Error: Metal error Error while loading function: "Function 'cast_bf16_f16' does not exist" with llama3

I made some modifications to the example code in llama3 for it to run locally, but I encountered an error during execution. I am using a MacBook with an M3 chip. Below is the Rust code (I have omitted some irrelevant parts):

```rust
mod token;
use candle_core::{backend::BackendDevice, safetensors, DType, Device, MetalDevice, Tensor};
use candle_nn::VarBuilder;
use candle_transformers::{
generation::{LogitsProcessor, Sampling},
models::llama::Config,
};

use std::{error::Error, io::Write};

use candle_transformers::models::llama as model;
use model::{Llama, LlamaConfig};

const EOS_TOKEN: &str = "";
const DEFAULT_PROMPT: &str = "My favorite theorem is ";

fn main() -> anyhow::Result<()> {
let device = Device::new_metal(0)?;
let dtype = DType::F16;
let (llama, tokenizer_filename, mut cache, config) = {
let config: LlamaConfig =
serde_json::from_slice(&std::fs::read("model/config.json").unwrap()).unwrap();
let filenames = vec![
"model/model-00001-of-00005.safetensors",
"model/model-00002-of-00005.safetensors",
"model/model-00003-of-00005.safetensors",
"model/model-00004-of-00005.safetensors",
"model/model-00005-of-00005.safetensors",
];
let config = config.into_config(true);
let cache = model::Cache::new(false, dtype, &config, &device)?;

let vb = unsafe { VarBuilder::from_mmaped_safetensors(&filenames, dtype, &device)? };
(
Llama::load(vb, &config)?,
"model/tokenizer.json",
cache,
config,
)
};
let tokenizer = tokenizers::Tokenizer::from_file(tokenizer_filename).unwrap();
let eos_token_id = config
.eos_token_id
.or_else(|| tokenizer.token_to_id(EOS_TOKEN));
let prompt = DEFAULT_PROMPT;
let mut tokens = tokenizer.encode(prompt, true).unwrap().get_ids().to_vec();
let mut tokenizer = token::TokenOutputStream::new(tokenizer);

println!("starting the inference loop");
print!("{prompt}");
let mut logits_processor = {
let temperature = 0.8;
let sampling = if temperature <= 0. {
Sampling::ArgMax
} else {
match (None, None) {
(None, None) => Sampling::All { temperature },
(Some(k), None) => Sampling::TopK { k, temperature },
(None, Some(p)) => Sampling::TopP { p, temperature },
(Some(k), Some(p)) => Sampling::TopKThenTopP { k, p, temperature },
}
};
LogitsProcessor::from_sampling(299792458, sampling)
};

let mut start_gen = std::time::Instant::now();
let mut index_pos = 0;
let mut token_generated = 0;
for index in 0..10000 {
let (context_size, context_index) = if cache.use_kv_cache && index > 0 {
(1, index_pos)
} else {
(tokens.len(), 0)
};
if index == 1 {
start_gen = std::time::Instant::now()
}
let ctxt = &tokens[tokens.len().saturating_sub(context_size)..];
let input = Tensor::new(ctxt, &device)?.unsqueeze(0)?;
let logits = llama.forward(&input, context_index, &mut cache)?;
let logits = logits.squeeze(0)?;
let logits = if 1.1 == 1. {
logits
} else {
let start_at = tokens.len().saturating_sub(128);
candle_transformers::utils::apply_repeat_penalty(&logits, 1.1, &tokens[start_at..])?
};
index_pos += ctxt.len();

let next_token = logits_processor.sample(&logits)?;
token_generated += 1;
tokens.push(next_token);

if Some(next_token) == eos_token_id {
break;
}
if let Some(t) = tokenizer.next_token(next_token)? {
print!("{t}");
std::io::stdout().flush()?;
}
}
if let Some(rest) = tokenizer.decode_rest().unwrap() {
print!("{rest}");
}
let dt = start_gen.elapsed();
println!(
"\n\n{} tokens generated ({} token/s)\n",
token_generated,
(token_generated - 1) as f64 / dt.as_secs_f64(),
);
Ok(())
}
```
When I execute cargo run, the following error occurs:
```shell
Error: Metal error Error while loading function: "Function 'cast_bf16_f16' does not exist"

Caused by:
Error while loading function: "Function 'cast_bf16_f16' does not exist"
```

Reproduce the failure with the provided Rust llama3 example and `cargo run` on the M3 Metal device. Start by tracing Metal kernel loading for `cast_bf16_f16`; the issue is resolved when the example runs without this missing-function error.

Written by the indexing model from the issue text.