Re: gcc and compiling speed

[Zack Weinberg <zack at codesourcery dot com>]

Theo de Raadt <deraadt@cvs.openbsd.org> writes:

>> Theo de Raadt <deraadt@cvs.openbsd.org> writes:
>> 
>> >> Marc,
>> >> Now I know you have been asked before every time you bring up on the
>> >> GCC's mailing list about a set of preprocessed source for openbsd so
>> >> that the speed of GCC will improve.
>> >
>> > How will this improve the speed of gcc?
>> 
>> If Marc (or anyone) provides us with a test case for the performance
>> regression - for instance, the set of files produced by running gcc -E
>> over all of the openbsd kernel, which is what Andrew meant - then we
>> can find out why the compiler is slower, and fix it.
>> 
>> We do have our own test cases for compile time, and they have been
>> being fixed (mostly by Jan Hubicka) but we don't know that this will
>> help you.
>
> How big is your mailbox?
>
> I can compile the entire source tree for OpenBSD and mail you
> gcc -E output for every file.

Ideally you would create a .tar.bz2 of all the .i files and put them
on a web or FTP site.

We do *NOT* want performance numbers to go with these tarfiles, we
just want the raw preprocessed source, and only using one reference
compiler.

> I can then do that on 4 architectures.

Is there that much code that varies per architecture?  

> That is the performance test that matters.  Does gcc3 compile
> mozilla faster on any machine, than gcc2 did?

What you don't realize, perhaps, is just how data-driven gcc (any
version) is.  I could spend weeks tuning gcc to work well on mozilla
and it could make no. difference. whatsoever. to how long it takes to
compile OpenBSD core.

zw