Making __builtin_signbit type-generic

[FX <fxcoudert at gmail dot com>]

For use in both the Fortran front-end and in libgfortran, it would be really nice to have __builtin_signbit() be type-generic. It makes sense from the C point of view too, because itâs the only built-in from the C99 type-generic floating-point macros that is not type-generic.

So far, I have built a compiler with the trivial change attached (marking the built-in type-generic in gcc/builtins.def) on x86_64-apple-darwin14, where I can confirm that the built-in is correctly expanded (without function call) on all floating-point types. Is there something more to do (apart from adjusting the documentation)?


Joseph, Iâm CCâing you because of a 7-year old comment in PR 36757, where you said:

> It's necessary to avoid the type-generic signbit expanding to call a library
> function that may not exist, but as all currently supported floating-point
> formats do have a sign bit specified in signbit_ro I believe the case
> of failing to expand inline can be made into an abort.

I can confirm that even in 2015, the only format which has (signbit_ro < 0) is real_internal_format, which I think doesnât matter here. So: should I, in addition to the change in gcc/builtins.def, add some aborts() or sorry() in gcc/builtins.c if we canât expand (which should never happen)?


Thanks in advance for your help,
FX

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