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Date: Sat, 8 Dec 2012 20:48:19 -0500
From: Alain Espinosa <>
Subject: Re: GCN: indexed access to VGPRs

On 12/8/12, Solar Designer <> wrote:
> 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.

I think Nvidia cards supports this too, but using indexed registers is
slower than using "static" registers. In some fast kernels i get a
~50% speedup changing to normal registers.

> 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.

In OpenCL when you use a private array the compiler may use indexed registers.


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