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+/*
+ * Copyright (C) 2009 University of Szeged
+ * 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 UNIVERSITY OF SZEGED ``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 UNIVERSITY OF SZEGED 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 AssemblerBufferWithConstantPool_h
+#define AssemblerBufferWithConstantPool_h
+
+#if ENABLE(ASSEMBLER)
+
+#include "AssemblerBuffer.h"
+#include <wtf/SegmentedVector.h>
+
+#define ASSEMBLER_HAS_CONSTANT_POOL 1
+
+namespace JSC {
+
+/*
+    On a constant pool 4 or 8 bytes data can be stored. The values can be
+    constants or addresses. The addresses should be 32 or 64 bits. The constants
+    should be double-precisions float or integer numbers which are hard to be
+    encoded as few machine instructions.
+
+    TODO: The pool is desinged to handle both 32 and 64 bits values, but
+    currently only the 4 bytes constants are implemented and tested.
+
+    The AssemblerBuffer can contain multiple constant pools. Each pool is inserted
+    into the instruction stream - protected by a jump instruction from the
+    execution flow.
+
+    The flush mechanism is called when no space remain to insert the next instruction
+    into the pool. Three values are used to determine when the constant pool itself
+    have to be inserted into the instruction stream (Assembler Buffer):
+
+    - maxPoolSize: size of the constant pool in bytes, this value cannot be
+        larger than the maximum offset of a PC relative memory load
+
+    - barrierSize: size of jump instruction in bytes which protects the
+        constant pool from execution
+
+    - maxInstructionSize: maximum length of a machine instruction in bytes
+
+    There are some callbacks which solve the target architecture specific
+    address handling:
+
+    - TYPE patchConstantPoolLoad(TYPE load, int value):
+        patch the 'load' instruction with the index of the constant in the
+        constant pool and return the patched instruction.
+
+    - void patchConstantPoolLoad(void* loadAddr, void* constPoolAddr):
+        patch the a PC relative load instruction at 'loadAddr' address with the
+        final relative offset. The offset can be computed with help of
+        'constPoolAddr' (the address of the constant pool) and index of the
+        constant (which is stored previously in the load instruction itself).
+
+    - TYPE placeConstantPoolBarrier(int size):
+        return with a constant pool barrier instruction which jumps over the
+        constant pool.
+
+    The 'put*WithConstant*' functions should be used to place a data into the
+    constant pool.
+*/
+
+template <int maxPoolSize, int barrierSize, int maxInstructionSize, class AssemblerType>
+class AssemblerBufferWithConstantPool : public AssemblerBuffer {
+    typedef SegmentedVector<uint32_t, 512> LoadOffsets;
+    using AssemblerBuffer::putIntegral;
+    using AssemblerBuffer::putIntegralUnchecked;
+public:
+    typedef struct {
+        short high;
+        short low;
+    } TwoShorts;
+
+    enum {
+        UniqueConst,
+        ReusableConst,
+        UnusedEntry,
+    };
+
+    AssemblerBufferWithConstantPool()
+        : AssemblerBuffer()
+        , m_numConsts(0)
+        , m_maxDistance(maxPoolSize)
+        , m_lastConstDelta(0)
+    {
+        m_pool = static_cast<uint32_t*>(fastMalloc(maxPoolSize));
+        m_mask = static_cast<char*>(fastMalloc(maxPoolSize / sizeof(uint32_t)));
+    }
+
+    ~AssemblerBufferWithConstantPool()
+    {
+        fastFree(m_mask);
+        fastFree(m_pool);
+    }
+
+    void ensureSpace(int space)
+    {
+        flushIfNoSpaceFor(space);
+        AssemblerBuffer::ensureSpace(space);
+    }
+
+    void ensureSpace(int insnSpace, int constSpace)
+    {
+        flushIfNoSpaceFor(insnSpace, constSpace);
+        AssemblerBuffer::ensureSpace(insnSpace);
+    }
+
+    void ensureSpaceForAnyInstruction(int amount = 1)
+    {
+        flushIfNoSpaceFor(amount * maxInstructionSize, amount * sizeof(uint64_t));
+    }
+
+    bool isAligned(int alignment)
+    {
+        flushIfNoSpaceFor(alignment);
+        return AssemblerBuffer::isAligned(alignment);
+    }
+
+    void putByteUnchecked(int value)
+    {
+        AssemblerBuffer::putByteUnchecked(value);
+        correctDeltas(1);
+    }
+
+    void putByte(int value)
+    {
+        flushIfNoSpaceFor(1);
+        AssemblerBuffer::putByte(value);
+        correctDeltas(1);
+    }
+
+    void putShortUnchecked(int value)
+    {
+        AssemblerBuffer::putShortUnchecked(value);
+        correctDeltas(2);
+    }
+
+    void putShort(int value)
+    {
+        flushIfNoSpaceFor(2);
+        AssemblerBuffer::putShort(value);
+        correctDeltas(2);
+    }
+
+    void putIntUnchecked(int value)
+    {
+        AssemblerBuffer::putIntUnchecked(value);
+        correctDeltas(4);
+    }
+
+    void putInt(int value)
+    {
+        flushIfNoSpaceFor(4);
+        AssemblerBuffer::putInt(value);
+        correctDeltas(4);
+    }
+
+    void putInt64Unchecked(int64_t value)
+    {
+        AssemblerBuffer::putInt64Unchecked(value);
+        correctDeltas(8);
+    }
+
+    void putIntegral(TwoShorts value)
+    {
+        putIntegral(value.high);
+        putIntegral(value.low);
+    }
+
+    void putIntegralUnchecked(TwoShorts value)
+    {
+        putIntegralUnchecked(value.high);
+        putIntegralUnchecked(value.low);
+    }
+
+    PassRefPtr<ExecutableMemoryHandle> executableCopy(JSGlobalData& globalData, void* ownerUID, JITCompilationEffort effort)
+    {
+        flushConstantPool(false);
+        return AssemblerBuffer::executableCopy(globalData, ownerUID, effort);
+    }
+
+    void putShortWithConstantInt(uint16_t insn, uint32_t constant, bool isReusable = false)
+    {
+        putIntegralWithConstantInt(insn, constant, isReusable);
+    }
+
+    void putIntWithConstantInt(uint32_t insn, uint32_t constant, bool isReusable = false)
+    {
+        putIntegralWithConstantInt(insn, constant, isReusable);
+    }
+
+    // This flushing mechanism can be called after any unconditional jumps.
+    void flushWithoutBarrier(bool isForced = false)
+    {
+        // Flush if constant pool is more than 60% full to avoid overuse of this function.
+        if (isForced || 5 * static_cast<uint32_t>(m_numConsts) > 3 * maxPoolSize / sizeof(uint32_t))
+            flushConstantPool(false);
+    }
+
+    uint32_t* poolAddress()
+    {
+        return m_pool;
+    }
+
+    int sizeOfConstantPool()
+    {
+        return m_numConsts;
+    }
+
+private:
+    void correctDeltas(int insnSize)
+    {
+        m_maxDistance -= insnSize;
+        m_lastConstDelta -= insnSize;
+        if (m_lastConstDelta < 0)
+            m_lastConstDelta = 0;
+    }
+
+    void correctDeltas(int insnSize, int constSize)
+    {
+        correctDeltas(insnSize);
+
+        m_maxDistance -= m_lastConstDelta;
+        m_lastConstDelta = constSize;
+    }
+
+    template<typename IntegralType>
+    void putIntegralWithConstantInt(IntegralType insn, uint32_t constant, bool isReusable)
+    {
+        if (!m_numConsts)
+            m_maxDistance = maxPoolSize;
+        flushIfNoSpaceFor(sizeof(IntegralType), 4);
+
+        m_loadOffsets.append(codeSize());
+        if (isReusable) {
+            for (int i = 0; i < m_numConsts; ++i) {
+                if (m_mask[i] == ReusableConst && m_pool[i] == constant) {
+                    putIntegral(static_cast<IntegralType>(AssemblerType::patchConstantPoolLoad(insn, i)));
+                    correctDeltas(sizeof(IntegralType));
+                    return;
+                }
+            }
+        }
+
+        m_pool[m_numConsts] = constant;
+        m_mask[m_numConsts] = static_cast<char>(isReusable ? ReusableConst : UniqueConst);
+
+        putIntegral(static_cast<IntegralType>(AssemblerType::patchConstantPoolLoad(insn, m_numConsts)));
+        ++m_numConsts;
+
+        correctDeltas(sizeof(IntegralType), 4);
+    }
+
+    void flushConstantPool(bool useBarrier = true)
+    {
+        if (m_numConsts == 0)
+            return;
+        int alignPool = (codeSize() + (useBarrier ? barrierSize : 0)) & (sizeof(uint64_t) - 1);
+
+        if (alignPool)
+            alignPool = sizeof(uint64_t) - alignPool;
+
+        // Callback to protect the constant pool from execution
+        if (useBarrier)
+            putIntegral(AssemblerType::placeConstantPoolBarrier(m_numConsts * sizeof(uint32_t) + alignPool));
+
+        if (alignPool) {
+            if (alignPool & 1)
+                AssemblerBuffer::putByte(AssemblerType::padForAlign8);
+            if (alignPool & 2)
+                AssemblerBuffer::putShort(AssemblerType::padForAlign16);
+            if (alignPool & 4)
+                AssemblerBuffer::putInt(AssemblerType::padForAlign32);
+        }
+
+        int constPoolOffset = codeSize();
+        append(reinterpret_cast<char*>(m_pool), m_numConsts * sizeof(uint32_t));
+
+        // Patch each PC relative load
+        for (LoadOffsets::Iterator iter = m_loadOffsets.begin(); iter != m_loadOffsets.end(); ++iter) {
+            void* loadAddr = reinterpret_cast<char*>(data()) + *iter;
+            AssemblerType::patchConstantPoolLoad(loadAddr, reinterpret_cast<char*>(data()) + constPoolOffset);
+        }
+
+        m_loadOffsets.clear();
+        m_numConsts = 0;
+    }
+
+    void flushIfNoSpaceFor(int nextInsnSize)
+    {
+        if (m_numConsts == 0)
+            return;
+        int lastConstDelta = m_lastConstDelta > nextInsnSize ? m_lastConstDelta - nextInsnSize : 0;
+        if ((m_maxDistance < nextInsnSize + lastConstDelta + barrierSize + (int)sizeof(uint32_t)))
+            flushConstantPool();
+    }
+
+    void flushIfNoSpaceFor(int nextInsnSize, int nextConstSize)
+    {
+        if (m_numConsts == 0)
+            return;
+        if ((m_maxDistance < nextInsnSize + m_lastConstDelta + nextConstSize + barrierSize + (int)sizeof(uint32_t)) ||
+            (m_numConsts * sizeof(uint32_t) + nextConstSize >= maxPoolSize))
+            flushConstantPool();
+    }
+
+    uint32_t* m_pool;
+    char* m_mask;
+    LoadOffsets m_loadOffsets;
+
+    int m_numConsts;
+    int m_maxDistance;
+    int m_lastConstDelta;
+};
+
+} // namespace JSC
+
+#endif // ENABLE(ASSEMBLER)
+
+#endif // AssemblerBufferWithConstantPool_h