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      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 #ifndef LLVM_CODEGEN_SPLITKIT_H
     16 #define LLVM_CODEGEN_SPLITKIT_H
     17 
     18 #include "LiveRangeCalc.h"
     19 #include "llvm/ADT/ArrayRef.h"
     20 #include "llvm/ADT/DenseMap.h"
     21 #include "llvm/ADT/IntervalMap.h"
     22 #include "llvm/ADT/SmallPtrSet.h"
     23 
     24 namespace llvm {
     25 
     26 class ConnectedVNInfoEqClasses;
     27 class LiveInterval;
     28 class LiveIntervals;
     29 class LiveRangeEdit;
     30 class MachineBlockFrequencyInfo;
     31 class MachineInstr;
     32 class MachineLoopInfo;
     33 class MachineRegisterInfo;
     34 class TargetInstrInfo;
     35 class TargetRegisterInfo;
     36 class VirtRegMap;
     37 class VNInfo;
     38 class raw_ostream;
     39 
     40 /// SplitAnalysis - Analyze a LiveInterval, looking for live range splitting
     41 /// opportunities.
     42 class SplitAnalysis {
     43 public:
     44   const MachineFunction &MF;
     45   const VirtRegMap &VRM;
     46   const LiveIntervals &LIS;
     47   const MachineLoopInfo &Loops;
     48   const TargetInstrInfo &TII;
     49 
     50   /// Additional information about basic blocks where the current variable is
     51   /// live. Such a block will look like one of these templates:
     52   ///
     53   ///  1. |   o---x   | Internal to block. Variable is only live in this block.
     54   ///  2. |---x       | Live-in, kill.
     55   ///  3. |       o---| Def, live-out.
     56   ///  4. |---x   o---| Live-in, kill, def, live-out. Counted by NumGapBlocks.
     57   ///  5. |---o---o---| Live-through with uses or defs.
     58   ///  6. |-----------| Live-through without uses. Counted by NumThroughBlocks.
     59   ///
     60   /// Two BlockInfo entries are created for template 4. One for the live-in
     61   /// segment, and one for the live-out segment. These entries look as if the
     62   /// block were split in the middle where the live range isn't live.
     63   ///
     64   /// Live-through blocks without any uses don't get BlockInfo entries. They
     65   /// are simply listed in ThroughBlocks instead.
     66   ///
     67   struct BlockInfo {
     68     MachineBasicBlock *MBB;
     69     SlotIndex FirstInstr; ///< First instr accessing current reg.
     70     SlotIndex LastInstr;  ///< Last instr accessing current reg.
     71     SlotIndex FirstDef;   ///< First non-phi valno->def, or SlotIndex().
     72     bool LiveIn;          ///< Current reg is live in.
     73     bool LiveOut;         ///< Current reg is live out.
     74 
     75     /// isOneInstr - Returns true when this BlockInfo describes a single
     76     /// instruction.
     77     bool isOneInstr() const {
     78       return SlotIndex::isSameInstr(FirstInstr, LastInstr);
     79     }
     80   };
     81 
     82 private:
     83   // Current live interval.
     84   const LiveInterval *CurLI;
     85 
     86   // Sorted slot indexes of using instructions.
     87   SmallVector<SlotIndex, 8> UseSlots;
     88 
     89   /// LastSplitPoint - Last legal split point in each basic block in the current
     90   /// function. The first entry is the first terminator, the second entry is the
     91   /// last valid split point for a variable that is live in to a landing pad
     92   /// successor.
     93   SmallVector<std::pair<SlotIndex, SlotIndex>, 8> LastSplitPoint;
     94 
     95   /// UseBlocks - Blocks where CurLI has uses.
     96   SmallVector<BlockInfo, 8> UseBlocks;
     97 
     98   /// NumGapBlocks - Number of duplicate entries in UseBlocks for blocks where
     99   /// the live range has a gap.
    100   unsigned NumGapBlocks;
    101 
    102   /// ThroughBlocks - Block numbers where CurLI is live through without uses.
    103   BitVector ThroughBlocks;
    104 
    105   /// NumThroughBlocks - Number of live-through blocks.
    106   unsigned NumThroughBlocks;
    107 
    108   /// DidRepairRange - analyze was forced to shrinkToUses().
    109   bool DidRepairRange;
    110 
    111   SlotIndex computeLastSplitPoint(unsigned Num);
    112 
    113   // Sumarize statistics by counting instructions using CurLI.
    114   void analyzeUses();
    115 
    116   /// calcLiveBlockInfo - Compute per-block information about CurLI.
    117   bool calcLiveBlockInfo();
    118 
    119 public:
    120   SplitAnalysis(const VirtRegMap &vrm, const LiveIntervals &lis,
    121                 const MachineLoopInfo &mli);
    122 
    123   /// analyze - set CurLI to the specified interval, and analyze how it may be
    124   /// split.
    125   void analyze(const LiveInterval *li);
    126 
    127   /// didRepairRange() - Returns true if CurLI was invalid and has been repaired
    128   /// by analyze(). This really shouldn't happen, but sometimes the coalescer
    129   /// can create live ranges that end in mid-air.
    130   bool didRepairRange() const { return DidRepairRange; }
    131 
    132   /// clear - clear all data structures so SplitAnalysis is ready to analyze a
    133   /// new interval.
    134   void clear();
    135 
    136   /// getParent - Return the last analyzed interval.
    137   const LiveInterval &getParent() const { return *CurLI; }
    138 
    139   /// getLastSplitPoint - Return the base index of the last valid split point
    140   /// in the basic block numbered Num.
    141   SlotIndex getLastSplitPoint(unsigned Num) {
    142     // Inline the common simple case.
    143     if (LastSplitPoint[Num].first.isValid() &&
    144         !LastSplitPoint[Num].second.isValid())
    145       return LastSplitPoint[Num].first;
    146     return computeLastSplitPoint(Num);
    147   }
    148 
    149   /// getLastSplitPointIter - Returns the last split point as an iterator.
    150   MachineBasicBlock::iterator getLastSplitPointIter(MachineBasicBlock*);
    151 
    152   /// isOriginalEndpoint - Return true if the original live range was killed or
    153   /// (re-)defined at Idx. Idx should be the 'def' slot for a normal kill/def,
    154   /// and 'use' for an early-clobber def.
    155   /// This can be used to recognize code inserted by earlier live range
    156   /// splitting.
    157   bool isOriginalEndpoint(SlotIndex Idx) const;
    158 
    159   /// getUseSlots - Return an array of SlotIndexes of instructions using CurLI.
    160   /// This include both use and def operands, at most one entry per instruction.
    161   ArrayRef<SlotIndex> getUseSlots() const { return UseSlots; }
    162 
    163   /// getUseBlocks - Return an array of BlockInfo objects for the basic blocks
    164   /// where CurLI has uses.
    165   ArrayRef<BlockInfo> getUseBlocks() const { return UseBlocks; }
    166 
    167   /// getNumThroughBlocks - Return the number of through blocks.
    168   unsigned getNumThroughBlocks() const { return NumThroughBlocks; }
    169 
    170   /// isThroughBlock - Return true if CurLI is live through MBB without uses.
    171   bool isThroughBlock(unsigned MBB) const { return ThroughBlocks.test(MBB); }
    172 
    173   /// getThroughBlocks - Return the set of through blocks.
    174   const BitVector &getThroughBlocks() const { return ThroughBlocks; }
    175 
    176   /// getNumLiveBlocks - Return the number of blocks where CurLI is live.
    177   unsigned getNumLiveBlocks() const {
    178     return getUseBlocks().size() - NumGapBlocks + getNumThroughBlocks();
    179   }
    180 
    181   /// countLiveBlocks - Return the number of blocks where li is live. This is
    182   /// guaranteed to return the same number as getNumLiveBlocks() after calling
    183   /// analyze(li).
    184   unsigned countLiveBlocks(const LiveInterval *li) const;
    185 
    186   typedef SmallPtrSet<const MachineBasicBlock*, 16> BlockPtrSet;
    187 
    188   /// shouldSplitSingleBlock - Returns true if it would help to create a local
    189   /// live range for the instructions in BI. There is normally no benefit to
    190   /// creating a live range for a single instruction, but it does enable
    191   /// register class inflation if the instruction has a restricted register
    192   /// class.
    193   ///
    194   /// @param BI           The block to be isolated.
    195   /// @param SingleInstrs True when single instructions should be isolated.
    196   bool shouldSplitSingleBlock(const BlockInfo &BI, bool SingleInstrs) const;
    197 };
    198 
    199 
    200 /// SplitEditor - Edit machine code and LiveIntervals for live range
    201 /// splitting.
    202 ///
    203 /// - Create a SplitEditor from a SplitAnalysis.
    204 /// - Start a new live interval with openIntv.
    205 /// - Mark the places where the new interval is entered using enterIntv*
    206 /// - Mark the ranges where the new interval is used with useIntv*
    207 /// - Mark the places where the interval is exited with exitIntv*.
    208 /// - Finish the current interval with closeIntv and repeat from 2.
    209 /// - Rewrite instructions with finish().
    210 ///
    211 class SplitEditor {
    212   SplitAnalysis &SA;
    213   LiveIntervals &LIS;
    214   VirtRegMap &VRM;
    215   MachineRegisterInfo &MRI;
    216   MachineDominatorTree &MDT;
    217   const TargetInstrInfo &TII;
    218   const TargetRegisterInfo &TRI;
    219   const MachineBlockFrequencyInfo &MBFI;
    220 
    221 public:
    222 
    223   /// ComplementSpillMode - Select how the complement live range should be
    224   /// created.  SplitEditor automatically creates interval 0 to contain
    225   /// anything that isn't added to another interval.  This complement interval
    226   /// can get quite complicated, and it can sometimes be an advantage to allow
    227   /// it to overlap the other intervals.  If it is going to spill anyway, no
    228   /// registers are wasted by keeping a value in two places at the same time.
    229   enum ComplementSpillMode {
    230     /// SM_Partition(Default) - Try to create the complement interval so it
    231     /// doesn't overlap any other intervals, and the original interval is
    232     /// partitioned.  This may require a large number of back copies and extra
    233     /// PHI-defs.  Only segments marked with overlapIntv will be overlapping.
    234     SM_Partition,
    235 
    236     /// SM_Size - Overlap intervals to minimize the number of inserted COPY
    237     /// instructions.  Copies to the complement interval are hoisted to their
    238     /// common dominator, so only one COPY is required per value in the
    239     /// complement interval.  This also means that no extra PHI-defs need to be
    240     /// inserted in the complement interval.
    241     SM_Size,
    242 
    243     /// SM_Speed - Overlap intervals to minimize the expected execution
    244     /// frequency of the inserted copies.  This is very similar to SM_Size, but
    245     /// the complement interval may get some extra PHI-defs.
    246     SM_Speed
    247   };
    248 
    249 private:
    250 
    251   /// Edit - The current parent register and new intervals created.
    252   LiveRangeEdit *Edit;
    253 
    254   /// Index into Edit of the currently open interval.
    255   /// The index 0 is used for the complement, so the first interval started by
    256   /// openIntv will be 1.
    257   unsigned OpenIdx;
    258 
    259   /// The current spill mode, selected by reset().
    260   ComplementSpillMode SpillMode;
    261 
    262   typedef IntervalMap<SlotIndex, unsigned> RegAssignMap;
    263 
    264   /// Allocator for the interval map. This will eventually be shared with
    265   /// SlotIndexes and LiveIntervals.
    266   RegAssignMap::Allocator Allocator;
    267 
    268   /// RegAssign - Map of the assigned register indexes.
    269   /// Edit.get(RegAssign.lookup(Idx)) is the register that should be live at
    270   /// Idx.
    271   RegAssignMap RegAssign;
    272 
    273   typedef PointerIntPair<VNInfo*, 1> ValueForcePair;
    274   typedef DenseMap<std::pair<unsigned, unsigned>, ValueForcePair> ValueMap;
    275 
    276   /// Values - keep track of the mapping from parent values to values in the new
    277   /// intervals. Given a pair (RegIdx, ParentVNI->id), Values contains:
    278   ///
    279   /// 1. No entry - the value is not mapped to Edit.get(RegIdx).
    280   /// 2. (Null, false) - the value is mapped to multiple values in
    281   ///    Edit.get(RegIdx).  Each value is represented by a minimal live range at
    282   ///    its def.  The full live range can be inferred exactly from the range
    283   ///    of RegIdx in RegAssign.
    284   /// 3. (Null, true).  As above, but the ranges in RegAssign are too large, and
    285   ///    the live range must be recomputed using LiveRangeCalc::extend().
    286   /// 4. (VNI, false) The value is mapped to a single new value.
    287   ///    The new value has no live ranges anywhere.
    288   ValueMap Values;
    289 
    290   /// LRCalc - Cache for computing live ranges and SSA update.  Each instance
    291   /// can only handle non-overlapping live ranges, so use a separate
    292   /// LiveRangeCalc instance for the complement interval when in spill mode.
    293   LiveRangeCalc LRCalc[2];
    294 
    295   /// getLRCalc - Return the LRCalc to use for RegIdx.  In spill mode, the
    296   /// complement interval can overlap the other intervals, so it gets its own
    297   /// LRCalc instance.  When not in spill mode, all intervals can share one.
    298   LiveRangeCalc &getLRCalc(unsigned RegIdx) {
    299     return LRCalc[SpillMode != SM_Partition && RegIdx != 0];
    300   }
    301 
    302   /// defValue - define a value in RegIdx from ParentVNI at Idx.
    303   /// Idx does not have to be ParentVNI->def, but it must be contained within
    304   /// ParentVNI's live range in ParentLI. The new value is added to the value
    305   /// map.
    306   /// Return the new LI value.
    307   VNInfo *defValue(unsigned RegIdx, const VNInfo *ParentVNI, SlotIndex Idx);
    308 
    309   /// forceRecompute - Force the live range of ParentVNI in RegIdx to be
    310   /// recomputed by LiveRangeCalc::extend regardless of the number of defs.
    311   /// This is used for values whose live range doesn't match RegAssign exactly.
    312   /// They could have rematerialized, or back-copies may have been moved.
    313   void forceRecompute(unsigned RegIdx, const VNInfo *ParentVNI);
    314 
    315   /// defFromParent - Define Reg from ParentVNI at UseIdx using either
    316   /// rematerialization or a COPY from parent. Return the new value.
    317   VNInfo *defFromParent(unsigned RegIdx,
    318                         VNInfo *ParentVNI,
    319                         SlotIndex UseIdx,
    320                         MachineBasicBlock &MBB,
    321                         MachineBasicBlock::iterator I);
    322 
    323   /// removeBackCopies - Remove the copy instructions that defines the values
    324   /// in the vector in the complement interval.
    325   void removeBackCopies(SmallVectorImpl<VNInfo*> &Copies);
    326 
    327   /// getShallowDominator - Returns the least busy dominator of MBB that is
    328   /// also dominated by DefMBB.  Busy is measured by loop depth.
    329   MachineBasicBlock *findShallowDominator(MachineBasicBlock *MBB,
    330                                           MachineBasicBlock *DefMBB);
    331 
    332   /// hoistCopiesForSize - Hoist back-copies to the complement interval in a
    333   /// way that minimizes code size. This implements the SM_Size spill mode.
    334   void hoistCopiesForSize();
    335 
    336   /// transferValues - Transfer values to the new ranges.
    337   /// Return true if any ranges were skipped.
    338   bool transferValues();
    339 
    340   /// extendPHIKillRanges - Extend the ranges of all values killed by original
    341   /// parent PHIDefs.
    342   void extendPHIKillRanges();
    343 
    344   /// rewriteAssigned - Rewrite all uses of Edit.getReg() to assigned registers.
    345   void rewriteAssigned(bool ExtendRanges);
    346 
    347   /// deleteRematVictims - Delete defs that are dead after rematerializing.
    348   void deleteRematVictims();
    349 
    350 public:
    351   /// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
    352   /// Newly created intervals will be appended to newIntervals.
    353   SplitEditor(SplitAnalysis &SA, LiveIntervals&, VirtRegMap&,
    354               MachineDominatorTree&, MachineBlockFrequencyInfo &);
    355 
    356   /// reset - Prepare for a new split.
    357   void reset(LiveRangeEdit&, ComplementSpillMode = SM_Partition);
    358 
    359   /// Create a new virtual register and live interval.
    360   /// Return the interval index, starting from 1. Interval index 0 is the
    361   /// implicit complement interval.
    362   unsigned openIntv();
    363 
    364   /// currentIntv - Return the current interval index.
    365   unsigned currentIntv() const { return OpenIdx; }
    366 
    367   /// selectIntv - Select a previously opened interval index.
    368   void selectIntv(unsigned Idx);
    369 
    370   /// enterIntvBefore - Enter the open interval before the instruction at Idx.
    371   /// If the parent interval is not live before Idx, a COPY is not inserted.
    372   /// Return the beginning of the new live range.
    373   SlotIndex enterIntvBefore(SlotIndex Idx);
    374 
    375   /// enterIntvAfter - Enter the open interval after the instruction at Idx.
    376   /// Return the beginning of the new live range.
    377   SlotIndex enterIntvAfter(SlotIndex Idx);
    378 
    379   /// enterIntvAtEnd - Enter the open interval at the end of MBB.
    380   /// Use the open interval from the inserted copy to the MBB end.
    381   /// Return the beginning of the new live range.
    382   SlotIndex enterIntvAtEnd(MachineBasicBlock &MBB);
    383 
    384   /// useIntv - indicate that all instructions in MBB should use OpenLI.
    385   void useIntv(const MachineBasicBlock &MBB);
    386 
    387   /// useIntv - indicate that all instructions in range should use OpenLI.
    388   void useIntv(SlotIndex Start, SlotIndex End);
    389 
    390   /// leaveIntvAfter - Leave the open interval after the instruction at Idx.
    391   /// Return the end of the live range.
    392   SlotIndex leaveIntvAfter(SlotIndex Idx);
    393 
    394   /// leaveIntvBefore - Leave the open interval before the instruction at Idx.
    395   /// Return the end of the live range.
    396   SlotIndex leaveIntvBefore(SlotIndex Idx);
    397 
    398   /// leaveIntvAtTop - Leave the interval at the top of MBB.
    399   /// Add liveness from the MBB top to the copy.
    400   /// Return the end of the live range.
    401   SlotIndex leaveIntvAtTop(MachineBasicBlock &MBB);
    402 
    403   /// overlapIntv - Indicate that all instructions in range should use the open
    404   /// interval, but also let the complement interval be live.
    405   ///
    406   /// This doubles the register pressure, but is sometimes required to deal with
    407   /// register uses after the last valid split point.
    408   ///
    409   /// The Start index should be a return value from a leaveIntv* call, and End
    410   /// should be in the same basic block. The parent interval must have the same
    411   /// value across the range.
    412   ///
    413   void overlapIntv(SlotIndex Start, SlotIndex End);
    414 
    415   /// finish - after all the new live ranges have been created, compute the
    416   /// remaining live range, and rewrite instructions to use the new registers.
    417   /// @param LRMap When not null, this vector will map each live range in Edit
    418   ///              back to the indices returned by openIntv.
    419   ///              There may be extra indices created by dead code elimination.
    420   void finish(SmallVectorImpl<unsigned> *LRMap = nullptr);
    421 
    422   /// dump - print the current interval maping to dbgs().
    423   void dump() const;
    424 
    425   // ===--- High level methods ---===
    426 
    427   /// splitSingleBlock - Split CurLI into a separate live interval around the
    428   /// uses in a single block. This is intended to be used as part of a larger
    429   /// split, and doesn't call finish().
    430   void splitSingleBlock(const SplitAnalysis::BlockInfo &BI);
    431 
    432   /// splitLiveThroughBlock - Split CurLI in the given block such that it
    433   /// enters the block in IntvIn and leaves it in IntvOut. There may be uses in
    434   /// the block, but they will be ignored when placing split points.
    435   ///
    436   /// @param MBBNum      Block number.
    437   /// @param IntvIn      Interval index entering the block.
    438   /// @param LeaveBefore When set, leave IntvIn before this point.
    439   /// @param IntvOut     Interval index leaving the block.
    440   /// @param EnterAfter  When set, enter IntvOut after this point.
    441   void splitLiveThroughBlock(unsigned MBBNum,
    442                              unsigned IntvIn, SlotIndex LeaveBefore,
    443                              unsigned IntvOut, SlotIndex EnterAfter);
    444 
    445   /// splitRegInBlock - Split CurLI in the given block such that it enters the
    446   /// block in IntvIn and leaves it on the stack (or not at all). Split points
    447   /// are placed in a way that avoids putting uses in the stack interval. This
    448   /// may require creating a local interval when there is interference.
    449   ///
    450   /// @param BI          Block descriptor.
    451   /// @param IntvIn      Interval index entering the block. Not 0.
    452   /// @param LeaveBefore When set, leave IntvIn before this point.
    453   void splitRegInBlock(const SplitAnalysis::BlockInfo &BI,
    454                        unsigned IntvIn, SlotIndex LeaveBefore);
    455 
    456   /// splitRegOutBlock - Split CurLI in the given block such that it enters the
    457   /// block on the stack (or isn't live-in at all) and leaves it in IntvOut.
    458   /// Split points are placed to avoid interference and such that the uses are
    459   /// not in the stack interval. This may require creating a local interval
    460   /// when there is interference.
    461   ///
    462   /// @param BI          Block descriptor.
    463   /// @param IntvOut     Interval index leaving the block.
    464   /// @param EnterAfter  When set, enter IntvOut after this point.
    465   void splitRegOutBlock(const SplitAnalysis::BlockInfo &BI,
    466                         unsigned IntvOut, SlotIndex EnterAfter);
    467 };
    468 
    469 }
    470 
    471 #endif
    472