Don't use u8x16_bitmask for ASCII Check

Because `NEON` doesn't have an equivalent instruction, the WASM runtimes
have to emit fairly suboptimal instructions for bitmasks. Therefore it's
best to avoid it, if the code can be written in an alternative way.

src/implementation/wasm32/simd128.rs

@@ -1,8 +1,8 @@
 //! Contains the wasm32 UTF-8 validation implementation.
 
 use core::arch::wasm32::{
-    u8x16, u8x16_bitmask, u8x16_gt, u8x16_shr, u8x16_shuffle, u8x16_splat, u8x16_sub_sat,
-    u8x16_swizzle, v128, v128_and, v128_any_true, v128_or, v128_xor,
+    u8x16, u8x16_all_true, u8x16_bitmask, u8x16_gt, u8x16_lt, u8x16_shr, u8x16_shuffle,
+    u8x16_splat, u8x16_sub_sat, u8x16_swizzle, v128, v128_and, v128_any_true, v128_or, v128_xor,
 };
 
 use crate::implementation::helpers::Utf8CheckAlgorithm;
@@ -252,7 +252,9 @@ impl SimdU8Value {
 
     #[inline]
     unsafe fn is_ascii(self) -> bool {
-        u8x16_bitmask(self.0) == 0
+        // We don't want to use u8x16_bitmask as that is inefficient on NEON.
+        // For x86 shifts should also be avoided.
+        u8x16_all_true(u8x16_lt(self.0, u8x16_splat(0b1000_0000_u8)))
     }
 }