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

[Rafael Ávila de Espíndola via llvm-commits]

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.


http://reviews.llvm.org/D18252

Files:
  llvm/lib/Linker/LinkModules.cpp
  llvm/test/Linker/Inputs/comdat-rm-dst.ll
  llvm/test/Linker/comdat-rm-dst.ll

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