Delete no_nonzero_bitscan configuration

Author: dtolnay

build.rs

@@ -11,18 +11,8 @@ fn main() {
     };
 
     if compiler >= 80 {
-        println!("cargo:rustc-check-cfg=cfg(no_nonzero_bitscan)");
         println!("cargo:rustc-check-cfg=cfg(test_node_semver)");
     }
-
-    if compiler < 53 {
-        // Efficient intrinsics for count-leading-zeros and count-trailing-zeros
-        // on NonZero integers stabilized in 1.53.0. On many architectures these
-        // are more efficient than counting zeros on ordinary zeroable integers.
-        // https://doc.rust-lang.org/std/num/struct.NonZeroU64.html#method.leading_zeros
-        // https://doc.rust-lang.org/std/num/struct.NonZeroU64.html#method.trailing_zeros
-        println!("cargo:rustc-cfg=no_nonzero_bitscan");
-    }
 }
 
 fn rustc_minor_version() -> Option<u32> {

src/identifier.rs

@@ -320,13 +320,6 @@ unsafe fn inline_len(repr: &Identifier) -> NonZeroUsize {
     // because inline strings are at least 1 byte long and cannot contain \0.
     let repr = unsafe { ptr::read(repr as *const Identifier as *const NonZeroU64) };
 
-    // Rustc >=1.53 has intrinsics for counting zeros on a non-zeroable integer.
-    // On many architectures these are more efficient than counting on ordinary
-    // zeroable integers (bsf vs cttz). On rustc <1.53 without those intrinsics,
-    // we count zeros in the u64 rather than the NonZeroU64.
-    #[cfg(no_nonzero_bitscan)]
-    let repr = repr.get();
-
     #[cfg(target_endian = "little")]
     let zero_bits_on_string_end = repr.leading_zeros();
     #[cfg(target_endian = "big")]
@@ -413,9 +406,6 @@ unsafe fn ptr_as_str(repr: &NonNull<u8>) -> &str {
 
 // Number of base-128 digits required for the varint representation of a length.
 fn bytes_for_varint(len: NonZeroUsize) -> usize {
-    #[cfg(no_nonzero_bitscan)] // rustc <1.53
-    let len = len.get();
-
     let usize_bits = mem::size_of::<usize>() * 8;
     let len_bits = usize_bits - len.leading_zeros() as usize;
     (len_bits + 6) / 7