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From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug debug/99830] [11 Regression] ICE: in lra_eliminate_regs_1, at lra-eliminations.c:659 with -O2 -fno-expensive-optimizations -fno-split-wide-types -g
Date: Fri, 09 Apr 2021 18:01:38 +0000	[thread overview]
Message-ID: <bug-99830-4-m0oreOjENP@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-99830-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99830

--- Comment #12 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #11)
> I don't understand what is wrong about that.
> (clobber:TI (const_int 0 [0])) in there stands for couldn't figure out what
> this value is or how to represent it, so it is wildcard for I don't know
> what the value is.

That is not what it means.  It means "This instruction is invalid".  It should
never be "optimised" away.

> I'd think if one has say (and:TI (clobber:TI (const_int 0 [0])) (const_int 0
> [0])) one should be able to still simplify it into 0, etc.,

No.  That RTL has no meaning at all, you cannot use a clobber as a RHS!

> and what happens
> here is the same thing, the clobber value, whatever it is, doesn't influence
> in any way the whole expression value, therefore it is optimized away.
> If it remained there, sure, the instruction would fail recog_for_combine.

Yes.  And that is why it should never be removed!

  parent reply	other threads:[~2021-04-09 18:01 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-30 14:11 [Bug rtl-optimization/99830] New: " zsojka at seznam dot cz
2021-03-30 16:14 ` [Bug rtl-optimization/99830] " acoplan at gcc dot gnu.org
2021-03-31  7:53 ` rguenth at gcc dot gnu.org
2021-04-08 13:21 ` rguenth at gcc dot gnu.org
2021-04-08 13:27 ` jakub at gcc dot gnu.org
2021-04-08 14:45 ` [Bug debug/99830] " jakub at gcc dot gnu.org
2021-04-09 12:29 ` segher at gcc dot gnu.org
2021-04-09 12:36 ` jakub at gcc dot gnu.org
2021-04-09 12:38 ` segher at gcc dot gnu.org
2021-04-09 13:27 ` jakub at gcc dot gnu.org
2021-04-09 14:23 ` jakub at gcc dot gnu.org
2021-04-09 17:09 ` segher at gcc dot gnu.org
2021-04-09 17:31 ` jakub at gcc dot gnu.org
2021-04-09 18:01 ` segher at gcc dot gnu.org [this message]
2021-04-09 19:10 ` jakub at gcc dot gnu.org
2021-04-09 19:10 ` jakub at gcc dot gnu.org
2021-04-09 21:29 ` segher at gcc dot gnu.org
2021-04-12 16:20 ` jakub at gcc dot gnu.org
2021-04-12 23:01 ` cvs-commit at gcc dot gnu.org
2021-04-12 23:03 ` jakub at gcc dot gnu.org
2021-04-20  9:46 ` cvs-commit at gcc dot gnu.org
2021-04-20 23:34 ` cvs-commit at gcc dot gnu.org
2021-04-22 16:52 ` cvs-commit at gcc dot gnu.org

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