Index: include/llvm/Analysis/TargetTransformInfo.h
===================================================================
--- include/llvm/Analysis/TargetTransformInfo.h
+++ include/llvm/Analysis/TargetTransformInfo.h
@@ -264,6 +264,8 @@
     /// transformation will select an unrolling factor based on the current cost
     /// threshold and other factors.
     unsigned Count;
+    /// Default unroll count for loops with run-time trip count.
+    unsigned DefaultUnrollRuntimeCount;
     // Set the maximum unrolling factor. The unrolling factor may be selected
     // using the appropriate cost threshold, but may not exceed this number
     // (set to UINT_MAX to disable). This does not apply in cases where the
Index: lib/Target/SystemZ/SystemZTargetTransformInfo.h
===================================================================
--- lib/Target/SystemZ/SystemZTargetTransformInfo.h
+++ lib/Target/SystemZ/SystemZTargetTransformInfo.h
@@ -50,6 +50,8 @@
 
   TTI::PopcntSupportKind getPopcntSupport(unsigned TyWidth);
 
+  void getUnrollingPreferences(Loop *L, TTI::UnrollingPreferences &UP);
+
   /// @}
 
   /// \name Vector TTI Implementations
Index: lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
===================================================================
--- lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
+++ lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
@@ -238,6 +238,63 @@
   return TTI::PSK_Software;
 }
 
+void SystemZTTIImpl::getUnrollingPreferences(Loop *L,
+                                             TTI::UnrollingPreferences &UP) {
+  // Find out if L contains a call, what the machine instruction count
+  // estimate is, and how many stores there are.
+  bool HasCall = false;
+  unsigned NumStores = 0;
+  for (auto &BB : L->blocks())
+    for (auto &I : *BB) {
+      if (isa<CallInst>(&I) || isa<InvokeInst>(&I)) {
+        ImmutableCallSite CS(&I);
+        if (const Function *F = CS.getCalledFunction()) {
+          if (isLoweredToCall(F))
+            HasCall = true;
+          if (F->getIntrinsicID() == Intrinsic::memcpy ||
+              F->getIntrinsicID() == Intrinsic::memset)
+            NumStores++;
+        } else { // indirect call.
+          HasCall = true;
+        }
+      }
+      if (isa<StoreInst>(&I)) {
+        NumStores++;
+        Type *MemAccessTy = I.getOperand(0)->getType();
+        if((MemAccessTy->isIntegerTy() || MemAccessTy->isFloatingPointTy()) &&
+           (getDataLayout().getTypeSizeInBits(MemAccessTy) == 128))
+          NumStores++;  // 128 bit fp/int stores get split.
+      }
+    }
+
+  // The z13 processor will run out of store tags if too many stores
+  // are fed into it too quickly. Therefore make sure there are not
+  // too many stores in the resulting unrolled loop.
+  unsigned const Max = (NumStores ? (12 / NumStores) : UINT_MAX);
+
+  if (HasCall) {
+    // Only allow full unrolling if loop has any calls.
+    UP.FullUnrollMaxCount = Max;
+    UP.MaxCount = 1;
+    return;
+  }
+
+  UP.MaxCount = Max;
+  if (UP.MaxCount <= 1)
+    return;
+
+  // Allow partial and runtime trip count unrolling.
+  UP.Partial = UP.Runtime = true;
+
+  UP.PartialThreshold = 75;
+  UP.DefaultUnrollRuntimeCount = 4;
+
+  // Allow expensive instructions in the pre-header of the loop.
+  UP.AllowExpensiveTripCount = true;
+
+  UP.Force = true;
+}
+
 unsigned SystemZTTIImpl::getNumberOfRegisters(bool Vector) {
   if (!Vector)
     // Discount the stack pointer.  Also leave out %r0, since it can't
Index: lib/Transforms/Scalar/LoopUnrollPass.cpp
===================================================================
--- lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -102,10 +102,6 @@
 /// code expansion would result.
 static const unsigned NoThreshold = UINT_MAX;
 
-/// Default unroll count for loops with run-time trip count if
-/// -unroll-count is not set
-static const unsigned DefaultUnrollRuntimeCount = 8;
-
 /// Gather the various unrolling parameters based on the defaults, compiler
 /// flags, TTI overrides and user specified parameters.
 static TargetTransformInfo::UnrollingPreferences gatherUnrollingPreferences(
@@ -122,6 +118,7 @@
   UP.PartialThreshold = UP.Threshold;
   UP.PartialOptSizeThreshold = 0;
   UP.Count = 0;
+  UP.DefaultUnrollRuntimeCount = 8;
   UP.MaxCount = UINT_MAX;
   UP.FullUnrollMaxCount = UINT_MAX;
   UP.Partial = false;
@@ -803,7 +800,7 @@
         // largest power-of-two factor that satisfies the threshold limit.
         // As we'll create fixup loop, do the type of unrolling only if
         // remainder loop is allowed.
-        UP.Count = DefaultUnrollRuntimeCount;
+        UP.Count = UP.DefaultUnrollRuntimeCount;
         UnrolledSize = (LoopSize - BEInsns) * UP.Count + BEInsns;
         while (UP.Count != 0 && UnrolledSize > UP.PartialThreshold) {
           UP.Count >>= 1;
@@ -852,7 +849,7 @@
     return false;
   }
   if (UP.Count == 0)
-    UP.Count = DefaultUnrollRuntimeCount;
+    UP.Count = UP.DefaultUnrollRuntimeCount;
   UnrolledSize = (LoopSize - BEInsns) * UP.Count + BEInsns;
 
   // Reduce unroll count to be the largest power-of-two factor of