[PATCH] Fix PR86321

[Richard Biener]

On Thu, 28 Jun 2018, Richard Biener wrote:

> 
> The fortran FE creates array descriptor types via build_distinct_type_copy
> which ends up re-using the TYPE_FIELDs chain of FIELD_DECLs between
> types in different type-variant chains.  While that seems harmless
> in practice it breaks once we try to generate C-like debug info for
> it because dwarf2out doesn't expect such sharing to occur (and I
> wouldn't be surprised of other odd behavior elsewhere that simply
> doesn't manifest in a as fatal way as PR86321).
> 
> We generate C-like debug info when you use LTO and -g0 at compile-time
> and -g at link-time (that's the way targets w/o debug-copy implementation
> end up wired).  For non-LTO we avoid directly generating debug for
> the array descriptor types by detecting them via a langhook.
> 
> The solution seems to be to adhere to the invariant that TYPE_FIELDs
> (and thus FIELD_DECL) sharing is only valid between variant types
> and their main variant.  Thus, copy the chain.
> 
> Bootstrap / regtest pending on x86_64-unknown-linux-gnu.
> 
> I suppose verify_type () could check proper ownership of the
> FIELD_DECLs (simply verify that DECL_CONTEXT is TYPE_MAIN_VARIANT).
> But I guess this may break in different ways.  Honza - did you
> originally try to verify that?  It currently says
> 
>       for (tree fld = TYPE_FIELDS (t); fld; fld = TREE_CHAIN (fld))
>         {
>           /* TODO: verify properties of decls.  */
>           if (TREE_CODE (fld) == FIELD_DECL)
>             ;
> ...

So at least for class Foo { enum Bar { BAZ }; }; the CONST_DECL for
BAZ appears in the TYPE_FIELDS for Foo and has DECL_CONTEXT Bar ...

Likely dwarf2out also has the following "hack" to deal with this:

gen_decl_die (tree decl, tree origin, struct vlr_context *ctx,
              dw_die_ref context_die)
{
...
    case CONST_DECL:
      if (!is_fortran () && !is_ada ())
        {
          /* The individual enumerators of an enum type get output when we 
output
             the Dwarf representation of the relevant enum type itself.  
*/
          break;
        }

Richard.

> 
> OK for trunk?
> 
> Thanks,
> Richard.
> 
> 2018-06-28  Richard Biener  <rguenther@suse.de>
> 
> 	fortran/
> 	PR lto/86321
> 	* trans-types.c (gfc_get_array_type_bounds): Unshare TYPE_FIELDs
> 	for the distinct type copy.
> 
> Index: gcc/fortran/trans-types.c
> ===================================================================
> --- gcc/fortran/trans-types.c	(revision 262132)
> +++ gcc/fortran/trans-types.c	(working copy)
> @@ -1923,6 +1923,14 @@ gfc_get_array_type_bounds (tree etype, i
>  
>    base_type = gfc_get_array_descriptor_base (dimen, codimen, restricted);
>    fat_type = build_distinct_type_copy (base_type);
> +  /* Unshare TYPE_FIELDs.  */
> +  for (tree *tp = &TYPE_FIELDS (fat_type); *tp; tp = &DECL_CHAIN (*tp))
> +    {
> +      tree next = DECL_CHAIN (*tp);
> +      *tp = copy_node (*tp);
> +      DECL_CONTEXT (*tp) = fat_type;
> +      DECL_CHAIN (*tp) = next;
> +    }
>    /* Make sure that nontarget and target array type have the same canonical
>       type (and same stub decl for debug info).  */
>    base_type = gfc_get_array_descriptor_base (dimen, codimen, false);
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)