Add two-byte string support in codeunitAt intrinsic.

runtime/vm/intrinsifier_arm.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_ARM.
 #if defined(TARGET_ARCH_ARM)
 
 #include "vm/intrinsifier.h"
 
 #include "vm/assembler.h"
@@ skipping 1423 matching lines @@
 
 
 bool Intrinsifier::String_getLength(Assembler* assembler) {
   __ ldr(R0, Address(SP, 0 * kWordSize));
   __ ldr(R0, FieldAddress(R0, String::length_offset()));
   __ Ret();
   return true;
 }
 
 
-// TODO(srdjan): Implement for two and four byte strings as well.
 bool Intrinsifier::String_codeUnitAt(Assembler* assembler) {
-  Label fall_through;
+  Label fall_through, try_two_byte_string;
 
   __ ldr(R1, Address(SP, 0 * kWordSize));  // Index.
   __ ldr(R0, Address(SP, 1 * kWordSize));  // String.
   __ tst(R1, ShifterOperand(kSmiTagMask));
   __ b(&fall_through, NE);  // Index is not a Smi.
   // Range check.
   __ ldr(R2, FieldAddress(R0, String::length_offset()));
   __ cmp(R1, ShifterOperand(R2));
   __ b(&fall_through, CS);  // Runtime throws exception.
   __ CompareClassId(R0, kOneByteStringCid, R3);
-  __ b(&fall_through, NE);
+  __ b(&try_two_byte_string, NE);
   __ SmiUntag(R1);
   __ AddImmediate(R0, OneByteString::data_offset() - kHeapObjectTag);
   __ ldrb(R0, Address(R0, R1));
   __ SmiTag(R0);
   __ Ret();
+
+  __ Bind(&try_two_byte_string);
+  __ CompareClassId(R0, kTwoByteStringCid, R3);
+  __ b(&fall_through, NE);
+  ASSERT(kSmiTagShift == 1);
+  __ AddImmediate(R0, OneByteString::data_offset() - kHeapObjectTag);
+  __ ldrh(R0, Address(R0, R1));
+  __ SmiTag(R0);
+  __ Ret();
+
   __ Bind(&fall_through);
   return false;
 }
 
 
 bool Intrinsifier::String_getIsEmpty(Assembler* assembler) {
   __ ldr(R0, Address(SP, 0 * kWordSize));
   __ ldr(R0, FieldAddress(R0, String::length_offset()));
   __ cmp(R0, ShifterOperand(Smi::RawValue(0)));
   __ LoadObject(R0, Bool::True(), EQ);
@@ skipping 216 matching lines @@
   __ Bind(&ok);
   __ Ret();
 
   __ Bind(&fall_through);
   return false;
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM