1//===- SwitchLoweringUtils.h - Switch Lowering ------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef LLVM_CODEGEN_SWITCHLOWERINGUTILS_H
10#define LLVM_CODEGEN_SWITCHLOWERINGUTILS_H
11
12#include "llvm/ADT/SmallVector.h"
13#include "llvm/CodeGen/ISDOpcodes.h"
14#include "llvm/CodeGen/SelectionDAGNodes.h"
15#include "llvm/IR/InstrTypes.h"
16#include "llvm/Support/BranchProbability.h"
17#include <vector>
18
19namespace llvm {
20
21class BlockFrequencyInfo;
22class ConstantInt;
23class FunctionLoweringInfo;
24class MachineBasicBlock;
25class ProfileSummaryInfo;
26class TargetLowering;
27class TargetMachine;
28
29namespace SwitchCG {
30
31enum CaseClusterKind {
32 /// A cluster of adjacent case labels with the same destination, or just one
33 /// case.
34 CC_Range,
35 /// A cluster of cases suitable for jump table lowering.
36 CC_JumpTable,
37 /// A cluster of cases suitable for bit test lowering.
38 CC_BitTests
39};
40
41/// A cluster of case labels.
42struct CaseCluster {
43 CaseClusterKind Kind;
44 const ConstantInt *Low, *High;
45 union {
46 MachineBasicBlock *MBB;
47 unsigned JTCasesIndex;
48 unsigned BTCasesIndex;
49 };
50 BranchProbability Prob;
51
52 static CaseCluster range(const ConstantInt *Low, const ConstantInt *High,
53 MachineBasicBlock *MBB, BranchProbability Prob) {
54 CaseCluster C;
55 C.Kind = CC_Range;
56 C.Low = Low;
57 C.High = High;
58 C.MBB = MBB;
59 C.Prob = Prob;
60 return C;
61 }
62
63 static CaseCluster jumpTable(const ConstantInt *Low, const ConstantInt *High,
64 unsigned JTCasesIndex, BranchProbability Prob) {
65 CaseCluster C;
66 C.Kind = CC_JumpTable;
67 C.Low = Low;
68 C.High = High;
69 C.JTCasesIndex = JTCasesIndex;
70 C.Prob = Prob;
71 return C;
72 }
73
74 static CaseCluster bitTests(const ConstantInt *Low, const ConstantInt *High,
75 unsigned BTCasesIndex, BranchProbability Prob) {
76 CaseCluster C;
77 C.Kind = CC_BitTests;
78 C.Low = Low;
79 C.High = High;
80 C.BTCasesIndex = BTCasesIndex;
81 C.Prob = Prob;
82 return C;
83 }
84};
85
86using CaseClusterVector = std::vector<CaseCluster>;
87using CaseClusterIt = CaseClusterVector::iterator;
88
89/// Sort Clusters and merge adjacent cases.
90void sortAndRangeify(CaseClusterVector &Clusters);
91
92struct CaseBits {
93 uint64_t Mask = 0;
94 MachineBasicBlock *BB = nullptr;
95 unsigned Bits = 0;
96 BranchProbability ExtraProb;
97
98 CaseBits() = default;
99 CaseBits(uint64_t mask, MachineBasicBlock *bb, unsigned bits,
100 BranchProbability Prob)
101 : Mask(mask), BB(bb), Bits(bits), ExtraProb(Prob) {}
102};
103
104using CaseBitsVector = std::vector<CaseBits>;
105
106/// This structure is used to communicate between SelectionDAGBuilder and
107/// SDISel for the code generation of additional basic blocks needed by
108/// multi-case switch statements.
109struct CaseBlock {
110 // For the GISel interface.
111 struct PredInfoPair {
112 CmpInst::Predicate Pred;
113 // Set when no comparison should be emitted.
114 bool NoCmp;
115 };
116 union {
117 // The condition code to use for the case block's setcc node.
118 // Besides the integer condition codes, this can also be SETTRUE, in which
119 // case no comparison gets emitted.
120 ISD::CondCode CC;
121 struct PredInfoPair PredInfo;
122 };
123
124 // The LHS/MHS/RHS of the comparison to emit.
125 // Emit by default LHS op RHS. MHS is used for range comparisons:
126 // If MHS is not null: (LHS <= MHS) and (MHS <= RHS).
127 const Value *CmpLHS, *CmpMHS, *CmpRHS;
128
129 // The block to branch to if the setcc is true/false.
130 MachineBasicBlock *TrueBB, *FalseBB;
131
132 // The block into which to emit the code for the setcc and branches.
133 MachineBasicBlock *ThisBB;
134
135 /// The debug location of the instruction this CaseBlock was
136 /// produced from.
137 SDLoc DL;
138 DebugLoc DbgLoc;
139
140 // Branch weights.
141 BranchProbability TrueProb, FalseProb;
142
143 // Constructor for SelectionDAG.
144 CaseBlock(ISD::CondCode cc, const Value *cmplhs, const Value *cmprhs,
145 const Value *cmpmiddle, MachineBasicBlock *truebb,
146 MachineBasicBlock *falsebb, MachineBasicBlock *me, SDLoc dl,
147 BranchProbability trueprob = BranchProbability::getUnknown(),
148 BranchProbability falseprob = BranchProbability::getUnknown())
149 : CC(cc), CmpLHS(cmplhs), CmpMHS(cmpmiddle), CmpRHS(cmprhs),
150 TrueBB(truebb), FalseBB(falsebb), ThisBB(me), DL(dl),
151 TrueProb(trueprob), FalseProb(falseprob) {}
152
153 // Constructor for GISel.
154 CaseBlock(CmpInst::Predicate pred, bool nocmp, const Value *cmplhs,
155 const Value *cmprhs, const Value *cmpmiddle,
156 MachineBasicBlock *truebb, MachineBasicBlock *falsebb,
157 MachineBasicBlock *me, DebugLoc dl,
158 BranchProbability trueprob = BranchProbability::getUnknown(),
159 BranchProbability falseprob = BranchProbability::getUnknown())
160 : PredInfo({.Pred: pred, .NoCmp: nocmp}), CmpLHS(cmplhs), CmpMHS(cmpmiddle),
161 CmpRHS(cmprhs), TrueBB(truebb), FalseBB(falsebb), ThisBB(me),
162 DbgLoc(dl), TrueProb(trueprob), FalseProb(falseprob) {}
163};
164
165struct JumpTable {
166 /// The virtual register containing the index of the jump table entry
167 /// to jump to.
168 unsigned Reg;
169 /// The JumpTableIndex for this jump table in the function.
170 unsigned JTI;
171 /// The MBB into which to emit the code for the indirect jump.
172 MachineBasicBlock *MBB;
173 /// The MBB of the default bb, which is a successor of the range
174 /// check MBB. This is when updating PHI nodes in successors.
175 MachineBasicBlock *Default;
176
177 /// The debug location of the instruction this JumpTable was produced from.
178 std::optional<SDLoc> SL; // For SelectionDAG
179
180 JumpTable(unsigned R, unsigned J, MachineBasicBlock *M, MachineBasicBlock *D,
181 std::optional<SDLoc> SL)
182 : Reg(R), JTI(J), MBB(M), Default(D), SL(SL) {}
183};
184struct JumpTableHeader {
185 APInt First;
186 APInt Last;
187 const Value *SValue;
188 MachineBasicBlock *HeaderBB;
189 bool Emitted;
190 bool FallthroughUnreachable = false;
191
192 JumpTableHeader(APInt F, APInt L, const Value *SV, MachineBasicBlock *H,
193 bool E = false)
194 : First(std::move(F)), Last(std::move(L)), SValue(SV), HeaderBB(H),
195 Emitted(E) {}
196};
197using JumpTableBlock = std::pair<JumpTableHeader, JumpTable>;
198
199struct BitTestCase {
200 uint64_t Mask;
201 MachineBasicBlock *ThisBB;
202 MachineBasicBlock *TargetBB;
203 BranchProbability ExtraProb;
204
205 BitTestCase(uint64_t M, MachineBasicBlock *T, MachineBasicBlock *Tr,
206 BranchProbability Prob)
207 : Mask(M), ThisBB(T), TargetBB(Tr), ExtraProb(Prob) {}
208};
209
210using BitTestInfo = SmallVector<BitTestCase, 3>;
211
212struct BitTestBlock {
213 APInt First;
214 APInt Range;
215 const Value *SValue;
216 unsigned Reg;
217 MVT RegVT;
218 bool Emitted;
219 bool ContiguousRange;
220 MachineBasicBlock *Parent;
221 MachineBasicBlock *Default;
222 BitTestInfo Cases;
223 BranchProbability Prob;
224 BranchProbability DefaultProb;
225 bool FallthroughUnreachable = false;
226
227 BitTestBlock(APInt F, APInt R, const Value *SV, unsigned Rg, MVT RgVT, bool E,
228 bool CR, MachineBasicBlock *P, MachineBasicBlock *D,
229 BitTestInfo C, BranchProbability Pr)
230 : First(std::move(F)), Range(std::move(R)), SValue(SV), Reg(Rg),
231 RegVT(RgVT), Emitted(E), ContiguousRange(CR), Parent(P), Default(D),
232 Cases(std::move(C)), Prob(Pr) {}
233};
234
235/// Return the range of values within a range.
236uint64_t getJumpTableRange(const CaseClusterVector &Clusters, unsigned First,
237 unsigned Last);
238
239/// Return the number of cases within a range.
240uint64_t getJumpTableNumCases(const SmallVectorImpl<unsigned> &TotalCases,
241 unsigned First, unsigned Last);
242
243struct SwitchWorkListItem {
244 MachineBasicBlock *MBB = nullptr;
245 CaseClusterIt FirstCluster;
246 CaseClusterIt LastCluster;
247 const ConstantInt *GE = nullptr;
248 const ConstantInt *LT = nullptr;
249 BranchProbability DefaultProb;
250};
251using SwitchWorkList = SmallVector<SwitchWorkListItem, 4>;
252
253class SwitchLowering {
254public:
255 SwitchLowering(FunctionLoweringInfo &funcinfo) : FuncInfo(funcinfo) {}
256
257 void init(const TargetLowering &tli, const TargetMachine &tm,
258 const DataLayout &dl) {
259 TLI = &tli;
260 TM = &tm;
261 DL = &dl;
262 }
263
264 /// Vector of CaseBlock structures used to communicate SwitchInst code
265 /// generation information.
266 std::vector<CaseBlock> SwitchCases;
267
268 /// Vector of JumpTable structures used to communicate SwitchInst code
269 /// generation information.
270 std::vector<JumpTableBlock> JTCases;
271
272 /// Vector of BitTestBlock structures used to communicate SwitchInst code
273 /// generation information.
274 std::vector<BitTestBlock> BitTestCases;
275
276 void findJumpTables(CaseClusterVector &Clusters, const SwitchInst *SI,
277 std::optional<SDLoc> SL, MachineBasicBlock *DefaultMBB,
278 ProfileSummaryInfo *PSI, BlockFrequencyInfo *BFI);
279
280 bool buildJumpTable(const CaseClusterVector &Clusters, unsigned First,
281 unsigned Last, const SwitchInst *SI,
282 const std::optional<SDLoc> &SL,
283 MachineBasicBlock *DefaultMBB, CaseCluster &JTCluster);
284
285 void findBitTestClusters(CaseClusterVector &Clusters, const SwitchInst *SI);
286
287 /// Build a bit test cluster from Clusters[First..Last]. Returns false if it
288 /// decides it's not a good idea.
289 bool buildBitTests(CaseClusterVector &Clusters, unsigned First, unsigned Last,
290 const SwitchInst *SI, CaseCluster &BTCluster);
291
292 virtual void addSuccessorWithProb(
293 MachineBasicBlock *Src, MachineBasicBlock *Dst,
294 BranchProbability Prob = BranchProbability::getUnknown()) = 0;
295
296 /// Determine the rank by weight of CC in [First,Last]. If CC has more weight
297 /// than each cluster in the range, its rank is 0.
298 unsigned caseClusterRank(const CaseCluster &CC, CaseClusterIt First,
299 CaseClusterIt Last);
300
301 struct SplitWorkItemInfo {
302 CaseClusterIt LastLeft;
303 CaseClusterIt FirstRight;
304 BranchProbability LeftProb;
305 BranchProbability RightProb;
306 };
307 /// Compute information to balance the tree based on branch probabilities to
308 /// create a near-optimal (in terms of search time given key frequency) binary
309 /// search tree. See e.g. Kurt Mehlhorn "Nearly Optimal Binary Search Trees"
310 /// (1975).
311 SplitWorkItemInfo computeSplitWorkItemInfo(const SwitchWorkListItem &W);
312 virtual ~SwitchLowering() = default;
313
314private:
315 const TargetLowering *TLI = nullptr;
316 const TargetMachine *TM = nullptr;
317 const DataLayout *DL = nullptr;
318 FunctionLoweringInfo &FuncInfo;
319};
320
321} // namespace SwitchCG
322} // namespace llvm
323
324#endif // LLVM_CODEGEN_SWITCHLOWERINGUTILS_H
325

source code of llvm/include/llvm/CodeGen/SwitchLoweringUtils.h