On Tue, 10 Aug 2021, Eric Botcazou wrote:
> > The question is whether we instead want to amend build3 to
> > set TREE_THIS_VOLATILE automatically when the FIELD_DECL has
> > it set. At least for the Fortran FE cases the gimplifier
> > fails to see some volatile references and thus can generate
> > wrong code which is a latent issue.
>
> What do we do for other similar flags, e.g. TREE_READONLY?
build3 currently does no special processing for the FIELD_DECL operand,
it just sets TREE_THIS_VOLATILE from operand zero for tcc_references.
The C and C++ frontends have repeated patterns like
ref = build3 (COMPONENT_REF, subtype, datum, subdatum,
NULL_TREE);
SET_EXPR_LOCATION (ref, loc);
if (TREE_READONLY (subdatum)
|| (use_datum_quals && TREE_READONLY (datum)))
TREE_READONLY (ref) = 1;
if (TREE_THIS_VOLATILE (subdatum)
|| (use_datum_quals && TREE_THIS_VOLATILE (datum)))
TREE_THIS_VOLATILE (ref) = 1;
Leaving out TREE_READONLY shouldn't have any correctness issue. It's
just that when adjusting the SSA operand scanner to correctly interpret
GENERIC that this uncovers pre-existing issues in the Fortran frontend
(one manifests in a testsuite FAIL - otherwise I wouldn't have noticed).
I'm fine with just plugging the Fortran FE holes as we discover them
but I did not check other frontends and testsuite coverage is weak.
Now - I wonder if there's a reason a frontend might _not_ want to
set TREE_THIS_VOLATILE on a COMPONENT_REF when the FIELD_DECL has
TREE_THIS_VOLATILE set.
I guess I'll do one more experiment and add verification that
TREE_THIS_VOLATILE on COMPONENT_REFs and FIELD_DECLs is consistent
and see where that trips.
Richard.
