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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/ArrayRef.h"
26 : #include "llvm/ADT/BitVector.h"
27 : #include "llvm/ADT/DenseMap.h"
28 : #include "llvm/ADT/IndexedMap.h"
29 : #include "llvm/ADT/SmallVector.h"
30 : #include "llvm/CodeGen/LiveInterval.h"
31 : #include "llvm/CodeGen/MachineBasicBlock.h"
32 : #include "llvm/CodeGen/SlotIndexes.h"
33 : #include "llvm/MC/LaneBitmask.h"
34 : #include <utility>
35 :
36 : namespace llvm {
37 :
38 : template <class NodeT> class DomTreeNodeBase;
39 : class MachineDominatorTree;
40 : class MachineFunction;
41 : class MachineRegisterInfo;
42 :
43 : using MachineDomTreeNode = DomTreeNodeBase<MachineBasicBlock>;
44 :
45 : class LiveRangeCalc {
46 : const MachineFunction *MF = nullptr;
47 : const MachineRegisterInfo *MRI = nullptr;
48 : SlotIndexes *Indexes = nullptr;
49 : MachineDominatorTree *DomTree = nullptr;
50 : VNInfo::Allocator *Alloc = nullptr;
51 :
52 : /// LiveOutPair - A value and the block that defined it. The domtree node is
53 : /// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)].
54 : using LiveOutPair = std::pair<VNInfo *, MachineDomTreeNode *>;
55 :
56 : /// LiveOutMap - Map basic blocks to the value leaving the block.
57 : using LiveOutMap = IndexedMap<LiveOutPair, MBB2NumberFunctor>;
58 :
59 : /// Bit vector of active entries in LiveOut, also used as a visited set by
60 : /// findReachingDefs. One entry per basic block, indexed by block number.
61 : /// This is kept as a separate bit vector because it can be cleared quickly
62 : /// when switching live ranges.
63 : BitVector Seen;
64 :
65 : /// Map LiveRange to sets of blocks (represented by bit vectors) that
66 : /// in the live range are defined on entry and undefined on entry.
67 : /// A block is defined on entry if there is a path from at least one of
68 : /// the defs in the live range to the entry of the block, and conversely,
69 : /// a block is undefined on entry, if there is no such path (i.e. no
70 : /// definition reaches the entry of the block). A single LiveRangeCalc
71 : /// object is used to track live-out information for multiple registers
72 : /// in live range splitting (which is ok, since the live ranges of these
73 : /// registers do not overlap), but the defined/undefined information must
74 : /// be kept separate for each individual range.
75 : /// By convention, EntryInfoMap[&LR] = { Defined, Undefined }.
76 : using EntryInfoMap = DenseMap<LiveRange *, std::pair<BitVector, BitVector>>;
77 : EntryInfoMap EntryInfos;
78 :
79 : /// Map each basic block where a live range is live out to the live-out value
80 : /// and its defining block.
81 : ///
82 : /// For every basic block, MBB, one of these conditions shall be true:
83 : ///
84 : /// 1. !Seen.count(MBB->getNumber())
85 : /// Blocks without a Seen bit are ignored.
86 : /// 2. LiveOut[MBB].second.getNode() == MBB
87 : /// The live-out value is defined in MBB.
88 : /// 3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB]
89 : /// The live-out value passses through MBB. All predecessors must carry
90 : /// the same value.
91 : ///
92 : /// The domtree node may be null, it can be computed.
93 : ///
94 : /// The map can be shared by multiple live ranges as long as no two are
95 : /// live-out of the same block.
96 : LiveOutMap Map;
97 :
98 : /// LiveInBlock - Information about a basic block where a live range is known
99 : /// to be live-in, but the value has not yet been determined.
100 : struct LiveInBlock {
101 : // The live range set that is live-in to this block. The algorithms can
102 : // handle multiple non-overlapping live ranges simultaneously.
103 : LiveRange &LR;
104 :
105 : // DomNode - Dominator tree node for the block.
106 : // Cleared when the final value has been determined and LI has been updated.
107 : MachineDomTreeNode *DomNode;
108 :
109 : // Position in block where the live-in range ends, or SlotIndex() if the
110 : // range passes through the block. When the final value has been
111 : // determined, the range from the block start to Kill will be added to LI.
112 : SlotIndex Kill;
113 :
114 : // Live-in value filled in by updateSSA once it is known.
115 : VNInfo *Value = nullptr;
116 :
117 : LiveInBlock(LiveRange &LR, MachineDomTreeNode *node, SlotIndex kill)
118 179844 : : LR(LR), DomNode(node), Kill(kill) {}
119 : };
120 :
121 : /// LiveIn - Work list of blocks where the live-in value has yet to be
122 : /// determined. This list is typically computed by findReachingDefs() and
123 : /// used as a work list by updateSSA(). The low-level interface may also be
124 : /// used to add entries directly.
125 : SmallVector<LiveInBlock, 16> LiveIn;
126 :
127 : /// Check if the entry to block @p MBB can be reached by any of the defs
128 : /// in @p LR. Return true if none of the defs reach the entry to @p MBB.
129 : bool isDefOnEntry(LiveRange &LR, ArrayRef<SlotIndex> Undefs,
130 : MachineBasicBlock &MBB, BitVector &DefOnEntry,
131 : BitVector &UndefOnEntry);
132 :
133 : /// Find the set of defs that can reach @p Kill. @p Kill must belong to
134 : /// @p UseMBB.
135 : ///
136 : /// If exactly one def can reach @p UseMBB, and the def dominates @p Kill,
137 : /// all paths from the def to @p UseMBB are added to @p LR, and the function
138 : /// returns true.
139 : ///
140 : /// If multiple values can reach @p UseMBB, the blocks that need @p LR to be
141 : /// live in are added to the LiveIn array, and the function returns false.
142 : ///
143 : /// The array @p Undef provides the locations where the range @p LR becomes
144 : /// undefined by <def,read-undef> operands on other subranges. If @p Undef
145 : /// is non-empty and @p Kill is jointly dominated only by the entries of
146 : /// @p Undef, the function returns false.
147 : ///
148 : /// PhysReg, when set, is used to verify live-in lists on basic blocks.
149 : bool findReachingDefs(LiveRange &LR, MachineBasicBlock &UseMBB,
150 : SlotIndex Use, unsigned PhysReg,
151 : ArrayRef<SlotIndex> Undefs);
152 :
153 : /// updateSSA - Compute the values that will be live in to all requested
154 : /// blocks in LiveIn. Create PHI-def values as required to preserve SSA form.
155 : ///
156 : /// Every live-in block must be jointly dominated by the added live-out
157 : /// blocks. No values are read from the live ranges.
158 : void updateSSA();
159 :
160 : /// Transfer information from the LiveIn vector to the live ranges and update
161 : /// the given @p LiveOuts.
162 : void updateFromLiveIns();
163 :
164 : /// Extend the live range of @p LR to reach all uses of Reg.
165 : ///
166 : /// If @p LR is a main range, or if @p LI is null, then all uses must be
167 : /// jointly dominated by the definitions from @p LR. If @p LR is a subrange
168 : /// of the live interval @p LI, corresponding to lane mask @p LaneMask,
169 : /// all uses must be jointly dominated by the definitions from @p LR
170 : /// together with definitions of other lanes where @p LR becomes undefined
171 : /// (via <def,read-undef> operands).
172 : /// If @p LR is a main range, the @p LaneMask should be set to ~0, i.e.
173 : /// LaneBitmask::getAll().
174 : void extendToUses(LiveRange &LR, unsigned Reg, LaneBitmask LaneMask,
175 : LiveInterval *LI = nullptr);
176 :
177 : /// Reset Map and Seen fields.
178 : void resetLiveOutMap();
179 :
180 : public:
181 1526432 : LiveRangeCalc() = default;
182 :
183 : //===--------------------------------------------------------------------===//
184 : // High-level interface.
185 : //===--------------------------------------------------------------------===//
186 : //
187 : // Calculate live ranges from scratch.
188 : //
189 :
190 : /// reset - Prepare caches for a new set of non-overlapping live ranges. The
191 : /// caches must be reset before attempting calculations with a live range
192 : /// that may overlap a previously computed live range, and before the first
193 : /// live range in a function. If live ranges are not known to be
194 : /// non-overlapping, call reset before each.
195 : void reset(const MachineFunction *mf, SlotIndexes *SI,
196 : MachineDominatorTree *MDT, VNInfo::Allocator *VNIA);
197 :
198 : //===--------------------------------------------------------------------===//
199 : // Mid-level interface.
200 : //===--------------------------------------------------------------------===//
201 : //
202 : // Modify existing live ranges.
203 : //
204 :
205 : /// Extend the live range of @p LR to reach @p Use.
206 : ///
207 : /// The existing values in @p LR must be live so they jointly dominate @p Use.
208 : /// If @p Use is not dominated by a single existing value, PHI-defs are
209 : /// inserted as required to preserve SSA form.
210 : ///
211 : /// PhysReg, when set, is used to verify live-in lists on basic blocks.
212 : void extend(LiveRange &LR, SlotIndex Use, unsigned PhysReg,
213 : ArrayRef<SlotIndex> Undefs);
214 :
215 : /// createDeadDefs - Create a dead def in LI for every def operand of Reg.
216 : /// Each instruction defining Reg gets a new VNInfo with a corresponding
217 : /// minimal live range.
218 : void createDeadDefs(LiveRange &LR, unsigned Reg);
219 :
220 : /// Extend the live range of @p LR to reach all uses of Reg.
221 : ///
222 : /// All uses must be jointly dominated by existing liveness. PHI-defs are
223 : /// inserted as needed to preserve SSA form.
224 : void extendToUses(LiveRange &LR, unsigned PhysReg) {
225 788034 : extendToUses(LR, PhysReg, LaneBitmask::getAll());
226 : }
227 :
228 : /// Calculates liveness for the register specified in live interval @p LI.
229 : /// Creates subregister live ranges as needed if subreg liveness tracking is
230 : /// enabled.
231 : void calculate(LiveInterval &LI, bool TrackSubRegs);
232 :
233 : /// For live interval \p LI with correct SubRanges construct matching
234 : /// information for the main live range. Expects the main live range to not
235 : /// have any segments or value numbers.
236 : void constructMainRangeFromSubranges(LiveInterval &LI);
237 :
238 : //===--------------------------------------------------------------------===//
239 : // Low-level interface.
240 : //===--------------------------------------------------------------------===//
241 : //
242 : // These functions can be used to compute live ranges where the live-in and
243 : // live-out blocks are already known, but the SSA value in each block is
244 : // unknown.
245 : //
246 : // After calling reset(), add known live-out values and known live-in blocks.
247 : // Then call calculateValues() to compute the actual value that is
248 : // live-in to each block, and add liveness to the live ranges.
249 : //
250 :
251 : /// setLiveOutValue - Indicate that VNI is live out from MBB. The
252 : /// calculateValues() function will not add liveness for MBB, the caller
253 : /// should take care of that.
254 : ///
255 : /// VNI may be null only if MBB is a live-through block also passed to
256 : /// addLiveInBlock().
257 : void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
258 1906271 : Seen.set(MBB->getNumber());
259 : Map[MBB] = LiveOutPair(VNI, nullptr);
260 : }
261 :
262 : /// addLiveInBlock - Add a block with an unknown live-in value. This
263 : /// function can only be called once per basic block. Once the live-in value
264 : /// has been determined, calculateValues() will add liveness to LI.
265 : ///
266 : /// @param LR The live range that is live-in to the block.
267 : /// @param DomNode The domtree node for the block.
268 : /// @param Kill Index in block where LI is killed. If the value is
269 : /// live-through, set Kill = SLotIndex() and also call
270 : /// setLiveOutValue(MBB, 0).
271 : void addLiveInBlock(LiveRange &LR,
272 : MachineDomTreeNode *DomNode,
273 : SlotIndex Kill = SlotIndex()) {
274 179844 : LiveIn.push_back(LiveInBlock(LR, DomNode, Kill));
275 : }
276 :
277 : /// calculateValues - Calculate the value that will be live-in to each block
278 : /// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA
279 : /// form. Add liveness to all live-in blocks up to the Kill point, or the
280 : /// whole block for live-through blocks.
281 : ///
282 : /// Every predecessor of a live-in block must have been given a value with
283 : /// setLiveOutValue, the value may be null for live-trough blocks.
284 : void calculateValues();
285 :
286 : /// A diagnostic function to check if the end of the block @p MBB is
287 : /// jointly dominated by the blocks corresponding to the slot indices
288 : /// in @p Defs. This function is mainly for use in self-verification
289 : /// checks.
290 : LLVM_ATTRIBUTE_UNUSED
291 : static bool isJointlyDominated(const MachineBasicBlock *MBB,
292 : ArrayRef<SlotIndex> Defs,
293 : const SlotIndexes &Indexes);
294 : };
295 :
296 : } // end namespace llvm
297 :
298 : #endif // LLVM_LIB_CODEGEN_LIVERANGECALC_H
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