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Re: Recent dataflow branch SPEC2000 benchmarking


On 4/12/07, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
On 4/12/07, Vladimir Makarov <vmakarov@redhat.com> wrote:
> An interesting observation is that the more hard registers the processor
> has, the bigger slowdown is.  Although it might be a coincidence.

Yes, I noticed this too.  I don't believe this is a coincidence.  It's
the first thing I was planning to look into, in fact.

The problem seems to have to do with how the RTL loop optimizers work. They analyze a subcfg with df, and this is incredibly slow right now.

To give you some idea, we spend more than 35% of the total compile
time in "loop analysis" (TV_LOOP) for a fairly typical Fortran 90
program with lots of small loops, and almost all that extra time is
spent in df_reorganize_refs_by_reg.

So, Vlad, thanks for helping us identify a serious bottleneck! Kenny
said he has some ideas about how to fix this.

Gr.
Steven


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