RFR: Add support for ARMv6 to ARM JIT

[Andrew Haley]

On 01/22/2015 11:14 AM, Edward Nevill wrote:
> On Thu, Jan 22, 2015 at 10:00 AM, Andrew Haley <aph at redhat.com> wrote:
> 
>> So what is thumb2.cpp for?  I still don't get it.
> 
> The idea was to minimise the change to reduce the risk of breaking
> anything for distros. The migration from thumb2 JIT to arm JIT would
> be done in 3 stages.
> 
> Stage 1:
> 
> Introduced arm32JIT.cpp but still have the default build from the
> old thumb2.cpp which is unchanged apart from the one #ifndef
> ARM32JIT.
> 
> Distros can then elect to choose the arm32 JIT by applying the 1
> small patch which adds -DARM32JIT to zeroshark.make. This patch can
> be carried within the distro packaging. Alternatively distros can
> ignore the arm32 JIT and continue with the unchanged thumb2 JIT as
> before.
> 
> Stage 2:
> 
> When everyone is happy with the arm32 JIT make ARM32JIT the default.
> Distros can still elect to build the thumb2 JIT by backing out the
> -DARM32JIT in zeroshark.make
> 
> Stage 3:
> 
> Sometime in the future delete thumb2.cpp
> 
> Of course if people are happy to go straight to stage 3 that is fine
> by me.  The only question then is whether the changes should just be
> applied to thumb2.cpp which would now generate thumb2 or arm32 code
> or whether to rename it to arm32JIT.cpp.

This is a very different development model from what we use in
IcedTea.  There are stable branches we use for releases and the
development trunk for new code.  We don't need to keep old files
around because we have everything under source control.

IMO (and it is just my opinion) you should remove thumb2.cpp on the
development trunk.  I have no opinion about whether thumb2 or ARM
should be the default on systems which support both.  I'm guessing
that thumb2 might be a slightly better choice, but I doubt that it
will make any difference to most workloads.

Andrew.