Initial version of reverse mode autodiff

Author: apaszke

include/tc/core/autodiff.h

@@ -0,0 +1,26 @@
+/**
+ * Copyright (c) 2017-present, Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include "tc/lang/tree.h"
+
+#include <ostream>
+
+namespace tc {
+
+std::string differentiate(const std::string& source);
+
+} // namespace tc

include/tc/lang/sema.h

@@ -155,6 +155,8 @@ static inline TreeRef match_types(TreeRef a, TreeRef b) {
 /// - replace TK_APPLY with TK_BUILT_IN for built in functions
 /// - checks that all variables are defined, and creates index/reduction
 /// variable objects.
+//  - replaces augumented assignments that have no reduction variables
+//  with regular assignents
 struct Sema {
   std::unordered_map<TreeRef, TreeRef> expr_to_type;
 

include/tc/lang/tree_views.h

@@ -125,14 +125,19 @@ struct ListViewIterator {
   bool operator!=(const ListViewIterator& rhs) const {
     return it != rhs.it;
   }
+  bool operator==(const ListViewIterator& rhs) const {
+    return it == rhs.it;
+  }
   T operator*() const {
     return T(*it);
   }
-  void operator++() {
+  ListViewIterator& operator++() {
     ++it;
+    return *this;
   }
-  void operator--() {
+  ListViewIterator& operator--() {
     --it;
+    return *this;
   }
 
  private:

src/core/CMakeLists.txt

@@ -3,6 +3,7 @@ add_library(
 
   SHARED
 
+  autodiff.cc
   flags.cc
   mapping_options.cc
   mapping_options_cpp_printer.cc