecute = 0x4,
+  DataStatic = 0x8,
+  ValidFlags = 0xe,
+};
+
 enum class DescriptorRangeFlags : unsigned {
   None = 0,
   DescriptorsVolatile = 0x1,
@@ -91,6 +99,23 @@ struct RootParam {
   Register Reg;
   uint32_t Space = 0;
   ShaderVisibility Visibility = ShaderVisibility::All;
+  RootDescriptorFlags Flags;
+
+  void setDefaultFlags() {
+    assert(Type != ParamType::Sampler &&
+           "Sampler is not a valid type of ParamType");
+    switch (Type) {
+    case ParamType::CBuffer:
+    case ParamType::SRV:
+      Flags = RootDescriptorFlags::DataStaticWhileSetAtExecute;
+      break;
+    case ParamType::UAV:
+      Flags = RootDescriptorFlags::DataVolatile;
+      break;
+    case ParamType::Sampler:
+      break;
+    }
+  }
 };
 
 // Models the end of a descriptor table and stores its visibility
