c++: constexpr VEC_INIT_EXPR [PR118285]

cxx_eval_vec_init_1 was doing the wrong thing for an array of
self-referential class type; just evaluating the TARGET_EXPR initializer
creates a new object that refers to the TARGET_EXPR_SLOT, if we want it to
refer properly to the initialization target we need to provide it.

	PR c++/118285

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_vec_init_1): Build INIT_EXPR for
	initializing a class.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/initlist-opt7.C: New test.

2 files changed, 49 insertions, 1 deletions

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 94a4680..58bed6f 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -5624,7 +5624,11 @@ cxx_eval_vec_init_1 (const constexpr_ctx *ctx, tree atype, tree init,
 	  if (init == void_node)
 	    /* Trivial default-init, don't do anything to the CONSTRUCTOR.  */
 	    return ctx->ctor;
-	  eltinit = cxx_eval_constant_expression (&new_ctx, init, lval,
+	  eltinit = init;
+	  if (CLASS_TYPE_P (elttype) && new_ctx.object)
+	    /* Clarify what object is being initialized (118285).  */
+	    eltinit = build2 (INIT_EXPR, elttype, new_ctx.object, eltinit);
+	  eltinit = cxx_eval_constant_expression (&new_ctx, eltinit, lval,
 						  non_constant_p, overflow_p);
 	  reuse = i == 0;
 	}
@@ -5637,6 +5641,9 @@ cxx_eval_vec_init_1 (const constexpr_ctx *ctx, tree atype, tree init,
 	  eltinit = (perform_implicit_conversion_flags
 		     (elttype, eltinit, complain,
 		      LOOKUP_IMPLICIT|LOOKUP_NO_NARROWING));
+	  if (CLASS_TYPE_P (elttype) && new_ctx.object)
+	    /* Clarify what object is being initialized (118285).  */
+	    eltinit = build2 (INIT_EXPR, elttype, new_ctx.object, eltinit);
 	  eltinit = cxx_eval_constant_expression (&new_ctx, eltinit, lval,
 						  non_constant_p, overflow_p);
 	}
diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist-opt7.C b/gcc/testsuite/g++.dg/cpp0x/initlist-opt7.C
new file mode 100644
index 0000000..f55ef5b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist-opt7.C
@@ -0,0 +1,41 @@
+// PR c++/118285
+// { dg-do compile { target c++20 } }
+
+#include <initializer_list>
+
+struct A {
+  char *a;
+  union { char b[8]; long c; };
+  constexpr A (const char *x) : a(b)
+  {
+    for (int i = 0; i < 8; ++i)
+      b[i] = 0;
+  }
+  constexpr ~A ()
+  {
+    if (!foo ())
+      bar (c);
+  }
+  constexpr bool foo ()
+  {
+    char *x = a;
+    if (x == b)
+      return true;
+    return false;
+  }
+  constexpr void bar (long) {}
+};
+
+constexpr void
+baz (std::initializer_list<A>)
+{
+}
+
+constexpr bool
+qux ()
+{
+  baz ({""});
+  return true;
+}
+
+static_assert (qux (), "");