From: "Stefan Franke" <s.franke@bebbosoft.de>
To: <gcc-help@gcc.gnu.org>
Subject: AW: Correct way to express to the compiler "this does not get clobbered"?
Date: Fri, 4 Dec 2020 19:57:39 +0100 [thread overview]
Message-ID: <017801d6ca6f$56fed450$04fc7cf0$@bebbosoft.de> (raw)
In-Reply-To: <017701d6ca6d$7dc8dc90$795a95b0$@bebbosoft.de>
> > -----Ursprüngliche Nachricht-----
> > Von: Gcc-help <gcc-help-bounces@gcc.gnu.org> Im Auftrag von Segher
> > Boessenkool
> > Gesendet: Freitag, 4. Dezember 2020 19:33
> > An: Andrea Corallo <andrea.corallo@arm.com>
> > Cc: stefan@franke.ms; gcc-help@gcc.gnu.org
> > Betreff: Re: Correct way to express to the compiler "this does not get
> > clobbered"?
> >
> > On Fri, Dec 04, 2020 at 07:16:45PM +0100, Andrea Corallo via Gcc-help
> wrote:
> > > Segher Boessenkool <segher@kernel.crashing.org> writes:
> > >
> > > > On Fri, Dec 04, 2020 at 10:52:17AM +0100, Andrea Corallo via
> Gcc-help
> > wrote:
> > > >> stefan@franke.ms writes:
> > > >> I might open a bug but my understanding is that const is
> > > >> generally not used for optimizations. Am I wrong?
> > > >
> > > > extern const int x = 42;
> > > > int f(void) { return x; }
> > > >
> > > > The code generated for f does not load the value for x from memory:
> > > > it returns 42 always.
> >
> > > Are you suggesting we should treat this as a bug?
> >
> > Huh? No, I am just saying that const *is* used for optimisation, with
> > a
> dumb
> > simple example. Remove const from this code and you get different
> > generated machine code (that does load x from memory always).
> >
> > If you think you have found a missing optimisation, please make a
> > self- contained demonstrator for that, and a file a PR?
> >
> >
> > Segher
IMHO it's the cprop pass which should get enhanced.
Stefan
next prev parent reply other threads:[~2020-12-04 18:57 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-03 11:47 Andrea Corallo
2020-12-03 12:04 ` Richard Earnshaw
2020-12-03 12:28 ` Andrea Corallo
2020-12-03 13:06 ` Richard Earnshaw
2020-12-03 13:40 ` Andrea Corallo
2020-12-03 18:24 ` David Brown
2020-12-03 23:00 ` Andrea Corallo
2020-12-04 7:23 ` stefan
2020-12-04 9:52 ` Andrea Corallo
2020-12-04 17:27 ` Segher Boessenkool
2020-12-04 18:16 ` Andrea Corallo
2020-12-04 18:33 ` Segher Boessenkool
2020-12-04 18:45 ` Andrea Corallo
[not found] ` <017701d6ca6d$7dc8dc90$795a95b0$@bebbosoft.de>
2020-12-04 18:57 ` Stefan Franke [this message]
2020-12-04 22:52 ` AW: " Andrea Corallo
2020-12-05 14:01 ` David Brown
2020-12-05 14:17 ` AW: " Stefan Franke
2020-12-05 18:10 ` Andrea Corallo
2020-12-07 22:27 ` Segher Boessenkool
2020-12-05 19:03 ` David Brown
2020-12-06 11:29 ` AW: " Stefan Franke
2020-12-05 17:29 ` Andrea Corallo
2020-12-05 19:07 ` David Brown
2020-12-06 9:22 ` Jonathan Wakely
2020-12-04 8:27 ` David Brown
2020-12-04 10:05 ` Andrea Corallo
2020-12-05 8:06 ` Liu Hao
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