The simplest example is `memcpy(dst, src, len)` and similar iterative byte copying operations. If the function did not use noalias, the compiler wouldn't be free to optimize individual byte read/writes into register-sized writes, as the destination may overlap with the source. In practice this means 8x more CPU instructions per copy operation on a 64-bit machine.

Note that memcpy specifically may already be implemented this way under the hood because it requires noalias; but I imagine similar iterative copying operations can be optimized in a like manner ad-hoc when aliasing information is baked in like it is with Rust.