Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 447

The Speculative Operation fault handler does not need to check for unimplemented
instruction addresses. They will be checked automatically by processor hardware when
the handler executes its rfi. On processors which report unimplemented instruction
addresses with an Unimplemented Instruction Address (UIA) trap, if an emulated check
instruction targets an unimplemented address and also needs to take a Single Step trap
or Taken Branch trap (or both), the UIA trap will not be raised until after the Single Step
and/or Taken Branch trap has been handled, making it appear that the Unimplemented
Instruction Address trap has the wrong priority. A Speculative Operation fault handler
with this behavior is architecturally compliant. On processors which report
unimplemented instruction addresses with an Unimplemented Instruction Address fault,
the UIA fault will be taken at the target of the check rather than on the check
instruction itself, so any Single Step trap and/or Taken Branch trap on the check will
naturally become visible first.
Volume 2, Part 1: Interruption Vector Descriptions 2:199