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expr_range.c revision 1.5 
      1 /*	$NetBSD: expr_range.c,v 1.5 2023/03/28 14:44:34 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
     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: 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: statement not reached [193] */
     42 		println("7 is not reachable");
     43 		break;
     44 	}
     45 }
     46