[Bug c++/19763] New: surplus -Wuninitialized warnings

["oliverst at online dot de" <gcc-bugzilla at gcc dot gnu dot org>]

extern void foo(int);

void test()
{
 	 int change_y, y , new_y;
        {
            int save_y;
            if (change_y) save_y = y, y = new_y;
            if (change_y) y = save_y;
          }
          foo(y);
}

int main()
{
 	test();
 	return 0;
}

If I compile this code with "-Wuninitialized -O1" or "-Wuninitialized -O2" with
the MinGW 3.4.2 GCC I got those warnings:

test2.cpp: In function `void test()':
test2.cpp:5: warning: 'change_y' might be used uninitialized in this function
test2.cpp:5: warning: 'y' might be used uninitialized in this function

But I compile it with "-Wuninitialized -O3" I get this:

test2.cpp: In function `void test()':
test2.cpp:5: warning: 'change_y' might be used uninitialized in this function
test2.cpp:5: warning: 'y' might be used uninitialized in this function
test2.cpp: In function `int main()':
test2.cpp:5: warning: 'change_y' might be used uninitialized in this function
test2.cpp:5: warning: 'y' might be used uninitialized in this function

Which is obviously two surplus warnings and those two warnings also referencing
to the wrong function.

But when I comment the foo() call, then I get no warning at all, but I don't
know how the optimizations of GCC work, so it might be, because all the vars are
removed, because they aren't used at all and are "dead code".

MinGW GCC 3.3.3 and a linux GCC 3.2 also behaves the same.

-- 
           Summary: surplus -Wuninitialized warnings
           Product: gcc
           Version: 3.4.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: oliverst at online dot de
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19763