tree: Fix up the DECL_VALUE_EXPR GC marking [PR118790]

tree: Fix up the DECL_VALUE_EXPR GC marking [PR118790]

The ggc_set_mark call in gt_value_expr_mark_2 is actually wrong, that
just marks the VAR_DECL itself, but doesn't mark the subtrees of it (type
etc.).  So, I think we need to test gcc_marked_p for whether it is marked
or not, if not marked walk the DECL_VALUE_EXPR and then gt_ggc_mx mark
the VAR_DECL that was determined not marked and needs to be marked now.
One option would be to call gt_ggc_mx (t) right after the DECL_VALUE_EXPR
walking, but I'm a little bit worried that the subtree marking could mark
other VAR_DECLs (e.g. seen from DECL_SIZE or TREE_TYPE and the like) and
if they would be DECL_HAS_VALUE_EXPR_P we might not walk their
DECL_VALUE_EXPR anymore later.
So, the patch defers the gt_ggc_mx calls until we've walked all the
DECL_VALUE_EXPRs directly or indirectly connected to already marked
VAR_DECLs.

2025-02-14  Jakub Jelinek  <jakub@redhat.com>

	PR debug/118790
	* tree.cc (struct gt_value_expr_mark_data): New type.
	(gt_value_expr_mark_2): Don't call ggc_set_mark, instead check
	ggc_marked_p.  Treat data as gt_value_expr_mark_data * with pset
	in it rather than address of the pset itself and push to be marked
	VAR_DECLs into to_mark vec.
	(gt_value_expr_mark_1): Change argument from hash_set<tree> *
	to gt_value_expr_mark_data * and find pset in it.
	(gt_value_expr_mark): Pass to traverse_noresize address of
	gt_value_expr_mark_data object rather than hash_table<tree> and
	for all entries in the to_mark vector after the traversal call
	gt_ggc_mx.