Re: [google]: initialize language field for clone function struct

["Joseph S. Myers" <joseph@codesourcery.com>]

On Tue, 3 May 2011, Eric Botcazou wrote:

> > In my view we should require front ends to take responsibility for
> > variable-size types, and get rid of this language-independent function
> > (copying such parts as are needed into the front ends that need them).
> 
> I don't really see the point here.  GCC supports variable-sized types in the 
> middle-end (stor-layout.c, gimplifier) so why special-casing this function?

In general errors from outside the front end, but relating to problems 
with the user's source code, are suspicious; the front end should detect 
invalid code, diagnose it and not pass it to the language-independent 
compiler.  And the exact language semantics regarding where variable-size 
types are permitted and when the sizes should be evaluated are inherently 
front-end-specific and not easily represented in a generic function.

convert.c is another place with errors that I think ought to go in the 
front ends; having some generic conversion logic is fine, but the front 
ends should deal with diagnosing invalid cases and convert.c should ICE if 
asked to do a conversion it doesn't know how to do.

> > C for example uses its own version as the language-independent one isn't
> > right for C.
> 
> The C version looks an almost exact duplicate of the generic one though.  We 
> should probably try to reconciliate the different versions.

C doesn't want the language-independent errors (see above); they don't 
reflect the right logic for C.  It needs to override parts of the generic 
function when called from generic code, and so to replace it when called 
from the front end.

C returns -1 from global_bindings_p, as does Ada.  That the languages that 
probably care most about variable-size types find aspects of the generic 
function need overriding like that should be a good indication that it 
isn't really that generic - as I said above, semantics for variable sizes 
are very front-end-specific.

-- 
Joseph S. Myers
joseph@codesourcery.com