This is the mail archive of the
mailing list for the GCC project.
Re: New GCC releases comparison and comparison of GCC4.4 and LLVM2.5 on SPEC2000
> Paolo Bonzini wrote:
> >Rather, we should seriously understand what caused the compilation time
> >jump in 4.2, and whether those are still a problem. We made a good job
> >in 4.0 and 4.3 offsetting the slowdowns from infrastructure changes with
> >speedups from other changes; and 4.4 while slower than 4.3 at least
> >stays below 4.2. But, 4.2 was a disaster for compilation time.
> It was interesting for me that GCC4.4 is faster than GCC4.3 on Intel
> Core I7. This is not true for most other processors (at least for P4,
> Core2, Power4/5/6 etc). Intel Core I7 has 3rd level big and fast cache
> and memory controller on the chip. I guess that slowdown in GCC is
> mostly because of data and/or code locality.
Note that one of important reasons for slowdowns is the startup cost.
Binarry is bigger, we need more libraries and we do more initialization.
With per-function flags via attributes, we are now initializing all the
builtins and amount of builtins in i386 backend has grown to quite
extreme sizes. In 4.3 timeframe I did some work on optimizing startup
costs that translated quite noticeably to kernel compilation time. It
might be interesting to consider some scheme for initializing them
> Fortunately, GCC4.5 will be 5% faster because of Richard Guenter's work
> on improving aliasing (of course if it will be not eaten by a new
> optimization). People are complaining about GCC compilation speed and
> of course we should work on its speedup. But GCC is not so bad, for
> example SUN Studio compiler is almost 2 times slower than GCC. IMHO,
> GCC performace is still #1 priority for us (although people working on
> embedded processors could disagree with me). I think that because in my
> experience the performance improvement is much harder to achieve than
> compilation speed and code size improvements.