[clang][SourceManager] cache Macro Expansions pt.2

[nickdesaulniers]

Summary

Rebasing D80681 on D82497+D82498, I made a mistake and dropped this hunk
accidentally.

[nickdesaulniers]

Alternatively, I could revert dffc1420451f674, and reland with this hunk? That way if a revert is necessary in the future, it's only one. Also so that before/after metrics are together and not across two separate patches.

[kadircet]

yes let's revert dffc1420451f674 and reland with this change included, also please keep the Differential Revision: https://reviews.llvm.org/D80681 line on the commit message, so that it gets associated with the previous review, as it contains a lot of context.

[nickdesaulniers]

Reverted in 7c2cb1448ad2d20e251db5e3ae4a0c84c12aa970, relanded in 7b8cf98b4a9a2f5ea3667fdbf913a4f8952ed36a.

clang/lib/Basic/SourceManager.cpp

if (MidOffset > SLocOffset) {
       continue;
     }
 
     // If the middle index contains the value, succeed and return.
     if (MiddleIndex + 1 == LocalSLocEntryTable.size() ||
         SLocOffset < getLocalSLocEntry(MiddleIndex + 1).getOffset()) {
       FileID Res = FileID::get(MiddleIndex);
 
-      // If this isn't a macro expansion, remember it.  We have good locality
-      // across FileID lookups.
-      if (!LocalSLocEntryTable[MiddleIndex].isExpansion())
-        LastFileIDLookup = Res;
+      // Remember it.  We have good locality across FileID lookups.
       NumBinaryProbes += NumProbes;
       return Res;
     }
 
     // Otherwise, move the low-side up to the middle index.
     LessIndex = MiddleIndex;
   }
 }