Re: alloca and labels as values

["Marc Nieper-Wißkirchen" <marc@nieper-wisskirchen.de>]

Am Di., 18. Dez. 2018 um 15:02 Uhr schrieb David Malcolm <dmalcolm@redhat.com>:

[...]

> On Tue, 2018-12-18 at 08:12 +0100, Marc Nieper-Wißkirchen wrote:
> > > > Is `alloca' currently  possible with libgccjit? I haven't found

[...]

> >  > I haven't tested this, but I believe you ought to be able to
> > access it
> >  > via the "__builtin_alloca" builtin, via something like:

[...]

> > That was helpful; thank you very much. I overlooked the procedure
> > `gcc_jit_context_get_builtin_function' in the documentation. Is there
> > a
> > way to determine which builtins are supported by a specific version
> > of
> > the library or would I have to add a few scripts to my project's
> > `configure.ac' myself?
>
> I think you'd need a configure check.

[...]

Having thought about it once more I think the configure check I asked
about makes no sense. Configure can tell me the available builtins of
the host compiler but nothing about the available builtins of the
target system that eventually runs libgccjit (if we don't want to give
up the option of cross-compiling).

What we need, I think, is that <libgccjit.h> exports a number of
macros that define the

Thus we need that libgccjit's header defines a number of macros that
define the capabilities of the GCC embedded in libgccjit.so.

Concretely, source code that uses libgccjit can test the feature macro
__GNUC__. This, however, returns the GCC version of the build system.
What is missing is another macro like GCC_JIT_GNUC that is defined in
<libgccjit.h> and returns the GCC version of the libgccjit library.

It may also be worth to reflect some macros from
https://gcc.gnu.org/onlinedocs/gccint/Target-Macros.html as
GCC_JIT_XXX macros in <libgccjit.h>.

-- Marc