Why would you OR a value with itself before a call to jnz?

Question

I\'m reading some code that does the following:

OR al, al
JNZ loc_123456

If I am reading this correctly, the OR command just s

Answer 1

Using or x, x to test for zero is a common idiom, so it's perfectly readable.

You should prefer test x, x (also a common idiom) though, it macro-fuses with the branch on many processors.

Avoid cmp reg, 0. Having a lot of memory is no reason to waste it, and there's nothing to gain here. Even if there was a readability difference - this is assembly, readability is not the point. And cache space and instruction fetch bandwidth are still limited resources.