From: Nick Lewycky <nicholas@mxc.ca>
Date: Sat, 19 Sep 2009 19:00:06 +0000 (+0000)
Subject: Add a comment explaining why you would ever want to do this.
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=c2fc1fec6c8c5360828aa778e8fcc446bb9c6ae9;p=oota-llvm.git

Add a comment explaining why you would ever want to do this.


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 8a74745dd3f..b7844f02276 100644
--- 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())