GPUCompiler rewrite

[tshort]

This is a general issue to discuss plans on how to rewrite using GPUCompiler. Now that JuliaLang/julia#38642 is merged, it'll be easier for people to try out static compilation.

cc @jpsamaroo, @el-oso

[tshort]

I'll start on some housekeeping things like closing most of the PR's and issues.

[jpsamaroo]

I suspect you should still keep a lot of logic, but notably irgen, opt, and mcgen are replaceable by GPUCompiler.

[tshort]

I ditched all the existing code in #46.

One part I don't get is handling globals (string, symbols, and many others). I see placeholders for them. We need some way to populate those. I don't know if the code in libjulia can do that.

[jpsamaroo]

Where do see those placeholders? I couldn't find them when I looked for them.

[tshort]

I rechecked. I was wrong on that--must have misread it.

[jpsamaroo]

So I think the issue we'll run into is Julia's weird way of emitting globals, which sets them null with internal linkage. This already causes issues with GPUCompiler's optim pipeline, which does GlobalOpt and GlobalDCE, which causes such globals to be deleted and the null value inlined to loads of the global.

[dumblob]

This may sound rude, but I'll ask anyway 😉. What's the current state of this?

(I don't follow Julia development, so feel free to elaborate also about that as it seems tightly related)

[tshort]

The current state is stagnant. I don't know that anyone's doing much right now. The path forward (I think) involves finishing JuliaGPU/GPUCompiler.jl#125 and getting it to work with the latest version of LLVM.

The ongoing work on Julia compiler plugins (JuliaLang/julia#41632 and https://github.com/JuliaCompilerPlugins/) is also interesting. The ability to customize code generation may simplify GPUCompiler.

[jpsamaroo]

I agree with @tshort that Compiler Plugins will probably be the way to go for a purely static, no runtime approach. For most users, however, I think that JuliaLang/julia#41936 + PackageCompiler + "tree shaking" will do most of what we want. The sysimage generation system already does a lot of what we're trying to do here, and is very well tested (since every Julia user relies on it). JuliaLang/julia#40414 will make PC binaries much faster to generate too, making it a more enjoyable user experience.

[dumblob]

Thanks a lot for prompt pointers @tshort and @jpsamaroo . The links provide promising information - I'll follow them and see what'll happen as it seems to be a hot topic recently.

[MasonProtter]

Okay to close this issue? 😀