feat(wgpu): add to_dtype kernel (#906)

* feat(wgpu): add to_dtype kernel

* fix: add WebGPUNativeType

* style: clippy fix

---------

Co-authored-by: Corey Lowman <clowman1993@gmail.com>

dfdx-core/src/tensor/webgpu/device.rs

@@ -247,6 +247,36 @@ impl Webgpu {
     pub(crate) fn get_shader_module(&self, name: TypeId) -> Option<Arc<ShaderModule>> {
         self.cs_cache.read().get(&name).cloned()
     }
+    /// Submit a command buffer to the GPU.
+    ///
+    /// Note: Does not block until completion. If you need this, use
+    /// `self.dev.poll(Maintain::WaitForSubmissionIndex(idx))` using the
+    /// returned [`wgpu::SubmissionIndex`]
+    pub(crate) fn submit_commands<F>(
+        &self,
+        label: Option<&str>,
+        command_builder: F,
+    ) -> wgpu::SubmissionIndex
+    where
+        F: FnOnce(&mut wgpu::CommandEncoder),
+    {
+        let mut encoder = self
+            .dev
+            .create_command_encoder(&wgpu::CommandEncoderDescriptor {
+                label: label.clone(),
+            });
+
+        if let Some(label) = label {
+            encoder.push_debug_group(label);
+        }
+        command_builder(&mut encoder);
+        if labe.is_some() {
+            encoder.pop_debug_group();
+        }
+
+        let cmd = [encoder.finish()];
+        self.queue.submit(cmd)
+    }
 
     // #[allow(unused)]
     // pub(crate) unsafe fn get_workspace<E>(&self, len: usize) -> Result<MutexGuard<Buffer>, Error> {

dfdx-core/src/tensor/webgpu/mod.rs

@@ -1,8 +1,10 @@
 mod allocate;
 mod device;
+mod types;
 
 pub use device::Buffer;
 pub use device::Webgpu;
+pub use types::*;
 
 #[cfg(test)]
 mod tests {

dfdx-core/src/tensor/webgpu/types.rs

@@ -0,0 +1,56 @@
+use crate::shapes::Unit;
+
+/// A primitive data type natively supported by WebGPU.
+///
+/// See: https://www.w3.org/TR/WGSL/#types
+///
+/// todo: support packed types
+pub trait WebgpuNativeType: Unit {
+    /// Name of the data type in WGSL.
+    const NAME: &'static str;
+}
+
+macro_rules! webgpu_type {
+    ($RustTy:ty) => {
+        impl WebgpuNativeType for $RustTy {
+            const NAME: &'static str = stringify!($RustTy);
+        }
+    };
+    ($RustTy:ty, $WgpuTy:expr) => {
+        impl WebgpuNativeType for $RustTy {
+            const NAME: &'static str = $WgpuTy;
+        }
+    };
+}
+
+/*
+see:
+- https://docs.rs/wgpu/latest/wgpu/struct.Features.html#associatedconstant.SHADER_F16
+- https://docs.rs/wgpu/latest/wgpu/struct.Features.html#associatedconstant.SHADER_F64
+- https://docs.rs/wgpu/latest/wgpu/struct.Features.html#associatedconstant.SHADER_I16
+ */
+#[cfg(feature = "f16")]
+webgpu_type!(half::f16, "f16");
+webgpu_type!(f32);
+// todo: only enable when f64 feature is enabled
+#[cfg(feature = "f64")]
+webgpu_type!(f64);
+
+#[cfg(feature = "i16")]
+webgpu_type!(i16);
+webgpu_type!(i32);
+
+webgpu_type!(u32);
+webgpu_type!(bool);
+
+pub(crate) trait HasGlslType {
+    const TYPE: &'static str;
+}
+
+impl HasGlslType for f32 {
+    const TYPE: &'static str = "float";
+}
+
+impl HasGlslType for f64 {
+    const TYPE: &'static str = "double";
+}

dfdx-core/src/tensor_ops/to_dtype/to_dtype.wgsl

@@ -0,0 +1,16 @@
+alias T = __SRC__;
+alias U = __DST__;
+
+@group(0) @binding(0)
+var<storage, read> in: array<T>;
+
+@group(0) @binding(1)
+var<storage, read_write> out: array<U>;
+
+@compute @workgroup_size(1, 1, 1)
+fn main(
+    @builtin(global_invocation_id) global_id: vec3<u32>
+) {
+    let i = global_id.x;
+    out[i] = U(in[i]);
+}

dfdx-core/src/tensor_ops/to_dtype/webgpu_kernel.rs

@@ -1,9 +1,102 @@
-use crate::prelude::{Unit, Webgpu};
+use crate::{
+    prelude::Storage,
+    tensor::webgpu::{Webgpu, WebgpuNativeType},
+    tensor_ops::utilities::webgpu_kernels::webgpu_params,
+};
+use num_traits::AsPrimitive;
+use wgpu;
 
-impl<E1: Unit, E2: Unit> super::ToDtypeKernel<E1, E2> for Webgpu {
+/// kernel template
+const KERNEL: &'static str = include_str!("./to_dtype.wgsl");
+
+const LAYOUT_DESC: wgpu::BindGroupLayoutDescriptor = wgpu::BindGroupLayoutDescriptor {
+    label: Some("to-dtype"),
+    entries: &[
+        wgpu::BindGroupLayoutEntry {
+            binding: 0,
+            visibility: wgpu::ShaderStages::COMPUTE,
+            ty: wgpu::BindingType::Buffer {
+                ty: wgpu::BufferBindingType::Storage { read_only: true },
+                has_dynamic_offset: false,
+                min_binding_size: None,
+            },
+            count: None,
+        },
+        wgpu::BindGroupLayoutEntry {
+            binding: 1,
+            visibility: wgpu::ShaderStages::COMPUTE,
+            ty: wgpu::BindingType::Buffer {
+                ty: wgpu::BufferBindingType::Storage { read_only: false },
+                has_dynamic_offset: false,
+                min_binding_size: None,
+            },
+            count: None,
+        },
+    ],
+};
+
+impl<E1: WebgpuNativeType + AsPrimitive<E2>, E2: WebgpuNativeType> super::ToDtypeKernel<E1, E2>
+    for Webgpu
+{
     fn forward<S: crate::prelude::Shape>(
         inp: crate::prelude::Tensor<S, E1, Self>,
     ) -> Result<crate::prelude::Tensor<S, E2, Self>, crate::prelude::Error> {
-        todo!()
+        let module_name = std::format!("convert_{}_to_{}", E1::NAME, E2::NAME);
+        let label = Some(module_name.as_str());
+        let device = inp.device;
+
+        let layout = device.dev.create_bind_group_layout(&LAYOUT_DESC);
+        let shader_source: String = KERNEL
+            .replace("__SRC__", E1::NAME)
+            .replace("__DST__", E2::NAME);
+
+        // TODO: support WGSL shaders in device shader cache
+        let source = wgpu::ShaderSource::Wgsl(shader_source.into());
+        let shader_module = device
+            .dev
+            .create_shader_module(wgpu::ShaderModuleDescriptor {
+                label: Some(shader_name),
+                source,
+            });
+        let pipeline_layout = device
+            .dev
+            .create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
+                label: label.clone(),
+                bind_group_layouts: layouts,
+                // todo: these are useful and we should use them if the adapter supports them
+                push_constant_ranges: &push_constant_ranges,
+            });
+
+        let pipeline = device
+            .dev
+            .create_compute_pipeline(&wgpu::ComputePipelineDescriptor {
+                label: label.clone(),
+                layout: Some(&pipeline_layout),
+                module: &shader_module,
+                entry_point: fn_name,
+            });
+
+        let numel = inp.shape.num_elements();
+        let shape = inp.shape;
+        let strides = shape.strides();
+        let output = unsafe { device.alloc_empty::<E2>(numel) }?;
+
+        let params: wgpu::BindGroup = webgpu_params!(device, pipeline; inp.data, output);
+
+        let _idx = device.submit_commands(label.clone(), |encoder| {
+            let (x, y, z) = *work_groups;
+            let mut pass = encoder.begin_compute_pass(&wgpu::ComputePassDescriptor {
+                label: label.clone(),
+                ..Default::default()
+            });
+            // TODO: should this be called before the pass, as the pass is created, or before submission?
+            pass.set_pipeline(&pipeline);
+            pass.set_bind_group(0, &params, &[]);
+            pass.dispatch_workgroups(numel as u32, 1, 1);
+        });
+
+        // note: no need to sync here, buffer can remain on the gpu until to_array or to_vec gets called,
+        // and those functions sync the device before mapping the buffer
+        Ok(device.build_tensor(shape, strides, output))
     }
 }

dfdx-core/src/tensor_ops/utilities/webgpu_kernels.rs

@@ -6,6 +6,33 @@ use crate::{
 use core::any::TypeId;
 use std::{borrow::Cow, marker::PhantomData, sync::Arc, vec::Vec};
 
+use wgpu::{
+    BindingType, BufferBindingType, ComputePipelineDescriptor, Device, PipelineLayout, ShaderStages,
+};
+
+/// Creates a [`BindGroup`] for a pipeline from a set of [`wgpu::BindingResource`]s.
+macro_rules! webgpu_params {
+    ($self:expr, $pipeline:expr; $($x:expr),+ $(,)? ) => {
+        {
+            let bindings = [$($x.as_entire_binding()),+];
+            let entries: Vec<_> = bindings
+                .into_iter()
+                .enumerate()
+                .map(|(i, binding)| wgpu::BindGroupEntry {
+                    binding: i as u32,
+                    resource: binding,
+                })
+                .collect();
+            $self.dev.create_bind_group(&::wgpu::BindGroupDescriptor {
+                label: None,
+                layout: &($pipeline).get_bind_group_layout(0),
+                entries: &entries
+            })
+        }
+    }
+}
+pub(crate) use webgpu_params;
+
 pub(crate) trait UnaryOpWebgpuKernel<E> {
     const DF_USES_FX: bool;
     const HAS_CONST_DF: bool;
@@ -49,6 +76,7 @@ macro_rules! webgpu_unary {
         }
     };
 }
+pub(crate) use webgpu_unary;
 
 /// Zero-sized marker type for forward pass TypeId
 #[derive(Debug, Default)]
@@ -62,23 +90,6 @@ pub(crate) struct Backward<E: Dtype, K> {
     _phantom: PhantomData<(E, K)>,
 }
 
-pub(crate) trait HasGlslType {
-    const TYPE: &'static str;
-}
-
-impl HasGlslType for f32 {
-    const TYPE: &'static str = "float";
-}
-
-impl HasGlslType for f64 {
-    const TYPE: &'static str = "double";
-}
-
-pub(crate) use webgpu_unary;
-use wgpu::{
-    BindingType, BufferBindingType, ComputePipelineDescriptor, Device, PipelineLayout, ShaderStages,
-};
-
 impl<E: Dtype + HasGlslType, K: UnaryOpWebgpuKernel<E> + 'static> UnaryKernel<K, E> for Webgpu {
     const BACKWARD_WITHOUT_INP: bool = K::DF_USES_FX;
     const BACKWARD_WITHOUT_DATA: bool = K::HAS_CONST_DF;