[llvm] [KeyInstr] Hide new MDNodeKeyImpl<DILocation> fields (PR #138296)

[Orlando Cazalet-Hyams via llvm-commits]

OCHyams wrote:

> Are you expecting the perf drop to go away once KI is finished?

Hi :) As nikic says - we're going to mitigate it

https://github.com/llvm/llvm-project/pull/138296