On 11/13/24 15:12, Richard Biener wrote:
On Wed, Nov 13, 2024 at 3:05 PM Thomas Koenig <tkoe...@netcologne.de> wrote:
Hello world,
J3, the US Fortran standards committee, has passed
https://j3-fortran.org/doc/year/24/24-179.txt
which states (with a bit of an overabundance of
clarity) that, in Fortran, it is possible special-case
complex multiplication when one of the numbers is known
to have a zero component, for example when promoting
a real to complex for complex multiplication. For
example, multiplying a complex variable b with a real
variable a can be done with c%re = b%re * a, c%im = b%im * a,
without considering NaNs and infinities. Apparently, other
Fortran compilers do this.
They also stated that ISO/IEC 60559:2020 (aka IEEE 754) does
not specify complex arithmetic (I wouldn't know, because it is a
paywalled standard).
How do we want to deal with this? Do we want to implement this
(it's an obvious speed advantage)? Should it be the default?
Do we want to include this in -fcx-fortran-rules?
The middle-end complex lowering pass does this already, irrespective
of NaNs, same for some degenerate cases with division.
Are you sure ?
For this code:
$ cat complex.f90
complex function p(c, r)
complex, intent(in) :: c
real, intent(in) :: r
p = c * r
end
I definitely see a difference between
$ gfortran -O2 -S complex.f90
and
$ gfortran -O2 -ffast-math -S complex.f90
--
Toon Moene - e-mail: t...@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG Maartensdijk, The Netherlands
