[PATCH] D124168: DeadMachineInstructionElim: Switch to using LiveRegUnits

Mon Sep 12 14:56:19 PDT 2022

nikic added a comment.

In D124168#3784875 <https://reviews.llvm.org/D124168#3784875>, @arsenm wrote:

> In D124168#3784598 <https://reviews.llvm.org/D124168#3784598>, @arsenm wrote:
>
>> In D124168#3784108 <https://reviews.llvm.org/D124168#3784108>, @nikic wrote:
>>
>>>> Theoretically improves compile time for targets with many overlapping registers
>>>
>>> In practice, this is a major compile time regression instead: http://llvm-compile-time-tracker.com/compare.php?from=6c44a7179f1747ec38d580e6b50bde98555ad811&to=b5041527c75de2f409aa9e2e6deba12b17834c59&stat=instructions
>>
>> This doesn't make much sense. My preliminary analysis says that this is somehow phys_regs_and_masks fault (which really doesn't buy any real code simplification over iterating the operands)
>
> Hopefully d90f7cb559e32c2cbf1f9839d7e8e0cc0be189ba <https://reviews.llvm.org/rGd90f7cb559e32c2cbf1f9839d7e8e0cc0be189ba> fixes this

It does recover most of the regression: http://llvm-compile-time-tracker.com/compare.php?from=ab56719acd98778fb2e48fa425ac7c8d27bdea86&to=d90f7cb559e32c2cbf1f9839d7e8e0cc0be189ba&stat=instructions

There is still a bit of residual regression left though: http://llvm-compile-time-tracker.com/compare.php?from=6c44a7179f1747ec38d580e6b50bde98555ad811&to=d90f7cb559e32c2cbf1f9839d7e8e0cc0be189ba&stat=instructions

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D124168/new/

https://reviews.llvm.org/D124168