Если почитать талмуд внимательнее, то окажется, что "uCode ROM" применялось далеко не для всех инструкций. Мне лениво искать старый талмуд, где написано подробнее, вот из актуального:

16.2.1.1 Instruction Decoder
Some IA instructions that perform complex tasks require a lookup in the microcode sequencer ROM
(MSROM) to decode them into a multiple uop flow. To determine which instructions require an MSROM
lookup, see the instruction latency/bandwidth table in Section 16.3.
Fewer instructions require MSROM lookup in the Goldmont Plus and Goldmont microarchitecture than in
the Silvermont microarchitecture, though the Silvermont microarchitecture also improved significantly
over prior generations in this area; Section 16.3 provides more details. It is advisable to avoid ucode
flows where possible. Table 16-9 provides alternate non-MSROM instruction sequences that can replace
an instruction that decodes from MSROM.