C++ MIRGraph::end方法代码示例

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
}

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
}

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
}

bool
ion::BuildPhiReverseMapping(MIRGraph &graph)
{
    // Build a mapping such that given a basic block, whose successor has one or
    // more phis, we can find our specific input to that phi. To make this fast
    // mapping work we rely on a specific property of our structured control
    // flow graph: For a block with phis, its predecessors each have only one
    // successor with phis. Consider each case:
    //   * Blocks with less than two predecessors cannot have phis.
    //   * Breaks. A break always has exactly one successor, and the break
    //             catch block has exactly one predecessor for each break, as
    //             well as a final predecessor for the actual loop exit.
    //   * Continues. A continue always has exactly one successor, and the
    //             continue catch block has exactly one predecessor for each
    //             continue, as well as a final predecessor for the actual
    //             loop continuation. The continue itself has exactly one
    //             successor.
    //   * An if. Each branch as exactly one predecessor.
    //   * A switch. Each branch has exactly one predecessor.
    //   * Loop tail. A new block is always created for the exit, and if a
    //             break statement is present, the exit block will forward
    //             directly to the break block.
    for (MBasicBlockIterator block(graph.begin()); block != graph.end(); block++) {
        if (block->numPredecessors() < 2) {
            JS_ASSERT(block->phisEmpty());
            continue;
        }

        // Assert on the above.
        for (size_t j = 0; j < block->numPredecessors(); j++) {
            MBasicBlock *pred = block->getPredecessor(j);

#ifdef DEBUG
            size_t numSuccessorsWithPhis = 0;
            for (size_t k = 0; k < pred->numSuccessors(); k++) {
                MBasicBlock *successor = pred->getSuccessor(k);
                if (!successor->phisEmpty())
                    numSuccessorsWithPhis++;
            }
            JS_ASSERT(numSuccessorsWithPhis <= 1);
#endif

            pred->setSuccessorWithPhis(*block, j);
        }
    }

    return true;
}

bool
ion::BuildDominatorTree(MIRGraph &graph)
{
    ComputeImmediateDominators(graph);

    // Traversing through the graph in post-order means that every use
    // of a definition is visited before the def itself. Since a def
    // dominates its uses, by the time we reach a particular
    // block, we have processed all of its dominated children, so
    // block->numDominated() is accurate.
    for (PostorderIterator i(graph.poBegin()); i != graph.poEnd(); i++) {
        MBasicBlock *child = *i;
        MBasicBlock *parent = child->immediateDominator();

        // If the block only self-dominates, it has no definite parent.
        if (child == parent)
            continue;

        if (!parent->addImmediatelyDominatedBlock(child))
            return false;

        // An additional +1 for the child block.
        parent->addNumDominated(child->numDominated() + 1);
    }

#ifdef DEBUG
    // If compiling with OSR, many blocks will self-dominate.
    // Without OSR, there is only one root block which dominates all.
    if (!graph.osrBlock())
        JS_ASSERT(graph.begin()->numDominated() == graph.numBlocks() - 1);
#endif
    // Now, iterate through the dominator tree and annotate every
    // block with its index in the pre-order traversal of the
    // dominator tree.
    Vector<MBasicBlock *, 1, IonAllocPolicy> worklist;

    // The index of the current block in the CFG traversal.
    size_t index = 0;

    // Add all self-dominating blocks to the worklist.
    // This includes all roots. Order does not matter.
    for (MBasicBlockIterator i(graph.begin()); i != graph.end(); i++) {
        MBasicBlock *block = *i;
        if (block->immediateDominator() == block) {
            if (!worklist.append(block))
                return false;
        }
    }
    // Starting from each self-dominating block, traverse the CFG in pre-order.
    while (!worklist.empty()) {
        MBasicBlock *block = worklist.popCopy();
        block->setDomIndex(index);

        for (size_t i = 0; i < block->numImmediatelyDominatedBlocks(); i++) {
            if (!worklist.append(block->getImmediatelyDominatedBlock(i)))
                return false;
        }
        index++;
    }

    return true;
}

// Eliminate checks which are redundant given each other or other instructions.
//
// A type barrier is considered redundant if all missing types have been tested
// for by earlier control instructions.
//
// A bounds check is considered redundant if it's dominated by another bounds
// check with the same length and the indexes differ by only a constant amount.
// In this case we eliminate the redundant bounds check and update the other one
// to cover the ranges of both checks.
//
// Bounds checks are added to a hash map and since the hash function ignores
// differences in constant offset, this offers a fast way to find redundant
// checks.
bool
ion::EliminateRedundantChecks(MIRGraph &graph)
{
    BoundsCheckMap checks;

    if (!checks.init())
        return false;

    // Stack for pre-order CFG traversal.
    Vector<MBasicBlock *, 1, IonAllocPolicy> worklist;

    // The index of the current block in the CFG traversal.
    size_t index = 0;

    // Add all self-dominating blocks to the worklist.
    // This includes all roots. Order does not matter.
    for (MBasicBlockIterator i(graph.begin()); i != graph.end(); i++) {
        MBasicBlock *block = *i;
        if (block->immediateDominator() == block) {
            if (!worklist.append(block))
                return false;
        }
    }

    // Starting from each self-dominating block, traverse the CFG in pre-order.
    while (!worklist.empty()) {
        MBasicBlock *block = worklist.popCopy();

        // Add all immediate dominators to the front of the worklist.
        for (size_t i = 0; i < block->numImmediatelyDominatedBlocks(); i++) {
            if (!worklist.append(block->getImmediatelyDominatedBlock(i)))
                return false;
        }

        for (MDefinitionIterator iter(block); iter; ) {
            bool eliminated = false;

            if (iter->isBoundsCheck()) {
                if (!TryEliminateBoundsCheck(checks, index, iter->toBoundsCheck(), &eliminated))
                    return false;
            } else if (iter->isTypeBarrier()) {
                if (!TryEliminateTypeBarrier(iter->toTypeBarrier(), &eliminated))
                    return false;
            } else if (iter->isConvertElementsToDoubles()) {
                // Now that code motion passes have finished, replace any
                // ConvertElementsToDoubles with the actual elements.
                MConvertElementsToDoubles *ins = iter->toConvertElementsToDoubles();
                ins->replaceAllUsesWith(ins->elements());
            }

            if (eliminated)
                iter = block->discardDefAt(iter);
            else
                iter++;
        }
        index++;
    }

    JS_ASSERT(index == graph.numBlocks());
    return true;
}