expr_range.c revision 1.1 
1/*	$NetBSD: expr_range.c,v 1.1 2021/05/14 21:14:55 rillig Exp $	*/
2# 3 "expr_range.c"
3
4/*
5 * Test whether lint can detect switch branches that are impossible to reach.
6 * As of 2021-05-14, it cannot.  To do this, it would need to keep track of
7 * the possible values of each variable or expression.  To do this reliably,
8 * it would also need accurate control flow analysis, which as of 2021-05-14
9 * works only for functions without 'goto'.
10 *
11 * GCC 10 does not complain the unreachable branch.  It knows that the branch
12 * is unreachable though since it doesn't generate any code for it.  GCC once
13 * had the option -Wunreachable-code, but that option was made a no-op in
14 * 2011.
15 *
16 * Clang 10 does not complain about this either, and just like GCC it doesn't
17 * generate any code for this branch.  The code for tracking an expression's
18 * possible values may be related to RangeConstraintManager, just guessing.
19 *
20 * There should be at least one static analysis tool that warns about this.
21 */
22
23/* lint1-extra-flags: -chap */
24
25void
26example(unsigned x)
27{
28	switch (x & 6) {
29	case 1:
30		/* This branch is unreachable. */
31		printf("one\n");
32		break;
33	case 2:
34		printf("two\n");
35		break;
36	}
37}
38