[llvm] [llvm] Reduce memory footprint of Debug metadata nodes (PR #71227)

[via llvm-commits]

serge-sans-paille wrote:

> Is the use of SubclassData32 by each of the nodes documented somewhere?

https://github.com/llvm/llvm-project/blob/f1fdbcba5fc0f88a481f105c2a16f56db0dd2940/llvm/include/llvm/IR/Metadata.h#L74

No documentation, unfortunately :-/

https://github.com/llvm/llvm-project/pull/71227