C++ MDefinition::id方法代码示例

MDefinition *
ValueNumberer::simplify(MDefinition *def, bool useValueNumbers)
{
    if (def->isEffectful())
        return def;

    MDefinition *ins = def->foldsTo(useValueNumbers);

    if (ins == def || !ins->updateForFolding(def))
        return def;

    // ensure this instruction has a VN
    if (!ins->valueNumberData())
        ins->setValueNumberData(new ValueNumberData);
    if (!ins->block()) {
        // In this case, we made a new def by constant folding, for
        // example, we replaced add(#3,#4) with a new const(#7) node.

        // We will only fold a phi into one of its operands.
        JS_ASSERT(!def->isPhi());

        def->block()->insertAfter(def->toInstruction(), ins->toInstruction());
        ins->setValueNumber(lookupValue(ins));
    }

    JS_ASSERT(ins->id() != 0);

    def->replaceAllUsesWith(ins);

    IonSpew(IonSpew_GVN, "Folding %d to be %d", def->id(), ins->id());
    return ins;
}

bool
RangeAnalysis::removeBetaNobes()
{
    IonSpew(IonSpew_Range, "Removing beta nobes");

    for (PostorderIterator i(graph_.poBegin()); i != graph_.poEnd(); i++) {
        MBasicBlock *block = *i;
        for (MDefinitionIterator iter(*i); iter; ) {
            MDefinition *def = *iter;
            if (def->isBeta()) {
                MDefinition *op = def->getOperand(0);
                IonSpew(IonSpew_Range, "Removing beta node %d for %d",
                        def->id(), op->id());
                def->replaceAllUsesWith(op);
                iter = block->discardDefAt(iter);
            } else {
                // We only place Beta nodes at the beginning of basic
                // blocks, so if we see something else, we can move on
                // to the next block.
                break;
            }
        }
    }
    return true;
}

void
ValueNumberer::breakClass(MDefinition *def)
{
    if (def->valueNumber() == def->id()) {
        IonSpew(IonSpew_GVN, "Breaking congruence with itself: %d", def->id());
        ValueNumberData *defdata = def->valueNumberData();
        JS_ASSERT(defdata->classPrev == NULL);
        // If the def was the only member of the class, then there is nothing to do.
        if (defdata->classNext == NULL)
            return;
        // If upon closer inspection, we are still equivalent to this class
        // then there isn't anything for us to do.
        if (!needsSplit(def))
            return;

        // Get a new representative member
        MDefinition *newRep = defdata->classNext;

        // Chop off the head of the list (the old representative)
        newRep->valueNumberData()->classPrev = NULL;
        def->valueNumberData()->classNext = NULL;
        IonSpew(IonSpew_GVN, "Choosing a new representative: %d", newRep->id());

        // make the VN of every member in the class the VN of the new representative number.
        for (MDefinition *tmp = newRep; tmp != NULL; tmp = tmp->valueNumberData()->classNext) {
            // if this instruction is already scheduled to be processed, don't do anything.
            if (tmp->isInWorklist())
                continue;
            IonSpew(IonSpew_GVN, "Moving to a new congruence class: %d", tmp->id());
            tmp->setValueNumber(newRep->id());
            markConsumers(tmp);
            markDefinition(tmp);
        }

        // Insert the new representative => number mapping into the table
        // Logically, there should not be anything in the table currently, but
        // old values are never removed, so there's a good chance something will
        // already be there.
        values.put(newRep, newRep->id());
    } else {
        // The element that is breaking from the list isn't the representative element
        // just strip it from the list
        ValueNumberData *defdata = def->valueNumberData();
        if (defdata->classPrev)
            defdata->classPrev->valueNumberData()->classNext = defdata->classNext;
        if (defdata->classNext)
            defdata->classNext->valueNumberData()->classPrev = defdata->classPrev;

        // Make sure there is no nastinees accidentally linking elements into the old list later.
        defdata->classPrev = NULL;
        defdata->classNext = NULL;
    }
}

bool
RangeAnalysis::analyze()
{
    IonSpew(IonSpew_Range, "Doing range propagation");

    for (ReversePostorderIterator iter(graph_.rpoBegin()); iter != graph_.rpoEnd(); iter++) {
        MBasicBlock *block = *iter;

        for (MDefinitionIterator iter(block); iter; iter++) {
            MDefinition *def = *iter;

            def->computeRange();
            IonSpew(IonSpew_Range, "computing range on %d", def->id());
            SpewRange(def);
        }

        if (block->isLoopHeader())
            analyzeLoop(block);
    }

    return true;
}

// Visit |def|.
bool
ValueNumberer::visitDefinition(MDefinition* def)
{
    // Nop does not fit in any of the previous optimization, as its only purpose
    // is to reduce the register pressure by keeping additional resume
    // point. Still, there is no need consecutive list of MNop instructions, and
    // this will slow down every other iteration on the Graph.
    if (def->isNop()) {
        MNop* nop = def->toNop();
        MBasicBlock* block = nop->block();

        // We look backward to know if we can remove the previous Nop, we do not
        // look forward as we would not benefit from the folding made by GVN.
        MInstructionReverseIterator iter = ++block->rbegin(nop);

        // This nop is at the beginning of the basic block, just replace the
        // resume point of the basic block by the one from the resume point.
        if (iter == block->rend()) {
            JitSpew(JitSpew_GVN, "      Removing Nop%u", nop->id());
            nop->moveResumePointAsEntry();
            block->discard(nop);
            return true;
        }

        // The previous instruction is also a Nop, no need to keep it anymore.
        MInstruction* prev = *iter;
        if (prev->isNop()) {
            JitSpew(JitSpew_GVN, "      Removing Nop%u", prev->id());
            block->discard(prev);
            return true;
        }

        return true;
    }

    // If this instruction has a dependency() into an unreachable block, we'll
    // need to update AliasAnalysis.
    MInstruction* dep = def->dependency();
    if (dep != nullptr && (dep->isDiscarded() || dep->block()->isDead())) {
        JitSpew(JitSpew_GVN, "      AliasAnalysis invalidated");
        if (updateAliasAnalysis_ && !dependenciesBroken_) {
            // TODO: Recomputing alias-analysis could theoretically expose more
            // GVN opportunities.
            JitSpew(JitSpew_GVN, "        Will recompute!");
            dependenciesBroken_ = true;
        }
        // Temporarily clear its dependency, to protect foldsTo, which may
        // wish to use the dependency to do store-to-load forwarding.
        def->setDependency(def->toInstruction());
    } else {
        dep = nullptr;
    }

    // Look for a simplified form of |def|.
    MDefinition* sim = simplified(def);
    if (sim != def) {
        if (sim == nullptr)
            return false;

        // If |sim| doesn't belong to a block, insert it next to |def|.
        if (sim->block() == nullptr)
            def->block()->insertAfter(def->toInstruction(), sim->toInstruction());

#ifdef DEBUG
        JitSpew(JitSpew_GVN, "      Folded %s%u to %s%u",
                def->opName(), def->id(), sim->opName(), sim->id());
#endif
        MOZ_ASSERT(!sim->isDiscarded());
        ReplaceAllUsesWith(def, sim);

        // The node's foldsTo said |def| can be replaced by |rep|. If |def| is a
        // guard, then either |rep| is also a guard, or a guard isn't actually
        // needed, so we can clear |def|'s guard flag and let it be discarded.
        def->setNotGuardUnchecked();

        if (DeadIfUnused(def)) {
            if (!discardDefsRecursively(def))
                return false;

            // If that ended up discarding |sim|, then we're done here.
            if (sim->isDiscarded())
                return true;
        }

        // Otherwise, procede to optimize with |sim| in place of |def|.
        def = sim;
    }

    // Now that foldsTo is done, re-enable the original dependency. Even though
    // it may be pointing into a discarded block, it's still valid for the
    // purposes of detecting congruent loads.
    if (dep != nullptr)
        def->setDependency(dep);

    // Look for a dominating def which makes |def| redundant.
    MDefinition* rep = leader(def);
    if (rep != def) {
        if (rep == nullptr)
            return false;
//.........这里部分代码省略.........

// Visit |def|.
bool
ValueNumberer::visitDefinition(MDefinition *def)
{
    // If this instruction has a dependency() into an unreachable block, we'll
    // need to update AliasAnalysis.
    MDefinition *dep = def->dependency();
    if (dep != nullptr && (dep->isDiscarded() || dep->block()->isDead())) {
        JitSpew(JitSpew_GVN, "      AliasAnalysis invalidated");
        if (updateAliasAnalysis_ && !dependenciesBroken_) {
            // TODO: Recomputing alias-analysis could theoretically expose more
            // GVN opportunities.
            JitSpew(JitSpew_GVN, "        Will recompute!");
            dependenciesBroken_ = true;
        }
        // Temporarily clear its dependency, to protect foldsTo, which may
        // wish to use the dependency to do store-to-load forwarding.
        def->setDependency(def->toInstruction());
    } else {
        dep = nullptr;
    }

    // Look for a simplified form of |def|.
    MDefinition *sim = simplified(def);
    if (sim != def) {
        if (sim == nullptr)
            return false;

        // If |sim| doesn't belong to a block, insert it next to |def|.
        if (sim->block() == nullptr)
            def->block()->insertAfter(def->toInstruction(), sim->toInstruction());

#ifdef DEBUG
        JitSpew(JitSpew_GVN, "      Folded %s%u to %s%u",
                def->opName(), def->id(), sim->opName(), sim->id());
#endif
        ReplaceAllUsesWith(def, sim);

        // The node's foldsTo said |def| can be replaced by |rep|. If |def| is a
        // guard, then either |rep| is also a guard, or a guard isn't actually
        // needed, so we can clear |def|'s guard flag and let it be discarded.
        def->setNotGuardUnchecked();

        if (DeadIfUnused(def)) {
            if (!discardDefsRecursively(def))
                return false;
        }
        def = sim;
    }

    // Now that foldsTo is done, re-enable the original dependency. Even though
    // it may be pointing into a discarded block, it's still valid for the
    // purposes of detecting congruent loads.
    if (dep != nullptr)
        def->setDependency(dep);

    // Look for a dominating def which makes |def| redundant.
    MDefinition *rep = leader(def);
    if (rep != def) {
        if (rep == nullptr)
            return false;
        if (rep->updateForReplacement(def)) {
#ifdef DEBUG
            JitSpew(JitSpew_GVN,
                    "      Replacing %s%u with %s%u",
                    def->opName(), def->id(), rep->opName(), rep->id());
#endif
            ReplaceAllUsesWith(def, rep);

            // The node's congruentTo said |def| is congruent to |rep|, and it's
            // dominated by |rep|. If |def| is a guard, it's covered by |rep|,
            // so we can clear |def|'s guard flag and let it be discarded.
            def->setNotGuardUnchecked();

            if (DeadIfUnused(def)) {
                // discardDef should not add anything to the deadDefs, as the
                // redundant operation should have the same input operands.
                mozilla::DebugOnly<bool> r = discardDef(def);
                MOZ_ASSERT(r, "discardDef shouldn't have tried to add anything to the worklist, "
                              "so it shouldn't have failed");
                MOZ_ASSERT(deadDefs_.empty(),
                           "discardDef shouldn't have added anything to the worklist");
            }
            def = rep;
        }
    }

    return true;
}

// Visit |def|.
bool
ValueNumberer::visitDefinition(MDefinition* def)
{
    // Nop does not fit in any of the previous optimization, as its only purpose
    // is to reduce the register pressure by keeping additional resume
    // point. Still, there is no need consecutive list of MNop instructions, and
    // this will slow down every other iteration on the Graph.
    if (def->isNop()) {
        MNop* nop = def->toNop();
        MBasicBlock* block = nop->block();

        // We look backward to know if we can remove the previous Nop, we do not
        // look forward as we would not benefit from the folding made by GVN.
        MInstructionReverseIterator iter = ++block->rbegin(nop);

        // This nop is at the beginning of the basic block, just replace the
        // resume point of the basic block by the one from the resume point.
        if (iter == block->rend()) {
            JitSpew(JitSpew_GVN, "      Removing Nop%u", nop->id());
            nop->moveResumePointAsEntry();
            block->discard(nop);
            return true;
        }

        // The previous instruction is also a Nop, no need to keep it anymore.
        MInstruction* prev = *iter;
        if (prev->isNop()) {
            JitSpew(JitSpew_GVN, "      Removing Nop%u", prev->id());
            block->discard(prev);
            return true;
        }

        // The Nop is introduced to capture the result and make sure the operands
        // are not live anymore when there are no further uses. Though when
        // all operands are still needed the Nop doesn't decrease the liveness
        // and can get removed.
        MResumePoint* rp = nop->resumePoint();
        if (rp && rp->numOperands() > 0 &&
            rp->getOperand(rp->numOperands() - 1) == prev &&
            !nop->block()->lastIns()->isThrow() &&
            !prev->isAssertRecoveredOnBailout())
        {
            size_t numOperandsLive = 0;
            for (size_t j = 0; j < prev->numOperands(); j++) {
                for (size_t i = 0; i < rp->numOperands(); i++) {
                    if (prev->getOperand(j) == rp->getOperand(i)) {
                        numOperandsLive++;
                        break;
                    }
                }
            }

            if (numOperandsLive == prev->numOperands()) {
                JitSpew(JitSpew_GVN, "      Removing Nop%u", nop->id());
                block->discard(nop);
            }
        }

        return true;
    }

    // Skip optimizations on instructions which are recovered on bailout, to
    // avoid mixing instructions which are recovered on bailouts with
    // instructions which are not.
    if (def->isRecoveredOnBailout())
        return true;

    // If this instruction has a dependency() into an unreachable block, we'll
    // need to update AliasAnalysis.
    MDefinition* dep = def->dependency();
    if (dep != nullptr && (dep->isDiscarded() || dep->block()->isDead())) {
        JitSpew(JitSpew_GVN, "      AliasAnalysis invalidated");
        if (updateAliasAnalysis_ && !dependenciesBroken_) {
            // TODO: Recomputing alias-analysis could theoretically expose more
            // GVN opportunities.
            JitSpew(JitSpew_GVN, "        Will recompute!");
            dependenciesBroken_ = true;
        }
        // Temporarily clear its dependency, to protect foldsTo, which may
        // wish to use the dependency to do store-to-load forwarding.
        def->setDependency(def->toInstruction());
    } else {
        dep = nullptr;
    }

    // Look for a simplified form of |def|.
    MDefinition* sim = simplified(def);
    if (sim != def) {
        if (sim == nullptr)
            return false;

        bool isNewInstruction = sim->block() == nullptr;

        // If |sim| doesn't belong to a block, insert it next to |def|.
        if (isNewInstruction)
            def->block()->insertAfter(def->toInstruction(), sim->toInstruction());

#ifdef JS_JITSPEW
        JitSpew(JitSpew_GVN, "      Folded %s%u to %s%u",
//.........这里部分代码省略.........