modernc.org/ccgo/v3@v3.16.14/lib/testdata/tcc-0.9.27/tests/tests2/87_dead_code.c (about) 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 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 }