pre merge constant.

theano/gof/opt.py

@@ -344,6 +344,37 @@ def MergeOptMerge(opt):
     return SeqOptimizer([merger, opt, merger])
 
 
+def pre_constant_merge(vars):
+    """
+    Merge constants before the variables in the list `out`
+    Modify the nodes that are in the path to create out.
+
+    :note: This don't change node that are in an env.
+           This is used to pre-merge node generated in an optimization
+           that we don't want DebugMode to check as there is too many
+    """
+
+    seen_var = set()
+    const_sig = {}     # variable -> variable.signature()  (for constants)
+    const_sig_inv = {} # signature -> variable (for constants)
+    def recursive_merge(var):
+        if var in seen_var:
+            return var
+        if var.owner and hasattr(var.owner, "env"):
+            return var
+        seen_var.add(var)
+        if isinstance(var, graph.Constant):
+            sig = var.signature()
+            if sig in const_sig_inv:
+                return const_sig_inv[sig]
+            const_sig_inv[sig] = var
+            return var
+        if var.owner:
+            for idx,inp in enumerate(var.owner.inputs):
+                var.owner.inputs[idx] = recursive_merge(inp)
+        return var
+
+    return map(recursive_merge, vars)
 
 ########################
 ### Local Optimizers ###

theano/tensor/opt.py

@@ -25,7 +25,7 @@ import basic as T
 from theano import compile  #to register the optimizer built by this file
 
 from theano.gof.python25 import any, all
-from theano.gof.opt import Optimizer
+from theano.gof.opt import Optimizer, pre_constant_merge
 from theano.gof import toolbox, DestroyHandler
 from basic import get_constant_value
 
@@ -1415,9 +1415,9 @@ def merge_two_slices(slice1, len1, slice2, len2):
         stop  = greedy_local_optimizer( list_opt, stop)
         step  = greedy_local_optimizer( list_opt, step)
 
-        #start = theano.printing.Print('start')(start)
-        #stop  = theano.printing.Print('stop')(stop)
-        #step = theano.printing.Print('step')(step)
+        #Pre merge constant for the same reason.
+        start, stop, step = pre_constant_merge([start, stop, step])
+
         return slice(start, stop, step)
 
 @register_canonicalize