c++/7322: Code to Compute Numeric Limits "runs away" when -O<any> used

c++/7322: Code to Compute Numeric Limits "runs away" when -O<any> used

[lprimak]

>Number:         7322
>Category:       c++
>Synopsis:       Code to Compute Numeric Limits "runs away" when -O<any> used
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jul 15 19:56:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     Lenny Primak
>Release:        gcc version 3.1
>Organization:
>Environment:
(the OS is probably irrelevant)
Solaris 8/x86, Oct. 01 release,
gcc 3.1 as posted on Sunfreeware.com

ash-2.03$ gcc -v
Reading specs from /usr/local/lib/gcc-lib/i386-pc-solaris2.8/3.1/specs
Configured with: ../configure --with-as=/usr/ccs/bin/as --with-ld=/usr/ccs/bin/ld --disable-nls
Thread model: posix
bash-2.03$ gcc -v
Reading specs from /usr/local/lib/gcc-lib/i386-pc-solaris2.8/3.1/specs
Configured with: ../configure --with-as=/usr/ccs/bin/as --with-ld=/usr/ccs/bin/ld --disable-nls
Thread model: posix
gcc version 3.1
>Description:
The code works correctly when not using the optimize (-O) switch.
Incorrect code is produced that causes the process
to "run away" and eats 100% of the cpu when any kind
of optimization switch is used.
>How-To-Repeat:
bash-2.03$ c++ -O1 limits.cpp 
bash-2.03$ ./a.out
:
#undef _LPLIM_LIMITS
#define _LPLIM_CHAR_BIT 8
#define _LPLIM_BOOL_MIN !!0 /* sizeof (bool) = 1 */
#define _LPLIM_BOOL_MAX !0
#define _LPLIM_CHAR_MAX 127 /* sizeof (char) = 1 */
#define _LPLIM_CHAR_MIN (-_LPLIM_CHAR_MAX - 1)
(hangs/runs away here) ^C
bash-2.03$ 
>Fix:
None Available
>Release-Note:
>Audit-Trail:
>Unformatted:
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fQo=

Re: c++/7322: Code to Compute Numeric Limits "runs away" when -O<any> used

[nathan]

Synopsis: Code to Compute Numeric Limits "runs away" when -O<any> used

State-Changed-From-To: open->closed
State-Changed-By: nathan
State-Changed-When: Tue Jul 16 01:41:42 2002
State-Changed-Why:
    The code is ill formed.
    There are tests such as
    	if (T (max + 1) > max)
    where max & T are signed types. [5]/5 says that
    if the result is not in the range if representable values,
    the behaviour is undefined. gcc implements modulo arithmetic
    for unsigned types, and undefined behaviour for signed types.
    The optimized therefore knows that max + 1 must always
    be greater than max.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7322