[HLSL][RootSignature] Add parsing of Register in params for RootDescriptors (#140148)

- defines the `parseRootDescriptorParams` infrastructure for parsing the
params of a `RootDescriptor`
- defines the register type to illustrate use
- add tests to demonstrate functionality

Part 2 of https://github.com/llvm/llvm-project/issues/126577

clang/include/clang/Parse/ParseHLSLRootSignature.h

@@ -89,6 +89,12 @@ private:
   };
   std::optional<ParsedConstantParams> parseRootConstantParams();
 
+  struct ParsedRootDescriptorParams {
+    std::optional<llvm::hlsl::rootsig::Register> Reg;
+  };
+  std::optional<ParsedRootDescriptorParams>
+  parseRootDescriptorParams(RootSignatureToken::Kind RegType);
+
   struct ParsedClauseParams {
     std::optional<llvm::hlsl::rootsig::Register> Reg;
     std::optional<uint32_t> NumDescriptors;

clang/lib/Parse/ParseHLSLRootSignature.cpp

@@ -176,20 +176,37 @@ std::optional<RootDescriptor> RootSignatureParser::parseRootDescriptor() {
     return std::nullopt;
 
   RootDescriptor Descriptor;
+  TokenKind ExpectedReg;
   switch (DescriptorKind) {
   default:
     llvm_unreachable("Switch for consumed token was not provided");
   case TokenKind::kw_CBV:
     Descriptor.Type = DescriptorType::CBuffer;
+    ExpectedReg = TokenKind::bReg;
     break;
   case TokenKind::kw_SRV:
     Descriptor.Type = DescriptorType::SRV;
+    ExpectedReg = TokenKind::tReg;
     break;
   case TokenKind::kw_UAV:
     Descriptor.Type = DescriptorType::UAV;
+    ExpectedReg = TokenKind::uReg;
     break;
   }
 
+  auto Params = parseRootDescriptorParams(ExpectedReg);
+  if (!Params.has_value())
+    return std::nullopt;
+
+  // Check mandatory parameters were provided
+  if (!Params->Reg.has_value()) {
+    getDiags().Report(CurToken.TokLoc, diag::err_hlsl_rootsig_missing_param)
+        << ExpectedReg;
+    return std::nullopt;
+  }
+
+  Descriptor.Reg = Params->Reg.value();
+
   if (consumeExpectedToken(TokenKind::pu_r_paren,
                            diag::err_hlsl_unexpected_end_of_params,
                            /*param of=*/TokenKind::kw_RootConstants))
@@ -398,6 +415,31 @@ RootSignatureParser::parseRootConstantParams() {
   return Params;
 }
 
+std::optional<RootSignatureParser::ParsedRootDescriptorParams>
+RootSignatureParser::parseRootDescriptorParams(TokenKind RegType) {
+  assert(CurToken.TokKind == TokenKind::pu_l_paren &&
+         "Expects to only be invoked starting at given token");
+
+  ParsedRootDescriptorParams Params;
+  do {
+    // ( `b` | `t` | `u`) POS_INT
+    if (tryConsumeExpectedToken(RegType)) {
+      if (Params.Reg.has_value()) {
+        getDiags().Report(CurToken.TokLoc, diag::err_hlsl_rootsig_repeat_param)
+            << CurToken.TokKind;
+        return std::nullopt;
+      }
+      auto Reg = parseRegister();
+      if (!Reg.has_value())
+        return std::nullopt;
+      Params.Reg = Reg;
+    }
+
+  } while (tryConsumeExpectedToken(TokenKind::pu_comma));
+
+  return Params;
+}
+
 std::optional<RootSignatureParser::ParsedClauseParams>
 RootSignatureParser::parseDescriptorTableClauseParams(TokenKind RegType) {
   assert(CurToken.TokKind == TokenKind::pu_l_paren &&

clang/unittests/Parse/ParseHLSLRootSignatureTest.cpp

@@ -346,9 +346,9 @@ TEST_F(ParseHLSLRootSignatureTest, ValidParseRootFlagsTest) {
 
 TEST_F(ParseHLSLRootSignatureTest, ValidParseRootDescriptorsTest) {
   const llvm::StringLiteral Source = R"cc(
-    CBV(),
-    SRV(),
-    UAV()
+    CBV(b0),
+    SRV(t42),
+    UAV(u34893247)
   )cc";
 
   TrivialModuleLoader ModLoader;
@@ -369,14 +369,20 @@ TEST_F(ParseHLSLRootSignatureTest, ValidParseRootDescriptorsTest) {
   RootElement Elem = Elements[0];
   ASSERT_TRUE(std::holds_alternative<RootDescriptor>(Elem));
   ASSERT_EQ(std::get<RootDescriptor>(Elem).Type, DescriptorType::CBuffer);
+  ASSERT_EQ(std::get<RootDescriptor>(Elem).Reg.ViewType, RegisterType::BReg);
+  ASSERT_EQ(std::get<RootDescriptor>(Elem).Reg.Number, 0u);
 
   Elem = Elements[1];
   ASSERT_TRUE(std::holds_alternative<RootDescriptor>(Elem));
   ASSERT_EQ(std::get<RootDescriptor>(Elem).Type, DescriptorType::SRV);
+  ASSERT_EQ(std::get<RootDescriptor>(Elem).Reg.ViewType, RegisterType::TReg);
+  ASSERT_EQ(std::get<RootDescriptor>(Elem).Reg.Number, 42u);
 
   Elem = Elements[2];
   ASSERT_TRUE(std::holds_alternative<RootDescriptor>(Elem));
   ASSERT_EQ(std::get<RootDescriptor>(Elem).Type, DescriptorType::UAV);
+  ASSERT_EQ(std::get<RootDescriptor>(Elem).Reg.ViewType, RegisterType::UReg);
+  ASSERT_EQ(std::get<RootDescriptor>(Elem).Reg.Number, 34893247u);
 
   ASSERT_TRUE(Consumer->isSatisfied());
 }
@@ -494,6 +500,28 @@ TEST_F(ParseHLSLRootSignatureTest, InvalidMissingDTParameterTest) {
   ASSERT_TRUE(Consumer->isSatisfied());
 }
 
+TEST_F(ParseHLSLRootSignatureTest, InvalidMissingRDParameterTest) {
+  // This test will check that the parsing fails due a mandatory
+  // parameter (register) not being specified
+  const llvm::StringLiteral Source = R"cc(
+    SRV()
+  )cc";
+
+  TrivialModuleLoader ModLoader;
+  auto PP = createPP(Source, ModLoader);
+  auto TokLoc = SourceLocation();
+
+  hlsl::RootSignatureLexer Lexer(Source, TokLoc);
+  SmallVector<RootElement> Elements;
+  hlsl::RootSignatureParser Parser(Elements, Lexer, *PP);
+
+  // Test correct diagnostic produced
+  Consumer->setExpected(diag::err_hlsl_rootsig_missing_param);
+  ASSERT_TRUE(Parser.parse());
+
+  ASSERT_TRUE(Consumer->isSatisfied());
+}
+
 TEST_F(ParseHLSLRootSignatureTest, InvalidMissingRCParameterTest) {
   // This test will check that the parsing fails due a mandatory
   // parameter (num32BitConstants) not being specified

llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h

@@ -89,6 +89,7 @@ using DescriptorType = llvm::dxil::ResourceClass;
 // Models RootDescriptor : CBV | SRV | UAV, by collecting like parameters
 struct RootDescriptor {
   DescriptorType Type;
+  Register Reg;
 };
 
 // Models the end of a descriptor table and stores its visibility