If you look at discussions about the instruction decoder of Intel processors, you often see it mentioned that they have something like three "simple" decoders and one "complex" decoder. The main difference is that the "complex" decoder is the only one which can decode instructions implemented in microcode (dispatching micro-operations from the microcode ROM), while the "simple" decoders can only output micro-operations directly (using something similar to hard-wired pattern matching on the instruction). So yes, many x86 instructions are not implemented in microcode.