C++ MIRGraph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;
}

bool
jit::LICM(MIRGenerator *mir, MIRGraph &graph)
{
    JitSpew(JitSpew_LICM, "Beginning LICM pass");

    // Iterate in RPO to visit outer loops before inner loops. We'd hoist the
    // same things either way, but outer first means we do a little less work.
    for (auto i(graph.rpoBegin()), e(graph.rpoEnd()); i != e; ++i) {
        MBasicBlock *header = *i;
        if (!header->isLoopHeader())
            continue;

        bool canOsr;
        MarkLoopBlocks(graph, header, &canOsr);

        // Hoisting out of a loop that has an entry from the OSR block in
        // addition to its normal entry is tricky. In theory we could clone
        // the instruction and insert phis.
        if (!canOsr)
            VisitLoop(graph, header);
        else
            JitSpew(JitSpew_LICM, "  Skipping loop with header block%u due to OSR", header->id());

        UnmarkLoopBlocks(graph, header);

        if (mir->shouldCancel("LICM (main loop)"))
            return false;
    }

    return true;
}

void
ion::AssertGraphCoherency(MIRGraph &graph)
{
#ifdef DEBUG
    // Assert successor and predecessor list coherency.
    uint32_t count = 0;
    for (MBasicBlockIterator block(graph.begin()); block != graph.end(); block++) {
        count++;

        for (size_t i = 0; i < block->numSuccessors(); i++)
            JS_ASSERT(CheckSuccessorImpliesPredecessor(*block, block->getSuccessor(i)));

        for (size_t i = 0; i < block->numPredecessors(); i++)
            JS_ASSERT(CheckPredecessorImpliesSuccessor(*block, block->getPredecessor(i)));

        for (MInstructionIterator ins = block->begin(); ins != block->end(); ins++) {
            for (uint32_t i = 0; i < ins->numOperands(); i++)
                JS_ASSERT(CheckMarkedAsUse(*ins, ins->getOperand(i)));
        }
    }

    JS_ASSERT(graph.numBlocks() == count);

    AssertReversePostOrder(graph);
#endif
}

MBasicBlock::MBasicBlock(MIRGraph &graph, CompileInfo &info, const BytecodeSite &site, Kind kind)
  : unreachable_(false),
    graph_(graph),
    info_(info),
    predecessors_(graph.alloc()),
    stackPosition_(info_.firstStackSlot()),
    lastIns_(nullptr),
    pc_(site.pc()),
    lir_(nullptr),
    start_(nullptr),
    entryResumePoint_(nullptr),
    successorWithPhis_(nullptr),
    positionInPhiSuccessor_(0),
    kind_(kind),
    loopDepth_(0),
    mark_(false),
    immediatelyDominated_(graph.alloc()),
    immediateDominator_(nullptr),
    numDominated_(0),
    trackedSite_(site)
#if defined (JS_ION_PERF)
    , lineno_(0u),
    columnIndex_(0u)
#endif
{
}

static void
VisitLoop(MIRGraph &graph, MBasicBlock *header)
{
    MInstruction *hoistPoint = header->loopPredecessor()->lastIns();

    JitSpew(JitSpew_LICM, "  Visiting loop with header block%u, hoisting to %s%u",
            header->id(), hoistPoint->opName(), hoistPoint->id());

    MBasicBlock *backedge = header->backedge();

    // This indicates whether the loop contains calls or other things which
    // clobber most or all floating-point registers. In such loops,
    // floating-point constants should not be hoisted unless it enables further
    // hoisting.
    bool hasCalls = LoopContainsPossibleCall(graph, header, backedge);

    for (auto i(graph.rpoBegin(header)); ; ++i) {
        MOZ_ASSERT(i != graph.rpoEnd(), "Reached end of graph searching for blocks in loop");
        MBasicBlock *block = *i;
        if (!block->isMarked())
            continue;

        VisitLoopBlock(block, header, hoistPoint, hasCalls);

        if (block == backedge)
            break;
    }
}

bool
ion::RenumberBlocks(MIRGraph &graph)
{
    size_t id = 0;
    for (ReversePostorderIterator block(graph.rpoBegin()); block != graph.rpoEnd(); block++)
        block->setId(id++);

    return true;
}

static void
AnalyzeAsmHeapAddress(MDefinition* ptr, MIRGraph& graph)
{
    // Fold (a+i)&m to (a&m)+i, provided that this doesn't change the result,
    // since the users of the BitAnd include heap accesses. This will expose
    // the redundancy for GVN when expressions like this:
    //   a&m
    //   (a+1)&m,
    //   (a+2)&m,
    // are transformed into this:
    //   a&m
    //   (a&m)+1
    //   (a&m)+2
    // and it will allow the constants to be folded by the
    // EffectiveAddressAnalysis pass.
    //
    // Putting the add on the outside might seem like it exposes other users of
    // the expression to the possibility of i32 overflow, if we aren't in wasm
    // and they aren't naturally truncating. However, since we use MAdd::New
    // with MIRType::Int32, we make sure that the value is truncated, just as it
    // would be by the MBitAnd.

    MOZ_ASSERT(IsCompilingWasm());

    if (!ptr->isBitAnd())
        return;

    MDefinition* lhs = ptr->toBitAnd()->getOperand(0);
    MDefinition* rhs = ptr->toBitAnd()->getOperand(1);
    if (lhs->isConstant())
        mozilla::Swap(lhs, rhs);
    if (!lhs->isAdd() || !rhs->isConstant())
        return;

    MDefinition* op0 = lhs->toAdd()->getOperand(0);
    MDefinition* op1 = lhs->toAdd()->getOperand(1);
    if (op0->isConstant())
        mozilla::Swap(op0, op1);
    if (!op1->isConstant())
        return;

    uint32_t i = op1->toConstant()->toInt32();
    uint32_t m = rhs->toConstant()->toInt32();
    if (!IsAlignmentMask(m) || (i & m) != i)
        return;

    // The pattern was matched! Produce the replacement expression.
    MInstruction* and_ = MBitAnd::New(graph.alloc(), op0, rhs, MIRType::Int32);
    ptr->block()->insertBefore(ptr->toBitAnd(), and_);
    MInstruction* add = MAdd::New(graph.alloc(), and_, op1, MIRType::Int32);
    ptr->block()->insertBefore(ptr->toBitAnd(), add);
    ptr->replaceAllUsesWith(add);
    ptr->block()->discard(ptr->toBitAnd());
}

ValueNumberer::ValueNumberer(MIRGenerator* mir, MIRGraph& graph)
  : mir_(mir), graph_(graph),
    values_(graph.alloc()),
    deadDefs_(graph.alloc()),
    remainingBlocks_(graph.alloc()),
    nextDef_(nullptr),
    totalNumVisited_(0),
    rerun_(false),
    blocksRemoved_(false),
    updateAliasAnalysis_(false),
    dependenciesBroken_(false)
{}

void
ion::AssertExtendedGraphCoherency(MIRGraph &graph)
{
    // Checks the basic GraphCoherency but also other conditions that
    // do not hold immediately (such as the fact that critical edges
    // are split)

#ifdef DEBUG
    AssertGraphCoherency(graph);

    uint32_t idx = 0;
    for (MBasicBlockIterator block(graph.begin()); block != graph.end(); block++) {
        JS_ASSERT(block->id() == idx++);

        // No critical edges:
        if (block->numSuccessors() > 1)
            for (size_t i = 0; i < block->numSuccessors(); i++)
                JS_ASSERT(block->getSuccessor(i)->numPredecessors() == 1);

        if (block->isLoopHeader()) {
            JS_ASSERT(block->numPredecessors() == 2);
            MBasicBlock *backedge = block->getPredecessor(1);
            JS_ASSERT(backedge->id() >= block->id());
            JS_ASSERT(backedge->numSuccessors() == 1);
            JS_ASSERT(backedge->getSuccessor(0) == *block);
        }

        if (!block->phisEmpty()) {
            for (size_t i = 0; i < block->numPredecessors(); i++) {
                MBasicBlock *pred = block->getPredecessor(i);
                JS_ASSERT(pred->successorWithPhis() == *block);
                JS_ASSERT(pred->positionInPhiSuccessor() == i);
            }
        }

        uint32_t successorWithPhis = 0;
        for (size_t i = 0; i < block->numSuccessors(); i++)
            if (!block->getSuccessor(i)->phisEmpty())
                successorWithPhis++;

        JS_ASSERT(successorWithPhis <= 1);
        JS_ASSERT_IF(successorWithPhis, block->successorWithPhis() != NULL);

        // I'd like to assert this, but it's not necc. true.  Sometimes we set this
        // flag to non-NULL just because a successor has multiple preds, even if it
        // does not actually have any phis.
        //
        // JS_ASSERT_IF(!successorWithPhis, block->successorWithPhis() == NULL);
    }
#endif
}

ValueNumberer::ValueNumberer(MIRGenerator *mir, MIRGraph &graph, bool optimistic)
  : mir(mir),
    graph_(graph),
    values(graph.alloc()),
    pessimisticPass_(!optimistic),
    count_(0)
{ }

static void
AssertReversePostOrder(MIRGraph &graph)
{
    // Check that every block is visited after all its predecessors (except backedges).
    for (ReversePostorderIterator block(graph.rpoBegin()); block != graph.rpoEnd(); block++) {
        JS_ASSERT(!block->isMarked());

        for (size_t i = 0; i < block->numPredecessors(); i++) {
            MBasicBlock *pred = block->getPredecessor(i);
            JS_ASSERT_IF(!pred->isLoopBackedge(), pred->isMarked());
        }

        block->mark();
    }

    graph.unmarkBlocks();
}

bool
FoldLinearArithConstants(MIRGenerator* mir, MIRGraph& graph)
{
    for (PostorderIterator block(graph.poBegin()); block != graph.poEnd(); block++) {
        if (mir->shouldCancel("Fold Linear Arithmetic Constants (main loop)"))
            return false;

        for (MInstructionIterator i = block->begin(); i != block->end(); i++) {
            if (!graph.alloc().ensureBallast())
                return false;

            if (mir->shouldCancel("Fold Linear Arithmetic Constants (inner loop)"))
                return false;

            if (i->isAdd())
                AnalyzeAdd(graph.alloc(), i->toAdd());
        }
    }
    return true;
}

// Test whether any instruction in the loop possiblyCalls().
static bool
LoopContainsPossibleCall(MIRGraph &graph, MBasicBlock *header, MBasicBlock *backedge)
{
    for (auto i(graph.rpoBegin(header)); ; ++i) {
        MOZ_ASSERT(i != graph.rpoEnd(), "Reached end of graph searching for blocks in loop");
        MBasicBlock *block = *i;
        if (!block->isMarked())
            continue;

        for (auto insIter(block->begin()), insEnd(block->end()); insIter != insEnd; ++insIter) {
            MInstruction *ins = *insIter;
            if (ins->possiblyCalls()) {
                JitSpew(JitSpew_LICM, "    Possile call found at %s%u", ins->opName(), ins->id());
                return true;
            }
        }

        if (block == backedge)
            break;
    }
    return false;
}

static void
UnboxSimdPhi(const JitCompartment* jitCompartment, MIRGraph& graph, MPhi* phi, SimdType unboxType)
{
    TempAllocator& alloc = graph.alloc();

    // Unbox and replace all operands.
    for (size_t i = 0, e = phi->numOperands(); i < e; i++) {
        MDefinition* op = phi->getOperand(i);
        MSimdUnbox* unbox = MSimdUnbox::New(alloc, op, unboxType);
        op->block()->insertAtEnd(unbox);
        phi->replaceOperand(i, unbox);
    }

    // Change the MIRType of the Phi.
    MIRType mirType = SimdTypeToMIRType(unboxType);
    phi->setResultType(mirType);

    MBasicBlock* phiBlock = phi->block();
    MInstruction* atRecover = phiBlock->safeInsertTop(nullptr, MBasicBlock::IgnoreRecover);
    MInstruction* at = phiBlock->safeInsertTop(atRecover);

    // Note, we capture the uses-list now, as new instructions are not visited.
    MUseIterator i(phi->usesBegin()), e(phi->usesEnd());

    // Add a MSimdBox, and replace all the Phi uses with it.
    JSObject* templateObject = jitCompartment->maybeGetSimdTemplateObjectFor(unboxType);
    InlineTypedObject* inlineTypedObject = &templateObject->as<InlineTypedObject>();
    MSimdBox* recoverBox = MSimdBox::New(alloc, nullptr, phi, inlineTypedObject, unboxType, gc::DefaultHeap);
    recoverBox->setRecoveredOnBailout();
    phiBlock->insertBefore(atRecover, recoverBox);

    MSimdBox* box = nullptr;
    while (i != e) {
        MUse* use = *i++;
        MNode* ins = use->consumer();

        if ((ins->isDefinition() && ins->toDefinition()->isRecoveredOnBailout()) ||
            (ins->isResumePoint() && ins->toResumePoint()->isRecoverableOperand(use)))
        {
            use->replaceProducer(recoverBox);
            continue;
        }

        if (!box) {
            box = MSimdBox::New(alloc, nullptr, phi, inlineTypedObject, unboxType, gc::DefaultHeap);
            phiBlock->insertBefore(at, box);
        }

        use->replaceProducer(box);
    }
}

static void
ComputeImmediateDominators(MIRGraph &graph)
{
    // The default start block is a root and therefore only self-dominates.
    MBasicBlock *startBlock = *graph.begin();
    startBlock->setImmediateDominator(startBlock);

    // Any OSR block is a root and therefore only self-dominates.
    MBasicBlock *osrBlock = graph.osrBlock();
    if (osrBlock)
        osrBlock->setImmediateDominator(osrBlock);

    bool changed = true;

    while (changed) {
        changed = false;

        ReversePostorderIterator block = graph.rpoBegin();

        // For each block in RPO, intersect all dominators.
        for (; block != graph.rpoEnd(); block++) {
            // If a node has once been found to have no exclusive dominator,
            // it will never have an exclusive dominator, so it may be skipped.
            if (block->immediateDominator() == *block)
                continue;

            MBasicBlock *newIdom = block->getPredecessor(0);

            // Find the first common dominator.
            for (size_t i = 1; i < block->numPredecessors(); i++) {
                MBasicBlock *pred = block->getPredecessor(i);
                if (pred->immediateDominator() != NULL)
                    newIdom = IntersectDominators(pred, newIdom);

                // If there is no common dominator, the block self-dominates.
                if (newIdom == NULL) {
                    block->setImmediateDominator(*block);
                    changed = true;
                    break;
                }
            }

            if (newIdom && block->immediateDominator() != newIdom) {
                block->setImmediateDominator(newIdom);
                changed = true;
            }
        }
    }

#ifdef DEBUG
    // Assert that all blocks have dominator information.
    for (MBasicBlockIterator block(graph.begin()); block != graph.end(); block++) {
        JS_ASSERT(block->immediateDominator() != NULL);
    }
#endif
}