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Date: Sun, 9 Dec 2012 05:12:41 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: GCN: indexed access to VGPRs

Sayantan, Milen, all -

On page 53 in AMD_Southern_Islands_Instruction_Set_Architecture.pdf
(SHA-1: c64c24077eab93b070d291da3624a8d988d70d5d), there's a mention
that VGPRs may be indexed - something I had thought was not possible.

This may let us use the vector register file to augment LDS, e.g. to
compute a larger number of bcrypt hashes in parallel (some will have
their S-boxes in LDS, and some more - in VGPRs).  I guess we have
spare VGPRs in our current bcrypt code (since we bump into LDS size
first).

I don't know if there's currently a way to access this functionality
without going to a level lower than OpenCL or not, though.

Alexander

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