Bug 1114351 - Use mozilla::IsNaN() in DOUBLE_TO_JSVAL(); r=Waldo

Note that this requires making sure that IsNaN is constexpr because it
needs to be passed to the constexpr IMPL_TO_JSVALUE() function in
DOUBLE_TO_JSVAL().

--HG--
extra : amend_source : dbd8bb0659b53e7d36d2600ac97f0a753ef772c7

js/public/Value.h

@@ -1922,7 +1922,7 @@ DOUBLE_TO_JSVAL(double d)
      * because GCC from XCode 3.1.4 miscompiles the above code.
      */
 #if defined(JS_VALUE_IS_CONSTEXPR)
-    return IMPL_TO_JSVAL(MOZ_UNLIKELY(d != d)
+    return IMPL_TO_JSVAL(MOZ_UNLIKELY(mozilla::IsNaN(d))
                          ? (jsval_layout) { .asBits = 0x7FF8000000000000LL }
                          : (jsval_layout) { .asDouble = d });
 #else

mfbt/FloatingPoint.h

@@ -115,9 +115,9 @@ struct FloatingPoint : public SelectTrait<T>
   static_assert(sizeof(T) == sizeof(Bits), "Bits must be same size as T");
 };
 
-/** Determines whether a double is NaN. */
+/** Determines whether a float/double is NaN. */
 template<typename T>
-static MOZ_ALWAYS_INLINE bool
+static MOZ_ALWAYS_INLINE MOZ_CONSTEXPR bool
 IsNaN(T aValue)
 {
   /*
@@ -126,9 +126,8 @@ IsNaN(T aValue)
    */
   typedef FloatingPoint<T> Traits;
   typedef typename Traits::Bits Bits;
-  Bits bits = BitwiseCast<Bits>(aValue);
-  return (bits & Traits::kExponentBits) == Traits::kExponentBits &&
-         (bits & Traits::kSignificandBits) != 0;
+  return (BitwiseCast<Bits>(aValue) & Traits::kExponentBits) == Traits::kExponentBits &&
+         (BitwiseCast<Bits>(aValue) & Traits::kSignificandBits) != 0;
 }
 
 /** Determines whether a float/double is +Infinity or -Infinity. */