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Re: New GCC releases comparison and comparison of GCC4.4 and LLVM2.5 on SPEC2000
Andi Kleen wrote:
> "Joseph S. Myers" <joseph@codesourcery.com> writes:
>
>> On Tue, 12 May 2009, Chris Lattner wrote:
>>
>>> 1. I have a hard time understanding the code size numbers. Does 10% mean that
>>> GCC is generating 10% bigger or 10% smaller code than llvm?
>> I have a different comment on the code size numbers: could we have
>> comparisons of code size for -Os rather than (or in addition to) -O2 and
>> -O3? If someone is particularly concerned with code size, -Os is what
>> they are expected to use.
>
> It's a slippery slope that -O2 is getting so bad regarding
> code size. What should people do who need performance, but cannot
> completely disregard code size (and can't use profile feedback for
> some reason).
>From looking http://vmakarov.fedorapeople.org/spec/I2Size32.png it does
not look that bad at all. For SpecFP it is different, but code size is
rarely a problem in FP benchmarks (hot loops are really small or really
huge anyway). So it looks like we're doing the right thing in that respect.
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.
Paolo