Add benches, examples for cached hashing.

Ignore flamegraph files

eth2/utils/cached_tree_hash/benches/benches.rs

@@ -0,0 +1,73 @@
+#[macro_use]
+extern crate criterion;
+
+use cached_tree_hash::TreeHashCache;
+use criterion::black_box;
+use criterion::{Benchmark, Criterion};
+use ethereum_types::H256 as Hash256;
+use hashing::hash;
+use tree_hash::TreeHash;
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let n = 1024;
+
+    let source_vec: Vec<Hash256> = (0..n).map(|_| Hash256::random()).collect();
+
+    let mut source_modified_vec = source_vec.clone();
+    source_modified_vec[n - 1] = Hash256::random();
+
+    let modified_vec = source_modified_vec.clone();
+    c.bench(
+        &format!("vec_of_{}_hashes", n),
+        Benchmark::new("standard", move |b| {
+            b.iter_with_setup(
+                || modified_vec.clone(),
+                |modified_vec| black_box(modified_vec.tree_hash_root()),
+            )
+        })
+        .sample_size(100),
+    );
+
+    let modified_vec = source_modified_vec.clone();
+    c.bench(
+        &format!("vec_of_{}_hashes", n),
+        Benchmark::new("build_cache", move |b| {
+            b.iter_with_setup(
+                || modified_vec.clone(),
+                |vec| black_box(TreeHashCache::new(&vec, 0)),
+            )
+        })
+        .sample_size(100),
+    );
+
+    let vec = source_vec.clone();
+    let modified_vec = source_modified_vec.clone();
+    c.bench(
+        &format!("vec_of_{}_hashes", n),
+        Benchmark::new("cache_update", move |b| {
+            b.iter_with_setup(
+                || {
+                    let cache = TreeHashCache::new(&vec, 0).unwrap();
+                    (cache, modified_vec.clone())
+                },
+                |(mut cache, modified_vec)| black_box(cache.update(&modified_vec)),
+            )
+        })
+        .sample_size(100),
+    );
+
+    c.bench(
+        &format!("{}_hashes", n),
+        Benchmark::new("hash_64_bytes", move |b| {
+            b.iter(|| {
+                for _ in 0..n {
+                    let _digest = hash(&[42; 64]);
+                }
+            })
+        })
+        .sample_size(100),
+    );
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);