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Use an unsafe trait to reinterpret packed struct references as bytes #7336

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19 changes: 13 additions & 6 deletions vortex-cuda/src/dynamic_dispatch/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,7 @@ pub use plan_builder::MaterializedPlan;

include!(concat!(env!("OUT_DIR"), "/dynamic_dispatch.rs"));

/// Reinterpret a `&T` as a byte slice for serialization into the packed plan.
/// Reinterpret a reference to a packed type as a raw bytes slice.
///
/// # Safety
///
Expand All @@ -58,10 +58,17 @@ include!(concat!(env!("OUT_DIR"), "/dynamic_dispatch.rs"));
/// `PackedStage`, `ScalarOp`) are bindgen-generated `#[repr(C)]` structs.
/// Padding bytes may be uninitialised on the Rust side, but the C reader
/// never inspects them, so the values are irrelevant.
fn as_bytes<T: Sized>(val: &T) -> &[u8] {
unsafe { from_raw_parts(std::ptr::addr_of!(*val).cast(), size_of::<T>()) }
unsafe trait AsPackedBytes: Sized {
/// Reinterpret a `&T` as a byte slice for serialization into the packed plan.
fn as_packed_bytes(&self) -> &[u8] {
unsafe { from_raw_parts(std::ptr::addr_of!(*self).cast(), size_of::<Self>()) }
}
}

unsafe impl AsPackedBytes for PlanHeader {}
unsafe impl AsPackedBytes for PackedStage {}
unsafe impl AsPackedBytes for ScalarOp {}

/// A stage used to build a [`CudaDispatchPlan`] on the host side.
///
/// This is NOT a C ABI struct — it exists purely on the Rust side and is
Expand Down Expand Up @@ -165,7 +172,7 @@ impl CudaDispatchPlan {
num_stages: stages.len() as u8,
plan_size_bytes: total_size as u16,
};
buffer.extend_from_slice(as_bytes(&header));
buffer.extend_from_slice(header.as_packed_bytes());

// Write each stage header followed by its scalar ops.
for stage in &stages {
Expand All @@ -176,9 +183,9 @@ impl CudaDispatchPlan {
source: stage.source,
num_scalar_ops: stage.scalar_ops.len() as u8,
};
buffer.extend_from_slice(as_bytes(&packed_stage));
buffer.extend_from_slice(packed_stage.as_packed_bytes());
for op in &stage.scalar_ops {
buffer.extend_from_slice(as_bytes(op));
buffer.extend_from_slice(op.as_packed_bytes());
}
}

Expand Down
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