lib/CodeGen/SplitKit.h

   1 //===-------- SplitKit.h - Toolkit for splitting live ranges ----*- C++ -*-===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file contains the SplitAnalysis class as well as mutator functions for
  11 // live range splitting.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/ADT/ArrayRef.h"
  16 #include "llvm/ADT/BitVector.h"
  17 #include "llvm/ADT/DenseMap.h"
  18 #include "llvm/ADT/IndexedMap.h"
  19 #include "llvm/ADT/IntervalMap.h"
  20 #include "llvm/ADT/SmallPtrSet.h"
  21 #include "llvm/CodeGen/SlotIndexes.h"
  22
  23 namespace llvm {
  24
  25 class ConnectedVNInfoEqClasses;
  26 class LiveInterval;
  27 class LiveIntervals;
  28 class LiveRangeEdit;
  29 class MachineInstr;
  30 class MachineLoopInfo;
  31 class MachineRegisterInfo;
  32 class TargetInstrInfo;
  33 class TargetRegisterInfo;
  34 class VirtRegMap;
  35 class VNInfo;
  36 class raw_ostream;
  37
  38 /// At some point we should just include MachineDominators.h:
  39 class MachineDominatorTree;
  40 template <class NodeT> class DomTreeNodeBase;
  41 typedef DomTreeNodeBase<MachineBasicBlock> MachineDomTreeNode;
  42
  43
  44 /// SplitAnalysis - Analyze a LiveInterval, looking for live range splitting
  45 /// opportunities.
  46 class SplitAnalysis {
  47 public:
  48   const MachineFunction &MF;
  49   const VirtRegMap &VRM;
  50   const LiveIntervals &LIS;
  51   const MachineLoopInfo &Loops;
  52   const TargetInstrInfo &TII;
  53
  54   // Sorted slot indexes of using instructions.
  55   SmallVector<SlotIndex, 8> UseSlots;
  56
  57   /// Additional information about basic blocks where the current variable is
  58   /// live. Such a block will look like one of these templates:
  59   ///
  60   ///  1. |   o---x   | Internal to block. Variable is only live in this block.
  61   ///  2. |---x       | Live-in, kill.
  62   ///  3. |       o---| Def, live-out.
  63   ///  4. |---x   o---| Live-in, kill, def, live-out.
  64   ///  5. |---o---o---| Live-through with uses or defs.
  65   ///  6. |-----------| Live-through without uses. Transparent.
  66   ///
  67   struct BlockInfo {
  68     MachineBasicBlock *MBB;
  69     SlotIndex FirstUse;   ///< First instr using current reg.
  70     SlotIndex LastUse;    ///< Last instr using current reg.
  71     SlotIndex Kill;       ///< Interval end point inside block.
  72     SlotIndex Def;        ///< Interval start point inside block.
  73     bool LiveThrough;     ///< Live in whole block (Templ 5. or 6. above).
  74     bool LiveIn;          ///< Current reg is live in.
  75     bool LiveOut;         ///< Current reg is live out.
  76   };
  77
  78 private:
  79   // Current live interval.
  80   const LiveInterval *CurLI;
  81
  82   /// LastSplitPoint - Last legal split point in each basic block in the current
  83   /// function. The first entry is the first terminator, the second entry is the
  84   /// last valid split point for a variable that is live in to a landing pad
  85   /// successor.
  86   SmallVector<std::pair<SlotIndex, SlotIndex>, 8> LastSplitPoint;
  87
  88   /// UseBlocks - Blocks where CurLI has uses.
  89   SmallVector<BlockInfo, 8> UseBlocks;
  90
  91   /// ThroughBlocks - Block numbers where CurLI is live through without uses.
  92   SmallVector<unsigned, 8> ThroughBlocks;
  93
  94   SlotIndex computeLastSplitPoint(unsigned Num);
  95
  96   // Sumarize statistics by counting instructions using CurLI.
  97   void analyzeUses();
  98
  99   /// calcLiveBlockInfo - Compute per-block information about CurLI.
 100   bool calcLiveBlockInfo();
 101
 102 public:
 103   SplitAnalysis(const VirtRegMap &vrm, const LiveIntervals &lis,
 104                 const MachineLoopInfo &mli);
 105
 106   /// analyze - set CurLI to the specified interval, and analyze how it may be
 107   /// split.
 108   void analyze(const LiveInterval *li);
 109
 110   /// clear - clear all data structures so SplitAnalysis is ready to analyze a
 111   /// new interval.
 112   void clear();
 113
 114   /// getParent - Return the last analyzed interval.
 115   const LiveInterval &getParent() const { return *CurLI; }
 116
 117   /// getLastSplitPoint - Return that base index of the last valid split point
 118   /// in the basic block numbered Num.
 119   SlotIndex getLastSplitPoint(unsigned Num) {
 120     // Inline the common simple case.
 121     if (LastSplitPoint[Num].first.isValid() &&
 122         !LastSplitPoint[Num].second.isValid())
 123       return LastSplitPoint[Num].first;
 124     return computeLastSplitPoint(Num);
 125   }
 126
 127   /// isOriginalEndpoint - Return true if the original live range was killed or
 128   /// (re-)defined at Idx. Idx should be the 'def' slot for a normal kill/def,
 129   /// and 'use' for an early-clobber def.
 130   /// This can be used to recognize code inserted by earlier live range
 131   /// splitting.
 132   bool isOriginalEndpoint(SlotIndex Idx) const;
 133
 134   /// getUseBlocks - Return an array of BlockInfo objects for the basic blocks
 135   /// where CurLI has uses.
 136   ArrayRef<BlockInfo> getUseBlocks() { return UseBlocks; }
 137
 138   /// getThroughBlocks - Return an array of block numbers where CurLI is live
 139   /// through without uses.
 140   ArrayRef<unsigned> getThroughBlocks() { return ThroughBlocks; }
 141
 142   typedef SmallPtrSet<const MachineBasicBlock*, 16> BlockPtrSet;
 143
 144   /// getMultiUseBlocks - Add basic blocks to Blocks that may benefit from
 145   /// having CurLI split to a new live interval. Return true if Blocks can be
 146   /// passed to SplitEditor::splitSingleBlocks.
 147   bool getMultiUseBlocks(BlockPtrSet &Blocks);
 148 };
 149
 150
 151 /// SplitEditor - Edit machine code and LiveIntervals for live range
 152 /// splitting.
 153 ///
 154 /// - Create a SplitEditor from a SplitAnalysis.
 155 /// - Start a new live interval with openIntv.
 156 /// - Mark the places where the new interval is entered using enterIntv*
 157 /// - Mark the ranges where the new interval is used with useIntv*
 158 /// - Mark the places where the interval is exited with exitIntv*.
 159 /// - Finish the current interval with closeIntv and repeat from 2.
 160 /// - Rewrite instructions with finish().
 161 ///
 162 class SplitEditor {
 163   SplitAnalysis &SA;
 164   LiveIntervals &LIS;
 165   VirtRegMap &VRM;
 166   MachineRegisterInfo &MRI;
 167   MachineDominatorTree &MDT;
 168   const TargetInstrInfo &TII;
 169   const TargetRegisterInfo &TRI;
 170
 171   /// Edit - The current parent register and new intervals created.
 172   LiveRangeEdit *Edit;
 173
 174   /// Index into Edit of the currently open interval.
 175   /// The index 0 is used for the complement, so the first interval started by
 176   /// openIntv will be 1.
 177   unsigned OpenIdx;
 178
 179   typedef IntervalMap<SlotIndex, unsigned> RegAssignMap;
 180
 181   /// Allocator for the interval map. This will eventually be shared with
 182   /// SlotIndexes and LiveIntervals.
 183   RegAssignMap::Allocator Allocator;
 184
 185   /// RegAssign - Map of the assigned register indexes.
 186   /// Edit.get(RegAssign.lookup(Idx)) is the register that should be live at
 187   /// Idx.
 188   RegAssignMap RegAssign;
 189
 190   typedef DenseMap<std::pair<unsigned, unsigned>, VNInfo*> ValueMap;
 191
 192   /// Values - keep track of the mapping from parent values to values in the new
 193   /// intervals. Given a pair (RegIdx, ParentVNI->id), Values contains:
 194   ///
 195   /// 1. No entry - the value is not mapped to Edit.get(RegIdx).
 196   /// 2. Null - the value is mapped to multiple values in Edit.get(RegIdx).
 197   ///    Each value is represented by a minimal live range at its def.
 198   /// 3. A non-null VNInfo - the value is mapped to a single new value.
 199   ///    The new value has no live ranges anywhere.
 200   ValueMap Values;
 201
 202   typedef std::pair<VNInfo*, MachineDomTreeNode*> LiveOutPair;
 203   typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap;
 204
 205   // LiveOutCache - Map each basic block where a new register is live out to the
 206   // live-out value and its defining block.
 207   // One of these conditions shall be true:
 208   //
 209   //  1. !LiveOutCache.count(MBB)
 210   //  2. LiveOutCache[MBB].second.getNode() == MBB
 211   //  3. forall P in preds(MBB): LiveOutCache[P] == LiveOutCache[MBB]
 212   //
 213   // This is only a cache, the values can be computed as:
 214   //
 215   //  VNI = Edit.get(RegIdx)->getVNInfoAt(LIS.getMBBEndIdx(MBB))
 216   //  Node = mbt_[LIS.getMBBFromIndex(VNI->def)]
 217   //
 218   // The cache is also used as a visited set by extendRange(). It can be shared
 219   // by all the new registers because at most one is live out of each block.
 220   LiveOutMap LiveOutCache;
 221
 222   // LiveOutSeen - Indexed by MBB->getNumber(), a bit is set for each valid
 223   // entry in LiveOutCache.
 224   BitVector LiveOutSeen;
 225
 226   /// defValue - define a value in RegIdx from ParentVNI at Idx.
 227   /// Idx does not have to be ParentVNI->def, but it must be contained within
 228   /// ParentVNI's live range in ParentLI. The new value is added to the value
 229   /// map.
 230   /// Return the new LI value.
 231   VNInfo *defValue(unsigned RegIdx, const VNInfo *ParentVNI, SlotIndex Idx);
 232
 233   /// markComplexMapped - Mark ParentVNI as complex mapped in RegIdx regardless
 234   /// of the number of defs.
 235   void markComplexMapped(unsigned RegIdx, const VNInfo *ParentVNI);
 236
 237   /// defFromParent - Define Reg from ParentVNI at UseIdx using either
 238   /// rematerialization or a COPY from parent. Return the new value.
 239   VNInfo *defFromParent(unsigned RegIdx,
 240                         VNInfo *ParentVNI,
 241                         SlotIndex UseIdx,
 242                         MachineBasicBlock &MBB,
 243                         MachineBasicBlock::iterator I);
 244
 245   /// extendRange - Extend the live range of Edit.get(RegIdx) so it reaches Idx.
 246   /// Insert PHIDefs as needed to preserve SSA form.
 247   void extendRange(unsigned RegIdx, SlotIndex Idx);
 248
 249   /// updateSSA - Insert PHIDefs as necessary and update LiveOutCache such that
 250   /// Edit.get(RegIdx) is live-in to all the blocks in LiveIn.
 251   /// Return the value that is eventually live-in to IdxMBB.
 252   VNInfo *updateSSA(unsigned RegIdx,
 253                     SmallVectorImpl<MachineDomTreeNode*> &LiveIn,
 254                     SlotIndex Idx,
 255                     const MachineBasicBlock *IdxMBB);
 256
 257   /// transferSimpleValues - Transfer simply defined values to the new ranges.
 258   /// Return true if any complex ranges were skipped.
 259   bool transferSimpleValues();
 260
 261   /// extendPHIKillRanges - Extend the ranges of all values killed by original
 262   /// parent PHIDefs.
 263   void extendPHIKillRanges();
 264
 265   /// rewriteAssigned - Rewrite all uses of Edit.getReg() to assigned registers.
 266   void rewriteAssigned(bool ExtendRanges);
 267
 268   /// deleteRematVictims - Delete defs that are dead after rematerializing.
 269   void deleteRematVictims();
 270
 271 public:
 272   /// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
 273   /// Newly created intervals will be appended to newIntervals.
 274   SplitEditor(SplitAnalysis &SA, LiveIntervals&, VirtRegMap&,
 275               MachineDominatorTree&);
 276
 277   /// reset - Prepare for a new split.
 278   void reset(LiveRangeEdit&);
 279
 280   /// Create a new virtual register and live interval.
 281   void openIntv();
 282
 283   /// enterIntvBefore - Enter the open interval before the instruction at Idx.
 284   /// If the parent interval is not live before Idx, a COPY is not inserted.
 285   /// Return the beginning of the new live range.
 286   SlotIndex enterIntvBefore(SlotIndex Idx);
 287
 288   /// enterIntvAtEnd - Enter the open interval at the end of MBB.
 289   /// Use the open interval from he inserted copy to the MBB end.
 290   /// Return the beginning of the new live range.
 291   SlotIndex enterIntvAtEnd(MachineBasicBlock &MBB);
 292
 293   /// useIntv - indicate that all instructions in MBB should use OpenLI.
 294   void useIntv(const MachineBasicBlock &MBB);
 295
 296   /// useIntv - indicate that all instructions in range should use OpenLI.
 297   void useIntv(SlotIndex Start, SlotIndex End);
 298
 299   /// leaveIntvAfter - Leave the open interval after the instruction at Idx.
 300   /// Return the end of the live range.
 301   SlotIndex leaveIntvAfter(SlotIndex Idx);
 302
 303   /// leaveIntvBefore - Leave the open interval before the instruction at Idx.
 304   /// Return the end of the live range.
 305   SlotIndex leaveIntvBefore(SlotIndex Idx);
 306
 307   /// leaveIntvAtTop - Leave the interval at the top of MBB.
 308   /// Add liveness from the MBB top to the copy.
 309   /// Return the end of the live range.
 310   SlotIndex leaveIntvAtTop(MachineBasicBlock &MBB);
 311
 312   /// overlapIntv - Indicate that all instructions in range should use the open
 313   /// interval, but also let the complement interval be live.
 314   ///
 315   /// This doubles the register pressure, but is sometimes required to deal with
 316   /// register uses after the last valid split point.
 317   ///
 318   /// The Start index should be a return value from a leaveIntv* call, and End
 319   /// should be in the same basic block. The parent interval must have the same
 320   /// value across the range.
 321   ///
 322   void overlapIntv(SlotIndex Start, SlotIndex End);
 323
 324   /// closeIntv - Indicate that we are done editing the currently open
 325   /// LiveInterval, and ranges can be trimmed.
 326   void closeIntv();
 327
 328   /// finish - after all the new live ranges have been created, compute the
 329   /// remaining live range, and rewrite instructions to use the new registers.
 330   void finish();
 331
 332   /// dump - print the current interval maping to dbgs().
 333   void dump() const;
 334
 335   // ===--- High level methods ---===
 336
 337   /// splitSingleBlocks - Split CurLI into a separate live interval inside each
 338   /// basic block in Blocks.
 339   void splitSingleBlocks(const SplitAnalysis::BlockPtrSet &Blocks);
 340 };
 341
 342 }