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
  36 namespace JSC { namespace DFG {
  37
  38 void* prepareOSREntry(ExecState* exec, CodeBlock* codeBlock, unsigned bytecodeIndex)
  39 {
  40 #if DFG_ENABLE(OSR_ENTRY)
  41     ASSERT(codeBlock->getJITType() == JITCode::DFGJIT);
  42     ASSERT(codeBlock->alternative());
  43     ASSERT(codeBlock->alternative()->getJITType() == JITCode::BaselineJIT);
  44     ASSERT(!codeBlock->jitCodeMap());
  45     ASSERT(codeBlock->numberOfDFGOSREntries());
  46
  47 #if ENABLE(JIT_VERBOSE_OSR)
  48     dataLog("OSR in %p(%p) from bc#%u\n", codeBlock, codeBlock->alternative(), bytecodeIndex);
  49 #endif
  50
  51     JSGlobalData* globalData = &exec->globalData();
  52     OSREntryData* entry = codeBlock->dfgOSREntryDataForBytecodeIndex(bytecodeIndex);
  53
  54     ASSERT(entry->m_bytecodeIndex == bytecodeIndex);
  55
  56     // The code below checks if it is safe to perform OSR entry. It may find
  57     // that it is unsafe to do so, for any number of reasons, which are documented
  58     // below. If the code decides not to OSR then it returns 0, and it's the caller's
  59     // responsibility to patch up the state in such a way as to ensure that it's
  60     // both safe and efficient to continue executing baseline code for now. This
  61     // should almost certainly include calling either codeBlock->optimizeAfterWarmUp()
  62     // or codeBlock->dontOptimizeAnytimeSoon().
  63
  64     // 1) Verify predictions. If the predictions are inconsistent with the actual
  65     //    values, then OSR entry is not possible at this time. It's tempting to
  66     //    assume that we could somehow avoid this case. We can certainly avoid it
  67     //    for first-time loop OSR - that is, OSR into a CodeBlock that we have just
  68     //    compiled. Then we are almost guaranteed that all of the predictions will
  69     //    check out. It would be pretty easy to make that a hard guarantee. But
  70     //    then there would still be the case where two call frames with the same
  71     //    baseline CodeBlock are on the stack at the same time. The top one
  72     //    triggers compilation and OSR. In that case, we may no longer have
  73     //    accurate value profiles for the one deeper in the stack. Hence, when we
  74     //    pop into the CodeBlock that is deeper on the stack, we might OSR and
  75     //    realize that the predictions are wrong. Probably, in most cases, this is
  76     //    just an anomaly in the sense that the older CodeBlock simply went off
  77     //    into a less-likely path. So, the wisest course of action is to simply not
  78     //    OSR at this time.
  79
  80     for (size_t argument = 0; argument < entry->m_expectedValues.numberOfArguments(); ++argument) {
  81         if (argument >= exec->argumentCountIncludingThis()) {
  82 #if ENABLE(JIT_VERBOSE_OSR)
  83             dataLog("    OSR failed because argument %zu was not passed, expected ", argument);
  84             entry->m_expectedValues.argument(argument).dump(WTF::dataFile());
  85             dataLog(".\n");
  86 #endif
  87             return 0;
  88         }
  89
  90         JSValue value;
  91         if (!argument)
  92             value = exec->hostThisValue();
  93         else
  94             value = exec->argument(argument - 1);
  95
  96         if (!entry->m_expectedValues.argument(argument).validate(value)) {
  97 #if ENABLE(JIT_VERBOSE_OSR)
  98             dataLog("    OSR failed because argument %zu is %s, expected ", argument, value.description());
  99             entry->m_expectedValues.argument(argument).dump(WTF::dataFile());
 100             dataLog(".\n");
 101 #endif
 102             return 0;
 103         }
 104     }
 105
 106     for (size_t local = 0; local < entry->m_expectedValues.numberOfLocals(); ++local) {
 107         if (entry->m_localsForcedDouble.get(local)) {
 108             if (!exec->registers()[local].jsValue().isNumber()) {
 109 #if ENABLE(JIT_VERBOSE_OSR)
 110                 dataLog("    OSR failed because variable %zu is %s, expected number.\n", local, exec->registers()[local].jsValue().description());
 111 #endif
 112                 return 0;
 113             }
 114             continue;
 115         }
 116         if (!entry->m_expectedValues.local(local).validate(exec->registers()[local].jsValue())) {
 117 #if ENABLE(JIT_VERBOSE_OSR)
 118             dataLog("    OSR failed because variable %zu is %s, expected ", local, exec->registers()[local].jsValue().description());
 119             entry->m_expectedValues.local(local).dump(WTF::dataFile());
 120             dataLog(".\n");
 121 #endif
 122             return 0;
 123         }
 124     }
 125
 126     // 2) Check the stack height. The DFG JIT may require a taller stack than the
 127     //    baseline JIT, in some cases. If we can't grow the stack, then don't do
 128     //    OSR right now. That's the only option we have unless we want basic block
 129     //    boundaries to start throwing RangeErrors. Although that would be possible,
 130     //    it seems silly: you'd be diverting the program to error handling when it
 131     //    would have otherwise just kept running albeit less quickly.
 132
 133     if (!globalData->interpreter->registerFile().grow(&exec->registers()[codeBlock->m_numCalleeRegisters])) {
 134 #if ENABLE(JIT_VERBOSE_OSR)
 135         dataLog("    OSR failed because stack growth failed.\n");
 136 #endif
 137         return 0;
 138     }
 139
 140 #if ENABLE(JIT_VERBOSE_OSR)
 141     dataLog("    OSR should succeed.\n");
 142 #endif
 143
 144     // 3) Perform data format conversions.
 145     for (size_t local = 0; local < entry->m_expectedValues.numberOfLocals(); ++local) {
 146         if (entry->m_localsForcedDouble.get(local))
 147             *bitwise_cast<double*>(exec->registers() + local) = exec->registers()[local].jsValue().asNumber();
 148     }
 149
 150     // 4) Fix the call frame.
 151
 152     exec->setCodeBlock(codeBlock);
 153
 154     // 5) Find and return the destination machine code address.
 155
 156     void* result = codeBlock->getJITCode().executableAddressAtOffset(entry->m_machineCodeOffset);
 157
 158 #if ENABLE(JIT_VERBOSE_OSR)
 159     dataLog("    OSR returning machine code address %p.\n", result);
 160 #endif
 161
 162     return result;
 163 #else // DFG_ENABLE(OSR_ENTRY)
 164     UNUSED_PARAM(exec);
 165     UNUSED_PARAM(codeBlock);
 166     UNUSED_PARAM(bytecodeIndex);
 167     return 0;
 168 #endif
 169 }
 170
 171 } } // namespace JSC::DFG
 172
 173 #endif // ENABLE(DFG_JIT)