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      1  1.6  rillig /*	$NetBSD: expr_range.c,v 1.6 2024/11/13 04:32:49 rillig Exp $	*/
      2  1.1  rillig # 3 "expr_range.c"
      3  1.1  rillig 
      4  1.1  rillig /*
      5  1.2  rillig  * In a switch statement that has (expr & constant) as the controlling
      6  1.3  rillig  * expression, complain if a case branch is unreachable because the case
      7  1.3  rillig  * label can never match the controlling expression.
      8  1.1  rillig  *
      9  1.2  rillig  * GCC 10 does not complain about the unreachable branch.  It knows that the
     10  1.3  rillig  * branch is unreachable though, since it doesn't generate any code for it.
     11  1.2  rillig  * GCC once had the option -Wunreachable-code, but that option was made a
     12  1.2  rillig  * no-op in 2011.
     13  1.1  rillig  *
     14  1.1  rillig  * Clang 10 does not complain about this either, and just like GCC it doesn't
     15  1.1  rillig  * generate any code for this branch.  The code for tracking an expression's
     16  1.1  rillig  * possible values may be related to RangeConstraintManager, just guessing.
     17  1.1  rillig  */
     18  1.1  rillig 
     19  1.5  rillig /* lint1-extra-flags: -chap -X 351 */
     20  1.1  rillig 
     21  1.2  rillig void println(const char *);
     22  1.2  rillig 
     23  1.1  rillig void
     24  1.1  rillig example(unsigned x)
     25  1.1  rillig {
     26  1.1  rillig 	switch (x & 6) {
     27  1.2  rillig 	case 0:
     28  1.2  rillig 		println("0 is reachable");
     29  1.2  rillig 		break;
     30  1.4  rillig 	case 1:
     31  1.6  rillig 		/* expect-1: warning: 'case' statement not reached [193] */
     32  1.2  rillig 		println("1 is not reachable");
     33  1.1  rillig 		break;
     34  1.1  rillig 	case 2:
     35  1.2  rillig 		println("2 is reachable");
     36  1.2  rillig 		break;
     37  1.2  rillig 	case 6:
     38  1.2  rillig 		println("6 is reachable");
     39  1.2  rillig 		break;
     40  1.4  rillig 	case 7:
     41  1.6  rillig 		/* expect-1: warning: 'case' statement not reached [193] */
     42  1.2  rillig 		println("7 is not reachable");
     43  1.1  rillig 		break;
     44  1.1  rillig 	}
     45  1.1  rillig }
     46