RISC-V LLVM sync-up call 16 Apr 2020

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 BST, via

I've created a shared calendar which may help in keeping track, which
is 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:
* LTO/ThinLTO for RISC-V https://reviews.llvm.org/D78035
* Initial bitmanip patches landed last week (thank you all!). Next steps
* Differential testing work from Luis on GCC vs Clang missed
optimisation opportunities
* FYI/reminders
  * DAGCombiner improvement from Roger for bool comparisons looks
almost good to land https://reviews.llvm.org/D65802
  * Evandro is still seeking compact code model feedback
  * vscale discussion on llvm-dev continues
  * FDPIC discussions on RISC-V sw-dev are still continuing
* No other topics were submitted, as always, please do submit things
you'd like to discuss