------- Comment #1 from lcwu at gcc dot gnu dot org 2009-04-17 23:07 -------
This bogus warning started to show up after the fix for PR c++/39551 was
submitted (at revision 146132). And the root cause for the issue is that C++
front-end generates the following code to initialize the local 'pair' array:
(see build_vec_init() in cp/init.c)
*(struct pair[3] *) ({
(D.2247 = (struct pair *) &components);
(D.2248 = D.2247);
(D.2249 = 2);
for_stmt
{
D.2249 != -1;
--D.2249;
__comp_ctor (NON_LVALUE_EXPR <D.2248>);
++D.2248;
}
D.2247; })
The INDIRECT_REF operation (*) in the above code was later determined useless
and therefore deleted. However, since we didn't know that the INDIRECT_REF
expression was actually created by the compiler (instead of coming from the
user code) and therefore mistakenly emit an 'unused value' warning.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39803
