[PATCH v4] c++: ICE with temporary of class type in DMI [PR100252]

[Marek Polacek <polacek@redhat.com>]

On Sat, May 07, 2022 at 06:02:13PM -0400, Jason Merrill wrote:
> On 5/7/22 15:11, Marek Polacek wrote:
> > On Tue, May 03, 2022 at 04:59:38PM -0400, Jason Merrill wrote:
> > > Does this testcase still work with this patch?
> > > 
> > > struct A {
> > >    const A* p = this;
> > > };
> > > 
> > > struct B {
> > >    A a = A{};
> > > };
> > > 
> > > constexpr B b;
> > > static_assert (b.a.p == &b.a);
> > 
> > Ouch, no.  Thanks for catching this, it would have been very unpleasant
> > to hit this problem later...
> > 
> > The reason your testcase was rejected is that replacing a PLACEHOLDER
> > in the outermost TARGET_EXPR broke guaranteed copy elision.  Now that
> > I've spent another day on this, I still think we have to replace the
> > placeholders created when temporary materialization takes place in an
> > NSDMI, but it must happen in digest_nsdmi_init (as Patrick suggested),
> > where we can see the full initializer.  That way I can avoid breaking
> > copy elision.
> > 
> > I've added a bunch of new testcases and updated the
> > (already long) description.  The yuge comment hopefully also explains
> > how this problem is avoided.  Thanks again,
> > 
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > 
> > -- >8 --
> > Consider
> > 
> >    struct A {
> >      int x;
> >      int y = x;
> >    };
> > 
> >    struct B {
> >      int x = 0;
> >      int y = A{x}.y; // #1
> >    };
> > 
> > where for #1 we end up with
> > 
> >    {.x=(&<PLACEHOLDER_EXPR struct B>)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}
> > 
> > that is, two PLACEHOLDER_EXPRs for different types on the same level in
> > a {}.  This crashes because our CONSTRUCTOR_PLACEHOLDER_BOUNDARY mechanism to
> > avoid replacing unrelated PLACEHOLDER_EXPRs cannot deal with it.
> > 
> > Here's why we wound up with those PLACEHOLDER_EXPRs: When we're performing
> > cp_parser_late_parsing_nsdmi for "int y = A{x}.y;" we use finish_compound_literal
> > on type=A, compound_literal={((struct B *) this)->x}.  When digesting this
> > initializer, we call get_nsdmi which creates a PLACEHOLDER_EXPR for A -- we don't
> > have any object to refer to yet.  After digesting, we have
> > 
> >    {.x=((struct B *) this)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}
> > 
> > and since we've created a PLACEHOLDER_EXPR inside it, we marked the whole ctor
> > CONSTRUCTOR_PLACEHOLDER_BOUNDARY.  f_c_l creates a TARGET_EXPR and returns
> > 
> >    TARGET_EXPR <D.2384, {.x=((struct B *) this)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}>
> > 
> > Then we get to
> > 
> >    B b = {};
> > 
> > and call store_init_value, which digests the {}, which produces
> > 
> >    {.x=NON_LVALUE_EXPR <0>, .y=(TARGET_EXPR <D.2395, {.x=(&<PLACEHOLDER_EXPR struct B>)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}>).y}
> > 
> > lookup_placeholder in constexpr won't find an object to replace the
> > PLACEHOLDER_EXPR for B, because ctx->object will be D.2395 of type A, and we
> > cannot search outward from D.2395 to find 'b'.
> > 
> > The call to replace_placeholders in store_init_value will not do anything:
> > we've marked the inner { } CONSTRUCTOR_PLACEHOLDER_BOUNDARY, and it's only
> > a sub-expression, so replace_placeholders does nothing, so the <P_E struct B>
> > stays even though now is the perfect time to replace it because we have an
> > object for it: 'b'.
> > 
> > Later, in cp_gimplify_init_expr the *expr_p is
> > 
> >    D.2395 = {.x=(&<PLACEHOLDER_EXPR struct B>)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}
> > 
> > where D.2395 is of type A, but we crash because we hit <P_E struct B>, which
> > has a different type.
> > 
> > My idea was to replace <P_E struct A> with D.2384 after creating the
> > TARGET_EXPR because that means we have an object we can refer to.
> > Then clear CONSTRUCTOR_PLACEHOLDER_BOUNDARY because we no longer have
> > a PLACEHOLDER_EXPR in the {}.  Then store_init_value will be able to
> > replace <P_E struct B> with 'b', and we should be good to go.  We must
> > be careful not to break guaranteed copy elision, so this replacement
> > happens in digest_nsdmi_init where we can see the whole initializer,
> > and avoid replacing any placeholders in the outermost TARGET_EXPR.
> > 
> > 	PR c++/100252
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* typeck2.cc (replace_placeholders_for_class_temp_r): New.
> > 	(digest_nsdmi_init): Call it.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	* g++.dg/cpp1y/nsdmi-aggr14.C: New test.
> > 	* g++.dg/cpp1y/nsdmi-aggr15.C: New test.
> > 	* g++.dg/cpp1y/nsdmi-aggr16.C: New test.
> > 	* g++.dg/cpp1y/nsdmi-aggr17.C: New test.
> > 	* g++.dg/cpp1y/nsdmi-aggr18.C: New test.
> > ---
> >   gcc/cp/typeck2.cc                         | 54 +++++++++++++++++++++++
> >   gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr14.C | 46 +++++++++++++++++++
> >   gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr15.C | 29 ++++++++++++
> >   gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C | 19 ++++++++
> >   gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C | 47 ++++++++++++++++++++
> >   gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr18.C | 25 +++++++++++
> >   6 files changed, 220 insertions(+)
> >   create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr14.C
> >   create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr15.C
> >   create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C
> >   create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C
> >   create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr18.C
> > 
> > diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
> > index 63d95c1529a..72d7cfaf1d3 100644
> > --- a/gcc/cp/typeck2.cc
> > +++ b/gcc/cp/typeck2.cc
> > @@ -1371,6 +1371,34 @@ digest_init_flags (tree type, tree init, int flags, tsubst_flags_t complain)
> >     return digest_init_r (type, init, 0, flags, complain);
> >   }
> > +/* Callback to replace PLACEHOLDER_EXPRs in a TARGET_EXPR (which isn't used
> > +   in the context of guaranteed copy elision).  */
> > +
> > +static tree
> > +replace_placeholders_for_class_temp_r (tree *tp, int *walk_subtrees, void *data)
> > +{
> > +  tree t = *tp;
> > +  tree full_expr = *static_cast<tree *>(data);
> > +
> > +  /* We're looking for a TARGET_EXPR nested in the whole expression.  */
> > +  if (TREE_CODE (t) == TARGET_EXPR && t != full_expr)
> 
> Just comparing to full_expr doesn't seem enough to catch all the cases where
> a prvalue is used as an initializer rather than for temporary
> materialization; you will also need to handle comma and conditional
> expressions.  And probably PAREN_EXPR.
> 
> I'm failing to find a term for this in the standard; "potential result" also
> includes objects that the result is an xvalue subobject of (as in #1 below).
> Maybe "potential prvalue result", to exclude the xvalue cases?  So,
> 
> && !potential_prvalue_result_of (t, full_expr)
> 
> ?

Thanks, the previous version indeed did have problems when ?: or , was used.
I've greatly enhanced the tests to detect more cases, and added
potential_prvalue_result_of.

While looking into this, I found PR105550, which turned out to be a big
can of worms.  So, XFAIL for now.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

-- >8 --
Consider

  struct A {
    int x;
    int y = x;
  };

  struct B {
    int x = 0;
    int y = A{x}.y; // #1
  };

where for #1 we end up with

  {.x=(&<PLACEHOLDER_EXPR struct B>)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}

that is, two PLACEHOLDER_EXPRs for different types on the same level in
a {}.  This crashes because our CONSTRUCTOR_PLACEHOLDER_BOUNDARY mechanism to
avoid replacing unrelated PLACEHOLDER_EXPRs cannot deal with it.

Here's why we wound up with those PLACEHOLDER_EXPRs: When we're performing
cp_parser_late_parsing_nsdmi for "int y = A{x}.y;" we use finish_compound_literal
on type=A, compound_literal={((struct B *) this)->x}.  When digesting this
initializer, we call get_nsdmi which creates a PLACEHOLDER_EXPR for A -- we don't
have any object to refer to yet.  After digesting, we have

  {.x=((struct B *) this)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}

and since we've created a PLACEHOLDER_EXPR inside it, we marked the whole ctor
CONSTRUCTOR_PLACEHOLDER_BOUNDARY.  f_c_l creates a TARGET_EXPR and returns

  TARGET_EXPR <D.2384, {.x=((struct B *) this)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}>

Then we get to

  B b = {};

and call store_init_value, which digests the {}, which produces

  {.x=NON_LVALUE_EXPR <0>, .y=(TARGET_EXPR <D.2395, {.x=(&<PLACEHOLDER_EXPR struct B>)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}>).y}

lookup_placeholder in constexpr won't find an object to replace the
PLACEHOLDER_EXPR for B, because ctx->object will be D.2395 of type A, and we
cannot search outward from D.2395 to find 'b'.

The call to replace_placeholders in store_init_value will not do anything:
we've marked the inner { } CONSTRUCTOR_PLACEHOLDER_BOUNDARY, and it's only
a sub-expression, so replace_placeholders does nothing, so the <P_E struct B>
stays even though now is the perfect time to replace it because we have an
object for it: 'b'.

Later, in cp_gimplify_init_expr the *expr_p is

  D.2395 = {.x=(&<PLACEHOLDER_EXPR struct B>)->x, .y=(&<PLACEHOLDER_EXPR struct A>)->x}

where D.2395 is of type A, but we crash because we hit <P_E struct B>, which
has a different type.

My idea was to replace <P_E struct A> with D.2384 after creating the
TARGET_EXPR because that means we have an object we can refer to.
Then clear CONSTRUCTOR_PLACEHOLDER_BOUNDARY because we no longer have
a PLACEHOLDER_EXPR in the {}.  Then store_init_value will be able to
replace <P_E struct B> with 'b', and we should be good to go.  We must
be careful not to break guaranteed copy elision, so this replacement
happens in digest_nsdmi_init where we can see the whole initializer,
and avoid replacing any placeholders in TARGET_EXPRs used in the context
of initialization/copy elision.  This is achieved via the new function
called potential_prvalue_result_of.

While fixing this problem, I found PR105550, thus the FIXMEs in the
tests.

	PR c++/100252

gcc/cp/ChangeLog:

	* typeck2.cc (potential_prvalue_result_of): New.
	(replace_placeholders_for_class_temp_r): New.
	(digest_nsdmi_init): Call it.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/nsdmi-aggr14.C: New test.
	* g++.dg/cpp1y/nsdmi-aggr15.C: New test.
	* g++.dg/cpp1y/nsdmi-aggr16.C: New test.
	* g++.dg/cpp1y/nsdmi-aggr17.C: New test.
	* g++.dg/cpp1y/nsdmi-aggr18.C: New test.
	* g++.dg/cpp1y/nsdmi-aggr19.C: New test.
---
 gcc/cp/typeck2.cc                         |  90 ++++++++++++++
 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr14.C | 131 ++++++++++++++++++++
 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr15.C |  80 +++++++++++++
 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C |  58 +++++++++
 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C | 138 ++++++++++++++++++++++
 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr18.C |  56 +++++++++
 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr19.C |  28 +++++
 7 files changed, 581 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr14.C
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr15.C
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr18.C
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr19.C

diff --git a/gcc/cp/typeck2.cc b/gcc/cp/typeck2.cc
index 1d92310edd0..f60e1df4c27 100644
--- a/gcc/cp/typeck2.cc
+++ b/gcc/cp/typeck2.cc
@@ -1371,6 +1371,70 @@ digest_init_flags (tree type, tree init, int flags, tsubst_flags_t complain)
   return digest_init_r (type, init, 0, flags, complain);
 }
 
+/* Return true if a prvalue is used as an initializer rather than for
+   temporary materialization.  For instance:
+
+     A a = A{};		      // initializer
+     A a = (A{});	      // initializer
+     A a = (1, A{});	      // initializer
+     A a = true ? A{} : A{};  // initializer
+     auto x = A{}.x;	      // temporary materialization
+     auto x = foo(A{});	      // temporary materialization
+
+   FULL_EXPR is the whole expression, SUBOB is its TARGET_EXPR subobject.  */
+
+static bool
+potential_prvalue_result_of (tree subob, tree full_expr)
+{
+  if (subob == full_expr)
+    return true;
+  else if (TREE_CODE (full_expr) == TARGET_EXPR)
+    {
+      tree init = TARGET_EXPR_INITIAL (full_expr);
+      if (TREE_CODE (init) == COND_EXPR)
+	return (potential_prvalue_result_of (subob, TREE_OPERAND (init, 1))
+		|| potential_prvalue_result_of (subob, TREE_OPERAND (init, 2)));
+      else if (TREE_CODE (init) == COMPOUND_EXPR)
+	return (potential_prvalue_result_of (subob, TREE_OPERAND (init, 0))
+		|| potential_prvalue_result_of (subob, TREE_OPERAND (init, 1)));
+      /* ??? I don't know if this can be hit.  If so, look inside the ( )
+	 instead of the assert.  */
+      else if (TREE_CODE (init) == PAREN_EXPR)
+	gcc_checking_assert (false);
+    }
+  return false;
+}
+
+/* Callback to replace PLACEHOLDER_EXPRs in a TARGET_EXPR (which isn't used
+   in the context of guaranteed copy elision).  */
+
+static tree
+replace_placeholders_for_class_temp_r (tree *tp, int *, void *data)
+{
+  tree t = *tp;
+  tree full_expr = *static_cast<tree *>(data);
+
+  /* We're looking for a TARGET_EXPR nested in the whole expression.  */
+  if (TREE_CODE (t) == TARGET_EXPR
+      && !potential_prvalue_result_of (t, full_expr))
+    {
+      tree init = TARGET_EXPR_INITIAL (t);
+      while (TREE_CODE (init) == COMPOUND_EXPR)
+	init = TREE_OPERAND (init, 1);
+      if (TREE_CODE (init) == CONSTRUCTOR
+	  && CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init))
+	{
+	  tree obj = TARGET_EXPR_SLOT (t);
+	  replace_placeholders (init, obj);
+	  /* We should have dealt with all PLACEHOLDER_EXPRs.  */
+	  CONSTRUCTOR_PLACEHOLDER_BOUNDARY (init) = false;
+	  gcc_checking_assert (!find_placeholders (init));
+	}
+    }
+
+  return NULL_TREE;
+}
+
 /* Process the initializer INIT for an NSDMI DECL (a FIELD_DECL).  */
 tree
 digest_nsdmi_init (tree decl, tree init, tsubst_flags_t complain)
@@ -1390,6 +1454,32 @@ digest_nsdmi_init (tree decl, tree init, tsubst_flags_t complain)
       && CP_AGGREGATE_TYPE_P (type))
     init = reshape_init (type, init, complain);
   init = digest_init_flags (type, init, flags, complain);
+
+  /* We may have temporary materialization in a NSDMI, if the initializer
+     has something like A{} in it.  Digesting the {} could have introduced
+     a PLACEHOLDER_EXPR referring to A.  Now that we've got a TARGET_EXPR,
+     we have an object we can refer to.  The reason we bother doing this
+     here is for code like
+
+       struct A {
+	 int x;
+	 int y = x;
+       };
+
+       struct B {
+	 int x = 0;
+	 int y = A{x}.y; // #1
+       };
+
+     where in #1 we don't want to end up with two PLACEHOLDER_EXPRs for
+     different types on the same level in a {} when lookup_placeholder
+     wouldn't find a named object for the PLACEHOLDER_EXPR for A.  Note,
+     temporary materialization does not occur when initializing an object
+     from a prvalue of the same type, therefore we must not replace the
+     placeholder with a temporary object so that it can be elided.  */
+  cp_walk_tree (&init, replace_placeholders_for_class_temp_r, &init,
+		nullptr);
+
   return init;
 }
 \f
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr14.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr14.C
new file mode 100644
index 00000000000..28b908a0a1a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr14.C
@@ -0,0 +1,131 @@
+// PR c++/100252
+// { dg-do run { target c++14 } }
+
+#define SA(X) static_assert ((X),#X)
+
+struct A {
+  int x;
+  int y = x;
+};
+
+struct B {
+  int x = 0;
+  int y = A{x}.y;
+};
+
+constexpr B csb1 = { };
+SA(csb1.x == 0 && csb1.y == csb1.x);
+constexpr B csb2 = { 1 };
+SA(csb2.x == 1 && csb2.y == csb2.x);
+constexpr B csb3 = { 1, 2 };
+SA(csb3.x == 1 && csb3.y == 2);
+
+B sb1 = { };
+B sb2 = { 1 };
+B sb3 = { 1, 2};
+
+struct C {
+  int x = 0;
+  int y = (true, A{x}.y) + (A{x}.y, 0);
+};
+
+constexpr C csc1 = { };
+SA(csc1.x == 0 && csc1.y == csc1.x);
+constexpr C csc2 = { 1 };
+SA(csc2.x == 1 && csc2.y == csc2.x);
+constexpr C csc3 = { 1, 2 };
+SA(csc3.x == 1 && csc3.y == 2);
+
+C sc1 = { };
+C sc2 = { 1 };
+C sc3 = { 1, 2};
+
+struct D {
+  int x = 0;
+  int y = (A{x}.y);
+};
+
+constexpr D csd1 = { };
+SA(csd1.x == 0 && csd1.y == csd1.x);
+constexpr D csd2 = { 1 };
+SA(csd2.x == 1 && csd2.y == csd2.x);
+constexpr D csd3 = { 1, 2 };
+SA(csd3.x == 1 && csd3.y == 2);
+
+D sd1 = { };
+D sd2 = { 1 };
+D sd3 = { 1, 2};
+
+struct E {
+  int x = 0;
+  int y = x ? A{x}.y : A{x}.y;
+};
+
+constexpr E cse1 = { };
+SA(cse1.x == 0 && cse1.y == cse1.x);
+constexpr E cse2 = { 1 };
+SA(cse2.x == 1 && cse2.y == cse2.x);
+constexpr E cse3 = { 1, 2 };
+SA(cse3.x == 1 && cse3.y == 2);
+
+E se1 = { };
+E se2 = { 1 };
+E se3 = { 1, 2};
+
+int
+main ()
+{
+  if (sb1.x != 0 || sb1.x != sb1.y)
+    __builtin_abort();
+  if (sb2.x != 1 || sb2.x != sb2.y)
+    __builtin_abort();
+  if (sb3.x != 1 || sb3.y != 2)
+    __builtin_abort();
+
+  if (sc1.x != 0 || sc1.x != sc1.y)
+    __builtin_abort();
+  if (sc2.x != 1 || sc2.x != sc2.y)
+    __builtin_abort();
+  if (sc3.x != 1 || sc3.y != 2)
+    __builtin_abort();
+
+  B b1 = { };
+  B b2 = { 1 };
+  B b3 = { 1, 2};
+  if (b1.x != 0 || b1.x != b1.y)
+    __builtin_abort();
+  if (b2.x != 1 || b2.x != b2.y)
+    __builtin_abort();
+  if (b3.x != 1 || b3.y != 2)
+    __builtin_abort();
+
+  C c1 = { };
+  C c2 = { 1 };
+  C c3 = { 1, 2};
+  if (c1.x != 0 || c1.x != c1.y)
+    __builtin_abort();
+  if (c2.x != 1 || c2.x != c2.y)
+    __builtin_abort();
+  if (c3.x != 1 || c3.y != 2)
+    __builtin_abort();
+
+  D d1 = { };
+  D d2 = { 1 };
+  D d3 = { 1, 2};
+  if (d1.x != 0 || d1.x != d1.y)
+    __builtin_abort();
+  if (d2.x != 1 || d2.x != d2.y)
+    __builtin_abort();
+  if (d3.x != 1 || d3.y != 2)
+    __builtin_abort();
+
+  E e1 = { };
+  E e2 = { 1 };
+  E e3 = { 1, 2};
+  if (e1.x != 0 || e1.x != e1.y)
+    __builtin_abort();
+  if (e2.x != 1 || e2.x != e2.y)
+    __builtin_abort();
+  if (e3.x != 1 || e3.y != 2)
+    __builtin_abort();
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr15.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr15.C
new file mode 100644
index 00000000000..d091d693042
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr15.C
@@ -0,0 +1,80 @@
+// PR c++/100252
+// { dg-do run { target c++14 } }
+
+struct A {
+  int x;
+  int y = x;
+};
+
+struct B {
+  int x = 0;
+  int y = A{x}.y;
+};
+
+static void
+test_b (B b1 = B{}, B b2 = B{1}, B b3 = B{1, 2})
+{
+  if (b1.x != 0 || b1.y != b1.x)
+    __builtin_abort();
+  if (b2.x != 1 || b2.y != b2.x)
+    __builtin_abort();
+  if (b3.x != 1 || b3.y != 2)
+    __builtin_abort();
+}
+
+struct C {
+  int x = 0;
+  int y = (true, A{x}.y) + (A{x}.y, 0);
+};
+
+static void
+test_c (C c1 = C{}, C c2 = C{1}, C c3 = C{1, 2})
+{
+  if (c1.x != 0 || c1.y != c1.x)
+    __builtin_abort();
+  if (c2.x != 1 || c2.y != c2.x)
+    __builtin_abort();
+  if (c3.x != 1 || c3.y != 2)
+    __builtin_abort();
+}
+
+struct D {
+  int x = 0;
+  int y = (A{x}.y);
+};
+
+static void
+test_d (D d1 = D{}, D d2 = D{1}, D d3 = D{1, 2})
+{
+  if (d1.x != 0 || d1.y != d1.x)
+    __builtin_abort();
+  if (d2.x != 1 || d2.y != d2.x)
+    __builtin_abort();
+  if (d3.x != 1 || d3.y != 2)
+    __builtin_abort();
+}
+
+struct E {
+  int x = 0;
+  int y = x ? A{x}.y : A{x}.y;
+};
+
+static void
+test_e (E e1 = E{}, E e2 = E{1}, E e3 = E{1, 2})
+{
+  if (e1.x != 0 || e1.y != e1.x)
+    __builtin_abort();
+  if (e2.x != 1 || e2.y != e2.x)
+    __builtin_abort();
+  if (e3.x != 1 || e3.y != 2)
+    __builtin_abort();
+}
+
+int
+main ()
+{
+  test_b ();
+  test_c ();
+  test_d ();
+  test_e ();
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C
new file mode 100644
index 00000000000..dc6492c1b0b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr16.C
@@ -0,0 +1,58 @@
+// PR c++/100252
+// { dg-do compile { target c++14 } }
+
+#define SA(X) static_assert ((X),#X)
+
+struct A {
+  const A* p = this;
+};
+
+struct B {
+  A a = A{};
+};
+
+constexpr B b;
+SA(b.a.p == &b.a);
+B b1 = { };
+
+struct C {
+  A a = (true, A{});
+};
+
+constexpr C c;
+SA(c.a.p == &c.a);
+C c1 = { };
+
+struct D {
+  A a = (A{});
+};
+
+constexpr D d;
+SA(d.a.p == &d.a);
+D d1 = { };
+
+static constexpr A global_a;
+
+struct E {
+  A a = true ? A{} : A{};
+  A b = true ? global_a : (false ? A{} : A{});
+  A c = true ? (false ? A{} : A{}) : global_a;
+  A d = true ? (false ? A{} : A{}) : (false ? A{} : A{});
+};
+
+// FIXME: When fixing this, also fix nsdmi-aggr17.C.
+constexpr E e;	    // { dg-bogus "" "PR105550" { xfail *-*-* } }
+SA (e.a.p == &e.a); // { dg-bogus "" "PR105550" { xfail *-*-* } }
+
+E e1 = { };
+
+struct F {
+  bool b = (A{}, true);
+};
+
+constexpr F f;
+
+void
+g (B b2 = B{}, C c2 = C{}, D d2 = D{}, E e2 = E{})
+{
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C
new file mode 100644
index 00000000000..fc27a2cdac7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr17.C
@@ -0,0 +1,138 @@
+// PR c++/100252
+// { dg-do run { target c++14 } }
+
+#define SA(X) static_assert ((X),#X)
+
+struct A {
+  int x;
+  int y = x;
+  const A* p = this;
+};
+
+struct B {
+  int x = 42;
+  A a = A{x};
+};
+
+constexpr B b;
+SA(b.a.p == &b.a);
+SA(b.x == 42);
+B b2 = { };
+B b3 = { 42 };
+
+struct C {
+  int x = 42;
+  B b = B{x};
+};
+
+constexpr C c;
+C c2;
+C c3;
+
+struct D {
+  int x = 42;
+  A a = (true, A{x});
+};
+
+constexpr D d;
+SA(d.a.p == &d.a);
+SA(d.x == 42);
+D d2 = { };
+D d3 = { 42 };
+
+struct E {
+  int x = 42;
+  A a = (A{x});
+};
+
+constexpr E e;
+SA(e.a.p == &e.a);
+SA(e.x == 42);
+E e2 = { };
+E e3 = { 42 };
+
+struct F {
+  int x = 42;
+  A a = true ? A{x} : A{x};
+};
+
+// FIXME: Doesn't work due to PR105550.
+//constexpr F f;
+//SA (f.a.p == &f.a);
+SA (e.x == 42);
+F f2 = { };
+F f3 = { 42 };
+
+static void
+test_b (B b4 = B{}, B b5 = B{ 42 })
+{
+  if (b2.x != 42 || b2.a.x != 42 || b2.a.y != b2.a.x)
+    __builtin_abort ();
+  if (b3.x != 42 || b3.a.x != 42 || b3.a.y != b3.a.x)
+    __builtin_abort ();
+  if (b4.x != 42 || b4.a.x != 42 || b4.a.y != b4.a.x)
+    __builtin_abort ();
+  if (b5.x != 42 || b5.a.x != 42 || b5.a.y != b5.a.x)
+    __builtin_abort ();
+}
+
+static void
+test_c (C c4 = C{}, C c5 = C{ 42 })
+{
+  if (c2.b.x != 42 || c2.b.a.x != 42 || c2.b.a.y != c2.b.a.x)
+    __builtin_abort ();
+  if (c3.b.x != 42 || c3.b.a.x != 42 || c3.b.a.y != c3.b.a.x)
+    __builtin_abort ();
+  if (c4.b.x != 42 || c4.b.a.x != 42 || c4.b.a.y != c4.b.a.x)
+    __builtin_abort ();
+  if (c5.b.x != 42 || c5.b.a.x != 42 || c5.b.a.y != c5.b.a.x)
+    __builtin_abort ();
+}
+
+static void
+test_d (D d4 = D{}, D d5 = D{ 42 })
+{
+  if (d2.x != 42 || d2.a.x != 42 || d2.a.y != d2.a.x)
+    __builtin_abort ();
+  if (d3.x != 42 || d3.a.x != 42 || d3.a.y != d3.a.x)
+    __builtin_abort ();
+  if (d4.x != 42 || d4.a.x != 42 || d4.a.y != d4.a.x)
+    __builtin_abort ();
+  if (d5.x != 42 || d5.a.x != 42 || d5.a.y != d5.a.x)
+    __builtin_abort ();
+}
+
+static void
+test_e (E e4 = E{}, E e5 = E{ 42 })
+{
+  if (e2.x != 42 || e2.a.x != 42 || e2.a.y != e2.a.x)
+    __builtin_abort ();
+  if (e3.x != 42 || e3.a.x != 42 || e3.a.y != e3.a.x)
+    __builtin_abort ();
+  if (e4.x != 42 || e4.a.x != 42 || e4.a.y != e4.a.x)
+    __builtin_abort ();
+  if (e5.x != 42 || e5.a.x != 42 || e5.a.y != e5.a.x)
+    __builtin_abort ();
+}
+
+static void
+test_f (F f4 = F{}, F f5 = F{ 42 })
+{
+  if (f2.x != 42 || f2.a.x != 42 || f2.a.y != f2.a.x)
+    __builtin_abort ();
+  if (f3.x != 42 || f3.a.x != 42 || f3.a.y != f3.a.x)
+    __builtin_abort ();
+  if (f4.x != 42 || f4.a.x != 42 || f4.a.y != f4.a.x)
+    __builtin_abort ();
+  if (f5.x != 42 || f5.a.x != 42 || f5.a.y != f5.a.x)
+    __builtin_abort ();
+}
+int
+main ()
+{
+  test_b ();
+  test_c ();
+  test_d ();
+  test_e ();
+  test_f ();
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr18.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr18.C
new file mode 100644
index 00000000000..567b8ee96d9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr18.C
@@ -0,0 +1,56 @@
+// PR c++/100252
+// { dg-do compile { target c++14 } }
+
+struct B { };
+
+struct A {
+  int x;
+  int y = x;
+  constexpr operator B() { return B{}; }
+};
+
+struct C {
+  int x = 42;
+  B b = A{x};
+};
+
+C c1 = {};
+C c2 = { 42 };
+constexpr C c3 = {};
+constexpr C c4 = { 42 };
+
+struct D {
+  int x = 42;
+  B b = (true, A{x});
+};
+
+D d1 = {};
+D d2 = { 42 };
+constexpr D d3 = {};
+constexpr D d4 = { 42 };
+
+struct E {
+  int x = 42;
+  B b = (A{x});
+};
+
+E e1 = {};
+E e2 = { 42 };
+constexpr E e3 = {};
+constexpr E e4 = { 42 };
+
+struct F {
+  int x = 42;
+  B b = (A{x});
+};
+
+F f1 = {};
+F f2 = { 42 };
+constexpr F f3 = {};
+constexpr F f4 = { 42 };
+
+void
+g (C c5 = C{}, C c6 = C{ 42 }, D d5 = D{}, D d6 = D{ 42 },
+   E e5 = E{}, E e6 = E{ 42 }, F f5 = F{}, F f6 = F{ 42 })
+{
+}
diff --git a/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr19.C b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr19.C
new file mode 100644
index 00000000000..f4892e3379b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/nsdmi-aggr19.C
@@ -0,0 +1,28 @@
+// PR c++/100252
+// { dg-do compile { target c++14 } }
+
+#define SA(X) static_assert ((X),#X)
+
+struct A {
+  const A* p = this;
+};
+
+struct B {
+  A a = (A{}, A{});
+};
+
+constexpr B b;
+SA(b.a.p == &b.a);
+
+struct C { 
+  int x;
+  int y = x;
+};
+
+struct D { 
+  int x = 0;
+  int y = (C{x}.y, C{x}.y);
+};
+
+constexpr D d = { };
+D d2 = {};

base-commit: dd7813f05df50d2ad8e0dc34503f2dff0b521d89
-- 
2.36.1