C++ VM::getAllCalleeSaveRegisterOffsets方法代码示例

//.........这里部分代码省略.........

    // 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.
    
    unsigned frameSizeForCheck = jitCode->common.requiredRegisterCountForExecutionAndExit();
    if (!vm->interpreter->stack().ensureCapacityFor(&exec->registers()[virtualRegisterForLocal(frameSizeForCheck - 1).offset()])) {
        if (Options::verboseOSR())
            dataLogF("    OSR failed because stack growth failed.\n");
        return 0;
    }
    
    if (Options::verboseOSR())
        dataLogF("    OSR should succeed.\n");

    // At this point we're committed to entering. We will do some work to set things up,
    // but we also rely on our caller recognizing that when we return a non-null pointer,
    // that means that we're already past the point of no return and we must succeed at
    // entering.
    
    // 3) Set up the data in the scratch buffer and perform data format conversions.

    unsigned frameSize = jitCode->common.frameRegisterCount;
    unsigned baselineFrameSize = entry->m_expectedValues.numberOfLocals();
    unsigned maxFrameSize = std::max(frameSize, baselineFrameSize);

    Register* scratch = bitwise_cast<Register*>(vm->scratchBufferForSize(sizeof(Register) * (2 + JSStack::CallFrameHeaderSize + maxFrameSize))->dataBuffer());
    
    *bitwise_cast<size_t*>(scratch + 0) = frameSize;
    
    void* targetPC = codeBlock->jitCode()->executableAddressAtOffset(entry->m_machineCodeOffset);
    if (Options::verboseOSR())
        dataLogF("    OSR using target PC %p.\n", targetPC);
    RELEASE_ASSERT(targetPC);
    *bitwise_cast<void**>(scratch + 1) = targetPC;
    
    Register* pivot = scratch + 2 + JSStack::CallFrameHeaderSize;
    
    for (int index = -JSStack::CallFrameHeaderSize; index < static_cast<int>(baselineFrameSize); ++index) {
        VirtualRegister reg(-1 - index);
        
        if (reg.isLocal()) {
            if (entry->m_localsForcedDouble.get(reg.toLocal())) {
                *bitwise_cast<double*>(pivot + index) = exec->registers()[reg.offset()].asanUnsafeJSValue().asNumber();
                continue;
            }
            
            if (entry->m_localsForcedAnyInt.get(reg.toLocal())) {
                *bitwise_cast<int64_t*>(pivot + index) = exec->registers()[reg.offset()].asanUnsafeJSValue().asAnyInt() << JSValue::int52ShiftAmount;
                continue;
            }
        }
        
        pivot[index] = exec->registers()[reg.offset()].asanUnsafeJSValue();
    }
    
    // 4) Reshuffle those registers that need reshuffling.
    Vector<JSValue> temporaryLocals(entry->m_reshufflings.size());
    for (unsigned i = entry->m_reshufflings.size(); i--;)
        temporaryLocals[i] = pivot[VirtualRegister(entry->m_reshufflings[i].fromOffset).toLocal()].asanUnsafeJSValue();
    for (unsigned i = entry->m_reshufflings.size(); i--;)
        pivot[VirtualRegister(entry->m_reshufflings[i].toOffset).toLocal()] = temporaryLocals[i];
    
    // 5) Clear those parts of the call frame that the DFG ain't using. This helps GC on
    //    some programs by eliminating some stale pointer pathologies.
    for (unsigned i = frameSize; i--;) {
        if (entry->m_machineStackUsed.get(i))
            continue;
        pivot[i] = JSValue();
    }

    // 6) Copy our callee saves to buffer.
#if NUMBER_OF_CALLEE_SAVES_REGISTERS > 0
    RegisterAtOffsetList* registerSaveLocations = codeBlock->calleeSaveRegisters();
    RegisterAtOffsetList* allCalleeSaves = vm->getAllCalleeSaveRegisterOffsets();
    RegisterSet dontSaveRegisters = RegisterSet(RegisterSet::stackRegisters(), RegisterSet::allFPRs());

    unsigned registerCount = registerSaveLocations->size();
    VMEntryRecord* record = vmEntryRecord(vm->topVMEntryFrame);
    for (unsigned i = 0; i < registerCount; i++) {
        RegisterAtOffset currentEntry = registerSaveLocations->at(i);
        if (dontSaveRegisters.get(currentEntry.reg()))
            continue;
        RegisterAtOffset* calleeSavesEntry = allCalleeSaves->find(currentEntry.reg());
        
        *(bitwise_cast<intptr_t*>(pivot - 1) - currentEntry.offsetAsIndex()) = record->calleeSaveRegistersBuffer[calleeSavesEntry->offsetAsIndex()];
    }
#endif
    
    // 7) Fix the call frame to have the right code block.
    
    *bitwise_cast<CodeBlock**>(pivot - 1 - JSStack::CodeBlock) = codeBlock;
    
    if (Options::verboseOSR())
        dataLogF("    OSR returning data buffer %p.\n", scratch);
    return scratch;
}