[HLSL] Rework semantic handling as attributes (#166796)

Previously, we had 2 level of attributes:
 - HLSLUnparsedSemantic
 - N attributes, one for each known system semantic.

The first was assigned during parsing, and carried no other meaning than
"there is a semantic token". It was then converted to one of the N
attributes later during Sema.
Those attributes also carried informations like "is indexable" or "is
index explicit".

This had a few issues:
- there was no difference between a semantic attribute applied to a
decl, and the effective semantic in the entrypoint use context.
 - having the indexable bit was not useful.
 - semantic constraints checks were split between .td files and sema.

Also, existing implementation had effective attributes attached to the
type decl or parameters, meaning struct decl reuse across entrypoints of
in a nested type was not supported, even if legal in HLSL.

This PR tried to simplifies semantic attribute by having 3 attributes:

 - HLSLUnpasedSemantic
 - HLSLParsedSemantic
 - HLSLAppliedSemantic

Initial parsing emits an `HLSLUnparsedSemantic`. We simply say "here is
an HLSL semantic token", but we don't do any semantic check.

Then, Sema does initial validation and transforms an UnparseSemantic
into a ParsedSemantic. This validates a system semantic is known, or
that the associated type is valid (like uint3 for a ThreadIndex).

Then, once we parse an actual shader entrypoint, we can know how
semantics are used in a real context. This step emits a list of
AppliedSemantic. Those are the actual semantic in use for this specific
entrypoint.
Those attributes are attached to each entrypoint parameter, as a flat
list matching the semantic structure flattening HLSL defines. At this
stage of sema, index collision or other stage compabitility checkes are
carried.

This allows codegen to simply iterate over this list and emit the proper
DXIL or SPIR-V codegen.

Author: Keenuts

clang/include/clang/AST/Attr.h

@@ -233,44 +233,19 @@ class HLSLAnnotationAttr : public InheritableAttr {
   }
 };
 
-class HLSLSemanticAttr : public HLSLAnnotationAttr {
-  unsigned SemanticIndex = 0;
-  LLVM_PREFERRED_TYPE(bool)
-  unsigned SemanticIndexable : 1;
-  LLVM_PREFERRED_TYPE(bool)
-  unsigned SemanticExplicitIndex : 1;
-
-  Decl *TargetDecl = nullptr;
-
+class HLSLSemanticBaseAttr : public HLSLAnnotationAttr {
 protected:
-  HLSLSemanticAttr(ASTContext &Context, const AttributeCommonInfo &CommonInfo,
-                   attr::Kind AK, bool IsLateParsed,
-                   bool InheritEvenIfAlreadyPresent, bool SemanticIndexable)
+  HLSLSemanticBaseAttr(ASTContext &Context,
+                       const AttributeCommonInfo &CommonInfo, attr::Kind AK,
+                       bool IsLateParsed, bool InheritEvenIfAlreadyPresent)
       : HLSLAnnotationAttr(Context, CommonInfo, AK, IsLateParsed,
-                           InheritEvenIfAlreadyPresent) {
-    this->SemanticIndexable = SemanticIndexable;
-    this->SemanticExplicitIndex = false;
-  }
+                           InheritEvenIfAlreadyPresent) {}
 
 public:
-  bool isSemanticIndexable() const { return SemanticIndexable; }
-
-  void setSemanticIndex(unsigned SemanticIndex) {
-    this->SemanticIndex = SemanticIndex;
-    this->SemanticExplicitIndex = true;
-  }
-
-  unsigned getSemanticIndex() const { return SemanticIndex; }
-
-  bool isSemanticIndexExplicit() const { return SemanticExplicitIndex; }
-
-  void setTargetDecl(Decl *D) { TargetDecl = D; }
-  Decl *getTargetDecl() const { return TargetDecl; }
-
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Attr *A) {
-    return A->getKind() >= attr::FirstHLSLSemanticAttr &&
-           A->getKind() <= attr::LastHLSLSemanticAttr;
+    return A->getKind() >= attr::FirstHLSLSemanticBaseAttr &&
+           A->getKind() <= attr::LastHLSLSemanticBaseAttr;
   }
 };
 

clang/include/clang/Basic/Attr.td

@@ -783,18 +783,6 @@ class DeclOrStmtAttr : InheritableAttr;
 /// An attribute class for HLSL Annotations.
 class HLSLAnnotationAttr : InheritableAttr;
 
-class HLSLSemanticAttr<bit Indexable> : HLSLAnnotationAttr {
-  bit SemanticIndexable = Indexable;
-  int SemanticIndex = 0;
-  bit SemanticExplicitIndex = 0;
-
-  let Spellings = [];
-  let Subjects = SubjectList<[ParmVar, Field, Function]>;
-  let LangOpts = [HLSL];
-  let Args = [DeclArgument<Named, "Target">, IntArgument<"SemanticIndex">,
-              BoolArgument<"SemanticExplicitIndex">];
-}
-
 /// A target-specific attribute.  This class is meant to be used as a mixin
 /// with InheritableAttr or Attr depending on the attribute's needs.
 class TargetSpecificAttr<TargetSpec target> {
@@ -5021,28 +5009,28 @@ def HLSLUnparsedSemantic : HLSLAnnotationAttr {
   let Documentation = [InternalOnly];
 }
 
-def HLSLUserSemantic : HLSLSemanticAttr</* Indexable= */ 1> {
-  let Documentation = [InternalOnly];
-}
-
-def HLSLSV_Position : HLSLSemanticAttr</* Indexable= */ 1> {
-  let Documentation = [HLSLSV_PositionDocs];
-}
+class HLSLSemanticBaseAttr : HLSLAnnotationAttr {
+  int SemanticIndex = 0;
 
-def HLSLSV_GroupThreadID : HLSLSemanticAttr</* Indexable= */ 0> {
-  let Documentation = [HLSLSV_GroupThreadIDDocs];
-}
+  let Spellings = [];
+  let Subjects = SubjectList<[ParmVar, Field, Function]>;
+  let LangOpts = [HLSL];
 
-def HLSLSV_GroupID : HLSLSemanticAttr</* Indexable= */ 0> {
-  let Documentation = [HLSLSV_GroupIDDocs];
+  let Args = [StringArgument<"SemanticName">, IntArgument<"SemanticIndex">];
 }
 
-def HLSLSV_GroupIndex : HLSLSemanticAttr</* Indexable= */ 0> {
-  let Documentation = [HLSLSV_GroupIndexDocs];
+def HLSLParsedSemantic : HLSLSemanticBaseAttr {
+  let Spellings = [];
+  let Subjects = SubjectList<[ParmVar, Field, Function]>;
+  let LangOpts = [HLSL];
+  let Documentation = [InternalOnly];
 }
 
-def HLSLSV_DispatchThreadID : HLSLSemanticAttr</* Indexable= */ 0> {
-  let Documentation = [HLSLSV_DispatchThreadIDDocs];
+def HLSLAppliedSemantic : HLSLSemanticBaseAttr {
+  let Spellings = [];
+  let Subjects = SubjectList<[ParmVar, Field, Function]>;
+  let LangOpts = [HLSL];
+  let Documentation = [InternalOnly];
 }
 
 def HLSLPackOffset: HLSLAnnotationAttr {

clang/include/clang/Basic/AttrDocs.td

@@ -8672,38 +8672,6 @@ randomized.
   }];
 }
 
-def HLSLSV_GroupThreadIDDocs : Documentation {
-  let Category = DocHLSLSemantics;
-  let Content = [{
-The ``SV_GroupThreadID`` semantic, when applied to an input parameter, specifies which
-individual thread within a thread group is executing in. This attribute is
-only supported in compute shaders.
-
-The full documentation is available here: https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/sv-groupthreadid
-  }];
-}
-
-def HLSLSV_GroupIDDocs : Documentation {
-  let Category = DocHLSLSemantics;
-  let Content = [{
-The ``SV_GroupID`` semantic, when applied to an input parameter, specifies which
-thread group a shader is executing in. This attribute is only supported in compute shaders.
-
-The full documentation is available here: https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/sv-groupid
-  }];
-}
-
-def HLSLSV_GroupIndexDocs : Documentation {
-  let Category = DocHLSLSemantics;
-  let Content = [{
-The ``SV_GroupIndex`` semantic, when applied to an input parameter, specifies a
-data binding to map the group index to the specified parameter. This attribute
-is only supported in compute shaders.
-
-The full documentation is available here: https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/sv-groupindex
-  }];
-}
-
 def HLSLResourceBindingDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{
@@ -8750,35 +8718,6 @@ The full documentation is available here: https://learn.microsoft.com/en-us/wind
   }];
 }
 
-def HLSLSV_DispatchThreadIDDocs : Documentation {
-  let Category = DocHLSLSemantics;
-  let Content = [{
-The ``SV_DispatchThreadID`` semantic, when applied to an input parameter,
-specifies a data binding to map the global thread offset within the Dispatch
-call (per dimension of the group) to the specified parameter.
-When applied to a field of a struct, the data binding is specified to the field
-when the struct is used as a parameter type.
-The semantic on the field is ignored when not used as a parameter.
-This attribute is only supported in compute shaders.
-
-The full documentation is available here: https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/sv-dispatchthreadid
-  }];
-}
-
-def HLSLSV_PositionDocs : Documentation {
-  let Category = DocHLSLSemantics;
-  let Content = [{
-The ``SV_Position`` semantic, when applied to an input parameter in a pixel
-shader, contains the location of the pixel center (x, y) in screen space.
-This semantic can be applied to the parameter, or a field in a struct used
-as an input parameter.
-This attribute is supported as an input in pixel, hull, domain and mesh shaders.
-This attribute is supported as an output in vertex, geometry and domain shaders.
-
-The full documentation is available here: https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-semantics
-  }];
-}
-
 def HLSLGroupSharedAddressSpaceDocs : Documentation {
   let Category = DocCatVariable;
   let Content = [{

clang/include/clang/Sema/SemaHLSL.h

@@ -178,18 +178,11 @@ class SemaHLSL : public SemaBase {
   bool handleResourceTypeAttr(QualType T, const ParsedAttr &AL);
 
   template <typename T>
-  T *createSemanticAttr(const AttributeCommonInfo &ACI, NamedDecl *TargetDecl,
+  T *createSemanticAttr(const AttributeCommonInfo &ACI,
                         std::optional<unsigned> Location) {
-    T *Attr =
-        ::new (getASTContext()) T(getASTContext(), ACI, TargetDecl,
-                                  Location.value_or(0), Location.has_value());
-
-    if (!Attr->isSemanticIndexable() && Location.has_value()) {
-      Diag(Attr->getLocation(), diag::err_hlsl_semantic_indexing_not_supported)
-          << Attr->getAttrName()->getName();
-      return nullptr;
-    }
-    return Attr;
+    return ::new (getASTContext())
+        T(getASTContext(), ACI, ACI.getAttrName()->getName(),
+          Location.value_or(0));
   }
 
   void diagnoseSystemSemanticAttr(Decl *D, const ParsedAttr &AL,
@@ -247,7 +240,7 @@ class SemaHLSL : public SemaBase {
   IdentifierInfo *RootSigOverrideIdent = nullptr;
 
   struct SemanticInfo {
-    HLSLSemanticAttr *Semantic;
+    HLSLParsedSemanticAttr *Semantic;
     std::optional<uint32_t> Index;
   };
 
@@ -257,14 +250,14 @@ class SemaHLSL : public SemaBase {
                                                const RecordType *RT);
 
   void checkSemanticAnnotation(FunctionDecl *EntryPoint, const Decl *Param,
-                               const HLSLSemanticAttr *SemanticAttr);
-  HLSLSemanticAttr *createSemantic(const SemanticInfo &Semantic,
-                                   DeclaratorDecl *TargetDecl);
-  bool determineActiveSemanticOnScalar(FunctionDecl *FD, DeclaratorDecl *D,
+                               const HLSLAppliedSemanticAttr *SemanticAttr);
+  bool determineActiveSemanticOnScalar(FunctionDecl *FD,
+                                       DeclaratorDecl *OutputDecl,
+                                       DeclaratorDecl *D,
                                        SemanticInfo &ActiveSemantic,
                                        llvm::StringSet<> &ActiveInputSemantics);
-  bool determineActiveSemantic(FunctionDecl *FD, DeclaratorDecl *D,
-                               SemanticInfo &ActiveSemantic,
+  bool determineActiveSemantic(FunctionDecl *FD, DeclaratorDecl *OutputDecl,
+                               DeclaratorDecl *D, SemanticInfo &ActiveSemantic,
                                llvm::StringSet<> &ActiveInputSemantics);
 
   void processExplicitBindingsOnDecl(VarDecl *D);