avoid runtime 'in' tests for dict literals when we can determine at compile...

avoid runtime 'in' tests for dict literals when we can determine at compile time that there are no duplicate keys

Cython/Compiler/ExprNodes.py

@@ -7391,24 +7391,47 @@ class DictNode(ExprNode):
                 code.globalstate.use_utility_code(
                     UtilityCode.load_cached("RaiseDoubleKeywords", "FunctionArguments.c"))
 
-        for i, item in enumerate(self.key_value_pairs):
+        keys_seen = set()
+        key_type = None
+
+        for item in self.key_value_pairs:
             item.generate_evaluation_code(code)
             if is_dict:
                 if self.exclude_null_values:
                     code.putln('if (%s) {' % item.value.py_result())
-                if self.reject_duplicates and i >= 1:
+                key = item.key
+                if self.reject_duplicates:
+                    if keys_seen is not None:
+                        # avoid runtime 'in' checks for literals that we can do at compile time
+                        if not key.is_string_literal:
+                            keys_seen = None
+                        elif key.value in keys_seen:
+                            # FIXME: this could be a compile time error, at least in Cython code
+                            keys_seen = None
+                        elif key_type is not type(key.value):
+                            if key_type is None:
+                                key_type = type(key.value)
+                                keys_seen.add(key.value)
+                            else:
+                                # different types => may not be able to compare at compile time
+                                keys_seen = None
+                        else:
+                            keys_seen.add(key.value)
+
+                    if keys_seen is None:
                         code.putln('if (unlikely(PyDict_Contains(%s, %s))) {' % (
-                        self.result(), item.key.py_result()))
+                            self.result(), key.py_result()))
                         # currently only used in function calls
                         code.putln('__Pyx_RaiseDoubleKeywordsError("function", %s); %s' % (
-                        item.key.py_result(),
+                            key.py_result(),
                             code.error_goto(item.pos)))
                         code.putln("} else {")
+
                 code.put_error_if_neg(self.pos, "PyDict_SetItem(%s, %s, %s)" % (
                     self.result(),
                     item.key.py_result(),
                     item.value.py_result()))
-                if self.reject_duplicates and i >= 1:
+                if self.reject_duplicates and keys_seen is None:
                     code.putln('}')
                 if self.exclude_null_values:
                     code.putln('}')