From: Jeff Law <jeffreyalaw@gmail.com>
To: Philipp Tomsich <philipp.tomsich@vrull.eu>
Cc: gcc-patches@gcc.gnu.org,
Christoph Muellner <christoph.muellner@vrull.eu>,
Kito Cheng <kito.cheng@gmail.com>,
Vineet Gupta <vineetg@rivosinc.com>,
Jeff Law <jlaw@ventanamicro.com>,
Palmer Dabbelt <palmer@rivosinc.com>
Subject: Re: [PATCH] RISC-V: Handle "(a & twobits) == singlebit" in branches using Zbs
Date: Thu, 17 Nov 2022 09:39:49 -0700 [thread overview]
Message-ID: <b622499f-eed1-fd43-cc18-ac828dd916d4@gmail.com> (raw)
In-Reply-To: <CAAeLtUAMq=XiECQp=giT6o=oeZeAg4W-3f_OH6p3=TeFt6GsFQ@mail.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
next prev parent reply other threads:[~2022-11-17 16:39 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-13 20:48 Philipp Tomsich
2022-11-17 14:58 ` Jeff Law
2022-11-17 15:12 ` Philipp Tomsich
2022-11-17 16:39 ` Jeff Law [this message]
2022-11-17 16:46 ` Philipp Tomsich
2022-11-17 18:25 ` Andrew Pinski
2022-11-17 18:27 ` Andrew Pinski
2022-11-17 18:57 ` Philipp Tomsich
2022-11-17 18:33 ` Andrew Waterman
2022-11-17 18:51 ` Philipp Tomsich
2022-11-17 18:56 ` Andrew Waterman
2022-11-17 18:59 ` Philipp Tomsich
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