Re: [PATCH] fortran/69121 -- Make IEEE_SCALB generic

[Sudakshina Das <Sudi dot Das at arm dot com>]

Hi Steve

On 21/12/18 8:01 PM, Steve Kargl wrote:
> On Fri, Dec 21, 2018 at 07:39:45PM +0000, Joseph Myers wrote:
>> On Fri, 21 Dec 2018, Steve Kargl wrote:
>>
>>> scalbln(double x, long n)
>>> {
>>>
>>>          return (scalbn(x, (n > NMAX) ? NMAX : (n < NMIN) ? NMIN : (int)n));
>>> }
>>>
>>> A search for glibc's libm locateshttps://tinyurl.com/ybcy8w4t
>>> which is a bit-twiddling routine.  Not sure it's worth the
>>> effort.  Joseph Myers might have an opinion.
>> Such comparisons are needed in the scalbn / scalbln implementations anyway
>> to deal with large exponents.  I suppose where there's a suitable scalbln
>> implementation, and you don't know if the arguments are within the range
>> of int, calling scalbln at least saves code size in the caller and avoids
>> duplicating those range checks.
>>
> I was thinking along the lines of -ffast-math and whether
> __builtin_scalbn and __builtin_scalbln are then inlined.
> The comparisons may inhibit inlining __builtin_scalbn;
> while, if gfortran used __builtin_scalbln, inlining would
> occur.
>
> As it is, for
>
>     function foo(x,i)
>       use ieee_arithmetic
>       real(8) foo, c
>       integer(8) i
>       foo = ieee_scalb(c, i)
>     end function foo
>
> the options -ffast-math -O3 -fdump-tree-optimized give
>
>    <bb 2> [local count: 1073741824]:
>    _gfortran_ieee_procedure_entry (&fpstate.0);
>    _8 = *i_7(D);
>    _1 = MIN_EXPR <_8, 2147483647>;
>    _2 = MAX_EXPR <_1, -2147483647>;
>    _3 = (integer(kind=4)) _2;
>    _4 = __builtin_scalbn (c_9(D), _3);
>    _gfortran_ieee_procedure_exit (&fpstate.0);
>    fpstate.0 ={v} {CLOBBER};
>    return _4;
>
> It seems this could be
>
>    <bb 2> [local count: 1073741824]:
>    _gfortran_ieee_procedure_entry (&fpstate.0);
>    _3 = (integer(kind=4)) *i_7(D);
>    _4 = __builtin_scalbn (c_9(D), _3
>    _gfortran_ieee_procedure_exit (&fpstate.0);
>    fpstate.0 ={v} {CLOBBER};
>
I am observing your new test pr88328.f90 failing on 
arm-none-linux-gnueabihf:
Excess errors:
/build/src/gcc/gcc/testsuite/gfortran.dg/ieee/ieee_9.f90:20:36: Error: 
Invalid kind for REAL at (1)
/build/src/gcc/gcc/testsuite/gfortran.dg/ieee/ieee_9.f90:35:36: Error: 
Invalid kind for REAL at (1)
/build/src/gcc/gcc/testsuite/gfortran.dg/ieee/ieee_9.f90:50:36: Error: 
Invalid kind for REAL at (1)
/build/src/gcc/gcc/testsuite/gfortran.dg/ieee/ieee_9.f90:65:36: Error: 
Invalid kind for REAL at (1)