On Mon, Oct 26, 2015 at 1:33 PM, Alan Hayward <alan.hayw...@arm.com> wrote:
> There is a potential bug in vectorizable_live_operation.
>
> Consider the case where the first op for stmt is valid, but the second is
> null.
> The first time through the for () loop, it will call out to
> vect_is_simple_use () which will set dt.
> The second time, because op is null, vect_is_simple_use () will not be
> called.
> However, dt is still set to a valid value, therefore the loop will
> continue.
>
> Note this is different from the case where the first op is null, which
> will cause the loop not call vect_is_simple_use () and then return false.
>
> It is possible that this was intentional, however that is not clear from
> the code.
>
> The fix is to simply ensure dt is initialized to a default value on each
> iteration.
I think the patch is a strict improvement, thus OK. Still a NULL operand
is not possible in GIMPLE so the op && check is not necessary. The way
it iterates over all stmt uses is a bit scary anyway. As it is ok with
all invariants it should probably simply do sth like
FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_USE)
if (!vect_is_simple_use (op, ....))
and be done with that. Unvisited uses can only be constants (ok).
Care to rework the funtion like that if you are here?
Thanks,
Richard.
>
> 2015-09-07 Alan Hayward alan.hayw...@arm.com
> * tree-vect-looop.c (vectorizable_live_operation): localize variable.
>
>
> Cheers,
> Alan
>
