Should Julia use MLIR in the future?

I saw that MLIR technology is already driving a new programming language called MOJO with the ability to be very fast, make difficult-to-do optimizations and give instructions to many types of hardware such as CPU, GPU, TPU, etc.

Does Julia have plans to use MLIR technology in the future as an intermediate level IR or something similar?

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Generating MLIR from julia was experimented on with a project called brutus GitHub - JuliaLabs/brutus, it was early days of MLIR so performance wasn’t really good. Currently I don’t see any plans of switching julia from it’s LLVM IR backend to a MLIR one, but one could use it do specialized codegen, maybe through GitHub - JuliaLabs/MLIR.jl. But it’s all in an early stage.


Lord help me for saying this - and I say it in the spirit of welcoming @dafmdev

Look at this talk by Moses Giardano on porting Julia to the Graphcore IPU

This does of course not answer your question!


Welcome! :slight_smile:

ability to be very fast, make difficult-to-do optimizations and give instructions to many types of hardware such as CPU, GPU, TPU, etc.

I don’t think it should ever become a priority to switch to MLIR, since you could say mostly the same for for Julia (runs on TPU, GPU and is very fast on CPU)!

It would be a huge project, with lots of problems and not that many improvements above the current state of Julia.

What @gbaraldi linked will be a much more likely integration if someone sees worth in it.

I think MLIR is cool, but Julia has been getting similar features via other means so far (e.g. GPUCompiler.jl, LoopVectorization.jl, and all the automatic differentiation packages).


I don’t have any insights into MLIR, just wanted to link also to this project: GitHub - Pangoraw/Coil.jl: ꩜ Lift Julia array operations to MLIR dialects and run using IREE.. Maybe having the option to use MLIR for specific functions (instead of everywhere) could be attractive.

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To add onto this, it’s worth pointing out that MLIR and Mojo are not magic. The “ML” in MLIR stands for “multi-level”; think Inception for LLVM rather than Machine Learning. In fact, LLVM IR is a MLIR “dialect”. Most Mojo code running on CPU (and likely a lot running on GPU) is “lowered” from a higher-level dialect into LLVM IR, while all Julia code is lowered from a higher-level IR which is not a MLIR dialect into LLVM IR.

This should offer some insight into why just making Julia use MLIR instead of LLVM IR directly wouldn’t change much. Does that mean there’s no benefit to using MLIR? No. You could imagine how a library like Coil.jl could benefit if Julia IR was a MLIR dialect. Other non-LLVM MLIR dialects help Mojo achieve functionality like auto-vectorization at the language level, while the Julia ecosystem has to deal with issues like Why is LoopVectorization deprecated? because trying to integrate with the compiler is far more fragile.

Lastly, I should point out that neither Mojo nor the Julia ecosystem support TPUs right now. There have been attempts to get Julia code running on TPUs, but see above about fragile compiler integration. Additionally, TPUs speak a very limited set of high-level array operations and nothing else. Given most Julia and Mojo code is being written at a significantly lower level and using constructs (e.g. complex loops, lazy conditionals with side effects) that are not supported in the XLA IR TPUs use, it’s unlikely either will get great language-level support any time soon. The best path is likely via some high-level DSL, which is basically what JAX is for Python.


You may also be interested in the recent work towards compiler plugins in Julia#52964.


Doesn’t Julia SSA serve the same function as MLIR?

Yes and no. Some MLIR dialects allow for specific optimizations we don’t perform i.e in areas like linear Algebra


Is it possible to mix Julia SSA with other MLIR dialects? If not, would it be possible to adapt Julia SSA to become an MLIR dialect and mix it with other MLIR dialects?

At last year’s FOSDEM there was a presentation on how to build your own MLIR dialect.

Hi Xiaoxi, Julia is lowered to LLVM IR (see code_llvm in julia doc) which exists as a ML IR dialect ( so it’s inevitably compatible with other MLIR dialects.

I’m not sure what you’re looking for exactly, ML IR use SSA form too maybe this can help you:
To develop a julia ML IR dialect, imo the best way is to start from LLVM IR, and implements progressively julia specific operations in a dialect, if you want want higher level implementation in ML IR like type checking… this discussion may interest you:

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In case it wasn’t clear from @gbaraldi’s earlier comment, this is exactly what GitHub - JuliaLabs/brutus does.


I don’t think MLIR is needed for Julia, for speed (or for Mojo?).

Mojo was recently claimed 50% faster than Rust for some code, and then Mojo was beat by Julia (I believe Julia could always match, depends on how good the programmer is and if using good tools e.g. Bumper.jl which sort of amends a downside vs Mojo). Julia has the performance ceiling of C/C++, i.e. as fast as possible, is in practice often faster. You often get less if you’re new to Julia or haven’t read the performance section of the manual.

I’m mostly ignorant of MLIR, but not what’s needed for speed. I’m less ignorant of Mojo (and Rust that inspired it, its borrow checker).

Allocations aren’t slow in Julia (or Mojo) but they imply GC pressure, which can be a performance killer, but that is (fully) avoidable.

I’m a bit ignorant of GPU use; with Julia, but GPUs/CUDA.jl don’t have the GC pressure problem, and Julia is already about 3% faster than CUDA C. Julia is already ease/r to code for GPUs than many/most/all? languages.

[In a recent benchmark Mojo was actually slower than Python, because of their Dict implementation, Python’s is good. That problem may apply to Julia too, though I doubt it. Julia’s should be good, it was strictly because of Strings used in Dicts, and they could be improved in Julia (and Mojo I guess).]

To be fair (while still can be used, and for years, 1.10 will likely become LTS), this is non-ideal (LoopModels will likely replace this project, if not already):

NOTE: Deprecated for Julia v1.11 and above!

LoopVectorization only works for Julia 1.3 through 1.10. For 1.11 and newer, it simply uses @inbounds @fastmath instead, so it should still get roughly the same answer, but both runtime and compile time performance may change dramatically.

It was my favourite Julia package, seeing what (speed) it enabled, and others built on it e.g. Gaius.jl. @Elrod deprecated it but not (yet?) VectorizationBase.jl it depends on, which I’ve not looked much into. Gaius depends on both but some, at least, AccurateArithmetic.jl, depend on only the Base package.

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