[Bug preprocessor/17315] Strange compile-time regression in cpp against gcc3.4.1

["giovannibajo at libero dot it" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From giovannibajo at libero dot it  2004-09-08 00:19 -------
Subject: Re:  Strange compile-time regression in cpp against gcc3.4.1

pcarlini at suse dot de wrote:

> I have no idea whether cpp is involved or not...

It is not, because it can be reproduced with .ii files, where the preprocessed
is not even invoked.

>  it's not, as you are saying. I have only removed the wrong
> categorization libstdc++ which is
> certainly wrong, since it's used for bugs in the library. Please
> notice that I have *not* confirmed the bug!

The *only* difference between the two preprocessed files is libstdc++.

Let's say for a moment that, for some absurd reason, including <iostream> in
3.5 brings into scope 4000 new instantiations that where not present in 3.4.
This would cause a compile-time regression for any program including iostream.
How would you mark such a bug, if not with libstdc++?

There is only one data point in this bug: including libstdc++ from 3.5 causes
*at least* 10% compile-time regression compared to libstdc++ from 3.4. Now,
either the new libstdc++ exploits by mere chance some special bottleneck in the
compiler while the old libstdc++ didn't, or the code itself is slower to
compile for some reason. This is kind of hard to analyze and surely an
interesting issue (the regression is enough to totally destroy the compile-time
improvements that the tree-ssa folks brought to us), so I would appreciate some
help, and not only something like "please this is not my bug, go away".

Giovanni Bajo




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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315