On 3/18/22 17:55, Marek Polacek wrote:
On Fri, Mar 11, 2022 at 06:46:42PM -0500, Jason Merrill wrote:
On 3/10/22 18:04, Marek Polacek wrote:
Since r9-6073 cxx_eval_store_expression preevaluates the value to
be stored, and that revealed a crash where a template code (here,
code=IMPLICIT_CONV_EXPR) leaks into cxx_eval*.
It happens because we're performing build_vec_init while processing
a template
Hmm, that seems like the bug. Where's that call coming from?
From build_aggr_init. So we're handling e.g.
template<class>
constexpr void g () {
constexpr S s2[]{{'a'}};
}
cp_finish_decl (decl=s2, init={{'a'}}) sees we're in processing_template_decl,
but also that we have a constexpr var which is not dependent, nor is its
initializer:
else if (init
&& (init_const_expr_p || DECL_DECLARED_CONSTEXPR_P (decl))
&& !TYPE_REF_P (type)
&& decl_maybe_constant_var_p (decl)
&& !(dep_init = value_dependent_init_p (init)))
{
/* This variable seems to be a non-dependent constant, so process
its initializer. If check_initializer returns non-null the
initialization wasn't constant after all. */
tree init_code;
cleanups = make_tree_vector ();
init_code = check_initializer (decl, init, flags, &cleanups);
so we call check_initializer, where we go down this path:
init_code = build_aggr_init_full_exprs (decl, init, flags);
build_aggr_init sees that the type of 's2' is ARRAY_TYPE, so it calls
build_vec_init.
I now recall that we've discussed build_vec_init in a template in the
past, for example in the context of c++/93676. So I agree we ought to
make an effort to avoid calling build_vec_init in a template. Perhaps
like this: use an INIT_EXPR. With that, we should call build_vec_init
if needed while instantiating. Does that make any sense?
Hmm. If we do that, then we get back to
if (TREE_CODE (init_code) == INIT_EXPR)
in check_initializer, and pull out the same init again, and set
LOOKUP_ALREADY_DIGESTED. But I think that's wrong, we haven't digested
it yet.
Maybe we could avoid entering the below block of check_initializer at
all in this situation?
if (((type_build_ctor_call (type) || CLASS_TYPE_P (type))
&& !(flags & LOOKUP_ALREADY_DIGESTED)
&& !(init && BRACE_ENCLOSED_INITIALIZER_P (init)
&& CP_AGGREGATE_TYPE_P (type)
&& (CLASS_TYPE_P (type)
Maybe by adding || processing_template_decl here?
|| !TYPE_NEEDS_CONSTRUCTING (type)
|| type_has_extended_temps (type))))
|| (DECL_DECOMPOSITION_P (decl) && TREE_CODE (type) == ARRAY_TYPE))
Jason
