C++ MControlInstruction::numSuccessors方法代码示例

// Visit the control instruction at the end of |block|.
bool
ValueNumberer::visitControlInstruction(MBasicBlock* block, const MBasicBlock* dominatorRoot)
{
    // Look for a simplified form of the control instruction.
    MControlInstruction* control = block->lastIns();
    MDefinition* rep = simplified(control);
    if (rep == control)
        return true;

    if (rep == nullptr)
        return false;

    MControlInstruction* newControl = rep->toControlInstruction();
    MOZ_ASSERT(!newControl->block(),
               "Control instruction replacement shouldn't already be in a block");
#ifdef DEBUG
    JitSpew(JitSpew_GVN, "      Folded control instruction %s%u to %s%u",
            control->opName(), control->id(), newControl->opName(), graph_.getNumInstructionIds());
#endif

    // If the simplification removes any CFG edges, update the CFG and remove
    // any blocks that become dead.
    size_t oldNumSuccs = control->numSuccessors();
    size_t newNumSuccs = newControl->numSuccessors();
    if (newNumSuccs != oldNumSuccs) {
        MOZ_ASSERT(newNumSuccs < oldNumSuccs, "New control instruction has too many successors");
        for (size_t i = 0; i != oldNumSuccs; ++i) {
            MBasicBlock* succ = control->getSuccessor(i);
            if (HasSuccessor(newControl, succ))
                continue;
            if (succ->isMarked())
                continue;
            if (!removePredecessorAndCleanUp(succ, block))
                return false;
            if (succ->isMarked())
                continue;
            if (!rerun_) {
                if (!remainingBlocks_.append(succ))
                    return false;
            }
        }
    }

    if (!releaseOperands(control))
        return false;
    block->discardIgnoreOperands(control);
    block->end(newControl);
    if (block->entryResumePoint() && newNumSuccs != oldNumSuccs)
        block->flagOperandsOfPrunedBranches(newControl);
    return processDeadDefs();
}

//.........这里部分代码省略.........
    // Assign unique value numbers if pessimistic.
    // It might be productive to do this in the MDefinition constructor or
    // possibly in a previous pass, if it seems reasonable.
    if (pessimisticPass_) {
        for (ReversePostorderIterator block(graph_.rpoBegin()); block != graph_.rpoEnd(); block++) {
            for (MDefinitionIterator iter(*block); iter; iter++)
                iter->setValueNumber(iter->id());
        }
    } else {
        // For each root block, add all of its instructions to the worklist.
        markBlock(*(graph_.begin()));
        if (graph_.osrBlock())
            markBlock(graph_.osrBlock());
    }

    while (count_ > 0) {
#ifdef DEBUG
        if (!pessimisticPass_) {
            size_t debugCount = 0;
            IonSpew(IonSpew_GVN, "The following instructions require processing:");
            for (ReversePostorderIterator block(graph_.rpoBegin()); block != graph_.rpoEnd(); block++) {
                for (MDefinitionIterator iter(*block); iter; iter++) {
                    if (iter->isInWorklist()) {
                        IonSpew(IonSpew_GVN, "\t%d", iter->id());
                        debugCount++;
                    }
                }
                if (block->lastIns()->isInWorklist()) {
                    IonSpew(IonSpew_GVN, "\t%d", block->lastIns()->id());
                    debugCount++;
                }
            }
            if (!debugCount)
                IonSpew(IonSpew_GVN, "\tNone");
            JS_ASSERT(debugCount == count_);
        }
#endif
        for (ReversePostorderIterator block(graph_.rpoBegin()); block != graph_.rpoEnd(); block++) {
            for (MDefinitionIterator iter(*block); iter; ) {

                if (!isMarked(*iter)) {
                    iter++;
                    continue;
                }

                JS_ASSERT_IF(!pessimisticPass_, count_ > 0);
                unmarkDefinition(*iter);

                MDefinition *ins = simplify(*iter, false);

                if (ins != *iter) {
                    iter = block->discardDefAt(iter);
                    continue;
                }

                uint32 value = lookupValue(ins);

                if (!value)
                    return false; // Hashtable insertion failed

                if (ins->valueNumber() != value) {
                    IonSpew(IonSpew_GVN,
                            "Broke congruence for instruction %d (%p) with VN %d (now using %d)",
                            ins->id(), (void *) ins, ins->valueNumber(), value);
                    ins->setValueNumber(value);
                    markConsumers(ins);
                }

                iter++;
            }
            // Process control flow instruction:
            MControlInstruction *jump = block->lastIns();

            // If we are pessimistic, then this will never get set.
            if (!jump->isInWorklist())
                continue;
            unmarkDefinition(jump);
            if (jump->valueNumber() == 0) {
                jump->setValueNumber(jump->id());
                for (size_t i = 0; i < jump->numSuccessors(); i++)
                    markBlock(jump->getSuccessor(i));
            }

        }

        // If we are doing a pessimistic pass, we only go once through the
        // instruction list.
        if (pessimisticPass_)
            break;
    }
#ifdef DEBUG
    for (ReversePostorderIterator block(graph_.rpoBegin()); block != graph_.rpoEnd(); block++) {
        for (MDefinitionIterator iter(*block); iter; iter++) {
            JS_ASSERT(!iter->isInWorklist());
            JS_ASSERT(iter->valueNumber() != 0);
        }
    }
#endif
    return true;
}