Add a write barrier elimination pass

We can eliminate redundant write barriers as we don't need several
for the same receiver. For example:

```
MyObject o;
o.inner_obj = io;
o.inner_obj2 = io2;
o.inner_obj3 = io3;
```

We can keep the write barrier for `inner_obj` and remove the other
two.

Note that we cannot perform this optimization across
invokes, suspend check, or instructions that can throw.

Local improvements (pixel 5, speed compile):
 * System server: -280KB (-0.56%)
 * SystemUIGoogle: -330KB (-1.16%)
 * AGSA: -3876KB (-1.19%)

Bug: 260843353
Fixes: 260843353
Change-Id: Ibf98efbe891ee00e46125853c3e97ae30aa3ff30

1 files changed, 6 insertions, 0 deletions

diff --git a/compiler/optimizing/optimization.cc b/compiler/optimizing/optimization.cc
index e0c5933657..73a47517bf 100644
--- a/compiler/optimizing/optimization.cc
+++ b/compiler/optimizing/optimization.cc
@@ -55,6 +55,7 @@
 #include "select_generator.h"
 #include "sharpening.h"
 #include "side_effects_analysis.h"
+#include "write_barrier_elimination.h"
 
 // Decide between default or alternative pass name.
 
@@ -95,6 +96,8 @@ const char* OptimizationPassName(OptimizationPass pass) {
       return ConstructorFenceRedundancyElimination::kCFREPassName;
     case OptimizationPass::kScheduling:
       return HInstructionScheduling::kInstructionSchedulingPassName;
+    case OptimizationPass::kWriteBarrierElimination:
+      return WriteBarrierElimination::kWBEPassName;
 #ifdef ART_ENABLE_CODEGEN_arm
     case OptimizationPass::kInstructionSimplifierArm:
       return arm::InstructionSimplifierArm::kInstructionSimplifierArmPassName;
@@ -268,6 +271,9 @@ ArenaVector<HOptimization*> ConstructOptimizations(
       case OptimizationPass::kLoadStoreElimination:
         opt = new (allocator) LoadStoreElimination(graph, stats, pass_name);
         break;
+      case OptimizationPass::kWriteBarrierElimination:
+        opt = new (allocator) WriteBarrierElimination(graph, stats, pass_name);
+        break;
       case OptimizationPass::kScheduling:
         opt = new (allocator) HInstructionScheduling(
             graph, codegen->GetCompilerOptions().GetInstructionSet(), codegen, pass_name);