ch 2, select instr and assign homes

book.tex

@@ -3527,12 +3527,11 @@ $\Tail$.}
 \python{We recommend implementing an auxiliary function
   named \code{select\_stmt} for the $\Stmt$ non-terminal.}
 
-\racket{
-The cases for $\Atm$ are straightforward; variables stay
-the same and integer constants change to immediates:
-$\INT{n}$ changes to $\IMM{n}$.}
+\racket{The cases for $\Atm$ are straightforward; variables stay the
+  same and integer constants change to immediates, that is, $\INT{n}$
+  changes to $\IMM{n}$.}
 
-We consider the cases for the $\Stmt$ non-terminal, starting with
+Next consider the cases for the $\Stmt$ non-terminal, starting with
 arithmetic operations. For example, consider the addition operation
 below, on the left side. There is an \key{addq} instruction in x86,
 but it performs an in-place update.  So we could move $\Arg_1$
@@ -3674,9 +3673,9 @@ programs.
 \section{Assign Homes}
 \label{sec:assign-Lvar}
 
-The \key{assign\_homes} pass compiles \LangXVar{} programs to
+The \code{assign\_homes} pass compiles \LangXVar{} programs to
 \LangXVar{} programs that no longer use program variables.
-Thus, the \key{assign-homes} pass is responsible for placing all of
+Thus, the \code{assign\_homes} pass is responsible for placing all of
 the program variables in registers or on the stack. For runtime
 efficiency, it is better to place variables in registers, but as there
 are only 16 registers, some programs must necessarily resort to
@@ -3722,24 +3721,29 @@ movq -16(%rbp), %rax
 \end{lstlisting}
 \end{transformation}
 
-\racket{The \code{locals-types} entry in the $\itm{info}$ of the
-  \code{X86Program} node is an alist mapping all the variables in the
-  program to their types (for now just \code{Integer}).  The
-  \code{assign\_homes} pass should replace all uses of those variables
-  with stack locations.  As an aside, the \code{locals-types} entry is
+\racket{
+  The \code{assign\_homes} pass should replace all variables
+  with stack locations.
+  The list of variables can be obtain from 
+  the \code{locals-types} entry in the $\itm{info}$ of the
+  \code{X86Program} node. The \code{locals-types} entry is an alist
+  mapping all the variables in the program to their types
+  (for now just \code{Integer}).
+  As an aside, the \code{locals-types} entry is
   computed by \code{type-check-Cvar} in the support code, which
   installs it in the $\itm{info}$ field of the \code{CProgram} node,
-  which should be propagated to the \code{X86Program} node.}
+  which you should propagate to the \code{X86Program} node.}
 %
 \python{The \code{assign\_homes} pass should replace all uses of
   variables with stack locations.}
 %
 In the process of assigning variables to stack locations, it is
 convenient for you to compute and store the size of the frame (in
-bytes) in%
-\racket{the $\itm{info}$ field of the \key{X86Program} node, with the key \code{stack-space}}
+bytes) in
+\racket{the $\itm{info}$ field of the \key{X86Program} node, with the key \code{stack-space},}
+%
+\python{the field \code{stack\_space} of the \key{X86Program} node,}
 %
-\python{the field \code{stack\_space} of the \key{X86Program} node},
 which is needed later to generate the conclusion of the \code{main}
 procedure. The x86-64 standard requires the frame size to be a
 multiple of 16 bytes.\index{subject}{frame}
@@ -3747,7 +3751,7 @@ multiple of 16 bytes.\index{subject}{frame}
 % TODO: store the number of variables instead? -Jeremy
 
 \begin{exercise}\normalfont
-Implement the \key{assign\_homes} pass in
+Implement the \code{assign\_homes} pass in
 \racket{\code{compiler.rkt}}\python{\code{compiler.py}}, defining
 auxiliary functions for each of the non-terminals in the \LangXVar{}
 grammar.  We recommend that the auxiliary functions take an extra
@@ -3794,7 +3798,7 @@ print(b)
 \end{lstlisting}
 \fi}
 \end{minipage}\\
-The \key{assign\_homes} pass produces the following translation. \\
+The \code{assign\_homes} pass produces the following translation. \\
 \begin{minipage}{0.5\textwidth}
 {\if\edition\racketEd
 \begin{lstlisting}