C++ MInstructionReverseIterator类代码示例

bool
EagerSimdUnbox(MIRGenerator* mir, MIRGraph& graph)
{
    const JitCompartment* jitCompartment = GetJitContext()->compartment->jitCompartment();
    for (PostorderIterator block = graph.poBegin(); block != graph.poEnd(); block++) {
        if (mir->shouldCancel("Eager Simd Unbox"))
            return false;

        for (MInstructionReverseIterator ins = block->rbegin(); ins != block->rend(); ins++) {
            if (!ins->isSimdUnbox())
                continue;

            MSimdUnbox* unbox = ins->toSimdUnbox();
            if (!unbox->input()->isPhi())
                continue;

            MPhi* phi = unbox->input()->toPhi();
            if (!CanUnboxSimdPhi(jitCompartment, phi, unbox->simdType()))
                continue;

            UnboxSimdPhi(jitCompartment, graph, phi, unbox->simdType());
        }
    }

    return true;
}

void
MBasicBlock::flagOperandsOfPrunedBranches(MInstruction* ins)
{
    // Find the previous resume point which would be used for bailing out.
    MResumePoint* rp = nullptr;
    for (MInstructionReverseIterator iter = rbegin(ins); iter != rend(); iter++) {
        rp = iter->resumePoint();
        if (rp)
            break;
    }

    // If none, take the entry resume point.
    if (!rp)
        rp = entryResumePoint();

    // The only blocks which do not have any entryResumePoint in Ion, are the
    // SplitEdge blocks.  SplitEdge blocks only have a Goto instruction before
    // Range Analysis phase.  In adjustInputs, we are manipulating instructions
    // which have a TypePolicy.  So, as a Goto has no operand and no type
    // policy, the entry resume point should exists.
    MOZ_ASSERT(rp);

    // Flag all operand as being potentially used.
    while (rp) {
        for (size_t i = 0, end = rp->numOperands(); i < end; i++)
            rp->getOperand(i)->setUseRemovedUnchecked();
        rp = rp->caller();
    }
}

MInstructionReverseIterator
MBasicBlock::discardAt(MInstructionReverseIterator &iter)
{
    for (size_t i = 0; i < iter->numOperands(); i++)
        iter->replaceOperand(i, NULL);

    return instructions_.removeAt(iter);
}

MInstructionReverseIterator
MBasicBlock::discardAt(MInstructionReverseIterator &iter)
{
    AssertSafelyDiscardable(*iter);
    for (size_t i = 0; i < iter->numOperands(); i++)
        iter->discardOperand(i);

    return instructions_.removeAt(iter);
}

// Instructions are useless if they are unused and have no side effects.
// This pass eliminates useless instructions.
// The graph itself is unchanged.
bool
ion::EliminateDeadCode(MIRGenerator *mir, MIRGraph &graph)
{
    // Traverse in postorder so that we hit uses before definitions.
    // Traverse instruction list backwards for the same reason.
    for (PostorderIterator block = graph.poBegin(); block != graph.poEnd(); block++) {
        if (mir->shouldCancel("Eliminate Dead Code (main loop)"))
            return false;

        // Remove unused instructions.
        for (MInstructionReverseIterator inst = block->rbegin(); inst != block->rend(); ) {
            if (!inst->isEffectful() && !inst->hasUses() && !inst->isGuard() &&
                !inst->isControlInstruction()) {
                inst = block->discardAt(inst);
            } else {
                inst++;
            }
        }
    }

    return true;
}