[clang] [clang] Emit @llvm.assume when we know the streaming mode of the function (PR #121917)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

I really don't see why we'd want to implement the optimization this way; can't we just add an instcombine for calls to `llvm.aarch64.sme.in.streaming.mode`?

https://github.com/llvm/llvm-project/pull/121917