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diff --git a/src/ir/manipulation.h b/src/ir/manipulation.h
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+++ b/src/ir/manipulation.h
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+/*
+ * Copyright 2017 WebAssembly Community Group participants
+ *
+ * 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.
+ */
+
+#ifndef wasm_ir_manipulation_h
+#define wasm_ir_manipulation_h
+
+#include "wasm.h"
+
+namespace wasm {
+
+namespace ExpressionManipulator {
+  // Re-use a node's memory. This helps avoid allocation when optimizing.
+  template<typename InputType, typename OutputType>
+  inline OutputType* convert(InputType *input) {
+    static_assert(sizeof(OutputType) <= sizeof(InputType),
+                  "Can only convert to a smaller size Expression node");
+    input->~InputType(); // arena-allocaed, so no destructor, but avoid UB.
+    OutputType* output = (OutputType*)(input);
+    new (output) OutputType;
+    return output;
+  }
+
+  // Convenience method for nop, which is a common conversion
+  template<typename InputType>
+  inline Nop* nop(InputType* target) {
+    return convert<InputType, Nop>(target);
+  }
+
+  // Convert a node that allocates
+  template<typename InputType, typename OutputType>
+  inline OutputType* convert(InputType *input, MixedArena& allocator) {
+    assert(sizeof(OutputType) <= sizeof(InputType));
+    input->~InputType(); // arena-allocaed, so no destructor, but avoid UB.
+    OutputType* output = (OutputType*)(input);
+    new (output) OutputType(allocator);
+    return output;
+  }
+
+  using CustomCopier = std::function<Expression*(Expression*)>;
+  Expression* flexibleCopy(Expression* original, Module& wasm, CustomCopier custom);
+
+  inline Expression* copy(Expression* original, Module& wasm) {
+    auto copy = [](Expression* curr) {
+        return nullptr;
+    };
+    return flexibleCopy(original, wasm, copy);
+  }
+
+  // Splice an item into the middle of a block's list
+  void spliceIntoBlock(Block* block, Index index, Expression* add);
+}
+
+} // wasm
+
+#endif // wams_ir_manipulation_h
+