C++ LUse类代码示例

bool
GreedyAllocator::allocateInputs(LInstruction *ins)
{
    // First deal with fixed-register policies and policies that require
    // registers.
    for (size_t i = 0; i < ins->numOperands(); i++) {
        LAllocation *a = ins->getOperand(i);
        if (!a->isUse())
            continue;
        LUse *use = a->toUse();
        VirtualRegister *vr = getVirtualRegister(use);
        if (use->policy() == LUse::FIXED) {
            if (!allocateFixedOperand(a, vr))
                return false;
        } else if (use->policy() == LUse::REGISTER) {
            if (!allocateRegisterOperand(a, vr))
                return false;
        }
    }

    // Finally, deal with things that take either registers or memory.
    for (size_t i = 0; i < ins->numOperands(); i++) {
        LAllocation *a = ins->getOperand(i);
        if (!a->isUse())
            continue;

        VirtualRegister *vr = getVirtualRegister(a->toUse());
        if (!allocateAnyOperand(a, vr))
            return false;
    }

    return true;
}

void
LSnapshot::rewriteRecoveredInput(LUse input)
{
    // Mark any operands to this snapshot with the same value as input as being
    // equal to the instruction's result.
    for (size_t i = 0; i < numEntries(); i++) {
        if (getEntry(i)->isUse() && getEntry(i)->toUse()->virtualRegister() == input.virtualRegister())
            setEntry(i, LUse(input.virtualRegister(), LUse::RECOVERED_INPUT));
    }
}

bool
GreedyAllocator::prescanUses(LInstruction *ins)
{
    for (size_t i = 0; i < ins->numOperands(); i++) {
        LAllocation *a = ins->getOperand(i);
        if (!a->isUse()) {
            JS_ASSERT(a->isConstant());
            continue;
        }

        LUse *use = a->toUse();
        VirtualRegister *vr = getVirtualRegister(use);
        if (use->policy() == LUse::FIXED) {
            // A def or temp may use the same register, so we have to use the
            // unchecked version.
            disallowed.addUnchecked(GetFixedRegister(vr->def, use));
        } else if (vr->hasRegister()) {
            discouraged.addUnchecked(vr->reg());
        }
    }
    return true;
}

//.........这里部分代码省略.........
                            return false;
                    }
                }
            }

            for (size_t i = 0; i < ins->numDefs(); i++) {
                if (ins->getDef(i)->policy() != LDefinition::PASSTHROUGH) {
                    LDefinition *def = ins->getDef(i);

                    CodePosition from;
                    if (def->policy() == LDefinition::PRESET && def->output()->isRegister() && forLSRA) {
                        // The fixed range covers the current instruction so the
                        // interval for the virtual register starts at the next
                        // instruction. If the next instruction has a fixed use,
                        // this can lead to unnecessary register moves. To avoid
                        // special handling for this, assert the next instruction
                        // has no fixed uses. defineFixed guarantees this by inserting
                        // an LNop.
                        JS_ASSERT(!NextInstructionHasFixedUses(block, *ins));
                        AnyRegister reg = def->output()->toRegister();
                        if (!addFixedRangeAtHead(reg, inputOf(*ins), outputOf(*ins).next()))
                            return false;
                        from = outputOf(*ins).next();
                    } else {
                        from = forLSRA ? inputOf(*ins) : outputOf(*ins);
                    }

                    if (def->policy() == LDefinition::MUST_REUSE_INPUT) {
                        // MUST_REUSE_INPUT is implemented by allocating an output
                        // register and moving the input to it. Register hints are
                        // used to avoid unnecessary moves. We give the input an
                        // LUse::ANY policy to avoid allocating a register for the
                        // input.
                        LUse *inputUse = ins->getOperand(def->getReusedInput())->toUse();
                        JS_ASSERT(inputUse->policy() == LUse::REGISTER);
                        JS_ASSERT(inputUse->usedAtStart());
                        *inputUse = LUse(inputUse->virtualRegister(), LUse::ANY, /* usedAtStart = */ true);
                    }

                    LiveInterval *interval = vregs[def].getInterval(0);
                    interval->setFrom(from);

                    // Ensure that if there aren't any uses, there's at least
                    // some interval for the output to go into.
                    if (interval->numRanges() == 0) {
                        if (!interval->addRangeAtHead(from, from.next()))
                            return false;
                    }
                    live->remove(def->virtualRegister());
                }
            }

            for (size_t i = 0; i < ins->numTemps(); i++) {
                LDefinition *temp = ins->getTemp(i);
                if (temp->isBogusTemp())
                    continue;

                if (forLSRA) {
                    if (temp->policy() == LDefinition::PRESET) {
                        if (ins->isCall())
                            continue;
                        AnyRegister reg = temp->output()->toRegister();
                        if (!addFixedRangeAtHead(reg, inputOf(*ins), outputOf(*ins)))
                            return false;

                        // Fixed intervals are not added to safepoints, so do it

void
StupidAllocator::allocateForInstruction(LInstruction *ins)
{
    // Sync all registers before making a call.
    if (ins->isCall()) {
        for (size_t i = 0; i < registerCount; i++)
            syncRegister(ins, i);
    }

    // Allocate for inputs which are required to be in registers.
    for (LInstruction::InputIterator alloc(*ins); alloc.more(); alloc.next()) {
        if (!alloc->isUse())
            continue;
        LUse *use = alloc->toUse();
        uint32_t vreg = use->virtualRegister();
        if (use->policy() == LUse::REGISTER) {
            AnyRegister reg = ensureHasRegister(ins, vreg);
            alloc.replace(LAllocation(reg));
        } else if (use->policy() == LUse::FIXED) {
            AnyRegister reg = GetFixedRegister(virtualRegisters[use->virtualRegister()], use);
            RegisterIndex index = registerIndex(reg);
            if (registers[index].vreg != vreg) {
                evictRegister(ins, index);
                RegisterIndex existing = findExistingRegister(vreg);
                if (existing != UINT32_MAX)
                    evictRegister(ins, existing);
                loadRegister(ins, vreg, index);
            }
            alloc.replace(LAllocation(reg));
        } else {
            // Inputs which are not required to be in a register are not
            // allocated until after temps/definitions, as the latter may need
            // to evict registers which hold these inputs.
        }
    }

    // Find registers to hold all temporaries and outputs of the instruction.
    for (size_t i = 0; i < ins->numTemps(); i++) {
        LDefinition *def = ins->getTemp(i);
        if (!def->isBogusTemp())
            allocateForDefinition(ins, def);
    }
    for (size_t i = 0; i < ins->numDefs(); i++) {
        LDefinition *def = ins->getDef(i);
        if (def->policy() != LDefinition::PASSTHROUGH)
            allocateForDefinition(ins, def);
    }

    // Allocate for remaining inputs which do not need to be in registers.
    for (LInstruction::InputIterator alloc(*ins); alloc.more(); alloc.next()) {
        if (!alloc->isUse())
            continue;
        LUse *use = alloc->toUse();
        uint32_t vreg = use->virtualRegister();
        JS_ASSERT(use->policy() != LUse::REGISTER && use->policy() != LUse::FIXED);

        RegisterIndex index = findExistingRegister(vreg);
        if (index == UINT32_MAX) {
            LAllocation *stack = stackLocation(use->virtualRegister());
            alloc.replace(*stack);
        } else {
            registers[index].age = ins->id();
            alloc.replace(LAllocation(registers[index].reg));
        }
    }

    // If this is a call, evict all registers except for those holding outputs.
    if (ins->isCall()) {
        for (size_t i = 0; i < registerCount; i++) {
            if (!registers[i].dirty)
                registers[i].set(MISSING_ALLOCATION);
        }
    }
}