LLVM did do some with noalias, but it wasn’t very mature because it wasn’t broadly useful in C/C++, because it was too hard to use correctly.

Then Rust made it trivial to use correctly, and found that what LLVM did have was quite buggy, because it hadn’t been exercised. These were bugs that could in theory have been found in C/C++, but in practice never would have been. And so for quite some years Rust would toggle the noalias optimisations on and off, depending on whether there were any known bad-codegen issues at the time. I think the last toggle was a few years ago by now, this stuff is finally actually stable and appreciated.

My recollection is that the figures for the Rust compiler are in the vicinity of a 5% improvement from emitting noalias in the LLVM IR.

And it’s likely that quite a bit more is possible.