public inbox for gcc-patches@gcc.gnu.org
 help / color / mirror / Atom feed
From: Jeff Law <jeffreyalaw@gmail.com>
To: Philipp Tomsich <philipp.tomsich@vrull.eu>, gcc-patches@gcc.gnu.org
Cc: Jeff Law <jlaw@ventanamicro.com>,
	Palmer Dabbelt <palmer@rivosinc.com>,
	Christoph Muellner <christoph.muellner@vrull.eu>,
	Kito Cheng <kito.cheng@gmail.com>,
	Vineet Gupta <vineetg@rivosinc.com>
Subject: Re: [PATCH] RISC-V: Split "(a & (1UL << bitno)) ? 0 : 1" to bext + xori
Date: Tue, 15 Nov 2022 10:36:37 -0700	[thread overview]
Message-ID: <cbbe20b9-98fc-6c78-6a05-5aff602dac5a@gmail.com> (raw)
In-Reply-To: <20221113204849.4062129-1-philipp.tomsich@vrull.eu>


On 11/13/22 13:48, Philipp Tomsich wrote:
> We avoid reassociating "(~(a >> BIT_NO)) & 1" into "((~a) >> BIT_NO) & 1"
> by splitting it into a zero-extraction (bext) and an xori.  This both
> avoids burning a register on a temporary and generates a sequence that
> clearly captures 'extract bit, then invert bit'.
>
> This change improves the previously generated
>      srl   a0,a0,a1
>      not	  a0,a0
>      andi  a0,a0,1
> into
>      bext  a0,a0,a1
>      xori  a0,a0,1
>
> Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
>
> gcc/ChangeLog:
>
> 	* config/riscv/bitmanip.md: Add split covering
> 	"(a & (1 << BIT_NO)) ? 0 : 1".
>
> gcc/testsuite/ChangeLog:
>
> 	* gcc.target/riscv/zbs-bext.c: Add testcases.
> 	* gcc.target/riscv/zbs-bexti.c: Add testcases.

OK.   Not terribly happy with the SUBREG, but I can guess that's an 
artifact of other patterns which require that operand to be QImode.


Jeff



  reply	other threads:[~2022-11-15 17:36 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-13 20:48 Philipp Tomsich
2022-11-15 17:36 ` Jeff Law [this message]
2022-11-16 20:01   ` Philipp Tomsich

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=cbbe20b9-98fc-6c78-6a05-5aff602dac5a@gmail.com \
    --to=jeffreyalaw@gmail.com \
    --cc=christoph.muellner@vrull.eu \
    --cc=gcc-patches@gcc.gnu.org \
    --cc=jlaw@ventanamicro.com \
    --cc=kito.cheng@gmail.com \
    --cc=palmer@rivosinc.com \
    --cc=philipp.tomsich@vrull.eu \
    --cc=vineetg@rivosinc.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).