Add m-esr52 at 52.6.0

1 files changed, 1350 insertions, 0 deletions

diff --git a/js/src/jit/ScalarReplacement.cpp b/js/src/jit/ScalarReplacement.cpp
new file mode 100644
index 000000000..4614b2162
--- /dev/null
+++ b/js/src/jit/ScalarReplacement.cpp
@@ -0,0 +1,1350 @@
+/* -*- 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/ScalarReplacement.h"
+
+#include "mozilla/Vector.h"
+
+#include "jit/IonAnalysis.h"
+#include "jit/JitSpewer.h"
+#include "jit/MIR.h"
+#include "jit/MIRGenerator.h"
+#include "jit/MIRGraph.h"
+#include "vm/UnboxedObject.h"
+
+#include "jsobjinlines.h"
+
+namespace js {
+namespace jit {
+
+template <typename MemoryView>
+class EmulateStateOf
+{
+  private:
+    typedef typename MemoryView::BlockState BlockState;
+
+    MIRGenerator* mir_;
+    MIRGraph& graph_;
+
+    // Block state at the entrance of all basic blocks.
+    Vector<BlockState*, 8, SystemAllocPolicy> states_;
+
+  public:
+    EmulateStateOf(MIRGenerator* mir, MIRGraph& graph)
+      : mir_(mir),
+        graph_(graph)
+    {
+    }
+
+    bool run(MemoryView& view);
+};
+
+template <typename MemoryView>
+bool
+EmulateStateOf<MemoryView>::run(MemoryView& view)
+{
+    // Initialize the current block state of each block to an unknown state.
+    if (!states_.appendN(nullptr, graph_.numBlocks()))
+        return false;
+
+    // Initialize the first block which needs to be traversed in RPO.
+    MBasicBlock* startBlock = view.startingBlock();
+    if (!view.initStartingState(&states_[startBlock->id()]))
+        return false;
+
+    // Iterate over each basic block which has a valid entry state, and merge
+    // the state in the successor blocks.
+    for (ReversePostorderIterator block = graph_.rpoBegin(startBlock); block != graph_.rpoEnd(); block++) {
+        if (mir_->shouldCancel(MemoryView::phaseName))
+            return false;
+
+        // Get the block state as the result of the merge of all predecessors
+        // which have already been visited in RPO.  This means that backedges
+        // are not yet merged into the loop.
+        BlockState* state = states_[block->id()];
+        if (!state)
+            continue;
+        view.setEntryBlockState(state);
+
+        // Iterates over resume points, phi and instructions.
+        for (MNodeIterator iter(*block); iter; ) {
+            // Increment the iterator before visiting the instruction, as the
+            // visit function might discard itself from the basic block.
+            MNode* ins = *iter++;
+            if (ins->isDefinition())
+                ins->toDefinition()->accept(&view);
+            else
+                view.visitResumePoint(ins->toResumePoint());
+            if (view.oom())
+                return false;
+        }
+
+        // For each successor, merge the current state into the state of the
+        // successors.
+        for (size_t s = 0; s < block->numSuccessors(); s++) {
+            MBasicBlock* succ = block->getSuccessor(s);
+            if (!view.mergeIntoSuccessorState(*block, succ, &states_[succ->id()]))
+                return false;
+        }
+    }
+
+    states_.clear();
+    return true;
+}
+
+static bool
+IsObjectEscaped(MInstruction* ins, JSObject* objDefault = nullptr);
+
+// Returns False if the lambda is not escaped and if it is optimizable by
+// ScalarReplacementOfObject.
+static bool
+IsLambdaEscaped(MLambda* lambda, JSObject* obj)
+{
+    JitSpewDef(JitSpew_Escape, "Check lambda\n", lambda);
+    JitSpewIndent spewIndent(JitSpew_Escape);
+
+    // The scope chain is not escaped if none of the Lambdas which are
+    // capturing it are escaped.
+    for (MUseIterator i(lambda->usesBegin()); i != lambda->usesEnd(); i++) {
+        MNode* consumer = (*i)->consumer();
+        if (!consumer->isDefinition()) {
+            // Cannot optimize if it is observable from fun.arguments or others.
+            if (!consumer->toResumePoint()->isRecoverableOperand(*i)) {
+                JitSpew(JitSpew_Escape, "Observable lambda cannot be recovered");
+                return true;
+            }
+            continue;
+        }
+
+        MDefinition* def = consumer->toDefinition();
+        if (!def->isFunctionEnvironment()) {
+            JitSpewDef(JitSpew_Escape, "is escaped by\n", def);
+            return true;
+        }
+
+        if (IsObjectEscaped(def->toInstruction(), obj)) {
+            JitSpewDef(JitSpew_Escape, "is indirectly escaped by\n", def);
+            return true;
+        }
+    }
+    JitSpew(JitSpew_Escape, "Lambda is not escaped");
+    return false;
+}
+
+// Returns False if the object is not escaped and if it is optimizable by
+// ScalarReplacementOfObject.
+//
+// For the moment, this code is dumb as it only supports objects which are not
+// changing shape, and which are known by TI at the object creation.
+static bool
+IsObjectEscaped(MInstruction* ins, JSObject* objDefault)
+{
+    MOZ_ASSERT(ins->type() == MIRType::Object);
+    MOZ_ASSERT(ins->isNewObject() || ins->isGuardShape() || ins->isCreateThisWithTemplate() ||
+               ins->isNewCallObject() || ins->isFunctionEnvironment());
+
+    JitSpewDef(JitSpew_Escape, "Check object\n", ins);
+    JitSpewIndent spewIndent(JitSpew_Escape);
+
+    JSObject* obj = objDefault;
+    if (!obj)
+        obj = MObjectState::templateObjectOf(ins);
+
+    if (!obj) {
+        JitSpew(JitSpew_Escape, "No template object defined.");
+        return true;
+    }
+
+    // Check if the object is escaped. If the object is not the first argument
+    // of either a known Store / Load, then we consider it as escaped. This is a
+    // cheap and conservative escape analysis.
+    for (MUseIterator i(ins->usesBegin()); i != ins->usesEnd(); i++) {
+        MNode* consumer = (*i)->consumer();
+        if (!consumer->isDefinition()) {
+            // Cannot optimize if it is observable from fun.arguments or others.
+            if (!consumer->toResumePoint()->isRecoverableOperand(*i)) {
+                JitSpew(JitSpew_Escape, "Observable object cannot be recovered");
+                return true;
+            }
+            continue;
+        }
+
+        MDefinition* def = consumer->toDefinition();
+        switch (def->op()) {
+          case MDefinition::Op_StoreFixedSlot:
+          case MDefinition::Op_LoadFixedSlot:
+            // Not escaped if it is the first argument.
+            if (def->indexOf(*i) == 0)
+                break;
+
+            JitSpewDef(JitSpew_Escape, "is escaped by\n", def);
+            return true;
+
+          case MDefinition::Op_LoadUnboxedScalar:
+          case MDefinition::Op_StoreUnboxedScalar:
+          case MDefinition::Op_LoadUnboxedObjectOrNull:
+          case MDefinition::Op_StoreUnboxedObjectOrNull:
+          case MDefinition::Op_LoadUnboxedString:
+          case MDefinition::Op_StoreUnboxedString:
+            // Not escaped if it is the first argument.
+            if (def->indexOf(*i) != 0) {
+                JitSpewDef(JitSpew_Escape, "is escaped by\n", def);
+                return true;
+            }
+
+            if (!def->getOperand(1)->isConstant()) {
+                JitSpewDef(JitSpew_Escape, "is addressed with unknown index\n", def);
+                return true;
+            }
+
+            break;
+
+          case MDefinition::Op_PostWriteBarrier:
+            break;
+
+          case MDefinition::Op_Slots: {
+#ifdef DEBUG
+            // Assert that MSlots are only used by MStoreSlot and MLoadSlot.
+            MSlots* ins = def->toSlots();
+            MOZ_ASSERT(ins->object() != 0);
+            for (MUseIterator i(ins->usesBegin()); i != ins->usesEnd(); i++) {
+                // toDefinition should normally never fail, since they don't get
+                // captured by resume points.
+                MDefinition* def = (*i)->consumer()->toDefinition();
+                MOZ_ASSERT(def->op() == MDefinition::Op_StoreSlot ||
+                           def->op() == MDefinition::Op_LoadSlot);
+            }
+#endif
+            break;
+          }
+
+          case MDefinition::Op_GuardShape: {
+            MGuardShape* guard = def->toGuardShape();
+            MOZ_ASSERT(!ins->isGuardShape());
+            if (obj->maybeShape() != guard->shape()) {
+                JitSpewDef(JitSpew_Escape, "has a non-matching guard shape\n", guard);
+                return true;
+            }
+            if (IsObjectEscaped(def->toInstruction(), obj)) {
+                JitSpewDef(JitSpew_Escape, "is indirectly escaped by\n", def);
+                return true;
+            }
+            break;
+          }
+
+          case MDefinition::Op_Lambda: {
+            MLambda* lambda = def->toLambda();
+            if (IsLambdaEscaped(lambda, obj)) {
+                JitSpewDef(JitSpew_Escape, "is indirectly escaped by\n", lambda);
+                return true;
+            }
+            break;
+          }
+
+          // This instruction is a no-op used to verify that scalar replacement
+          // is working as expected in jit-test.
+          case MDefinition::Op_AssertRecoveredOnBailout:
+            break;
+
+          default:
+            JitSpewDef(JitSpew_Escape, "is escaped by\n", def);
+            return true;
+        }
+    }
+
+    JitSpew(JitSpew_Escape, "Object is not escaped");
+    return false;
+}
+
+class ObjectMemoryView : public MDefinitionVisitorDefaultNoop
+{
+  public:
+    typedef MObjectState BlockState;
+    static const char* phaseName;
+
+  private:
+    TempAllocator& alloc_;
+    MConstant* undefinedVal_;
+    MInstruction* obj_;
+    MBasicBlock* startBlock_;
+    BlockState* state_;
+
+    // Used to improve the memory usage by sharing common modification.
+    const MResumePoint* lastResumePoint_;
+
+    bool oom_;
+
+  public:
+    ObjectMemoryView(TempAllocator& alloc, MInstruction* obj);
+
+    MBasicBlock* startingBlock();
+    bool initStartingState(BlockState** pState);
+
+    void setEntryBlockState(BlockState* state);
+    bool mergeIntoSuccessorState(MBasicBlock* curr, MBasicBlock* succ, BlockState** pSuccState);
+
+#ifdef DEBUG
+    void assertSuccess();
+#else
+    void assertSuccess() {}
+#endif
+
+    bool oom() const { return oom_; }
+
+  public:
+    void visitResumePoint(MResumePoint* rp);
+    void visitObjectState(MObjectState* ins);
+    void visitStoreFixedSlot(MStoreFixedSlot* ins);
+    void visitLoadFixedSlot(MLoadFixedSlot* ins);
+    void visitPostWriteBarrier(MPostWriteBarrier* ins);
+    void visitStoreSlot(MStoreSlot* ins);
+    void visitLoadSlot(MLoadSlot* ins);
+    void visitGuardShape(MGuardShape* ins);
+    void visitFunctionEnvironment(MFunctionEnvironment* ins);
+    void visitLambda(MLambda* ins);
+    void visitStoreUnboxedScalar(MStoreUnboxedScalar* ins);
+    void visitLoadUnboxedScalar(MLoadUnboxedScalar* ins);
+    void visitStoreUnboxedObjectOrNull(MStoreUnboxedObjectOrNull* ins);
+    void visitLoadUnboxedObjectOrNull(MLoadUnboxedObjectOrNull* ins);
+    void visitStoreUnboxedString(MStoreUnboxedString* ins);
+    void visitLoadUnboxedString(MLoadUnboxedString* ins);
+
+  private:
+    void storeOffset(MInstruction* ins, size_t offset, MDefinition* value);
+    void loadOffset(MInstruction* ins, size_t offset);
+};
+
+const char* ObjectMemoryView::phaseName = "Scalar Replacement of Object";
+
+ObjectMemoryView::ObjectMemoryView(TempAllocator& alloc, MInstruction* obj)
+  : alloc_(alloc),
+    obj_(obj),
+    startBlock_(obj->block()),
+    state_(nullptr),
+    lastResumePoint_(nullptr),
+    oom_(false)
+{
+    // Annotate snapshots RValue such that we recover the store first.
+    obj_->setIncompleteObject();
+
+    // Annotate the instruction such that we do not replace it by a
+    // Magic(JS_OPTIMIZED_OUT) in case of removed uses.
+    obj_->setImplicitlyUsedUnchecked();
+}
+
+MBasicBlock*
+ObjectMemoryView::startingBlock()
+{
+    return startBlock_;
+}
+
+bool
+ObjectMemoryView::initStartingState(BlockState** pState)
+{
+    // Uninitialized slots have an "undefined" value.
+    undefinedVal_ = MConstant::New(alloc_, UndefinedValue());
+    startBlock_->insertBefore(obj_, undefinedVal_);
+
+    // Create a new block state and insert at it at the location of the new object.
+    BlockState* state = BlockState::New(alloc_, obj_);
+    if (!state)
+        return false;
+
+    startBlock_->insertAfter(obj_, state);
+
+    // Initialize the properties of the object state.
+    if (!state->initFromTemplateObject(alloc_, undefinedVal_))
+        return false;
+
+    // Hold out of resume point until it is visited.
+    state->setInWorklist();
+
+    *pState = state;
+    return true;
+}
+
+void
+ObjectMemoryView::setEntryBlockState(BlockState* state)
+{
+    state_ = state;
+}
+
+bool
+ObjectMemoryView::mergeIntoSuccessorState(MBasicBlock* curr, MBasicBlock* succ,
+                                          BlockState** pSuccState)
+{
+    BlockState* succState = *pSuccState;
+
+    // When a block has no state yet, create an empty one for the
+    // successor.
+    if (!succState) {
+        // If the successor is not dominated then the object cannot flow
+        // in this basic block without a Phi.  We know that no Phi exist
+        // in non-dominated successors as the conservative escaped
+        // analysis fails otherwise.  Such condition can succeed if the
+        // successor is a join at the end of a if-block and the object
+        // only exists within the branch.
+        if (!startBlock_->dominates(succ))
+            return true;
+
+        // If there is only one predecessor, carry over the last state of the
+        // block to the successor.  As the block state is immutable, if the
+        // current block has multiple successors, they will share the same entry
+        // state.
+        if (succ->numPredecessors() <= 1 || !state_->numSlots()) {
+            *pSuccState = state_;
+            return true;
+        }
+
+        // If we have multiple predecessors, then we allocate one Phi node for
+        // each predecessor, and create a new block state which only has phi
+        // nodes.  These would later be removed by the removal of redundant phi
+        // nodes.
+        succState = BlockState::Copy(alloc_, state_);
+        if (!succState)
+            return false;
+
+        size_t numPreds = succ->numPredecessors();
+        for (size_t slot = 0; slot < state_->numSlots(); slot++) {
+            MPhi* phi = MPhi::New(alloc_);
+            if (!phi->reserveLength(numPreds))
+                return false;
+
+            // Fill the input of the successors Phi with undefined
+            // values, and each block later fills the Phi inputs.
+            for (size_t p = 0; p < numPreds; p++)
+                phi->addInput(undefinedVal_);
+
+            // Add Phi in the list of Phis of the basic block.
+            succ->addPhi(phi);
+            succState->setSlot(slot, phi);
+        }
+
+        // Insert the newly created block state instruction at the beginning
+        // of the successor block, after all the phi nodes.  Note that it
+        // would be captured by the entry resume point of the successor
+        // block.
+        succ->insertBefore(succ->safeInsertTop(), succState);
+        *pSuccState = succState;
+    }
+
+    MOZ_ASSERT_IF(succ == startBlock_, startBlock_->isLoopHeader());
+    if (succ->numPredecessors() > 1 && succState->numSlots() && succ != startBlock_) {
+        // We need to re-compute successorWithPhis as the previous EliminatePhis
+        // phase might have removed all the Phis from the successor block.
+        size_t currIndex;
+        MOZ_ASSERT(!succ->phisEmpty());
+        if (curr->successorWithPhis()) {
+            MOZ_ASSERT(curr->successorWithPhis() == succ);
+            currIndex = curr->positionInPhiSuccessor();
+        } else {
+            currIndex = succ->indexForPredecessor(curr);
+            curr->setSuccessorWithPhis(succ, currIndex);
+        }
+        MOZ_ASSERT(succ->getPredecessor(currIndex) == curr);
+
+        // Copy the current slot states to the index of current block in all the
+        // Phi created during the first visit of the successor.
+        for (size_t slot = 0; slot < state_->numSlots(); slot++) {
+            MPhi* phi = succState->getSlot(slot)->toPhi();
+            phi->replaceOperand(currIndex, state_->getSlot(slot));
+        }
+    }
+
+    return true;
+}
+
+#ifdef DEBUG
+void
+ObjectMemoryView::assertSuccess()
+{
+    for (MUseIterator i(obj_->usesBegin()); i != obj_->usesEnd(); i++) {
+        MNode* ins = (*i)->consumer();
+        MDefinition* def = nullptr;
+
+        // Resume points have been replaced by the object state.
+        if (ins->isResumePoint() || (def = ins->toDefinition())->isRecoveredOnBailout()) {
+            MOZ_ASSERT(obj_->isIncompleteObject());
+            continue;
+        }
+
+        // The only remaining uses would be removed by DCE, which will also
+        // recover the object on bailouts.
+        MOZ_ASSERT(def->isSlots() || def->isLambda());
+        MOZ_ASSERT(!def->hasDefUses());
+    }
+}
+#endif
+
+void
+ObjectMemoryView::visitResumePoint(MResumePoint* rp)
+{
+    // As long as the MObjectState is not yet seen next to the allocation, we do
+    // not patch the resume point to recover the side effects.
+    if (!state_->isInWorklist()) {
+        rp->addStore(alloc_, state_, lastResumePoint_);
+        lastResumePoint_ = rp;
+    }
+}
+
+void
+ObjectMemoryView::visitObjectState(MObjectState* ins)
+{
+    if (ins->isInWorklist())
+        ins->setNotInWorklist();
+}
+
+void
+ObjectMemoryView::visitStoreFixedSlot(MStoreFixedSlot* ins)
+{
+    // Skip stores made on other objects.
+    if (ins->object() != obj_)
+        return;
+
+    // Clone the state and update the slot value.
+    if (state_->hasFixedSlot(ins->slot())) {
+        state_ = BlockState::Copy(alloc_, state_);
+        if (!state_) {
+            oom_ = true;
+            return;
+        }
+
+        state_->setFixedSlot(ins->slot(), ins->value());
+        ins->block()->insertBefore(ins->toInstruction(), state_);
+    } else {
+        // UnsafeSetReserveSlot can access baked-in slots which are guarded by
+        // conditions, which are not seen by the escape analysis.
+        MBail* bailout = MBail::New(alloc_, Bailout_Inevitable);
+        ins->block()->insertBefore(ins, bailout);
+    }
+
+    // Remove original instruction.
+    ins->block()->discard(ins);
+}
+
+void
+ObjectMemoryView::visitLoadFixedSlot(MLoadFixedSlot* ins)
+{
+    // Skip loads made on other objects.
+    if (ins->object() != obj_)
+        return;
+
+    // Replace load by the slot value.
+    if (state_->hasFixedSlot(ins->slot())) {
+        ins->replaceAllUsesWith(state_->getFixedSlot(ins->slot()));
+    } else {
+        // UnsafeGetReserveSlot can access baked-in slots which are guarded by
+        // conditions, which are not seen by the escape analysis.
+        MBail* bailout = MBail::New(alloc_, Bailout_Inevitable);
+        ins->block()->insertBefore(ins, bailout);
+        ins->replaceAllUsesWith(undefinedVal_);
+    }
+
+    // Remove original instruction.
+    ins->block()->discard(ins);
+}
+
+void
+ObjectMemoryView::visitPostWriteBarrier(MPostWriteBarrier* ins)
+{
+    // Skip loads made on other objects.
+    if (ins->object() != obj_)
+        return;
+
+    // Remove original instruction.
+    ins->block()->discard(ins);
+}
+
+void
+ObjectMemoryView::visitStoreSlot(MStoreSlot* ins)
+{
+    // Skip stores made on other objects.
+    MSlots* slots = ins->slots()->toSlots();
+    if (slots->object() != obj_) {
+        // Guard objects are replaced when they are visited.
+        MOZ_ASSERT(!slots->object()->isGuardShape() || slots->object()->toGuardShape()->object() != obj_);
+        return;
+    }
+
+    // Clone the state and update the slot value.
+    if (state_->hasDynamicSlot(ins->slot())) {
+        state_ = BlockState::Copy(alloc_, state_);
+        if (!state_) {
+            oom_ = true;
+            return;
+        }
+
+        state_->setDynamicSlot(ins->slot(), ins->value());
+        ins->block()->insertBefore(ins->toInstruction(), state_);
+    } else {
+        // UnsafeSetReserveSlot can access baked-in slots which are guarded by
+        // conditions, which are not seen by the escape analysis.
+        MBail* bailout = MBail::New(alloc_, Bailout_Inevitable);
+        ins->block()->insertBefore(ins, bailout);
+    }
+
+    // Remove original instruction.
+    ins->block()->discard(ins);
+}
+
+void
+ObjectMemoryView::visitLoadSlot(MLoadSlot* ins)
+{
+    // Skip loads made on other objects.
+    MSlots* slots = ins->slots()->toSlots();
+    if (slots->object() != obj_) {
+        // Guard objects are replaced when they are visited.
+        MOZ_ASSERT(!slots->object()->isGuardShape() || slots->object()->toGuardShape()->object() != obj_);
+        return;
+    }
+
+    // Replace load by the slot value.
+    if (state_->hasDynamicSlot(ins->slot())) {
+        ins->replaceAllUsesWith(state_->getDynamicSlot(ins->slot()));
+    } else {
+        // UnsafeGetReserveSlot can access baked-in slots which are guarded by
+        // conditions, which are not seen by the escape analysis.
+        MBail* bailout = MBail::New(alloc_, Bailout_Inevitable);
+        ins->block()->insertBefore(ins, bailout);
+        ins->replaceAllUsesWith(undefinedVal_);
+    }
+
+    // Remove original instruction.
+    ins->block()->discard(ins);
+}
+
+void
+ObjectMemoryView::visitGuardShape(MGuardShape* ins)
+{
+    // Skip loads made on other objects.
+    if (ins->object() != obj_)
+        return;
+
+    // Replace the shape guard by its object.
+    ins->replaceAllUsesWith(obj_);
+
+    // Remove original instruction.
+    ins->block()->discard(ins);
+}
+
+void
+ObjectMemoryView::visitFunctionEnvironment(MFunctionEnvironment* ins)
+{
+    // Skip function environment which are not aliases of the NewCallObject.
+    MDefinition* input = ins->input();
+    if (!input->isLambda() || input->toLambda()->environmentChain() != obj_)
+        return;
+
+    // Replace the function environment by the scope chain of the lambda.
+    ins->replaceAllUsesWith(obj_);
+
+    // Remove original instruction.
+    ins->block()->discard(ins);
+}
+
+void
+ObjectMemoryView::visitLambda(MLambda* ins)
+{
+    if (ins->environmentChain() != obj_)
+        return;
+
+    // In order to recover the lambda we need to recover the scope chain, as the
+    // lambda is holding it.
+    ins->setIncompleteObject();
+}
+
+static size_t
+GetOffsetOf(MDefinition* index, size_t width, int32_t baseOffset)
+{
+    int32_t idx = index->toConstant()->toInt32();
+    MOZ_ASSERT(idx >= 0);
+    MOZ_ASSERT(baseOffset >= 0 && size_t(baseOffset) >= UnboxedPlainObject::offsetOfData());
+    return idx * width + baseOffset - UnboxedPlainObject::offsetOfData();
+}
+
+static size_t
+GetOffsetOf(MDefinition* index, Scalar::Type type, int32_t baseOffset)
+{
+    return GetOffsetOf(index, Scalar::byteSize(type), baseOffset);
+}
+
+void
+ObjectMemoryView::storeOffset(MInstruction* ins, size_t offset, MDefinition* value)
+{
+    // Clone the state and update the slot value.
+    MOZ_ASSERT(state_->hasOffset(offset));
+    state_ = BlockState::Copy(alloc_, state_);
+    if (!state_) {
+        oom_ = true;
+        return;
+    }
+
+    state_->setOffset(offset, value);
+    ins->block()->insertBefore(ins, state_);
+
+    // Remove original instruction.
+    ins->block()->discard(ins);
+}
+
+void
+ObjectMemoryView::loadOffset(MInstruction* ins, size_t offset)
+{
+    // Replace load by the slot value.
+    MOZ_ASSERT(state_->hasOffset(offset));
+    ins->replaceAllUsesWith(state_->getOffset(offset));
+
+    // Remove original instruction.
+    ins->block()->discard(ins);
+}
+
+void
+ObjectMemoryView::visitStoreUnboxedScalar(MStoreUnboxedScalar* ins)
+{
+    // Skip stores made on other objects.
+    if (ins->elements() != obj_)
+        return;
+
+    size_t offset = GetOffsetOf(ins->index(), ins->storageType(), ins->offsetAdjustment());
+    storeOffset(ins, offset, ins->value());
+}
+
+void
+ObjectMemoryView::visitLoadUnboxedScalar(MLoadUnboxedScalar* ins)
+{
+    // Skip loads made on other objects.
+    if (ins->elements() != obj_)
+        return;
+
+    // Replace load by the slot value.
+    size_t offset = GetOffsetOf(ins->index(), ins->storageType(), ins->offsetAdjustment());
+    loadOffset(ins, offset);
+}
+
+void
+ObjectMemoryView::visitStoreUnboxedObjectOrNull(MStoreUnboxedObjectOrNull* ins)
+{
+    // Skip stores made on other objects.
+    if (ins->elements() != obj_)
+        return;
+
+    // Clone the state and update the slot value.
+    size_t offset = GetOffsetOf(ins->index(), sizeof(uintptr_t), ins->offsetAdjustment());
+    storeOffset(ins, offset, ins->value());
+}
+
+void
+ObjectMemoryView::visitLoadUnboxedObjectOrNull(MLoadUnboxedObjectOrNull* ins)
+{
+    // Skip loads made on other objects.
+    if (ins->elements() != obj_)
+        return;
+
+    // Replace load by the slot value.
+    size_t offset = GetOffsetOf(ins->index(), sizeof(uintptr_t), ins->offsetAdjustment());
+    loadOffset(ins, offset);
+}
+
+void
+ObjectMemoryView::visitStoreUnboxedString(MStoreUnboxedString* ins)
+{
+    // Skip stores made on other objects.
+    if (ins->elements() != obj_)
+        return;
+
+    // Clone the state and update the slot value.
+    size_t offset = GetOffsetOf(ins->index(), sizeof(uintptr_t), ins->offsetAdjustment());
+    storeOffset(ins, offset, ins->value());
+}
+
+void
+ObjectMemoryView::visitLoadUnboxedString(MLoadUnboxedString* ins)
+{
+    // Skip loads made on other objects.
+    if (ins->elements() != obj_)
+        return;
+
+    // Replace load by the slot value.
+    size_t offset = GetOffsetOf(ins->index(), sizeof(uintptr_t), ins->offsetAdjustment());
+    loadOffset(ins, offset);
+}
+
+static bool
+IndexOf(MDefinition* ins, int32_t* res)
+{
+    MOZ_ASSERT(ins->isLoadElement() || ins->isStoreElement());
+    MDefinition* indexDef = ins->getOperand(1); // ins->index();
+    if (indexDef->isBoundsCheck())
+        indexDef = indexDef->toBoundsCheck()->index();
+    if (indexDef->isToInt32())
+        indexDef = indexDef->toToInt32()->getOperand(0);
+    MConstant* indexDefConst = indexDef->maybeConstantValue();
+    if (!indexDefConst || indexDefConst->type() != MIRType::Int32)
+        return false;
+    *res = indexDefConst->toInt32();
+    return true;
+}
+
+// Returns False if the elements is not escaped and if it is optimizable by
+// ScalarReplacementOfArray.
+static bool
+IsElementEscaped(MElements* def, uint32_t arraySize)
+{
+    JitSpewDef(JitSpew_Escape, "Check elements\n", def);
+    JitSpewIndent spewIndent(JitSpew_Escape);
+
+    for (MUseIterator i(def->usesBegin()); i != def->usesEnd(); i++) {
+        // The MIRType::Elements cannot be captured in a resume point as
+        // it does not represent a value allocation.
+        MDefinition* access = (*i)->consumer()->toDefinition();
+
+        switch (access->op()) {
+          case MDefinition::Op_LoadElement: {
+            MOZ_ASSERT(access->toLoadElement()->elements() == def);
+
+            // If we need hole checks, then the array cannot be escaped
+            // as the array might refer to the prototype chain to look
+            // for properties, thus it might do additional side-effects
+            // which are not reflected by the alias set, is we are
+            // bailing on holes.
+            if (access->toLoadElement()->needsHoleCheck()) {
+                JitSpewDef(JitSpew_Escape,
+                           "has a load element with a hole check\n", access);
+                return true;
+            }
+
+            // If the index is not a constant then this index can alias
+            // all others. We do not handle this case.
+            int32_t index;
+            if (!IndexOf(access, &index)) {
+                JitSpewDef(JitSpew_Escape,
+                           "has a load element with a non-trivial index\n", access);
+                return true;
+            }
+            if (index < 0 || arraySize <= uint32_t(index)) {
+                JitSpewDef(JitSpew_Escape,
+                           "has a load element with an out-of-bound index\n", access);
+                return true;
+            }
+            break;
+          }
+
+          case MDefinition::Op_StoreElement: {
+            MOZ_ASSERT(access->toStoreElement()->elements() == def);
+
+            // If we need hole checks, then the array cannot be escaped
+            // as the array might refer to the prototype chain to look
+            // for properties, thus it might do additional side-effects
+            // which are not reflected by the alias set, is we are
+            // bailing on holes.
+            if (access->toStoreElement()->needsHoleCheck()) {
+                JitSpewDef(JitSpew_Escape,
+                           "has a store element with a hole check\n", access);
+                return true;
+            }
+
+            // If the index is not a constant then this index can alias
+            // all others. We do not handle this case.
+            int32_t index;
+            if (!IndexOf(access, &index)) {
+                JitSpewDef(JitSpew_Escape, "has a store element with a non-trivial index\n", access);
+                return true;
+            }
+            if (index < 0 || arraySize <= uint32_t(index)) {
+                JitSpewDef(JitSpew_Escape, "has a store element with an out-of-bound index\n", access);
+                return true;
+            }
+
+            // We are not yet encoding magic hole constants in resume points.
+            if (access->toStoreElement()->value()->type() == MIRType::MagicHole) {
+                JitSpewDef(JitSpew_Escape, "has a store element with an magic-hole constant\n", access);
+                return true;
+            }
+            break;
+          }
+
+          case MDefinition::Op_SetInitializedLength:
+            MOZ_ASSERT(access->toSetInitializedLength()->elements() == def);
+            break;
+
+          case MDefinition::Op_InitializedLength:
+            MOZ_ASSERT(access->toInitializedLength()->elements() == def);
+            break;
+
+          case MDefinition::Op_ArrayLength:
+            MOZ_ASSERT(access->toArrayLength()->elements() == def);
+            break;
+
+          default:
+            JitSpewDef(JitSpew_Escape, "is escaped by\n", access);
+            return true;
+        }
+    }
+    JitSpew(JitSpew_Escape, "Elements is not escaped");
+    return false;
+}
+
+// Returns False if the array is not escaped and if it is optimizable by
+// ScalarReplacementOfArray.
+//
+// For the moment, this code is dumb as it only supports arrays which are not
+// changing length, with only access with known constants.
+static bool
+IsArrayEscaped(MInstruction* ins)
+{
+    MOZ_ASSERT(ins->type() == MIRType::Object);
+    MOZ_ASSERT(ins->isNewArray());
+    uint32_t length = ins->toNewArray()->length();
+
+    JitSpewDef(JitSpew_Escape, "Check array\n", ins);
+    JitSpewIndent spewIndent(JitSpew_Escape);
+
+    JSObject* obj = ins->toNewArray()->templateObject();
+    if (!obj) {
+        JitSpew(JitSpew_Escape, "No template object defined.");
+        return true;
+    }
+
+    if (obj->is<UnboxedArrayObject>()) {
+        JitSpew(JitSpew_Escape, "Template object is an unboxed plain object.");
+        return true;
+    }
+
+    if (length >= 16) {
+        JitSpew(JitSpew_Escape, "Array has too many elements");
+        return true;
+    }
+
+    // Check if the object is escaped. If the object is not the first argument
+    // of either a known Store / Load, then we consider it as escaped. This is a
+    // cheap and conservative escape analysis.
+    for (MUseIterator i(ins->usesBegin()); i != ins->usesEnd(); i++) {
+        MNode* consumer = (*i)->consumer();
+        if (!consumer->isDefinition()) {
+            // Cannot optimize if it is observable from fun.arguments or others.
+            if (!consumer->toResumePoint()->isRecoverableOperand(*i)) {
+                JitSpew(JitSpew_Escape, "Observable array cannot be recovered");
+                return true;
+            }
+            continue;
+        }
+
+        MDefinition* def = consumer->toDefinition();
+        switch (def->op()) {
+          case MDefinition::Op_Elements: {
+            MElements *elem = def->toElements();
+            MOZ_ASSERT(elem->object() == ins);
+            if (IsElementEscaped(elem, length)) {
+                JitSpewDef(JitSpew_Escape, "is indirectly escaped by\n", elem);
+                return true;
+            }
+
+            break;
+          }
+
+          // This instruction is a no-op used to verify that scalar replacement
+          // is working as expected in jit-test.
+          case MDefinition::Op_AssertRecoveredOnBailout:
+            break;
+
+          default:
+            JitSpewDef(JitSpew_Escape, "is escaped by\n", def);
+            return true;
+        }
+    }
+
+    JitSpew(JitSpew_Escape, "Array is not escaped");
+    return false;
+}
+
+// This class replaces every MStoreElement and MSetInitializedLength by an
+// MArrayState which emulates the content of the array. All MLoadElement,
+// MInitializedLength and MArrayLength are replaced by the corresponding value.
+//
+// In order to restore the value of the array correctly in case of bailouts, we
+// replace all reference of the allocation by the MArrayState definition.
+class ArrayMemoryView : public MDefinitionVisitorDefaultNoop
+{
+  public:
+    typedef MArrayState BlockState;
+    static const char* phaseName;
+
+  private:
+    TempAllocator& alloc_;
+    MConstant* undefinedVal_;
+    MConstant* length_;
+    MInstruction* arr_;
+    MBasicBlock* startBlock_;
+    BlockState* state_;
+
+    // Used to improve the memory usage by sharing common modification.
+    const MResumePoint* lastResumePoint_;
+
+    bool oom_;
+
+  public:
+    ArrayMemoryView(TempAllocator& alloc, MInstruction* arr);
+
+    MBasicBlock* startingBlock();
+    bool initStartingState(BlockState** pState);
+
+    void setEntryBlockState(BlockState* state);
+    bool mergeIntoSuccessorState(MBasicBlock* curr, MBasicBlock* succ, BlockState** pSuccState);
+
+#ifdef DEBUG
+    void assertSuccess();
+#else
+    void assertSuccess() {}
+#endif
+
+    bool oom() const { return oom_; }
+
+  private:
+    bool isArrayStateElements(MDefinition* elements);
+    void discardInstruction(MInstruction* ins, MDefinition* elements);
+
+  public:
+    void visitResumePoint(MResumePoint* rp);
+    void visitArrayState(MArrayState* ins);
+    void visitStoreElement(MStoreElement* ins);
+    void visitLoadElement(MLoadElement* ins);
+    void visitSetInitializedLength(MSetInitializedLength* ins);
+    void visitInitializedLength(MInitializedLength* ins);
+    void visitArrayLength(MArrayLength* ins);
+};
+
+const char* ArrayMemoryView::phaseName = "Scalar Replacement of Array";
+
+ArrayMemoryView::ArrayMemoryView(TempAllocator& alloc, MInstruction* arr)
+  : alloc_(alloc),
+    undefinedVal_(nullptr),
+    length_(nullptr),
+    arr_(arr),
+    startBlock_(arr->block()),
+    state_(nullptr),
+    lastResumePoint_(nullptr),
+    oom_(false)
+{
+    // Annotate snapshots RValue such that we recover the store first.
+    arr_->setIncompleteObject();
+
+    // Annotate the instruction such that we do not replace it by a
+    // Magic(JS_OPTIMIZED_OUT) in case of removed uses.
+    arr_->setImplicitlyUsedUnchecked();
+}
+
+MBasicBlock*
+ArrayMemoryView::startingBlock()
+{
+    return startBlock_;
+}
+
+bool
+ArrayMemoryView::initStartingState(BlockState** pState)
+{
+    // Uninitialized elements have an "undefined" value.
+    undefinedVal_ = MConstant::New(alloc_, UndefinedValue());
+    MConstant* initLength = MConstant::New(alloc_, Int32Value(0));
+    arr_->block()->insertBefore(arr_, undefinedVal_);
+    arr_->block()->insertBefore(arr_, initLength);
+
+    // Create a new block state and insert at it at the location of the new array.
+    BlockState* state = BlockState::New(alloc_, arr_, undefinedVal_, initLength);
+    if (!state)
+        return false;
+
+    startBlock_->insertAfter(arr_, state);
+
+    // Hold out of resume point until it is visited.
+    state->setInWorklist();
+
+    *pState = state;
+    return true;
+}
+
+void
+ArrayMemoryView::setEntryBlockState(BlockState* state)
+{
+    state_ = state;
+}
+
+bool
+ArrayMemoryView::mergeIntoSuccessorState(MBasicBlock* curr, MBasicBlock* succ,
+                                          BlockState** pSuccState)
+{
+    BlockState* succState = *pSuccState;
+
+    // When a block has no state yet, create an empty one for the
+    // successor.
+    if (!succState) {
+        // If the successor is not dominated then the array cannot flow
+        // in this basic block without a Phi.  We know that no Phi exist
+        // in non-dominated successors as the conservative escaped
+        // analysis fails otherwise.  Such condition can succeed if the
+        // successor is a join at the end of a if-block and the array
+        // only exists within the branch.
+        if (!startBlock_->dominates(succ))
+            return true;
+
+        // If there is only one predecessor, carry over the last state of the
+        // block to the successor.  As the block state is immutable, if the
+        // current block has multiple successors, they will share the same entry
+        // state.
+        if (succ->numPredecessors() <= 1 || !state_->numElements()) {
+            *pSuccState = state_;
+            return true;
+        }
+
+        // If we have multiple predecessors, then we allocate one Phi node for
+        // each predecessor, and create a new block state which only has phi
+        // nodes.  These would later be removed by the removal of redundant phi
+        // nodes.
+        succState = BlockState::Copy(alloc_, state_);
+        if (!succState)
+            return false;
+
+        size_t numPreds = succ->numPredecessors();
+        for (size_t index = 0; index < state_->numElements(); index++) {
+            MPhi* phi = MPhi::New(alloc_);
+            if (!phi->reserveLength(numPreds))
+                return false;
+
+            // Fill the input of the successors Phi with undefined
+            // values, and each block later fills the Phi inputs.
+            for (size_t p = 0; p < numPreds; p++)
+                phi->addInput(undefinedVal_);
+
+            // Add Phi in the list of Phis of the basic block.
+            succ->addPhi(phi);
+            succState->setElement(index, phi);
+        }
+
+        // Insert the newly created block state instruction at the beginning
+        // of the successor block, after all the phi nodes.  Note that it
+        // would be captured by the entry resume point of the successor
+        // block.
+        succ->insertBefore(succ->safeInsertTop(), succState);
+        *pSuccState = succState;
+    }
+
+    MOZ_ASSERT_IF(succ == startBlock_, startBlock_->isLoopHeader());
+    if (succ->numPredecessors() > 1 && succState->numElements() && succ != startBlock_) {
+        // We need to re-compute successorWithPhis as the previous EliminatePhis
+        // phase might have removed all the Phis from the successor block.
+        size_t currIndex;
+        MOZ_ASSERT(!succ->phisEmpty());
+        if (curr->successorWithPhis()) {
+            MOZ_ASSERT(curr->successorWithPhis() == succ);
+            currIndex = curr->positionInPhiSuccessor();
+        } else {
+            currIndex = succ->indexForPredecessor(curr);
+            curr->setSuccessorWithPhis(succ, currIndex);
+        }
+        MOZ_ASSERT(succ->getPredecessor(currIndex) == curr);
+
+        // Copy the current element states to the index of current block in all
+        // the Phi created during the first visit of the successor.
+        for (size_t index = 0; index < state_->numElements(); index++) {
+            MPhi* phi = succState->getElement(index)->toPhi();
+            phi->replaceOperand(currIndex, state_->getElement(index));
+        }
+    }
+
+    return true;
+}
+
+#ifdef DEBUG
+void
+ArrayMemoryView::assertSuccess()
+{
+    MOZ_ASSERT(!arr_->hasLiveDefUses());
+}
+#endif
+
+void
+ArrayMemoryView::visitResumePoint(MResumePoint* rp)
+{
+    // As long as the MArrayState is not yet seen next to the allocation, we do
+    // not patch the resume point to recover the side effects.
+    if (!state_->isInWorklist()) {
+        rp->addStore(alloc_, state_, lastResumePoint_);
+        lastResumePoint_ = rp;
+    }
+}
+
+void
+ArrayMemoryView::visitArrayState(MArrayState* ins)
+{
+    if (ins->isInWorklist())
+        ins->setNotInWorklist();
+}
+
+bool
+ArrayMemoryView::isArrayStateElements(MDefinition* elements)
+{
+    return elements->isElements() && elements->toElements()->object() == arr_;
+}
+
+void
+ArrayMemoryView::discardInstruction(MInstruction* ins, MDefinition* elements)
+{
+    MOZ_ASSERT(elements->isElements());
+    ins->block()->discard(ins);
+    if (!elements->hasLiveDefUses())
+        elements->block()->discard(elements->toInstruction());
+}
+
+void
+ArrayMemoryView::visitStoreElement(MStoreElement* ins)
+{
+    // Skip other array objects.
+    MDefinition* elements = ins->elements();
+    if (!isArrayStateElements(elements))
+        return;
+
+    // Register value of the setter in the state.
+    int32_t index;
+    MOZ_ALWAYS_TRUE(IndexOf(ins, &index));
+    state_ = BlockState::Copy(alloc_, state_);
+    if (!state_) {
+        oom_ = true;
+        return;
+    }
+
+    state_->setElement(index, ins->value());
+    ins->block()->insertBefore(ins, state_);
+
+    // Remove original instruction.
+    discardInstruction(ins, elements);
+}
+
+void
+ArrayMemoryView::visitLoadElement(MLoadElement* ins)
+{
+    // Skip other array objects.
+    MDefinition* elements = ins->elements();
+    if (!isArrayStateElements(elements))
+        return;
+
+    // Replace by the value contained at the index.
+    int32_t index;
+    MOZ_ALWAYS_TRUE(IndexOf(ins, &index));
+    ins->replaceAllUsesWith(state_->getElement(index));
+
+    // Remove original instruction.
+    discardInstruction(ins, elements);
+}
+
+void
+ArrayMemoryView::visitSetInitializedLength(MSetInitializedLength* ins)
+{
+    // Skip other array objects.
+    MDefinition* elements = ins->elements();
+    if (!isArrayStateElements(elements))
+        return;
+
+    // Replace by the new initialized length.  Note that the argument of
+    // MSetInitalizedLength is the last index and not the initialized length.
+    // To obtain the length, we need to add 1 to it, and thus we need to create
+    // a new constant that we register in the ArrayState.
+    state_ = BlockState::Copy(alloc_, state_);
+    if (!state_) {
+        oom_ = true;
+        return;
+    }
+
+    int32_t initLengthValue = ins->index()->maybeConstantValue()->toInt32() + 1;
+    MConstant* initLength = MConstant::New(alloc_, Int32Value(initLengthValue));
+    ins->block()->insertBefore(ins, initLength);
+    ins->block()->insertBefore(ins, state_);
+    state_->setInitializedLength(initLength);
+
+    // Remove original instruction.
+    discardInstruction(ins, elements);
+}
+
+void
+ArrayMemoryView::visitInitializedLength(MInitializedLength* ins)
+{
+    // Skip other array objects.
+    MDefinition* elements = ins->elements();
+    if (!isArrayStateElements(elements))
+        return;
+
+    // Replace by the value of the length.
+    ins->replaceAllUsesWith(state_->initializedLength());
+
+    // Remove original instruction.
+    discardInstruction(ins, elements);
+}
+
+void
+ArrayMemoryView::visitArrayLength(MArrayLength* ins)
+{
+    // Skip other array objects.
+    MDefinition* elements = ins->elements();
+    if (!isArrayStateElements(elements))
+        return;
+
+    // Replace by the value of the length.
+    if (!length_) {
+        length_ = MConstant::New(alloc_, Int32Value(state_->numElements()));
+        arr_->block()->insertBefore(arr_, length_);
+    }
+    ins->replaceAllUsesWith(length_);
+
+    // Remove original instruction.
+    discardInstruction(ins, elements);
+}
+
+bool
+ScalarReplacement(MIRGenerator* mir, MIRGraph& graph)
+{
+    EmulateStateOf<ObjectMemoryView> replaceObject(mir, graph);
+    EmulateStateOf<ArrayMemoryView> replaceArray(mir, graph);
+    bool addedPhi = false;
+
+    for (ReversePostorderIterator block = graph.rpoBegin(); block != graph.rpoEnd(); block++) {
+        if (mir->shouldCancel("Scalar Replacement (main loop)"))
+            return false;
+
+        for (MInstructionIterator ins = block->begin(); ins != block->end(); ins++) {
+            if ((ins->isNewObject() || ins->isCreateThisWithTemplate() || ins->isNewCallObject()) &&
+                !IsObjectEscaped(*ins))
+            {
+                ObjectMemoryView view(graph.alloc(), *ins);
+                if (!replaceObject.run(view))
+                    return false;
+                view.assertSuccess();
+                addedPhi = true;
+                continue;
+            }
+
+            if (ins->isNewArray() && !IsArrayEscaped(*ins)) {
+                ArrayMemoryView view(graph.alloc(), *ins);
+                if (!replaceArray.run(view))
+                    return false;
+                view.assertSuccess();
+                addedPhi = true;
+                continue;
+            }
+        }
+    }
+
+    if (addedPhi) {
+        // Phis added by Scalar Replacement are only redundant Phis which are
+        // not directly captured by any resume point but only by the MDefinition
+        // state. The conservative observability only focuses on Phis which are
+        // not used as resume points operands.
+        AssertExtendedGraphCoherency(graph);
+        if (!EliminatePhis(mir, graph, ConservativeObservability))
+            return false;
+    }
+
+    return true;
+}
+
+} /* namespace jit */
+} /* namespace js */