re PR c++/83634 (ICE in useless_type_conversion_p, at gimple-expr.c:86)

	PR c++/83634
	* cp-gimplify.c (cp_fold) <case NOP_EXPR>: If the operand folds to
	error_mark_node, return error_mark_node.

	* g++.dg/parse/pr83634.C: New test.

From-SVN: r256174

gcc/cp/ChangeLog

 2018-01-03  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/83634
+	* cp-gimplify.c (cp_fold) <case NOP_EXPR>: If the operand folds to
+	error_mark_node, return error_mark_node.
+
 	Update copyright years.
 
 2018-01-02  Jakub Jelinek  <jakub@redhat.com>

gcc/cp/cp-gimplify.c

@@ -2112,7 +2112,20 @@ cp_fold (tree x)
     case NON_LVALUE_EXPR:
 
       if (VOID_TYPE_P (TREE_TYPE (x)))
-	return x;
+	{
+	  /* This is just to make sure we don't end up with casts to
+	     void from error_mark_node.  If we just return x, then
+	     cp_fold_r might fold the operand into error_mark_node and
+	     leave the conversion in the IR.  STRIP_USELESS_TYPE_CONVERSION
+	     during gimplification doesn't like such casts.
+	     Don't create a new tree if op0 != TREE_OPERAND (x, 0), the
+	     folding of the operand should be in the caches and if in cp_fold_r
+	     it will modify it in place.  */
+	  op0 = cp_fold (TREE_OPERAND (x, 0));
+	  if (op0 == error_mark_node)
+	    x = error_mark_node;
+	  break;
+	}
 
       loc = EXPR_LOCATION (x);
       op0 = cp_fold_maybe_rvalue (TREE_OPERAND (x, 0), rval_ops);

gcc/testsuite/ChangeLog

+2018-01-03  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/83634
+	* g++.dg/parse/pr83634.C: New test.
+
 2018-01-03  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
 	PR fortran/83664

gcc/testsuite/g++.dg/parse/pr83634.C

+// PR c++/83634
+// { dg-do compile }
+
+void
+foo ()
+{
+  const int x = fn ();		// { dg-error "was not declared in this scope" }
+  short n;
+  for (n = x; n < 100; ++n)
+    ;
+}