// Assumes that the following costs from https://gmplib.org/~tege/x86-timing.pdf:
//    1 - addq, shlq, leaq, negq, subq
//    3 - imulq
// This limits the rewrites to two instructions.
// Note that negq always operates in-place,
// which can require a register-register move
// to preserve the original value,
// so it must be used with care.
(MUL(Q|L)const [-9] x) => (NEG(Q|L) (LEA(Q|L)8 <v.Type> x x))