Index: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -441,6 +441,10 @@
   /// respective conditions.
   void predicateInstructions();
 
+  /// Collect the instructions from the original loop that would be trivially
+  /// dead in the vectorized loop if generated.
+  void collectTriviallyDeadInstructions();
+
   /// Shrinks vector element sizes to the smallest bitwidth they can be legally
   /// represented as.
   void truncateToMinimalBitwidths();
@@ -763,6 +767,14 @@
 
   // Record whether runtime checks are added.
   bool AddedSafetyChecks;
+
+  // Holds instructions from the original loop whose counterparts in the
+  // vectorized loop would be trivially dead if generated. For example,
+  // original induction update instructions can become dead because we
+  // separately emit induction "steps" when generating code for the new loop.
+  // Similarly, we create a new latch condition when setting up the structure
+  // of the new loop, so the old one can become dead.
+  SmallPtrSet<Instruction *, 4> DeadInstructions;
 };
 
 class InnerLoopUnroller : public InnerLoopVectorizer {
@@ -3802,6 +3814,11 @@
   // are vectorized, so we can use them to construct the PHI.
   PhiVector PHIsToFix;
 
+  // Collect instructions from the original loop that will become trivially
+  // dead in the vectorized loop. We don't need to vectorize these
+  // instructions.
+  collectTriviallyDeadInstructions();
+
   // Scan the loop in a topological order to ensure that defs are vectorized
   // before users.
   LoopBlocksDFS DFS(OrigLoop);
@@ -4209,6 +4226,29 @@
   }
 }
 
+void InnerLoopVectorizer::collectTriviallyDeadInstructions() {
+  BasicBlock *Latch = OrigLoop->getLoopLatch();
+
+  // We create new control-flow for the vectorized loop, so the original
+  // condition will be dead after vectorization if it's only used by the
+  // branch.
+  auto *Cmp = dyn_cast<Instruction>(Latch->getTerminator()->getOperand(0));
+  if (Cmp && Cmp->hasOneUse())
+    DeadInstructions.insert(Cmp);
+
+  // We create new "steps" for induction variable updates to which the original
+  // induction variables map. An original update instruction will be dead if
+  // all its users except the induction variable are dead.
+  for (auto &Induction : *Legal->getInductionVars()) {
+    PHINode *Ind = Induction.first;
+    auto *IndUpdate = cast<Instruction>(Ind->getIncomingValueForBlock(Latch));
+    if (all_of(IndUpdate->users(), [&](User *U) -> bool {
+          return U == Ind || DeadInstructions.count(cast<Instruction>(U));
+        }))
+      DeadInstructions.insert(IndUpdate);
+  }
+}
+
 void InnerLoopVectorizer::predicateInstructions() {
 
   // For each instruction I marked for predication on value C, split I into its
@@ -4536,6 +4576,11 @@
   // For each instruction in the old loop.
   for (Instruction &I : *BB) {
 
+    // If the instruction will become trivially dead when vectorized, we don't
+    // need to generate it.
+    if (DeadInstructions.count(&I))
+      continue;
+
     // Scalarize instructions that should remain scalar after vectorization.
     if (!(isa<BranchInst>(&I) || isa<PHINode>(&I) ||
           isa<DbgInfoIntrinsic>(&I)) &&
Index: llvm/trunk/test/Transforms/LoopVectorize/dead_instructions.ll
===================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/dead_instructions.ll
+++ llvm/trunk/test/Transforms/LoopVectorize/dead_instructions.ll
@@ -0,0 +1,42 @@
+; RUN: opt < %s -force-vector-width=2 -force-vector-interleave=2 -loop-vectorize -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-i128:128-n32:64-S128"
+
+; CHECK-LABEL: @dead_instructions_01
+;
+; This test ensures that we don't generate trivially dead instructions prior to
+; instruction simplification. We don't need to generate instructions
+; corresponding to the original induction variable update or branch condition,
+; since we rewrite the loop structure.
+;
+; CHECK:     vector.body:
+; CHECK:       %index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
+; CHECK:       %[[I0:.+]] = add i64 %index, 0
+; CHECK:       %[[I2:.+]] = add i64 %index, 2
+; CHECK:       getelementptr inbounds i64, i64* %a, i64 %[[I0]]
+; CHECK:       getelementptr inbounds i64, i64* %a, i64 %[[I2]]
+; CHECK-NOT:   add nuw nsw i64 %[[I0]], 1
+; CHECK-NOT:   add nuw nsw i64 %[[I2]], 1
+; CHECK-NOT:   icmp slt i64 {{.*}}, %n
+; CHECK:       %index.next = add i64 %index, 4
+; CHECK:       %[[CMP:.+]] = icmp eq i64 %index.next, %n.vec
+; CHECK:       br i1 %[[CMP]], label %middle.block, label %vector.body
+;
+define i64 @dead_instructions_01(i64 *%a, i64 %n) {
+entry:
+  br label %for.body
+
+for.body:
+  %i = phi i64 [ %i.next, %for.body ], [ 0, %entry ]
+  %r = phi i64 [ %tmp2, %for.body ], [ 0, %entry ]
+  %tmp0 = getelementptr inbounds i64, i64* %a, i64 %i
+  %tmp1 = load i64, i64* %tmp0, align 8
+  %tmp2 = add i64 %tmp1, %r
+  %i.next = add nuw nsw i64 %i, 1
+  %cond = icmp slt i64 %i.next, %n
+  br i1 %cond, label %for.body, label %for.end
+
+for.end:
+  %tmp3  = phi i64 [ %tmp2, %for.body ]
+  ret i64 %tmp3
+}