From 5b1c896c605ed1047fc17a437e0b58792a778e2d Mon Sep 17 00:00:00 2001
From: Maxim Vezenov <mvezenov@gmail.com>
Date: Tue, 24 Sep 2024 12:17:23 -0400
Subject: [PATCH] fix(ssa): RC correctness issue  (#6134)

# Description

## Problem\*

Resolves #6123

## Summary\*

Still a draft as I want to test it a bit more and am not fully sure if
it is the best solution.

## Additional Context



## Documentation\*

Check one:
- [X] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [X] I have tested the changes locally.
- [X] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.
---
 .../src/ssa/ssa_gen/context.rs                |  4 ++
 .../brillig_rc_regression_6123/Nargo.toml     |  7 ++++
 .../brillig_rc_regression_6123/src/main.nr    | 41 +++++++++++++++++++
 tooling/debugger/ignored-tests.txt            |  3 +-
 4 files changed, 54 insertions(+), 1 deletion(-)
 create mode 100644 test_programs/execution_success/brillig_rc_regression_6123/Nargo.toml
 create mode 100644 test_programs/execution_success/brillig_rc_regression_6123/src/main.nr

diff --git a/compiler/noirc_evaluator/src/ssa/ssa_gen/context.rs b/compiler/noirc_evaluator/src/ssa/ssa_gen/context.rs
index fb7091a8854..c71c3a33edf 100644
--- a/compiler/noirc_evaluator/src/ssa/ssa_gen/context.rs
+++ b/compiler/noirc_evaluator/src/ssa/ssa_gen/context.rs
@@ -732,6 +732,10 @@ impl<'a> FunctionContext<'a> {
         let element_types = Self::convert_type(element_type);
         values.map_both(element_types, |value, element_type| {
             let reference = value.eval_reference();
+            // Reference counting in brillig relies on us incrementing reference
+            // counts when arrays/slices are constructed or indexed.
+            // Thus, if we dereference an lvalue which happens to be array/slice we should increment its reference counter.
+            self.builder.increment_array_reference_count(reference);
             self.builder.insert_load(reference, element_type).into()
         })
     }
diff --git a/test_programs/execution_success/brillig_rc_regression_6123/Nargo.toml b/test_programs/execution_success/brillig_rc_regression_6123/Nargo.toml
new file mode 100644
index 00000000000..533777df67f
--- /dev/null
+++ b/test_programs/execution_success/brillig_rc_regression_6123/Nargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "brillig_rc_regression_6123"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.34.0"
+
+[dependencies]
\ No newline at end of file
diff --git a/test_programs/execution_success/brillig_rc_regression_6123/src/main.nr b/test_programs/execution_success/brillig_rc_regression_6123/src/main.nr
new file mode 100644
index 00000000000..3eb29659944
--- /dev/null
+++ b/test_programs/execution_success/brillig_rc_regression_6123/src/main.nr
@@ -0,0 +1,41 @@
+struct Builder {
+    note_hashes: BoundedVec<Field, 2>,
+    nullifiers: BoundedVec<Field, 2>,
+}
+
+impl Builder {
+    fn append_note_hashes_with_logs(&mut self, num_note_hashes: u32) {
+        let index_offset = self.note_hashes.len();
+        for i in 0..self.note_hashes.max_len() {
+            if i < num_note_hashes {
+                self.add_new_note_hash((index_offset + i) as Field);
+            }
+        }
+    }
+
+    fn add_new_note_hash(&mut self, value: Field) {
+        self.note_hashes.push(value);
+    }
+}
+
+fn swap_items<T, let N: u32>(vec: &mut BoundedVec<T, N>, from_index: u32, to_index: u32) {
+    let tmp = vec.storage[from_index];
+    vec.storage[from_index] = vec.storage[to_index];
+    vec.storage[to_index] = tmp;
+}
+
+unconstrained fn main() {
+    let mut builder = Builder { note_hashes: BoundedVec::new(), nullifiers: BoundedVec::new() };
+
+    builder.append_note_hashes_with_logs(2);
+    builder.nullifiers.storage[1] = 27;
+    // Get ordered items before shuffling.
+    let note_hashes = builder.note_hashes.storage;
+    let original_first_note_hash = note_hashes[0];
+    // Shuffle.
+    swap_items(&mut builder.note_hashes, 1, 0);
+
+    for i in 0..1 {
+        assert_eq(note_hashes[i], original_first_note_hash);
+    }
+}
diff --git a/tooling/debugger/ignored-tests.txt b/tooling/debugger/ignored-tests.txt
index 78e14397938..0037b8e5d5f 100644
--- a/tooling/debugger/ignored-tests.txt
+++ b/tooling/debugger/ignored-tests.txt
@@ -4,4 +4,5 @@ is_unconstrained
 macros
 references
 regression_4709
-reference_only_used_as_alias
\ No newline at end of file
+reference_only_used_as_alias
+brillig_rc_regression_6123
\ No newline at end of file