From 910d20f6a51a91374facd1462b927bdb7e6eb0a9 Mon Sep 17 00:00:00 2001
From: Jason Williams <jwilliams720@bloomberg.net>
Date: Wed, 18 Sep 2019 21:24:40 +0100
Subject: [PATCH] support early returns, fixes #101

---
 Cargo.toml       |  4 ++++
 benches/fib.rs   | 30 ++++++++++++++++++++++++++++++
 src/lib/exec.rs  | 23 ++++++++++++++++++-----
 tests/js/test.js | 14 ++++++++++++--
 4 files changed, 64 insertions(+), 7 deletions(-)
 create mode 100644 benches/fib.rs

diff --git a/Cargo.toml b/Cargo.toml
index 16d5145dae..45e845f5f8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -36,6 +36,10 @@ path = "src/lib/lib.rs"
 name = "string"
 harness = false
 
+[[bench]]
+name = "fib"
+harness = false
+
 [[bin]]
 name = "boa"
 path = "src/bin/bin.rs"
diff --git a/benches/fib.rs b/benches/fib.rs
new file mode 100644
index 0000000000..1ef30fbdec
--- /dev/null
+++ b/benches/fib.rs
@@ -0,0 +1,30 @@
+#[macro_use]
+extern crate criterion;
+
+use boa::exec;
+use boa::syntax::lexer::Lexer;
+use boa::syntax::parser::Parser;
+use criterion::black_box;
+use criterion::Criterion;
+
+static SRC: &str = r#"
+let num = 12;
+
+function fib(n) {
+  if (n <= 1) return 1;
+  return fib(n - 1) + fib(n - 2);
+}
+
+let res = fib(num);
+
+res;
+"#;
+
+fn fibonacci(c: &mut Criterion) {
+    c.bench_function("fibonacci (Execution)", move |b| {
+        b.iter(|| exec(black_box(SRC)))
+    });
+}
+
+criterion_group!(benches, fibonacci);
+criterion_main!(benches);
diff --git a/src/lib/exec.rs b/src/lib/exec.rs
index c4e843d9d3..4b42a2e196 100644
--- a/src/lib/exec.rs
+++ b/src/lib/exec.rs
@@ -30,6 +30,7 @@ pub trait Executor {
 pub struct Interpreter {
     /// An object representing the global object
     environment: LexicalEnvironment,
+    is_return: bool,
 }
 
 /// Builder for the [`Interpreter`]
@@ -62,7 +63,13 @@ impl Executor for Interpreter {
                 let mut obj = to_value(None::<()>);
                 for e in es.iter() {
                     let val = self.run(e)?;
-                    if e == es.last().unwrap() {
+                    // early return
+                    if self.is_return {
+                        obj = val;
+                        self.is_return = false;
+                        break;
+                    }
+                    if e == es.last().expect("unable to get last value") {
                         obj = val;
                     }
                 }
@@ -312,10 +319,15 @@ impl Executor for Interpreter {
                     _ => Ok(Gc::new(ValueData::Undefined)),
                 }
             }
-            ExprDef::Return(ref ret) => match *ret {
-                Some(ref v) => self.run(v),
-                None => Ok(Gc::new(ValueData::Undefined)),
-            },
+            ExprDef::Return(ref ret) => {
+                let result = match *ret {
+                    Some(ref v) => self.run(v),
+                    None => Ok(Gc::new(ValueData::Undefined)),
+                };
+                // Set flag for return
+                self.is_return = true;
+                result
+            }
             ExprDef::Throw(ref ex) => Err(self.run(ex)?),
             ExprDef::Assign(ref ref_e, ref val_e) => {
                 let val = self.run(val_e)?;
@@ -410,6 +422,7 @@ impl InterpreterBuilder {
     pub fn build(self) -> Interpreter {
         Interpreter {
             environment: LexicalEnvironment::new(self.global.clone()),
+            is_return: false,
         }
     }
 }
diff --git a/tests/js/test.js b/tests/js/test.js
index ffbdea4081..1946d591b6 100644
--- a/tests/js/test.js
+++ b/tests/js/test.js
@@ -1,2 +1,12 @@
-let a = "hello";
-print(a);
+let num = 12;
+
+function fib(n) {
+  if (n <= 1) return 1;
+  return fib(n - 1) + fib(n - 2);
+}
+
+let res = fib(num);
+
+res;
+
+// (2 - 1 = 1) + (2 - 2 = rt 1)