C++ SelectionDAGBuilder::ExportFromCurrentBlock方法代码示例

//.........这里部分代码省略.........
    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);
    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 =
    StatepointSite.getCallSite().getInstruction();
  FunctionLoweringInfo::StatepointSpilledValueMapTy &SpillMap =
    Builder.FuncInfo.StatepointRelocatedValues[StatepointInstr];

  for (GCRelocateOperands RelocateOpers : StatepointSite.getRelocates()) {
    const Value *V = RelocateOpers.getDerivedPtr();
    SDValue SDV = Builder.getValue(V);
    SDValue Loc = Builder.StatepointLowering.getLocation(SDV);

    if (Loc.getNode()) {
      SpillMap[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 emiting 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[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 corresponging values so that it would automatically
      // export them. Relocates of the spilled values does not use original
      // value.
      if (StatepointSite.getCallSite().isInvoke())
        Builder.ExportFromCurrentBlock(V);
    }
  }
}

//.........这里部分代码省略.........
  // 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
      assert(Incoming.getValueType() == Builder.getFrameIndexTy() &&
             "Incoming value is a frame index!");
      Ops.push_back(Builder.DAG.getTargetFrameIndex(FI->getIndex(),
                                                    Builder.getFrameIndexTy()));
    }
  }

  // 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);
    }
  }
}