ASTWriter: Cache some DenseMaps we use repeatedly.
 - This reduces our total # of allocations building a PCH for Cocoa.h by almost
   a whopping 50%.
 - A SmallPtrMap would be cleaner, but since we don't have one yet...

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151697 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed