ART: Add two extra DCE passes

Add two DCE passes to eliminate dead instructions left by:
- Loop optimization unrolling. After loop optimization, dead
  instructions are often left that, when removed can simplify the
  structure of the loop and remove basic blocks. This extra DCE pass
  creates an opportunity for the load store elimination pass to
  remove some loads/stores.
- The last instruction simplification pass.

Authors: Hari Limaye, Chris Jones

Test: 458-checker-instruct-simplification
Test: 530-checker-lse, 530-checker-lse-simd, 706-checker-scheduler
Test: test-art-target, test-art-host

Change-Id: I6e14cbfc3c320af5f507135a067bb7b5bc4df8f4

1 files changed, 10 insertions, 2 deletions

diff --git a/compiler/optimizing/optimizing_compiler.cc b/compiler/optimizing/optimizing_compiler.cc
index f394635ede..7cb4b29c87 100644
--- a/compiler/optimizing/optimizing_compiler.cc
+++ b/compiler/optimizing/optimizing_compiler.cc
@@ -670,17 +670,25 @@ void OptimizingCompiler::RunOptimizations(HGraph* graph,
            "constant_folding$after_bce"),
     OptDef(OptimizationPass::kAggressiveInstructionSimplifier,
            "instruction_simplifier$after_bce"),
+    OptDef(OptimizationPass::kDeadCodeElimination,
+           "dead_code_elimination$after_bce"),
     // Other high-level optimizations.
     OptDef(OptimizationPass::kLoadStoreElimination),
-    OptDef(OptimizationPass::kCHAGuardOptimization),
     OptDef(OptimizationPass::kDeadCodeElimination,
-           "dead_code_elimination$after_bce"),
+           "dead_code_elimination$after_lse",
+           OptimizationPass::kLoadStoreElimination),
+    OptDef(OptimizationPass::kCHAGuardOptimization),
     OptDef(OptimizationPass::kCodeSinking),
     // The codegen has a few assumptions that only the instruction simplifier
     // can satisfy. For example, the code generator does not expect to see a
     // HTypeConversion from a type to the same type.
     OptDef(OptimizationPass::kAggressiveInstructionSimplifier,
            "instruction_simplifier$before_codegen"),
+    // Simplification may result in dead code that should be removed prior to
+    // code generation.
+    OptDef(OptimizationPass::kDeadCodeElimination,
+           "dead_code_elimination$before_codegen",
+           OptimizationPass::kAggressiveInstructionSimplifier),
     // Eliminate constructor fences after code sinking to avoid
     // complicated sinking logic to split a fence with many inputs.
     OptDef(OptimizationPass::kConstructorFenceRedundancyElimination)