Amend r138129 (reduction of SLocEntries) which introduced performance regression due

to increased calls to SourceManager::getFileID. (rdar://9992664)

Use a slightly different approach that is more efficient both in terms of speed
(no extra getFileID calls) and in SLocEntries reduction.

Comparing pre-r138129 and this patch we get:

For compiling SemaExpr.cpp reduction of SLocEntries by 26%.
For the boost enum library:
  -SLocEntries -34% (note that this was -5% for r138129)
  -Memory consumption -50%
  -PCH size -31%

Reduced SLocEntries also benefit the hot function SourceManager::getFileID,
evident by the reduced "FileID scans".

llvm-svn: 138380

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index bf2c8be4679..66ae4861a6a 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -834,10 +834,11 @@ SourceManager::getDecomposedSpellingLocSlowCase(const SrcMgr::SLocEntry *E,
   SourceLocation Loc;
   do {
     Loc = E->getExpansion().getSpellingLoc();
+    Loc = Loc.getFileLocWithOffset(Offset);
 
     FID = getFileID(Loc);
     E = &getSLocEntry(FID);
-    Offset += Loc.getOffset()-E->getOffset();
+    Offset = Loc.getOffset()-E->getOffset();
   } while (!Loc.isFileID());
 
   return std::make_pair(FID, Offset);