diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6529,17 +6529,22 @@
     // Only look at the first use, avoid hurting compile time with long uselists
     User *Use = *I->user_begin();
 
+    auto *UseI = dyn_cast<Instruction>(Use);
+    // Bail out if Use is not in the same BB as I or UseI == I or UseI comes
+    // before I in the block. The latter two can be the case if UseI is a PHI
+    // node.
+    if (!UseI || UseI->getParent() != I->getParent() || UseI == I ||
+        UseI->comesBefore(I))
+      return false;
+
     // Now make sure that there are no instructions in between that can alter
     // control flow (eg. calls)
-    for (BasicBlock::iterator
-             i = ++BasicBlock::iterator(I),
-             UI = BasicBlock::iterator(dyn_cast<Instruction>(Use));
-         i != UI; ++i) {
-      if (i == I->getParent()->end())
-        return false;
-      if (!isGuaranteedToTransferExecutionToSuccessor(&*i))
-        return false;
-    }
+    auto InstrRange =
+        make_range(std::next(I->getIterator()), UseI->getIterator());
+    if (any_of(InstrRange, [](Instruction &I) {
+          return !isGuaranteedToTransferExecutionToSuccessor(&I);
+        }))
+      return false;
 
     // Look through GEPs. A load from a GEP derived from NULL is still undefined
     if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))