[PATCH] Fix PR86321

[Richard Biener]

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)
;
...

OK for trunk?

Thanks,
Richard.

2018-06-28 Richard Biener <***@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);

[Dominique d'Humières]

The patch fixes PR86321 without regression.

Thanks,

Dominique

[Janne Blomqvist]

Post by Richard Biener
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)
;
...
OK for trunk?

Ok, thanks for the patch, and to Dominique for testing!