[clang] [HLSL][RootSignature] Define and integrate rootsig clang attr and decl (PR #137690)

[Finn Plummer via cfe-commits]

================
@@ -5209,6 +5211,97 @@ void Parser::ParseMicrosoftUuidAttributeArgs(ParsedAttributes &Attrs) {
   }
 }
 
+void Parser::ParseMicrosoftRootSignatureAttributeArgs(ParsedAttributes &Attrs) {
+  assert(Tok.is(tok::identifier) &&
+         "Expected an identifier to denote which MS attribute to consider");
+  IdentifierInfo *RootSignatureIdent = Tok.getIdentifierInfo();
+  assert(RootSignatureIdent->getName() == "RootSignature" &&
+         "Expected RootSignature identifier for root signature attribute");
+
+  SourceLocation RootSignatureLoc = Tok.getLocation();
+  ConsumeToken();
+
+  // Ignore the left paren location for now.
+  BalancedDelimiterTracker T(*this, tok::l_paren);
+  if (T.consumeOpen()) {
+    Diag(Tok, diag::err_expected) << tok::l_paren;
+    return;
+  }
+
+  auto ProcessStringLiteral = [this]() -> std::optional<StringLiteral *> {
+    if (!isTokenStringLiteral())
+      return std::nullopt;
+
+    ExprResult StringResult = ParseUnevaluatedStringLiteralExpression();
+    if (StringResult.isInvalid())
+      return std::nullopt;
+
+    if (auto Lit = dyn_cast<StringLiteral>(StringResult.get()))
+      return Lit;
+
+    return std::nullopt;
+  };
+
+  auto StrLiteral = ProcessStringLiteral();
+  if (!StrLiteral.has_value()) {
+    Diag(Tok, diag::err_expected_string_literal)
+        << /*in attributes...*/ 4 << RootSignatureIdent->getName();
+    SkipUntil(tok::r_paren, StopAtSemi | StopBeforeMatch);
+    T.consumeClose();
+    return;
+  }
+
+  // Construct our identifier
+  StringRef Signature = StrLiteral.value()->getString();
+  auto Hash = llvm::hash_value(Signature);
+  std::string IdStr = "__hlsl_rootsig_decl_" + std::to_string(Hash);
+  IdentifierInfo *DeclIdent = &(Actions.getASTContext().Idents.get(IdStr));
+
+  LookupResult R(Actions, DeclIdent, SourceLocation(),
+                 Sema::LookupOrdinaryName);
+  // Check if we have already found a decl of the same name, if we haven't
+  // then parse the root signature string and construct the in-memory elements
+  if (!Actions.LookupQualifiedName(R, Actions.CurContext)) {
+    SourceLocation SignatureLoc =
+        StrLiteral.value()->getExprLoc().getLocWithOffset(
+            1); // offset 1 for '"'
+    // Invoke the root signature parser to construct the in-memory constructs
+    hlsl::RootSignatureLexer Lexer(Signature, SignatureLoc);
+    SmallVector<llvm::hlsl::rootsig::RootElement> Elements;
+    hlsl::RootSignatureParser Parser(Elements, Lexer, PP);
+    if (Parser.parse()) {
+      T.consumeClose();
+      return;
+    }
+
+    // Allocate the root elements onto ASTContext
+    unsigned N = Elements.size();
+    auto RootElements = MutableArrayRef<llvm::hlsl::rootsig::RootElement>(
+        ::new (Actions.getASTContext()) llvm::hlsl::rootsig::RootElement[N], N);
+    for (unsigned I = 0; I < N; ++I)
+      RootElements[I] = Elements[I];
----------------
inbelic wrote:

Whoops this should be able to get deleted now and we can just pass `Elements` where `RootElements is below

https://github.com/llvm/llvm-project/pull/137690