[llvm] [BOLT][Perf2bolt] Add support to generate pre-parsed perf data (PR #171144)

[Ádám Kallai via llvm-commits]

kaadam wrote:

> During the last office hours, @aaupov asked about motivation. On our end, it was to exercise as much of the flow as possible in tests (perf2bolt/bolt), without a hard dependency on the `perf` binary. Not sure if @kaadam had other user cases as well.

My main motivation is to add an end-to-end test for SPE Aggregation based on this [comment](https://github.com/llvm/llvm-project/pull/129231#pullrequestreview-2936814302). As SPE is new CPU extension, to collect this type of profile needs to have an arm developer device which has Spe support. To decode Spe data, it also needs to have the proper version of Linux Perf (minimum v6.15).
Using pre-parsed text profile bypasses this technical difficulties, of course it could be used any other cases as well.
The generator itself is just a tool to help the developer/user to create a standard pre-parsed text profile. 

@aaupov  If you have any other idea or suggestion please let me know. Thanks. 


https://github.com/llvm/llvm-project/pull/171144