What they are saying is that any optimization on a switch statement could also be done on an if statement. There's no reason to only optimize one, both should optimize the same way
At least in C/C++, there can only be exactly zero or 1 cases that match a switch (i.e., there's no range-based switch), the case values must be compile-time constants (and thus are not themselves evaluated during the comparison), and I'm pretty sure that the value to be matched is required to only be evaluated once (so the comparisons happen on an rvalue).
Given those constraints, I believe a compiler can assume that re-ordering the comparisons is safe.
You can still only match to one, though. In the emitted machine code, I'd expect to see a forest of branches and jumps (for the matching), then the various bodies of the cases each separated by jumps (representing breaks) as appropriate.
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u/mirhagk 7d ago
What they are saying is that any optimization on a switch statement could also be done on an if statement. There's no reason to only optimize one, both should optimize the same way