[clang] [HLSL] cbuffer: Create host layout structs (PR #122820)

[Helena Kotas via cfe-commits]

================
@@ -253,12 +257,229 @@ static void validatePackoffset(Sema &S, HLSLBufferDecl *BufDecl) {
   }
 }
 
+// Returns true if the array has a zero size = if any of the dimensions is 0
+static bool isZeroSizedArray(const ConstantArrayType *CAT) {
+  while (CAT && !CAT->isZeroSize())
+    CAT = dyn_cast<ConstantArrayType>(
+        CAT->getElementType()->getUnqualifiedDesugaredType());
+  return CAT != nullptr;
+}
+
+// Returns true if the struct contains at least one element that prevents it
+// from being included inside HLSL Buffer as is, such as an intangible type,
+// empty struct, or zero-sized array. If it does, a new implicit layout struct
+// needs to be created for HLSL Buffer use that will exclude these unwanted
+// declarations (see createHostLayoutStruct function).
+static bool requiresImplicitBufferLayoutStructure(const CXXRecordDecl *RD) {
+  if (RD->getTypeForDecl()->isHLSLIntangibleType() || RD->isEmpty())
+    return true;
+  // check fields
+  for (const FieldDecl *Field : RD->fields()) {
+    QualType Ty = Field->getType();
+    if (Ty->isRecordType()) {
+      if (requiresImplicitBufferLayoutStructure(Ty->getAsCXXRecordDecl()))
+        return true;
+    } else if (Ty->isConstantArrayType()) {
+      if (isZeroSizedArray(cast<ConstantArrayType>(Ty)))
+        return true;
+    }
+  }
+  // check bases
+  for (const CXXBaseSpecifier &Base : RD->bases())
+    if (requiresImplicitBufferLayoutStructure(
+            Base.getType()->getAsCXXRecordDecl()))
+      return true;
+  return false;
+}
+
+static CXXRecordDecl *findRecordDecl(Sema &S, IdentifierInfo *II,
+                                     DeclContext *DC) {
+  DeclarationNameInfo NameInfo =
+      DeclarationNameInfo(DeclarationName(II), SourceLocation());
+  LookupResult R(S, NameInfo, Sema::LookupOrdinaryName);
+  S.LookupName(R, S.getScopeForContext(DC));
+  if (R.isSingleResult())
+    return R.getAsSingle<CXXRecordDecl>();
+  return nullptr;
+}
+
+// Creates a name for buffer layout struct using the provide name base.
+// If the name must be unique (not previously defined), a suffix is added
+// until a unique name is found.
+static IdentifierInfo *getHostLayoutStructName(Sema &S,
+                                               IdentifierInfo *NameBaseII,
+                                               bool MustBeUnique,
+                                               DeclContext *DC) {
+  ASTContext &AST = S.getASTContext();
+  std::string NameBase;
+  if (NameBaseII) {
+    NameBase = NameBaseII->getName().str();
+  } else {
+    // anonymous struct
+    NameBase = "anon";
+    MustBeUnique = true;
+  }
+
+  std::string Name = "__layout_" + NameBase;
+  IdentifierInfo *II = &AST.Idents.get(Name, tok::TokenKind::identifier);
+  if (!MustBeUnique)
+    return II;
+
+  unsigned suffix = 0;
+  while (true) {
+    if (suffix != 0)
+      II = &AST.Idents.get((llvm::Twine(Name) + "_" + Twine(suffix)).str(),
+                           tok::TokenKind::identifier);
+    if (!findRecordDecl(S, II, DC))
+      return II;
+    // declaration with that name already exists - increment suffix and try
+    // again until unique name is found
+    suffix++;
+  };
+}
+
+// Returns true if the record type is an HLSL resource class
+static bool isResourceRecordType(const Type *Ty) {
+  return HLSLAttributedResourceType::findHandleTypeOnResource(Ty) != nullptr;
+}
+
+static CXXRecordDecl *createHostLayoutStruct(Sema &S, CXXRecordDecl *StructDecl,
+                                             HLSLBufferDecl *BufDecl);
+
+// Creates a field declaration of given name and type for HLSL buffer layout
+// struct. Returns nullptr if the type cannot be use in HLSL Buffer layout.
+static FieldDecl *createFieldForHostLayoutStruct(Sema &S, const Type *Ty,
+                                                 IdentifierInfo *II,
+                                                 CXXRecordDecl *LayoutStruct,
+                                                 HLSLBufferDecl *BufDecl) {
+  if (Ty->isRecordType()) {
+    if (isResourceRecordType(Ty))
+      return nullptr;
+    CXXRecordDecl *RD = Ty->getAsCXXRecordDecl();
+    if (requiresImplicitBufferLayoutStructure(RD)) {
+      RD = createHostLayoutStruct(S, RD, BufDecl);
+      if (!RD)
+        return nullptr;
+      Ty = RD->getTypeForDecl();
+    }
+  } else if (Ty->isConstantArrayType()) {
+    if (isZeroSizedArray(cast<ConstantArrayType>(Ty)))
+      return nullptr;
+  }
+  QualType QT = QualType(Ty, 0);
+  ASTContext &AST = S.getASTContext();
+  TypeSourceInfo *TSI = AST.getTrivialTypeSourceInfo(QT, SourceLocation());
+  auto *Field = FieldDecl::Create(AST, LayoutStruct, SourceLocation(),
+                                  SourceLocation(), II, QT, TSI, nullptr, false,
+                                  InClassInitStyle::ICIS_NoInit);
+  Field->setAccess(AccessSpecifier::AS_private);
+  return Field;
+}
+
+// Creates host layout struct for a struct included in HLSL Buffer.
+// The layout struct will include only fields that are allowed in HLSL buffer.
+// These fields will be filtered out:
+// - resource classes
+// - empty structs
+// - zero-sized arrays
+// Returns nullptr if the resulting layout struct would be empty.
+static CXXRecordDecl *createHostLayoutStruct(Sema &S, CXXRecordDecl *StructDecl,
+                                             HLSLBufferDecl *BufDecl) {
+  assert(requiresImplicitBufferLayoutStructure(StructDecl) &&
+         "struct is already HLSL buffer compatible");
+
+  ASTContext &AST = S.getASTContext();
+  DeclContext *DC = StructDecl->getDeclContext();
+  IdentifierInfo *II = getHostLayoutStructName(
+      S, StructDecl->getIdentifier(), false, BufDecl->getDeclContext());
+
+  // reuse existing if the layout struct if it already exists
+  if (CXXRecordDecl *RD = findRecordDecl(S, II, DC))
+    return RD;
+
+  CXXRecordDecl *LS =
+      CXXRecordDecl::Create(AST, TagDecl::TagKind::Class, BufDecl,
+                            SourceLocation(), SourceLocation(), II);
+  LS->setImplicit(true);
+  LS->startDefinition();
+
+  // copy base struct, create HLSL Buffer compatible version if needed
+  if (unsigned NumBases = StructDecl->getNumBases()) {
+    assert(NumBases == 1 && "HLSL supports only one base type");
----------------
hekota wrote:

It looks like we might not be supporting interfaces in Clang, so I'll remove the FIXME.

https://github.com/llvm/llvm-project/pull/122820