Purely based on experience (without understanding precise details of SIMD execution) I'd say yes, it's an optimization
And my experience so far has been that any expression that at compile time can be guaranteed to return the same value for all elements will be executed/printed only once as the value is gonna be the same for all (as there is no need to run something 100million times if you already know all will be 0 or any other constant value)
It's not a valid optimization tho (if you can call it that). printf() has side effect and no proper compiler should merge several printf() calls into one like that. It's only a valid optimization for pure functions.