[lld] [ELF] Avoid repeated scans when merging strings (PR #219071)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay requested changes to this pull request.

> Unfortunately, I ran this at Meta on a production-scale check, a large optimized binary with tens of thousands of direct object inputs and several thousand archives but showed no measurable end-to-end change.

Then what's the point of this change that significantly increases code complexity? FWIW I've also tried optimizing this function but haven't managed to do so...

Also, thanks for providing such detailed motivation notes. But please move them to a comment since the PR description is used as the default commit message.

https://github.com/llvm/llvm-project/pull/219071