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expr_range.c revision 1.2.2.2 
      1  1.2.2.2  cjep /*	$NetBSD: expr_range.c,v 1.2.2.2 2021/05/31 22:15:24 cjep Exp $	*/
      2  1.2.2.2  cjep # 3 "expr_range.c"
      3  1.2.2.2  cjep 
      4  1.2.2.2  cjep /*
      5  1.2.2.2  cjep  * In a switch statement that has (expr & constant) as the controlling
      6  1.2.2.2  cjep  * expression, complain if one of the case branches is unreachable because
      7  1.2.2.2  cjep  * the case label does can never match the controlling expression.
      8  1.2.2.2  cjep  *
      9  1.2.2.2  cjep  * GCC 10 does not complain about the unreachable branch.  It knows that the
     10  1.2.2.2  cjep  * branch is unreachable though since it doesn't generate any code for it.
     11  1.2.2.2  cjep  * GCC once had the option -Wunreachable-code, but that option was made a
     12  1.2.2.2  cjep  * no-op in 2011.
     13  1.2.2.2  cjep  *
     14  1.2.2.2  cjep  * Clang 10 does not complain about this either, and just like GCC it doesn't
     15  1.2.2.2  cjep  * generate any code for this branch.  The code for tracking an expression's
     16  1.2.2.2  cjep  * possible values may be related to RangeConstraintManager, just guessing.
     17  1.2.2.2  cjep  */
     18  1.2.2.2  cjep 
     19  1.2.2.2  cjep /* lint1-extra-flags: -chap */
     20  1.2.2.2  cjep 
     21  1.2.2.2  cjep void println(const char *);
     22  1.2.2.2  cjep 
     23  1.2.2.2  cjep void
     24  1.2.2.2  cjep example(unsigned x)
     25  1.2.2.2  cjep {
     26  1.2.2.2  cjep 	switch (x & 6) {
     27  1.2.2.2  cjep 	case 0:
     28  1.2.2.2  cjep 		println("0 is reachable");
     29  1.2.2.2  cjep 		break;
     30  1.2.2.2  cjep 	case 1:			/* expect: statement not reached */
     31  1.2.2.2  cjep 		println("1 is not reachable");
     32  1.2.2.2  cjep 		break;
     33  1.2.2.2  cjep 	case 2:
     34  1.2.2.2  cjep 		println("2 is reachable");
     35  1.2.2.2  cjep 		break;
     36  1.2.2.2  cjep 	case 6:
     37  1.2.2.2  cjep 		println("6 is reachable");
     38  1.2.2.2  cjep 		break;
     39  1.2.2.2  cjep 	case 7:			/* expect: statement not reached */
     40  1.2.2.2  cjep 		println("7 is not reachable");
     41  1.2.2.2  cjep 		break;
     42  1.2.2.2  cjep 	}
     43  1.2.2.2  cjep }
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