Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -560,6 +560,9 @@
   PMBuilder.LoopVectorize = CodeGenOpts.VectorizeLoop;
 
   PMBuilder.DisableUnrollLoops = !CodeGenOpts.UnrollLoops;
+  // Loop interleaving in the loop vectorizer has historically been set to be
+  // enabled when loop unrolling is enabled.
+  PMBuilder.LoopsInterleaved = CodeGenOpts.UnrollLoops;
   PMBuilder.MergeFunctions = CodeGenOpts.MergeFunctions;
   PMBuilder.PrepareForThinLTO = CodeGenOpts.PrepareForThinLTO;
   PMBuilder.PrepareForLTO = CodeGenOpts.PrepareForLTO;