[cfe-dev] Implicit declarations of builtins

Douglas Gregor dgregor at apple.com
Sun Jan 22 22:32:52 PST 2012

Sent from my iPhone

On Jan 22, 2012, at 2:54 PM, Eli Friedman <eli.friedman at gmail.com> wrote:

> On Sun, Jan 22, 2012 at 2:37 PM, Joerg Sonnenberger
> <joerg at britannica.bec.de> wrote:
>> Hi all,
>> I've just stumbled over a nasty surprise with the implicit prototypes
>> for library builtins. Consider the following input:
>> int main() { char *p = powl; return 0; }
>> This is from a configure test and expected to fail on NetBSD. Compiling
>> it with -O2 gives the expected
>> warning: implicitly declaring C library function 'powl' with type
>> 'long double (long double, long double)'
>> warning, but the undefined reference gets optimised away. Dow.
> Hmm... IIRC, gcc only does implicit builtin declarations in contexts
> where the builtin is used as a function call.  Might be worth changing
> clang to follow gcc's example.

I agree. Clang should do the same. I could swear that it worked that way at one point. 

>> Even more
>> nasty: -Werror=implicit-function-declaration makes it still continue.
> That's definitely a bug.
> -Eli
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