Change generated code for substring not to bail out to runtime system.

src/arm/code-stubs-arm.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 5797 matching lines @@
   __ jmp(&return_r0);
 
   if (FLAG_string_slices) {
     __ bind(&create_slice);
     // r0: original string
     // r1: instance type
     // r2: length
     // r3: from index (untagged smi)
     // r6 (a.k.a. to): to (smi)
     // r7 (a.k.a. from): from offset (smi)
-    Label allocate_slice, sliced_string, seq_string;
-    STATIC_ASSERT(kSeqStringTag == 0);
-    __ tst(r1, Operand(kStringRepresentationMask));
-    __ b(eq, &seq_string);
+    Label allocate_slice, sliced_string, seq_or_external_string;
     STATIC_ASSERT(kIsIndirectStringMask == (kSlicedStringTag & kConsStringTag));
     STATIC_ASSERT(kIsIndirectStringMask != 0);
     __ tst(r1, Operand(kIsIndirectStringMask));
-    // External string.  Jump to runtime.
-    __ b(eq, &runtime);
+    __ b(eq, &seq_or_external_string);
 
     __ tst(r1, Operand(kSlicedNotConsMask));
     __ b(ne, &sliced_string);
     // Cons string.  Check whether it is flat, then fetch first part.
     __ ldr(r5, FieldMemOperand(r0, ConsString::kSecondOffset));
     __ LoadRoot(r9, Heap::kEmptyStringRootIndex);
     __ cmp(r5, r9);
     __ b(ne, &runtime);
     __ ldr(r5, FieldMemOperand(r0, ConsString::kFirstOffset));
     __ jmp(&allocate_slice);
 
     __ bind(&sliced_string);
     // Sliced string.  Fetch parent and correct start index by offset.
     __ ldr(r5, FieldMemOperand(r0, SlicedString::kOffsetOffset));
     __ add(r7, r7, r5);
     __ ldr(r5, FieldMemOperand(r0, SlicedString::kParentOffset));
     __ jmp(&allocate_slice);
 
-    __ bind(&seq_string);
-    // Sequential string.  Just move string to the right register.
+    __ bind(&seq_or_external_string);
+    // Sequential or external string.  Just move string to the correct register.
     __ mov(r5, r0);
 
     __ bind(&allocate_slice);
     // r1: instance type of original string
     // r2: length
     // r5: underlying subject string
     // r7 (a.k.a. from): from offset (smi)
     // Allocate new sliced string.  At this point we do not reload the instance
     // type including the string encoding because we simply rely on the info
     // provided by the original string.  It does not matter if the original
@@ skipping 1325 matching lines @@
   __ StoreNumberToDoubleElements(r0, r3, r1, r5, r6, r7, r9, r10,
                                  &slow_elements);
   __ Ret();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM