[Clang] Reduce the size of Decl and classes derived from it (#87361)

Class | Old size (in bytes) | New size (in bytes) ----------------------------------|---------------------|-------------------- Decl | 40 | 32 AccessSpecDecl | 40 | 40 BlockDecl | 128 | 120 CapturedDecl | 88 | 80 EmptyDecl | 40 | 32 ExportDecl | 80 | 72 ExternCContextDecl | 72 | 64 FileScopeAsmDecl | 56 | 48 FriendDecl | 64 | 56 FriendTemplateDecl | 64 | 64 ImplicitConceptSpecializationDecl | 40 | 40 ImportDecl | 56 | 48 LifetimeExtendedTemporaryDecl | 72 | 64 LinkageSpecDecl | 80 | 72 NamedDecl | 48 | 40 ObjCPropertyImplDecl | 96 | 88 PragmaCommentDecl | 40 | 40 PragmaDetectMismatchDecl | 48 | 40 RequiresExprBodyDecl | 72 | 64 StaticAssertDecl | 64 | 56 TopLevelStmtDecl | 88 | 80 TranslationUnitDecl | 104 | 96 BaseUsingDecl | 56 | 48 UsingDecl | 88 | 80 UsingEnumDecl | 72 | 64 HLSLBufferDecl | 96 | 88 LabelDecl | 80 | 72 NamespaceAliasDecl | 96 | 88 NamespaceDecl | 112 | 104 ObjCCompatibleAliasDecl | 56 | 48 ObjCContainerDecl | 88 | 80 ObjCMethodDecl | 136 | 128 ObjCPropertyDecl | 128 | 120 TemplateDecl | 64 | 56 BuiltinTemplateDecl | 72 | 64 TypeDecl | 64 | 56 UnresolvedUsingIfExistsDecl | 48 | 40 UsingDirectiveDecl | 88 | 80 UsingPackDecl | 64 | 56 UsingShadowDecl | 80 | 72 ValueDecl | 56 | 48 When parsing libc++'s `<string>` header the used memory is reduced from 42.8MB to 42.5MB.
llvm · Apr 14, 2024 · c6f9c84 · c6f9c84
1 parent 09327ef
commit c6f9c84
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Showing 3 changed files with 70 additions and 35 deletions.
diff --git a/clang/include/clang/AST/DeclBase.h b/clang/include/clang/AST/DeclBase.h
@@ -268,17 +268,37 @@ class alignas(8) Decl {
   ///   }
   ///   void A::f(); // SemanticDC == namespace 'A'
   ///                // LexicalDC == global namespace
-  llvm::PointerUnion<DeclContext*, MultipleDC*> DeclCtx;
 
-  bool isInSemaDC() const { return DeclCtx.is<DeclContext*>(); }
-  bool isOutOfSemaDC() const { return DeclCtx.is<MultipleDC*>(); }
+  // Compress the InvalidDecl and HasAttrs bits into DeclCtx to keep Decl below
+  // 32 bytes in size
+  llvm::PointerIntPair<
+      llvm::PointerIntPair<llvm::PointerUnion<DeclContext *, MultipleDC *>, 1,
+                           bool>,
+      1, bool>
+      DeclCtxWithInvalidDeclAndHasAttrs;
+
+  bool isInSemaDC() const {
+    return DeclCtxWithInvalidDeclAndHasAttrs.getPointer()
+        .getPointer()
+        .is<DeclContext *>();
+  }
+
+  bool isOutOfSemaDC() const {
+    return DeclCtxWithInvalidDeclAndHasAttrs.getPointer()
+        .getPointer()
+        .is<MultipleDC *>();
+  }
 
   MultipleDC *getMultipleDC() const {
-    return DeclCtx.get<MultipleDC*>();
+    return DeclCtxWithInvalidDeclAndHasAttrs.getPointer()
+        .getPointer()
+        .get<MultipleDC *>();
   }
 
   DeclContext *getSemanticDC() const {
-    return DeclCtx.get<DeclContext*>();
+    return DeclCtxWithInvalidDeclAndHasAttrs.getPointer()
+        .getPointer()
+        .get<DeclContext *>();
   }
 
   /// Loc - The location of this decl.
@@ -288,14 +308,6 @@ class alignas(8) Decl {
   LLVM_PREFERRED_TYPE(Kind)
   unsigned DeclKind : 7;
 
-  /// InvalidDecl - This indicates a semantic error occurred.
-  LLVM_PREFERRED_TYPE(bool)
-  unsigned InvalidDecl :  1;
-
-  /// HasAttrs - This indicates whether the decl has attributes or not.
-  LLVM_PREFERRED_TYPE(bool)
-  unsigned HasAttrs : 1;
-
   /// Implicit - Whether this declaration was implicitly generated by
   /// the implementation rather than explicitly written by the user.
   LLVM_PREFERRED_TYPE(bool)
@@ -393,21 +405,22 @@ class alignas(8) Decl {
 protected:
   Decl(Kind DK, DeclContext *DC, SourceLocation L)
       : NextInContextAndBits(nullptr, getModuleOwnershipKindForChildOf(DC)),
-        DeclCtx(DC), Loc(L), DeclKind(DK), InvalidDecl(false), HasAttrs(false),
-        Implicit(false), Used(false), Referenced(false),
+        DeclCtxWithInvalidDeclAndHasAttrs({DC, false}, false), Loc(L),
+        DeclKind(DK), Implicit(false), Used(false), Referenced(false),
         TopLevelDeclInObjCContainer(false), Access(AS_none), FromASTFile(0),
         IdentifierNamespace(getIdentifierNamespaceForKind(DK)),
         CacheValidAndLinkage(llvm::to_underlying(Linkage::Invalid)) {
-    if (StatisticsEnabled) add(DK);
+    if (StatisticsEnabled)
+      add(DK);
   }
 
   Decl(Kind DK, EmptyShell Empty)
-      : DeclKind(DK), InvalidDecl(false), HasAttrs(false), Implicit(false),
-        Used(false), Referenced(false), TopLevelDeclInObjCContainer(false),
-        Access(AS_none), FromASTFile(0),
+      : DeclKind(DK), Implicit(false), Used(false), Referenced(false),
+        TopLevelDeclInObjCContainer(false), Access(AS_none), FromASTFile(0),
         IdentifierNamespace(getIdentifierNamespaceForKind(DK)),
         CacheValidAndLinkage(llvm::to_underlying(Linkage::Invalid)) {
-    if (StatisticsEnabled) add(DK);
+    if (StatisticsEnabled)
+      add(DK);
   }
 
   virtual ~Decl();
@@ -520,7 +533,9 @@ class alignas(8) Decl {
     return AccessSpecifier(Access);
   }
 
-  bool hasAttrs() const { return HasAttrs; }
+  bool hasAttrs() const {
+    return DeclCtxWithInvalidDeclAndHasAttrs.getPointer().getInt();
+  }
 
   void setAttrs(const AttrVec& Attrs) {
     return setAttrsImpl(Attrs, getASTContext());
@@ -549,13 +564,17 @@ class alignas(8) Decl {
   }
 
   template <typename... Ts> void dropAttrs() {
-    if (!HasAttrs) return;
+    if (!hasAttrs())
+      return;
 
     AttrVec &Vec = getAttrs();
     llvm::erase_if(Vec, [](Attr *A) { return isa<Ts...>(A); });
 
-    if (Vec.empty())
-      HasAttrs = false;
+    if (Vec.empty()) {
+      auto InnerPtr = DeclCtxWithInvalidDeclAndHasAttrs.getPointer();
+      InnerPtr.setInt(false);
+      DeclCtxWithInvalidDeclAndHasAttrs.setPointer(InnerPtr);
+    }
   }
 
   template <typename T> void dropAttr() { dropAttrs<T>(); }
@@ -590,7 +609,10 @@ class alignas(8) Decl {
   /// setInvalidDecl - Indicates the Decl had a semantic error. This
   /// allows for graceful error recovery.
   void setInvalidDecl(bool Invalid = true);
-  bool isInvalidDecl() const { return (bool) InvalidDecl; }
+
+  bool isInvalidDecl() const {
+    return DeclCtxWithInvalidDeclAndHasAttrs.getInt();
+  }
 
   /// isImplicit - Indicates whether the declaration was implicitly
   /// generated by the implementation. If false, this declaration

diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
@@ -52,6 +52,8 @@
 
 using namespace clang;
 
+static_assert(sizeof(Decl) <= 32, "Decl grew beyond 32 bytes!");
+
 //===----------------------------------------------------------------------===//
 //  Statistics
 //===----------------------------------------------------------------------===//
@@ -130,7 +132,7 @@ const char *Decl::getDeclKindName() const {
 }
 
 void Decl::setInvalidDecl(bool Invalid) {
-  InvalidDecl = Invalid;
+  DeclCtxWithInvalidDeclAndHasAttrs.setInt(Invalid);
   assert(!isa<TagDecl>(this) || !cast<TagDecl>(this)->isCompleteDefinition());
   if (!Invalid) {
     return;
@@ -334,7 +336,9 @@ void PrettyStackTraceDecl::print(raw_ostream &OS) const {
 Decl::~Decl() = default;
 
 void Decl::setDeclContext(DeclContext *DC) {
-  DeclCtx = DC;
+  auto InnerPtr = DeclCtxWithInvalidDeclAndHasAttrs.getPointer();
+  InnerPtr.setPointer(DC);
+  DeclCtxWithInvalidDeclAndHasAttrs.setPointer(InnerPtr);
 }
 
 void Decl::setLexicalDeclContext(DeclContext *DC) {
@@ -364,12 +368,16 @@ void Decl::setLexicalDeclContext(DeclContext *DC) {
 void Decl::setDeclContextsImpl(DeclContext *SemaDC, DeclContext *LexicalDC,
                                ASTContext &Ctx) {
   if (SemaDC == LexicalDC) {
-    DeclCtx = SemaDC;
+    auto InnerPtr = DeclCtxWithInvalidDeclAndHasAttrs.getPointer();
+    InnerPtr.setPointer(SemaDC);
+    DeclCtxWithInvalidDeclAndHasAttrs.setPointer(InnerPtr);
   } else {
     auto *MDC = new (Ctx) Decl::MultipleDC();
     MDC->SemanticDC = SemaDC;
     MDC->LexicalDC = LexicalDC;
-    DeclCtx = MDC;
+    auto InnerPtr = DeclCtxWithInvalidDeclAndHasAttrs.getPointer();
+    InnerPtr.setPointer(MDC);
+    DeclCtxWithInvalidDeclAndHasAttrs.setPointer(InnerPtr);
   }
 }
 
@@ -956,19 +964,24 @@ unsigned Decl::getIdentifierNamespaceForKind(Kind DeclKind) {
 }
 
 void Decl::setAttrsImpl(const AttrVec &attrs, ASTContext &Ctx) {
-  assert(!HasAttrs && "Decl already contains attrs.");
+  assert(!hasAttrs() && "Decl already contains attrs.");
 
   AttrVec &AttrBlank = Ctx.getDeclAttrs(this);
   assert(AttrBlank.empty() && "HasAttrs was wrong?");
 
   AttrBlank = attrs;
-  HasAttrs = true;
+  auto InnerPtr = DeclCtxWithInvalidDeclAndHasAttrs.getPointer();
+  InnerPtr.setInt(true);
+  DeclCtxWithInvalidDeclAndHasAttrs.setPointer(InnerPtr);
 }
 
 void Decl::dropAttrs() {
-  if (!HasAttrs) return;
+  if (!hasAttrs())
+    return;
 
-  HasAttrs = false;
+  auto InnerPtr = DeclCtxWithInvalidDeclAndHasAttrs.getPointer();
+  InnerPtr.setInt(false);
+  DeclCtxWithInvalidDeclAndHasAttrs.setPointer(InnerPtr);
   getASTContext().eraseDeclAttrs(this);
 }
 
@@ -996,7 +1009,7 @@ void Decl::addAttr(Attr *A) {
 }
 
 const AttrVec &Decl::getAttrs() const {
-  assert(HasAttrs && "No attrs to get!");
+  assert(hasAttrs() && "No attrs to get!");
   return getASTContext().getDeclAttrs(this);
 }
 

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -588,7 +588,7 @@ void ASTDeclReader::VisitDecl(Decl *D) {
   bool HasStandaloneLexicalDC = DeclBits.getNextBit();
   bool HasAttrs = DeclBits.getNextBit();
   D->setTopLevelDeclInObjCContainer(DeclBits.getNextBit());
-  D->InvalidDecl = DeclBits.getNextBit();
+  D->DeclCtxWithInvalidDeclAndHasAttrs.setInt(DeclBits.getNextBit());
   D->FromASTFile = true;
 
   if (D->isTemplateParameter() || D->isTemplateParameterPack() ||