C: PR c/79412: Poison decls with error_mark_node after type mismatch
This patch fixes an ICE during error-recovery regression in the C front-end.
The symptom is that the middle-end's sanity checking assertions fail during
gimplification when being asked to increment an array, which is non-sense.
The issue is that the C-front end has detected the type mismatch and
reported an error to the user, but hasn't provided any indication of this
to the middle-end, simply passing bogus trees that the optimizers recognize
as invalid.
This appears to be a frequently reported ICE with 94730, 94731, 101036
and 101365 all marked as duplicates.
I believe the correct (polite) fix is to mark the mismatched types as
problematic/dubious in the front-end, when the error is spotted, so that
the middle-end has a heads-up and can be a little more forgiving. This
patch to c-decl.c's duplicate_decls sets (both) mismatched types to
error_mark_node if they are significantly different, and we've issued
an error message. Alas, this is too punitive for FUNCTION_DECLs where
we store return types, parameter lists, parameter types and attributes
in the type, but fortunately the middle-end is already more cautious
about trusting possibly suspect function types.
This fix required one minor change to the testsuite, typedef-var-2.c
where after conflicting type definitions, we now no longer assume that
the (first or) second definition is the correct one. This change only
affects the behaviour after seen_error(), so should be relatively safe.
2021-09-01 Roger Sayle <roger@nextmovesoftware.com>
Joseph Myers <joseph@codesourcery.com>
gcc/c/ChangeLog
PR c/79412
* c-decl.c (duplicate_decls): On significant mismatches, mark the
types of both (non-function) decls as error_mark_node, so that the
middle-end can see the code is malformed.
(free_attr_access_data): Don't process if the type has been set to
error_mark_node.
gcc/testsuite/ChangeLog
PR c/79412
* gcc.dg/pr79412.c: New test case.
* gcc.dg/typedef-var-2.c: Update expeted errors.