Compile a simple function (#2)

* Implement basics.

* Execute code

* Add wasm2wat test cases.

* abi_loc_for_arg for stack.

* Assert that sp_depth is 0 at the epilogue

* Do 32bit add.

* Assert that RAX can be used as a scratch register

* Reuse assembler.

* Align stack slots.

src/tests.rs

@@ -0,0 +1,34 @@
+use super::{translate, TranslatedModule};
+use wabt;
+
+fn translate_wat(wat: &str) -> TranslatedModule {
+    let wasm = wabt::wat2wasm(wat).unwrap();
+    let compiled = translate(&wasm).unwrap();
+    compiled
+}
+
+/// Execute the first function in the module.
+fn execute_wat(wat: &str, a: usize, b: usize) -> usize {
+    let translated = translate_wat(wat);
+    translated.execute_func(0, a, b)
+}
+
+#[test]
+fn adds() {
+    const CASES: &[(usize, usize, usize)] = &[
+        (5, 3, 8),
+        (0, 228, 228),
+        (usize::max_value(), 1, 0),
+    ];
+
+    let code = r#"
+(module
+  (func (param i32) (param i32) (result i32) (i32.add (get_local 0) (get_local 1)))
+)
+    "#;
+    for (a, b, expected) in CASES {
+        assert_eq!(execute_wat(code, *a, *b), *expected);
+    }
+}
+
+// TODO: Add a test that checks argument passing via the stack.