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_LIB_CODEGEN_SPLITKIT_H
16 #define LLVM_LIB_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.
isOneInstrBlockInfo77     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.
didRepairRange()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.
getParent()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.
getLastSplitPoint(unsigned 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.
getUseSlots()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.
getUseBlocks()165   ArrayRef<BlockInfo> getUseBlocks() const { return UseBlocks; }
166 
167   /// getNumThroughBlocks - Return the number of through blocks.
getNumThroughBlocks()168   unsigned getNumThroughBlocks() const { return NumThroughBlocks; }
169 
170   /// isThroughBlock - Return true if CurLI is live through MBB without uses.
isThroughBlock(unsigned MBB)171   bool isThroughBlock(unsigned MBB) const { return ThroughBlocks.test(MBB); }
172 
173   /// getThroughBlocks - Return the set of through blocks.
getThroughBlocks()174   const BitVector &getThroughBlocks() const { return ThroughBlocks; }
175 
176   /// getNumLiveBlocks - Return the number of blocks where CurLI is live.
getNumLiveBlocks()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.
getLRCalc(unsigned RegIdx)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.
currentIntv()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