ART: Boolean simplifier

The optimization recognizes the negation pattern generated by 'javac'
and replaces it with a single condition. To this end, boolean values
are now consistently assumed to be represented by an integer.

This is a first optimization which deletes blocks from the HGraph and
does so by replacing the corresponding entries with null. Hence,
existing code can continue indexing the list of blocks with the block
ID, but must check for null when iterating over the list.

Change-Id: I7779da69cfa925c6521938ad0bcc11bc52335583

19 files changed, 642 insertions, 63 deletions

diff --git a/compiler/Android.mk b/compiler/Android.mk
index 0906753..6b0e6ff 100644
--- a/compiler/Android.mk
+++ b/compiler/Android.mk
@@ -94,6 +94,7 @@ LIBART_COMPILER_SRC_FILES := \
 	jni/quick/x86_64/calling_convention_x86_64.cc \
 	jni/quick/calling_convention.cc \
 	jni/quick/jni_compiler.cc \
+	optimizing/boolean_simplifier.cc \
 	optimizing/builder.cc \
 	optimizing/bounds_check_elimination.cc \
 	optimizing/code_generator.cc \
diff --git a/compiler/optimizing/boolean_simplifier.cc b/compiler/optimizing/boolean_simplifier.cc
new file mode 100644
index 0000000..ecf9fa2
--- /dev/null
+++ b/compiler/optimizing/boolean_simplifier.cc
@@ -0,0 +1,140 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "boolean_simplifier.h"
+
+namespace art {
+
+static bool EndsWithAnIf(HBasicBlock* block) {
+  return block->GetLastInstruction()->IsIf();
+}
+
+static bool HasSinglePhi(HBasicBlock* block) {
+  return !block->GetPhis().IsEmpty()
+      && block->GetFirstPhi()->GetNext() == nullptr;
+}
+
+// Returns true if 'block1' and 'block2' are empty, merge into the same single
+// successor and the successor can only be reached from them.
+static bool BlocksDoMergeTogether(HBasicBlock* block1, HBasicBlock* block2) {
+  if (!block1->IsSingleGoto() || !block2->IsSingleGoto()) return false;
+  HBasicBlock* succ1 = block1->GetSuccessors().Get(0);
+  HBasicBlock* succ2 = block2->GetSuccessors().Get(0);
+  return succ1 == succ2 && succ1->GetPredecessors().Size() == 2u;
+}
+
+// Returns true if the outcome of the branching matches the boolean value of
+// the branching condition.
+static bool PreservesCondition(HInstruction* input_true, HInstruction* input_false) {
+  return input_true->IsIntConstant() && input_true->AsIntConstant()->GetValue() == 1
+         && input_false->IsIntConstant() && input_false->AsIntConstant()->GetValue() == 0;
+}
+
+// Returns true if the outcome of the branching is exactly opposite of the
+// boolean value of the branching condition.
+static bool NegatesCondition(HInstruction* input_true, HInstruction* input_false) {
+  return input_true->IsIntConstant() && input_true->AsIntConstant()->GetValue() == 0
+         && input_false->IsIntConstant() && input_false->AsIntConstant()->GetValue() == 1;
+}
+
+// Returns an instruction with the opposite boolean value from 'cond'.
+static HInstruction* GetOppositeCondition(HInstruction* cond) {
+  HGraph* graph = cond->GetBlock()->GetGraph();
+  ArenaAllocator* allocator = graph->GetArena();
+
+  if (cond->IsCondition()) {
+    HInstruction* lhs = cond->InputAt(0);
+    HInstruction* rhs = cond->InputAt(1);
+    if (cond->IsEqual()) {
+      return new (allocator) HNotEqual(lhs, rhs);
+    } else if (cond->IsNotEqual()) {
+      return new (allocator) HEqual(lhs, rhs);
+    } else if (cond->IsLessThan()) {
+      return new (allocator) HGreaterThanOrEqual(lhs, rhs);
+    } else if (cond->IsLessThanOrEqual()) {
+      return new (allocator) HGreaterThan(lhs, rhs);
+    } else if (cond->IsGreaterThan()) {
+      return new (allocator) HLessThanOrEqual(lhs, rhs);
+    } else if (cond->IsGreaterThanOrEqual()) {
+      return new (allocator) HLessThan(lhs, rhs);
+    }
+  } else if (cond->IsIntConstant()) {
+    int32_t value = cond->AsIntConstant()->GetValue();
+    if (value == 0) {
+      return graph->GetIntConstant1();
+    } else {
+      DCHECK_EQ(value, 1);
+      return graph->GetIntConstant0();
+    }
+  }
+
+  LOG(FATAL) << "Instruction " << cond->DebugName() << " used as a condition";
+  UNREACHABLE();
+}
+
+void HBooleanSimplifier::Run() {
+  // Iterate in post order in the unlikely case that removing one occurrence of
+  // the pattern empties a branch block of another occurrence. Otherwise the
+  // order does not matter.
+  for (HPostOrderIterator it(*graph_); !it.Done(); it.Advance()) {
+    HBasicBlock* block = it.Current();
+    if (!EndsWithAnIf(block)) continue;
+
+    // Find elements of the pattern.
+    HIf* if_instruction = block->GetLastInstruction()->AsIf();
+    HBasicBlock* true_block = if_instruction->IfTrueSuccessor();
+    HBasicBlock* false_block = if_instruction->IfFalseSuccessor();
+    if (!BlocksDoMergeTogether(true_block, false_block)) {
+      continue;
+    }
+    HBasicBlock* merge_block = true_block->GetSuccessors().Get(0);
+    if (!HasSinglePhi(merge_block)) {
+      continue;
+    }
+    HPhi* phi = merge_block->GetFirstPhi()->AsPhi();
+    HInstruction* true_value = phi->InputAt(merge_block->GetPredecessorIndexOf(true_block));
+    HInstruction* false_value = phi->InputAt(merge_block->GetPredecessorIndexOf(false_block));
+
+    // Check if the selection negates/preserves the value of the condition and
+    // if so, generate a suitable replacement instruction.
+    HInstruction* if_condition = if_instruction->InputAt(0);
+    HInstruction* replacement;
+    if (NegatesCondition(true_value, false_value)) {
+      replacement = GetOppositeCondition(if_condition);
+      if (replacement->GetBlock() == nullptr) {
+        block->InsertInstructionBefore(replacement, if_instruction);
+      }
+    } else if (PreservesCondition(true_value, false_value)) {
+      replacement = if_condition;
+    } else {
+      continue;
+    }
+
+    // Replace the selection outcome with the new instruction.
+    phi->ReplaceWith(replacement);
+    merge_block->RemovePhi(phi);
+
+    // Link the start/end blocks and remove empty branches.
+    graph_->MergeEmptyBranches(block, merge_block);
+
+    // Remove the original condition if it is now unused.
+    if (!if_condition->HasUses()) {
+      if_condition->GetBlock()->RemoveInstruction(if_condition);
+    }
+  }
+}
+
+}  // namespace art
diff --git a/compiler/optimizing/boolean_simplifier.h b/compiler/optimizing/boolean_simplifier.h
new file mode 100644
index 0000000..9fa9c5a
--- /dev/null
+++ b/compiler/optimizing/boolean_simplifier.h
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// This optimization recognizes a common pattern where a boolean value is
+// either casted to an integer or negated by selecting from zero/one integer
+// constants with an If statement. Because boolean values are internally
+// represented as zero/one, we can safely replace the pattern with a suitable
+// condition instruction.
+
+// Example: Negating a boolean value
+//     B1:
+//       z1   ParameterValue
+//       i2   IntConstant 0
+//       i3   IntConstant 1
+//       v4   Goto B2
+//     B2:
+//       z5   NotEquals [ z1 i2 ]
+//       v6   If [ z5 ] then B3 else B4
+//     B3:
+//       v7   Goto B5
+//     B4:
+//       v8   Goto B5
+//     B5:
+//       i9   Phi [ i3 i2 ]
+//       v10  Return [ i9 ]
+// turns into
+//     B1:
+//       z1   ParameterValue
+//       i2   IntConstant 0
+//       v4   Goto B2
+//     B2:
+//       z11  Equals [ z1 i2 ]
+//       v10  Return [ z11 ]
+//     B3, B4, B5: removed
+
+// Note: in order to recognize empty blocks, this optimization must be run
+// after the instruction simplifier has removed redundant suspend checks.
+
+#ifndef ART_COMPILER_OPTIMIZING_BOOLEAN_SIMPLIFIER_H_
+#define ART_COMPILER_OPTIMIZING_BOOLEAN_SIMPLIFIER_H_
+
+#include "optimization.h"
+
+namespace art {
+
+class HBooleanSimplifier : public HOptimization {
+ public:
+  explicit HBooleanSimplifier(HGraph* graph)
+    : HOptimization(graph, true, kBooleanSimplifierPassName) {}
+
+  void Run() OVERRIDE;
+
+  static constexpr const char* kBooleanSimplifierPassName = "boolean_simplifier";
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(HBooleanSimplifier);
+};
+
+}  // namespace art
+
+#endif  // ART_COMPILER_OPTIMIZING_BOOLEAN_SIMPLIFIER_H_
diff --git a/compiler/optimizing/builder.cc b/compiler/optimizing/builder.cc
index cbb41b1..75b114b 100644
--- a/compiler/optimizing/builder.cc
+++ b/compiler/optimizing/builder.cc
@@ -2060,31 +2060,13 @@ bool HGraphBuilder::AnalyzeDexInstruction(const Instruction& instruction, uint32
   return true;
 }  // NOLINT(readability/fn_size)
 
-HIntConstant* HGraphBuilder::GetIntConstant0() {
-  if (constant0_ != nullptr) {
-    return constant0_;
-  }
-  constant0_ = new(arena_) HIntConstant(0);
-  entry_block_->AddInstruction(constant0_);
-  return constant0_;
-}
-
-HIntConstant* HGraphBuilder::GetIntConstant1() {
-  if (constant1_ != nullptr) {
-    return constant1_;
-  }
-  constant1_ = new(arena_) HIntConstant(1);
-  entry_block_->AddInstruction(constant1_);
-  return constant1_;
-}
-
 HIntConstant* HGraphBuilder::GetIntConstant(int32_t constant) {
   switch (constant) {
-    case 0: return GetIntConstant0();
-    case 1: return GetIntConstant1();
+    case 0: return graph_->GetIntConstant0();
+    case 1: return graph_->GetIntConstant1();
     default: {
       HIntConstant* instruction = new (arena_) HIntConstant(constant);
-      entry_block_->AddInstruction(instruction);
+      graph_->AddConstant(instruction);
       return instruction;
     }
   }
@@ -2092,7 +2074,7 @@ HIntConstant* HGraphBuilder::GetIntConstant(int32_t constant) {
 
 HLongConstant* HGraphBuilder::GetLongConstant(int64_t constant) {
   HLongConstant* instruction = new (arena_) HLongConstant(constant);
-  entry_block_->AddInstruction(instruction);
+  graph_->AddConstant(instruction);
   return instruction;
 }
 
diff --git a/compiler/optimizing/builder.h b/compiler/optimizing/builder.h
index 96196de..c70170b 100644
--- a/compiler/optimizing/builder.h
+++ b/compiler/optimizing/builder.h
@@ -47,8 +47,6 @@ class HGraphBuilder : public ValueObject {
         exit_block_(nullptr),
         current_block_(nullptr),
         graph_(graph),
-        constant0_(nullptr),
-        constant1_(nullptr),
         dex_file_(dex_file),
         dex_compilation_unit_(dex_compilation_unit),
         compiler_driver_(driver),
@@ -67,8 +65,6 @@ class HGraphBuilder : public ValueObject {
         exit_block_(nullptr),
         current_block_(nullptr),
         graph_(graph),
-        constant0_(nullptr),
-        constant1_(nullptr),
         dex_file_(nullptr),
         dex_compilation_unit_(nullptr),
         compiler_driver_(nullptr),
@@ -100,8 +96,6 @@ class HGraphBuilder : public ValueObject {
   void MaybeUpdateCurrentBlock(size_t index);
   HBasicBlock* FindBlockStartingAt(int32_t index) const;
 
-  HIntConstant* GetIntConstant0();
-  HIntConstant* GetIntConstant1();
   HIntConstant* GetIntConstant(int32_t constant);
   HLongConstant* GetLongConstant(int64_t constant);
   void InitializeLocals(uint16_t count);
@@ -253,9 +247,6 @@ class HGraphBuilder : public ValueObject {
   HBasicBlock* current_block_;
   HGraph* const graph_;
 
-  HIntConstant* constant0_;
-  HIntConstant* constant1_;
-
   // The dex file where the method being compiled is.
   const DexFile* const dex_file_;
 
diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index 561dcb7..22d5ac6 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -40,16 +40,6 @@ size_t CodeGenerator::GetCacheOffset(uint32_t index) {
   return mirror::ObjectArray<mirror::Object>::OffsetOfElement(index).SizeValue();
 }
 
-static bool IsSingleGoto(HBasicBlock* block) {
-  HLoopInformation* loop_info = block->GetLoopInformation();
-  // TODO: Remove the null check b/19084197.
-  return (block->GetFirstInstruction() != nullptr)
-      && (block->GetFirstInstruction() == block->GetLastInstruction())
-      && block->GetLastInstruction()->IsGoto()
-      // Back edges generate the suspend check.
-      && (loop_info == nullptr || !loop_info->IsBackEdge(block));
-}
-
 void CodeGenerator::CompileBaseline(CodeAllocator* allocator, bool is_leaf) {
   Initialize();
   if (!is_leaf) {
@@ -74,7 +64,7 @@ bool CodeGenerator::GoesToNextBlock(HBasicBlock* current, HBasicBlock* next) con
 HBasicBlock* CodeGenerator::GetNextBlockToEmit() const {
   for (size_t i = current_block_index_ + 1; i < block_order_->Size(); ++i) {
     HBasicBlock* block = block_order_->Get(i);
-    if (!IsSingleGoto(block)) {
+    if (!block->IsSingleGoto()) {
       return block;
     }
   }
@@ -82,7 +72,7 @@ HBasicBlock* CodeGenerator::GetNextBlockToEmit() const {
 }
 
 HBasicBlock* CodeGenerator::FirstNonEmptyBlock(HBasicBlock* block) const {
-  while (IsSingleGoto(block)) {
+  while (block->IsSingleGoto()) {
     block = block->GetSuccessors().Get(0);
   }
   return block;
@@ -97,7 +87,7 @@ void CodeGenerator::CompileInternal(CodeAllocator* allocator, bool is_baseline)
     // Don't generate code for an empty block. Its predecessors will branch to its successor
     // directly. Also, the label of that block will not be emitted, so this helps catch
     // errors where we reference that label.
-    if (IsSingleGoto(block)) continue;
+    if (block->IsSingleGoto()) continue;
     Bind(block);
     for (HInstructionIterator it(block->GetInstructions()); !it.Done(); it.Advance()) {
       HInstruction* current = it.Current();
diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index 0a069a7..d783903 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -883,7 +883,7 @@ void InstructionCodeGeneratorARM::VisitGoto(HGoto* got) {
   HInstruction* previous = got->GetPrevious();
 
   HLoopInformation* info = block->GetLoopInformation();
-  if (info != nullptr && info->IsBackEdge(block) && info->HasSuspendCheck()) {
+  if (info != nullptr && info->IsBackEdge(*block) && info->HasSuspendCheck()) {
     codegen_->ClearSpillSlotsFromLoopPhisInStackMap(info->GetSuspendCheck());
     GenerateSuspendCheck(info->GetSuspendCheck(), successor);
     return;
@@ -1388,9 +1388,14 @@ void LocationsBuilderARM::VisitTypeConversion(HTypeConversion* conversion) {
   LocationSummary* locations =
       new (GetGraph()->GetArena()) LocationSummary(conversion, call_kind);
 
+  // Java language does not allow treating boolean as an integral type but our
+  // bit representation makes it safe.
+
   switch (result_type) {
     case Primitive::kPrimByte:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1407,6 +1412,8 @@ void LocationsBuilderARM::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimShort:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1451,6 +1458,8 @@ void LocationsBuilderARM::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimLong:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1487,6 +1496,8 @@ void LocationsBuilderARM::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimChar:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1503,6 +1514,8 @@ void LocationsBuilderARM::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimFloat:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1536,6 +1549,8 @@ void LocationsBuilderARM::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimDouble:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1582,6 +1597,8 @@ void InstructionCodeGeneratorARM::VisitTypeConversion(HTypeConversion* conversio
   switch (result_type) {
     case Primitive::kPrimByte:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1597,6 +1614,8 @@ void InstructionCodeGeneratorARM::VisitTypeConversion(HTypeConversion* conversio
 
     case Primitive::kPrimShort:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1654,6 +1673,8 @@ void InstructionCodeGeneratorARM::VisitTypeConversion(HTypeConversion* conversio
 
     case Primitive::kPrimLong:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1692,6 +1713,8 @@ void InstructionCodeGeneratorARM::VisitTypeConversion(HTypeConversion* conversio
 
     case Primitive::kPrimChar:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1707,6 +1730,8 @@ void InstructionCodeGeneratorARM::VisitTypeConversion(HTypeConversion* conversio
 
     case Primitive::kPrimFloat:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1773,6 +1798,8 @@ void InstructionCodeGeneratorARM::VisitTypeConversion(HTypeConversion* conversio
 
     case Primitive::kPrimDouble:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index 99283a0..9455a91 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -1621,7 +1621,7 @@ void InstructionCodeGeneratorARM64::VisitGoto(HGoto* got) {
   HInstruction* previous = got->GetPrevious();
   HLoopInformation* info = block->GetLoopInformation();
 
-  if (info != nullptr && info->IsBackEdge(block) && info->HasSuspendCheck()) {
+  if (info != nullptr && info->IsBackEdge(*block) && info->HasSuspendCheck()) {
     codegen_->ClearSpillSlotsFromLoopPhisInStackMap(info->GetSuspendCheck());
     GenerateSuspendCheck(info->GetSuspendCheck(), successor);
     return;
diff --git a/compiler/optimizing/code_generator_x86.cc b/compiler/optimizing/code_generator_x86.cc
index 02b9b32..86ee459 100644
--- a/compiler/optimizing/code_generator_x86.cc
+++ b/compiler/optimizing/code_generator_x86.cc
@@ -792,7 +792,7 @@ void InstructionCodeGeneratorX86::VisitGoto(HGoto* got) {
   HInstruction* previous = got->GetPrevious();
 
   HLoopInformation* info = block->GetLoopInformation();
-  if (info != nullptr && info->IsBackEdge(block) && info->HasSuspendCheck()) {
+  if (info != nullptr && info->IsBackEdge(*block) && info->HasSuspendCheck()) {
     codegen_->ClearSpillSlotsFromLoopPhisInStackMap(info->GetSuspendCheck());
     GenerateSuspendCheck(info->GetSuspendCheck(), successor);
     return;
@@ -1370,9 +1370,14 @@ void LocationsBuilderX86::VisitTypeConversion(HTypeConversion* conversion) {
   LocationSummary* locations =
       new (GetGraph()->GetArena()) LocationSummary(conversion, call_kind);
 
+  // Java language does not allow treating boolean as an integral type but our
+  // bit representation makes it safe.
+
   switch (result_type) {
     case Primitive::kPrimByte:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1391,6 +1396,8 @@ void LocationsBuilderX86::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimShort:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1435,6 +1442,8 @@ void LocationsBuilderX86::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimLong:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1464,6 +1473,8 @@ void LocationsBuilderX86::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimChar:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1480,6 +1491,8 @@ void LocationsBuilderX86::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimFloat:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1511,6 +1524,8 @@ void LocationsBuilderX86::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimDouble:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1556,6 +1571,8 @@ void InstructionCodeGeneratorX86::VisitTypeConversion(HTypeConversion* conversio
   switch (result_type) {
     case Primitive::kPrimByte:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1577,6 +1594,8 @@ void InstructionCodeGeneratorX86::VisitTypeConversion(HTypeConversion* conversio
 
     case Primitive::kPrimShort:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1672,6 +1691,8 @@ void InstructionCodeGeneratorX86::VisitTypeConversion(HTypeConversion* conversio
 
     case Primitive::kPrimLong:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1703,6 +1724,8 @@ void InstructionCodeGeneratorX86::VisitTypeConversion(HTypeConversion* conversio
 
     case Primitive::kPrimChar:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1726,6 +1749,8 @@ void InstructionCodeGeneratorX86::VisitTypeConversion(HTypeConversion* conversio
 
     case Primitive::kPrimFloat:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1783,6 +1808,8 @@ void InstructionCodeGeneratorX86::VisitTypeConversion(HTypeConversion* conversio
 
     case Primitive::kPrimDouble:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
diff --git a/compiler/optimizing/code_generator_x86_64.cc b/compiler/optimizing/code_generator_x86_64.cc
index d09c8f8..0fb8cd5 100644
--- a/compiler/optimizing/code_generator_x86_64.cc
+++ b/compiler/optimizing/code_generator_x86_64.cc
@@ -729,7 +729,7 @@ void InstructionCodeGeneratorX86_64::VisitGoto(HGoto* got) {
   HInstruction* previous = got->GetPrevious();
 
   HLoopInformation* info = block->GetLoopInformation();
-  if (info != nullptr && info->IsBackEdge(block) && info->HasSuspendCheck()) {
+  if (info != nullptr && info->IsBackEdge(*block) && info->HasSuspendCheck()) {
     codegen_->ClearSpillSlotsFromLoopPhisInStackMap(info->GetSuspendCheck());
     GenerateSuspendCheck(info->GetSuspendCheck(), successor);
     return;
@@ -1409,9 +1409,15 @@ void LocationsBuilderX86_64::VisitTypeConversion(HTypeConversion* conversion) {
   Primitive::Type result_type = conversion->GetResultType();
   Primitive::Type input_type = conversion->GetInputType();
   DCHECK_NE(result_type, input_type);
+
+  // Java language does not allow treating boolean as an integral type but our
+  // bit representation makes it safe.
+
   switch (result_type) {
     case Primitive::kPrimByte:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1428,6 +1434,8 @@ void LocationsBuilderX86_64::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimShort:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1472,6 +1480,8 @@ void LocationsBuilderX86_64::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimLong:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1505,6 +1515,8 @@ void LocationsBuilderX86_64::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimChar:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1521,6 +1533,8 @@ void LocationsBuilderX86_64::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimFloat:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1550,6 +1564,8 @@ void LocationsBuilderX86_64::VisitTypeConversion(HTypeConversion* conversion) {
 
     case Primitive::kPrimDouble:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1593,6 +1609,8 @@ void InstructionCodeGeneratorX86_64::VisitTypeConversion(HTypeConversion* conver
   switch (result_type) {
     case Primitive::kPrimByte:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1617,6 +1635,8 @@ void InstructionCodeGeneratorX86_64::VisitTypeConversion(HTypeConversion* conver
 
     case Primitive::kPrimShort:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimInt:
         case Primitive::kPrimChar:
@@ -1715,6 +1735,8 @@ void InstructionCodeGeneratorX86_64::VisitTypeConversion(HTypeConversion* conver
     case Primitive::kPrimLong:
       switch (input_type) {
         DCHECK(out.IsRegister());
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1782,6 +1804,8 @@ void InstructionCodeGeneratorX86_64::VisitTypeConversion(HTypeConversion* conver
 
     case Primitive::kPrimChar:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1806,6 +1830,8 @@ void InstructionCodeGeneratorX86_64::VisitTypeConversion(HTypeConversion* conver
 
     case Primitive::kPrimFloat:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
@@ -1832,6 +1858,8 @@ void InstructionCodeGeneratorX86_64::VisitTypeConversion(HTypeConversion* conver
 
     case Primitive::kPrimDouble:
       switch (input_type) {
+        case Primitive::kPrimBoolean:
+          // Boolean input is a result of code transformations.
         case Primitive::kPrimByte:
         case Primitive::kPrimShort:
         case Primitive::kPrimInt:
diff --git a/compiler/optimizing/graph_checker.cc b/compiler/optimizing/graph_checker.cc
index 76b9f4f..09a3ae4 100644
--- a/compiler/optimizing/graph_checker.cc
+++ b/compiler/optimizing/graph_checker.cc
@@ -227,13 +227,13 @@ void SSAChecker::CheckLoop(HBasicBlock* loop_header) {
   } else {
     HLoopInformation* loop_information = loop_header->GetLoopInformation();
     HBasicBlock* first_predecessor = loop_header->GetPredecessors().Get(0);
-    if (loop_information->IsBackEdge(first_predecessor)) {
+    if (loop_information->IsBackEdge(*first_predecessor)) {
       AddError(StringPrintf(
           "First predecessor of loop header %d is a back edge.",
           id));
     }
     HBasicBlock* second_predecessor = loop_header->GetPredecessors().Get(1);
-    if (!loop_information->IsBackEdge(second_predecessor)) {
+    if (!loop_information->IsBackEdge(*second_predecessor)) {
       AddError(StringPrintf(
           "Second predecessor of loop header %d is not a back edge.",
           id));
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index a90ebce..6009cb5 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -185,7 +185,7 @@ void HGraph::SplitCriticalEdge(HBasicBlock* block, HBasicBlock* successor) {
   if (successor->IsLoopHeader()) {
     // If we split at a back edge boundary, make the new block the back edge.
     HLoopInformation* info = successor->GetLoopInformation();
-    if (info->IsBackEdge(block)) {
+    if (info->IsBackEdge(*block)) {
       info->RemoveBackEdge(block);
       info->AddBackEdge(new_block);
     }
@@ -287,19 +287,49 @@ bool HGraph::AnalyzeNaturalLoops() const {
   return true;
 }
 
+void HGraph::AddConstant(HConstant* instruction) {
+  HInstruction* last_instruction = entry_block_->GetLastInstruction();
+  if (last_instruction == nullptr || !last_instruction->IsControlFlow()) {
+    // Called from the builder. Insert at the end of the block.
+    entry_block_->AddInstruction(instruction);
+  } else {
+    // Entry block ends with control-flow. Insert before the last instruction.
+    entry_block_->InsertInstructionBefore(instruction, last_instruction);
+  }
+}
+
 HNullConstant* HGraph::GetNullConstant() {
   if (cached_null_constant_ == nullptr) {
     cached_null_constant_ = new (arena_) HNullConstant();
-    entry_block_->InsertInstructionBefore(cached_null_constant_,
-                                          entry_block_->GetLastInstruction());
+    AddConstant(cached_null_constant_);
   }
   return cached_null_constant_;
 }
 
+HIntConstant* HGraph::GetIntConstant0() {
+  if (cached_int_constant0_ == nullptr) {
+    cached_int_constant0_ = new (arena_) HIntConstant(0);
+    AddConstant(cached_int_constant0_);
+  }
+  return cached_int_constant0_;
+}
+
+HIntConstant* HGraph::GetIntConstant1() {
+  if (cached_int_constant1_ == nullptr) {
+    cached_int_constant1_ = new (arena_) HIntConstant(1);
+    AddConstant(cached_int_constant1_);
+  }
+  return cached_int_constant1_;
+}
+
 void HLoopInformation::Add(HBasicBlock* block) {
   blocks_.SetBit(block->GetBlockId());
 }
 
+void HLoopInformation::Remove(HBasicBlock* block) {
+  blocks_.ClearBit(block->GetBlockId());
+}
+
 void HLoopInformation::PopulateRecursive(HBasicBlock* block) {
   if (blocks_.IsBitSet(block->GetBlockId())) {
     return;
@@ -621,7 +651,10 @@ FOR_EACH_INSTRUCTION(DEFINE_ACCEPT)
 void HGraphVisitor::VisitInsertionOrder() {
   const GrowableArray<HBasicBlock*>& blocks = graph_->GetBlocks();
   for (size_t i = 0 ; i < blocks.Size(); i++) {
-    VisitBasicBlock(blocks.Get(i));
+    HBasicBlock* block = blocks.Get(i);
+    if (block != nullptr) {
+      VisitBasicBlock(block);
+    }
   }
 }
 
@@ -788,6 +821,17 @@ HBasicBlock* HBasicBlock::SplitAfter(HInstruction* cursor) {
   return new_block;
 }
 
+bool HBasicBlock::IsSingleGoto() const {
+  HLoopInformation* loop_info = GetLoopInformation();
+  // TODO: Remove the null check b/19084197.
+  return GetFirstInstruction() != nullptr
+         && GetPhis().IsEmpty()
+         && GetFirstInstruction() == GetLastInstruction()
+         && GetLastInstruction()->IsGoto()
+         // Back edges generate the suspend check.
+         && (loop_info == nullptr || !loop_info->IsBackEdge(*this));
+}
+
 void HInstructionList::SetBlockOfInstructions(HBasicBlock* block) const {
   for (HInstruction* current = first_instruction_;
        current != nullptr;
@@ -811,14 +855,35 @@ void HInstructionList::AddAfter(HInstruction* cursor, const HInstructionList& in
 }
 
 void HInstructionList::Add(const HInstructionList& instruction_list) {
-  DCHECK(!IsEmpty());
-  AddAfter(last_instruction_, instruction_list);
+  if (IsEmpty()) {
+    first_instruction_ = instruction_list.first_instruction_;
+    last_instruction_ = instruction_list.last_instruction_;
+  } else {
+    AddAfter(last_instruction_, instruction_list);
+  }
+}
+
+void HBasicBlock::DisconnectFromAll() {
+  DCHECK(dominated_blocks_.IsEmpty()) << "Unimplemented scenario";
+
+  for (size_t i = 0, e = predecessors_.Size(); i < e; ++i) {
+    predecessors_.Get(i)->successors_.Delete(this);
+  }
+  for (size_t i = 0, e = successors_.Size(); i < e; ++i) {
+    successors_.Get(i)->predecessors_.Delete(this);
+  }
+  dominator_->dominated_blocks_.Delete(this);
+
+  predecessors_.Reset();
+  successors_.Reset();
+  dominator_ = nullptr;
+  graph_ = nullptr;
 }
 
 void HBasicBlock::MergeWith(HBasicBlock* other) {
   DCHECK(successors_.IsEmpty()) << "Unimplemented block merge scenario";
-  DCHECK(dominated_blocks_.IsEmpty()) << "Unimplemented block merge scenario";
-  DCHECK(other->GetDominator()->IsEntryBlock() && other->GetGraph() != graph_)
+  DCHECK(dominated_blocks_.IsEmpty()
+         || (dominated_blocks_.Size() == 1 && dominated_blocks_.Get(0) == other))
       << "Unimplemented block merge scenario";
   DCHECK(other->GetPhis().IsEmpty());
 
@@ -1006,7 +1071,7 @@ void HGraph::InlineInto(HGraph* outer_graph, HInvoke* invoke) {
     if (info != nullptr) {
       info->Add(to);
       to->SetLoopInformation(info);
-      if (info->IsBackEdge(at)) {
+      if (info->IsBackEdge(*at)) {
         // Only `at` can become a back edge, as the inlined blocks
         // are predecessors of `at`.
         DCHECK_EQ(1u, info->NumberOfBackEdges());
@@ -1020,6 +1085,57 @@ void HGraph::InlineInto(HGraph* outer_graph, HInvoke* invoke) {
   invoke->GetBlock()->RemoveInstruction(invoke);
 }
 
+void HGraph::MergeEmptyBranches(HBasicBlock* start_block, HBasicBlock* end_block) {
+  // Make sure this is a diamond control-flow path, find the two branches.
+  DCHECK_EQ(start_block->GetSuccessors().Size(), 2u);
+  DCHECK_EQ(end_block->GetPredecessors().Size(), 2u);
+  HBasicBlock* left_branch = start_block->GetSuccessors().Get(0);
+  HBasicBlock* right_branch = start_block->GetSuccessors().Get(1);
+  DCHECK_EQ(left_branch->GetSuccessors().Get(0), end_block);
+  DCHECK_EQ(right_branch->GetSuccessors().Get(0), end_block);
+  DCHECK_EQ(start_block, end_block->GetDominator());
+
+  // Disconnect the branches and merge the two blocks. This will move
+  // all instructions from 'end_block' to 'start_block'.
+  DCHECK(left_branch->IsSingleGoto());
+  DCHECK(right_branch->IsSingleGoto());
+  left_branch->DisconnectFromAll();
+  right_branch->DisconnectFromAll();
+  start_block->RemoveInstruction(start_block->GetLastInstruction());
+  start_block->MergeWith(end_block);
+
+  // Delete the now redundant blocks from the graph.
+  blocks_.Put(left_branch->GetBlockId(), nullptr);
+  blocks_.Put(right_branch->GetBlockId(), nullptr);
+  blocks_.Put(end_block->GetBlockId(), nullptr);
+
+  // Update reverse post order.
+  reverse_post_order_.Delete(left_branch);
+  reverse_post_order_.Delete(right_branch);
+  reverse_post_order_.Delete(end_block);
+
+  // Update loop information.
+  HLoopInformation* loop_info = start_block->GetLoopInformation();
+  if (kIsDebugBuild) {
+    if (loop_info != nullptr) {
+      DCHECK_EQ(loop_info, left_branch->GetLoopInformation());
+      DCHECK_EQ(loop_info, right_branch->GetLoopInformation());
+      DCHECK_EQ(loop_info, end_block->GetLoopInformation());
+    }
+  }
+  while (loop_info != nullptr) {
+    loop_info->Remove(left_branch);
+    loop_info->Remove(right_branch);
+    loop_info->Remove(end_block);
+    if (loop_info->IsBackEdge(*end_block)) {
+      loop_info->RemoveBackEdge(end_block);
+      loop_info->AddBackEdge(start_block);
+    }
+    // Move to parent loop if nested.
+    loop_info = loop_info->GetHeader()->GetDominator()->GetLoopInformation();
+  }
+}
+
 std::ostream& operator<<(std::ostream& os, const ReferenceTypeInfo& rhs) {
   ScopedObjectAccess soa(Thread::Current());
   os << "["
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index 07ff8ba..7c84f95 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -128,6 +128,7 @@ class HGraph : public ArenaObject<kArenaAllocMisc> {
   void SetExitBlock(HBasicBlock* block) { exit_block_ = block; }
 
   void AddBlock(HBasicBlock* block);
+  void AddConstant(HConstant* instruction);
 
   // Try building the SSA form of this graph, with dominance computation and loop
   // recognition. Returns whether it was successful in doing all these steps.
@@ -154,6 +155,8 @@ class HGraph : public ArenaObject<kArenaAllocMisc> {
   // Inline this graph in `outer_graph`, replacing the given `invoke` instruction.
   void InlineInto(HGraph* outer_graph, HInvoke* invoke);
 
+  void MergeEmptyBranches(HBasicBlock* start_block, HBasicBlock* end_block);
+
   void SplitCriticalEdge(HBasicBlock* block, HBasicBlock* successor);
   void SimplifyLoop(HBasicBlock* header);
 
@@ -217,6 +220,8 @@ class HGraph : public ArenaObject<kArenaAllocMisc> {
   bool IsDebuggable() const { return debuggable_; }
 
   HNullConstant* GetNullConstant();
+  HIntConstant* GetIntConstant0();
+  HIntConstant* GetIntConstant1();
 
  private:
   HBasicBlock* FindCommonDominator(HBasicBlock* first, HBasicBlock* second) const;
@@ -267,6 +272,10 @@ class HGraph : public ArenaObject<kArenaAllocMisc> {
   // Cached null constant that might be created when building SSA form.
   HNullConstant* cached_null_constant_;
 
+  // Cached common constants often needed by optimization passes.
+  HIntConstant* cached_int_constant0_;
+  HIntConstant* cached_int_constant1_;
+
   ART_FRIEND_TEST(GraphTest, IfSuccessorSimpleJoinBlock1);
   DISALLOW_COPY_AND_ASSIGN(HGraph);
 };
@@ -300,9 +309,9 @@ class HLoopInformation : public ArenaObject<kArenaAllocMisc> {
     back_edges_.Delete(back_edge);
   }
 
-  bool IsBackEdge(HBasicBlock* block) {
+  bool IsBackEdge(const HBasicBlock& block) const {
     for (size_t i = 0, e = back_edges_.Size(); i < e; ++i) {
-      if (back_edges_.Get(i) == block) return true;
+      if (back_edges_.Get(i) == &block) return true;
     }
     return false;
   }
@@ -336,6 +345,7 @@ class HLoopInformation : public ArenaObject<kArenaAllocMisc> {
   const ArenaBitVector& GetBlocks() const { return blocks_; }
 
   void Add(HBasicBlock* block);
+  void Remove(HBasicBlock* block);
 
  private:
   // Internal recursive implementation of `Populate`.
@@ -391,6 +401,8 @@ class HBasicBlock : public ArenaObject<kArenaAllocMisc> {
     return graph_->GetExitBlock() == this;
   }
 
+  bool IsSingleGoto() const;
+
   void AddBackEdge(HBasicBlock* back_edge) {
     if (loop_information_ == nullptr) {
       loop_information_ = new (graph_->GetArena()) HLoopInformation(this, graph_);
@@ -512,8 +524,16 @@ class HBasicBlock : public ArenaObject<kArenaAllocMisc> {
   // of `this` are moved to `other`.
   // Note that this method does not update the graph, reverse post order, loop
   // information, nor make sure the blocks are consistent (for example ending
+  // with a control flow instruction).
   void ReplaceWith(HBasicBlock* other);
 
+  // Disconnects `this` from all its predecessors, successors and the dominator.
+  // It assumes that `this` does not dominate any blocks.
+  // Note that this method does not update the graph, reverse post order, loop
+  // information, nor make sure the blocks are consistent (for example ending
+  // with a control flow instruction).
+  void DisconnectFromAll();
+
   void AddInstruction(HInstruction* instruction);
   void InsertInstructionBefore(HInstruction* instruction, HInstruction* cursor);
   // Replace instruction `initial` with `replacement` within this block.
diff --git a/compiler/optimizing/optimizing_compiler.cc b/compiler/optimizing/optimizing_compiler.cc
index 933a8a0..ea969dc 100644
--- a/compiler/optimizing/optimizing_compiler.cc
+++ b/compiler/optimizing/optimizing_compiler.cc
@@ -22,6 +22,7 @@
 #include "base/arena_allocator.h"
 #include "base/dumpable.h"
 #include "base/timing_logger.h"
+#include "boolean_simplifier.h"
 #include "bounds_check_elimination.h"
 #include "builder.h"
 #include "code_generator.h"
@@ -313,6 +314,7 @@ static void RunOptimizations(HGraph* graph,
   HDeadCodeElimination dce(graph);
   HConstantFolding fold1(graph);
   InstructionSimplifier simplify1(graph, stats);
+  HBooleanSimplifier boolean_not(graph);
 
   HInliner inliner(graph, dex_compilation_unit, driver, stats);
 
@@ -331,6 +333,9 @@ static void RunOptimizations(HGraph* graph,
     &dce,
     &fold1,
     &simplify1,
+    // BooleanSimplifier depends on the InstructionSimplifier removing redundant
+    // suspend checks to recognize empty blocks.
+    &boolean_not,
     &inliner,
     &fold2,
     &side_effects,
diff --git a/compiler/optimizing/ssa_liveness_analysis.cc b/compiler/optimizing/ssa_liveness_analysis.cc
index c0d6f42..56ccd71 100644
--- a/compiler/optimizing/ssa_liveness_analysis.cc
+++ b/compiler/optimizing/ssa_liveness_analysis.cc
@@ -71,8 +71,8 @@ void SsaLivenessAnalysis::LinearizeGraph() {
   //      for it.
   GrowableArray<uint32_t> forward_predecessors(graph_.GetArena(), graph_.GetBlocks().Size());
   forward_predecessors.SetSize(graph_.GetBlocks().Size());
-  for (size_t i = 0, e = graph_.GetBlocks().Size(); i < e; ++i) {
-    HBasicBlock* block = graph_.GetBlocks().Get(i);
+  for (HReversePostOrderIterator it(graph_); !it.Done(); it.Advance()) {
+    HBasicBlock* block = it.Current();
     size_t number_of_forward_predecessors = block->GetPredecessors().Size();
     if (block->IsLoopHeader()) {
       // We rely on having simplified the CFG.
diff --git a/runtime/primitive.h b/runtime/primitive.h
index 2d6b6b3..d11f1e9 100644
--- a/runtime/primitive.h
+++ b/runtime/primitive.h
@@ -153,7 +153,10 @@ class Primitive {
   }
 
   static bool IsIntegralType(Type type) {
+    // Java language does not allow treating boolean as an integral type but our
+    // bit representation makes it safe.
     switch (type) {
+      case kPrimBoolean:
       case kPrimByte:
       case kPrimChar:
       case kPrimShort:
diff --git a/test/463-checker-boolean-simplifier/expected.txt b/test/463-checker-boolean-simplifier/expected.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/test/463-checker-boolean-simplifier/expected.txt
diff --git a/test/463-checker-boolean-simplifier/info.txt b/test/463-checker-boolean-simplifier/info.txt
new file mode 100644
index 0000000..9c0493a
--- /dev/null
+++ b/test/463-checker-boolean-simplifier/info.txt
@@ -0,0 +1 @@
+Tests simplification of boolean NOT in optimizing compiler.
diff --git a/test/463-checker-boolean-simplifier/src/Main.java b/test/463-checker-boolean-simplifier/src/Main.java
new file mode 100644
index 0000000..25f58b4
--- /dev/null
+++ b/test/463-checker-boolean-simplifier/src/Main.java
@@ -0,0 +1,174 @@
+/*
+* Copyright (C) 2015 The Android Open Source Project
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*      http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+public class Main {
+
+  // Note #1: `javac` flips the conditions of If statements.
+  // Note #2: In the optimizing compiler, the first input of Phi is always
+  //          the fall-through path, i.e. the false branch.
+
+  public static void assertBoolEquals(boolean expected, boolean result) {
+    if (expected != result) {
+      throw new Error("Expected: " + expected + ", found: " + result);
+    }
+  }
+
+  /*
+   * Elementary test negating a boolean. Verifies that the condition is replaced,
+   * blocks merged and empty branches removed.
+   */
+
+  // CHECK-START: boolean Main.BooleanNot(boolean) boolean_simplifier (before)
+  // CHECK-DAG:     [[Param:z\d+]]    ParameterValue
+  // CHECK-DAG:     [[Const0:i\d+]]   IntConstant 0
+  // CHECK-DAG:     [[Const1:i\d+]]   IntConstant 1
+  // CHECK-DAG:     [[NotEq:z\d+]]    NotEqual [ [[Param]] [[Const0]] ]
+  // CHECK-DAG:                       If [ [[NotEq]] ]
+  // CHECK-DAG:     [[Phi:i\d+]]      Phi [ [[Const1]] [[Const0]] ]
+  // CHECK-DAG:                       Return [ [[Phi]] ]
+
+  // CHECK-START: boolean Main.BooleanNot(boolean) boolean_simplifier (before)
+  // CHECK:                           Goto
+  // CHECK:                           Goto
+  // CHECK:                           Goto
+  // CHECK-NOT:                       Goto
+
+  // CHECK-START: boolean Main.BooleanNot(boolean) boolean_simplifier (after)
+  // CHECK-DAG:     [[Param:z\d+]]    ParameterValue
+  // CHECK-DAG:     [[Const0:i\d+]]   IntConstant 0
+  // CHECK-DAG:     [[Eq:z\d+]]       Equal [ [[Param]] [[Const0]] ]
+  // CHECK-DAG:                       Return [ [[Eq]] ]
+
+  // CHECK-START: boolean Main.BooleanNot(boolean) boolean_simplifier (after)
+  // CHECK-NOT:                       NotEqual
+  // CHECK-NOT:                       If
+  // CHECK-NOT:                       Phi
+
+  // CHECK-START: boolean Main.BooleanNot(boolean) boolean_simplifier (after)
+  // CHECK:                           Goto
+  // CHECK-NOT:                       Goto
+
+  public static boolean BooleanNot(boolean x) {
+    return !x;
+  }
+
+  /*
+   * Program which only delegates the condition, i.e. returns 1 when True
+   * and 0 when False.
+   */
+
+  // CHECK-START: boolean Main.GreaterThan(int, int) boolean_simplifier (before)
+  // CHECK-DAG:     [[ParamX:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[ParamY:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[Const0:i\d+]]   IntConstant 0
+  // CHECK-DAG:     [[Const1:i\d+]]   IntConstant 1
+  // CHECK-DAG:     [[Cond:z\d+]]     GreaterThan [ [[ParamX]] [[ParamY]] ]
+  // CHECK-DAG:                       If [ [[Cond]] ]
+  // CHECK-DAG:     [[Phi:i\d+]]      Phi [ [[Const0]] [[Const1]] ]
+  // CHECK-DAG:                       Return [ [[Phi]] ]
+
+  // CHECK-START: boolean Main.GreaterThan(int, int) boolean_simplifier (after)
+  // CHECK-DAG:     [[ParamX:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[ParamY:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[Const0:i\d+]]   IntConstant 0
+  // CHECK-DAG:     [[Const1:i\d+]]   IntConstant 1
+  // CHECK-DAG:     [[Cond:z\d+]]     GreaterThan [ [[ParamX]] [[ParamY]] ]
+  // CHECK-DAG:                       Return [ [[Cond]] ]
+
+  public static boolean GreaterThan(int x, int y) {
+    return (x <= y) ? false : true;
+  }
+
+  /*
+   * Program which negates a condition, i.e. returns 0 when True
+   * and 1 when False.
+   */
+
+  // CHECK-START: boolean Main.LessThan(int, int) boolean_simplifier (before)
+  // CHECK-DAG:     [[ParamX:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[ParamY:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[Const0:i\d+]]   IntConstant 0
+  // CHECK-DAG:     [[Const1:i\d+]]   IntConstant 1
+  // CHECK-DAG:     [[Cond:z\d+]]     GreaterThanOrEqual [ [[ParamX]] [[ParamY]] ]
+  // CHECK-DAG:                       If [ [[Cond]] ]
+  // CHECK-DAG:     [[Phi:i\d+]]      Phi [ [[Const1]] [[Const0]] ]
+  // CHECK-DAG:                       Return [ [[Phi]] ]
+
+  // CHECK-START: boolean Main.LessThan(int, int) boolean_simplifier (after)
+  // CHECK-DAG:     [[ParamX:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[ParamY:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[Const0:i\d+]]   IntConstant 0
+  // CHECK-DAG:     [[Const1:i\d+]]   IntConstant 1
+  // CHECK-DAG:     [[Cond:z\d+]]     LessThan [ [[ParamX]] [[ParamY]] ]
+  // CHECK-DAG:                       Return [ [[Cond]] ]
+
+  public static boolean LessThan(int x, int y) {
+    return x < y;
+  }
+
+  /*
+   * Program which further uses negated conditions.
+   * Note that Phis are discovered retrospectively.
+   */
+
+  // CHECK-START: boolean Main.ValuesOrdered(int, int, int) boolean_simplifier (before)
+  // CHECK-DAG:     [[ParamX:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[ParamY:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[ParamZ:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[Const0:i\d+]]   IntConstant 0
+  // CHECK-DAG:     [[Const1:i\d+]]   IntConstant 1
+  // CHECK-DAG:     [[CondXY:z\d+]]   GreaterThan [ [[ParamX]] [[ParamY]] ]
+  // CHECK-DAG:                       If [ [[CondXY]] ]
+  // CHECK-DAG:     [[CondYZ:z\d+]]   GreaterThan [ [[ParamY]] [[ParamZ]] ]
+  // CHECK-DAG:                       If [ [[CondYZ]] ]
+  // CHECK-DAG:     [[CondXYZ:z\d+]]  NotEqual [ [[PhiXY:i\d+]] [[PhiYZ:i\d+]] ]
+  // CHECK-DAG:                       If [ [[CondXYZ]] ]
+  // CHECK-DAG:                       Return [ [[PhiXYZ:i\d+]] ]
+  // CHECK-DAG:     [[PhiXY]]         Phi [ [[Const1]] [[Const0]] ]
+  // CHECK-DAG:     [[PhiYZ]]         Phi [ [[Const1]] [[Const0]] ]
+  // CHECK-DAG:     [[PhiXYZ]]        Phi [ [[Const1]] [[Const0]] ]
+
+  // CHECK-START: boolean Main.ValuesOrdered(int, int, int) boolean_simplifier (after)
+  // CHECK-DAG:     [[ParamX:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[ParamY:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[ParamZ:i\d+]]   ParameterValue
+  // CHECK-DAG:     [[CmpXY:z\d+]]    LessThanOrEqual [ [[ParamX]] [[ParamY]] ]
+  // CHECK-DAG:     [[CmpYZ:z\d+]]    LessThanOrEqual [ [[ParamY]] [[ParamZ]] ]
+  // CHECK-DAG:     [[CmpXYZ:z\d+]]   Equal [ [[CmpXY]] [[CmpYZ]] ]
+  // CHECK-DAG:                       Return [ [[CmpXYZ]] ]
+
+  public static boolean ValuesOrdered(int x, int y, int z) {
+    return (x <= y) == (y <= z);
+  }
+
+  public static void main(String[] args) {
+    assertBoolEquals(false, BooleanNot(true));
+    assertBoolEquals(true, BooleanNot(false));
+    assertBoolEquals(true, GreaterThan(10, 5));
+    assertBoolEquals(false, GreaterThan(10, 10));
+    assertBoolEquals(false, GreaterThan(5, 10));
+    assertBoolEquals(true, LessThan(5, 10));
+    assertBoolEquals(false, LessThan(10, 10));
+    assertBoolEquals(false, LessThan(10, 5));
+    assertBoolEquals(true, ValuesOrdered(1, 3, 5));
+    assertBoolEquals(true, ValuesOrdered(5, 3, 1));
+    assertBoolEquals(false, ValuesOrdered(1, 3, 2));
+    assertBoolEquals(false, ValuesOrdered(2, 3, 1));
+    assertBoolEquals(true, ValuesOrdered(3, 3, 3));
+    assertBoolEquals(true, ValuesOrdered(3, 3, 5));
+    assertBoolEquals(false, ValuesOrdered(5, 5, 3));
+  }
+}