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diff --git a/Source/JavaScriptCore/b3/B3Effects.h b/Source/JavaScriptCore/b3/B3Effects.h
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+/*
+ * Copyright (C) 2015-2016 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. 
+ */
+
+#pragma once
+
+#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. For example,
+    // loads are usually control-dependent because we must assume that any control construct (either
+    // a terminal like Branch or anything that exits sideways, like Check) validates whether the
+    // pointer is valid. Hoisting the load above control may cause the load to trap even though it
+    // would not have otherwise trapped.
+    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, Sets, and Fences.
+    // This is a way of saying: even though this operation is not a terminal, does not exit sideways,
+    // and does not write to the heap, you still cannot kill this operation.
+    bool writesLocalState { false };
+
+    // True if this reads from the local state. This is only used for Phi and Get.
+    bool readsLocalState { false };
+
+    // B3 understands things about pinned registers. Therefore, it needs to know who reads them and
+    // who writes them. We don't track this on a per-register basis because that would be harder and
+    // we don't need it. Note that if you want to construct an immutable pinned register while also
+    // having other pinned registers that are mutable, then you can use ArgumentReg. Also note that
+    // nobody will stop you from making this get out-of-sync with your clobbered register sets in
+    // Patchpoint. It's recommended that you err on the side of being conservative.
+    // FIXME: Explore making these be RegisterSets. That's mainly hard because it would be awkward to
+    // reconcile with StackmapValue's support for clobbered regs.
+    // https://bugs.webkit.org/show_bug.cgi?id=163173
+    bool readsPinned { false };
+    bool writesPinned { 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();
+        result.readsPinned = true;
+        result.writesPinned = true;
+        return result;
+    }
+
+    static Effects forCheck()
+    {
+        Effects result;
+        result.exitsSideways = true;
+        // The program could read anything after exiting, and it's on us to declare this.
+        result.reads = HeapRange::top();
+        return result;
+    }
+
+    bool mustExecute() const
+    {
+        return terminal || exitsSideways || writesLocalState || writes || writesPinned;
+    }
+
+    // Returns true if reordering instructions with these respective effects would change program
+    // behavior in an observable way.
+    bool interferes(const Effects&) const;
+    
+    JS_EXPORT_PRIVATE bool operator==(const Effects&) const;
+    JS_EXPORT_PRIVATE bool operator!=(const Effects&) const;
+
+    JS_EXPORT_PRIVATE void dump(PrintStream& out) const;
+};
+
+} } // namespace JSC::B3
+
+#endif // ENABLE(B3_JIT)