This should not be a primary degredation of performance since the
redirection gets on seperately from this update which will only affect
future predictions.
improvements that can be upstreamed.
Basically, only use addresses in these predictors rather than
capabilities, and just pass an address in from the FetchStage.
Sc is unique in that it writes both memory and a register value.
This implementation works around the fact that the memory store data and
the register write data are sharing the same field in the reorder buffer
by inferring the writeback value of Sc from the byteEnable field.
All of St, Amo, Lr and Sc use the normal 3-bit encoding for the width;
rather than add Lr and Sc to the list, switch it just to exclude Ld as
the special case that's handled by the other half of the expression.
Previously LR.C and SC.C were decoded as LR.BU and SC.BU.
nextPc only reflected things known in the Decode stage, but not before
(i.e. BTB predictions).
This meant that we were pretty much always redirecting JRs.
I needed to pipe through whether a jump was predicted by the BTB or not,
and then only stop predicting if there is no nextPc prediction and also
no BTB prediction. This should actually reasonably approximate SBC.
Also, this one is not "redirecting", it's just flushing (flipping
decode_epoch_local), trusting that we'll get a later redirection.
We think that we were wedging on IFetch bus error.
It appears that we didn't make the last instruction fragment valid in the bus error case, and expect that this path was not previously exercised.
This change returns 0s (to hopefully make the error less subtle) in exactly the right number of fragments.
These checks were broken in several ways:
1) a missing 'else' inverted the priority of PermitStoreViolation vs. PermitStore[Local]Cap exceptions
2) another missing 'else' inverted the priority of PermitStoreCap and PermitStoreLocalCap exceptions
3) No store checks were performed when mem_func == Amo because of the preceding if clause for loads
I decided to flatten the nested if statements by pulling out the conditions into boolean local variables. Hopefully this makes it clearer (as well as fixing the bugs).
