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Re: [PATCH] Enabling Software Prefetching by Default at -O3
- From: Andreas Krebbel <krebbel at linux dot vnet dot ibm dot com>
- To: "Fang, Changpeng" <Changpeng dot Fang at amd dot com>
- Cc: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, borntraeger at de dot ibm dot com
- Date: Fri, 18 Jun 2010 10:38:31 +0200
- Subject: Re: [PATCH] Enabling Software Prefetching by Default at -O3
- References: <D4C76825A6780047854A11E93CDE84D02F7743@SAUSEXMBP01.amd.com>
Hi,
> This patch serves as a proposal to turn on software prefetching by default at -O3.
On S/390 I ran into a problem with the runtime of the prefetching pass when using
aggressive loop unrolling. There is an algorithm with quadratic runtime regarding the
memory references which causes a very long compile time. Christian already opened a
bugzilla for that (PR 44576). It probably would make sense to have a closer look at this
before enabling the pass by default. Perhaps we could simply limit the miss rate
computation to a certain amount of memory references?
Besides of that enabling the prefetching pass by default is ok with me. I think it would
help getting more people into improving it.
Bye,
-Andreas-