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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/78103] Failure to optimize with __builtin_clzl
Date: Mon, 26 Jul 2021 21:08:27 +0000 [thread overview]
Message-ID: <bug-78103-4-gUIyqW86Ts@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-78103-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78103
--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #13)
> (In reply to Jakub Jelinek from comment #10)
> > Unfortunately, it doesn't work for the #c0 testcase, after the combiner
> > splitter kicks in, the combiner doesn't even try that 4 insn combination.
>
> It does for me?
But only in the unpatched gcc, no?
For #c0 findLastSet I actually need to combine 5 original instructions, and
what I was hoping for is to first combine first 3 instructions into 2,
9, 10 -> 12 to get rid of the useless sign-extension, the value is known to be
0..63, so zero extension is fine, into 10 (bsr) and 12 (xor with zero extend),
which is what the #c9 patch does.
And then I was hoping 10, 12, 13 -> 14 would be attempted to be combined
because 13 is mov of a constant. But that doesn't happen because the 9, 10 ->
12 combination with the #c9 patch throws away the 12 -> 10 LOG_LINKS and
doesn't add a new one, even when 10 is a setter of a fresh new pseudo and 12 is
the only use of that pseudo.
next prev parent reply other threads:[~2021-07-26 21:08 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-78103-4@http.gcc.gnu.org/bugzilla/>
2021-07-24 6:20 ` pinskia at gcc dot gnu.org
2021-07-24 12:28 ` jakub at gcc dot gnu.org
2021-07-26 10:57 ` jakub at gcc dot gnu.org
2021-07-26 11:14 ` jakub at gcc dot gnu.org
2021-07-26 11:22 ` jakub at gcc dot gnu.org
2021-07-26 12:11 ` jakub at gcc dot gnu.org
2021-07-26 21:01 ` segher at gcc dot gnu.org
2021-07-26 21:08 ` jakub at gcc dot gnu.org [this message]
2021-07-26 21:26 ` segher at gcc dot gnu.org
2021-07-27 8:52 ` jakub at gcc dot gnu.org
2021-07-27 12:35 ` segher at gcc dot gnu.org
2021-07-27 12:41 ` jakub at gcc dot gnu.org
2021-07-27 13:53 ` jakub at gcc dot gnu.org
2021-07-27 15:25 ` segher at gcc dot gnu.org
2021-07-27 15:37 ` segher at gcc dot gnu.org
2021-07-31 7:21 ` cvs-commit at gcc dot gnu.org
2021-07-31 8:24 ` jakub at gcc dot gnu.org
2021-08-01 20:33 ` cvs-commit at gcc dot gnu.org
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