LLVM 19.0.0git
DFAJumpThreading.cpp
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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 case1ยง
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
61#include "llvm/ADT/APInt.h"
62#include "llvm/ADT/DenseMap.h"
63#include "llvm/ADT/SmallSet.h"
64#include "llvm/ADT/Statistic.h"
70#include "llvm/IR/CFG.h"
71#include "llvm/IR/Constants.h"
74#include "llvm/Support/Debug.h"
78#include <algorithm>
79#include <deque>
80
81#ifdef EXPENSIVE_CHECKS
82#include "llvm/IR/Verifier.h"
83#endif
84
85using namespace llvm;
86
87#define DEBUG_TYPE "dfa-jump-threading"
88
89STATISTIC(NumTransforms, "Number of transformations done");
90STATISTIC(NumCloned, "Number of blocks cloned");
91STATISTIC(NumPaths, "Number of individual paths threaded");
92
93static cl::opt<bool>
94 ClViewCfgBefore("dfa-jump-view-cfg-before",
95 cl::desc("View the CFG before DFA Jump Threading"),
96 cl::Hidden, cl::init(false));
97
99 "dfa-max-path-length",
100 cl::desc("Max number of blocks searched to find a threading path"),
101 cl::Hidden, cl::init(20));
102
104 MaxNumPaths("dfa-max-num-paths",
105 cl::desc("Max number of paths enumerated around a switch"),
106 cl::Hidden, cl::init(200));
107
109 CostThreshold("dfa-cost-threshold",
110 cl::desc("Maximum cost accepted for the transformation"),
111 cl::Hidden, cl::init(50));
112
113namespace {
114
115class SelectInstToUnfold {
116 SelectInst *SI;
117 PHINode *SIUse;
118
119public:
120 SelectInstToUnfold(SelectInst *SI, PHINode *SIUse) : SI(SI), SIUse(SIUse) {}
121
122 SelectInst *getInst() { return SI; }
123 PHINode *getUse() { return SIUse; }
124
125 explicit operator bool() const { return SI && SIUse; }
126};
127
128void unfold(DomTreeUpdater *DTU, SelectInstToUnfold SIToUnfold,
129 std::vector<SelectInstToUnfold> *NewSIsToUnfold,
130 std::vector<BasicBlock *> *NewBBs);
131
132class DFAJumpThreading {
133public:
134 DFAJumpThreading(AssumptionCache *AC, DominatorTree *DT,
136 : AC(AC), DT(DT), TTI(TTI), ORE(ORE) {}
137
138 bool run(Function &F);
139
140private:
141 void
142 unfoldSelectInstrs(DominatorTree *DT,
143 const SmallVector<SelectInstToUnfold, 4> &SelectInsts) {
144 DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
146 for (SelectInstToUnfold SIToUnfold : SelectInsts)
147 Stack.push_back(SIToUnfold);
148
149 while (!Stack.empty()) {
150 SelectInstToUnfold SIToUnfold = Stack.pop_back_val();
151
152 std::vector<SelectInstToUnfold> NewSIsToUnfold;
153 std::vector<BasicBlock *> NewBBs;
154 unfold(&DTU, SIToUnfold, &NewSIsToUnfold, &NewBBs);
155
156 // Put newly discovered select instructions into the work list.
157 for (const SelectInstToUnfold &NewSIToUnfold : NewSIsToUnfold)
158 Stack.push_back(NewSIToUnfold);
159 }
160 }
161
162 AssumptionCache *AC;
163 DominatorTree *DT;
166};
167
168} // end anonymous namespace
169
170namespace {
171
172/// Create a new basic block and sink \p SIToSink into it.
173void createBasicBlockAndSinkSelectInst(
174 DomTreeUpdater *DTU, SelectInst *SI, PHINode *SIUse, SelectInst *SIToSink,
175 BasicBlock *EndBlock, StringRef NewBBName, BasicBlock **NewBlock,
176 BranchInst **NewBranch, std::vector<SelectInstToUnfold> *NewSIsToUnfold,
177 std::vector<BasicBlock *> *NewBBs) {
178 assert(SIToSink->hasOneUse());
179 assert(NewBlock);
180 assert(NewBranch);
181 *NewBlock = BasicBlock::Create(SI->getContext(), NewBBName,
182 EndBlock->getParent(), EndBlock);
183 NewBBs->push_back(*NewBlock);
184 *NewBranch = BranchInst::Create(EndBlock, *NewBlock);
185 SIToSink->moveBefore(*NewBranch);
186 NewSIsToUnfold->push_back(SelectInstToUnfold(SIToSink, SIUse));
187 DTU->applyUpdates({{DominatorTree::Insert, *NewBlock, EndBlock}});
188}
189
190/// Unfold the select instruction held in \p SIToUnfold by replacing it with
191/// control flow.
192///
193/// Put newly discovered select instructions into \p NewSIsToUnfold. Put newly
194/// created basic blocks into \p NewBBs.
195///
196/// TODO: merge it with CodeGenPrepare::optimizeSelectInst() if possible.
197void unfold(DomTreeUpdater *DTU, SelectInstToUnfold SIToUnfold,
198 std::vector<SelectInstToUnfold> *NewSIsToUnfold,
199 std::vector<BasicBlock *> *NewBBs) {
200 SelectInst *SI = SIToUnfold.getInst();
201 PHINode *SIUse = SIToUnfold.getUse();
202 BasicBlock *StartBlock = SI->getParent();
203 BasicBlock *EndBlock = SIUse->getParent();
204 BranchInst *StartBlockTerm =
205 dyn_cast<BranchInst>(StartBlock->getTerminator());
206
207 assert(StartBlockTerm && StartBlockTerm->isUnconditional());
208 assert(SI->hasOneUse());
209
210 // These are the new basic blocks for the conditional branch.
211 // At least one will become an actual new basic block.
212 BasicBlock *TrueBlock = nullptr;
213 BasicBlock *FalseBlock = nullptr;
214 BranchInst *TrueBranch = nullptr;
215 BranchInst *FalseBranch = nullptr;
216
217 // Sink select instructions to be able to unfold them later.
218 if (SelectInst *SIOp = dyn_cast<SelectInst>(SI->getTrueValue())) {
219 createBasicBlockAndSinkSelectInst(DTU, SI, SIUse, SIOp, EndBlock,
220 "si.unfold.true", &TrueBlock, &TrueBranch,
221 NewSIsToUnfold, NewBBs);
222 }
223 if (SelectInst *SIOp = dyn_cast<SelectInst>(SI->getFalseValue())) {
224 createBasicBlockAndSinkSelectInst(DTU, SI, SIUse, SIOp, EndBlock,
225 "si.unfold.false", &FalseBlock,
226 &FalseBranch, NewSIsToUnfold, NewBBs);
227 }
228
229 // If there was nothing to sink, then arbitrarily choose the 'false' side
230 // for a new input value to the PHI.
231 if (!TrueBlock && !FalseBlock) {
232 FalseBlock = BasicBlock::Create(SI->getContext(), "si.unfold.false",
233 EndBlock->getParent(), EndBlock);
234 NewBBs->push_back(FalseBlock);
235 BranchInst::Create(EndBlock, FalseBlock);
236 DTU->applyUpdates({{DominatorTree::Insert, FalseBlock, EndBlock}});
237 }
238
239 // Insert the real conditional branch based on the original condition.
240 // If we did not create a new block for one of the 'true' or 'false' paths
241 // of the condition, it means that side of the branch goes to the end block
242 // directly and the path originates from the start block from the point of
243 // view of the new PHI.
244 BasicBlock *TT = EndBlock;
245 BasicBlock *FT = EndBlock;
246 if (TrueBlock && FalseBlock) {
247 // A diamond.
248 TT = TrueBlock;
249 FT = FalseBlock;
250
251 // Update the phi node of SI.
252 SIUse->addIncoming(SI->getTrueValue(), TrueBlock);
253 SIUse->addIncoming(SI->getFalseValue(), FalseBlock);
254
255 // Update any other PHI nodes in EndBlock.
256 for (PHINode &Phi : EndBlock->phis()) {
257 if (&Phi != SIUse) {
258 Value *OrigValue = Phi.getIncomingValueForBlock(StartBlock);
259 Phi.addIncoming(OrigValue, TrueBlock);
260 Phi.addIncoming(OrigValue, FalseBlock);
261 }
262
263 // Remove incoming place of original StartBlock, which comes in a indirect
264 // way (through TrueBlock and FalseBlock) now.
265 Phi.removeIncomingValue(StartBlock, /* DeletePHIIfEmpty = */ false);
266 }
267 } else {
268 BasicBlock *NewBlock = nullptr;
269 Value *SIOp1 = SI->getTrueValue();
270 Value *SIOp2 = SI->getFalseValue();
271
272 // A triangle pointing right.
273 if (!TrueBlock) {
274 NewBlock = FalseBlock;
275 FT = FalseBlock;
276 }
277 // A triangle pointing left.
278 else {
279 NewBlock = TrueBlock;
280 TT = TrueBlock;
281 std::swap(SIOp1, SIOp2);
282 }
283
284 // Update the phi node of SI.
285 for (unsigned Idx = 0; Idx < SIUse->getNumIncomingValues(); ++Idx) {
286 if (SIUse->getIncomingBlock(Idx) == StartBlock)
287 SIUse->setIncomingValue(Idx, SIOp1);
288 }
289 SIUse->addIncoming(SIOp2, NewBlock);
290
291 // Update any other PHI nodes in EndBlock.
292 for (auto II = EndBlock->begin(); PHINode *Phi = dyn_cast<PHINode>(II);
293 ++II) {
294 if (Phi != SIUse)
295 Phi->addIncoming(Phi->getIncomingValueForBlock(StartBlock), NewBlock);
296 }
297 }
298 StartBlockTerm->eraseFromParent();
299 BranchInst::Create(TT, FT, SI->getCondition(), StartBlock);
300 DTU->applyUpdates({{DominatorTree::Insert, StartBlock, TT},
301 {DominatorTree::Insert, StartBlock, FT}});
302
303 // The select is now dead.
304 assert(SI->use_empty() && "Select must be dead now");
305 SI->eraseFromParent();
306}
307
308struct ClonedBlock {
309 BasicBlock *BB;
310 APInt State; ///< \p State corresponds to the next value of a switch stmnt.
311};
312
313typedef std::deque<BasicBlock *> PathType;
314typedef std::vector<PathType> PathsType;
315typedef SmallPtrSet<const BasicBlock *, 8> VisitedBlocks;
316typedef std::vector<ClonedBlock> CloneList;
317
318// This data structure keeps track of all blocks that have been cloned. If two
319// different ThreadingPaths clone the same block for a certain state it should
320// be reused, and it can be looked up in this map.
321typedef DenseMap<BasicBlock *, CloneList> DuplicateBlockMap;
322
323// This map keeps track of all the new definitions for an instruction. This
324// information is needed when restoring SSA form after cloning blocks.
326
327inline raw_ostream &operator<<(raw_ostream &OS, const PathType &Path) {
328 OS << "< ";
329 for (const BasicBlock *BB : Path) {
330 std::string BBName;
331 if (BB->hasName())
332 raw_string_ostream(BBName) << BB->getName();
333 else
334 raw_string_ostream(BBName) << BB;
335 OS << BBName << " ";
336 }
337 OS << ">";
338 return OS;
339}
340
341/// ThreadingPath is a path in the control flow of a loop that can be threaded
342/// by cloning necessary basic blocks and replacing conditional branches with
343/// unconditional ones. A threading path includes a list of basic blocks, the
344/// exit state, and the block that determines the next state.
345struct ThreadingPath {
346 /// Exit value is DFA's exit state for the given path.
347 APInt getExitValue() const { return ExitVal; }
348 void setExitValue(const ConstantInt *V) {
349 ExitVal = V->getValue();
350 IsExitValSet = true;
351 }
352 bool isExitValueSet() const { return IsExitValSet; }
353
354 /// Determinator is the basic block that determines the next state of the DFA.
355 const BasicBlock *getDeterminatorBB() const { return DBB; }
356 void setDeterminator(const BasicBlock *BB) { DBB = BB; }
357
358 /// Path is a list of basic blocks.
359 const PathType &getPath() const { return Path; }
360 void setPath(const PathType &NewPath) { Path = NewPath; }
361
362 void print(raw_ostream &OS) const {
363 OS << Path << " [ " << ExitVal << ", " << DBB->getName() << " ]";
364 }
365
366private:
367 PathType Path;
368 APInt ExitVal;
369 const BasicBlock *DBB = nullptr;
370 bool IsExitValSet = false;
371};
372
373#ifndef NDEBUG
374inline raw_ostream &operator<<(raw_ostream &OS, const ThreadingPath &TPath) {
375 TPath.print(OS);
376 return OS;
377}
378#endif
379
380struct MainSwitch {
381 MainSwitch(SwitchInst *SI, OptimizationRemarkEmitter *ORE) {
382 if (isCandidate(SI)) {
383 Instr = SI;
384 } else {
385 ORE->emit([&]() {
386 return OptimizationRemarkMissed(DEBUG_TYPE, "SwitchNotPredictable", SI)
387 << "Switch instruction is not predictable.";
388 });
389 }
390 }
391
392 virtual ~MainSwitch() = default;
393
394 SwitchInst *getInstr() const { return Instr; }
395 const SmallVector<SelectInstToUnfold, 4> getSelectInsts() {
396 return SelectInsts;
397 }
398
399private:
400 /// Do a use-def chain traversal starting from the switch condition to see if
401 /// \p SI is a potential condidate.
402 ///
403 /// Also, collect select instructions to unfold.
404 bool isCandidate(const SwitchInst *SI) {
405 std::deque<Value *> Q;
406 SmallSet<Value *, 16> SeenValues;
407 SelectInsts.clear();
408
409 Value *SICond = SI->getCondition();
410 LLVM_DEBUG(dbgs() << "\tSICond: " << *SICond << "\n");
411 if (!isa<PHINode>(SICond))
412 return false;
413
414 addToQueue(SICond, Q, SeenValues);
415
416 while (!Q.empty()) {
417 Value *Current = Q.front();
418 Q.pop_front();
419
420 if (auto *Phi = dyn_cast<PHINode>(Current)) {
421 for (Value *Incoming : Phi->incoming_values()) {
422 addToQueue(Incoming, Q, SeenValues);
423 }
424 LLVM_DEBUG(dbgs() << "\tphi: " << *Phi << "\n");
425 } else if (SelectInst *SelI = dyn_cast<SelectInst>(Current)) {
426 if (!isValidSelectInst(SelI))
427 return false;
428 addToQueue(SelI->getTrueValue(), Q, SeenValues);
429 addToQueue(SelI->getFalseValue(), Q, SeenValues);
430 LLVM_DEBUG(dbgs() << "\tselect: " << *SelI << "\n");
431 if (auto *SelIUse = dyn_cast<PHINode>(SelI->user_back()))
432 SelectInsts.push_back(SelectInstToUnfold(SelI, SelIUse));
433 } else if (isa<Constant>(Current)) {
434 LLVM_DEBUG(dbgs() << "\tconst: " << *Current << "\n");
435 continue;
436 } else {
437 LLVM_DEBUG(dbgs() << "\tother: " << *Current << "\n");
438 // Allow unpredictable values. The hope is that those will be the
439 // initial switch values that can be ignored (they will hit the
440 // unthreaded switch) but this assumption will get checked later after
441 // paths have been enumerated (in function getStateDefMap).
442 continue;
443 }
444 }
445
446 return true;
447 }
448
449 void addToQueue(Value *Val, std::deque<Value *> &Q,
450 SmallSet<Value *, 16> &SeenValues) {
451 if (SeenValues.contains(Val))
452 return;
453 Q.push_back(Val);
454 SeenValues.insert(Val);
455 }
456
457 bool isValidSelectInst(SelectInst *SI) {
458 if (!SI->hasOneUse())
459 return false;
460
461 Instruction *SIUse = dyn_cast<Instruction>(SI->user_back());
462 // The use of the select inst should be either a phi or another select.
463 if (!SIUse && !(isa<PHINode>(SIUse) || isa<SelectInst>(SIUse)))
464 return false;
465
466 BasicBlock *SIBB = SI->getParent();
467
468 // Currently, we can only expand select instructions in basic blocks with
469 // one successor.
470 BranchInst *SITerm = dyn_cast<BranchInst>(SIBB->getTerminator());
471 if (!SITerm || !SITerm->isUnconditional())
472 return false;
473
474 // Only fold the select coming from directly where it is defined.
475 PHINode *PHIUser = dyn_cast<PHINode>(SIUse);
476 if (PHIUser && PHIUser->getIncomingBlock(*SI->use_begin()) != SIBB)
477 return false;
478
479 // If select will not be sunk during unfolding, and it is in the same basic
480 // block as another state defining select, then cannot unfold both.
481 for (SelectInstToUnfold SIToUnfold : SelectInsts) {
482 SelectInst *PrevSI = SIToUnfold.getInst();
483 if (PrevSI->getTrueValue() != SI && PrevSI->getFalseValue() != SI &&
484 PrevSI->getParent() == SI->getParent())
485 return false;
486 }
487
488 return true;
489 }
490
491 SwitchInst *Instr = nullptr;
493};
494
495struct AllSwitchPaths {
496 AllSwitchPaths(const MainSwitch *MSwitch, OptimizationRemarkEmitter *ORE)
497 : Switch(MSwitch->getInstr()), SwitchBlock(Switch->getParent()),
498 ORE(ORE) {}
499
500 std::vector<ThreadingPath> &getThreadingPaths() { return TPaths; }
501 unsigned getNumThreadingPaths() { return TPaths.size(); }
502 SwitchInst *getSwitchInst() { return Switch; }
503 BasicBlock *getSwitchBlock() { return SwitchBlock; }
504
505 void run() {
506 VisitedBlocks Visited;
507 PathsType LoopPaths = paths(SwitchBlock, Visited, /* PathDepth = */ 1);
508 StateDefMap StateDef = getStateDefMap(LoopPaths);
509
510 if (StateDef.empty()) {
511 ORE->emit([&]() {
512 return OptimizationRemarkMissed(DEBUG_TYPE, "SwitchNotPredictable",
513 Switch)
514 << "Switch instruction is not predictable.";
515 });
516 return;
517 }
518
519 for (PathType Path : LoopPaths) {
520 ThreadingPath TPath;
521
522 const BasicBlock *PrevBB = Path.back();
523 for (const BasicBlock *BB : Path) {
524 if (StateDef.contains(BB)) {
525 const PHINode *Phi = dyn_cast<PHINode>(StateDef[BB]);
526 assert(Phi && "Expected a state-defining instr to be a phi node.");
527
528 const Value *V = Phi->getIncomingValueForBlock(PrevBB);
529 if (const ConstantInt *C = dyn_cast<const ConstantInt>(V)) {
530 TPath.setExitValue(C);
531 TPath.setDeterminator(BB);
532 TPath.setPath(Path);
533 }
534 }
535
536 // Switch block is the determinator, this is the final exit value.
537 if (TPath.isExitValueSet() && BB == Path.front())
538 break;
539
540 PrevBB = BB;
541 }
542
543 if (TPath.isExitValueSet() && isSupported(TPath))
544 TPaths.push_back(TPath);
545 }
546 }
547
548private:
549 // Value: an instruction that defines a switch state;
550 // Key: the parent basic block of that instruction.
552
553 PathsType paths(BasicBlock *BB, VisitedBlocks &Visited,
554 unsigned PathDepth) const {
555 PathsType Res;
556
557 // Stop exploring paths after visiting MaxPathLength blocks
558 if (PathDepth > MaxPathLength) {
559 ORE->emit([&]() {
560 return OptimizationRemarkAnalysis(DEBUG_TYPE, "MaxPathLengthReached",
561 Switch)
562 << "Exploration stopped after visiting MaxPathLength="
563 << ore::NV("MaxPathLength", MaxPathLength) << " blocks.";
564 });
565 return Res;
566 }
567
568 Visited.insert(BB);
569
570 // Some blocks have multiple edges to the same successor, and this set
571 // is used to prevent a duplicate path from being generated
572 SmallSet<BasicBlock *, 4> Successors;
573 for (BasicBlock *Succ : successors(BB)) {
574 if (!Successors.insert(Succ).second)
575 continue;
576
577 // Found a cycle through the SwitchBlock
578 if (Succ == SwitchBlock) {
579 Res.push_back({BB});
580 continue;
581 }
582
583 // We have encountered a cycle, do not get caught in it
584 if (Visited.contains(Succ))
585 continue;
586
587 PathsType SuccPaths = paths(Succ, Visited, PathDepth + 1);
588 for (const PathType &Path : SuccPaths) {
589 PathType NewPath(Path);
590 NewPath.push_front(BB);
591 Res.push_back(NewPath);
592 if (Res.size() >= MaxNumPaths) {
593 return Res;
594 }
595 }
596 }
597 // This block could now be visited again from a different predecessor. Note
598 // that this will result in exponential runtime. Subpaths could possibly be
599 // cached but it takes a lot of memory to store them.
600 Visited.erase(BB);
601 return Res;
602 }
603
604 /// Walk the use-def chain and collect all the state-defining instructions.
605 ///
606 /// Return an empty map if unpredictable values encountered inside the basic
607 /// blocks of \p LoopPaths.
608 StateDefMap getStateDefMap(const PathsType &LoopPaths) const {
609 StateDefMap Res;
610
611 // Basic blocks belonging to any of the loops around the switch statement.
613 for (const PathType &Path : LoopPaths) {
614 for (BasicBlock *BB : Path)
615 LoopBBs.insert(BB);
616 }
617
618 Value *FirstDef = Switch->getOperand(0);
619
620 assert(isa<PHINode>(FirstDef) && "The first definition must be a phi.");
621
623 Stack.push_back(dyn_cast<PHINode>(FirstDef));
624 SmallSet<Value *, 16> SeenValues;
625
626 while (!Stack.empty()) {
627 PHINode *CurPhi = Stack.pop_back_val();
628
629 Res[CurPhi->getParent()] = CurPhi;
630 SeenValues.insert(CurPhi);
631
632 for (BasicBlock *IncomingBB : CurPhi->blocks()) {
633 Value *Incoming = CurPhi->getIncomingValueForBlock(IncomingBB);
634 bool IsOutsideLoops = LoopBBs.count(IncomingBB) == 0;
635 if (Incoming == FirstDef || isa<ConstantInt>(Incoming) ||
636 SeenValues.contains(Incoming) || IsOutsideLoops) {
637 continue;
638 }
639
640 // Any unpredictable value inside the loops means we must bail out.
641 if (!isa<PHINode>(Incoming))
642 return StateDefMap();
643
644 Stack.push_back(cast<PHINode>(Incoming));
645 }
646 }
647
648 return Res;
649 }
650
651 /// The determinator BB should precede the switch-defining BB.
652 ///
653 /// Otherwise, it is possible that the state defined in the determinator block
654 /// defines the state for the next iteration of the loop, rather than for the
655 /// current one.
656 ///
657 /// Currently supported paths:
658 /// \code
659 /// < switch bb1 determ def > [ 42, determ ]
660 /// < switch_and_def bb1 determ > [ 42, determ ]
661 /// < switch_and_def_and_determ bb1 > [ 42, switch_and_def_and_determ ]
662 /// \endcode
663 ///
664 /// Unsupported paths:
665 /// \code
666 /// < switch bb1 def determ > [ 43, determ ]
667 /// < switch_and_determ bb1 def > [ 43, switch_and_determ ]
668 /// \endcode
669 bool isSupported(const ThreadingPath &TPath) {
670 Instruction *SwitchCondI = dyn_cast<Instruction>(Switch->getCondition());
671 assert(SwitchCondI);
672 if (!SwitchCondI)
673 return false;
674
675 const BasicBlock *SwitchCondDefBB = SwitchCondI->getParent();
676 const BasicBlock *SwitchCondUseBB = Switch->getParent();
677 const BasicBlock *DeterminatorBB = TPath.getDeterminatorBB();
678
679 assert(
680 SwitchCondUseBB == TPath.getPath().front() &&
681 "The first BB in a threading path should have the switch instruction");
682 if (SwitchCondUseBB != TPath.getPath().front())
683 return false;
684
685 // Make DeterminatorBB the first element in Path.
686 PathType Path = TPath.getPath();
687 auto ItDet = llvm::find(Path, DeterminatorBB);
688 std::rotate(Path.begin(), ItDet, Path.end());
689
690 bool IsDetBBSeen = false;
691 bool IsDefBBSeen = false;
692 bool IsUseBBSeen = false;
693 for (BasicBlock *BB : Path) {
694 if (BB == DeterminatorBB)
695 IsDetBBSeen = true;
696 if (BB == SwitchCondDefBB)
697 IsDefBBSeen = true;
698 if (BB == SwitchCondUseBB)
699 IsUseBBSeen = true;
700 if (IsDetBBSeen && IsUseBBSeen && !IsDefBBSeen)
701 return false;
702 }
703
704 return true;
705 }
706
708 BasicBlock *SwitchBlock;
710 std::vector<ThreadingPath> TPaths;
711};
712
713struct TransformDFA {
714 TransformDFA(AllSwitchPaths *SwitchPaths, DominatorTree *DT,
718 : SwitchPaths(SwitchPaths), DT(DT), AC(AC), TTI(TTI), ORE(ORE),
719 EphValues(EphValues) {}
720
721 void run() {
722 if (isLegalAndProfitableToTransform()) {
723 createAllExitPaths();
724 NumTransforms++;
725 }
726 }
727
728private:
729 /// This function performs both a legality check and profitability check at
730 /// the same time since it is convenient to do so. It iterates through all
731 /// blocks that will be cloned, and keeps track of the duplication cost. It
732 /// also returns false if it is illegal to clone some required block.
733 bool isLegalAndProfitableToTransform() {
735 SwitchInst *Switch = SwitchPaths->getSwitchInst();
736
737 // Don't thread switch without multiple successors.
738 if (Switch->getNumSuccessors() <= 1)
739 return false;
740
741 // Note that DuplicateBlockMap is not being used as intended here. It is
742 // just being used to ensure (BB, State) pairs are only counted once.
743 DuplicateBlockMap DuplicateMap;
744
745 for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) {
746 PathType PathBBs = TPath.getPath();
747 APInt NextState = TPath.getExitValue();
748 const BasicBlock *Determinator = TPath.getDeterminatorBB();
749
750 // Update Metrics for the Switch block, this is always cloned
751 BasicBlock *BB = SwitchPaths->getSwitchBlock();
752 BasicBlock *VisitedBB = getClonedBB(BB, NextState, DuplicateMap);
753 if (!VisitedBB) {
754 Metrics.analyzeBasicBlock(BB, *TTI, EphValues);
755 DuplicateMap[BB].push_back({BB, NextState});
756 }
757
758 // If the Switch block is the Determinator, then we can continue since
759 // this is the only block that is cloned and we already counted for it.
760 if (PathBBs.front() == Determinator)
761 continue;
762
763 // Otherwise update Metrics for all blocks that will be cloned. If any
764 // block is already cloned and would be reused, don't double count it.
765 auto DetIt = llvm::find(PathBBs, Determinator);
766 for (auto BBIt = DetIt; BBIt != PathBBs.end(); BBIt++) {
767 BB = *BBIt;
768 VisitedBB = getClonedBB(BB, NextState, DuplicateMap);
769 if (VisitedBB)
770 continue;
771 Metrics.analyzeBasicBlock(BB, *TTI, EphValues);
772 DuplicateMap[BB].push_back({BB, NextState});
773 }
774
775 if (Metrics.notDuplicatable) {
776 LLVM_DEBUG(dbgs() << "DFA Jump Threading: Not jump threading, contains "
777 << "non-duplicatable instructions.\n");
778 ORE->emit([&]() {
779 return OptimizationRemarkMissed(DEBUG_TYPE, "NonDuplicatableInst",
780 Switch)
781 << "Contains non-duplicatable instructions.";
782 });
783 return false;
784 }
785
786 if (Metrics.convergent) {
787 LLVM_DEBUG(dbgs() << "DFA Jump Threading: Not jump threading, contains "
788 << "convergent instructions.\n");
789 ORE->emit([&]() {
790 return OptimizationRemarkMissed(DEBUG_TYPE, "ConvergentInst", Switch)
791 << "Contains convergent instructions.";
792 });
793 return false;
794 }
795
796 if (!Metrics.NumInsts.isValid()) {
797 LLVM_DEBUG(dbgs() << "DFA Jump Threading: Not jump threading, contains "
798 << "instructions with invalid cost.\n");
799 ORE->emit([&]() {
800 return OptimizationRemarkMissed(DEBUG_TYPE, "ConvergentInst", Switch)
801 << "Contains instructions with invalid cost.";
802 });
803 return false;
804 }
805 }
806
807 InstructionCost DuplicationCost = 0;
808
809 unsigned JumpTableSize = 0;
810 TTI->getEstimatedNumberOfCaseClusters(*Switch, JumpTableSize, nullptr,
811 nullptr);
812 if (JumpTableSize == 0) {
813 // Factor in the number of conditional branches reduced from jump
814 // threading. Assume that lowering the switch block is implemented by
815 // using binary search, hence the LogBase2().
816 unsigned CondBranches =
817 APInt(32, Switch->getNumSuccessors()).ceilLogBase2();
818 assert(CondBranches > 0 &&
819 "The threaded switch must have multiple branches");
820 DuplicationCost = Metrics.NumInsts / CondBranches;
821 } else {
822 // Compared with jump tables, the DFA optimizer removes an indirect branch
823 // on each loop iteration, thus making branch prediction more precise. The
824 // more branch targets there are, the more likely it is for the branch
825 // predictor to make a mistake, and the more benefit there is in the DFA
826 // optimizer. Thus, the more branch targets there are, the lower is the
827 // cost of the DFA opt.
828 DuplicationCost = Metrics.NumInsts / JumpTableSize;
829 }
830
831 LLVM_DEBUG(dbgs() << "\nDFA Jump Threading: Cost to jump thread block "
832 << SwitchPaths->getSwitchBlock()->getName()
833 << " is: " << DuplicationCost << "\n\n");
834
835 if (DuplicationCost > CostThreshold) {
836 LLVM_DEBUG(dbgs() << "Not jump threading, duplication cost exceeds the "
837 << "cost threshold.\n");
838 ORE->emit([&]() {
839 return OptimizationRemarkMissed(DEBUG_TYPE, "NotProfitable", Switch)
840 << "Duplication cost exceeds the cost threshold (cost="
841 << ore::NV("Cost", DuplicationCost)
842 << ", threshold=" << ore::NV("Threshold", CostThreshold) << ").";
843 });
844 return false;
845 }
846
847 ORE->emit([&]() {
848 return OptimizationRemark(DEBUG_TYPE, "JumpThreaded", Switch)
849 << "Switch statement jump-threaded.";
850 });
851
852 return true;
853 }
854
855 /// Transform each threading path to effectively jump thread the DFA.
856 void createAllExitPaths() {
857 DomTreeUpdater DTU(*DT, DomTreeUpdater::UpdateStrategy::Eager);
858
859 // Move the switch block to the end of the path, since it will be duplicated
860 BasicBlock *SwitchBlock = SwitchPaths->getSwitchBlock();
861 for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) {
862 LLVM_DEBUG(dbgs() << TPath << "\n");
863 PathType NewPath(TPath.getPath());
864 NewPath.push_back(SwitchBlock);
865 TPath.setPath(NewPath);
866 }
867
868 // Transform the ThreadingPaths and keep track of the cloned values
869 DuplicateBlockMap DuplicateMap;
870 DefMap NewDefs;
871
872 SmallSet<BasicBlock *, 16> BlocksToClean;
873 for (BasicBlock *BB : successors(SwitchBlock))
874 BlocksToClean.insert(BB);
875
876 for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths()) {
877 createExitPath(NewDefs, TPath, DuplicateMap, BlocksToClean, &DTU);
878 NumPaths++;
879 }
880
881 // After all paths are cloned, now update the last successor of the cloned
882 // path so it skips over the switch statement
883 for (ThreadingPath &TPath : SwitchPaths->getThreadingPaths())
884 updateLastSuccessor(TPath, DuplicateMap, &DTU);
885
886 // For each instruction that was cloned and used outside, update its uses
887 updateSSA(NewDefs);
888
889 // Clean PHI Nodes for the newly created blocks
890 for (BasicBlock *BB : BlocksToClean)
891 cleanPhiNodes(BB);
892 }
893
894 /// For a specific ThreadingPath \p Path, create an exit path starting from
895 /// the determinator block.
896 ///
897 /// To remember the correct destination, we have to duplicate blocks
898 /// corresponding to each state. Also update the terminating instruction of
899 /// the predecessors, and phis in the successor blocks.
900 void createExitPath(DefMap &NewDefs, ThreadingPath &Path,
901 DuplicateBlockMap &DuplicateMap,
902 SmallSet<BasicBlock *, 16> &BlocksToClean,
903 DomTreeUpdater *DTU) {
904 APInt NextState = Path.getExitValue();
905 const BasicBlock *Determinator = Path.getDeterminatorBB();
906 PathType PathBBs = Path.getPath();
907
908 // Don't select the placeholder block in front
909 if (PathBBs.front() == Determinator)
910 PathBBs.pop_front();
911
912 auto DetIt = llvm::find(PathBBs, Determinator);
913 // When there is only one BB in PathBBs, the determinator takes itself as a
914 // direct predecessor.
915 BasicBlock *PrevBB = PathBBs.size() == 1 ? *DetIt : *std::prev(DetIt);
916 for (auto BBIt = DetIt; BBIt != PathBBs.end(); BBIt++) {
917 BasicBlock *BB = *BBIt;
918 BlocksToClean.insert(BB);
919
920 // We already cloned BB for this NextState, now just update the branch
921 // and continue.
922 BasicBlock *NextBB = getClonedBB(BB, NextState, DuplicateMap);
923 if (NextBB) {
924 updatePredecessor(PrevBB, BB, NextBB, DTU);
925 PrevBB = NextBB;
926 continue;
927 }
928
929 // Clone the BB and update the successor of Prev to jump to the new block
930 BasicBlock *NewBB = cloneBlockAndUpdatePredecessor(
931 BB, PrevBB, NextState, DuplicateMap, NewDefs, DTU);
932 DuplicateMap[BB].push_back({NewBB, NextState});
933 BlocksToClean.insert(NewBB);
934 PrevBB = NewBB;
935 }
936 }
937
938 /// Restore SSA form after cloning blocks.
939 ///
940 /// Each cloned block creates new defs for a variable, and the uses need to be
941 /// updated to reflect this. The uses may be replaced with a cloned value, or
942 /// some derived phi instruction. Note that all uses of a value defined in the
943 /// same block were already remapped when cloning the block.
944 void updateSSA(DefMap &NewDefs) {
945 SSAUpdaterBulk SSAUpdate;
946 SmallVector<Use *, 16> UsesToRename;
947
948 for (const auto &KV : NewDefs) {
949 Instruction *I = KV.first;
950 BasicBlock *BB = I->getParent();
951 std::vector<Instruction *> Cloned = KV.second;
952
953 // Scan all uses of this instruction to see if it is used outside of its
954 // block, and if so, record them in UsesToRename.
955 for (Use &U : I->uses()) {
956 Instruction *User = cast<Instruction>(U.getUser());
957 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
958 if (UserPN->getIncomingBlock(U) == BB)
959 continue;
960 } else if (User->getParent() == BB) {
961 continue;
962 }
963
964 UsesToRename.push_back(&U);
965 }
966
967 // If there are no uses outside the block, we're done with this
968 // instruction.
969 if (UsesToRename.empty())
970 continue;
971 LLVM_DEBUG(dbgs() << "DFA-JT: Renaming non-local uses of: " << *I
972 << "\n");
973
974 // We found a use of I outside of BB. Rename all uses of I that are
975 // outside its block to be uses of the appropriate PHI node etc. See
976 // ValuesInBlocks with the values we know.
977 unsigned VarNum = SSAUpdate.AddVariable(I->getName(), I->getType());
978 SSAUpdate.AddAvailableValue(VarNum, BB, I);
979 for (Instruction *New : Cloned)
980 SSAUpdate.AddAvailableValue(VarNum, New->getParent(), New);
981
982 while (!UsesToRename.empty())
983 SSAUpdate.AddUse(VarNum, UsesToRename.pop_back_val());
984
985 LLVM_DEBUG(dbgs() << "\n");
986 }
987 // SSAUpdater handles phi placement and renaming uses with the appropriate
988 // value.
989 SSAUpdate.RewriteAllUses(DT);
990 }
991
992 /// Clones a basic block, and adds it to the CFG.
993 ///
994 /// This function also includes updating phi nodes in the successors of the
995 /// BB, and remapping uses that were defined locally in the cloned BB.
996 BasicBlock *cloneBlockAndUpdatePredecessor(BasicBlock *BB, BasicBlock *PrevBB,
997 const APInt &NextState,
998 DuplicateBlockMap &DuplicateMap,
999 DefMap &NewDefs,
1000 DomTreeUpdater *DTU) {
1001 ValueToValueMapTy VMap;
1002 BasicBlock *NewBB = CloneBasicBlock(
1003 BB, VMap, ".jt" + std::to_string(NextState.getLimitedValue()),
1004 BB->getParent());
1005 NewBB->moveAfter(BB);
1006 NumCloned++;
1007
1008 for (Instruction &I : *NewBB) {
1009 // Do not remap operands of PHINode in case a definition in BB is an
1010 // incoming value to a phi in the same block. This incoming value will
1011 // be renamed later while restoring SSA.
1012 if (isa<PHINode>(&I))
1013 continue;
1014 RemapInstruction(&I, VMap,
1016 if (AssumeInst *II = dyn_cast<AssumeInst>(&I))
1017 AC->registerAssumption(II);
1018 }
1019
1020 updateSuccessorPhis(BB, NewBB, NextState, VMap, DuplicateMap);
1021 updatePredecessor(PrevBB, BB, NewBB, DTU);
1022 updateDefMap(NewDefs, VMap);
1023
1024 // Add all successors to the DominatorTree
1026 for (auto *SuccBB : successors(NewBB)) {
1027 if (SuccSet.insert(SuccBB).second)
1028 DTU->applyUpdates({{DominatorTree::Insert, NewBB, SuccBB}});
1029 }
1030 SuccSet.clear();
1031 return NewBB;
1032 }
1033
1034 /// Update the phi nodes in BB's successors.
1035 ///
1036 /// This means creating a new incoming value from NewBB with the new
1037 /// instruction wherever there is an incoming value from BB.
1038 void updateSuccessorPhis(BasicBlock *BB, BasicBlock *ClonedBB,
1039 const APInt &NextState, ValueToValueMapTy &VMap,
1040 DuplicateBlockMap &DuplicateMap) {
1041 std::vector<BasicBlock *> BlocksToUpdate;
1042
1043 // If BB is the last block in the path, we can simply update the one case
1044 // successor that will be reached.
1045 if (BB == SwitchPaths->getSwitchBlock()) {
1046 SwitchInst *Switch = SwitchPaths->getSwitchInst();
1047 BasicBlock *NextCase = getNextCaseSuccessor(Switch, NextState);
1048 BlocksToUpdate.push_back(NextCase);
1049 BasicBlock *ClonedSucc = getClonedBB(NextCase, NextState, DuplicateMap);
1050 if (ClonedSucc)
1051 BlocksToUpdate.push_back(ClonedSucc);
1052 }
1053 // Otherwise update phis in all successors.
1054 else {
1055 for (BasicBlock *Succ : successors(BB)) {
1056 BlocksToUpdate.push_back(Succ);
1057
1058 // Check if a successor has already been cloned for the particular exit
1059 // value. In this case if a successor was already cloned, the phi nodes
1060 // in the cloned block should be updated directly.
1061 BasicBlock *ClonedSucc = getClonedBB(Succ, NextState, DuplicateMap);
1062 if (ClonedSucc)
1063 BlocksToUpdate.push_back(ClonedSucc);
1064 }
1065 }
1066
1067 // If there is a phi with an incoming value from BB, create a new incoming
1068 // value for the new predecessor ClonedBB. The value will either be the same
1069 // value from BB or a cloned value.
1070 for (BasicBlock *Succ : BlocksToUpdate) {
1071 for (auto II = Succ->begin(); PHINode *Phi = dyn_cast<PHINode>(II);
1072 ++II) {
1073 Value *Incoming = Phi->getIncomingValueForBlock(BB);
1074 if (Incoming) {
1075 if (isa<Constant>(Incoming)) {
1076 Phi->addIncoming(Incoming, ClonedBB);
1077 continue;
1078 }
1079 Value *ClonedVal = VMap[Incoming];
1080 if (ClonedVal)
1081 Phi->addIncoming(ClonedVal, ClonedBB);
1082 else
1083 Phi->addIncoming(Incoming, ClonedBB);
1084 }
1085 }
1086 }
1087 }
1088
1089 /// Sets the successor of PrevBB to be NewBB instead of OldBB. Note that all
1090 /// other successors are kept as well.
1091 void updatePredecessor(BasicBlock *PrevBB, BasicBlock *OldBB,
1092 BasicBlock *NewBB, DomTreeUpdater *DTU) {
1093 // When a path is reused, there is a chance that predecessors were already
1094 // updated before. Check if the predecessor needs to be updated first.
1095 if (!isPredecessor(OldBB, PrevBB))
1096 return;
1097
1098 Instruction *PrevTerm = PrevBB->getTerminator();
1099 for (unsigned Idx = 0; Idx < PrevTerm->getNumSuccessors(); Idx++) {
1100 if (PrevTerm->getSuccessor(Idx) == OldBB) {
1101 OldBB->removePredecessor(PrevBB, /* KeepOneInputPHIs = */ true);
1102 PrevTerm->setSuccessor(Idx, NewBB);
1103 }
1104 }
1105 DTU->applyUpdates({{DominatorTree::Delete, PrevBB, OldBB},
1106 {DominatorTree::Insert, PrevBB, NewBB}});
1107 }
1108
1109 /// Add new value mappings to the DefMap to keep track of all new definitions
1110 /// for a particular instruction. These will be used while updating SSA form.
1111 void updateDefMap(DefMap &NewDefs, ValueToValueMapTy &VMap) {
1113 NewDefsVector.reserve(VMap.size());
1114
1115 for (auto Entry : VMap) {
1116 Instruction *Inst =
1117 dyn_cast<Instruction>(const_cast<Value *>(Entry.first));
1118 if (!Inst || !Entry.second || isa<BranchInst>(Inst) ||
1119 isa<SwitchInst>(Inst)) {
1120 continue;
1121 }
1122
1123 Instruction *Cloned = dyn_cast<Instruction>(Entry.second);
1124 if (!Cloned)
1125 continue;
1126
1127 NewDefsVector.push_back({Inst, Cloned});
1128 }
1129
1130 // Sort the defs to get deterministic insertion order into NewDefs.
1131 sort(NewDefsVector, [](const auto &LHS, const auto &RHS) {
1132 if (LHS.first == RHS.first)
1133 return LHS.second->comesBefore(RHS.second);
1134 return LHS.first->comesBefore(RHS.first);
1135 });
1136
1137 for (const auto &KV : NewDefsVector)
1138 NewDefs[KV.first].push_back(KV.second);
1139 }
1140
1141 /// Update the last branch of a particular cloned path to point to the correct
1142 /// case successor.
1143 ///
1144 /// Note that this is an optional step and would have been done in later
1145 /// optimizations, but it makes the CFG significantly easier to work with.
1146 void updateLastSuccessor(ThreadingPath &TPath,
1147 DuplicateBlockMap &DuplicateMap,
1148 DomTreeUpdater *DTU) {
1149 APInt NextState = TPath.getExitValue();
1150 BasicBlock *BB = TPath.getPath().back();
1151 BasicBlock *LastBlock = getClonedBB(BB, NextState, DuplicateMap);
1152
1153 // Note multiple paths can end at the same block so check that it is not
1154 // updated yet
1155 if (!isa<SwitchInst>(LastBlock->getTerminator()))
1156 return;
1157 SwitchInst *Switch = cast<SwitchInst>(LastBlock->getTerminator());
1158 BasicBlock *NextCase = getNextCaseSuccessor(Switch, NextState);
1159
1160 std::vector<DominatorTree::UpdateType> DTUpdates;
1162 for (BasicBlock *Succ : successors(LastBlock)) {
1163 if (Succ != NextCase && SuccSet.insert(Succ).second)
1164 DTUpdates.push_back({DominatorTree::Delete, LastBlock, Succ});
1165 }
1166
1167 Switch->eraseFromParent();
1168 BranchInst::Create(NextCase, LastBlock);
1169
1170 DTU->applyUpdates(DTUpdates);
1171 }
1172
1173 /// After cloning blocks, some of the phi nodes have extra incoming values
1174 /// that are no longer used. This function removes them.
1175 void cleanPhiNodes(BasicBlock *BB) {
1176 // If BB is no longer reachable, remove any remaining phi nodes
1177 if (pred_empty(BB)) {
1178 std::vector<PHINode *> PhiToRemove;
1179 for (auto II = BB->begin(); PHINode *Phi = dyn_cast<PHINode>(II); ++II) {
1180 PhiToRemove.push_back(Phi);
1181 }
1182 for (PHINode *PN : PhiToRemove) {
1183 PN->replaceAllUsesWith(PoisonValue::get(PN->getType()));
1184 PN->eraseFromParent();
1185 }
1186 return;
1187 }
1188
1189 // Remove any incoming values that come from an invalid predecessor
1190 for (auto II = BB->begin(); PHINode *Phi = dyn_cast<PHINode>(II); ++II) {
1191 std::vector<BasicBlock *> BlocksToRemove;
1192 for (BasicBlock *IncomingBB : Phi->blocks()) {
1193 if (!isPredecessor(BB, IncomingBB))
1194 BlocksToRemove.push_back(IncomingBB);
1195 }
1196 for (BasicBlock *BB : BlocksToRemove)
1197 Phi->removeIncomingValue(BB);
1198 }
1199 }
1200
1201 /// Checks if BB was already cloned for a particular next state value. If it
1202 /// was then it returns this cloned block, and otherwise null.
1203 BasicBlock *getClonedBB(BasicBlock *BB, const APInt &NextState,
1204 DuplicateBlockMap &DuplicateMap) {
1205 CloneList ClonedBBs = DuplicateMap[BB];
1206
1207 // Find an entry in the CloneList with this NextState. If it exists then
1208 // return the corresponding BB
1209 auto It = llvm::find_if(ClonedBBs, [NextState](const ClonedBlock &C) {
1210 return C.State == NextState;
1211 });
1212 return It != ClonedBBs.end() ? (*It).BB : nullptr;
1213 }
1214
1215 /// Helper to get the successor corresponding to a particular case value for
1216 /// a switch statement.
1217 BasicBlock *getNextCaseSuccessor(SwitchInst *Switch, const APInt &NextState) {
1218 BasicBlock *NextCase = nullptr;
1219 for (auto Case : Switch->cases()) {
1220 if (Case.getCaseValue()->getValue() == NextState) {
1221 NextCase = Case.getCaseSuccessor();
1222 break;
1223 }
1224 }
1225 if (!NextCase)
1226 NextCase = Switch->getDefaultDest();
1227 return NextCase;
1228 }
1229
1230 /// Returns true if IncomingBB is a predecessor of BB.
1231 bool isPredecessor(BasicBlock *BB, BasicBlock *IncomingBB) {
1232 return llvm::is_contained(predecessors(BB), IncomingBB);
1233 }
1234
1235 AllSwitchPaths *SwitchPaths;
1236 DominatorTree *DT;
1237 AssumptionCache *AC;
1241 std::vector<ThreadingPath> TPaths;
1242};
1243
1244bool DFAJumpThreading::run(Function &F) {
1245 LLVM_DEBUG(dbgs() << "\nDFA Jump threading: " << F.getName() << "\n");
1246
1247 if (F.hasOptSize()) {
1248 LLVM_DEBUG(dbgs() << "Skipping due to the 'minsize' attribute\n");
1249 return false;
1250 }
1251
1252 if (ClViewCfgBefore)
1253 F.viewCFG();
1254
1255 SmallVector<AllSwitchPaths, 2> ThreadableLoops;
1256 bool MadeChanges = false;
1257
1258 for (BasicBlock &BB : F) {
1259 auto *SI = dyn_cast<SwitchInst>(BB.getTerminator());
1260 if (!SI)
1261 continue;
1262
1263 LLVM_DEBUG(dbgs() << "\nCheck if SwitchInst in BB " << BB.getName()
1264 << " is a candidate\n");
1265 MainSwitch Switch(SI, ORE);
1266
1267 if (!Switch.getInstr())
1268 continue;
1269
1270 LLVM_DEBUG(dbgs() << "\nSwitchInst in BB " << BB.getName() << " is a "
1271 << "candidate for jump threading\n");
1272 LLVM_DEBUG(SI->dump());
1273
1274 unfoldSelectInstrs(DT, Switch.getSelectInsts());
1275 if (!Switch.getSelectInsts().empty())
1276 MadeChanges = true;
1277
1278 AllSwitchPaths SwitchPaths(&Switch, ORE);
1279 SwitchPaths.run();
1280
1281 if (SwitchPaths.getNumThreadingPaths() > 0) {
1282 ThreadableLoops.push_back(SwitchPaths);
1283
1284 // For the time being limit this optimization to occurring once in a
1285 // function since it can change the CFG significantly. This is not a
1286 // strict requirement but it can cause buggy behavior if there is an
1287 // overlap of blocks in different opportunities. There is a lot of room to
1288 // experiment with catching more opportunities here.
1289 break;
1290 }
1291 }
1292
1294 if (ThreadableLoops.size() > 0)
1295 CodeMetrics::collectEphemeralValues(&F, AC, EphValues);
1296
1297 for (AllSwitchPaths SwitchPaths : ThreadableLoops) {
1298 TransformDFA Transform(&SwitchPaths, DT, AC, TTI, ORE, EphValues);
1299 Transform.run();
1300 MadeChanges = true;
1301 }
1302
1303#ifdef EXPENSIVE_CHECKS
1304 assert(DT->verify(DominatorTree::VerificationLevel::Full));
1305 verifyFunction(F, &dbgs());
1306#endif
1307
1308 return MadeChanges;
1309}
1310
1311} // end anonymous namespace
1312
1313/// Integrate with the new Pass Manager
1320
1321 if (!DFAJumpThreading(&AC, &DT, &TTI, &ORE).run(F))
1322 return PreservedAnalyses::all();
1323
1326 return PA;
1327}
This file implements a class to represent arbitrary precision integral constant values and operations...
static void print(raw_ostream &Out, object::Archive::Kind Kind, T Val)
static const Function * getParent(const Value *V)
This file contains the declarations for the subclasses of Constant, which represent the different fla...
static cl::opt< unsigned > MaxPathLength("dfa-max-path-length", cl::desc("Max number of blocks searched to find a threading path"), cl::Hidden, cl::init(20))
static cl::opt< bool > ClViewCfgBefore("dfa-jump-view-cfg-before", cl::desc("View the CFG before DFA Jump Threading"), cl::Hidden, cl::init(false))
static cl::opt< unsigned > CostThreshold("dfa-cost-threshold", cl::desc("Maximum cost accepted for the transformation"), cl::Hidden, cl::init(50))
static cl::opt< unsigned > MaxNumPaths("dfa-max-num-paths", cl::desc("Max number of paths enumerated around a switch"), cl::Hidden, cl::init(200))
#define DEBUG_TYPE
Returns the sub type a function will return at a given Idx Should correspond to the result type of an ExtractValue instruction executed with just that one unsigned Idx
#define LLVM_DEBUG(X)
Definition: Debug.h:101
This file defines the DenseMap class.
This file provides various utilities for inspecting and working with the control flow graph in LLVM I...
#define F(x, y, z)
Definition: MD5.cpp:55
#define I(x, y, z)
Definition: MD5.cpp:58
static bool isCandidate(const MachineInstr *MI, Register &DefedReg, Register FrameReg)
Machine Trace Metrics
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
raw_pwrite_stream & OS
This file defines the SmallSet class.
This file defines the 'Statistic' class, which is designed to be an easy way to expose various metric...
#define STATISTIC(VARNAME, DESC)
Definition: Statistic.h:167
This pass exposes codegen information to IR-level passes.
Value * RHS
Value * LHS
Class for arbitrary precision integers.
Definition: APInt.h:76
unsigned ceilLogBase2() const
Definition: APInt.h:1699
uint64_t getLimitedValue(uint64_t Limit=UINT64_MAX) const
If this value is smaller than the specified limit, return it, otherwise return the limit value.
Definition: APInt.h:453
A container for analyses that lazily runs them and caches their results.
Definition: PassManager.h:348
PassT::Result & getResult(IRUnitT &IR, ExtraArgTs... ExtraArgs)
Get the result of an analysis pass for a given IR unit.
Definition: PassManager.h:500
This represents the llvm.assume intrinsic.
A function analysis which provides an AssumptionCache.
A cache of @llvm.assume calls within a function.
LLVM Basic Block Representation.
Definition: BasicBlock.h:60
iterator begin()
Instruction iterator methods.
Definition: BasicBlock.h:438
iterator_range< const_phi_iterator > phis() const
Returns a range that iterates over the phis in the basic block.
Definition: BasicBlock.h:507
static BasicBlock * Create(LLVMContext &Context, const Twine &Name="", Function *Parent=nullptr, BasicBlock *InsertBefore=nullptr)
Creates a new BasicBlock.
Definition: BasicBlock.h:207
void moveAfter(BasicBlock *MovePos)
Unlink this basic block from its current function and insert it right after MovePos in the function M...
Definition: BasicBlock.cpp:329
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:214
size_t size() const
Definition: BasicBlock.h:459
const Instruction * getTerminator() const LLVM_READONLY
Returns the terminator instruction if the block is well formed or null if the block is not well forme...
Definition: BasicBlock.h:229
const Instruction & back() const
Definition: BasicBlock.h:463
void removePredecessor(BasicBlock *Pred, bool KeepOneInputPHIs=false)
Update PHI nodes in this BasicBlock before removal of predecessor Pred.
Definition: BasicBlock.cpp:552
Conditional or Unconditional Branch instruction.
static BranchInst * Create(BasicBlock *IfTrue, Instruction *InsertBefore=nullptr)
bool isUnconditional() const
This is the shared class of boolean and integer constants.
Definition: Constants.h:79
void applyUpdates(ArrayRef< DominatorTree::UpdateType > Updates)
Submit updates to all available trees.
Analysis pass which computes a DominatorTree.
Definition: Dominators.h:275
bool verify(VerificationLevel VL=VerificationLevel::Full) const
verify - checks if the tree is correct.
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree.
Definition: Dominators.h:162
unsigned getNumSuccessors() const LLVM_READONLY
Return the number of successors that this instruction has.
const BasicBlock * getParent() const
Definition: Instruction.h:150
InstListType::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
Definition: Instruction.cpp:93
BasicBlock * getSuccessor(unsigned Idx) const LLVM_READONLY
Return the specified successor. This instruction must be a terminator.
void setSuccessor(unsigned Idx, BasicBlock *BB)
Update the specified successor to point at the provided block.
void moveBefore(Instruction *MovePos)
Unlink this instruction from its current basic block and insert it into the basic block that MovePos ...
This class implements a map that also provides access to all stored values in a deterministic order.
Definition: MapVector.h:36
Diagnostic information for optimization analysis remarks.
The optimization diagnostic interface.
void emit(DiagnosticInfoOptimizationBase &OptDiag)
Output the remark via the diagnostic handler and to the optimization record file.
Diagnostic information for missed-optimization remarks.
Diagnostic information for applied optimization remarks.
void addIncoming(Value *V, BasicBlock *BB)
Add an incoming value to the end of the PHI list.
iterator_range< const_block_iterator > blocks() const
void setIncomingValue(unsigned i, Value *V)
Value * getIncomingValueForBlock(const BasicBlock *BB) const
BasicBlock * getIncomingBlock(unsigned i) const
Return incoming basic block number i.
unsigned getNumIncomingValues() const
Return the number of incoming edges.
static PoisonValue * get(Type *T)
Static factory methods - Return an 'poison' object of the specified type.
Definition: Constants.cpp:1743
A set of analyses that are preserved following a run of a transformation pass.
Definition: Analysis.h:109
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: Analysis.h:115
void preserve()
Mark an analysis as preserved.
Definition: Analysis.h:129
Helper class for SSA formation on a set of values defined in multiple blocks.
unsigned AddVariable(StringRef Name, Type *Ty)
Add a new variable to the SSA rewriter.
void AddAvailableValue(unsigned Var, BasicBlock *BB, Value *V)
Indicate that a rewritten value is available in the specified block with the specified value.
void RewriteAllUses(DominatorTree *DT, SmallVectorImpl< PHINode * > *InsertedPHIs=nullptr)
Perform all the necessary updates, including new PHI-nodes insertion and the requested uses update.
void AddUse(unsigned Var, Use *U)
Record a use of the symbolic value.
This class represents the LLVM 'select' instruction.
const Value * getFalseValue() const
const Value * getTrueValue() const
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:360
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:342
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
Definition: SmallPtrSet.h:427
SmallSet - This maintains a set of unique values, optimizing for the case when the set is small (less...
Definition: SmallSet.h:135
void clear()
Definition: SmallSet.h:218
bool contains(const T &V) const
Check if the SmallSet contains the given element.
Definition: SmallSet.h:236
std::pair< const_iterator, bool > insert(const T &V)
insert - Insert an element into the set if it isn't already there.
Definition: SmallSet.h:179
bool empty() const
Definition: SmallVector.h:94
size_t size() const
Definition: SmallVector.h:91
void reserve(size_type N)
Definition: SmallVector.h:676
void push_back(const T &Elt)
Definition: SmallVector.h:426
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1209
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:50
Multiway switch.
Analysis pass providing the TargetTransformInfo.
This pass provides access to the codegen interfaces that are needed for IR-level transformations.
unsigned getEstimatedNumberOfCaseClusters(const SwitchInst &SI, unsigned &JTSize, ProfileSummaryInfo *PSI, BlockFrequencyInfo *BFI) const
A Use represents the edge between a Value definition and its users.
Definition: Use.h:43
size_type size() const
Definition: ValueMap.h:140
LLVM Value Representation.
Definition: Value.h:74
bool hasOneUse() const
Return true if there is exactly one use of this value.
Definition: Value.h:434
StringRef getName() const
Return a constant reference to the value's name.
Definition: Value.cpp:309
This class implements an extremely fast bulk output stream that can only output to a stream.
Definition: raw_ostream.h:52
A raw_ostream that writes to an std::string.
Definition: raw_ostream.h:660
@ C
The default llvm calling convention, compatible with C.
Definition: CallingConv.h:34
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:450
@ Switch
The "resume-switch" lowering, where there are separate resume and destroy functions that are shared b...
PointerTypeMap run(const Module &M)
Compute the PointerTypeMap for the module M.
DiagnosticInfoOptimizationBase::Argument NV
NodeAddr< InstrNode * > Instr
Definition: RDFGraph.h:389
NodeAddr< PhiNode * > Phi
Definition: RDFGraph.h:390
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
auto find(R &&Range, const T &Val)
Provide wrappers to std::find which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1751
bool verifyFunction(const Function &F, raw_ostream *OS=nullptr)
Check a function for errors, useful for use when debugging a pass.
Definition: Verifier.cpp:6710
auto successors(const MachineBasicBlock *BB)
BasicBlock * CloneBasicBlock(const BasicBlock *BB, ValueToValueMapTy &VMap, const Twine &NameSuffix="", Function *F=nullptr, ClonedCodeInfo *CodeInfo=nullptr, DebugInfoFinder *DIFinder=nullptr)
Return a copy of the specified basic block, but without embedding the block into a particular functio...
void sort(IteratorTy Start, IteratorTy End)
Definition: STLExtras.h:1656
@ RF_IgnoreMissingLocals
If this flag is set, the remapper ignores missing function-local entries (Argument,...
Definition: ValueMapper.h:94
@ RF_NoModuleLevelChanges
If this flag is set, the remapper knows that only local values within a function (such as an instruct...
Definition: ValueMapper.h:76
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
void RemapInstruction(Instruction *I, ValueToValueMapTy &VM, RemapFlags Flags=RF_None, ValueMapTypeRemapper *TypeMapper=nullptr, ValueMaterializer *Materializer=nullptr)
Convert the instruction operands from referencing the current values into those specified by VM.
Definition: ValueMapper.h:263
raw_ostream & operator<<(raw_ostream &OS, const APFixedPoint &FX)
Definition: APFixedPoint.h:293
auto find_if(R &&Range, UnaryPredicate P)
Provide wrappers to std::find_if which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1758
auto predecessors(const MachineBasicBlock *BB)
bool is_contained(R &&Range, const E &Element)
Returns true if Element is found in Range.
Definition: STLExtras.h:1888
bool pred_empty(const BasicBlock *BB)
Definition: CFG.h:118
void swap(llvm::BitVector &LHS, llvm::BitVector &RHS)
Implement std::swap in terms of BitVector swap.
Definition: BitVector.h:860
Utility to calculate the size and a few similar metrics for a set of basic blocks.
Definition: CodeMetrics.h:31
static void collectEphemeralValues(const Loop *L, AssumptionCache *AC, SmallPtrSetImpl< const Value * > &EphValues)
Collect a loop's ephemeral values (those used only by an assume or similar intrinsics in the loop).
Definition: CodeMetrics.cpp:70
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Integrate with the new Pass Manager.
Incoming for lane maks phi as machine instruction, incoming register Reg and incoming block Block are...