Exemplo n.º 1
0
void
FrameState::pushCopyOf(uint32 index)
{
    FrameEntry *backing = entryFor(index);
    FrameEntry *fe = rawPush();
    fe->resetUnsynced();
    if (backing->isConstant()) {
        fe->setConstant(Jsvalify(backing->getValue()));
    } else {
        if (backing->isTypeKnown())
            fe->setType(backing->getKnownType());
        else
            fe->type.invalidate();
        fe->isNumber = backing->isNumber;
        fe->data.invalidate();
        if (backing->isCopy()) {
            backing = backing->copyOf();
            fe->setCopyOf(backing);
        } else {
            fe->setCopyOf(backing);
            backing->setCopied();
        }

        /* Maintain tracker ordering guarantees for copies. */
        JS_ASSERT(backing->isCopied());
        if (fe->trackerIndex() < backing->trackerIndex())
            swapInTracker(fe, backing);
    }
}
Exemplo n.º 2
0
void
FrameState::storeLocal(uint32 n, bool popGuaranteed, bool typeChange)
{
    FrameEntry *localFe = getLocal(n);
    bool cacheable = !eval && !escaping[n];

    if (!popGuaranteed && !cacheable) {
        JS_ASSERT_IF(base[localIndex(n)] && (!eval || n < script->nfixed),
                     entries[localIndex(n)].type.inMemory() &&
                     entries[localIndex(n)].data.inMemory());
        Address local(JSFrameReg, sizeof(JSStackFrame) + n * sizeof(Value));
        storeTo(peek(-1), local, false);
        forgetAllRegs(getLocal(n));
        localFe->resetSynced();
        return;
    }

    bool wasSynced = localFe->type.synced();

    /* Detect something like (x = x) which is a no-op. */
    FrameEntry *top = peek(-1);
    if (top->isCopy() && top->copyOf() == localFe) {
        JS_ASSERT(localFe->isCopied());
        return;
    }

    /* Completely invalidate the local variable. */
    if (localFe->isCopied()) {
        uncopy(localFe);
        if (!localFe->isCopied())
            forgetAllRegs(localFe);
    } else {
        forgetAllRegs(localFe);
    }

    localFe->resetUnsynced();

    /* Constants are easy to propagate. */
    if (top->isConstant()) {
        localFe->setCopyOf(NULL);
        localFe->setNotCopied();
        localFe->setConstant(Jsvalify(top->getValue()));
        return;
    }

    /*
     * When dealing with copies, there are two important invariants:
     *
     * 1) The backing store precedes all copies in the tracker.
     * 2) The backing store of a local is never a stack slot, UNLESS the local
     *    variable itself is a stack slot (blocks) that precedes the stack
     *    slot.
     *
     * If the top is a copy, and the second condition holds true, the local
     * can be rewritten as a copy of the original backing slot. If the first
     * condition does not hold, force it to hold by swapping in-place.
     */
    FrameEntry *backing = top;
    if (top->isCopy()) {
        backing = top->copyOf();
        JS_ASSERT(backing->trackerIndex() < top->trackerIndex());

        uint32 backingIndex = indexOfFe(backing);
        uint32 tol = uint32(spBase - base);
        if (backingIndex < tol || backingIndex < localIndex(n)) {
            /* local.idx < backing.idx means local cannot be a copy yet */
            if (localFe->trackerIndex() < backing->trackerIndex())
                swapInTracker(backing, localFe);
            localFe->setNotCopied();
            localFe->setCopyOf(backing);
            if (backing->isTypeKnown())
                localFe->setType(backing->getKnownType());
            else
                localFe->type.invalidate();
            localFe->data.invalidate();
            localFe->isNumber = backing->isNumber;
            return;
        }

        /*
         * If control flow lands here, then there was a bytecode sequence like
         *
         *  ENTERBLOCK 2
         *  GETLOCAL 1
         *  SETLOCAL 0
         *
         * The problem is slot N can't be backed by M if M could be popped
         * before N. We want a guarantee that when we pop M, even if it was
         * copied, it has no outstanding copies.
         * 
         * Because of |let| expressions, it's kind of hard to really know
         * whether a region on the stack will be popped all at once. Bleh!
         *
         * This should be rare except in browser code (and maybe even then),
         * but even so there's a quick workaround. We take all copies of the
         * backing fe, and redirect them to be copies of the destination.
         */
        FrameEntry *tos = tosFe();
        for (uint32 i = backing->trackerIndex() + 1; i < tracker.nentries; i++) {
            FrameEntry *fe = tracker[i];
            if (fe >= tos)
                continue;
            if (fe->isCopy() && fe->copyOf() == backing)
                fe->setCopyOf(localFe);
        }
    }
    backing->setNotCopied();
    
    /*
     * This is valid from the top->isCopy() path because we're guaranteed a
     * consistent ordering - all copies of |backing| are tracked after 
     * |backing|. Transitively, only one swap is needed.
     */
    if (backing->trackerIndex() < localFe->trackerIndex())
        swapInTracker(backing, localFe);

    /*
     * Move the backing store down - we spill registers here, but we could be
     * smarter and re-use the type reg.
     */
    RegisterID reg = tempRegForData(backing);
    localFe->data.setRegister(reg);
    moveOwnership(reg, localFe);

    if (typeChange) {
        if (backing->isTypeKnown()) {
            localFe->setType(backing->getKnownType());
        } else {
            RegisterID reg = tempRegForType(backing);
            localFe->type.setRegister(reg);
            moveOwnership(reg, localFe);
        }
    } else {
        if (!wasSynced)
            masm.storeTypeTag(ImmType(backing->getKnownType()), addressOf(localFe));
        localFe->type.setMemory();
    }

    if (!backing->isTypeKnown())
        backing->type.invalidate();
    backing->data.invalidate();
    backing->setCopyOf(localFe);
    backing->isNumber = localFe->isNumber;
    localFe->setCopied();

    if (!cacheable) {
        /* TODO: x64 optimization */
        if (!localFe->type.synced())
            syncType(localFe, addressOf(localFe), masm);
        if (!localFe->data.synced())
            syncData(localFe, addressOf(localFe), masm);
        forgetAllRegs(localFe);
        localFe->type.setMemory();
        localFe->data.setMemory();
    }

    JS_ASSERT(top->copyOf() == localFe);
}