Add a benchmark of the hang-on-test-failure code path

Author: saethlin

bench-cargo-miri/slice-get-unchecked/Cargo.lock

@@ -0,0 +1,8 @@
+[package]
+name = "slice-get-unchecked"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

bench-cargo-miri/slice-get-unchecked/Cargo.toml

@@ -0,0 +1,12 @@
+//! This is a stripped-down version of the code pattern that causes runtime blowup when printing
+//! backtraces in a failed test under cargo miri test with -Zmiri-disable-isolation.
+//! See https://github.com/rust-lang/miri/issues/2273
+
+fn main() {
+    let x = vec![0u8; 4096];
+    let mut i = 0;
+    while i < x.len() {
+        let _element = unsafe { *x.get_unchecked(i) };
+        i += 1;
+    }
+}