[HLSL] Implement default constant buffer $Globals (2nd attempt)

clang/include/clang/AST/Decl.h

@@ -5045,22 +5045,26 @@ class HLSLBufferDecl final : public NamedDecl, public DeclContext {
   // LayoutStruct - Layout struct for the buffer
   CXXRecordDecl *LayoutStruct;
 
-  // For default (implicit) constant buffer, a lisf of references of global
+  // For default (implicit) constant buffer, an array of references of global
   // decls that belong to the buffer. The decls are already parented by the
-  // translation unit context.
-  SmallVector<Decl *> DefaultBufferDecls;
+  // translation unit context. The array is allocated by the ASTContext
+  // allocator in HLSLBufferDecl::CreateDefaultCBuffer.
+  ArrayRef<Decl *> DefaultBufferDecls;
 
   HLSLBufferDecl(DeclContext *DC, bool CBuffer, SourceLocation KwLoc,
                  IdentifierInfo *ID, SourceLocation IDLoc,
                  SourceLocation LBrace);
 
+  void setDefaultBufferDecls(ArrayRef<Decl *> Decls);
+
 public:
   static HLSLBufferDecl *Create(ASTContext &C, DeclContext *LexicalParent,
                                 bool CBuffer, SourceLocation KwLoc,
                                 IdentifierInfo *ID, SourceLocation IDLoc,
                                 SourceLocation LBrace);
-  static HLSLBufferDecl *CreateDefaultCBuffer(ASTContext &C,
-                                              DeclContext *LexicalParent);
+  static HLSLBufferDecl *
+  CreateDefaultCBuffer(ASTContext &C, DeclContext *LexicalParent,
+                       ArrayRef<Decl *> DefaultCBufferDecls);
   static HLSLBufferDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   SourceRange getSourceRange() const override LLVM_READONLY {
@@ -5075,7 +5079,6 @@ class HLSLBufferDecl final : public NamedDecl, public DeclContext {
   bool hasValidPackoffset() const { return HasValidPackoffset; }
   const CXXRecordDecl *getLayoutStruct() const { return LayoutStruct; }
   void addLayoutStruct(CXXRecordDecl *LS);
-  void addDefaultBufferDecl(Decl *D);
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }

clang/include/clang/Sema/SemaHLSL.h

@@ -168,8 +168,9 @@ class SemaHLSL : public SemaBase {
   // List of all resource bindings
   ResourceBindings Bindings;
 
-  // default constant buffer $Globals
-  HLSLBufferDecl *DefaultCBuffer;
+  // Global declaration collected for the $Globals default constant
+  // buffer which will be created at the end of the translation unit.
+  llvm::SmallVector<Decl *> DefaultCBufferDecls;
 
 private:
   void collectResourceBindingsOnVarDecl(VarDecl *D);

clang/lib/AST/Decl.cpp

@@ -5747,13 +5747,20 @@ HLSLBufferDecl *HLSLBufferDecl::Create(ASTContext &C,
 }
 
 HLSLBufferDecl *
-HLSLBufferDecl::CreateDefaultCBuffer(ASTContext &C,
-                                     DeclContext *LexicalParent) {
+HLSLBufferDecl::CreateDefaultCBuffer(ASTContext &C, DeclContext *LexicalParent,
+                                     ArrayRef<Decl *> DefaultCBufferDecls) {
   DeclContext *DC = LexicalParent;
   IdentifierInfo *II = &C.Idents.get("$Globals", tok::TokenKind::identifier);
   HLSLBufferDecl *Result = new (C, DC) HLSLBufferDecl(
       DC, true, SourceLocation(), II, SourceLocation(), SourceLocation());
   Result->setImplicit(true);
+
+  // allocate array for default decls with ASTContext allocator
+  assert(!DefaultCBufferDecls.empty());
+  Decl **DeclsArray = new (C) Decl *[DefaultCBufferDecls.size()];
+  std::copy(DefaultCBufferDecls.begin(), DefaultCBufferDecls.end(), DeclsArray);
+  Result->setDefaultBufferDecls(
+      ArrayRef<Decl *>(DeclsArray, DefaultCBufferDecls.size()));
   return Result;
 }
 
@@ -5769,11 +5776,11 @@ void HLSLBufferDecl::addLayoutStruct(CXXRecordDecl *LS) {
   addDecl(LS);
 }
 
-void HLSLBufferDecl::addDefaultBufferDecl(Decl *D) {
+void HLSLBufferDecl::setDefaultBufferDecls(ArrayRef<Decl *> Decls) {
   assert(isImplicit() &&
          "default decls can only be added to the implicit/default constant "
          "buffer $Globals");
-  DefaultBufferDecls.push_back(D);
+  DefaultBufferDecls = Decls;
 }
 
 HLSLBufferDecl::buffer_decl_iterator

clang/lib/Sema/SemaHLSL.cpp

@@ -148,7 +148,7 @@ bool ResourceBindings::hasBindingInfoForDecl(const VarDecl *VD) const {
   return DeclToBindingListIndex.contains(VD);
 }
 
-SemaHLSL::SemaHLSL(Sema &S) : SemaBase(S), DefaultCBuffer(nullptr) {}
+SemaHLSL::SemaHLSL(Sema &S) : SemaBase(S) {}
 
 Decl *SemaHLSL::ActOnStartBuffer(Scope *BufferScope, bool CBuffer,
                                  SourceLocation KwLoc, IdentifierInfo *Ident,
@@ -1931,7 +1931,10 @@ void DiagnoseHLSLAvailability::CheckDeclAvailability(NamedDecl *D,
 
 void SemaHLSL::ActOnEndOfTranslationUnit(TranslationUnitDecl *TU) {
   // process default CBuffer - create buffer layout struct and invoke codegenCGH
-  if (DefaultCBuffer) {
+  if (!DefaultCBufferDecls.empty()) {
+    HLSLBufferDecl *DefaultCBuffer = HLSLBufferDecl::CreateDefaultCBuffer(
+        SemaRef.getASTContext(), SemaRef.getCurLexicalContext(),
+        DefaultCBufferDecls);
     SemaRef.getCurLexicalContext()->addDecl(DefaultCBuffer);
     createHostLayoutStructForBuffer(SemaRef, DefaultCBuffer);
 
@@ -3025,16 +3028,13 @@ void SemaHLSL::ActOnVariableDeclarator(VarDecl *VD) {
 
     // Global variables outside a cbuffer block that are not a resource, static,
     // groupshared, or an empty array or struct belong to the default constant
-    // buffer $Globals
+    // buffer $Globals (to be created at the end of the translation unit).
     if (IsDefaultBufferConstantDecl(VD)) {
-      if (DefaultCBuffer == nullptr)
-        DefaultCBuffer = HLSLBufferDecl::CreateDefaultCBuffer(
-            SemaRef.getASTContext(), SemaRef.getCurLexicalContext());
       // update address space to hlsl_constant
       QualType NewTy = getASTContext().getAddrSpaceQualType(
           VD->getType(), LangAS::hlsl_constant);
       VD->setType(NewTy);
-      DefaultCBuffer->addDefaultBufferDecl(VD);
+      DefaultCBufferDecls.push_back(VD);
     }
 
     // find all resources bindings on decl