[llvm] [llvm][IR] Extend BranchWeightMetadata to track provenance of weights (PR #86609)

[Nikita Popov via llvm-commits]

nikic wrote:

This change causes compile-time regressions for stage2 builds only (https://llvm-compile-time-tracker.com/compare.php?from=3254f31a66263ea9647c9547f1531c3123444fcd&to=c5978f1eb5eeca8610b9dfce1fcbf1f473911cd8&stat=instructions:u). This indicates that it makes clang codegen worse in some way that affects clang itself.

I assume this was intended to be NFC in terms of generated code, so something is probably not handling the new format correctly?

https://github.com/llvm/llvm-project/pull/86609