C++ LBlock::rbegin方法代码示例

bool
StupidAllocator::go()
{
    // This register allocator is intended to be as simple as possible, while
    // still being complicated enough to share properties with more complicated
    // allocators. Namely, physical registers may be used to carry virtual
    // registers across LIR instructions, but not across basic blocks.
    //
    // This algorithm does not pay any attention to liveness. It is performed
    // as a single forward pass through the basic blocks in the program. As
    // virtual registers and temporaries are defined they are assigned physical
    // registers, evicting existing allocations in an LRU fashion.

    // For virtual registers not carried in a register, a canonical spill
    // location is used. Each vreg has a different spill location; since we do
    // not track liveness we cannot determine that two vregs have disjoint
    // lifetimes. Thus, the maximum stack height is the number of vregs (scaled
    // by two on 32 bit platforms to allow storing double values).
    graph.setLocalSlotCount(DefaultStackSlot(graph.numVirtualRegisters() - 1) + 1);

    if (!init())
        return false;

    for (size_t blockIndex = 0; blockIndex < graph.numBlocks(); blockIndex++) {
        LBlock *block = graph.getBlock(blockIndex);
        JS_ASSERT(block->mir()->id() == blockIndex);

        for (size_t i = 0; i < registerCount; i++)
            registers[i].set(MISSING_ALLOCATION);

        for (LInstructionIterator iter = block->begin(); iter != block->end(); iter++) {
            LInstruction *ins = *iter;

            if (ins == *block->rbegin())
                syncForBlockEnd(block, ins);

            allocateForInstruction(ins);
        }
    }

    return true;
}

bool
AllocationIntegrityState::check(bool populateSafepoints)
{
    MOZ_ASSERT(!instructions.empty());

#ifdef DEBUG
    if (JitSpewEnabled(JitSpew_RegAlloc))
        dump();

    for (size_t blockIndex = 0; blockIndex < graph.numBlocks(); blockIndex++) {
        LBlock* block = graph.getBlock(blockIndex);

        // Check that all instruction inputs and outputs have been assigned an allocation.
        for (LInstructionIterator iter = block->begin(); iter != block->end(); iter++) {
            LInstruction* ins = *iter;

            for (LInstruction::InputIterator alloc(*ins); alloc.more(); alloc.next())
                MOZ_ASSERT(!alloc->isUse());

            for (size_t i = 0; i < ins->numDefs(); i++) {
                LDefinition* def = ins->getDef(i);
                MOZ_ASSERT(!def->output()->isUse());

                LDefinition oldDef = instructions[ins->id()].outputs[i];
                MOZ_ASSERT_IF(oldDef.policy() == LDefinition::MUST_REUSE_INPUT,
                              *def->output() == *ins->getOperand(oldDef.getReusedInput()));
            }

            for (size_t i = 0; i < ins->numTemps(); i++) {
                LDefinition* temp = ins->getTemp(i);
                MOZ_ASSERT_IF(!temp->isBogusTemp(), temp->output()->isRegister());

                LDefinition oldTemp = instructions[ins->id()].temps[i];
                MOZ_ASSERT_IF(oldTemp.policy() == LDefinition::MUST_REUSE_INPUT,
                              *temp->output() == *ins->getOperand(oldTemp.getReusedInput()));
            }
        }
    }
#endif

    // Check that the register assignment and move groups preserve the original
    // semantics of the virtual registers. Each virtual register has a single
    // write (owing to the SSA representation), but the allocation may move the
    // written value around between registers and memory locations along
    // different paths through the script.
    //
    // For each use of an allocation, follow the physical value which is read
    // backward through the script, along all paths to the value's virtual
    // register's definition.
    for (size_t blockIndex = 0; blockIndex < graph.numBlocks(); blockIndex++) {
        LBlock* block = graph.getBlock(blockIndex);
        for (LInstructionIterator iter = block->begin(); iter != block->end(); iter++) {
            LInstruction* ins = *iter;
            const InstructionInfo& info = instructions[ins->id()];

            LSafepoint* safepoint = ins->safepoint();
            if (safepoint) {
                for (size_t i = 0; i < ins->numTemps(); i++) {
                    if (ins->getTemp(i)->isBogusTemp())
                        continue;
                    uint32_t vreg = info.temps[i].virtualRegister();
                    LAllocation* alloc = ins->getTemp(i)->output();
                    if (!checkSafepointAllocation(ins, vreg, *alloc, populateSafepoints))
                        return false;
                }
                MOZ_ASSERT_IF(ins->isCall() && !populateSafepoints,
                              safepoint->liveRegs().emptyFloat() &&
                              safepoint->liveRegs().emptyGeneral());
            }

            size_t inputIndex = 0;
            for (LInstruction::InputIterator alloc(*ins); alloc.more(); alloc.next()) {
                LAllocation oldInput = info.inputs[inputIndex++];
                if (!oldInput.isUse())
                    continue;

                uint32_t vreg = oldInput.toUse()->virtualRegister();

                if (safepoint && !oldInput.toUse()->usedAtStart()) {
                    if (!checkSafepointAllocation(ins, vreg, **alloc, populateSafepoints))
                        return false;
                }

                // Start checking at the previous instruction, in case this
                // instruction reuses its input register for an output.
                LInstructionReverseIterator riter = block->rbegin(ins);
                riter++;
                checkIntegrity(block, *riter, vreg, **alloc, populateSafepoints);

                while (!worklist.empty()) {
                    IntegrityItem item = worklist.popCopy();
                    checkIntegrity(item.block, *item.block->rbegin(), item.vreg, item.alloc, populateSafepoints);
                }
            }
        }
    }

    return true;
}

bool
LiveRangeAllocator<VREG>::buildLivenessInfo()
{
    if (!init())
        return false;

    Vector<MBasicBlock *, 1, SystemAllocPolicy> loopWorkList;
    BitSet *loopDone = BitSet::New(alloc(), graph.numBlockIds());
    if (!loopDone)
        return false;

    for (size_t i = graph.numBlocks(); i > 0; i--) {
        if (mir->shouldCancel("Build Liveness Info (main loop)"))
            return false;

        LBlock *block = graph.getBlock(i - 1);
        MBasicBlock *mblock = block->mir();

        BitSet *live = BitSet::New(alloc(), graph.numVirtualRegisters());
        if (!live)
            return false;
        liveIn[mblock->id()] = live;

        // Propagate liveIn from our successors to us
        for (size_t i = 0; i < mblock->lastIns()->numSuccessors(); i++) {
            MBasicBlock *successor = mblock->lastIns()->getSuccessor(i);
            // Skip backedges, as we fix them up at the loop header.
            if (mblock->id() < successor->id())
                live->insertAll(liveIn[successor->id()]);
        }

        // Add successor phis
        if (mblock->successorWithPhis()) {
            LBlock *phiSuccessor = mblock->successorWithPhis()->lir();
            for (unsigned int j = 0; j < phiSuccessor->numPhis(); j++) {
                LPhi *phi = phiSuccessor->getPhi(j);
                LAllocation *use = phi->getOperand(mblock->positionInPhiSuccessor());
                uint32_t reg = use->toUse()->virtualRegister();
                live->insert(reg);
            }
        }

        // Variables are assumed alive for the entire block, a define shortens
        // the interval to the point of definition.
        for (BitSet::Iterator liveRegId(*live); liveRegId; liveRegId++) {
            if (!vregs[*liveRegId].getInterval(0)->addRangeAtHead(inputOf(block->firstId()),
                                                                  outputOf(block->lastId()).next()))
            {
                return false;
            }
        }

        // Shorten the front end of live intervals for live variables to their
        // point of definition, if found.
        for (LInstructionReverseIterator ins = block->rbegin(); ins != block->rend(); ins++) {
            // Calls may clobber registers, so force a spill and reload around the callsite.
            if (ins->isCall()) {
                for (AnyRegisterIterator iter(allRegisters_); iter.more(); iter++) {
                    if (forLSRA) {
                        if (!addFixedRangeAtHead(*iter, inputOf(*ins), outputOf(*ins)))
                            return false;
                    } else {
                        bool found = false;
                        for (size_t i = 0; i < ins->numDefs(); i++) {
                            if (ins->getDef(i)->isPreset() &&
                                *ins->getDef(i)->output() == LAllocation(*iter)) {
                                found = true;
                                break;
                            }
                        }
                        if (!found && !addFixedRangeAtHead(*iter, outputOf(*ins), outputOf(*ins).next()))
                            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
//.........这里部分代码省略.........