Auto merge of rust-lang#93455 - asquared31415:vec-zero-opts, r=thomcc

Implement internal `IsZero` for Wrapping and Saturating for `Vec` optimizations

This implements the `IsZero` trait for the `Wrapping` and `Saturating` types so that users of these types can get the improved performance from the specialization of creating a `Vec` from a single element repeated when it has a zero bit pattern (example `vec![0_i32; 500]`, or after this PR `vec![Wrapping(0_i32); 500]`)

CC rust-lang#60978

Author: bors

library/alloc/src/lib.rs

@@ -134,6 +134,7 @@
 #![feature(ptr_metadata)]
 #![feature(ptr_sub_ptr)]
 #![feature(receiver_trait)]
+#![feature(saturating_int_impl)]
 #![feature(set_ptr_value)]
 #![feature(slice_from_ptr_range)]
 #![feature(slice_group_by)]

library/alloc/src/vec/is_zero.rs

@@ -1,3 +1,5 @@
+use core::num::{Saturating, Wrapping};
+
 use crate::boxed::Box;
 
 #[rustc_specialization_trait]
@@ -144,3 +146,17 @@ impl_is_zero_option_of_nonzero!(
     NonZeroUsize,
     NonZeroIsize,
 );
+
+unsafe impl<T: IsZero> IsZero for Wrapping<T> {
+    #[inline]
+    fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+}
+
+unsafe impl<T: IsZero> IsZero for Saturating<T> {
+    #[inline]
+    fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+}