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diff --git a/Source/JavaScriptCore/b3/air/AirTmpWidth.h b/Source/JavaScriptCore/b3/air/AirTmpWidth.h
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+++ b/Source/JavaScriptCore/b3/air/AirTmpWidth.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 "AirArg.h"
+
+namespace JSC { namespace B3 { namespace Air {
+
+class Code;
+
+class TmpWidth {
+public:
+    TmpWidth();
+    TmpWidth(Code&);
+    ~TmpWidth();
+
+    void recompute(Code&);
+
+    // The width of a Tmp is the number of bits that you need to be able to track without some trivial
+    // recovery. A Tmp may have a "subwidth" (say, Width32 on a 64-bit system) if either of the following
+    // is true:
+    //
+    // - The high bits are never read.
+    // - The high bits are always zero.
+    //
+    // This doesn't tell you which of those properties holds, but you can query that using the other
+    // methods.
+    Arg::Width width(Tmp tmp) const
+    {
+        auto iter = m_width.find(tmp);
+        if (iter == m_width.end())
+            return Arg::minimumWidth(Arg(tmp).type());
+        return std::min(iter->value.use, iter->value.def);
+    }
+
+    // Return the minimum required width for all defs/uses of this Tmp.
+    Arg::Width requiredWidth(Tmp tmp)
+    {
+        auto iter = m_width.find(tmp);
+        if (iter == m_width.end())
+            return Arg::minimumWidth(Arg(tmp).type());
+        return std::max(iter->value.use, iter->value.def);
+    }
+
+    // This indirectly tells you how much of the tmp's high bits are guaranteed to be zero. The number of
+    // high bits that are zero are:
+    //
+    //     TotalBits - defWidth(tmp)
+    //
+    // Where TotalBits are the total number of bits in the register, so 64 on a 64-bit system.
+    Arg::Width defWidth(Tmp tmp) const
+    {
+        auto iter = m_width.find(tmp);
+        if (iter == m_width.end())
+            return Arg::minimumWidth(Arg(tmp).type());
+        return iter->value.def;
+    }
+
+    // This tells you how much of Tmp is going to be read.
+    Arg::Width useWidth(Tmp tmp) const
+    {
+        auto iter = m_width.find(tmp);
+        if (iter == m_width.end())
+            return Arg::minimumWidth(Arg(tmp).type());
+        return iter->value.use;
+    }
+    
+private:
+    struct Widths {
+        Widths() { }
+
+        Widths(Arg::Type type)
+        {
+            use = Arg::minimumWidth(type);
+            def = Arg::minimumWidth(type);
+        }
+
+        void dump(PrintStream& out) const;
+        
+        Arg::Width use;
+        Arg::Width def;
+    };
+    
+    HashMap<Tmp, Widths> m_width;
+};
+
+} } } // namespace JSC::B3::Air
+
+#endif // ENABLE(B3_JIT)