Re: [PATCH] Simple optimization for MASK_STORE.

[Yuri Rumyantsev <ysrumyan@gmail.com>]

Richard,

What we should do to cope with this problem (structure size increasing)?
Should we return to vector comparison version?

Thanks.
Yuri.

2015-11-11 12:18 GMT+03:00 Richard Biener <richard.guenther@gmail.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.
>>>>>>
>>>>>>