Re: [www] Document C++ -O0 improvements

["Giovanni Bajo" <giovannibajo at libero dot it>]

Bonzini Paolo wrote:

>> ...though, given the quote above, isn't the statement a bit too
>> strong ("any previous version")?
>
> any 3.x version?

No, it is faster than 2.95 as well. I would argue that, in the worse cases, it
is about the same speed or just a tad slower, but for many others it is much
faster.

For compilations which are template-bound like PR8361, the gain is smaller, at
least for the average users. To me, for instance, this already means a lot
because we go almost the same speed *and* do two-phase template lookup instead
of just one-phase lookup (just to name one thing G++ 4.0 and 2.95 did not).

Moreover, to tell you everything, much of the point of this patch is to tell
users that we *are* doing progress even compared to 2.95. What I often hear
from the "field" is that most people do not know why they should upgrade from
2.95, and the only things they *all* know is that newer versions of GCC are
much slower. This is why, for instance, I believe that gcc-4.0/changes.html is
still totally incomplete: it does not say -- in user terms -- why we bumped the
big number. The paragraph about tree-ssa is just a list of techinical names
which mean nothing to non compiler developers. I am actually planning to
rewrite that adding many examples of code snippets that we now optimize better,
with side-by-side assembly comparison with 2.95 or 3.4.

The patch is now in, thanks Gerald!

Giovanni Bajo