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

src/ia32/macro-assembler-ia32.cc

 // Copyright 2006-2009 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 301 matching lines @@
 }
 
 
 void MacroAssembler::CmpInstanceType(Register map, InstanceType type) {
   cmpb(FieldOperand(map, Map::kInstanceTypeOffset),
        static_cast<int8_t>(type));
 }
 
 
 void MacroAssembler::FCmp() {
-  fcompp();
-  push(eax);
-  fnstsw_ax();
-  sahf();
-  pop(eax);
+  if (CpuFeatures::IsSupported(CpuFeatures::CMOV)) {
+    fucomip();
+    ffree(0);
+    fincstp();
+  } else {
+    fucompp();
+    push(eax);
+    fnstsw_ax();
+    sahf();
+    pop(eax);
+  }
 }
 
 
 void MacroAssembler::EnterFrame(StackFrame::Type type) {
   push(ebp);
   mov(ebp, Operand(esp));
   push(esi);
   push(Immediate(Smi::FromInt(type)));
   push(Immediate(CodeObject()));
   if (FLAG_debug_code) {
@@ skipping 840 matching lines @@
   // Indicate that code has changed.
   CPU::FlushICache(address_, size_);
 
   // Check that the code was patched as expected.
   ASSERT(masm_.pc_ == address_ + size_);
   ASSERT(masm_.reloc_info_writer.pos() == address_ + size_ + Assembler::kGap);
 }
 
 
 } }  // namespace v8::internal