Parallel flowcharts: conjoined nodes, arrow routing and alignment

Question

Transitioning from GraphViz to TikZ is hurting my brain...

My task is to generate flowcharts of the following variety:

In particular, I need a method to position nodes that share borders (preferably independent of their width and height) while adhering to a grid. Extra credit for explanations of how to draw brackets that indicate node grouping, as well as how to draw orthogonal arrows whose endpoints do not coincide (preferably without specifying exact coordinates or angles) or that align with specific columns, such as the load -> add arrow.

Answer 1

There were three main requests:

1. A method to position nodes that share borders. One possibility here is to use the key node distance and the positioning library. An example:

   \documentclass{standalone}
   \usepackage{tikz}
   \usetikzlibrary{positioning}
   
   \begin{document}
   
   \begin{tikzpicture}[every node/.style={draw}]
   \node (a) {A};
   \node[right=of a] (b) {B};
   \node[right=of b] (c) {C};
   \begin{scope}[yshift=-1cm,node distance=-\pgflinewidth,every node/.append style={fill=blue!20}]
   \node (a) {A};
   \node[right=of a] (b) {B};
   \node[right=of b] (c) {C};
   \end{scope}
   \end{tikzpicture}
   
   \end{document}
   

   

2. How to draw orthogonal arrows whose endpoints do not coincide (preferably without specifying exact coordinates or angles) or that align with specific columns. The main tool here is the implicit syntax for the perpendicular coordinate system. The expression ( p |- q ) or ( q -| p ). For example, (0,1 |- 2,3) and (2,3 -| 0,1) both produce the same as (0,3); the following example shows this syntax in action:

   \documentclass{standalone}
   \usepackage{tikz}
   
   \begin{document}
   
   \begin{tikzpicture}
   \node at (0,0) (a) {A};
   \node at (2,2) (b) {B};
   \node at (4,-1) (c) {C};
   \node at (4,-2) (d) {D};
   
   \draw[red] (a) |- (b);
   \draw[blue] (a) -| (b);
   \draw[green] (c) -- (a|-c) -- (a|-d) -- (d);
   \end{tikzpicture}
   
   \end{document}
   

   

3. How to draw brackets that indicate node grouping. The idea here is to use decorations; particularly, the brace decoration offered by the decorations.pathreplacing library. A little example:

   \documentclass{standalone}
   \usepackage{tikz}
   \usetikzlibrary{decorations.pathreplacing}
   
   \begin{document}
   
   \begin{tikzpicture}
   \node (a) {A};
   \node at (2,2) (b) {B};
   \node at (4,0) (c) {C};
   \draw[decorate,decoration=brace] (a) -- (b);
   \draw[decorate,decoration=brace] (b) -- (c);
   \draw[decorate,decoration={brace,mirror}] (a) -- (c);
   \end{tikzpicture}
   
   \end{document}
   

   

Combining these ideas and defining some styles for the nodes, the original diagram can be produced. The complete code:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{calc,positioning,arrows,decorations.pathreplacing}

\definecolor{myblue}{RGB}{170,223,249}
\begin{document}

\begin{tikzpicture}[
  >={stealth'},
  every node/.style={node distance=-\pgflinewidth},
  exx/.style={rectangle,draw,fill=gray!30,text width=0.9cm,align=center,font=\ttfamily},
  sblue/.style={rectangle,rounded corners,draw,fill=myblue,text width=1.25cm,
    align=center,text height=9pt,text depth=3pt,font=\sffamily},
  mtext/.style={text width=4cm,align=left,text height=9pt,text depth=3pt,font=\ttfamily}
]

% the upper eax,..., edx nodes
\node[exx] (eax) {\%eax};
\node[exx,right= of eax] (ebx) {\%ebx};
\node[exx,right= of ebx] (ecx) {\%ecx};
\node[exx,right= of ecx] (edx) {\%edx};

% the vertical blue nodes
\node[sblue,below right = 10pt of edx] (sadd) {s\_addr};
\node[sblue,below = of sadd] (sdata) {s\_data};
\node[sblue,below = of sdata] (load) {load};
\node[sblue,below = of load] (add) {add};
\node[sblue,below = of add] (sub) {sub};
\node[sblue,below = of sub] (jne) {jne};

% some vertical nodes to place text to the right of the blue nodes
\node[mtext,right = 20pt of sadd] (tsadd) {};
\node[mtext,below = of tsadd] (tsdata) {};
\node[mtext,below = -9pt of tsadd] {movl \%eax,(\%ecx)};
\node[mtext,right = 20pt of load] (tload) {movl (\%ebx),\%eax};
\node[mtext,below = of tload] (tadd) {addl \$1,\%eax};
\node[mtext,below = of tadd] (tsub) {subl \$1,\%edx};
\node[mtext,below = of tsub] (tjne) {jne loop};

% the lower eax,..., edx nodes
\node[exx,below left = 10pt of jne] (edx1) {\%edx};
\node[exx,left= of edx1] (ecx1) {\%ecx};
\node[exx,left= of ecx1] (ebx1) {\%ebx};
\node[exx,left= of ebx1] (eax1) {\%eax};

% the straight lines with arrow tips
\draw[->] (eax) |- (sdata);
\draw[->] (ebx) -- (ebx1);
\draw[->] (ecx) -- (ecx1);
\draw[->] (edx) |- (sub.170);
\draw[->] (sub.190) -| (edx1);
\draw[*->] (ecx|-sadd) |- (sadd);
\draw[*->] (ebx|-load.170) |- (load.170);
\draw[->] (load.190) -- (eax|-load.190) -- (eax|-add.170) -- (add.170);
\draw[->] (add.190) -| (eax1);

% the curved arrows
\draw[->] (sadd.355) to[out=-30,in=30] (sdata.5);
\draw[->] (sadd.0) to[out=-30,in=30] (load.350);
\draw[->,dashed] (sdata.355) to[out=-30,in=30] (load.5);
\draw[->] (sub.0) to[out=-30,in=30] (jne.0);

% the brace
\draw[decorate,decoration=brace] ( $(sadd.north)!.35!(tsadd.north) $ ) -- ( $(sdata.south)!.35!(tsdata.south) $ );

\end{tikzpicture}

\end{document}