The following snippet generates branches (with -C opt-level=3)

pub fn func1(a: u16, b: u16, v: u16) -> u16 { match (a == v, b == v) { (true, false) => 0, (false, true) => u16::MAX, _ => 1 << 15, // half } }

whereas spelling it out to the compiler does not:

pub fn func2(a: u16, b: u16, v: u16) -> u16 { match (a == v, b == v) { (true, false) => 0, (false, true) => u16::MAX, (true, true) => 1 << 15, // half (false, false) => 1 << 15, // half } }

I believe this breaks the zero cost abstraction promise.
In theory these do mean different things but for constant 16-bit integers on a modern 64-bit system they should be optimized away.

Other quirks:

• only partially spelling it out to the compiler with (true, true) | (false, false) still generates branches
• using guard clauses generates branchless code but with more instructions

Godbolt link: https://rust.godbolt.org/z/cWoboKM3d