[LLVMdev] [llvm-commits] RFC: Merge branches/R600 into TOT for 3.2 release

[Benjamin Kramer]

On 01.11.2012, at 14:44, Tom Stellard <tom at stellard.net> wrote:

> Moving this thread to llvmdev.
> 
> On Tue, Oct 30, 2012 at 11:09:34PM -0700, Chris Lattner wrote:
>> On Oct 30, 2012, at 11:35 AM, Tom Stellard <tom at stellard.net> wrote:
>>>> Hi Tom,
>>>> 
>>>> Time is running short, but this would be great.  The best place to start is to begin decomposing the mega-patch into individual pieces that makes sense.  Do you have changes outside Target/AMDGPU?  Those would be the be place to start.
>>> 
>>> Not counting test cases, new intrinsics, and configuration files,
>>> there are no changes outside of Target/AMDGPU.  I always submit patches
>>> for changes I make outside of Target/AMDGPU.  Isn't that how Open Source
>>> is supposed to work? ;)
>> 
>> Well yeah, but sometimes you still have to ask :).  Can the intrinsics be pulled into the target directory ala Targets/MBlaze/MBlazeIntrinsics.td or Targets/NVPTX/NVPTXIntrinsics.td?
>> 
>>> What's the best way to break up the patch?  In the past I have divided it up
>>> into 4 patches:
>>> 
>>> 1. Core Target files (*TargetMachine, *InstInfo, etc.)
>>> 2. Target specific passes
>>> 3. .td files
>>> 4. Configuration / Intrinsic additions
>>> 
>>> Would something like this work?
>> 
>> Any way that you can slices it to land it in stages would be preferred.  Another major challenge will be to find someone to review the patch.  You don't need detailed comments on every design aspect, but it is important to give you a basic "yeah, the structure looks fine and there aren't any obviously gratuitous code style violations" is the sort of review I'm looking for.  I'm not sure a great way to get this, but asking on llvmdev is probably a good start.
>> 
> 
> Hi LLVM Developers,
> 
> I would like to merge the R600 backend from branches/R600 into TOT
> prior to the LLVM 3.2 release.  As you can see in the above paragraph,
> Chris has asked me to find someone to review the code.  If there is
> anyone that would be willing to take the time and look at the code,
> I would really appreciate it.  For your convenience, I have split the
> code into two patches:
> 
> http://people.freedesktop.org/~tstellar/llvm/R600.patch
> http://people.freedesktop.org/~tstellar/llvm/SI.patch
> 
> R600.patch adds the code required to support the R600 generation of GPUs,
> and SI.patch adds the code required to support the Southern Islands
> generation of GPUs.
> 
> In addition, this code can be found in the branches/R600 branch of the
> llvm SVN repository, as well as in my git repo:
> 
> git fetch git://people.freedesktop.org/~tstellar/llvm master
> gitweb: http://cgit.freedesktop.org/~tstellar/llvm/
> 
> In the attached patches, the R600 backend is not built by default,
> so you need to pass the --enable-experimental-targets=AMDGPU to build
> it.  If the backend is merged into TOT, I was planning to keep the
> build disabled by default, but I don't mind enabling it if someone wants
> to approve that change.
> 
> I will also be changing the name of the backend directory from AMDGPU to
> R600 per Chris' suggestion.  These patches still use the AMDGPU
> directory, but I'll be updating the R600 branch with this change
> as soon as I am able to pass along updated build instructions to our users.
> 
> Looking forward to your comments.

I went over the patches today and I must say that it looks a lot better than when you started getting it in shape for inclusion in LLVM. Great Job!

While I can't comment on technical details of the architecture, here are my high level style comments:

- The prevailing style of brace placement in LLVM is to never put the opening brace on it's own line. There are different styles used in your patches.
- In some places the indentation uses 4 or more spaces instead of the preferred two.
- There's commented out code in both c++ source and the .td files. Please either document why it's commented out or remove the code. "//FIXME: gcc complains on this." isn't helpful at all.
- Macros like
#define FirstNonDebugInstr(A) A->begin()
are not only confusing, the name also says something that the definition doesn't provide. Please audit the macros and change them to UPPERCASE so it's obvious that there's some macro magic at work.

Overall I think this should go in as soon as possible. It has been around for a while and you have been actively maintaining it over the whole timespan since it was first proposed for inclusion. I'm afraid it's too late for 3.2, but we're now early in the 3.3 cycle and it would be really nice to have a stable R600 backend in 3.3.

- Ben