tests/tests2/87_dead_code.c

   1 /* This checks various ways of dead code inside if statements
   2    where there are non-obvious ways of how the code is actually
   3    not dead due to reachable by labels.  */
   4 extern int printf (const char *, ...);
   5 static void kb_wait_1(void)
   6 {
   7   unsigned long timeout = 2;
   8   do {
   9       /* Here the else arm is a statement expression that's supposed
  10          to be suppressed.  The label inside the while would unsuppress
  11          code generation again if not handled correctly.  And that
  12          would wreak havok to the cond-expression because there's no
  13          jump-around emitted, the whole statement expression really
  14          needs to not generate code (perhaps except useless forward jumps).  */
  15       (1 ?
  16        printf("timeout=%ld\n", timeout) :
  17        ({
  18         int i = 1;
  19         while (1)
  20           while (i--)
  21             some_label:
  22               printf("error\n");
  23         goto some_label;
  24         })
  25       );
  26       timeout--;
  27   } while (timeout);
  28 }
  29 int main (void)
  30 {
  31   int i = 1;
  32   kb_wait_1();
  33
  34   /* Simple test of dead code at first sight which isn't actually dead. */
  35   if (0) {
  36 yeah:
  37       printf ("yeah\n");
  38   } else {
  39       printf ("boo\n");
  40   }
  41   if (i--)
  42     goto yeah;
  43
  44   /* Some more non-obvious uses where the problems are loops, so that even
  45      the first loop statements aren't actually dead.  */
  46   i = 1;
  47   if (0) {
  48       while (i--) {
  49           printf ("once\n");
  50 enterloop:
  51           printf ("twice\n");
  52       }
  53   }
  54   if (i >= 0)
  55     goto enterloop;
  56
  57   /* The same with statement expressions.  One might be tempted to
  58      handle them specially by counting if inside statement exprs and
  59      not unsuppressing code at loops at all then.
  60      See kb_wait_1 for the other side of the medal where that wouldn't work.  */
  61   i = ({
  62       int j = 1;
  63       if (0) {
  64           while (j--) {
  65               printf ("SEonce\n");
  66     enterexprloop:
  67               printf ("SEtwice\n");
  68           }
  69       }
  70       if (j >= 0)
  71         goto enterexprloop;
  72       j; });
  73
  74   /* The other two loop forms: */
  75   i = 1;
  76   if (0) {
  77       for (i = 1; i--;) {
  78           printf ("once2\n");
  79 enterloop2:
  80           printf ("twice2\n");
  81       }
  82   }
  83   if (i > 0)
  84     goto enterloop2;
  85
  86   i = 1;
  87   if (0) {
  88       do {
  89           printf ("once3\n");
  90 enterloop3:
  91           printf ("twice3\n");
  92       } while (i--);
  93   }
  94   if (i > 0)
  95     goto enterloop3;
  96
  97   /* And check that case and default labels have the same effect
  98      of disabling code suppression.  */
  99   i = 41;
 100   switch (i) {
 101       if (0) {
 102           printf ("error\n");
 103       case 42:
 104           printf ("error2\n");
 105       case 41:
 106           printf ("caseok\n");
 107       }
 108   }
 109
 110   i = 41;
 111   switch (i) {
 112       if (0) {
 113           printf ("error3\n");
 114       default:
 115           printf ("caseok2\n");
 116           break;
 117       case 42:
 118           printf ("error4\n");
 119       }
 120   }
 121   return 0;
 122 }