JavaScriptCore-1097.3.tar.gz

[apple/javascriptcore.git] / dfg / DFGOSREntry.cpp

/*
 * Copyright (C) 2011 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,
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#include "config.h"
#include "DFGOSREntry.h"

#if ENABLE(DFG_JIT)

#include "CallFrame.h"
#include "CodeBlock.h"
#include "DFGNode.h"
#include "JIT.h"

namespace JSC { namespace DFG {

void* prepareOSREntry(ExecState* exec, CodeBlock* codeBlock, unsigned bytecodeIndex)
{
#if DFG_ENABLE(OSR_ENTRY)
    ASSERT(codeBlock->getJITType() == JITCode::DFGJIT);
    ASSERT(codeBlock->alternative());
    ASSERT(codeBlock->alternative()->getJITType() == JITCode::BaselineJIT);
    ASSERT(!codeBlock->jitCodeMap());
    ASSERT(codeBlock->numberOfDFGOSREntries());

#if ENABLE(JIT_VERBOSE_OSR)
    dataLog("OSR in %p(%p) from bc#%u\n", codeBlock, codeBlock->alternative(), bytecodeIndex);
#endif
    
    JSGlobalData* globalData = &exec->globalData();
    OSREntryData* entry = codeBlock->dfgOSREntryDataForBytecodeIndex(bytecodeIndex);
    
    ASSERT(entry->m_bytecodeIndex == bytecodeIndex);
    
    // The code below checks if it is safe to perform OSR entry. It may find
    // that it is unsafe to do so, for any number of reasons, which are documented
    // below. If the code decides not to OSR then it returns 0, and it's the caller's
    // responsibility to patch up the state in such a way as to ensure that it's
    // both safe and efficient to continue executing baseline code for now. This
    // should almost certainly include calling either codeBlock->optimizeAfterWarmUp()
    // or codeBlock->dontOptimizeAnytimeSoon().
    
    // 1) Verify predictions. If the predictions are inconsistent with the actual
    //    values, then OSR entry is not possible at this time. It's tempting to
    //    assume that we could somehow avoid this case. We can certainly avoid it
    //    for first-time loop OSR - that is, OSR into a CodeBlock that we have just
    //    compiled. Then we are almost guaranteed that all of the predictions will
    //    check out. It would be pretty easy to make that a hard guarantee. But
    //    then there would still be the case where two call frames with the same
    //    baseline CodeBlock are on the stack at the same time. The top one
    //    triggers compilation and OSR. In that case, we may no longer have
    //    accurate value profiles for the one deeper in the stack. Hence, when we
    //    pop into the CodeBlock that is deeper on the stack, we might OSR and
    //    realize that the predictions are wrong. Probably, in most cases, this is
    //    just an anomaly in the sense that the older CodeBlock simply went off
    //    into a less-likely path. So, the wisest course of action is to simply not
    //    OSR at this time.
    
    for (size_t argument = 0; argument < entry->m_expectedValues.numberOfArguments(); ++argument) {
        if (argument >= exec->argumentCountIncludingThis()) {
#if ENABLE(JIT_VERBOSE_OSR)
            dataLog("    OSR failed because argument %zu was not passed, expected ", argument);
            entry->m_expectedValues.argument(argument).dump(WTF::dataFile());
            dataLog(".\n");
#endif
            return 0;
        }
        
        JSValue value;
        if (!argument)
            value = exec->hostThisValue();
        else
            value = exec->argument(argument - 1);
        
        if (!entry->m_expectedValues.argument(argument).validate(value)) {
#if ENABLE(JIT_VERBOSE_OSR)
            dataLog("    OSR failed because argument %zu is %s, expected ", argument, value.description());
            entry->m_expectedValues.argument(argument).dump(WTF::dataFile());
            dataLog(".\n");
#endif
            return 0;
        }
    }
    
    for (size_t local = 0; local < entry->m_expectedValues.numberOfLocals(); ++local) {
        if (entry->m_localsForcedDouble.get(local)) {
            if (!exec->registers()[local].jsValue().isNumber()) {
#if ENABLE(JIT_VERBOSE_OSR)
                dataLog("    OSR failed because variable %zu is %s, expected number.\n", local, exec->registers()[local].jsValue().description());
#endif
                return 0;
            }
            continue;
        }
        if (!entry->m_expectedValues.local(local).validate(exec->registers()[local].jsValue())) {
#if ENABLE(JIT_VERBOSE_OSR)
            dataLog("    OSR failed because variable %zu is %s, expected ", local, exec->registers()[local].jsValue().description());
            entry->m_expectedValues.local(local).dump(WTF::dataFile());
            dataLog(".\n");
#endif
            return 0;
        }
    }

    // 2) Check the stack height. The DFG JIT may require a taller stack than the
    //    baseline JIT, in some cases. If we can't grow the stack, then don't do
    //    OSR right now. That's the only option we have unless we want basic block
    //    boundaries to start throwing RangeErrors. Although that would be possible,
    //    it seems silly: you'd be diverting the program to error handling when it
    //    would have otherwise just kept running albeit less quickly.
    
    if (!globalData->interpreter->registerFile().grow(&exec->registers()[codeBlock->m_numCalleeRegisters])) {
#if ENABLE(JIT_VERBOSE_OSR)
        dataLog("    OSR failed because stack growth failed.\n");
#endif
        return 0;
    }
    
#if ENABLE(JIT_VERBOSE_OSR)
    dataLog("    OSR should succeed.\n");
#endif
    
    // 3) Perform data format conversions.
    for (size_t local = 0; local < entry->m_expectedValues.numberOfLocals(); ++local) {
        if (entry->m_localsForcedDouble.get(local))
            *bitwise_cast<double*>(exec->registers() + local) = exec->registers()[local].jsValue().asNumber();
    }
    
    // 4) Fix the call frame.
    
    exec->setCodeBlock(codeBlock);
    
    // 5) Find and return the destination machine code address.
    
    void* result = codeBlock->getJITCode().executableAddressAtOffset(entry->m_machineCodeOffset);
    
#if ENABLE(JIT_VERBOSE_OSR)
    dataLog("    OSR returning machine code address %p.\n", result);
#endif
    
    return result;
#else // DFG_ENABLE(OSR_ENTRY)
    UNUSED_PARAM(exec);
    UNUSED_PARAM(codeBlock);
    UNUSED_PARAM(bytecodeIndex);
    return 0;
#endif
}

} } // namespace JSC::DFG

#endif // ENABLE(DFG_JIT)