sdcc/support/regression/tcc/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 int main (void)
  60 {
  61   int i = 1;
  62   kb_wait_1();
  63
  64   /* Simple test of dead code at first sight which isn't actually dead. */
  65   if (0) {
  66 yeah:
  67       printf ("yeah\n");
  68   } else {
  69       printf ("boo\n");
  70   }
  71   if (i--)
  72     goto yeah;
  73
  74   /* Some more non-obvious uses where the problems are loops, so that even
  75      the first loop statements aren't actually dead.  */
  76   i = 1;
  77   if (0) {
  78       while (i--) {
  79           printf ("once\n");
  80 enterloop:
  81           printf ("twice\n");
  82       }
  83   }
  84   if (i >= 0)
  85     goto enterloop;
  86
  87   /* The same with statement expressions.  One might be tempted to
  88      handle them specially by counting if inside statement exprs and
  89      not unsuppressing code at loops at all then.
  90      See kb_wait_1 for the other side of the medal where that wouldn't work.  */
  91   i = ({
  92       int j = 1;
  93       if (0) {
  94           while (j--) {
  95               printf ("SEonce\n");
  96     enterexprloop:
  97               printf ("SEtwice\n");
  98           }
  99       }
 100       if (j >= 0)
 101         goto enterexprloop;
 102       j; });
 103
 104   /* The other two loop forms: */
 105   i = 1;
 106   if (0) {
 107       for (i = 1; i--;) {
 108           printf ("once2\n");
 109 enterloop2:
 110           printf ("twice2\n");
 111       }
 112   }
 113   if (i > 0)
 114     goto enterloop2;
 115
 116   i = 1;
 117   if (0) {
 118       do {
 119           printf ("once3\n");
 120 enterloop3:
 121           printf ("twice3\n");
 122       } while (i--);
 123   }
 124   if (i > 0)
 125     goto enterloop3;
 126
 127   /* And check that case and default labels have the same effect
 128      of disabling code suppression.  */
 129   i = 41;
 130   switch (i) {
 131       if (0) {
 132           printf ("error\n");
 133       case 42:
 134           printf ("error2\n");
 135       case 41:
 136           printf ("caseok\n");
 137       }
 138   }
 139
 140   i = 41;
 141   switch (i) {
 142       if (0) {
 143           printf ("error3\n");
 144       default:
 145           printf ("caseok2\n");
 146           break;
 147       case 42:
 148           printf ("error4\n");
 149       }
 150   }
 151
 152   dowhile();
 153
 154   return 0;
 155 }