1//===- LowerSwitch.cpp - Eliminate Switch instructions --------------------===//
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// The LowerSwitch transformation rewrites switch instructions with a sequence
10// of branches, which allows targets to get away with not implementing the
11// switch instruction until it is convenient.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/Transforms/Utils/LowerSwitch.h"
16#include "llvm/ADT/DenseMap.h"
17#include "llvm/ADT/STLExtras.h"
18#include "llvm/ADT/SmallPtrSet.h"
19#include "llvm/ADT/SmallVector.h"
20#include "llvm/Analysis/AssumptionCache.h"
21#include "llvm/Analysis/LazyValueInfo.h"
22#include "llvm/Analysis/ValueTracking.h"
23#include "llvm/IR/BasicBlock.h"
24#include "llvm/IR/CFG.h"
25#include "llvm/IR/ConstantRange.h"
26#include "llvm/IR/Constants.h"
27#include "llvm/IR/Function.h"
28#include "llvm/IR/InstrTypes.h"
29#include "llvm/IR/Instructions.h"
30#include "llvm/IR/PassManager.h"
31#include "llvm/IR/Value.h"
32#include "llvm/InitializePasses.h"
33#include "llvm/Pass.h"
34#include "llvm/Support/Casting.h"
35#include "llvm/Support/Compiler.h"
36#include "llvm/Support/Debug.h"
37#include "llvm/Support/KnownBits.h"
38#include "llvm/Support/raw_ostream.h"
39#include "llvm/Transforms/Utils.h"
40#include "llvm/Transforms/Utils/BasicBlockUtils.h"
41#include <cassert>
42#include <iterator>
43#include <vector>
44
45using namespace llvm;
46
47#define DEBUG_TYPE "lower-switch"
48
49namespace {
50
51struct IntRange {
52 APInt Low, High;
53};
54
55} // end anonymous namespace
56
57namespace {
58// Return true iff R is covered by Ranges.
59bool IsInRanges(const IntRange &R, const std::vector<IntRange> &Ranges) {
60 // Note: Ranges must be sorted, non-overlapping and non-adjacent.
61
62 // Find the first range whose High field is >= R.High,
63 // then check if the Low field is <= R.Low. If so, we
64 // have a Range that covers R.
65 auto I = llvm::lower_bound(
66 Range: Ranges, Value: R, C: [](IntRange A, IntRange B) { return A.High.slt(RHS: B.High); });
67 return I != Ranges.end() && I->Low.sle(RHS: R.Low);
68}
69
70struct CaseRange {
71 ConstantInt *Low;
72 ConstantInt *High;
73 BasicBlock *BB;
74
75 CaseRange(ConstantInt *low, ConstantInt *high, BasicBlock *bb)
76 : Low(low), High(high), BB(bb) {}
77};
78
79using CaseVector = std::vector<CaseRange>;
80using CaseItr = std::vector<CaseRange>::iterator;
81
82/// The comparison function for sorting the switch case values in the vector.
83/// WARNING: Case ranges should be disjoint!
84struct CaseCmp {
85 bool operator()(const CaseRange &C1, const CaseRange &C2) {
86 const ConstantInt *CI1 = cast<const ConstantInt>(Val: C1.Low);
87 const ConstantInt *CI2 = cast<const ConstantInt>(Val: C2.High);
88 return CI1->getValue().slt(RHS: CI2->getValue());
89 }
90};
91
92/// Used for debugging purposes.
93LLVM_ATTRIBUTE_USED
94raw_ostream &operator<<(raw_ostream &O, const CaseVector &C) {
95 O << "[";
96
97 for (CaseVector::const_iterator B = C.begin(), E = C.end(); B != E;) {
98 O << "[" << B->Low->getValue() << ", " << B->High->getValue() << "]";
99 if (++B != E)
100 O << ", ";
101 }
102
103 return O << "]";
104}
105
106/// Update the first occurrence of the "switch statement" BB in the PHI
107/// node with the "new" BB. The other occurrences will:
108///
109/// 1) Be updated by subsequent calls to this function. Switch statements may
110/// have more than one outcoming edge into the same BB if they all have the same
111/// value. When the switch statement is converted these incoming edges are now
112/// coming from multiple BBs.
113/// 2) Removed if subsequent incoming values now share the same case, i.e.,
114/// multiple outcome edges are condensed into one. This is necessary to keep the
115/// number of phi values equal to the number of branches to SuccBB.
116void FixPhis(BasicBlock *SuccBB, BasicBlock *OrigBB, BasicBlock *NewBB,
117 const APInt &NumMergedCases) {
118 for (auto &I : SuccBB->phis()) {
119 PHINode *PN = cast<PHINode>(Val: &I);
120
121 // Only update the first occurrence if NewBB exists.
122 unsigned Idx = 0, E = PN->getNumIncomingValues();
123 APInt LocalNumMergedCases = NumMergedCases;
124 for (; Idx != E && NewBB; ++Idx) {
125 if (PN->getIncomingBlock(i: Idx) == OrigBB) {
126 PN->setIncomingBlock(i: Idx, BB: NewBB);
127 break;
128 }
129 }
130
131 // Skip the updated incoming block so that it will not be removed.
132 if (NewBB)
133 ++Idx;
134
135 // Remove additional occurrences coming from condensed cases and keep the
136 // number of incoming values equal to the number of branches to SuccBB.
137 SmallVector<unsigned, 8> Indices;
138 for (; LocalNumMergedCases.ugt(RHS: 0) && Idx < E; ++Idx)
139 if (PN->getIncomingBlock(i: Idx) == OrigBB) {
140 Indices.push_back(Elt: Idx);
141 LocalNumMergedCases -= 1;
142 }
143 // Remove incoming values in the reverse order to prevent invalidating
144 // *successive* index.
145 for (unsigned III : llvm::reverse(C&: Indices))
146 PN->removeIncomingValue(Idx: III);
147 }
148}
149
150/// Create a new leaf block for the binary lookup tree. It checks if the
151/// switch's value == the case's value. If not, then it jumps to the default
152/// branch. At this point in the tree, the value can't be another valid case
153/// value, so the jump to the "default" branch is warranted.
154BasicBlock *NewLeafBlock(CaseRange &Leaf, Value *Val, ConstantInt *LowerBound,
155 ConstantInt *UpperBound, BasicBlock *OrigBlock,
156 BasicBlock *Default) {
157 Function *F = OrigBlock->getParent();
158 BasicBlock *NewLeaf = BasicBlock::Create(Context&: Val->getContext(), Name: "LeafBlock");
159 F->insert(Position: ++OrigBlock->getIterator(), BB: NewLeaf);
160
161 // Emit comparison
162 ICmpInst *Comp = nullptr;
163 if (Leaf.Low == Leaf.High) {
164 // Make the seteq instruction...
165 Comp =
166 new ICmpInst(NewLeaf, ICmpInst::ICMP_EQ, Val, Leaf.Low, "SwitchLeaf");
167 } else {
168 // Make range comparison
169 if (Leaf.Low == LowerBound) {
170 // Val >= Min && Val <= Hi --> Val <= Hi
171 Comp = new ICmpInst(NewLeaf, ICmpInst::ICMP_SLE, Val, Leaf.High,
172 "SwitchLeaf");
173 } else if (Leaf.High == UpperBound) {
174 // Val <= Max && Val >= Lo --> Val >= Lo
175 Comp = new ICmpInst(NewLeaf, ICmpInst::ICMP_SGE, Val, Leaf.Low,
176 "SwitchLeaf");
177 } else if (Leaf.Low->isZero()) {
178 // Val >= 0 && Val <= Hi --> Val <=u Hi
179 Comp = new ICmpInst(NewLeaf, ICmpInst::ICMP_ULE, Val, Leaf.High,
180 "SwitchLeaf");
181 } else {
182 // Emit V-Lo <=u Hi-Lo
183 Constant *NegLo = ConstantExpr::getNeg(C: Leaf.Low);
184 Instruction *Add = BinaryOperator::CreateAdd(
185 V1: Val, V2: NegLo, Name: Val->getName() + ".off", InsertBefore: NewLeaf);
186 Constant *UpperBound = ConstantExpr::getAdd(C1: NegLo, C2: Leaf.High);
187 Comp = new ICmpInst(NewLeaf, ICmpInst::ICMP_ULE, Add, UpperBound,
188 "SwitchLeaf");
189 }
190 }
191
192 // Make the conditional branch...
193 BasicBlock *Succ = Leaf.BB;
194 BranchInst::Create(IfTrue: Succ, IfFalse: Default, Cond: Comp, InsertBefore: NewLeaf);
195
196 // Update the PHI incoming value/block for the default.
197 for (auto &I : Default->phis()) {
198 PHINode *PN = cast<PHINode>(Val: &I);
199 auto *V = PN->getIncomingValueForBlock(BB: OrigBlock);
200 PN->addIncoming(V, BB: NewLeaf);
201 }
202
203 // If there were any PHI nodes in this successor, rewrite one entry
204 // from OrigBlock to come from NewLeaf.
205 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(Val: I); ++I) {
206 PHINode *PN = cast<PHINode>(Val&: I);
207 // Remove all but one incoming entries from the cluster
208 APInt Range = Leaf.High->getValue() - Leaf.Low->getValue();
209 for (APInt j(Range.getBitWidth(), 0, false); j.ult(RHS: Range); ++j) {
210 PN->removeIncomingValue(BB: OrigBlock);
211 }
212
213 int BlockIdx = PN->getBasicBlockIndex(BB: OrigBlock);
214 assert(BlockIdx != -1 && "Switch didn't go to this successor??");
215 PN->setIncomingBlock(i: (unsigned)BlockIdx, BB: NewLeaf);
216 }
217
218 return NewLeaf;
219}
220
221/// Convert the switch statement into a binary lookup of the case values.
222/// The function recursively builds this tree. LowerBound and UpperBound are
223/// used to keep track of the bounds for Val that have already been checked by
224/// a block emitted by one of the previous calls to switchConvert in the call
225/// stack.
226BasicBlock *SwitchConvert(CaseItr Begin, CaseItr End, ConstantInt *LowerBound,
227 ConstantInt *UpperBound, Value *Val,
228 BasicBlock *Predecessor, BasicBlock *OrigBlock,
229 BasicBlock *Default,
230 const std::vector<IntRange> &UnreachableRanges) {
231 assert(LowerBound && UpperBound && "Bounds must be initialized");
232 unsigned Size = End - Begin;
233
234 if (Size == 1) {
235 // Check if the Case Range is perfectly squeezed in between
236 // already checked Upper and Lower bounds. If it is then we can avoid
237 // emitting the code that checks if the value actually falls in the range
238 // because the bounds already tell us so.
239 if (Begin->Low == LowerBound && Begin->High == UpperBound) {
240 APInt NumMergedCases = UpperBound->getValue() - LowerBound->getValue();
241 FixPhis(SuccBB: Begin->BB, OrigBB: OrigBlock, NewBB: Predecessor, NumMergedCases);
242 return Begin->BB;
243 }
244 return NewLeafBlock(Leaf&: *Begin, Val, LowerBound, UpperBound, OrigBlock,
245 Default);
246 }
247
248 unsigned Mid = Size / 2;
249 std::vector<CaseRange> LHS(Begin, Begin + Mid);
250 LLVM_DEBUG(dbgs() << "LHS: " << LHS << "\n");
251 std::vector<CaseRange> RHS(Begin + Mid, End);
252 LLVM_DEBUG(dbgs() << "RHS: " << RHS << "\n");
253
254 CaseRange &Pivot = *(Begin + Mid);
255 LLVM_DEBUG(dbgs() << "Pivot ==> [" << Pivot.Low->getValue() << ", "
256 << Pivot.High->getValue() << "]\n");
257
258 // NewLowerBound here should never be the integer minimal value.
259 // This is because it is computed from a case range that is never
260 // the smallest, so there is always a case range that has at least
261 // a smaller value.
262 ConstantInt *NewLowerBound = Pivot.Low;
263
264 // Because NewLowerBound is never the smallest representable integer
265 // it is safe here to subtract one.
266 ConstantInt *NewUpperBound = ConstantInt::get(Context&: NewLowerBound->getContext(),
267 V: NewLowerBound->getValue() - 1);
268
269 if (!UnreachableRanges.empty()) {
270 // Check if the gap between LHS's highest and NewLowerBound is unreachable.
271 APInt GapLow = LHS.back().High->getValue() + 1;
272 APInt GapHigh = NewLowerBound->getValue() - 1;
273 IntRange Gap = {.Low: GapLow, .High: GapHigh};
274 if (GapHigh.sge(RHS: GapLow) && IsInRanges(R: Gap, Ranges: UnreachableRanges))
275 NewUpperBound = LHS.back().High;
276 }
277
278 LLVM_DEBUG(dbgs() << "LHS Bounds ==> [" << LowerBound->getValue() << ", "
279 << NewUpperBound->getValue() << "]\n"
280 << "RHS Bounds ==> [" << NewLowerBound->getValue() << ", "
281 << UpperBound->getValue() << "]\n");
282
283 // Create a new node that checks if the value is < pivot. Go to the
284 // left branch if it is and right branch if not.
285 Function *F = OrigBlock->getParent();
286 BasicBlock *NewNode = BasicBlock::Create(Context&: Val->getContext(), Name: "NodeBlock");
287
288 ICmpInst *Comp = new ICmpInst(ICmpInst::ICMP_SLT, Val, Pivot.Low, "Pivot");
289
290 BasicBlock *LBranch =
291 SwitchConvert(Begin: LHS.begin(), End: LHS.end(), LowerBound, UpperBound: NewUpperBound, Val,
292 Predecessor: NewNode, OrigBlock, Default, UnreachableRanges);
293 BasicBlock *RBranch =
294 SwitchConvert(Begin: RHS.begin(), End: RHS.end(), LowerBound: NewLowerBound, UpperBound, Val,
295 Predecessor: NewNode, OrigBlock, Default, UnreachableRanges);
296
297 F->insert(Position: ++OrigBlock->getIterator(), BB: NewNode);
298 Comp->insertInto(ParentBB: NewNode, It: NewNode->end());
299
300 BranchInst::Create(IfTrue: LBranch, IfFalse: RBranch, Cond: Comp, InsertBefore: NewNode);
301 return NewNode;
302}
303
304/// Transform simple list of \p SI's cases into list of CaseRange's \p Cases.
305/// \post \p Cases wouldn't contain references to \p SI's default BB.
306/// \returns Number of \p SI's cases that do not reference \p SI's default BB.
307unsigned Clusterify(CaseVector &Cases, SwitchInst *SI) {
308 unsigned NumSimpleCases = 0;
309
310 // Start with "simple" cases
311 for (auto Case : SI->cases()) {
312 if (Case.getCaseSuccessor() == SI->getDefaultDest())
313 continue;
314 Cases.push_back(x: CaseRange(Case.getCaseValue(), Case.getCaseValue(),
315 Case.getCaseSuccessor()));
316 ++NumSimpleCases;
317 }
318
319 llvm::sort(C&: Cases, Comp: CaseCmp());
320
321 // Merge case into clusters
322 if (Cases.size() >= 2) {
323 CaseItr I = Cases.begin();
324 for (CaseItr J = std::next(x: I), E = Cases.end(); J != E; ++J) {
325 const APInt &nextValue = J->Low->getValue();
326 const APInt &currentValue = I->High->getValue();
327 BasicBlock *nextBB = J->BB;
328 BasicBlock *currentBB = I->BB;
329
330 // If the two neighboring cases go to the same destination, merge them
331 // into a single case.
332 assert(nextValue.sgt(currentValue) &&
333 "Cases should be strictly ascending");
334 if ((nextValue == currentValue + 1) && (currentBB == nextBB)) {
335 I->High = J->High;
336 // FIXME: Combine branch weights.
337 } else if (++I != J) {
338 *I = *J;
339 }
340 }
341 Cases.erase(first: std::next(x: I), last: Cases.end());
342 }
343
344 return NumSimpleCases;
345}
346
347/// Replace the specified switch instruction with a sequence of chained if-then
348/// insts in a balanced binary search.
349void ProcessSwitchInst(SwitchInst *SI,
350 SmallPtrSetImpl<BasicBlock *> &DeleteList,
351 AssumptionCache *AC, LazyValueInfo *LVI) {
352 BasicBlock *OrigBlock = SI->getParent();
353 Function *F = OrigBlock->getParent();
354 Value *Val = SI->getCondition(); // The value we are switching on...
355 BasicBlock *Default = SI->getDefaultDest();
356
357 // Don't handle unreachable blocks. If there are successors with phis, this
358 // would leave them behind with missing predecessors.
359 if ((OrigBlock != &F->getEntryBlock() && pred_empty(BB: OrigBlock)) ||
360 OrigBlock->getSinglePredecessor() == OrigBlock) {
361 DeleteList.insert(Ptr: OrigBlock);
362 return;
363 }
364
365 // Prepare cases vector.
366 CaseVector Cases;
367 const unsigned NumSimpleCases = Clusterify(Cases, SI);
368 IntegerType *IT = cast<IntegerType>(Val: SI->getCondition()->getType());
369 const unsigned BitWidth = IT->getBitWidth();
370 // Explicitly use higher precision to prevent unsigned overflow where
371 // `UnsignedMax - 0 + 1 == 0`
372 APInt UnsignedZero(BitWidth + 1, 0);
373 APInt UnsignedMax = APInt::getMaxValue(numBits: BitWidth);
374 LLVM_DEBUG(dbgs() << "Clusterify finished. Total clusters: " << Cases.size()
375 << ". Total non-default cases: " << NumSimpleCases
376 << "\nCase clusters: " << Cases << "\n");
377
378 // If there is only the default destination, just branch.
379 if (Cases.empty()) {
380 BranchInst::Create(IfTrue: Default, InsertBefore: OrigBlock);
381 // Remove all the references from Default's PHIs to OrigBlock, but one.
382 FixPhis(SuccBB: Default, OrigBB: OrigBlock, NewBB: OrigBlock, NumMergedCases: UnsignedMax);
383 SI->eraseFromParent();
384 return;
385 }
386
387 ConstantInt *LowerBound = nullptr;
388 ConstantInt *UpperBound = nullptr;
389 bool DefaultIsUnreachableFromSwitch = false;
390
391 if (SI->defaultDestUnreachable()) {
392 // Make the bounds tightly fitted around the case value range, because we
393 // know that the value passed to the switch must be exactly one of the case
394 // values.
395 LowerBound = Cases.front().Low;
396 UpperBound = Cases.back().High;
397 DefaultIsUnreachableFromSwitch = true;
398 } else {
399 // Constraining the range of the value being switched over helps eliminating
400 // unreachable BBs and minimizing the number of `add` instructions
401 // newLeafBlock ends up emitting. Running CorrelatedValuePropagation after
402 // LowerSwitch isn't as good, and also much more expensive in terms of
403 // compile time for the following reasons:
404 // 1. it processes many kinds of instructions, not just switches;
405 // 2. even if limited to icmp instructions only, it will have to process
406 // roughly C icmp's per switch, where C is the number of cases in the
407 // switch, while LowerSwitch only needs to call LVI once per switch.
408 const DataLayout &DL = F->getDataLayout();
409 KnownBits Known = computeKnownBits(V: Val, DL, AC, CxtI: SI);
410 // TODO Shouldn't this create a signed range?
411 ConstantRange KnownBitsRange =
412 ConstantRange::fromKnownBits(Known, /*IsSigned=*/false);
413 const ConstantRange LVIRange =
414 LVI->getConstantRange(V: Val, CxtI: SI, /*UndefAllowed*/ false);
415 ConstantRange ValRange = KnownBitsRange.intersectWith(CR: LVIRange);
416 // We delegate removal of unreachable non-default cases to other passes. In
417 // the unlikely event that some of them survived, we just conservatively
418 // maintain the invariant that all the cases lie between the bounds. This
419 // may, however, still render the default case effectively unreachable.
420 const APInt &Low = Cases.front().Low->getValue();
421 const APInt &High = Cases.back().High->getValue();
422 APInt Min = APIntOps::smin(A: ValRange.getSignedMin(), B: Low);
423 APInt Max = APIntOps::smax(A: ValRange.getSignedMax(), B: High);
424
425 LowerBound = ConstantInt::get(Context&: SI->getContext(), V: Min);
426 UpperBound = ConstantInt::get(Context&: SI->getContext(), V: Max);
427 DefaultIsUnreachableFromSwitch = (Min + (NumSimpleCases - 1) == Max);
428 }
429
430 std::vector<IntRange> UnreachableRanges;
431
432 if (DefaultIsUnreachableFromSwitch) {
433 DenseMap<BasicBlock *, APInt> Popularity;
434 APInt MaxPop(UnsignedZero);
435 BasicBlock *PopSucc = nullptr;
436
437 APInt SignedMax = APInt::getSignedMaxValue(numBits: BitWidth);
438 APInt SignedMin = APInt::getSignedMinValue(numBits: BitWidth);
439 IntRange R = {.Low: SignedMin, .High: SignedMax};
440 UnreachableRanges.push_back(x: R);
441 for (const auto &I : Cases) {
442 const APInt &Low = I.Low->getValue();
443 const APInt &High = I.High->getValue();
444
445 IntRange &LastRange = UnreachableRanges.back();
446 if (LastRange.Low.eq(RHS: Low)) {
447 // There is nothing left of the previous range.
448 UnreachableRanges.pop_back();
449 } else {
450 // Terminate the previous range.
451 assert(Low.sgt(LastRange.Low));
452 LastRange.High = Low - 1;
453 }
454 if (High.ne(RHS: SignedMax)) {
455 IntRange R = {.Low: High + 1, .High: SignedMax};
456 UnreachableRanges.push_back(x: R);
457 }
458
459 // Count popularity.
460 assert(High.sge(Low) && "Popularity shouldn't be negative.");
461 APInt N = High.sext(width: BitWidth + 1) - Low.sext(width: BitWidth + 1) + 1;
462 // Explict insert to make sure the bitwidth of APInts match
463 APInt &Pop = Popularity.insert(KV: {I.BB, APInt(UnsignedZero)}).first->second;
464 if ((Pop += N).ugt(RHS: MaxPop)) {
465 MaxPop = Pop;
466 PopSucc = I.BB;
467 }
468 }
469#ifndef NDEBUG
470 /* UnreachableRanges should be sorted and the ranges non-adjacent. */
471 for (auto I = UnreachableRanges.begin(), E = UnreachableRanges.end();
472 I != E; ++I) {
473 assert(I->Low.sle(I->High));
474 auto Next = I + 1;
475 if (Next != E) {
476 assert(Next->Low.sgt(I->High));
477 }
478 }
479#endif
480
481 // As the default block in the switch is unreachable, update the PHI nodes
482 // (remove all of the references to the default block) to reflect this.
483 const unsigned NumDefaultEdges = SI->getNumCases() + 1 - NumSimpleCases;
484 for (unsigned I = 0; I < NumDefaultEdges; ++I)
485 Default->removePredecessor(Pred: OrigBlock);
486
487 // Use the most popular block as the new default, reducing the number of
488 // cases.
489 Default = PopSucc;
490 llvm::erase_if(C&: Cases,
491 P: [PopSucc](const CaseRange &R) { return R.BB == PopSucc; });
492
493 // If there are no cases left, just branch.
494 if (Cases.empty()) {
495 BranchInst::Create(IfTrue: Default, InsertBefore: OrigBlock);
496 SI->eraseFromParent();
497 // As all the cases have been replaced with a single branch, only keep
498 // one entry in the PHI nodes.
499 if (!MaxPop.isZero())
500 for (APInt I(UnsignedZero); I.ult(RHS: MaxPop - 1); ++I)
501 PopSucc->removePredecessor(Pred: OrigBlock);
502 return;
503 }
504
505 // If the condition was a PHI node with the switch block as a predecessor
506 // removing predecessors may have caused the condition to be erased.
507 // Getting the condition value again here protects against that.
508 Val = SI->getCondition();
509 }
510
511 BasicBlock *SwitchBlock =
512 SwitchConvert(Begin: Cases.begin(), End: Cases.end(), LowerBound, UpperBound, Val,
513 Predecessor: OrigBlock, OrigBlock, Default, UnreachableRanges);
514
515 // We have added incoming values for newly-created predecessors in
516 // NewLeafBlock(). The only meaningful work we offload to FixPhis() is to
517 // remove the incoming values from OrigBlock. There might be a special case
518 // that SwitchBlock is the same as Default, under which the PHIs in Default
519 // are fixed inside SwitchConvert().
520 if (SwitchBlock != Default)
521 FixPhis(SuccBB: Default, OrigBB: OrigBlock, NewBB: nullptr, NumMergedCases: UnsignedMax);
522
523 // Branch to our shiny new if-then stuff...
524 BranchInst::Create(IfTrue: SwitchBlock, InsertBefore: OrigBlock);
525
526 // We are now done with the switch instruction, delete it.
527 BasicBlock *OldDefault = SI->getDefaultDest();
528 SI->eraseFromParent();
529
530 // If the Default block has no more predecessors just add it to DeleteList.
531 if (pred_empty(BB: OldDefault))
532 DeleteList.insert(Ptr: OldDefault);
533}
534
535bool LowerSwitch(Function &F, LazyValueInfo *LVI, AssumptionCache *AC) {
536 bool Changed = false;
537 SmallPtrSet<BasicBlock *, 8> DeleteList;
538
539 // We use make_early_inc_range here so that we don't traverse new blocks.
540 for (BasicBlock &Cur : llvm::make_early_inc_range(Range&: F)) {
541 // If the block is a dead Default block that will be deleted later, don't
542 // waste time processing it.
543 if (DeleteList.count(Ptr: &Cur))
544 continue;
545
546 if (SwitchInst *SI = dyn_cast<SwitchInst>(Val: Cur.getTerminator())) {
547 Changed = true;
548 ProcessSwitchInst(SI, DeleteList, AC, LVI);
549 }
550 }
551
552 for (BasicBlock *BB : DeleteList) {
553 LVI->eraseBlock(BB);
554 DeleteDeadBlock(BB);
555 }
556
557 return Changed;
558}
559
560/// Replace all SwitchInst instructions with chained branch instructions.
561class LowerSwitchLegacyPass : public FunctionPass {
562public:
563 // Pass identification, replacement for typeid
564 static char ID;
565
566 LowerSwitchLegacyPass() : FunctionPass(ID) {
567 initializeLowerSwitchLegacyPassPass(*PassRegistry::getPassRegistry());
568 }
569
570 bool runOnFunction(Function &F) override;
571
572 void getAnalysisUsage(AnalysisUsage &AU) const override {
573 AU.addRequired<LazyValueInfoWrapperPass>();
574 }
575};
576
577} // end anonymous namespace
578
579char LowerSwitchLegacyPass::ID = 0;
580
581// Publicly exposed interface to pass...
582char &llvm::LowerSwitchID = LowerSwitchLegacyPass::ID;
583
584INITIALIZE_PASS_BEGIN(LowerSwitchLegacyPass, "lowerswitch",
585 "Lower SwitchInst's to branches", false, false)
586INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
587INITIALIZE_PASS_DEPENDENCY(LazyValueInfoWrapperPass)
588INITIALIZE_PASS_END(LowerSwitchLegacyPass, "lowerswitch",
589 "Lower SwitchInst's to branches", false, false)
590
591// createLowerSwitchPass - Interface to this file...
592FunctionPass *llvm::createLowerSwitchPass() {
593 return new LowerSwitchLegacyPass();
594}
595
596bool LowerSwitchLegacyPass::runOnFunction(Function &F) {
597 LazyValueInfo *LVI = &getAnalysis<LazyValueInfoWrapperPass>().getLVI();
598 auto *ACT = getAnalysisIfAvailable<AssumptionCacheTracker>();
599 AssumptionCache *AC = ACT ? &ACT->getAssumptionCache(F) : nullptr;
600 return LowerSwitch(F, LVI, AC);
601}
602
603PreservedAnalyses LowerSwitchPass::run(Function &F,
604 FunctionAnalysisManager &AM) {
605 LazyValueInfo *LVI = &AM.getResult<LazyValueAnalysis>(IR&: F);
606 AssumptionCache *AC = AM.getCachedResult<AssumptionAnalysis>(IR&: F);
607 return LowerSwitch(F, LVI, AC) ? PreservedAnalyses::none()
608 : PreservedAnalyses::all();
609}
610