Changes to IdentifierTable:
- High-level summary: StringMap never owns IdentifierInfos. It just
references them.
- The string map now has StringMapEntry<IdentifierInfo*> instead of
StringMapEntry<IdentifierInfo>. The IdentifierInfo object is
allocated using the same bump pointer allocator as used by the
StringMap.
Changes to IdentifierInfo:
- Added an extra pointer to point to the
StringMapEntry<IdentifierInfo*> in the string map. This pointer
will be null if the IdentifierInfo* is *only* used by the PTHLexer
(that is it isn't in the StringMap).
Algorithmic changes:
- Non-PTH case:
IdentifierInfo::get() will always consult the StringMap first to
see if we have an IdentifierInfo object. If that StringMapEntry
references a null pointer, we allocate a new one from the BumpPtrAllocator
and update the reference in the StringMapEntry.
- PTH case:
We do the same lookup as with the non-PTH case, but if we don't get
a hit in the StringMap we do a secondary lookup in the PTHManager for
the IdentifierInfo. If we don't find an IdentifierInfo we create a
new one as in the non-PTH case. If we do find and IdentifierInfo
in the PTHManager, we update the StringMapEntry to refer to it so
that the IdentifierInfo will be found on the next StringMap lookup.
This way we only do a binary search in the PTH file at most once
for a given IdentifierInfo. This greatly speeds things up for source
files containing a non-trivial amount of code.
Performance impact:
While these changes do add some extra indirection in
IdentifierTable to access an IdentifierInfo*, I saw speedups even
in the non-PTH case as well.
Non-PTH: For -fsyntax-only on Cocoa.h, we see a 6% speedup.
PTH (with Cocoa.h in token cache): 11% speedup.
I also did an experiment where we did -fsyntax-only on a source file
including a large header and Cocoa.h, but the token cache did not
contain the larger header. For this file, we were seeing a performance
*regression* when using PTH of 3% over non-PTH. Now we are seeing
a performance improvement of 9%!
Tests:
The serialization tests are now failing. I looked at this extensively,
and I my belief is that this change is unmasking a bug rather than
introducing a new one. I have disabled the serialization tests for now.
llvm-svn: 62636
52f73cad4a