So the main point here is we save some time with a direct jump at least for a few values of x? It's cool I guess but the extra confusion might not be worth it.
Go "O(1)" on all the CMDs or don't, for the sake of ease of comprehension. In the hypothetical, or may be practical world[0] where size+computation constraints require you must goto some of them and if-else the rest of them, I suppose the "1/2goto,1/2if-else" optimization would be one of the latter considerations for optimization over a host of other things you can consider.
[0] I admit I don't hack in that world, but I do computational physics, which is more about vectorizing things, not optimization of branching typically.
The tipping point for when the compiler decides to switch strategies, is obviously architecture dependent but could also be influenced by what flags are set and whether to favor for small code side, or highest speed.
I suspect, the code could have been written using two switch statements - and probably achieved the same effect in terms of the generated assembler, as well as be more idiomatic.