[BUG]: bfloat16 cast fails

[jon-chuang]

Bug description

[User] error: Couldn't lookup symbols:
  __truncsfbf2

Steps to reproduce

Repro

from random import rand
let image = rand[DType.float32](10)
a = image.data().simd_load[1]().cast[DType.bfloat16]()

System information

- What OS did you do install Mojo on ? Ubuntu 22.04
- Provide version information for Mojo by pasting the output of `mojo -v` mojo 0.5.0 (6e50a738)
- Provide Modular CLI version by pasting the output of `modular -v` modular 0.2.1 (5144fffe)

[willghatch]

I failed to reproduce this on MacOS. I'll try again later on Ubuntu.

[jon-chuang]

__truncsfbf2 is an x86 symbol. Are you using ARM Mac?

[jon-chuang]

Possibly related: JuliaLang/julia#52067

My device is an Intel on an ASUS machine.

[Sharktheone]

I also can't reproduce this. In the repl I get this:

(SIMD[bf16, 1]) a = {
  (scalar<bf16>) value = {
    (bf16) [0] = 1.5068
  }
}
(Tensor[f32]) image = {
  (TensorSpec) _spec = {
    (TensorShape) shape = {
      (_TensorShapeStorage) _rep = {
        (DTypePointer[invalid]) ptr = {
          (pointer<scalar<invalid>>) address = 0x000000000000000a
        }
        (SIMD[si64, 1]) idx = {
          (scalar<si64>) value = {
            (si64) [0] = 4756083780991582208
          }
        }
      }
    }
  }
  (DTypePointer[f32]) _ptr = {
    (pointer<scalar<f32>>) address = 0x000055c49a85f830
  }
}

and when i run it in a file, i also doesn't give me an error.
Note, that i've added let before a

[jon-chuang]

I get the error regardless of let

Expressions are delimited by a blank line.
Type `:quit` to exit the REPL and `:mojo help` for further assistance.

  1> from random import rand 
  2. let image = rand[DType.float32](10) 
  3. let a = image.data().simd_load[1]().cast[DType.bfloat16]()
[User] error: Couldn't lookup symbols:
  __truncsfbf2

[jon-chuang]

Maybe it's the clang/LLVM version on my machine?

Regardless, it's bad that it happens.

[Sharktheone]

Hmm, it seems like, you don't have the newest version of modular installed. Can you update it and reinstall mojo? I don't really think that is fixing that, but it was at leased tried then.

[willghatch]

OK, I spun up an Intel Ubuntu VM and was able to reproduce this in the repl but not in a file. We'll look into this.

[Sharktheone]

Interesting though I couldn't reproduce this. This might be for the same reason it also doesn't fail on MacOS. Might be depending on some CPU features

[jon-chuang]

Hmm, weird, when I run on file, it prints nothing.

def main():
    from random import rand
    let image = rand[DType.float32](10)
    let a = image.data().simd_load[1]().cast[DType.bfloat16]()
    print(a, "something")  # prints ' something'

[HJLebbink]

On mojo 0.7.0 (af002202) I get the same error:

from random import rand

fn main():
    let image = rand[DType.float32](10)
    let a = image.data().simd_load[1]().cast[DType.bfloat16]()
    let b = a.cast[DType.float32]()
    print(str(b))

gives:

JIT session error: Symbols not found: [ __truncsfbf2 ]
mojo: error: Failed to materialize symbols: { (exec, { main }) }

This is on a Intel(R) Xeon(R) w5-2455X

[River707]

This should be fixed in the next release!