text: //===-- StatepointLowering.cpp - SDAGBuilder's statepoint code -----------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file includes support code use by SelectionDAGBuilder when lowering a
  // statepoint sequence in SelectionDAG IR.
  //
  //===----------------------------------------------------------------------===//
  
  #include "StatepointLowering.h"
  #include "SelectionDAGBuilder.h"
  #include "llvm/ADT/SmallSet.h"
  #include "llvm/ADT/Statistic.h"
  #include "llvm/CodeGen/FunctionLoweringInfo.h"
  #include "llvm/CodeGen/MachineFrameInfo.h"
  #include "llvm/CodeGen/GCMetadata.h"
  #include "llvm/CodeGen/GCStrategy.h"
  #include "llvm/CodeGen/SelectionDAG.h"
  #include "llvm/CodeGen/StackMaps.h"
  #include "llvm/IR/CallingConv.h"
  #include "llvm/IR/Instructions.h"
  #include "llvm/IR/IntrinsicInst.h"
  #include "llvm/IR/Intrinsics.h"
  #include "llvm/IR/Statepoint.h"
  #include "llvm/Target/TargetLowering.h"
  #include <algorithm>
  using namespace llvm;
  
  #define DEBUG_TYPE "statepoint-lowering"
  
  STATISTIC(NumSlotsAllocatedForStatepoints,
            "Number of stack slots allocated for statepoints");
  STATISTIC(NumOfStatepoints, "Number of statepoint nodes encountered");
  STATISTIC(StatepointMaxSlotsRequired,
            "Maximum number of stack slots required for a singe statepoint");
  
  static void pushStackMapConstant(SmallVectorImpl<SDValue>& Ops,
                                   SelectionDAGBuilder &Builder, uint64_t Value) {
    SDLoc L = Builder.getCurSDLoc();
    Ops.push_back(Builder.DAG.getTargetConstant(StackMaps::ConstantOp, L,
                                                MVT::i64));
    Ops.push_back(Builder.DAG.getTargetConstant(Value, L, MVT::i64));
  }
  
  void StatepointLoweringState::startNewStatepoint(SelectionDAGBuilder &Builder) {
    // Consistency check
    assert(PendingGCRelocateCalls.empty() &&
           "Trying to visit statepoint before finished processing previous one");
    Locations.clear();
    NextSlotToAllocate = 0;
    // Need to resize this on each safepoint - we need the two to stay in sync and
    // the clear patterns of a SelectionDAGBuilder have no relation to
    // FunctionLoweringInfo.  Also need to ensure used bits get cleared.
    AllocatedStackSlots.clear();
    AllocatedStackSlots.resize(Builder.FuncInfo.StatepointStackSlots.size());
  }
  
  void StatepointLoweringState::clear() {
    Locations.clear();
    AllocatedStackSlots.clear();
    assert(PendingGCRelocateCalls.empty() &&
           "cleared before statepoint sequence completed");
  }
  
  SDValue
  StatepointLoweringState::allocateStackSlot(EVT ValueType,
                                             SelectionDAGBuilder &Builder) {
    NumSlotsAllocatedForStatepoints++;
    MachineFrameInfo &MFI = Builder.DAG.getMachineFunction().getFrameInfo();
  
    unsigned SpillSize = ValueType.getSizeInBits() / 8;
    assert((SpillSize * 8) == ValueType.getSizeInBits() && "Size not in bytes?");
  
    // First look for a previously created stack slot which is not in
    // use (accounting for the fact arbitrary slots may already be
    // reserved), or to create a new stack slot and use it.
  
    const size_t NumSlots = AllocatedStackSlots.size();
    assert(NextSlotToAllocate <= NumSlots && "Broken invariant");
  
    assert(AllocatedStackSlots.size() ==
           Builder.FuncInfo.StatepointStackSlots.size() &&
           "Broken invariant");
  
    for (; NextSlotToAllocate < NumSlots; NextSlotToAllocate++) {
      if (!AllocatedStackSlots.test(NextSlotToAllocate)) {
        const int FI = Builder.FuncInfo.StatepointStackSlots[NextSlotToAllocate];
        if (MFI.getObjectSize(FI) == SpillSize) {
          AllocatedStackSlots.set(NextSlotToAllocate);
          // TODO: Is ValueType the right thing to use here?
          return Builder.DAG.getFrameIndex(FI, ValueType);
        }
      }
    }
  
    // Couldn't find a free slot, so create a new one:
  
    SDValue SpillSlot = Builder.DAG.CreateStackTemporary(ValueType);
    const unsigned FI = cast<FrameIndexSDNode>(SpillSlot)->getIndex();
    MFI.markAsStatepointSpillSlotObjectIndex(FI);
  
    Builder.FuncInfo.StatepointStackSlots.push_back(FI);
    AllocatedStackSlots.resize(AllocatedStackSlots.size()+1, true);
    assert(AllocatedStackSlots.size() ==
           Builder.FuncInfo.StatepointStackSlots.size() &&
           "Broken invariant");
  
    StatepointMaxSlotsRequired = std::max<unsigned long>(
        StatepointMaxSlotsRequired, Builder.FuncInfo.StatepointStackSlots.size());
  
    return SpillSlot;
  }
  
  /// Utility function for reservePreviousStackSlotForValue. Tries to find
  /// stack slot index to which we have spilled value for previous statepoints.
  /// LookUpDepth specifies maximum DFS depth this function is allowed to look.
  static Optional<int> findPreviousSpillSlot(const Value *Val,
                                             SelectionDAGBuilder &Builder,
                                             int LookUpDepth) {
    // Can not look any further - give up now
    if (LookUpDepth <= 0)
      return None;
  
    // Spill location is known for gc relocates
    if (const auto *Relocate = dyn_cast<GCRelocateInst>(Val)) {
      const auto &SpillMap =
          Builder.FuncInfo.StatepointSpillMaps[Relocate->getStatepoint()];
  
      auto It = SpillMap.find(Relocate->getDerivedPtr());
      if (It == SpillMap.end())
        return None;
  
      return It->second;
    }
  
    // Look through bitcast instructions.
    if (const BitCastInst *Cast = dyn_cast<BitCastInst>(Val))
      return findPreviousSpillSlot(Cast->getOperand(0), Builder, LookUpDepth - 1);
  
    // Look through phi nodes
    // All incoming values should have same known stack slot, otherwise result
    // is unknown.
    if (const PHINode *Phi = dyn_cast<PHINode>(Val)) {
      Optional<int> MergedResult = None;
  
      for (auto &IncomingValue : Phi->incoming_values()) {
        Optional<int> SpillSlot =
            findPreviousSpillSlot(IncomingValue, Builder, LookUpDepth - 1);
        if (!SpillSlot.hasValue())
          return None;
  
        if (MergedResult.hasValue() && *MergedResult != *SpillSlot)
          return None;
  
        MergedResult = SpillSlot;
      }
      return MergedResult;
    }
  
    // TODO: We can do better for PHI nodes. In cases like this:
    //   ptr = phi(relocated_pointer, not_relocated_pointer)
    //   statepoint(ptr)
    // We will return that stack slot for ptr is unknown. And later we might
    // assign different stack slots for ptr and relocated_pointer. This limits
    // llvm's ability to remove redundant stores.
    // Unfortunately it's hard to accomplish in current infrastructure.
    // We use this function to eliminate spill store completely, while
    // in example we still need to emit store, but instead of any location
    // we need to use special "preferred" location.
  
    // TODO: handle simple updates.  If a value is modified and the original
    // value is no longer live, it would be nice to put the modified value in the
    // same slot.  This allows folding of the memory accesses for some
    // instructions types (like an increment).
    //   statepoint (i)
    //   i1 = i+1
    //   statepoint (i1)
    // However we need to be careful for cases like this:
    //   statepoint(i)
    //   i1 = i+1
    //   statepoint(i, i1)
    // Here we want to reserve spill slot for 'i', but not for 'i+1'. If we just
    // put handling of simple modifications in this function like it's done
    // for bitcasts we might end up reserving i's slot for 'i+1' because order in
    // which we visit values is unspecified.
  
    // Don't know any information about this instruction
    return None;
  }
  
  /// Try to find existing copies of the incoming values in stack slots used for
  /// statepoint spilling.  If we can find a spill slot for the incoming value,
  /// mark that slot as allocated, and reuse the same slot for this safepoint.
  /// This helps to avoid series of loads and stores that only serve to reshuffle
  /// values on the stack between calls.
  static void reservePreviousStackSlotForValue(const Value *IncomingValue,
                                               SelectionDAGBuilder &Builder) {
  
    SDValue Incoming = Builder.getValue(IncomingValue);
  
    if (isa<ConstantSDNode>(Incoming) || isa<FrameIndexSDNode>(Incoming)) {
      // We won't need to spill this, so no need to check for previously
      // allocated stack slots
      return;
    }
  
    SDValue OldLocation = Builder.StatepointLowering.getLocation(Incoming);
    if (OldLocation.getNode())
      // Duplicates in input
      return;
  
    const int LookUpDepth = 6;
    Optional<int> Index =
        findPreviousSpillSlot(IncomingValue, Builder, LookUpDepth);
    if (!Index.hasValue())
      return;
  
    const auto &StatepointSlots = Builder.FuncInfo.StatepointStackSlots;
  
    auto SlotIt = find(StatepointSlots, *Index);
    assert(SlotIt != StatepointSlots.end() &&
           "Value spilled to the unknown stack slot");
  
    // This is one of our dedicated lowering slots
    const int Offset = std::distance(StatepointSlots.begin(), SlotIt);
    if (Builder.StatepointLowering.isStackSlotAllocated(Offset)) {
      // stack slot already assigned to someone else, can't use it!
      // TODO: currently we reserve space for gc arguments after doing
      // normal allocation for deopt arguments.  We should reserve for
      // _all_ deopt and gc arguments, then start allocating.  This
      // will prevent some moves being inserted when vm state changes,
      // but gc state doesn't between two calls.
      return;
    }
    // Reserve this stack slot
    Builder.StatepointLowering.reserveStackSlot(Offset);
  
    // Cache this slot so we find it when going through the normal
    // assignment loop.
    SDValue Loc = Builder.DAG.getTargetFrameIndex(*Index, Incoming.getValueType());
    Builder.StatepointLowering.setLocation(Incoming, Loc);
  }
  
  /// Remove any duplicate (as SDValues) from the derived pointer pairs.  This
  /// is not required for correctness.  It's purpose is to reduce the size of
  /// StackMap section.  It has no effect on the number of spill slots required
  /// or the actual lowering.
  static void
  removeDuplicateGCPtrs(SmallVectorImpl<const Value *> &Bases,
                        SmallVectorImpl<const Value *> &Ptrs,
                        SmallVectorImpl<const GCRelocateInst *> &Relocs,
                        SelectionDAGBuilder &Builder,
                        FunctionLoweringInfo::StatepointSpillMap &SSM) {
    DenseMap<SDValue, const Value *> Seen;
  
    SmallVector<const Value *, 64> NewBases, NewPtrs;
    SmallVector<const GCRelocateInst *, 64> NewRelocs;
    for (size_t i = 0, e = Ptrs.size(); i < e; i++) {
      SDValue SD = Builder.getValue(Ptrs[i]);
      auto SeenIt = Seen.find(SD);
  
      if (SeenIt == Seen.end()) {
        // Only add non-duplicates
        NewBases.push_back(Bases[i]);
        NewPtrs.push_back(Ptrs[i]);
        NewRelocs.push_back(Relocs[i]);
        Seen[SD] = Ptrs[i];
      } else {
        // Duplicate pointer found, note in SSM and move on:
        SSM.DuplicateMap[Ptrs[i]] = SeenIt->second;
      }
    }
    assert(Bases.size() >= NewBases.size());
    assert(Ptrs.size() >= NewPtrs.size());
    assert(Relocs.size() >= NewRelocs.size());
    Bases = NewBases;
    Ptrs = NewPtrs;
    Relocs = NewRelocs;
    assert(Ptrs.size() == Bases.size());
    assert(Ptrs.size() == Relocs.size());
  }
  
  /// Extract call from statepoint, lower it and return pointer to the
  /// call node. Also update NodeMap so that getValue(statepoint) will
  /// reference lowered call result
  static std::pair<SDValue, SDNode *> lowerCallFromStatepointLoweringInfo(
      SelectionDAGBuilder::StatepointLoweringInfo &SI,
      SelectionDAGBuilder &Builder, SmallVectorImpl<SDValue> &PendingExports) {
  
    SDValue ReturnValue, CallEndVal;
    std::tie(ReturnValue, CallEndVal) =
        Builder.lowerInvokable(SI.CLI, SI.EHPadBB);
    SDNode *CallEnd = CallEndVal.getNode();
  
    // Get a call instruction from the call sequence chain.  Tail calls are not
    // allowed.  The following code is essentially reverse engineering X86's
    // LowerCallTo.
    //
    // We are expecting DAG to have the following form:
    //
    // ch = eh_label (only in case of invoke statepoint)
    //   ch, glue = callseq_start ch
    //   ch, glue = X86::Call ch, glue
    //   ch, glue = callseq_end ch, glue
    //   get_return_value ch, glue
    //
    // get_return_value can either be a sequence of CopyFromReg instructions
    // to grab the return value from the return register(s), or it can be a LOAD
    // to load a value returned by reference via a stack slot.
  
    bool HasDef = !SI.CLI.RetTy->isVoidTy();
    if (HasDef) {
      if (CallEnd->getOpcode() == ISD::LOAD)
        CallEnd = CallEnd->getOperand(0).getNode();
      else
        while (CallEnd->getOpcode() == ISD::CopyFromReg)
          CallEnd = CallEnd->getOperand(0).getNode();
    }
  
    assert(CallEnd->getOpcode() == ISD::CALLSEQ_END && "expected!");
    return std::make_pair(ReturnValue, CallEnd->getOperand(0).getNode());
  }
  
  /// Spill a value incoming to the statepoint. It might be either part of
  /// vmstate
  /// or gcstate. In both cases unconditionally spill it on the stack unless it
  /// is a null constant. Return pair with first element being frame index
  /// containing saved value and second element with outgoing chain from the
  /// emitted store
  static std::pair<SDValue, SDValue>
  spillIncomingStatepointValue(SDValue Incoming, SDValue Chain,
                               SelectionDAGBuilder &Builder) {
    SDValue Loc = Builder.StatepointLowering.getLocation(Incoming);
  
    // Emit new store if we didn't do it for this ptr before
    if (!Loc.getNode()) {
      Loc = Builder.StatepointLowering.allocateStackSlot(Incoming.getValueType(),
                                                         Builder);
      int Index = cast<FrameIndexSDNode>(Loc)->getIndex();
      // We use TargetFrameIndex so that isel will not select it into LEA
      Loc = Builder.DAG.getTargetFrameIndex(Index, Incoming.getValueType());
  
      // TODO: We can create TokenFactor node instead of
      //       chaining stores one after another, this may allow
      //       a bit more optimal scheduling for them
  
  #ifndef NDEBUG
      // Right now we always allocate spill slots that are of the same
      // size as the value we're about to spill (the size of spillee can
      // vary since we spill vectors of pointers too).  At some point we
      // can consider allowing spills of smaller values to larger slots
      // (i.e. change the '==' in the assert below to a '>=').
      MachineFrameInfo &MFI = Builder.DAG.getMachineFunction().getFrameInfo();
      assert((MFI.getObjectSize(Index) * 8) == Incoming.getValueSizeInBits() &&
             "Bad spill:  stack slot does not match!");
  #endif
  
      Chain = Builder.DAG.getStore(Chain, Builder.getCurSDLoc(), Incoming, Loc,
                                   MachinePointerInfo::getFixedStack(
                                       Builder.DAG.getMachineFunction(), Index));
  
      Builder.StatepointLowering.setLocation(Incoming, Loc);
    }
  
    assert(Loc.getNode());
    return std::make_pair(Loc, Chain);
  }
  
  /// Lower a single value incoming to a statepoint node.  This value can be
  /// either a deopt value or a gc value, the handling is the same.  We special
  /// case constants and allocas, then fall back to spilling if required.
  static void lowerIncomingStatepointValue(SDValue Incoming, bool LiveInOnly,
                                           SmallVectorImpl<SDValue> &Ops,
                                           SelectionDAGBuilder &Builder) {
    SDValue Chain = Builder.getRoot();
  
    if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Incoming)) {
      // If the original value was a constant, make sure it gets recorded as
      // such in the stackmap.  This is required so that the consumer can
      // parse any internal format to the deopt state.  It also handles null
      // pointers and other constant pointers in GC states.  Note the constant
      // vectors do not appear to actually hit this path and that anything larger
      // than an i64 value (not type!) will fail asserts here.
      pushStackMapConstant(Ops, Builder, C->getSExtValue());
    } else if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Incoming)) {
      // This handles allocas as arguments to the statepoint (this is only
      // really meaningful for a deopt value.  For GC, we'd be trying to
      // relocate the address of the alloca itself?)
      Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(),
                                                    Incoming.getValueType()));
    } else if (LiveInOnly) {
      // If this value is live in (not live-on-return, or live-through), we can
      // treat it the same way patchpoint treats it's "live in" values.  We'll 
      // end up folding some of these into stack references, but they'll be 
      // handled by the register allocator.  Note that we do not have the notion
      // of a late use so these values might be placed in registers which are 
      // clobbered by the call.  This is fine for live-in.
      Ops.push_back(Incoming);
    } else {
      // Otherwise, locate a spill slot and explicitly spill it so it
      // can be found by the runtime later.  We currently do not support
      // tracking values through callee saved registers to their eventual
      // spill location.  This would be a useful optimization, but would
      // need to be optional since it requires a lot of complexity on the
      // runtime side which not all would support.
      auto Res = spillIncomingStatepointValue(Incoming, Chain, Builder);
      Ops.push_back(Res.first);
      Chain = Res.second;
    }
  
    Builder.DAG.setRoot(Chain);
  }
  
  /// Lower deopt state and gc pointer arguments of the statepoint.  The actual
  /// lowering is described in lowerIncomingStatepointValue.  This function is
  /// responsible for lowering everything in the right position and playing some
  /// tricks to avoid redundant stack manipulation where possible.  On
  /// completion, 'Ops' will contain ready to use operands for machine code
  /// statepoint. The chain nodes will have already been created and the DAG root
  /// will be set to the last value spilled (if any were).
  static void
  lowerStatepointMetaArgs(SmallVectorImpl<SDValue> &Ops,
                          SelectionDAGBuilder::StatepointLoweringInfo &SI,
                          SelectionDAGBuilder &Builder) {
    // Lower the deopt and gc arguments for this statepoint.  Layout will be:
    // deopt argument length, deopt arguments.., gc arguments...
  #ifndef NDEBUG
    if (auto *GFI = Builder.GFI) {
      // Check that each of the gc pointer and bases we've gotten out of the
      // safepoint is something the strategy thinks might be a pointer (or vector
      // of pointers) into the GC heap.  This is basically just here to help catch
      // errors during statepoint insertion. TODO: This should actually be in the
      // Verifier, but we can't get to the GCStrategy from there (yet).
      GCStrategy &S = GFI->getStrategy();
      for (const Value *V : SI.Bases) {
        auto Opt = S.isGCManagedPointer(V->getType()->getScalarType());
        if (Opt.hasValue()) {
          assert(Opt.getValue() &&
                 "non gc managed base pointer found in statepoint");
        }
      }
      for (const Value *V : SI.Ptrs) {
        auto Opt = S.isGCManagedPointer(V->getType()->getScalarType());
        if (Opt.hasValue()) {
          assert(Opt.getValue() &&
                 "non gc managed derived pointer found in statepoint");
        }
      }
      assert(SI.Bases.size() == SI.Ptrs.size() && "Pointer without base!");
    } else {
      assert(SI.Bases.empty() && "No gc specified, so cannot relocate pointers!");
      assert(SI.Ptrs.empty() && "No gc specified, so cannot relocate pointers!");
    }
  #endif
  
    // Figure out what lowering strategy we're going to use for each part
    // Note: Is is conservatively correct to lower both "live-in" and "live-out"
    // as "live-through". A "live-through" variable is one which is "live-in",
    // "live-out", and live throughout the lifetime of the call (i.e. we can find
    // it from any PC within the transitive callee of the statepoint).  In
    // particular, if the callee spills callee preserved registers we may not
    // be able to find a value placed in that register during the call.  This is
    // fine for live-out, but not for live-through.  If we were willing to make
    // assumptions about the code generator producing the callee, we could
    // potentially allow live-through values in callee saved registers.
    const bool LiveInDeopt =
      SI.StatepointFlags & (uint64_t)StatepointFlags::DeoptLiveIn;
  
    auto isGCValue =[&](const Value *V) {
      return is_contained(SI.Ptrs, V) || is_contained(SI.Bases, V);
    };
    
    // Before we actually start lowering (and allocating spill slots for values),
    // reserve any stack slots which we judge to be profitable to reuse for a
    // particular value.  This is purely an optimization over the code below and
    // doesn't change semantics at all.  It is important for performance that we
    // reserve slots for both deopt and gc values before lowering either.
    for (const Value *V : SI.DeoptState) {
      if (!LiveInDeopt || isGCValue(V))
        reservePreviousStackSlotForValue(V, Builder);
    }
    for (unsigned i = 0; i < SI.Bases.size(); ++i) {
      reservePreviousStackSlotForValue(SI.Bases[i], Builder);
      reservePreviousStackSlotForValue(SI.Ptrs[i], Builder);
    }
  
    // First, prefix the list with the number of unique values to be
    // lowered.  Note that this is the number of *Values* not the
    // number of SDValues required to lower them.
    const int NumVMSArgs = SI.DeoptState.size();
    pushStackMapConstant(Ops, Builder, NumVMSArgs);
  
    // The vm state arguments are lowered in an opaque manner.  We do not know
    // what type of values are contained within.
    for (const Value *V : SI.DeoptState) {
      SDValue Incoming = Builder.getValue(V);
      const bool LiveInValue = LiveInDeopt && !isGCValue(V);
      lowerIncomingStatepointValue(Incoming, LiveInValue, Ops, Builder);
    }
  
    // Finally, go ahead and lower all the gc arguments.  There's no prefixed
    // length for this one.  After lowering, we'll have the base and pointer
    // arrays interwoven with each (lowered) base pointer immediately followed by
    // it's (lowered) derived pointer.  i.e
    // (base[0], ptr[0], base[1], ptr[1], ...)
    for (unsigned i = 0; i < SI.Bases.size(); ++i) {
      const Value *Base = SI.Bases[i];
      lowerIncomingStatepointValue(Builder.getValue(Base), /*LiveInOnly*/ false,
                                   Ops, Builder);
  
      const Value *Ptr = SI.Ptrs[i];
      lowerIncomingStatepointValue(Builder.getValue(Ptr), /*LiveInOnly*/ false,
                                   Ops, Builder);
    }
  
    // If there are any explicit spill slots passed to the statepoint, record
    // them, but otherwise do not do anything special.  These are user provided
    // allocas and give control over placement to the consumer.  In this case,
    // it is the contents of the slot which may get updated, not the pointer to
    // the alloca
    for (Value *V : SI.GCArgs) {
      SDValue Incoming = Builder.getValue(V);
      if (FrameIndexSDNode *FI = dyn_cast<FrameIndexSDNode>(Incoming)) {
        // This handles allocas as arguments to the statepoint
        Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(),
                                                      Incoming.getValueType()));
      }
    }
  
    // Record computed locations for all lowered values.
    // This can not be embedded in lowering loops as we need to record *all*
    // values, while previous loops account only values with unique SDValues.
    const Instruction *StatepointInstr = SI.StatepointInstr;
    auto &SpillMap = Builder.FuncInfo.StatepointSpillMaps[StatepointInstr];
  
    for (const GCRelocateInst *Relocate : SI.GCRelocates) {
      const Value *V = Relocate->getDerivedPtr();
      SDValue SDV = Builder.getValue(V);
      SDValue Loc = Builder.StatepointLowering.getLocation(SDV);
  
      if (Loc.getNode()) {
        SpillMap.SlotMap[V] = cast<FrameIndexSDNode>(Loc)->getIndex();
      } else {
        // Record value as visited, but not spilled. This is case for allocas
        // and constants. For this values we can avoid emitting spill load while
        // visiting corresponding gc_relocate.
        // Actually we do not need to record them in this map at all.
        // We do this only to check that we are not relocating any unvisited
        // value.
        SpillMap.SlotMap[V] = None;
  
        // Default llvm mechanisms for exporting values which are used in
        // different basic blocks does not work for gc relocates.
        // Note that it would be incorrect to teach llvm that all relocates are
        // uses of the corresponding values so that it would automatically
        // export them. Relocates of the spilled values does not use original
        // value.
        if (Relocate->getParent() != StatepointInstr->getParent())
          Builder.ExportFromCurrentBlock(V);
      }
    }
  }
  
  SDValue SelectionDAGBuilder::LowerAsSTATEPOINT(
      SelectionDAGBuilder::StatepointLoweringInfo &SI) {
    // The basic scheme here is that information about both the original call and
    // the safepoint is encoded in the CallInst.  We create a temporary call and
    // lower it, then reverse engineer the calling sequence.
  
    NumOfStatepoints++;
    // Clear state
    StatepointLowering.startNewStatepoint(*this);
  
  #ifndef NDEBUG
    // We schedule gc relocates before removeDuplicateGCPtrs since we _will_
    // encounter the duplicate gc relocates we elide in removeDuplicateGCPtrs.
    for (auto *Reloc : SI.GCRelocates)
      if (Reloc->getParent() == SI.StatepointInstr->getParent())
        StatepointLowering.scheduleRelocCall(*Reloc);
  #endif
  
    // Remove any redundant llvm::Values which map to the same SDValue as another
    // input.  Also has the effect of removing duplicates in the original
    // llvm::Value input list as well.  This is a useful optimization for
    // reducing the size of the StackMap section.  It has no other impact.
    removeDuplicateGCPtrs(SI.Bases, SI.Ptrs, SI.GCRelocates, *this,
                          FuncInfo.StatepointSpillMaps[SI.StatepointInstr]);
    assert(SI.Bases.size() == SI.Ptrs.size() &&
           SI.Ptrs.size() == SI.GCRelocates.size());
  
    // Lower statepoint vmstate and gcstate arguments
    SmallVector<SDValue, 10> LoweredMetaArgs;
    lowerStatepointMetaArgs(LoweredMetaArgs, SI, *this);
  
    // Now that we've emitted the spills, we need to update the root so that the
    // call sequence is ordered correctly.
    SI.CLI.setChain(getRoot());
  
    // Get call node, we will replace it later with statepoint
    SDValue ReturnVal;
    SDNode *CallNode;
    std::tie(ReturnVal, CallNode) =
        lowerCallFromStatepointLoweringInfo(SI, *this, PendingExports);
  
    // Construct the actual GC_TRANSITION_START, STATEPOINT, and GC_TRANSITION_END
    // nodes with all the appropriate arguments and return values.
  
    // Call Node: Chain, Target, {Args}, RegMask, [Glue]
    SDValue Chain = CallNode->getOperand(0);
  
    SDValue Glue;
    bool CallHasIncomingGlue = CallNode->getGluedNode();
    if (CallHasIncomingGlue) {
      // Glue is always last operand
      Glue = CallNode->getOperand(CallNode->getNumOperands() - 1);
    }
  
    // Build the GC_TRANSITION_START node if necessary.
    //
    // The operands to the GC_TRANSITION_{START,END} nodes are laid out in the
    // order in which they appear in the call to the statepoint intrinsic. If
    // any of the operands is a pointer-typed, that operand is immediately
    // followed by a SRCVALUE for the pointer that may be used during lowering
    // (e.g. to form MachinePointerInfo values for loads/stores).
    const bool IsGCTransition =
        (SI.StatepointFlags & (uint64_t)StatepointFlags::GCTransition) ==
        (uint64_t)StatepointFlags::GCTransition;
    if (IsGCTransition) {
      SmallVector<SDValue, 8> TSOps;
  
      // Add chain
      TSOps.push_back(Chain);
  
      // Add GC transition arguments
      for (const Value *V : SI.GCTransitionArgs) {
        TSOps.push_back(getValue(V));
        if (V->getType()->isPointerTy())
          TSOps.push_back(DAG.getSrcValue(V));
      }
  
      // Add glue if necessary
      if (CallHasIncomingGlue)
        TSOps.push_back(Glue);
  
      SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
  
      SDValue GCTransitionStart =
          DAG.getNode(ISD::GC_TRANSITION_START, getCurSDLoc(), NodeTys, TSOps);
  
      Chain = GCTransitionStart.getValue(0);
      Glue = GCTransitionStart.getValue(1);
    }
  
    // TODO: Currently, all of these operands are being marked as read/write in
    // PrologEpilougeInserter.cpp, we should special case the VMState arguments
    // and flags to be read-only.
    SmallVector<SDValue, 40> Ops;
  
    // Add the <id> and <numBytes> constants.
    Ops.push_back(DAG.getTargetConstant(SI.ID, getCurSDLoc(), MVT::i64));
    Ops.push_back(
        DAG.getTargetConstant(SI.NumPatchBytes, getCurSDLoc(), MVT::i32));
  
    // Calculate and push starting position of vmstate arguments
    // Get number of arguments incoming directly into call node
    unsigned NumCallRegArgs =
        CallNode->getNumOperands() - (CallHasIncomingGlue ? 4 : 3);
    Ops.push_back(DAG.getTargetConstant(NumCallRegArgs, getCurSDLoc(), MVT::i32));
  
    // Add call target
    SDValue CallTarget = SDValue(CallNode->getOperand(1).getNode(), 0);
    Ops.push_back(CallTarget);
  
    // Add call arguments
    // Get position of register mask in the call
    SDNode::op_iterator RegMaskIt;
    if (CallHasIncomingGlue)
      RegMaskIt = CallNode->op_end() - 2;
    else
      RegMaskIt = CallNode->op_end() - 1;
    Ops.insert(Ops.end(), CallNode->op_begin() + 2, RegMaskIt);
  
    // Add a constant argument for the calling convention
    pushStackMapConstant(Ops, *this, SI.CLI.CallConv);
  
    // Add a constant argument for the flags
    uint64_t Flags = SI.StatepointFlags;
    assert(((Flags & ~(uint64_t)StatepointFlags::MaskAll) == 0) &&
           "Unknown flag used");
    pushStackMapConstant(Ops, *this, Flags);
  
    // Insert all vmstate and gcstate arguments
    Ops.insert(Ops.end(), LoweredMetaArgs.begin(), LoweredMetaArgs.end());
  
    // Add register mask from call node
    Ops.push_back(*RegMaskIt);
  
    // Add chain
    Ops.push_back(Chain);
  
    // Same for the glue, but we add it only if original call had it
    if (Glue.getNode())
      Ops.push_back(Glue);
  
    // Compute return values.  Provide a glue output since we consume one as
    // input.  This allows someone else to chain off us as needed.
    SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
  
    SDNode *StatepointMCNode =
        DAG.getMachineNode(TargetOpcode::STATEPOINT, getCurSDLoc(), NodeTys, Ops);
  
    SDNode *SinkNode = StatepointMCNode;
  
    // Build the GC_TRANSITION_END node if necessary.
    //
    // See the comment above regarding GC_TRANSITION_START for the layout of
    // the operands to the GC_TRANSITION_END node.
    if (IsGCTransition) {
      SmallVector<SDValue, 8> TEOps;
  
      // Add chain
      TEOps.push_back(SDValue(StatepointMCNode, 0));
  
      // Add GC transition arguments
      for (const Value *V : SI.GCTransitionArgs) {
        TEOps.push_back(getValue(V));
        if (V->getType()->isPointerTy())
          TEOps.push_back(DAG.getSrcValue(V));
      }
  
      // Add glue
      TEOps.push_back(SDValue(StatepointMCNode, 1));
  
      SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
  
      SDValue GCTransitionStart =
          DAG.getNode(ISD::GC_TRANSITION_END, getCurSDLoc(), NodeTys, TEOps);
  
      SinkNode = GCTransitionStart.getNode();
    }
  
    // Replace original call
    DAG.ReplaceAllUsesWith(CallNode, SinkNode); // This may update Root
    // Remove original call node
    DAG.DeleteNode(CallNode);
  
    // DON'T set the root - under the assumption that it's already set past the
    // inserted node we created.
  
    // TODO: A better future implementation would be to emit a single variable
    // argument, variable return value STATEPOINT node here and then hookup the
    // return value of each gc.relocate to the respective output of the
    // previously emitted STATEPOINT value.  Unfortunately, this doesn't appear
    // to actually be possible today.
  
    return ReturnVal;
  }
  
  void
  SelectionDAGBuilder::LowerStatepoint(ImmutableStatepoint ISP,
                                       const BasicBlock *EHPadBB /*= nullptr*/) {
    assert(ISP.getCallSite().getCallingConv() != CallingConv::AnyReg &&
           "anyregcc is not supported on statepoints!");
  
  #ifndef NDEBUG
    // If this is a malformed statepoint, report it early to simplify debugging.
    // This should catch any IR level mistake that's made when constructing or
    // transforming statepoints.
    ISP.verify();
  
    // Check that the associated GCStrategy expects to encounter statepoints.
    assert(GFI->getStrategy().useStatepoints() &&
           "GCStrategy does not expect to encounter statepoints");
  #endif
  
    SDValue ActualCallee;
  
    if (ISP.getNumPatchBytes() > 0) {
      // If we've been asked to emit a nop sequence instead of a call instruction
      // for this statepoint then don't lower the call target, but use a constant
      // `null` instead.  Not lowering the call target lets statepoint clients get
      // away without providing a physical address for the symbolic call target at
      // link time.
  
      const auto &TLI = DAG.getTargetLoweringInfo();
      const auto &DL = DAG.getDataLayout();
  
      unsigned AS = ISP.getCalledValue()->getType()->getPointerAddressSpace();
      ActualCallee = DAG.getConstant(0, getCurSDLoc(), TLI.getPointerTy(DL, AS));
    } else {
      ActualCallee = getValue(ISP.getCalledValue());
    }
  
    StatepointLoweringInfo SI(DAG);
    populateCallLoweringInfo(SI.CLI, ISP.getCallSite(),
                             ImmutableStatepoint::CallArgsBeginPos,
                             ISP.getNumCallArgs(), ActualCallee,
                             ISP.getActualReturnType(), false /* IsPatchPoint */);
  
    for (const GCRelocateInst *Relocate : ISP.getRelocates()) {
      SI.GCRelocates.push_back(Relocate);
      SI.Bases.push_back(Relocate->getBasePtr());
      SI.Ptrs.push_back(Relocate->getDerivedPtr());
    }
  
    SI.GCArgs = ArrayRef<const Use>(ISP.gc_args_begin(), ISP.gc_args_end());
    SI.StatepointInstr = ISP.getInstruction();
    SI.GCTransitionArgs =
        ArrayRef<const Use>(ISP.gc_args_begin(), ISP.gc_args_end());
    SI.ID = ISP.getID();
    SI.DeoptState = ArrayRef<const Use>(ISP.vm_state_begin(), ISP.vm_state_end());
    SI.StatepointFlags = ISP.getFlags();
    SI.NumPatchBytes = ISP.getNumPatchBytes();
    SI.EHPadBB = EHPadBB;
  
    SDValue ReturnValue = LowerAsSTATEPOINT(SI);
  
    // Export the result value if needed
    const GCResultInst *GCResult = ISP.getGCResult();
    Type *RetTy = ISP.getActualReturnType();
    if (!RetTy->isVoidTy() && GCResult) {
      if (GCResult->getParent() != ISP.getCallSite().getParent()) {
        // Result value will be used in a different basic block so we need to
        // export it now.  Default exporting mechanism will not work here because
        // statepoint call has a different type than the actual call. It means
        // that by default llvm will create export register of the wrong type
        // (always i32 in our case). So instead we need to create export register
        // with correct type manually.
        // TODO: To eliminate this problem we can remove gc.result intrinsics
        //       completely and make statepoint call to return a tuple.
        unsigned Reg = FuncInfo.CreateRegs(RetTy);
        RegsForValue RFV(*DAG.getContext(), DAG.getTargetLoweringInfo(),
                         DAG.getDataLayout(), Reg, RetTy);
        SDValue Chain = DAG.getEntryNode();
  
        RFV.getCopyToRegs(ReturnValue, DAG, getCurSDLoc(), Chain, nullptr);
        PendingExports.push_back(Chain);
        FuncInfo.ValueMap[ISP.getInstruction()] = Reg;
      } else {
        // Result value will be used in a same basic block. Don't export it or
        // perform any explicit register copies.
        // We'll replace the actuall call node shortly. gc_result will grab
        // this value.
        setValue(ISP.getInstruction(), ReturnValue);
      }
    } else {
      // The token value is never used from here on, just generate a poison value
      setValue(ISP.getInstruction(), DAG.getIntPtrConstant(-1, getCurSDLoc()));
    }
  }
  
  void SelectionDAGBuilder::LowerCallSiteWithDeoptBundleImpl(
      ImmutableCallSite CS, SDValue Callee, const BasicBlock *EHPadBB,
      bool VarArgDisallowed, bool ForceVoidReturnTy) {
    StatepointLoweringInfo SI(DAG);
    unsigned ArgBeginIndex = CS.arg_begin() - CS.getInstruction()->op_begin();
    populateCallLoweringInfo(
        SI.CLI, CS, ArgBeginIndex, CS.getNumArgOperands(), Callee,
        ForceVoidReturnTy ? Type::getVoidTy(*DAG.getContext()) : CS.getType(),
        false);
    if (!VarArgDisallowed)
      SI.CLI.IsVarArg = CS.getFunctionType()->isVarArg();
  
    auto DeoptBundle = *CS.getOperandBundle(LLVMContext::OB_deopt);
  
    unsigned DefaultID = StatepointDirectives::DeoptBundleStatepointID;
  
    auto SD = parseStatepointDirectivesFromAttrs(CS.getAttributes());
    SI.ID = SD.StatepointID.getValueOr(DefaultID);
    SI.NumPatchBytes = SD.NumPatchBytes.getValueOr(0);
  
    SI.DeoptState =
        ArrayRef<const Use>(DeoptBundle.Inputs.begin(), DeoptBundle.Inputs.end());
    SI.StatepointFlags = static_cast<uint64_t>(StatepointFlags::None);
    SI.EHPadBB = EHPadBB;
  
    // NB! The GC arguments are deliberately left empty.
  
    if (SDValue ReturnVal = LowerAsSTATEPOINT(SI)) {
      const Instruction *Inst = CS.getInstruction();
      ReturnVal = lowerRangeToAssertZExt(DAG, *Inst, ReturnVal);
      setValue(Inst, ReturnVal);
    }
  }
  
  void SelectionDAGBuilder::LowerCallSiteWithDeoptBundle(
      ImmutableCallSite CS, SDValue Callee, const BasicBlock *EHPadBB) {
    LowerCallSiteWithDeoptBundleImpl(CS, Callee, EHPadBB,
                                     /* VarArgDisallowed = */ false,
                                     /* ForceVoidReturnTy  = */ false);
  }
  
  void SelectionDAGBuilder::visitGCResult(const GCResultInst &CI) {
    // The result value of the gc_result is simply the result of the actual
    // call.  We've already emitted this, so just grab the value.
    const Instruction *I = CI.getStatepoint();
  
    if (I->getParent() != CI.getParent()) {
      // Statepoint is in different basic block so we should have stored call
      // result in a virtual register.
      // We can not use default getValue() functionality to copy value from this
      // register because statepoint and actual call return types can be
      // different, and getValue() will use CopyFromReg of the wrong type,
      // which is always i32 in our case.
      PointerType *CalleeType = cast<PointerType>(
          ImmutableStatepoint(I).getCalledValue()->getType());
      Type *RetTy =
          cast<FunctionType>(CalleeType->getElementType())->getReturnType();
      SDValue CopyFromReg = getCopyFromRegs(I, RetTy);
  
      assert(CopyFromReg.getNode());
      setValue(&CI, CopyFromReg);
    } else {
      setValue(&CI, getValue(I));
    }
  }
  
  void SelectionDAGBuilder::visitGCRelocate(const GCRelocateInst &Relocate) {
  #ifndef NDEBUG
    // Consistency check
    // We skip this check for relocates not in the same basic block as their
    // statepoint. It would be too expensive to preserve validation info through
    // different basic blocks.
    if (Relocate.getStatepoint()->getParent() == Relocate.getParent())
      StatepointLowering.relocCallVisited(Relocate);
  
    auto *Ty = Relocate.getType()->getScalarType();
    if (auto IsManaged = GFI->getStrategy().isGCManagedPointer(Ty))
      assert(*IsManaged && "Non gc managed pointer relocated!");
  #endif
  
    const Value *DerivedPtr = Relocate.getDerivedPtr();
    SDValue SD = getValue(DerivedPtr);
  
    auto &SpillMap = FuncInfo.StatepointSpillMaps[Relocate.getStatepoint()];
    auto SlotIt = SpillMap.find(DerivedPtr);
    assert(SlotIt != SpillMap.end() && "Relocating not lowered gc value");
    Optional<int> DerivedPtrLocation = SlotIt->second;
  
    // We didn't need to spill these special cases (constants and allocas).
    // See the handling in spillIncomingValueForStatepoint for detail.
    if (!DerivedPtrLocation) {
      setValue(&Relocate, SD);
      return;
    }
  
    SDValue SpillSlot = DAG.getTargetFrameIndex(*DerivedPtrLocation,
                                                SD.getValueType());
  
    // Be conservative: flush all pending loads
    // TODO: Probably we can be less restrictive on this,
    // it may allow more scheduling opportunities.
    SDValue Chain = getRoot();
  
    SDValue SpillLoad =
        DAG.getLoad(SpillSlot.getValueType(), getCurSDLoc(), Chain, SpillSlot,
                    MachinePointerInfo::getFixedStack(DAG.getMachineFunction(),
                                                      *DerivedPtrLocation));
  
    // Again, be conservative, don't emit pending loads
    DAG.setRoot(SpillLoad.getValue(1));
  
    assert(SpillLoad.getNode());
    setValue(&Relocate, SpillLoad);
  }
  
  void SelectionDAGBuilder::LowerDeoptimizeCall(const CallInst *CI) {
    const auto &TLI = DAG.getTargetLoweringInfo();
    SDValue Callee = DAG.getExternalSymbol(TLI.getLibcallName(RTLIB::DEOPTIMIZE),
                                           TLI.getPointerTy(DAG.getDataLayout()));
  
    // We don't lower calls to __llvm_deoptimize as varargs, but as a regular
    // call.  We also do not lower the return value to any virtual register, and
    // change the immediately following return to a trap instruction.
    LowerCallSiteWithDeoptBundleImpl(CI, Callee, /* EHPadBB = */ nullptr,
                                     /* VarArgDisallowed = */ true,
                                     /* ForceVoidReturnTy = */ true);
  }
  
  void SelectionDAGBuilder::LowerDeoptimizingReturn() {
    // We do not lower the return value from llvm.deoptimize to any virtual
    // register, and change the immediately following return to a trap
    // instruction.
    if (DAG.getTarget().Options.TrapUnreachable)
      DAG.setRoot(
          DAG.getNode(ISD::TRAP, getCurSDLoc(), MVT::Other, DAG.getRoot()));
  }
  