The most important optimization of control is recognizing when an if test is known at compile time, then deleting theif, the test expression, and the unreachable branch of theif. This can be considered a special case of constant folding, although the test doesn't have to be truly constant as long as it is definitely not nil. Note also, that type inference propagates the result of an if test to the true and false branches, see section constraint-propagation.
A related if optimization is this transformation:5.2
In Python, all the Common Lisp macros really are macros, written in terms of if, block and tagbody, so user-defined control macros can be just as efficient as the standard ones. Python emits basic blocks using a heuristic that minimizes the number of unconditional branches. The code in a tagbody will not be emitted in the order it appeared in the source, so there is no point in arranging the code to make control drop through to the target.