Improvements for x87 stack handling

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index ad036871802b32b0ad9646e480fd43339444ce0f..a0d61add5d0f3b14f788fe42e2073e2297bb3739 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -3196,7 +3196,8 @@ class HConstant: public HTemplateInstruction<0> {
     }
     if (has_double_value_) {
       if (BitCast<int64_t>(double_value_) == BitCast<int64_t>(-0.0) ||
-          isnan(double_value_)) {
+          isnan(double_value_) ||
+          FixedDoubleArray::is_the_hole_nan(double_value_)) {
         return true;
       }
       return false;
@@ -3227,7 +3228,9 @@ class HConstant: public HTemplateInstruction<0> {
     return has_int32_value_;
   }
 
-  virtual bool EmitAtUses() { return !representation().IsDouble(); }
+  virtual bool EmitAtUses() {
+    return !representation().IsDouble() || ImmortalImmovable();

[danno, 2013/04/08 12:57:27]

Maybe it's better to factor our the special cases for doubles into another
predicate, like IsSpecialDouble() that is used both here and in
ImmortalImmovable.

[mvstanton, 2013/04/08 16:10:14]

I did this kind of refactoring but more in the methods ImmortalImmovable(), and
then below with the new IsTheHole() method. Does that correspond?

+  }
   virtual void PrintDataTo(StringStream* stream);
   virtual HType CalculateInferredType();
   bool IsInteger() { return handle()->IsSmi(); }
@@ -3246,6 +3249,10 @@ class HConstant: public HTemplateInstruction<0> {
     ASSERT(HasDoubleValue());
     return double_value_;
   }
+  bool IsDoubleCanonicalHole() const {
+    ASSERT(HasDoubleValue());
+    return FixedDoubleArray::is_the_hole_nan(double_value_);
+  }
   bool HasNumberValue() const { return has_double_value_; }
   int32_t NumberValueAsInteger32() const {
     ASSERT(HasNumberValue());
@@ -5677,6 +5684,11 @@ class HStoreKeyed
   bool IsDehoisted() { return is_dehoisted_; }
   void SetDehoisted(bool is_dehoisted) { is_dehoisted_ = is_dehoisted; }
 
+  bool IsConstantHoleStore() {
+    return value()->IsConstant() &&
+        HConstant::cast(value())->IsDoubleCanonicalHole();

[danno, 2013/04/08 12:57:27]

This predicate seems misleading... it checks only for the double canonical hold,
but not the real hole. Either rename the predicate or add support for testing
for the the_hole constant tagged value.

[mvstanton, 2013/04/08 16:10:14]

Done.

+  }
+
   virtual void SetSideEffectDominator(GVNFlag side_effect, HValue* dominator) {
     ASSERT(side_effect == kChangesNewSpacePromotion);
     new_space_dominator_ = dominator;