generate dependency graph and remove dead instructions

src/ram.py

@@ -97,6 +97,49 @@ class Ram(object):
             print(*self.instr[self.current]['args'])
             self.instr[self.current]['op'](self, *self.instr[self.current]['args'])
 
+    def generate_graph(self):
+        graph_edges = []
+        n_instr = len(self.instr)
+        for (n,instr) in enumerate(self.instr):
+            if ((instr['op'] == Ram.op) and (n<n_instr-1)):
+                graph_edges.append((n, n+1))
+            elif (instr['args'][0] == 'JUMP'):
+                dest = n+instr['args'][1]
+                if dest<n_instr:
+                    graph_edges.append((n, dest))
+            elif ((instr['args'][0] == 'JL') or (instr['args'][0] == 'JE')):
+                if (n<n_instr-1):
+                    graph_edges.append((n, n+1))
+                graph_edges.append((n, n+instr['args'][1]))
+        return graph_edges
+
+    def accessible_instr(self):
+        graph_edges = self.generate_graph()
+        accessible_from_instr = dict()
+        for edge in graph_edges:
+            accessible_from_instr.setdefault(edge[0], []).append(edge[1])
+        waitlist = [0]
+        accessible = []
+        while len(waitlist)>0:
+            current = waitlist.pop()
+            accessible.append(current)
+            try:
+                temp = accessible_from_instr[current]
+            except KeyError: # no node reachable from this node
+                pass
+            for elem in temp:
+                if elem not in accessible and elem not in waitlist:
+                    waitlist.append(elem)
+        return sorted(accessible)
+
+    def remove_unreachable_instr(self):
+        accessible = self.accessible_instr()
+        new_instr = [instr for (i,instr) in enumerate(self.instr) if i in accessible]
+        for instr in new_instr:
+            print(instr)
+        self.instr = new_instr
+
+
 
 
 ### example