[PATCH] D107249: [GlobalOpt] Don't replace alias with aliasee if either alias/aliasee may be preemptible

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

In D107249#3285600 <https://reviews.llvm.org/D107249#3285600>, @efriedma wrote:

> Do we need to fix other places?  I tried grepping for GlobalAlias, and at least BasicAliasAnalysis.cpp and MemoryBuiltins.cpp and StackSafetyAnalysis.cpp contain similar isInterposable() checks.

Maybe. Perhaps cross that bridge when we come to it.

> In D107249#2919094 <https://reviews.llvm.org/D107249#2919094>, @efriedma wrote:
>
>> 2. Can we forbid aliases that refer to globals that are interposable, or use weak linkage?  In theory, this prohibition doesn't cause any loss of generality in IR: we can turn a weak definition into an alias pointing to an internal definition, which should be essentially equivalent.
>
> Any comment on this?

We cannot reject such aliases. GCC supports:

  int aliasee __attribute__((weak));
  extern int alias __attribute__((alias("aliasee")));

Perhaps LLVM's instrumentations are better of not creating such aliases, but the IR needs to be handled.


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https://reviews.llvm.org/D107249