[llvm] [DebugInfo] Make DISubprogram's hashing always produce the same result (PR #90770)

[David Blaikie via llvm-commits]

https://github.com/dwblaikie commented:

What about cases where the mangled name is not included - I guess, for subprogram definitions, maybe that only comes up in something like C?

https://github.com/llvm/llvm-project/pull/90770