Index: llvm/include/llvm/Transforms/Vectorize/LoopVectorize.h
===================================================================
--- llvm/include/llvm/Transforms/Vectorize/LoopVectorize.h
+++ llvm/include/llvm/Transforms/Vectorize/LoopVectorize.h
@@ -116,6 +116,15 @@
   }
 };
 
+/// Storage for information about made changes.
+struct LoopVectorizeResult {
+  bool MadeAnyChange;
+  bool MadeCFGChange;
+
+  LoopVectorizeResult(bool MadeAnyChange, bool MadeCFGChange)
+      : MadeAnyChange(MadeAnyChange), MadeCFGChange(MadeCFGChange) {}
+};
+
 /// The LoopVectorize Pass.
 struct LoopVectorizePass : public PassInfoMixin<LoopVectorizePass> {
 private:
@@ -146,12 +155,13 @@
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 
   // Shim for old PM.
-  bool runImpl(Function &F, ScalarEvolution &SE_, LoopInfo &LI_,
-               TargetTransformInfo &TTI_, DominatorTree &DT_,
-               BlockFrequencyInfo &BFI_, TargetLibraryInfo *TLI_,
-               DemandedBits &DB_, AliasAnalysis &AA_, AssumptionCache &AC_,
-               std::function<const LoopAccessInfo &(Loop &)> &GetLAA_,
-               OptimizationRemarkEmitter &ORE_, ProfileSummaryInfo *PSI_);
+  LoopVectorizeResult
+  runImpl(Function &F, ScalarEvolution &SE_, LoopInfo &LI_,
+          TargetTransformInfo &TTI_, DominatorTree &DT_,
+          BlockFrequencyInfo &BFI_, TargetLibraryInfo *TLI_, DemandedBits &DB_,
+          AliasAnalysis &AA_, AssumptionCache &AC_,
+          std::function<const LoopAccessInfo &(Loop &)> &GetLAA_,
+          OptimizationRemarkEmitter &ORE_, ProfileSummaryInfo *PSI_);
 
   bool processLoop(Loop *L);
 };
Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -1625,7 +1625,7 @@
         [&](Loop &L) -> const LoopAccessInfo & { return LAA->getInfo(&L); };
 
     return Impl.runImpl(F, *SE, *LI, *TTI, *DT, *BFI, TLI, *DB, *AA, *AC,
-                        GetLAA, *ORE, PSI);
+                        GetLAA, *ORE, PSI).MadeAnyChange;
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
@@ -7944,7 +7944,7 @@
   return true;
 }
 
-bool LoopVectorizePass::runImpl(
+LoopVectorizeResult LoopVectorizePass::runImpl(
     Function &F, ScalarEvolution &SE_, LoopInfo &LI_, TargetTransformInfo &TTI_,
     DominatorTree &DT_, BlockFrequencyInfo &BFI_, TargetLibraryInfo *TLI_,
     DemandedBits &DB_, AliasAnalysis &AA_, AssumptionCache &AC_,
@@ -7972,9 +7972,9 @@
   // interleaving.
   if (!TTI->getNumberOfRegisters(TTI->getRegisterClassForType(true)) &&
       TTI->getMaxInterleaveFactor(1) < 2)
-    return false;
+    return LoopVectorizeResult(false, false);
 
-  bool Changed = false;
+  bool Changed = false, CFGChanged = false;
 
   // The vectorizer requires loops to be in simplified form.
   // Since simplification may add new inner loops, it has to run before the
@@ -7982,7 +7982,7 @@
   // will simplify all loops, regardless of whether anything end up being
   // vectorized.
   for (auto &L : *LI)
-    Changed |=
+    Changed |= CFGChanged |=
         simplifyLoop(L, DT, LI, SE, AC, nullptr, false /* PreserveLCSSA */);
 
   // Build up a worklist of inner-loops to vectorize. This is necessary as
@@ -8003,11 +8003,11 @@
     // transform.
     Changed |= formLCSSARecursively(*L, *DT, LI, SE);
 
-    Changed |= processLoop(L);
+    Changed |= CFGChanged |= processLoop(L);
   }
 
   // Process each loop nest in the function.
-  return Changed;
+  return LoopVectorizeResult(Changed, CFGChanged);
 }
 
 PreservedAnalyses LoopVectorizePass::run(Function &F,
@@ -8036,9 +8036,9 @@
         AM.getResult<ModuleAnalysisManagerFunctionProxy>(F).getManager();
     ProfileSummaryInfo *PSI =
         MAM.getCachedResult<ProfileSummaryAnalysis>(*F.getParent());
-    bool Changed =
+    LoopVectorizeResult Result =
         runImpl(F, SE, LI, TTI, DT, BFI, &TLI, DB, AA, AC, GetLAA, ORE, PSI);
-    if (!Changed)
+    if (!Result.MadeAnyChange)
       return PreservedAnalyses::all();
     PreservedAnalyses PA;
 
@@ -8052,5 +8052,7 @@
     }
     PA.preserve<BasicAA>();
     PA.preserve<GlobalsAA>();
+    if (!Result.MadeCFGChange)
+      PA.preserveSet<CFGAnalyses>();
     return PA;
 }