[clang] [clang] Optimize SourceManager.getSpellingLocSlowCase and SourceManager.getFileLocSlowCase (PR #164269)

[Aaron Ballman via cfe-commits]

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@@ -908,19 +908,23 @@ getExpansionLocSlowCase(SourceLocation Loc) const {
 
 SourceLocation SourceManager::getSpellingLocSlowCase(SourceLocation Loc) const {
   do {
-    FileIDAndOffset LocInfo = getDecomposedLoc(Loc);
-    Loc = getSLocEntry(LocInfo.first).getExpansion().getSpellingLoc();
-    Loc = Loc.getLocWithOffset(LocInfo.second);
+    const SLocEntry &Entry = getSLocEntry(getFileID(Loc));
+    Loc = Entry.getExpansion().getSpellingLoc().getLocWithOffset(
+        Loc.getOffset() - Entry.getOffset());
   } while (!Loc.isFileID());
   return Loc;
 }
 
 SourceLocation SourceManager::getFileLocSlowCase(SourceLocation Loc) const {
   do {
-    if (isMacroArgExpansion(Loc))
-      Loc = getImmediateSpellingLoc(Loc);
-    else
-      Loc = getImmediateExpansionRange(Loc).getBegin();
+    const SLocEntry &Entry = getSLocEntry(getFileID(Loc));
+    const ExpansionInfo &ExpInfo = Entry.getExpansion();
+    if (ExpInfo.isMacroArgExpansion()) {
+      Loc = ExpInfo.getSpellingLoc().getLocWithOffset(Loc.getOffset() -
+                                                      Entry.getOffset());
+    } else {
+      Loc = ExpInfo.getExpansionLocStart();
+    }
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AaronBallman wrote:

> Can we run the performance test on this RP somehow? Although I doubt that there will be any significant change.

Unfortunately, not trivially; you can contact Nikita to have your fork added (https://llvm-compile-time-tracker.com/about.php) but that may take a while given the upcoming dev conference and folks being busy with that. I think it'd be fine if there were some local tests on whatever project you have that's super macro heavy, something as simple as "average of 1234ms before this patch and 567ms after the patch on my machine" would perhaps help.

Basically, if there's a measurable performance improvement, we can hold our nose on slightly reduced readability, but if there's no measurable performance improvement, there's less of a case for taking the patch..

https://github.com/llvm/llvm-project/pull/164269