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//===- SplitKit.h - Toolkit for splitting live ranges -----------*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This file contains the SplitAnalysis class as well as mutator functions for
// live range splitting.
#include "LiveRangeCalc.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/IntervalMap.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/MC/LaneBitmask.h"
#include "llvm/Support/Compiler.h"
#include <utility>
namespace llvm {
class LiveIntervals;
class LiveRangeEdit;
class MachineBlockFrequencyInfo;
class MachineDominatorTree;
class MachineLoopInfo;
class MachineRegisterInfo;
class TargetInstrInfo;
class TargetRegisterInfo;
class VirtRegMap;
/// Determines the latest safe point in a block in which we can insert a split,
/// spill or other instruction related with CurLI.
class LLVM_LIBRARY_VISIBILITY InsertPointAnalysis {
const LiveIntervals &LIS;
/// Last legal insert point in each basic block in the current function.
/// The first entry is the first terminator, the second entry is the
/// last valid point to insert a split or spill for a variable that is
/// live into a landing pad successor.
SmallVector<std::pair<SlotIndex, SlotIndex>, 8> LastInsertPoint;
SlotIndex computeLastInsertPoint(const LiveInterval &CurLI,
const MachineBasicBlock &MBB);
InsertPointAnalysis(const LiveIntervals &lis, unsigned BBNum);
/// Return the base index of the last valid insert point for \pCurLI in \pMBB.
SlotIndex getLastInsertPoint(const LiveInterval &CurLI,
const MachineBasicBlock &MBB) {
unsigned Num = MBB.getNumber();
// Inline the common simple case.
if (LastInsertPoint[Num].first.isValid() &&
return LastInsertPoint[Num].first;
return computeLastInsertPoint(CurLI, MBB);
/// Returns the last insert point as an iterator for \pCurLI in \pMBB.
MachineBasicBlock::iterator getLastInsertPointIter(const LiveInterval &CurLI,
MachineBasicBlock &MBB);
/// Return the base index of the first insert point in \pMBB.
SlotIndex getFirstInsertPoint(MachineBasicBlock &MBB) {
SlotIndex Res = LIS.getMBBStartIdx(&MBB);
if (!MBB.empty()) {
MachineBasicBlock::iterator MII = MBB.SkipPHIsLabelsAndDebug(MBB.begin());
if (MII != MBB.end())
Res = LIS.getInstructionIndex(*MII);
return Res;
/// SplitAnalysis - Analyze a LiveInterval, looking for live range splitting
/// opportunities.
const MachineFunction &MF;
const VirtRegMap &VRM;
const LiveIntervals &LIS;
const MachineLoopInfo &Loops;
const TargetInstrInfo &TII;
/// Additional information about basic blocks where the current variable is
/// live. Such a block will look like one of these templates:
/// 1. | o---x | Internal to block. Variable is only live in this block.
/// 2. |---x | Live-in, kill.
/// 3. | o---| Def, live-out.
/// 4. |---x o---| Live-in, kill, def, live-out. Counted by NumGapBlocks.
/// 5. |---o---o---| Live-through with uses or defs.
/// 6. |-----------| Live-through without uses. Counted by NumThroughBlocks.
/// Two BlockInfo entries are created for template 4. One for the live-in
/// segment, and one for the live-out segment. These entries look as if the
/// block were split in the middle where the live range isn't live.
/// Live-through blocks without any uses don't get BlockInfo entries. They
/// are simply listed in ThroughBlocks instead.
struct BlockInfo {
MachineBasicBlock *MBB;
SlotIndex FirstInstr; ///< First instr accessing current reg.
SlotIndex LastInstr; ///< Last instr accessing current reg.
SlotIndex FirstDef; ///< First non-phi valno->def, or SlotIndex().
bool LiveIn; ///< Current reg is live in.
bool LiveOut; ///< Current reg is live out.
/// isOneInstr - Returns true when this BlockInfo describes a single
/// instruction.
bool isOneInstr() const {
return SlotIndex::isSameInstr(FirstInstr, LastInstr);
// Current live interval.
const LiveInterval *CurLI = nullptr;
/// Insert Point Analysis.
InsertPointAnalysis IPA;
// Sorted slot indexes of using instructions.
SmallVector<SlotIndex, 8> UseSlots;
/// UseBlocks - Blocks where CurLI has uses.
SmallVector<BlockInfo, 8> UseBlocks;
/// NumGapBlocks - Number of duplicate entries in UseBlocks for blocks where
/// the live range has a gap.
unsigned NumGapBlocks;
/// ThroughBlocks - Block numbers where CurLI is live through without uses.
BitVector ThroughBlocks;
/// NumThroughBlocks - Number of live-through blocks.
unsigned NumThroughBlocks;
/// DidRepairRange - analyze was forced to shrinkToUses().
bool DidRepairRange;
// Sumarize statistics by counting instructions using CurLI.
void analyzeUses();
/// calcLiveBlockInfo - Compute per-block information about CurLI.
bool calcLiveBlockInfo();
SplitAnalysis(const VirtRegMap &vrm, const LiveIntervals &lis,
const MachineLoopInfo &mli);
/// analyze - set CurLI to the specified interval, and analyze how it may be
/// split.
void analyze(const LiveInterval *li);
/// didRepairRange() - Returns true if CurLI was invalid and has been repaired
/// by analyze(). This really shouldn't happen, but sometimes the coalescer
/// can create live ranges that end in mid-air.
bool didRepairRange() const { return DidRepairRange; }
/// clear - clear all data structures so SplitAnalysis is ready to analyze a
/// new interval.
void clear();
/// getParent - Return the last analyzed interval.
const LiveInterval &getParent() const { return *CurLI; }
/// isOriginalEndpoint - Return true if the original live range was killed or
/// (re-)defined at Idx. Idx should be the 'def' slot for a normal kill/def,
/// and 'use' for an early-clobber def.
/// This can be used to recognize code inserted by earlier live range
/// splitting.
bool isOriginalEndpoint(SlotIndex Idx) const;
/// getUseSlots - Return an array of SlotIndexes of instructions using CurLI.
/// This include both use and def operands, at most one entry per instruction.
ArrayRef<SlotIndex> getUseSlots() const { return UseSlots; }
/// getUseBlocks - Return an array of BlockInfo objects for the basic blocks
/// where CurLI has uses.
ArrayRef<BlockInfo> getUseBlocks() const { return UseBlocks; }
/// getNumThroughBlocks - Return the number of through blocks.
unsigned getNumThroughBlocks() const { return NumThroughBlocks; }
/// isThroughBlock - Return true if CurLI is live through MBB without uses.
bool isThroughBlock(unsigned MBB) const { return ThroughBlocks.test(MBB); }
/// getThroughBlocks - Return the set of through blocks.
const BitVector &getThroughBlocks() const { return ThroughBlocks; }
/// getNumLiveBlocks - Return the number of blocks where CurLI is live.
unsigned getNumLiveBlocks() const {
return getUseBlocks().size() - NumGapBlocks + getNumThroughBlocks();
/// countLiveBlocks - Return the number of blocks where li is live. This is
/// guaranteed to return the same number as getNumLiveBlocks() after calling
/// analyze(li).
unsigned countLiveBlocks(const LiveInterval *li) const;
using BlockPtrSet = SmallPtrSet<const MachineBasicBlock *, 16>;
/// shouldSplitSingleBlock - Returns true if it would help to create a local
/// live range for the instructions in BI. There is normally no benefit to
/// creating a live range for a single instruction, but it does enable
/// register class inflation if the instruction has a restricted register
/// class.
/// @param BI The block to be isolated.
/// @param SingleInstrs True when single instructions should be isolated.
bool shouldSplitSingleBlock(const BlockInfo &BI, bool SingleInstrs) const;
SlotIndex getLastSplitPoint(unsigned Num) {
return IPA.getLastInsertPoint(*CurLI, *MF.getBlockNumbered(Num));
MachineBasicBlock::iterator getLastSplitPointIter(MachineBasicBlock *BB) {
return IPA.getLastInsertPointIter(*CurLI, *BB);
SlotIndex getFirstSplitPoint(unsigned Num) {
return IPA.getFirstInsertPoint(*MF.getBlockNumbered(Num));
/// SplitEditor - Edit machine code and LiveIntervals for live range
/// splitting.
/// - Create a SplitEditor from a SplitAnalysis.
/// - Start a new live interval with openIntv.
/// - Mark the places where the new interval is entered using enterIntv*
/// - Mark the ranges where the new interval is used with useIntv*
/// - Mark the places where the interval is exited with exitIntv*.
/// - Finish the current interval with closeIntv and repeat from 2.
/// - Rewrite instructions with finish().
SplitAnalysis &SA;
AliasAnalysis &AA;
LiveIntervals &LIS;
VirtRegMap &VRM;
MachineRegisterInfo &MRI;
MachineDominatorTree &MDT;
const TargetInstrInfo &TII;
const TargetRegisterInfo &TRI;
const MachineBlockFrequencyInfo &MBFI;
/// ComplementSpillMode - Select how the complement live range should be
/// created. SplitEditor automatically creates interval 0 to contain
/// anything that isn't added to another interval. This complement interval
/// can get quite complicated, and it can sometimes be an advantage to allow
/// it to overlap the other intervals. If it is going to spill anyway, no
/// registers are wasted by keeping a value in two places at the same time.
enum ComplementSpillMode {
/// SM_Partition(Default) - Try to create the complement interval so it
/// doesn't overlap any other intervals, and the original interval is
/// partitioned. This may require a large number of back copies and extra
/// PHI-defs. Only segments marked with overlapIntv will be overlapping.
/// SM_Size - Overlap intervals to minimize the number of inserted COPY
/// instructions. Copies to the complement interval are hoisted to their
/// common dominator, so only one COPY is required per value in the
/// complement interval. This also means that no extra PHI-defs need to be
/// inserted in the complement interval.
/// SM_Speed - Overlap intervals to minimize the expected execution
/// frequency of the inserted copies. This is very similar to SM_Size, but
/// the complement interval may get some extra PHI-defs.
/// Edit - The current parent register and new intervals created.
LiveRangeEdit *Edit = nullptr;
/// Index into Edit of the currently open interval.
/// The index 0 is used for the complement, so the first interval started by
/// openIntv will be 1.
unsigned OpenIdx = 0;
/// The current spill mode, selected by reset().
ComplementSpillMode SpillMode = SM_Partition;
using RegAssignMap = IntervalMap<SlotIndex, unsigned>;
/// Allocator for the interval map. This will eventually be shared with
/// SlotIndexes and LiveIntervals.
RegAssignMap::Allocator Allocator;
/// RegAssign - Map of the assigned register indexes.
/// Edit.get(RegAssign.lookup(Idx)) is the register that should be live at
/// Idx.
RegAssignMap RegAssign;
using ValueForcePair = PointerIntPair<VNInfo *, 1>;
using ValueMap = DenseMap<std::pair<unsigned, unsigned>, ValueForcePair>;
/// Values - keep track of the mapping from parent values to values in the new
/// intervals. Given a pair (RegIdx, ParentVNI->id), Values contains:
/// 1. No entry - the value is not mapped to Edit.get(RegIdx).
/// 2. (Null, false) - the value is mapped to multiple values in
/// Edit.get(RegIdx). Each value is represented by a minimal live range at
/// its def. The full live range can be inferred exactly from the range
/// of RegIdx in RegAssign.
/// 3. (Null, true). As above, but the ranges in RegAssign are too large, and
/// the live range must be recomputed using LiveRangeCalc::extend().
/// 4. (VNI, false) The value is mapped to a single new value.
/// The new value has no live ranges anywhere.
ValueMap Values;
/// LRCalc - Cache for computing live ranges and SSA update. Each instance
/// can only handle non-overlapping live ranges, so use a separate
/// LiveRangeCalc instance for the complement interval when in spill mode.
LiveRangeCalc LRCalc[2];
/// getLRCalc - Return the LRCalc to use for RegIdx. In spill mode, the
/// complement interval can overlap the other intervals, so it gets its own
/// LRCalc instance. When not in spill mode, all intervals can share one.
LiveRangeCalc &getLRCalc(unsigned RegIdx) {
return LRCalc[SpillMode != SM_Partition && RegIdx != 0];
/// Find a subrange corresponding to the lane mask @p LM in the live
/// interval @p LI. The interval @p LI is assumed to contain such a subrange.
/// This function is used to find corresponding subranges between the
/// original interval and the new intervals.
LiveInterval::SubRange &getSubRangeForMask(LaneBitmask LM, LiveInterval &LI);
/// Add a segment to the interval LI for the value number VNI. If LI has
/// subranges, corresponding segments will be added to them as well, but
/// with newly created value numbers. If Original is true, dead def will
/// only be added a subrange of LI if the corresponding subrange of the
/// original interval has a def at this index. Otherwise, all subranges
/// of LI will be updated.
void addDeadDef(LiveInterval &LI, VNInfo *VNI, bool Original);
/// defValue - define a value in RegIdx from ParentVNI at Idx.
/// Idx does not have to be ParentVNI->def, but it must be contained within
/// ParentVNI's live range in ParentLI. The new value is added to the value
/// map. The value being defined may either come from rematerialization
/// (or an inserted copy), or it may be coming from the original interval.
/// The parameter Original should be true in the latter case, otherwise
/// it should be false.
/// Return the new LI value.
VNInfo *defValue(unsigned RegIdx, const VNInfo *ParentVNI, SlotIndex Idx,
bool Original);
/// forceRecompute - Force the live range of ParentVNI in RegIdx to be
/// recomputed by LiveRangeCalc::extend regardless of the number of defs.
/// This is used for values whose live range doesn't match RegAssign exactly.
/// They could have rematerialized, or back-copies may have been moved.
void forceRecompute(unsigned RegIdx, const VNInfo &ParentVNI);
/// Calls forceRecompute() on any affected regidx and on ParentVNI
/// predecessors in case of a phi definition.
void forceRecomputeVNI(const VNInfo &ParentVNI);
/// defFromParent - Define Reg from ParentVNI at UseIdx using either
/// rematerialization or a COPY from parent. Return the new value.
VNInfo *defFromParent(unsigned RegIdx,
VNInfo *ParentVNI,
SlotIndex UseIdx,
MachineBasicBlock &MBB,
MachineBasicBlock::iterator I);
/// removeBackCopies - Remove the copy instructions that defines the values
/// in the vector in the complement interval.
void removeBackCopies(SmallVectorImpl<VNInfo*> &Copies);
/// getShallowDominator - Returns the least busy dominator of MBB that is
/// also dominated by DefMBB. Busy is measured by loop depth.
MachineBasicBlock *findShallowDominator(MachineBasicBlock *MBB,
MachineBasicBlock *DefMBB);
/// Find out all the backCopies dominated by others.
void computeRedundantBackCopies(DenseSet<unsigned> &NotToHoistSet,
SmallVectorImpl<VNInfo *> &BackCopies);
/// Hoist back-copies to the complement interval. It tries to hoist all
/// the back-copies to one BB if it is beneficial, or else simply remove
/// redundant backcopies dominated by others.
void hoistCopies();
/// transferValues - Transfer values to the new ranges.
/// Return true if any ranges were skipped.
bool transferValues();
/// Live range @p LR corresponding to the lane Mask @p LM has a live
/// PHI def at the beginning of block @p B. Extend the range @p LR of
/// all predecessor values that reach this def. If @p LR is a subrange,
/// the array @p Undefs is the set of all locations where it is undefined
/// via <def,read-undef> in other subranges for the same register.
void extendPHIRange(MachineBasicBlock &B, LiveRangeCalc &LRC,
LiveRange &LR, LaneBitmask LM,
ArrayRef<SlotIndex> Undefs);
/// extendPHIKillRanges - Extend the ranges of all values killed by original
/// parent PHIDefs.
void extendPHIKillRanges();
/// rewriteAssigned - Rewrite all uses of Edit.getReg() to assigned registers.
void rewriteAssigned(bool ExtendRanges);
/// deleteRematVictims - Delete defs that are dead after rematerializing.
void deleteRematVictims();
/// Add a copy instruction copying \p FromReg to \p ToReg before
/// \p InsertBefore. This can be invoked with a \p LaneMask which may make it
/// necessary to construct a sequence of copies to cover it exactly.
SlotIndex buildCopy(unsigned FromReg, unsigned ToReg, LaneBitmask LaneMask,
MachineBasicBlock &MBB, MachineBasicBlock::iterator InsertBefore,
bool Late, unsigned RegIdx);
SlotIndex buildSingleSubRegCopy(unsigned FromReg, unsigned ToReg,
MachineBasicBlock &MB, MachineBasicBlock::iterator InsertBefore,
unsigned SubIdx, LiveInterval &DestLI, bool Late, SlotIndex Def);
/// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
/// Newly created intervals will be appended to newIntervals.
SplitEditor(SplitAnalysis &sa, AliasAnalysis &aa, LiveIntervals &lis,
VirtRegMap &vrm, MachineDominatorTree &mdt,
MachineBlockFrequencyInfo &mbfi);
/// reset - Prepare for a new split.
void reset(LiveRangeEdit&, ComplementSpillMode = SM_Partition);
/// Create a new virtual register and live interval.
/// Return the interval index, starting from 1. Interval index 0 is the
/// implicit complement interval.
unsigned openIntv();
/// currentIntv - Return the current interval index.
unsigned currentIntv() const { return OpenIdx; }
/// selectIntv - Select a previously opened interval index.
void selectIntv(unsigned Idx);
/// enterIntvBefore - Enter the open interval before the instruction at Idx.
/// If the parent interval is not live before Idx, a COPY is not inserted.
/// Return the beginning of the new live range.
SlotIndex enterIntvBefore(SlotIndex Idx);
/// enterIntvAfter - Enter the open interval after the instruction at Idx.
/// Return the beginning of the new live range.
SlotIndex enterIntvAfter(SlotIndex Idx);
/// enterIntvAtEnd - Enter the open interval at the end of MBB.
/// Use the open interval from the inserted copy to the MBB end.
/// Return the beginning of the new live range.
SlotIndex enterIntvAtEnd(MachineBasicBlock &MBB);
/// useIntv - indicate that all instructions in MBB should use OpenLI.
void useIntv(const MachineBasicBlock &MBB);
/// useIntv - indicate that all instructions in range should use OpenLI.
void useIntv(SlotIndex Start, SlotIndex End);
/// leaveIntvAfter - Leave the open interval after the instruction at Idx.
/// Return the end of the live range.
SlotIndex leaveIntvAfter(SlotIndex Idx);
/// leaveIntvBefore - Leave the open interval before the instruction at Idx.
/// Return the end of the live range.
SlotIndex leaveIntvBefore(SlotIndex Idx);
/// leaveIntvAtTop - Leave the interval at the top of MBB.
/// Add liveness from the MBB top to the copy.
/// Return the end of the live range.
SlotIndex leaveIntvAtTop(MachineBasicBlock &MBB);
/// overlapIntv - Indicate that all instructions in range should use the open
/// interval, but also let the complement interval be live.
/// This doubles the register pressure, but is sometimes required to deal with
/// register uses after the last valid split point.
/// The Start index should be a return value from a leaveIntv* call, and End
/// should be in the same basic block. The parent interval must have the same
/// value across the range.
void overlapIntv(SlotIndex Start, SlotIndex End);
/// finish - after all the new live ranges have been created, compute the
/// remaining live range, and rewrite instructions to use the new registers.
/// @param LRMap When not null, this vector will map each live range in Edit
/// back to the indices returned by openIntv.
/// There may be extra indices created by dead code elimination.
void finish(SmallVectorImpl<unsigned> *LRMap = nullptr);
/// dump - print the current interval mapping to dbgs().
void dump() const;
// ===--- High level methods ---===
/// splitSingleBlock - Split CurLI into a separate live interval around the
/// uses in a single block. This is intended to be used as part of a larger
/// split, and doesn't call finish().
void splitSingleBlock(const SplitAnalysis::BlockInfo &BI);
/// splitLiveThroughBlock - Split CurLI in the given block such that it
/// enters the block in IntvIn and leaves it in IntvOut. There may be uses in
/// the block, but they will be ignored when placing split points.
/// @param MBBNum Block number.
/// @param IntvIn Interval index entering the block.
/// @param LeaveBefore When set, leave IntvIn before this point.
/// @param IntvOut Interval index leaving the block.
/// @param EnterAfter When set, enter IntvOut after this point.
void splitLiveThroughBlock(unsigned MBBNum,
unsigned IntvIn, SlotIndex LeaveBefore,
unsigned IntvOut, SlotIndex EnterAfter);
/// splitRegInBlock - Split CurLI in the given block such that it enters the
/// block in IntvIn and leaves it on the stack (or not at all). Split points
/// are placed in a way that avoids putting uses in the stack interval. This
/// may require creating a local interval when there is interference.
/// @param BI Block descriptor.
/// @param IntvIn Interval index entering the block. Not 0.
/// @param LeaveBefore When set, leave IntvIn before this point.
void splitRegInBlock(const SplitAnalysis::BlockInfo &BI,
unsigned IntvIn, SlotIndex LeaveBefore);
/// splitRegOutBlock - Split CurLI in the given block such that it enters the
/// block on the stack (or isn't live-in at all) and leaves it in IntvOut.
/// Split points are placed to avoid interference and such that the uses are
/// not in the stack interval. This may require creating a local interval
/// when there is interference.
/// @param BI Block descriptor.
/// @param IntvOut Interval index leaving the block.
/// @param EnterAfter When set, enter IntvOut after this point.
void splitRegOutBlock(const SplitAnalysis::BlockInfo &BI,
unsigned IntvOut, SlotIndex EnterAfter);
} // end namespace llvm