Implement some missing maths-related intrinsics

[tomaka]

These intrinsics are used by the Rust compiler.

[juj]

Are there such things as llvm_trunc_f32 and llvm_floor_f32? If so, could add those as well?

[tomaka]

Will do.

[juj]

Is Math.trunc an asm.js import? It is not listed here at least: http://asmjs.org/spec/latest/#standard-library

[tomaka]

@juj Oh I didn't realize these functions were part of an asm.js standard library. I just looked at a reference for the standard javascript Math object.

[tomaka]

It also looks like trunc is in fact not standard Javascript but an extension (or maybe it's ECMAScript 6, I'm not sure).
However it's quite simple to implement manually. Should that be done on the emscripten side or on the Rust side?

[kripken]

Emscripten side makes sense for things that are not asm.js builtins (then other projects can use them too). See e.g. llvm_uadd_with_overflow_i64 for an example.

For things that are asm.js builtins, adding them to library.js makes them work, but to make them fast we'd need them in the asm.js backend in LLVM. (But that can be done later, if needed.)

[juj]

I don't think we should reuse anything from Math if it means an FFI call, but have all of those in asm.js side. @kripken, @lukewagner: do you know if this list http://asmjs.org/spec/latest/#standard-library is out of date? It does not list Math.clz32 for example.

[kripken]

Yes, that does look out of date. @lukewagner, do you know what the correct list is?

[lukewagner]

Looks like Math.trunc is new with ES6 so it's not in the asm.js stdlib. There are several trunc operators in wasm. I'd recommend inlining trunc in Emscripten for now.

[kripken]

since trunc is fairly new in ES6, we should have a pollyfill.

[kripken]

Ok, given the optimization discussion, this looks good to go aside from needing a trunc polyfill, and also let's add some testing. Can add to test_llvm_intrinsics in tests/test_core.py, or an LLVM IR test in tests/cases would be ok as well.

[kripken]

What's the status here? Anything I can do to help?

[tomaka]

Sorry, I was taken by the release of Vulkan. It should be good now.

[kripken]

Thanks, merged!

This uncovered a backend bug with powi, where asm.js wants their types to be the same. Fixed in the fastcomp repo.