Index: lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- lib/Transforms/Vectorize/LoopVectorize.cpp
+++ lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -6099,13 +6099,12 @@
     // If the user doesn't provide a vectorization factor, determine a
     // reasonable one.
     if (!UserVF) {
-      // We set VF to 4 for stress testing.
-      if (VPlanBuildStressTest)
-        VF = 4;
-      else
         VF = determineVPlanVF(TTI->getRegisterBitWidth(true /* Vector*/), CM);
-    }
 
+        // Make sure we have a VF > 1 for stress testing.
+        if (VPlanBuildStressTest && VF < 2)
+          VF = 4;
+    }
     assert(EnableVPlanNativePath && "VPlan-native path is not enabled.");
     assert(isPowerOf2_32(VF) && "VF needs to be a power of two");
     LLVM_DEBUG(dbgs() << "LV: Using " << (UserVF ? "user VF " : "computed VF ")