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LiveRangeCalc.h
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1 //===- LiveRangeCalc.h - Calculate 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 // The LiveRangeCalc class can be used to compute live ranges from scratch. It
11 // caches information about values in the CFG to speed up repeated operations
12 // on the same live range. The cache can be shared by non-overlapping live
13 // ranges. SplitKit uses that when computing the live range of split products.
14 //
15 // A low-level interface is available to clients that know where a variable is
16 // live, but don't know which value it has as every point. LiveRangeCalc will
17 // propagate values down the dominator tree, and even insert PHI-defs where
18 // needed. SplitKit uses this faster interface when possible.
19 //
20 //===----------------------------------------------------------------------===//
21 
22 #ifndef LLVM_LIB_CODEGEN_LIVERANGECALC_H
23 #define LLVM_LIB_CODEGEN_LIVERANGECALC_H
24 
25 #include "llvm/ADT/ArrayRef.h"
26 #include "llvm/ADT/BitVector.h"
27 #include "llvm/ADT/DenseMap.h"
28 #include "llvm/ADT/IndexedMap.h"
29 #include "llvm/ADT/SmallVector.h"
33 #include "llvm/MC/LaneBitmask.h"
34 #include <utility>
35 
36 namespace llvm {
37 
38 template <class NodeT> class DomTreeNodeBase;
39 class MachineDominatorTree;
40 class MachineFunction;
41 class MachineRegisterInfo;
42 
43 using MachineDomTreeNode = DomTreeNodeBase<MachineBasicBlock>;
44 
46  const MachineFunction *MF = nullptr;
47  const MachineRegisterInfo *MRI = nullptr;
48  SlotIndexes *Indexes = nullptr;
49  MachineDominatorTree *DomTree = nullptr;
50  VNInfo::Allocator *Alloc = nullptr;
51 
52  /// LiveOutPair - A value and the block that defined it. The domtree node is
53  /// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)].
54  using LiveOutPair = std::pair<VNInfo *, MachineDomTreeNode *>;
55 
56  /// LiveOutMap - Map basic blocks to the value leaving the block.
58 
59  /// Bit vector of active entries in LiveOut, also used as a visited set by
60  /// findReachingDefs. One entry per basic block, indexed by block number.
61  /// This is kept as a separate bit vector because it can be cleared quickly
62  /// when switching live ranges.
63  BitVector Seen;
64 
65  /// Map LiveRange to sets of blocks (represented by bit vectors) that
66  /// in the live range are defined on entry and undefined on entry.
67  /// A block is defined on entry if there is a path from at least one of
68  /// the defs in the live range to the entry of the block, and conversely,
69  /// a block is undefined on entry, if there is no such path (i.e. no
70  /// definition reaches the entry of the block). A single LiveRangeCalc
71  /// object is used to track live-out information for multiple registers
72  /// in live range splitting (which is ok, since the live ranges of these
73  /// registers do not overlap), but the defined/undefined information must
74  /// be kept separate for each individual range.
75  /// By convention, EntryInfoMap[&LR] = { Defined, Undefined }.
77  EntryInfoMap EntryInfos;
78 
79  /// Map each basic block where a live range is live out to the live-out value
80  /// and its defining block.
81  ///
82  /// For every basic block, MBB, one of these conditions shall be true:
83  ///
84  /// 1. !Seen.count(MBB->getNumber())
85  /// Blocks without a Seen bit are ignored.
86  /// 2. LiveOut[MBB].second.getNode() == MBB
87  /// The live-out value is defined in MBB.
88  /// 3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB]
89  /// The live-out value passses through MBB. All predecessors must carry
90  /// the same value.
91  ///
92  /// The domtree node may be null, it can be computed.
93  ///
94  /// The map can be shared by multiple live ranges as long as no two are
95  /// live-out of the same block.
96  LiveOutMap Map;
97 
98  /// LiveInBlock - Information about a basic block where a live range is known
99  /// to be live-in, but the value has not yet been determined.
100  struct LiveInBlock {
101  // The live range set that is live-in to this block. The algorithms can
102  // handle multiple non-overlapping live ranges simultaneously.
103  LiveRange &LR;
104 
105  // DomNode - Dominator tree node for the block.
106  // Cleared when the final value has been determined and LI has been updated.
107  MachineDomTreeNode *DomNode;
108 
109  // Position in block where the live-in range ends, or SlotIndex() if the
110  // range passes through the block. When the final value has been
111  // determined, the range from the block start to Kill will be added to LI.
112  SlotIndex Kill;
113 
114  // Live-in value filled in by updateSSA once it is known.
115  VNInfo *Value = nullptr;
116 
117  LiveInBlock(LiveRange &LR, MachineDomTreeNode *node, SlotIndex kill)
118  : LR(LR), DomNode(node), Kill(kill) {}
119  };
120 
121  /// LiveIn - Work list of blocks where the live-in value has yet to be
122  /// determined. This list is typically computed by findReachingDefs() and
123  /// used as a work list by updateSSA(). The low-level interface may also be
124  /// used to add entries directly.
126 
127  /// Check if the entry to block @p MBB can be reached by any of the defs
128  /// in @p LR. Return true if none of the defs reach the entry to @p MBB.
129  bool isDefOnEntry(LiveRange &LR, ArrayRef<SlotIndex> Undefs,
130  MachineBasicBlock &MBB, BitVector &DefOnEntry,
131  BitVector &UndefOnEntry);
132 
133  /// Find the set of defs that can reach @p Kill. @p Kill must belong to
134  /// @p UseMBB.
135  ///
136  /// If exactly one def can reach @p UseMBB, and the def dominates @p Kill,
137  /// all paths from the def to @p UseMBB are added to @p LR, and the function
138  /// returns true.
139  ///
140  /// If multiple values can reach @p UseMBB, the blocks that need @p LR to be
141  /// live in are added to the LiveIn array, and the function returns false.
142  ///
143  /// The array @p Undef provides the locations where the range @p LR becomes
144  /// undefined by <def,read-undef> operands on other subranges. If @p Undef
145  /// is non-empty and @p Kill is jointly dominated only by the entries of
146  /// @p Undef, the function returns false.
147  ///
148  /// PhysReg, when set, is used to verify live-in lists on basic blocks.
149  bool findReachingDefs(LiveRange &LR, MachineBasicBlock &UseMBB,
150  SlotIndex Kill, unsigned PhysReg,
151  ArrayRef<SlotIndex> Undefs);
152 
153  /// updateSSA - Compute the values that will be live in to all requested
154  /// blocks in LiveIn. Create PHI-def values as required to preserve SSA form.
155  ///
156  /// Every live-in block must be jointly dominated by the added live-out
157  /// blocks. No values are read from the live ranges.
158  void updateSSA();
159 
160  /// Transfer information from the LiveIn vector to the live ranges and update
161  /// the given @p LiveOuts.
162  void updateFromLiveIns();
163 
164  /// Extend the live range of @p LR to reach all uses of Reg.
165  ///
166  /// If @p LR is a main range, or if @p LI is null, then all uses must be
167  /// jointly dominated by the definitions from @p LR. If @p LR is a subrange
168  /// of the live interval @p LI, corresponding to lane mask @p LaneMask,
169  /// all uses must be jointly dominated by the definitions from @p LR
170  /// together with definitions of other lanes where @p LR becomes undefined
171  /// (via <def,read-undef> operands).
172  /// If @p LR is a main range, the @p LaneMask should be set to ~0, i.e.
173  /// LaneBitmask::getAll().
174  void extendToUses(LiveRange &LR, unsigned Reg, LaneBitmask LaneMask,
175  LiveInterval *LI = nullptr);
176 
177  /// Reset Map and Seen fields.
178  void resetLiveOutMap();
179 
180 public:
181  LiveRangeCalc() = default;
182 
183  //===--------------------------------------------------------------------===//
184  // High-level interface.
185  //===--------------------------------------------------------------------===//
186  //
187  // Calculate live ranges from scratch.
188  //
189 
190  /// reset - Prepare caches for a new set of non-overlapping live ranges. The
191  /// caches must be reset before attempting calculations with a live range
192  /// that may overlap a previously computed live range, and before the first
193  /// live range in a function. If live ranges are not known to be
194  /// non-overlapping, call reset before each.
195  void reset(const MachineFunction *mf, SlotIndexes *SI,
197 
198  //===--------------------------------------------------------------------===//
199  // Mid-level interface.
200  //===--------------------------------------------------------------------===//
201  //
202  // Modify existing live ranges.
203  //
204 
205  /// Extend the live range of @p LR to reach @p Use.
206  ///
207  /// The existing values in @p LR must be live so they jointly dominate @p Use.
208  /// If @p Use is not dominated by a single existing value, PHI-defs are
209  /// inserted as required to preserve SSA form.
210  ///
211  /// PhysReg, when set, is used to verify live-in lists on basic blocks.
212  void extend(LiveRange &LR, SlotIndex Use, unsigned PhysReg,
213  ArrayRef<SlotIndex> Undefs);
214 
215  /// createDeadDefs - Create a dead def in LI for every def operand of Reg.
216  /// Each instruction defining Reg gets a new VNInfo with a corresponding
217  /// minimal live range.
218  void createDeadDefs(LiveRange &LR, unsigned Reg);
219 
220  /// Extend the live range of @p LR to reach all uses of Reg.
221  ///
222  /// All uses must be jointly dominated by existing liveness. PHI-defs are
223  /// inserted as needed to preserve SSA form.
224  void extendToUses(LiveRange &LR, unsigned PhysReg) {
225  extendToUses(LR, PhysReg, LaneBitmask::getAll());
226  }
227 
228  /// Calculates liveness for the register specified in live interval @p LI.
229  /// Creates subregister live ranges as needed if subreg liveness tracking is
230  /// enabled.
231  void calculate(LiveInterval &LI, bool TrackSubRegs);
232 
233  /// For live interval \p LI with correct SubRanges construct matching
234  /// information for the main live range. Expects the main live range to not
235  /// have any segments or value numbers.
237 
238  //===--------------------------------------------------------------------===//
239  // Low-level interface.
240  //===--------------------------------------------------------------------===//
241  //
242  // These functions can be used to compute live ranges where the live-in and
243  // live-out blocks are already known, but the SSA value in each block is
244  // unknown.
245  //
246  // After calling reset(), add known live-out values and known live-in blocks.
247  // Then call calculateValues() to compute the actual value that is
248  // live-in to each block, and add liveness to the live ranges.
249  //
250 
251  /// setLiveOutValue - Indicate that VNI is live out from MBB. The
252  /// calculateValues() function will not add liveness for MBB, the caller
253  /// should take care of that.
254  ///
255  /// VNI may be null only if MBB is a live-through block also passed to
256  /// addLiveInBlock().
258  Seen.set(MBB->getNumber());
259  Map[MBB] = LiveOutPair(VNI, nullptr);
260  }
261 
262  /// addLiveInBlock - Add a block with an unknown live-in value. This
263  /// function can only be called once per basic block. Once the live-in value
264  /// has been determined, calculateValues() will add liveness to LI.
265  ///
266  /// @param LR The live range that is live-in to the block.
267  /// @param DomNode The domtree node for the block.
268  /// @param Kill Index in block where LI is killed. If the value is
269  /// live-through, set Kill = SLotIndex() and also call
270  /// setLiveOutValue(MBB, 0).
272  MachineDomTreeNode *DomNode,
273  SlotIndex Kill = SlotIndex()) {
274  LiveIn.push_back(LiveInBlock(LR, DomNode, Kill));
275  }
276 
277  /// calculateValues - Calculate the value that will be live-in to each block
278  /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA
279  /// form. Add liveness to all live-in blocks up to the Kill point, or the
280  /// whole block for live-through blocks.
281  ///
282  /// Every predecessor of a live-in block must have been given a value with
283  /// setLiveOutValue, the value may be null for live-trough blocks.
284  void calculateValues();
285 };
286 
287 } // end namespace llvm
288 
289 #endif // LLVM_LIB_CODEGEN_LIVERANGECALC_H
void push_back(const T &Elt)
Definition: SmallVector.h:212
BitVector & set()
Definition: BitVector.h:398
A common definition of LaneBitmask for use in TableGen and CodeGen.
void createDeadDefs(LiveRange &LR, unsigned Reg)
createDeadDefs - Create a dead def in LI for every def operand of Reg.
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI)
setLiveOutValue - Indicate that VNI is live out from MBB.
static LaneBitmask getAll()
Definition: LaneBitmask.h:84
LiveInterval - This class represents the liveness of a register, or stack slot.
Definition: LiveInterval.h:638
void constructMainRangeFromSubranges(LiveInterval &LI)
For live interval LI with correct SubRanges construct matching information for the main live range...
VNInfo - Value Number Information.
Definition: LiveInterval.h:53
This class represents the liveness of a register, stack slot, etc.
Definition: LiveInterval.h:157
DomTreeNodeBase< MachineBasicBlock > MachineDomTreeNode
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
Reg
All possible values of the reg field in the ModR/M byte.
LiveRangeCalc()=default
SlotIndexes pass.
Definition: SlotIndexes.h:331
void addLiveInBlock(LiveRange &LR, MachineDomTreeNode *DomNode, SlotIndex Kill=SlotIndex())
addLiveInBlock - Add a block with an unknown live-in value.
Base class for the actual dominator tree node.
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory)...
Definition: APInt.h:33
void extend(LiveRange &LR, SlotIndex Use, unsigned PhysReg, ArrayRef< SlotIndex > Undefs)
Extend the live range of LR to reach Use.
int getNumber() const
MachineBasicBlocks are uniquely numbered at the function level, unless they&#39;re not in a MachineFuncti...
Allocate memory in an ever growing pool, as if by bump-pointer.
Definition: Allocator.h:138
void reset(const MachineFunction *mf, SlotIndexes *SI, MachineDominatorTree *MDT, VNInfo::Allocator *VNIA)
reset - Prepare caches for a new set of non-overlapping live ranges.
void calculate(LiveInterval &LI, bool TrackSubRegs)
Calculates liveness for the register specified in live interval LI.
MachineRegisterInfo - Keep track of information for virtual and physical registers, including vreg register classes, use/def chains for registers, etc.
void extendToUses(LiveRange &LR, unsigned PhysReg)
Extend the live range of LR to reach all uses of Reg.
LLVM Value Representation.
Definition: Value.h:73
SlotIndex - An opaque wrapper around machine indexes.
Definition: SlotIndexes.h:84
void calculateValues()
calculateValues - Calculate the value that will be live-in to each block added with addLiveInBlock...
DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to compute a normal dominat...