[Patch, fortran] PR35339 Optimize implied do loops in io statements

[Nicolas Koenig]

Hello Dominique,

attached is the next try, this time without stupidities (I hope). Both 
test cases you posted don't ICE anymore.

Ok for trunk?

Nicolas

Regression tested for x86_64-pc-linux-gnu.

Changelog (still the same):
2017-05-27  Nicolas Koenig  <koenigni@student.ethz.ch>

         PR fortran/35339
         * frontend-passes.c (traverse_io_block): New function.
         (simplify_io_impl_do): New function.
         (optimize_namespace): Invoke gfc_code_walker with
         simplify_io_impl_do.

2017-05-27  Nicolas Koenig  <koenigni@student.ethz.ch>

         PR fortran/35339
         * gfortran.dg/implied_do_io_1.f90: New Test.

On 05/31/2017 05:49 PM, Dominique d'Humières wrote:
>> Le 31 mai 2017 à 17:40, Dominique d'Humières <dominiq@lps.ens.fr> a écrit :
>>
>> If I am not mistaken, compiling the following code with the patch applied
> simpler test
>
>    print *,(huge(0),i=1,6)
> !  print*,(i,i=1,6)
> !  print*,(i,i=10000,60000,10000)
>    end
>
>> gives an ICE.
>>
>> TIA
>>
>> Dominique

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