How can a front-end know what integer mode corresponds to int_fastN_t?

[Geoffrey Keating]

FX Coudert <fxcoudert@gmail.com> writes:

> Hi all,
> 
> For Fortran 2003 standard conformance, the Fortran front-end has to
> know at compile-time what integer mode corresponds to some C99 types,
> like intmax_t, intN_t, int_leastN_t, int_fastN_t.
> 
> For intN_t and int_leastN_t, I can see how to get them by looking at
> the width of the different integer modes. For intmax_t, it is defined
> in c-common.h as:
> 
> #define INTMAX_TYPE ((INT_TYPE_SIZE == LONG_LONG_TYPE_SIZE)     \
>                       ? "int"                                    \
>                       : ((LONG_TYPE_SIZE == LONG_LONG_TYPE_SIZE) \
>                          ? "long int"                            \
>                          : "long long int"))
> 
> But I cannot see how the front-end can know the integer mode for
> int_leastN_t. We're likely to include this functionality for the 4.3
> release, so I'll be happy to get a large number of suggestions around
> on how to implement that.

It's a property of the ABI on the target.  The only way to know is to
have someone (or something) tell you.  Even the macro above can be
redefined by a target.

One nice thing would be that if we actually had GCC know about all the
contents of stdint.h, then maybe GCC could provide it; we have a
policy that GCC provides all the headers of a freestanding
implementation, and this is the only one missing.