lib/CodeGen/SplitKit.h

//===-------- SplitKit.cpp - Toolkit for splitting live ranges --*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the SplitAnalysis class as well as mutator functions for
// live range splitting.
//
//===----------------------------------------------------------------------===//

#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/CodeGen/SlotIndexes.h"

namespace llvm {

class LiveInterval;
class LiveIntervals;
class LiveRangeEdit;
class MachineInstr;
class MachineDominatorTree;
class MachineLoop;
class MachineLoopInfo;
class MachineRegisterInfo;
class TargetInstrInfo;
class VirtRegMap;
class VNInfo;
class raw_ostream;

/// SplitAnalysis - Analyze a LiveInterval, looking for live range splitting
/// opportunities.
class SplitAnalysis {
public:
  const MachineFunction &mf_;
  const LiveIntervals &lis_;
  const MachineLoopInfo &loops_;
  const TargetInstrInfo &tii_;

  // Instructions using the the current register.
  typedef SmallPtrSet<const MachineInstr*, 16> InstrPtrSet;
  InstrPtrSet usingInstrs_;

  // The number of instructions using curli in each basic block.
  typedef DenseMap<const MachineBasicBlock*, unsigned> BlockCountMap;
  BlockCountMap usingBlocks_;

  // The number of basic block using curli in each loop.
  typedef DenseMap<const MachineLoop*, unsigned> LoopCountMap;
  LoopCountMap usingLoops_;

private:
  // Current live interval.
  const LiveInterval *curli_;

  // Sumarize statistics by counting instructions using curli_.
  void analyzeUses();

  /// canAnalyzeBranch - Return true if MBB ends in a branch that can be
  /// analyzed.
  bool canAnalyzeBranch(const MachineBasicBlock *MBB);

public:
  SplitAnalysis(const MachineFunction &mf, const LiveIntervals &lis,
                const MachineLoopInfo &mli);

  /// analyze - set curli to the specified interval, and analyze how it may be
  /// split.
  void analyze(const LiveInterval *li);

  /// clear - clear all data structures so SplitAnalysis is ready to analyze a
  /// new interval.
  void clear();

  typedef SmallPtrSet<const MachineBasicBlock*, 16> BlockPtrSet;
  typedef SmallPtrSet<const MachineLoop*, 16> LoopPtrSet;

  // Print a set of blocks with use counts.
  void print(const BlockPtrSet&, raw_ostream&) const;

  // Sets of basic blocks surrounding a machine loop.
  struct LoopBlocks {
    BlockPtrSet Loop;  // Blocks in the loop.
    BlockPtrSet Preds; // Loop predecessor blocks.
    BlockPtrSet Exits; // Loop exit blocks.

    void clear() {
      Loop.clear();
      Preds.clear();
      Exits.clear();
    }
  };

  // Print loop blocks with use counts.
  void print(const LoopBlocks&, raw_ostream&) const;

  // Calculate the block sets surrounding the loop.
  void getLoopBlocks(const MachineLoop *Loop, LoopBlocks &Blocks);

  /// LoopPeripheralUse - how is a variable used in and around a loop?
  /// Peripheral blocks are the loop predecessors and exit blocks.
  enum LoopPeripheralUse {
    ContainedInLoop,  // All uses are inside the loop.
    SinglePeripheral, // At most one instruction per peripheral block.
    MultiPeripheral,  // Multiple instructions in some peripheral blocks.
    OutsideLoop       // Uses outside loop periphery.
  };

  /// analyzeLoopPeripheralUse - Return an enum describing how curli_ is used in
  /// and around the Loop.
  LoopPeripheralUse analyzeLoopPeripheralUse(const LoopBlocks&);

  /// getCriticalExits - It may be necessary to partially break critical edges
  /// leaving the loop if an exit block has phi uses of curli. Collect the exit
  /// blocks that need special treatment into CriticalExits.
  void getCriticalExits(const LoopBlocks &Blocks, BlockPtrSet &CriticalExits);

  /// canSplitCriticalExits - Return true if it is possible to insert new exit
  /// blocks before the blocks in CriticalExits.
  bool canSplitCriticalExits(const LoopBlocks &Blocks,
                             BlockPtrSet &CriticalExits);

  /// getCriticalPreds - Get the set of loop predecessors with critical edges to
  /// blocks outside the loop that have curli live in. We don't have to break
  /// these edges, but they do require special treatment.
  void getCriticalPreds(const LoopBlocks &Blocks, BlockPtrSet &CriticalPreds);

  /// getBestSplitLoop - Return the loop where curli may best be split to a
  /// separate register, or NULL.
  const MachineLoop *getBestSplitLoop();

  /// getMultiUseBlocks - Add basic blocks to Blocks that may benefit from
  /// having curli split to a new live interval. Return true if Blocks can be
  /// passed to SplitEditor::splitSingleBlocks.
  bool getMultiUseBlocks(BlockPtrSet &Blocks);

  /// getBlockForInsideSplit - If curli is contained inside a single basic block,
  /// and it wou pay to subdivide the interval inside that block, return it.
  /// Otherwise return NULL. The returned block can be passed to
  /// SplitEditor::splitInsideBlock.
  const MachineBasicBlock *getBlockForInsideSplit();
};


/// LiveIntervalMap - Map values from a large LiveInterval into a small
/// interval that is a subset. Insert phi-def values as needed. This class is
/// used by SplitEditor to create new smaller LiveIntervals.
///
/// parentli_ is the larger interval, li_ is the subset interval. Every value
/// in li_ corresponds to exactly one value in parentli_, and the live range
/// of the value is contained within the live range of the parentli_ value.
/// Values in parentli_ may map to any number of openli_ values, including 0.
class LiveIntervalMap {
  LiveIntervals &lis_;
  MachineDominatorTree &mdt_;

  // The parent interval is never changed.
  const LiveInterval &parentli_;

  // The child interval's values are fully contained inside parentli_ values.
  LiveInterval *li_;

  typedef DenseMap<const VNInfo*, VNInfo*> ValueMap;

  // Map parentli_ values to simple values in li_ that are defined at the same
  // SlotIndex, or NULL for parentli_ values that have complex li_ defs.
  // Note there is a difference between values mapping to NULL (complex), and
  // values not present (unknown/unmapped).
  ValueMap valueMap_;

public:
  LiveIntervalMap(LiveIntervals &lis,
                  MachineDominatorTree &mdt,
                  const LiveInterval &parentli)
    : lis_(lis), mdt_(mdt), parentli_(parentli), li_(0) {}

  /// reset - clear all data structures and start a new live interval.
  void reset(LiveInterval *);

  /// getLI - return the current live interval.
  LiveInterval *getLI() const { return li_; }

  /// defValue - define a value in li_ from the parentli_ value VNI and Idx.
  /// Idx does not have to be ParentVNI->def, but it must be contained within
  /// ParentVNI's live range in parentli_.
  /// Return the new li_ value.
  VNInfo *defValue(const VNInfo *ParentVNI, SlotIndex Idx);

  /// mapValue - map ParentVNI to the corresponding li_ value at Idx. It is
  /// assumed that ParentVNI is live at Idx.
  /// If ParentVNI has not been defined by defValue, it is assumed that
  /// ParentVNI->def dominates Idx.
  /// If ParentVNI has been defined by defValue one or more times, a value that
  /// dominates Idx will be returned. This may require creating extra phi-def
  /// values and adding live ranges to li_.
  /// If simple is not NULL, *simple will indicate if ParentVNI is a simply
  /// mapped value.
  VNInfo *mapValue(const VNInfo *ParentVNI, SlotIndex Idx, bool *simple = 0);

  // extendTo - Find the last li_ value defined in MBB at or before Idx. The
  // parentli is assumed to be live at Idx. Extend the live range to include
  // Idx. Return the found VNInfo, or NULL.
  VNInfo *extendTo(const MachineBasicBlock *MBB, SlotIndex Idx);

  /// isMapped - Return true is ParentVNI is a known mapped value. It may be a
  /// simple 1-1 mapping or a complex mapping to later defs.
  bool isMapped(const VNInfo *ParentVNI) const {
    return valueMap_.count(ParentVNI);
  }

  /// isComplexMapped - Return true if ParentVNI has received new definitions
  /// with defValue.
  bool isComplexMapped(const VNInfo *ParentVNI) const;

  // addSimpleRange - Add a simple range from parentli_ to li_.
  // ParentVNI must be live in the [Start;End) interval.
  void addSimpleRange(SlotIndex Start, SlotIndex End, const VNInfo *ParentVNI);

  /// addRange - Add live ranges to li_ where [Start;End) intersects parentli_.
  /// All needed values whose def is not inside [Start;End) must be defined
  /// beforehand so mapValue will work.
  void addRange(SlotIndex Start, SlotIndex End);

  /// defByCopyFrom - Insert a copy from Reg to li, assuming that Reg carries
  /// ParentVNI. Add a minimal live range for the new value and return it.
  VNInfo *defByCopyFrom(unsigned Reg,
                        const VNInfo *ParentVNI,
                        MachineBasicBlock &MBB,
                        MachineBasicBlock::iterator I);

};


/// SplitEditor - Edit machine code and LiveIntervals for live range
/// splitting.
///
/// - Create a SplitEditor from a SplitAnalysis.
/// - Start a new live interval with openIntv.
/// - Mark the places where the new interval is entered using enterIntv*
/// - Mark the ranges where the new interval is used with useIntv* 
/// - Mark the places where the interval is exited with exitIntv*.
/// - Finish the current interval with closeIntv and repeat from 2.
/// - Rewrite instructions with finish().
///
class SplitEditor {
  SplitAnalysis &sa_;
  LiveIntervals &lis_;
  VirtRegMap &vrm_;
  MachineRegisterInfo &mri_;
  const TargetInstrInfo &tii_;

  /// edit_ - The current parent register and new intervals created.
  LiveRangeEdit &edit_;

  /// dupli_ - Created as a copy of curli_, ranges are carved out as new
  /// intervals get added through openIntv / closeIntv. This is used to avoid
  /// editing curli_.
  LiveIntervalMap dupli_;

  /// Currently open LiveInterval.
  LiveIntervalMap openli_;

  /// intervalsLiveAt - Return true if any member of intervals_ is live at Idx.
  bool intervalsLiveAt(SlotIndex Idx) const;

  /// Values in curli whose live range has been truncated when entering an open
  /// li.
  SmallPtrSet<const VNInfo*, 8> truncatedValues;

  /// addTruncSimpleRange - Add the given simple range to dupli_ after
  /// truncating any overlap with intervals_.
  void addTruncSimpleRange(SlotIndex Start, SlotIndex End, VNInfo *VNI);

  /// criticalPreds_ - Set of basic blocks where both dupli and openli should be
  /// live out because of a critical edge.
  SplitAnalysis::BlockPtrSet criticalPreds_;

  /// computeRemainder - Compute the dupli liveness as the complement of all the
  /// new intervals.
  void computeRemainder();

  /// rewrite - Rewrite all uses of reg to use the new registers.
  void rewrite(unsigned reg);

public:
  /// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
  /// Newly created intervals will be appended to newIntervals.
  SplitEditor(SplitAnalysis &SA, LiveIntervals&, VirtRegMap&,
              MachineDominatorTree&, LiveRangeEdit&);

  /// getAnalysis - Get the corresponding analysis.
  SplitAnalysis &getAnalysis() { return sa_; }

  /// Create a new virtual register and live interval.
  void openIntv();

  /// enterIntvBefore - Enter openli before the instruction at Idx. If curli is
  /// not live before Idx, a COPY is not inserted.
  void enterIntvBefore(SlotIndex Idx);

  /// enterIntvAtEnd - Enter openli at the end of MBB.
  void enterIntvAtEnd(MachineBasicBlock &MBB);

  /// useIntv - indicate that all instructions in MBB should use openli.
  void useIntv(const MachineBasicBlock &MBB);

  /// useIntv - indicate that all instructions in range should use openli.
  void useIntv(SlotIndex Start, SlotIndex End);

  /// leaveIntvAfter - Leave openli after the instruction at Idx.
  void leaveIntvAfter(SlotIndex Idx);

  /// leaveIntvAtTop - Leave the interval at the top of MBB.
  /// Currently, only one value can leave the interval.
  void leaveIntvAtTop(MachineBasicBlock &MBB);

  /// closeIntv - Indicate that we are done editing the currently open
  /// LiveInterval, and ranges can be trimmed.
  void closeIntv();

  /// finish - after all the new live ranges have been created, compute the
  /// remaining live range, and rewrite instructions to use the new registers.
  void finish();

  // ===--- High level methods ---===

  /// splitAroundLoop - Split curli into a separate live interval inside
  /// the loop.
  void splitAroundLoop(const MachineLoop*);

  /// splitSingleBlocks - Split curli into a separate live interval inside each
  /// basic block in Blocks.
  void splitSingleBlocks(const SplitAnalysis::BlockPtrSet &Blocks);

  /// splitInsideBlock - Split curli into multiple intervals inside MBB.
  void splitInsideBlock(const MachineBasicBlock *);
};

}