How to use LLVM as backend in other language (not in C++)?

Question

I'm trying to write a programming language and being stuck at code generation phase.

After thorough consideration, I decide to use LLVM as my back-end because I don't want to deal with obscure low-level stuff (generating assembly is fine to me, but I need more knowledge on linking to accomplish my work).

One stumbling block is that my work is not on C++. It means I could not use ready LLVM classes in my code.

Could I generate LLVM IR code in the form of characters string, save it to file (or no need?) and then compile it? In the case I could, is there any other form that I can generate to help LLVM run faster?

Special thanks to any advice.

One Lyner · Accepted Answer · 2020-08-03 15:17:22Z

4

Copying the LLVM documentation

Your compiler front-end will communicate with LLVM by creating a module in the LLVM intermediate representation (IR) format. Assuming you want to write your language’s compiler in [something else than C++], there are 3 major ways to tackle generating LLVM IR from a front-end:

Call into the LLVM libraries code using your language’s FFI (foreign function interface).

for: best tracks changes to the LLVM IR, .ll syntax, and .bc format

for: enables running LLVM optimization passes without a emit/parse overhead

for: adapts well to a JIT context

against: lots of ugly glue code to write

Emit LLVM assembly from your compiler’s native language.

for: very straightforward to get started

against: the .ll parser is slower than the bitcode reader when interfacing to the middle end

against: it may be harder to track changes to the IR

Emit LLVM bitcode from your compiler’s native language.

for: can use the more-efficient bitcode reader when interfacing to the middle end

against: you’ll have to re-engineer the LLVM IR object model and bitcode writer in your language

against: it may be harder to track changes to the IR

The option you mention is number 2.

answered Aug 3, 2020 at 15:17

One Lyner

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tandat Over a year ago

Another question. In the option number 2, should I include pre-built clang compiler (with a copy of its license) in my project or ask user to install it themselves?

arrowd · Accepted Answer · 2020-08-03 07:23:19Z

1

Could I generate LLVM IR code in the form of characters string, save it to file (or no need?) and then compile it?

This approach is being used by some projects (GHC, for instance), but it is not recommended. Instead, you can use LLVM C bindings. Interfacing with C is a common feature for many languages, so it shouldn't be a problem.

answered Aug 3, 2020 at 7:23

arrowd

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