Autovectorize is_four_byte()

src/unicode.rs

@@ -34,4 +34,5 @@
 const STATE_COMPACT: u32 = 0b00000000000000000000000000100000;
 
 fn is_four_byte(buf: &str) -> bool {
+    let mut ret = false;
     for &each in buf.as_bytes() {
@@ -37,4 +38,3 @@
     for &each in buf.as_bytes() {
-        if unlikely!(each >= 240) {
-            return true;
+        ret |= each >= 240;
     }
@@ -40,6 +40,5 @@
     }
-    }
-    false
+    ret
 }
 
 enum PyUnicodeKind {