[llvm-commits] [llvm] r122689 - /llvm/trunk/include/llvm/Analysis/DominatorInternals.h
zwarich at apple.com
Sun Jan 2 02:40:14 PST 2011
Date: Sun Jan 2 04:40:14 2011
New Revision: 122689
Add the explanatory comment from r122680's commit message to the code itself.
--- llvm/trunk/include/llvm/Analysis/DominatorInternals.h (original)
+++ llvm/trunk/include/llvm/Analysis/DominatorInternals.h Sun Jan 2 04:40:14 2011
@@ -195,6 +195,16 @@
// infinite loops). In these cases an artificial exit node is required.
MultipleRoots |= (DT.isPostDominator() && N != F.size());
+ // When naively implemented, the Lengauer-Tarjan algorithm requires a separate
+ // bucket for each vertex. However, this is unnecessary, because each vertex
+ // is only placed into a single bucket (that of its semidominator), and each
+ // vertex's bucket is processed before it is added to any bucket itself.
+ // Instead of using a bucket per vertex, we use a single array Buckets that
+ // has two purposes. Before the vertex V with preorder number i is processed,
+ // Buckets[i] stores the index of the first element in V's bucket. After V's
+ // bucket is processed, Buckets[i] stores the index of the next element in the
+ // bucket containing V, if any.
Buckets.resize(N + 1);
for (unsigned i = 1; i <= N; ++i)
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