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_CODEGEN_LIVERANGECALC_H
23 #define LLVM_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 /// Seen - Bit vector of active entries in LiveOut, also used as a visited
44 /// set by findReachingDefs. One entry per basic block, indexed by block
45 /// number. This is kept as a separate bit vector because it can be cleared
46 /// quickly when switching live ranges.
49 /// LiveOutPair - A value and the block that defined it. The domtree node is
50 /// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)].
51 typedef std::pair<VNInfo*, MachineDomTreeNode*> LiveOutPair;
53 /// LiveOutMap - Map basic blocks to the value leaving the block.
54 typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap;
56 /// LiveOut - Map each basic block where a live range is live out to the
57 /// live-out value 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 // LI - The live range 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(LiveInterval *li, MachineDomTreeNode *node, SlotIndex kill)
95 : LI(li), DomNode(node), Kill(kill), Value(0) {}
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(LiveInterval *LI,
115 MachineBasicBlock *KillMBB,
119 /// updateSSA - Compute the values that will be live in to all requested
120 /// blocks in LiveIn. Create PHI-def values as required to preserve SSA form.
122 /// Every live-in block must be jointly dominated by the added live-out
123 /// blocks. No values are read from the live ranges.
126 /// Add liveness as specified in the LiveIn vector.
127 void updateLiveIns();
130 LiveRangeCalc() : MF(0), MRI(0), Indexes(0), DomTree(0), Alloc(0) {}
132 //===--------------------------------------------------------------------===//
133 // High-level interface.
134 //===--------------------------------------------------------------------===//
136 // Calculate live ranges from scratch.
139 /// reset - Prepare caches for a new set of non-overlapping live ranges. The
140 /// caches must be reset before attempting calculations with a live range
141 /// that may overlap a previously computed live range, and before the first
142 /// live range in a function. If live ranges are not known to be
143 /// non-overlapping, call reset before each.
144 void reset(const MachineFunction *MF,
146 MachineDominatorTree*,
149 //===--------------------------------------------------------------------===//
150 // Mid-level interface.
151 //===--------------------------------------------------------------------===//
153 // Modify existing live ranges.
156 /// extend - Extend the live range of LI to reach Kill.
158 /// The existing values in LI must be live so they jointly dominate Kill. If
159 /// Kill is not dominated by a single existing value, PHI-defs are inserted
160 /// as required to preserve SSA form. If Kill is known to be dominated by a
161 /// single existing value, Alloc may be null.
163 /// PhysReg, when set, is used to verify live-in lists on basic blocks.
164 void extend(LiveInterval *LI, SlotIndex Kill, unsigned PhysReg = 0);
166 /// createDeadDefs - Create a dead def in LI for every def operand of Reg.
167 /// Each instruction defining Reg gets a new VNInfo with a corresponding
168 /// minimal live range.
169 void createDeadDefs(LiveInterval *LI, unsigned Reg);
171 /// createDeadDefs - Create a dead def in LI for every def of LI->reg.
172 void createDeadDefs(LiveInterval *LI) {
173 createDeadDefs(LI, LI->reg);
176 /// extendToUses - Extend the live range of LI to reach all uses of Reg.
178 /// All uses must be jointly dominated by existing liveness. PHI-defs are
179 /// inserted as needed to preserve SSA form.
180 void extendToUses(LiveInterval *LI, unsigned Reg);
182 /// extendToUses - Extend the live range of LI to reach all uses of LI->reg.
183 void extendToUses(LiveInterval *LI) {
184 extendToUses(LI, LI->reg);
187 //===--------------------------------------------------------------------===//
188 // Low-level interface.
189 //===--------------------------------------------------------------------===//
191 // These functions can be used to compute live ranges where the live-in and
192 // live-out blocks are already known, but the SSA value in each block is
195 // After calling reset(), add known live-out values and known live-in blocks.
196 // Then call calculateValues() to compute the actual value that is
197 // live-in to each block, and add liveness to the live ranges.
200 /// setLiveOutValue - Indicate that VNI is live out from MBB. The
201 /// calculateValues() function will not add liveness for MBB, the caller
202 /// should take care of that.
204 /// VNI may be null only if MBB is a live-through block also passed to
205 /// addLiveInBlock().
206 void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
207 Seen.set(MBB->getNumber());
208 LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0);
211 /// addLiveInBlock - Add a block with an unknown live-in value. This
212 /// function can only be called once per basic block. Once the live-in value
213 /// has been determined, calculateValues() will add liveness to LI.
215 /// @param LI The live range that is live-in to the block.
216 /// @param DomNode The domtree node for the block.
217 /// @param Kill Index in block where LI is killed. If the value is
218 /// live-through, set Kill = SLotIndex() and also call
219 /// setLiveOutValue(MBB, 0).
220 void addLiveInBlock(LiveInterval *LI,
221 MachineDomTreeNode *DomNode,
222 SlotIndex Kill = SlotIndex()) {
223 LiveIn.push_back(LiveInBlock(LI, DomNode, Kill));
226 /// calculateValues - Calculate the value that will be live-in to each block
227 /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA
228 /// form. Add liveness to all live-in blocks up to the Kill point, or the
229 /// whole block for live-through blocks.
231 /// Every predecessor of a live-in block must have been given a value with
232 /// setLiveOutValue, the value may be null for live-trough blocks.
233 void calculateValues();
236 } // end namespace llvm