> On Oct 7, 2022, at 2:34 AM, Richard Biener <richard.guent...@gmail.com> wrote: > > On Thu, Oct 6, 2022 at 3:18 PM Qing Zhao <qing.z...@oracle.com> wrote: >> >> >> >>> On Oct 6, 2022, at 4:29 AM, Richard Biener <richard.guent...@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 <mli...@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.
