Add text explaining an assertion.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122617 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/StrongPHIElimination.cpp b/lib/CodeGen/StrongPHIElimination.cpp
index 5713e6a..4749d8e 100644
--- a/lib/CodeGen/StrongPHIElimination.cpp
+++ b/lib/CodeGen/StrongPHIElimination.cpp
@@ -283,7 +283,9 @@
LiveInterval& DestLI = LI->getInterval(DestReg);
LiveInterval& NewLI = LI->getInterval(NewReg);
- assert(DestLI.ranges.size() == 1);
+ assert(DestLI.ranges.size() == 1
+ && "PHI destination copy's live interval should be a single live "
+ "range from the beginning of the BB to the copy instruction.");
LiveRange* DestLR = DestLI.begin();
VNInfo* NewVNI = NewLI.getVNInfoAt(DestLR->start);
if (!NewVNI) {