Clusterfuzz identified overflow check needed in dehoisting.

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HYDROGEN_INSTRUCTIONS_H_
 #define V8_HYDROGEN_INSTRUCTIONS_H_
 
 #include "src/v8.h"
 
 #include "src/allocation.h"
@@ skipping 6381 matching lines @@
     SetFlag(kUseGVN);
     SetDependsOnFlag(kCalls);
   }
 };
 
 class ArrayInstructionInterface {
  public:
   virtual HValue* GetKey() = 0;
   virtual void SetKey(HValue* key) = 0;
   virtual ElementsKind elements_kind() const = 0;
-  virtual void IncreaseBaseOffset(uint32_t base_offset) = 0;
-  virtual int MaxBaseOffsetBits() = 0;
+  // increase_by_value should be non-negative
+  virtual bool CanIncreaseBaseOffset(int32_t increase_by_value) = 0;
+  virtual void IncreaseBaseOffset(int32_t increase_by_value) = 0;
   virtual bool IsDehoisted() = 0;
   virtual void SetDehoisted(bool is_dehoisted) = 0;
   virtual ~ArrayInstructionInterface() { }
 
   static Representation KeyedAccessIndexRequirement(Representation r) {
     return r.IsInteger32() || SmiValuesAre32Bits()
         ? Representation::Integer32() : Representation::Smi();
   }
 };
 
@@ skipping 25 matching lines @@
   bool is_typed_elements() const {
     return is_external() || is_fixed_typed_array();
   }
   HValue* elements() { return OperandAt(0); }
   HValue* key() { return OperandAt(1); }
   HValue* dependency() {
     ASSERT(HasDependency());
     return OperandAt(2);
   }
   bool HasDependency() const { return OperandAt(0) != OperandAt(2); }
-  uint32_t base_offset() { return BaseOffsetField::decode(bit_field_); }
-  void IncreaseBaseOffset(uint32_t base_offset) {
-    base_offset += BaseOffsetField::decode(bit_field_);
-    bit_field_ = BaseOffsetField::update(bit_field_, base_offset);
+  uint32_t base_offset() {
+    int32_t base_offset_value = BaseOffsetField::decode(bit_field_);
+    ASSERT(base_offset_value >= 0);
+    return static_cast<uint32_t>(base_offset_value);
   }
-  virtual int MaxBaseOffsetBits() {
-    return kBitsForBaseOffset;
+  bool CanIncreaseBaseOffset(int32_t increase_by_value) {
+    ASSERT(increase_by_value >= 0);
+    int32_t new_value = BaseOffsetField::decode(bit_field_) + increase_by_value;
+    return (new_value >= 0 || BaseOffsetField::is_valid(new_value));
+  }
+  void IncreaseBaseOffset(int32_t increase_by_value) {
+    ASSERT(increase_by_value >= 0);
+    increase_by_value += BaseOffsetField::decode(bit_field_);
+    bit_field_ = BaseOffsetField::update(bit_field_, increase_by_value);
   }
   HValue* GetKey() { return key(); }
   void SetKey(HValue* key) { SetOperandAt(1, key); }
   bool IsDehoisted() { return IsDehoistedField::decode(bit_field_); }
   void SetDehoisted(bool is_dehoisted) {
     bit_field_ = IsDehoistedField::update(bit_field_, is_dehoisted);
   }
   ElementsKind elements_kind() const {
     return ElementsKindField::decode(bit_field_);
   }
@@ skipping 129 matching lines @@
   STATIC_ASSERT((kBitsForElementsKind + kBitsForBaseOffset +
                  kBitsForIsDehoisted) <= sizeof(uint32_t)*8);
   STATIC_ASSERT(kElementsKindCount <= (1 << kBitsForElementsKind));
   class ElementsKindField:
     public BitField<ElementsKind, kStartElementsKind, kBitsForElementsKind>
     {};  // NOLINT
   class HoleModeField:
     public BitField<LoadKeyedHoleMode, kStartHoleMode, kBitsForHoleMode>
     {};  // NOLINT
   class BaseOffsetField:
-    public BitField<uint32_t, kStartBaseOffset, kBitsForBaseOffset>
+    public BitField<int32_t, kStartBaseOffset, kBitsForBaseOffset>
     {};  // NOLINT
   class IsDehoistedField:
     public BitField<bool, kStartIsDehoisted, kBitsForIsDehoisted>
     {};  // NOLINT
   uint32_t bit_field_;
 };
 
 
 class HLoadKeyedGeneric V8_FINAL : public HTemplateInstruction<3> {
  public:
@@ skipping 293 matching lines @@
   }
 
   HValue* elements() const { return OperandAt(0); }
   HValue* key() const { return OperandAt(1); }
   HValue* value() const { return OperandAt(2); }
   bool value_is_smi() const {
     return IsFastSmiElementsKind(elements_kind_);
   }
   StoreFieldOrKeyedMode store_mode() const { return store_mode_; }
   ElementsKind elements_kind() const { return elements_kind_; }
-  uint32_t base_offset() { return base_offset_; }
-  void IncreaseBaseOffset(uint32_t base_offset) {
-    base_offset_ += base_offset;
+  uint32_t base_offset() {
+    ASSERT(base_offset_ >= 0);
+    return static_cast<uint32_t>(base_offset_);
   }
-  virtual int MaxBaseOffsetBits() {
-    return 31 - ElementsKindToShiftSize(elements_kind_);
+  bool CanIncreaseBaseOffset(int32_t increase_by_value) {
+    ASSERT(increase_by_value >= 0);
+    // Guard against overflow
+    return (increase_by_value + base_offset_) >= 0;
+  }
+  void IncreaseBaseOffset(int32_t increase_by_value) {
+    ASSERT(increase_by_value >= 0);
+    base_offset_ += increase_by_value;
   }
   HValue* GetKey() { return key(); }
   void SetKey(HValue* key) { SetOperandAt(1, key); }
   bool IsDehoisted() { return is_dehoisted_; }
   void SetDehoisted(bool is_dehoisted) { is_dehoisted_ = is_dehoisted; }
   bool IsUninitialized() { return is_uninitialized_; }
   void SetUninitialized(bool is_uninitialized) {
     is_uninitialized_ = is_uninitialized;
   }
 
@@ skipping 70 matching lines @@
     // EXTERNAL_{UNSIGNED_,}{BYTE,SHORT,INT}_ELEMENTS are truncating.
     if ((elements_kind >= EXTERNAL_INT8_ELEMENTS &&
         elements_kind <= EXTERNAL_UINT32_ELEMENTS) ||
         (elements_kind >= UINT8_ELEMENTS &&
         elements_kind <= INT32_ELEMENTS)) {
       SetFlag(kTruncatingToInt32);
     }
   }
 
   ElementsKind elements_kind_;
-  uint32_t base_offset_;
+  int32_t base_offset_;
   bool is_dehoisted_ : 1;
   bool is_uninitialized_ : 1;
   StoreFieldOrKeyedMode store_mode_: 1;
   HValue* dominator_;
 };
 
 
 class HStoreKeyedGeneric V8_FINAL : public HTemplateInstruction<4> {
  public:
   DECLARE_INSTRUCTION_WITH_CONTEXT_FACTORY_P4(HStoreKeyedGeneric, HValue*,
@@ skipping 675 matching lines @@
   virtual bool IsDeletable() const V8_OVERRIDE { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_