Fixing issue 1757 (string slices of external strings).

src/mips/code-stubs-mips.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 5112 matching lines @@
   // 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;
   __ lw(result_, FieldMemOperand(object_, ConsString::kSecondOffset));
   __ LoadRoot(t0, Heap::kEmptyStringRootIndex);
   __ Branch(&call_runtime_, ne, result_, Operand(t0));
 
   // Get the first of the two strings and load its instance type.
-  __ lw(object_, FieldMemOperand(object_, ConsString::kFirstOffset));
+  __ lw(result_, FieldMemOperand(object_, ConsString::kFirstOffset));
   __ jmp(&assure_seq_string);
 
   // SlicedString, unpack and add offset.
   __ bind(&sliced_string);
   __ lw(result_, FieldMemOperand(object_, SlicedString::kOffsetOffset));
   __ addu(scratch_, scratch_, result_);
-  __ lw(object_, FieldMemOperand(object_, SlicedString::kParentOffset));
+  __ lw(result_, FieldMemOperand(object_, SlicedString::kParentOffset));
 
   // Assure that we are dealing with a sequential string. Go to runtime if not.
   __ bind(&assure_seq_string);
-  __ lw(result_, FieldMemOperand(object_, HeapObject::kMapOffset));
+  __ lw(result_, FieldMemOperand(result_, HeapObject::kMapOffset));
   __ lbu(result_, FieldMemOperand(result_, Map::kInstanceTypeOffset));
   // Check that parent is not an external string. Go to runtime otherwise.
   STATIC_ASSERT(kSeqStringTag == 0);
 
   __ And(t0, result_, Operand(kStringRepresentationMask));
   __ Branch(&call_runtime_, ne, t0, Operand(zero_reg));
+  // Actually fetch the parent string if it is confirmed to be sequential.
+  STATIC_ASSERT(SlicedString::kParentOffset == ConsString::kFirstOffset);
+  __ lw(object_, FieldMemOperand(object_, SlicedString::kParentOffset));
 
   // Check for 1-byte or 2-byte string.
   __ bind(&flat_string);
   STATIC_ASSERT((kStringEncodingMask & kAsciiStringTag) != 0);
   STATIC_ASSERT((kStringEncodingMask & kTwoByteStringTag) == 0);
   __ And(t0, result_, Operand(kStringEncodingMask));
   __ Branch(&ascii_string, ne, t0, Operand(zero_reg));
 
   // 2-byte string.
   // Load the 2-byte character code into the result register. We can
@@ skipping 1859 matching lines @@
   __ mov(result, zero_reg);
   __ Ret();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS