[Bug tree-optimization/33498] Optimizer (-O2) may convert a normal loop to infinite

["rakdver at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #15 from rakdver at gcc dot gnu dot org  2007-09-20 18:47 -------
> I see.  I thought we might be able to recognize the overflow in computing
> the final value of val and as val is signed, not use that for the exit 
> test.  Or simply give up in computing the final value for val if it 
> invokes signed overflow.  I agree the code invokes undefined behavior, 
> just from a QOI perspective it might be nice to not produce the endless
> loop here ;)

More appropriate place to "fix" this (assuming that we want to do something
about this) would be VRP, as it will use the assumption that val does not
overflow regardless (if something more complicated than just assigning it were
done with val).

We might also issue warnings for signed variables that provably overflow;
although it probably would not be very useful, as we are very rarely able to
prove that.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33498