[llvm-dev] RFC: Mark BasicAA as a CFG-only pass.

Hal Finkel via llvm-dev
2020-02-10T21:48:12Z

On 2/10/20 2:35 PM, Alina Sbirlea wrote:
> Hi,
>
> Here's a tentative patch of the changes for this: D74353
> <https://reviews.llvm.org/D74353>.


I suppose that, as expected, it's invalidated less often this way. Given
that it's generally stateless, does this really represent a cost savings?

  -Hal


>
> Thank you,
> Alina
>
>
> On Mon, Feb 10, 2020 at 11:34 AM Alina Sbirlea
> <alina.sbirlea at gmail.com <mailto:alina.sbirlea at
gmail.com>> wrote:
>
>     Hi,
>
>     I'd like to understand if it makes sense to keep BasicAA as a not
>     CFG-only pass, or if it can be updated to CFG-only. The change was
>     made in D44564 <https://reviews.llvm.org/D44564>.
>
>     From what I gathered the motivation was PhiValuesAnalysis not
>     being properly updated, and BasicAA having an instance of it.
>     PhiValuesAnalysis now uses callback values to invalidate deleted
>     values (r340613
>     <https://reviews.llvm.org/rL340613>),PhiValuesAnalysis is also
>     being updated in MemDepAnalysis (D48489
>     <https://reviews.llvm.org/D48489>) and BasicAA is invalidated if
>     PhiValuesAnalysis gets invalidated.
>
>     I may not have the full context here, so I'd like some feedback:
>     does it make sense to make BasicAA a CFG-only pass again?
>
>     Thank you,
>     Alina
>
--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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