c-family: Fix up MEM_REF printing [PR95580]

The C FE in the MEM_REF printing ICEs if the type of the first argument
(which due to useless pointer conversions can be an arbitrary type) is a
pointer to an incomplete type.  The code just wants to avoid printing a cast
if it is a pointer to single byte elements.

2020-06-09  Jakub Jelinek  <jakub@redhat.com>

	PR c/95580
	* c-pretty-print.c (c_pretty_printer::unary_expression): Handle the
	case when MEM_REF's first argument has type pointer to incomplete type.

	* gcc.dg/pr95580.c: New test.

(cherry picked from commit d6dbb71e468d0db561cc9eca99eeaca1efb81c11)

gcc/c-family/c-pretty-print.c

@@ -1789,8 +1789,9 @@ c_pretty_printer::unary_expression (tree e)
 	  if (!integer_zerop (TREE_OPERAND (e, 1)))
 	    {
 	      pp_c_left_paren (this);
-	      if (!integer_onep (TYPE_SIZE_UNIT
-				 (TREE_TYPE (TREE_TYPE (TREE_OPERAND (e, 0))))))
+	      tree type = TREE_TYPE (TREE_TYPE (TREE_OPERAND (e, 0)));
+	      if (TYPE_SIZE_UNIT (type) == NULL_TREE
+		  || !integer_onep (TYPE_SIZE_UNIT (type)))
 		pp_c_type_cast (this, ptr_type_node);
 	    }
 	  pp_c_cast_expression (this, TREE_OPERAND (e, 0));

gcc/testsuite/gcc.dg/pr95580.c

+/* PR c/95580 */
+/* { dg-do compile } */
+/* { dg-options "-O1 -W -fno-tree-dce" } */
+
+void bar (void);
+
+void
+foo (int x)
+{
+  if (x == 0)
+    {
+      void *p = __builtin_malloc (4);
+      ((char *)p)[1] ^= 1;	/* { dg-warning "may be used uninitialized" "" { xfail *-*-* } } */
+    }
+  bar ();
+}