Fix a bug in the x64 elements transition code.

src/x64/codegen-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 210 matching lines @@
 void ElementsTransitionGenerator::GenerateSmiOnlyToDouble(
     MacroAssembler* masm, Label* fail) {
   // ----------- S t a t e -------------
   //  -- rax    : value
   //  -- rbx    : target map
   //  -- rcx    : key
   //  -- rdx    : receiver
   //  -- rsp[0] : return address
   // -----------------------------------
   // The fail label is not actually used since we do not allocate.
-  Label allocated, cow_array, only_change_map, done;
+  Label allocated, new_backing_store, only_change_map, done;
 
   // Check for empty arrays, which only require a map transition and no changes
   // to the backing store.
   __ movq(r8, FieldOperand(rdx, JSObject::kElementsOffset));
   __ CompareRoot(r8, Heap::kEmptyFixedArrayRootIndex);
   __ j(equal, &only_change_map);
 
-  // Check backing store for COW-ness.  If the negative case, we do not have to
-  // allocate a new array, since FixedArray and FixedDoubleArray do not differ
-  // in size.
+  // Check backing store for COW-ness.  For COW arrays we have to
+  // allocate a new backing store.
   __ SmiToInteger32(r9, FieldOperand(r8, FixedDoubleArray::kLengthOffset));
   __ CompareRoot(FieldOperand(r8, HeapObject::kMapOffset),
                  Heap::kFixedCOWArrayMapRootIndex);
-  __ j(equal, &cow_array);
+  __ j(equal, &new_backing_store);
+  // Check if the backing store is in new-space. If not, we need to allocate
+  // a new one since the old one is in pointer-space.
+  // If in new space, we can reuse the old backing store because it is
+  // the same size.
+  __ JumpIfNotInNewSpace(r8, rdi, &new_backing_store);
+
   __ movq(r14, r8);  // Destination array equals source array.
 
-  __ bind(&allocated);
   // r8 : source FixedArray
   // r9 : elements array length
   // r14: destination FixedDoubleArray
   // Set backing store's map
   __ LoadRoot(rdi, Heap::kFixedDoubleArrayMapRootIndex);
   __ movq(FieldOperand(r14, HeapObject::kMapOffset), rdi);
 
+  __ bind(&allocated);
   // Set transitioned map.
   __ movq(FieldOperand(rdx, HeapObject::kMapOffset), rbx);
   __ RecordWriteField(rdx,
                       HeapObject::kMapOffset,
                       rbx,
                       rdi,
                       kDontSaveFPRegs,
                       EMIT_REMEMBERED_SET,
                       OMIT_SMI_CHECK);
 
   // Convert smis to doubles and holes to hole NaNs.  The Array's length
   // remains unchanged.
   STATIC_ASSERT(FixedDoubleArray::kLengthOffset == FixedArray::kLengthOffset);
   STATIC_ASSERT(FixedDoubleArray::kHeaderSize == FixedArray::kHeaderSize);
 
   Label loop, entry, convert_hole;
   __ movq(r15, BitCast<int64_t, uint64_t>(kHoleNanInt64), RelocInfo::NONE);
   // r15: the-hole NaN
   __ jmp(&entry);
 
-  // Allocate new array if the source array is a COW array.
-  __ bind(&cow_array);
+  // Allocate new backing store.
+  __ bind(&new_backing_store);
   __ lea(rdi, Operand(r9, times_pointer_size, FixedArray::kHeaderSize));
   __ AllocateInNewSpace(rdi, r14, r11, r15, fail, TAG_OBJECT);
+  // Set backing store's map
+  __ LoadRoot(rdi, Heap::kFixedDoubleArrayMapRootIndex);
+  __ movq(FieldOperand(r14, HeapObject::kMapOffset), rdi);
   // Set receiver's backing store.
   __ movq(FieldOperand(rdx, JSObject::kElementsOffset), r14);
   __ movq(r11, r14);
   __ RecordWriteField(rdx,
                       JSObject::kElementsOffset,
                       r11,
                       r15,
                       kDontSaveFPRegs,
                       EMIT_REMEMBERED_SET,
                       OMIT_SMI_CHECK);
@@ skipping 252 matching lines @@
                                   times_1,
                                   SeqAsciiString::kHeaderSize));
   __ bind(&done);
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64