Re: [PATCH] Simple optimization for MASK_STORE.

[Richard Biener <richard dot guenther at gmail dot com>]

On Tue, Nov 10, 2015 at 3:56 PM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
> 2015-11-10 17:46 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
>> On Tue, Nov 10, 2015 at 1:48 PM, Ilya Enkovich <enkovich.gnu@gmail.com> wrote:
>>> 2015-11-10 15:33 GMT+03:00 Richard Biener <richard.guenther@gmail.com>:
>>>> On Fri, Nov 6, 2015 at 2:28 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>>>>> Richard,
>>>>>
>>>>> I tried it but 256-bit precision integer type is not yet supported.
>>>>
>>>> What's the symptom?  The compare cannot be expanded?  Just add a pattern then.
>>>> After all we have modes up to XImode.
>>>
>>> I suppose problem may be in:
>>>
>>> gcc/config/i386/i386-modes.def:#define MAX_BITSIZE_MODE_ANY_INT (128)
>>>
>>> which doesn't allow to create constants of bigger size.  Changing it
>>> to maximum vector size (512) would mean we increase wide_int structure
>>> size significantly. New patterns are probably also needed.
>>
>> Yes, new patterns are needed but wide-int should be fine (we only need to create
>> a literal zero AFACS).  The "new pattern" would be equality/inequality
>> against zero
>> compares only.
>
> Currently 256bit integer creation fails because wide_int for max and
> min values cannot be created.

Hmm, indeed:

#1  0x000000000072dab5 in wi::extended_tree<192>::extended_tree (
    this=0x7fffffffd950, t=0x7ffff6a000b0)
    at /space/rguenther/src/svn/trunk/gcc/tree.h:5125
5125      gcc_checking_assert (TYPE_PRECISION (TREE_TYPE (t)) <= N);

but that's not that the constants fail to be created but

#5  0x00000000010d8828 in build_nonstandard_integer_type (precision=512,
    unsignedp=65) at /space/rguenther/src/svn/trunk/gcc/tree.c:8051
8051      if (tree_fits_uhwi_p (TYPE_MAX_VALUE (itype)))
(gdb) l
8046        fixup_unsigned_type (itype);
8047      else
8048        fixup_signed_type (itype);
8049
8050      ret = itype;
8051      if (tree_fits_uhwi_p (TYPE_MAX_VALUE (itype)))
8052        ret = type_hash_canon (tree_to_uhwi (TYPE_MAX_VALUE
(itype)), itype);

thus the integer type hashing being "interesting".  tree_fits_uhwi_p
fails because
it does

7289    bool
7290    tree_fits_uhwi_p (const_tree t)
7291    {
7292      return (t != NULL_TREE
7293              && TREE_CODE (t) == INTEGER_CST
7294              && wi::fits_uhwi_p (wi::to_widest (t)));
7295    }

and wi::to_widest () fails with doing

5121    template <int N>
5122    inline wi::extended_tree <N>::extended_tree (const_tree t)
5123      : m_t (t)
5124    {
5125      gcc_checking_assert (TYPE_PRECISION (TREE_TYPE (t)) <= N);
5126    }

fixing the hashing then runs into type_cache_hasher::equal doing
tree_int_cst_equal
which again uses to_widest (it should be easier and cheaper to do the compare on
the actual tree representation, but well, seems to be just the first
of various issues
we'd run into).

We eventually could fix the assert above (but then need to hope we assert
when a computation overflows the narrower precision of widest_int) or use
a special really_widest_int (ugh).

> It is fixed by increasing MAX_BITSIZE_MODE_ANY_INT, but it increases
> WIDE_INT_MAX_ELTS
> and thus increases wide_int structure. If we use 512 for
> MAX_BITSIZE_MODE_ANY_INT then
> wide_int structure would grow by 48 bytes (16 bytes if use 256 for
> MAX_BITSIZE_MODE_ANY_INT).
> Is it OK for such narrow usage?

widest_int is used in some long-living structures (which is the reason for
MAX_BITSIZE_MODE_ANY_INT in the first place).  So I don't think so.

Richard.

> Ilya
>
>>
>> Richard.
>>
>>> Ilya
>>>
>>>>
>>>> Richard.
>>>>
>>>>> Yuri.
>>>>>
>>>>>