From: Martin Sebor <msebor@gmail.com>
To: "Kewen.Lin" <linkw@linux.ibm.com>,
Richard Biener <richard.guenther@gmail.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>,
Jakub Jelinek <jakub@redhat.com>,
Jonathan Wakely <jwakely.gcc@gmail.com>,
Segher Boessenkool <segher@kernel.crashing.org>,
Richard Sandiford <richard.sandiford@arm.com>,
Trevor Saunders <tbsaunde@tbsaunde.org>,
Bill Schmidt <wschmidt@linux.ibm.com>
Subject: Re: [PATCH] Make loops_list support an optional loop_p root
Date: Fri, 23 Jul 2021 10:26:20 -0600 [thread overview]
Message-ID: <0fd941f1-a69a-ad2b-3dea-75dcc50a747b@gmail.com> (raw)
In-Reply-To: <61ac669c-7293-f53a-20c7-158b5a813cee@linux.ibm.com>
On 7/23/21 2:41 AM, Kewen.Lin wrote:
> on 2021/7/22 下午8:56, Richard Biener wrote:
>> On Tue, Jul 20, 2021 at 4:37
>> PM Kewen.Lin <linkw@linux.ibm.com> wrote:
>>>
>>> Hi,
>>>
>>> This v2 has addressed some review comments/suggestions:
>>>
>>> - Use "!=" instead of "<" in function operator!= (const Iter &rhs)
>>> - Add new CTOR loops_list (struct loops *loops, unsigned flags)
>>> to support loop hierarchy tree rather than just a function,
>>> and adjust to use loops* accordingly.
>>
>> I actually meant struct loop *, not struct loops * ;) At the point
>> we pondered to make loop invariant motion work on single
>> loop nests we gave up not only but also because it iterates
>> over the loop nest but all the iterators only ever can process
>> all loops, not say, all loops inside a specific 'loop' (and
>> including that 'loop' if LI_INCLUDE_ROOT). So the
>> CTOR would take the 'root' of the loop tree as argument.
>>
>> I see that doesn't trivially fit how loops_list works, at least
>> not for LI_ONLY_INNERMOST. But I guess FROM_INNERMOST
>> could be adjusted to do ONLY_INNERMOST as well?
>>
>
>
> Thanks for the clarification! I just realized that the previous
> version with struct loops* is problematic, all traversal is
> still bounded with outer_loop == NULL. I think what you expect
> is to respect the given loop_p root boundary. Since we just
> record the loops' nums, I think we still need the function* fn?
> So I add one optional argument loop_p root and update the
> visiting codes accordingly. Before this change, the previous
> visiting uses the outer_loop == NULL as the termination condition,
> it perfectly includes the root itself, but with this given root,
> we have to use it as the termination condition to avoid to iterate
> onto its possible existing next.
>
> For LI_ONLY_INNERMOST, I was thinking whether we can use the
> code like:
>
> struct loops *fn_loops = loops_for_fn (fn)->larray;
> for (i = 0; vec_safe_iterate (fn_loops, i, &aloop); i++)
> if (aloop != NULL
> && aloop->inner == NULL
> && flow_loop_nested_p (tree_root, aloop))
> this->to_visit.quick_push (aloop->num);
>
> it has the stable bound, but if the given root only has several
> child loops, it can be much worse if there are many loops in fn.
> It seems impossible to predict the given root loop hierarchy size,
> maybe we can still use the original linear searching for the case
> loops_for_fn (fn) == root? But since this visiting seems not so
> performance critical, I chose to share the code originally used
> for FROM_INNERMOST, hope it can have better readability and
> maintainability.
I might be mixing up the two patches (they both seem to touch
the same functions), but in this one the loops_list ctor looks
like a sizeable function with at least one loop. Since the ctor
is used in the initialization of each of the many range-for loops,
that could result in inlining of a lot of these calls and so quite
a bit code bloat. Unless this is necessary for efficiency (not
my area) I would recommend to consider defining the loops_list
ctor out-of-line in some .c or .cc file.
(Also, if you agree with the rationale, I'd replace loop_p with
loop * in the new code.)
Thanks
Martin
>
> Bootstrapped and regtested on powerpc64le-linux-gnu P9,
> x86_64-redhat-linux and aarch64-linux-gnu, also
> bootstrapped on ppc64le P9 with bootstrap-O3 config.
>
> Does the attached patch meet what you expect?
>
> BR,
> Kewen
> -----
> gcc/ChangeLog:
>
> * cfgloop.h (loops_list::loops_list): Add one optional argument root
> and adjust accordingly.
>
next prev parent reply other threads:[~2021-07-23 16:26 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-19 6:20 [RFC/PATCH] Use range-based for loops for traversing loops Kewen.Lin
2021-07-19 6:26 ` Andrew Pinski
2021-07-20 8:56 ` Kewen.Lin
2021-07-19 14:08 ` Jonathan Wakely
2021-07-20 8:56 ` Kewen.Lin
2021-07-19 14:34 ` Richard Biener
2021-07-20 8:57 ` Kewen.Lin
2021-07-19 15:59 ` Martin Sebor
2021-07-20 8:58 ` Kewen.Lin
2021-07-20 9:49 ` Jonathan Wakely
2021-07-20 9:50 ` Jonathan Wakely
2021-07-20 14:42 ` Kewen.Lin
2021-07-20 14:36 ` [PATCH v2] " Kewen.Lin
2021-07-22 12:56 ` Richard Biener
2021-07-22 12:56 ` Richard Biener
2021-07-23 8:41 ` [PATCH] Make loops_list support an optional loop_p root Kewen.Lin
2021-07-23 16:26 ` Martin Sebor [this message]
2021-07-27 2:25 ` Kewen.Lin
2021-07-29 8:01 ` Richard Biener
2021-07-30 5:20 ` [PATCH v2] " Kewen.Lin
2021-08-03 12:08 ` Richard Biener
2021-08-04 2:36 ` [PATCH v3] " Kewen.Lin
2021-08-04 10:01 ` Richard Biener
2021-08-04 10:47 ` Kewen.Lin
2021-08-04 12:04 ` Richard Biener
2021-08-05 8:50 ` Kewen.Lin
2021-07-23 8:35 ` [PATCH v3] Use range-based for loops for traversing loops Kewen.Lin
2021-07-23 16:10 ` Martin Sebor
2021-07-27 2:10 ` [PATCH v4] " Kewen.Lin
2021-07-29 7:48 ` Richard Biener
2021-07-30 7:18 ` Thomas Schwinge
2021-07-30 7:58 ` Kewen.Lin
2021-11-24 14:24 ` Reduce scope of a few 'class loop *loop' variables (was: [PATCH v4] Use range-based for loops for traversing loops) Thomas Schwinge
2021-11-24 16:58 ` Martin Jambor
2021-11-24 19:44 ` Jeff Law
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