Merge pull request #5480 from notoraptor/fix-old-backend-compilation

doc/library/config.txt

@@ -671,6 +671,14 @@ import theano and print the config variable, as in:
 
     A directory with bin/, lib/, include/ folders containing cuda utilities.
 
+.. attribute:: config.cuda.enabled
+
+    Bool value: either ``True`` of ``False``
+
+    Default: ``True``
+
+    If set to `False`, C code in old backend is not compiled.
+
 .. attribute:: config.dnn.enabled
 
     String value: ``'auto'``, ``'True'``, ``'False'``

theano/configdefaults.py

@@ -199,6 +199,12 @@ AddConfigVar(
     StrParam(default_cuda_root),
     in_c_key=False)
 
+AddConfigVar(
+    'cuda.enabled',
+    'If false, C code in old backend is not compiled.',
+    BoolParam(True),
+    in_c_key=False)
+
 
 def filter_nvcc_flags(s):
     assert isinstance(s, str)

theano/sandbox/cuda/nvcc_compiler.py

@@ -27,6 +27,9 @@ def is_nvcc_available():
     Return True iff the nvcc compiler is found.
 
     """
+    if not config.cuda.enabled:
+        return False
+
     def set_version():
         p_out = output_subprocess_Popen([nvcc_path, '--version'])
         ver_line = decode(p_out[0]).strip().split('\n')[-1]