Initial commit from sysy-main

test/21_test_cse.sy

@@ -0,0 +1,18 @@
+//test file for common subexpression eliminiation (cse)
+int main(){
+
+    int a = 1;
+    int b = 2; 
+    int c, d, e, f;
+
+    c = a + b;
+
+    if(c > 0){
+        b = 3;
+        d = a + b;
+    }
+    
+    e = a + b;
+
+    return e;
+}