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Re: [PATCH GCC][1/2]Feed bound computation to folder in loop split


On Fri, Jun 16, 2017 at 2:10 PM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Fri, Jun 16, 2017 at 3:06 PM, Bin.Cheng <amker.cheng@gmail.com> wrote:
>> On Fri, Jun 16, 2017 at 11:49 AM, Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>> On Wed, Jun 14, 2017 at 3:07 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
>>>> Hi,
>>>> Loop split forces intermediate computation to gimple operands all the time when
>>>> computing bound information.  This is not good since folding opportunities are
>>>> missed.  This patch fixes the issue by feeding all computation to folder and only
>>>> forcing to gimple operand at last.
>>>>
>>>> Bootstrap and test on x86_64 and AArch64.  Is it OK?
>>>
>>> Hm?  It uses gimple_build () which should do the same as fold_buildN in terms
>>> of simplification.
>>>
>>> So where does that not work?  It is supposed to be the prefered way and no
>>> new code should use force_gimple_operand (unless dealing with generic
>>> coming from other middle-end infrastructure like SCEV or niter analysis)
>> Hmm, current code calls force_gimpele operand several times which
>> causes the inefficiency.  The patch avoids that and does one call at
>> the end.
>
> But it forces to the same sequence that is used for extending the expression
> so folding should work.  Where do you see that it does not?  Note the
> code uses gimple_build (), not gimple_build_assign ().
In spec2k6/hmmer, when building fast_algorithms.c with below command line:
./gcc -Ofast -S fast_algorithms.c -o fast_algorithms.S -fdump-tree-all
-fdump-tree-lsplit
The lsplit dump contains:
  <bb 11> [12.75%]:
  _124 = _197 + 1;
  _123 = _124 + -1;
  _115 = MIN_EXPR <_197, _124>;
Which is generated here.

Thanks,
bin
>
> Richard.
>
>> Thanks,
>> bin
>>>
>>> Richard.
>>>
>>>>
>>>> Thanks,
>>>> bin
>>>> 2017-06-12  Bin Cheng  <bin.cheng@arm.com>
>>>>
>>>>         * tree-ssa-loop-split.c (compute_new_first_bound): Feed bound
>>>>         computation to folder, rather than force to gimple operands too
>>>>         early.


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