Re: Buggy ceill on OpenBSD, and possible gnulib test problem

[Paul Eggert]

Assaf Gordon wrote:
> 1. Based on a long list of GCC builtins
> (https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html), perhaps add
> "-fno-builtin" to all the gnulib tests? or at least the math related ones?

That'd have to be done conditionally, no?  Not every compiler supports 
-fno-builtin.  And perhaps the tests should be done once with -fno-builtin, and 
once without.  This is lower priority than #2, tho.

> 2. Similar to 'gl_cv_func_expl_buggy' in 'm4/expl.m4',
> add 'gl_cv_func_ceill_buggy' in 'm4/ceill.m4'.
> Possible patch attached (tested on OpenBSD5.7+gcc 4.2.1, but not much 
> elsewhere).

If I understand you correctly the patch detects the bug only when compiling with 
CFLAGS='-g -O0 -fno-builtin' or something like that.  Can you redo the patch so 
that it detects the bug with the default CFLAGS and GCC?  Something like the 
following, say:

#include <math.h>
long double d = 0.3;
int main (void) { return ceill (d) != 1; }

so that the compiler can't constant-fold the ceill call.