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From: Eric Botcazou <ebotcazou@libertysurf.fr>
To: Hiroshi Fujishima <hiroshi.fujishima@gmail.com>
Subject: Re: isinf
Date: Thu, 14 Jul 2005 06:27:00 -0000
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Cc: gcc@gcc.gnu.org,
 Joe Buck <Joe.Buck@synopsys.com>
References: <7cfyui3a9r.fsf@gmail.com> <20050713232903.GA14174@synopsys.com> <7cr7e28e13.fsf@gmail.com>
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> Oops, the configure script compiling with -O2 optimization.

Clearly not the best option for this kind of tests.

> The compilation of the following code still suceesss.
>
> #include <math.h>
>
> int a;
>
> int
> main ()
> {
>   float f = 0.0;
>   a = isinf (f);
>   return 0;
> }

The compiler knows the answer of isinf (0) so it again optimizes away the 
call.  Try something like:

int a;

int
main (int argc, char *argv[])
{
  a = isinf ((double) argc);
  return 0;
}

or additionally compile with -fno-builtin.

-- 
Eric Botcazou