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Re: Compile time improvement, runtime regression (ia64)



On Jun 13, 2004, at 8:18 AM, Richard Guenther wrote:


Since the last two days I experience a compile time improvement both in bootstrap times (50min vs. 60min before - but also switched host compiler to 3.4.0 from 3.3.4) and tramp3d-v3 (non-leafified) testcase
(2min30 vs. 3min before). Unfortunately tramp3d-v3 performance regressed from about 7.5s/it to 8s/it.


There's a hole in testing due to various bootstrapping problems on ia64 in the last week, so the precise cause remains uncertain.

Any ideas what causes the performance drop?


It's quite possible it's GVN-PRE.
It doesn't perform load motion, which SSAPRE did.
This is being worked on.
It also can find so many partially redundant values (compared to SSAPRE) that it can increase register pressure.
I'm working on this too.
The easy way to tell if either of these could be the problem is to turn off PRE and see what timings you get.




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