[AST] Store the OwnedTagDecl as a trailing object in ElaboratedType.

The TagDecl *OwnedTagDecl in ElaboratedType is quite commonly
null (at least when parsing all of Boost, it is non-null for only about 600
of the 66k ElaboratedType). Therefore we can save a pointer in the
common case by storing it as a trailing object, and storing a bit in the
bit-fields of Type indicating when the pointer is null.

Reviewed By: rjmccall

Differential Revision: https://reviews.llvm.org/D50715

llvm-svn: 339862

1 files changed, 4 insertions, 2 deletions

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 91e9f3ed873..0a40ee5de9d 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -4136,8 +4136,10 @@ QualType ASTContext::getElaboratedType(ElaboratedTypeKeyword Keyword,
     (void)CheckT;
   }
 
-  T = new (*this, TypeAlignment)
-      ElaboratedType(Keyword, NNS, NamedType, Canon, OwnedTagDecl);
+  void *Mem = Allocate(ElaboratedType::totalSizeToAlloc<TagDecl *>(!!OwnedTagDecl),
+                       TypeAlignment);
+  T = new (Mem) ElaboratedType(Keyword, NNS, NamedType, Canon, OwnedTagDecl);
+
   Types.push_back(T);
   ElaboratedTypes.InsertNode(T, InsertPos);
   return QualType(T, 0);