add parser benchmark for expressions (#226)

Cargo.toml

@@ -46,6 +46,10 @@ harness = false
 name = "exec"
 harness = false
 
+[[bench]]
+name = "parser"
+harness = false
+
 [[bin]]
 name = "boa"
 path = "src/bin/bin.rs"

benches/parser.rs

@@ -0,0 +1,30 @@
+#[macro_use]
+extern crate criterion;
+
+use boa::syntax::lexer::Lexer;
+use boa::syntax::parser::Parser;
+use criterion::black_box;
+use criterion::Criterion;
+
+static EXPRESSION: &str = r#"
+1 + 1 + 1 + 1 + 1 + 1 / 1 + 1 + 1 * 1 + 1 + 1 + 1;
+"#;
+
+fn expression_parser(c: &mut Criterion) {
+    // Don't include lexing as part of the parser benchmark
+    let mut lexer = Lexer::new(EXPRESSION);
+    lexer.lex().expect("failed to lex");
+    let tokens = lexer.tokens;
+    c.bench_function_over_inputs(
+        "Expression (Parser)",
+        move |b, tok| {
+            b.iter(|| {
+                Parser::new(black_box(tok.to_vec())).parse_all().unwrap();
+            })
+        },
+        vec![tokens],
+    );
+}
+
+criterion_group!(benches, expression_parser);
+criterion_main!(benches);