https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64130
--- Comment #10 from kugan at gcc dot gnu.org ---
(In reply to Marc Glisse from comment #6)
> (In reply to kugan from comment #5)
> > I think it should be in from front-end?
>
> ?
Sorry for the confusing terminology.
for the case
int fsigned(int a)
{
return 0xffffffffffffffL / a == 0;
}
004t.gimple has:
int D.4228;
long long int D.4229;
long long int D.4230;
_Bool D.4231;
D.4229 = (long long int) a;
D.4230 = 72057594037927935 / D.4229;
D.4231 = D.4230 == 0;
So based on the "x >= maxval(typeof(a)), x / a cannot be 0" the
maxval(typeof(a)) is now maxval(long long int) in the case of ARM. Thats why I
was asking if it is to be done before gimple is generated. As I see, the above
statement does not rely on value ranges.
>
> > Tried fixing it in VRP like:
>
> You don't seem to use ranges at all. This might be the right place to
> implement the suggestion from comment #2 (though if it does not use ranges,
> match.pd would be better), but for the original optimization, what you want
> to improve is the computation of the range of a division. When a has range
> [0, 4294967295] we compute for 2305843009213693951 / a the range [0,
> 2305843009213693951] which is not optimal, the left bound should be
> 536870912 not 0. If the good interval is computed, VRP will automatically
> fold == 0 to false without extra code. We already get this right when a has
> range [1, 4294967295].
How about something like this:
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -3158,7 +3158,14 @@ extract_range_from_binary_expr_1 (value_range_t *vr,
type = VR_VARYING;
cmp = compare_values (vr0.min, zero);
if (cmp == 1)
- min = zero;
+ {
+ if (vr1.type == VR_RANGE
+ && !symbolic_range_p (&vr0)
+ && !symbolic_range_p (&vr1))
+ min = int_const_binop (code, vr0.min, vr1.max);
+ else
+ min = zero;
+ }
else if (cmp == 0 || cmp == -1)
min = vr0.min;
else
