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From: "jv244 at cam dot ac dot uk" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/25620] Missed optimization with power
Date: Mon, 04 Sep 2006 14:10:00 -0000 [thread overview]
Message-ID: <20060904141034.12947.qmail@sourceware.org> (raw)
In-Reply-To: <bug-25620-6642@http.gcc.gnu.org/bugzilla/>
------- Comment #9 from jv244 at cam dot ac dot uk 2006-09-04 14:10 -------
(In reply to comment #7)
> Looking at how we deal with all this, we seem to like pow() very much during
> folding, even doing the reverse transformations you suggest. The
> transformation
> back to sqrt ( x**N ) with N being an integer could be done by
> expand_builtin_pow
> in case that computation of sqrt is cheap. Other than that, exposing integer
> powers is only a win if theres some CSE possibility.
Despite this PR being a bit old, I'd like to add another (similar example, also
from real code) where other compilers generate much better code:
subroutine t(x)
x=x**1.5
end subroutine t
pgf90:
# lineno: 0
sqrtss (%rdi), %xmm0
mulss (%rdi), %xmm0
movss %xmm0, (%rdi)
gfortran -S -O3 -ffast-math:
movss (%rdi), %xmm0
movq %rdi, %rbx
movss .LC0(%rip), %xmm1
call powf
movss %xmm0, (%rbx)
popq %rbx
ret
trying to time this with the following fragment:
y=0.
DO i=1,10000000
x=i
y=y+x**1.5
ENDDO
write(6,*) y
END
pgf90 is about 10 times faster than gfortran
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25620
next prev parent reply other threads:[~2006-09-04 14:10 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-01 12:29 [Bug tree-optimization/25620] New: Missed optimisation " jv244 at cam dot ac dot uk
2006-01-06 14:07 ` [Bug tree-optimization/25620] Missed optimization with power (only with -ffast-math) pinskia at gcc dot gnu dot org
2006-01-13 16:37 ` [Bug tree-optimization/25620] Missed optimization with power pinskia at gcc dot gnu dot org
2006-01-13 16:44 ` [Bug fortran/25620] " rguenth at gcc dot gnu dot org
2006-01-13 17:33 ` jv244 at cam dot ac dot uk
2006-01-13 17:38 ` jv244 at cam dot ac dot uk
2006-01-13 18:15 ` jv244 at cam dot ac dot uk
2006-01-13 18:42 ` rguenth at gcc dot gnu dot org
2006-01-13 19:58 ` kargl at gcc dot gnu dot org
2006-09-04 14:10 ` jv244 at cam dot ac dot uk [this message]
2006-09-04 14:17 ` rguenther at suse dot de
2006-11-04 15:01 ` rguenth at gcc dot gnu dot org
2006-11-05 20:39 ` [Bug middle-end/25620] " patchapp at dberlin dot org
2006-11-26 14:30 ` patchapp at dberlin dot org
2006-11-27 11:39 ` rguenth at gcc dot gnu dot org
2006-11-27 11:52 ` [Bug fortran/25620] " rguenth at gcc dot gnu dot org
2006-11-27 16:49 ` jv244 at cam dot ac dot uk
2007-01-22 22:02 ` fxcoudert at gcc dot gnu dot org
2010-03-18 14:37 ` vincent at vinc17 dot org
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