On Mon, Oct 19, 2020 at 12:55:38PM +0200, Aldy Hernandez wrote:
> > Shifts are undefined already when the shift count is equal to the precision.
> > And arbitrarily choosing one of the values as the shift count seems risky to
> > me (and even when used, the most natural would be truncating the excess bits
> > rather than saturating), can't it just punt (return VARYING) for the UB
> > shifts?
>
> Good point. It looks cleaner too.
>
> How about this?
>
> diff --git a/gcc/range-op.cc b/gcc/range-op.cc
> index 30d2a4d3987..0ab5e62be7f 100644
> --- a/gcc/range-op.cc
> +++ b/gcc/range-op.cc
> @@ -1579,6 +1579,9 @@ operator_lshift::op1_range (irange &r,
> wide_int shift = wi::to_wide (shift_amount);
> if (wi::lt_p (shift, 0, SIGNED))
> return false;
> + if (wi::gt_p (shift, wi::uhwi (TYPE_PRECISION (type),
> + TYPE_PRECISION (op2.type ()))))
> + return false;
If you use wi::ge_p instead, then LGTM.
Jakub
