Manually implement for supported lanes

Author: calebzulawski

crates/core_simd/src/masks/full_masks.rs

@@ -114,8 +114,7 @@ where
     #[must_use = "method returns a new array and does not mutate the original value"]
     pub fn to_bitmask(self) -> [u8; super::bitmask_len(LANES)] {
         unsafe {
-            let mut bitmask: [u8; super::bitmask_len(LANES)] =
-                intrinsics::simd_bitmask(self.0);
+            let mut bitmask: [u8; super::bitmask_len(LANES)] = intrinsics::simd_bitmask(self.0);
 
             // There is a bug where LLVM appears to implement this operation with the wrong
             // bit order.

crates/core_simd/src/masks/to_bitmask.rs

@@ -85,15 +85,31 @@ pub const fn bitmask_len(lanes: usize) -> usize {
 }
 
 #[cfg(feature = "generic_const_exprs")]
-impl<T: MaskElement, const LANES: usize> ToBitMask<[u8; bitmask_len(LANES)]> for Mask<T, LANES>
-where
-    LaneCount<LANES>: SupportedLaneCount,
-{
-    fn to_bitmask(self) -> [u8; bitmask_len(LANES)] {
-        self.0.to_bitmask()
-    }
+macro_rules! impl_array_bitmask {
+    { $(impl ToBitMask<[u8; _]> for Mask<_, $lanes:literal>)* } => {
+        $(
+        impl<T: MaskElement> ToBitMask<[u8; bitmask_len($lanes)]> for Mask<T, $lanes>
+        {
+            fn to_bitmask(self) -> [u8; bitmask_len($lanes)] {
+                self.0.to_bitmask()
+            }
 
-    fn from_bitmask(bitmask: [u8; bitmask_len(LANES)]) -> Self {
-        Mask(mask_impl::Mask::from_bitmask(bitmask))
+            fn from_bitmask(bitmask: [u8; bitmask_len($lanes)]) -> Self {
+                Mask(mask_impl::Mask::from_bitmask(bitmask))
+            }
+        }
+        )*
     }
 }
+
+// FIXME this should be specified generically, but it doesn't seem to work with rustc, yet
+#[cfg(feature = "generic_const_exprs")]
+impl_array_bitmask! {
+    impl ToBitMask<[u8; _]> for Mask<_, 1>
+    impl ToBitMask<[u8; _]> for Mask<_, 2>
+    impl ToBitMask<[u8; _]> for Mask<_, 4>
+    impl ToBitMask<[u8; _]> for Mask<_, 8>
+    impl ToBitMask<[u8; _]> for Mask<_, 16>
+    impl ToBitMask<[u8; _]> for Mask<_, 32>
+    impl ToBitMask<[u8; _]> for Mask<_, 64>
+}

crates/core_simd/tests/masks.rs

@@ -81,7 +81,6 @@ macro_rules! test_mask_api {
                 assert_eq!(core_simd::Mask::<$type, 16>::from_bitmask(bitmask), mask);
             }
 
-            /*
             #[cfg(feature = "generic_const_exprs")]
             #[test]
             fn roundtrip_bitmask_array_conversion() {
@@ -95,7 +94,6 @@ macro_rules! test_mask_api {
                 assert_eq!(bitmask, [0b01001001, 0b10000011]);
                 assert_eq!(core_simd::Mask::<$type, 16>::from_bitmask(bitmask), mask);
             }
-            */
         }
     }
 }