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lang-cpp
-O0is kind of pointless, at least if you're going to scrutinize its efficiency.movwould ever be useful. On a side note, optimizing with -02 removes the redundant operation.b=++a. It is effectively the same asb=(a+=1);so you computea+1and store that intoaand then copy fromatob. An unoptimized compile is not supposed to notice that the value just stored intoais still in eax, so you don't need to read it back fromawhen copyingatob. An unoptimized compile forgets the register contents after each step.++aand the final 2 do theb = a(whereaalready has the incremented value). Due to no optimization, the compiler didn't eliminate the reload ofeax.