[HLSL][RootSignature] Define and integrate rootsig clang attr and decl

inbelic · inbelic · commit 87680ba4a99d · 2025-05-09T19:47:56.000Z
- Defines a new declaration node `HLSLRootSignature` in `DeclNodes.td`
that will hold a reference to an in-memory construction of the root
signature, namely an array of `hlsl::rootsig::RootElement`s

- Defines a new clang attr `RootSignature` which simply holds an
identifier to a corresponding root signature declration as above

It was previously proposed that we could have the root elements
reference be stored directly as an additional member of the attribute
and to not have a seperate root signature decl. In contrast, by defining
them seperately as this change proposes, we will allow a unique root
signature to have its own declaration in the AST tree. This allows us
to only construct a single root signature for all duplicate rootsignature
attributes. Having it located directly as a declaration might also prove
advantageous when we consider root signature libraries.
diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
@@ -41,6 +41,7 @@
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/iterator_range.h"
+#include "llvm/Frontend/HLSL/HLSLRootSignature.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/TrailingObjects.h"
@@ -5178,6 +5179,29 @@ class HLSLBufferDecl final : public NamedDecl, public DeclContext {
   friend class ASTDeclWriter;
 };
 
+class HLSLRootSignatureDecl final : public NamedDecl {
+  ArrayRef<llvm::hlsl::rootsig::RootElement> RootElements;
+
+  HLSLRootSignatureDecl(
+      DeclContext *DC, SourceLocation Loc, IdentifierInfo *ID,
+      ArrayRef<llvm::hlsl::rootsig::RootElement> RootElements);
+
+public:
+  static HLSLRootSignatureDecl *
+  Create(ASTContext &C, DeclContext *DC, SourceLocation Loc, IdentifierInfo *ID,
+         ArrayRef<llvm::hlsl::rootsig::RootElement> RootElements);
+  static HLSLRootSignatureDecl *CreateDeserialized(ASTContext &C,
+                                                   GlobalDeclID ID);
+
+  ArrayRef<llvm::hlsl::rootsig::RootElement> &getRootElements() {
+    return RootElements;
+  }
+
+  // Implement isa/cast/dyncast/etc.
+  static bool classof(const Decl *D) { return classofKind(D->getKind()); }
+  static bool classofKind(Kind K) { return K == HLSLRootSignature; }
+};
+
 /// Insertion operator for diagnostics.  This allows sending NamedDecl's
 /// into a diagnostic with <<.
 inline const StreamingDiagnostic &operator<<(const StreamingDiagnostic &PD,
diff --git a/clang/include/clang/AST/RecursiveASTVisitor.h b/clang/include/clang/AST/RecursiveASTVisitor.h
@@ -1599,6 +1599,8 @@ DEF_TRAVERSE_DECL(EmptyDecl, {})
 
 DEF_TRAVERSE_DECL(HLSLBufferDecl, {})
 
+DEF_TRAVERSE_DECL(HLSLRootSignatureDecl, {})
+
 DEF_TRAVERSE_DECL(LifetimeExtendedTemporaryDecl, {
   TRY_TO(TraverseStmt(D->getTemporaryExpr()));
 })
diff --git a/clang/include/clang/AST/TextNodeDumper.h b/clang/include/clang/AST/TextNodeDumper.h
@@ -408,6 +408,7 @@ class TextNodeDumper
   void
   VisitLifetimeExtendedTemporaryDecl(const LifetimeExtendedTemporaryDecl *D);
   void VisitHLSLBufferDecl(const HLSLBufferDecl *D);
+  void VisitHLSLRootSignatureDecl(const HLSLRootSignatureDecl *D);
   void VisitHLSLOutArgExpr(const HLSLOutArgExpr *E);
   void VisitOpenACCConstructStmt(const OpenACCConstructStmt *S);
   void VisitOpenACCLoopConstruct(const OpenACCLoopConstruct *S);
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
@@ -4735,6 +4735,17 @@ def Error : InheritableAttr {
   let Documentation = [ErrorAttrDocs];
 }
 
+/// HLSL Root Signature Attribute
+def RootSignature : Attr {
+  /// [RootSignature(Signature)]
+  let Spellings = [Microsoft<"RootSignature">];
+  let Args = [IdentifierArgument<"Signature">];
+  let Subjects = SubjectList<[Function],
+                             ErrorDiag, "'function'">;
+  let LangOpts = [HLSL];
+  let Documentation = [RootSignatureDocs];
+}
+
 def HLSLNumThreads: InheritableAttr {
   let Spellings = [Microsoft<"numthreads">];
   let Args = [IntArgument<"X">, IntArgument<"Y">, IntArgument<"Z">];
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
@@ -8195,6 +8195,17 @@ and https://microsoft.github.io/hlsl-specs/proposals/0013-wave-size-range.html
   }];
 }
 
+def RootSignatureDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+The ``RootSignature`` attribute applies to HLSL entry functions to define what
+types of resources are bound to the graphics pipeline.
+
+For details about the use and specification of Root Signatures please see here:
+https://learn.microsoft.com/en-us/windows/win32/direct3d12/root-signatures
+  }];
+}
+
 def NumThreadsDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{
diff --git a/clang/include/clang/Basic/DeclNodes.td b/clang/include/clang/Basic/DeclNodes.td
@@ -111,5 +111,6 @@ def Empty : DeclNode<Decl>;
 def RequiresExprBody : DeclNode<Decl>, DeclContext;
 def LifetimeExtendedTemporary : DeclNode<Decl>;
 def HLSLBuffer : DeclNode<Named, "HLSLBuffer">, DeclContext;
+def HLSLRootSignature : DeclNode<Named, "HLSLRootSignature">;
 def OpenACCDeclare : DeclNode<Decl, "#pragma acc declare">;
 def OpenACCRoutine : DeclNode<Decl, "#pragma acc routine">;
diff --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
@@ -3093,6 +3093,7 @@ class Parser : public CodeCompletionHandler {
     return AttrsParsed;
   }
   void ParseMicrosoftUuidAttributeArgs(ParsedAttributes &Attrs);
+  void ParseMicrosoftRootSignatureAttributeArgs(ParsedAttributes &Attrs);
   void ParseMicrosoftAttributes(ParsedAttributes &Attrs);
   bool MaybeParseMicrosoftDeclSpecs(ParsedAttributes &Attrs) {
     if (getLangOpts().DeclSpecKeyword && Tok.is(tok::kw___declspec)) {
diff --git a/clang/include/clang/Sema/SemaHLSL.h b/clang/include/clang/Sema/SemaHLSL.h
@@ -119,6 +119,7 @@ class SemaHLSL : public SemaBase {
                                        bool IsCompAssign);
   void emitLogicalOperatorFixIt(Expr *LHS, Expr *RHS, BinaryOperatorKind Opc);
 
+  void handleRootSignatureAttr(Decl *D, const ParsedAttr &AL);
   void handleNumThreadsAttr(Decl *D, const ParsedAttr &AL);
   void handleWaveSizeAttr(Decl *D, const ParsedAttr &AL);
   void handleSV_DispatchThreadIDAttr(Decl *D, const ParsedAttr &AL);
diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
@@ -5847,6 +5847,31 @@ bool HLSLBufferDecl::buffer_decls_empty() {
   return DefaultBufferDecls.empty() && decls_empty();
 }
 
+//===----------------------------------------------------------------------===//
+// HLSLRootSignatureDecl Implementation
+//===----------------------------------------------------------------------===//
+
+HLSLRootSignatureDecl::HLSLRootSignatureDecl(
+    DeclContext *DC, SourceLocation Loc, IdentifierInfo *ID,
+    ArrayRef<llvm::hlsl::rootsig::RootElement> RootElements)
+    : NamedDecl(Decl::Kind::HLSLRootSignature, DC, Loc, DeclarationName(ID)),
+      RootElements(RootElements) {}
+
+HLSLRootSignatureDecl *HLSLRootSignatureDecl::Create(
+    ASTContext &C, DeclContext *DC, SourceLocation Loc, IdentifierInfo *ID,
+    ArrayRef<llvm::hlsl::rootsig::RootElement> RootElements) {
+  HLSLRootSignatureDecl *Result =
+      new (C, DC) HLSLRootSignatureDecl(DC, Loc, ID, RootElements);
+  return Result;
+}
+
+HLSLRootSignatureDecl *
+HLSLRootSignatureDecl::CreateDeserialized(ASTContext &C, GlobalDeclID ID) {
+  HLSLRootSignatureDecl *Result =
+      new (C, ID) HLSLRootSignatureDecl(nullptr, SourceLocation(), nullptr, {});
+  return Result;
+}
+
 //===----------------------------------------------------------------------===//
 // ImportDecl Implementation
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
@@ -886,6 +886,7 @@ unsigned Decl::getIdentifierNamespaceForKind(Kind DeclKind) {
     case ObjCProperty:
     case MSProperty:
     case HLSLBuffer:
+    case HLSLRootSignature:
       return IDNS_Ordinary;
     case Label:
       return IDNS_Label;
diff --git a/clang/lib/AST/TextNodeDumper.cpp b/clang/lib/AST/TextNodeDumper.cpp
@@ -3037,6 +3037,10 @@ void TextNodeDumper::VisitHLSLBufferDecl(const HLSLBufferDecl *D) {
   dumpName(D);
 }
 
+void TextNodeDumper::VisitHLSLRootSignatureDecl(const HLSLRootSignatureDecl *D) {
+  dumpName(D);
+}
+
 void TextNodeDumper::VisitHLSLOutArgExpr(const HLSLOutArgExpr *E) {
   OS << (E->isInOut() ? " inout" : " out");
 }
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
@@ -106,6 +106,7 @@ void CodeGenFunction::EmitDecl(const Decl &D, bool EvaluateConditionDecl) {
   case Decl::Binding:
   case Decl::UnresolvedUsingIfExists:
   case Decl::HLSLBuffer:
+  case Decl::HLSLRootSignature:
     llvm_unreachable("Declaration should not be in declstmts!");
   case Decl::Record:    // struct/union/class X;
   case Decl::CXXRecord: // struct/union/class X; [C++]
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -21,10 +21,12 @@
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/TokenKinds.h"
 #include "clang/Lex/LiteralSupport.h"
+#include "clang/Parse/ParseHLSLRootSignature.h"
 #include "clang/Parse/Parser.h"
 #include "clang/Parse/RAIIObjectsForParser.h"
 #include "clang/Sema/DeclSpec.h"
 #include "clang/Sema/EnterExpressionEvaluationContext.h"
+#include "clang/Sema/Lookup.h"
 #include "clang/Sema/ParsedTemplate.h"
 #include "clang/Sema/Scope.h"
 #include "clang/Sema/SemaCodeCompletion.h"
@@ -5311,6 +5313,92 @@ void Parser::ParseMicrosoftUuidAttributeArgs(ParsedAttributes &Attrs) {
   }
 }
 
+void Parser::ParseMicrosoftRootSignatureAttributeArgs(ParsedAttributes &Attrs) {
+  assert(Tok.is(tok::identifier) && "Not a Microsoft attribute list");
+  IdentifierInfo *RootSignatureIdent = Tok.getIdentifierInfo();
+  assert(RootSignatureIdent->getName() == "RootSignature" &&
+         "Not a Microsoft attribute list");
+
+  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;
+  }
+
+  if (!isTokenStringLiteral()) {
+    Diag(Tok, diag::err_expected_string_literal)
+        << /*in attributes...*/ 4 << RootSignatureIdent->getName();
+    SkipUntil(tok::r_square, StopAtSemi | StopBeforeMatch);
+    if (Tok.is(tok::r_paren))
+      T.consumeClose();
+    return;
+  }
+
+  ExprResult StringResult = ParseUnevaluatedStringLiteralExpression();
+  if (StringResult.isInvalid()) {
+    SkipUntil(tok::r_square, StopAtSemi | StopBeforeMatch);
+    if (Tok.is(tok::r_paren))
+      T.consumeClose();
+    return;
+  }
+
+  ArgsVector Args;
+  if (auto Lit = dyn_cast<StringLiteral>(StringResult.get())) {
+    // Construct our identifier
+    StringRef Signature = Lit->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)) {
+      // Invoke the root signature parser to construct the in-memory constructs
+      hlsl::RootSignatureLexer Lexer(Signature, RootSignatureLoc);
+      SmallVector<llvm::hlsl::rootsig::RootElement> Elements;
+      hlsl::RootSignatureParser Parser(Elements, Lexer, PP);
+      if (Parser.parse()) {
+        SkipUntil(tok::r_square, StopAtSemi | StopBeforeMatch);
+        if (Tok.is(tok::r_paren))
+          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];
+
+      // Create the Root Signature
+      auto *SignatureDecl = HLSLRootSignatureDecl::Create(
+          Actions.getASTContext(), /*FIXME?*/ Actions.CurContext,
+          RootSignatureLoc, DeclIdent, RootElements);
+      SignatureDecl->setImplicit();
+      Actions.PushOnScopeChains(SignatureDecl, getCurScope());
+    }
+
+    // Create the arg for the ParsedAttr
+    IdentifierLoc *ILoc = ::new (Actions.getASTContext())
+        IdentifierLoc(RootSignatureLoc, DeclIdent);
+    Args.push_back(ILoc);
+  }
+
+  if (!T.consumeClose())
+    Attrs.addNew(RootSignatureIdent,
+                 SourceRange(RootSignatureLoc, T.getCloseLocation()), nullptr,
+                 SourceLocation(), Args.data(), Args.size(),
+                 ParsedAttr::Form::Microsoft());
+}
+
 /// ParseMicrosoftAttributes - Parse Microsoft attributes [Attr]
 ///
 /// [MS] ms-attribute:
@@ -5345,6 +5433,8 @@ void Parser::ParseMicrosoftAttributes(ParsedAttributes &Attrs) {
         break;
       if (Tok.getIdentifierInfo()->getName() == "uuid")
         ParseMicrosoftUuidAttributeArgs(Attrs);
+      else if (Tok.getIdentifierInfo()->getName() == "RootSignature")
+        ParseMicrosoftRootSignatureAttributeArgs(Attrs);
       else {
         IdentifierInfo *II = Tok.getIdentifierInfo();
         SourceLocation NameLoc = Tok.getLocation();
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -7481,6 +7481,9 @@ ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D, const ParsedAttr &AL,
     break;
 
   // HLSL attributes:
+  case ParsedAttr::AT_RootSignature:
+    S.HLSL().handleRootSignatureAttr(D, AL);
+    break;
   case ParsedAttr::AT_HLSLNumThreads:
     S.HLSL().handleNumThreadsAttr(D, AL);
     break;
diff --git a/clang/lib/Sema/SemaHLSL.cpp b/clang/lib/Sema/SemaHLSL.cpp
@@ -29,6 +29,7 @@
 #include "clang/Basic/Specifiers.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Sema/Initialization.h"
+#include "clang/Sema/Lookup.h"
 #include "clang/Sema/ParsedAttr.h"
 #include "clang/Sema/Sema.h"
 #include "clang/Sema/Template.h"
@@ -950,6 +951,23 @@ void SemaHLSL::emitLogicalOperatorFixIt(Expr *LHS, Expr *RHS,
       << NewFnName << FixItHint::CreateReplacement(FullRange, OS.str());
 }
 
+void SemaHLSL::handleRootSignatureAttr(Decl *D, const ParsedAttr &AL) {
+  if (AL.getNumArgs() != 1) {
+    Diag(AL.getLoc(), diag::err_attribute_wrong_number_arguments) << AL << 1;
+    return;
+  }
+
+  IdentifierInfo *Ident = AL.getArgAsIdent(0)->getIdentifierInfo();
+  LookupResult R(SemaRef, Ident, SourceLocation(), Sema::LookupOrdinaryName);
+  if (SemaRef.LookupQualifiedName(R, D->getDeclContext()))
+    if (auto *SignatureDecl =
+            dyn_cast<HLSLRootSignatureDecl>(R.getFoundDecl())) {
+      // Perform validation of constructs here
+      D->addAttr(::new (getASTContext())
+                     RootSignatureAttr(getASTContext(), AL, Ident));
+    }
+}
+
 void SemaHLSL::handleNumThreadsAttr(Decl *D, const ParsedAttr &AL) {
   llvm::VersionTuple SMVersion =
       getASTContext().getTargetInfo().getTriple().getOSVersion();
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -999,6 +999,11 @@ Decl *TemplateDeclInstantiator::VisitHLSLBufferDecl(HLSLBufferDecl *Decl) {
   llvm_unreachable("HLSL buffer declarations cannot be instantiated");
 }
 
+Decl *TemplateDeclInstantiator::VisitHLSLRootSignatureDecl(
+    HLSLRootSignatureDecl *Decl) {
+  llvm_unreachable("HLSL root signature declarations cannot be instantiated");
+}
+
 Decl *
 TemplateDeclInstantiator::VisitPragmaCommentDecl(PragmaCommentDecl *D) {
   llvm_unreachable("pragma comment cannot be instantiated");
diff --git a/clang/lib/Serialization/ASTCommon.cpp b/clang/lib/Serialization/ASTCommon.cpp
@@ -458,6 +458,7 @@ bool serialization::isRedeclarableDeclKind(unsigned Kind) {
   case Decl::RequiresExprBody:
   case Decl::UnresolvedUsingIfExists:
   case Decl::HLSLBuffer:
+  case Decl::HLSLRootSignature:
   case Decl::OpenACCDeclare:
   case Decl::OpenACCRoutine:
     return false;
diff --git a/clang/test/AST/HLSL/RootSignatures-AST.hlsl b/clang/test/AST/HLSL/RootSignatures-AST.hlsl
diff --git a/clang/test/SemaHLSL/RootSignature-err.hlsl b/clang/test/SemaHLSL/RootSignature-err.hlsl
diff --git a/clang/tools/libclang/CIndex.cpp b/clang/tools/libclang/CIndex.cpp

Original file line number	Diff line number	Diff line change
`@@ -3093,6 +3093,7 @@ class Parser : public CodeCompletionHandler {`
`3093`	`3093`	`return AttrsParsed;`
`3094`	`3094`	`}`
`3095`	`3095`	`void ParseMicrosoftUuidAttributeArgs(ParsedAttributes &Attrs);`
	`3096`	`+ void ParseMicrosoftRootSignatureAttributeArgs(ParsedAttributes &Attrs);`
`3096`	`3097`	`void ParseMicrosoftAttributes(ParsedAttributes &Attrs);`
`3097`	`3098`	`bool MaybeParseMicrosoftDeclSpecs(ParsedAttributes &Attrs) {`
`3098`	`3099`	`if (getLangOpts().DeclSpecKeyword && Tok.is(tok::kw___declspec)) {`