[Bug tree-optimization/81346] Missed constant propagation into comparison

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81346

--- Comment #10 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #9)
> (In reply to Marc Glisse from comment #8)
> > I think always using an unsigned type for the range check would be simpler.
> > If we try to check that x>=INT_MIN+2 && x<=INT_MAX-2 with -fwrapv, int is
> > still not a suitable type in which to do
> > x-(INT_MIN+2)<=INT_MAX-2-(INT_MIN+2), while the issue doesn't exist with an
> > unsigned type.
> 
> I'm trying to preserve what we did before, it can be tweaked incrementally
> if needed.

Then you may need to check for overflow in "hi = const_binop (MINUS_EXPR,
etype, hi, lo);", current build_range_check has "if (value != 0 &&
!TREE_OVERFLOW (value))" for the result of that operation. That should matter
for instance when simplifying X/INT_MAX==0.