Identical code folding

Since Rust can't do polymorphization properly yet, using generics generates a lot of duplicated functions because of monomorphization. These functions take space in the binary, even though they have completely the same instructions.

Some linkers (gold, lld) can deduplicate these identical functions using Identical Code Folding, and thus reduce binary size (and potentially also improve usage of the i-cache).

You can specify this linker option using a linker flag, for example like this:

$ RUSTFLAGS="-Clink-args=-fuse-ld=lld -Clink-args=-Wl,--icf=all" cargo build

I measured the binary size change for the following program:

fn foo() {
    let mut a: Vec<u8> = vec![1, 2, 3];
    a.pop();

    let mut b: Vec<u32> = vec![1, 2, 3];
    b.pop();

    let mut c: Vec<i32> = vec![1, 2, 3];
    c.pop();
}

fn main() {
    foo();
}

Here are binary sizes are after running strip on them: