[Mesa-dev] [PATCH 2/2] radeonsi: Use pointers rather than resource descriptors for shader constants v3

[Michel Dänzer]

On Mon, 2013-08-05 at 14:58 -0400, Tom Stellard wrote:
> From: Tom Stellard <thomas.stellard at amd.com>
> 
> The TGSI->LLVM pass for radeonsi preloads constants and relies on LLVM's
> sinking pass to reduce SGPR usage by lowering constant reads to an
> optimal place in the code.  However, LLVM's machine sink pass will not
> lower instructions that have been selected from llvm.SI.load.const
> intrinsics, because these instructions do not have a MachineMemOperand,
> which LLVM needs in order to determine whether or not it is safe to sink
> a load.  Replacing this intrinsic with a real load instruction will
> enable the sinking optimization and probably a few others.
> 
> The other advantages of using pointers are:
> + Reduced register usage (pointers take 2 registers, descriptors take 4)
> + More code sharing with compute

OTOH, one advantage of using descriptors is more graceful behaviour if
the shader tries to access beyond the constant buffer's extents. Would
it be possible to get the benefits of the machine sink pass with a
descriptor based solution as well?


> diff --git a/src/gallium/drivers/radeonsi/radeonsi_shader.c b/src/gallium/drivers/radeonsi/radeonsi_shader.c
> index 4d8a479..d251252 100644
> --- a/src/gallium/drivers/radeonsi/radeonsi_shader.c
> +++ b/src/gallium/drivers/radeonsi/radeonsi_shader.c
> @@ -115,20 +115,31 @@ static LLVMValueRef build_indexed_load(
>  	return result;
>  }
>  
> -static LLVMValueRef build_constant_load(
> +static LLVMValueRef build_load_constant(

Any particular reason for changing the helper function name in this
patch? The patch could be smaller and cleaner otherwise.


-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer