Index: llvm/trunk/include/llvm/Passes/PassBuilder.h
===================================================================
--- llvm/trunk/include/llvm/Passes/PassBuilder.h
+++ llvm/trunk/include/llvm/Passes/PassBuilder.h
@@ -88,6 +88,10 @@
   /// Tuning option to enable/disable loop unrolling. Its default value is true.
   bool LoopUnrolling;
 
+  /// Tuning option to forget all SCEV loops in LoopUnroll. Its default value
+  /// is that of the flag: `-forget-scev-loop-unroll`.
+  bool ForgetAllSCEVInLoopUnroll;
+
   /// Tuning option to cap the number of calls to retrive clobbering accesses in
   /// MemorySSA, in LICM.
   unsigned LicmMssaOptCap;
Index: llvm/trunk/include/llvm/Transforms/Scalar/LoopUnrollPass.h
===================================================================
--- llvm/trunk/include/llvm/Transforms/Scalar/LoopUnrollPass.h
+++ llvm/trunk/include/llvm/Transforms/Scalar/LoopUnrollPass.h
@@ -15,6 +15,8 @@
 
 namespace llvm {
 
+extern cl::opt<bool> ForgetSCEVInLoopUnroll;
+
 class Function;
 class Loop;
 class LPMUpdater;
@@ -28,9 +30,16 @@
   /// metadata are considered. All other loops are skipped.
   const bool OnlyWhenForced;
 
+  /// If true, forget all loops when unrolling. If false, forget top-most loop
+  /// of the currently processed loops, which removes one entry at a time from
+  /// the internal SCEV records. For large loops, the former is faster.
+  const bool ForgetSCEV;
+
 public:
-  explicit LoopFullUnrollPass(int OptLevel = 2, bool OnlyWhenForced = false)
-      : OptLevel(OptLevel), OnlyWhenForced(OnlyWhenForced) {}
+  explicit LoopFullUnrollPass(int OptLevel = 2, bool OnlyWhenForced = false,
+                              bool ForgetSCEV = false)
+      : OptLevel(OptLevel), OnlyWhenForced(OnlyWhenForced),
+        ForgetSCEV(ForgetSCEV) {}
 
   PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM,
                         LoopStandardAnalysisResults &AR, LPMUpdater &U);
@@ -60,8 +69,15 @@
   /// metadata are considered. All other loops are skipped.
   bool OnlyWhenForced;
 
-  LoopUnrollOptions(int OptLevel = 2, bool OnlyWhenForced = false)
-      : OptLevel(OptLevel), OnlyWhenForced(OnlyWhenForced) {}
+  /// If true, forget all loops when unrolling. If false, forget top-most loop
+  /// of the currently processed loops, which removes one entry at a time from
+  /// the internal SCEV records. For large loops, the former is faster.
+  const bool ForgetSCEV;
+
+  LoopUnrollOptions(int OptLevel = 2, bool OnlyWhenForced = false,
+                    bool ForgetSCEV = false)
+      : OptLevel(OptLevel), OnlyWhenForced(OnlyWhenForced),
+        ForgetSCEV(ForgetSCEV) {}
 
   /// Enables or disables partial unrolling. When disabled only full unrolling
   /// is allowed.
Index: llvm/trunk/lib/Passes/PassBuilder.cpp
===================================================================
--- llvm/trunk/lib/Passes/PassBuilder.cpp
+++ llvm/trunk/lib/Passes/PassBuilder.cpp
@@ -218,6 +218,7 @@
   LoopVectorization = EnableLoopVectorization;
   SLPVectorization = RunSLPVectorization;
   LoopUnrolling = true;
+  ForgetAllSCEVInLoopUnroll = ForgetSCEVInLoopUnroll;
   LicmMssaOptCap = SetLicmMssaOptCap;
   LicmMssaNoAccForPromotionCap = SetLicmMssaNoAccForPromotionCap;
 }
@@ -463,7 +464,8 @@
   if ((Phase != ThinLTOPhase::PreLink || !PGOOpt ||
        PGOOpt->Action != PGOOptions::SampleUse) &&
       PTO.LoopUnrolling)
-    LPM2.addPass(LoopFullUnrollPass(Level));
+    LPM2.addPass(
+        LoopFullUnrollPass(Level, false, PTO.ForgetAllSCEVInLoopUnroll));
 
   for (auto &C : LoopOptimizerEndEPCallbacks)
     C(LPM2, Level);
@@ -910,7 +912,8 @@
         createFunctionToLoopPassAdaptor(LoopUnrollAndJamPass(Level)));
   }
   if (PTO.LoopUnrolling)
-    OptimizePM.addPass(LoopUnrollPass(LoopUnrollOptions(Level)));
+    OptimizePM.addPass(LoopUnrollPass(
+        LoopUnrollOptions(Level, false, PTO.ForgetAllSCEVInLoopUnroll)));
   OptimizePM.addPass(WarnMissedTransformationsPass());
   OptimizePM.addPass(InstCombinePass());
   OptimizePM.addPass(RequireAnalysisPass<OptimizationRemarkEmitterAnalysis, Function>());
Index: llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
===================================================================
--- llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ llvm/trunk/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -39,6 +39,7 @@
 #include "llvm/Transforms/Scalar/GVN.h"
 #include "llvm/Transforms/Scalar/InstSimplifyPass.h"
 #include "llvm/Transforms/Scalar/LICM.h"
+#include "llvm/Transforms/Scalar/LoopUnrollPass.h"
 #include "llvm/Transforms/Scalar/SimpleLoopUnswitch.h"
 #include "llvm/Transforms/Utils.h"
 #include "llvm/Transforms/Vectorize.h"
@@ -145,12 +146,6 @@
     "enable-order-file-instrumentation", cl::init(false), cl::Hidden,
     cl::desc("Enable order file instrumentation (default = off)"));
 
-cl::opt<bool> ForgetSCEVInLoopUnroll(
-    "forget-scev-loop-unroll", cl::init(false), cl::Hidden,
-    cl::desc("Forget everything in SCEV when doing LoopUnroll, instead of just"
-             " the current top-most loop. This is somtimes preferred to reduce"
-             " compile time."));
-
 PassManagerBuilder::PassManagerBuilder() {
     OptLevel = 2;
     SizeLevel = 0;
Index: llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -71,6 +71,12 @@
 
 #define DEBUG_TYPE "loop-unroll"
 
+cl::opt<bool> llvm::ForgetSCEVInLoopUnroll(
+    "forget-scev-loop-unroll", cl::init(false), cl::Hidden,
+    cl::desc("Forget everything in SCEV when doing LoopUnroll, instead of just"
+             " the current top-most loop. This is somtimes preferred to reduce"
+             " compile time."));
+
 static cl::opt<unsigned>
     UnrollThreshold("unroll-threshold", cl::Hidden,
                     cl::desc("The cost threshold for loop unrolling"));
@@ -1281,7 +1287,7 @@
       tryToUnrollLoop(&L, AR.DT, &AR.LI, AR.SE, AR.TTI, AR.AC, *ORE,
                       /*BFI*/ nullptr, /*PSI*/ nullptr,
                       /*PreserveLCSSA*/ true, OptLevel, OnlyWhenForced,
-                      /*ForgetAllSCEV*/ false, /*Count*/ None,
+                      ForgetSCEV, /*Count*/ None,
                       /*Threshold*/ None, /*AllowPartial*/ false,
                       /*Runtime*/ false, /*UpperBound*/ false,
                       /*AllowPeeling*/ false) != LoopUnrollResult::Unmodified;
@@ -1422,7 +1428,7 @@
     LoopUnrollResult Result = tryToUnrollLoop(
         &L, DT, &LI, SE, TTI, AC, ORE, BFI, PSI,
         /*PreserveLCSSA*/ true, UnrollOpts.OptLevel, UnrollOpts.OnlyWhenForced,
-        /*ForgetAllSCEV*/ false, /*Count*/ None,
+        UnrollOpts.ForgetSCEV, /*Count*/ None,
         /*Threshold*/ None, UnrollOpts.AllowPartial, UnrollOpts.AllowRuntime,
         UnrollOpts.AllowUpperBound, LocalAllowPeeling);
     Changed |= Result != LoopUnrollResult::Unmodified;