c++: -fmerge-all-constants vs. destructors [PR91529]

cp_finish_decl avoids setting TREE_READONLY on TREE_STATIC variables that
have non-constant construction or destruction, but -fmerge-all-constants was
converting an automatic variable to static while leaving TREE_READONLY set.

Fixed by clearing the flag in cp_finish_decl in the presence of
-fmerge-all-constants.

gcc/cp/ChangeLog
2020-05-01  Jason Merrill  <jason@redhat.com>

	PR c++/91529
	* decl.c (cp_finish_decl): Also clear TREE_READONLY if
	-fmerge-all-constants.

gcc/cp/ChangeLog

@@ -1,3 +1,9 @@
+2020-05-01  Jason Merrill  <jason@redhat.com>
+
+	PR c++/91529
+	* decl.c (cp_finish_decl): Also clear TREE_READONLY if
+	-fmerge-all-constants.
+
 2020-05-01  Jason Merrill  <jason@redhat.com>
 
 	PR c++/93822

gcc/cp/decl.c

@@ -7833,7 +7833,10 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
 	    maybe_commonize_var (decl);
 	}
 
-      if (var_definition_p && TREE_STATIC (decl))
+      if (var_definition_p
+	  /* With -fmerge-all-constants, gimplify_init_constructor
+	     might add TREE_STATIC to the variable.  */
+	  && (TREE_STATIC (decl) || flag_merge_constants >= 2))
 	{
 	  /* If a TREE_READONLY variable needs initialization
 	     at runtime, it is no longer readonly and we need to

gcc/testsuite/g++.dg/init/const14.C

@@ -0,0 +1,14 @@
+// PR c++/91529
+// { dg-do run }
+// { dg-additional-options -fmerge-all-constants }
+
+struct A
+{
+  int i[2];
+  ~A() { i[0] = 0; }
+};
+
+int main()
+{
+  const A a = { 1,2 };
+}