Initial commit from sysy-main

test/23_test_vn.sy

@@ -0,0 +1,11 @@
+//test file for value numbering (vn)
+int main(){
+
+    int a, b, c, d;
+    a = 1;
+    b = a + 1;
+    c = a;
+    d = c + 1;
+
+    return d;
+}