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

[Richard Kenner]

> Note the interesting places in VRP where it assumes undefined signed
> overflow is in compare_values -- we use the undefinedness to fold
> comparisons.

Unfortunately, comparisons are the trickiest case because you have to
be careful to avoid deleting a comparison that exists to see if overflow
occured: this is perhaps the most common place where wrapping is assumed.