Tom Lane wrote:
It seems that gcc is up to some creative reinterpretation of basic C
semantics again; specifically, you can no longer trust that traditional
C semantics of integer overflow hold:
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=175462
While I don't think we are anywhere using exactly the same trick that
the referenced mysql code is using, it certainly seems likely to me that
a compiler that is willing to replace "x < 0 && -x < 0" with "false"
might be able to break some of the integer overflow checks we do use.
I think we need to add -fwrapv to CFLAGS anytime the compiler will take
it, same as we recently started doing with -fno-strict-aliasing.
What about this one from the bug (by Jakub Jelinek):
Now, -fwrapv can be an answer if you are unwilling to fix the broken code,
but be prepared that the performance will be terrible, as GCC will not be
able to optimize many loops in a way that it is allowed by the standard.
"Performance will be terrible" does not sound that good.
Is there any other GCC guy you could talk about this? I don't think
GCC==Jakub Jelinek? What do others suggest? There should be a portable way
to detect overflow, no?
Best Regards,
Michael Paesold
[Tom, I removed you from CC: because your spam filter tends to eat my mail;
you should get it through the lists, though.]
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