[clang] [clang] SourceManager: Cache offsets for LastFileIDLookup to speed up getFileID (PR #146782)

[Haojian Wu via cfe-commits]

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@@ -1901,9 +1903,8 @@ class SourceManager : public RefCountedBase<SourceManager> {
 
   FileID getFileID(SourceLocation::UIntTy SLocOffset) const {
     // If our one-entry cache covers this offset, just return it.
-    if (isOffsetInFileID(LastFileIDLookup, SLocOffset))
+    if (SLocOffset >= LastLookupStartOffset && SLocOffset < LastLookupEndOffset)
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hokein wrote:

I’ve reverted the changes to `isOffsetInFileID` in this patch to maximize the overall performance gain.

I have some ideas for improving `isOffsetInFileID` and might explore them later -- though it’s not clear whether `isOffsetInFileID` will still be a hot method after this change.



https://github.com/llvm/llvm-project/pull/146782