Index: llvm/include/llvm/Transforms/Utils/UnrollLoop.h
===================================================================
--- llvm/include/llvm/Transforms/Utils/UnrollLoop.h
+++ llvm/include/llvm/Transforms/Utils/UnrollLoop.h
@@ -71,7 +71,6 @@
   bool AllowRuntime;
   bool AllowExpensiveTripCount;
   bool PreserveCondBr;
-  bool PreserveOnlyFirst;
   unsigned TripMultiple;
   unsigned PeelCount;
   bool UnrollRemainder;
Index: llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -1166,7 +1166,7 @@
   LoopUnrollResult UnrollResult = UnrollLoop(
       L,
       {UP.Count, TripCount, UP.Force, UP.Runtime, UP.AllowExpensiveTripCount,
-       UseUpperBound, MaxOrZero, TripMultiple, PP.PeelCount, UP.UnrollRemainder,
+       UseUpperBound, TripMultiple, PP.PeelCount, UP.UnrollRemainder,
        ForgetAllSCEV},
       LI, &SE, &DT, &AC, &TTI, &ORE, PreserveLCSSA, &RemainderLoop);
   if (UnrollResult == LoopUnrollResult::Unmodified)
Index: llvm/lib/Transforms/Utils/LoopUnroll.cpp
===================================================================
--- llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -256,8 +256,7 @@
 ///
 /// PreserveCondBr indicates whether the conditional branch of the LatchBlock
 /// needs to be preserved.  It is needed when we use trip count upper bound to
-/// fully unroll the loop. If PreserveOnlyFirst is also set then only the first
-/// conditional branch needs to be preserved.
+/// fully unroll the loop.
 ///
 /// Similarly, TripMultiple divides the number of times that the LatchBlock may
 /// execute without exiting the loop.
@@ -381,6 +380,11 @@
       any_of(ExitBlocks,
              [](const BasicBlock *BB) { return isa<PHINode>(BB->begin()); });
 
+  const unsigned MaxTripCount = SE->getSmallConstantMaxTripCount(L);
+  const bool MaxOrZero = SE->isBackedgeTakenCountMaxOrZero(L);
+
+  const bool PreserveOnlyFirst = ULO.Count == MaxTripCount && MaxOrZero;
+
   // The current loop unroll pass can unroll loops that have
   // (1) single latch; and
   // (2a) latch is unconditional; or
@@ -755,7 +759,7 @@
 
     auto WillExit = [&](unsigned i, unsigned j) -> Optional<bool> {
       if (CompletelyUnroll) {
-        if (ULO.PreserveCondBr && j && !(ULO.PreserveOnlyFirst && i != 0))
+        if (ULO.PreserveCondBr && j && !(PreserveOnlyFirst && i != 0))
           return None;
         return j == 0;
       }
Index: llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
===================================================================
--- llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -987,7 +987,7 @@
                    {/*Count*/ Count - 1, /*TripCount*/ Count - 1,
                     /*Force*/ false, /*AllowRuntime*/ false,
                     /*AllowExpensiveTripCount*/ false, /*PreserveCondBr*/ true,
-                    /*PreserveOnlyFirst*/ false, /*TripMultiple*/ 1,
+                    /*TripMultiple*/ 1,
                     /*PeelCount*/ 0, /*UnrollRemainder*/ false, ForgetAllSCEV},
                    LI, SE, DT, AC, TTI, /*ORE*/ nullptr, PreserveLCSSA);
   }