From 4c5740779a88059e2fa547bfac2b275cc886e869 Mon Sep 17 00:00:00 2001
From: Waleed Khan <me@waleedkhan.name>
Date: Sun, 5 Sep 2021 00:09:02 -0500
Subject: [PATCH] bench: add `cherrypick_fast` benchmark

The results on the gecko-dev repository (https://github.com/mozilla/gecko-dev) show around 500x speedup for in-memory cherry-picks:

```
$ PATH_TO_REPO="$HOME/workspace/gecko-dev" cargo bench cherrypick
Benchmarking Cherrypick/Repo::cherrypick_commit: Warming up for 3.0000 s
Warning: Unable to complete 10 samples in 5.0s. You may wish to increase target time to 19.0s.
Cherrypick/Repo::cherrypick_commit
                        time:   [1.8935 s 1.9011 s 1.9088 s]
                        change: [-1.7816% +2.5204% +7.0223%] (p = 0.29 > 0.05)
                        No change in performance detected.
Cherrypick/Repo::cherrypick_fast
                        time:   [2.7665 ms 2.8209 ms 2.9297 ms]
                        change: [-1.1128% +1.4992% +4.9619%] (p = 0.38 > 0.05)
                        No change in performance detected.
```
---
 CHANGELOG.md       |  1 +
 benches/benches.rs | 41 +++++++++++++++++++++++++++++++++++++++--
 2 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index abd79b94c..892fb529a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fixed: Flickering in `git undo`'s rendering has been reduced.
 - Fixed: Commits made via `git merge` are now recorded in the event log.
 - Fixed: Long progress messages are now truncated on narrow screens.
+- Fixed: In-memory rebases on large repositories are now up to 500x faster.
 
 ## [0.3.4] - 2021-08-12
 
diff --git a/benches/benches.rs b/benches/benches.rs
index 4deffe240..f79eec65f 100644
--- a/benches/benches.rs
+++ b/benches/benches.rs
@@ -5,7 +5,7 @@ use branchless::core::formatting::Glyphs;
 use branchless::core::graph::{make_graph, BranchOids, HeadOid, MainBranchOid};
 use branchless::core::mergebase::{make_merge_base_db, MergeBaseDb};
 use branchless::core::rewrite::{BuildRebasePlanOptions, RebasePlanBuilder};
-use branchless::git::{Commit, Repo};
+use branchless::git::{CherryPickFastOptions, Commit, Repo};
 use branchless::tui::Effects;
 use criterion::{criterion_group, criterion_main, BatchSize, Criterion};
 
@@ -111,9 +111,46 @@ fn bench_find_path_to_merge_base(c: &mut Criterion) {
     });
 }
 
+fn bench_cherrypick_fast(c: &mut Criterion) {
+    let mut group = c.benchmark_group("Cherrypick");
+    group.sample_size(10);
+    group.bench_function("Repo::cherrypick_commit", |b| {
+        let repo = get_repo();
+        let head_oid = repo.get_head_info().unwrap().oid.unwrap();
+        let head_commit = repo.find_commit_or_fail(head_oid).unwrap();
+        let target_commit = nth_parent(head_commit.clone(), 1);
+
+        b.iter(|| {
+            let mut index = repo
+                .cherrypick_commit(&head_commit, &target_commit, 0)
+                .unwrap();
+            let tree_oid = repo.write_index_to_tree(&mut index).unwrap();
+            repo.find_tree(tree_oid).unwrap().unwrap()
+        })
+    });
+    group.bench_function("Repo::cherrypick_fast", |b| {
+        let repo = get_repo();
+        let head_oid = repo.get_head_info().unwrap().oid.unwrap();
+        let head_commit = repo.find_commit_or_fail(head_oid).unwrap();
+        let target_commit = nth_parent(head_commit.clone(), 1);
+
+        b.iter(|| {
+            repo.cherrypick_fast(
+                &head_commit,
+                &target_commit,
+                &CherryPickFastOptions {
+                    reuse_parent_tree_if_possible: false,
+                },
+            )
+            .unwrap()
+            .unwrap();
+        });
+    });
+}
+
 criterion_group!(
     name = benches;
     config = Criterion::default().sample_size(10);
-    targets = bench_rebase_plan, bench_find_path_to_merge_base
+    targets = bench_rebase_plan, bench_find_path_to_merge_base, bench_cherrypick_fast
 );
 criterion_main!(benches);