Index: lib/Target/AArch64/AArch64TargetTransformInfo.cpp
===================================================================
--- lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -490,6 +490,10 @@
 
   // Disable partial & runtime unrolling on -Os.
   UP.PartialOptSizeThreshold = 0;
+
+  // the benefits of unrolling often outweigh the cost of a division to compute
+  // the trip count.
+  UP.AllowExpensiveTripCount = true;
 }
 
 Value *AArch64TTIImpl::getOrCreateResultFromMemIntrinsic(IntrinsicInst *Inst,