when insts execute, they mark the time they finish to be used for subsequent isnts
they may need forwarding of data. However, the regdepmap was using the wrong
value to index into the destination operands of the instruction to be forwarded.
Thus, in some cases, we are checking to see if the 3rd destination register
for an instruction is executed at a certain time, when there is only 1 dest. register
valid. Thus, we get a bad, uninitialized time value that will stall forwarding
causing performance loss but still the correct execution.
This model currently only works in MIPS_SE mode, so it will take some effort
to clean it up and make it generally useful. Hopefully people are willing to
help make that happen!
