On Wed, Aug 10, 2016 at 5:57 PM, Jason Merrill <jason@redhat.com> wrote:
> This patch implements the C++17 constexpr if feature.  The primary use
> is in templates, where the non-taken branch of the constexpr
> if-statement is not instantiated.  But it can also be used outside of
> templates, where the branches are parsed and discarded, and discarded
> return statements are not used for return type deduction.

...and the feature test macro.