Fixing issue 1757 (string slices of external strings).

src/x64/code-stubs-x64.cc

 // Copyright 2011 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 4066 matching lines @@
   // ConsString.
   // Check whether the right hand side is the empty string (i.e. if
   // this is really a flat string in a cons string). If that is not
   // the case we would rather go to the runtime system now to flatten
   // the string.
   Label assure_seq_string;
   __ CompareRoot(FieldOperand(object_, ConsString::kSecondOffset),
                  Heap::kEmptyStringRootIndex);
   __ j(not_equal, &call_runtime_);
   // Get the first of the two strings and load its instance type.
-  __ movq(object_, FieldOperand(object_, ConsString::kFirstOffset));
+  __ movq(kScratchRegister, FieldOperand(object_, ConsString::kFirstOffset));
   __ jmp(&assure_seq_string, Label::kNear);
 
   // SlicedString, unpack and add offset.
   __ bind(&sliced_string);
   __ addq(scratch_, FieldOperand(object_, SlicedString::kOffsetOffset));
-  __ movq(object_, FieldOperand(object_, SlicedString::kParentOffset));
+  __ movq(kScratchRegister, FieldOperand(object_, SlicedString::kParentOffset));
 
   __ bind(&assure_seq_string);
-  __ movq(result_, FieldOperand(object_, HeapObject::kMapOffset));
+  __ movq(result_, FieldOperand(kScratchRegister, HeapObject::kMapOffset));
   __ movzxbl(result_, FieldOperand(result_, Map::kInstanceTypeOffset));
   // If the first cons component is also non-flat, then go to runtime.
   STATIC_ASSERT(kSeqStringTag == 0);
   __ testb(result_, Immediate(kStringRepresentationMask));
   __ j(not_zero, &call_runtime_);
-  __ jmp(&flat_string);
+  __ movq(object_, kScratchRegister);
 
   // Check for 1-byte or 2-byte string.
   __ bind(&flat_string);
   STATIC_ASSERT((kStringEncodingMask & kAsciiStringTag) != 0);
   STATIC_ASSERT((kStringEncodingMask & kTwoByteStringTag) == 0);
   __ testb(result_, Immediate(kStringEncodingMask));
   __ j(not_zero, &ascii_string);
 
   // 2-byte string.
   // Load the 2-byte character code into the result register.
@@ skipping 1801 matching lines @@
 
   // Fall through when we need to inform the incremental marker.
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64