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Diffstat (limited to 'js/src/jit/BacktrackingAllocator.cpp')
| -rw-r--r-- | js/src/jit/BacktrackingAllocator.cpp | 3124 |
1 files changed, 3124 insertions, 0 deletions
diff --git a/js/src/jit/BacktrackingAllocator.cpp b/js/src/jit/BacktrackingAllocator.cpp new file mode 100644 index 000000000..94ef25785 --- /dev/null +++ b/js/src/jit/BacktrackingAllocator.cpp @@ -0,0 +1,3124 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- + * vim: set ts=8 sts=4 et sw=4 tw=99: + * This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +#include "jit/BacktrackingAllocator.h" + +#include "jsprf.h" + +#include "jit/BitSet.h" + +using namespace js; +using namespace js::jit; + +using mozilla::DebugOnly; + +///////////////////////////////////////////////////////////////////// +// Utility +///////////////////////////////////////////////////////////////////// + +static inline bool +SortBefore(UsePosition* a, UsePosition* b) +{ + return a->pos <= b->pos; +} + +static inline bool +SortBefore(LiveRange::BundleLink* a, LiveRange::BundleLink* b) +{ + LiveRange* rangea = LiveRange::get(a); + LiveRange* rangeb = LiveRange::get(b); + MOZ_ASSERT(!rangea->intersects(rangeb)); + return rangea->from() < rangeb->from(); +} + +static inline bool +SortBefore(LiveRange::RegisterLink* a, LiveRange::RegisterLink* b) +{ + return LiveRange::get(a)->from() <= LiveRange::get(b)->from(); +} + +template <typename T> +static inline void +InsertSortedList(InlineForwardList<T> &list, T* value) +{ + if (list.empty()) { + list.pushFront(value); + return; + } + + if (SortBefore(list.back(), value)) { + list.pushBack(value); + return; + } + + T* prev = nullptr; + for (InlineForwardListIterator<T> iter = list.begin(); iter; iter++) { + if (SortBefore(value, *iter)) + break; + prev = *iter; + } + + if (prev) + list.insertAfter(prev, value); + else + list.pushFront(value); +} + +///////////////////////////////////////////////////////////////////// +// LiveRange +///////////////////////////////////////////////////////////////////// + +void +LiveRange::addUse(UsePosition* use) +{ + MOZ_ASSERT(covers(use->pos)); + InsertSortedList(uses_, use); +} + +void +LiveRange::distributeUses(LiveRange* other) +{ + MOZ_ASSERT(other->vreg() == vreg()); + MOZ_ASSERT(this != other); + + // Move over all uses which fit in |other|'s boundaries. + for (UsePositionIterator iter = usesBegin(); iter; ) { + UsePosition* use = *iter; + if (other->covers(use->pos)) { + uses_.removeAndIncrement(iter); + other->addUse(use); + } else { + iter++; + } + } + + // Distribute the definition to |other| as well, if possible. + if (hasDefinition() && from() == other->from()) + other->setHasDefinition(); +} + +bool +LiveRange::contains(LiveRange* other) const +{ + return from() <= other->from() && to() >= other->to(); +} + +void +LiveRange::intersect(LiveRange* other, Range* pre, Range* inside, Range* post) const +{ + MOZ_ASSERT(pre->empty() && inside->empty() && post->empty()); + + CodePosition innerFrom = from(); + if (from() < other->from()) { + if (to() < other->from()) { + *pre = range_; + return; + } + *pre = Range(from(), other->from()); + innerFrom = other->from(); + } + + CodePosition innerTo = to(); + if (to() > other->to()) { + if (from() >= other->to()) { + *post = range_; + return; + } + *post = Range(other->to(), to()); + innerTo = other->to(); + } + + if (innerFrom != innerTo) + *inside = Range(innerFrom, innerTo); +} + +bool +LiveRange::intersects(LiveRange* other) const +{ + Range pre, inside, post; + intersect(other, &pre, &inside, &post); + return !inside.empty(); +} + +///////////////////////////////////////////////////////////////////// +// SpillSet +///////////////////////////////////////////////////////////////////// + +void +SpillSet::setAllocation(LAllocation alloc) +{ + for (size_t i = 0; i < numSpilledBundles(); i++) + spilledBundle(i)->setAllocation(alloc); +} + +///////////////////////////////////////////////////////////////////// +// LiveBundle +///////////////////////////////////////////////////////////////////// + +#ifdef DEBUG +size_t +LiveBundle::numRanges() const +{ + size_t count = 0; + for (LiveRange::BundleLinkIterator iter = rangesBegin(); iter; iter++) + count++; + return count; +} +#endif // DEBUG + +LiveRange* +LiveBundle::rangeFor(CodePosition pos) const +{ + for (LiveRange::BundleLinkIterator iter = rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + if (range->covers(pos)) + return range; + } + return nullptr; +} + +void +LiveBundle::addRange(LiveRange* range) +{ + MOZ_ASSERT(!range->bundle()); + range->setBundle(this); + InsertSortedList(ranges_, &range->bundleLink); +} + +bool +LiveBundle::addRange(TempAllocator& alloc, uint32_t vreg, CodePosition from, CodePosition to) +{ + LiveRange* range = LiveRange::FallibleNew(alloc, vreg, from, to); + if (!range) + return false; + addRange(range); + return true; +} + +bool +LiveBundle::addRangeAndDistributeUses(TempAllocator& alloc, LiveRange* oldRange, + CodePosition from, CodePosition to) +{ + LiveRange* range = LiveRange::FallibleNew(alloc, oldRange->vreg(), from, to); + if (!range) + return false; + addRange(range); + oldRange->distributeUses(range); + return true; +} + +LiveRange* +LiveBundle::popFirstRange() +{ + LiveRange::BundleLinkIterator iter = rangesBegin(); + if (!iter) + return nullptr; + + LiveRange* range = LiveRange::get(*iter); + ranges_.removeAt(iter); + + range->setBundle(nullptr); + return range; +} + +void +LiveBundle::removeRange(LiveRange* range) +{ + for (LiveRange::BundleLinkIterator iter = rangesBegin(); iter; iter++) { + LiveRange* existing = LiveRange::get(*iter); + if (existing == range) { + ranges_.removeAt(iter); + return; + } + } + MOZ_CRASH(); +} + +///////////////////////////////////////////////////////////////////// +// VirtualRegister +///////////////////////////////////////////////////////////////////// + +bool +VirtualRegister::addInitialRange(TempAllocator& alloc, CodePosition from, CodePosition to) +{ + MOZ_ASSERT(from < to); + + // Mark [from,to) as a live range for this register during the initial + // liveness analysis, coalescing with any existing overlapping ranges. + + LiveRange* prev = nullptr; + LiveRange* merged = nullptr; + for (LiveRange::RegisterLinkIterator iter(rangesBegin()); iter; ) { + LiveRange* existing = LiveRange::get(*iter); + + if (from > existing->to()) { + // The new range should go after this one. + prev = existing; + iter++; + continue; + } + + if (to.next() < existing->from()) { + // The new range should go before this one. + break; + } + + if (!merged) { + // This is the first old range we've found that overlaps the new + // range. Extend this one to cover its union with the new range. + merged = existing; + + if (from < existing->from()) + existing->setFrom(from); + if (to > existing->to()) + existing->setTo(to); + + // Continue searching to see if any other old ranges can be + // coalesced with the new merged range. + iter++; + continue; + } + + // Coalesce this range into the previous range we merged into. + MOZ_ASSERT(existing->from() >= merged->from()); + if (existing->to() > merged->to()) + merged->setTo(existing->to()); + + MOZ_ASSERT(!existing->hasDefinition()); + existing->distributeUses(merged); + MOZ_ASSERT(!existing->hasUses()); + + ranges_.removeAndIncrement(iter); + } + + if (!merged) { + // The new range does not overlap any existing range for the vreg. + LiveRange* range = LiveRange::FallibleNew(alloc, vreg(), from, to); + if (!range) + return false; + + if (prev) + ranges_.insertAfter(&prev->registerLink, &range->registerLink); + else + ranges_.pushFront(&range->registerLink); + } + + return true; +} + +void +VirtualRegister::addInitialUse(UsePosition* use) +{ + LiveRange::get(*rangesBegin())->addUse(use); +} + +void +VirtualRegister::setInitialDefinition(CodePosition from) +{ + LiveRange* first = LiveRange::get(*rangesBegin()); + MOZ_ASSERT(from >= first->from()); + first->setFrom(from); + first->setHasDefinition(); +} + +LiveRange* +VirtualRegister::rangeFor(CodePosition pos, bool preferRegister /* = false */) const +{ + LiveRange* found = nullptr; + for (LiveRange::RegisterLinkIterator iter = rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + if (range->covers(pos)) { + if (!preferRegister || range->bundle()->allocation().isRegister()) + return range; + if (!found) + found = range; + } + } + return found; +} + +void +VirtualRegister::addRange(LiveRange* range) +{ + InsertSortedList(ranges_, &range->registerLink); +} + +void +VirtualRegister::removeRange(LiveRange* range) +{ + for (LiveRange::RegisterLinkIterator iter = rangesBegin(); iter; iter++) { + LiveRange* existing = LiveRange::get(*iter); + if (existing == range) { + ranges_.removeAt(iter); + return; + } + } + MOZ_CRASH(); +} + +///////////////////////////////////////////////////////////////////// +// BacktrackingAllocator +///////////////////////////////////////////////////////////////////// + +// This function pre-allocates and initializes as much global state as possible +// to avoid littering the algorithms with memory management cruft. +bool +BacktrackingAllocator::init() +{ + if (!RegisterAllocator::init()) + return false; + + liveIn = mir->allocate<BitSet>(graph.numBlockIds()); + if (!liveIn) + return false; + + size_t numVregs = graph.numVirtualRegisters(); + if (!vregs.init(mir->alloc(), numVregs)) + return false; + memset(&vregs[0], 0, sizeof(VirtualRegister) * numVregs); + for (uint32_t i = 0; i < numVregs; i++) + new(&vregs[i]) VirtualRegister(); + + // Build virtual register objects. + for (size_t i = 0; i < graph.numBlocks(); i++) { + if (mir->shouldCancel("Create data structures (main loop)")) + return false; + + LBlock* block = graph.getBlock(i); + for (LInstructionIterator ins = block->begin(); ins != block->end(); ins++) { + if (mir->shouldCancel("Create data structures (inner loop 1)")) + return false; + + for (size_t j = 0; j < ins->numDefs(); j++) { + LDefinition* def = ins->getDef(j); + if (def->isBogusTemp()) + continue; + vreg(def).init(*ins, def, /* isTemp = */ false); + } + + for (size_t j = 0; j < ins->numTemps(); j++) { + LDefinition* def = ins->getTemp(j); + if (def->isBogusTemp()) + continue; + vreg(def).init(*ins, def, /* isTemp = */ true); + } + } + for (size_t j = 0; j < block->numPhis(); j++) { + LPhi* phi = block->getPhi(j); + LDefinition* def = phi->getDef(0); + vreg(def).init(phi, def, /* isTemp = */ false); + } + } + + LiveRegisterSet remainingRegisters(allRegisters_.asLiveSet()); + while (!remainingRegisters.emptyGeneral()) { + AnyRegister reg = AnyRegister(remainingRegisters.takeAnyGeneral()); + registers[reg.code()].allocatable = true; + } + while (!remainingRegisters.emptyFloat()) { + AnyRegister reg = AnyRegister(remainingRegisters.takeAnyFloat()); + registers[reg.code()].allocatable = true; + } + + LifoAlloc* lifoAlloc = mir->alloc().lifoAlloc(); + for (size_t i = 0; i < AnyRegister::Total; i++) { + registers[i].reg = AnyRegister::FromCode(i); + registers[i].allocations.setAllocator(lifoAlloc); + } + + hotcode.setAllocator(lifoAlloc); + callRanges.setAllocator(lifoAlloc); + + // Partition the graph into hot and cold sections, for helping to make + // splitting decisions. Since we don't have any profiling data this is a + // crapshoot, so just mark the bodies of inner loops as hot and everything + // else as cold. + + LBlock* backedge = nullptr; + for (size_t i = 0; i < graph.numBlocks(); i++) { + LBlock* block = graph.getBlock(i); + + // If we see a loop header, mark the backedge so we know when we have + // hit the end of the loop. Don't process the loop immediately, so that + // if there is an inner loop we will ignore the outer backedge. + if (block->mir()->isLoopHeader()) + backedge = block->mir()->backedge()->lir(); + + if (block == backedge) { + LBlock* header = block->mir()->loopHeaderOfBackedge()->lir(); + LiveRange* range = LiveRange::FallibleNew(alloc(), 0, entryOf(header), + exitOf(block).next()); + if (!range || !hotcode.insert(range)) + return false; + } + } + + return true; +} + +bool +BacktrackingAllocator::addInitialFixedRange(AnyRegister reg, CodePosition from, CodePosition to) +{ + LiveRange* range = LiveRange::FallibleNew(alloc(), 0, from, to); + return range && registers[reg.code()].allocations.insert(range); +} + +#ifdef DEBUG +// Returns true iff ins has a def/temp reusing the input allocation. +static bool +IsInputReused(LInstruction* ins, LUse* use) +{ + for (size_t i = 0; i < ins->numDefs(); i++) { + if (ins->getDef(i)->policy() == LDefinition::MUST_REUSE_INPUT && + ins->getOperand(ins->getDef(i)->getReusedInput())->toUse() == use) + { + return true; + } + } + + for (size_t i = 0; i < ins->numTemps(); i++) { + if (ins->getTemp(i)->policy() == LDefinition::MUST_REUSE_INPUT && + ins->getOperand(ins->getTemp(i)->getReusedInput())->toUse() == use) + { + return true; + } + } + + return false; +} +#endif + +/* + * This function builds up liveness ranges for all virtual registers + * defined in the function. + * + * The algorithm is based on the one published in: + * + * Wimmer, Christian, and Michael Franz. "Linear Scan Register Allocation on + * SSA Form." Proceedings of the International Symposium on Code Generation + * and Optimization. Toronto, Ontario, Canada, ACM. 2010. 170-79. PDF. + * + * The algorithm operates on blocks ordered such that dominators of a block + * are before the block itself, and such that all blocks of a loop are + * contiguous. It proceeds backwards over the instructions in this order, + * marking registers live at their uses, ending their live ranges at + * definitions, and recording which registers are live at the top of every + * block. To deal with loop backedges, registers live at the beginning of + * a loop gain a range covering the entire loop. + */ +bool +BacktrackingAllocator::buildLivenessInfo() +{ + JitSpew(JitSpew_RegAlloc, "Beginning liveness analysis"); + + Vector<MBasicBlock*, 1, SystemAllocPolicy> loopWorkList; + BitSet loopDone(graph.numBlockIds()); + if (!loopDone.init(alloc())) + return false; + + for (size_t i = graph.numBlocks(); i > 0; i--) { + if (mir->shouldCancel("Build Liveness Info (main loop)")) + return false; + + LBlock* block = graph.getBlock(i - 1); + MBasicBlock* mblock = block->mir(); + + BitSet& live = liveIn[mblock->id()]; + new (&live) BitSet(graph.numVirtualRegisters()); + if (!live.init(alloc())) + return false; + + // Propagate liveIn from our successors to us. + for (size_t i = 0; i < mblock->lastIns()->numSuccessors(); i++) { + MBasicBlock* successor = mblock->lastIns()->getSuccessor(i); + // Skip backedges, as we fix them up at the loop header. + if (mblock->id() < successor->id()) + live.insertAll(liveIn[successor->id()]); + } + + // Add successor phis. + if (mblock->successorWithPhis()) { + LBlock* phiSuccessor = mblock->successorWithPhis()->lir(); + for (unsigned int j = 0; j < phiSuccessor->numPhis(); j++) { + LPhi* phi = phiSuccessor->getPhi(j); + LAllocation* use = phi->getOperand(mblock->positionInPhiSuccessor()); + uint32_t reg = use->toUse()->virtualRegister(); + live.insert(reg); + vreg(use).setUsedByPhi(); + } + } + + // Registers are assumed alive for the entire block, a define shortens + // the range to the point of definition. + for (BitSet::Iterator liveRegId(live); liveRegId; ++liveRegId) { + if (!vregs[*liveRegId].addInitialRange(alloc(), entryOf(block), exitOf(block).next())) + return false; + } + + // Shorten the front end of ranges for live variables to their point of + // definition, if found. + for (LInstructionReverseIterator ins = block->rbegin(); ins != block->rend(); ins++) { + // Calls may clobber registers, so force a spill and reload around the callsite. + if (ins->isCall()) { + for (AnyRegisterIterator iter(allRegisters_.asLiveSet()); iter.more(); ++iter) { + bool found = false; + for (size_t i = 0; i < ins->numDefs(); i++) { + if (ins->getDef(i)->isFixed() && + ins->getDef(i)->output()->aliases(LAllocation(*iter))) { + found = true; + break; + } + } + // If this register doesn't have an explicit def above, mark + // it as clobbered by the call unless it is actually + // call-preserved. + if (!found && !ins->isCallPreserved(*iter)) { + if (!addInitialFixedRange(*iter, outputOf(*ins), outputOf(*ins).next())) + return false; + } + } + + CallRange* callRange = + new(alloc().fallible()) CallRange(outputOf(*ins), outputOf(*ins).next()); + if (!callRange) + return false; + + callRangesList.pushFront(callRange); + if (!callRanges.insert(callRange)) + return false; + } + DebugOnly<bool> hasDoubleDef = false; + DebugOnly<bool> hasFloat32Def = false; + for (size_t i = 0; i < ins->numDefs(); i++) { + LDefinition* def = ins->getDef(i); + if (def->isBogusTemp()) + continue; +#ifdef DEBUG + if (def->type() == LDefinition::DOUBLE) + hasDoubleDef = true; + if (def->type() == LDefinition::FLOAT32) + hasFloat32Def = true; +#endif + CodePosition from = outputOf(*ins); + + if (def->policy() == LDefinition::MUST_REUSE_INPUT) { + // MUST_REUSE_INPUT is implemented by allocating an output + // register and moving the input to it. Register hints are + // used to avoid unnecessary moves. We give the input an + // LUse::ANY policy to avoid allocating a register for the + // input. + LUse* inputUse = ins->getOperand(def->getReusedInput())->toUse(); + MOZ_ASSERT(inputUse->policy() == LUse::REGISTER); + MOZ_ASSERT(inputUse->usedAtStart()); + *inputUse = LUse(inputUse->virtualRegister(), LUse::ANY, /* usedAtStart = */ true); + } + + if (!vreg(def).addInitialRange(alloc(), from, from.next())) + return false; + vreg(def).setInitialDefinition(from); + live.remove(def->virtualRegister()); + } + + for (size_t i = 0; i < ins->numTemps(); i++) { + LDefinition* temp = ins->getTemp(i); + if (temp->isBogusTemp()) + continue; + + // Normally temps are considered to cover both the input + // and output of the associated instruction. In some cases + // though we want to use a fixed register as both an input + // and clobbered register in the instruction, so watch for + // this and shorten the temp to cover only the output. + CodePosition from = inputOf(*ins); + if (temp->policy() == LDefinition::FIXED) { + AnyRegister reg = temp->output()->toRegister(); + for (LInstruction::InputIterator alloc(**ins); alloc.more(); alloc.next()) { + if (alloc->isUse()) { + LUse* use = alloc->toUse(); + if (use->isFixedRegister()) { + if (GetFixedRegister(vreg(use).def(), use) == reg) + from = outputOf(*ins); + } + } + } + } + + CodePosition to = + ins->isCall() ? outputOf(*ins) : outputOf(*ins).next(); + + if (!vreg(temp).addInitialRange(alloc(), from, to)) + return false; + vreg(temp).setInitialDefinition(from); + } + + DebugOnly<bool> hasUseRegister = false; + DebugOnly<bool> hasUseRegisterAtStart = false; + + for (LInstruction::InputIterator inputAlloc(**ins); inputAlloc.more(); inputAlloc.next()) { + if (inputAlloc->isUse()) { + LUse* use = inputAlloc->toUse(); + + // Call uses should always be at-start, since calls use all + // registers. + MOZ_ASSERT_IF(ins->isCall() && !inputAlloc.isSnapshotInput(), + use->usedAtStart()); + +#ifdef DEBUG + // Don't allow at-start call uses if there are temps of the same kind, + // so that we don't assign the same register. Only allow this when the + // use and temp are fixed registers, as they can't alias. + if (ins->isCall() && use->usedAtStart()) { + for (size_t i = 0; i < ins->numTemps(); i++) { + MOZ_ASSERT(vreg(ins->getTemp(i)).type() != vreg(use).type() || + (use->isFixedRegister() && ins->getTemp(i)->isFixed())); + } + } + + // If there are both useRegisterAtStart(x) and useRegister(y) + // uses, we may assign the same register to both operands + // (bug 772830). Don't allow this for now. + if (use->policy() == LUse::REGISTER) { + if (use->usedAtStart()) { + if (!IsInputReused(*ins, use)) + hasUseRegisterAtStart = true; + } else { + hasUseRegister = true; + } + } + MOZ_ASSERT(!(hasUseRegister && hasUseRegisterAtStart)); +#endif + + // Don't treat RECOVERED_INPUT uses as keeping the vreg alive. + if (use->policy() == LUse::RECOVERED_INPUT) + continue; + + CodePosition to = use->usedAtStart() ? inputOf(*ins) : outputOf(*ins); + if (use->isFixedRegister()) { + LAllocation reg(AnyRegister::FromCode(use->registerCode())); + for (size_t i = 0; i < ins->numDefs(); i++) { + LDefinition* def = ins->getDef(i); + if (def->policy() == LDefinition::FIXED && *def->output() == reg) + to = inputOf(*ins); + } + } + + if (!vreg(use).addInitialRange(alloc(), entryOf(block), to.next())) + return false; + UsePosition* usePosition = new(alloc().fallible()) UsePosition(use, to); + if (!usePosition) + return false; + vreg(use).addInitialUse(usePosition); + live.insert(use->virtualRegister()); + } + } + } + + // Phis have simultaneous assignment semantics at block begin, so at + // the beginning of the block we can be sure that liveIn does not + // contain any phi outputs. + for (unsigned int i = 0; i < block->numPhis(); i++) { + LDefinition* def = block->getPhi(i)->getDef(0); + if (live.contains(def->virtualRegister())) { + live.remove(def->virtualRegister()); + } else { + // This is a dead phi, so add a dummy range over all phis. This + // can go away if we have an earlier dead code elimination pass. + CodePosition entryPos = entryOf(block); + if (!vreg(def).addInitialRange(alloc(), entryPos, entryPos.next())) + return false; + } + } + + if (mblock->isLoopHeader()) { + // A divergence from the published algorithm is required here, as + // our block order does not guarantee that blocks of a loop are + // contiguous. As a result, a single live range spanning the + // loop is not possible. Additionally, we require liveIn in a later + // pass for resolution, so that must also be fixed up here. + MBasicBlock* loopBlock = mblock->backedge(); + while (true) { + // Blocks must already have been visited to have a liveIn set. + MOZ_ASSERT(loopBlock->id() >= mblock->id()); + + // Add a range for this entire loop block + CodePosition from = entryOf(loopBlock->lir()); + CodePosition to = exitOf(loopBlock->lir()).next(); + + for (BitSet::Iterator liveRegId(live); liveRegId; ++liveRegId) { + if (!vregs[*liveRegId].addInitialRange(alloc(), from, to)) + return false; + } + + // Fix up the liveIn set. + liveIn[loopBlock->id()].insertAll(live); + + // Make sure we don't visit this node again + loopDone.insert(loopBlock->id()); + + // If this is the loop header, any predecessors are either the + // backedge or out of the loop, so skip any predecessors of + // this block + if (loopBlock != mblock) { + for (size_t i = 0; i < loopBlock->numPredecessors(); i++) { + MBasicBlock* pred = loopBlock->getPredecessor(i); + if (loopDone.contains(pred->id())) + continue; + if (!loopWorkList.append(pred)) + return false; + } + } + + // Terminate loop if out of work. + if (loopWorkList.empty()) + break; + + // Grab the next block off the work list, skipping any OSR block. + MBasicBlock* osrBlock = graph.mir().osrBlock(); + while (!loopWorkList.empty()) { + loopBlock = loopWorkList.popCopy(); + if (loopBlock != osrBlock) + break; + } + + // If end is reached without finding a non-OSR block, then no more work items were found. + if (loopBlock == osrBlock) { + MOZ_ASSERT(loopWorkList.empty()); + break; + } + } + + // Clear the done set for other loops + loopDone.clear(); + } + + MOZ_ASSERT_IF(!mblock->numPredecessors(), live.empty()); + } + + JitSpew(JitSpew_RegAlloc, "Liveness analysis complete"); + + if (JitSpewEnabled(JitSpew_RegAlloc)) + dumpInstructions(); + + return true; +} + +bool +BacktrackingAllocator::go() +{ + JitSpew(JitSpew_RegAlloc, "Beginning register allocation"); + + if (!init()) + return false; + + if (!buildLivenessInfo()) + return false; + + if (!allocationQueue.reserve(graph.numVirtualRegisters() * 3 / 2)) + return false; + + JitSpew(JitSpew_RegAlloc, "Beginning grouping and queueing registers"); + if (!mergeAndQueueRegisters()) + return false; + + if (JitSpewEnabled(JitSpew_RegAlloc)) + dumpVregs(); + + JitSpew(JitSpew_RegAlloc, "Beginning main allocation loop"); + + // Allocate, spill and split bundles until finished. + while (!allocationQueue.empty()) { + if (mir->shouldCancel("Backtracking Allocation")) + return false; + + QueueItem item = allocationQueue.removeHighest(); + if (!processBundle(mir, item.bundle)) + return false; + } + JitSpew(JitSpew_RegAlloc, "Main allocation loop complete"); + + if (!pickStackSlots()) + return false; + + if (JitSpewEnabled(JitSpew_RegAlloc)) + dumpAllocations(); + + if (!resolveControlFlow()) + return false; + + if (!reifyAllocations()) + return false; + + if (!populateSafepoints()) + return false; + + if (!annotateMoveGroups()) + return false; + + return true; +} + +static bool +IsArgumentSlotDefinition(LDefinition* def) +{ + return def->policy() == LDefinition::FIXED && def->output()->isArgument(); +} + +static bool +IsThisSlotDefinition(LDefinition* def) +{ + return IsArgumentSlotDefinition(def) && + def->output()->toArgument()->index() < THIS_FRAME_ARGSLOT + sizeof(Value); +} + +bool +BacktrackingAllocator::tryMergeBundles(LiveBundle* bundle0, LiveBundle* bundle1) +{ + // See if bundle0 and bundle1 can be merged together. + if (bundle0 == bundle1) + return true; + + // Get a representative virtual register from each bundle. + VirtualRegister& reg0 = vregs[bundle0->firstRange()->vreg()]; + VirtualRegister& reg1 = vregs[bundle1->firstRange()->vreg()]; + + if (!reg0.isCompatible(reg1)) + return true; + + // Registers which might spill to the frame's |this| slot can only be + // grouped with other such registers. The frame's |this| slot must always + // hold the |this| value, as required by JitFrame tracing and by the Ion + // constructor calling convention. + if (IsThisSlotDefinition(reg0.def()) || IsThisSlotDefinition(reg1.def())) { + if (*reg0.def()->output() != *reg1.def()->output()) + return true; + } + + // Registers which might spill to the frame's argument slots can only be + // grouped with other such registers if the frame might access those + // arguments through a lazy arguments object or rest parameter. + if (IsArgumentSlotDefinition(reg0.def()) || IsArgumentSlotDefinition(reg1.def())) { + if (graph.mir().entryBlock()->info().mayReadFrameArgsDirectly()) { + if (*reg0.def()->output() != *reg1.def()->output()) + return true; + } + } + + // Limit the number of times we compare ranges if there are many ranges in + // one of the bundles, to avoid quadratic behavior. + static const size_t MAX_RANGES = 200; + + // Make sure that ranges in the bundles do not overlap. + LiveRange::BundleLinkIterator iter0 = bundle0->rangesBegin(), iter1 = bundle1->rangesBegin(); + size_t count = 0; + while (iter0 && iter1) { + if (++count >= MAX_RANGES) + return true; + + LiveRange* range0 = LiveRange::get(*iter0); + LiveRange* range1 = LiveRange::get(*iter1); + + if (range0->from() >= range1->to()) + iter1++; + else if (range1->from() >= range0->to()) + iter0++; + else + return true; + } + + // Move all ranges from bundle1 into bundle0. + while (LiveRange* range = bundle1->popFirstRange()) + bundle0->addRange(range); + + return true; +} + +static inline LDefinition* +FindReusingDefOrTemp(LNode* ins, LAllocation* alloc) +{ + for (size_t i = 0; i < ins->numDefs(); i++) { + LDefinition* def = ins->getDef(i); + if (def->policy() == LDefinition::MUST_REUSE_INPUT && + ins->getOperand(def->getReusedInput()) == alloc) + return def; + } + for (size_t i = 0; i < ins->numTemps(); i++) { + LDefinition* def = ins->getTemp(i); + if (def->policy() == LDefinition::MUST_REUSE_INPUT && + ins->getOperand(def->getReusedInput()) == alloc) + return def; + } + return nullptr; +} + +static inline size_t +NumReusingDefs(LNode* ins) +{ + size_t num = 0; + for (size_t i = 0; i < ins->numDefs(); i++) { + LDefinition* def = ins->getDef(i); + if (def->policy() == LDefinition::MUST_REUSE_INPUT) + num++; + } + return num; +} + +bool +BacktrackingAllocator::tryMergeReusedRegister(VirtualRegister& def, VirtualRegister& input) +{ + // def is a vreg which reuses input for its output physical register. Try + // to merge ranges for def with those of input if possible, as avoiding + // copies before def's instruction is crucial for generated code quality + // (MUST_REUSE_INPUT is used for all arithmetic on x86/x64). + + if (def.rangeFor(inputOf(def.ins()))) { + MOZ_ASSERT(def.isTemp()); + def.setMustCopyInput(); + return true; + } + + LiveRange* inputRange = input.rangeFor(outputOf(def.ins())); + if (!inputRange) { + // The input is not live after the instruction, either in a safepoint + // for the instruction or in subsequent code. The input and output + // can thus be in the same group. + return tryMergeBundles(def.firstBundle(), input.firstBundle()); + } + + // The input is live afterwards, either in future instructions or in a + // safepoint for the reusing instruction. This is impossible to satisfy + // without copying the input. + // + // It may or may not be better to split the input into two bundles at the + // point of the definition, which may permit merging. One case where it is + // definitely better to split is if the input never has any register uses + // after the instruction. Handle this splitting eagerly. + + LBlock* block = def.ins()->block(); + + // The input's lifetime must end within the same block as the definition, + // otherwise it could live on in phis elsewhere. + if (inputRange != input.lastRange() || inputRange->to() > exitOf(block)) { + def.setMustCopyInput(); + return true; + } + + // If we already split the input for some other register, don't make a + // third bundle. + if (inputRange->bundle() != input.firstRange()->bundle()) { + def.setMustCopyInput(); + return true; + } + + // If the input will start out in memory then adding a separate bundle for + // memory uses after the def won't help. + if (input.def()->isFixed() && !input.def()->output()->isRegister()) { + def.setMustCopyInput(); + return true; + } + + // The input cannot have register or reused uses after the definition. + for (UsePositionIterator iter = inputRange->usesBegin(); iter; iter++) { + if (iter->pos <= inputOf(def.ins())) + continue; + + LUse* use = iter->use(); + if (FindReusingDefOrTemp(insData[iter->pos], use)) { + def.setMustCopyInput(); + return true; + } + if (iter->usePolicy() != LUse::ANY && iter->usePolicy() != LUse::KEEPALIVE) { + def.setMustCopyInput(); + return true; + } + } + + LiveRange* preRange = LiveRange::FallibleNew(alloc(), input.vreg(), + inputRange->from(), outputOf(def.ins())); + if (!preRange) + return false; + + // The new range starts at reg's input position, which means it overlaps + // with the old range at one position. This is what we want, because we + // need to copy the input before the instruction. + LiveRange* postRange = LiveRange::FallibleNew(alloc(), input.vreg(), + inputOf(def.ins()), inputRange->to()); + if (!postRange) + return false; + + inputRange->distributeUses(preRange); + inputRange->distributeUses(postRange); + MOZ_ASSERT(!inputRange->hasUses()); + + JitSpew(JitSpew_RegAlloc, " splitting reused input at %u to try to help grouping", + inputOf(def.ins()).bits()); + + LiveBundle* firstBundle = inputRange->bundle(); + input.removeRange(inputRange); + input.addRange(preRange); + input.addRange(postRange); + + firstBundle->removeRange(inputRange); + firstBundle->addRange(preRange); + + // The new range goes in a separate bundle, where it will be spilled during + // allocation. + LiveBundle* secondBundle = LiveBundle::FallibleNew(alloc(), nullptr, nullptr); + if (!secondBundle) + return false; + secondBundle->addRange(postRange); + + return tryMergeBundles(def.firstBundle(), input.firstBundle()); +} + +bool +BacktrackingAllocator::mergeAndQueueRegisters() +{ + MOZ_ASSERT(!vregs[0u].hasRanges()); + + // Create a bundle for each register containing all its ranges. + for (size_t i = 1; i < graph.numVirtualRegisters(); i++) { + VirtualRegister& reg = vregs[i]; + if (!reg.hasRanges()) + continue; + + LiveBundle* bundle = LiveBundle::FallibleNew(alloc(), nullptr, nullptr); + if (!bundle) + return false; + for (LiveRange::RegisterLinkIterator iter = reg.rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + bundle->addRange(range); + } + } + + // If there is an OSR block, merge parameters in that block with the + // corresponding parameters in the initial block. + if (MBasicBlock* osr = graph.mir().osrBlock()) { + size_t original = 1; + for (LInstructionIterator iter = osr->lir()->begin(); iter != osr->lir()->end(); iter++) { + if (iter->isParameter()) { + for (size_t i = 0; i < iter->numDefs(); i++) { + DebugOnly<bool> found = false; + VirtualRegister ¶mVreg = vreg(iter->getDef(i)); + for (; original < paramVreg.vreg(); original++) { + VirtualRegister &originalVreg = vregs[original]; + if (*originalVreg.def()->output() == *iter->getDef(i)->output()) { + MOZ_ASSERT(originalVreg.ins()->isParameter()); + if (!tryMergeBundles(originalVreg.firstBundle(), paramVreg.firstBundle())) + return false; + found = true; + break; + } + } + MOZ_ASSERT(found); + } + } + } + } + + // Try to merge registers with their reused inputs. + for (size_t i = 1; i < graph.numVirtualRegisters(); i++) { + VirtualRegister& reg = vregs[i]; + if (!reg.hasRanges()) + continue; + + if (reg.def()->policy() == LDefinition::MUST_REUSE_INPUT) { + LUse* use = reg.ins()->getOperand(reg.def()->getReusedInput())->toUse(); + if (!tryMergeReusedRegister(reg, vreg(use))) + return false; + } + } + + // Try to merge phis with their inputs. + for (size_t i = 0; i < graph.numBlocks(); i++) { + LBlock* block = graph.getBlock(i); + for (size_t j = 0; j < block->numPhis(); j++) { + LPhi* phi = block->getPhi(j); + VirtualRegister &outputVreg = vreg(phi->getDef(0)); + for (size_t k = 0, kend = phi->numOperands(); k < kend; k++) { + VirtualRegister& inputVreg = vreg(phi->getOperand(k)->toUse()); + if (!tryMergeBundles(inputVreg.firstBundle(), outputVreg.firstBundle())) + return false; + } + } + } + + // Add all bundles to the allocation queue, and create spill sets for them. + for (size_t i = 1; i < graph.numVirtualRegisters(); i++) { + VirtualRegister& reg = vregs[i]; + for (LiveRange::RegisterLinkIterator iter = reg.rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + LiveBundle* bundle = range->bundle(); + if (range == bundle->firstRange()) { + if (!alloc().ensureBallast()) + return false; + + SpillSet* spill = SpillSet::New(alloc()); + if (!spill) + return false; + bundle->setSpillSet(spill); + + size_t priority = computePriority(bundle); + if (!allocationQueue.insert(QueueItem(bundle, priority))) + return false; + } + } + } + + return true; +} + +static const size_t MAX_ATTEMPTS = 2; + +bool +BacktrackingAllocator::tryAllocateFixed(LiveBundle* bundle, Requirement requirement, + bool* success, bool* pfixed, + LiveBundleVector& conflicting) +{ + // Spill bundles which are required to be in a certain stack slot. + if (!requirement.allocation().isRegister()) { + JitSpew(JitSpew_RegAlloc, " stack allocation requirement"); + bundle->setAllocation(requirement.allocation()); + *success = true; + return true; + } + + AnyRegister reg = requirement.allocation().toRegister(); + return tryAllocateRegister(registers[reg.code()], bundle, success, pfixed, conflicting); +} + +bool +BacktrackingAllocator::tryAllocateNonFixed(LiveBundle* bundle, + Requirement requirement, Requirement hint, + bool* success, bool* pfixed, + LiveBundleVector& conflicting) +{ + // If we want, but do not require a bundle to be in a specific register, + // only look at that register for allocating and evict or spill if it is + // not available. Picking a separate register may be even worse than + // spilling, as it will still necessitate moves and will tie up more + // registers than if we spilled. + if (hint.kind() == Requirement::FIXED) { + AnyRegister reg = hint.allocation().toRegister(); + if (!tryAllocateRegister(registers[reg.code()], bundle, success, pfixed, conflicting)) + return false; + if (*success) + return true; + } + + // Spill bundles which have no hint or register requirement. + if (requirement.kind() == Requirement::NONE && hint.kind() != Requirement::REGISTER) { + if (!spill(bundle)) + return false; + *success = true; + return true; + } + + if (conflicting.empty() || minimalBundle(bundle)) { + // Search for any available register which the bundle can be + // allocated to. + for (size_t i = 0; i < AnyRegister::Total; i++) { + if (!tryAllocateRegister(registers[i], bundle, success, pfixed, conflicting)) + return false; + if (*success) + return true; + } + } + + // Spill bundles which have no register requirement if they didn't get + // allocated. + if (requirement.kind() == Requirement::NONE) { + if (!spill(bundle)) + return false; + *success = true; + return true; + } + + // We failed to allocate this bundle. + MOZ_ASSERT(!*success); + return true; +} + +bool +BacktrackingAllocator::processBundle(MIRGenerator* mir, LiveBundle* bundle) +{ + if (JitSpewEnabled(JitSpew_RegAlloc)) { + JitSpew(JitSpew_RegAlloc, "Allocating %s [priority %" PRIuSIZE "] [weight %" PRIuSIZE "]", + bundle->toString().get(), computePriority(bundle), computeSpillWeight(bundle)); + } + + // A bundle can be processed by doing any of the following: + // + // - Assigning the bundle a register. The bundle cannot overlap any other + // bundle allocated for that physical register. + // + // - Spilling the bundle, provided it has no register uses. + // + // - Splitting the bundle into two or more bundles which cover the original + // one. The new bundles are placed back onto the priority queue for later + // processing. + // + // - Evicting one or more existing allocated bundles, and then doing one + // of the above operations. Evicted bundles are placed back on the + // priority queue. Any evicted bundles must have a lower spill weight + // than the bundle being processed. + // + // As long as this structure is followed, termination is guaranteed. + // In general, we want to minimize the amount of bundle splitting (which + // generally necessitates spills), so allocate longer lived, lower weight + // bundles first and evict and split them later if they prevent allocation + // for higher weight bundles. + + Requirement requirement, hint; + bool canAllocate = computeRequirement(bundle, &requirement, &hint); + + bool fixed; + LiveBundleVector conflicting; + for (size_t attempt = 0;; attempt++) { + if (mir->shouldCancel("Backtracking Allocation (processBundle loop)")) + return false; + + if (canAllocate) { + bool success = false; + fixed = false; + conflicting.clear(); + + // Ok, let's try allocating for this bundle. + if (requirement.kind() == Requirement::FIXED) { + if (!tryAllocateFixed(bundle, requirement, &success, &fixed, conflicting)) + return false; + } else { + if (!tryAllocateNonFixed(bundle, requirement, hint, &success, &fixed, conflicting)) + return false; + } + + // If that worked, we're done! + if (success) + return true; + + // If that didn't work, but we have one or more non-fixed bundles + // known to be conflicting, maybe we can evict them and try again. + if ((attempt < MAX_ATTEMPTS || minimalBundle(bundle)) && + !fixed && + !conflicting.empty() && + maximumSpillWeight(conflicting) < computeSpillWeight(bundle)) + { + for (size_t i = 0; i < conflicting.length(); i++) { + if (!evictBundle(conflicting[i])) + return false; + } + continue; + } + } + + // A minimal bundle cannot be split any further. If we try to split it + // it at this point we will just end up with the same bundle and will + // enter an infinite loop. Weights and the initial live ranges must + // be constructed so that any minimal bundle is allocatable. + MOZ_ASSERT(!minimalBundle(bundle)); + + LiveBundle* conflict = conflicting.empty() ? nullptr : conflicting[0]; + return chooseBundleSplit(bundle, canAllocate && fixed, conflict); + } +} + +bool +BacktrackingAllocator::computeRequirement(LiveBundle* bundle, + Requirement *requirement, Requirement *hint) +{ + // Set any requirement or hint on bundle according to its definition and + // uses. Return false if there are conflicting requirements which will + // require the bundle to be split. + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + VirtualRegister ® = vregs[range->vreg()]; + + if (range->hasDefinition()) { + // Deal with any definition constraints/hints. + LDefinition::Policy policy = reg.def()->policy(); + if (policy == LDefinition::FIXED) { + // Fixed policies get a FIXED requirement. + JitSpew(JitSpew_RegAlloc, " Requirement %s, fixed by definition", + reg.def()->output()->toString().get()); + if (!requirement->merge(Requirement(*reg.def()->output()))) + return false; + } else if (reg.ins()->isPhi()) { + // Phis don't have any requirements, but they should prefer their + // input allocations. This is captured by the group hints above. + } else { + // Non-phis get a REGISTER requirement. + if (!requirement->merge(Requirement(Requirement::REGISTER))) + return false; + } + } + + // Search uses for requirements. + for (UsePositionIterator iter = range->usesBegin(); iter; iter++) { + LUse::Policy policy = iter->usePolicy(); + if (policy == LUse::FIXED) { + AnyRegister required = GetFixedRegister(reg.def(), iter->use()); + + JitSpew(JitSpew_RegAlloc, " Requirement %s, due to use at %u", + required.name(), iter->pos.bits()); + + // If there are multiple fixed registers which the bundle is + // required to use, fail. The bundle will need to be split before + // it can be allocated. + if (!requirement->merge(Requirement(LAllocation(required)))) + return false; + } else if (policy == LUse::REGISTER) { + if (!requirement->merge(Requirement(Requirement::REGISTER))) + return false; + } else if (policy == LUse::ANY) { + // ANY differs from KEEPALIVE by actively preferring a register. + if (!hint->merge(Requirement(Requirement::REGISTER))) + return false; + } + } + } + + return true; +} + +bool +BacktrackingAllocator::tryAllocateRegister(PhysicalRegister& r, LiveBundle* bundle, + bool* success, bool* pfixed, LiveBundleVector& conflicting) +{ + *success = false; + + if (!r.allocatable) + return true; + + LiveBundleVector aliasedConflicting; + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + VirtualRegister ® = vregs[range->vreg()]; + + if (!reg.isCompatible(r.reg)) + return true; + + for (size_t a = 0; a < r.reg.numAliased(); a++) { + PhysicalRegister& rAlias = registers[r.reg.aliased(a).code()]; + LiveRange* existing; + if (!rAlias.allocations.contains(range, &existing)) + continue; + if (existing->hasVreg()) { + MOZ_ASSERT(existing->bundle()->allocation().toRegister() == rAlias.reg); + bool duplicate = false; + for (size_t i = 0; i < aliasedConflicting.length(); i++) { + if (aliasedConflicting[i] == existing->bundle()) { + duplicate = true; + break; + } + } + if (!duplicate && !aliasedConflicting.append(existing->bundle())) + return false; + } else { + JitSpew(JitSpew_RegAlloc, " %s collides with fixed use %s", + rAlias.reg.name(), existing->toString().get()); + *pfixed = true; + return true; + } + } + } + + if (!aliasedConflicting.empty()) { + // One or more aliased registers is allocated to another bundle + // overlapping this one. Keep track of the conflicting set, and in the + // case of multiple conflicting sets keep track of the set with the + // lowest maximum spill weight. + + // The #ifdef guards against "unused variable 'existing'" bustage. +#ifdef JS_JITSPEW + if (JitSpewEnabled(JitSpew_RegAlloc)) { + if (aliasedConflicting.length() == 1) { + LiveBundle* existing = aliasedConflicting[0]; + JitSpew(JitSpew_RegAlloc, " %s collides with %s [weight %" PRIuSIZE "]", + r.reg.name(), existing->toString().get(), computeSpillWeight(existing)); + } else { + JitSpew(JitSpew_RegAlloc, " %s collides with the following", r.reg.name()); + for (size_t i = 0; i < aliasedConflicting.length(); i++) { + LiveBundle* existing = aliasedConflicting[i]; + JitSpew(JitSpew_RegAlloc, " %s [weight %" PRIuSIZE "]", + existing->toString().get(), computeSpillWeight(existing)); + } + } + } +#endif + + if (conflicting.empty()) { + if (!conflicting.appendAll(aliasedConflicting)) + return false; + } else { + if (maximumSpillWeight(aliasedConflicting) < maximumSpillWeight(conflicting)) { + conflicting.clear(); + if (!conflicting.appendAll(aliasedConflicting)) + return false; + } + } + return true; + } + + JitSpew(JitSpew_RegAlloc, " allocated to %s", r.reg.name()); + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + if (!alloc().ensureBallast()) + return false; + if (!r.allocations.insert(range)) + return false; + } + + bundle->setAllocation(LAllocation(r.reg)); + *success = true; + return true; +} + +bool +BacktrackingAllocator::evictBundle(LiveBundle* bundle) +{ + if (JitSpewEnabled(JitSpew_RegAlloc)) { + JitSpew(JitSpew_RegAlloc, " Evicting %s [priority %" PRIuSIZE "] [weight %" PRIuSIZE "]", + bundle->toString().get(), computePriority(bundle), computeSpillWeight(bundle)); + } + + AnyRegister reg(bundle->allocation().toRegister()); + PhysicalRegister& physical = registers[reg.code()]; + MOZ_ASSERT(physical.reg == reg && physical.allocatable); + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + physical.allocations.remove(range); + } + + bundle->setAllocation(LAllocation()); + + size_t priority = computePriority(bundle); + return allocationQueue.insert(QueueItem(bundle, priority)); +} + +bool +BacktrackingAllocator::splitAndRequeueBundles(LiveBundle* bundle, + const LiveBundleVector& newBundles) +{ + if (JitSpewEnabled(JitSpew_RegAlloc)) { + JitSpew(JitSpew_RegAlloc, " splitting bundle %s into:", bundle->toString().get()); + for (size_t i = 0; i < newBundles.length(); i++) + JitSpew(JitSpew_RegAlloc, " %s", newBundles[i]->toString().get()); + } + + // Remove all ranges in the old bundle from their register's list. + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + vregs[range->vreg()].removeRange(range); + } + + // Add all ranges in the new bundles to their register's list. + for (size_t i = 0; i < newBundles.length(); i++) { + LiveBundle* newBundle = newBundles[i]; + for (LiveRange::BundleLinkIterator iter = newBundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + vregs[range->vreg()].addRange(range); + } + } + + // Queue the new bundles for register assignment. + for (size_t i = 0; i < newBundles.length(); i++) { + LiveBundle* newBundle = newBundles[i]; + size_t priority = computePriority(newBundle); + if (!allocationQueue.insert(QueueItem(newBundle, priority))) + return false; + } + + return true; +} + +bool +BacktrackingAllocator::spill(LiveBundle* bundle) +{ + JitSpew(JitSpew_RegAlloc, " Spilling bundle"); + MOZ_ASSERT(bundle->allocation().isBogus()); + + if (LiveBundle* spillParent = bundle->spillParent()) { + JitSpew(JitSpew_RegAlloc, " Using existing spill bundle"); + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + LiveRange* parentRange = spillParent->rangeFor(range->from()); + MOZ_ASSERT(parentRange->contains(range)); + MOZ_ASSERT(range->vreg() == parentRange->vreg()); + range->distributeUses(parentRange); + MOZ_ASSERT(!range->hasUses()); + vregs[range->vreg()].removeRange(range); + } + return true; + } + + return bundle->spillSet()->addSpilledBundle(bundle); +} + +bool +BacktrackingAllocator::pickStackSlots() +{ + for (size_t i = 1; i < graph.numVirtualRegisters(); i++) { + VirtualRegister& reg = vregs[i]; + + if (mir->shouldCancel("Backtracking Pick Stack Slots")) + return false; + + for (LiveRange::RegisterLinkIterator iter = reg.rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + LiveBundle* bundle = range->bundle(); + + if (bundle->allocation().isBogus()) { + if (!pickStackSlot(bundle->spillSet())) + return false; + MOZ_ASSERT(!bundle->allocation().isBogus()); + } + } + } + + return true; +} + +bool +BacktrackingAllocator::pickStackSlot(SpillSet* spillSet) +{ + // Look through all ranges that have been spilled in this set for a + // register definition which is fixed to a stack or argument slot. If we + // find one, use it for all bundles that have been spilled. tryMergeBundles + // makes sure this reuse is possible when an initial bundle contains ranges + // from multiple virtual registers. + for (size_t i = 0; i < spillSet->numSpilledBundles(); i++) { + LiveBundle* bundle = spillSet->spilledBundle(i); + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + if (range->hasDefinition()) { + LDefinition* def = vregs[range->vreg()].def(); + if (def->policy() == LDefinition::FIXED) { + MOZ_ASSERT(!def->output()->isRegister()); + MOZ_ASSERT(!def->output()->isStackSlot()); + spillSet->setAllocation(*def->output()); + return true; + } + } + } + } + + LDefinition::Type type = vregs[spillSet->spilledBundle(0)->firstRange()->vreg()].type(); + + SpillSlotList* slotList; + switch (StackSlotAllocator::width(type)) { + case 4: slotList = &normalSlots; break; + case 8: slotList = &doubleSlots; break; + case 16: slotList = &quadSlots; break; + default: + MOZ_CRASH("Bad width"); + } + + // Maximum number of existing spill slots we will look at before giving up + // and allocating a new slot. + static const size_t MAX_SEARCH_COUNT = 10; + + size_t searches = 0; + SpillSlot* stop = nullptr; + while (!slotList->empty()) { + SpillSlot* spillSlot = *slotList->begin(); + if (!stop) { + stop = spillSlot; + } else if (stop == spillSlot) { + // We looked through every slot in the list. + break; + } + + bool success = true; + for (size_t i = 0; i < spillSet->numSpilledBundles(); i++) { + LiveBundle* bundle = spillSet->spilledBundle(i); + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + LiveRange* existing; + if (spillSlot->allocated.contains(range, &existing)) { + success = false; + break; + } + } + if (!success) + break; + } + if (success) { + // We can reuse this physical stack slot for the new bundles. + // Update the allocated ranges for the slot. + for (size_t i = 0; i < spillSet->numSpilledBundles(); i++) { + LiveBundle* bundle = spillSet->spilledBundle(i); + if (!insertAllRanges(spillSlot->allocated, bundle)) + return false; + } + spillSet->setAllocation(spillSlot->alloc); + return true; + } + + // On a miss, move the spill to the end of the list. This will cause us + // to make fewer attempts to allocate from slots with a large and + // highly contended range. + slotList->popFront(); + slotList->pushBack(spillSlot); + + if (++searches == MAX_SEARCH_COUNT) + break; + } + + // We need a new physical stack slot. + uint32_t stackSlot = stackSlotAllocator.allocateSlot(type); + + SpillSlot* spillSlot = new(alloc().fallible()) SpillSlot(stackSlot, alloc().lifoAlloc()); + if (!spillSlot) + return false; + + for (size_t i = 0; i < spillSet->numSpilledBundles(); i++) { + LiveBundle* bundle = spillSet->spilledBundle(i); + if (!insertAllRanges(spillSlot->allocated, bundle)) + return false; + } + + spillSet->setAllocation(spillSlot->alloc); + + slotList->pushFront(spillSlot); + return true; +} + +bool +BacktrackingAllocator::insertAllRanges(LiveRangeSet& set, LiveBundle* bundle) +{ + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + if (!alloc().ensureBallast()) + return false; + if (!set.insert(range)) + return false; + } + return true; +} + +bool +BacktrackingAllocator::deadRange(LiveRange* range) +{ + // Check for direct uses of this range. + if (range->hasUses() || range->hasDefinition()) + return false; + + CodePosition start = range->from(); + LNode* ins = insData[start]; + if (start == entryOf(ins->block())) + return false; + + VirtualRegister& reg = vregs[range->vreg()]; + + // Check if there are later ranges for this vreg. + LiveRange::RegisterLinkIterator iter = reg.rangesBegin(range); + for (iter++; iter; iter++) { + LiveRange* laterRange = LiveRange::get(*iter); + if (laterRange->from() > range->from()) + return false; + } + + // Check if this range ends at a loop backedge. + LNode* last = insData[range->to().previous()]; + if (last->isGoto() && last->toGoto()->target()->id() < last->block()->mir()->id()) + return false; + + // Check if there are phis which this vreg flows to. + if (reg.usedByPhi()) + return false; + + return true; +} + +bool +BacktrackingAllocator::resolveControlFlow() +{ + // Add moves to handle changing assignments for vregs over their lifetime. + JitSpew(JitSpew_RegAlloc, "Resolving control flow (vreg loop)"); + + // Look for places where a register's assignment changes in the middle of a + // basic block. + MOZ_ASSERT(!vregs[0u].hasRanges()); + for (size_t i = 1; i < graph.numVirtualRegisters(); i++) { + VirtualRegister& reg = vregs[i]; + + if (mir->shouldCancel("Backtracking Resolve Control Flow (vreg outer loop)")) + return false; + + for (LiveRange::RegisterLinkIterator iter = reg.rangesBegin(); iter; ) { + LiveRange* range = LiveRange::get(*iter); + + if (mir->shouldCancel("Backtracking Resolve Control Flow (vreg inner loop)")) + return false; + + // Remove ranges which will never be used. + if (deadRange(range)) { + reg.removeRangeAndIncrement(iter); + continue; + } + + // The range which defines the register does not have a predecessor + // to add moves from. + if (range->hasDefinition()) { + iter++; + continue; + } + + // Ignore ranges that start at block boundaries. We will handle + // these in the next phase. + CodePosition start = range->from(); + LNode* ins = insData[start]; + if (start == entryOf(ins->block())) { + iter++; + continue; + } + + // If we already saw a range which covers the start of this range + // and has the same allocation, we don't need an explicit move at + // the start of this range. + bool skip = false; + for (LiveRange::RegisterLinkIterator prevIter = reg.rangesBegin(); + prevIter != iter; + prevIter++) + { + LiveRange* prevRange = LiveRange::get(*prevIter); + if (prevRange->covers(start) && + prevRange->bundle()->allocation() == range->bundle()->allocation()) + { + skip = true; + break; + } + } + if (skip) { + iter++; + continue; + } + + if (!alloc().ensureBallast()) + return false; + + LiveRange* predecessorRange = reg.rangeFor(start.previous(), /* preferRegister = */ true); + if (start.subpos() == CodePosition::INPUT) { + if (!moveInput(ins->toInstruction(), predecessorRange, range, reg.type())) + return false; + } else { + if (!moveAfter(ins->toInstruction(), predecessorRange, range, reg.type())) + return false; + } + + iter++; + } + } + + JitSpew(JitSpew_RegAlloc, "Resolving control flow (block loop)"); + + for (size_t i = 0; i < graph.numBlocks(); i++) { + if (mir->shouldCancel("Backtracking Resolve Control Flow (block loop)")) + return false; + + LBlock* successor = graph.getBlock(i); + MBasicBlock* mSuccessor = successor->mir(); + if (mSuccessor->numPredecessors() < 1) + continue; + + // Resolve phis to moves. + for (size_t j = 0; j < successor->numPhis(); j++) { + LPhi* phi = successor->getPhi(j); + MOZ_ASSERT(phi->numDefs() == 1); + LDefinition* def = phi->getDef(0); + VirtualRegister& reg = vreg(def); + LiveRange* to = reg.rangeFor(entryOf(successor)); + MOZ_ASSERT(to); + + for (size_t k = 0; k < mSuccessor->numPredecessors(); k++) { + LBlock* predecessor = mSuccessor->getPredecessor(k)->lir(); + MOZ_ASSERT(predecessor->mir()->numSuccessors() == 1); + + LAllocation* input = phi->getOperand(k); + LiveRange* from = vreg(input).rangeFor(exitOf(predecessor), /* preferRegister = */ true); + MOZ_ASSERT(from); + + if (!alloc().ensureBallast()) + return false; + if (!moveAtExit(predecessor, from, to, def->type())) + return false; + } + } + } + + // Add moves to resolve graph edges with different allocations at their + // source and target. + for (size_t i = 1; i < graph.numVirtualRegisters(); i++) { + VirtualRegister& reg = vregs[i]; + for (LiveRange::RegisterLinkIterator iter = reg.rangesBegin(); iter; iter++) { + LiveRange* targetRange = LiveRange::get(*iter); + + size_t firstBlockId = insData[targetRange->from()]->block()->mir()->id(); + if (!targetRange->covers(entryOf(graph.getBlock(firstBlockId)))) + firstBlockId++; + for (size_t id = firstBlockId; id < graph.numBlocks(); id++) { + LBlock* successor = graph.getBlock(id); + if (!targetRange->covers(entryOf(successor))) + break; + + BitSet& live = liveIn[id]; + if (!live.contains(i)) + continue; + + for (size_t j = 0; j < successor->mir()->numPredecessors(); j++) { + LBlock* predecessor = successor->mir()->getPredecessor(j)->lir(); + if (targetRange->covers(exitOf(predecessor))) + continue; + + if (!alloc().ensureBallast()) + return false; + LiveRange* from = reg.rangeFor(exitOf(predecessor), true); + if (successor->mir()->numPredecessors() > 1) { + MOZ_ASSERT(predecessor->mir()->numSuccessors() == 1); + if (!moveAtExit(predecessor, from, targetRange, reg.type())) + return false; + } else { + if (!moveAtEntry(successor, from, targetRange, reg.type())) + return false; + } + } + } + } + } + + return true; +} + +bool +BacktrackingAllocator::isReusedInput(LUse* use, LNode* ins, bool considerCopy) +{ + if (LDefinition* def = FindReusingDefOrTemp(ins, use)) + return considerCopy || !vregs[def->virtualRegister()].mustCopyInput(); + return false; +} + +bool +BacktrackingAllocator::isRegisterUse(UsePosition* use, LNode* ins, bool considerCopy) +{ + switch (use->usePolicy()) { + case LUse::ANY: + return isReusedInput(use->use(), ins, considerCopy); + + case LUse::REGISTER: + case LUse::FIXED: + return true; + + default: + return false; + } +} + +bool +BacktrackingAllocator::isRegisterDefinition(LiveRange* range) +{ + if (!range->hasDefinition()) + return false; + + VirtualRegister& reg = vregs[range->vreg()]; + if (reg.ins()->isPhi()) + return false; + + if (reg.def()->policy() == LDefinition::FIXED && !reg.def()->output()->isRegister()) + return false; + + return true; +} + +bool +BacktrackingAllocator::reifyAllocations() +{ + JitSpew(JitSpew_RegAlloc, "Reifying Allocations"); + + MOZ_ASSERT(!vregs[0u].hasRanges()); + for (size_t i = 1; i < graph.numVirtualRegisters(); i++) { + VirtualRegister& reg = vregs[i]; + + if (mir->shouldCancel("Backtracking Reify Allocations (main loop)")) + return false; + + for (LiveRange::RegisterLinkIterator iter = reg.rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + + if (range->hasDefinition()) { + reg.def()->setOutput(range->bundle()->allocation()); + if (reg.ins()->recoversInput()) { + LSnapshot* snapshot = reg.ins()->toInstruction()->snapshot(); + for (size_t i = 0; i < snapshot->numEntries(); i++) { + LAllocation* entry = snapshot->getEntry(i); + if (entry->isUse() && entry->toUse()->policy() == LUse::RECOVERED_INPUT) + *entry = *reg.def()->output(); + } + } + } + + for (UsePositionIterator iter(range->usesBegin()); iter; iter++) { + LAllocation* alloc = iter->use(); + *alloc = range->bundle()->allocation(); + + // For any uses which feed into MUST_REUSE_INPUT definitions, + // add copies if the use and def have different allocations. + LNode* ins = insData[iter->pos]; + if (LDefinition* def = FindReusingDefOrTemp(ins, alloc)) { + LiveRange* outputRange = vreg(def).rangeFor(outputOf(ins)); + LAllocation res = outputRange->bundle()->allocation(); + LAllocation sourceAlloc = range->bundle()->allocation(); + + if (res != *alloc) { + if (!this->alloc().ensureBallast()) + return false; + if (NumReusingDefs(ins) <= 1) { + LMoveGroup* group = getInputMoveGroup(ins->toInstruction()); + if (!group->addAfter(sourceAlloc, res, reg.type())) + return false; + } else { + LMoveGroup* group = getFixReuseMoveGroup(ins->toInstruction()); + if (!group->add(sourceAlloc, res, reg.type())) + return false; + } + *alloc = res; + } + } + } + + addLiveRegistersForRange(reg, range); + } + } + + graph.setLocalSlotCount(stackSlotAllocator.stackHeight()); + return true; +} + +size_t +BacktrackingAllocator::findFirstNonCallSafepoint(CodePosition from) +{ + size_t i = 0; + for (; i < graph.numNonCallSafepoints(); i++) { + const LInstruction* ins = graph.getNonCallSafepoint(i); + if (from <= inputOf(ins)) + break; + } + return i; +} + +void +BacktrackingAllocator::addLiveRegistersForRange(VirtualRegister& reg, LiveRange* range) +{ + // Fill in the live register sets for all non-call safepoints. + LAllocation a = range->bundle()->allocation(); + if (!a.isRegister()) + return; + + // Don't add output registers to the safepoint. + CodePosition start = range->from(); + if (range->hasDefinition() && !reg.isTemp()) { +#ifdef CHECK_OSIPOINT_REGISTERS + // We don't add the output register to the safepoint, + // but it still might get added as one of the inputs. + // So eagerly add this reg to the safepoint clobbered registers. + if (reg.ins()->isInstruction()) { + if (LSafepoint* safepoint = reg.ins()->toInstruction()->safepoint()) + safepoint->addClobberedRegister(a.toRegister()); + } +#endif + start = start.next(); + } + + size_t i = findFirstNonCallSafepoint(start); + for (; i < graph.numNonCallSafepoints(); i++) { + LInstruction* ins = graph.getNonCallSafepoint(i); + CodePosition pos = inputOf(ins); + + // Safepoints are sorted, so we can shortcut out of this loop + // if we go out of range. + if (range->to() <= pos) + break; + + MOZ_ASSERT(range->covers(pos)); + + LSafepoint* safepoint = ins->safepoint(); + safepoint->addLiveRegister(a.toRegister()); + +#ifdef CHECK_OSIPOINT_REGISTERS + if (reg.isTemp()) + safepoint->addClobberedRegister(a.toRegister()); +#endif + } +} + +static inline bool +IsNunbox(VirtualRegister& reg) +{ +#ifdef JS_NUNBOX32 + return reg.type() == LDefinition::TYPE || + reg.type() == LDefinition::PAYLOAD; +#else + return false; +#endif +} + +static inline bool +IsSlotsOrElements(VirtualRegister& reg) +{ + return reg.type() == LDefinition::SLOTS; +} + +static inline bool +IsTraceable(VirtualRegister& reg) +{ + if (reg.type() == LDefinition::OBJECT) + return true; +#ifdef JS_PUNBOX64 + if (reg.type() == LDefinition::BOX) + return true; +#endif + return false; +} + +size_t +BacktrackingAllocator::findFirstSafepoint(CodePosition pos, size_t startFrom) +{ + size_t i = startFrom; + for (; i < graph.numSafepoints(); i++) { + LInstruction* ins = graph.getSafepoint(i); + if (pos <= inputOf(ins)) + break; + } + return i; +} + +bool +BacktrackingAllocator::populateSafepoints() +{ + JitSpew(JitSpew_RegAlloc, "Populating Safepoints"); + + size_t firstSafepoint = 0; + + MOZ_ASSERT(!vregs[0u].def()); + for (uint32_t i = 1; i < graph.numVirtualRegisters(); i++) { + VirtualRegister& reg = vregs[i]; + + if (!reg.def() || (!IsTraceable(reg) && !IsSlotsOrElements(reg) && !IsNunbox(reg))) + continue; + + firstSafepoint = findFirstSafepoint(inputOf(reg.ins()), firstSafepoint); + if (firstSafepoint >= graph.numSafepoints()) + break; + + for (LiveRange::RegisterLinkIterator iter = reg.rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + + for (size_t j = firstSafepoint; j < graph.numSafepoints(); j++) { + LInstruction* ins = graph.getSafepoint(j); + + if (!range->covers(inputOf(ins))) { + if (inputOf(ins) >= range->to()) + break; + continue; + } + + // Include temps but not instruction outputs. Also make sure + // MUST_REUSE_INPUT is not used with gcthings or nunboxes, or + // we would have to add the input reg to this safepoint. + if (ins == reg.ins() && !reg.isTemp()) { + DebugOnly<LDefinition*> def = reg.def(); + MOZ_ASSERT_IF(def->policy() == LDefinition::MUST_REUSE_INPUT, + def->type() == LDefinition::GENERAL || + def->type() == LDefinition::INT32 || + def->type() == LDefinition::FLOAT32 || + def->type() == LDefinition::DOUBLE); + continue; + } + + LSafepoint* safepoint = ins->safepoint(); + + LAllocation a = range->bundle()->allocation(); + if (a.isGeneralReg() && ins->isCall()) + continue; + + switch (reg.type()) { + case LDefinition::OBJECT: + if (!safepoint->addGcPointer(a)) + return false; + break; + case LDefinition::SLOTS: + if (!safepoint->addSlotsOrElementsPointer(a)) + return false; + break; +#ifdef JS_NUNBOX32 + case LDefinition::TYPE: + if (!safepoint->addNunboxType(i, a)) + return false; + break; + case LDefinition::PAYLOAD: + if (!safepoint->addNunboxPayload(i, a)) + return false; + break; +#else + case LDefinition::BOX: + if (!safepoint->addBoxedValue(a)) + return false; + break; +#endif + default: + MOZ_CRASH("Bad register type"); + } + } + } + } + + return true; +} + +bool +BacktrackingAllocator::annotateMoveGroups() +{ + // Annotate move groups in the LIR graph with any register that is not + // allocated at that point and can be used as a scratch register. This is + // only required for x86, as other platforms always have scratch registers + // available for use. +#ifdef JS_CODEGEN_X86 + LiveRange* range = LiveRange::FallibleNew(alloc(), 0, CodePosition(), CodePosition().next()); + if (!range) + return false; + + for (size_t i = 0; i < graph.numBlocks(); i++) { + if (mir->shouldCancel("Backtracking Annotate Move Groups")) + return false; + + LBlock* block = graph.getBlock(i); + LInstruction* last = nullptr; + for (LInstructionIterator iter = block->begin(); iter != block->end(); ++iter) { + if (iter->isMoveGroup()) { + CodePosition from = last ? outputOf(last) : entryOf(block); + range->setTo(from.next()); + range->setFrom(from); + + for (size_t i = 0; i < AnyRegister::Total; i++) { + PhysicalRegister& reg = registers[i]; + if (reg.reg.isFloat() || !reg.allocatable) + continue; + + // This register is unavailable for use if (a) it is in use + // by some live range immediately before the move group, + // or (b) it is an operand in one of the group's moves. The + // latter case handles live ranges which end immediately + // before the move group or start immediately after. + // For (b) we need to consider move groups immediately + // preceding or following this one. + + if (iter->toMoveGroup()->uses(reg.reg.gpr())) + continue; + bool found = false; + LInstructionIterator niter(iter); + for (niter++; niter != block->end(); niter++) { + if (niter->isMoveGroup()) { + if (niter->toMoveGroup()->uses(reg.reg.gpr())) { + found = true; + break; + } + } else { + break; + } + } + if (iter != block->begin()) { + LInstructionIterator riter(iter); + do { + riter--; + if (riter->isMoveGroup()) { + if (riter->toMoveGroup()->uses(reg.reg.gpr())) { + found = true; + break; + } + } else { + break; + } + } while (riter != block->begin()); + } + + LiveRange* existing; + if (found || reg.allocations.contains(range, &existing)) + continue; + + iter->toMoveGroup()->setScratchRegister(reg.reg.gpr()); + break; + } + } else { + last = *iter; + } + } + } +#endif + + return true; +} + +///////////////////////////////////////////////////////////////////// +// Debugging methods +///////////////////////////////////////////////////////////////////// + +#ifdef JS_JITSPEW + +UniqueChars +LiveRange::toString() const +{ + AutoEnterOOMUnsafeRegion oomUnsafe; + + char* buf = JS_smprintf("v%u [%u,%u)", hasVreg() ? vreg() : 0, from().bits(), to().bits()); + + if (buf && bundle() && !bundle()->allocation().isBogus()) + buf = JS_sprintf_append(buf, " %s", bundle()->allocation().toString().get()); + + if (buf && hasDefinition()) + buf = JS_sprintf_append(buf, " (def)"); + + for (UsePositionIterator iter = usesBegin(); buf && iter; iter++) + buf = JS_sprintf_append(buf, " %s@%u", iter->use()->toString().get(), iter->pos.bits()); + + if (!buf) + oomUnsafe.crash("LiveRange::toString()"); + + return UniqueChars(buf); +} + +UniqueChars +LiveBundle::toString() const +{ + AutoEnterOOMUnsafeRegion oomUnsafe; + + // Suppress -Wformat warning. + char *buf = JS_smprintf("%s", ""); + + for (LiveRange::BundleLinkIterator iter = rangesBegin(); buf && iter; iter++) { + buf = JS_sprintf_append(buf, "%s %s", + (iter == rangesBegin()) ? "" : " ##", + LiveRange::get(*iter)->toString().get()); + } + + if (!buf) + oomUnsafe.crash("LiveBundle::toString()"); + + return UniqueChars(buf); +} + +#endif // JS_JITSPEW + +void +BacktrackingAllocator::dumpVregs() +{ +#ifdef JS_JITSPEW + MOZ_ASSERT(!vregs[0u].hasRanges()); + + fprintf(stderr, "Live ranges by virtual register:\n"); + + for (uint32_t i = 1; i < graph.numVirtualRegisters(); i++) { + fprintf(stderr, " "); + VirtualRegister& reg = vregs[i]; + for (LiveRange::RegisterLinkIterator iter = reg.rangesBegin(); iter; iter++) { + if (iter != reg.rangesBegin()) + fprintf(stderr, " ## "); + fprintf(stderr, "%s", LiveRange::get(*iter)->toString().get()); + } + fprintf(stderr, "\n"); + } + + fprintf(stderr, "\nLive ranges by bundle:\n"); + + for (uint32_t i = 1; i < graph.numVirtualRegisters(); i++) { + VirtualRegister& reg = vregs[i]; + for (LiveRange::RegisterLinkIterator baseIter = reg.rangesBegin(); baseIter; baseIter++) { + LiveRange* range = LiveRange::get(*baseIter); + LiveBundle* bundle = range->bundle(); + if (range == bundle->firstRange()) { + fprintf(stderr, " "); + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + if (iter != bundle->rangesBegin()) + fprintf(stderr, " ## "); + fprintf(stderr, "%s", LiveRange::get(*iter)->toString().get()); + } + fprintf(stderr, "\n"); + } + } + } +#endif +} + +#ifdef JS_JITSPEW +struct BacktrackingAllocator::PrintLiveRange +{ + bool& first_; + + explicit PrintLiveRange(bool& first) : first_(first) {} + + void operator()(const LiveRange* range) + { + if (first_) + first_ = false; + else + fprintf(stderr, " /"); + fprintf(stderr, " %s", range->toString().get()); + } +}; +#endif + +void +BacktrackingAllocator::dumpAllocations() +{ +#ifdef JS_JITSPEW + fprintf(stderr, "Allocations:\n"); + + dumpVregs(); + + fprintf(stderr, "Allocations by physical register:\n"); + + for (size_t i = 0; i < AnyRegister::Total; i++) { + if (registers[i].allocatable && !registers[i].allocations.empty()) { + fprintf(stderr, " %s:", AnyRegister::FromCode(i).name()); + bool first = true; + registers[i].allocations.forEach(PrintLiveRange(first)); + fprintf(stderr, "\n"); + } + } + + fprintf(stderr, "\n"); +#endif // JS_JITSPEW +} + +/////////////////////////////////////////////////////////////////////////////// +// Heuristic Methods +/////////////////////////////////////////////////////////////////////////////// + +size_t +BacktrackingAllocator::computePriority(LiveBundle* bundle) +{ + // The priority of a bundle is its total length, so that longer lived + // bundles will be processed before shorter ones (even if the longer ones + // have a low spill weight). See processBundle(). + size_t lifetimeTotal = 0; + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + lifetimeTotal += range->to() - range->from(); + } + + return lifetimeTotal; +} + +bool +BacktrackingAllocator::minimalDef(LiveRange* range, LNode* ins) +{ + // Whether this is a minimal range capturing a definition at ins. + return (range->to() <= minimalDefEnd(ins).next()) && + ((!ins->isPhi() && range->from() == inputOf(ins)) || range->from() == outputOf(ins)); +} + +bool +BacktrackingAllocator::minimalUse(LiveRange* range, UsePosition* use) +{ + // Whether this is a minimal range capturing |use|. + LNode* ins = insData[use->pos]; + return (range->from() == inputOf(ins)) && + (range->to() == (use->use()->usedAtStart() ? outputOf(ins) : outputOf(ins).next())); +} + +bool +BacktrackingAllocator::minimalBundle(LiveBundle* bundle, bool* pfixed) +{ + LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); + LiveRange* range = LiveRange::get(*iter); + + if (!range->hasVreg()) { + *pfixed = true; + return true; + } + + // If a bundle contains multiple ranges, splitAtAllRegisterUses will split + // each range into a separate bundle. + if (++iter) + return false; + + if (range->hasDefinition()) { + VirtualRegister& reg = vregs[range->vreg()]; + if (pfixed) + *pfixed = reg.def()->policy() == LDefinition::FIXED && reg.def()->output()->isRegister(); + return minimalDef(range, reg.ins()); + } + + bool fixed = false, minimal = false, multiple = false; + + for (UsePositionIterator iter = range->usesBegin(); iter; iter++) { + if (iter != range->usesBegin()) + multiple = true; + + switch (iter->usePolicy()) { + case LUse::FIXED: + if (fixed) + return false; + fixed = true; + if (minimalUse(range, *iter)) + minimal = true; + break; + + case LUse::REGISTER: + if (minimalUse(range, *iter)) + minimal = true; + break; + + default: + break; + } + } + + // If a range contains a fixed use and at least one other use, + // splitAtAllRegisterUses will split each use into a different bundle. + if (multiple && fixed) + minimal = false; + + if (pfixed) + *pfixed = fixed; + return minimal; +} + +size_t +BacktrackingAllocator::computeSpillWeight(LiveBundle* bundle) +{ + // Minimal bundles have an extremely high spill weight, to ensure they + // can evict any other bundles and be allocated to a register. + bool fixed; + if (minimalBundle(bundle, &fixed)) + return fixed ? 2000000 : 1000000; + + size_t usesTotal = 0; + fixed = false; + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + + if (range->hasDefinition()) { + VirtualRegister& reg = vregs[range->vreg()]; + if (reg.def()->policy() == LDefinition::FIXED && reg.def()->output()->isRegister()) { + usesTotal += 2000; + fixed = true; + } else if (!reg.ins()->isPhi()) { + usesTotal += 2000; + } + } + + for (UsePositionIterator iter = range->usesBegin(); iter; iter++) { + switch (iter->usePolicy()) { + case LUse::ANY: + usesTotal += 1000; + break; + + case LUse::FIXED: + fixed = true; + MOZ_FALLTHROUGH; + case LUse::REGISTER: + usesTotal += 2000; + break; + + case LUse::KEEPALIVE: + break; + + default: + // Note: RECOVERED_INPUT will not appear in UsePositionIterator. + MOZ_CRASH("Bad use"); + } + } + } + + // Bundles with fixed uses are given a higher spill weight, since they must + // be allocated to a specific register. + if (testbed && fixed) + usesTotal *= 2; + + // Compute spill weight as a use density, lowering the weight for long + // lived bundles with relatively few uses. + size_t lifetimeTotal = computePriority(bundle); + return lifetimeTotal ? usesTotal / lifetimeTotal : 0; +} + +size_t +BacktrackingAllocator::maximumSpillWeight(const LiveBundleVector& bundles) +{ + size_t maxWeight = 0; + for (size_t i = 0; i < bundles.length(); i++) + maxWeight = Max(maxWeight, computeSpillWeight(bundles[i])); + return maxWeight; +} + +bool +BacktrackingAllocator::trySplitAcrossHotcode(LiveBundle* bundle, bool* success) +{ + // If this bundle has portions that are hot and portions that are cold, + // split it at the boundaries between hot and cold code. + + LiveRange* hotRange = nullptr; + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + if (hotcode.contains(range, &hotRange)) + break; + } + + // Don't split if there is no hot code in the bundle. + if (!hotRange) { + JitSpew(JitSpew_RegAlloc, " bundle does not contain hot code"); + return true; + } + + // Don't split if there is no cold code in the bundle. + bool coldCode = false; + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + if (!hotRange->contains(range)) { + coldCode = true; + break; + } + } + if (!coldCode) { + JitSpew(JitSpew_RegAlloc, " bundle does not contain cold code"); + return true; + } + + JitSpew(JitSpew_RegAlloc, " split across hot range %s", hotRange->toString().get()); + + // Tweak the splitting method when compiling wasm code to look at actual + // uses within the hot/cold code. This heuristic is in place as the below + // mechanism regresses several asm.js tests. Hopefully this will be fixed + // soon and this special case removed. See bug 948838. + if (compilingWasm()) { + SplitPositionVector splitPositions; + if (!splitPositions.append(hotRange->from()) || !splitPositions.append(hotRange->to())) + return false; + *success = true; + return splitAt(bundle, splitPositions); + } + + LiveBundle* hotBundle = LiveBundle::FallibleNew(alloc(), bundle->spillSet(), + bundle->spillParent()); + if (!hotBundle) + return false; + LiveBundle* preBundle = nullptr; + LiveBundle* postBundle = nullptr; + LiveBundle* coldBundle = nullptr; + + if (testbed) { + coldBundle = LiveBundle::FallibleNew(alloc(), bundle->spillSet(), bundle->spillParent()); + if (!coldBundle) + return false; + } + + // Accumulate the ranges of hot and cold code in the bundle. Note that + // we are only comparing with the single hot range found, so the cold code + // may contain separate hot ranges. + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + LiveRange::Range hot, coldPre, coldPost; + range->intersect(hotRange, &coldPre, &hot, &coldPost); + + if (!hot.empty()) { + if (!hotBundle->addRangeAndDistributeUses(alloc(), range, hot.from, hot.to)) + return false; + } + + if (!coldPre.empty()) { + if (testbed) { + if (!coldBundle->addRangeAndDistributeUses(alloc(), range, coldPre.from, coldPre.to)) + return false; + } else { + if (!preBundle) { + preBundle = LiveBundle::FallibleNew(alloc(), bundle->spillSet(), + bundle->spillParent()); + if (!preBundle) + return false; + } + if (!preBundle->addRangeAndDistributeUses(alloc(), range, coldPre.from, coldPre.to)) + return false; + } + } + + if (!coldPost.empty()) { + if (testbed) { + if (!coldBundle->addRangeAndDistributeUses(alloc(), range, coldPost.from, coldPost.to)) + return false; + } else { + if (!postBundle) { + postBundle = LiveBundle::FallibleNew(alloc(), bundle->spillSet(), + bundle->spillParent()); + if (!postBundle) + return false; + } + if (!postBundle->addRangeAndDistributeUses(alloc(), range, coldPost.from, coldPost.to)) + return false; + } + } + } + + MOZ_ASSERT(hotBundle->numRanges() != 0); + + LiveBundleVector newBundles; + if (!newBundles.append(hotBundle)) + return false; + + if (testbed) { + MOZ_ASSERT(coldBundle->numRanges() != 0); + if (!newBundles.append(coldBundle)) + return false; + } else { + MOZ_ASSERT(preBundle || postBundle); + if (preBundle && !newBundles.append(preBundle)) + return false; + if (postBundle && !newBundles.append(postBundle)) + return false; + } + + *success = true; + return splitAndRequeueBundles(bundle, newBundles); +} + +bool +BacktrackingAllocator::trySplitAfterLastRegisterUse(LiveBundle* bundle, LiveBundle* conflict, + bool* success) +{ + // If this bundle's later uses do not require it to be in a register, + // split it after the last use which does require a register. If conflict + // is specified, only consider register uses before the conflict starts. + + CodePosition lastRegisterFrom, lastRegisterTo, lastUse; + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + + // If the range defines a register, consider that a register use for + // our purposes here. + if (isRegisterDefinition(range)) { + CodePosition spillStart = minimalDefEnd(insData[range->from()]).next(); + if (!conflict || spillStart < conflict->firstRange()->from()) { + lastUse = lastRegisterFrom = range->from(); + lastRegisterTo = spillStart; + } + } + + for (UsePositionIterator iter(range->usesBegin()); iter; iter++) { + LNode* ins = insData[iter->pos]; + + // Uses in the bundle should be sorted. + MOZ_ASSERT(iter->pos >= lastUse); + lastUse = inputOf(ins); + + if (!conflict || outputOf(ins) < conflict->firstRange()->from()) { + if (isRegisterUse(*iter, ins, /* considerCopy = */ true)) { + lastRegisterFrom = inputOf(ins); + lastRegisterTo = iter->pos.next(); + } + } + } + } + + // Can't trim non-register uses off the end by splitting. + if (!lastRegisterFrom.bits()) { + JitSpew(JitSpew_RegAlloc, " bundle has no register uses"); + return true; + } + if (lastUse < lastRegisterTo) { + JitSpew(JitSpew_RegAlloc, " bundle's last use is a register use"); + return true; + } + + JitSpew(JitSpew_RegAlloc, " split after last register use at %u", + lastRegisterTo.bits()); + + SplitPositionVector splitPositions; + if (!splitPositions.append(lastRegisterTo)) + return false; + *success = true; + return splitAt(bundle, splitPositions); +} + +bool +BacktrackingAllocator::trySplitBeforeFirstRegisterUse(LiveBundle* bundle, LiveBundle* conflict, bool* success) +{ + // If this bundle's earlier uses do not require it to be in a register, + // split it before the first use which does require a register. If conflict + // is specified, only consider register uses after the conflict ends. + + if (isRegisterDefinition(bundle->firstRange())) { + JitSpew(JitSpew_RegAlloc, " bundle is defined by a register"); + return true; + } + if (!bundle->firstRange()->hasDefinition()) { + JitSpew(JitSpew_RegAlloc, " bundle does not have definition"); + return true; + } + + CodePosition firstRegisterFrom; + + CodePosition conflictEnd; + if (conflict) { + for (LiveRange::BundleLinkIterator iter = conflict->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + if (range->to() > conflictEnd) + conflictEnd = range->to(); + } + } + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + + if (!conflict || range->from() > conflictEnd) { + if (range->hasDefinition() && isRegisterDefinition(range)) { + firstRegisterFrom = range->from(); + break; + } + } + + for (UsePositionIterator iter(range->usesBegin()); iter; iter++) { + LNode* ins = insData[iter->pos]; + + if (!conflict || outputOf(ins) >= conflictEnd) { + if (isRegisterUse(*iter, ins, /* considerCopy = */ true)) { + firstRegisterFrom = inputOf(ins); + break; + } + } + } + if (firstRegisterFrom.bits()) + break; + } + + if (!firstRegisterFrom.bits()) { + // Can't trim non-register uses off the beginning by splitting. + JitSpew(JitSpew_RegAlloc, " bundle has no register uses"); + return true; + } + + JitSpew(JitSpew_RegAlloc, " split before first register use at %u", + firstRegisterFrom.bits()); + + SplitPositionVector splitPositions; + if (!splitPositions.append(firstRegisterFrom)) + return false; + *success = true; + return splitAt(bundle, splitPositions); +} + +// When splitting a bundle according to a list of split positions, return +// whether a use or range at |pos| should use a different bundle than the last +// position this was called for. +static bool +UseNewBundle(const SplitPositionVector& splitPositions, CodePosition pos, + size_t* activeSplitPosition) +{ + if (splitPositions.empty()) { + // When the split positions are empty we are splitting at all uses. + return true; + } + + if (*activeSplitPosition == splitPositions.length()) { + // We've advanced past all split positions. + return false; + } + + if (splitPositions[*activeSplitPosition] > pos) { + // We haven't gotten to the next split position yet. + return false; + } + + // We've advanced past the next split position, find the next one which we + // should split at. + while (*activeSplitPosition < splitPositions.length() && + splitPositions[*activeSplitPosition] <= pos) + { + (*activeSplitPosition)++; + } + return true; +} + +static bool +HasPrecedingRangeSharingVreg(LiveBundle* bundle, LiveRange* range) +{ + MOZ_ASSERT(range->bundle() == bundle); + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* prevRange = LiveRange::get(*iter); + if (prevRange == range) + return false; + if (prevRange->vreg() == range->vreg()) + return true; + } + + MOZ_CRASH(); +} + +static bool +HasFollowingRangeSharingVreg(LiveBundle* bundle, LiveRange* range) +{ + MOZ_ASSERT(range->bundle() == bundle); + + bool foundRange = false; + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* prevRange = LiveRange::get(*iter); + if (foundRange && prevRange->vreg() == range->vreg()) + return true; + if (prevRange == range) + foundRange = true; + } + + MOZ_ASSERT(foundRange); + return false; +} + +bool +BacktrackingAllocator::splitAt(LiveBundle* bundle, const SplitPositionVector& splitPositions) +{ + // Split the bundle at the given split points. Register uses which have no + // intervening split points are consolidated into the same bundle. If the + // list of split points is empty, then all register uses are placed in + // minimal bundles. + + // splitPositions should be sorted. + for (size_t i = 1; i < splitPositions.length(); ++i) + MOZ_ASSERT(splitPositions[i-1] < splitPositions[i]); + + // We don't need to create a new spill bundle if there already is one. + bool spillBundleIsNew = false; + LiveBundle* spillBundle = bundle->spillParent(); + if (!spillBundle) { + spillBundle = LiveBundle::FallibleNew(alloc(), bundle->spillSet(), nullptr); + if (!spillBundle) + return false; + spillBundleIsNew = true; + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + + CodePosition from = range->from(); + if (isRegisterDefinition(range)) + from = minimalDefEnd(insData[from]).next(); + + if (from < range->to()) { + if (!spillBundle->addRange(alloc(), range->vreg(), from, range->to())) + return false; + + if (range->hasDefinition() && !isRegisterDefinition(range)) + spillBundle->lastRange()->setHasDefinition(); + } + } + } + + LiveBundleVector newBundles; + + // The bundle which ranges are currently being added to. + LiveBundle* activeBundle = LiveBundle::FallibleNew(alloc(), bundle->spillSet(), spillBundle); + if (!activeBundle || !newBundles.append(activeBundle)) + return false; + + // State for use by UseNewBundle. + size_t activeSplitPosition = 0; + + // Make new bundles according to the split positions, and distribute ranges + // and uses to them. + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + + if (UseNewBundle(splitPositions, range->from(), &activeSplitPosition)) { + activeBundle = LiveBundle::FallibleNew(alloc(), bundle->spillSet(), spillBundle); + if (!activeBundle || !newBundles.append(activeBundle)) + return false; + } + + LiveRange* activeRange = LiveRange::FallibleNew(alloc(), range->vreg(), + range->from(), range->to()); + if (!activeRange) + return false; + activeBundle->addRange(activeRange); + + if (isRegisterDefinition(range)) + activeRange->setHasDefinition(); + + while (range->hasUses()) { + UsePosition* use = range->popUse(); + LNode* ins = insData[use->pos]; + + // Any uses of a register that appear before its definition has + // finished must be associated with the range for that definition. + if (isRegisterDefinition(range) && use->pos <= minimalDefEnd(insData[range->from()])) { + activeRange->addUse(use); + } else if (isRegisterUse(use, ins)) { + // Place this register use into a different bundle from the + // last one if there are any split points between the two uses. + // UseNewBundle always returns true if we are splitting at all + // register uses, but we can still reuse the last range and + // bundle if they have uses at the same position, except when + // either use is fixed (the two uses might require incompatible + // registers.) + if (UseNewBundle(splitPositions, use->pos, &activeSplitPosition) && + (!activeRange->hasUses() || + activeRange->usesBegin()->pos != use->pos || + activeRange->usesBegin()->usePolicy() == LUse::FIXED || + use->usePolicy() == LUse::FIXED)) + { + activeBundle = LiveBundle::FallibleNew(alloc(), bundle->spillSet(), + spillBundle); + if (!activeBundle || !newBundles.append(activeBundle)) + return false; + activeRange = LiveRange::FallibleNew(alloc(), range->vreg(), + range->from(), range->to()); + if (!activeRange) + return false; + activeBundle->addRange(activeRange); + } + + activeRange->addUse(use); + } else { + MOZ_ASSERT(spillBundleIsNew); + spillBundle->rangeFor(use->pos)->addUse(use); + } + } + } + + LiveBundleVector filteredBundles; + + // Trim the ends of ranges in each new bundle when there are no other + // earlier or later ranges in the same bundle with the same vreg. + for (size_t i = 0; i < newBundles.length(); i++) { + LiveBundle* bundle = newBundles[i]; + + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; ) { + LiveRange* range = LiveRange::get(*iter); + + if (!range->hasDefinition()) { + if (!HasPrecedingRangeSharingVreg(bundle, range)) { + if (range->hasUses()) { + UsePosition* use = *range->usesBegin(); + range->setFrom(inputOf(insData[use->pos])); + } else { + bundle->removeRangeAndIncrementIterator(iter); + continue; + } + } + } + + if (!HasFollowingRangeSharingVreg(bundle, range)) { + if (range->hasUses()) { + UsePosition* use = range->lastUse(); + range->setTo(use->pos.next()); + } else if (range->hasDefinition()) { + range->setTo(minimalDefEnd(insData[range->from()]).next()); + } else { + bundle->removeRangeAndIncrementIterator(iter); + continue; + } + } + + iter++; + } + + if (bundle->hasRanges() && !filteredBundles.append(bundle)) + return false; + } + + if (spillBundleIsNew && !filteredBundles.append(spillBundle)) + return false; + + return splitAndRequeueBundles(bundle, filteredBundles); +} + +bool +BacktrackingAllocator::splitAcrossCalls(LiveBundle* bundle) +{ + // Split the bundle to separate register uses and non-register uses and + // allow the vreg to be spilled across its range. + + // Find the locations of all calls in the bundle's range. + SplitPositionVector callPositions; + for (LiveRange::BundleLinkIterator iter = bundle->rangesBegin(); iter; iter++) { + LiveRange* range = LiveRange::get(*iter); + CallRange searchRange(range->from(), range->to()); + CallRange* callRange; + if (!callRanges.contains(&searchRange, &callRange)) { + // There are no calls inside this range. + continue; + } + MOZ_ASSERT(range->covers(callRange->range.from)); + + // The search above returns an arbitrary call within the range. Walk + // backwards to find the first call in the range. + for (CallRangeList::reverse_iterator riter = callRangesList.rbegin(callRange); + riter != callRangesList.rend(); + ++riter) + { + CodePosition pos = riter->range.from; + if (range->covers(pos)) + callRange = *riter; + else + break; + } + + // Add all call positions within the range, by walking forwards. + for (CallRangeList::iterator iter = callRangesList.begin(callRange); + iter != callRangesList.end(); + ++iter) + { + CodePosition pos = iter->range.from; + if (!range->covers(pos)) + break; + + // Calls at the beginning of the range are ignored; there is no splitting to do. + if (range->covers(pos.previous())) { + MOZ_ASSERT_IF(callPositions.length(), pos > callPositions.back()); + if (!callPositions.append(pos)) + return false; + } + } + } + MOZ_ASSERT(callPositions.length()); + +#ifdef JS_JITSPEW + JitSpewStart(JitSpew_RegAlloc, " split across calls at "); + for (size_t i = 0; i < callPositions.length(); ++i) + JitSpewCont(JitSpew_RegAlloc, "%s%u", i != 0 ? ", " : "", callPositions[i].bits()); + JitSpewFin(JitSpew_RegAlloc); +#endif + + return splitAt(bundle, callPositions); +} + +bool +BacktrackingAllocator::chooseBundleSplit(LiveBundle* bundle, bool fixed, LiveBundle* conflict) +{ + bool success = false; + + if (!trySplitAcrossHotcode(bundle, &success)) + return false; + if (success) + return true; + + if (fixed) + return splitAcrossCalls(bundle); + + if (!trySplitBeforeFirstRegisterUse(bundle, conflict, &success)) + return false; + if (success) + return true; + + if (!trySplitAfterLastRegisterUse(bundle, conflict, &success)) + return false; + if (success) + return true; + + // Split at all register uses. + SplitPositionVector emptyPositions; + return splitAt(bundle, emptyPositions); +} |