--- Comment #12 from rsandifo at gcc dot <rsandifo at gcc dot> 
(In reply to Jakub Jelinek from comment #11)
> (In reply to from comment #10)
> > I'd tried doing this in set_nonzero_bits first, before adding
> > intersect_range_with_nonzero_bits.  See
> > for why it didn't
> > work.
> IMHO that is a risk of all the VRP changes that some case will regress, the
> more important question is how much it will help in general, and I think it
> would.

Yeah I'd hoped so too, but...

> If it is only done in this special case, other passes can't benefit from the
> more accurate range info.

...when I did a comparison of the testsuite assembly output on a range
of targets, I didn't find any examples of things benefiting outside of
split_constant_offset, but quite a few regressions caused by trying
to interesect a VR_ANTI_RANGE with a reduced VR_RANGE.

The testsuite isn't the most representative codebase around, but still,
it suggests that we'd need to add some special cases elsewhere to

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