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@@ -6803,7 +6803,7 @@ addition of \key{if} expressions to \LangIf{}, \code{explicate-control}
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produces many basic blocks arranged in a control-flow graph. We
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recommend that you create a new auxiliary function named
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\code{uncover-live-CFG} that applies liveness analysis to a
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-control-flow graph.
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+control-flow graph. \ocaml{This structuring suggestion is not crucial.}
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The first question we is: what order should we process the basic
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blocks in the control-flow graph? Recall that to perform liveness
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@@ -6867,11 +6867,22 @@ instruction's argument and for computing the variables read-from ($R$)
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or written-to ($W$) by an instruction need to be updated to handle the
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new kinds of arguments and instructions in \LangXIfVar{}.
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+\begin{ocamlx}
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+ It will now become convenient to process the \code{main} and \code{conclusion}
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+ blocks uniformly with the others. That should be straightforward, but note
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+ two things: (a) to avoid having \code{`framesize} appear as a live variable,
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+ we should avoid adding it to the set of read variables; (b) The
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+ \code{\%rbp} register may show up in some live sets; this is harmless,
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+ so long as it is precolored with a negative color in {\tt AllocateRegisters}.
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+\end{ocamlx}
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+
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\begin{exercise}\normalfont
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Update the \code{uncover-live} pass and implement the
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\code{uncover-live-CFG} auxiliary function to apply liveness analysis
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to the control-flow graph.
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-\ocaml{This is in the \code{UncoverLive} submodule of \code{Chapter4.ml}.}
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+\ocaml{Place your solution in the \code{UncoverLive} submodule of \code{Chapter4.ml}.
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+ You don't have to structure it with an auxiliary function unless
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+ you find that useful.}
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Add the following entry to the list of
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\code{passes} in the \code{run-tests.rkt} script.
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\begin{lstlisting}
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Andrew Tolmach