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

[Richard Biener <richard.guenther@gmail.com>]

On June 16, 2017 3:31:32 PM GMT+02:00, "Bin.Cheng" <amker.cheng@gmail.com> wrote:
>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.

That means we miss a pattern in match.PD to handle this case.

Richard.

>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.