//===-- StatepointLowering.h - SDAGBuilder's statepoint code -*- C++ -*---===//
//
//                     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.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIB_CODEGEN_SELECTIONDAG_STATEPOINTLOWERING_H
#define LLVM_LIB_CODEGEN_SELECTIONDAG_STATEPOINTLOWERING_H

#include "llvm/ADT/DenseMap.h"
#include "llvm/CodeGen/SelectionDAG.h"
#include "llvm/CodeGen/SelectionDAGNodes.h"
#include <vector>

namespace llvm {
class SelectionDAGBuilder;

/// This class tracks both per-statepoint and per-selectiondag information.
/// For each statepoint it tracks locations of it's gc valuess (incoming and
/// relocated) and list of gcreloc calls scheduled for visiting (this is
/// used for a debug mode consistency check only).  The spill slot tracking
/// works in concert with information in FunctionLoweringInfo.
class StatepointLoweringState {
public:
  StatepointLoweringState() : NextSlotToAllocate(0) {
  }

  /// Reset all state tracking for a newly encountered safepoint.  Also
  /// performs some consistency checking.
  void startNewStatepoint(SelectionDAGBuilder &Builder);

  /// Clear the memory usage of this object.  This is called from
  /// SelectionDAGBuilder::clear.  We require this is never called in the
  /// midst of processing a statepoint sequence.
  void clear();

  /// Returns the spill location of a value incoming to the current
  /// statepoint.  Will return SDValue() if this value hasn't been
  /// spilled.  Otherwise, the value has already been spilled and no
  /// further action is required by the caller.
  SDValue getLocation(SDValue val) {
    if (!Locations.count(val))
      return SDValue();
    return Locations[val];
  }
  void setLocation(SDValue val, SDValue Location) {
    assert(!Locations.count(val) &&
           "Trying to allocate already allocated location");
    Locations[val] = Location;
  }

  /// Returns the relocated value for a given input pointer. Will
  /// return SDValue() if this value hasn't yet been reloaded from
  /// it's stack slot after the statepoint.  Otherwise, the value
  /// has already been reloaded and the SDValue of that reload will
  /// be returned. Note that VMState values are spilled but not
  /// reloaded (since they don't change at the safepoint unless
  /// also listed in the GC pointer section) and will thus never
  /// be in this map
  SDValue getRelocLocation(SDValue val) {
    if (!RelocLocations.count(val))
      return SDValue();
    return RelocLocations[val];
  }
  void setRelocLocation(SDValue val, SDValue Location) {
    assert(!RelocLocations.count(val) &&
           "Trying to allocate already allocated location");
    RelocLocations[val] = Location;
  }

  /// Record the fact that we expect to encounter a given gc_relocate
  /// before the next statepoint.  If we don't see it, we'll report
  /// an assertion.
  void scheduleRelocCall(const CallInst &RelocCall) {
    PendingGCRelocateCalls.push_back(&RelocCall);
  }
  /// Remove this gc_relocate from the list we're expecting to see
  /// before the next statepoint.  If we weren't expecting to see
  /// it, we'll report an assertion.
  void relocCallVisited(const CallInst &RelocCall) {
    SmallVectorImpl<const CallInst *>::iterator itr =
        std::find(PendingGCRelocateCalls.begin(), PendingGCRelocateCalls.end(),
                  &RelocCall);
    assert(itr != PendingGCRelocateCalls.end() &&
           "Visited unexpected gcrelocate call");
    PendingGCRelocateCalls.erase(itr);
  }

  // TODO: Should add consistency tracking to ensure we encounter
  // expected gc_result calls too.

  /// Get a stack slot we can use to store an value of type ValueType.  This
  /// will hopefully be a recylced slot from another statepoint.
  SDValue allocateStackSlot(EVT ValueType, SelectionDAGBuilder &Builder);

  void reserveStackSlot(int Offset) {
    assert(Offset >= 0 && Offset < (int)AllocatedStackSlots.size() &&
           "out of bounds");
    assert(!AllocatedStackSlots[Offset] && "already reserved!");
    assert(NextSlotToAllocate <= (unsigned)Offset && "consistency!");
    AllocatedStackSlots[Offset] = true;
  }
  bool isStackSlotAllocated(int Offset) {
    assert(Offset >= 0 && Offset < (int)AllocatedStackSlots.size() &&
           "out of bounds");
    return AllocatedStackSlots[Offset];
  }

private:
  /// Maps pre-relocation value (gc pointer directly incoming into statepoint)
  /// into it's location (currently only stack slots)
  DenseMap<SDValue, SDValue> Locations;
  /// Map pre-relocated value into it's new relocated location
  DenseMap<SDValue, SDValue> RelocLocations;

  /// A boolean indicator for each slot listed in the FunctionInfo as to
  /// whether it has been used in the current statepoint.  Since we try to
  /// preserve stack slots across safepoints, there can be gaps in which
  /// slots have been allocated.
  SmallVector<bool, 50> AllocatedStackSlots;

  /// Points just beyond the last slot known to have been allocated
  unsigned NextSlotToAllocate;

  /// Keep track of pending gcrelocate calls for consistency check
  SmallVector<const CallInst *, 10> PendingGCRelocateCalls;
};
} // end namespace llvm

#endif // LLVM_LIB_CODEGEN_SELECTIONDAG_STATEPOINTLOWERING_H