Fix shuffle index constant not being monomorphized.

src/test/ui/simd/monomorphize-shuffle-index.rs

@@ -0,0 +1,40 @@
+//run-pass
+#![feature(repr_simd, platform_intrinsics)]
+
+extern "platform-intrinsic" {
+    fn simd_shuffle<T, I, U>(a: T, b: T, i: I) -> U;
+}
+
+#[derive(Copy, Clone)]
+#[repr(simd)]
+struct Simd<T, const N: usize>([T; N]);
+
+trait Shuffle<const N: usize> {
+    const I: [u32; N];
+
+    unsafe fn shuffle<T, const M: usize>(&self, a: Simd<T, M>, b: Simd<T, M>) -> Simd<T, N> {
+        simd_shuffle(a, b, Self::I)
+    }
+}
+
+fn main() {
+    struct I1;
+    impl Shuffle<4> for I1 {
+        const I: [u32; 4] = [0, 2, 4, 6];
+    }
+
+    struct I2;
+    impl Shuffle<2> for I2 {
+        const I: [u32; 2] = [1, 5];
+    }
+
+    let a = Simd::<u8, 4>([0, 1, 2, 3]);
+    let b = Simd::<u8, 4>([4, 5, 6, 7]);
+    unsafe {
+        let x: Simd<u8, 4> = I1.shuffle(a, b);
+        assert_eq!(x.0, [0, 2, 4, 6]);
+
+        let y: Simd<u8, 2> = I2.shuffle(a, b);
+        assert_eq!(y.0, [1, 5]);
+    }
+}