[Bug fortran/67531] No IEEE rounding support for powerpc long double type

["pthaugen at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67531

--- Comment #5 from Pat Haugen <pthaugen at gcc dot gnu.org> ---
(In reply to Francois-Xavier Coudert from comment #3)
> How about with this? I'm trying to come as close as possible to the exact
> sequence of fe.etround() calls as the Fortran front-end and runtime library
> would end up performing…
> 
> 
> #include <fenv.h>
> #include <stdio.h>
> 
> int main (void)
> {
>   int r;
>   long double x1, x2, x;
> 
>   x1 = 1;
>   x = 3;
>   r = fegetround ();
>   fesetround (FE_UPWARD);
>   x1 = x1 / x;
>   fesetround (r);
> 
>   x2 = 1;
>   x = 3;
>   r = fegetround ();
>   fesetround (FE_DOWNWARD);
>   x2 = x2 / x;
>   fesetround (r);
> 
>   printf ("%.40Lg\n", x1);
>   printf ("%.40Lg\n", x2);
> }

pthaugen@genoa:~$ ~/install/gcc/trunk/bin/gcc junk.c -lm && ./a.out
0.3333333333333333333333333333333353876586
0.3333333333333333333333333333333292246828
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From: "olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/59478] Optimize variable access via byte copy
Date: Fri, 11 Sep 2015 13:51:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idY478

--- Comment #1 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Oleg Endo from comment #0)
> This happens at least on SH with trunk rev 205905 (4.9).
> I'm not sure whether these are target specific or not.
>
> Accessing float values as integers can be done in various ways.  One way is
> to do a byte copy...
>
> int float_as_int (float val)
> {
>   char valbytes[sizeof (float)];
>   __builtin_memcpy (valbytes, &val, sizeof (float));
>
>   int result;
>   __builtin_memcpy (&result, valbytes, sizeof (float));
>
>   return result;
> }
>
> The above compiled with -m4-single -ml -O2 results in:
>
>         add     #-8,r15
>         fmov.s  fr5,@r15
>         mov.l   @r15,r0
>         rts
>         add     #8,r15
>
> which is not so bad actually, but could be done better by utilizing the fpul
> register, as it is done when using the union approach:

This case got better.  It now produces the expected sequence:

        flds    fr5,fpul
        rts
        sts     fpul,r0