[llvm-commits] [llvm] r122689 - /llvm/trunk/include/llvm/Analysis/DominatorInternals.h

[Cameron Zwarich]

Author: zwarich
Date: Sun Jan  2 04:40:14 2011
New Revision: 122689

URL: http://llvm.org/viewvc/llvm-project?rev=122689&view=rev
Log:
Add the explanatory comment from r122680's commit message to the code itself.

Modified:
    llvm/trunk/include/llvm/Analysis/DominatorInternals.h

Modified: llvm/trunk/include/llvm/Analysis/DominatorInternals.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/DominatorInternals.h?rev=122689&r1=122688&r2=122689&view=diff
==============================================================================
--- 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.
   std::vector<unsigned> Buckets;
   Buckets.resize(N + 1);
   for (unsigned i = 1; i <= N; ++i)