[HLSL][RootSignature] Handle an empty root signature

- Define the Parser struct
- Model RootElements as a variant of the different types
- Create a basic test case for unit testing

Author: inbelic

clang/include/clang/Parse/ParseHLSLRootSignature.h

@@ -22,9 +22,13 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
 
+#include "llvm/Frontend/HLSL/HLSLRootSignature.h"
+
 namespace clang {
 namespace hlsl {
 
+namespace rs = llvm::hlsl::root_signature;
+
 struct RootSignatureToken {
   enum Kind {
 #define TOK(X) X,
@@ -80,6 +84,28 @@ class RootSignatureLexer {
   }
 };
 
+class RootSignatureParser {
+public:
+  RootSignatureParser(SmallVector<rs::RootElement> &Elements,
+                      const SmallVector<RootSignatureToken> &Tokens,
+                      DiagnosticsEngine &Diags);
+
+  // Iterates over the provided tokens and constructs the in-memory
+  // representations of the RootElements.
+  //
+  // The return value denotes if there was a failure and the method will
+  // return on the first encountered failure, or, return false if it
+  // can sucessfully reach the end of the tokens.
+  bool Parse();
+
+private:
+  SmallVector<rs::RootElement> &Elements;
+  SmallVector<RootSignatureToken>::const_iterator CurTok;
+  SmallVector<RootSignatureToken>::const_iterator LastTok;
+
+  DiagnosticsEngine &Diags;
+};
+
 } // namespace hlsl
 } // namespace clang
 

clang/lib/Parse/ParseHLSLRootSignature.cpp

@@ -1,5 +1,7 @@
 #include "clang/Parse/ParseHLSLRootSignature.h"
 
+using namespace llvm::hlsl::root_signature;
+
 namespace clang {
 namespace hlsl {
 
@@ -169,5 +171,22 @@ bool RootSignatureLexer::LexToken(RootSignatureToken &Result) {
   return false;
 }
 
+// Parser Definitions
+
+RootSignatureParser::RootSignatureParser(
+    SmallVector<RootElement> &Elements,
+    const SmallVector<RootSignatureToken> &Tokens, DiagnosticsEngine &Diags)
+    : Elements(Elements), Diags(Diags) {
+  CurTok = Tokens.begin();
+  LastTok = Tokens.end();
+}
+
+bool RootSignatureParser::Parse() {
+  // Handle edge-case of empty RootSignature()
+  if (CurTok == LastTok)
+    return false;
+
+  return true;
+}
 } // namespace hlsl
 } // namespace clang

clang/unittests/Parse/ParseHLSLRootSignatureTest.cpp

@@ -24,6 +24,7 @@
 #include "gtest/gtest.h"
 
 using namespace clang;
+using namespace llvm::hlsl::root_signature;
 
 namespace {
 
@@ -279,4 +280,29 @@ TEST_F(ParseHLSLRootSignatureTest, InvalidLexIdentifierTest) {
   ASSERT_TRUE(Consumer->IsSatisfied());
 }
 
+// Valid Parser Tests
+
+TEST_F(ParseHLSLRootSignatureTest, ValidParseEmptyTest) {
+  const llvm::StringLiteral Source = R"cc()cc";
+
+  TrivialModuleLoader ModLoader;
+  auto PP = CreatePP(Source, ModLoader);
+  auto TokLoc = SourceLocation();
+
+  // Test no diagnostics produced
+  Consumer->SetNoDiag();
+  hlsl::RootSignatureLexer Lexer(Source, TokLoc, *PP);
+
+  SmallVector<hlsl::RootSignatureToken> Tokens;
+  ASSERT_FALSE(Lexer.Lex(Tokens));
+
+  SmallVector<RootElement> Elements;
+  hlsl::RootSignatureParser Parser(Elements, Tokens, Diags);
+
+  ASSERT_FALSE(Parser.Parse());
+  ASSERT_EQ((int)Elements.size(), 0);
+
+  ASSERT_TRUE(Consumer->IsSatisfied());
+}
+
 } // anonymous namespace

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

@@ -0,0 +1,30 @@
+//===- HLSLRootSignature.h - HLSL Root Signature helper objects -----------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file This file contains helper objects for working with HLSL Root
+/// Signatures.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_FRONTEND_HLSL_HLSLROOTSIGNATURE_H
+#define LLVM_FRONTEND_HLSL_HLSLROOTSIGNATURE_H
+
+#include <variant>
+
+namespace llvm {
+namespace hlsl {
+namespace root_signature {
+
+// Models RootElement
+using RootElement = std::variant<std::monostate>;
+
+} // namespace root_signature
+} // namespace hlsl
+} // namespace llvm
+
+#endif // LLVM_FRONTEND_HLSL_HLSLROOTSIGNATURE_H