They're not the same thing semantically, even though the final x86/64 assembly might be the same after a compiler is done with it. '+' is addition but '+=' is a

They're not the same thing semantically, even though the final x86/64 assembly might be the same after a compiler is done with it. '+' is addition but '+=' is addition "in place" which means that the calculation is performed in the location where it will be stored (although, again, these might look identical when talking about register allocation and whatnot in the final assembly). This is relevant to reordering compilers because it allows them to do certain optimizations that are normally hard to prove safe because of aliasing rules, especially in lower level intermediate forms where typing and other information might be lost.