ART: Removes SuspendCheck for plain loops with a low trip count.

This change removes SuspendCheck for plain loops with a low trip count.

The SuspendCheck in the codegen makes sure that the thread can be
interrupted during execution for GC. Not being able to do so might
decrease the responsiveness of GC in the case when a very long loop
or a long recursion is being executed.

However, for plain loops with a small trip count, the removal of
SuspendCheck should not affect the GC's responsiveness by a large
margin. Consequently, since the thread won't be interrupted for
plain loops, it is assumed that the performance might increase
by removing SuspendCheck.

Test: art/test.py -v -j12 --host --64 -t 2233-checker\
-remove-loop-suspend-check --run-test --optimizing

Change-Id: Ic9f1387059669645ad836d8277bfbc7553aa6e2f

1 files changed, 18 insertions, 2 deletions

diff --git a/compiler/optimizing/loop_optimization.h b/compiler/optimizing/loop_optimization.h
index d3583ed8a6..0ca16b543d 100644
--- a/compiler/optimizing/loop_optimization.h
+++ b/compiler/optimizing/loop_optimization.h
@@ -47,6 +47,11 @@ class HLoopOptimization : public HOptimization {
 
   static constexpr const char* kLoopOptimizationPassName = "loop_optimization";
 
+  // The maximum number of total instructions (trip_count * instruction_count),
+  // where the optimization of removing SuspendChecks from the loop header could
+  // be performed.
+  static constexpr int64_t kMaxTotalInstRemoveSuspendCheck = 128;
+
  private:
   /**
    * A single loop inside the loop hierarchy representation.
@@ -163,8 +168,19 @@ class HLoopOptimization : public HOptimization {
   // should be actually applied.
   bool TryFullUnrolling(LoopAnalysisInfo* analysis_info, bool generate_code = true);
 
-  // Tries to apply scalar loop peeling and unrolling.
-  bool TryPeelingAndUnrolling(LoopNode* node);
+  // Tries to remove SuspendCheck for plain loops with a low trip count. The
+  // SuspendCheck in the codegen makes sure that the thread can be interrupted
+  // during execution for GC. Not being able to do so might decrease the
+  // responsiveness of GC when a very long loop or a long recursion is being
+  // executed. However, for plain loops with a small trip count, the removal of
+  // SuspendCheck should not affect the GC's responsiveness by a large margin.
+  // Consequently, since the thread won't be interrupted for plain loops, it is
+  // assumed that the performance might increase by removing SuspendCheck.
+  bool TryToRemoveSuspendCheckFromLoopHeader(LoopAnalysisInfo* analysis_info,
+                                             bool generate_code = true);
+
+  // Tries to apply scalar loop optimizations.
+  bool TryLoopScalarOpts(LoopNode* node);
 
   //
   // Vectorization analysis and synthesis.