dfg/DFGOSREntry.cpp

   1 /*
   2  * Copyright (C) 2011 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "config.h"
  27 #include "DFGOSREntry.h"
  28
  29 #if ENABLE(DFG_JIT)
  30
  31 #include "CallFrame.h"
  32 #include "CodeBlock.h"
  33 #include "DFGNode.h"
  34 #include "JIT.h"
  35 #include "Operations.h"
  36
  37 namespace JSC { namespace DFG {
  38
  39 void* prepareOSREntry(ExecState* exec, CodeBlock* codeBlock, unsigned bytecodeIndex)
  40 {
  41 #if DFG_ENABLE(OSR_ENTRY)
  42     ASSERT(codeBlock->getJITType() == JITCode::DFGJIT);
  43     ASSERT(codeBlock->alternative());
  44     ASSERT(codeBlock->alternative()->getJITType() == JITCode::BaselineJIT);
  45     ASSERT(!codeBlock->jitCodeMap());
  46
  47 #if ENABLE(JIT_VERBOSE_OSR)
  48     dataLog("OSR in ", *codeBlock->alternative(), " -> ", *codeBlock, " from bc#", bytecodeIndex, "\n");
  49 #endif
  50
  51     VM* vm = &exec->vm();
  52     OSREntryData* entry = codeBlock->dfgOSREntryDataForBytecodeIndex(bytecodeIndex);
  53
  54     if (!entry) {
  55 #if ENABLE(JIT_VERBOSE_OSR)
  56         dataLogF("    OSR failed because the entrypoint was optimized out.\n");
  57 #endif
  58         return 0;
  59     }
  60
  61     ASSERT(entry->m_bytecodeIndex == bytecodeIndex);
  62
  63     // The code below checks if it is safe to perform OSR entry. It may find
  64     // that it is unsafe to do so, for any number of reasons, which are documented
  65     // below. If the code decides not to OSR then it returns 0, and it's the caller's
  66     // responsibility to patch up the state in such a way as to ensure that it's
  67     // both safe and efficient to continue executing baseline code for now. This
  68     // should almost certainly include calling either codeBlock->optimizeAfterWarmUp()
  69     // or codeBlock->dontOptimizeAnytimeSoon().
  70
  71     // 1) Verify predictions. If the predictions are inconsistent with the actual
  72     //    values, then OSR entry is not possible at this time. It's tempting to
  73     //    assume that we could somehow avoid this case. We can certainly avoid it
  74     //    for first-time loop OSR - that is, OSR into a CodeBlock that we have just
  75     //    compiled. Then we are almost guaranteed that all of the predictions will
  76     //    check out. It would be pretty easy to make that a hard guarantee. But
  77     //    then there would still be the case where two call frames with the same
  78     //    baseline CodeBlock are on the stack at the same time. The top one
  79     //    triggers compilation and OSR. In that case, we may no longer have
  80     //    accurate value profiles for the one deeper in the stack. Hence, when we
  81     //    pop into the CodeBlock that is deeper on the stack, we might OSR and
  82     //    realize that the predictions are wrong. Probably, in most cases, this is
  83     //    just an anomaly in the sense that the older CodeBlock simply went off
  84     //    into a less-likely path. So, the wisest course of action is to simply not
  85     //    OSR at this time.
  86
  87     for (size_t argument = 0; argument < entry->m_expectedValues.numberOfArguments(); ++argument) {
  88         if (argument >= exec->argumentCountIncludingThis()) {
  89 #if ENABLE(JIT_VERBOSE_OSR)
  90             dataLogF("    OSR failed because argument %zu was not passed, expected ", argument);
  91             entry->m_expectedValues.argument(argument).dump(WTF::dataFile());
  92             dataLogF(".\n");
  93 #endif
  94             return 0;
  95         }
  96
  97         JSValue value;
  98         if (!argument)
  99             value = exec->hostThisValue();
 100         else
 101             value = exec->argument(argument - 1);
 102
 103         if (!entry->m_expectedValues.argument(argument).validate(value)) {
 104 #if ENABLE(JIT_VERBOSE_OSR)
 105             dataLog("    OSR failed because argument ", argument, " is ", value, ", expected ", entry->m_expectedValues.argument(argument), ".\n");
 106 #endif
 107             return 0;
 108         }
 109     }
 110
 111     for (size_t local = 0; local < entry->m_expectedValues.numberOfLocals(); ++local) {
 112         if (entry->m_localsForcedDouble.get(local)) {
 113             if (!exec->registers()[local].jsValue().isNumber()) {
 114 #if ENABLE(JIT_VERBOSE_OSR)
 115                 dataLog("    OSR failed because variable ", local, " is ", exec->registers()[local].jsValue(), ", expected number.\n");
 116 #endif
 117                 return 0;
 118             }
 119             continue;
 120         }
 121         if (!entry->m_expectedValues.local(local).validate(exec->registers()[local].jsValue())) {
 122 #if ENABLE(JIT_VERBOSE_OSR)
 123             dataLog("    OSR failed because variable ", local, " is ", exec->registers()[local].jsValue(), ", expected ", entry->m_expectedValues.local(local), ".\n");
 124 #endif
 125             return 0;
 126         }
 127     }
 128
 129     // 2) Check the stack height. The DFG JIT may require a taller stack than the
 130     //    baseline JIT, in some cases. If we can't grow the stack, then don't do
 131     //    OSR right now. That's the only option we have unless we want basic block
 132     //    boundaries to start throwing RangeErrors. Although that would be possible,
 133     //    it seems silly: you'd be diverting the program to error handling when it
 134     //    would have otherwise just kept running albeit less quickly.
 135
 136     if (!vm->interpreter->stack().grow(&exec->registers()[codeBlock->m_numCalleeRegisters])) {
 137 #if ENABLE(JIT_VERBOSE_OSR)
 138         dataLogF("    OSR failed because stack growth failed.\n");
 139 #endif
 140         return 0;
 141     }
 142
 143 #if ENABLE(JIT_VERBOSE_OSR)
 144     dataLogF("    OSR should succeed.\n");
 145 #endif
 146
 147     // 3) Perform data format conversions.
 148     for (size_t local = 0; local < entry->m_expectedValues.numberOfLocals(); ++local) {
 149         if (entry->m_localsForcedDouble.get(local))
 150             *bitwise_cast<double*>(exec->registers() + local) = exec->registers()[local].jsValue().asNumber();
 151     }
 152
 153     // 4) Fix the call frame.
 154
 155     exec->setCodeBlock(codeBlock);
 156
 157     // 5) Find and return the destination machine code address.
 158
 159     void* result = codeBlock->getJITCode().executableAddressAtOffset(entry->m_machineCodeOffset);
 160
 161 #if ENABLE(JIT_VERBOSE_OSR)
 162     dataLogF("    OSR returning machine code address %p.\n", result);
 163 #endif
 164
 165     return result;
 166 #else // DFG_ENABLE(OSR_ENTRY)
 167     UNUSED_PARAM(exec);
 168     UNUSED_PARAM(codeBlock);
 169     UNUSED_PARAM(bytecodeIndex);
 170     return 0;
 171 #endif
 172 }
 173
 174 } } // namespace JSC::DFG
 175
 176 #endif // ENABLE(DFG_JIT)