[lld] [lld][MachO]Multi-threaded i/o. Twice as fast linking a large project. (PR #147134)

[John Holdsworth via llvm-commits]

johnno1962 wrote:

@drodriguez, Thanks for persisting with this PR. I get that `paralellFor` may not use exactly `readThreads` threads the limit in practice being the number of CPUs on the host which is the default value for the -threads option. My point is it doesn't actually matter the precise number of threads as long as it is more than one tickling the flies into memory. The code using `paralellFor` at least I understand and it is performant. It's unfortunate that we are having to develop our own background threading abstraction but platform agnostic alternatives don't seem to be readily available and there is no point running the risk of having existing code regress by trying to restructure it for our limited use case. We are beginning to cycle on this PR reverting changes that it was suggested be put in which is a sign it is ready enough and we're getting down to fairly minor nits. If there is something you really can't live with let me know or suggest a specific alternative and I can test it.

https://github.com/llvm/llvm-project/pull/147134