[PATCH] D138027: Clean up CFG on JumpThreading

[Nikita Popov via Phabricator via llvm-commits]

nikic requested changes to this revision.
nikic added a comment.

In D138027#4004683 <https://reviews.llvm.org/D138027#4004683>, @arkangath wrote:

> In D138027#4004662 <https://reviews.llvm.org/D138027#4004662>, @nikic wrote:
>
>> This doesn't really make sense to me. It deletes trivial cycles, but there may be dead cycles that are larger.
>
> I don't understand what you mean.
> Should the patch be rejected because it doesn't clean *everything* ?

Yes. Doing this in JumpThreading makes sense only if it avoids issues related to self-referential instructions (inside JumpThreading), and it cannot do so unless it removes all unreachable blocks. For example, I don't think it covers the case from https://reviews.llvm.org/D139783.

If this is *not* about self-referential instructions breaking JumpThreading itself, then you need to make the motivation for this clearer -- for example, are you addressing a phase ordering problem? (If so, please add a phase ordering test.)


Repository:
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  https://reviews.llvm.org/D138027/new/

https://reviews.llvm.org/D138027