[llvm] [llvm-profgen] Add Arm SPE branch profile support (PR #223237)

[via llvm-commits]

jacobhodgsonARM wrote:

Looks good overall. The design is similar to ours.
One concern with the range counting: code after an SVC system call can get weight from both a sampled
branch into the block and a sampled return from the kernel. AutoFDO’s LLVM SPE reader has the same
issue, so I don’t think this should hold up the pull request.

I’d also like us to extend AutoFDO’s approach by using SPE’s previous branch target information to
reconstruct ranges ending at the sampled branch. That may give us a better profile, but we can leave it
for a follow-up.

https://github.com/llvm/llvm-project/pull/223237