cpu-o3: Don't add non-speculative mem barriers to the IQ twice

There are cases where the IEW adds a non-speculative instruction to
the IQ twice. This can happen if an instruction is flagged as
IsMemBarrier and IsNonSpeculative. Avoid adding non-speculative
instructions in the IEW to the IQ by checking if it has been added
already.

Change-Id: Ifcff676a451b57b2406ce00ed8dae19ed399515f
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Javier Setoain <javier.setoain@arm.com>
Reviewed-by: Giacomo Gabrielli <giacomo.gabrielli@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/8374
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

src/cpu/o3/iew_impl.hh

@@ -1100,7 +1100,7 @@ DefaultIEW<Impl>::dispatchInsts(ThreadID tid)
             add_to_iq = true;
         }
 
-        if (inst->isNonSpeculative()) {
+        if (add_to_iq && inst->isNonSpeculative()) {
             DPRINTF(IEW, "[tid:%i]: Issue: Nonspeculative instruction "
                     "encountered, skipping.\n", tid);