Address review comments.

Author: hokein

clang/include/clang/Basic/SourceManager.h

@@ -1903,7 +1903,7 @@ class SourceManager : public RefCountedBase<SourceManager> {
 
   FileID getFileID(SourceLocation::UIntTy SLocOffset) const {
     // If our one-entry cache covers this offset, just return it.
-    if (SLocOffset >= LastLookupStartOffset && SLocOffset < LastLookupEndOffset)
+    if (isOffsetInFileID(LastFileIDLookup, SLocOffset))
       return LastFileIDLookup;
     return getFileIDSlow(SLocOffset);
   }
@@ -1927,6 +1927,10 @@ class SourceManager : public RefCountedBase<SourceManager> {
   /// specified SourceLocation offset.  This is a very hot method.
   inline bool isOffsetInFileID(FileID FID,
                                SourceLocation::UIntTy SLocOffset) const {
+    if (FID == LastFileIDLookup)
+      return SLocOffset >= LastLookupStartOffset &&
+             SLocOffset < LastLookupEndOffset;
+
     const SrcMgr::SLocEntry &Entry = getSLocEntry(FID);
     // If the entry is after the offset, it can't contain it.
     if (SLocOffset < Entry.getOffset()) return false;

clang/lib/Basic/SourceManager.cpp

@@ -814,8 +814,9 @@ FileID SourceManager::getFileIDSlow(SourceLocation::UIntTy SLocOffset) const {
 /// loaded one.
 FileID SourceManager::getFileIDLocal(SourceLocation::UIntTy SLocOffset) const {
   assert(SLocOffset < NextLocalOffset && "Bad function choice");
-  assert(SLocOffset >= LocalSLocEntryTable[0].getOffset() &&
+  assert(SLocOffset >= LocalSLocEntryTable[0].getOffset() && SLocOffset > 0 &&
          "Invalid SLocOffset");
+  assert(LastFileIDLookup.ID >= 0 && "Only cache local file sloc entry");
 
   // After the first and second level caches, I see two common sorts of
   // behavior: 1) a lot of searched FileID's are "near" the cached file