r323528 - [AST] Use bit packing to reduce sizeof(TypedefNameDecl) from 88 to 80.

[Benjamin Kramer via cfe-commits]

Author: d0k
Date: Fri Jan 26 06:14:11 2018
New Revision: 323528

URL: http://llvm.org/viewvc/llvm-project?rev=323528&view=rev
Log:
[AST] Use bit packing to reduce sizeof(TypedefNameDecl) from 88 to 80.

We can stash the cached transparent tag bit in existing pointer padding.
Everything coming out of ASTContext is always aligned to a multiple of
8, so we have 8 spare bits.

Modified:
    cfe/trunk/include/clang/AST/Decl.h
    cfe/trunk/lib/AST/Decl.cpp

Modified: cfe/trunk/include/clang/AST/Decl.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/AST/Decl.h?rev=323528&r1=323527&r2=323528&view=diff
==============================================================================
--- cfe/trunk/include/clang/AST/Decl.h (original)
+++ cfe/trunk/include/clang/AST/Decl.h Fri Jan 26 06:14:11 2018
@@ -2814,12 +2814,12 @@ public:
 /// Base class for declarations which introduce a typedef-name.
 class TypedefNameDecl : public TypeDecl, public Redeclarable<TypedefNameDecl> {
   using ModedTInfo = std::pair<TypeSourceInfo *, QualType>;
-  llvm::PointerUnion<TypeSourceInfo *, ModedTInfo *> MaybeModedTInfo;
 
-  // FIXME: This can be packed into the bitfields in Decl.
-  /// If 0, we have not computed IsTransparentTag.
-  /// Otherwise, IsTransparentTag is (CacheIsTransparentTag >> 1).
-  mutable unsigned CacheIsTransparentTag : 2;
+  /// If int part is 0, we have not computed IsTransparentTag.
+  /// Otherwise, IsTransparentTag is (getInt() >> 1).
+  mutable llvm::PointerIntPair<
+      llvm::PointerUnion<TypeSourceInfo *, ModedTInfo *>, 2>
+      MaybeModedTInfo;
 
   void anchor() override;
 
@@ -2828,7 +2828,7 @@ protected:
                   SourceLocation StartLoc, SourceLocation IdLoc,
                   IdentifierInfo *Id, TypeSourceInfo *TInfo)
       : TypeDecl(DK, DC, IdLoc, Id, StartLoc), redeclarable_base(C),
-        MaybeModedTInfo(TInfo), CacheIsTransparentTag(0) {}
+        MaybeModedTInfo(TInfo, 0) {}
 
   using redeclarable_base = Redeclarable<TypedefNameDecl>;
 
@@ -2855,26 +2855,29 @@ public:
   using redeclarable_base::getMostRecentDecl;
   using redeclarable_base::isFirstDecl;
 
-  bool isModed() const { return MaybeModedTInfo.is<ModedTInfo*>(); }
+  bool isModed() const {
+    return MaybeModedTInfo.getPointer().is<ModedTInfo *>();
+  }
 
   TypeSourceInfo *getTypeSourceInfo() const {
-    return isModed()
-      ? MaybeModedTInfo.get<ModedTInfo*>()->first
-      : MaybeModedTInfo.get<TypeSourceInfo*>();
+    return isModed() ? MaybeModedTInfo.getPointer().get<ModedTInfo *>()->first
+                     : MaybeModedTInfo.getPointer().get<TypeSourceInfo *>();
   }
 
   QualType getUnderlyingType() const {
-    return isModed()
-      ? MaybeModedTInfo.get<ModedTInfo*>()->second
-      : MaybeModedTInfo.get<TypeSourceInfo*>()->getType();
+    return isModed() ? MaybeModedTInfo.getPointer().get<ModedTInfo *>()->second
+                     : MaybeModedTInfo.getPointer()
+                           .get<TypeSourceInfo *>()
+                           ->getType();
   }
 
   void setTypeSourceInfo(TypeSourceInfo *newType) {
-    MaybeModedTInfo = newType;
+    MaybeModedTInfo.setPointer(newType);
   }
 
   void setModedTypeSourceInfo(TypeSourceInfo *unmodedTSI, QualType modedTy) {
-    MaybeModedTInfo = new (getASTContext()) ModedTInfo(unmodedTSI, modedTy);
+    MaybeModedTInfo.setPointer(new (getASTContext(), 8)
+                                   ModedTInfo(unmodedTSI, modedTy));
   }
 
   /// Retrieves the canonical declaration of this typedef-name.
@@ -2891,8 +2894,8 @@ public:
   /// Determines if this typedef shares a name and spelling location with its
   /// underlying tag type, as is the case with the NS_ENUM macro.
   bool isTransparentTag() const {
-    if (CacheIsTransparentTag)
-      return CacheIsTransparentTag & 0x2;
+    if (MaybeModedTInfo.getInt())
+      return MaybeModedTInfo.getInt() & 0x2;
     return isTransparentTagSlow();
   }
 

Modified: cfe/trunk/lib/AST/Decl.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/Decl.cpp?rev=323528&r1=323527&r2=323528&view=diff
==============================================================================
--- cfe/trunk/lib/AST/Decl.cpp (original)
+++ cfe/trunk/lib/AST/Decl.cpp Fri Jan 26 06:14:11 2018
@@ -4372,9 +4372,7 @@ bool TypedefNameDecl::isTransparentTagSl
   };
 
   bool isTransparent = determineIsTransparent();
-  CacheIsTransparentTag = 1;
-  if (isTransparent)
-    CacheIsTransparentTag |= 0x2;
+  MaybeModedTInfo.setInt((isTransparent << 1) | 1);
   return isTransparent;
 }