Including jemallocator-global doesn't actually enable jemalloc on MacOS X

[jorendorff]

I took an existing program, added a dependency on jemallocator-global in its Cargo.toml, built it with --release, and ran it under a profiler (Instruments). Observed: The profiler found stacks under libsystem_malloc.dylib. Expected: stacks under a statically linked jemalloc.

Depending directly on the jemallocator crate instead, and declaring a #[global_allocator] static Jemalloc in the binary crate, works fine.

I'm using stable Rust 1.37: rustc 1.37.0 (eae3437df 2019-08-13)

[jorendorff]

I think this is an upstream bug. Filed rust-lang/rust#64402 .

[gnzlbg]

Oh, so if the edition is set to Rust 2018, and one does not use extern crate jemallocator_global;, the whole crate is optimized away?

[gnzlbg]

@jorendorff we can probably add #[used] here to work around this, could you give it a try and see if adding #[used] to the jemallocator-global crate fixes this ?