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From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/114515] [14 Regression] Failure to use aarch64 lane forms after PR101523
Date: Thu, 28 Mar 2024 10:09:58 +0000	[thread overview]
Message-ID: <bug-114515-4-uiztCZ3DzG@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-114515-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114515

--- Comment #2 from Segher Boessenkool <segher at gcc dot gnu.org> ---
The PR101523 fix makes sure we do not get the same I2 back, because that
violates algorithmic assumptions of combine.  Importantly, the way it was
things can be changed back time and time again, and that actually happened.
There is no "canonical form" in combine, it all depends on what little
piece of context is and is not considered what form combine prefers.  Things
can -- and DID -- oscillate.

So, what is happening here?  The "dup" here is really a "splat"?  Should the
backend have some extra define_insn or define_split, or maybe even a peephole?

  parent reply	other threads:[~2024-03-28 10:09 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-03-28 10:01 [Bug rtl-optimization/114515] New: " rsandifo at gcc dot gnu.org
2024-03-28 10:05 ` [Bug rtl-optimization/114515] " rguenth at gcc dot gnu.org
2024-03-28 10:06 ` rguenth at gcc dot gnu.org
2024-03-28 10:09 ` segher at gcc dot gnu.org [this message]
2024-03-28 10:19 ` rsandifo at gcc dot gnu.org
2024-03-28 10:29 ` rsandifo at gcc dot gnu.org
2024-03-28 12:43 ` rsandifo at gcc dot gnu.org
2024-03-29 23:47 ` law at gcc dot gnu.org
2024-04-02  8:05 ` rguenth at gcc dot gnu.org
2024-04-02 18:42 ` rdapp at gcc dot gnu.org
2024-04-02 20:24 ` ewlu at rivosinc dot com
2024-04-02 20:45 ` law at gcc dot gnu.org
2024-04-03 15:20 ` tnfchris at gcc dot gnu.org
2024-04-10  6:01 ` [Bug rtl-optimization/114515] [15 " rguenth at gcc dot gnu.org

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