Re: [PATCH] Remove poly_int_pod

[Jason Merrill <jason@redhat.com>]

On 9/28/23 05:55, Richard Sandiford wrote:
> poly_int was written before the switch to C++11 and so couldn't
> use explicit default constructors.  This led to an awkward split
> between poly_int_pod and poly_int.  poly_int simply inherited from
> poly_int_pod and added constructors, with the argumentless constructor
> having an empty body.  But inheritance meant that poly_int had to
> repeat the assignment operators from poly_int_pod (again, no C++11,
> so no "using" to inherit base-class implementations).
> 
> All that goes away if we switch to using default constructors.
> 
> The main complication is ensuring that braced initialisation still
> gives a constexpr, so that static variables can be initialised without
> runtime code.  The two problems here are:
> 
> (1) When initialising a poly_int<N, wide_int> with fewer than N
>      coefficients, the other coefficients need to be a zero of
>      the same precision as the explicit coefficients.  This was
>      previously done in a for loop using wi::ints_for<...>::zero,
>      but C++11 constexpr constructors can't have function bodies.
>      The patch instead uses a series of delegated initialisers to
>      fill in the implicit coefficients.

Perhaps it's time to update the bootstrap requirement to C++14 (i.e. GCC 
5, from eight years ago).  Not that this would affect this particular patch.

Jason