Re: [PATCH] Fix PR66705

[Jan Hubicka <hubicka@ucw.cz>]

> 
> I was naiively using ->get_constructor in IPA PTA without proper
> checking on wheter that succeeds.  Now I tried to use ctor_for_folding
> but that isn't good as we want to analyze non-const globals in IPA
> PTA and we need to analyze their initialiers as well.
> 
> Thus I'm trying below with ctor_for_analysis, but I really "just"
> need the initializer or a "not available" for conservative handling.
> 
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
> 
> Honza - I suppose you should doble-check this and suggest sth
> different (or implement sth more generic in the IPA infrastructure).

Yep, you are correct that we don't currently have way to look into ctor
without actually loading. But do you need something more than just walking
references that you already have in ipa-ref lists?
> 
> Thanks,
> Richard.
> 
> 2015-09-02  Richard Biener  <rguenther@suse.de>
> 
> 	PR ipa/66705
> 	* tree-ssa-structalias.c (ctor_for_analysis): New function.
> 	(create_variable_info_for_1): Use ctor_for_analysis instead
> 	of get_constructor.
> 	(create_variable_info_for): Likewise.

Otherwise I would go for making ctor_for_analysis a method of varpool_node and...
> 
> 	* g++.dg/lto/pr66705_0.C: New testcase.
> 
> Index: gcc/tree-ssa-structalias.c
> ===================================================================
> --- gcc/tree-ssa-structalias.c	(revision 227207)
> +++ gcc/tree-ssa-structalias.c	(working copy)
> @@ -5637,6 +5637,26 @@ check_for_overlaps (vec<fieldoff_s> fiel
>    return false;
>  }
>  
> +/* We can't use ctor_for_folding as that only returns constant constructors.  */
> +
> +static tree
> +ctor_for_analysis (tree decl)
> +{
> +  varpool_node *node = varpool_node::get (decl);
> +  if (!node)
> +    return error_mark_node;
> +  node = node->ultimate_alias_target ();
> +  if (DECL_INITIAL (node->decl) != error_mark_node
> +      || !in_lto_p)
> +    return (DECL_INITIAL (node->decl)
> +	    ? DECL_INITIAL (node->decl) : error_mark_node);

I think returning NULL here is just fine. 
error_mark_node means constructor is not really available. NULL is
the usual way to say that the variable is not initialized.