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 havoc 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
  30 static int global;
  31
  32 static void foo(int i)
  33 {
  34   global+=i;
  35   printf ("g=%d\n", global);
  36 }
  37
  38 static int check(void)
  39 {
  40   printf ("check %d\n", global);
  41   return 1;
  42 }
  43
  44 static void dowhile(void)
  45 {
  46   do {
  47       foo(1);
  48       if (global == 1) {
  49           continue;
  50       } else if (global == 2) {
  51           continue;
  52       }
  53       /* The following break shouldn't disable the check() call,
  54          as it's reachable by the continues above.  */
  55       break;
  56   } while (check());
  57 }
  58
  59 static void nondead_after_dead_return(void)
  60 {
  61   /* This statement expr is not entered, and hence that fact that it
  62      doesn't fall-through should not influence the surrounding code.  */
  63   0 && ({ return; 0;});
  64   printf ("nondead works\n");
  65   return;
  66 }
  67
  68 int main (void)
  69 {
  70   int i = 1;
  71   kb_wait_1();
  72
  73   /* Simple test of dead code at first sight which isn't actually dead. */
  74   if (0) {
  75 yeah:
  76       printf ("yeah\n");
  77   } else {
  78       printf ("boo\n");
  79   }
  80   if (i--)
  81     goto yeah;
  82
  83   /* Some more non-obvious uses where the problems are loops, so that even
  84      the first loop statements aren't actually dead.  */
  85   i = 1;
  86   if (0) {
  87       while (i--) {
  88           printf ("once\n");
  89 enterloop:
  90           printf ("twice\n");
  91       }
  92   }
  93   if (i >= 0)
  94     goto enterloop;
  95
  96   /* The same with statement expressions.  One might be tempted to
  97      handle them specially by counting if inside statement exprs and
  98      not unsuppressing code at loops at all then.
  99      See kb_wait_1 for the other side of the medal where that wouldn't work.  */
 100   i = ({
 101       int j = 1;
 102       if (0) {
 103           while (j--) {
 104               printf ("SEonce\n");
 105     enterexprloop:
 106               printf ("SEtwice\n");
 107           }
 108       }
 109       if (j >= 0)
 110         goto enterexprloop;
 111       j; });
 112
 113   /* The other two loop forms: */
 114   i = 1;
 115   if (0) {
 116       for (i = 1; i--;) {
 117           printf ("once2\n");
 118 enterloop2:
 119           printf ("twice2\n");
 120       }
 121   }
 122   if (i > 0)
 123     goto enterloop2;
 124
 125   i = 1;
 126   if (0) {
 127       do {
 128           printf ("once3\n");
 129 enterloop3:
 130           printf ("twice3\n");
 131       } while (i--);
 132   }
 133   if (i > 0)
 134     goto enterloop3;
 135
 136   /* And check that case and default labels have the same effect
 137      of disabling code suppression.  */
 138   i = 41;
 139   switch (i) {
 140       if (0) {
 141           printf ("error\n");
 142       case 42:
 143           printf ("error2\n");
 144       case 41:
 145           printf ("caseok\n");
 146       }
 147   }
 148
 149   i = 41;
 150   switch (i) {
 151       if (0) {
 152           printf ("error3\n");
 153       default:
 154           printf ("caseok2\n");
 155           break;
 156       case 42:
 157           printf ("error4\n");
 158       }
 159   }
 160
 161   dowhile();
 162   nondead_after_dead_return();
 163
 164   return 0;
 165 }