[331] | 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 | }
|
---|