Add an optimization for removing redundant suspend tests in ART

This CL:
(1) eliminates redundant suspend checks (dominated by another check),

(2) removes the special treatment of the R4 register, which got
reset on every native call, possibly yielding long execution
sequences without any suspend checks, and

(3) fixes the absence of suspend checks in leaf methods.

(2) and (3) increase the frequency of suspend checks, which improves
the performance of GC and the accuracy of profile data.  To
compensate for the increased number of checks, we implemented an
optimization that leverages dominance information to remove
redundant suspend checks on back edges.  Based on the results of
running the Caffeine benchmark on Nexus 7, the patch performs
roughly 30% more useful suspend checks, spreading them much more
evenly along the execution trace, while incurring less than 1%
overhead.  For flexibility consideration, this CL defines two flags
to control the enabling of optimizations.  The original
implementation is the default.

Change-Id: I31e81a5b3c53030444dbe0434157274c9ab8640f
Signed-off-by: Wei Jin <wejin@google.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/compiler/dex/mir_graph.h b/compiler/dex/mir_graph.h
index 38cd5ee449..b6cec662c3 100644
--- a/compiler/dex/mir_graph.h
+++ b/compiler/dex/mir_graph.h
@@ -192,6 +192,7 @@ enum OatMethodAttributes {
 
 typedef uint16_t BasicBlockId;
 static const BasicBlockId NullBasicBlockId = 0;
+static constexpr bool kLeafOptimization = false;
 
 /*
  * In general, vreg/sreg describe Dalvik registers that originated with dx.  However,
@@ -1055,6 +1056,20 @@ class MIRGraph {
   void HandleSSADef(int* defs, int dalvik_reg, int reg_index);
   bool InferTypeAndSize(BasicBlock* bb, MIR* mir, bool changed);
 
+  // Used for removing redudant suspend tests
+  void AppendGenSuspendTestList(BasicBlock* bb) {
+    if (gen_suspend_test_list_.Size() == 0 ||
+        gen_suspend_test_list_.Get(gen_suspend_test_list_.Size() - 1) != bb) {
+      gen_suspend_test_list_.Insert(bb);
+    }
+  }
+
+  /* This is used to check if there is already a method call dominating the
+   * source basic block of a backedge and being dominated by the target basic
+   * block of the backedge.
+   */
+  bool HasSuspendTestBetween(BasicBlock* source, BasicBlockId target_id);
+
  protected:
   int FindCommonParent(int block1, int block2);
   void ComputeSuccLineIn(ArenaBitVector* dest, const ArenaBitVector* src1,
@@ -1162,6 +1177,7 @@ class MIRGraph {
   GrowableArray<MirSFieldLoweringInfo> sfield_lowering_infos_;
   GrowableArray<MirMethodLoweringInfo> method_lowering_infos_;
   static const uint64_t oat_data_flow_attributes_[kMirOpLast];
+  GrowableArray<BasicBlock*> gen_suspend_test_list_;  // List of blocks containing suspend tests
 
   friend class ClassInitCheckEliminationTest;
   friend class LocalValueNumberingTest;