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"
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 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.
48  typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap;
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.
89    SlotIndex Kill;
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.
102  SmallVector<LiveInBlock, 16> LiveIn;
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, LaneBitmask LaneMask);
133
134  /// Reset Map and Seen fields.
135  void resetLiveOutMap();
136
137public:
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*,
155             MachineDominatorTree*,
156             VNInfo::Allocator*);
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  /// For live interval \p LI with correct SubRanges construct matching
193  /// information for the main live range. Expects the main live range to not
194  /// have any segments or value numbers.
195  void constructMainRangeFromSubranges(LiveInterval &LI);
196
197  //===--------------------------------------------------------------------===//
198  // Low-level interface.
199  //===--------------------------------------------------------------------===//
200  //
201  // These functions can be used to compute live ranges where the live-in and
202  // live-out blocks are already known, but the SSA value in each block is
203  // unknown.
204  //
205  // After calling reset(), add known live-out values and known live-in blocks.
206  // Then call calculateValues() to compute the actual value that is
207  // live-in to each block, and add liveness to the live ranges.
208  //
209
210  /// setLiveOutValue - Indicate that VNI is live out from MBB.  The
211  /// calculateValues() function will not add liveness for MBB, the caller
212  /// should take care of that.
213  ///
214  /// VNI may be null only if MBB is a live-through block also passed to
215  /// addLiveInBlock().
216  void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
217    Seen.set(MBB->getNumber());
218    Map[MBB] = LiveOutPair(VNI, nullptr);
219  }
220
221  /// addLiveInBlock - Add a block with an unknown live-in value.  This
222  /// function can only be called once per basic block.  Once the live-in value
223  /// has been determined, calculateValues() will add liveness to LI.
224  ///
225  /// @param LR      The live range that is live-in to the block.
226  /// @param DomNode The domtree node for the block.
227  /// @param Kill    Index in block where LI is killed.  If the value is
228  ///                live-through, set Kill = SLotIndex() and also call
229  ///                setLiveOutValue(MBB, 0).
230  void addLiveInBlock(LiveRange &LR,
231                      MachineDomTreeNode *DomNode,
232                      SlotIndex Kill = SlotIndex()) {
233    LiveIn.push_back(LiveInBlock(LR, DomNode, Kill));
234  }
235
236  /// calculateValues - Calculate the value that will be live-in to each block
237  /// added with addLiveInBlock.  Add PHI-def values as needed to preserve SSA
238  /// form.  Add liveness to all live-in blocks up to the Kill point, or the
239  /// whole block for live-through blocks.
240  ///
241  /// Every predecessor of a live-in block must have been given a value with
242  /// setLiveOutValue, the value may be null for live-trough blocks.
243  void calculateValues();
244};
245
246} // end namespace llvm
247
248#endif
249