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diff --git a/Source/JavaScriptCore/b3/B3Effects.h b/Source/JavaScriptCore/b3/B3Effects.h
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+/*
+ * Copyright (C) 2015 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 B3Effects_h
+#define B3Effects_h
+
+#if ENABLE(B3_JIT)
+
+#include "B3HeapRange.h"
+#include <wtf/PrintStream.h>
+
+namespace JSC { namespace B3 {
+
+struct Effects {
+    // True if this cannot continue execution in the current block.
+    bool terminal { false };
+
+    // True if this value can cause execution to terminate abruptly, and that this abrupt termination is
+    // observable. An example of how this gets used is to limit the hoisting of controlDependent values.
+    // Note that if exitsSideways is set to true but reads is bottom, then B3 is free to assume that
+    // after abrupt termination of this procedure, none of the heap will be read. That's usually false,
+    // so make sure that reads corresponds to the set of things that are readable after this function
+    // terminates abruptly.
+    bool exitsSideways { false };
+
+    // True if the instruction may change semantics if hoisted above some control flow.
+    bool controlDependent { false };
+
+    // True if this writes to the local state. Operations that write local state don't write to anything
+    // in "memory" but they have a side-effect anyway. This is for modeling Upsilons and Sets. You can ignore
+    // this if you have your own way of modeling Upsilons and Sets or if you intend to just rebuild them
+    // anyway.
+    bool writesLocalState { false };
+
+    // True if this reads from the local state. This is only used for Phi and Get.
+    bool readsLocalState { false };
+
+    HeapRange writes;
+    HeapRange reads;
+
+    static Effects none()
+    {
+        return Effects();
+    }
+
+    static Effects forCall()
+    {
+        Effects result;
+        result.exitsSideways = true;
+        result.controlDependent = true;
+        result.writes = HeapRange::top();
+        result.reads = HeapRange::top();
+        return result;
+    }
+
+    bool mustExecute() const
+    {
+        return terminal || exitsSideways || writesLocalState || writes;
+    }
+
+    // Returns true if reordering instructions with these respective effects would change program
+    // behavior in an observable way.
+    bool interferes(const Effects&) const;
+
+    void dump(PrintStream& out) const;
+};
+
+} } // namespace JSC::B3
+
+#endif // ENABLE(B3_JIT)
+
+#endif // B3Effects_h
+