[Bug middle-end/88345] -Os overrides -falign-functions=N on the command line

["matz at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345

--- Comment #19 from Michael Matz <matz at gcc dot gnu.org> ---
(In reply to Jan Hubicka from comment #18)
> Reading all the discussion again, I am leaning towards -falign-all-functions
> + documentation update explaining that -falign-functions/-falign-loops are
> optimizations and ignored for -Os.
> 
> I do use -falign-functions/-falign-loops when tuning for new generations of
> CPUs and I definitely want to have way to specify alignment that is ignored
> for cold functions (as perforance optimization) and we have this behavior
> since profile code was introduced in 2002.
> 
> As an optimization, we also want to have hot functions aligned more than 8
> byte boundary needed for patching.
> 
> I will prepare patch for this and send it for disucssion.  Pehraps we want
> -flive-patching to also imply FUNCTION_BOUNDARY increase on x86-64? Or is
> live patching useful if function entries are not aligned?

Live patching (user-space) doesn't depend on any particular alignment of
functions, on x86-64 at least.  (The plan for other architectures wouldn't need
any specific alignment either).  Note that the above complaints about missing
alignment is for kernel (!) ftrace/livepatching on arm64 (!), not on x86_64.