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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82319 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/SparsePropagation.cpp b/lib/Analysis/SparsePropagation.cpp
index 8a74745dd3fb62c379f3e9bbc0079117fd10234d..b7844f022765cb4a31ff174c3dbe78724548151a 100644 (file)
--- a/lib/Analysis/SparsePropagation.cpp
+++ b/lib/Analysis/SparsePropagation.cpp
@@ -223,6 +223,9 @@ void SparseSolver::visitTerminatorInst(TerminatorInst &TI) {
 }
 
 void SparseSolver::visitPHINode(PHINode &PN) {
+  // The lattice function may store more information on a PHINode than could be
+  // computed from its incoming values.  For example, SSI form stores its sigma
+  // functions as PHINodes with a single incoming value.
   if (LatticeFunc->IsSpecialCasedPHI(&PN)) {
     LatticeVal IV = LatticeFunc->ComputeInstructionState(PN, *this);
     if (IV != LatticeFunc->getUntrackedVal())