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_CODEGEN_LIVERANGECALC_H
23#define LLVM_CODEGEN_LIVERANGECALC_H
24
25#include "llvm/ADT/BitVector.h"
26#include "llvm/ADT/IndexedMap.h"
27#include "llvm/CodeGen/LiveInterval.h"
28
29namespace llvm {
30
31/// Forward declarations for MachineDominators.h:
32class MachineDominatorTree;
33template <class NodeT> class DomTreeNodeBase;
34typedef DomTreeNodeBase<MachineBasicBlock> MachineDomTreeNode;
35
36class LiveRangeCalc {
37  const MachineRegisterInfo *MRI;
38  SlotIndexes *Indexes;
39  MachineDominatorTree *DomTree;
40  VNInfo::Allocator *Alloc;
41
42  /// Seen - Bit vector of active entries in LiveOut, also used as a visited
43  /// set by findReachingDefs.  One entry per basic block, indexed by block
44  /// number.  This is kept as a separate bit vector because it can be cleared
45  /// quickly when switching live ranges.
46  BitVector Seen;
47
48  /// LiveOutPair - A value and the block that defined it.  The domtree node is
49  /// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)].
50  typedef std::pair<VNInfo*, MachineDomTreeNode*> LiveOutPair;
51
52  /// LiveOutMap - Map basic blocks to the value leaving the block.
53  typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap;
54
55  /// LiveOut - Map each basic block where a live range is live out to the
56  /// live-out value and its defining block.
57  ///
58  /// For every basic block, MBB, one of these conditions shall be true:
59  ///
60  ///  1. !Seen.count(MBB->getNumber())
61  ///     Blocks without a Seen bit are ignored.
62  ///  2. LiveOut[MBB].second.getNode() == MBB
63  ///     The live-out value is defined in MBB.
64  ///  3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB]
65  ///     The live-out value passses through MBB. All predecessors must carry
66  ///     the same value.
67  ///
68  /// The domtree node may be null, it can be computed.
69  ///
70  /// The map can be shared by multiple live ranges as long as no two are
71  /// live-out of the same block.
72  LiveOutMap LiveOut;
73
74  /// LiveInBlock - Information about a basic block where a live range is known
75  /// to be live-in, but the value has not yet been determined.
76  struct LiveInBlock {
77    // LI - The live range that is live-in to this block.  The algorithms can
78    // handle multiple non-overlapping live ranges simultaneously.
79    LiveInterval *LI;
80
81    // DomNode - Dominator tree node for the block.
82    // Cleared when the final value has been determined and LI has been updated.
83    MachineDomTreeNode *DomNode;
84
85    // Position in block where the live-in range ends, or SlotIndex() if the
86    // range passes through the block.  When the final value has been
87    // determined, the range from the block start to Kill will be added to LI.
88    SlotIndex Kill;
89
90    // Live-in value filled in by updateSSA once it is known.
91    VNInfo *Value;
92
93    LiveInBlock(LiveInterval *li, MachineDomTreeNode *node, SlotIndex kill)
94      : LI(li), DomNode(node), Kill(kill), Value(0) {}
95  };
96
97  /// LiveIn - Work list of blocks where the live-in value has yet to be
98  /// determined.  This list is typically computed by findReachingDefs() and
99  /// used as a work list by updateSSA().  The low-level interface may also be
100  /// used to add entries directly.
101  SmallVector<LiveInBlock, 16> LiveIn;
102
103  /// findReachingDefs - Assuming that LI is live-in to KillMBB and killed at
104  /// Kill, search for values that can reach KillMBB.  All blocks that need LI
105  /// to be live-in are added to LiveIn.  If a unique reaching def is found,
106  /// its value is returned, if Kill is jointly dominated by multiple values,
107  /// NULL is returned.
108  ///
109  /// PhysReg, when set, is used to verify live-in lists on basic blocks.
110  VNInfo *findReachingDefs(LiveInterval *LI,
111                           MachineBasicBlock *KillMBB,
112                           SlotIndex Kill,
113                           unsigned PhysReg);
114
115  /// updateSSA - Compute the values that will be live in to all requested
116  /// blocks in LiveIn.  Create PHI-def values as required to preserve SSA form.
117  ///
118  /// Every live-in block must be jointly dominated by the added live-out
119  /// blocks.  No values are read from the live ranges.
120  void updateSSA();
121
122  /// updateLiveIns - Add liveness as specified in the LiveIn vector, using VNI
123  /// as a wildcard value for LiveIn entries without a value.
124  void updateLiveIns(VNInfo *VNI);
125
126public:
127  LiveRangeCalc() : MRI(0), Indexes(0), DomTree(0), Alloc(0) {}
128
129  //===--------------------------------------------------------------------===//
130  // High-level interface.
131  //===--------------------------------------------------------------------===//
132  //
133  // Calculate live ranges from scratch.
134  //
135
136  /// reset - Prepare caches for a new set of non-overlapping live ranges.  The
137  /// caches must be reset before attempting calculations with a live range
138  /// that may overlap a previously computed live range, and before the first
139  /// live range in a function.  If live ranges are not known to be
140  /// non-overlapping, call reset before each.
141  void reset(const MachineFunction *MF,
142             SlotIndexes*,
143             MachineDominatorTree*,
144             VNInfo::Allocator*);
145
146  /// calculate - Calculate the live range of a virtual register from its defs
147  /// and uses.  LI must be empty with no values.
148  void calculate(LiveInterval *LI);
149
150  //===--------------------------------------------------------------------===//
151  // Mid-level interface.
152  //===--------------------------------------------------------------------===//
153  //
154  // Modify existing live ranges.
155  //
156
157  /// extend - Extend the live range of LI to reach Kill.
158  ///
159  /// The existing values in LI must be live so they jointly dominate Kill.  If
160  /// Kill is not dominated by a single existing value, PHI-defs are inserted
161  /// as required to preserve SSA form.  If Kill is known to be dominated by a
162  /// single existing value, Alloc may be null.
163  ///
164  /// PhysReg, when set, is used to verify live-in lists on basic blocks.
165  void extend(LiveInterval *LI, SlotIndex Kill, unsigned PhysReg = 0);
166
167  /// createDeadDefs - Create a dead def in LI for every def operand of Reg.
168  /// Each instruction defining Reg gets a new VNInfo with a corresponding
169  /// minimal live range.
170  void createDeadDefs(LiveInterval *LI, unsigned Reg);
171
172  /// createDeadDefs - Create a dead def in LI for every def of LI->reg.
173  void createDeadDefs(LiveInterval *LI) {
174    createDeadDefs(LI, LI->reg);
175  }
176
177  /// extendToUses - Extend the live range of LI to reach all uses of Reg.
178  ///
179  /// All uses must be jointly dominated by existing liveness.  PHI-defs are
180  /// inserted as needed to preserve SSA form.
181  void extendToUses(LiveInterval *LI, unsigned Reg);
182
183  /// extendToUses - Extend the live range of LI to reach all uses of LI->reg.
184  void extendToUses(LiveInterval *LI) {
185    extendToUses(LI, LI->reg);
186  }
187
188  //===--------------------------------------------------------------------===//
189  // Low-level interface.
190  //===--------------------------------------------------------------------===//
191  //
192  // These functions can be used to compute live ranges where the live-in and
193  // live-out blocks are already known, but the SSA value in each block is
194  // unknown.
195  //
196  // After calling reset(), add known live-out values and known live-in blocks.
197  // Then call calculateValues() to compute the actual value that is
198  // live-in to each block, and add liveness to the live ranges.
199  //
200
201  /// setLiveOutValue - Indicate that VNI is live out from MBB.  The
202  /// calculateValues() function will not add liveness for MBB, the caller
203  /// should take care of that.
204  ///
205  /// VNI may be null only if MBB is a live-through block also passed to
206  /// addLiveInBlock().
207  void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
208    Seen.set(MBB->getNumber());
209    LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0);
210  }
211
212  /// addLiveInBlock - Add a block with an unknown live-in value.  This
213  /// function can only be called once per basic block.  Once the live-in value
214  /// has been determined, calculateValues() will add liveness to LI.
215  ///
216  /// @param LI      The live range that is live-in to the block.
217  /// @param DomNode The domtree node for the block.
218  /// @param Kill    Index in block where LI is killed.  If the value is
219  ///                live-through, set Kill = SLotIndex() and also call
220  ///                setLiveOutValue(MBB, 0).
221  void addLiveInBlock(LiveInterval *LI,
222                      MachineDomTreeNode *DomNode,
223                      SlotIndex Kill = SlotIndex()) {
224    LiveIn.push_back(LiveInBlock(LI, DomNode, Kill));
225  }
226
227  /// calculateValues - Calculate the value that will be live-in to each block
228  /// added with addLiveInBlock.  Add PHI-def values as needed to preserve SSA
229  /// form.  Add liveness to all live-in blocks up to the Kill point, or the
230  /// whole block for live-through blocks.
231  ///
232  /// Every predecessor of a live-in block must have been given a value with
233  /// setLiveOutValue, the value may be null for live-trough blocks.
234  void calculateValues();
235};
236
237} // end namespace llvm
238
239#endif
240