Improved and simplified loop optimizations.

Rationale:
Empty preheader simplification has been simplified
to a much more general empty block removal optimization
step. Incremental updating of induction variable
analysis enables repeated elimination or simplification
of induction cycles.

This enabled an extra layer of optimization for
e.g. Benchpress Loop (17.5us. -> 0.24us. -> 0.08us).
So the original 73x speedup is now multiplied
by another 3x, for a total of about 218x.

Test: 618-checker-induction et al.
Change-Id: I394699981481cdd5357e0531bce88cd48bd32879

1 files changed, 8 insertions, 2 deletions

diff --git a/compiler/optimizing/loop_optimization.h b/compiler/optimizing/loop_optimization.h
index b2bf1c8507..9c4b462a1f 100644
--- a/compiler/optimizing/loop_optimization.h
+++ b/compiler/optimizing/loop_optimization.h
@@ -46,7 +46,7 @@ class HLoopOptimization : public HOptimization {
           inner(nullptr),
           previous(nullptr),
           next(nullptr) {}
-    const HLoopInformation* const loop_info;
+    HLoopInformation* const loop_info;
     LoopNode* outer;
     LoopNode* inner;
     LoopNode* previous;
@@ -61,9 +61,10 @@ class HLoopOptimization : public HOptimization {
   void TraverseLoopsInnerToOuter(LoopNode* node);
 
   void SimplifyInduction(LoopNode* node);
+  void SimplifyBlocks(LoopNode* node);
   void RemoveIfEmptyLoop(LoopNode* node);
 
-  bool IsOnlyUsedAfterLoop(const HLoopInformation& loop_info,
+  bool IsOnlyUsedAfterLoop(HLoopInformation* loop_info,
                            HInstruction* instruction,
                            /*out*/ int32_t* use_count);
   void ReplaceAllUses(HInstruction* instruction, HInstruction* replacement);
@@ -87,6 +88,11 @@ class HLoopOptimization : public HOptimization {
   // Contents reside in phase-local heap memory.
   ArenaSet<HInstruction*>* iset_;
 
+  // Counter that tracks how many induction cycles have been simplified. Useful
+  // to trigger incremental updates of induction variable analysis of outer loops
+  // when the induction of inner loops has changed.
+  int32_t induction_simplication_count_;
+
   friend class LoopOptimizationTest;
 
   DISALLOW_COPY_AND_ASSIGN(HLoopOptimization);