alloca and labels as values

[David Malcolm]

On Tue, 2018-12-18 at 08:12 +0100, Marc Nieper-Wißkirchen wrote:
> > > Is `alloca' currently  possible with libgccjit? I haven't found
> 
>  > > anything
>  > > about it in the documentation. If it isn't possible at the
> moment,
>  > > I'd
>  > > love to see it added to libgccjit very soon. (One use case would
> be
>  > > a
>  > > compiler like the Chicken Scheme compiler that employs Cheney-
> on-the-
>  > > MTA
>  > > where the youngest heap generation is allocated on the stack.)
>  >
>  > I haven't tested this, but I believe you ought to be able to
> access it
>  > via the "__builtin_alloca" builtin, via something like:
>  >
>  >
>  > gcc_jit_function *fn_alloca
>  >   = gcc_jit_context_get_builtin_function (ctxt,
> "__builtin_alloca");
>  >
>  >
>  > gcc_jit_rvalue *call =
>  >         gcc_jit_context_new_call (ctxt,
>  >                                   loc,
>  >                                   fn_alloc_a,
>  >                                   1, &size_t_arg);
>  >
>  >  gcc_jit_block_add_assignment (block, loc,
>  >                                dst_lvalue,
>  >                                call);
>  >
>  > ...or something like that.
> 
> 
> 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 <http://configure.ac>' myself?

I think you'd need a configure check.

> -- Marc
> 
> P.S.: Another thing I wasn't able to find so far was how to declare 
> variables as thread local (i.e. GCC's __thread or C11's
> thread_local).

There isn't currently a way to do thread local variables.  I suspect
that something like a variant of gcc_jit_context_new_global could do
it, e.g. "gcc_jit_context_new_thread_local" or somesuch.  Or maybe a
way to mark the result of gcc_jit_context_new_global as being thread-
local.

Dave