optimization/1762: treatment of NaNs violates IEEE 754

[reichelt@igpm.rwth-aachen.de]

>Number:         1762
>Category:       optimization
>Synopsis:       treatment of NaNs violates IEEE 754
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Wed Jan 24 10:56:00 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     Volker Reichelt
>Release:        gcc 2.95, 2.96.20000920 on IRIX6.5
>Organization:
>Environment:
SGI O2, IRIX 6.5
CPU: MIPS R5000 Processor Chip Revision: 2.1
FPU: MIPS R5000 Floating Point Coprocessor Revision: 1.0
>Description:
The following program shows some problems with the
treatment of NaNs. According to IEEE 754 the result
of "0 < NaN" should be false. Therefore the result
of "less" and the return value of the program should
be "0". This is the case, if I compile the program
without optimization. With optimization enabled,
however, I get the result "1" instead.
(The same problem arises, when "a<b?b:a" is evaluated.)


double less(double a, double b)
{
  return a < b;
}

int main()
{
  const double NaN = 0.0/0.0;
  return (int)less(0.0,NaN);
}
>How-To-Repeat:
gcc -O1 NaN.cpp; ./a.out; echo $?
(assuming the file is called NaN.cpp)
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:
>From Gabriel.Dos-Reis@cmla.ens-cachan.fr Sun Apr 01 00:00:00 2001
From: Gabriel Dos Reis <Gabriel.Dos-Reis@cmla.ens-cachan.fr>
To: nobody@gcc.gnu.org
Cc: gcc-prs@gcc.gnu.org
Subject: Re: libstdc++/1755: libstdc++-v3 gen-num-limits fails on mips-sgi-irix5.3
Date: Sun, 01 Apr 2001 00:00:00 -0000
Message-id: <20010124112601.13983.qmail@sourceware.cygnus.com>
X-SW-Source: 2001-q1/msg00649.html
Content-length: 991

The following reply was made to PR libstdc++/1755; it has been noted by GNATS.

From: Gabriel Dos Reis <Gabriel.Dos-Reis@cmla.ens-cachan.fr>
To: fleming.151@osu.edu
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: libstdc++/1755: libstdc++-v3 gen-num-limits fails on mips-sgi-irix5.3
Date: 24 Jan 2001 12:20:10 +0100

 fleming.151@osu.edu writes:
 
 | >Number:         1755
 | >Category:       libstdc++
 | >Synopsis:       libstdc++-v3 gen-num-limits fails on mips-sgi-irix5.3
 | >Confidential:   no
 | >Severity:       serious
 | >Priority:       medium
 | >Responsible:    unassigned
 | >State:          open
 | >Class:          sw-bug
 | >Submitter-Id:   net
 | >Arrival-Date:   Tue Jan 23 23:36:00 PST 2001
 | >Closed-Date:
 | >Last-Modified:
 | >Originator:     George T. Fleming
 | >Release:        gcc version 2.97 20010115 (experimental)
 
 A patch was checked in recently.  Please update and give it a new try.
 
 -- Gaby
 CodeSourcery, LLC                       http://www.codesourcery.com
>From aoliva@gcc.gnu.org Sun Apr 01 00:00:00 2001
From: aoliva@gcc.gnu.org
To: nobody@gcc.gnu.org
Cc: gcc-prs@gcc.gnu.org
Subject: Re: web/1817
Date: Sun, 01 Apr 2001 00:00:00 -0000
Message-id: <20010311174601.17227.qmail@sourceware.cygnus.com>
X-SW-Source: 2001-q1/msg02203.html
Content-length: 547

The following reply was made to PR web/1817; it has been noted by GNATS.

From: aoliva@gcc.gnu.org
To: gcc-gnats@gcc.gnu.org, nobody@gcc.gnu.org, slager@hydra.accu.uu.nl
Cc:  
Subject: Re: web/1817
Date: 11 Mar 2001 17:43:40 -0000

 Synopsis: gnatsweb.pl has fault -after not accepting empty submitter-id
 
 State-Changed-From-To: open->closed
 State-Changed-By: aoliva
 State-Changed-When: Sun Mar 11 09:43:40 2001
 State-Changed-Why:
     Problem in Gnatsweb, not in GCC.
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view&pr=1817&database=gcc