Re: [PATCH] IPA: support -flto + -flive-patching=inline-clone

[Qing Zhao <qing.zhao@oracle.com>]

> 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?

thanks.

Qing

> 
> Martin
> 
>> 
>> thanks.
>