On Mon, 26 Feb 2024, Jakub Jelinek wrote:
> On Mon, Feb 26, 2024 at 03:15:02PM +0100, Richard Biener wrote:
> > When folding a multiply CHRECs are handled like {a, +, b} * c
> > is {a*c, +, b*c} but that isn't generally correct when overflow
> > invokes undefined behavior. The following uses unsigned arithmetic
> > unless either a is zero or a and b have the same sign.
> >
> > I've used simple early outs for INTEGER_CSTs and otherwise use
> > a range-query since we lack a tree_expr_nonpositive_p.
>
> What about testing
> (get_range_pos_neg (CHREC_LEFT (op0))
> | get_range_pos_neg (CHREC_RIGHT (op0))) != 3
> ?
Ah, didn't know about that. It seems to treat zero as "always
positive", so for 0 and -1 I'd get 3. OK as I check for
zero CHREC_LEFT separately.
I'll note that get_range_pos_neg only asks global range query
and for SSA names (but not sure if range_of_expr handles aribitrary
GENERIC as SCEV tends to have here ...).
Will update the patch, I think any improvement should be done
to get_range_pos_neg (it's a bit odd in behavior for unsigned
but I have only signed things incoming).
Richard.
