[PATCH] Implement ADRP CSE for global symbols

[Tim Northover]

Hi Jiangning,

> Tim, Do you mean we should move it out of PreISel stage and hoist it to middle end which can really be covered by opt? If yes, do you have any suggestions, where we should drop this pass?

I didn't mean any change in the order (I've no idea where it would be
best placed, though "as late as possible" seems reasonable so PreISel
may be right), just that it would be good to be able to run it via opt
instead of llc. I did the same recently to the Atomics pass I've been
working on.

Cheers.

Tim