On Wed, 29 Jun 2005, Daniel Berlin wrote:
So i would advise anyone arguing against turning on -fwrapv simply
because it doesn't seem to hurt us at O2.
And i'll again point out that the exact opposite is the default in every
other compiler i'm aware of.
Sorry, I couldn't parse those sentences... are you saying the -fwrapv
behaviour (ie. wrap-on-signed-integer-overflow) is the default or not the
default in these other compilers?
XLC at O2 has qstrict_induction on by default (the equivalent), and
warns the user when it sees a loop where it's making the assumption[1]
Which assumption?
The XLC people told me since they turned this on in 1998, they have had
one real piece of code where it actually mattered, and that was a char
induction variable.
ICC does the same, though i don't think it bothers to warn.
Open64 does the same, but no warning.
Not sure about Sun CC, but i'd be very surprised if they did it.
Personally, i only care about wrapping for induction variables. If you
guys want to leave regular variables to do whatever, fine.
Are you saying you don't want induction variables to have to wrap, but you
don't care about non-induction variables?
Sorry if I'm being dim... I think it's excellent you're discussing what
other compilers do, I just can't understand what you've said as expressed
:)
Nick
