Index: lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp
===================================================================
--- lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp
+++ lib/StaticAnalyzer/Checkers/UndefResultChecker.cpp
@@ -61,7 +61,7 @@
     SmallString<256> sbuf;
     llvm::raw_svector_ostream OS(sbuf);
     const Expr *Ex = nullptr;
-    bool isLeft = true;
+    bool isLeft;
 
     if (state->getSVal(B->getLHS(), LCtx).isUndef()) {
       Ex = B->getLHS()->IgnoreParenCasts();
@@ -73,6 +73,24 @@
     }
 
     if (Ex) {
+      if (isa<ArraySubscriptExpr>(Ex)) {
+        SVal Loc = state->getSVal(Ex,LCtx);
+        if (Loc.isValid()) {
+          const MemRegion *MR = Loc.castAs<loc::MemRegionVal>().getRegion();
+          if (const ElementRegion *ER = dyn_cast<ElementRegion>(MR)) {
+            DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
+            DefinedOrUnknownSVal NumElements
+              = C.getStoreManager().getSizeInElements(state, ER->getSuperRegion(),
+                ER->getValueType());
+            ProgramStateRef StInBound = state->assumeInBound(Idx, NumElements, true);
+            ProgramStateRef StOutBound = state->assumeInBound(Idx, NumElements, false);
+            if (StOutBound && !StInBound) {
+              return;
+            }
+          }
+        }
+      }
+
       OS << "The " << (isLeft ? "left" : "right")
          << " operand of '"
          << BinaryOperator::getOpcodeStr(B->getOpcode())