Index: include/llvm/IR/IRBuilder.h
===================================================================
--- include/llvm/IR/IRBuilder.h
+++ include/llvm/IR/IRBuilder.h
@@ -188,6 +188,24 @@
   /// \brief Set the fast-math flags to be used with generated fp-math operators
   void SetFastMathFlags(FastMathFlags NewFMF) { FMF = NewFMF; }
 
+  class Marker {
+    BasicBlock::iterator Prev;
+    BasicBlock *BB;
+  public:
+    Marker(BasicBlock::iterator InsertionPoint) : BB(nullptr) {
+      if (InsertionPoint == InsertionPoint->getParent()->begin())
+        BB = InsertionPoint->getParent();
+      else
+        Prev = std::prev(InsertionPoint);
+    }
+    BasicBlock::iterator get() const {
+      if (BB)
+        return BB->begin();
+      else
+        return std::next(Prev);
+    }
+  };
+
   //===--------------------------------------------------------------------===//
   // RAII helpers.
   //===--------------------------------------------------------------------===//
Index: lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- lib/Transforms/Vectorize/LoopVectorize.cpp
+++ lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -2050,6 +2050,8 @@
   }
 
   IRBuilder<> ChkBuilder(Loc);
+  IRBuilder<>::Marker BeforeInsertionMarker(Loc);
+
   // Our instructions might fold to a constant.
   Value *MemoryRuntimeCheck = nullptr;
   for (unsigned i = 0; i < NumPointers; ++i) {
@@ -2102,6 +2104,14 @@
                                                  ConstantInt::getTrue(Ctx));
   ChkBuilder.Insert(Check, "memcheck.conflict");
   FirstInst = getFirstInst(FirstInst, Check, Loc);
+
+  Instruction *AnotherFirst = BeforeInsertionMarker.get();
+  assert(std::find_if(BasicBlock::iterator(AnotherFirst),
+                      Loc->getParent()->end(),
+                      [&](Instruction &I) {
+                        return &I == FirstInst;
+                      }) !=  Loc->getParent()->end());
+
   return std::make_pair(FirstInst, Check);
 }