http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56273
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-11
09:32:31 UTC ---
(In reply to comment #2)
> The problem is a missing VRP. Basically ivopts changes:
> if (j_10 != 9)
>
> Which works into:
>
> j_10 = ivtmp.12_56;
> if (ivtmp.12_56 != 9)
> goto <bb 7>;
> else
> goto <bb 6>;
>
>
> Which does not work as VRP cannot figure out j_10 will never be 9.
> I have some patches to VRP which improves this but I don't remember if it
> fixes
> this case where there is an assignment which is used later on.
A similar case was PR55079 which was
j_10 = ivtmp.12_56 + 1;
if (ivtmp.12_56 == 5)
...
I handled already. Extending this to copies should be easy. If I do that
it still doesn't work.
That's because we warn for stuff[j_15] and j_15 is [9, 16] (we completely
peel the loop). The access is guarded with
<bb 30>:
j_55 = ivtmp.12_56 + 8;
j_72 = ivtmp.12_56 + 8;
if (j_72 != 9)
goto <bb 31>;
else
goto <bb 3>;
<bb 31>:
# j_15 = PHI <j_55(30)>
_12 = stuff[j_15].a;
if (_12 != 0)
but j_72 is [9, 16] as well and ivtmp.12_56: [1, 9]. Improving VRP to
see that j_55 is != 9 in bb31 will only lead to [10, 16] which is also
out-of-bounds.
It might very well be that folding the < test to != in VRP1 causes most
of the issues. Indeed -fdisable-tree-vrp1 "fixes" the testcase. We
should probably delay that optimization to VRP2 only, thus don't do
Folding statement: if (i_1 <= 8)
Simplified relational if (i_1 <= 8)
into if (i_1 != 9)
(simplify_cond_using_ranges).
