RISC-V LLVM sync-up call 21st Nov 2019

For background on these calls, see

Reminder: the purpose is to co-ordinate between active contributors.
If you have support questions etc then it's best to post to llvm-dev.

We have a call each Thursday at 4pm GMT, via

I've created a shared calendar which may help in keeping track, which
is hopefully accessible at:
  * <https://calendar.google.com/calendar/b/1?cid=bG93cmlzYy5vcmdfMG41cGtlc2ZqY25wMGJoNWhwczFwMGJkODBAZ3JvdXAuY2FsZW5kYXIuZ29vZ2xlLmNvbQ>
  * <https://calendar.google.com/calendar/ical/lowrisc.org_0n5pkesfjcnp0bh5hps1p0bd80%40group.calendar.google.com/public/basic.ics>

Issues to discuss today include the following:
* Heads up: the lowRISC toolchain team is starting to get a bit more
involved in Rust RISC-V related issues due to ongoing work to port
Oreboot and TockOS to the OpenTitan platform. See e.g.
<https://github.com/rust-lang/rust/pull/66548>, and if you're involved
in the Rust RISC-V community please do flag things to us if you think
we can help.
* fcopysign: Luis has posted a more minimal approach as
<https://reviews.llvm.org/D70426> which we'd really like help in
reviewing and landing, as this bug is causing issues in e.g. FreeBSD
base system rebuilds
* The march/mabi behaviour changer (D69383) has now landed.
  * Thank you everyone for your input and to Sam for driving.
  * As noted, we may want to tackle multilib reuse soon
* ilp32e ABI support: Sam has posted <https://reviews.llvm.org/D70401>
for review. There are currently some issues related to stack
realignment and the recent base pointer work
* SET6/SUB6 relocations: Luis has posted
<https://reviews.llvm.org/D70396> to fix resolution. There seem to be
some inconsistencies in GCC/binutils behaviour for these relocations,
which we're investigating
* Shrink wrapping, machine outliner, save/restore libcalls - are there
outstanding issues here? How can we get this landed?
* Other
  * The libunwind RISC-V patch seems effectively ready
<https://reviews.llvm.org/D68362>, there is some discussion there
about cross-unwinding, which is a future goal of libunwind
  * Work is underway to enable RISC-V in the Fuchsia toolchain build