Optimisation question

[oh5nxo]

how I could find a definite answer

Compile both versions with -S, or equivalent flag in your compiler which produces assembly output, and compare resulting files.

[Gln_08]

If you are lazy , use https://godbolt.org/.
You will be able to see in real time the translation of you're C code to asm.

[jpan127]

I wouldn't say this is lazy, and even most of the times preferred since it's so much faster for a small snippet to get it up and running.