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Add the explanatory comment from r122680's commit message to the code itself.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122689 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Cameron Zwarich 2011-01-02 10:40:14 +00:00
parent 19feb4ca8a
commit 2a8c22aa68
1 changed files with 10 additions and 0 deletions
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10
include/llvm/Analysis/DominatorInternals.h
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@ -195,6 +195,16 @@ void Calculate(DominatorTreeBase<typename GraphTraits<NodeT>::NodeType>& DT,
// 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.
std::vector<unsigned> Buckets;
Buckets.resize(N + 1);
for (unsigned i = 1; i <= N; ++i)