typo

book.tex

@@ -3474,7 +3474,7 @@ for the compilation of $R_2$.
 \label{sec:opt-if}
 
 A close inspection of the x86 code generated in
-Figure~\ref{fig:R2-passes} reveals some redundant computation
+Figure~\ref{fig:if-example-x86} reveals some redundant computation
 regarding the condition of the \key{if}. We compare \key{rcx} to $1$
 twice using \key{cmpq} as follows.
 \begin{lstlisting}