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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/51954] __int128_t (and long long on x86) negation can be optimized
Date: Mon, 21 Feb 2022 06:29:17 +0000 [thread overview]
Message-ID: <bug-51954-4-nI6VtLc8hV@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-51954-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51954
--- Comment #4 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Andrew Pinski from comment #2)
> We get this now:
>
> movq %rdi, %rax
> movq %rsi, %rdx
> negq %rax
> adcq $0, %rdx
> negq %rdx
>
> ICC produces:
> xorl %edx, %edx #3.10
> xorl %eax, %eax #3.10
> subq %rdi, %rax #3.10
> sbbq %rsi, %rdx #3.10
> ret #3.10
>
> Which seems even better.
>
> LLVM does produce:
> movq %rdi, %rax
> xorl %edx, %edx
> negq %rax
> sbbq %rsi, %rdx
>
> Which basically combines the addcq and negq together and changes one mov
> into an exor.
Yes, neg rdx = (0 - rdx) = (0 - (rdx + CF)(last def)) = (sbb 0, rdx)
next prev parent reply other threads:[~2022-02-21 6:29 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-23 1:43 [Bug rtl-optimization/51954] New: __int128_t " svfuerst at gmail dot com
2012-01-23 4:00 ` [Bug rtl-optimization/51954] __int128_t (and long long on x86) " pinskia at gcc dot gnu.org
2021-12-26 22:34 ` [Bug target/51954] " pinskia at gcc dot gnu.org
2022-02-21 5:57 ` pinskia at gcc dot gnu.org
2022-02-21 6:29 ` crazylht at gmail dot com [this message]
2022-02-21 6:49 ` crazylht at gmail dot com
2022-02-21 7:45 ` ubizjak at gmail dot com
2022-02-21 7:52 ` ubizjak at gmail dot com
2022-02-21 7:57 ` ubizjak at gmail dot com
2022-04-29 11:31 ` cvs-commit at gcc dot gnu.org
2022-04-29 11:33 ` ubizjak at gmail dot com
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