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/BitVector.h"
21 #include "llvm/ADT/DenseMap.h"
22 #include "llvm/ADT/DenseSet.h"
23 #include "llvm/ADT/IntervalMap.h"
24 #include "llvm/ADT/PointerIntPair.h"
25 #include "llvm/ADT/SmallPtrSet.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/CodeGen/LiveInterval.h"
28 #include "llvm/CodeGen/LiveIntervals.h"
29 #include "llvm/CodeGen/MachineBasicBlock.h"
30 #include "llvm/CodeGen/MachineFunction.h"
31 #include "llvm/CodeGen/SlotIndexes.h"
32 #include "llvm/MC/LaneBitmask.h"
33 #include "llvm/Support/Compiler.h"
40 class MachineBlockFrequencyInfo;
41 class MachineDominatorTree;
42 class MachineLoopInfo;
43 class MachineRegisterInfo;
44 class TargetInstrInfo;
45 class TargetRegisterInfo;
48 /// Determines the latest safe point in a block in which we can insert a split,
49 /// spill or other instruction related with CurLI.
50 class LLVM_LIBRARY_VISIBILITY InsertPointAnalysis {
52 const LiveIntervals &LIS;
54 /// Last legal insert point in each basic block in the current function.
55 /// The first entry is the first terminator, the second entry is the
56 /// last valid point to insert a split or spill for a variable that is
57 /// live into a landing pad successor.
58 SmallVector<std::pair<SlotIndex, SlotIndex>, 8> LastInsertPoint;
60 SlotIndex computeLastInsertPoint(const LiveInterval &CurLI,
61 const MachineBasicBlock &MBB);
64 InsertPointAnalysis(const LiveIntervals &lis, unsigned BBNum);
66 /// Return the base index of the last valid insert point for \pCurLI in \pMBB.
67 SlotIndex getLastInsertPoint(const LiveInterval &CurLI,
68 const MachineBasicBlock &MBB) {
69 unsigned Num = MBB.getNumber();
70 // Inline the common simple case.
71 if (LastInsertPoint[Num].first.isValid() &&
72 !LastInsertPoint[Num].second.isValid())
73 return LastInsertPoint[Num].first;
74 return computeLastInsertPoint(CurLI, MBB);
77 /// Returns the last insert point as an iterator for \pCurLI in \pMBB.
78 MachineBasicBlock::iterator getLastInsertPointIter(const LiveInterval &CurLI,
79 MachineBasicBlock &MBB);
81 /// Return the base index of the first insert point in \pMBB.
82 SlotIndex getFirstInsertPoint(MachineBasicBlock &MBB) {
83 SlotIndex Res = LIS.getMBBStartIdx(&MBB);
85 MachineBasicBlock::iterator MII = MBB.SkipPHIsLabelsAndDebug(MBB.begin());
87 Res = LIS.getInstructionIndex(*MII);
94 /// SplitAnalysis - Analyze a LiveInterval, looking for live range splitting
96 class LLVM_LIBRARY_VISIBILITY SplitAnalysis {
98 const MachineFunction &MF;
99 const VirtRegMap &VRM;
100 const LiveIntervals &LIS;
101 const MachineLoopInfo &Loops;
102 const TargetInstrInfo &TII;
104 /// Additional information about basic blocks where the current variable is
105 /// live. Such a block will look like one of these templates:
107 /// 1. | o---x | Internal to block. Variable is only live in this block.
108 /// 2. |---x | Live-in, kill.
109 /// 3. | o---| Def, live-out.
110 /// 4. |---x o---| Live-in, kill, def, live-out. Counted by NumGapBlocks.
111 /// 5. |---o---o---| Live-through with uses or defs.
112 /// 6. |-----------| Live-through without uses. Counted by NumThroughBlocks.
114 /// Two BlockInfo entries are created for template 4. One for the live-in
115 /// segment, and one for the live-out segment. These entries look as if the
116 /// block were split in the middle where the live range isn't live.
118 /// Live-through blocks without any uses don't get BlockInfo entries. They
119 /// are simply listed in ThroughBlocks instead.
122 MachineBasicBlock *MBB;
123 SlotIndex FirstInstr; ///< First instr accessing current reg.
124 SlotIndex LastInstr; ///< Last instr accessing current reg.
125 SlotIndex FirstDef; ///< First non-phi valno->def, or SlotIndex().
126 bool LiveIn; ///< Current reg is live in.
127 bool LiveOut; ///< Current reg is live out.
129 /// isOneInstr - Returns true when this BlockInfo describes a single
131 bool isOneInstr() const {
132 return SlotIndex::isSameInstr(FirstInstr, LastInstr);
137 // Current live interval.
138 const LiveInterval *CurLI = nullptr;
140 /// Insert Point Analysis.
141 InsertPointAnalysis IPA;
143 // Sorted slot indexes of using instructions.
144 SmallVector<SlotIndex, 8> UseSlots;
146 /// UseBlocks - Blocks where CurLI has uses.
147 SmallVector<BlockInfo, 8> UseBlocks;
149 /// NumGapBlocks - Number of duplicate entries in UseBlocks for blocks where
150 /// the live range has a gap.
151 unsigned NumGapBlocks;
153 /// ThroughBlocks - Block numbers where CurLI is live through without uses.
154 BitVector ThroughBlocks;
156 /// NumThroughBlocks - Number of live-through blocks.
157 unsigned NumThroughBlocks;
159 /// DidRepairRange - analyze was forced to shrinkToUses().
162 // Sumarize statistics by counting instructions using CurLI.
165 /// calcLiveBlockInfo - Compute per-block information about CurLI.
166 bool calcLiveBlockInfo();
169 SplitAnalysis(const VirtRegMap &vrm, const LiveIntervals &lis,
170 const MachineLoopInfo &mli);
172 /// analyze - set CurLI to the specified interval, and analyze how it may be
174 void analyze(const LiveInterval *li);
176 /// didRepairRange() - Returns true if CurLI was invalid and has been repaired
177 /// by analyze(). This really shouldn't happen, but sometimes the coalescer
178 /// can create live ranges that end in mid-air.
179 bool didRepairRange() const { return DidRepairRange; }
181 /// clear - clear all data structures so SplitAnalysis is ready to analyze a
185 /// getParent - Return the last analyzed interval.
186 const LiveInterval &getParent() const { return *CurLI; }
188 /// isOriginalEndpoint - Return true if the original live range was killed or
189 /// (re-)defined at Idx. Idx should be the 'def' slot for a normal kill/def,
190 /// and 'use' for an early-clobber def.
191 /// This can be used to recognize code inserted by earlier live range
193 bool isOriginalEndpoint(SlotIndex Idx) const;
195 /// getUseSlots - Return an array of SlotIndexes of instructions using CurLI.
196 /// This include both use and def operands, at most one entry per instruction.
197 ArrayRef<SlotIndex> getUseSlots() const { return UseSlots; }
199 /// getUseBlocks - Return an array of BlockInfo objects for the basic blocks
200 /// where CurLI has uses.
201 ArrayRef<BlockInfo> getUseBlocks() const { return UseBlocks; }
203 /// getNumThroughBlocks - Return the number of through blocks.
204 unsigned getNumThroughBlocks() const { return NumThroughBlocks; }
206 /// isThroughBlock - Return true if CurLI is live through MBB without uses.
207 bool isThroughBlock(unsigned MBB) const { return ThroughBlocks.test(MBB); }
209 /// getThroughBlocks - Return the set of through blocks.
210 const BitVector &getThroughBlocks() const { return ThroughBlocks; }
212 /// getNumLiveBlocks - Return the number of blocks where CurLI is live.
213 unsigned getNumLiveBlocks() const {
214 return getUseBlocks().size() - NumGapBlocks + getNumThroughBlocks();
217 /// countLiveBlocks - Return the number of blocks where li is live. This is
218 /// guaranteed to return the same number as getNumLiveBlocks() after calling
220 unsigned countLiveBlocks(const LiveInterval *li) const;
222 using BlockPtrSet = SmallPtrSet<const MachineBasicBlock *, 16>;
224 /// shouldSplitSingleBlock - Returns true if it would help to create a local
225 /// live range for the instructions in BI. There is normally no benefit to
226 /// creating a live range for a single instruction, but it does enable
227 /// register class inflation if the instruction has a restricted register
230 /// @param BI The block to be isolated.
231 /// @param SingleInstrs True when single instructions should be isolated.
232 bool shouldSplitSingleBlock(const BlockInfo &BI, bool SingleInstrs) const;
234 SlotIndex getLastSplitPoint(unsigned Num) {
235 return IPA.getLastInsertPoint(*CurLI, *MF.getBlockNumbered(Num));
238 MachineBasicBlock::iterator getLastSplitPointIter(MachineBasicBlock *BB) {
239 return IPA.getLastInsertPointIter(*CurLI, *BB);
242 SlotIndex getFirstSplitPoint(unsigned Num) {
243 return IPA.getFirstInsertPoint(*MF.getBlockNumbered(Num));
247 /// SplitEditor - Edit machine code and LiveIntervals for live range
250 /// - Create a SplitEditor from a SplitAnalysis.
251 /// - Start a new live interval with openIntv.
252 /// - Mark the places where the new interval is entered using enterIntv*
253 /// - Mark the ranges where the new interval is used with useIntv*
254 /// - Mark the places where the interval is exited with exitIntv*.
255 /// - Finish the current interval with closeIntv and repeat from 2.
256 /// - Rewrite instructions with finish().
258 class LLVM_LIBRARY_VISIBILITY SplitEditor {
263 MachineRegisterInfo &MRI;
264 MachineDominatorTree &MDT;
265 const TargetInstrInfo &TII;
266 const TargetRegisterInfo &TRI;
267 const MachineBlockFrequencyInfo &MBFI;
270 /// ComplementSpillMode - Select how the complement live range should be
271 /// created. SplitEditor automatically creates interval 0 to contain
272 /// anything that isn't added to another interval. This complement interval
273 /// can get quite complicated, and it can sometimes be an advantage to allow
274 /// it to overlap the other intervals. If it is going to spill anyway, no
275 /// registers are wasted by keeping a value in two places at the same time.
276 enum ComplementSpillMode {
277 /// SM_Partition(Default) - Try to create the complement interval so it
278 /// doesn't overlap any other intervals, and the original interval is
279 /// partitioned. This may require a large number of back copies and extra
280 /// PHI-defs. Only segments marked with overlapIntv will be overlapping.
283 /// SM_Size - Overlap intervals to minimize the number of inserted COPY
284 /// instructions. Copies to the complement interval are hoisted to their
285 /// common dominator, so only one COPY is required per value in the
286 /// complement interval. This also means that no extra PHI-defs need to be
287 /// inserted in the complement interval.
290 /// SM_Speed - Overlap intervals to minimize the expected execution
291 /// frequency of the inserted copies. This is very similar to SM_Size, but
292 /// the complement interval may get some extra PHI-defs.
297 /// Edit - The current parent register and new intervals created.
298 LiveRangeEdit *Edit = nullptr;
300 /// Index into Edit of the currently open interval.
301 /// The index 0 is used for the complement, so the first interval started by
302 /// openIntv will be 1.
303 unsigned OpenIdx = 0;
305 /// The current spill mode, selected by reset().
306 ComplementSpillMode SpillMode = SM_Partition;
308 using RegAssignMap = IntervalMap<SlotIndex, unsigned>;
310 /// Allocator for the interval map. This will eventually be shared with
311 /// SlotIndexes and LiveIntervals.
312 RegAssignMap::Allocator Allocator;
314 /// RegAssign - Map of the assigned register indexes.
315 /// Edit.get(RegAssign.lookup(Idx)) is the register that should be live at
317 RegAssignMap RegAssign;
319 using ValueForcePair = PointerIntPair<VNInfo *, 1>;
320 using ValueMap = DenseMap<std::pair<unsigned, unsigned>, ValueForcePair>;
322 /// Values - keep track of the mapping from parent values to values in the new
323 /// intervals. Given a pair (RegIdx, ParentVNI->id), Values contains:
325 /// 1. No entry - the value is not mapped to Edit.get(RegIdx).
326 /// 2. (Null, false) - the value is mapped to multiple values in
327 /// Edit.get(RegIdx). Each value is represented by a minimal live range at
328 /// its def. The full live range can be inferred exactly from the range
329 /// of RegIdx in RegAssign.
330 /// 3. (Null, true). As above, but the ranges in RegAssign are too large, and
331 /// the live range must be recomputed using LiveRangeCalc::extend().
332 /// 4. (VNI, false) The value is mapped to a single new value.
333 /// The new value has no live ranges anywhere.
336 /// LRCalc - Cache for computing live ranges and SSA update. Each instance
337 /// can only handle non-overlapping live ranges, so use a separate
338 /// LiveRangeCalc instance for the complement interval when in spill mode.
339 LiveRangeCalc LRCalc[2];
341 /// getLRCalc - Return the LRCalc to use for RegIdx. In spill mode, the
342 /// complement interval can overlap the other intervals, so it gets its own
343 /// LRCalc instance. When not in spill mode, all intervals can share one.
344 LiveRangeCalc &getLRCalc(unsigned RegIdx) {
345 return LRCalc[SpillMode != SM_Partition && RegIdx != 0];
348 /// Find a subrange corresponding to the lane mask @p LM in the live
349 /// interval @p LI. The interval @p LI is assumed to contain such a subrange.
350 /// This function is used to find corresponding subranges between the
351 /// original interval and the new intervals.
352 LiveInterval::SubRange &getSubRangeForMask(LaneBitmask LM, LiveInterval &LI);
354 /// Add a segment to the interval LI for the value number VNI. If LI has
355 /// subranges, corresponding segments will be added to them as well, but
356 /// with newly created value numbers. If Original is true, dead def will
357 /// only be added a subrange of LI if the corresponding subrange of the
358 /// original interval has a def at this index. Otherwise, all subranges
359 /// of LI will be updated.
360 void addDeadDef(LiveInterval &LI, VNInfo *VNI, bool Original);
362 /// defValue - define a value in RegIdx from ParentVNI at Idx.
363 /// Idx does not have to be ParentVNI->def, but it must be contained within
364 /// ParentVNI's live range in ParentLI. The new value is added to the value
365 /// map. The value being defined may either come from rematerialization
366 /// (or an inserted copy), or it may be coming from the original interval.
367 /// The parameter Original should be true in the latter case, otherwise
368 /// it should be false.
369 /// Return the new LI value.
370 VNInfo *defValue(unsigned RegIdx, const VNInfo *ParentVNI, SlotIndex Idx,
373 /// forceRecompute - Force the live range of ParentVNI in RegIdx to be
374 /// recomputed by LiveRangeCalc::extend regardless of the number of defs.
375 /// This is used for values whose live range doesn't match RegAssign exactly.
376 /// They could have rematerialized, or back-copies may have been moved.
377 void forceRecompute(unsigned RegIdx, const VNInfo &ParentVNI);
379 /// Calls forceRecompute() on any affected regidx and on ParentVNI
380 /// predecessors in case of a phi definition.
381 void forceRecomputeVNI(const VNInfo &ParentVNI);
383 /// defFromParent - Define Reg from ParentVNI at UseIdx using either
384 /// rematerialization or a COPY from parent. Return the new value.
385 VNInfo *defFromParent(unsigned RegIdx,
388 MachineBasicBlock &MBB,
389 MachineBasicBlock::iterator I);
391 /// removeBackCopies - Remove the copy instructions that defines the values
392 /// in the vector in the complement interval.
393 void removeBackCopies(SmallVectorImpl<VNInfo*> &Copies);
395 /// getShallowDominator - Returns the least busy dominator of MBB that is
396 /// also dominated by DefMBB. Busy is measured by loop depth.
397 MachineBasicBlock *findShallowDominator(MachineBasicBlock *MBB,
398 MachineBasicBlock *DefMBB);
400 /// Find out all the backCopies dominated by others.
401 void computeRedundantBackCopies(DenseSet<unsigned> &NotToHoistSet,
402 SmallVectorImpl<VNInfo *> &BackCopies);
404 /// Hoist back-copies to the complement interval. It tries to hoist all
405 /// the back-copies to one BB if it is beneficial, or else simply remove
406 /// redundant backcopies dominated by others.
409 /// transferValues - Transfer values to the new ranges.
410 /// Return true if any ranges were skipped.
411 bool transferValues();
413 /// Live range @p LR corresponding to the lane Mask @p LM has a live
414 /// PHI def at the beginning of block @p B. Extend the range @p LR of
415 /// all predecessor values that reach this def. If @p LR is a subrange,
416 /// the array @p Undefs is the set of all locations where it is undefined
417 /// via <def,read-undef> in other subranges for the same register.
418 void extendPHIRange(MachineBasicBlock &B, LiveRangeCalc &LRC,
419 LiveRange &LR, LaneBitmask LM,
420 ArrayRef<SlotIndex> Undefs);
422 /// extendPHIKillRanges - Extend the ranges of all values killed by original
424 void extendPHIKillRanges();
426 /// rewriteAssigned - Rewrite all uses of Edit.getReg() to assigned registers.
427 void rewriteAssigned(bool ExtendRanges);
429 /// deleteRematVictims - Delete defs that are dead after rematerializing.
430 void deleteRematVictims();
432 /// Add a copy instruction copying \p FromReg to \p ToReg before
433 /// \p InsertBefore. This can be invoked with a \p LaneMask which may make it
434 /// necessary to construct a sequence of copies to cover it exactly.
435 SlotIndex buildCopy(unsigned FromReg, unsigned ToReg, LaneBitmask LaneMask,
436 MachineBasicBlock &MBB, MachineBasicBlock::iterator InsertBefore,
437 bool Late, unsigned RegIdx);
439 SlotIndex buildSingleSubRegCopy(unsigned FromReg, unsigned ToReg,
440 MachineBasicBlock &MB, MachineBasicBlock::iterator InsertBefore,
441 unsigned SubIdx, LiveInterval &DestLI, bool Late, SlotIndex Def);
444 /// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
445 /// Newly created intervals will be appended to newIntervals.
446 SplitEditor(SplitAnalysis &sa, AliasAnalysis &aa, LiveIntervals &lis,
447 VirtRegMap &vrm, MachineDominatorTree &mdt,
448 MachineBlockFrequencyInfo &mbfi);
450 /// reset - Prepare for a new split.
451 void reset(LiveRangeEdit&, ComplementSpillMode = SM_Partition);
453 /// Create a new virtual register and live interval.
454 /// Return the interval index, starting from 1. Interval index 0 is the
455 /// implicit complement interval.
458 /// currentIntv - Return the current interval index.
459 unsigned currentIntv() const { return OpenIdx; }
461 /// selectIntv - Select a previously opened interval index.
462 void selectIntv(unsigned Idx);
464 /// enterIntvBefore - Enter the open interval before the instruction at Idx.
465 /// If the parent interval is not live before Idx, a COPY is not inserted.
466 /// Return the beginning of the new live range.
467 SlotIndex enterIntvBefore(SlotIndex Idx);
469 /// enterIntvAfter - Enter the open interval after the instruction at Idx.
470 /// Return the beginning of the new live range.
471 SlotIndex enterIntvAfter(SlotIndex Idx);
473 /// enterIntvAtEnd - Enter the open interval at the end of MBB.
474 /// Use the open interval from the inserted copy to the MBB end.
475 /// Return the beginning of the new live range.
476 SlotIndex enterIntvAtEnd(MachineBasicBlock &MBB);
478 /// useIntv - indicate that all instructions in MBB should use OpenLI.
479 void useIntv(const MachineBasicBlock &MBB);
481 /// useIntv - indicate that all instructions in range should use OpenLI.
482 void useIntv(SlotIndex Start, SlotIndex End);
484 /// leaveIntvAfter - Leave the open interval after the instruction at Idx.
485 /// Return the end of the live range.
486 SlotIndex leaveIntvAfter(SlotIndex Idx);
488 /// leaveIntvBefore - Leave the open interval before the instruction at Idx.
489 /// Return the end of the live range.
490 SlotIndex leaveIntvBefore(SlotIndex Idx);
492 /// leaveIntvAtTop - Leave the interval at the top of MBB.
493 /// Add liveness from the MBB top to the copy.
494 /// Return the end of the live range.
495 SlotIndex leaveIntvAtTop(MachineBasicBlock &MBB);
497 /// overlapIntv - Indicate that all instructions in range should use the open
498 /// interval, but also let the complement interval be live.
500 /// This doubles the register pressure, but is sometimes required to deal with
501 /// register uses after the last valid split point.
503 /// The Start index should be a return value from a leaveIntv* call, and End
504 /// should be in the same basic block. The parent interval must have the same
505 /// value across the range.
507 void overlapIntv(SlotIndex Start, SlotIndex End);
509 /// finish - after all the new live ranges have been created, compute the
510 /// remaining live range, and rewrite instructions to use the new registers.
511 /// @param LRMap When not null, this vector will map each live range in Edit
512 /// back to the indices returned by openIntv.
513 /// There may be extra indices created by dead code elimination.
514 void finish(SmallVectorImpl<unsigned> *LRMap = nullptr);
516 /// dump - print the current interval mapping to dbgs().
519 // ===--- High level methods ---===
521 /// splitSingleBlock - Split CurLI into a separate live interval around the
522 /// uses in a single block. This is intended to be used as part of a larger
523 /// split, and doesn't call finish().
524 void splitSingleBlock(const SplitAnalysis::BlockInfo &BI);
526 /// splitLiveThroughBlock - Split CurLI in the given block such that it
527 /// enters the block in IntvIn and leaves it in IntvOut. There may be uses in
528 /// the block, but they will be ignored when placing split points.
530 /// @param MBBNum Block number.
531 /// @param IntvIn Interval index entering the block.
532 /// @param LeaveBefore When set, leave IntvIn before this point.
533 /// @param IntvOut Interval index leaving the block.
534 /// @param EnterAfter When set, enter IntvOut after this point.
535 void splitLiveThroughBlock(unsigned MBBNum,
536 unsigned IntvIn, SlotIndex LeaveBefore,
537 unsigned IntvOut, SlotIndex EnterAfter);
539 /// splitRegInBlock - Split CurLI in the given block such that it enters the
540 /// block in IntvIn and leaves it on the stack (or not at all). Split points
541 /// are placed in a way that avoids putting uses in the stack interval. This
542 /// may require creating a local interval when there is interference.
544 /// @param BI Block descriptor.
545 /// @param IntvIn Interval index entering the block. Not 0.
546 /// @param LeaveBefore When set, leave IntvIn before this point.
547 void splitRegInBlock(const SplitAnalysis::BlockInfo &BI,
548 unsigned IntvIn, SlotIndex LeaveBefore);
550 /// splitRegOutBlock - Split CurLI in the given block such that it enters the
551 /// block on the stack (or isn't live-in at all) and leaves it in IntvOut.
552 /// Split points are placed to avoid interference and such that the uses are
553 /// not in the stack interval. This may require creating a local interval
554 /// when there is interference.
556 /// @param BI Block descriptor.
557 /// @param IntvOut Interval index leaving the block.
558 /// @param EnterAfter When set, enter IntvOut after this point.
559 void splitRegOutBlock(const SplitAnalysis::BlockInfo &BI,
560 unsigned IntvOut, SlotIndex EnterAfter);
563 } // end namespace llvm
565 #endif // LLVM_LIB_CODEGEN_SPLITKIT_H