Intel ARCHITECTURE IA-32 - Manual (Page 137)

General Optimization Guidelines
2
2-65
If there is more than one change to rounding, precision and infinity bits
and the rounding mode is not important to the result; use the algorithm
in Example 2-23 to avoid synchronization issues, the overhead of the
fldcw instruction and having to change the rounding mode. The
provided example suffers from a store-forwarding problem which will
lead to a performance penalty. However, its performance is still better
than changing the rounding, precision and infinity bits among more than
two values.