const weak variables are inlined.

[Richard Guenther]

On Wed, May 7, 2008 at 8:38 PM, Joseph S. Myers <joseph@codesourcery.com> wrote:
> On Wed, 7 May 2008, Mark Mitchell wrote:
>
>  > Christian BRUEL wrote:
>  >
>  > > This is a problem if the variable is replaced at link time by a strong one,
>  > > like in:
>  >
>  > > const int  __attribute__((weak)) vaca = 0;
>  >
>  > This one is a little tricky, actually.
>  >
>  > I think we need to actually have some documentation that says what this means.
>  > Normally, of course, doing the substitution of a const variable with its
>  > initializer is valid.  In fact, in C++ it's *required*.
>
>  (The above example is only valid in C++ with "extern" added; otherwise the
>  compiler gives an error.)
>
>  I think this is similar to the issue of not analysing the contents of a
>  function, where it was said
>  <http://gcc.gnu.org/ml/gcc/2008-01/msg00171.html> that marking the
>  function weak will achieve that effect.  So for C I think neither const
>  volatile nor const weak variables should have their initializers used for
>  optimization.  (I do not think this optimization belongs in the C front
>  end at the early stage where it's presently handled; the earliest point it
>  should be done is gimplification-time folding along with most of the other
>  folding presently done at parse time.  But that's a separate matter.)

CCP and SCCVN do this optimization as well.  I don't see why volatile const
should disable the optimization.  The problem with disabling it for const weak
is that basically propagation from constant extern initializers in
libraries built
with -fPIC would be disabled.

So I am all for option 2) which we currently implement and suggest to emit
a warning for explicitly weaked constants.

Richard.