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From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/107172] [13 Regression] wrong code with "-O1 -ftree-vrp" on x86_64-linux-gnu since r13-1268-g8c99e307b20c502e
Date: Wed, 12 Oct 2022 17:50:22 +0000 [thread overview]
Message-ID: <bug-107172-4-ZwI7tLwBy5@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-107172-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107172
--- Comment #22 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Segher Boessenkool from comment #21)
> (In reply to Hongtao.liu from comment #19)
> > (In reply to H.J. Lu from comment #18)
> > > (In reply to Segher Boessenkool from comment #16)
> > > > Hi Roger,
> > > >
> > > > (In reply to Roger Sayle from comment #15)
> > > > > Yes, a COMPARE rtx can be used to set various flags on x86, but many other
> > > > > operations also legitimately set and/or use MODE_CC, often in a parallel
> > > > > with the primary operation.
> > > >
> > > > *Any* MODE_CC setter sets the flags as-if from a compare. This is what
> > > > MODE_CC *is*.
> > > >
> > > > Setting something as ne:CC and then using it as somethingelse:CC has no
> > > > defined meaning.
> > >
> > > This
> > >
> > > (parallel [
> > > (set (reg:SI 97)
> > > (neg:SI (ltu:SI (reg:CCC 17 flags)
> > > (const_int 0 [0]))))
> > > (clobber (reg:CC 17 flags))
> > > ])
> > >
> > > still won't work correctly if reg:CCC 17 flags is set by a compare of
> > > 2 known values.
> >
> > I guess Segher means it should be NE instead of LTU in the
> > x86_mov<mode>cc_0_m1_neg, since the setters is NE to const 0.
>
> Yes.
So the issue is with the consumer:
(insn 50 49 51 2 (parallel [
(set (reg:SI 93)
(neg:SI (ltu:SI (reg:CCC 17 flags)
(const_int 0 [0]))))
(clobber (reg:CC 17 flags))
]) "107172.c":4:10 1258 {*x86_movsicc_0_m1_neg}
(expr_list:REG_DEAD (reg:CCC 17 flags)
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil))))
There are many similar patterns in different backends. They work as long as
the flags register isn't a known constant since simplify-rtx.cc leaves them
alone. They become a problem only when the flags register is a known constant.
next prev parent reply other threads:[~2022-10-12 17:50 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-06 17:51 [Bug tree-optimization/107172] New: wrong code with "-O1 -ftree-vrp" on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
2022-10-06 18:02 ` [Bug tree-optimization/107172] [13 Regression] " pinskia at gcc dot gnu.org
2022-10-06 18:46 ` [Bug tree-optimization/107172] [13 Regression] wrong code with "-O1 -ftree-vrp" on x86_64-linux-gnu since r13-1268-g8c99e307b20c502e marxin at gcc dot gnu.org
2022-10-07 7:21 ` rguenth at gcc dot gnu.org
2022-10-07 12:17 ` aldyh at gcc dot gnu.org
2022-10-07 21:04 ` [Bug target/107172] " hjl.tools at gmail dot com
2022-10-07 22:20 ` hjl.tools at gmail dot com
2022-10-09 21:51 ` roger at nextmovesoftware dot com
2022-10-10 18:32 ` segher at gcc dot gnu.org
2022-10-10 18:34 ` segher at gcc dot gnu.org
2022-10-10 19:16 ` hjl.tools at gmail dot com
2022-10-10 20:55 ` segher at gcc dot gnu.org
2022-10-11 0:10 ` hjl.tools at gmail dot com
2022-10-11 16:16 ` segher at gcc dot gnu.org
2022-10-11 17:16 ` hjl.tools at gmail dot com
2022-10-11 18:05 ` segher at gcc dot gnu.org
2022-10-11 19:49 ` roger at nextmovesoftware dot com
2022-10-11 20:26 ` segher at gcc dot gnu.org
2022-10-11 22:30 ` hjl.tools at gmail dot com
2022-10-11 22:38 ` hjl.tools at gmail dot com
2022-10-12 7:17 ` crazylht at gmail dot com
2022-10-12 7:25 ` crazylht at gmail dot com
2022-10-12 8:11 ` segher at gcc dot gnu.org
2022-10-12 17:50 ` hjl.tools at gmail dot com [this message]
2022-10-13 3:38 ` crazylht at gmail dot com
2022-10-13 8:14 ` ubizjak at gmail dot com
2022-10-13 12:31 ` crazylht at gmail dot com
2022-10-13 16:54 ` hjl.tools at gmail dot com
2022-10-13 17:49 ` hjl.tools at gmail dot com
2022-10-13 22:07 ` segher at gcc dot gnu.org
2022-10-13 22:12 ` segher at gcc dot gnu.org
2022-10-13 22:20 ` segher at gcc dot gnu.org
2022-10-13 22:23 ` hjl.tools at gmail dot com
2022-10-13 22:34 ` hjl.tools at gmail dot com
2022-10-15 14:53 ` segher at gcc dot gnu.org
2022-10-17 3:28 ` crazylht at gmail dot com
2022-10-17 7:48 ` rguenth at gcc dot gnu.org
2022-10-17 7:55 ` rguenth at gcc dot gnu.org
2022-10-17 15:59 ` hjl.tools at gmail dot com
2022-10-17 22:01 ` segher at gcc dot gnu.org
2022-10-18 0:19 ` hjl.tools at gmail dot com
2022-10-18 14:44 ` segher at gcc dot gnu.org
2022-10-18 19:54 ` hjl.tools at gmail dot com
2022-10-18 20:14 ` segher at gcc dot gnu.org
2022-10-20 17:25 ` pinskia at gcc dot gnu.org
2022-10-20 19:03 ` hjl.tools at gmail dot com
2022-10-22 21:14 ` segher at gcc dot gnu.org
2022-10-27 18:42 ` cvs-commit at gcc dot gnu.org
2022-10-28 9:11 ` roger at nextmovesoftware dot com
2022-10-28 15:48 ` hjl.tools at gmail dot com
2022-11-30 17:33 ` jakub at gcc dot gnu.org
2022-11-30 21:52 ` hjl.tools at gmail dot com
2023-05-30 13:44 ` cvs-commit at gcc dot gnu.org
2023-07-27 14:47 ` shaohua.li at inf dot ethz.ch
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