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Renamed opt_const to opt_expr

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Clifford Wolf 2016-03-31 08:43:28 +02:00
parent d31c968d76
commit 1d0f0d668a
14 changed files with 84 additions and 83 deletions
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16
manual/CHAPTER_Optimize.tex
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@ -15,7 +15,7 @@ passes that each perform a simple optimization:
\begin{itemize}
\item Once at the beginning of {\tt opt}:
\begin{itemize}
\item {\tt opt\_const}
\item {\tt opt\_expr}
\item {\tt opt\_share -nomux}
\end{itemize}
\item Repeat until result is stable:
@ -25,13 +25,13 @@ passes that each perform a simple optimization:
\item {\tt opt\_share}
\item {\tt opt\_rmdff}
\item {\tt opt\_clean}
\item {\tt opt\_const}
\item {\tt opt\_expr}
\end{itemize}
\end{itemize}
The following section describes each of the {\tt opt\_*} passes.
\subsection{The opt\_const pass}
\subsection{The opt\_expr pass}
This pass performs const folding on the internal combinational cell types
described in Chap.~\ref{chapter:celllib}. This means a cell with all constant
@ -57,11 +57,11 @@ this pass can also optimize cells with some constant inputs.
$a$ & 1 & $a$ \\
1 & $b$ & $b$ \\
\end{tabular}
\caption{Const folding rules for {\tt\$\_AND\_} cells as used in {\tt opt\_const}.}
\label{tab:opt_const_and}
\caption{Const folding rules for {\tt\$\_AND\_} cells as used in {\tt opt\_expr}.}
\label{tab:opt_expr_and}
\end{table}
Table~\ref{tab:opt_const_and} shows the replacement rules used for optimizing
Table~\ref{tab:opt_expr_and} shows the replacement rules used for optimizing
an {\tt\$\_AND\_} gate. The first three rules implement the obvious const folding
rules. Note that `any' might include dynamic values calculated by other parts
of the circuit. The following three lines propagate undef (X) states.
@ -76,10 +76,10 @@ an undef value or a 1 and therefore the output can be set to undef.
The last two lines simply replace an {\tt\$\_AND\_} gate with one constant-1
input with a buffer.
Besides this basic const folding the {\tt opt\_const} pass can replace 1-bit wide
Besides this basic const folding the {\tt opt\_expr} pass can replace 1-bit wide
{\tt \$eq} and {\tt \$ne} cells with buffers or not-gates if one input is constant.
The {\tt opt\_const} pass is very conservative regarding optimizing {\tt \$mux} cells,
The {\tt opt\_expr} pass is very conservative regarding optimizing {\tt \$mux} cells,
as these cells are often used to model decision-trees and breaking these trees can
interfere with other optimizations.