c++: ICE with aggregate assignment and DMI [PR104583]

c++: ICE with aggregate assignment and DMI [PR104583]

The attached 93280 test no longer ICEs but looks like it was never added to the
testsuite.  The 104583 test, modified so that it closely resembles 93280, still
ICEs.

The problem is that in 104583 we have a value-init from {} (the line A a{};),
so this code in convert_like_internal

 7960         /* If we're initializing from {}, it's value-initialization.  */
 7961         if (BRACE_ENCLOSED_INITIALIZER_P (expr)
 7962             && CONSTRUCTOR_NELTS (expr) == 0
 7963             && TYPE_HAS_DEFAULT_CONSTRUCTOR (totype)
 7964             && !processing_template_decl)
 7965           {
 7966             bool direct = CONSTRUCTOR_IS_DIRECT_INIT (expr);
...
 7974                 TARGET_EXPR_DIRECT_INIT_P (expr) = direct;

sets TARGET_EXPR_DIRECT_INIT_P.  This does not happen in 93280 where we
initialize from {0}.

In 104583, when gimplifying, the d = {}; line, we have

d = {.a=TARGET_EXPR <D.2474, <<< Unknown tree: aggr_init_expr
  4
  __ct_comp
  D.2474
  (struct A *) <<< Unknown tree: void_cst >>> >>>>}

where the TARGET_EXPR is the one with TARGET_EXPR_DIRECT_INIT_P set.  In
gimplify_init_ctor_preeval we do

 4724       FOR_EACH_VEC_SAFE_ELT (v, ix, ce)
 4725         gimplify_init_ctor_preeval (&ce->value, pre_p, post_p, data);

so we gimplify the TARGET_EXPR, crashing at

 744     case TARGET_EXPR:
 745       /* A TARGET_EXPR that expresses direct-initialization should have
been
 746          elided by cp_gimplify_init_expr.  */
 747       gcc_checking_assert (!TARGET_EXPR_DIRECT_INIT_P (*expr_p));

but there is no INIT_EXPR so cp_gimplify_init_expr was never called!

Now, the fix for c++/93280
<https://gcc.gnu.org/pipermail/gcc-patches/2020-January/538414.html>
says "let's only set TARGET_EXPR_DIRECT_INIT_P when we're using the DMI in
a constructor." and the comment talks about the full initialization.  Is
is accurate to say that our TARGET_EXPR does not represent the full
initialization, because it only initializes the 'a' subobject?  If so,
then maybe get_nsdmi should clear TARGET_EXPR_DIRECT_INIT_P when in_ctor
is false.

I've compared the 93280.s and 104583.s files, they differ only in one
movl $0, so there are no extra calls and similar.

	PR c++/93280
	PR c++/104583

gcc/cp/ChangeLog:

	* init.cc (get_nsdmi): Set TARGET_EXPR_DIRECT_INIT_P to in_ctor.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/nsdmi-list7.C: New test.
	* g++.dg/cpp0x/nsdmi-list8.C: New test.