Matmul after reshape crashes on Metal

[laptou]

Doing a matrix multiplication after transpose() calls / after permute() crashes on Metal backend.
Here's a reproduction of the bug:

use candle_core::{DType, Device, Tensor};

pub fn main() -> candle_core::Result<()> {
    let dev = Device::Cpu;
    let x = Tensor::zeros(&[1, 8, 52, 1250], DType::F32, &dev)?;
    let y = Tensor::zeros(&[1, 8, 1250, 52], DType::F32, &dev)?;
    let z = x.matmul(&y)?; // works fine
    dbg!(z.shape());

    let x = Tensor::zeros(&[1, 8, 1250, 52], DType::F32, &dev)?;
    let y = Tensor::zeros(&[1, 8, 52, 1250], DType::F32, &dev)?;
    let z = x.matmul(&y)?; // works fine
    dbg!(z.shape());

    let x = Tensor::zeros(&[1, 1250, 416], DType::F32, &dev)?;
    let y = Tensor::zeros(&[1, 1250, 416], DType::F32, &dev)?;

    let x = x.reshape((1, 1250, 8, 52))?.transpose(1, 2)?;
    let y = y
        .reshape((1, 1250, 8, 52))?
        .transpose(1, 2)?
        .transpose(2, 3)?;

    let z = x.matmul(&y)?; // works fine
    dbg!(z.shape());

    let dev = Device::new_metal(0)?;
    let x = Tensor::zeros(&[1, 8, 52, 1250], DType::F32, &dev)?;
    let y = Tensor::zeros(&[1, 8, 1250, 52], DType::F32, &dev)?;
    let z = x.matmul(&y)?; // works fine
    dbg!(z.shape());

    let x = Tensor::zeros(&[1, 8, 1250, 52], DType::F32, &dev)?;
    let y = Tensor::zeros(&[1, 8, 52, 1250], DType::F32, &dev)?;
    let z = x.matmul(&y)?; // works fine
    dbg!(z.shape());

    let x = Tensor::zeros(&[1, 1250, 416], DType::F32, &dev)?;
    let y = Tensor::zeros(&[1, 1250, 416], DType::F32, &dev)?;

    let x = x.reshape((1, 1250, 8, 52))?.transpose(1, 2)?;
    let y = y
        .reshape((1, 1250, 8, 52))?
        .transpose(1, 2)?
        .transpose(2, 3)?;
      // also crashes if you do permute(0, 2, 3, 1)
      // also crashes if you create the array with shape (1, 1250, 8, 52) without reshaping

    let z = x.matmul(&y)?; // crashes
    dbg!(z.shape());

    Ok(())
}

[laptou]

The error message says "Invalid matmul arguments" which is not very clear. The error in the code is called MatMulNonContiguous. The error goes away if I call .contiguous() on x and y before calling matmul. Can I send a PR to update this error message to be clearer?