C++ compile time (again)

[Wolfgang Bangerth]

It's C++-compile-time-regression-rant time again. Compile times for a
complete build of the deal.II library on a PIII 800 MHz:

  gcc2.95 :  46 min
  mainline:  89 min
  tree-ssa: 118 min

The last two numbers are generated with --enable-checking, but apart
from that I don't think further comments are necessary. Switching to a
new compiler can be frustrating if you have to wait 2 hours when you
know it could be less than one...

Now, what troubles me (and Gerald, who has been pointing this out for
ages now) is that it seems as if these numbers don't change
anything. Everytime Gerald brings this up, answers are "Oh, yes, good 
you remind us that there is C++ out there, we seem to have forgotten".

Why is it that everyone is always looking at C code for compile time?
I don't know about Gerald's library, but to get a good piece of C++,
it's as easy as
  - going to  http://www.dealii.org/
  - go to "download"
  - download version 4.0.0
  - tar xvzf
  - ./configure
  - time make all
If there are questions, I would be more than willing to answer any and
all of them if that helps. If I shall write up some instructions, tell
me where, I'll do so immediately.

It just doesn't make sense if we constantly surprise ourselves by
pointing out the existence of real-life C++ codes. Testing compile
time speed for C++ needs to be done as a normal part of gcc
development. It's just impossible to figure out what made gcc slow if
Gerald, I, or someone else has the time for testing these issues every
second month or so. Even more so, since none of us really has any
knowledge of what's going on inside gcc.

W.

</rant>

-------------------------------------------------------------------------
Wolfgang Bangerth              email:            bangerth@ices.utexas.edu
                               www: http://www.ices.utexas.edu/~bangerth/