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From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/102840] [12 Regression] gcc.target/i386/pr22076.c by r12-4475
Date: Tue, 19 Oct 2021 15:36:03 +0000 [thread overview]
Message-ID: <bug-102840-4-7wZvRzjcR4@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-102840-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102840
--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Roger Sayle from comment #1)
> I believe this test case is poorly written, and not correctly testing the
> original issue in PR target/22076 which concerned suboptimal moving of
> arguments via memory (fixed by prohibiting reload using mmx registers).
>
> Prior to my patch, with -m32 -O2 -fomit-frame-pointer -mmmx -mno-sse2, GCC
> generated:
>
> test: movq .LC1, %mm0
> paddb .LC0, %mm0
> movq %mm0, x
> ret
>
> .x: .zero 8
> .LC0: .byte 1
> .byte 2
> .byte 3
> .byte 4
> .byte 5
> .byte 6
> .byte 7
> .byte 8
> .LC1: .byte 11
> .byte 22
> .byte 33
> .byte 44
> .byte 55
> .byte 66
> .byte 77
> .byte 88
>
> which indeed doesn't use movl, and requires two movq.
>
> After my patch, we now generate the much more efficient (dare I say optimal):
> test: movl $807671820, %eax
> movl $1616136252, %edx
> movl %eax, x
> movl %edx, x+4
> ret
>
> which has evaluated the _mm_add_pi8 at compile-time, and effectively memsets
> x to the correct value in the minimum possible number of cycles. In fact,
> failing to evaluate this at compile-time is a regression since v4.1
> (according to godbolt)
If your analysis is correct, why does -m64 stay the same?
next prev parent reply other threads:[~2021-10-19 15:36 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-19 13:39 [Bug rtl-optimization/102840] New: " hjl.tools at gmail dot com
2021-10-19 14:12 ` [Bug rtl-optimization/102840] " rguenth at gcc dot gnu.org
2021-10-19 14:48 ` roger at nextmovesoftware dot com
2021-10-19 15:36 ` hjl.tools at gmail dot com [this message]
2021-10-19 17:42 ` roger at nextmovesoftware dot com
2021-10-19 18:08 ` hjl.tools at gmail dot com
2021-10-21 18:58 ` cvs-commit at gcc dot gnu.org
2021-10-21 18:59 ` ubizjak at gmail dot com
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