Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."

[Gabriel Dos Reis <gdr at integrable-solutions dot net>]

Andrew Pinski <pinskia@physics.uc.edu.integrable-solutions.net> writes:

| > 
| > Paul Eggert <eggert@CS.UCLA.EDU> writes:
| > 
| > > 	* NEWS: AC_PROG_CC, AC_PROG_CXX, and AC_PROG_OBJC now take an
| > > 	optional second argument specifying the default optimization
| > > 	options for GCC.  These optimizations now default to "-O2 -fwrapv"
| > > 	instead of to "-O2".  This partly attacks the problem reported by
| > > 	Ralf Wildenhues in
| > > 	<http://lists.gnu.org/archive/html/bug-gnulib/2006-12/msg00084.html>
| > > 	and in <http://gcc.gnu.org/ml/gcc/2006-12/msg00459.html>.
| > 
| > Does anybody think that Paul's proposed patch to autoconf would be
| > better than changing VRP?
| 
| I think both ways are incorrect way forward.
| What about coding the loops like:
| 
| if (sizeof(time_t) == sizeof(unsigned int))
| {
|   // do loop using unsigned int
|   // convert to time_t and then see if an overflow happened
| }
| //etc. for the other type

Yuck.


If the above is the only without Autoconf change, I would highly
recommend Autoconf change if GCC optimizers highly value benchmarks
over running real world code.

-- Gaby