The FP-classification builtins (__builtin_isfinite, etc) use variadic
packs in the definition file to mean an overload set. Because of that,
floats were converted to doubles, which is incorrect. There WAS a patch
to remove the cast after the fact.
THis patch switches these builtins to just be custom type checking,
calls the implicit conversions for the integer members, and makes sure
the correct L->R casts are put into place, then does type checking like
normal.
A future direction (that wouldn't be NFC) would consider making
conversions for the floating point parameter legal.
Note: The initial patch for this missed that certain systems need to
still convert half to float, since they dont' support that type.
As brought up in D71467, a group of floating point builtins
automatically promoted floats to doubles because they used the variadic
builtin tag to support an overload set. The result is that the
parameters were treated as a variadic pack, which always promots
float->double.
This resulted in the wrong answer being given in cases with certain
values of NaN.
Erich Keane