X64: Implement StringCharAtStub which is used from lithium codegen....

src/x64/lithium-codegen-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 687 matching lines @@
       RegExpExecStub stub;
       CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);
       break;
     }
     case CodeStub::SubString: {
       SubStringStub stub;
       CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);
       break;
     }
     case CodeStub::StringCharAt: {
-      // TODO(1116): Add StringCharAt stub to x64.
-      Abort("Unimplemented: %s", "StringCharAt Stub");
+      StringCharAtStub stub;
+      CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);
       break;
     }
     case CodeStub::MathPow: {
       MathPowStub stub;
       CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);
       break;
     }
     case CodeStub::NumberToString: {
       NumberToStringStub stub;
       CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);
@@ skipping 2900 matching lines @@
   RegisterEnvironmentForDeoptimization(environment);
   ASSERT(osr_pc_offset_ == -1);
   osr_pc_offset_ = masm()->pc_offset();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64