[llvm] Introduction of typified section in ExtBinary format (PR #166553)

[Sergey Shcherbinin via llvm-commits]

SergeyShch01 wrote:

Well, let's take load latency profile as an example: a profiled latency value is given to a load. 

Load can be pointed to by line:descriminator (probe doesn't work). Also, such feedback can be unrelated to call context (which can be important in LBR case).

In ExtBinary file a new profile type is introduced (say ProfTypeLoadLat) and then it will be possible to have a sub-record inside a function record in SecTypifiedProfile section for this new profile type. This sub-record for ProfTypeLoadLat can contain a list of [line:descriminator, profiled_latency] pairs.

Then, when ExtBinary file is loaded, this new profile is read and [line:descriminator, profiled_latency] pairs are moved to a new map in FunctionSamples (e.g. std::map<LineLocation, ProfiledLoadLat> LoadLatencies).

Then latencies from LoadLatencies can be put to instruction metadata in LLVM IR.

Generally this should look similar to current LBR feedback processing.

https://github.com/llvm/llvm-project/pull/166553