[PATCH] D68930: [InstCombine] Shift amount reassociation in shifty sign bit test (PR43595)

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In D68930#1714878 <https://reviews.llvm.org/D68930#1714878>, @lebedev.ri wrote:

> In D68930#1714856 <https://reviews.llvm.org/D68930#1714856>, @xbolva00 wrote:
>
> > >> sadly i'm still seeing regressions (although smaller!) in target benchmark, and analysis of IR points to *this* missing pattern
> >
> > But does this or base pattern shows up somewhere else (test suite/clang/chromium) than in your benchmark?
>
>
> It's not "'your benchmark'", that is a real code. I'm not pulling it out of a thin air.


I don't think the intent was to disrespect whatever code this pattern showed up in, but to ask if there are any stats for common clang benchmarks. That's the only way we can draw a line on these kinds of decisions. Every pattern is presumably showing up somewhere real for someone, so we can't distinguish where it belongs just based on existence.

My opinion (and others have disagreed with this) is that we always want the fold somewhere; it's just a question of where does it go to minimize cost/maximize benefit.


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