Emit slightly more compact code in untag double.

Review URL: http://codereview.chromium.org/6677111

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7243 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/assembler.cc

@@ -67,6 +67,7 @@ namespace internal {
 const double DoubleConstant::min_int = kMinInt;
 const double DoubleConstant::one_half = 0.5;
 const double DoubleConstant::minus_zero = -0.0;
+const double DoubleConstant::nan = OS::nan_value();
 const double DoubleConstant::negative_infinity = -V8_INFINITY;
 const char* RelocInfo::kFillerCommentString = "DEOPTIMIZATION PADDING";
 
@@ -745,6 +746,12 @@ ExternalReference ExternalReference::address_of_negative_infinity() {
 }
 
 
+ExternalReference ExternalReference::address_of_nan() {
+  return ExternalReference(reinterpret_cast<void*>(
+      const_cast<double*>(&DoubleConstant::nan)));
+}
+
+
 #ifndef V8_INTERPRETED_REGEXP
 
 ExternalReference ExternalReference::re_check_stack_guard_state() {

src/assembler.h

@@ -53,6 +53,7 @@ class DoubleConstant: public AllStatic {
   static const double one_half;
   static const double minus_zero;
   static const double negative_infinity;
+  static const double nan;
 };
 
 
@@ -590,6 +591,7 @@ class ExternalReference BASE_EMBEDDED {
   static ExternalReference address_of_one_half();
   static ExternalReference address_of_minus_zero();
   static ExternalReference address_of_negative_infinity();
+  static ExternalReference address_of_nan();
 
   static ExternalReference math_sin_double_function();
   static ExternalReference math_cos_double_function();

src/ia32/lithium-codegen-ia32.cc

@@ -3276,10 +3276,8 @@ void LCodeGen::EmitNumberUntagD(Register input_reg,
   DeoptimizeIf(not_equal, env);
 
   // Convert undefined to NaN.
-  __ push(input_reg);
-  __ mov(input_reg, Factory::nan_value());
-  __ movdbl(result_reg, FieldOperand(input_reg, HeapNumber::kValueOffset));
-  __ pop(input_reg);
+  ExternalReference nan = ExternalReference::address_of_nan();
+  __ movdbl(result_reg, Operand::StaticVariable(nan));
   __ jmp(&done);
 
   // Heap number to XMM conversion.