"uninitialized variable" warning from compiler

["Umashankar V.K." <shankar dot vk at gmail dot com>]

Hi,

      I have few questions about  inbuilt mechanism of  gcc/g++  for
warning about ?uninitialized variable.

I am interested in cases where  compiler is unable to warn.  I  am
aware that all the known bugs about  warning-failure are
mentioned  at  bugzilla   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24639

a)  The compiler activates the warning mechanism only if  optimisation
is enabled  at compilation time with -O option.
For all the bugs that I went  through at bugzilla,  the failure is not
 -O level dependent.  The warning-failure occurs  for  all levels of
optimisation.
So, I believe this is the general case.

But then I came across the following  failure case.  This one  fails
to  warn when compiled with any  level  below 3.
With -O3,  gcc  is able to warn.   Can someone tell me which is the
corresponding bug logged at bugzilla ?

Are there any more such bugs which  disappear when compiled with
specific -O level ?

b)  Are there any known  "fail to do uninitialised-warning"   gcc bugs
which are language-dependent ?   I mean bugs which occur only in C++ ,
but not in C.
( Bugs which arise out of  C++ language features/syntax. ) .    If so,
I would  like to know.

                  thanks for your time
                    Uma shankar