Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -1566,14 +1566,14 @@
 
   /// Returns true if we're required to use a scalar epilogue for at least
   /// the final iteration of the original loop.
-  bool requiresScalarEpilogue() const {
+  bool requiresScalarEpilogue(ElementCount VF) const {
     if (!isScalarEpilogueAllowed())
       return false;
     // If we might exit from anywhere but the latch, must run the exiting
     // iteration in scalar form.
     if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch())
       return true;
-    return InterleaveInfo.requiresScalarEpilogue();
+    return VF.isVector() && InterleaveInfo.requiresScalarEpilogue();
   }
 
   /// Returns true if a scalar epilogue is not allowed due to optsize or a
@@ -3183,18 +3183,13 @@
   // unroll factor (number of SIMD instructions).
   Value *R = Builder.CreateURem(TC, Step, "n.mod.vf");
 
-  // There are two cases where we need to ensure (at least) the last iteration
-  // runs in the scalar remainder loop. Thus, if the step evenly divides
-  // the trip count, we set the remainder to be equal to the step. If the step
-  // does not evenly divide the trip count, no adjustment is necessary since
-  // there will already be scalar iterations. Note that the minimum iterations
-  // check ensures that N >= Step. The cases are:
-  // 1) If there is a non-reversed interleaved group that may speculatively
-  //    access memory out-of-bounds.
-  // 2) If any instruction may follow a conditionally taken exit. That is, if
-  //    the loop contains multiple exiting blocks, or a single exiting block
-  //    which is not the latch.
-  if (VF.isVector() && Cost->requiresScalarEpilogue()) {
+  // There are cases where we *must* run at least one iteration in the remainder
+  // loop.  See the cost model for when this can happen.  If the step evenly
+  // divides the trip count, we set the remainder to be equal to the step. If
+  // the step does not evenly divide the trip count, no adjustment is necessary
+  // since there will already be scalar iterations. Note that the minimum
+  // iterations check ensures that N >= Step.
+  if (Cost->requiresScalarEpilogue(VF)) {
     auto *IsZero = Builder.CreateICmpEQ(R, ConstantInt::get(R->getType(), 0));
     R = Builder.CreateSelect(IsZero, Step, R);
   }
@@ -3248,8 +3243,8 @@
   // vector trip count is zero. This check also covers the case where adding one
   // to the backedge-taken count overflowed leading to an incorrect trip count
   // of zero. In this case we will also jump to the scalar loop.
-  auto P = Cost->requiresScalarEpilogue() ? ICmpInst::ICMP_ULE
-                                          : ICmpInst::ICMP_ULT;
+  auto P = Cost->requiresScalarEpilogue(VF) ? ICmpInst::ICMP_ULE
+                                            : ICmpInst::ICMP_ULT;
 
   // If tail is to be folded, vector loop takes care of all iterations.
   Value *CheckMinIters = Builder.getFalse();
@@ -8324,7 +8319,7 @@
   // Generate code to check if the loop's trip count is less than VF * UF of the
   // main vector loop.
   auto P =
-      Cost->requiresScalarEpilogue() ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_ULT;
+    Cost->requiresScalarEpilogue(VF) ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_ULT;
 
   Value *CheckMinIters = Builder.CreateICmp(
       P, Count, ConstantInt::get(Count->getType(), VFactor * UFactor),
@@ -8468,7 +8463,7 @@
   // Generate code to check if the loop's trip count is less than VF * UF of the
   // vector epilogue loop.
   auto P =
-      Cost->requiresScalarEpilogue() ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_ULT;
+    Cost->requiresScalarEpilogue(VF) ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_ULT;
 
   Value *CheckMinIters = Builder.CreateICmp(
       P, Count,
Index: llvm/test/Transforms/LoopVectorize/unroll_nonlatch.ll
===================================================================
--- llvm/test/Transforms/LoopVectorize/unroll_nonlatch.ll
+++ llvm/test/Transforms/LoopVectorize/unroll_nonlatch.ll
@@ -27,7 +27,7 @@
 ; CHECK-NEXT:    [[TMP9:%.*]] = fneg double [[TMP7]]
 ; CHECK-NEXT:    store double [[TMP8]], double* [[TMP4]], align 8
 ; CHECK-NEXT:    store double [[TMP9]], double* [[TMP5]], align 8
-; CHECK-NEXT:    [[INDEX_NEXT]] = add i64 [[INDEX]], 2
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 2
 ; CHECK-NEXT:    [[TMP10:%.*]] = icmp eq i64 [[INDEX_NEXT]], 1022
 ; CHECK-NEXT:    br i1 [[TMP10]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
 ; CHECK:       middle.block: