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 8a74745..b7844f0 100644
--- a/lib/Analysis/SparsePropagation.cpp
+++ b/lib/Analysis/SparsePropagation.cpp
@@ -223,6 +223,9 @@
}
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())