This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH 3/9] Use murmurhash3 for pointer map hashing
- From: Andi Kleen <ak at linux dot intel dot com>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: Andi Kleen <andi at firstfloor dot org>, gcc-patches at gcc dot gnu dot org, hubicka at ucw dot cz
- Date: Mon, 22 Apr 2013 08:42:41 -0700
- Subject: Re: [PATCH 3/9] Use murmurhash3 for pointer map hashing
- References: <1366407117-18462-1-git-send-email-andi at firstfloor dot org> <1366407117-18462-4-git-send-email-andi at firstfloor dot org> <CAFiYyc3btjf-4X2ozSw+9pAEtuzOyoaPejzoJQ-Myvf27e2S=A at mail dot gmail dot com>
On Mon, Apr 22, 2013 at 01:46:58PM +0200, Richard Biener wrote:
> On Fri, Apr 19, 2013 at 11:31 PM, Andi Kleen <andi@firstfloor.org> wrote:
> > From: Andi Kleen <ak@linux.intel.com>
> >
> > For a large LTO test case The previous pointer hash change brought
> > the collision rate for the WPA gimple type hash table from 90% to
> > 70. This patch uses the well known murmur3 to improve it further
> > to 64%.
>
> But if they are pointers then pointer_hash should be good enough... ?
The original pointer hash (ptr >> 3) % hashsize and throwing away most bits is
very poor.
The evahash based on I sent earlier is better, but murmur3 is even better than
that, at least for this case.
-Andi