Merge "Add CHECKs to help diagnose a crash seen internally."
diff --git a/compiler/optimizing/induction_var_range.cc b/compiler/optimizing/induction_var_range.cc
index c0ec58f..f35aace 100644
--- a/compiler/optimizing/induction_var_range.cc
+++ b/compiler/optimizing/induction_var_range.cc
@@ -373,21 +373,23 @@
 
 bool InductionVarRange::IsUnitStride(HInstruction* context,
                                      HInstruction* instruction,
+                                     HGraph* graph,
                                      /*out*/ HInstruction** offset) const {
   HLoopInformation* loop = nullptr;
   HInductionVarAnalysis::InductionInfo* info = nullptr;
   HInductionVarAnalysis::InductionInfo* trip = nullptr;
   if (HasInductionInfo(context, instruction, &loop, &info, &trip)) {
     if (info->induction_class == HInductionVarAnalysis::kLinear &&
-        info->op_b->operation == HInductionVarAnalysis::kFetch &&
         !HInductionVarAnalysis::IsNarrowingLinear(info)) {
       int64_t stride_value = 0;
       if (IsConstant(info->op_a, kExact, &stride_value) && stride_value == 1) {
         int64_t off_value = 0;
-        if (IsConstant(info->op_b, kExact, &off_value) && off_value == 0) {
-          *offset = nullptr;
-        } else {
+        if (IsConstant(info->op_b, kExact, &off_value)) {
+          *offset = graph->GetConstant(info->op_b->type, off_value);
+        } else if (info->op_b->operation == HInductionVarAnalysis::kFetch) {
           *offset = info->op_b->fetch;
+        } else {
+          return false;
         }
         return true;
       }
diff --git a/compiler/optimizing/induction_var_range.h b/compiler/optimizing/induction_var_range.h
index a8ee829..ab1772b 100644
--- a/compiler/optimizing/induction_var_range.h
+++ b/compiler/optimizing/induction_var_range.h
@@ -163,6 +163,7 @@
    */
   bool IsUnitStride(HInstruction* context,
                     HInstruction* instruction,
+                    HGraph* graph,
                     /*out*/ HInstruction** offset) const;
 
   /**
diff --git a/compiler/optimizing/induction_var_range_test.cc b/compiler/optimizing/induction_var_range_test.cc
index d01d314..67d2093 100644
--- a/compiler/optimizing/induction_var_range_test.cc
+++ b/compiler/optimizing/induction_var_range_test.cc
@@ -770,8 +770,8 @@
   EXPECT_TRUE(range_.IsFinite(loop_header_->GetLoopInformation(), &tc));
   EXPECT_EQ(1000, tc);
   HInstruction* offset = nullptr;
-  EXPECT_TRUE(range_.IsUnitStride(phi, phi, &offset));
-  EXPECT_TRUE(offset == nullptr);
+  EXPECT_TRUE(range_.IsUnitStride(phi, phi, graph_, &offset));
+  ExpectInt(0, offset);
   HInstruction* tce = range_.GenerateTripCount(
       loop_header_->GetLoopInformation(), graph_, loop_preheader_);
   ASSERT_TRUE(tce != nullptr);
@@ -826,7 +826,7 @@
   EXPECT_TRUE(range_.IsFinite(loop_header_->GetLoopInformation(), &tc));
   EXPECT_EQ(1000, tc);
   HInstruction* offset = nullptr;
-  EXPECT_FALSE(range_.IsUnitStride(phi, phi, &offset));
+  EXPECT_FALSE(range_.IsUnitStride(phi, phi, graph_, &offset));
   HInstruction* tce = range_.GenerateTripCount(
       loop_header_->GetLoopInformation(), graph_, loop_preheader_);
   ASSERT_TRUE(tce != nullptr);
@@ -908,8 +908,8 @@
   EXPECT_TRUE(range_.IsFinite(loop_header_->GetLoopInformation(), &tc));
   EXPECT_EQ(0, tc);  // unknown
   HInstruction* offset = nullptr;
-  EXPECT_TRUE(range_.IsUnitStride(phi, phi, &offset));
-  EXPECT_TRUE(offset == nullptr);
+  EXPECT_TRUE(range_.IsUnitStride(phi, phi, graph_, &offset));
+  ExpectInt(0, offset);
   HInstruction* tce = range_.GenerateTripCount(
       loop_header_->GetLoopInformation(), graph_, loop_preheader_);
   ASSERT_TRUE(tce != nullptr);
@@ -994,7 +994,7 @@
   EXPECT_TRUE(range_.IsFinite(loop_header_->GetLoopInformation(), &tc));
   EXPECT_EQ(0, tc);  // unknown
   HInstruction* offset = nullptr;
-  EXPECT_FALSE(range_.IsUnitStride(phi, phi, &offset));
+  EXPECT_FALSE(range_.IsUnitStride(phi, phi, graph_, &offset));
   HInstruction* tce = range_.GenerateTripCount(
       loop_header_->GetLoopInformation(), graph_, loop_preheader_);
   ASSERT_TRUE(tce != nullptr);
diff --git a/compiler/optimizing/loop_optimization.cc b/compiler/optimizing/loop_optimization.cc
index 32f4002..b61d7b8 100644
--- a/compiler/optimizing/loop_optimization.cc
+++ b/compiler/optimizing/loop_optimization.cc
@@ -620,12 +620,15 @@
           // Conservatively assume a potential loop-carried data dependence otherwise, avoided by
           // generating an explicit a != b disambiguation runtime test on the two references.
           if (x != y) {
-            // For now, we reject after one test to avoid excessive overhead.
-            if (vector_runtime_test_a_ != nullptr) {
-              return false;
+            // To avoid excessive overhead, we only accept one a != b test.
+            if (vector_runtime_test_a_ == nullptr) {
+              // First test found.
+              vector_runtime_test_a_ = a;
+              vector_runtime_test_b_ = b;
+            } else if ((vector_runtime_test_a_ != a || vector_runtime_test_b_ != b) &&
+                       (vector_runtime_test_a_ != b || vector_runtime_test_b_ != a)) {
+              return false;  // second test would be needed
             }
-            vector_runtime_test_a_ = a;
-            vector_runtime_test_b_ = b;
           }
         }
       }
@@ -842,7 +845,7 @@
     HInstruction* offset = nullptr;
     if (TrySetVectorType(type, &restrictions) &&
         node->loop_info->IsDefinedOutOfTheLoop(base) &&
-        induction_range_.IsUnitStride(instruction, index, &offset) &&
+        induction_range_.IsUnitStride(instruction, index, graph_, &offset) &&
         VectorizeUse(node, value, generate_code, type, restrictions)) {
       if (generate_code) {
         GenerateVecSub(index, offset);
@@ -900,7 +903,7 @@
     HInstruction* offset = nullptr;
     if (type == instruction->GetType() &&
         node->loop_info->IsDefinedOutOfTheLoop(base) &&
-        induction_range_.IsUnitStride(instruction, index, &offset)) {
+        induction_range_.IsUnitStride(instruction, index, graph_, &offset)) {
       if (generate_code) {
         GenerateVecSub(index, offset);
         GenerateVecMem(instruction, vector_map_->Get(index), nullptr, offset, type);
@@ -1216,7 +1219,8 @@
 void HLoopOptimization::GenerateVecSub(HInstruction* org, HInstruction* offset) {
   if (vector_map_->find(org) == vector_map_->end()) {
     HInstruction* subscript = vector_index_;
-    if (offset != nullptr) {
+    int64_t value = 0;
+    if (!IsInt64AndGet(offset, &value) || value != 0) {
       subscript = new (global_allocator_) HAdd(Primitive::kPrimInt, subscript, offset);
       if (org->IsPhi()) {
         Insert(vector_body_, subscript);  // lacks layout placeholder
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index b21c4a5..5e072cd 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -421,7 +421,7 @@
   void SimplifyLoop(HBasicBlock* header);
 
   int32_t GetNextInstructionId() {
-    DCHECK_NE(current_instruction_id_, INT32_MAX);
+    CHECK_NE(current_instruction_id_, INT32_MAX);
     return current_instruction_id_++;
   }
 
@@ -430,7 +430,7 @@
   }
 
   void SetCurrentInstructionId(int32_t id) {
-    DCHECK_GE(id, current_instruction_id_);
+    CHECK_GE(id, current_instruction_id_);
     current_instruction_id_ = id;
   }
 
diff --git a/compiler/optimizing/ssa_liveness_analysis.cc b/compiler/optimizing/ssa_liveness_analysis.cc
index 7b7495b..185303b 100644
--- a/compiler/optimizing/ssa_liveness_analysis.cc
+++ b/compiler/optimizing/ssa_liveness_analysis.cc
@@ -197,7 +197,7 @@
           HInstruction* instruction = environment->GetInstructionAt(i);
           bool should_be_live = ShouldBeLiveForEnvironment(current, instruction);
           if (should_be_live) {
-            DCHECK(instruction->HasSsaIndex());
+            CHECK(instruction->HasSsaIndex()) << instruction->DebugName();
             live_in->SetBit(instruction->GetSsaIndex());
           }
           if (instruction != nullptr) {
diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index 928645a..10e0bd2 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -4064,7 +4064,10 @@
     while (old_status == mirror::Class::kStatusVerifying ||
         old_status == mirror::Class::kStatusVerifyingAtRuntime) {
       lock.WaitIgnoringInterrupts();
-      CHECK(klass->IsErroneous() || (klass->GetStatus() > old_status))
+      // WaitIgnoringInterrupts can still receive an interrupt and return early, in this
+      // case we may see the same status again. b/62912904. This is why the check is
+      // greater or equal.
+      CHECK(klass->IsErroneous() || (klass->GetStatus() >= old_status))
           << "Class '" << klass->PrettyClass()
           << "' performed an illegal verification state transition from " << old_status
           << " to " << klass->GetStatus();
diff --git a/runtime/interpreter/interpreter_switch_impl.cc b/runtime/interpreter/interpreter_switch_impl.cc
index de8c44e..0a2705d 100644
--- a/runtime/interpreter/interpreter_switch_impl.cc
+++ b/runtime/interpreter/interpreter_switch_impl.cc
@@ -17,7 +17,6 @@
 #include "interpreter_switch_impl.h"
 
 #include "base/enums.h"
-#include "base/memory_tool.h"
 #include "experimental_flags.h"
 #include "interpreter_common.h"
 #include "jit/jit.h"
@@ -119,15 +118,12 @@
 // to detect exceptions thrown by the DexPcMovedEvent itself. These exceptions could be thrown by
 // jvmti-agents while handling breakpoint or single step events. We had to move this into its own
 // function because it was making ExecuteSwitchImpl have too large a stack.
-#ifdef ADDRESS_SANITIZER
-NO_INLINE
-#endif  // ADDRESS_SANITIZER
-static bool DoDexPcMoveEvent(Thread* self,
-                             const DexFile::CodeItem* code_item,
-                             const ShadowFrame& shadow_frame,
-                             uint32_t dex_pc,
-                             const instrumentation::Instrumentation* instrumentation,
-                             JValue* save_ref)
+NO_INLINE static bool DoDexPcMoveEvent(Thread* self,
+                                       const DexFile::CodeItem* code_item,
+                                       const ShadowFrame& shadow_frame,
+                                       uint32_t dex_pc,
+                                       const instrumentation::Instrumentation* instrumentation,
+                                       JValue* save_ref)
     REQUIRES_SHARED(Locks::mutator_lock_) {
   DCHECK(instrumentation->HasDexPcListeners());
   StackHandleScope<2> hs(self);
diff --git a/runtime/thread.cc b/runtime/thread.cc
index be1614b..5edd071 100644
--- a/runtime/thread.cc
+++ b/runtime/thread.cc
@@ -549,27 +549,40 @@
   //
   // We map in the stack by reading every page from the stack bottom (highest address)
   // to the stack top. (We then madvise this away.) This must be done by reading from the
-  // current stack pointer downwards. Any access more than a page below the current SP
-  // might cause a segv.
-  // TODO: This comment may be out of date. It seems possible to speed this up. As
-  //       this is normally done once in the zygote on startup, ignore for now.
+  // current stack pointer downwards.
   //
-  // AddressSanitizer does not like the part of this functions that reads every stack page.
-  // Looks a lot like an out-of-bounds access.
+  // Accesses too far below the current machine register corresponding to the stack pointer (e.g.,
+  // ESP on x86[-32], SP on ARM) might cause a SIGSEGV (at least on x86 with newer kernels). We
+  // thus have to move the stack pointer. We do this portably by using a recursive function with a
+  // large stack frame size.
 
-  // (Defensively) first remove the protection on the protected region as will want to read
+  // (Defensively) first remove the protection on the protected region as we'll want to read
   // and write it. Ignore errors.
   UnprotectStack();
 
   VLOG(threads) << "Need to map in stack for thread at " << std::hex <<
       static_cast<void*>(pregion);
 
-  // Read every page from the high address to the low.
-  volatile uint8_t dont_optimize_this;
-  UNUSED(dont_optimize_this);
-  for (uint8_t* p = stack_top; p >= pregion; p -= kPageSize) {
-    dont_optimize_this = *p;
-  }
+  struct RecurseDownStack {
+    // This function has an intentionally large stack size.
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wframe-larger-than="
+    NO_INLINE
+    static void Touch(uintptr_t target) {
+      volatile size_t zero = 0;
+      // Use a large local volatile array to ensure a large frame size. Do not use anything close
+      // to a full page for ASAN. It would be nice to ensure the frame size is at most a page, but
+      // there is no pragma support for this.
+      volatile char space[kPageSize - 256];
+      char sink ATTRIBUTE_UNUSED = space[zero];
+      if (reinterpret_cast<uintptr_t>(space) >= target + kPageSize) {
+        Touch(target);
+      }
+      zero *= 2;  // Try to avoid tail recursion.
+    }
+#pragma GCC diagnostic pop
+  };
+  RecurseDownStack::Touch(reinterpret_cast<uintptr_t>(pregion));
 
   VLOG(threads) << "(again) installing stack protected region at " << std::hex <<
       static_cast<void*>(pregion) << " to " <<
diff --git a/test/656-checker-simd-opt/src/Main.java b/test/656-checker-simd-opt/src/Main.java
index 0d0885c..794c9b6 100644
--- a/test/656-checker-simd-opt/src/Main.java
+++ b/test/656-checker-simd-opt/src/Main.java
@@ -46,6 +46,37 @@
     }
   }
 
+  /// CHECK-START: void Main.stencil(int[], int[], int) loop_optimization (before)
+  /// CHECK-DAG: <<CP1:i\d+>>   IntConstant 1                        loop:none
+  /// CHECK-DAG: <<CM1:i\d+>>   IntConstant -1                       loop:none
+  /// CHECK-DAG: <<Phi:i\d+>>   Phi                                  loop:<<Loop:B\d+>> outer_loop:none
+  /// CHECK-DAG: <<Add1:i\d+>>  Add [<<Phi>>,<<CM1>>]                loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Get1:i\d+>>  ArrayGet [{{l\d+}},<<Add1>>]         loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Get2:i\d+>>  ArrayGet [{{l\d+}},<<Phi>>]          loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Add2:i\d+>>  Add [<<Get1>>,<<Get2>>]              loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Add3:i\d+>>  Add [<<Phi>>,<<CP1>>]                loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Get3:i\d+>>  ArrayGet [{{l\d+}},<<Add3>>]         loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Add4:i\d+>>  Add [<<Add2>>,<<Get3>>]              loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG:                ArraySet [{{l\d+}},<<Phi>>,<<Add4>>] loop:<<Loop>>      outer_loop:none
+  //
+  /// CHECK-START-ARM64: void Main.stencil(int[], int[], int) loop_optimization (after)
+  /// CHECK-DAG: <<CP1:i\d+>>   IntConstant 1                         loop:none
+  /// CHECK-DAG: <<CP2:i\d+>>   IntConstant 2                         loop:none
+  /// CHECK-DAG: <<Phi:i\d+>>   Phi                                   loop:<<Loop:B\d+>> outer_loop:none
+  /// CHECK-DAG: <<Add1:i\d+>>  Add [<<Phi>>,<<CP1>>]                 loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Get1:d\d+>>  VecLoad [{{l\d+}},<<Phi>>]            loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Get2:d\d+>>  VecLoad [{{l\d+}},<<Add1>>]           loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Add2:d\d+>>  VecAdd [<<Get1>>,<<Get2>>]            loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Add3:i\d+>>  Add [<<Phi>>,<<CP2>>]                 loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Get3:d\d+>>  VecLoad [{{l\d+}},<<Add3>>]           loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG: <<Add4:d\d+>>  VecAdd [<<Add2>>,<<Get3>>]            loop:<<Loop>>      outer_loop:none
+  /// CHECK-DAG:                VecStore [{{l\d+}},<<Add1>>,<<Add4>>] loop:<<Loop>>      outer_loop:none
+  private static void stencil(int[] a, int[] b, int n) {
+    for (int i = 1; i < n - 1; i++) {
+      a[i] = b[i - 1] + b[i] + b[i + 1];
+    }
+  }
+
   public static void main(String[] args) {
     float[] x = new float[100];
     float[] y = new float[100];
@@ -58,6 +89,18 @@
       expectEquals(5.0f, x[i]);
       expectEquals(2.0f, y[i]);
     }
+    int[] a = new int[100];
+    int[] b = new int[100];
+    for (int i = 0; i < 100; i++) {
+      a[i] = 0;
+      b[i] = i;
+    }
+    stencil(a, b, 100);
+    for (int i = 1; i < 99; i++) {
+      int e = i + i + i;
+      expectEquals(e, a[i]);
+      expectEquals(i, b[i]);
+    }
     System.out.println("passed");
   }
 
diff --git a/tools/dexfuzz/README b/tools/dexfuzz/README
index 78f73f5..3c0c65e 100644
--- a/tools/dexfuzz/README
+++ b/tools/dexfuzz/README
@@ -139,7 +139,9 @@
 InstructionSwapper 80
 NewMethodCaller 10
 NonsenseStringPrinter 10
+OppositeBranchChanger 40
 PoolIndexChanger 30
+RandomBranchChanger 30
 RandomInstructionGenerator 30
 SwitchBranchShifter 30
 TryBlockShifter 40
diff --git a/tools/dexfuzz/src/dexfuzz/DexFuzz.java b/tools/dexfuzz/src/dexfuzz/DexFuzz.java
index 3b28754..41ce7b2 100644
--- a/tools/dexfuzz/src/dexfuzz/DexFuzz.java
+++ b/tools/dexfuzz/src/dexfuzz/DexFuzz.java
@@ -34,7 +34,7 @@
  */
 public class DexFuzz {
   private static int majorVersion = 1;
-  private static int minorVersion = 1;
+  private static int minorVersion = 2;
   private static int seedChangeVersion = 0;
 
   /**
diff --git a/tools/dexfuzz/src/dexfuzz/program/Program.java b/tools/dexfuzz/src/dexfuzz/program/Program.java
index 286fe52..e550d30 100644
--- a/tools/dexfuzz/src/dexfuzz/program/Program.java
+++ b/tools/dexfuzz/src/dexfuzz/program/Program.java
@@ -32,7 +32,9 @@
 import dexfuzz.program.mutators.InstructionSwapper;
 import dexfuzz.program.mutators.NewMethodCaller;
 import dexfuzz.program.mutators.NonsenseStringPrinter;
+import dexfuzz.program.mutators.OppositeBranchChanger;
 import dexfuzz.program.mutators.PoolIndexChanger;
+import dexfuzz.program.mutators.RandomBranchChanger;
 import dexfuzz.program.mutators.RandomInstructionGenerator;
 import dexfuzz.program.mutators.SwitchBranchShifter;
 import dexfuzz.program.mutators.TryBlockShifter;
@@ -199,7 +201,9 @@
     registerMutator(new InstructionSwapper(rng, mutationStats, mutations));
     registerMutator(new NewMethodCaller(rng, mutationStats, mutations));
     registerMutator(new NonsenseStringPrinter(rng, mutationStats, mutations));
+    registerMutator(new OppositeBranchChanger(rng, mutationStats, mutations));
     registerMutator(new PoolIndexChanger(rng, mutationStats, mutations));
+    registerMutator(new RandomBranchChanger(rng, mutationStats, mutations));
     registerMutator(new RandomInstructionGenerator(rng, mutationStats, mutations));
     registerMutator(new SwitchBranchShifter(rng, mutationStats, mutations));
     registerMutator(new TryBlockShifter(rng, mutationStats, mutations));
diff --git a/tools/dexfuzz/src/dexfuzz/program/mutators/IfBranchChanger.java b/tools/dexfuzz/src/dexfuzz/program/mutators/IfBranchChanger.java
new file mode 100644
index 0000000..872b297
--- /dev/null
+++ b/tools/dexfuzz/src/dexfuzz/program/mutators/IfBranchChanger.java
@@ -0,0 +1,158 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+
+package dexfuzz.program.mutators;
+
+import dexfuzz.Log;
+import dexfuzz.MutationStats;
+import dexfuzz.program.MInsn;
+import dexfuzz.program.MutatableCode;
+import dexfuzz.program.Mutation;
+import dexfuzz.rawdex.Instruction;
+import dexfuzz.rawdex.Opcode;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+
+/**
+ * This class mutates the comparison operator of the if
+ * statements by taking in a random instruction, checking whether
+ * it is an if statement and, if so, changing the comparison
+ * operator. The inheriting classes implement the way comparison
+ * operator changes. For example, by choosing the opposite
+ * comparison operator or by choosing a random comparison operator.
+ */
+public abstract class IfBranchChanger extends CodeMutator {
+  /**
+   * Every CodeMutator has an AssociatedMutation, representing the
+   * mutation that this CodeMutator can perform, to allow separate
+   * generateMutation() and applyMutation() phases, allowing serialization.
+   */
+  public static class AssociatedMutation extends Mutation {
+    public int ifBranchInsnIdx;
+
+    @Override
+    public String getString() {
+      return Integer.toString(ifBranchInsnIdx);
+    }
+
+    @Override
+    public void parseString(String[] elements) {
+      ifBranchInsnIdx = Integer.parseInt(elements[2]);
+    }
+  }
+
+  // The following two methods are here for the benefit of MutationSerializer,
+  // so it can create a CodeMutator and get the correct associated Mutation, as it
+  // reads in mutations from a dump of mutations.
+  @Override
+  public Mutation getNewMutation() {
+    return new AssociatedMutation();
+  }
+
+  public IfBranchChanger() { }
+
+  public IfBranchChanger(Random rng, MutationStats stats, List<Mutation> mutations) {
+    super(rng, stats, mutations);
+  }
+
+  // A cache that should only exist between generateMutation() and applyMutation(),
+  // or be created at the start of applyMutation(), if we're reading in mutations from
+  // a file.
+  private List<MInsn> ifBranchInsns = null;
+
+  private void generateCachedifBranchInsns(MutatableCode mutatableCode) {
+    if (ifBranchInsns != null) {
+      return;
+    }
+
+    ifBranchInsns = new ArrayList<MInsn>();
+
+    for (MInsn mInsn : mutatableCode.getInstructions()) {
+      if (isIfBranchOperation(mInsn)) {
+        ifBranchInsns.add(mInsn);
+      }
+    }
+  }
+
+  @Override
+  protected boolean canMutate(MutatableCode mutatableCode) {
+    for (MInsn mInsn : mutatableCode.getInstructions()) {
+      if (isIfBranchOperation(mInsn)) {
+        return true;
+      }
+    }
+
+    Log.debug("No if branch operation, skipping...");
+    return false;
+  }
+
+  @Override
+  protected Mutation generateMutation(MutatableCode mutatableCode) {
+    generateCachedifBranchInsns(mutatableCode);
+
+    int ifBranchInsnIdx = rng.nextInt(ifBranchInsns.size());
+
+    AssociatedMutation mutation = new AssociatedMutation();
+    mutation.setup(this.getClass(), mutatableCode);
+    mutation.ifBranchInsnIdx = ifBranchInsnIdx;
+    return mutation;
+  }
+
+  @Override
+  protected void applyMutation(Mutation uncastMutation) {
+    AssociatedMutation mutation = (AssociatedMutation) uncastMutation;
+    MutatableCode mutatableCode = mutation.mutatableCode;
+
+    generateCachedifBranchInsns(mutatableCode);
+
+    MInsn ifBranchInsn = ifBranchInsns.get(mutation.ifBranchInsnIdx);
+
+    String oldInsnString = ifBranchInsn.toString();
+
+    Opcode newOpcode = getModifiedOpcode(ifBranchInsn);
+
+    ifBranchInsn.insn.info = Instruction.getOpcodeInfo(newOpcode);
+
+    Log.info("Changed " + oldInsnString + " to " + ifBranchInsn);
+
+    stats.incrementStat("Changed if branch operator to " + getMutationTag() + " operator");
+
+    // Clear cache.
+    ifBranchInsns = null;
+  }
+
+  /**
+   * Get a different if branch instruction.
+   * @return opcode of the new comparison operator.
+   */
+  protected abstract Opcode getModifiedOpcode(MInsn mInsn);
+
+  /**
+   * Get the tag of the mutation that fired.
+   * @return string tag of the type of mutation used
+   */
+  protected abstract String getMutationTag();
+
+  private boolean isIfBranchOperation(MInsn mInsn) {
+    Opcode opcode = mInsn.insn.info.opcode;
+    if (Opcode.isBetween(opcode, Opcode.IF_EQ, Opcode.IF_LEZ)) {
+      return true;
+    }
+    return false;
+  }
+}
\ No newline at end of file
diff --git a/tools/dexfuzz/src/dexfuzz/program/mutators/OppositeBranchChanger.java b/tools/dexfuzz/src/dexfuzz/program/mutators/OppositeBranchChanger.java
new file mode 100644
index 0000000..cb25b64
--- /dev/null
+++ b/tools/dexfuzz/src/dexfuzz/program/mutators/OppositeBranchChanger.java
@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+
+package dexfuzz.program.mutators;
+
+import dexfuzz.Log;
+import dexfuzz.MutationStats;
+import dexfuzz.program.MInsn;
+import dexfuzz.program.Mutation;
+import dexfuzz.rawdex.Opcode;
+import java.util.List;
+import java.util.Random;
+
+public class OppositeBranchChanger extends IfBranchChanger {
+
+  public OppositeBranchChanger(Random rng, MutationStats stats, List<Mutation> mutations) {
+    super(rng, stats, mutations);
+    likelihood = 40;
+  }
+
+  @Override
+  protected Opcode getModifiedOpcode(MInsn mInsn) {
+    Opcode opcode = mInsn.insn.info.opcode;
+    switch (opcode) {
+      case IF_EQ:
+        return Opcode.IF_NE;
+      case IF_NE:
+        return Opcode.IF_EQ;
+      case IF_LT:
+        return Opcode.IF_GE;
+      case IF_GT:
+        return Opcode.IF_LE;
+      case IF_GE:
+        return Opcode.IF_LT;
+      case IF_LE:
+        return Opcode.IF_GT;
+      case IF_EQZ:
+        return Opcode.IF_NEZ;
+      case IF_NEZ:
+        return Opcode.IF_EQZ;
+      case IF_LTZ:
+        return Opcode.IF_GEZ;
+      case IF_GTZ:
+        return Opcode.IF_LEZ;
+      case IF_GEZ:
+        return Opcode.IF_LTZ;
+      case IF_LEZ:
+        return Opcode.IF_GTZ;
+      default:
+        Log.errorAndQuit("Could not find if branch.");
+        return opcode;
+    }
+  }
+
+  @Override
+  protected String getMutationTag() {
+    return "opposite";
+  }
+}
\ No newline at end of file
diff --git a/tools/dexfuzz/src/dexfuzz/program/mutators/RandomBranchChanger.java b/tools/dexfuzz/src/dexfuzz/program/mutators/RandomBranchChanger.java
new file mode 100644
index 0000000..fc42c2e
--- /dev/null
+++ b/tools/dexfuzz/src/dexfuzz/program/mutators/RandomBranchChanger.java
@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+
+package dexfuzz.program.mutators;
+
+import dexfuzz.MutationStats;
+import dexfuzz.program.MInsn;
+import dexfuzz.program.Mutation;
+import dexfuzz.rawdex.Opcode;
+import java.util.List;
+import java.util.Random;
+
+public class RandomBranchChanger extends IfBranchChanger {
+
+  private static final Opcode[] EQUALITY_CMP_OP_LIST = {
+    Opcode.IF_EQ,
+    Opcode.IF_NE,
+    Opcode.IF_LT,
+    Opcode.IF_GE,
+    Opcode.IF_GT,
+    Opcode.IF_LE
+  };
+
+  private static final Opcode[] ZERO_CMP_OP_LIST = {
+    Opcode.IF_EQZ,
+    Opcode.IF_NEZ,
+    Opcode.IF_LTZ,
+    Opcode.IF_GEZ,
+    Opcode.IF_GTZ,
+    Opcode.IF_LEZ
+  };
+
+  public RandomBranchChanger(Random rng, MutationStats stats, List<Mutation> mutations) {
+    super(rng, stats, mutations);
+    likelihood = 30;
+  }
+
+  @Override
+  protected Opcode getModifiedOpcode(MInsn mInsn) {
+    Opcode opcode = mInsn.insn.info.opcode;
+    if (Opcode.isBetween(opcode, Opcode.IF_EQ, Opcode.IF_LE)) {
+      int index = opcode.ordinal() - Opcode.IF_EQ.ordinal();
+      int length = EQUALITY_CMP_OP_LIST.length;
+      return EQUALITY_CMP_OP_LIST[(index + 1 + rng.nextInt(length - 1)) % length];
+    } else if (Opcode.isBetween(opcode, Opcode.IF_EQZ, Opcode.IF_LEZ)) {
+      int index = opcode.ordinal() - Opcode.IF_EQZ.ordinal();
+      int length = ZERO_CMP_OP_LIST.length;
+      return ZERO_CMP_OP_LIST[(index + 1 + rng.nextInt(length - 1)) % length];
+    }
+    return opcode;
+  }
+
+  @Override
+  protected String getMutationTag() {
+    return "random";
+  }
+}
\ No newline at end of file