PR c++/93143 - incorrect tree sharing with constexpr.

We don't unshare CONSTRUCTORs as often during constexpr evaluation, so we
need to unshare them here.

	* constexpr.c (cxx_eval_outermost_constant_expr): Don't assume
	CONSTRUCTORs are already unshared.

From-SVN: r280127

gcc/cp/ChangeLog

 2020-01-10  Jason Merrill  <jason@redhat.com>
 
+	PR c++/93143 - incorrect tree sharing with constexpr.
+	* constexpr.c (cxx_eval_outermost_constant_expr): Don't assume
+	CONSTRUCTORs are already unshared.
+
 	PR c++/93173 - incorrect tree sharing.
 	PR c++/93033
 	* cp-gimplify.c (cp_gimplify_init_expr, cp_gimplify_expr): Use

gcc/cp/constexpr.c

@@ -6347,10 +6347,10 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant,
   if (!non_constant_p && overflow_p)
     non_constant_p = true;
 
-  /* Unshare the result unless it's a CONSTRUCTOR in which case it's already
-     unshared.  */
+  /* Unshare the result.  */
   bool should_unshare = true;
-  if (r == t || TREE_CODE (r) == CONSTRUCTOR)
+  if (r == t || (TREE_CODE (t) == TARGET_EXPR
+		 && TARGET_EXPR_INITIAL (t) == r))
     should_unshare = false;
 
   if (non_constant_p && !allow_non_constant)

gcc/testsuite/g++.dg/cpp0x/constexpr-array22.C

+// PR c++/93143
+// { dg-do run { target c++11 } }
+
+struct A { char a[2]; };
+
+static constexpr A foo () { return A{1}; }
+
+void bar ()
+{
+  A a = foo ();
+  if (a.a[0] != 1)
+    __builtin_abort(); 
+}
+
+void foobar ()
+{
+  A x[] = { foo (), foo () };
+  A a = foo ();
+  if (a.a[0] != 1)
+    __builtin_abort(); 
+}
+
+int main()
+{
+  bar();
+  foobar();
+}