It's a little bit surprising to me that LLVM can't eliminate the grow_one check. It looks like there's a test ensure it's not needed in the easier case of vec.p

It's a little bit surprising to me that LLVM can't eliminate the grow_one check. It looks like there's a test ensure it's not needed in the easier case of vec.push(vec.pop()) [0]. With the iterator the optimization is handled in the standard library using specialization and TrustedLen[1]. [0]: https://github.com/rust-lang/rust/blob/master/tests/codegen/vec_pop_push_noop.rs#L8 https://github.com/rust-lang/rust/blob/master/tests/codegen/... [1]: https://github.com/rust-lang/rust/blob/d4025ee454169fbd22f5773f54348310ab6a47bb/library/alloc/src/vec/mod.rs#L3543 https://github.com/rust-lang/rust/blob/d4025ee454169fbd22f57...