optimise set([x,y,z]) into a set literal

--HG--
extra : rebase_source : 55b0537a6e3c5a410956fb55e2dafc2bf8b30439

Cython/Compiler/Optimize.py

@@ -1957,6 +1957,27 @@ class OptimizeBuiltinCalls(Visitor.EnvTransform):
         exception_value = "((double)-1)",
         exception_check = True)
 
+    def _handle_simple_function_set(self, node, pos_args):
+        if len(pos_args) == 1 and isinstance(pos_args[0], (ExprNodes.ListNode,
+                                                           ExprNodes.TupleNode)):
+            # We can optimise set([x,y,z]) safely into a set literal,
+            # but only if we create all items before adding them -
+            # adding an item may raise an exception if it is not
+            # hashable, but creating the later items may have
+            # side-effects.
+            args = []
+            temps = []
+            for arg in pos_args[0].args:
+                if not arg.is_simple():
+                    arg = UtilNodes.LetRefNode(arg)
+                    temps.append(arg)
+                args.append(arg)
+            result = ExprNodes.SetNode(node.pos, is_temp=1, args=args)
+            for temp in temps[::-1]:
+                result = UtilNodes.EvalWithTempExprNode(temp, result)
+            return result
+        return node
+
     def _handle_simple_function_float(self, node, pos_args):
         """Transform float() into either a C type cast or a faster C
         function call.

tests/run/set.pyx

@@ -123,6 +123,30 @@ def test_set_sideeffect_unhashable_failure():
     else: assert False, "expected exception not raised"
     return L
 
+@cython.test_assert_path_exists("//SetNode")
+@cython.test_fail_if_path_exists("//SimpleCallNode")
+def test_set_of_list():
+    """
+    >>> s = test_set_of_list()
+    >>> isinstance(s, _set)
+    True
+    >>> sorted(s)
+    [1, 2, 3]
+    """
+    return set([1, 2, 3])
+
+@cython.test_assert_path_exists("//SetNode")
+@cython.test_fail_if_path_exists("//SimpleCallNode")
+def test_set_of_tuple():
+    """
+    >>> s = test_set_of_tuple()
+    >>> isinstance(s, _set)
+    True
+    >>> sorted(s)
+    [1, 2, 3]
+    """
+    return set([1, 2, 3])
+
 def sorted(it):
     # Py3 can't compare strings to ints
     chars = []