Inline ordered relative compares of mixed double/undefined values.

src/hydrogen-instructions.cc

 // Copyright 2012 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 1439 matching lines @@
 
 
 void HGoto::PrintDataTo(StringStream* stream) {
   stream->Add("B%d", SuccessorAt(0)->block_id());
 }
 
 
 void HCompareIDAndBranch::SetInputRepresentation(Representation r) {
   input_representation_ = r;
   if (r.IsDouble()) {
-    SetFlag(kDeoptimizeOnUndefined);
+    // ==, === and != have special handling of undefined, specifically undeifned

[fschneider, 2012/03/02 12:39:15]

s/undeifned/undefined

[danno, 2012/03/02 13:28:45]

Done.

+    // == undefined is 'true' but the standard Crankshaft tagged-to-double
+    // conversion to ensure the HCompareIDAndBranch's inputs, including
+    // undefined values, are doubles will convert undefined to NaN, and NaN ==
+    // NaN is 'false'. So all comparisons that aren't explicitly defined by the
+    // spec to call ToPrimitive() (i.e. anything not an ordered relational
+    // comparison) must deopt when one of the arguments is undefined.
+    // See v8:1434

[fschneider, 2012/03/02 12:39:15]

I'd also refer to the corresponding sections in the ES5 spec (11.9.3, 11.8.5)
and use the same terms "relational comparison" and "equality comparison".

[danno, 2012/03/02 13:28:45]

Done.

+    if (!Token::IsOrderedCompareOp(token_)) {

[fschneider, 2012/03/02 12:39:15]

maybe rename to IsRelationalCompareOp.

[danno, 2012/03/02 13:28:45]

Done.

+      SetFlag(kDeoptimizeOnUndefined);
+    }
   } else {
     ASSERT(r.IsInteger32());
   }
 }
 
 
 void HParameter::PrintDataTo(StringStream* stream) {
   stream->Add("%u", index());
 }
 
@@ skipping 779 matching lines @@
 
 
 void HCheckPrototypeMaps::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal