7039652: Performance regression after 7004547 changes
Summary: Use unrolled_count() to limit unrolling and use the stride check only for initial stride value.
Reviewed-by: never
--- a/hotspot/src/share/vm/opto/loopTransform.cpp Thu Apr 28 14:00:13 2011 -0700
+++ b/hotspot/src/share/vm/opto/loopTransform.cpp Thu Apr 28 16:40:23 2011 -0700
@@ -632,6 +632,8 @@
}
+#define MAX_UNROLL 16 // maximum number of unrolls for main loop
+
//------------------------------policy_unroll----------------------------------
// Return TRUE or FALSE if the loop should be unrolled or not. Unroll if
// the loop is a CountedLoop and the body is small enough.
@@ -646,10 +648,11 @@
// protect against over-unrolling
if (cl->trip_count() <= 1) return false;
- // Check for stride being a small enough constant
- if (abs(cl->stride_con()) > (1<<3)) return false;
+ int future_unroll_ct = cl->unrolled_count() * 2;
+ if (future_unroll_ct > MAX_UNROLL) return false;
- int future_unroll_ct = cl->unrolled_count() * 2;
+ // Check for initial stride being a small enough constant
+ if (abs(cl->stride_con()) > (1<<2)*future_unroll_ct) return false;
// Don't unroll if the next round of unrolling would push us
// over the expected trip count of the loop. One is subtracted