[LLVMdev] R600, a new backend for AMD GPUs

[Villmow, Micah]

Tom,
 Two things. One is missing tests.  I have some I could send you, but they are mainly OpenCL based for the AMDIL backend, not for the R600.

That brings me to the second thing. Are the AMDIL backend and the R600 backend the same, or not? At this point, they really do feel like they are separate back ends, with one dependent on the other. 

As there is no other backend that is dependent on another backend in the tree, how would that work if the back ends diverge? Should we work on integrating both closer, or separate them completely?

Micah
> -----Original Message-----
> From: Stellard, Thomas
> Sent: Monday, March 26, 2012 9:50 AM
> To: llvmdev at cs.uiuc.edu
> Cc: Villmow, Micah
> Subject: RFC: R600, a new backend for AMD GPUs
> 
> Hi,
> 
> We've been working on an LLVM backend for the previous generation of
> AMD
> GPUs (HD 2XXX - HD 6XXX) and we would like submit it for inclusion in
> the
> main LLVM tree.  The latest code can be found in this git repository:
> http://cgit.freedesktop.org/~tstellar/llvm/ in the r600-initial-review
> branch or if you prefer you can download the entire tree with this
> link:
> http://cgit.freedesktop.org/~tstellar/llvm/snapshot/llvm-r600-initial-
> review.tar.gz
> The R600 backend is located in lib/Target/AMDIL
> 
> First, a brief description of the backend:
> 
> The r600 backend is being developed as a part of the Open Source
> compute
> stack in Mesa (http://www.mesa3d.org/), which uses the Gallium API.
> It uses large portions of the AMDIL backend which was open-sourced
> last December and you'll notice the TargetMachine for this backend
> (AMDGPUTargetMachine) is a sub-class of AMDILTargetMachine.  We are
> also
> currently working on an LLVM backend for Southern Islands GPUs, and we
> would like to get that code into the LLVM tree as well, once it has
> been
> approved for release.  The Southern Islands backend will be used for
> compute shaders and also graphics shaders in the AMD open source 3D
> driver.
> 
> One thing that I would like to point out is that all of the
> code from the AMDIL backend is licensed under a BSD license with an
> additional clause that deals with United States export laws (non-AMDIL
> code is licensed with the University of Illinois Open Source License).
> Will the LLVM project accept a backend with code licensed under this
> BSD
> license?  We would prefer to keep this license, but if it isn't
> acceptable, we can try to relicense it.
> 
> Second, I am looking for two categories of feedback for the r600
> backend:
> 
> 1. What changes do I need to make to get the backend included in the
> LLVM tree.
> 2. What changes can I make to improve the backend overall.
> 
> My top priority is to get the backend into the LLVM tree, so
> when you provide feedback if you could be clear about what
> changes are needed to get the backend into the tree versus what changes
> are just general improvements, I would appreciate it.
> 
> Lastly, I did a very brief run through of the code to check the coding
> style,
> but I know there are still some violations.  For example, a lot of the
> file headers are missing file descriptions.  I didn't want to spend a
> lot of time on coding style changes prior to the initial review in case
> I was asked to make big changes to the code, so I will address these
> issues once I have received an OK on the organization of the code.
> However, please still point out coding style errors to me, and I'll be
> sure to fix them during the final pass.
> 
> Looking forward to your feedback.
> 
> Thanks,
> Tom Stellard