[HLSL] cbuffer: Create host layout struct and add resource handle to AST

Creates layout struct for `cbuffer` in Sema which will contains only declarations
contributing to the constant buffer layout. Anything else will be filtered out,
such as static variables decls, struct and function definitions, resources,
or empty struct and zero-sized arrays.

If the constant buffer includes a struct that contains any of the above undesirable
declarations, a new version of this struct should be created with these declarations
filtered out as well.

The definition of buffer layour struct is added to the HLSLBufferDecl node and is followed
by 'cbuffer` resource handle decl referencing the layout struct as its contained type.

Fixes #122553

clang/include/clang/AST/Decl.h

@@ -4967,6 +4967,7 @@ class HLSLBufferDecl final : public NamedDecl, public DeclContext {
   SourceLocation getRBraceLoc() const { return RBraceLoc; }
   void setRBraceLoc(SourceLocation L) { RBraceLoc = L; }
   bool isCBuffer() const { return IsCBuffer; }
+  const Type *getResourceHandleType() const;
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }

clang/lib/AST/Decl.cpp

@@ -5693,6 +5693,19 @@ HLSLBufferDecl *HLSLBufferDecl::CreateDeserialized(ASTContext &C,
                                     SourceLocation(), SourceLocation());
 }
 
+const Type *HLSLBufferDecl::getResourceHandleType() const {
+  // Resource handle is the last decl in the HLSLBufferDecl.
+  // If it is not present, it probably means the buffer is empty.
+  if (VarDecl *VD = llvm::dyn_cast_or_null<VarDecl>(LastDecl)) {
+    const Type *Ty = VD->getType().getTypePtr();
+    if (Ty->isHLSLAttributedResourceType()) {
+      assert(VD->getNameAsString() == "__handle");
+      return Ty;
+    }
+  }
+  return nullptr;
+}
+
 //===----------------------------------------------------------------------===//
 // ImportDecl Implementation
 //===----------------------------------------------------------------------===//

clang/lib/CodeGen/CGHLSLRuntime.cpp

@@ -159,10 +159,12 @@ void CGHLSLRuntime::addConstant(VarDecl *D, Buffer &CB) {
   CB.Constants.emplace_back(std::make_pair(GV, LowerBound));
 }
 
-void CGHLSLRuntime::addBufferDecls(const DeclContext *DC, Buffer &CB) {
-  for (Decl *it : DC->decls()) {
+void CGHLSLRuntime::addBufferDecls(const HLSLBufferDecl *D, Buffer &CB) {
+  for (Decl *it : D->decls()) {
     if (auto *ConstDecl = dyn_cast<VarDecl>(it)) {
-      addConstant(ConstDecl, CB);
+      if (ConstDecl->getType().getTypePtr() != D->getResourceHandleType()) {
+        addConstant(ConstDecl, CB);
+      }
     } else if (isa<CXXRecordDecl, EmptyDecl>(it)) {
       // Nothing to do for this declaration.
     } else if (isa<FunctionDecl>(it)) {

clang/lib/CodeGen/CGHLSLRuntime.h

@@ -169,7 +169,7 @@ class CGHLSLRuntime {
                                    llvm::hlsl::ElementType ET,
                                    BufferResBinding &Binding);
   void addConstant(VarDecl *D, Buffer &CB);
-  void addBufferDecls(const DeclContext *DC, Buffer &CB);
+  void addBufferDecls(const HLSLBufferDecl *D, Buffer &CB);
   llvm::Triple::ArchType getArch();
   llvm::SmallVector<Buffer> Buffers;
 

clang/lib/Sema/SemaHLSL.cpp

@@ -21,22 +21,26 @@
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/Builtins.h"
 #include "clang/Basic/DiagnosticSema.h"
+#include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/SourceLocation.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"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/Twine.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/DXILABI.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/TargetParser/Triple.h"
 #include <iterator>
+#include <string>
 #include <utility>
 
 using namespace clang;
@@ -253,12 +257,253 @@ 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 can be used inside HLSL Buffer which means
+// that it does not contain intangible types, empty structs, zero-sized arrays,
+// and the same is true for its base or embedded structs.
+bool isStructHLSLBufferCompatible(const CXXRecordDecl *RD) {
+  if (RD->getTypeForDecl()->isHLSLIntangibleType() ||
+      (RD->field_empty() && RD->getNumBases() == 0))
+    return false;
+  // check fields
+  for (const FieldDecl *Field : RD->fields()) {
+    QualType Ty = Field->getType();
+    if (Ty->isRecordType()) {
+      if (!isStructHLSLBufferCompatible(Ty->getAsCXXRecordDecl()))
+        return false;
+    } else if (Ty->isConstantArrayType()) {
+      if (isZeroSizedArray(cast<ConstantArrayType>(Ty)))
+        return false;
+    }
+  }
+  // check bases
+  for (const CXXBaseSpecifier &Base : RD->bases())
+    if (!isStructHLSLBufferCompatible(Base.getType()->getAsCXXRecordDecl()))
+      return false;
+  return true;
+}
+
+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 = "__hostlayout.struct." + 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 (!isStructHLSLBufferCompatible(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(!isStructHLSLBufferCompatible(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");
+    CXXBaseSpecifier Base = *StructDecl->bases_begin();
+    CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
+    if (!isStructHLSLBufferCompatible(BaseDecl)) {
+      BaseDecl = createHostLayoutStruct(S, BaseDecl, BufDecl);
+      if (BaseDecl) {
+        TypeSourceInfo *TSI = AST.getTrivialTypeSourceInfo(
+            QualType(BaseDecl->getTypeForDecl(), 0));
+        Base = CXXBaseSpecifier(SourceRange(), false, StructDecl->isClass(),
+                                AS_none, TSI, SourceLocation());
+      }
+    }
+    if (BaseDecl) {
+      const CXXBaseSpecifier *BasesArray[1] = {&Base};
+      LS->setBases(BasesArray, 1);
+    }
+  }
+
+  // filter struct fields
+  for (const FieldDecl *FD : StructDecl->fields()) {
+    const Type *Ty = FD->getType()->getUnqualifiedDesugaredType();
+    if (FieldDecl *NewFD = createFieldForHostLayoutStruct(
+            S, Ty, FD->getIdentifier(), LS, BufDecl))
+      LS->addDecl(NewFD);
+  }
+  LS->completeDefinition();
+
+  if (LS->field_empty() && LS->getNumBases() == 0)
+    return nullptr;
+  BufDecl->addDecl(LS);
+  return LS;
+}
+
+// Creates host layout struct for HLSL Buffer. The struct will include only
+// fields of types that are allowed in HLSL buffer and it will filter out:
+// - static variable declarations
+// - resource classes
+// - empty structs
+// - zero-sized arrays
+// - non-variable declarations
+static CXXRecordDecl *createHostLayoutStructForBuffer(Sema &S,
+                                                      HLSLBufferDecl *BufDecl) {
+  ASTContext &AST = S.getASTContext();
+  IdentifierInfo *II = getHostLayoutStructName(S, BufDecl->getIdentifier(),
+                                               true, BufDecl->getDeclContext());
+
+  CXXRecordDecl *LS =
+      CXXRecordDecl::Create(AST, TagDecl::TagKind::Class, BufDecl,
+                            SourceLocation(), SourceLocation(), II);
+  LS->setImplicit(true);
+  LS->startDefinition();
+
+  for (const Decl *D : BufDecl->decls()) {
+    const VarDecl *VD = dyn_cast<VarDecl>(D);
+    if (!VD || VD->getStorageClass() == SC_Static)
+      continue;
+    const Type *Ty = VD->getType()->getUnqualifiedDesugaredType();
+    if (FieldDecl *FD = createFieldForHostLayoutStruct(
+            S, Ty, VD->getIdentifier(), LS, BufDecl))
+      LS->addDecl(FD);
+  }
+  LS->completeDefinition();
+  BufDecl->addDecl(LS);
+  return LS;
+}
+
+// Creates a "__handle" declaration for the HLSL Buffer type
+// with the corresponding HLSL resource type and adds it to the HLSLBufferDecl
+static void createHLSLBufferHandle(Sema &S, HLSLBufferDecl *BufDecl,
+                                   CXXRecordDecl *LayoutStruct) {
+  ASTContext &AST = S.getASTContext();
+
+  HLSLAttributedResourceType::Attributes ResAttrs(
+      BufDecl->isCBuffer() ? ResourceClass::CBuffer : ResourceClass::SRV, false,
+      false);
+  QualType ResHandleTy = AST.getHLSLAttributedResourceType(
+      AST.HLSLResourceTy, QualType(LayoutStruct->getTypeForDecl(), 0),
+      ResAttrs);
+
+  IdentifierInfo *II = &AST.Idents.get("__handle", tok::TokenKind::identifier);
+  VarDecl *VD = VarDecl::Create(
+      BufDecl->getASTContext(), BufDecl, SourceLocation(), SourceLocation(), II,
+      ResHandleTy, AST.getTrivialTypeSourceInfo(ResHandleTy, SourceLocation()),
+      SC_None);
+  BufDecl->addDecl(VD);
+}
+
+// Handle end of cbuffer/tbuffer declaration
 void SemaHLSL::ActOnFinishBuffer(Decl *Dcl, SourceLocation RBrace) {
   auto *BufDecl = cast<HLSLBufferDecl>(Dcl);
   BufDecl->setRBraceLoc(RBrace);
 
   validatePackoffset(SemaRef, BufDecl);
 
+  // create buffer layout struct
+  CXXRecordDecl *LayoutStruct =
+      createHostLayoutStructForBuffer(SemaRef, BufDecl);
+
+  // create buffer resource handle
+  createHLSLBufferHandle(SemaRef, BufDecl, LayoutStruct);
+
   SemaRef.PopDeclContext();
 }
 

clang/test/AST/HLSL/ast-dump-comment-cbuffe-tbufferr.hlsl

@@ -44,12 +44,23 @@ tbuffer B {
 // AST-NEXT:`-ParagraphComment {{.*}}<col:4, col:17>
 // AST-NEXT:`-TextComment {{.*}}<col:4, col:17> Text=" CBuffer decl."
 // AST-NEXT:-VarDecl {{.*}}<line:15:5, col:11> col:11 a 'float'
-// AST-NEXT:`-VarDecl {{.*}}<line:19:5, col:9> col:9 b 'int'
+// AST-NEXT:-VarDecl {{.*}}<line:19:5, col:9> col:9 b 'int'
+// AST-NEXT:CXXRecordDecl 0x[[CB:[0-9a-f]+]] {{.*}} implicit class __hostlayout.struct.A definition
+// AST:FieldDecl 0x[[CB:[0-9a-f]+]] {{.*}} a 'float'
+// AST-NEXT:FieldDecl 0x[[CB:[0-9a-f]+]] {{.*}} b 'int'
+// AST-NEXT:VarDecl 0x[[CB:[0-9a-f]+]] {{.*}} __handle '__hlsl_resource_t 
+// AST-SAME{LITERAL}: [[hlsl::resource_class(CBuffer)]] [[hlsl::contained_type(__hostlayout.struct.A)]]'
+
 // AST-NEXT:HLSLBufferDecl {{.*}}<line:29:1, line:38:1> line:29:9 tbuffer B
 // AST-NEXT:-HLSLResourceClassAttr {{.*}} <<invalid sloc>> Implicit SRV
 // AST-NEXT:-HLSLResourceAttr {{.*}} <<invalid sloc>> Implicit TBuffer
 // AST-NEXT:-FullComment {{.*}}<line:28:4, col:17>
 // AST-NEXT: `-ParagraphComment {{.*}}<col:4, col:17>
 // AST-NEXT:  `-TextComment {{.*}}<col:4, col:17> Text=" TBuffer decl."
 // AST-NEXT:-VarDecl {{.*}}<line:33:5, col:11> col:11 c 'float'
-// AST-NEXT:`-VarDecl {{.*}} <line:37:5, col:9> col:9 d 'int'
+// AST-NEXT:-VarDecl {{.*}} <line:37:5, col:9> col:9 d 'int'
+// AST-NEXT:CXXRecordDecl 0x[[CB:[0-9a-f]+]] {{.*}} implicit class __hostlayout.struct.B definition
+// AST:FieldDecl 0x[[CB:[0-9a-f]+]] {{.*}} c 'float'
+// AST-NEXT:FieldDecl 0x[[CB:[0-9a-f]+]] {{.*}} d 'int'
+// AST-NEXT:VarDecl 0x[[CB:[0-9a-f]+]] {{.*}} __handle '__hlsl_resource_t
+// AST-SAME{LITERAL}: [[hlsl::resource_class(SRV)]] [[hlsl::contained_type(__hostlayout.struct.B)]]'