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Re: New GCC releases comparison and comparison of GCC4.4 and LLVM2.5 on SPEC2000
Paolo Bonzini wrote:
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.
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.
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.