[PATCH] D115755: [InstSimplify] Fold logic And to Zero

[Mehrnoosh Heidarpour via Phabricator via llvm-commits]

MehrHeidar added a comment.

In D115755#3204863 <https://reviews.llvm.org/D115755#3204863>, @spatel wrote:

> In D115755#3204851 <https://reviews.llvm.org/D115755#3204851>, @MehrHeidar wrote:
>
>> But, this one is not complicated enough to catch this pattern : )   -->`(Y ^ (Y | X) ) & ((X | Y) ^ X) --> 0`
>>
>>   %or1 = or i32 %y, %x
>>    %or2 = or i32 %x, %y
>>    %xor1 = xor i32 %y, %or1
>>    %xor2 = xor i32 %or2, %x
>>    %and = and i32 %xor1, %xor2
>>    ret i32 %and
>
> Unless we have some evidence that this pattern can escape a typical -O1 pipeline, I don't think we need to care about it. `%or1` and `%or2` should be CSE'd independently of instsimplify. In other words, I think the positive tests only need to include a single 'or' instruction. If you want to include a test with different 'or' instructions to show the limits of instsimplify, that's fine.

Thank you for explaining the reason behind this. I checked the test case and it did get simplified and we ended up with a single `or`; So I updated the code and test cases.


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