Re: Avoid generating useless range info

[Aldy Hernandez <aldyh@redhat.com>]

[one more time, but without sending html which the list refuses :-/]

On Fri, Jun 16, 2017 at 4:00 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Wed, Jun 14, 2017 at 6:41 PM, Aldy Hernandez <aldyh@redhat.com> wrote:
>> Hi!
>>
>> As discovered in my range class work, we seem to generate a significant
>> amount of useless range info out of VRP.
>>
>> Is there any reason why we can't avoid generating any range info that spans
>> the entire domain, and yet contains nothing in the non-zero bitmask?
>>
>> The attached patch passes bootstrap, and the one regression it causes is
>> because now the -Walloca-larger-than= pass is better able to determine that
>> there is no range information at all, and the testcase is unbounded.
>> So...win, win.
>>
>> OK for trunk?
>
> Can you please do this in set_range_info itself?  Thus, if min ==
> wi::min_value && max == wi::max_value
> simply return?  (do not use TYPE_MIN?MAX_VALUE please)


The reason I did it in vrp_finalize is because if you do it in
set_range_info, you break set_nonzero_bits when setting bits on an SSA
that currently has no range info:

void
set_nonzero_bits (tree name, const wide_int_ref &mask)
{
  gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
  if (SSA_NAME_RANGE_INFO (name) == NULL)
    set_range_info (name, VR_RANGE,
   TYPE_MIN_VALUE (TREE_TYPE (name)),
   TYPE_MAX_VALUE (TREE_TYPE (name)));
  range_info_def *ri = SSA_NAME_RANGE_INFO (name);
  ri->set_nonzero_bits (mask);
}

Let me know how you'd like me to proceed.
Aldy

>
> Thanks,
> Richard.
>
>> Aldy