Author: Carl Friedrich Bolz <[email protected]>
Branch: extradoc
Changeset: r4668:d12df5c678eb
Date: 2012-08-17 12:27 +0200
http://bitbucket.org/pypy/extradoc/changeset/d12df5c678eb/
Log: describe control dependencies
diff --git a/talk/dls2012/paper.tex b/talk/dls2012/paper.tex
--- a/talk/dls2012/paper.tex
+++ b/talk/dls2012/paper.tex
@@ -742,6 +742,17 @@
In the optimized trace $J$ is replaced by $\hat J$ and $K$ by $\hat
K$.
+It is interesting to note that the described approach automatically deals with
+implicit control dependencies correctly, whereas in other approaches this needs
+to be carefully programmed in. A commonly used example for a control dependency
+is a division operation that needs to be preceded by a check for the second
+argument being 0. In a trace, such a check would be done with a guard. The
+division operation must not be moved before that guard, and indeed, this is
+never done. If the division is loop invariant, the result computed in copy of
+the division operation in the preamble is reused. This division operation is
+preceded by a copy of the non-null guard, which ensures that it can be executed
+correctly.
+
\subsection{Allocation Removal}
\label{sub:allocation}
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