1 //===---- LiveRangeCalc.h - Calculate live ranges ---------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
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.
20 //===----------------------------------------------------------------------===//
22 #ifndef LLVM_LIB_CODEGEN_LIVERANGECALC_H
23 #define LLVM_LIB_CODEGEN_LIVERANGECALC_H
25 #include "llvm/ADT/BitVector.h"
26 #include "llvm/ADT/IndexedMap.h"
27 #include "llvm/CodeGen/LiveInterval.h"
31 /// Forward declarations for MachineDominators.h:
32 class MachineDominatorTree;
33 template <class NodeT> class DomTreeNodeBase;
34 typedef DomTreeNodeBase<MachineBasicBlock> MachineDomTreeNode;
37 const MachineFunction *MF;
38 const MachineRegisterInfo *MRI;
40 MachineDominatorTree *DomTree;
41 VNInfo::Allocator *Alloc;
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;
47 /// LiveOutMap - Map basic blocks to the value leaving the block.
48 typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap;
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.
56 /// Map each basic block where a live range is live out to the live-out value
57 /// and its defining block.
59 /// For every basic block, MBB, one of these conditions shall be true:
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
69 /// The domtree node may be null, it can be computed.
71 /// The map can be shared by multiple live ranges as long as no two are
72 /// live-out of the same block.
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.
78 // The live range set that is live-in to this block. The algorithms can
79 // handle multiple non-overlapping live ranges simultaneously.
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;
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.
91 // Live-in value filled in by updateSSA once it is known.
94 LiveInBlock(LiveRange &LR, MachineDomTreeNode *node, SlotIndex kill)
95 : LR(LR), DomNode(node), Kill(kill), Value(nullptr) {}
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;
104 /// Assuming that LI is live-in to KillMBB and killed at Kill, find the set
105 /// of defs that can reach it.
107 /// If only one def can reach Kill, all paths from the def to kill are added
108 /// to LI, and the function returns true.
110 /// If multiple values can reach Kill, the blocks that need LI to be live in
111 /// are added to the LiveIn array, and the function returns false.
113 /// PhysReg, when set, is used to verify live-in lists on basic blocks.
114 bool findReachingDefs(LiveRange &LR, MachineBasicBlock &KillMBB,
115 SlotIndex Kill, unsigned PhysReg);
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.
120 /// Every live-in block must be jointly dominated by the added live-out
121 /// blocks. No values are read from the live ranges.
124 /// Transfer information from the LiveIn vector to the live ranges and update
125 /// the given @p LiveOuts.
126 void updateFromLiveIns();
128 /// Extend the live range of @p LR to reach all uses of Reg.
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);
134 /// Reset Map and Seen fields.
135 void resetLiveOutMap();
138 LiveRangeCalc() : MF(nullptr), MRI(nullptr), Indexes(nullptr),
139 DomTree(nullptr), Alloc(nullptr) {}
141 //===--------------------------------------------------------------------===//
142 // High-level interface.
143 //===--------------------------------------------------------------------===//
145 // Calculate live ranges from scratch.
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,
155 MachineDominatorTree*,
158 //===--------------------------------------------------------------------===//
159 // Mid-level interface.
160 //===--------------------------------------------------------------------===//
162 // Modify existing live ranges.
165 /// extend - Extend the live range of LI to reach Kill.
167 /// The existing values in LI must be live so they jointly dominate Kill. If
168 /// Kill is not dominated by a single existing value, PHI-defs are inserted
169 /// as required to preserve SSA form. If Kill is known to be dominated by a
170 /// single existing value, Alloc may be null.
172 /// PhysReg, when set, is used to verify live-in lists on basic blocks.
173 void extend(LiveRange &LR, SlotIndex Kill, unsigned PhysReg = 0);
175 /// createDeadDefs - Create a dead def in LI for every def operand of Reg.
176 /// Each instruction defining Reg gets a new VNInfo with a corresponding
177 /// minimal live range.
178 void createDeadDefs(LiveRange &LR, unsigned Reg);
180 /// Extend the live range of @p LR to reach all uses of Reg.
182 /// All uses must be jointly dominated by existing liveness. PHI-defs are
183 /// inserted as needed to preserve SSA form.
184 void extendToUses(LiveRange &LR, unsigned PhysReg) {
185 extendToUses(LR, PhysReg, ~0u);
188 /// Calculates liveness for the register specified in live interval @p LI.
189 /// Creates subregister live ranges as needed if subreg liveness tracking is
191 void calculate(LiveInterval &LI);
193 //===--------------------------------------------------------------------===//
194 // Low-level interface.
195 //===--------------------------------------------------------------------===//
197 // These functions can be used to compute live ranges where the live-in and
198 // live-out blocks are already known, but the SSA value in each block is
201 // After calling reset(), add known live-out values and known live-in blocks.
202 // Then call calculateValues() to compute the actual value that is
203 // live-in to each block, and add liveness to the live ranges.
206 /// setLiveOutValue - Indicate that VNI is live out from MBB. The
207 /// calculateValues() function will not add liveness for MBB, the caller
208 /// should take care of that.
210 /// VNI may be null only if MBB is a live-through block also passed to
211 /// addLiveInBlock().
212 void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
213 Seen.set(MBB->getNumber());
214 Map[MBB] = LiveOutPair(VNI, nullptr);
217 /// addLiveInBlock - Add a block with an unknown live-in value. This
218 /// function can only be called once per basic block. Once the live-in value
219 /// has been determined, calculateValues() will add liveness to LI.
221 /// @param LR The live range that is live-in to the block.
222 /// @param DomNode The domtree node for the block.
223 /// @param Kill Index in block where LI is killed. If the value is
224 /// live-through, set Kill = SLotIndex() and also call
225 /// setLiveOutValue(MBB, 0).
226 void addLiveInBlock(LiveRange &LR,
227 MachineDomTreeNode *DomNode,
228 SlotIndex Kill = SlotIndex()) {
229 LiveIn.push_back(LiveInBlock(LR, DomNode, Kill));
232 /// calculateValues - Calculate the value that will be live-in to each block
233 /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA
234 /// form. Add liveness to all live-in blocks up to the Kill point, or the
235 /// whole block for live-through blocks.
237 /// Every predecessor of a live-in block must have been given a value with
238 /// setLiveOutValue, the value may be null for live-trough blocks.
239 void calculateValues();
242 } // end namespace llvm