[llvm] [BOLT][AArch64] Introduce SPE mode in BasicAggregation (PR #120741)

[Amir Ayupov via llvm-commits]

aaupov wrote:

> This PR is an implementation of the (4a) approach of:
> 
> * [[AArch64] BOLT does not support SPE branch data #115333](https://github.com/llvm/llvm-project/issues/115333)
> 
> We did some limited, quick testing and there was no clear winner between the two approaches, but the `--spe` flag is introduced in a way to accommodate both.

Missed this comment. Am I reading it right that you didn't see a perf difference between registering SPE as two basic events or one branch event? In this case, can you please try `-infer-fall-throughs` option with the latter? 

https://github.com/llvm/llvm-project/pull/120741