re PR c++/83993 (ICE: constant not recomputed when ADDR_EXPR changed)

	PR c++/83993
	* constexpr.c (cxx_eval_outermost_constant_expr): Build NOP_EXPR
	around non-constant ADDR_EXPRs rather than clearing TREE_CONSTANT
	on ADDR_EXPR.

	* g++.dg/init/pr83993-2.C: New test.

From-SVN: r257265

gcc/cp/ChangeLog

+2018-01-31  Jason Merrill  <jason@redhat.com>
+	    Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/83993
+	* constexpr.c (cxx_eval_outermost_constant_expr): Build NOP_EXPR
+	around non-constant ADDR_EXPRs rather than clearing TREE_CONSTANT
+	on ADDR_EXPR.
+
 2018-01-31  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/83993

gcc/cp/constexpr.c

@@ -4840,8 +4840,12 @@ cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant,
     return error_mark_node;
   else if (non_constant_p && TREE_CONSTANT (r))
     {
-      /* This isn't actually constant, so unset TREE_CONSTANT.  */
-      if (EXPR_P (r))
+      /* This isn't actually constant, so unset TREE_CONSTANT.
+	 Don't clear TREE_CONSTANT on ADDR_EXPR, as the middle-end requires
+	 it to be set if it is invariant address, even when it is not
+	 a valid C++ constant expression.  Wrap it with a NOP_EXPR
+	 instead.  */
+      if (EXPR_P (r) && TREE_CODE (r) != ADDR_EXPR)
 	r = copy_node (r);
       else if (TREE_CODE (r) == CONSTRUCTOR)
 	r = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (r), r);

gcc/testsuite/ChangeLog

 2018-01-31  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/83993
+	* g++.dg/init/pr83993-2.C: New test.
+
+	PR c++/83993
 	* g++.dg/init/pr83993-1.C: New test.
 	* g++.dg/cpp0x/pr83993.C: New test.
 

gcc/testsuite/g++.dg/init/pr83993-2.C

+// PR c++/83993
+// { dg-do compile }
+// { dg-options "-w" }
+
+int a[5];
+extern int b[];
+int *const c = &a[6];
+int *const d = &b[1];
+
+int
+foo ()
+{
+  return c[-4] + d[-1];
+}