C++ SelectionDAGBuilder类代码示例

/// 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);
    assert(isa<FrameIndexSDNode>(Loc));
    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
    Chain = Builder.DAG.getStore(Chain, Builder.getCurSDLoc(), Incoming, Loc,
                                 MachinePointerInfo::getFixedStack(Index),
                                 false, false, 0);

    Builder.StatepointLowering.setLocation(Incoming, Loc);
  }

  assert(Loc.getNode());
  return std::make_pair(Loc, Chain);
}

/// 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 removeDuplicatesGCPtrs(SmallVectorImpl<const Value *> &Bases,
                                   SmallVectorImpl<const Value *> &Ptrs,
                                   SmallVectorImpl<const Value *> &Relocs,
                                   SelectionDAGBuilder &Builder) {

  // This is horribly ineffecient, but I don't care right now
  SmallSet<SDValue, 64> Seen;

  SmallVector<const Value *, 64> NewBases, NewPtrs, NewRelocs;
  for (size_t i = 0; i < Ptrs.size(); i++) {
    SDValue SD = Builder.getValue(Ptrs[i]);
    // Only add non-duplicates
    if (Seen.count(SD) == 0) {
      NewBases.push_back(Bases[i]);
      NewPtrs.push_back(Ptrs[i]);
      NewRelocs.push_back(Relocs[i]);
    }
    Seen.insert(SD);
  }
  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());
}

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));
}

/// 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,
                                         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
    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 {
    // 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.
    std::pair<SDValue, SDValue> Res =
        spillIncomingStatepointValue(Incoming, Chain, Builder);
    Ops.push_back(Res.first);
    Chain = Res.second;
  }

  Builder.DAG.setRoot(Chain);
}

/// 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());
}

/// 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?)
    assert(Incoming.getValueType() == Builder.getFrameIndexTy() &&
           "Incoming value is a frame index!");
    Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(),
                                                  Builder.getFrameIndexTy()));
  } 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);
}

/// 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, Builder.getFrameIndexTy());

    // 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);
}

/// 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 resuffle
/// 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;

  auto Itr = std::find(Builder.FuncInfo.StatepointStackSlots.begin(),
                       Builder.FuncInfo.StatepointStackSlots.end(), *Index);
  assert(Itr != Builder.FuncInfo.StatepointStackSlots.end() &&
         "value spilled to the unknown stack slot");

  // This is one of our dedicated lowering slots
  const int Offset =
      std::distance(Builder.FuncInfo.StatepointStackSlots.begin(), Itr);
  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);
}

/// 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());
}

/// 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,
                                    ImmutableStatepoint StatepointSite,
                                    SelectionDAGBuilder &Builder) {

  // Lower the deopt and gc arguments for this statepoint.  Layout will
  // be: deopt argument length, deopt arguments.., gc arguments...

  SmallVector<const Value *, 64> Bases, Ptrs, Relocations;
  getIncomingStatepointGCValues(Bases, Ptrs, Relocations, StatepointSite,
                                Builder);

#ifndef NDEBUG
  // 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 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 = Builder.GFI->getStrategy();
  for (const Value *V : Bases) {
    auto Opt = S.isGCManagedPointer(V);
    if (Opt.hasValue()) {
      assert(Opt.getValue() &&
             "non gc managed base pointer found in statepoint");
    }
  }
  for (const Value *V : Ptrs) {
    auto Opt = S.isGCManagedPointer(V);
    if (Opt.hasValue()) {
      assert(Opt.getValue() &&
             "non gc managed derived pointer found in statepoint");
    }
  }
  for (const Value *V : Relocations) {
    auto Opt = S.isGCManagedPointer(V);
    if (Opt.hasValue()) {
      assert(Opt.getValue() && "non gc managed pointer relocated");
    }
  }
#endif

  // 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 : StatepointSite.vm_state_args()) {
    reservePreviousStackSlotForValue(V, Builder);
  }
  for (unsigned i = 0; i < Bases.size(); ++i) {
    reservePreviousStackSlotForValue(Bases[i], Builder);
    reservePreviousStackSlotForValue(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 = StatepointSite.getNumTotalVMSArgs();
  pushStackMapConstant(Ops, Builder, NumVMSArgs);

  assert(NumVMSArgs == std::distance(StatepointSite.vm_state_begin(),
                                     StatepointSite.vm_state_end()));

  // The vm state arguments are lowered in an opaque manner.  We do
  // not know what type of values are contained within.  We skip the
  // first one since that happens to be the total number we lowered
  // explicitly just above.  We could have left it in the loop and
  // not done it explicitly, but it's far easier to understand this
  // way.
  for (const Value *V : StatepointSite.vm_state_args()) {
    SDValue Incoming = Builder.getValue(V);
    lowerIncomingStatepointValue(Incoming, 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 < Bases.size(); ++i) {
    const Value *Base = Bases[i];
    lowerIncomingStatepointValue(Builder.getValue(Base), Ops, Builder);

    const Value *Ptr = Ptrs[i];
    lowerIncomingStatepointValue(Builder.getValue(Ptr), 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 : StatepointSite.gc_args()) {
    SDValue Incoming = Builder.getValue(V);
//.........这里部分代码省略.........

/// 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,
                                    ImmutableStatepoint StatepointSite,
                                    SelectionDAGBuilder &Builder) {

  // Lower the deopt and gc arguments for this statepoint.  Layout will
  // be: deopt argument length, deopt arguments.., gc arguments...

  SmallVector<const Value *, 64> Bases, Ptrs, Relocations;
  getIncomingStatepointGCValues(Bases, Ptrs, Relocations, StatepointSite,
                                Builder);

#ifndef NDEBUG
  // 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 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 = Builder.GFI->getStrategy();
  for (const Value *V : Bases) {
    auto Opt = S.isGCManagedPointer(V);
    if (Opt.hasValue()) {
      assert(Opt.getValue() &&
             "non gc managed base pointer found in statepoint");
    }
  }
  for (const Value *V : Ptrs) {
    auto Opt = S.isGCManagedPointer(V);
    if (Opt.hasValue()) {
      assert(Opt.getValue() &&
             "non gc managed derived pointer found in statepoint");
    }
  }
  for (const Value *V : Relocations) {
    auto Opt = S.isGCManagedPointer(V);
    if (Opt.hasValue()) {
      assert(Opt.getValue() && "non gc managed pointer relocated");
    }
  }
#endif

  // 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 : StatepointSite.vm_state_args()) {
    SDValue Incoming = Builder.getValue(V);
    reservePreviousStackSlotForValue(Incoming, Builder);
  }
  for (unsigned i = 0; i < Bases.size(); ++i) {
    const Value *Base = Bases[i];
    reservePreviousStackSlotForValue(Builder.getValue(Base), Builder);

    const Value *Ptr = Ptrs[i];
    reservePreviousStackSlotForValue(Builder.getValue(Ptr), 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 = StatepointSite.getNumTotalVMSArgs();
  pushStackMapConstant(Ops, Builder, NumVMSArgs);

  assert(NumVMSArgs == std::distance(StatepointSite.vm_state_begin(),
                                     StatepointSite.vm_state_end()));

  // The vm state arguments are lowered in an opaque manner.  We do
  // not know what type of values are contained within.  We skip the
  // first one since that happens to be the total number we lowered
  // explicitly just above.  We could have left it in the loop and
  // not done it explicitly, but it's far easier to understand this
  // way.
  for (const Value *V : StatepointSite.vm_state_args()) {
    SDValue Incoming = Builder.getValue(V);
    lowerIncomingStatepointValue(Incoming, 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 < Bases.size(); ++i) {
    const Value *Base = Bases[i];
    lowerIncomingStatepointValue(Builder.getValue(Base), Ops, Builder);

    const Value *Ptr = Ptrs[i];
    lowerIncomingStatepointValue(Builder.getValue(Ptr), 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,
//.........这里部分代码省略.........

/// 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);
//.........这里部分代码省略.........