[PATCH] D135014: [lld][ELF] Fix lazy ThinLTO index writing in thin archives

[Aiden Grossman via Phabricator via llvm-commits]

aidengrossman added a comment.

The path that is written to without this patch is the path to the object file relative from the path of the thin archive, but it expands this path over the current working directory rather than the path of the thin archive. For example if the thin archive is in `./test-folder-2/lib.a`, pointing to archive files in `./test-folder-1`, the `thinLTOCreateEmptyIndexFiles()` function will try and write the `*.thinlto.bc` files to `../test-folder-1/*` relative to the current working directory (set up in the examples as containing `test-folder-1` and `test-folder-2`, ie one level up). Even just fixing the path issue, the current implementation also names the files differently (ie `c.o.thinlto.bc` instead of in the non-lazy case `lib.a(c.o at xxx).thinlto.bc`.

I have just tested this on a ThinLTO Chromium compile for preparing a corpus for MLGO. I don't believe this patch will make this case work for distributed ThinLTO all the way through the backends, but I'm not familiar enough with how distributed ThinLTO picks up all the necessary files in order to say anything conclusive.


Repository:
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https://reviews.llvm.org/D135014