Bug#826749: clang: enable FPXX for o32 by default

[Matthew Fortune]

YunQiang Su <wzssyqa at gmail.com> writes:
> On Fri, Jun 10, 2016 at 12:10 AM, Pablo Oliveira <pablo at sifflez.org>
> wrote:
> > Dear YunQiang Su,
> >
> > On Wed, 8 Jun 2016 23:49:17 +0800 YunQiang Su <wzssyqa at gmail.com>
> wrote:
> >> Package: src:llvm-toolchain-snapshot
> >>
> >> We are working on moving all packages mips/mipsel built with
> >> fpxx-enabled by default.
> >>
> >> While, now fpxx is not enabled by default in clang.
> >> So please apply the attached patch to 3.5/3.6/3.7/3.8/snapshot.
> >>
> >> About FPXX and the transaction, please see:
> >>
> >> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=825342
> >
> > Are you sure it is ok to modify the default behavior of FPXXDefault
> > only for Debian clang packages (this could lead to surprise and hard
> > to track bugs for users) ?
> 
> The clang guy in IMG told me that this the only way currently.
> 
> >
> > To me it makes more sense to:
> >
> > 1) either submit this patch upstream, so that every clang distribution
> > has the same common behavior regarding FPXX
> 
> I also prefer this way.

We cannot do this as the topic we are discussing here is inherently a
decision for distributions and not upstream. Please note the setting for
this in GCC is a build time setting so upstream GCC does not set FPXX
by default. Fedora or other distros can choose different compatibility
levels that suit their user base and hence may not use FPXX.

There is a longer term plan to get a build time configuration option into
CLANG/LLVM but this will take time to plan and implement. When ready
you can switch to it but there is no ETA.

> >
> > 2) change the default flags used when building mips/mipsel packages,
> > and keep the default clang behavior.
> 
> I don't this is ideal for us.
> It also will make people confused.

The FPXX setting is almost entirely invisible to end users it is a
distro level decision on how compatible the resulting objects are. Only
a handful of packages will do special things depending on this setting
and they will be designed to cope with all possibilities eventually.

> > Could you please clarify this issue ?
> 
> CC'd the toolchain guys in IMG.

Hope that clears it up a bit.

Matthew