Silence unused variable warning in -asserts build

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161256 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/StrongPHIElimination.cpp b/lib/CodeGen/StrongPHIElimination.cpp
index 9a8e745..5b06195 100644
--- a/lib/CodeGen/StrongPHIElimination.cpp
+++ b/lib/CodeGen/StrongPHIElimination.cpp
@@ -672,6 +672,7 @@
       LiveInterval &SrcInterval = LI->getInterval(SrcReg);
       SlotIndex PredIndex = LI->getMBBEndIdx(PredBB);
       VNInfo *SrcVNI = SrcInterval.getVNInfoBefore(PredIndex);
+      (void)SrcVNI;
       assert(SrcVNI);
       continue;
     }