[PATCH] D110171: [VectorCombine] Switch to using a worklist.

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

In D110171#3012936 <https://reviews.llvm.org/D110171#3012936>, @fhahn wrote:

> In D110171#3012911 <https://reviews.llvm.org/D110171#3012911>, @lebedev.ri wrote:
>
>> Hmm, but this still doesn't do instcombine-style whole-function reprocessing ("iteration"), but only reprocesses the ones explicitly added to worklist.
>> This is intentional?
>
> At the moment, the first combining round is done by iterating over the function without the worklist. Only if something gets simplified, the modified instructions are added. Is this what you are referring to? I did not add all instructions to the worklist up front intentionally.
>
> The number of combines is quite limited at the moment and I expect there are a lot of functions where no combine triggers at all. In those cases, adding everything to the worklist first seems a bit of unnecessary overhead.

Instcombine roughly does the following:

1. add all instructions into worklist
2. pop from worklist until it's empty
3. if made any changes, goto 1.

This essentially does 1. and 2., but not 3.
This may either be an oversight, or an intentional improvement that guarantees that in this pass we don't repeat instcombine's mistake
of relying on 3., but consistently add everything we want reprocessed into worklist.
Thus, i'm asking.


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https://reviews.llvm.org/D110171