Bug#956418: src:glibc: Please provide optimized builds for ARMv8.1

[Florian Weimer <fw@deneb.enyo.de>]

* Noah Meyerhans:

> On Sat, Apr 11, 2020 at 09:14:11PM +0200, Florian Weimer wrote:
>> > At least if I'm reading the code right (which I may very well not be
>> > doing, being generally unfamiliar with gcc internals), -mtune=generic
>> > enables the equivalent of ARMv8 support:
>> >
>> > https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/common/config/aarch64/aarch64-common.c;h=0bddcc8c3e9282a957c5479b4df7f68058093bab;hb=HEAD#l176
>> >
>> > https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/aarch64/aarch64-cores.def;h=ea9b98b4b0ad2a578755561bba5b6d5c56115994;hb=HEAD
>> >
>> > https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/aarch64/aarch64.h;h=8f08bad3562c4cbe8acdf5891e84f89d23ea6784;hb=HEAD#l226
>> 
>> Hmm.  I don't see anything that sets TARGET_OUTLINE_ATOMICS by
>> default.
>
> Only -moutline-atomics enables that.  Otherwise, unconditional support
> for atomics is enabled by TARGET_LSE, which itself is enabled by a
> number of options, e.g. -marmv8-a+lse, -marmv8.1-a, etc.
>
> See
> https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/aarch64/aarch64.c;h=4af562a81ea760891fac3cf7101b8bf887fe7a0d;hb=HEAD#l18961

Sorry, I have a feeling that we are discussing different matters.

I believe that ideally, Debian (and Fedora etc.) should follow
upstream GCC defaults.  I don't think we are in this state
(code_for_aarch64_compare_and_swap uses the atomics.md patterns to
call aarch64_split_compare_and_swap, as far as I can see).

Or put differently: If upstream doesn't want to default to
-moutline-atomics, why should Debian?