Internal llvm failure if using -O2 with thumbv7em-linux-eabi target

[farcaller]

On cross-compiling libcore, if cpu is locked in to cortex-m4 and -O2 is used, llvm fails with unreachable:

rustc --target thumbv7em-linux-eabi -Ctarget-cpu=cortex-m4 --opt-level 2 libcore/lib.rs
Unexpected member type for HA
UNREACHABLE executed at /Users/farcaller/temp/rust/src/llvm/lib/Target/ARM/ARMCallingConv.h:213!

Compiling without --opt-level 2 or -Ctarget-cpu=cortex-m4 works as expected.

PS: I think this is an LLVM bug, but I cannot figure out a small test case.

[alexcrichton]

This is the IR run through bugpoint: https://gist.github.com/ff0487dadc8576d07bdf.

This isn't very actionable on our end as this definitely looks like an LLVM bug, so I'm going to close this. I would recommend reporting the bugpoint output upstream after trying to minimize it further.

[farcaller]

It seems that this one is actually fixed at r209650 of llvm. What's the rust policy to bump tracking llvm version?

[alexcrichton]

If you make a pull request against rust-lang/llvm with the new commits, I can push so you can update the submodule.