[PATCH] D18252: Drop comdats from the dst module if they are not selected

Rafael Ávila de Espíndola via llvm-commits llvm-commits at lists.llvm.org
Thu Mar 17 13:25:29 PDT 2016

rafael created this revision.
rafael added reviewers: majnemer, joker.eph.
rafael added a subscriber: llvm-commits.

A really unfortunate design of llvm-link and related libraries is that they operate one module at a time.

This means they can copy a GV to the destination module that should not be there in the final result because a later bitcode file takes precedence.

We already handled cases like a strong GV replacing a weak for example.

One case that is not currently handled is a comdat replacing another. This doesn't happen in ELF, but with COFF largest selection kind it is possible.

In "llvm-link a.ll b.ll" if the selected comdat was from a.ll, everything will work and we will not copy the comdat from b.ll.

But if we run "llvm-link b.ll a.ll", we fail to delete the already copied comdat from b.ll. This patch fixes that.



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