It seems that there already was a bug about this: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35903 It's old, but active. I have put the test case in that bug. Thanks for your help. 2009/10/16 Ian Lance Taylor <iant@xxxxxxxxxx>: > You didn't mention the machine you are using, nor the version of gcc. > However, I hypothesize that you are using GNU/Linux. On GNU/Linux, > <string.h> includes <bits/string2.h>. When optimizing, > <bits/string2.h> defines strcmp as a macro, as follows: > > # define strcmp(s1, s2) \ > __extension__ \ > ({ size_t __s1_len, __s2_len; \ > (__builtin_constant_p (s1) && __builtin_constant_p (s2) \ > && (__s1_len = strlen (s1), __s2_len = strlen (s2), \ > (!__string2_1bptr_p (s1) || __s1_len >= 4) \ > && (!__string2_1bptr_p (s2) || __s2_len >= 4)) \ > ? __builtin_strcmp (s1, s2) \ > : (__builtin_constant_p (s1) && __string2_1bptr_p (s1) \ > && (__s1_len = strlen (s1), __s1_len < 4) \ > ? (__builtin_constant_p (s2) && __string2_1bptr_p (s2) \ > ? __builtin_strcmp (s1, s2) \ > : __strcmp_cg (s1, s2, __s1_len)) \ > : (__builtin_constant_p (s2) && __string2_1bptr_p (s2) \ > && (__s2_len = strlen (s2), __s2_len < 4) \ > ? (__builtin_constant_p (s1) && __string2_1bptr_p (s1) \ > ? __builtin_strcmp (s1, s2) \ > : __strcmp_gc (s1, s2, __s2_len)) \ > : __builtin_strcmp (s1, s2)))); }) > > The warning is coming from a reference in that macro. At a guess, the > macro somehow gets too complicated for gcc to sort out that some code > is never executed. I'm not sure why that only occurs in one case but > not the others. > > It's probably worth filing a bug report on this. Please follow the > directions at http://gcc.gnu.org/bugs.html . In particular, please > include the preprocessed source code. Thanks. > > Ian > -- Alfonso Cepeda
