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

[Jeff Law <jeffreyalaw@gmail.com>]

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.

Sure.

jeff