Certain corner-case operations cannot be handled
natively by the execution pipeline and must be performed by the microcode
sequencer (MS), where 1 or more uOps are issued. The microcode sequencer
performs microcode assists (small programs injected into the execution stream),
inserting flows, and writing to the instruction queue (IQ). For example, when
working with very small floating point values (so-called denormals), the
floating-point units are not set up to perform these operations natively.
Instead, a sequence of instructions to perform the computation on the denormal
is injected into the pipeline. Since these microcode sequences might be
hundreds of instructions long, these microcode assists are extremely
deleterious to performance.