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Commit bd8913da authored by Taddeus Kroes's avatar Taddeus Kroes
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Final changes to report

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...@@ -7,9 +7,10 @@ ...@@ -7,9 +7,10 @@
\setlength{\parindent}{0pt} \setlength{\parindent}{0pt}
\setlength{\parskip}{1ex plus 0.5ex minus 0.2ex} \setlength{\parskip}{1ex plus 0.5ex minus 0.2ex}
\title{Peephole Optimizer} \title{Compilerbouw - Peephole Optimizer}
\author{Jayke Meijer (6049885), Richard Torenvliet (6138861), Tadde\"us Kroes \author{Jayke Meijer (6049885), \\
(6054129)} Richard Torenvliet (6138861), \\
Tadde\"us Kroes (6054129)}
\begin{document} \begin{document}
...@@ -140,7 +141,17 @@ redefinition of x. ...@@ -140,7 +141,17 @@ redefinition of x.
Arithmetics in Assembly are always performed between two registers or a Arithmetics in Assembly are always performed between two registers or a
register and a constant. If the current value of all used registers is known, register and a constant. If the current value of all used registers is known,
The expression can be executed at-compile-time and the instruction can be The expression can be executed at-compile-time and the instruction can be
replaced by an immediate load of the result. See \ref{opt} for an example. replaced by an immediate load of the result. The following example illustrates
this:
\begin{verbatim}
li $2, 2 # $2 = 2
sw $2, 16($fp) # 16($fp) = 2
li $2, 3 # $2 = 3
sw $2, 20($fp) # 20($fp) = 3
lw $2, 16($fp) # $2 = 16($fp) = 2
lw $3, 20($fp) # $3 = 20($fp) = 3
addu $2, $2, $3 # change to "li $2, 0x00000005"
\end{verbatim}
%In other words until the current definition of \texttt{x} becomes dead. %In other words until the current definition of \texttt{x} becomes dead.
%Therefore reaching definitions analysis is needed. Reaching definitions is a %Therefore reaching definitions analysis is needed. Reaching definitions is a
...@@ -151,8 +162,8 @@ During the constant folding, so-called algebraic transformations are performed ...@@ -151,8 +162,8 @@ During the constant folding, so-called algebraic transformations are performed
as well. When calculations are performed using constants, some calculations can as well. When calculations are performed using constants, some calculations can
be replaced by a load- or move-instruction. An example is the statement be replaced by a load- or move-instruction. An example is the statement
$x = y + 0$, or in Assembly: \texttt{addu \$1, \$2, 0}. This can be replaced by $x = y + 0$, or in Assembly: \texttt{addu \$1, \$2, 0}. This can be replaced by
$x = y$ or \texttt{move \$1, \$2}. A list of transformations that are performed $x = y$ or \texttt{move \$1, \$2}. To see all transformations that are
can be found in appendix \ref{opt}. performed, read the inline comment blocks in the corresponding code.
\subsubsection{Copy propagation} \subsubsection{Copy propagation}
...@@ -433,7 +444,7 @@ clinpack & 3523 & 231 & 1543746 & 1457479 & 5.59\% \\ ...@@ -433,7 +444,7 @@ clinpack & 3523 & 231 & 1543746 & 1457479 & 5.59\% \\
\pagebreak \pagebreak
\appendix \appendix
\section{List of all optimizations} \section{List of straight-forward optimizations}
\label{opt} \label{opt}
...@@ -477,44 +488,5 @@ shift $regA,$regA,0 -> --- // remove it ...@@ -477,44 +488,5 @@ shift $regA,$regA,0 -> --- // remove it
add $regA,$regA,X -> lw ...,X($regA) add $regA,$regA,X -> lw ...,X($regA)
lw ...,0($regA) lw ...,0($regA)
\end{verbatim} \end{verbatim}
\textbf{Advanced basic block optimizations}
\begin{verbatim}
# Common subexpression elimination
addu $regA, $regB, 4 addu $regD, $regB, 4
... move $regA, $regD
Code not writing $regB -> ...
... ...
addu $regC, $regB, 4 move $regC, $regD
# Constant folding
li $2, 2 $2 = 2
sw $2, 16($fp) 16($fp) = 2
li $2, 3 $2 = 3
sw $2, 20($fp) -> 20($fp) = 3
lw $2, 16($fp) $2 = 16($fp) = 2
lw $3, 20($fp) $3 = 20($fp) = 3
addu $2, $2, $3 change to "li $2, 0x00000005"
# Copy propagation
move $regA, $regB move $regA, $regB
... ...
Code not writing $regA, -> ...
$regB ...
... ...
addu $regC, $regA, ... addu $regC, $regB, ...
# Algebraic transformations
addu $regA, $regB, 0 -> move $regA, $regB
subu $regA, $regB, 0 -> move $regA, $regB
mult $regA, $regB, 1 -> move $regA, $regB
mult $regA, $regB, 0 -> li $regA, 0
mult $regA, $regB, 2 -> sll $regA, $regB, 1
\end{verbatim}
\end{document} \end{document}
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