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From: Eric Botcazou <ebotcazou@libertysurf.fr>
To: Michael Veksler <VEKSLER@il.ibm.com>
Subject: Re: isinf
Date: Thu, 14 Jul 2005 07:33:00 -0000
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Cc: gcc@gcc.gnu.org,
 Hiroshi Fujishima <hiroshi.fujishima@gmail.com>,
 Joe Buck <Joe.Buck@synopsys.com>
References: <OF26D9F22F.D3621F38-ON4325703E.0024F6B2-4325703E.0025BCF5@il.ibm.com>
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> This may work today, but and still break in the future. This
> will not work (possibly) years from now when gcc will start
> doing VRP on math functions like isinf.
>
> MIN_INT <= argc <= MAX_INT falls well into representable
> values of double (assuming 32 bit int or less). This means
> that the compiler may deduce that isinf((double)argc) always
> returns false, without ever calling the function.

You're too clever. :-)

union U {
  int i;
  double d;
};

volatile int a;

int
main (int argc, char *argv[])
{
  union U u;
  u.i = argc;
  a = isinf (u.d);
  return 0;
}

-- 
Eric Botcazou