Re: GCC options for kernel live-patching (Was: Add a new option to control inlining only on static functions)

[Jan Hubicka <hubicka@ucw.cz>]

> On 11/5/18 10:51 AM, Jan Hubicka wrote:
> >> @honza: PING
> >>
> >> On 10/3/18 12:53 PM, Martin Liška wrote:
> >>> On 10/3/18 11:04 AM, Jan Hubicka wrote:
> >>>>>
> >>>>> That was promised to be done by Honza Hubièka. He's very skilled in IPA optimizations and he's aware
> >>>>> of optimizations that cause troubles for live-patching.
> >>>>
> >>>> :) I am not sure how skilful I am, but here is what I arrived to.
> >>>
> >>> Heh! Thanks for the analysis.
> >>>
> >>>>
> >>>>  We have transformations that are modeled as clonning, which are
> >>>>   - inlining  (can't be disabled completely because of always inline, but -fno-inline
> >>>>     does most of stuff)
> >>>>   - cloning (disabled via -fno-ipa-cp)
> >>>>   - ipa-sra (-fno-ipa-sra)
> >>>>   - splitting (-fno-partial-inlining)
> >>>>  These should play well with Martin's tracking code
> >>>
> >>> I hope so!
> >>>
> >>>>
> >>>>  We propagate info about side effects of function:
> >>>>   - function attribute discovery (pure, const, nothrow, malloc)
> >>>>     Some of this can be disabled by -fno-ipa-pure-const, but not all
> >>>>     of it.
> >>>
> >>> Would it be possible to add option for the remaining ones?
> > 
> > Sure, I can prepare patch unless you beat me :)
> 
> Are you sure there's a call to 'analyze_function' where the analysis is done
> when one sets -fno-ipa-pure-const?

In set_nothrow_function_flags.  Probably would be good to grep for
places where node->set_XXXX_flag is used.
> 2018-11-07  Martin Liska  <mliska@suse.cz>
> 
> 	* common.opt: Add -fipa-stack-alignment flag.
> 	* doc/invoke.texi: Document it.
> 	* final.c (rest_of_clean_state): Guard stack
> 	shrinking with flag.
> 
> gcc/testsuite/ChangeLog:
> 
> 2018-11-07  Martin Liska  <mliska@suse.cz>
> 
> 	* gcc.target/i386/ipa-stack-alignment.c: New test.
> From 8691490a142228021ed65313a72d176d06966829 Mon Sep 17 00:00:00 2001
> From: marxin <mliska@suse.cz>
> Date: Wed, 7 Nov 2018 13:31:41 +0100
> Subject: [PATCH 1/2] Come up with -fipa-reference-addressable flag.
> 
> gcc/ChangeLog:
> 
> 2018-11-07  Martin Liska  <mliska@suse.cz>
> 
> 	* cgraph.h (ipa_discover_readonly_nonaddressable_vars): Rename
> 	to ...
> 	(ipa_discover_nonaddressable_vars): ... this.
> 	* common.opt: Come up with new flag -fipa-reference-addressable.
> 	* doc/invoke.texi: Document it.
> 	* ipa-reference.c (propagate): Call the renamed fn.
> 	* ipa-visibility.c (whole_program_function_and_variable_visibility):
> 	Likewise.
> 	* ipa.c (ipa_discover_readonly_nonaddressable_vars): Renamed to
> 	...
> 	(ipa_discover_nonaddressable_vars): ... this.  Discove
> 	non-addressable variables only with the newly added flag.
> 	* opts.c: Enable the newly added flag with -O1 and higher
> 	optimization level.

Hmm, the write-only and readonly flags are not handled in here?

Honza