From: Richard Biener <richard.guenther@gmail.com>
To: GCC Patches <gcc-patches@gcc.gnu.org>
Cc: "Hurugalawadi, Naveen" <Naveen.Hurugalawadi@caviumnetworks.com>
Subject: Re: Move some flag_unsafe_math_optimizations using simplify and match
Date: Thu, 20 Aug 2015 08:22:00 -0000 [thread overview]
Message-ID: <CAFiYyc1TTP9xixrB3Aw3eGYN+kYue+r3MH1dUQUmuWXRsHtRdw@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1508200726580.1547@laptop-mg.saclay.inria.fr>
On Thu, Aug 20, 2015 at 7:38 AM, Marc Glisse <marc.glisse@inria.fr> wrote:
> On Thu, 20 Aug 2015, Hurugalawadi, Naveen wrote:
>
>> The following testcase does not generate "x" as needed.
>> ====================
>> double t (double x)
>> {
>> x = sqrt (x) * sqrt (x);
>> return x;
>> }
>> ====================
>
>
> With -fno-math-errno, we CSE the calls to sqrt, so I would expect this to
> match:
>
> (mult (SQRT@1 @0) @1)
>
> Without the flag, I expect that one will apply
>
> (simplify
> (mult (SQRT:s @0) (SQRT:s @1))
> (SQRT (mult @0 @1)))
>
> and then maybe we have something converting sqrt(x*x) to abs(x) or maybe
> not.
ICK. I'd rather have CSE still CSE the two calls by adding some
tricks regarding
to errno ...
> I wonder if all the unsafe math optimizations are really ok without
> -fno-math-errno...
Well, on GIMPLE they will preserve the original calls because of their
side-effects
setting errno... on GENERIC probably not.
Richard.
> --
> Marc Glisse
next prev parent reply other threads:[~2015-08-20 8:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-17 5:29 Hurugalawadi, Naveen
2015-08-18 10:24 ` Richard Biener
2015-08-19 6:47 ` Hurugalawadi, Naveen
2015-08-19 10:06 ` Richard Biener
2015-08-20 5:38 ` Hurugalawadi, Naveen
2015-08-20 6:20 ` Marc Glisse
2015-08-20 8:22 ` Richard Biener [this message]
2015-08-20 9:18 ` Marc Glisse
2015-08-20 8:17 ` Richard Biener
2015-08-20 9:24 ` Hurugalawadi, Naveen
2015-08-20 11:00 ` Richard Biener
2015-08-21 8:51 ` Richard Biener
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