Re: [PATCH] RISC-V: Handle "(a & twobits) == singlebit" in branches using Zbs

[Philipp Tomsich <philipp.tomsich@vrull.eu>]

On Thu, 17 Nov 2022 at 17:39, Jeff Law <jeffreyalaw@gmail.com> wrote:
>
>
> On 11/17/22 08:12, Philipp Tomsich wrote:
> >
> > This serves as an assertion only, as that case is non-sensical and
> > will be optimized away by earlier passes (as "a & C == T" with C and T
> > sharing no bits will always be false).
> > IFAIK the preceding transforms should always clean such a check up,
> > but we can't exclude the possibility that with enough command line
> > overrides and params we might see such a non-sensical test making it
> > all the way to the backend.
>
> Good!  I was thinking in the back of my mind that the no-sharing-bits
> case should have been handled in the generic optimizers.  Thanks for
> clarifying.
>
>
> >
> > What would you recommend? Adding this to the pattern's condition feels
> > a bit redundant.
>
> We can leave it in the splitter.
>
>
> > In fact, I am leaning towards hiding the !SMALL_OPERAND check in yet
> > another predicate that combines const_twobits_operand with a
> > match_test for !SMALL_OPERAND.

I'll send a v2 with this cleaned up (and look into clarifying things
around the FAIL).

Philipp.