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expr_range.c revision 1.2.2.2 
      1 /*	$NetBSD: expr_range.c,v 1.2.2.2 2021/05/31 22:15:24 cjep Exp $	*/
      2 # 3 "expr_range.c"
      3 
      4 /*
      5  * In a switch statement that has (expr & constant) as the controlling
      6  * expression, complain if one of the case branches is unreachable because
      7  * the case label does 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 */
     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:			/* expect: statement not reached */
     31 		println("1 is not reachable");
     32 		break;
     33 	case 2:
     34 		println("2 is reachable");
     35 		break;
     36 	case 6:
     37 		println("6 is reachable");
     38 		break;
     39 	case 7:			/* expect: statement not reached */
     40 		println("7 is not reachable");
     41 		break;
     42 	}
     43 }
     44