Re-land Clusterfuzz identified overflow check needed in dehoisting.

src/hydrogen-dehoist.cc

 // Copyright 2013 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.
 
 #include "src/hydrogen-dehoist.h"
 
 namespace v8 {
 namespace internal {
 
 static void DehoistArrayIndex(ArrayInstructionInterface* array_operation) {
@@ skipping 10 matching lines @@
   } else if (binary_operation->right()->IsConstant()) {
     subexpression = binary_operation->left();
     constant = HConstant::cast(binary_operation->right());
   } else {
     return;
   }
 
   if (!constant->HasInteger32Value()) return;
   int32_t sign = binary_operation->IsSub() ? -1 : 1;
   int32_t value = constant->Integer32Value() * sign;
-  // We limit offset values to 30 bits because we want to avoid the risk of
-  // overflows when the offset is added to the object header size.
-  if (value >= 1 << array_operation->MaxBaseOffsetBits() || value < 0) return;
+  if (value < 0) return;
+
+  // Check for overflow.
+  // TODO(mvstanton): replace with safe_math.h operations when that code is
+  // integrated.
+  int32_t shift_amount =
+      1 << ElementsKindToShiftSize(array_operation->elements_kind());
+  int32_t multiplication_result = value * shift_amount;
+  if ((multiplication_result >> shift_amount) != value) return;
+  value = multiplication_result;
+
+  // Ensure that the array operation can add value to existing base offset
+  // without overflowing.
+  if (!array_operation->CanIncreaseBaseOffset(value)) return;
   array_operation->SetKey(subexpression);
   if (binary_operation->HasNoUses()) {
     binary_operation->DeleteAndReplaceWith(NULL);
   }
-  value <<= ElementsKindToShiftSize(array_operation->elements_kind());
-  array_operation->IncreaseBaseOffset(static_cast<uint32_t>(value));
+  array_operation->IncreaseBaseOffset(value);
   array_operation->SetDehoisted(true);
 }
 
 
 void HDehoistIndexComputationsPhase::Run() {
   const ZoneList<HBasicBlock*>* blocks(graph()->blocks());
   for (int i = 0; i < blocks->length(); ++i) {
     for (HInstructionIterator it(blocks->at(i)); !it.Done(); it.Advance()) {
       HInstruction* instr = it.Current();
       if (instr->IsLoadKeyed()) {
         DehoistArrayIndex(HLoadKeyed::cast(instr));
       } else if (instr->IsStoreKeyed()) {
         DehoistArrayIndex(HStoreKeyed::cast(instr));
       }
     }
   }
 }
 
 } }  // namespace v8::internal