Fixed an optimization crash during gemm optimization related to complex

theano/tensor/blas.py

@@ -1120,8 +1120,17 @@ def _gemm_from_factored_list(lst):
             return True
         except Exception:
             return False
-    lst = [(T.cast(sM[0],sM[1].type.dtype), sM[1])
-            for sM in lst if is_pair(sM)]
+
+    lst2 = []
+    # Remove the tuple that can't be casted correctly.
+    # This can happen when we try to cast a complex to a real
+    for sM in lst:
+        if is_pair(sM):
+            try:
+                lst2.append(T.cast(sM[0],sM[1].type.dtype), sM[1])
+            except TypeError:
+                pass
+    lst = lst2
 
     # Try every pair in the sM_list, trying to turn it into a gemm operation
     for i in xrange(len(lst) - 1):

theano/tensor/tests/test_blas.py

@@ -577,6 +577,17 @@ def test_upcasting_scalar_nogemm():
     assert numpy.sum([isinstance(n.op, Gemm) for n in t]) == 0
     theano.printing.debugprint(f, print_type=True)
 
+    v = T.fmatrix('v')
+    w = T.fmatrix('w')
+    t = T.fmatrix('t')
+    alpha = T.cscalar('a')
+
+    rval = T.dot(w, v) * alpha + t
+    f = theano.function([w, v, t, alpha], rval)
+    t = f.maker.env.toposort()
+    assert numpy.sum([isinstance(n.op, Gemm) for n in t]) == 0
+    theano.printing.debugprint(f, print_type=True)
+
 def test_gemm_nested():
     X,Y,Z,a,b = T.dmatrix('X'), T.dmatrix('Y'), T.dmatrix('Z'), T.dscalar('a'), T.dscalar('b')
     R,S,U,c,d = T.dmatrix('R'), T.dmatrix('S'), T.dmatrix('U'), T.dscalar('c'), T.dscalar('d')