updated description for ex 11

book.tex

@@ -2814,20 +2814,33 @@ shown in Figure~\ref{fig:reg-alloc-passes}.
 \end{figure}
 
 \begin{exercise}\normalfont
-Implement the pass \code{allocate-registers} and test it by creating
-new example programs that exercise all of the register allocation
-algorithm, such as forcing variables to be spilled to the stack.
-
-We recommend that you create a helper function named
-\code{color-graph} that takes an interference graph and a list of all
-the variables in the program. This function should return a mapping of
-variables to their colors. By creating this helper function, we will
-be able to reuse it in Chapter~\ref{ch:functions} when we add support
-for functions.  Once you have obtained the coloring from
-\code{color-graph}, you can assign the variables to registers or stack
-locations based on their color and then use the \code{assign-homes}
-function from Section~\ref{sec:assign-s0} to replace the variables
-with their assigned location.
+  Implement the pass \code{allocate-registers}, which should come
+  after the \code{build-interference} pass. The three new passes,
+  \code{uncover-live}, \code{build-interference}, and
+  \code{allocate-registers} replace the \code{assign-homes} pass of
+  Section~\ref{sec:assign-s0}.  Just like \code{assign-homes}, the
+  output of \code{allocate-registers} should be in the form
+  \[
+  (\key{program}\;\Int\;\Instr^{+})
+  \]
+  
+  We recommend that you create a helper function named
+  \code{color-graph} that takes an interference graph and a list of
+  all the variables in the program. This function should return a
+  mapping of variables to their colors (represented as natural
+  numbers). By creating this helper function, you will be able to
+  reuse it in Chapter~\ref{ch:functions} when you add support for
+  functions.
+
+  Once you have obtained the coloring from \code{color-graph}, you can
+  assign the variables to registers or stack locations and then reuse
+  code from the \code{assign-homes} pass from
+  Section~\ref{sec:assign-s0} to replace the variables with their
+  assigned location.
+  
+  Test your updated compiler by creating new example programs that
+  exercise all of the register allocation algorithm, such as forcing
+  variables to be spilled to the stack.
 \end{exercise}