LLVM  4.0.0
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/IndexedMap.h"
29 
30 namespace llvm {
31 
32 /// Forward declarations for MachineDominators.h:
33 class MachineDominatorTree;
34 template <class NodeT> class DomTreeNodeBase;
35 typedef DomTreeNodeBase<MachineBasicBlock> MachineDomTreeNode;
36 
38  const MachineFunction *MF;
39  const MachineRegisterInfo *MRI;
40  SlotIndexes *Indexes;
41  MachineDominatorTree *DomTree;
42  VNInfo::Allocator *Alloc;
43 
44  /// LiveOutPair - A value and the block that defined it. The domtree node is
45  /// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)].
46  typedef std::pair<VNInfo*, MachineDomTreeNode*> LiveOutPair;
47 
48  /// LiveOutMap - Map basic blocks to the value leaving the block.
50 
51  /// Bit vector of active entries in LiveOut, also used as a visited set by
52  /// findReachingDefs. One entry per basic block, indexed by block number.
53  /// This is kept as a separate bit vector because it can be cleared quickly
54  /// when switching live ranges.
55  BitVector Seen;
56 
57  /// Map LiveRange to sets of blocks (represented by bit vectors) that
58  /// in the live range are defined on entry and undefined on entry.
59  /// A block is defined on entry if there is a path from at least one of
60  /// the defs in the live range to the entry of the block, and conversely,
61  /// a block is undefined on entry, if there is no such path (i.e. no
62  /// definition reaches the entry of the block). A single LiveRangeCalc
63  /// object is used to track live-out information for multiple registers
64  /// in live range splitting (which is ok, since the live ranges of these
65  /// registers do not overlap), but the defined/undefined information must
66  /// be kept separate for each individual range.
67  /// By convention, EntryInfoMap[&LR] = { Defined, Undefined }.
68  std::map<LiveRange*,std::pair<BitVector,BitVector>> EntryInfoMap;
69 
70  /// Map each basic block where a live range is live out to the live-out value
71  /// and its defining block.
72  ///
73  /// For every basic block, MBB, one of these conditions shall be true:
74  ///
75  /// 1. !Seen.count(MBB->getNumber())
76  /// Blocks without a Seen bit are ignored.
77  /// 2. LiveOut[MBB].second.getNode() == MBB
78  /// The live-out value is defined in MBB.
79  /// 3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB]
80  /// The live-out value passses through MBB. All predecessors must carry
81  /// the same value.
82  ///
83  /// The domtree node may be null, it can be computed.
84  ///
85  /// The map can be shared by multiple live ranges as long as no two are
86  /// live-out of the same block.
87  LiveOutMap Map;
88 
89  /// LiveInBlock - Information about a basic block where a live range is known
90  /// to be live-in, but the value has not yet been determined.
91  struct LiveInBlock {
92  // The live range set that is live-in to this block. The algorithms can
93  // handle multiple non-overlapping live ranges simultaneously.
94  LiveRange &LR;
95 
96  // DomNode - Dominator tree node for the block.
97  // Cleared when the final value has been determined and LI has been updated.
98  MachineDomTreeNode *DomNode;
99 
100  // Position in block where the live-in range ends, or SlotIndex() if the
101  // range passes through the block. When the final value has been
102  // determined, the range from the block start to Kill will be added to LI.
103  SlotIndex Kill;
104 
105  // Live-in value filled in by updateSSA once it is known.
106  VNInfo *Value;
107 
108  LiveInBlock(LiveRange &LR, MachineDomTreeNode *node, SlotIndex kill)
109  : LR(LR), DomNode(node), Kill(kill), Value(nullptr) {}
110  };
111 
112  /// LiveIn - Work list of blocks where the live-in value has yet to be
113  /// determined. This list is typically computed by findReachingDefs() and
114  /// used as a work list by updateSSA(). The low-level interface may also be
115  /// used to add entries directly.
117 
118  /// Check if the entry to block @p MBB can be reached by any of the defs
119  /// in @p LR. Return true if none of the defs reach the entry to @p MBB.
120  bool isDefOnEntry(LiveRange &LR, ArrayRef<SlotIndex> Undefs,
121  MachineBasicBlock &MBB, BitVector &DefOnEntry,
122  BitVector &UndefOnEntry);
123 
124  /// Find the set of defs that can reach @p Kill. @p Kill must belong to
125  /// @p UseMBB.
126  ///
127  /// If exactly one def can reach @p UseMBB, and the def dominates @p Kill,
128  /// all paths from the def to @p UseMBB are added to @p LR, and the function
129  /// returns true.
130  ///
131  /// If multiple values can reach @p UseMBB, the blocks that need @p LR to be
132  /// live in are added to the LiveIn array, and the function returns false.
133  ///
134  /// The array @p Undef provides the locations where the range @p LR becomes
135  /// undefined by <def,read-undef> operands on other subranges. If @p Undef
136  /// is non-empty and @p Kill is jointly dominated only by the entries of
137  /// @p Undef, the function returns false.
138  ///
139  /// PhysReg, when set, is used to verify live-in lists on basic blocks.
140  bool findReachingDefs(LiveRange &LR, MachineBasicBlock &UseMBB,
141  SlotIndex Kill, unsigned PhysReg,
142  ArrayRef<SlotIndex> Undefs);
143 
144  /// updateSSA - Compute the values that will be live in to all requested
145  /// blocks in LiveIn. Create PHI-def values as required to preserve SSA form.
146  ///
147  /// Every live-in block must be jointly dominated by the added live-out
148  /// blocks. No values are read from the live ranges.
149  void updateSSA();
150 
151  /// Transfer information from the LiveIn vector to the live ranges and update
152  /// the given @p LiveOuts.
153  void updateFromLiveIns();
154 
155  /// Extend the live range of @p LR to reach all uses of Reg.
156  ///
157  /// If @p LR is a main range, or if @p LI is null, then all uses must be
158  /// jointly dominated by the definitions from @p LR. If @p LR is a subrange
159  /// of the live interval @p LI, corresponding to lane mask @p LaneMask,
160  /// all uses must be jointly dominated by the definitions from @p LR
161  /// together with definitions of other lanes where @p LR becomes undefined
162  /// (via <def,read-undef> operands).
163  /// If @p LR is a main range, the @p LaneMask should be set to ~0, i.e.
164  /// LaneBitmask::getAll().
165  void extendToUses(LiveRange &LR, unsigned Reg, LaneBitmask LaneMask,
166  LiveInterval *LI = nullptr);
167 
168  /// Reset Map and Seen fields.
169  void resetLiveOutMap();
170 
171 public:
172  LiveRangeCalc() : MF(nullptr), MRI(nullptr), Indexes(nullptr),
173  DomTree(nullptr), Alloc(nullptr) {}
174 
175  //===--------------------------------------------------------------------===//
176  // High-level interface.
177  //===--------------------------------------------------------------------===//
178  //
179  // Calculate live ranges from scratch.
180  //
181 
182  /// reset - Prepare caches for a new set of non-overlapping live ranges. The
183  /// caches must be reset before attempting calculations with a live range
184  /// that may overlap a previously computed live range, and before the first
185  /// live range in a function. If live ranges are not known to be
186  /// non-overlapping, call reset before each.
187  void reset(const MachineFunction *MF,
188  SlotIndexes*,
191 
192  //===--------------------------------------------------------------------===//
193  // Mid-level interface.
194  //===--------------------------------------------------------------------===//
195  //
196  // Modify existing live ranges.
197  //
198 
199  /// Extend the live range of @p LR to reach @p Use.
200  ///
201  /// The existing values in @p LR must be live so they jointly dominate @p Use.
202  /// If @p Use is not dominated by a single existing value, PHI-defs are
203  /// inserted as required to preserve SSA form.
204  ///
205  /// PhysReg, when set, is used to verify live-in lists on basic blocks.
206  void extend(LiveRange &LR, SlotIndex Use, unsigned PhysReg,
207  ArrayRef<SlotIndex> Undefs);
208 
209  /// createDeadDefs - Create a dead def in LI for every def operand of Reg.
210  /// Each instruction defining Reg gets a new VNInfo with a corresponding
211  /// minimal live range.
212  void createDeadDefs(LiveRange &LR, unsigned Reg);
213 
214  /// Extend the live range of @p LR to reach all uses of Reg.
215  ///
216  /// All uses must be jointly dominated by existing liveness. PHI-defs are
217  /// inserted as needed to preserve SSA form.
218  void extendToUses(LiveRange &LR, unsigned PhysReg) {
219  extendToUses(LR, PhysReg, LaneBitmask::getAll());
220  }
221 
222  /// Calculates liveness for the register specified in live interval @p LI.
223  /// Creates subregister live ranges as needed if subreg liveness tracking is
224  /// enabled.
225  void calculate(LiveInterval &LI, bool TrackSubRegs);
226 
227  /// For live interval \p LI with correct SubRanges construct matching
228  /// information for the main live range. Expects the main live range to not
229  /// have any segments or value numbers.
231 
232  //===--------------------------------------------------------------------===//
233  // Low-level interface.
234  //===--------------------------------------------------------------------===//
235  //
236  // These functions can be used to compute live ranges where the live-in and
237  // live-out blocks are already known, but the SSA value in each block is
238  // unknown.
239  //
240  // After calling reset(), add known live-out values and known live-in blocks.
241  // Then call calculateValues() to compute the actual value that is
242  // live-in to each block, and add liveness to the live ranges.
243  //
244 
245  /// setLiveOutValue - Indicate that VNI is live out from MBB. The
246  /// calculateValues() function will not add liveness for MBB, the caller
247  /// should take care of that.
248  ///
249  /// VNI may be null only if MBB is a live-through block also passed to
250  /// addLiveInBlock().
252  Seen.set(MBB->getNumber());
253  Map[MBB] = LiveOutPair(VNI, nullptr);
254  }
255 
256  /// addLiveInBlock - Add a block with an unknown live-in value. This
257  /// function can only be called once per basic block. Once the live-in value
258  /// has been determined, calculateValues() will add liveness to LI.
259  ///
260  /// @param LR The live range that is live-in to the block.
261  /// @param DomNode The domtree node for the block.
262  /// @param Kill Index in block where LI is killed. If the value is
263  /// live-through, set Kill = SLotIndex() and also call
264  /// setLiveOutValue(MBB, 0).
266  MachineDomTreeNode *DomNode,
267  SlotIndex Kill = SlotIndex()) {
268  LiveIn.push_back(LiveInBlock(LR, DomNode, Kill));
269  }
270 
271  /// calculateValues - Calculate the value that will be live-in to each block
272  /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA
273  /// form. Add liveness to all live-in blocks up to the Kill point, or the
274  /// whole block for live-through blocks.
275  ///
276  /// Every predecessor of a live-in block must have been given a value with
277  /// setLiveOutValue, the value may be null for live-trough blocks.
278  void calculateValues();
279 };
280 
281 } // end namespace llvm
282 
283 #endif
void push_back(const T &Elt)
Definition: SmallVector.h:211
BitVector & set()
Definition: BitVector.h:219
void createDeadDefs(LiveRange &LR, unsigned Reg)
createDeadDefs - Create a dead def in LI for every def operand of Reg.
int getNumber() const
MachineBasicBlocks are uniquely numbered at the function level, unless they're not in a MachineFuncti...
void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI)
setLiveOutValue - Indicate that VNI is live out from MBB.
static LaneBitmask getAll()
Definition: LaneBitmask.h:75
LiveInterval - This class represents the liveness of a register, or stack slot.
Definition: LiveInterval.h:625
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:45
This class represents the liveness of a register, stack slot, etc.
Definition: LiveInterval.h:153
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.
SlotIndexes pass.
Definition: SlotIndexes.h:323
void addLiveInBlock(LiveRange &LR, MachineDomTreeNode *DomNode, SlotIndex Kill=SlotIndex())
addLiveInBlock - Add a block with an unknown live-in value.
MachineBasicBlock * MBB
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.
void reset(const MachineFunction *MF, SlotIndexes *, MachineDominatorTree *, VNInfo::Allocator *)
reset - Prepare caches for a new set of non-overlapping live ranges.
Allocate memory in an ever growing pool, as if by bump-pointer.
Definition: Allocator.h:138
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:71
SlotIndex - An opaque wrapper around machine indexes.
Definition: SlotIndexes.h:76
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...