Re: Will tree-ssa be GCC 3.5?

[Jim Wilson <wilson at specifixinc dot com>]

On Sat, 2003-11-29 at 15:58, Zack Weinberg wrote:
> I don't agree.  Major version number bumps should be reserved for
> changes which are guaranteed to break compatibility for everyone.

We will never be able to do that, and hence by this criteria, we will
never be able to change the major version number again.

Even for the gcc 2.x to gcc 3.x change we did not have this level of
change.  There were major compatibility problems for C++ users, and for
OS vendors that rely on gcc, but there certainly weren't major problems
for everyone.

I think the main problem with gcc 3.0 was that it had too many bugs, and
we dropped gcc 2.x support before people were able to switch to gcc
3.x.  These are potential issues for tree-ssa as well.

There are a number of issues with tree-ssa that will cause problems for
lots of people.
1) Loss of Ada support, until such time as the Ada front end is
gimplified.  This will be a major problem for all Ada users.
2) Replacing the f77 front end with the f95 front end.  This will be
noticed by many Fortran users.
3) Loss of all externally maintained front ends, such as Pascal and
Mercury, until such time that they are all gimplified.
4) The addition of new infrastructure, which will require all gcc
developers to re-educate themselves.
5) The addition of new optimization passes which are likely to cause new
classes of bugs for users, and also probably new classes of features.
I think these things are more easily explained with a major version
number change.

If we maintain gcc3 in parallel with gcc4 for a while, then this gives
us a chance to add in the tree-ssa stuff now even if it isn't perfect
yet.  People can continue to use gcc3 if necessary until gcc4
stabilizes.

If people really don't want to change the version number to 4.0 then I
can live with that.  I just wanted to make sure it was considered as an
option.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com