commit e178f469655dd0e1a17318e649848e21ed2f9360
author Sanjoy Das <sanjoy@playingwithpointers.com> Tue Apr 14 03:20:38 2015 +0000
committer Sanjoy Das <sanjoy@playingwithpointers.com> Tue Apr 14 03:20:38 2015 +0000
tree 819fba9b0780f554a5f8eb83afe0091545258560
parent a9f1e27a0493892005c1602ffdf76a3a7ff19d73

[LoopUnrollRuntime] Avoid high-cost trip count computation.

Summary:
Runtime unrolling of loops needs to emit an expression to compute the
loop's runtime trip-count.  Avoid runtime unrolling if this computation
will be expensive.

Depends on D8993.

Reviewers: atrick

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8994

llvm-svn: 234846

llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp

diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index 600cbde..3de3b3d 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -165,6 +165,7 @@
       UP.MaxCount = UINT_MAX;
       UP.Partial = CurrentAllowPartial;
       UP.Runtime = CurrentRuntime;
+      UP.AllowExpensiveTripCount = false;
       TTI.getUnrollingPreferences(L, UP);
     }
 
@@ -886,8 +887,8 @@
   }
 
   // Unroll the loop.
-  if (!UnrollLoop(L, Count, TripCount, AllowRuntime, TripMultiple, LI, this,
-                  &LPM, &AC))
+  if (!UnrollLoop(L, Count, TripCount, AllowRuntime, UP.AllowExpensiveTripCount,
+                  TripMultiple, LI, this, &LPM, &AC))
     return false;
 
   return true;