From: Qing Zhao <qing.zhao@oracle.com>
To: Richard Biener <richard.guenther@gmail.com>
Cc: "Martin Liška" <mliska@suse.cz>,
"gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>,
"Jan Hubicka" <hubicka@ucw.cz>
Subject: Re: [PATCH] IPA: support -flto + -flive-patching=inline-clone
Date: Fri, 7 Oct 2022 13:04:43 +0000 [thread overview]
Message-ID: <03E958B0-A70F-48BA-A28E-A365B9B70981@oracle.com> (raw)
In-Reply-To: <CAFiYyc13_qJXB6KQWBk6Yzi7T1CWUNrwXFZEQyYJSKF5YXH2-A@mail.gmail.com>
> On Oct 7, 2022, at 2:34 AM, Richard Biener <richard.guenther@gmail.com> wrote:
>
> On Thu, Oct 6, 2022 at 3:18 PM Qing Zhao <qing.zhao@oracle.com> wrote:
>>
>>
>>
>>> On Oct 6, 2022, at 4:29 AM, Richard Biener <richard.guenther@gmail.com> wrote:
>>>
>>> On Wed, Oct 5, 2022 at 8:18 PM Qing Zhao via Gcc-patches
>>> <gcc-patches@gcc.gnu.org> wrote:
>>>>
>>>>
>>>>
>>>>> On Oct 5, 2022, at 1:36 PM, Martin Liška <mliska@suse.cz> wrote:
>>>>>
>>>>> On 10/5/22 16:50, Qing Zhao wrote:
>>>>>> I have two questions on this:
>>>>>
>>>>> Hello.
>>>>>
>>>>>>
>>>>>> 1. What’s the motivation to enable -flive-patching with -flto? Is there any application that will try -flive-patching with -flto now?
>>>>>
>>>>> We're planning supporting GCC LTO Linux kernel support, so that's one motivation. And the second one is a possible
>>>>> use in user-space livepatching. Note majority of modern distros default to -flto (openSUSE, Fedora, Debian, Ubuntu, ...).
>>>>
>>>> Okay, I see. That’s reasonable.
>>>>>
>>>>>>
>>>>>> 2. Why only enable -flive-patching=inline-clone with -flto?
>>>>>
>>>>> Because the inline-only-static level (which you added/requested) would have to properly
>>>>> block inter-procedural inlining that happens in LTO (can_inline_edge_by_limits_p) and
>>>>> I'm not sure it would be properly blocked. So, feel free to extend my patch if you want?
>>>>
>>>> -flive-patching=inline-only-static
>>>>
>>>> Only enable static functions inlining, all the inlining of external visible functions are blocked, So, LTO should be compatible with this naturally without any issue, I think.
>>>>
>>>> i.e, when "-flive-patching=inline-only-static -flto" present together, all the inter-procedural inlining should be automatically blocked by -flive-patching=inline-only-static already.
>>>>
>>>> Do I miss anything here?
>>>
>>> WPA will promote externally visible functions static when all accesses
>>> are from LTO IR, I don't think we preserve
>>> the "original" visibility for IPA inlining heuristics.
>>
>> WPA is Whole Program Analysis?
>
> Yes.
>
>> Okay, then It will promote all static function to extern functions. That’s reasonable.
>
> No, all extern functions to static functions.
Oh, really? Why change “extern” to “static”? (I recall that studio compiler promote static to extern for inter-procedural inlining)
>
>> Is it hard to preserve the original “static” visibility in the IR?
>
> Probably not hard, and the IPA pass adjusting visbility could as well
> mark the functions
> as not to be inlined with -flive-patching=inline-only-static.
Okay, then the implementation should be doable?
>
>>>
>>> OTOH inline-only-static could disable WPA inlining and do all inlining early ...
>>
>> Inline-only-static ONLY inlines static functions, how can it disable WPA inlining? Don’t quite understand here.
>
> it's a flag so it can be used to control other things.
When -flive-patching=inline-only-static is specified by the user, user explicitly request ONLY inlining static functions.
Even when LTO is enabled, if only static function inlining is enabled, user gets what he/she want. So I didn’t see any issue here.
Let me know if I still miss anything here.
Thanks.
Qing
>
>> thanks.
>>
>> Qing
>>>
>>> Richard,
>>>
>>>>
>>>> thanks.
>>>>
>>>> Qing
>>>>
>>>>>
>>>>> Martin
>>>>>
>>>>>>
>>>>>> thanks.
next prev parent reply other threads:[~2022-10-07 13:04 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-05 11:41 Martin Liška
2022-10-05 14:50 ` Qing Zhao
2022-10-05 17:36 ` Martin Liška
2022-10-05 18:18 ` Qing Zhao
2022-10-06 8:29 ` Richard Biener
2022-10-06 8:40 ` Martin Liška
2022-10-06 13:18 ` Qing Zhao
2022-10-07 6:34 ` Richard Biener
2022-10-07 13:03 ` Jan Hubicka
2022-10-07 14:30 ` Qing Zhao
2022-10-07 14:43 ` Jan Hubicka
2022-10-07 15:36 ` Qing Zhao
2022-10-07 13:04 ` Qing Zhao [this message]
2022-10-07 13:50 ` Martin Liška
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