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Danila Fedorin 2020-12-07 15:51:17 -08:00
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@ -44,7 +44,7 @@ As expected, the two stateless predictors, \emph{Taken}
and \emph{Not Taken}, perform significantly worse than the
others. These predictors do not keep track of the behavior
of various branches, and thus have limited ability
to predict the direction of a branch. Out of the stateful
to predict the direction or target of a branch. Out of the stateful
predictors, the \emph{2-level} predictor seems to perform the worst.
Unsurprisingly, the \emph{Combined} predictor, which is
a combination of the other two stateful predictors, performs
@ -102,7 +102,9 @@ since the code in \texttt{sim-outorder.c} converts zero to \texttt{PC+1}),
or, in the case of unconditional jumps, it returns the expected target
address (zero), which is \textit{also} \texttt{PC+1}! The fact that
the two predictors have the same address prediction rate seems
to be due to the ``FIXME'' in the simulator code.
to be due to the ``FIXME'' in the simulator code. By the way,
I write \texttt{PC+1} to mean ``the next program counter'', since
I do not know the width in bytes of the simulated instructions.
\section*{Part 2: IPC Benchmarks}
In this section, we present the IPC results from the previously listed
@ -212,6 +214,11 @@ tolerate at most one use of the wrong branch predictor before
switching to the other (if the current predictor is ``strongly''
predicted).
Of course, a combined predictor need not specifically consist of
a bimodal and a 2-level predictor. This approach can be applied
to combine any two predictors. However, in the code for the simulator,
it seems like only this specific combination is possible.
\section*{Part 5 - 3-Bit Branch Predictor}
For this part, I modified the SimpleScalar codebase to add
a 3-bit branch predictor. The code will be included with this