[patch, fortran] Fix PR 85544

[Paul Richard Thomas]

Hi Thomas,

That's OK for 7-  through 9-branches.

Thanks for the fix.

Paul

On Sun, 16 Dec 2018 at 22:01, Thomas Koenig <tkoenig@netcologne.de> wrote:
>
> Hello world,
>
> the PR pointed out an old regression because the front-end optimization
> pass was substituting 2**n with ishift(1,n), where n was an array.
>
> Simply removing the optimization for that case would have been easy,
> but also introduced a performance regression.
>
> So, for this, I moved the optimization to trans-*, where it makes more
> sense.
>
> Regression-tested.  This turned up that one of our tests, mvbits_1.f90,
> depends on the behavior that 2**32 is zero.  This is certainly not
> guaranteed by the standard, but I chose to keep the behavior as not
> to introduce any changes in behavior.
>
> This fixes a regression, so I would like to backport to all active
> branches if this if possible.
>
> Oh yes, if anybody feels strongly that we should also optimize 32**n
> and powers of other powers to two, now is the time to speak up :-)
>
> OK for affected branches?
>
> Regards
>
>         Thomas
>
> 2018-12-16  Thomas Koenig  <tkoenig@gcc.gnu.org>
>
>          PR fortran/85544
>          * frontend-passes.c (optimize_power): Remove.
>          (optimize_op): Remove call to optimize_power.
>          * trans-expr.c (gfc_conv_power_op): Handle cases of 1**integer,
>          (2|4|8|16) ** integer and (-1) ** integer.
>
> 2018-12-16  Thomas Koenig  <tkoenig@gcc.gnu.org>
>
>          PR fortran/85544
>          * gfortran.dg/power_7.f90: New test.



-- 
"If you can't explain it simply, you don't understand it well enough"
- Albert Einstein