optimizing: Add statistics for # of constructor fences added/removed

Statistics are attributed as follows:

Added because:
* HNewInstances requires a HConstructorFence following it.
* HReturn requires a HConstructorFence (for final fields) preceding it.

Removed because:
* Optimized in Load-Store-Elimination.
* Optimized in Prepare-For-Register-Allocation.

Test: art/test.py
Bug: 36656456
Change-Id: Ic119441c5151a5a840fc6532b411340e2d68e5eb

1 files changed, 7 insertions, 1 deletions

diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 3a1864b2ae..8644f676e8 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -1198,11 +1198,14 @@ void HVariableInputSizeInstruction::RemoveAllInputs() {
   DCHECK_EQ(0u, InputCount());
 }
 
-void HConstructorFence::RemoveConstructorFences(HInstruction* instruction) {
+size_t HConstructorFence::RemoveConstructorFences(HInstruction* instruction) {
   DCHECK(instruction->GetBlock() != nullptr);
   // Removing constructor fences only makes sense for instructions with an object return type.
   DCHECK_EQ(Primitive::kPrimNot, instruction->GetType());
 
+  // Return how many instructions were removed for statistic purposes.
+  size_t remove_count = 0;
+
   // Efficient implementation that simultaneously (in one pass):
   // * Scans the uses list for all constructor fences.
   // * Deletes that constructor fence from the uses list of `instruction`.
@@ -1250,6 +1253,7 @@ void HConstructorFence::RemoveConstructorFences(HInstruction* instruction) {
       // is removed.
       if (ctor_fence->InputCount() == 0u) {
         ctor_fence->GetBlock()->RemoveInstruction(ctor_fence);
+        ++remove_count;
       }
     }
   }
@@ -1263,6 +1267,8 @@ void HConstructorFence::RemoveConstructorFences(HInstruction* instruction) {
     }
     CHECK(instruction->GetBlock() != nullptr);
   }
+
+  return remove_count;
 }
 
 HInstruction* HConstructorFence::GetAssociatedAllocation() {