clang miscompiles OpenLibm on i686-*-freebsd

[Steve Kargl]

On Mon, Sep 07, 2020 at 07:10:02PM -0700, Steve Kargl wrote:
> 
> Interval tested for exp2f: [1,8]
>        ulp <= 0.5:  0.056%     14072 |   0.056%     14072
> 0.5 <  ulp <  0.6:  0.000%         8 |   0.056%     14080
> 3.0 <  ulp <  0.0: 99.944%  25151744 | 100.000%  25165824
> Max ulp: 22729.386719 at 1.00195301e+00
> 

Note, compiling s_exp2f.c with gcc9 gives the above
result with -O3 -march=i686 -m32. So, gcc9 is not
nearly as bad as clang, but both give bad results.
Comparing OpenLibm's s_exp2f.c and FreeBSD's s_exp2f.c,
one sees that the files are almost identical.

Note, FreeBSD's libm gives 

% ./tlibm_libm -DEfP exp2
Interval tested for exp2f: [1,8]
       ulp <= 0.5: 99.959%  25155610 |  99.959%  25155610
0.5 <  ulp <  0.6:  0.041%     10214 | 100.000%  25165824
Max ulp: 0.500980 at 1.97115958e+00

which is good, but this is compiled with CPUTYPE ?= core2
in /etc/make.conf.

-- 
Steve