Add codegen test

tests/codegen/simd/repr-packed.rs

@@ -0,0 +1,30 @@
+#![crate_type = "lib"]
+#![feature(repr_simd, platform_intrinsics)]
+
+#[repr(simd, packed)]
+pub struct Simd<T, const N: usize>([T; N]);
+
+#[repr(simd)]
+#[derive(Copy, Clone)]
+pub struct FullSimd<T, const N: usize>([T; N]);
+
+extern "platform-intrinsic" {
+    fn simd_mul<T>(a: T, b: T) -> T;
+}
+
+// non-powers-of-two have padding and need to be expanded to full vectors
+fn load<T, const N: usize>(v: Simd<T, N>) -> FullSimd<T, N> {
+    unsafe {
+        let mut tmp = core::mem::MaybeUninit::<FullSimd<T, N>>::uninit();
+        std::ptr::copy_nonoverlapping(&v as *const _, tmp.as_mut_ptr().cast(), 1);
+        tmp.assume_init()
+    }
+}
+
+// CHECK-LABEL: @square_packed
+#[no_mangle]
+pub fn square_packed(x: Simd<f32, 3>) -> FullSimd<f32, 3> {
+    // CHECK: load <3 x float>, ptr %x, align 4
+    let x = load(x);
+    unsafe { simd_mul(x, x) }
+}