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Message-ID: <20121209233619.GC4261@openwall.com>
Date: Mon, 10 Dec 2012 03:36:19 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: GCN: indexed access to VGPRs
On Sun, Dec 09, 2012 at 06:52:30PM +0530, Sayantan Datta wrote:
> Each 512 bit VGPR can hold 16 32bit ints. By indexed access to VGPRs ,
> I think he(solar) means each component of a VGPR can be indexed, right ? Or
> is it that the 256 different VGPRs can be indexed, not their individual
> components? Although the later would make more sense given that they are
> VGPRs.
We only need to index entire VGPRs, as with OpenCL different vector
components correspond to different work-items and there's no reason for
us to mix them up (nor should OpenCL allow us to do that).
(I recall reading that, surprisingly, on GCN it's technically possible
to index portions of VGPRs as well - or rather, make "not fully aligned"
accesses within the VGPR register file - but we don't need it, and
OpenCL should not make this functionality available to us.)
Alexander
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