add slice cast support

crates/rustc_codegen_spirv/src/builder/builder_methods.rs

@@ -2423,7 +2423,46 @@ impl<'a, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'tcx> {
                 "pointercast called on non-pointer dest type: {other:?}"
             )),
         };
-        let dest_pointee_size = self.lookup_type(dest_pointee).sizeof(self);
+
+        let dst_pointee_ty = self.lookup_type(dest_pointee);
+        let dest_pointee_size = dst_pointee_ty.sizeof(self);
+        let src_pointee_ty = self.lookup_type(ptr_pointee);
+
+        //  array -> element: *[T; N] -> *T
+        if let SpirvType::Array {
+            element: elem_ty, ..
+        } = src_pointee_ty
+            && elem_ty == dest_pointee
+        {
+            let zero = self.constant_u32(self.span(), 0).def(self);
+            return self
+                .emit()
+                .in_bounds_access_chain(dest_ty, None, ptr.def(self), [zero])
+                .unwrap()
+                .with_type(dest_ty);
+        }
+
+        // array -> RuntimeArray: *[T; N] -> *[T]
+        if let SpirvType::Array {
+            element: elem_ty, ..
+        } = src_pointee_ty
+            && let SpirvType::RuntimeArray {
+                element: rt_elem_ty,
+            } = dst_pointee_ty
+            && elem_ty == rt_elem_ty
+        {
+            let zero = self.constant_u32(self.span(), 0).def(self);
+            let elem_ptr_ty = self.type_ptr_to(elem_ty);
+            let elem_ptr = self
+                .emit()
+                .in_bounds_access_chain(elem_ptr_ty, None, ptr.def(self), [zero])
+                .unwrap();
+            return self
+                .emit()
+                .bitcast(dest_ty, None, elem_ptr)
+                .unwrap()
+                .with_type(dest_ty);
+        }
 
         if let Some((indices, _)) = self.recover_access_chain_from_offset(
             ptr_pointee,

tests/compiletests/ui/lang/core/slice.rs

@@ -0,0 +1,20 @@
+// build-pass
+
+use spirv_std::spirv;
+
+#[spirv(compute(threads(64)))]
+pub fn main(
+    #[spirv(storage_buffer, descriptor_set = 0, binding = 0)] input: &[u32; 3],
+    #[spirv(storage_buffer, descriptor_set = 0, binding = 1)] output: &mut u32,
+) {
+    // &[u32] fat pointer from a runtime storage buffer array
+    let slice: &[u32] = input;
+    let val = slice[1];
+
+    // *[u32; 3] -> *u32 via AccessChain (array->element path)
+    let array_ptr: *const [u32; 3] = input;
+    let element_ptr: *const u32 = array_ptr as *const u32;
+    let val2 = unsafe { *element_ptr };
+
+    *output = val + val2;
+}