fix(ssa refactor): Implement array equality in SSA-gen (#1704)

* Implement array equality

* chore(ssa refactor): elements -> composite_type

---------

Co-authored-by: Joss <joss@aztecprotocol.com>

crates/noirc_evaluator/src/ssa_refactor/ssa_gen/context.rs

@@ -226,6 +226,10 @@ impl<'a> FunctionContext<'a> {
     ) -> Values {
         let op = convert_operator(operator);
 
+        if op == BinaryOp::Eq && matches!(self.builder.type_of_value(lhs), Type::Array(..)) {
+            return self.insert_array_equality(lhs, operator, rhs);
+        }
+
         if operator_requires_swapped_operands(operator) {
             std::mem::swap(&mut lhs, &mut rhs);
         }
@@ -255,6 +259,93 @@ impl<'a> FunctionContext<'a> {
         result.into()
     }
 
+    /// The frontend claims to support equality (==) on arrays, so we must support it in SSA here.
+    /// The actual BinaryOp::Eq in SSA is meant only for primitive numeric types so we encode an
+    /// entire equality loop on each array element. The generated IR is as follows:
+    ///
+    ///   ...
+    ///   result_alloc = allocate
+    ///   store u1 1 in result_alloc
+    ///   jmp loop_start(0)
+    /// loop_start(i: Field):
+    ///   v0 = lt i, array_len
+    ///   jmpif v0, then: loop_body, else: loop_end
+    /// loop_body():
+    ///   v1 = array_get lhs, index i
+    ///   v2 = array_get rhs, index i
+    ///   v3 = eq v1, v2
+    ///   v4 = load result_alloc
+    ///   v5 = and v4, v3
+    ///   store v5 in result_alloc
+    ///   v6 = add i, Field 1
+    ///   jmp loop_start(v6)
+    /// loop_end():
+    ///   result = load result_alloc
+    fn insert_array_equality(
+        &mut self,
+        lhs: ValueId,
+        operator: noirc_frontend::BinaryOpKind,
+        rhs: ValueId,
+    ) -> Values {
+        let lhs_type = self.builder.type_of_value(lhs);
+        let rhs_type = self.builder.type_of_value(rhs);
+
+        let (array_length, element_type) = match (lhs_type, rhs_type) {
+            (
+                Type::Array(lhs_composite_type, lhs_length),
+                Type::Array(rhs_composite_type, rhs_length),
+            ) => {
+                assert!(
+                    lhs_composite_type.len() == 1 && rhs_composite_type.len() == 1,
+                    "== is unimplemented for arrays of structs"
+                );
+                assert_eq!(lhs_composite_type[0], rhs_composite_type[0]);
+                assert_eq!(lhs_length, rhs_length, "Expected two arrays of equal length");
+                (lhs_length, lhs_composite_type[0].clone())
+            }
+            _ => unreachable!("Expected two array values"),
+        };
+
+        let loop_start = self.builder.insert_block();
+        let loop_body = self.builder.insert_block();
+        let loop_end = self.builder.insert_block();
+
+        // pre-loop
+        let result_alloc = self.builder.insert_allocate();
+        let true_value = self.builder.numeric_constant(1u128, Type::bool());
+        self.builder.insert_store(result_alloc, true_value);
+        let zero = self.builder.field_constant(0u128);
+        self.builder.terminate_with_jmp(loop_start, vec![zero]);
+
+        // loop_start
+        self.builder.switch_to_block(loop_start);
+        let i = self.builder.add_block_parameter(loop_start, Type::field());
+        let array_length = self.builder.field_constant(array_length as u128);
+        let v0 = self.builder.insert_binary(i, BinaryOp::Lt, array_length);
+        self.builder.terminate_with_jmpif(v0, loop_body, loop_end);
+
+        // loop body
+        self.builder.switch_to_block(loop_body);
+        let v1 = self.builder.insert_array_get(lhs, i, element_type.clone());
+        let v2 = self.builder.insert_array_get(rhs, i, element_type);
+        let v3 = self.builder.insert_binary(v1, BinaryOp::Eq, v2);
+        let v4 = self.builder.insert_load(result_alloc, Type::bool());
+        let v5 = self.builder.insert_binary(v4, BinaryOp::And, v3);
+        self.builder.insert_store(result_alloc, v5);
+        let one = self.builder.field_constant(1u128);
+        let v6 = self.builder.insert_binary(i, BinaryOp::Add, one);
+        self.builder.terminate_with_jmp(loop_start, vec![v6]);
+
+        // loop end
+        self.builder.switch_to_block(loop_end);
+        let mut result = self.builder.insert_load(result_alloc, Type::bool());
+
+        if operator_requires_not(operator) {
+            result = self.builder.insert_not(result);
+        }
+        result.into()
+    }
+
     /// Inserts a call instruction at the end of the current block and returns the results
     /// of the call.
     ///