1 //===---- MachineOutliner.h - Outliner data structures ------*- 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 //===----------------------------------------------------------------------===//
11 /// Contains all data structures shared between the outliner implemented in
12 /// MachineOutliner.cpp and target implementations of the outliner.
14 //===----------------------------------------------------------------------===//
16 #ifndef LLVM_MACHINEOUTLINER_H
17 #define LLVM_MACHINEOUTLINER_H
19 #include "llvm/CodeGen/LiveRegUnits.h"
20 #include "llvm/CodeGen/MachineFunction.h"
21 #include "llvm/CodeGen/TargetRegisterInfo.h"
22 #include "llvm/CodeGen/LivePhysRegs.h"
27 /// Represents how an instruction should be mapped by the outliner.
28 /// \p Legal instructions are those which are safe to outline.
29 /// \p LegalTerminator instructions are safe to outline, but only as the
30 /// last instruction in a sequence.
31 /// \p Illegal instructions are those which cannot be outlined.
32 /// \p Invisible instructions are instructions which can be outlined, but
33 /// shouldn't actually impact the outlining result.
34 enum InstrType { Legal, LegalTerminator, Illegal, Invisible };
36 /// An individual sequence of instructions to be replaced with a call to
37 /// an outlined function.
40 /// The start index of this \p Candidate in the instruction list.
43 /// The number of instructions in this \p Candidate.
46 // The first instruction in this \p Candidate.
47 MachineBasicBlock::iterator FirstInst;
49 // The last instruction in this \p Candidate.
50 MachineBasicBlock::iterator LastInst;
52 // The basic block that contains this Candidate.
53 MachineBasicBlock *MBB;
55 /// Cost of calling an outlined function from this point as defined by the
57 unsigned CallOverhead;
60 /// The index of this \p Candidate's \p OutlinedFunction in the list of
61 /// \p OutlinedFunctions.
64 /// Set to false if the candidate overlapped with another candidate.
65 bool InCandidateList = true;
67 /// Identifier denoting the instructions to emit to call an outlined function
68 /// from this point. Defined by the target.
69 unsigned CallConstructionID;
71 /// Contains physical register liveness information for the MBB containing
72 /// this \p Candidate.
74 /// This is optionally used by the target to calculate more fine-grained
75 /// cost model information.
78 /// Contains the accumulated register liveness information for the
79 /// instructions in this \p Candidate.
81 /// This is optionally used by the target to determine which registers have
82 /// been used across the sequence.
83 LiveRegUnits UsedInSequence;
85 /// Return the number of instructions in this Candidate.
86 unsigned getLength() const { return Len; }
88 /// Return the start index of this candidate.
89 unsigned getStartIdx() const { return StartIdx; }
91 /// Return the end index of this candidate.
92 unsigned getEndIdx() const { return StartIdx + Len - 1; }
94 /// Set the CallConstructionID and CallOverhead of this candidate to CID and
96 void setCallInfo(unsigned CID, unsigned CO) {
97 CallConstructionID = CID;
101 /// Returns the call overhead of this candidate if it is in the list.
102 unsigned getCallOverhead() const {
103 return InCandidateList ? CallOverhead : 0;
106 MachineBasicBlock::iterator &front() { return FirstInst; }
107 MachineBasicBlock::iterator &back() { return LastInst; }
108 MachineFunction *getMF() const { return MBB->getParent(); }
109 MachineBasicBlock *getMBB() const { return MBB; }
111 /// The number of instructions that would be saved by outlining every
112 /// candidate of this type.
114 /// This is a fixed value which is not updated during the candidate pruning
115 /// process. It is only used for deciding which candidate to keep if two
116 /// candidates overlap. The true benefit is stored in the OutlinedFunction
117 /// for some given candidate.
118 unsigned Benefit = 0;
120 Candidate(unsigned StartIdx, unsigned Len,
121 MachineBasicBlock::iterator &FirstInst,
122 MachineBasicBlock::iterator &LastInst, MachineBasicBlock *MBB,
123 unsigned FunctionIdx)
124 : StartIdx(StartIdx), Len(Len), FirstInst(FirstInst), LastInst(LastInst),
125 MBB(MBB), FunctionIdx(FunctionIdx) {}
128 /// Used to ensure that \p Candidates are outlined in an order that
129 /// preserves the start and end indices of other \p Candidates.
130 bool operator<(const Candidate &RHS) const {
131 return getStartIdx() > RHS.getStartIdx();
134 /// Compute the registers that are live across this Candidate.
135 /// Used by targets that need this information for cost model calculation.
136 /// If a target does not need this information, then this should not be
138 void initLRU(const TargetRegisterInfo &TRI) {
139 assert(MBB->getParent()->getRegInfo().tracksLiveness() &&
140 "Candidate's Machine Function must track liveness");
142 LRU.addLiveOuts(*MBB);
144 // Compute liveness from the end of the block up to the beginning of the
145 // outlining candidate.
146 std::for_each(MBB->rbegin(), (MachineBasicBlock::reverse_iterator)front(),
147 [this](MachineInstr &MI) { LRU.stepBackward(MI); });
149 // Walk over the sequence itself and figure out which registers were used
151 UsedInSequence.init(TRI);
152 std::for_each(front(), std::next(back()),
153 [this](MachineInstr &MI) { UsedInSequence.accumulate(MI); });
157 /// The information necessary to create an outlined function for some
158 /// class of candidate.
159 struct OutlinedFunction {
162 /// The number of candidates for this \p OutlinedFunction.
163 unsigned OccurrenceCount = 0;
166 std::vector<std::shared_ptr<Candidate>> Candidates;
168 /// The actual outlined function created.
169 /// This is initialized after we go through and create the actual function.
170 MachineFunction *MF = nullptr;
172 /// A number assigned to this function which appears at the end of its name.
175 /// The sequence of integers corresponding to the instructions in this
177 std::vector<unsigned> Sequence;
179 /// Represents the size of a sequence in bytes. (Some instructions vary
180 /// widely in size, so just counting the instructions isn't very useful.)
181 unsigned SequenceSize;
183 /// Target-defined overhead of constructing a frame for this function.
184 unsigned FrameOverhead;
186 /// Target-defined identifier for constructing a frame for this function.
187 unsigned FrameConstructionID;
189 /// Return the number of candidates for this \p OutlinedFunction.
190 unsigned getOccurrenceCount() { return OccurrenceCount; }
192 /// Decrement the occurrence count of this OutlinedFunction and return the
194 unsigned decrement() {
195 assert(OccurrenceCount > 0 && "Can't decrement an empty function!");
197 return getOccurrenceCount();
200 /// Return the number of bytes it would take to outline this
202 unsigned getOutliningCost() {
203 unsigned CallOverhead = 0;
204 for (std::shared_ptr<Candidate> &C : Candidates)
205 CallOverhead += C->getCallOverhead();
206 return CallOverhead + SequenceSize + FrameOverhead;
209 /// Return the size in bytes of the unoutlined sequences.
210 unsigned getNotOutlinedCost() { return OccurrenceCount * SequenceSize; }
212 /// Return the number of instructions that would be saved by outlining
214 unsigned getBenefit() {
215 unsigned NotOutlinedCost = getNotOutlinedCost();
216 unsigned OutlinedCost = getOutliningCost();
217 return (NotOutlinedCost < OutlinedCost) ? 0
218 : NotOutlinedCost - OutlinedCost;
221 OutlinedFunction(std::vector<Candidate> &Cands,
222 unsigned SequenceSize, unsigned FrameOverhead,
223 unsigned FrameConstructionID)
224 : SequenceSize(SequenceSize), FrameOverhead(FrameOverhead),
225 FrameConstructionID(FrameConstructionID) {
226 OccurrenceCount = Cands.size();
227 for (Candidate &C : Cands)
228 Candidates.push_back(std::make_shared<outliner::Candidate>(C));
230 unsigned B = getBenefit();
231 for (std::shared_ptr<Candidate> &C : Candidates)
235 OutlinedFunction() {}
237 } // namespace outliner