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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/97832] AoSoA complex caxpy-like loops: AVX2+FMA -Ofast 7 times slower than -O3
Date: Fri, 25 Nov 2022 20:46:42 +0000 [thread overview]
Message-ID: <bug-97832-4-MqkCn0Xs7c@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-97832-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97832
--- Comment #17 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Michael_S from comment #16)
> On unrelated note, why loop overhead uses so many instructions?
> Assuming that I am as misguided as gcc about load-op combining, I would
> write it as:
> sub %rax, %rdx
> .L3:
> vmovupd (%rdx,%rax), %ymm1
> vmovupd 32(%rdx,%rax), %ymm0
> vfmadd213pd 32(%rax), %ymm3, %ymm1
> vfnmadd213pd (%rax), %ymm2, %ymm0
> vfnmadd231pd 32(%rdx,%rax), %ymm3, %ymm0
> vfnmadd231pd (%rdx,%rax), %ymm2, %ymm1
> vmovupd %ymm0, (%rax)
> vmovupd %ymm1, 32(%rax)
> addq $64, %rax
> decl %esi
> jb .L3
>
> The loop overhead in my variant is 3 x86 instructions==2 macro-ops,
> vs 5 x86 instructions==4 macro-ops in gcc variant.
> Also, in gcc variant all memory accesses have displacement that makes them
> 1 byte longer. In my variant only half of accesses have displacement.
>
> I think, in the past I had seen cases where gcc generates optimal or
> near-optimal
> code sequences for loop overhead. I wonder why it can not do it here.
I don't think we currently consider IVs based on the difference of two
addresses. The cost benefit of no displacement is only size, otherwise
I have no idea why we have biased the %rax accesses by -32. Why we
fail to consider decrement-to-zero for the counter IV is probably because
IVCANON would add such IV but the vectorizer replaces that and IVOPTs
doesn't consider re-adding that.
next prev parent reply other threads:[~2022-11-25 20:46 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-14 20:44 [Bug target/97832] New: " already5chosen at yahoo dot com
2020-11-16 7:21 ` [Bug target/97832] " rguenth at gcc dot gnu.org
2020-11-16 11:11 ` rguenth at gcc dot gnu.org
2020-11-16 20:11 ` already5chosen at yahoo dot com
2020-11-17 9:21 ` [Bug tree-optimization/97832] " rguenth at gcc dot gnu.org
2020-11-17 10:18 ` rguenth at gcc dot gnu.org
2020-11-18 8:53 ` rguenth at gcc dot gnu.org
2020-11-18 9:15 ` rguenth at gcc dot gnu.org
2020-11-18 13:23 ` rguenth at gcc dot gnu.org
2020-11-18 13:39 ` rguenth at gcc dot gnu.org
2020-11-19 19:55 ` already5chosen at yahoo dot com
2020-11-20 7:10 ` rguenth at gcc dot gnu.org
2021-06-09 12:41 ` cvs-commit at gcc dot gnu.org
2021-06-09 12:54 ` rguenth at gcc dot gnu.org
2022-01-21 0:16 ` pinskia at gcc dot gnu.org
2022-11-24 23:22 ` already5chosen at yahoo dot com
2022-11-25 8:16 ` rguenth at gcc dot gnu.org
2022-11-25 13:19 ` already5chosen at yahoo dot com
2022-11-25 20:46 ` rguenth at gcc dot gnu.org [this message]
2022-11-25 21:27 ` amonakov at gcc dot gnu.org
2022-11-26 18:27 ` already5chosen at yahoo dot com
2022-11-26 18:36 ` already5chosen at yahoo dot com
2022-11-26 19:36 ` amonakov at gcc dot gnu.org
2022-11-26 22:00 ` already5chosen at yahoo dot com
2022-11-28 6:29 ` crazylht at gmail dot com
2022-11-28 6:42 ` crazylht at gmail dot com
2022-11-28 7:21 ` rguenther at suse dot de
2022-11-28 7:24 ` crazylht at gmail dot com
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