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diff --git a/Source/JavaScriptCore/b3/B3BlockInsertionSet.h b/Source/JavaScriptCore/b3/B3BlockInsertionSet.h
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+/*
+ * Copyright (C) 2015-2016 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
+ */
+
+#ifndef B3BlockInsertionSet_h
+#define B3BlockInsertionSet_h
+
+#if ENABLE(B3_JIT)
+
+#include "B3Procedure.h"
+#include <wtf/Insertion.h>
+#include <wtf/Vector.h>
+
+namespace JSC { namespace B3 {
+
+class InsertionSet;
+
+typedef WTF::Insertion<std::unique_ptr<BasicBlock>> BlockInsertion;
+
+class BlockInsertionSet {
+public:
+    BlockInsertionSet(Procedure&);
+    ~BlockInsertionSet();
+    
+    void insert(BlockInsertion&&);
+
+    // Insert a new block at a given index.
+    BasicBlock* insert(unsigned index, double frequency = PNaN);
+
+    // Inserts a new block before the given block. Usually you will not pass the frequency
+    // argument. Passing PNaN causes us to just use the frequency of the 'before' block. That's
+    // usually what you want.
+    BasicBlock* insertBefore(BasicBlock* before, double frequency = PNaN);
+
+    // Inserts a new block after the given block.
+    BasicBlock* insertAfter(BasicBlock* after, double frequency = PNaN);
+
+    // A helper to split a block when forward iterating over it. It creates a new block to hold
+    // everything before the instruction at valueIndex. The current block is left with
+    // everything at and after valueIndex. If the optional InsertionSet is provided, it will get
+    // executed on the newly created block - this makes sense if you had previously inserted
+    // things into the original block, since the newly created block will be indexed identically
+    // to how this block was indexed for all values prior to valueIndex. After this runs, it sets
+    // valueIndex to zero. This allows you to use this method for things like:
+    //
+    // for (unsigned valueIndex = 0; valueIndex < block->size(); ++valueIndex) {
+    //     Value* value = block->at(valueIndex);
+    //     if (value->opcode() == Foo) {
+    //         BasicBlock* predecessor =
+    //             m_blockInsertionSet.splitForward(block, valueIndex, &m_insertionSet);
+    //         ... // Now you can append to predecessor, insert new blocks before 'block', and
+    //         ... // you can use m_insertionSet to insert more thing before 'value'.
+    //         predecessor->updatePredecessorsAfter();
+    //     }
+    // }
+    //
+    // Note how usually this idiom ends in a all to updatePredecessorsAftter(), which ensures
+    // that the predecessors involved in any of the new control flow that you've created are up
+    // to date.
+    BasicBlock* splitForward(
+        BasicBlock*, unsigned& valueIndex, InsertionSet* = nullptr,
+        double frequency = PNaN);
+    
+    bool execute();
+
+private:
+    Procedure& m_proc;
+    Vector<BlockInsertion, 8> m_insertions;
+};
+
+} } // namespace JSC::B3
+
+#endif // ENABLE(B3_JIT)
+
+#endif // B3BlockInsertionSet_h
+