Clarify result returned by remainder intrinsics.

runtime/vm/intrinsifier_x64.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_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intrinsifier.h"
 
 #include "vm/assembler.h"
@@ skipping 318 matching lines @@
 
 
 // Optimizations:
 // - result is 0 if:
 //   - left is 0
 //   - left equals right
 // - result is left if
 //   - left > 0 && left < right
 // RAX: Tagged left (dividend).
 // RCX: Tagged right (divisor).
-// RAX: Untagged result (remainder).
+// Returns:
+//   RAX: Untagged fallthrough result (remainder to be adjusted), or
+//   RAX: Tagged return result (remainder).
 static void EmitRemainderOperation(Assembler* assembler) {
   Label return_zero, try_modulo, not_32bit, done;
   // Check for quick zero results.
   __ cmpq(RAX, Immediate(0));
   __ j(EQUAL, &return_zero, Assembler::kNearJump);
   __ cmpq(RAX, RCX);
   __ j(EQUAL, &return_zero, Assembler::kNearJump);
 
   // Check if result equals left.
   __ cmpq(RAX, Immediate(0));
@@ skipping 1561 matching lines @@
   // Set return value to Isolate::current_tag_.
   __ movq(RAX, Address(RBX, Isolate::current_tag_offset()));
   __ ret();
 }
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64