You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: roundtrip.rs
    path of file: ./repos/phaser/phaser/vendor/jemallocator/benches
    
    the code of the file until where you have to start completion: //! Benchmarks the cost of the different allocation functions by doing a
//! roundt
    
            fn [<rt_mallocx_zeroed_size_ $size _align_ $align>](b: &mut Bencher) {
                b.iter(|| unsafe {
                    use jemalloc_sys as jemalloc;
                    let flags = layout_to_flags(&Layout::from_size_align($size, $align).unwrap());
                    let ptr = jemalloc::mallocx($size, flags | jemalloc::MALLOCX_ZERO);
                    test::black_box(ptr);
                    jemalloc::sdallocx(ptr, $size, flags);
                });
            }