Implement SquaredDifference

We do this as a simplification on the tensorflow graph itself.
We transform SquaredDifference(a,b) into (a-b) * (a-b).

Athos/TFCompiler/Graph.py

@@ -501,11 +501,14 @@ class Value:
         return self.__val
 
 class Node:
-    def __init__(self):
-        self.__name = ""        #Name of node
-        self.__op = ""          #Name of operation carried out by node
-        self.__inputs = []      #List of all inputs to the current node
-        self.__attr = {}        #Map of (attrName, Value) of all attributes for the current node
+    def __init__(self, op="", inputs=None, name=""):
+        self.__name = name          #Name of node
+        self.__op = op              #Name of operation carried out by node
+        if inputs is None:
+            self.__inputs = []      #List of all inputs to the current node
+        else:
+            self.__inputs = inputs
+        self.__attr = {}            #Map of (attrName, Value) of all attributes for the current node
 
     def getName(self):
         return self.__name

Athos/TFCompiler/ProcessTFGraph.py

@@ -112,6 +112,32 @@ def prefixAllPlaceHolderNodes(graph):
 			remNodes.append(curNode)
 	graph.setNodesList(placeHolderNodes + remNodes)
 
+
+# List of Optimisations
+# 1. Split squared difference into (a-b)*(a-b)
+def simplifyGraph(graph):
+	allNodes = graph.getAllNodesRef()
+	nodesMap = graph.getAllNodes()
+	newNodes = []
+	inputsFixup = {}
+	for curNode in allNodes:
+		inputs = curNode.getInputsRef()
+		for i in range(len(inputs)):
+			if inputs[i] in inputsFixup:
+				inputs[i] = inputsFixup[inputs[i]]
+		if (curNode.getOp() == "SquaredDifference"):
+			sub = Graph.Node("Sub", inputs.copy(), curNode.getName() + "__sub")
+			mul = Graph.Node("Mul", [sub.getName(), sub.getName()], curNode.getName() + "__mul")
+			newNodes.append(sub)
+			newNodes.append(mul)
+			nodesMap[sub.getName()] = sub
+			nodesMap[mul.getName()] = mul
+			inputsFixup[curNode.getName()] = mul.getName()
+			nodesMap.pop(curNode.getName())
+		else:
+			newNodes.append(curNode)
+	graph.setNodesList(newNodes)
+
 def main():
 	sys.setrecursionlimit(10000)
 
@@ -131,6 +157,8 @@ def main():
 	sizeInfoFileName = os.path.join(folderName, 'sizeInfo.mtdata')
 	sizeInfo = readSizeInfo(sizeInfoFileName)
 
+	# Tensorflow graph level optimisations
+	simplifyGraph(graph)
 	# Place all PlaceHolder nodes together at the beginning
 	prefixAllPlaceHolderNodes(graph)