Paul Eggert <[EMAIL PROTECTED]> 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>.
I fully appreciate that there is a real problem here which needs to be addressed, but this does not seem like the best solution to me. A great number of C programs are built using autoconf. If we make this change, then they will all be built with -fwrapv. That will disable useful loop optimizations, optimizations which are enabled by default by gcc's competitors. The result will be to make gcc look worse than it is. You will recall that the problem with the original code was not in the loop optimizers; it was in VRP. I think we would be better served by changing VRP to not rely on undefined signed overflow. Or, at least, to not rely on it without some additional option. If we make that change on the 4.2 branch and on mainline, then no autoconf change is necessary, and the default gcc behaviour will be less confusing. Does anybody think that Paul's proposed patch to autoconf would be better than changing VRP? Ian
