Rust sort_unstable_by with more complex closure unexpectedly shrunk binary

Thing I stumbled upon:

I added boolean argument & if statement inside sort_unstable_by closure:

 rust

    
//from
|&a, &b| compare(a, b) 

//to
|&a, &b| if is_reverse { compare(b, a) } else { compare(a, b) }


  

I expected binary to grow slightly, but actually got 1KB smaller.

I dug into & found that the reason is: quicksort fn became 980 bytes smaller.

Why? Not sure. Inlining looks same, quicksort just has fewer instructions.

target: arm-unknown-linux-gnueabihf

commit: https://github.com/tracyspacy/fli/commit/a87a98be77cc1972a53e6399716a227d1135e76b

details: https://pastebin.com/qJdTw49n

OC by @[email protected]