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

[Nikita Popov via llvm-commits]

nikic wrote:

@ilovepi Yes, the stage2 build uses ThinLTO.

Maybe a more convenient investigation target than clang bootstrap would be tramp3d-v4 with LTO, which shows a size change in the text segment: https://llvm-compile-time-tracker.com/compare.php?from=3254f31a66263ea9647c9547f1531c3123444fcd&to=c5978f1eb5eeca8610b9dfce1fcbf1f473911cd8&stat=size-text Root cause is probably the same.

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