Use fucomi instruction to compare floats and put results directly into EFLAGS...

src/x64/assembler-x64.cc

 // Copyright 2009 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 2064 matching lines @@
 
 
 void Assembler::fucompp() {
   EnsureSpace ensure_space(this);
   last_pc_ = pc_;
   emit(0xDA);
   emit(0xE9);
 }
 
 
+void Assembler::fucomip() {
+  EnsureSpace ensure_space(this);
+  last_pc_ = pc_;
+  emit(0xDF);
+  emit(0xE9);
+}
+
+
 void Assembler::fcompp() {
   EnsureSpace ensure_space(this);
   last_pc_ = pc_;
   emit(0xDE);
   emit(0xD9);
 }
 
 
 void Assembler::fnstsw_ax() {
   EnsureSpace ensure_space(this);
@@ skipping 263 matching lines @@
     RecordRelocInfo(RelocInfo::POSITION, current_position_);
     written_position_ = current_position_;
   }
 }
 
 
 const int RelocInfo::kApplyMask = 1 << RelocInfo::INTERNAL_REFERENCE;
 
 
 } }  // namespace v8::internal