LLVM  3.7.0
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/BitVector.h"
26 #include "llvm/ADT/IndexedMap.h"
28 
29 namespace llvm {
30 
31 /// Forward declarations for MachineDominators.h:
32 class MachineDominatorTree;
33 template <class NodeT> class DomTreeNodeBase;
34 typedef DomTreeNodeBase<MachineBasicBlock> MachineDomTreeNode;
35 
37  const MachineFunction *MF;
38  const MachineRegisterInfo *MRI;
39  SlotIndexes *Indexes;
40  MachineDominatorTree *DomTree;
41  VNInfo::Allocator *Alloc;
42 
43  /// LiveOutPair - A value and the block that defined it. The domtree node is
44  /// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)].
45  typedef std::pair<VNInfo*, MachineDomTreeNode*> LiveOutPair;
46 
47  /// LiveOutMap - Map basic blocks to the value leaving the block.
49 
50  /// Bit vector of active entries in LiveOut, also used as a visited set by
51  /// findReachingDefs. One entry per basic block, indexed by block number.
52  /// This is kept as a separate bit vector because it can be cleared quickly
53  /// when switching live ranges.
54  BitVector Seen;
55 
56  /// Map each basic block where a live range is live out to the live-out value
57  /// and its defining block.
58  ///
59  /// For every basic block, MBB, one of these conditions shall be true:
60  ///
61  /// 1. !Seen.count(MBB->getNumber())
62  /// Blocks without a Seen bit are ignored.
63  /// 2. LiveOut[MBB].second.getNode() == MBB
64  /// The live-out value is defined in MBB.
65  /// 3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB]
66  /// The live-out value passses through MBB. All predecessors must carry
67  /// the same value.
68  ///
69  /// The domtree node may be null, it can be computed.
70  ///
71  /// The map can be shared by multiple live ranges as long as no two are
72  /// live-out of the same block.
73  LiveOutMap Map;
74 
75  /// LiveInBlock - Information about a basic block where a live range is known
76  /// to be live-in, but the value has not yet been determined.
77  struct LiveInBlock {
78  // The live range set that is live-in to this block. The algorithms can
79  // handle multiple non-overlapping live ranges simultaneously.
80  LiveRange &LR;
81 
82  // DomNode - Dominator tree node for the block.
83  // Cleared when the final value has been determined and LI has been updated.
84  MachineDomTreeNode *DomNode;
85 
86  // Position in block where the live-in range ends, or SlotIndex() if the
87  // range passes through the block. When the final value has been
88  // determined, the range from the block start to Kill will be added to LI.
90 
91  // Live-in value filled in by updateSSA once it is known.
92  VNInfo *Value;
93 
94  LiveInBlock(LiveRange &LR, MachineDomTreeNode *node, SlotIndex kill)
95  : LR(LR), DomNode(node), Kill(kill), Value(nullptr) {}
96  };
97 
98  /// LiveIn - Work list of blocks where the live-in value has yet to be
99  /// determined. This list is typically computed by findReachingDefs() and
100  /// used as a work list by updateSSA(). The low-level interface may also be
101  /// used to add entries directly.
103 
104  /// Assuming that @p LR is live-in to @p UseMBB, find the set of defs that can
105  /// reach it.
106  ///
107  /// If only one def can reach @p UseMBB, all paths from the def to @p UseMBB
108  /// are added to @p LR, and the function returns true.
109  ///
110  /// If multiple values can reach @p UseMBB, the blocks that need @p LR to be
111  /// live in are added to the LiveIn array, and the function returns false.
112  ///
113  /// PhysReg, when set, is used to verify live-in lists on basic blocks.
114  bool findReachingDefs(LiveRange &LR, MachineBasicBlock &UseMBB,
115  SlotIndex Kill, unsigned PhysReg);
116 
117  /// updateSSA - Compute the values that will be live in to all requested
118  /// blocks in LiveIn. Create PHI-def values as required to preserve SSA form.
119  ///
120  /// Every live-in block must be jointly dominated by the added live-out
121  /// blocks. No values are read from the live ranges.
122  void updateSSA();
123 
124  /// Transfer information from the LiveIn vector to the live ranges and update
125  /// the given @p LiveOuts.
126  void updateFromLiveIns();
127 
128  /// Extend the live range of @p LR to reach all uses of Reg.
129  ///
130  /// All uses must be jointly dominated by existing liveness. PHI-defs are
131  /// inserted as needed to preserve SSA form.
132  void extendToUses(LiveRange &LR, unsigned Reg, unsigned LaneMask);
133 
134  /// Reset Map and Seen fields.
135  void resetLiveOutMap();
136 
137 public:
138  LiveRangeCalc() : MF(nullptr), MRI(nullptr), Indexes(nullptr),
139  DomTree(nullptr), Alloc(nullptr) {}
140 
141  //===--------------------------------------------------------------------===//
142  // High-level interface.
143  //===--------------------------------------------------------------------===//
144  //
145  // Calculate live ranges from scratch.
146  //
147 
148  /// reset - Prepare caches for a new set of non-overlapping live ranges. The
149  /// caches must be reset before attempting calculations with a live range
150  /// that may overlap a previously computed live range, and before the first
151  /// live range in a function. If live ranges are not known to be
152  /// non-overlapping, call reset before each.
153  void reset(const MachineFunction *MF,
154  SlotIndexes*,
157 
158  //===--------------------------------------------------------------------===//
159  // Mid-level interface.
160  //===--------------------------------------------------------------------===//
161  //
162  // Modify existing live ranges.
163  //
164 
165  /// Extend the live range of @p LR to reach @p Use.
166  ///
167  /// The existing values in @p LR must be live so they jointly dominate @p Use.
168  /// If @p Use is not dominated by a single existing value, PHI-defs are
169  /// inserted as required to preserve SSA form.
170  ///
171  /// PhysReg, when set, is used to verify live-in lists on basic blocks.
172  void extend(LiveRange &LR, SlotIndex Use, unsigned PhysReg = 0);
173 
174  /// createDeadDefs - Create a dead def in LI for every def operand of Reg.
175  /// Each instruction defining Reg gets a new VNInfo with a corresponding
176  /// minimal live range.
177  void createDeadDefs(LiveRange &LR, unsigned Reg);
178 
179  /// Extend the live range of @p LR to reach all uses of Reg.
180  ///
181  /// All uses must be jointly dominated by existing liveness. PHI-defs are
182  /// inserted as needed to preserve SSA form.
183  void extendToUses(LiveRange &LR, unsigned PhysReg) {
184  extendToUses(LR, PhysReg, ~0u);
185  }
186 
187  /// Calculates liveness for the register specified in live interval @p LI.
188  /// Creates subregister live ranges as needed if subreg liveness tracking is
189  /// enabled.
190  void calculate(LiveInterval &LI, bool TrackSubRegs);
191 
192  //===--------------------------------------------------------------------===//
193  // Low-level interface.
194  //===--------------------------------------------------------------------===//
195  //
196  // These functions can be used to compute live ranges where the live-in and
197  // live-out blocks are already known, but the SSA value in each block is
198  // unknown.
199  //
200  // After calling reset(), add known live-out values and known live-in blocks.
201  // Then call calculateValues() to compute the actual value that is
202  // live-in to each block, and add liveness to the live ranges.
203  //
204 
205  /// setLiveOutValue - Indicate that VNI is live out from MBB. The
206  /// calculateValues() function will not add liveness for MBB, the caller
207  /// should take care of that.
208  ///
209  /// VNI may be null only if MBB is a live-through block also passed to
210  /// addLiveInBlock().
212  Seen.set(MBB->getNumber());
213  Map[MBB] = LiveOutPair(VNI, nullptr);
214  }
215 
216  /// addLiveInBlock - Add a block with an unknown live-in value. This
217  /// function can only be called once per basic block. Once the live-in value
218  /// has been determined, calculateValues() will add liveness to LI.
219  ///
220  /// @param LR The live range that is live-in to the block.
221  /// @param DomNode The domtree node for the block.
222  /// @param Kill Index in block where LI is killed. If the value is
223  /// live-through, set Kill = SLotIndex() and also call
224  /// setLiveOutValue(MBB, 0).
226  MachineDomTreeNode *DomNode,
227  SlotIndex Kill = SlotIndex()) {
228  LiveIn.push_back(LiveInBlock(LR, DomNode, Kill));
229  }
230 
231  /// calculateValues - Calculate the value that will be live-in to each block
232  /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA
233  /// form. Add liveness to all live-in blocks up to the Kill point, or the
234  /// whole block for live-through blocks.
235  ///
236  /// Every predecessor of a live-in block must have been given a value with
237  /// setLiveOutValue, the value may be null for live-trough blocks.
238  void calculateValues();
239 };
240 
241 } // end namespace llvm
242 
243 #endif
void push_back(const T &Elt)
Definition: SmallVector.h:222
void extend(LiveRange &LR, SlotIndex Use, unsigned PhysReg=0)
Extend the live range of LR to reach Use.
BitVector & set()
Definition: BitVector.h:218
void createDeadDefs(LiveRange &LR, unsigned Reg)
createDeadDefs - Create a dead def in LI for every def operand of Reg.
int getNumber() const
getNumber - MachineBasicBlocks are uniquely numbered at the function level, unless they're not in a M...
void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI)
setLiveOutValue - Indicate that VNI is live out from MBB.
LiveInterval - This class represents the liveness of a register, or stack slot.
Definition: LiveInterval.h:588
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:69
Reg
All possible values of the reg field in the ModR/M byte.
SlotIndexes pass.
Definition: SlotIndexes.h:334
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.
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:135
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:69
SlotIndex - An opaque wrapper around machine indexes.
Definition: SlotIndexes.h:92
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...