1 //===-------- SplitKit.h - Toolkit for splitting live ranges ----*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file contains the SplitAnalysis class as well as mutator functions for
11 // live range splitting.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_LIB_CODEGEN_SPLITKIT_H
16 #define LLVM_LIB_CODEGEN_SPLITKIT_H
18 #include "LiveRangeCalc.h"
19 #include "llvm/ADT/ArrayRef.h"
20 #include "llvm/ADT/DenseMap.h"
21 #include "llvm/ADT/DenseSet.h"
22 #include "llvm/ADT/IntervalMap.h"
23 #include "llvm/ADT/SmallPtrSet.h"
27 class ConnectedVNInfoEqClasses;
31 class MachineBlockFrequencyInfo;
33 class MachineLoopInfo;
34 class MachineRegisterInfo;
35 class TargetInstrInfo;
36 class TargetRegisterInfo;
41 /// Determines the latest safe point in a block in which we can insert a split,
42 /// spill or other instruction related with CurLI.
43 class LLVM_LIBRARY_VISIBILITY InsertPointAnalysis {
45 const LiveIntervals &LIS;
47 /// Last legal insert point in each basic block in the current function.
48 /// The first entry is the first terminator, the second entry is the
49 /// last valid point to insert a split or spill for a variable that is
50 /// live into a landing pad successor.
51 SmallVector<std::pair<SlotIndex, SlotIndex>, 8> LastInsertPoint;
53 SlotIndex computeLastInsertPoint(const LiveInterval &CurLI,
54 const MachineBasicBlock &MBB);
57 InsertPointAnalysis(const LiveIntervals &lis, unsigned BBNum);
59 /// Return the base index of the last valid insert point for \pCurLI in \pMBB.
60 SlotIndex getLastInsertPoint(const LiveInterval &CurLI,
61 const MachineBasicBlock &MBB) {
62 unsigned Num = MBB.getNumber();
63 // Inline the common simple case.
64 if (LastInsertPoint[Num].first.isValid() &&
65 !LastInsertPoint[Num].second.isValid())
66 return LastInsertPoint[Num].first;
67 return computeLastInsertPoint(CurLI, MBB);
70 /// Returns the last insert point as an iterator for \pCurLI in \pMBB.
71 MachineBasicBlock::iterator getLastInsertPointIter(const LiveInterval &CurLI,
72 MachineBasicBlock &MBB);
75 /// SplitAnalysis - Analyze a LiveInterval, looking for live range splitting
77 class LLVM_LIBRARY_VISIBILITY SplitAnalysis {
79 const MachineFunction &MF;
80 const VirtRegMap &VRM;
81 const LiveIntervals &LIS;
82 const MachineLoopInfo &Loops;
83 const TargetInstrInfo &TII;
85 /// Additional information about basic blocks where the current variable is
86 /// live. Such a block will look like one of these templates:
88 /// 1. | o---x | Internal to block. Variable is only live in this block.
89 /// 2. |---x | Live-in, kill.
90 /// 3. | o---| Def, live-out.
91 /// 4. |---x o---| Live-in, kill, def, live-out. Counted by NumGapBlocks.
92 /// 5. |---o---o---| Live-through with uses or defs.
93 /// 6. |-----------| Live-through without uses. Counted by NumThroughBlocks.
95 /// Two BlockInfo entries are created for template 4. One for the live-in
96 /// segment, and one for the live-out segment. These entries look as if the
97 /// block were split in the middle where the live range isn't live.
99 /// Live-through blocks without any uses don't get BlockInfo entries. They
100 /// are simply listed in ThroughBlocks instead.
103 MachineBasicBlock *MBB;
104 SlotIndex FirstInstr; ///< First instr accessing current reg.
105 SlotIndex LastInstr; ///< Last instr accessing current reg.
106 SlotIndex FirstDef; ///< First non-phi valno->def, or SlotIndex().
107 bool LiveIn; ///< Current reg is live in.
108 bool LiveOut; ///< Current reg is live out.
110 /// isOneInstr - Returns true when this BlockInfo describes a single
112 bool isOneInstr() const {
113 return SlotIndex::isSameInstr(FirstInstr, LastInstr);
118 // Current live interval.
119 const LiveInterval *CurLI;
121 /// Insert Point Analysis.
122 InsertPointAnalysis IPA;
124 // Sorted slot indexes of using instructions.
125 SmallVector<SlotIndex, 8> UseSlots;
127 /// UseBlocks - Blocks where CurLI has uses.
128 SmallVector<BlockInfo, 8> UseBlocks;
130 /// NumGapBlocks - Number of duplicate entries in UseBlocks for blocks where
131 /// the live range has a gap.
132 unsigned NumGapBlocks;
134 /// ThroughBlocks - Block numbers where CurLI is live through without uses.
135 BitVector ThroughBlocks;
137 /// NumThroughBlocks - Number of live-through blocks.
138 unsigned NumThroughBlocks;
140 /// DidRepairRange - analyze was forced to shrinkToUses().
143 // Sumarize statistics by counting instructions using CurLI.
146 /// calcLiveBlockInfo - Compute per-block information about CurLI.
147 bool calcLiveBlockInfo();
150 SplitAnalysis(const VirtRegMap &vrm, const LiveIntervals &lis,
151 const MachineLoopInfo &mli);
153 /// analyze - set CurLI to the specified interval, and analyze how it may be
155 void analyze(const LiveInterval *li);
157 /// didRepairRange() - Returns true if CurLI was invalid and has been repaired
158 /// by analyze(). This really shouldn't happen, but sometimes the coalescer
159 /// can create live ranges that end in mid-air.
160 bool didRepairRange() const { return DidRepairRange; }
162 /// clear - clear all data structures so SplitAnalysis is ready to analyze a
166 /// getParent - Return the last analyzed interval.
167 const LiveInterval &getParent() const { return *CurLI; }
169 /// isOriginalEndpoint - Return true if the original live range was killed or
170 /// (re-)defined at Idx. Idx should be the 'def' slot for a normal kill/def,
171 /// and 'use' for an early-clobber def.
172 /// This can be used to recognize code inserted by earlier live range
174 bool isOriginalEndpoint(SlotIndex Idx) const;
176 /// getUseSlots - Return an array of SlotIndexes of instructions using CurLI.
177 /// This include both use and def operands, at most one entry per instruction.
178 ArrayRef<SlotIndex> getUseSlots() const { return UseSlots; }
180 /// getUseBlocks - Return an array of BlockInfo objects for the basic blocks
181 /// where CurLI has uses.
182 ArrayRef<BlockInfo> getUseBlocks() const { return UseBlocks; }
184 /// getNumThroughBlocks - Return the number of through blocks.
185 unsigned getNumThroughBlocks() const { return NumThroughBlocks; }
187 /// isThroughBlock - Return true if CurLI is live through MBB without uses.
188 bool isThroughBlock(unsigned MBB) const { return ThroughBlocks.test(MBB); }
190 /// getThroughBlocks - Return the set of through blocks.
191 const BitVector &getThroughBlocks() const { return ThroughBlocks; }
193 /// getNumLiveBlocks - Return the number of blocks where CurLI is live.
194 unsigned getNumLiveBlocks() const {
195 return getUseBlocks().size() - NumGapBlocks + getNumThroughBlocks();
198 /// countLiveBlocks - Return the number of blocks where li is live. This is
199 /// guaranteed to return the same number as getNumLiveBlocks() after calling
201 unsigned countLiveBlocks(const LiveInterval *li) const;
203 typedef SmallPtrSet<const MachineBasicBlock*, 16> BlockPtrSet;
205 /// shouldSplitSingleBlock - Returns true if it would help to create a local
206 /// live range for the instructions in BI. There is normally no benefit to
207 /// creating a live range for a single instruction, but it does enable
208 /// register class inflation if the instruction has a restricted register
211 /// @param BI The block to be isolated.
212 /// @param SingleInstrs True when single instructions should be isolated.
213 bool shouldSplitSingleBlock(const BlockInfo &BI, bool SingleInstrs) const;
215 SlotIndex getLastSplitPoint(unsigned Num) {
216 return IPA.getLastInsertPoint(*CurLI, *MF.getBlockNumbered(Num));
219 MachineBasicBlock::iterator getLastSplitPointIter(MachineBasicBlock *BB) {
220 return IPA.getLastInsertPointIter(*CurLI, *BB);
225 /// SplitEditor - Edit machine code and LiveIntervals for live range
228 /// - Create a SplitEditor from a SplitAnalysis.
229 /// - Start a new live interval with openIntv.
230 /// - Mark the places where the new interval is entered using enterIntv*
231 /// - Mark the ranges where the new interval is used with useIntv*
232 /// - Mark the places where the interval is exited with exitIntv*.
233 /// - Finish the current interval with closeIntv and repeat from 2.
234 /// - Rewrite instructions with finish().
236 class LLVM_LIBRARY_VISIBILITY SplitEditor {
241 MachineRegisterInfo &MRI;
242 MachineDominatorTree &MDT;
243 const TargetInstrInfo &TII;
244 const TargetRegisterInfo &TRI;
245 const MachineBlockFrequencyInfo &MBFI;
249 /// ComplementSpillMode - Select how the complement live range should be
250 /// created. SplitEditor automatically creates interval 0 to contain
251 /// anything that isn't added to another interval. This complement interval
252 /// can get quite complicated, and it can sometimes be an advantage to allow
253 /// it to overlap the other intervals. If it is going to spill anyway, no
254 /// registers are wasted by keeping a value in two places at the same time.
255 enum ComplementSpillMode {
256 /// SM_Partition(Default) - Try to create the complement interval so it
257 /// doesn't overlap any other intervals, and the original interval is
258 /// partitioned. This may require a large number of back copies and extra
259 /// PHI-defs. Only segments marked with overlapIntv will be overlapping.
262 /// SM_Size - Overlap intervals to minimize the number of inserted COPY
263 /// instructions. Copies to the complement interval are hoisted to their
264 /// common dominator, so only one COPY is required per value in the
265 /// complement interval. This also means that no extra PHI-defs need to be
266 /// inserted in the complement interval.
269 /// SM_Speed - Overlap intervals to minimize the expected execution
270 /// frequency of the inserted copies. This is very similar to SM_Size, but
271 /// the complement interval may get some extra PHI-defs.
277 /// Edit - The current parent register and new intervals created.
280 /// Index into Edit of the currently open interval.
281 /// The index 0 is used for the complement, so the first interval started by
282 /// openIntv will be 1.
285 /// The current spill mode, selected by reset().
286 ComplementSpillMode SpillMode;
288 typedef IntervalMap<SlotIndex, unsigned> RegAssignMap;
290 /// Allocator for the interval map. This will eventually be shared with
291 /// SlotIndexes and LiveIntervals.
292 RegAssignMap::Allocator Allocator;
294 /// RegAssign - Map of the assigned register indexes.
295 /// Edit.get(RegAssign.lookup(Idx)) is the register that should be live at
297 RegAssignMap RegAssign;
299 typedef PointerIntPair<VNInfo*, 1> ValueForcePair;
300 typedef DenseMap<std::pair<unsigned, unsigned>, ValueForcePair> ValueMap;
302 /// Values - keep track of the mapping from parent values to values in the new
303 /// intervals. Given a pair (RegIdx, ParentVNI->id), Values contains:
305 /// 1. No entry - the value is not mapped to Edit.get(RegIdx).
306 /// 2. (Null, false) - the value is mapped to multiple values in
307 /// Edit.get(RegIdx). Each value is represented by a minimal live range at
308 /// its def. The full live range can be inferred exactly from the range
309 /// of RegIdx in RegAssign.
310 /// 3. (Null, true). As above, but the ranges in RegAssign are too large, and
311 /// the live range must be recomputed using LiveRangeCalc::extend().
312 /// 4. (VNI, false) The value is mapped to a single new value.
313 /// The new value has no live ranges anywhere.
316 /// LRCalc - Cache for computing live ranges and SSA update. Each instance
317 /// can only handle non-overlapping live ranges, so use a separate
318 /// LiveRangeCalc instance for the complement interval when in spill mode.
319 LiveRangeCalc LRCalc[2];
321 /// getLRCalc - Return the LRCalc to use for RegIdx. In spill mode, the
322 /// complement interval can overlap the other intervals, so it gets its own
323 /// LRCalc instance. When not in spill mode, all intervals can share one.
324 LiveRangeCalc &getLRCalc(unsigned RegIdx) {
325 return LRCalc[SpillMode != SM_Partition && RegIdx != 0];
328 /// Find a subrange corresponding to the lane mask @p LM in the live
329 /// interval @p LI. The interval @p LI is assumed to contain such a subrange.
330 /// This function is used to find corresponding subranges between the
331 /// original interval and the new intervals.
332 LiveInterval::SubRange &getSubRangeForMask(LaneBitmask LM, LiveInterval &LI);
334 /// Add a segment to the interval LI for the value number VNI. If LI has
335 /// subranges, corresponding segments will be added to them as well, but
336 /// with newly created value numbers. If Original is true, dead def will
337 /// only be added a subrange of LI if the corresponding subrange of the
338 /// original interval has a def at this index. Otherwise, all subranges
339 /// of LI will be updated.
340 void addDeadDef(LiveInterval &LI, VNInfo *VNI, bool Original);
342 /// defValue - define a value in RegIdx from ParentVNI at Idx.
343 /// Idx does not have to be ParentVNI->def, but it must be contained within
344 /// ParentVNI's live range in ParentLI. The new value is added to the value
345 /// map. The value being defined may either come from rematerialization
346 /// (or an inserted copy), or it may be coming from the original interval.
347 /// The parameter Original should be true in the latter case, otherwise
348 /// it should be false.
349 /// Return the new LI value.
350 VNInfo *defValue(unsigned RegIdx, const VNInfo *ParentVNI, SlotIndex Idx,
353 /// forceRecompute - Force the live range of ParentVNI in RegIdx to be
354 /// recomputed by LiveRangeCalc::extend regardless of the number of defs.
355 /// This is used for values whose live range doesn't match RegAssign exactly.
356 /// They could have rematerialized, or back-copies may have been moved.
357 void forceRecompute(unsigned RegIdx, const VNInfo *ParentVNI);
359 /// defFromParent - Define Reg from ParentVNI at UseIdx using either
360 /// rematerialization or a COPY from parent. Return the new value.
361 VNInfo *defFromParent(unsigned RegIdx,
364 MachineBasicBlock &MBB,
365 MachineBasicBlock::iterator I);
367 /// removeBackCopies - Remove the copy instructions that defines the values
368 /// in the vector in the complement interval.
369 void removeBackCopies(SmallVectorImpl<VNInfo*> &Copies);
371 /// getShallowDominator - Returns the least busy dominator of MBB that is
372 /// also dominated by DefMBB. Busy is measured by loop depth.
373 MachineBasicBlock *findShallowDominator(MachineBasicBlock *MBB,
374 MachineBasicBlock *DefMBB);
376 /// Find out all the backCopies dominated by others.
377 void computeRedundantBackCopies(DenseSet<unsigned> &NotToHoistSet,
378 SmallVectorImpl<VNInfo *> &BackCopies);
380 /// Hoist back-copies to the complement interval. It tries to hoist all
381 /// the back-copies to one BB if it is beneficial, or else simply remove
382 /// redundant backcopies dominated by others.
385 /// transferValues - Transfer values to the new ranges.
386 /// Return true if any ranges were skipped.
387 bool transferValues();
389 /// Live range @p LR corresponding to the lane Mask @p LM has a live
390 /// PHI def at the beginning of block @p B. Extend the range @p LR of
391 /// all predecessor values that reach this def. If @p LR is a subrange,
392 /// the array @p Undefs is the set of all locations where it is undefined
393 /// via <def,read-undef> in other subranges for the same register.
394 void extendPHIRange(MachineBasicBlock &B, LiveRangeCalc &LRC,
395 LiveRange &LR, LaneBitmask LM,
396 ArrayRef<SlotIndex> Undefs);
398 /// extendPHIKillRanges - Extend the ranges of all values killed by original
400 void extendPHIKillRanges();
402 /// rewriteAssigned - Rewrite all uses of Edit.getReg() to assigned registers.
403 void rewriteAssigned(bool ExtendRanges);
405 /// deleteRematVictims - Delete defs that are dead after rematerializing.
406 void deleteRematVictims();
408 /// Add a copy instruction copying \p FromReg to \p ToReg before
409 /// \p InsertBefore. This can be invoked with a \p LaneMask which may make it
410 /// necessary to construct a sequence of copies to cover it exactly.
411 SlotIndex buildCopy(unsigned FromReg, unsigned ToReg, LaneBitmask LaneMask,
412 MachineBasicBlock &MBB, MachineBasicBlock::iterator InsertBefore,
413 bool Late, unsigned RegIdx);
415 SlotIndex buildSingleSubRegCopy(unsigned FromReg, unsigned ToReg,
416 MachineBasicBlock &MB, MachineBasicBlock::iterator InsertBefore,
417 unsigned SubIdx, LiveInterval &DestLI, bool Late, SlotIndex PrevCopy);
420 /// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
421 /// Newly created intervals will be appended to newIntervals.
422 SplitEditor(SplitAnalysis &SA, AliasAnalysis &AA, LiveIntervals&,
423 VirtRegMap&, MachineDominatorTree&,
424 MachineBlockFrequencyInfo &);
426 /// reset - Prepare for a new split.
427 void reset(LiveRangeEdit&, ComplementSpillMode = SM_Partition);
429 /// Create a new virtual register and live interval.
430 /// Return the interval index, starting from 1. Interval index 0 is the
431 /// implicit complement interval.
434 /// currentIntv - Return the current interval index.
435 unsigned currentIntv() const { return OpenIdx; }
437 /// selectIntv - Select a previously opened interval index.
438 void selectIntv(unsigned Idx);
440 /// enterIntvBefore - Enter the open interval before the instruction at Idx.
441 /// If the parent interval is not live before Idx, a COPY is not inserted.
442 /// Return the beginning of the new live range.
443 SlotIndex enterIntvBefore(SlotIndex Idx);
445 /// enterIntvAfter - Enter the open interval after the instruction at Idx.
446 /// Return the beginning of the new live range.
447 SlotIndex enterIntvAfter(SlotIndex Idx);
449 /// enterIntvAtEnd - Enter the open interval at the end of MBB.
450 /// Use the open interval from the inserted copy to the MBB end.
451 /// Return the beginning of the new live range.
452 SlotIndex enterIntvAtEnd(MachineBasicBlock &MBB);
454 /// useIntv - indicate that all instructions in MBB should use OpenLI.
455 void useIntv(const MachineBasicBlock &MBB);
457 /// useIntv - indicate that all instructions in range should use OpenLI.
458 void useIntv(SlotIndex Start, SlotIndex End);
460 /// leaveIntvAfter - Leave the open interval after the instruction at Idx.
461 /// Return the end of the live range.
462 SlotIndex leaveIntvAfter(SlotIndex Idx);
464 /// leaveIntvBefore - Leave the open interval before the instruction at Idx.
465 /// Return the end of the live range.
466 SlotIndex leaveIntvBefore(SlotIndex Idx);
468 /// leaveIntvAtTop - Leave the interval at the top of MBB.
469 /// Add liveness from the MBB top to the copy.
470 /// Return the end of the live range.
471 SlotIndex leaveIntvAtTop(MachineBasicBlock &MBB);
473 /// overlapIntv - Indicate that all instructions in range should use the open
474 /// interval, but also let the complement interval be live.
476 /// This doubles the register pressure, but is sometimes required to deal with
477 /// register uses after the last valid split point.
479 /// The Start index should be a return value from a leaveIntv* call, and End
480 /// should be in the same basic block. The parent interval must have the same
481 /// value across the range.
483 void overlapIntv(SlotIndex Start, SlotIndex End);
485 /// finish - after all the new live ranges have been created, compute the
486 /// remaining live range, and rewrite instructions to use the new registers.
487 /// @param LRMap When not null, this vector will map each live range in Edit
488 /// back to the indices returned by openIntv.
489 /// There may be extra indices created by dead code elimination.
490 void finish(SmallVectorImpl<unsigned> *LRMap = nullptr);
492 /// dump - print the current interval mapping to dbgs().
495 // ===--- High level methods ---===
497 /// splitSingleBlock - Split CurLI into a separate live interval around the
498 /// uses in a single block. This is intended to be used as part of a larger
499 /// split, and doesn't call finish().
500 void splitSingleBlock(const SplitAnalysis::BlockInfo &BI);
502 /// splitLiveThroughBlock - Split CurLI in the given block such that it
503 /// enters the block in IntvIn and leaves it in IntvOut. There may be uses in
504 /// the block, but they will be ignored when placing split points.
506 /// @param MBBNum Block number.
507 /// @param IntvIn Interval index entering the block.
508 /// @param LeaveBefore When set, leave IntvIn before this point.
509 /// @param IntvOut Interval index leaving the block.
510 /// @param EnterAfter When set, enter IntvOut after this point.
511 void splitLiveThroughBlock(unsigned MBBNum,
512 unsigned IntvIn, SlotIndex LeaveBefore,
513 unsigned IntvOut, SlotIndex EnterAfter);
515 /// splitRegInBlock - Split CurLI in the given block such that it enters the
516 /// block in IntvIn and leaves it on the stack (or not at all). Split points
517 /// are placed in a way that avoids putting uses in the stack interval. This
518 /// may require creating a local interval when there is interference.
520 /// @param BI Block descriptor.
521 /// @param IntvIn Interval index entering the block. Not 0.
522 /// @param LeaveBefore When set, leave IntvIn before this point.
523 void splitRegInBlock(const SplitAnalysis::BlockInfo &BI,
524 unsigned IntvIn, SlotIndex LeaveBefore);
526 /// splitRegOutBlock - Split CurLI in the given block such that it enters the
527 /// block on the stack (or isn't live-in at all) and leaves it in IntvOut.
528 /// Split points are placed to avoid interference and such that the uses are
529 /// not in the stack interval. This may require creating a local interval
530 /// when there is interference.
532 /// @param BI Block descriptor.
533 /// @param IntvOut Interval index leaving the block.
534 /// @param EnterAfter When set, enter IntvOut after this point.
535 void splitRegOutBlock(const SplitAnalysis::BlockInfo &BI,
536 unsigned IntvOut, SlotIndex EnterAfter);