[LLVMdev] RFC: Remove AArch64 backend & rename ARM64 -> AArch64

[Tim Northover]

Hi all,

Thanks to everyone's hard work over the last few months, the last
child of the AArch64/ARM64 merge issue (http://llvm.org/PR19392) has
just been resolved. So I think it's time to finish the job.

I'd like to delete the AArch64 target and move ARM64 into its place:
for now we'll accept both aarch64 and arm64 triples in all places, and
they will all be redirected to the backend residing in
lib/Target/AArch64.

This is going to be a big change, and will severely disrupt any
in-progress patches (not just the files moving, but from the
"s/ARM64/AArch64/g" we'll be doing for consistency and subsequent
clang-formatting to preserve column count). So I'd like to make sure
that these disruptions are kept to a minimum. Currently, the patches I
know about are:

+ Bradley is working on basic-a64-diagnostics.s. I propose to wait
until this is finished before moving.
+ I've got 1 or 2 things going on, I can work around those easily enough.
+ James has discovered the joys big-endian interactions with ACLE.
Fortunately this appears to be mostly Clang-based, so shouldn't affect
things much.
+ Dave is working on improving the A53 scheduler model. I'll wait
until that's committed.

So, does anyone have extra work they'd like to get in first, or any
other problems with the current state of the ARM64 backend that they
think should block this?

If not, I'd suggest I start work either next weekend (if I'm feeling
keen, to minimize disruption) or on Monday 26th (if not). I expect it
to take a day or so to disentangle things; but after the move commit
(while I'm doing final tidying up of tests & such), work should be
able to start again without issue.

Looks like we might make 3.5 comfortably!

Cheers.

Tim.

(Oh, and I'm away this weekend and early next week; without any net
for the weekend bit, so don't worry if it takes me a while to reply).