Rollup merge of #77504 - Amanieu:select_simd_bitmask, r=ecstatic-morse

Support vectors with fewer than 8 elements for simd_select_bitmask

Resolves the issue raised here: https://github.com/rust-lang/stdarch/issues/310#issuecomment-693730094

src/test/ui/simd-intrinsic/simd-intrinsic-generic-select.rs

@@ -49,8 +49,8 @@ fn main() {
         simd_select(m4, 0u32, 1u32);
         //~^ ERROR found non-SIMD `u32`
 
-        simd_select_bitmask(0u8, x, x);
-        //~^ ERROR mask length `8` != other vector length `4`
+        simd_select_bitmask(0u16, x, x);
+        //~^ ERROR mask length `16` != other vector length `4`
         //
         simd_select_bitmask(0u8, 1u32, 2u32);
         //~^ ERROR found non-SIMD `u32`

src/test/ui/simd-intrinsic/simd-intrinsic-generic-select.stderr

@@ -22,11 +22,11 @@ error[E0511]: invalid monomorphization of `simd_select` intrinsic: expected SIMD
 LL |         simd_select(m4, 0u32, 1u32);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0511]: invalid monomorphization of `simd_select_bitmask` intrinsic: mismatched lengths: mask length `8` != other vector length `4`
+error[E0511]: invalid monomorphization of `simd_select_bitmask` intrinsic: mismatched lengths: mask length `16` != other vector length `4`
   --> $DIR/simd-intrinsic-generic-select.rs:52:9
    |
-LL |         simd_select_bitmask(0u8, x, x);
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |         simd_select_bitmask(0u16, x, x);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0511]: invalid monomorphization of `simd_select_bitmask` intrinsic: expected SIMD argument type, found non-SIMD `u32`
   --> $DIR/simd-intrinsic-generic-select.rs:55:9

src/test/ui/simd/simd-intrinsic-generic-select.rs

@@ -167,4 +167,29 @@ fn main() {
         let e = u32x8(8, 9, 10, 11, 4, 5, 6, 7);
         assert_eq!(r, e);
     }
+
+    unsafe {
+        let a = u32x4(0, 1, 2, 3);
+        let b = u32x4(4, 5, 6, 7);
+
+        let r: u32x4 = simd_select_bitmask(0u8, a, b);
+        let e = b;
+        assert_eq!(r, e);
+
+        let r: u32x4 = simd_select_bitmask(0xfu8, a, b);
+        let e = a;
+        assert_eq!(r, e);
+
+        let r: u32x4 = simd_select_bitmask(0b0101u8, a, b);
+        let e = u32x4(0, 5, 2, 7);
+        assert_eq!(r, e);
+
+        let r: u32x4 = simd_select_bitmask(0b1010u8, a, b);
+        let e = u32x4(4, 1, 6, 3);
+        assert_eq!(r, e);
+
+        let r: u32x4 = simd_select_bitmask(0b1100u8, a, b);
+        let e = u32x4(4, 5, 2, 3);
+        assert_eq!(r, e);
+    }
 }