rust: import alloc

This brings the `alloc` crate in-tree.

The code comes from Rust 1.54.0-beta.1, i.e. commit `bf62f4de3`.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

rust/alloc/alloc.rs

@@ -0,0 +1,30 @@
+use super::*;
+
+extern crate test;
+use crate::boxed::Box;
+use test::Bencher;
+
+#[test]
+fn allocate_zeroed() {
+    unsafe {
+        let layout = Layout::from_size_align(1024, 1).unwrap();
+        let ptr =
+            Global.allocate_zeroed(layout.clone()).unwrap_or_else(|_| handle_alloc_error(layout));
+
+        let mut i = ptr.as_non_null_ptr().as_ptr();
+        let end = i.add(layout.size());
+        while i < end {
+            assert_eq!(*i, 0);
+            i = i.offset(1);
+        }
+        Global.deallocate(ptr.as_non_null_ptr(), layout);
+    }
+}
+
+#[bench]
+#[cfg_attr(miri, ignore)] // isolated Miri does not support benchmarks
+fn alloc_owned_small(b: &mut Bencher) {
+    b.iter(|| {
+        let _: Box<_> = box 10;
+    })
+}