C++ MInstruction::isInterruptCheck方法代码示例

void
LoopUnroller::go(LoopIterationBound *bound)
{
    // For now we always unroll loops the same number of times.
    static const size_t UnrollCount = 10;

    JitSpew(JitSpew_Unrolling, "Attempting to unroll loop");

    header = bound->header;

    // UCE might have determined this isn't actually a loop.
    if (!header->isLoopHeader())
        return;

    backedge = header->backedge();
    oldPreheader = header->loopPredecessor();

    JS_ASSERT(oldPreheader->numSuccessors() == 1);

    // Only unroll loops with two blocks: an initial one ending with the
    // bound's test, and the body ending with the backedge.
    MTest *test = bound->test;
    if (header->lastIns() != test)
        return;
    if (test->ifTrue() == backedge) {
        if (test->ifFalse()->id() <= backedge->id())
            return;
    } else if (test->ifFalse() == backedge) {
        if (test->ifTrue()->id() <= backedge->id())
            return;
    } else {
        return;
    }
    if (backedge->numPredecessors() != 1 || backedge->numSuccessors() != 1)
        return;
    JS_ASSERT(backedge->phisEmpty());

    MBasicBlock *bodyBlocks[] = { header, backedge };

    // All instructions in the header and body must be clonable.
    for (size_t i = 0; i < ArrayLength(bodyBlocks); i++) {
        MBasicBlock *block = bodyBlocks[i];
        for (MInstructionIterator iter(block->begin()); iter != block->end(); iter++) {
            MInstruction *ins = *iter;
            if (ins->canClone())
                continue;
            if (ins->isTest() || ins->isGoto() || ins->isInterruptCheck())
                continue;
#ifdef DEBUG
            JitSpew(JitSpew_Unrolling, "Aborting: can't clone instruction %s", ins->opName());
#endif
            return;
        }
    }

    // Compute the linear inequality we will use for exiting the unrolled loop:
    //
    // iterationBound - iterationCount - UnrollCount >= 0
    //
    LinearSum remainingIterationsInequality(bound->boundSum);
    if (!remainingIterationsInequality.add(bound->currentSum, -1))
        return;
    if (!remainingIterationsInequality.add(-int32_t(UnrollCount)))
        return;

    // Terms in the inequality need to be either loop invariant or phis from
    // the original header.
    for (size_t i = 0; i < remainingIterationsInequality.numTerms(); i++) {
        MDefinition *def = remainingIterationsInequality.term(i).term;
        if (def->block()->id() < header->id())
            continue;
        if (def->block() == header && def->isPhi())
            continue;
        return;
    }

    // OK, we've checked everything, now unroll the loop.

    JitSpew(JitSpew_Unrolling, "Unrolling loop");

    // The old preheader will go before the unrolled loop, and the old loop
    // will need a new empty preheader.
    CompileInfo &info = oldPreheader->info();
    if (header->trackedSite().pc()) {
        unrolledHeader =
            MBasicBlock::New(graph, nullptr, info,
                             oldPreheader, header->trackedSite(), MBasicBlock::LOOP_HEADER);
        unrolledBackedge =
            MBasicBlock::New(graph, nullptr, info,
                             unrolledHeader, backedge->trackedSite(), MBasicBlock::NORMAL);
        newPreheader =
            MBasicBlock::New(graph, nullptr, info,
                             unrolledHeader, oldPreheader->trackedSite(), MBasicBlock::NORMAL);
    } else {
        unrolledHeader = MBasicBlock::NewAsmJS(graph, info, oldPreheader, MBasicBlock::LOOP_HEADER);
        unrolledBackedge = MBasicBlock::NewAsmJS(graph, info, unrolledHeader, MBasicBlock::NORMAL);
        newPreheader = MBasicBlock::NewAsmJS(graph, info, unrolledHeader, MBasicBlock::NORMAL);
    }

    unrolledHeader->discardAllResumePoints();
//.........这里部分代码省略.........

bool
jit::ReorderInstructions(MIRGraph& graph)
{
    // Renumber all instructions in the graph as we go.
    size_t nextId = 0;

    // List of the headers of any loops we are in.
    Vector<MBasicBlock*, 4, SystemAllocPolicy> loopHeaders;

    for (ReversePostorderIterator block(graph.rpoBegin()); block != graph.rpoEnd(); block++) {
        // Renumber all definitions inside the basic blocks.
        for (MPhiIterator iter(block->phisBegin()); iter != block->phisEnd(); iter++)
            iter->setId(nextId++);

        for (MInstructionIterator iter(block->begin()); iter != block->end(); iter++)
            iter->setId(nextId++);

        // Don't reorder instructions within entry blocks, which have special requirements.
        if (*block == graph.entryBlock() || *block == graph.osrBlock())
            continue;

        if (block->isLoopHeader()) {
            if (!loopHeaders.append(*block))
                return false;
        }

        MBasicBlock* innerLoop = loopHeaders.empty() ? nullptr : loopHeaders.back();

        MInstruction* top = block->safeInsertTop();
        MInstructionReverseIterator rtop = ++block->rbegin(top);
        for (MInstructionIterator iter(block->begin(top)); iter != block->end(); ) {
            MInstruction* ins = *iter;

            // Filter out some instructions which are never reordered.
            if (ins->isEffectful() ||
                !ins->isMovable() ||
                ins->resumePoint() ||
                ins == block->lastIns())
            {
                iter++;
                continue;
            }

            // Move constants with a single use in the current block to the
            // start of the block. Constants won't be reordered by the logic
            // below, as they have no inputs. Moving them up as high as
            // possible can allow their use to be moved up further, though,
            // and has no cost if the constant is emitted at its use.
            if (ins->isConstant() &&
                ins->hasOneUse() &&
                ins->usesBegin()->consumer()->block() == *block &&
                !IsFloatingPointType(ins->type()))
            {
                iter++;
                MInstructionIterator targetIter = block->begin();
                while (targetIter->isConstant() || targetIter->isInterruptCheck()) {
                    if (*targetIter == ins)
                        break;
                    targetIter++;
                }
                MoveBefore(*block, *targetIter, ins);
                continue;
            }

            // Look for inputs where this instruction is the last use of that
            // input. If we move this instruction up, the input's lifetime will
            // be shortened, modulo resume point uses (which don't need to be
            // stored in a register, and can be handled by the register
            // allocator by just spilling at some point with no reload).
            Vector<MDefinition*, 4, SystemAllocPolicy> lastUsedInputs;
            for (size_t i = 0; i < ins->numOperands(); i++) {
                MDefinition* input = ins->getOperand(i);
                if (!input->isConstant() && IsLastUse(ins, input, innerLoop)) {
                    if (!lastUsedInputs.append(input))
                        return false;
                }
            }

            // Don't try to move instructions which aren't the last use of any
            // of their inputs (we really ought to move these down instead).
            if (lastUsedInputs.length() < 2) {
                iter++;
                continue;
            }

            MInstruction* target = ins;
            for (MInstructionReverseIterator riter = ++block->rbegin(ins); riter != rtop; riter++) {
                MInstruction* prev = *riter;
                if (prev->isInterruptCheck())
                    break;

                // The instruction can't be moved before any of its uses.
                bool isUse = false;
                for (size_t i = 0; i < ins->numOperands(); i++) {
                    if (ins->getOperand(i) == prev) {
                        isUse = true;
                        break;
                    }
                }
                if (isUse)
//.........这里部分代码省略.........