00213.c (3110B)
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 }