MULX
emit_alu_K(MULX, dst, imm, ctx);
emit(MULX | IMMED | RS1(tmp) | S13(imm) | RD(tmp), ctx);
emit(MULX | RS1(tmp) | RS2(tmp1) | RD(tmp), ctx);
emit_alu(MULX, src, dst, ctx);
emit_alu3(MULX, tmp, src, tmp, ctx);
emit_alu3(MULX, tmp, src, tmp, ctx);