[cfe-commits] False positive for -Wunreachable-code
Jordan Rose
jordan_rose at apple.com
Tue Oct 30 09:25:06 PDT 2012
On Oct 30, 2012, at 2:34 , Abramo Bagnara <abramo.bagnara at bugseng.com> wrote:
> Il 28/10/2012 08:12, Abramo Bagnara ha scritto:
>> $ cat p.c
>> #include <stdio.h>
>>
>> enum e { a, b = 4 } x = 3;
>>
>> void g(int v) {
>> printf("%d\n", v);
>> }
>>
>> int main(int argc, char **argv) {
>> switch (x) {
>> case a:
>> g(0);
>> break;
>> case b:
>> g(1);
>> break;
>> default:
>> g(2);
>> break;
>> }
>> }
>> $ _clang -Wunreachable-code -Wcovered-switch-default -O2 p.c
>> p.c:17:3: warning: default label in switch which covers all enumeration
>> values
>> [-Wcovered-switch-default]
>> default:
>> ^
>> p.c:18:7: warning: will never be executed [-Wunreachable-code]
>> g(2);
>> ^
>> $ ./a.out
>> 2
>>
>> Of course -Wcovered-switch-default warning is a perfectly true positive.
>>
>> My reading of the standard is that nothing prevent an enum to have a
>> value different from listed enum constants if this value is compatible
>> with enum range (and code generation seems to agree on that).
>
> I've attached the patch for review.
>
> The fixed testcase shows well why to hide warnings about undefined
> behaviour in code actually generated is a bad thing.
If we do this, we're going to want this under a CFG option at the very least. The static analyzer should continue assuming that an enum input to a switch is always a valid enum constant, in order to keep our false positive rate down.
Jordan
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