1 /* $NetBSD: expr_range.c,v 1.6 2024/11/13 04:32:49 rillig Exp $ */
2 # 3 "expr_range.c"
3
4 /*
5 * In a switch statement that has (expr & constant) as the controlling
6 * expression, complain if a case branch is unreachable because the case
7 * label can never match the controlling expression.
8 *
9 * GCC 10 does not complain about the unreachable branch. It knows that the
10 * branch is unreachable though, since it doesn't generate any code for it.
11 * GCC once had the option -Wunreachable-code, but that option was made a
12 * no-op in 2011.
13 *
14 * Clang 10 does not complain about this either, and just like GCC it doesn't
15 * generate any code for this branch. The code for tracking an expression's
16 * possible values may be related to RangeConstraintManager, just guessing.
17 */
18
19 /* lint1-extra-flags: -chap -X 351 */
20
21 void println(const char *);
22
23 void
example(unsigned x)24 example(unsigned x)
25 {
26 switch (x & 6) {
27 case 0:
28 println("0 is reachable");
29 break;
30 case 1:
31 /* expect-1: warning: 'case' statement not reached [193] */
32 println("1 is not reachable");
33 break;
34 case 2:
35 println("2 is reachable");
36 break;
37 case 6:
38 println("6 is reachable");
39 break;
40 case 7:
41 /* expect-1: warning: 'case' statement not reached [193] */
42 println("7 is not reachable");
43 break;
44 }
45 }
46