File: | llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp |
Warning: | line 335, column 3 Called C++ object pointer is null |
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1 | //===- DFAJumpThreading.cpp - Threads a switch statement inside a loop ----===// | ||||
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 | // Transform each threading path to effectively jump thread the DFA. For | ||||
10 | // example, the CFG below could be transformed as follows, where the cloned | ||||
11 | // blocks unconditionally branch to the next correct case based on what is | ||||
12 | // identified in the analysis. | ||||
13 | // | ||||
14 | // sw.bb sw.bb | ||||
15 | // / | \ / | \ | ||||
16 | // case1 case2 case3 case1 case2 case3 | ||||
17 | // \ | / | | | | ||||
18 | // determinator det.2 det.3 det.1 | ||||
19 | // br sw.bb / | \ | ||||
20 | // sw.bb.2 sw.bb.3 sw.bb.1 | ||||
21 | // br case2 br case3 br case1§ | ||||
22 | // | ||||
23 | // Definitions and Terminology: | ||||
24 | // | ||||
25 | // * Threading path: | ||||
26 | // a list of basic blocks, the exit state, and the block that determines | ||||
27 | // the next state, for which the following notation will be used: | ||||
28 | // < path of BBs that form a cycle > [ state, determinator ] | ||||
29 | // | ||||
30 | // * Predictable switch: | ||||
31 | // The switch variable is always a known constant so that all conditional | ||||
32 | // jumps based on switch variable can be converted to unconditional jump. | ||||
33 | // | ||||
34 | // * Determinator: | ||||
35 | // The basic block that determines the next state of the DFA. | ||||
36 | // | ||||
37 | // Representing the optimization in C-like pseudocode: the code pattern on the | ||||
38 | // left could functionally be transformed to the right pattern if the switch | ||||
39 | // condition is predictable. | ||||
40 | // | ||||
41 | // X = A goto A | ||||
42 | // for (...) A: | ||||
43 | // switch (X) ... | ||||
44 | // case A goto B | ||||
45 | // X = B B: | ||||
46 | // case B ... | ||||
47 | // X = C goto C | ||||
48 | // | ||||
49 | // The pass first checks that switch variable X is decided by the control flow | ||||
50 | // path taken in the loop; for example, in case B, the next value of X is | ||||
51 | // decided to be C. It then enumerates through all paths in the loop and labels | ||||
52 | // the basic blocks where the next state is decided. | ||||
53 | // | ||||
54 | // Using this information it creates new paths that unconditionally branch to | ||||
55 | // the next case. This involves cloning code, so it only gets triggered if the | ||||
56 | // amount of code duplicated is below a threshold. | ||||
57 | // | ||||
58 | //===----------------------------------------------------------------------===// | ||||
59 | |||||
60 | #include "llvm/Transforms/Scalar/DFAJumpThreading.h" | ||||
61 | #include "llvm/ADT/APInt.h" | ||||
62 | #include "llvm/ADT/DenseMap.h" | ||||
63 | #include "llvm/ADT/DepthFirstIterator.h" | ||||
64 | #include "llvm/ADT/SmallSet.h" | ||||
65 | #include "llvm/ADT/Statistic.h" | ||||
66 | #include "llvm/Analysis/AssumptionCache.h" | ||||
67 | #include "llvm/Analysis/CodeMetrics.h" | ||||
68 | #include "llvm/Analysis/LoopIterator.h" | ||||
69 | #include "llvm/Analysis/OptimizationRemarkEmitter.h" | ||||
70 | #include "llvm/Analysis/TargetTransformInfo.h" | ||||
71 | #include "llvm/IR/CFG.h" | ||||
72 | #include "llvm/IR/Constants.h" | ||||
73 | #include "llvm/IR/IntrinsicInst.h" | ||||
74 | #include "llvm/IR/Verifier.h" | ||||
75 | #include "llvm/InitializePasses.h" | ||||
76 | #include "llvm/Pass.h" | ||||
77 | #include "llvm/Support/CommandLine.h" | ||||
78 | #include "llvm/Support/Debug.h" | ||||
79 | #include "llvm/Transforms/Scalar.h" | ||||
80 | #include "llvm/Transforms/Utils/BasicBlockUtils.h" | ||||
81 | #include "llvm/Transforms/Utils/Cloning.h" | ||||
82 | #include "llvm/Transforms/Utils/SSAUpdaterBulk.h" | ||||
83 | #include "llvm/Transforms/Utils/ValueMapper.h" | ||||
84 | #include <algorithm> | ||||
85 | #include <deque> | ||||
86 | |||||
87 | using namespace llvm; | ||||
88 | |||||
89 | #define DEBUG_TYPE"dfa-jump-threading" "dfa-jump-threading" | ||||
90 | |||||
91 | STATISTIC(NumTransforms, "Number of transformations done")static llvm::Statistic NumTransforms = {"dfa-jump-threading", "NumTransforms", "Number of transformations done"}; | ||||
92 | STATISTIC(NumCloned, "Number of blocks cloned")static llvm::Statistic NumCloned = {"dfa-jump-threading", "NumCloned" , "Number of blocks cloned"}; | ||||
93 | STATISTIC(NumPaths, "Number of individual paths threaded")static llvm::Statistic NumPaths = {"dfa-jump-threading", "NumPaths" , "Number of individual paths threaded"}; | ||||
94 | |||||
95 | static cl::opt<bool> | ||||
96 | ClViewCfgBefore("dfa-jump-view-cfg-before", | ||||
97 | cl::desc("View the CFG before DFA Jump Threading"), | ||||
98 | cl::Hidden, cl::init(false)); | ||||
99 | |||||
100 | static cl::opt<unsigned> MaxPathLength( | ||||
101 | "dfa-max-path-length", | ||||
102 | cl::desc("Max number of blocks searched to find a threading path"), | ||||
103 | cl::Hidden, cl::init(20)); | ||||
104 | |||||
105 | static cl::opt<unsigned> | ||||
106 | CostThreshold("dfa-cost-threshold", | ||||
107 | cl::desc("Maximum cost accepted for the transformation"), | ||||
108 | cl::Hidden, cl::init(50)); | ||||
109 | |||||
110 | namespace { | ||||
111 | |||||
112 | class SelectInstToUnfold { | ||||
113 | SelectInst *SI; | ||||
114 | PHINode *SIUse; | ||||
115 | |||||
116 | public: | ||||
117 | SelectInstToUnfold(SelectInst *SI, PHINode *SIUse) : SI(SI), SIUse(SIUse) {} | ||||
118 | |||||
119 | SelectInst *getInst() { return SI; } | ||||
120 | PHINode *getUse() { return SIUse; } | ||||
121 | |||||
122 | explicit operator bool() const { return SI && SIUse; } | ||||
123 | }; | ||||
124 | |||||
125 | void unfold(DomTreeUpdater *DTU, SelectInstToUnfold SIToUnfold, | ||||
126 | std::vector<SelectInstToUnfold> *NewSIsToUnfold, | ||||
127 | std::vector<BasicBlock *> *NewBBs); | ||||
128 | |||||
129 | class DFAJumpThreading { | ||||
130 | public: | ||||
131 | DFAJumpThreading(AssumptionCache *AC, DominatorTree *DT, | ||||
132 | TargetTransformInfo *TTI, OptimizationRemarkEmitter *ORE) | ||||
133 | : AC(AC), DT(DT), TTI(TTI), ORE(ORE) {} | ||||
134 | |||||
135 | bool run(Function &F); | ||||
136 | |||||
137 | private: | ||||
138 | void | ||||
139 | unfoldSelectInstrs(DominatorTree *DT, | ||||
140 | const SmallVector<SelectInstToUnfold, 4> &SelectInsts) { | ||||
141 | DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager); | ||||
142 | SmallVector<SelectInstToUnfold, 4> Stack; | ||||
143 | for (SelectInstToUnfold SIToUnfold : SelectInsts) | ||||
144 | Stack.push_back(SIToUnfold); | ||||
145 | |||||
146 | while (!Stack.empty()) { | ||||
147 | SelectInstToUnfold SIToUnfold = Stack.back(); | ||||
148 | Stack.pop_back(); | ||||
149 | |||||
150 | std::vector<SelectInstToUnfold> NewSIsToUnfold; | ||||
151 | std::vector<BasicBlock *> NewBBs; | ||||
152 | unfold(&DTU, SIToUnfold, &NewSIsToUnfold, &NewBBs); | ||||
153 | |||||
154 | // Put newly discovered select instructions into the work list. | ||||
155 | for (const SelectInstToUnfold &NewSIToUnfold : NewSIsToUnfold) | ||||
156 | Stack.push_back(NewSIToUnfold); | ||||
157 | } | ||||
158 | } | ||||
159 | |||||
160 | AssumptionCache *AC; | ||||
161 | DominatorTree *DT; | ||||
162 | TargetTransformInfo *TTI; | ||||
163 | OptimizationRemarkEmitter *ORE; | ||||
164 | }; | ||||
165 | |||||
166 | class DFAJumpThreadingLegacyPass : public FunctionPass { | ||||
167 | public: | ||||
168 | static char ID; // Pass identification | ||||
169 | DFAJumpThreadingLegacyPass() : FunctionPass(ID) {} | ||||
170 | |||||
171 | void getAnalysisUsage(AnalysisUsage &AU) const override { | ||||
172 | AU.addRequired<AssumptionCacheTracker>(); | ||||
173 | AU.addRequired<DominatorTreeWrapperPass>(); | ||||
174 | AU.addPreserved<DominatorTreeWrapperPass>(); | ||||
175 | AU.addRequired<TargetTransformInfoWrapperPass>(); | ||||
176 | AU.addRequired<OptimizationRemarkEmitterWrapperPass>(); | ||||
177 | } | ||||
178 | |||||
179 | bool runOnFunction(Function &F) override { | ||||
180 | if (skipFunction(F)) | ||||
181 | return false; | ||||
182 | |||||
183 | AssumptionCache *AC = | ||||
184 | &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); | ||||
185 | DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); | ||||
186 | TargetTransformInfo *TTI = | ||||
187 | &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F); | ||||
188 | OptimizationRemarkEmitter *ORE = | ||||
189 | &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE(); | ||||
190 | |||||
191 | return DFAJumpThreading(AC, DT, TTI, ORE).run(F); | ||||
192 | } | ||||
193 | }; | ||||
194 | } // end anonymous namespace | ||||
195 | |||||
196 | char DFAJumpThreadingLegacyPass::ID = 0; | ||||
197 | INITIALIZE_PASS_BEGIN(DFAJumpThreadingLegacyPass, "dfa-jump-threading",static void *initializeDFAJumpThreadingLegacyPassPassOnce(PassRegistry &Registry) { | ||||
198 | "DFA Jump Threading", false, false)static void *initializeDFAJumpThreadingLegacyPassPassOnce(PassRegistry &Registry) { | ||||
199 | INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)initializeAssumptionCacheTrackerPass(Registry); | ||||
200 | INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry); | ||||
201 | INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)initializeTargetTransformInfoWrapperPassPass(Registry); | ||||
202 | INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)initializeOptimizationRemarkEmitterWrapperPassPass(Registry); | ||||
203 | INITIALIZE_PASS_END(DFAJumpThreadingLegacyPass, "dfa-jump-threading",PassInfo *PI = new PassInfo( "DFA Jump Threading", "dfa-jump-threading" , &DFAJumpThreadingLegacyPass::ID, PassInfo::NormalCtor_t (callDefaultCtor<DFAJumpThreadingLegacyPass>), false, false ); Registry.registerPass(*PI, true); return PI; } static llvm ::once_flag InitializeDFAJumpThreadingLegacyPassPassFlag; void llvm::initializeDFAJumpThreadingLegacyPassPass(PassRegistry & Registry) { llvm::call_once(InitializeDFAJumpThreadingLegacyPassPassFlag , initializeDFAJumpThreadingLegacyPassPassOnce, std::ref(Registry )); } | ||||
204 | "DFA Jump Threading", false, false)PassInfo *PI = new PassInfo( "DFA Jump Threading", "dfa-jump-threading" , &DFAJumpThreadingLegacyPass::ID, PassInfo::NormalCtor_t (callDefaultCtor<DFAJumpThreadingLegacyPass>), false, false ); Registry.registerPass(*PI, true); return PI; } static llvm ::once_flag InitializeDFAJumpThreadingLegacyPassPassFlag; void llvm::initializeDFAJumpThreadingLegacyPassPass(PassRegistry & Registry) { llvm::call_once(InitializeDFAJumpThreadingLegacyPassPassFlag , initializeDFAJumpThreadingLegacyPassPassOnce, std::ref(Registry )); } | ||||
205 | |||||
206 | // Public interface to the DFA Jump Threading pass | ||||
207 | FunctionPass *llvm::createDFAJumpThreadingPass() { | ||||
208 | return new DFAJumpThreadingLegacyPass(); | ||||
209 | } | ||||
210 | |||||
211 | namespace { | ||||
212 | |||||
213 | /// Create a new basic block and sink \p SIToSink into it. | ||||
214 | void createBasicBlockAndSinkSelectInst( | ||||
215 | DomTreeUpdater *DTU, SelectInst *SI, PHINode *SIUse, SelectInst *SIToSink, | ||||
216 | BasicBlock *EndBlock, StringRef NewBBName, BasicBlock **NewBlock, | ||||
217 | BranchInst **NewBranch, std::vector<SelectInstToUnfold> *NewSIsToUnfold, | ||||
218 | std::vector<BasicBlock *> *NewBBs) { | ||||
219 | assert(SIToSink->hasOneUse())(static_cast<void> (0)); | ||||
220 | assert(NewBlock)(static_cast<void> (0)); | ||||
221 | assert(NewBranch)(static_cast<void> (0)); | ||||
222 | *NewBlock = BasicBlock::Create(SI->getContext(), NewBBName, | ||||
223 | EndBlock->getParent(), EndBlock); | ||||
224 | NewBBs->push_back(*NewBlock); | ||||
225 | *NewBranch = BranchInst::Create(EndBlock, *NewBlock); | ||||
226 | SIToSink->moveBefore(*NewBranch); | ||||
227 | NewSIsToUnfold->push_back(SelectInstToUnfold(SIToSink, SIUse)); | ||||
228 | DTU->applyUpdates({{DominatorTree::Insert, *NewBlock, EndBlock}}); | ||||
229 | } | ||||
230 | |||||
231 | /// Unfold the select instruction held in \p SIToUnfold by replacing it with | ||||
232 | /// control flow. | ||||
233 | /// | ||||
234 | /// Put newly discovered select instructions into \p NewSIsToUnfold. Put newly | ||||
235 | /// created basic blocks into \p NewBBs. | ||||
236 | /// | ||||
237 | /// TODO: merge it with CodeGenPrepare::optimizeSelectInst() if possible. | ||||
238 | void unfold(DomTreeUpdater *DTU, SelectInstToUnfold SIToUnfold, | ||||
239 | std::vector<SelectInstToUnfold> *NewSIsToUnfold, | ||||
240 | std::vector<BasicBlock *> *NewBBs) { | ||||
241 | SelectInst *SI = SIToUnfold.getInst(); | ||||
242 | PHINode *SIUse = SIToUnfold.getUse(); | ||||
243 | BasicBlock *StartBlock = SI->getParent(); | ||||
244 | BasicBlock *EndBlock = SIUse->getParent(); | ||||
245 | BranchInst *StartBlockTerm = | ||||
246 | dyn_cast<BranchInst>(StartBlock->getTerminator()); | ||||
247 | |||||
248 | assert(StartBlockTerm && StartBlockTerm->isUnconditional())(static_cast<void> (0)); | ||||
249 | assert(SI->hasOneUse())(static_cast<void> (0)); | ||||
250 | |||||
251 | // These are the new basic blocks for the conditional branch. | ||||
252 | // At least one will become an actual new basic block. | ||||
253 | BasicBlock *TrueBlock = nullptr; | ||||
254 | BasicBlock *FalseBlock = nullptr; | ||||
255 | BranchInst *TrueBranch = nullptr; | ||||
256 | BranchInst *FalseBranch = nullptr; | ||||
257 | |||||
258 | // Sink select instructions to be able to unfold them later. | ||||
259 | if (SelectInst *SIOp
| ||||
260 | createBasicBlockAndSinkSelectInst(DTU, SI, SIUse, SIOp, EndBlock, | ||||
261 | "si.unfold.true", &TrueBlock, &TrueBranch, | ||||
262 | NewSIsToUnfold, NewBBs); | ||||
263 | } | ||||
264 | if (SelectInst *SIOp
| ||||
265 | createBasicBlockAndSinkSelectInst(DTU, SI, SIUse, SIOp, EndBlock, | ||||
266 | "si.unfold.false", &FalseBlock, | ||||
267 | &FalseBranch, NewSIsToUnfold, NewBBs); | ||||
268 | } | ||||
269 | |||||
270 | // If there was nothing to sink, then arbitrarily choose the 'false' side | ||||
271 | // for a new input value to the PHI. | ||||
272 | if (!TrueBlock
| ||||
273 | FalseBlock = BasicBlock::Create(SI->getContext(), "si.unfold.false", | ||||
274 | EndBlock->getParent(), EndBlock); | ||||
275 | NewBBs->push_back(FalseBlock); | ||||
276 | BranchInst::Create(EndBlock, FalseBlock); | ||||
277 | DTU->applyUpdates({{DominatorTree::Insert, FalseBlock, EndBlock}}); | ||||
278 | } | ||||
279 | |||||
280 | // Insert the real conditional branch based on the original condition. | ||||
281 | // If we did not create a new block for one of the 'true' or 'false' paths | ||||
282 | // of the condition, it means that side of the branch goes to the end block | ||||
283 | // directly and the path originates from the start block from the point of | ||||
284 | // view of the new PHI. | ||||
285 | BasicBlock *TT = EndBlock; | ||||
286 | BasicBlock *FT = EndBlock; | ||||
287 | if (TrueBlock
| ||||
288 | // A diamond. | ||||
289 | TT = TrueBlock; | ||||
290 | FT = FalseBlock; | ||||
291 | |||||
292 | // Update the phi node of SI. | ||||
293 | SIUse->removeIncomingValue(StartBlock, /* DeletePHIIfEmpty = */ false); | ||||
294 | SIUse->addIncoming(SI->getTrueValue(), TrueBlock); | ||||
295 | SIUse->addIncoming(SI->getFalseValue(), FalseBlock); | ||||
296 | |||||
297 | // Update any other PHI nodes in EndBlock. | ||||
298 | for (PHINode &Phi : EndBlock->phis()) { | ||||
299 | if (&Phi != SIUse) { | ||||
300 | Phi.addIncoming(Phi.getIncomingValueForBlock(StartBlock), TrueBlock); | ||||
301 | Phi.addIncoming(Phi.getIncomingValueForBlock(StartBlock), FalseBlock); | ||||
302 | } | ||||
303 | } | ||||
304 | } else { | ||||
305 | BasicBlock *NewBlock = nullptr; | ||||
306 | Value *SIOp1 = SI->getTrueValue(); | ||||
307 | Value *SIOp2 = SI->getFalseValue(); | ||||
308 | |||||
309 | // A triangle pointing right. | ||||
310 | if (!TrueBlock
| ||||
311 | NewBlock = FalseBlock; | ||||
312 | FT = FalseBlock; | ||||
313 | } | ||||
314 | // A triangle pointing left. | ||||
315 | else { | ||||
316 | NewBlock = TrueBlock; | ||||
317 | TT = TrueBlock; | ||||
318 | std::swap(SIOp1, SIOp2); | ||||
319 | } | ||||
320 | |||||
321 | // Update the phi node of SI. | ||||
322 | for (unsigned Idx = 0; Idx < SIUse->getNumIncomingValues(); ++Idx) { | ||||
323 | if (SIUse->getIncomingBlock(Idx) == StartBlock) | ||||
324 | SIUse->setIncomingValue(Idx, SIOp1); | ||||
325 | } | ||||
326 | SIUse->addIncoming(SIOp2, NewBlock); | ||||
327 | |||||
328 | // Update any other PHI nodes in EndBlock. | ||||
329 | for (auto II = EndBlock->begin(); PHINode *Phi = dyn_cast<PHINode>(II); | ||||
330 | ++II) { | ||||
331 | if (Phi != SIUse) | ||||
332 | Phi->addIncoming(Phi->getIncomingValueForBlock(StartBlock), NewBlock); | ||||
333 | } | ||||
334 | } | ||||
335 | StartBlockTerm->eraseFromParent(); | ||||
| |||||
336 | BranchInst::Create(TT, FT, SI->getCondition(), StartBlock); | ||||
337 | DTU->applyUpdates({{DominatorTree::Insert, StartBlock, TT}, | ||||
338 | {DominatorTree::Insert, StartBlock, FT}}); | ||||
339 | |||||
340 | // The select is now dead. | ||||
341 | SI->eraseFromParent(); | ||||
342 | } | ||||
343 | |||||
344 | struct ClonedBlock { | ||||
345 | BasicBlock *BB; | ||||
346 | uint64_t State; ///< \p State corresponds to the next value of a switch stmnt. | ||||
347 | }; | ||||
348 | |||||
349 | typedef std::deque<BasicBlock *> PathType; | ||||
350 | typedef std::vector<PathType> PathsType; | ||||
351 | typedef SmallPtrSet<const BasicBlock *, 8> VisitedBlocks; | ||||
352 | typedef std::vector<ClonedBlock> CloneList; | ||||
353 | |||||
354 | // This data structure keeps track of all blocks that have been cloned. If two | ||||
355 | // different ThreadingPaths clone the same block for a certain state it should | ||||
356 | // be reused, and it can be looked up in this map. | ||||
357 | typedef DenseMap<BasicBlock *, CloneList> DuplicateBlockMap; | ||||
358 | |||||
359 | // This map keeps track of all the new definitions for an instruction. This | ||||
360 | // information is needed when restoring SSA form after cloning blocks. | ||||
361 | typedef DenseMap<Instruction *, std::vector<Instruction *>> DefMap; | ||||
362 | |||||
363 | inline raw_ostream &operator<<(raw_ostream &OS, const PathType &Path) { | ||||
364 | OS << "< "; | ||||
365 | for (const BasicBlock *BB : Path) { | ||||
366 | std::string BBName; | ||||
367 | if (BB->hasName()) | ||||
368 | raw_string_ostream(BBName) << BB->getName(); | ||||
369 | else | ||||
370 | raw_string_ostream(BBName) << BB; | ||||
371 | OS << BBName << " "; | ||||
372 | } | ||||
373 | OS << ">"; | ||||
374 | return OS; | ||||
375 | } | ||||
376 | |||||
377 | /// ThreadingPath is a path in the control flow of a loop that can be threaded | ||||
378 | /// by cloning necessary basic blocks and replacing conditional branches with | ||||
379 | /// unconditional ones. A threading path includes a list of basic blocks, the | ||||
380 | /// exit state, and the block that determines the next state. | ||||
381 | struct ThreadingPath { | ||||
382 | /// Exit value is DFA's exit state for the given path. | ||||
383 | uint64_t getExitValue() const { return ExitVal; } | ||||
384 | void setExitValue(const ConstantInt *V) { | ||||
385 | ExitVal = V->getZExtValue(); | ||||
386 | IsExitValSet = true; | ||||
387 | } | ||||
388 | bool isExitValueSet() const { return IsExitValSet; } | ||||
389 | |||||
390 | /// Determinator is the basic block that determines the next state of the DFA. | ||||
391 | const BasicBlock *getDeterminatorBB() const { return DBB; } | ||||
392 | void setDeterminator(const BasicBlock *BB) { DBB = BB; } | ||||
393 | |||||
394 | /// Path is a list of basic blocks. | ||||
395 | const PathType &getPath() const { return Path; } | ||||
396 | void setPath(const PathType &NewPath) { Path = NewPath; } | ||||
397 | |||||
398 | void print(raw_ostream &OS) const { | ||||
399 | OS << Path << " [ " << ExitVal << ", " << DBB->getName() << " ]"; | ||||
400 | } | ||||
401 | |||||
402 | private: | ||||
403 | PathType Path; | ||||
404 | uint64_t ExitVal; | ||||
405 | const BasicBlock *DBB = nullptr; | ||||
406 | bool IsExitValSet = false; | ||||
407 | }; | ||||
408 | |||||
409 | #ifndef NDEBUG1 | ||||
410 | inline raw_ostream &operator<<(raw_ostream &OS, const ThreadingPath &TPath) { | ||||
411 | TPath.print(OS); | ||||
412 | return OS; | ||||
413 | } | ||||
414 | #endif | ||||
415 | |||||
416 | struct MainSwitch { | ||||
417 | MainSwitch(SwitchInst *SI, OptimizationRemarkEmitter *ORE) { | ||||
418 | if (isPredictable(SI)) { | ||||
419 | Instr = SI; | ||||
420 | } else { | ||||
421 | ORE->emit([&]() { | ||||
422 | return OptimizationRemarkMissed(DEBUG_TYPE"dfa-jump-threading", "SwitchNotPredictable", SI) | ||||
423 | << "Switch instruction is not predictable."; | ||||
424 | }); | ||||
425 | } | ||||
426 | } | ||||
427 | |||||
428 | virtual ~MainSwitch() = default; | ||||
429 | |||||
430 | SwitchInst *getInstr() const { return Instr; } | ||||
431 | const SmallVector<SelectInstToUnfold, 4> getSelectInsts() { | ||||
432 | return SelectInsts; | ||||
433 | } | ||||
434 | |||||
435 | private: | ||||
436 | /// Do a use-def chain traversal. Make sure the value of the switch variable | ||||
437 | /// is always a known constant. This means that all conditional jumps based on | ||||
438 | /// switch variable can be converted to unconditional jumps. | ||||
439 | bool isPredictable(const SwitchInst *SI) { | ||||
440 | std::deque<Instruction *> Q; | ||||
441 | SmallSet<Value *, 16> SeenValues; | ||||
442 | SelectInsts.clear(); | ||||
443 | |||||
444 | Value *FirstDef = SI->getOperand(0); | ||||
445 | auto *Inst = dyn_cast<Instruction>(FirstDef); | ||||
446 | |||||
447 | // If this is a function argument or another non-instruction, then give up. | ||||
448 | // We are interested in loop local variables. | ||||
449 | if (!Inst) | ||||
450 | return false; | ||||
451 | |||||
452 | // Require the first definition to be a PHINode | ||||
453 | if (!isa<PHINode>(Inst)) | ||||
454 | return false; | ||||
455 | |||||
456 | LLVM_DEBUG(dbgs() << "\tisPredictable() FirstDef: " << *Inst << "\n")do { } while (false); | ||||
457 | |||||
458 | Q.push_back(Inst); | ||||
459 | SeenValues.insert(FirstDef); | ||||
460 | |||||
461 | while (!Q.empty()) { | ||||
462 | Instruction *Current = Q.front(); | ||||
463 | Q.pop_front(); | ||||
464 | |||||
465 | if (auto *Phi = dyn_cast<PHINode>(Current)) { | ||||
466 | for (Value *Incoming : Phi->incoming_values()) { | ||||
467 | if (!isPredictableValue(Incoming, SeenValues)) | ||||
468 | return false; | ||||
469 | addInstToQueue(Incoming, Q, SeenValues); | ||||
470 | } | ||||
471 | LLVM_DEBUG(dbgs() << "\tisPredictable() phi: " << *Phi << "\n")do { } while (false); | ||||
472 | } else if (SelectInst *SelI = dyn_cast<SelectInst>(Current)) { | ||||
473 | if (!isValidSelectInst(SelI)) | ||||
474 | return false; | ||||
475 | if (!isPredictableValue(SelI->getTrueValue(), SeenValues) || | ||||
476 | !isPredictableValue(SelI->getFalseValue(), SeenValues)) { | ||||
477 | return false; | ||||
478 | } | ||||
479 | addInstToQueue(SelI->getTrueValue(), Q, SeenValues); | ||||
480 | addInstToQueue(SelI->getFalseValue(), Q, SeenValues); | ||||
481 | LLVM_DEBUG(dbgs() << "\tisPredictable() select: " << *SelI << "\n")do { } while (false); | ||||
482 | if (auto *SelIUse = dyn_cast<PHINode>(SelI->user_back())) | ||||
483 | SelectInsts.push_back(SelectInstToUnfold(SelI, SelIUse)); | ||||
484 | } else { | ||||
485 | // If it is neither a phi nor a select, then we give up. | ||||
486 | return false; | ||||
487 | } | ||||
488 | } | ||||
489 | |||||
490 | return true; | ||||
491 | } | ||||
492 | |||||
493 | bool isPredictableValue(Value *InpVal, SmallSet<Value *, 16> &SeenValues) { | ||||
494 | if (SeenValues.find(InpVal) != SeenValues.end()) | ||||
495 | return true; | ||||
496 | |||||
497 | if (isa<ConstantInt>(InpVal)) | ||||
498 | return true; | ||||
499 | |||||
500 | // If this is a function argument or another non-instruction, then give up. | ||||
501 | if (!isa<Instruction>(InpVal)) | ||||
502 | return false; | ||||
503 | |||||
504 | return true; | ||||
505 | } | ||||
506 | |||||
507 | void addInstToQueue(Value *Val, std::deque<Instruction *> &Q, | ||||
508 | SmallSet<Value *, 16> &SeenValues) { | ||||
509 | if (SeenValues.find(Val) != SeenValues.end()) | ||||
510 | return; | ||||
511 | if (Instruction *I = dyn_cast<Instruction>(Val)) | ||||
512 | Q.push_back(I); | ||||
513 | SeenValues.insert(Val); | ||||
514 | } | ||||
515 | |||||
516 | bool isValidSelectInst(SelectInst *SI) { | ||||
517 | if (!SI->hasOneUse()) | ||||
518 | return false; | ||||
519 | |||||
520 | Instruction *SIUse = dyn_cast<Instruction>(SI->user_back()); | ||||
521 | // The use of the select inst should be either a phi or another select. | ||||
522 | if (!SIUse && !(isa<PHINode>(SIUse) || isa<SelectInst>(SIUse))) | ||||
523 | return false; | ||||
524 | |||||
525 | BasicBlock *SIBB = SI->getParent(); | ||||
526 | |||||
527 | // Currently, we can only expand select instructions in basic blocks with | ||||
528 | // one successor. | ||||
529 | BranchInst *SITerm = dyn_cast<BranchInst>(SIBB->getTerminator()); | ||||
530 | if (!SITerm || !SITerm->isUnconditional()) | ||||
531 | return false; | ||||
532 | |||||
533 | if (isa<PHINode>(SIUse) && | ||||
534 | SIBB->getSingleSuccessor() != cast<Instruction>(SIUse)->getParent()) | ||||
535 | return false; | ||||
536 | |||||
537 | // If select will not be sunk during unfolding, and it is in the same basic | ||||
538 | // block as another state defining select, then cannot unfold both. | ||||
539 | for (SelectInstToUnfold SIToUnfold : SelectInsts) { | ||||
540 | SelectInst *PrevSI = SIToUnfold.getInst(); | ||||
541 | if (PrevSI->getTrueValue() != SI && PrevSI->getFalseValue() != SI && | ||||
542 | PrevSI->getParent() == SI->getParent()) | ||||
543 | return false; | ||||
544 | } | ||||
545 | |||||
546 | return true; | ||||
547 | } | ||||
548 | |||||
549 | SwitchInst *Instr = nullptr; | ||||
550 | SmallVector<SelectInstToUnfold, 4> SelectInsts; | ||||
551 | }; | ||||
552 | |||||
553 | struct AllSwitchPaths { | ||||
554 | AllSwitchPaths(const MainSwitch *MSwitch, OptimizationRemarkEmitter *ORE) | ||||
555 | : Switch(MSwitch->getInstr()), SwitchBlock(Switch->getParent()), | ||||
556 | ORE(ORE) {} | ||||
557 | |||||
558 | std::vector<ThreadingPath> &getThreadingPaths() { return TPaths; } | ||||
559 | unsigned getNumThreadingPaths() { return TPaths.size(); } | ||||
560 | SwitchInst *getSwitchInst() { return Switch; } | ||||
561 | BasicBlock *getSwitchBlock() { return SwitchBlock; } | ||||
562 | |||||
563 | void run() { | ||||
564 | VisitedBlocks Visited; | ||||
565 | PathsType LoopPaths = paths(SwitchBlock, Visited, /* PathDepth = */ 1); | ||||
566 | StateDefMap StateDef = getStateDefMap(); | ||||
567 | |||||
568 | for (PathType Path : LoopPaths) { | ||||
569 | ThreadingPath TPath; | ||||
570 | |||||
571 | const BasicBlock *PrevBB = Path.back(); | ||||
572 | for (const BasicBlock *BB : Path) { | ||||
573 | if (StateDef.count(BB) != 0) { | ||||
574 | const PHINode *Phi = dyn_cast<PHINode>(StateDef[BB]); | ||||
575 | assert(Phi && "Expected a state-defining instr to be a phi node.")(static_cast<void> (0)); | ||||
576 | |||||
577 | const Value *V = Phi->getIncomingValueForBlock(PrevBB); | ||||
578 | if (const ConstantInt *C = dyn_cast<const ConstantInt>(V)) { | ||||
579 | TPath.setExitValue(C); | ||||
580 | TPath.setDeterminator(BB); | ||||
581 | TPath.setPath(Path); | ||||
582 | } | ||||
583 | } | ||||
584 | |||||
585 | // Switch block is the determinator, this is the final exit value. | ||||
586 | if (TPath.isExitValueSet() && BB == Path.front()) | ||||
587 | break; | ||||
588 | |||||
589 | PrevBB = BB; | ||||
590 | } | ||||
591 | |||||
592 | if (TPath.isExitValueSet()) | ||||
593 | TPaths.push_back(TPath); | ||||
594 | } | ||||
595 | } | ||||
596 | |||||
597 | private: | ||||
598 | // Value: an instruction that defines a switch state; | ||||
599 | // Key: the parent basic block of that instruction. | ||||
600 | typedef DenseMap<const BasicBlock *, const PHINode *> StateDefMap; | ||||
601 | |||||
602 | PathsType paths(BasicBlock *BB, VisitedBlocks &Visited, | ||||
603 | unsigned PathDepth) const { | ||||
604 | PathsType Res; | ||||
605 | |||||
606 | // Stop exploring paths after visiting MaxPathLength blocks | ||||
607 | if (PathDepth > MaxPathLength) { | ||||
608 | ORE->emit([&]() { | ||||
609 | return OptimizationRemarkAnalysis(DEBUG_TYPE"dfa-jump-threading", "MaxPathLengthReached", | ||||
610 | Switch) | ||||
611 | << "Exploration stopped after visiting MaxPathLength=" | ||||
612 | << ore::NV("MaxPathLength", MaxPathLength) << " blocks."; | ||||
613 | }); | ||||
614 | return Res; | ||||
615 | } | ||||
616 | |||||
617 | Visited.insert(BB); | ||||
618 | |||||
619 | // Some blocks have multiple edges to the same successor, and this set | ||||
620 | // is used to prevent a duplicate path from being generated | ||||
621 | SmallSet<BasicBlock *, 4> Successors; | ||||
622 | for (BasicBlock *Succ : successors(BB)) { | ||||
623 | if (!Successors.insert(Succ).second) | ||||
624 | continue; | ||||
625 | |||||
626 | // Found a cycle through the SwitchBlock | ||||
627 | if (Succ == SwitchBlock) { | ||||
628 | Res.push_back({BB}); | ||||
629 | continue; | ||||
630 | } | ||||
631 | |||||
632 | // We have encountered a cycle, do not get caught in it | ||||
633 | if (Visited.contains(Succ)) | ||||
634 | continue; | ||||
635 | |||||
636 | PathsType SuccPaths = paths(Succ, Visited, PathDepth + 1); | ||||
637 | for (PathType Path : SuccPaths) { | ||||
638 | PathType NewPath(Path); | ||||
639 | NewPath.push_front(BB); | ||||
640 | Res.push_back(NewPath); | ||||
641 | } | ||||
642 | } | ||||
643 | // This block could now be visited again from a different predecessor. Note | ||||
644 | // that this will result in exponential runtime. Subpaths could possibly be | ||||
645 | // cached but it takes a lot of memory to store them. | ||||
646 | Visited.erase(BB); | ||||
647 | return Res; | ||||
648 | } | ||||
649 | |||||
650 | /// Walk the use-def chain and collect all the state-defining instructions. | ||||
651 | StateDefMap getStateDefMap() const { | ||||
652 | StateDefMap Res; | ||||
653 | |||||
654 | Value *FirstDef = Switch->getOperand(0); | ||||
655 | |||||
656 | assert(isa<PHINode>(FirstDef) && "After select unfolding, all state "(static_cast<void> (0)) | ||||
657 | "definitions are expected to be phi "(static_cast<void> (0)) | ||||
658 | "nodes.")(static_cast<void> (0)); | ||||
659 | |||||
660 | SmallVector<PHINode *, 8> Stack; | ||||
661 | Stack.push_back(dyn_cast<PHINode>(FirstDef)); | ||||
662 | SmallSet<Value *, 16> SeenValues; | ||||
663 | |||||
664 | while (!Stack.empty()) { | ||||
665 | PHINode *CurPhi = Stack.back(); | ||||
666 | Stack.pop_back(); | ||||
667 | |||||
668 | Res[CurPhi->getParent()] = CurPhi; | ||||
669 | SeenValues.insert(CurPhi); | ||||
670 | |||||
671 | for (Value *Incoming : CurPhi->incoming_values()) { | ||||
672 | if (Incoming == FirstDef || isa<ConstantInt>(Incoming) || | ||||
673 | SeenValues.find(Incoming) != SeenValues.end()) { | ||||
674 | continue; | ||||
675 | } | ||||
676 | |||||
677 | assert(isa<PHINode>(Incoming) && "After select unfolding, all state "(static_cast<void> (0)) | ||||
678 | "definitions are expected to be phi "(static_cast<void> (0)) | ||||
679 | "nodes.")(static_cast<void> (0)); | ||||
680 | |||||
681 | Stack.push_back(cast<PHINode>(Incoming)); | ||||
682 | } | ||||
683 | } | ||||
684 | |||||
685 | return Res; | ||||
686 | } | ||||
687 | |||||
688 | SwitchInst *Switch; | ||||
689 | BasicBlock *SwitchBlock; | ||||
690 | OptimizationRemarkEmitter *ORE; | ||||
691 | std::vector<ThreadingPath> TPaths; | ||||
692 | }; | ||||
693 | |||||
694 | struct TransformDFA { | ||||
695 | TransformDFA(AllSwitchPaths *SwitchPaths, DominatorTree *DT, | ||||
696 | AssumptionCache *AC, TargetTransformInfo *TTI, | ||||
697 | OptimizationRemarkEmitter *ORE, | ||||
698 | SmallPtrSet<const Value *, 32> EphValues) | ||||
699 | : SwitchPaths(SwitchPaths), DT(DT), AC(AC), TTI(TTI), ORE(ORE), | ||||
700 | EphValues(EphValues) {} | ||||
701 | |||||
702 | void run() { | ||||
703 | if (isLegalAndProfitableToTransform()) { | ||||
704 | createAllExitPaths(); | ||||
705 | NumTransforms++; | ||||
706 | } | ||||
707 | } | ||||
708 | |||||
709 | private: | ||||
710 | /// This function performs both a legality check and profitability check at | ||||
711 | /// the same time since it is convenient to do so. It iterates through all | ||||
712 | /// blocks that will be cloned, and keeps track of the duplication cost. It | ||||
713 | /// also returns false if it is illegal to clone some required block. | ||||
714 | bool isLegalAndProfitableToTransform() { | ||||
715 | CodeMetrics Metrics; | ||||
716 | SwitchInst *Switch = SwitchPaths->getSwitchInst(); | ||||
717 | |||||
718 | // Note that DuplicateBlockMap is not being used as intended here. It is | ||||
719 | // just being used to ensure (BB, State) pairs are only counted once. | ||||
720 | DuplicateBlockMap DuplicateMap; | ||||
721 | |||||
722 | for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) { | ||||
723 | PathType PathBBs = TPath.getPath(); | ||||
724 | uint64_t NextState = TPath.getExitValue(); | ||||
725 | const BasicBlock *Determinator = TPath.getDeterminatorBB(); | ||||
726 | |||||
727 | // Update Metrics for the Switch block, this is always cloned | ||||
728 | BasicBlock *BB = SwitchPaths->getSwitchBlock(); | ||||
729 | BasicBlock *VisitedBB = getClonedBB(BB, NextState, DuplicateMap); | ||||
730 | if (!VisitedBB) { | ||||
731 | Metrics.analyzeBasicBlock(BB, *TTI, EphValues); | ||||
732 | DuplicateMap[BB].push_back({BB, NextState}); | ||||
733 | } | ||||
734 | |||||
735 | // If the Switch block is the Determinator, then we can continue since | ||||
736 | // this is the only block that is cloned and we already counted for it. | ||||
737 | if (PathBBs.front() == Determinator) | ||||
738 | continue; | ||||
739 | |||||
740 | // Otherwise update Metrics for all blocks that will be cloned. If any | ||||
741 | // block is already cloned and would be reused, don't double count it. | ||||
742 | auto DetIt = std::find(PathBBs.begin(), PathBBs.end(), Determinator); | ||||
743 | for (auto BBIt = DetIt; BBIt != PathBBs.end(); BBIt++) { | ||||
744 | BB = *BBIt; | ||||
745 | VisitedBB = getClonedBB(BB, NextState, DuplicateMap); | ||||
746 | if (VisitedBB) | ||||
747 | continue; | ||||
748 | Metrics.analyzeBasicBlock(BB, *TTI, EphValues); | ||||
749 | DuplicateMap[BB].push_back({BB, NextState}); | ||||
750 | } | ||||
751 | |||||
752 | if (Metrics.notDuplicatable) { | ||||
753 | LLVM_DEBUG(dbgs() << "DFA Jump Threading: Not jump threading, contains "do { } while (false) | ||||
754 | << "non-duplicatable instructions.\n")do { } while (false); | ||||
755 | ORE->emit([&]() { | ||||
756 | return OptimizationRemarkMissed(DEBUG_TYPE"dfa-jump-threading", "NonDuplicatableInst", | ||||
757 | Switch) | ||||
758 | << "Contains non-duplicatable instructions."; | ||||
759 | }); | ||||
760 | return false; | ||||
761 | } | ||||
762 | |||||
763 | if (Metrics.convergent) { | ||||
764 | LLVM_DEBUG(dbgs() << "DFA Jump Threading: Not jump threading, contains "do { } while (false) | ||||
765 | << "convergent instructions.\n")do { } while (false); | ||||
766 | ORE->emit([&]() { | ||||
767 | return OptimizationRemarkMissed(DEBUG_TYPE"dfa-jump-threading", "ConvergentInst", Switch) | ||||
768 | << "Contains convergent instructions."; | ||||
769 | }); | ||||
770 | return false; | ||||
771 | } | ||||
772 | } | ||||
773 | |||||
774 | unsigned DuplicationCost = 0; | ||||
775 | |||||
776 | unsigned JumpTableSize = 0; | ||||
777 | TTI->getEstimatedNumberOfCaseClusters(*Switch, JumpTableSize, nullptr, | ||||
778 | nullptr); | ||||
779 | if (JumpTableSize == 0) { | ||||
780 | // Factor in the number of conditional branches reduced from jump | ||||
781 | // threading. Assume that lowering the switch block is implemented by | ||||
782 | // using binary search, hence the LogBase2(). | ||||
783 | unsigned CondBranches = | ||||
784 | APInt(32, Switch->getNumSuccessors()).ceilLogBase2(); | ||||
785 | DuplicationCost = Metrics.NumInsts / CondBranches; | ||||
786 | } else { | ||||
787 | // Compared with jump tables, the DFA optimizer removes an indirect branch | ||||
788 | // on each loop iteration, thus making branch prediction more precise. The | ||||
789 | // more branch targets there are, the more likely it is for the branch | ||||
790 | // predictor to make a mistake, and the more benefit there is in the DFA | ||||
791 | // optimizer. Thus, the more branch targets there are, the lower is the | ||||
792 | // cost of the DFA opt. | ||||
793 | DuplicationCost = Metrics.NumInsts / JumpTableSize; | ||||
794 | } | ||||
795 | |||||
796 | LLVM_DEBUG(dbgs() << "\nDFA Jump Threading: Cost to jump thread block "do { } while (false) | ||||
797 | << SwitchPaths->getSwitchBlock()->getName()do { } while (false) | ||||
798 | << " is: " << DuplicationCost << "\n\n")do { } while (false); | ||||
799 | |||||
800 | if (DuplicationCost > CostThreshold) { | ||||
801 | LLVM_DEBUG(dbgs() << "Not jump threading, duplication cost exceeds the "do { } while (false) | ||||
802 | << "cost threshold.\n")do { } while (false); | ||||
803 | ORE->emit([&]() { | ||||
804 | return OptimizationRemarkMissed(DEBUG_TYPE"dfa-jump-threading", "NotProfitable", Switch) | ||||
805 | << "Duplication cost exceeds the cost threshold (cost=" | ||||
806 | << ore::NV("Cost", DuplicationCost) | ||||
807 | << ", threshold=" << ore::NV("Threshold", CostThreshold) << ")."; | ||||
808 | }); | ||||
809 | return false; | ||||
810 | } | ||||
811 | |||||
812 | ORE->emit([&]() { | ||||
813 | return OptimizationRemark(DEBUG_TYPE"dfa-jump-threading", "JumpThreaded", Switch) | ||||
814 | << "Switch statement jump-threaded."; | ||||
815 | }); | ||||
816 | |||||
817 | return true; | ||||
818 | } | ||||
819 | |||||
820 | /// Transform each threading path to effectively jump thread the DFA. | ||||
821 | void createAllExitPaths() { | ||||
822 | DomTreeUpdater DTU(*DT, DomTreeUpdater::UpdateStrategy::Eager); | ||||
823 | |||||
824 | // Move the switch block to the end of the path, since it will be duplicated | ||||
825 | BasicBlock *SwitchBlock = SwitchPaths->getSwitchBlock(); | ||||
826 | for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) { | ||||
827 | LLVM_DEBUG(dbgs() << TPath << "\n")do { } while (false); | ||||
828 | PathType NewPath(TPath.getPath()); | ||||
829 | NewPath.push_back(SwitchBlock); | ||||
830 | TPath.setPath(NewPath); | ||||
831 | } | ||||
832 | |||||
833 | // Transform the ThreadingPaths and keep track of the cloned values | ||||
834 | DuplicateBlockMap DuplicateMap; | ||||
835 | DefMap NewDefs; | ||||
836 | |||||
837 | SmallSet<BasicBlock *, 16> BlocksToClean; | ||||
838 | for (BasicBlock *BB : successors(SwitchBlock)) | ||||
839 | BlocksToClean.insert(BB); | ||||
840 | |||||
841 | for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) { | ||||
842 | createExitPath(NewDefs, TPath, DuplicateMap, BlocksToClean, &DTU); | ||||
843 | NumPaths++; | ||||
844 | } | ||||
845 | |||||
846 | // After all paths are cloned, now update the last successor of the cloned | ||||
847 | // path so it skips over the switch statement | ||||
848 | for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) | ||||
849 | updateLastSuccessor(TPath, DuplicateMap, &DTU); | ||||
850 | |||||
851 | // For each instruction that was cloned and used outside, update its uses | ||||
852 | updateSSA(NewDefs); | ||||
853 | |||||
854 | // Clean PHI Nodes for the newly created blocks | ||||
855 | for (BasicBlock *BB : BlocksToClean) | ||||
856 | cleanPhiNodes(BB); | ||||
857 | } | ||||
858 | |||||
859 | /// For a specific ThreadingPath \p Path, create an exit path starting from | ||||
860 | /// the determinator block. | ||||
861 | /// | ||||
862 | /// To remember the correct destination, we have to duplicate blocks | ||||
863 | /// corresponding to each state. Also update the terminating instruction of | ||||
864 | /// the predecessors, and phis in the successor blocks. | ||||
865 | void createExitPath(DefMap &NewDefs, ThreadingPath &Path, | ||||
866 | DuplicateBlockMap &DuplicateMap, | ||||
867 | SmallSet<BasicBlock *, 16> &BlocksToClean, | ||||
868 | DomTreeUpdater *DTU) { | ||||
869 | uint64_t NextState = Path.getExitValue(); | ||||
870 | const BasicBlock *Determinator = Path.getDeterminatorBB(); | ||||
871 | PathType PathBBs = Path.getPath(); | ||||
872 | |||||
873 | // Don't select the placeholder block in front | ||||
874 | if (PathBBs.front() == Determinator) | ||||
875 | PathBBs.pop_front(); | ||||
876 | |||||
877 | auto DetIt = std::find(PathBBs.begin(), PathBBs.end(), Determinator); | ||||
878 | auto Prev = std::prev(DetIt); | ||||
879 | BasicBlock *PrevBB = *Prev; | ||||
880 | for (auto BBIt = DetIt; BBIt != PathBBs.end(); BBIt++) { | ||||
881 | BasicBlock *BB = *BBIt; | ||||
882 | BlocksToClean.insert(BB); | ||||
883 | |||||
884 | // We already cloned BB for this NextState, now just update the branch | ||||
885 | // and continue. | ||||
886 | BasicBlock *NextBB = getClonedBB(BB, NextState, DuplicateMap); | ||||
887 | if (NextBB) { | ||||
888 | updatePredecessor(PrevBB, BB, NextBB, DTU); | ||||
889 | PrevBB = NextBB; | ||||
890 | continue; | ||||
891 | } | ||||
892 | |||||
893 | // Clone the BB and update the successor of Prev to jump to the new block | ||||
894 | BasicBlock *NewBB = cloneBlockAndUpdatePredecessor( | ||||
895 | BB, PrevBB, NextState, DuplicateMap, NewDefs, DTU); | ||||
896 | DuplicateMap[BB].push_back({NewBB, NextState}); | ||||
897 | BlocksToClean.insert(NewBB); | ||||
898 | PrevBB = NewBB; | ||||
899 | } | ||||
900 | } | ||||
901 | |||||
902 | /// Restore SSA form after cloning blocks. | ||||
903 | /// | ||||
904 | /// Each cloned block creates new defs for a variable, and the uses need to be | ||||
905 | /// updated to reflect this. The uses may be replaced with a cloned value, or | ||||
906 | /// some derived phi instruction. Note that all uses of a value defined in the | ||||
907 | /// same block were already remapped when cloning the block. | ||||
908 | void updateSSA(DefMap &NewDefs) { | ||||
909 | SSAUpdaterBulk SSAUpdate; | ||||
910 | SmallVector<Use *, 16> UsesToRename; | ||||
911 | |||||
912 | for (auto KV : NewDefs) { | ||||
913 | Instruction *I = KV.first; | ||||
914 | BasicBlock *BB = I->getParent(); | ||||
915 | std::vector<Instruction *> Cloned = KV.second; | ||||
916 | |||||
917 | // Scan all uses of this instruction to see if it is used outside of its | ||||
918 | // block, and if so, record them in UsesToRename. | ||||
919 | for (Use &U : I->uses()) { | ||||
920 | Instruction *User = cast<Instruction>(U.getUser()); | ||||
921 | if (PHINode *UserPN = dyn_cast<PHINode>(User)) { | ||||
922 | if (UserPN->getIncomingBlock(U) == BB) | ||||
923 | continue; | ||||
924 | } else if (User->getParent() == BB) { | ||||
925 | continue; | ||||
926 | } | ||||
927 | |||||
928 | UsesToRename.push_back(&U); | ||||
929 | } | ||||
930 | |||||
931 | // If there are no uses outside the block, we're done with this | ||||
932 | // instruction. | ||||
933 | if (UsesToRename.empty()) | ||||
934 | continue; | ||||
935 | LLVM_DEBUG(dbgs() << "DFA-JT: Renaming non-local uses of: " << *Ido { } while (false) | ||||
936 | << "\n")do { } while (false); | ||||
937 | |||||
938 | // We found a use of I outside of BB. Rename all uses of I that are | ||||
939 | // outside its block to be uses of the appropriate PHI node etc. See | ||||
940 | // ValuesInBlocks with the values we know. | ||||
941 | unsigned VarNum = SSAUpdate.AddVariable(I->getName(), I->getType()); | ||||
942 | SSAUpdate.AddAvailableValue(VarNum, BB, I); | ||||
943 | for (Instruction *New : Cloned) | ||||
944 | SSAUpdate.AddAvailableValue(VarNum, New->getParent(), New); | ||||
945 | |||||
946 | while (!UsesToRename.empty()) | ||||
947 | SSAUpdate.AddUse(VarNum, UsesToRename.pop_back_val()); | ||||
948 | |||||
949 | LLVM_DEBUG(dbgs() << "\n")do { } while (false); | ||||
950 | } | ||||
951 | // SSAUpdater handles phi placement and renaming uses with the appropriate | ||||
952 | // value. | ||||
953 | SSAUpdate.RewriteAllUses(DT); | ||||
954 | } | ||||
955 | |||||
956 | /// Clones a basic block, and adds it to the CFG. | ||||
957 | /// | ||||
958 | /// This function also includes updating phi nodes in the successors of the | ||||
959 | /// BB, and remapping uses that were defined locally in the cloned BB. | ||||
960 | BasicBlock *cloneBlockAndUpdatePredecessor(BasicBlock *BB, BasicBlock *PrevBB, | ||||
961 | uint64_t NextState, | ||||
962 | DuplicateBlockMap &DuplicateMap, | ||||
963 | DefMap &NewDefs, | ||||
964 | DomTreeUpdater *DTU) { | ||||
965 | ValueToValueMapTy VMap; | ||||
966 | BasicBlock *NewBB = CloneBasicBlock( | ||||
967 | BB, VMap, ".jt" + std::to_string(NextState), BB->getParent()); | ||||
968 | NewBB->moveAfter(BB); | ||||
969 | NumCloned++; | ||||
970 | |||||
971 | for (Instruction &I : *NewBB) { | ||||
972 | // Do not remap operands of PHINode in case a definition in BB is an | ||||
973 | // incoming value to a phi in the same block. This incoming value will | ||||
974 | // be renamed later while restoring SSA. | ||||
975 | if (isa<PHINode>(&I)) | ||||
976 | continue; | ||||
977 | RemapInstruction(&I, VMap, | ||||
978 | RF_IgnoreMissingLocals | RF_NoModuleLevelChanges); | ||||
979 | if (AssumeInst *II = dyn_cast<AssumeInst>(&I)) | ||||
980 | AC->registerAssumption(II); | ||||
981 | } | ||||
982 | |||||
983 | updateSuccessorPhis(BB, NewBB, NextState, VMap, DuplicateMap); | ||||
984 | updatePredecessor(PrevBB, BB, NewBB, DTU); | ||||
985 | updateDefMap(NewDefs, VMap); | ||||
986 | |||||
987 | // Add all successors to the DominatorTree | ||||
988 | SmallPtrSet<BasicBlock *, 4> SuccSet; | ||||
989 | for (auto *SuccBB : successors(NewBB)) { | ||||
990 | if (SuccSet.insert(SuccBB).second) | ||||
991 | DTU->applyUpdates({{DominatorTree::Insert, NewBB, SuccBB}}); | ||||
992 | } | ||||
993 | SuccSet.clear(); | ||||
994 | return NewBB; | ||||
995 | } | ||||
996 | |||||
997 | /// Update the phi nodes in BB's successors. | ||||
998 | /// | ||||
999 | /// This means creating a new incoming value from NewBB with the new | ||||
1000 | /// instruction wherever there is an incoming value from BB. | ||||
1001 | void updateSuccessorPhis(BasicBlock *BB, BasicBlock *ClonedBB, | ||||
1002 | uint64_t NextState, ValueToValueMapTy &VMap, | ||||
1003 | DuplicateBlockMap &DuplicateMap) { | ||||
1004 | std::vector<BasicBlock *> BlocksToUpdate; | ||||
1005 | |||||
1006 | // If BB is the last block in the path, we can simply update the one case | ||||
1007 | // successor that will be reached. | ||||
1008 | if (BB == SwitchPaths->getSwitchBlock()) { | ||||
1009 | SwitchInst *Switch = SwitchPaths->getSwitchInst(); | ||||
1010 | BasicBlock *NextCase = getNextCaseSuccessor(Switch, NextState); | ||||
1011 | BlocksToUpdate.push_back(NextCase); | ||||
1012 | BasicBlock *ClonedSucc = getClonedBB(NextCase, NextState, DuplicateMap); | ||||
1013 | if (ClonedSucc) | ||||
1014 | BlocksToUpdate.push_back(ClonedSucc); | ||||
1015 | } | ||||
1016 | // Otherwise update phis in all successors. | ||||
1017 | else { | ||||
1018 | for (BasicBlock *Succ : successors(BB)) { | ||||
1019 | BlocksToUpdate.push_back(Succ); | ||||
1020 | |||||
1021 | // Check if a successor has already been cloned for the particular exit | ||||
1022 | // value. In this case if a successor was already cloned, the phi nodes | ||||
1023 | // in the cloned block should be updated directly. | ||||
1024 | BasicBlock *ClonedSucc = getClonedBB(Succ, NextState, DuplicateMap); | ||||
1025 | if (ClonedSucc) | ||||
1026 | BlocksToUpdate.push_back(ClonedSucc); | ||||
1027 | } | ||||
1028 | } | ||||
1029 | |||||
1030 | // If there is a phi with an incoming value from BB, create a new incoming | ||||
1031 | // value for the new predecessor ClonedBB. The value will either be the same | ||||
1032 | // value from BB or a cloned value. | ||||
1033 | for (BasicBlock *Succ : BlocksToUpdate) { | ||||
1034 | for (auto II = Succ->begin(); PHINode *Phi = dyn_cast<PHINode>(II); | ||||
1035 | ++II) { | ||||
1036 | Value *Incoming = Phi->getIncomingValueForBlock(BB); | ||||
1037 | if (Incoming) { | ||||
1038 | if (isa<Constant>(Incoming)) { | ||||
1039 | Phi->addIncoming(Incoming, ClonedBB); | ||||
1040 | continue; | ||||
1041 | } | ||||
1042 | Value *ClonedVal = VMap[Incoming]; | ||||
1043 | if (ClonedVal) | ||||
1044 | Phi->addIncoming(ClonedVal, ClonedBB); | ||||
1045 | else | ||||
1046 | Phi->addIncoming(Incoming, ClonedBB); | ||||
1047 | } | ||||
1048 | } | ||||
1049 | } | ||||
1050 | } | ||||
1051 | |||||
1052 | /// Sets the successor of PrevBB to be NewBB instead of OldBB. Note that all | ||||
1053 | /// other successors are kept as well. | ||||
1054 | void updatePredecessor(BasicBlock *PrevBB, BasicBlock *OldBB, | ||||
1055 | BasicBlock *NewBB, DomTreeUpdater *DTU) { | ||||
1056 | // When a path is reused, there is a chance that predecessors were already | ||||
1057 | // updated before. Check if the predecessor needs to be updated first. | ||||
1058 | if (!isPredecessor(OldBB, PrevBB)) | ||||
1059 | return; | ||||
1060 | |||||
1061 | Instruction *PrevTerm = PrevBB->getTerminator(); | ||||
1062 | for (unsigned Idx = 0; Idx < PrevTerm->getNumSuccessors(); Idx++) { | ||||
1063 | if (PrevTerm->getSuccessor(Idx) == OldBB) { | ||||
1064 | OldBB->removePredecessor(PrevBB, /* KeepOneInputPHIs = */ true); | ||||
1065 | PrevTerm->setSuccessor(Idx, NewBB); | ||||
1066 | } | ||||
1067 | } | ||||
1068 | DTU->applyUpdates({{DominatorTree::Delete, PrevBB, OldBB}, | ||||
1069 | {DominatorTree::Insert, PrevBB, NewBB}}); | ||||
1070 | } | ||||
1071 | |||||
1072 | /// Add new value mappings to the DefMap to keep track of all new definitions | ||||
1073 | /// for a particular instruction. These will be used while updating SSA form. | ||||
1074 | void updateDefMap(DefMap &NewDefs, ValueToValueMapTy &VMap) { | ||||
1075 | for (auto Entry : VMap) { | ||||
1076 | Instruction *Inst = | ||||
1077 | dyn_cast<Instruction>(const_cast<Value *>(Entry.first)); | ||||
1078 | if (!Inst || !Entry.second || isa<BranchInst>(Inst) || | ||||
1079 | isa<SwitchInst>(Inst)) { | ||||
1080 | continue; | ||||
1081 | } | ||||
1082 | |||||
1083 | Instruction *Cloned = dyn_cast<Instruction>(Entry.second); | ||||
1084 | if (!Cloned) | ||||
1085 | continue; | ||||
1086 | |||||
1087 | if (NewDefs.find(Inst) == NewDefs.end()) | ||||
1088 | NewDefs[Inst] = {Cloned}; | ||||
1089 | else | ||||
1090 | NewDefs[Inst].push_back(Cloned); | ||||
1091 | } | ||||
1092 | } | ||||
1093 | |||||
1094 | /// Update the last branch of a particular cloned path to point to the correct | ||||
1095 | /// case successor. | ||||
1096 | /// | ||||
1097 | /// Note that this is an optional step and would have been done in later | ||||
1098 | /// optimizations, but it makes the CFG significantly easier to work with. | ||||
1099 | void updateLastSuccessor(ThreadingPath &TPath, | ||||
1100 | DuplicateBlockMap &DuplicateMap, | ||||
1101 | DomTreeUpdater *DTU) { | ||||
1102 | uint64_t NextState = TPath.getExitValue(); | ||||
1103 | BasicBlock *BB = TPath.getPath().back(); | ||||
1104 | BasicBlock *LastBlock = getClonedBB(BB, NextState, DuplicateMap); | ||||
1105 | |||||
1106 | // Note multiple paths can end at the same block so check that it is not | ||||
1107 | // updated yet | ||||
1108 | if (!isa<SwitchInst>(LastBlock->getTerminator())) | ||||
1109 | return; | ||||
1110 | SwitchInst *Switch = cast<SwitchInst>(LastBlock->getTerminator()); | ||||
1111 | BasicBlock *NextCase = getNextCaseSuccessor(Switch, NextState); | ||||
1112 | |||||
1113 | std::vector<DominatorTree::UpdateType> DTUpdates; | ||||
1114 | SmallPtrSet<BasicBlock *, 4> SuccSet; | ||||
1115 | for (BasicBlock *Succ : successors(LastBlock)) { | ||||
1116 | if (Succ != NextCase && SuccSet.insert(Succ).second) | ||||
1117 | DTUpdates.push_back({DominatorTree::Delete, LastBlock, Succ}); | ||||
1118 | } | ||||
1119 | |||||
1120 | Switch->eraseFromParent(); | ||||
1121 | BranchInst::Create(NextCase, LastBlock); | ||||
1122 | |||||
1123 | DTU->applyUpdates(DTUpdates); | ||||
1124 | } | ||||
1125 | |||||
1126 | /// After cloning blocks, some of the phi nodes have extra incoming values | ||||
1127 | /// that are no longer used. This function removes them. | ||||
1128 | void cleanPhiNodes(BasicBlock *BB) { | ||||
1129 | // If BB is no longer reachable, remove any remaining phi nodes | ||||
1130 | if (pred_empty(BB)) { | ||||
1131 | std::vector<PHINode *> PhiToRemove; | ||||
1132 | for (auto II = BB->begin(); PHINode *Phi = dyn_cast<PHINode>(II); ++II) { | ||||
1133 | PhiToRemove.push_back(Phi); | ||||
1134 | } | ||||
1135 | for (PHINode *PN : PhiToRemove) { | ||||
1136 | PN->replaceAllUsesWith(UndefValue::get(PN->getType())); | ||||
1137 | PN->eraseFromParent(); | ||||
1138 | } | ||||
1139 | return; | ||||
1140 | } | ||||
1141 | |||||
1142 | // Remove any incoming values that come from an invalid predecessor | ||||
1143 | for (auto II = BB->begin(); PHINode *Phi = dyn_cast<PHINode>(II); ++II) { | ||||
1144 | std::vector<BasicBlock *> BlocksToRemove; | ||||
1145 | for (BasicBlock *IncomingBB : Phi->blocks()) { | ||||
1146 | if (!isPredecessor(BB, IncomingBB)) | ||||
1147 | BlocksToRemove.push_back(IncomingBB); | ||||
1148 | } | ||||
1149 | for (BasicBlock *BB : BlocksToRemove) | ||||
1150 | Phi->removeIncomingValue(BB); | ||||
1151 | } | ||||
1152 | } | ||||
1153 | |||||
1154 | /// Checks if BB was already cloned for a particular next state value. If it | ||||
1155 | /// was then it returns this cloned block, and otherwise null. | ||||
1156 | BasicBlock *getClonedBB(BasicBlock *BB, uint64_t NextState, | ||||
1157 | DuplicateBlockMap &DuplicateMap) { | ||||
1158 | CloneList ClonedBBs = DuplicateMap[BB]; | ||||
1159 | |||||
1160 | // Find an entry in the CloneList with this NextState. If it exists then | ||||
1161 | // return the corresponding BB | ||||
1162 | auto It = llvm::find_if(ClonedBBs, [NextState](const ClonedBlock &C) { | ||||
1163 | return C.State == NextState; | ||||
1164 | }); | ||||
1165 | return It != ClonedBBs.end() ? (*It).BB : nullptr; | ||||
1166 | } | ||||
1167 | |||||
1168 | /// Helper to get the successor corresponding to a particular case value for | ||||
1169 | /// a switch statement. | ||||
1170 | BasicBlock *getNextCaseSuccessor(SwitchInst *Switch, uint64_t NextState) { | ||||
1171 | BasicBlock *NextCase = nullptr; | ||||
1172 | for (auto Case : Switch->cases()) { | ||||
1173 | if (Case.getCaseValue()->getZExtValue() == NextState) { | ||||
1174 | NextCase = Case.getCaseSuccessor(); | ||||
1175 | break; | ||||
1176 | } | ||||
1177 | } | ||||
1178 | if (!NextCase) | ||||
1179 | NextCase = Switch->getDefaultDest(); | ||||
1180 | return NextCase; | ||||
1181 | } | ||||
1182 | |||||
1183 | /// Returns true if IncomingBB is a predecessor of BB. | ||||
1184 | bool isPredecessor(BasicBlock *BB, BasicBlock *IncomingBB) { | ||||
1185 | return llvm::find(predecessors(BB), IncomingBB) != pred_end(BB); | ||||
1186 | } | ||||
1187 | |||||
1188 | AllSwitchPaths *SwitchPaths; | ||||
1189 | DominatorTree *DT; | ||||
1190 | AssumptionCache *AC; | ||||
1191 | TargetTransformInfo *TTI; | ||||
1192 | OptimizationRemarkEmitter *ORE; | ||||
1193 | SmallPtrSet<const Value *, 32> EphValues; | ||||
1194 | std::vector<ThreadingPath> TPaths; | ||||
1195 | }; | ||||
1196 | |||||
1197 | bool DFAJumpThreading::run(Function &F) { | ||||
1198 | LLVM_DEBUG(dbgs() << "\nDFA Jump threading: " << F.getName() << "\n")do { } while (false); | ||||
1199 | |||||
1200 | if (F.hasOptSize()) { | ||||
1201 | LLVM_DEBUG(dbgs() << "Skipping due to the 'minsize' attribute\n")do { } while (false); | ||||
1202 | return false; | ||||
1203 | } | ||||
1204 | |||||
1205 | if (ClViewCfgBefore) | ||||
1206 | F.viewCFG(); | ||||
1207 | |||||
1208 | SmallVector<AllSwitchPaths, 2> ThreadableLoops; | ||||
1209 | bool MadeChanges = false; | ||||
1210 | |||||
1211 | for (BasicBlock &BB : F) { | ||||
1212 | auto *SI = dyn_cast<SwitchInst>(BB.getTerminator()); | ||||
1213 | if (!SI
| ||||
1214 | continue; | ||||
1215 | |||||
1216 | LLVM_DEBUG(dbgs() << "\nCheck if SwitchInst in BB " << BB.getName()do { } while (false) | ||||
1217 | << " is predictable\n")do { } while (false); | ||||
1218 | MainSwitch Switch(SI, ORE); | ||||
1219 | |||||
1220 | if (!Switch.getInstr()) | ||||
1221 | continue; | ||||
1222 | |||||
1223 | LLVM_DEBUG(dbgs() << "\nSwitchInst in BB " << BB.getName() << " is a "do { } while (false) | ||||
1224 | << "candidate for jump threading\n")do { } while (false); | ||||
1225 | LLVM_DEBUG(SI->dump())do { } while (false); | ||||
1226 | |||||
1227 | unfoldSelectInstrs(DT, Switch.getSelectInsts()); | ||||
1228 | if (!Switch.getSelectInsts().empty()) | ||||
1229 | MadeChanges = true; | ||||
1230 | |||||
1231 | AllSwitchPaths SwitchPaths(&Switch, ORE); | ||||
1232 | SwitchPaths.run(); | ||||
1233 | |||||
1234 | if (SwitchPaths.getNumThreadingPaths() > 0) { | ||||
1235 | ThreadableLoops.push_back(SwitchPaths); | ||||
1236 | |||||
1237 | // For the time being limit this optimization to occurring once in a | ||||
1238 | // function since it can change the CFG significantly. This is not a | ||||
1239 | // strict requirement but it can cause buggy behavior if there is an | ||||
1240 | // overlap of blocks in different opportunities. There is a lot of room to | ||||
1241 | // experiment with catching more opportunities here. | ||||
1242 | break; | ||||
1243 | } | ||||
1244 | } | ||||
1245 | |||||
1246 | SmallPtrSet<const Value *, 32> EphValues; | ||||
1247 | if (ThreadableLoops.size() > 0) | ||||
1248 | CodeMetrics::collectEphemeralValues(&F, AC, EphValues); | ||||
1249 | |||||
1250 | for (AllSwitchPaths SwitchPaths : ThreadableLoops) { | ||||
1251 | TransformDFA Transform(&SwitchPaths, DT, AC, TTI, ORE, EphValues); | ||||
1252 | Transform.run(); | ||||
1253 | MadeChanges = true; | ||||
1254 | } | ||||
1255 | |||||
1256 | #ifdef EXPENSIVE_CHECKS | ||||
1257 | assert(DT->verify(DominatorTree::VerificationLevel::Full))(static_cast<void> (0)); | ||||
1258 | verifyFunction(F, &dbgs()); | ||||
1259 | #endif | ||||
1260 | |||||
1261 | return MadeChanges; | ||||
1262 | } | ||||
1263 | |||||
1264 | } // end anonymous namespace | ||||
1265 | |||||
1266 | /// Integrate with the new Pass Manager | ||||
1267 | PreservedAnalyses DFAJumpThreadingPass::run(Function &F, | ||||
1268 | FunctionAnalysisManager &AM) { | ||||
1269 | AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F); | ||||
1270 | DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F); | ||||
1271 | TargetTransformInfo &TTI = AM.getResult<TargetIRAnalysis>(F); | ||||
1272 | OptimizationRemarkEmitter ORE(&F); | ||||
1273 | |||||
1274 | if (!DFAJumpThreading(&AC, &DT, &TTI, &ORE).run(F)) | ||||
| |||||
1275 | return PreservedAnalyses::all(); | ||||
1276 | |||||
1277 | PreservedAnalyses PA; | ||||
1278 | PA.preserve<DominatorTreeAnalysis>(); | ||||
1279 | return PA; | ||||
1280 | } |