Re: [Patch/cfgexpand]: also consider assembler_name to call expand_main_function

[Jan Hubicka <hubicka at ucw dot cz>]

> On Tue, 20 Mar 2012, Tristan Gingold wrote:
> 
> > 
> > On Mar 15, 2012, at 10:37 AM, Richard Guenther wrote:
> > 
> > > On Wed, 14 Mar 2012, Tristan Gingold wrote:
> > [?]
> > 
> > > 
> > > Well.  To make this work in LTO the "main" function (thus, the program
> > > entry point) should be marked at cgraph level and all users of
> > > MAIN_NAME_P should instead check a flag on the cgraph node.
> > > 
> > >> Will write a predicate in tree.[ch].
> > > 
> > > Please instead transition "main-ness" to the graph.

Yep, I also agree that it is something cgraph code should care about instead of
random placess across the whole middle-end.
> > diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
> > index bd21169..7a7a774 100644
> > --- a/gcc/cfgexpand.c
> > +++ b/gcc/cfgexpand.c
> > @@ -4513,9 +4513,8 @@ gimple_expand_cfg (void)
> >  
> >    /* If this function is `main', emit a call to `__main'
> >       to run global initializers, etc.  */
> > -  if (DECL_NAME (current_function_decl)
> > -      && MAIN_NAME_P (DECL_NAME (current_function_decl))
> > -      && DECL_FILE_SCOPE_P (current_function_decl))
> > +  if (DECL_FILE_SCOPE_P (current_function_decl)
> > +      && cgraph_main_function_p (cgraph_get_node (current_function_decl)))
> >      expand_main_function ();
> 
> The DECL_FILE_SCOPE_P check is redundant, please remove them everywhere
> you call cgraph_main_function_p.  I suppose returning false if the
> cgraph node is NULL in cgraph_main_function_p would be good.

How do we handle the cases before cgraph is built with this approach?
> > +/* Return true iff NODE is the main function (main in C).  */
> > +static inline bool
> > +cgraph_main_function_p (struct cgraph_node *node)
> > +{
> > +  return node->local.main_function;
> 
> node && node->local.main_function

Well, cgraph strategy is ito ICE when NODE is NULL :)
We could have cgraph_main_function_decl_p wrapper that does the NULL handling, but I still don't
see how this helps - i.e. when you don't have cgraph node you don't have info whether function
is main or not, so you should not even try to ask.
In what cases we ICE here?
> 
> > +}
> > +
> >  /* Walk all functions with body defined.  */
> >  #define FOR_EACH_FUNCTION_WITH_GIMPLE_BODY(node) \
> >     for ((node) = cgraph_first_function_with_gimple_body (); (node); \
> > diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
> > index 516f187..4a59f63 100644
> > --- a/gcc/cgraphunit.c
> > +++ b/gcc/cgraphunit.c
> > @@ -346,6 +346,10 @@ cgraph_finalize_function (tree decl, bool nested)
> >    notice_global_symbol (decl);
> >    node->local.finalized = true;
> >    node->lowered = DECL_STRUCT_FUNCTION (decl)->cfg != NULL;
> > +  node->local.main_function =
> > +    DECL_FILE_SCOPE_P (decl)
> > +    && ((!DECL_ASSEMBLER_NAME_SET_P (decl) && MAIN_NAME_P (DECL_NAME (decl)))
> > +	|| decl_assembler_name_equal (decl, main_identifier_node));
> 
> If we finalize a function we should always create an assembler name,
> thus I'd change the above to
> 
>   node->local.main_function = decl_assembler_name_equal (decl, 
> main_identifier_node);
> 
> btw, decl_assembler_name_equal doesn't seem to remove target-specific
> mangling - do some OSes "mangle" main differently (I'm thinking of
> leading underscores or complete renames)?  Thus, I guess the
> targets might want to be able to provide the main_identifier_assember_name
> you use here.

Yes, name function is mangled, i.e. it is _main on djgpp as long as I remember.
This is why we have the main_identifier_node to go through the mandling procedure.

Honza