Emscripten incoming branch is now on LLVM 3.5

[kripken]

Hi there, I wanted to give you a heads up that emscripten's incoming branch now uses LLVM 3.5, which I know was waited on for rust integration.

Also, I'm curious to experiment with this myself and help out. I'll try to build this project and see how far I get. Please let me know if there's other stuff I can try or should do.

[thehydroimpulse]

👍

[tomaka]

Thanks for the message!
For the moment I'm encountering a compilation issue with the 3.5 merge (that I've posted in the fastcompo repo).

If you want to try this, I suggest to wait a few days/weeks until Rust becomes a bit more stable. For the moment you need to use the commit ad9e75938 of the Rust compiler for it to compile (Rust is that instable), so it's not really worth the pain :)

[kripken]

Heh, thanks, maybe I'll wait then. I did run into a build error now (that I started on rust master, before reading this).

[kripken]

No luck with that revision. I'm trying

./configure --llvm-root=/home/alon/Dev/fastcomp/build/Release+Asserts
make

and it works for a while, then

rustc: x86_64-unknown-linux-gnu/stage0/lib/rustlib/x86_64-unknown-linux-gnu/lib/librbml
compile: x86_64-unknown-linux-gnu/rustllvm/ExecutionEngineWrapper.o
/home/alon/Dev/rust/src/rustllvm/ExecutionEngineWrapper.cpp: In function ‘LLVMOpaqueExecutionEngine* LLVMBuildExecutionEngine(LLVMModuleRef, LLVMRustJITMemoryManagerRef)’:
/home/alon/Dev/rust/src/rustllvm/ExecutionEngineWrapper.cpp:94:53: error: no matching function for call to ‘llvm::EngineBuilder::EngineBuilder(std::remove_reference<std::unique_ptr<llvm::Module>&>::type)’
     ExecutionEngine *ee = EngineBuilder(std::move(m))
                                                     ^
/home/alon/Dev/rust/src/rustllvm/ExecutionEngineWrapper.cpp:94:53: note: candidates are:
In file included from /home/alon/Dev/rust/src/rustllvm/rustllvm.h:34:0,
                 from /home/alon/Dev/rust/src/rustllvm/ExecutionEngineWrapper.cpp:11:
/home/alon/Dev/fastcomp/include/llvm/ExecutionEngine/ExecutionEngine.h:594:3: note: llvm::EngineBuilder::EngineBuilder(llvm::Module*)
   EngineBuilder(Module *m) : M(m) {
   ^
/home/alon/Dev/fastcomp/include/llvm/ExecutionEngine/ExecutionEngine.h:594:3: note:   no known conversion for argument 1 from ‘std::remove_reference<std::unique_ptr<llvm::Module>&>::type {aka std::unique_ptr<llvm::Module>}’ to ‘llvm::Module*’
/home/alon/Dev/fastcomp/include/llvm/ExecutionEngine/ExecutionEngine.h:570:7: note: llvm::EngineBuilder::EngineBuilder(const llvm::EngineBuilder&)
 class EngineBuilder {
       ^
/home/alon/Dev/fastcomp/include/llvm/ExecutionEngine/ExecutionEngine.h:570:7: note:   no known conversion for argument 1 from ‘std::remove_reference<std::unique_ptr<llvm::Module>&>::type {aka std::unique_ptr<llvm::Module>}’ to ‘const llvm::EngineBuilder&’
/home/alon/Dev/fastcomp/include/llvm/ExecutionEngine/ExecutionEngine.h:570:7: note: llvm::EngineBuilder::EngineBuilder(llvm::EngineBuilder&&)
/home/alon/Dev/fastcomp/include/llvm/ExecutionEngine/ExecutionEngine.h:570:7: note:   no known conversion for argument 1 from ‘std::remove_reference<std::unique_ptr<llvm::Module>&>::type {aka std::unique_ptr<llvm::Module>}’ to ‘llvm::EngineBuilder&&’
make: *** [x86_64-unknown-linux-gnu/rustllvm/ExecutionEngineWrapper.o] Error 1

[tomaka]

I'm not compiling Rust with any specific option. I'm just using the regular Rust. In fact ad9e75938 is one of the nightlies that were released a few days ago. I'm going to make these things clearer in the README after Rust 1.0 alpha is released.

The way cargo-emscripten works is that it asks the Rust compiler to emit LLVM IR, which is then passed to emcc.
I expect problems due to platform incompatibilities with this method, but it is also possible to pass low-level informations to Rust (data layout, endianess, etc). I didn't implement this yet, though.

[emidoots]

What are the next steps that need to be done? For reference:

• Rust 1.0 has been released.
• From this document it looks like Rust is using LLVM 3.3.
• Emscripten is now using LLVM 3.7 it looks like.

[tomaka]

From this document it looks like Rust is using LLVM 3.3.

You're looking at the wrong branch. I think Rust 1.0 uses LLVM 3.6, and the nightlies and maybe 1.1 beta use 3.7.

A few months ago, someone forked this repo and managed to make it work: https://github.com/AerialX/cargo-build
There are some demos in the wild: http://bl.ocks.org/AerialX/1041460cb9dd5876658c http://myth.aaronlindsay.com/test/
However it isn't really easy to build.

I think the plan is the following:

• update https://github.com/AerialX/rust-rt-minimal, which is a fork of rust's stdlib that works with emscripten
• make the build script of this repo build https://github.com/AerialX/rust-rt-minimal
• pass --sysroot and --target automatically when compiling