------- Comment #18 from rakdver at kam dot mff dot cuni dot cz 2010-06-07 20:24 ------- Subject: Re: Big spec cpu2006 prefetch regressions on gcc 4.6 on x86
> ------- Comment #14 from changpeng dot fang at amd dot com 2010-06-07 18:27 > ------- > Here is the current status of my investigation: > > (1) 465.tonto regression (~9%): > The regressions mainly comes from loops which have array references with both > constant (prefetch_mod = 8) and non-constant (prefetch_mod=1) steps. The loops > are unrolled 8 times, and 8 non-constant step prefetches are inserted into the > unrolled loops. > > The ideal way to solve the problem is to compute the prefetch count > considering > the effect of unrolling, i.e. we should count 8 non-constant step prefetches > in stead of 1. > > (2) 416.gamess regression (~5%): > The regression is from non-constant-step prefetching for outer loops. I am > proposing not to do non-constant step prefetching for outer loops to solve the > problem. both of these sound reasonable to me, Zdenek -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44297