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@@ -3796,23 +3796,20 @@ Run the script to test the \code{patch-instructions} pass.
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\index{prelude}\index{conclusion}
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Recall that the \code{print-x86} pass generates the prelude and
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-conclusion instructions for the \code{main} function.
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+conclusion instructions to satisfy the x86 calling conventions
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+(Section~\ref{sec:calling-conventions}). With the addition of the
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+register allocator, the callee-saved registers used by the register
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+allocator must be saved in the prelude and restored in the conclusion.
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+In the \code{allocate-registers} pass, add an entry to the \itm{info}
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+of \code{X86Program} named \code{used-callee} that stores the set of
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+callee-saved registers that were assigned to variables. The
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+\code{print-x86} pass can then access this information to decide which
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+callee-saved registers need to be saved and restored.
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%
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-The prelude saved the values in \code{rbp} and \code{rsp} and the
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-conclusion returned those values to \code{rbp} and \code{rsp}. The
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-reason for this is that our \code{main} function must adhere to the
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-x86 calling conventions that we described in
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-Section~\ref{sec:calling-conventions}. Furthermore, if your register
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-allocator assigned variables to other callee-saved registers
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-(e.g. \code{rbx}, \code{r12}, etc.), then those variables must also be
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-saved to the stack in the prelude and restored in the conclusion. The
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-simplest approach is to save and restore all of the callee-saved
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-registers. The more efficient approach is to keep track of which
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-callee-saved registers were used and only save and restore
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-them. Either way, make sure to take this use of stack space into
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-account when you are calculating the size of the frame and adjusting
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-the \code{rsp} in the prelude. Also, don't forget that the size of the
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-frame needs to be a multiple of 16 bytes!
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+When calculating the size of the frame to adjust the \code{rsp} in the
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+prelude, make sure to take into account the space used for saving the
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+callee-saved registers. Also, don't forget that the frame needs to be
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+a multiple of 16 bytes!
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An overview of all of the passes involved in register allocation is
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shown in Figure~\ref{fig:reg-alloc-passes}.
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Jeremy Siek