[llvm] Constant Fold Logf128 calls (PR #84501)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Please fix commit message; I think you've addressed most of the "concerns".

I'm still not happy with the dependency on host libc, given the increasing pressure to have constant-folding functionality reliably available.  See also https://discourse.llvm.org/t/rfc-project-hand-in-hand-llvm-libc-libc-code-sharing/77701/18 .

Other than that, looks fine.

https://github.com/llvm/llvm-project/pull/84501