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\usepackage{../slides}

\usepackage{../graphics}

\usepackage{../langs}

\usepackage{../data}

\hfuzz=220pt 

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\newcommand{\bl}[1]{\textcolor{blue}{#1}}     

% beamer stuff 

\renewcommand{\slidecaption}{CFL 01, King's College London}

%% https://cs.rit.edu/~hh/teaching/_media/cc18/lectures/lect1/main.pdf

%% https://cs.rit.edu/~hh/teaching/_media/cc18/lectures/lect2/main.pdf

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\begin{document}

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\begin{frame}[t]

\frametitle{%  

  \begin{tabular}{@ {}c@ {}}

  \\[-3mm]

  \LARGE Compilers and \\[-1mm] 

  \LARGE Formal Languages (1)\\[-3mm] 

  \end{tabular}}

  \begin{center}

  %\includegraphics[scale=0.3]{pics/ante1.jpg}\hspace{5mm}

  %\includegraphics[scale=0.31]{pics/ante2.jpg}\\

  %\footnotesize\textcolor{gray}{Antikythera automaton, 100 BC (Archimedes?)}

  \end{center}

  \normalsize

  \begin{center}

  \begin{tabular}{ll}

  Email:  & christian.urban at kcl.ac.uk\\

  Office Hours: & Thursdays 12 -- 14\\

  Location: & N7.07 (North Wing, Bush House)\\

  Slides \& Progs: & KEATS\\

  \end{tabular}

  \end{center}

\end{frame}

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\begin{frame}[t]

\frametitle{Why Study Compilers?}

John Regehr {\small(Univ.~Utah, LLVM compiler hacker)}\smallskip\\

\begin{bubble}[10.5cm]

  \bf ``\ldots{}It’s effectively a perpetual

  employment act for solid compiler hackers.''

\end{bubble}

\onslide<1->{

\only<2>{

\begin{itemize}

\item {\bf Hardware is getting weirder

  rather than getting clocked faster.}

\begin{itemize}

\item[]  ``Almost all processors are multicores nowadays and it looks

  like there is increasing asymmetry in resources across cores.

  Processors come with vector units, crypto accelerators etc. We have

  DSPs, GPUs, ARM big.little, and Xeon Phi. This is only scratching the

  surface.''

\end{itemize}  

\end{itemize}}

\only<3>{

\begin{itemize}

\item {\bf We’re getting tired of low-level languages and

    their associated security disasters.}

\begin{itemize}

\item [] ``We want to write new code, to whatever extent possible, in

  safer, higher-level languages. Compilers are caught right in the

  middle of these opposing trends: one of their main jobs is to help

  bridge the large and growing gap between increasingly high-level

  languages and increasingly wacky platforms.''

\end{itemize}  

\end{itemize}}}

\end{frame}

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\begin{frame}[t]

  \frametitle{What are Compilers?}

\begin{center}

\begin{tikzpicture}[]

  \node (0) at (-2.3,0) {\includegraphics[scale=0.3]{pics/csource.png}};

  \node (1) [right=35mm] at (0) {\includegraphics[scale=0.3]{pics/cassmbl.png}}; 

  \draw [->,line width=4mm, red] (0) -- (1);   

  \node (2) [below=25mm] at (0) {\LARGE\bf``source''};

  \node (3) [right=35mm] at (2) {\LARGE\bf``binary''};

  \draw [->,line width=1mm] (2) -- (3);   

\end{tikzpicture}

\end{center}

\begin{textblock}{10}(1,13.5)

Compiler explorers, e.g.: \url{https://gcc.godbolt.org}

\end{textblock}

\end{frame} 

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\begin{frame}[c]

\frametitle{\begin{tabular}{c}Why Bother?\\[-2mm] Compilers \& Boeings 777\end{tabular}}

First flight in 1994. They want to achieve triple redundancy in hardware

faults.\bigskip

They compile 1 Ada program to\medskip

\begin{itemize}

  \item Intel 80486

  \item Motorola 68040 (old Macintosh's)

  \item AMD 29050 (RISC chips used often in laser printers)

\end{itemize}\medskip\medskip

using 3 independent compilers.\bigskip\pause

\small Airbus uses C and static analysers. Recently started using CompCert.

\end{frame}

%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{frame}[c]

\frametitle{Why Bother?}

\begin{columns}[t]

\begin{column}{.5\textwidth}

Ruby, Python, Java 8\medskip\\

\begin{tikzpicture}\footnotesize

\begin{axis}[

    xlabel={$n$},

    x label style={at={(1.05,0.0)}},

    ylabel={time in secs},

    enlargelimits=false,

    xtick={0,5,...,30},

    xmax=33,

    ymax=35,

    ytick={0,5,...,30},

    scaled ticks=false,

    axis lines=left,

    width=5.5cm,

    height=4cm, 

    legend entries={Python,Ruby},  

    legend pos=north west,

    legend cell align=left]

\addplot[blue,mark=*, mark options={fill=white}] table {re-python.data};

\addplot[brown,mark=triangle*, mark options={fill=white}] table {re-ruby.data};

\end{axis}

\end{tikzpicture}

\begin{tikzpicture}\footnotesize

\begin{axis}[

    xlabel={$n$},

    x label style={at={(1.05,0.0)}},

    ylabel={time in secs},

    enlargelimits=false,

    xtick={0,5,...,30},

    xmax=33,

    ymax=35,

    ytick={0,5,...,30},

    scaled ticks=false,

    axis lines=left,

    width=5.5cm,

    height=4cm, 

    legend entries={Python, Java 8, JavaScript},  

    legend pos=north west,

    legend cell align=left]

\addplot[blue,mark=*, mark options={fill=white}] table {re-python2.data};   

\addplot[cyan,mark=*, mark options={fill=white}] table {re-java.data};

\addplot[red,mark=*, mark options={fill=white}] table {re-js.data};

\end{axis}

\end{tikzpicture}

\end{column}

\begin{column}{.5\textwidth}

Us (after next lecture)\medskip\\

\begin{tikzpicture}\footnotesize

\begin{axis}[

    xlabel={$n$},

    x label style={at={(1.07,0.0)}},

    ylabel={time in secs},

    enlargelimits=false,

    xtick={0,5000,...,10000},

    xmax=11000,

    ymax=35,

    ytick={0,5,...,30},

    scaled ticks=false,

    axis lines=left,

    width=5.5cm,

    height=4cm]

\addplot[green,mark=square*,mark options={fill=white}] table {re2.data};

\addplot[black,mark=square*,mark options={fill=white}] table {re3.data};

\end{axis}

\end{tikzpicture}

\begin{tikzpicture}\footnotesize

\begin{axis}[

    xlabel={$n$},

    x label style={at={(1.07,0.0)}},

    ylabel={time in secs},

    enlargelimits=false,

    ymax=35,

    ytick={0,5,...,30},

    scaled ticks=false,

    axis lines=left,

    width=5.5cm,

    height=4cm]

\addplot[black,mark=square*,mark options={fill=white}] table {re3a.data};

\end{axis}

\end{tikzpicture}

\end{column}

\end{columns}\bigskip

\small\centering

matching \bl{\texttt{[a?]\{n\}[a]\{n\}}} and \bl{\texttt{(a*)*b}}

against \bl{$\underbrace{\texttt{a}...\texttt{a}}_n$}

\end{frame} 

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\begin{frame}[c,fragile]

  \frametitle{Incidents}

  \begin{itemize}

  \item a global outage on 2 July 2019 at \textbf{Cloudflare} 

  (first one for six years)\medskip

  \begin{center}\small\color{blue}

  \begin{verbatim}  

  (?:(?:\"|'|\]|\}|\\|\d|(?:nan|infinity|true|false|

  null|undefined|symbol|math)|\`|\-|\+)+[)]*;?((?:\s

  |-|~|!|{}|\|\||\+)*.*(?:.*=.*)))  

  \end{verbatim}

  \end{center}\bigskip\bigskip\bigskip\bigskip\bigskip\bigskip\bigskip    

  \item on 20 July 2016 the \textbf{Stack Exchange} webpage went down

  because of an evil regular expression

  \end{itemize}

  \begin{textblock}{6}(9,7.6)

    \includegraphics[scale=0.14]{cloudflare.png}\\

    \footnotesize

    It serves more web traffic than Twitter, Amazon, Apple, Instagram, Bing \& Wikipedia combined.

    \end{textblock}

  \end{frame}

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\begin{frame}[c]

\frametitle{Evil Regular Expressions}

\begin{itemize}

\item \alert{R}egular \alert{e}xpression \alert{D}enial \alert{o}f \alert{S}ervice (ReDoS)\medskip

\item Evil regular expressions\medskip

\begin{itemize}

\item \bl{$(a^{?\{n\}}) \cdot a^{\{n\}}$}

\item \bl{$(a^*)^*\cdot b$}

\item \bl{$([a-z]^+)^*$}

\item \bl{$(a + a \cdot a)^*$}

\item \bl{$(a + a^?)^*$}

\end{itemize}

\item sometimes also called \alert{catastrophic backtracking}

\item this is a problem for \alert{N}etwork \alert{I}ntrusion

  \alert{D}etection systems, Cloudflare, StackExchange, Atom editor

\item \url{https://vimeo.com/112065252}  

\end{itemize}

\end{frame}

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\begin{frame}[c]

\frametitle{The Goal of this Module}

\begin{center}

  \begin{tikzpicture}[scale=1,

                      node/.style={

                      rectangle,rounded corners=3mm,

                      very thick,draw=black!50,minimum height=18mm, minimum width=20mm,

                      top color=white,bottom color=black!20}]

  \node at (3.05, 1.8) {\Large\bf write a compiler};

  \node (0) at (-2.3,0) {};  

  \node [above=5mm of 0]

  {\makebox[0mm]{\footnotesize

      \begin{tabular}{@{}l@{}}input\\[-1mm]program\end{tabular}}}; 

  \node (A) at (0,0)  [node] {};

  \node [below right] at (A.north west) {lexer};

  \node (B) at (3,0)  [node] {};

  \node [below right=1mm] at (B.north west) {\mbox{}\hspace{-1mm}parser};

  \node (C) at (6,0)  [node] {};

  \node [below right] at (C.north west) {\mbox{}\hspace{-1mm}code gen};

  \node (1) at (8.4,0) {};

  \node [above=5mm of 1]

  {\makebox[0mm]{\footnotesize

      \begin{tabular}{@{}r@{}}binary\\[-1mm]code\end{tabular}}};

  \draw [->,line width=4mm] (0) -- (A); 

  \draw [->,line width=4mm] (A) -- (B); 

  \draw [->,line width=4mm] (B) -- (C); 

  \draw [->,line width=4mm] (C) -- (1); 

  \end{tikzpicture}

  \end{center}

\only<2,3,4>{

\begin{textblock}{1}(1,2.1)

\begin{bubble}[9.8cm]

\normalsize

lexer input: a string\smallskip\\

\hspace{5mm}\code{"read(n);"}\medskip\\

lexer output: a sequence of tokens\smallskip\\

\hspace{5mm}\code{key(read) lpar id(n) rpar semi}

\end{bubble}

\end{textblock}} 

\only<3,4>{

\begin{textblock}{1}(6,7.8)

\begin{tabular}{c}

\includegraphics[scale=0.2]{../pics/rosetta.jpg}\\[-2mm]

\footnotesize lexing $\Rightarrow$ recognising words (Stone of Rosetta)

\end{tabular}

\end{textblock}}

\only<4>{

\begin{textblock}{1}(0.5,12)\small

\begin{tabular}{l@{}c@{}l}

  \pcode{if}    & $\;\Rightarrow\;$ & keyword\\

  \pcode{iffoo} & $\;\Rightarrow\;$ & identifier\\

\end{tabular}  

\end{textblock}}

\only<5>{

\begin{textblock}{1}(1,1.5)

\begin{bubble}[8.5cm]

\normalsize

parser input: a sequence of tokens\smallskip\\

{\small\hspace{5mm}\code{key(read) lpar id(n) rpar semi}}\smallskip\\

parser output: an abstract syntax tree\smallskip\\

\footnotesize

\hspace{2cm}\begin{tikzpicture}

  \node {\code{read}}

    child {node {\code{lpar}}}

    child {node {\code{n}}}

    child {node {\code{rpar}}};

\end{tikzpicture}

\end{bubble}

\end{textblock}}

\only<6,7>{

\begin{textblock}{1}(1,1.5)

\begin{bubble}[4cm]

\normalsize

code generator:\smallskip\\

\hspace{5mm}\code{istore 2}\\ 

\hspace{5mm}\code{iload 2}\\ 

\hspace{5mm}\code{ldc 10}\\

\hspace{5mm}\code{isub}\\

\hspace{5mm}\code{ifeq Label2}\\ 

\hspace{5mm}\code{iload 2}\\

\hspace{5mm}\code{...}\\

\end{bubble}

\end{textblock}}

\only<7>{

\begin{textblock}{6}(8.4,7)

\begin{bubble}[5cm]

\mbox{\begin{tikzpicture}[scale=0.58,rounded corners=0mm]

\begin{axis}[axis x line=bottom, axis y line=left, ylabel=secs,

    xlabel=n,

    enlargelimits=0.05,

    ybar interval=0.7, legend style=small]

\addplot file {interpreted2.data};

\addplot file {compiled2.data};

%\legend{interpreted, compiled}

\end{axis}

\end{tikzpicture}}

\end{bubble}

\end{textblock}}

\end{frame}

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\begin{frame}[c]

\frametitle{The Acad.~Subject is Mature}

\bigskip

\begin{itemize}

\item Turing Machines, 1936 (a tape as memory)

\item Regular Expressions, 1956\\

\item The first compiler for COBOL, 1957\\ (Grace Hopper)\medskip

\item But surprisingly research papers are still published nowadays\\

\item ``Parsing: The Solved Problem That Isn't''

\end{itemize}

\begin{flushright}

\includegraphics[scale=0.3]{pics/hopper.jpg}\\

\footnotesize\textcolor{gray}{Grace Hopper}

\end{flushright}

\begin{flushright}

\mbox{}\\[-6mm]

{\footnotesize\textcolor{gray}{(she made it to David Letterman's Tonight Show,\\[-2mm]

 \url{https://youtu.be/3N_ywhx6_K0?t=31})}}

\end{flushright}

\end{frame}

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\begin{frame}[c]

\frametitle{Remember BF*** from PEP?}

\begin{center}

\begin{tabular}{lcl}

\bl{\texttt{>}} & $\Rightarrow$ & move one cell right\\

\bl{\texttt{<}} & $\Rightarrow$ & move one cell left\\

\bl{\texttt{+}} & $\Rightarrow$ & increase cell by one\\

\bl{\texttt{-}} & $\Rightarrow$ & decrease cell by one\\

\bl{\texttt{.}} & $\Rightarrow$ & print current cell\\

\bl{\texttt{,}} & $\Rightarrow$ & input current cell\\

\bl{\texttt{[}} & $\Rightarrow$ & loop begin\\

\bl{\texttt{]}} & $\Rightarrow$ & loop end\medskip\\

                & $\Rightarrow$ & everything else is a comment\\

\end{tabular}  

\end{center}  

\end{frame}

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\begin{frame}[c]

  \frametitle{A ``Compiler'' for BF***}

  \begin{center}

  \begin{tabular}{lcl}

  \bl{\texttt{>}} & $\Rightarrow$ & \texttt{ptr++}\\

  \bl{\texttt{<}} & $\Rightarrow$ & \texttt{ptr--}\\

  \bl{\texttt{+}} & $\Rightarrow$ & \texttt{(*ptr)++}\\

  \bl{\texttt{-}} & $\Rightarrow$ & \texttt{(*ptr)--}\\

  \bl{\texttt{.}} & $\Rightarrow$ & \texttt{putchar(*ptr)}\\

  \bl{\texttt{,}} & $\Rightarrow$ & \texttt{*ptr = getchar()}\\

  \bl{\texttt{[}} & $\Rightarrow$ & \texttt{while(*ptr)\{}\\

  \bl{\texttt{]}} & $\Rightarrow$ & \texttt{\}}\medskip\\

                  & $\Rightarrow$ & ignore everything else\\

  \end{tabular}  

  \end{center}\bigskip  

  \texttt{char field[30000]\\ char *ptr = &field[15000]}

\end{frame}

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\begin{frame}[c]

\frametitle{Lectures 1 - 5}

transforming strings into structured data\\[10mm]

{\LARGE\bf Lexing} {\hfill{}based on regular expressions}\medskip\\

\hspace{5mm}(recognising ``words'')\\[6mm]