Changeset 47ed726


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Timestamp:
Dec 8, 2018, 4:06:25 PM (3 years ago)
Author:
Aaron Moss <a3moss@…>
Branches:
aaron-thesis, arm-eh, cleanup-dtors, deferred_resn, jacob/cs343-translation, jenkins-sandbox, master, new-ast, new-ast-unique-expr, no_list, persistent-indexer
Children:
29207bf
Parents:
df43791
Message:

Added asymptotic analysis to type environment chapter of thesis

File:
1 edited

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  • doc/theses/aaron_moss_PhD/phd/type-environment.tex

    rdf43791 r47ed726  
    4949For instance, unifying !R*! with !S*! for type variables !R! and !S! will result in a call to $unify(T, find($!R!$), find($!S!$))$, while unifying !R*! with !int*! will result in a call to $unifyBound$ on !int! and the bound type of the class containing !R!.
    5050As such, a call to $unify(T, T_i, T_j)$ may touch every type class in $T$, not just $T_i$ and $T_j$, collapsing the entirety of $T$ into a single type class in extreme cases.
     51For more information on \CFA{} unification, see \cite{Bilson03}.
    5152The inverse of $unify$ is $split(T, T_i)$, which produces a new environment $T'$ which is the same as $T$ except that $T_i$ has been replaced by two classes corresponding to the arguments to the previous call to $unify$ on $T_i$.
    5253If there has been no call to $unify$ on $T_i$ (\ie{} $T_i$ is a single-element class) $T_i$ is absent in $T'$.
     
    5859The invalid state of $T$ on failure is not important, given that a combination failure will result in the resolution algorithm backtracking to a different environment.
    5960$combine$ proceeds by calls to $insert$, $add$, and $unify$ as needed, and can be roughly thought of as calling $unify$ on every pair of classes in $T$ that have variables $v'_{i,j}$ and $v'_{i,k}$ in the same class $T'_i$ in $T'$.
    60 Like in $unify$, $combine$ can always find a mutually-consistent partition of type variables into classes (in the extreme case, all type variables from $T$ and $T'$ in a single type class), but may fail due to inconsistent bounds on merged type classes.
     61Like $unify$, $combine$ can always find a mutually-consistent partition of type variables into classes (in the extreme case, all type variables from $T$ and $T'$ in a single type class), but may fail due to inconsistent bounds on merged type classes.
    6162
    6263Finally, the backtracking access patterns of the compiler can be exploited to reduce memory usage or runtime through use of an appropriately designed data structure.
     
    183184In this section I present asymptotic analyses of the various approaches to a type environment data structure discussed in the previous section.
    184185
     186\begin{table}
     187\caption[Type environment operation bounds]{Worst-case analysis of type environment operations. $n$ is the number of type classes, $m$ the maximum size of a type class, and $p$ the edit distance between two environments or a single environment and the empty environment; $u(n)$ captures the recursive cost of class unification.}
     188\label{env-bounds-table}
     189\centering
     190\begin{tabular}{rllll}
     191        \hline
     192                                & \textbf{Na\"{\i}ve}   & \textbf{Incremental}  & \textbf{Union-Find}           & \textbf{U-F with Classes}             \\
     193        \hline
     194        $find$          & $O(n)$                                & $O(p)$                                & $O(\alpha(m))$                        & $O(\log m)$                                   \\
     195        $report$        & $O(m)$                                & $O(m)$                                & $O(n \log m)$                         & $O(m)$                                                \\
     196        $bound$         & $O(1)$                                & $O(1)$                                & $O(1)$                                        & $O(1)$                                                \\
     197        $insert$        & $O(1)$                                & $O(1)$                                & $O(1)$                                        & $O(1)$                                                \\
     198        $add$           & $O(1)$                                & $O(1)$                                & $O(1)$                                        & $O(1)$                                                \\
     199        $bind$          & $O(1)$                                & $O(1)$                                & $O(1)$                                        & $O(1)$                                                \\
     200        $unify$         & $O(m + u(n))$                 & $O(m + u(n))$                 & $O(\log m + u(n))$            & $O(\log m + u(n))$                    \\
     201        $split$         & ---                                   & ---                                   & ---                                           & $O(\log m)$                                   \\
     202        $combine$       & $O(nm \cdot u(n))$    & $O(pm \cdot u(n))$    & $O(n \log m \cdot u(n))$      & $O(p \log m \cdot u(n))$              \\
     203        $save$          & $O(nm)$                               & $O(1)$                                & $O(nm)$                                       & $O(1)$                                                \\
     204        $backtrack$     & $O(nm)$                               & $O(pm)$                               & $O(nm)$                                       & $O(p)$                                                \\
     205        \hline
     206\end{tabular}
     207\end{table}
     208
    185209% Future work: design multi-threaded version of C&F persistent map --- core idea is some sort of thread-boundary edit node
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