1 //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Peephole optimize the CFG.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "simplifycfg"
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/Constants.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/Type.h"
19 #include "llvm/Support/CFG.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
28 /// SafeToMergeTerminators - Return true if it is safe to merge these two
29 /// terminator instructions together.
31 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
32 if (SI1 == SI2) return false; // Can't merge with self!
34 // It is not safe to merge these two switch instructions if they have a common
35 // successor, and if that successor has a PHI node, and if *that* PHI node has
36 // conflicting incoming values from the two switch blocks.
37 BasicBlock *SI1BB = SI1->getParent();
38 BasicBlock *SI2BB = SI2->getParent();
39 std::set<BasicBlock*> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
41 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
42 if (SI1Succs.count(*I))
43 for (BasicBlock::iterator BBI = (*I)->begin();
44 isa<PHINode>(BBI); ++BBI) {
45 PHINode *PN = cast<PHINode>(BBI);
46 if (PN->getIncomingValueForBlock(SI1BB) !=
47 PN->getIncomingValueForBlock(SI2BB))
54 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
55 /// now be entries in it from the 'NewPred' block. The values that will be
56 /// flowing into the PHI nodes will be the same as those coming in from
57 /// ExistPred, an existing predecessor of Succ.
58 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
59 BasicBlock *ExistPred) {
60 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
61 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
62 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
64 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
65 PHINode *PN = cast<PHINode>(I);
66 Value *V = PN->getIncomingValueForBlock(ExistPred);
67 PN->addIncoming(V, NewPred);
71 // CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
72 // almost-empty BB ending in an unconditional branch to Succ, into succ.
74 // Assumption: Succ is the single successor for BB.
76 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
77 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
79 // Check to see if one of the predecessors of BB is already a predecessor of
80 // Succ. If so, we cannot do the transformation if there are any PHI nodes
81 // with incompatible values coming in from the two edges!
83 if (isa<PHINode>(Succ->front())) {
84 std::set<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
85 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
87 if (std::find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) {
88 // Loop over all of the PHI nodes checking to see if there are
89 // incompatible values coming in.
90 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
91 PHINode *PN = cast<PHINode>(I);
92 // Loop up the entries in the PHI node for BB and for *PI if the
93 // values coming in are non-equal, we cannot merge these two blocks
94 // (instead we should insert a conditional move or something, then
96 if (PN->getIncomingValueForBlock(BB) !=
97 PN->getIncomingValueForBlock(*PI))
98 return false; // Values are not equal...
103 // Finally, if BB has PHI nodes that are used by things other than the PHIs in
104 // Succ and Succ has predecessors that are not Succ and not Pred, we cannot
105 // fold these blocks, as we don't know whether BB dominates Succ or not to
106 // update the PHI nodes correctly.
107 if (!isa<PHINode>(BB->begin()) || Succ->getSinglePredecessor()) return true;
109 // If the predecessors of Succ are only BB and Succ itself, we can handle this.
111 for (pred_iterator PI = pred_begin(Succ), E = pred_end(Succ); PI != E; ++PI)
112 if (*PI != Succ && *PI != BB) {
116 if (IsSafe) return true;
118 // If the PHI nodes in BB are only used by instructions in Succ, we are ok if
119 // BB and Succ have no common predecessors.
120 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I) && IsSafe; ++I) {
121 PHINode *PN = cast<PHINode>(I);
122 for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E;
124 if (cast<Instruction>(*UI)->getParent() != Succ)
128 // Scan the predecessor sets of BB and Succ, making sure there are no common
129 // predecessors. Common predecessors would cause us to build a phi node with
130 // differing incoming values, which is not legal.
131 std::set<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
132 for (pred_iterator PI = pred_begin(Succ), E = pred_end(Succ); PI != E; ++PI)
133 if (BBPreds.count(*PI))
139 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
140 /// branch to Succ, and contains no instructions other than PHI nodes and the
141 /// branch. If possible, eliminate BB.
142 static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
144 // If our successor has PHI nodes, then we need to update them to include
145 // entries for BB's predecessors, not for BB itself. Be careful though,
146 // if this transformation fails (returns true) then we cannot do this
149 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
151 DEBUG(std::cerr << "Killing Trivial BB: \n" << *BB);
153 if (isa<PHINode>(Succ->begin())) {
154 // If there is more than one pred of succ, and there are PHI nodes in
155 // the successor, then we need to add incoming edges for the PHI nodes
157 const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
159 // Loop over all of the PHI nodes in the successor of BB.
160 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
161 PHINode *PN = cast<PHINode>(I);
162 Value *OldVal = PN->removeIncomingValue(BB, false);
163 assert(OldVal && "No entry in PHI for Pred BB!");
165 // If this incoming value is one of the PHI nodes in BB, the new entries
166 // in the PHI node are the entries from the old PHI.
167 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
168 PHINode *OldValPN = cast<PHINode>(OldVal);
169 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
170 PN->addIncoming(OldValPN->getIncomingValue(i),
171 OldValPN->getIncomingBlock(i));
173 for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
174 End = BBPreds.end(); PredI != End; ++PredI) {
175 // Add an incoming value for each of the new incoming values...
176 PN->addIncoming(OldVal, *PredI);
182 if (isa<PHINode>(&BB->front())) {
183 std::vector<BasicBlock*>
184 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
186 // Move all PHI nodes in BB to Succ if they are alive, otherwise
188 while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
189 if (PN->use_empty()) {
190 // Just remove the dead phi. This happens if Succ's PHIs were the only
191 // users of the PHI nodes.
192 PN->eraseFromParent();
194 // The instruction is alive, so this means that Succ must have
195 // *ONLY* had BB as a predecessor, and the PHI node is still valid
196 // now. Simply move it into Succ, because we know that BB
197 // strictly dominated Succ.
198 Succ->getInstList().splice(Succ->begin(),
199 BB->getInstList(), BB->begin());
201 // We need to add new entries for the PHI node to account for
202 // predecessors of Succ that the PHI node does not take into
203 // account. At this point, since we know that BB dominated succ,
204 // this means that we should any newly added incoming edges should
205 // use the PHI node as the value for these edges, because they are
207 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
208 if (OldSuccPreds[i] != BB)
209 PN->addIncoming(PN, OldSuccPreds[i]);
213 // Everything that jumped to BB now goes to Succ.
214 std::string OldName = BB->getName();
215 BB->replaceAllUsesWith(Succ);
216 BB->eraseFromParent(); // Delete the old basic block.
218 if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can
219 Succ->setName(OldName);
223 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
224 /// presumably PHI nodes in it), check to see if the merge at this block is due
225 /// to an "if condition". If so, return the boolean condition that determines
226 /// which entry into BB will be taken. Also, return by references the block
227 /// that will be entered from if the condition is true, and the block that will
228 /// be entered if the condition is false.
231 static Value *GetIfCondition(BasicBlock *BB,
232 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
233 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
234 "Function can only handle blocks with 2 predecessors!");
235 BasicBlock *Pred1 = *pred_begin(BB);
236 BasicBlock *Pred2 = *++pred_begin(BB);
238 // We can only handle branches. Other control flow will be lowered to
239 // branches if possible anyway.
240 if (!isa<BranchInst>(Pred1->getTerminator()) ||
241 !isa<BranchInst>(Pred2->getTerminator()))
243 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
244 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
246 // Eliminate code duplication by ensuring that Pred1Br is conditional if
248 if (Pred2Br->isConditional()) {
249 // If both branches are conditional, we don't have an "if statement". In
250 // reality, we could transform this case, but since the condition will be
251 // required anyway, we stand no chance of eliminating it, so the xform is
252 // probably not profitable.
253 if (Pred1Br->isConditional())
256 std::swap(Pred1, Pred2);
257 std::swap(Pred1Br, Pred2Br);
260 if (Pred1Br->isConditional()) {
261 // If we found a conditional branch predecessor, make sure that it branches
262 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
263 if (Pred1Br->getSuccessor(0) == BB &&
264 Pred1Br->getSuccessor(1) == Pred2) {
267 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
268 Pred1Br->getSuccessor(1) == BB) {
272 // We know that one arm of the conditional goes to BB, so the other must
273 // go somewhere unrelated, and this must not be an "if statement".
277 // The only thing we have to watch out for here is to make sure that Pred2
278 // doesn't have incoming edges from other blocks. If it does, the condition
279 // doesn't dominate BB.
280 if (++pred_begin(Pred2) != pred_end(Pred2))
283 return Pred1Br->getCondition();
286 // Ok, if we got here, both predecessors end with an unconditional branch to
287 // BB. Don't panic! If both blocks only have a single (identical)
288 // predecessor, and THAT is a conditional branch, then we're all ok!
289 if (pred_begin(Pred1) == pred_end(Pred1) ||
290 ++pred_begin(Pred1) != pred_end(Pred1) ||
291 pred_begin(Pred2) == pred_end(Pred2) ||
292 ++pred_begin(Pred2) != pred_end(Pred2) ||
293 *pred_begin(Pred1) != *pred_begin(Pred2))
296 // Otherwise, if this is a conditional branch, then we can use it!
297 BasicBlock *CommonPred = *pred_begin(Pred1);
298 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
299 assert(BI->isConditional() && "Two successors but not conditional?");
300 if (BI->getSuccessor(0) == Pred1) {
307 return BI->getCondition();
313 // If we have a merge point of an "if condition" as accepted above, return true
314 // if the specified value dominates the block. We don't handle the true
315 // generality of domination here, just a special case which works well enough
318 // If AggressiveInsts is non-null, and if V does not dominate BB, we check to
319 // see if V (which must be an instruction) is cheap to compute and is
320 // non-trapping. If both are true, the instruction is inserted into the set and
322 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
323 std::set<Instruction*> *AggressiveInsts) {
324 Instruction *I = dyn_cast<Instruction>(V);
325 if (!I) return true; // Non-instructions all dominate instructions.
326 BasicBlock *PBB = I->getParent();
328 // We don't want to allow weird loops that might have the "if condition" in
329 // the bottom of this block.
330 if (PBB == BB) return false;
332 // If this instruction is defined in a block that contains an unconditional
333 // branch to BB, then it must be in the 'conditional' part of the "if
335 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
336 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
337 if (!AggressiveInsts) return false;
338 // Okay, it looks like the instruction IS in the "condition". Check to
339 // see if its a cheap instruction to unconditionally compute, and if it
340 // only uses stuff defined outside of the condition. If so, hoist it out.
341 switch (I->getOpcode()) {
342 default: return false; // Cannot hoist this out safely.
343 case Instruction::Load:
344 // We can hoist loads that are non-volatile and obviously cannot trap.
345 if (cast<LoadInst>(I)->isVolatile())
347 if (!isa<AllocaInst>(I->getOperand(0)) &&
348 !isa<Constant>(I->getOperand(0)))
351 // Finally, we have to check to make sure there are no instructions
352 // before the load in its basic block, as we are going to hoist the loop
353 // out to its predecessor.
354 if (PBB->begin() != BasicBlock::iterator(I))
357 case Instruction::Add:
358 case Instruction::Sub:
359 case Instruction::And:
360 case Instruction::Or:
361 case Instruction::Xor:
362 case Instruction::Shl:
363 case Instruction::Shr:
364 case Instruction::SetEQ:
365 case Instruction::SetNE:
366 case Instruction::SetLT:
367 case Instruction::SetGT:
368 case Instruction::SetLE:
369 case Instruction::SetGE:
370 break; // These are all cheap and non-trapping instructions.
373 // Okay, we can only really hoist these out if their operands are not
374 // defined in the conditional region.
375 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
376 if (!DominatesMergePoint(I->getOperand(i), BB, 0))
378 // Okay, it's safe to do this! Remember this instruction.
379 AggressiveInsts->insert(I);
385 // GatherConstantSetEQs - Given a potentially 'or'd together collection of seteq
386 // instructions that compare a value against a constant, return the value being
387 // compared, and stick the constant into the Values vector.
388 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
389 if (Instruction *Inst = dyn_cast<Instruction>(V))
390 if (Inst->getOpcode() == Instruction::SetEQ) {
391 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
393 return Inst->getOperand(0);
394 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
396 return Inst->getOperand(1);
398 } else if (Inst->getOpcode() == Instruction::Or) {
399 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
400 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
407 // GatherConstantSetNEs - Given a potentially 'and'd together collection of
408 // setne instructions that compare a value against a constant, return the value
409 // being compared, and stick the constant into the Values vector.
410 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
411 if (Instruction *Inst = dyn_cast<Instruction>(V))
412 if (Inst->getOpcode() == Instruction::SetNE) {
413 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
415 return Inst->getOperand(0);
416 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
418 return Inst->getOperand(1);
420 } else if (Inst->getOpcode() == Instruction::Cast) {
421 // Cast of X to bool is really a comparison against zero.
422 assert(Inst->getType() == Type::BoolTy && "Can only handle bool values!");
423 Values.push_back(ConstantInt::get(Inst->getOperand(0)->getType(), 0));
424 return Inst->getOperand(0);
425 } else if (Inst->getOpcode() == Instruction::And) {
426 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
427 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
436 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
437 /// bunch of comparisons of one value against constants, return the value and
438 /// the constants being compared.
439 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
440 std::vector<ConstantInt*> &Values) {
441 if (Cond->getOpcode() == Instruction::Or) {
442 CompVal = GatherConstantSetEQs(Cond, Values);
444 // Return true to indicate that the condition is true if the CompVal is
445 // equal to one of the constants.
447 } else if (Cond->getOpcode() == Instruction::And) {
448 CompVal = GatherConstantSetNEs(Cond, Values);
450 // Return false to indicate that the condition is false if the CompVal is
451 // equal to one of the constants.
457 /// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
458 /// has no side effects, nuke it. If it uses any instructions that become dead
459 /// because the instruction is now gone, nuke them too.
460 static void ErasePossiblyDeadInstructionTree(Instruction *I) {
461 if (isInstructionTriviallyDead(I)) {
462 std::vector<Value*> Operands(I->op_begin(), I->op_end());
463 I->getParent()->getInstList().erase(I);
464 for (unsigned i = 0, e = Operands.size(); i != e; ++i)
465 if (Instruction *OpI = dyn_cast<Instruction>(Operands[i]))
466 ErasePossiblyDeadInstructionTree(OpI);
470 // isValueEqualityComparison - Return true if the specified terminator checks to
471 // see if a value is equal to constant integer value.
472 static Value *isValueEqualityComparison(TerminatorInst *TI) {
473 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
474 // Do not permit merging of large switch instructions into their
475 // predecessors unless there is only one predecessor.
476 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
477 pred_end(SI->getParent())) > 128)
480 return SI->getCondition();
482 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
483 if (BI->isConditional() && BI->getCondition()->hasOneUse())
484 if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))
485 if ((SCI->getOpcode() == Instruction::SetEQ ||
486 SCI->getOpcode() == Instruction::SetNE) &&
487 isa<ConstantInt>(SCI->getOperand(1)))
488 return SCI->getOperand(0);
492 // Given a value comparison instruction, decode all of the 'cases' that it
493 // represents and return the 'default' block.
495 GetValueEqualityComparisonCases(TerminatorInst *TI,
496 std::vector<std::pair<ConstantInt*,
497 BasicBlock*> > &Cases) {
498 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
499 Cases.reserve(SI->getNumCases());
500 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
501 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
502 return SI->getDefaultDest();
505 BranchInst *BI = cast<BranchInst>(TI);
506 SetCondInst *SCI = cast<SetCondInst>(BI->getCondition());
507 Cases.push_back(std::make_pair(cast<ConstantInt>(SCI->getOperand(1)),
508 BI->getSuccessor(SCI->getOpcode() ==
509 Instruction::SetNE)));
510 return BI->getSuccessor(SCI->getOpcode() == Instruction::SetEQ);
514 // EliminateBlockCases - Given an vector of bb/value pairs, remove any entries
515 // in the list that match the specified block.
516 static void EliminateBlockCases(BasicBlock *BB,
517 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
518 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
519 if (Cases[i].second == BB) {
520 Cases.erase(Cases.begin()+i);
525 // ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
528 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
529 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
530 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
532 // Make V1 be smaller than V2.
533 if (V1->size() > V2->size())
536 if (V1->size() == 0) return false;
537 if (V1->size() == 1) {
539 ConstantInt *TheVal = (*V1)[0].first;
540 for (unsigned i = 0, e = V2->size(); i != e; ++i)
541 if (TheVal == (*V2)[i].first)
545 // Otherwise, just sort both lists and compare element by element.
546 std::sort(V1->begin(), V1->end());
547 std::sort(V2->begin(), V2->end());
548 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
549 while (i1 != e1 && i2 != e2) {
550 if ((*V1)[i1].first == (*V2)[i2].first)
552 if ((*V1)[i1].first < (*V2)[i2].first)
560 // SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
561 // terminator instruction and its block is known to only have a single
562 // predecessor block, check to see if that predecessor is also a value
563 // comparison with the same value, and if that comparison determines the outcome
564 // of this comparison. If so, simplify TI. This does a very limited form of
566 static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
568 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
569 if (!PredVal) return false; // Not a value comparison in predecessor.
571 Value *ThisVal = isValueEqualityComparison(TI);
572 assert(ThisVal && "This isn't a value comparison!!");
573 if (ThisVal != PredVal) return false; // Different predicates.
575 // Find out information about when control will move from Pred to TI's block.
576 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
577 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
579 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
581 // Find information about how control leaves this block.
582 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
583 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
584 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
586 // If TI's block is the default block from Pred's comparison, potentially
587 // simplify TI based on this knowledge.
588 if (PredDef == TI->getParent()) {
589 // If we are here, we know that the value is none of those cases listed in
590 // PredCases. If there are any cases in ThisCases that are in PredCases, we
592 if (ValuesOverlap(PredCases, ThisCases)) {
593 if (BranchInst *BTI = dyn_cast<BranchInst>(TI)) {
594 // Okay, one of the successors of this condbr is dead. Convert it to a
596 assert(ThisCases.size() == 1 && "Branch can only have one case!");
597 Value *Cond = BTI->getCondition();
598 // Insert the new branch.
599 Instruction *NI = new BranchInst(ThisDef, TI);
601 // Remove PHI node entries for the dead edge.
602 ThisCases[0].second->removePredecessor(TI->getParent());
604 DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator()
605 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
607 TI->eraseFromParent(); // Nuke the old one.
608 // If condition is now dead, nuke it.
609 if (Instruction *CondI = dyn_cast<Instruction>(Cond))
610 ErasePossiblyDeadInstructionTree(CondI);
614 SwitchInst *SI = cast<SwitchInst>(TI);
615 // Okay, TI has cases that are statically dead, prune them away.
616 std::set<Constant*> DeadCases;
617 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
618 DeadCases.insert(PredCases[i].first);
620 DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator()
621 << "Through successor TI: " << *TI);
623 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
624 if (DeadCases.count(SI->getCaseValue(i))) {
625 SI->getSuccessor(i)->removePredecessor(TI->getParent());
629 DEBUG(std::cerr << "Leaving: " << *TI << "\n");
635 // Otherwise, TI's block must correspond to some matched value. Find out
636 // which value (or set of values) this is.
637 ConstantInt *TIV = 0;
638 BasicBlock *TIBB = TI->getParent();
639 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
640 if (PredCases[i].second == TIBB)
642 TIV = PredCases[i].first;
644 return false; // Cannot handle multiple values coming to this block.
645 assert(TIV && "No edge from pred to succ?");
647 // Okay, we found the one constant that our value can be if we get into TI's
648 // BB. Find out which successor will unconditionally be branched to.
649 BasicBlock *TheRealDest = 0;
650 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
651 if (ThisCases[i].first == TIV) {
652 TheRealDest = ThisCases[i].second;
656 // If not handled by any explicit cases, it is handled by the default case.
657 if (TheRealDest == 0) TheRealDest = ThisDef;
659 // Remove PHI node entries for dead edges.
660 BasicBlock *CheckEdge = TheRealDest;
661 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
662 if (*SI != CheckEdge)
663 (*SI)->removePredecessor(TIBB);
667 // Insert the new branch.
668 Instruction *NI = new BranchInst(TheRealDest, TI);
670 DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator()
671 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
672 Instruction *Cond = 0;
673 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
674 Cond = dyn_cast<Instruction>(BI->getCondition());
675 TI->eraseFromParent(); // Nuke the old one.
677 if (Cond) ErasePossiblyDeadInstructionTree(Cond);
683 // FoldValueComparisonIntoPredecessors - The specified terminator is a value
684 // equality comparison instruction (either a switch or a branch on "X == c").
685 // See if any of the predecessors of the terminator block are value comparisons
686 // on the same value. If so, and if safe to do so, fold them together.
687 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
688 BasicBlock *BB = TI->getParent();
689 Value *CV = isValueEqualityComparison(TI); // CondVal
690 assert(CV && "Not a comparison?");
691 bool Changed = false;
693 std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
694 while (!Preds.empty()) {
695 BasicBlock *Pred = Preds.back();
698 // See if the predecessor is a comparison with the same value.
699 TerminatorInst *PTI = Pred->getTerminator();
700 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
702 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
703 // Figure out which 'cases' to copy from SI to PSI.
704 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
705 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
707 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
708 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
710 // Based on whether the default edge from PTI goes to BB or not, fill in
711 // PredCases and PredDefault with the new switch cases we would like to
713 std::vector<BasicBlock*> NewSuccessors;
715 if (PredDefault == BB) {
716 // If this is the default destination from PTI, only the edges in TI
717 // that don't occur in PTI, or that branch to BB will be activated.
718 std::set<ConstantInt*> PTIHandled;
719 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
720 if (PredCases[i].second != BB)
721 PTIHandled.insert(PredCases[i].first);
723 // The default destination is BB, we don't need explicit targets.
724 std::swap(PredCases[i], PredCases.back());
725 PredCases.pop_back();
729 // Reconstruct the new switch statement we will be building.
730 if (PredDefault != BBDefault) {
731 PredDefault->removePredecessor(Pred);
732 PredDefault = BBDefault;
733 NewSuccessors.push_back(BBDefault);
735 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
736 if (!PTIHandled.count(BBCases[i].first) &&
737 BBCases[i].second != BBDefault) {
738 PredCases.push_back(BBCases[i]);
739 NewSuccessors.push_back(BBCases[i].second);
743 // If this is not the default destination from PSI, only the edges
744 // in SI that occur in PSI with a destination of BB will be
746 std::set<ConstantInt*> PTIHandled;
747 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
748 if (PredCases[i].second == BB) {
749 PTIHandled.insert(PredCases[i].first);
750 std::swap(PredCases[i], PredCases.back());
751 PredCases.pop_back();
755 // Okay, now we know which constants were sent to BB from the
756 // predecessor. Figure out where they will all go now.
757 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
758 if (PTIHandled.count(BBCases[i].first)) {
759 // If this is one we are capable of getting...
760 PredCases.push_back(BBCases[i]);
761 NewSuccessors.push_back(BBCases[i].second);
762 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
765 // If there are any constants vectored to BB that TI doesn't handle,
766 // they must go to the default destination of TI.
767 for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
768 E = PTIHandled.end(); I != E; ++I) {
769 PredCases.push_back(std::make_pair(*I, BBDefault));
770 NewSuccessors.push_back(BBDefault);
774 // Okay, at this point, we know which new successor Pred will get. Make
775 // sure we update the number of entries in the PHI nodes for these
777 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
778 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
780 // Now that the successors are updated, create the new Switch instruction.
781 SwitchInst *NewSI = new SwitchInst(CV, PredDefault, PredCases.size(),PTI);
782 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
783 NewSI->addCase(PredCases[i].first, PredCases[i].second);
785 Instruction *DeadCond = 0;
786 if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
787 // If PTI is a branch, remember the condition.
788 DeadCond = dyn_cast<Instruction>(BI->getCondition());
789 Pred->getInstList().erase(PTI);
791 // If the condition is dead now, remove the instruction tree.
792 if (DeadCond) ErasePossiblyDeadInstructionTree(DeadCond);
794 // Okay, last check. If BB is still a successor of PSI, then we must
795 // have an infinite loop case. If so, add an infinitely looping block
796 // to handle the case to preserve the behavior of the code.
797 BasicBlock *InfLoopBlock = 0;
798 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
799 if (NewSI->getSuccessor(i) == BB) {
800 if (InfLoopBlock == 0) {
801 // Insert it at the end of the loop, because it's either code,
802 // or it won't matter if it's hot. :)
803 InfLoopBlock = new BasicBlock("infloop", BB->getParent());
804 new BranchInst(InfLoopBlock, InfLoopBlock);
806 NewSI->setSuccessor(i, InfLoopBlock);
815 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
816 /// BB2, hoist any common code in the two blocks up into the branch block. The
817 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
818 static bool HoistThenElseCodeToIf(BranchInst *BI) {
819 // This does very trivial matching, with limited scanning, to find identical
820 // instructions in the two blocks. In particular, we don't want to get into
821 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
822 // such, we currently just scan for obviously identical instructions in an
824 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
825 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
827 Instruction *I1 = BB1->begin(), *I2 = BB2->begin();
828 if (I1->getOpcode() != I2->getOpcode() || !I1->isIdenticalTo(I2) ||
832 // If we get here, we can hoist at least one instruction.
833 BasicBlock *BIParent = BI->getParent();
836 // If we are hoisting the terminator instruction, don't move one (making a
837 // broken BB), instead clone it, and remove BI.
838 if (isa<TerminatorInst>(I1))
839 goto HoistTerminator;
841 // For a normal instruction, we just move one to right before the branch,
842 // then replace all uses of the other with the first. Finally, we remove
843 // the now redundant second instruction.
844 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
845 if (!I2->use_empty())
846 I2->replaceAllUsesWith(I1);
847 BB2->getInstList().erase(I2);
851 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
856 // Okay, it is safe to hoist the terminator.
857 Instruction *NT = I1->clone();
858 BIParent->getInstList().insert(BI, NT);
859 if (NT->getType() != Type::VoidTy) {
860 I1->replaceAllUsesWith(NT);
861 I2->replaceAllUsesWith(NT);
862 NT->setName(I1->getName());
865 // Hoisting one of the terminators from our successor is a great thing.
866 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
867 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
868 // nodes, so we insert select instruction to compute the final result.
869 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
870 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
872 for (BasicBlock::iterator BBI = SI->begin();
873 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
874 Value *BB1V = PN->getIncomingValueForBlock(BB1);
875 Value *BB2V = PN->getIncomingValueForBlock(BB2);
877 // These values do not agree. Insert a select instruction before NT
878 // that determines the right value.
879 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
881 SI = new SelectInst(BI->getCondition(), BB1V, BB2V,
882 BB1V->getName()+"."+BB2V->getName(), NT);
883 // Make the PHI node use the select for all incoming values for BB1/BB2
884 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
885 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
886 PN->setIncomingValue(i, SI);
891 // Update any PHI nodes in our new successors.
892 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
893 AddPredecessorToBlock(*SI, BIParent, BB1);
895 BI->eraseFromParent();
899 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
900 /// across this block.
901 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
902 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
903 Value *Cond = BI->getCondition();
907 // If this basic block contains anything other than a PHI (which controls the
908 // branch) and branch itself, bail out. FIXME: improve this in the future.
909 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) {
910 if (Size > 10) return false; // Don't clone large BB's.
912 // We can only support instructions that are do not define values that are
913 // live outside of the current basic block.
914 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
916 Instruction *U = cast<Instruction>(*UI);
917 if (U->getParent() != BB || isa<PHINode>(U)) return false;
920 // Looks ok, continue checking.
926 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
927 /// that is defined in the same block as the branch and if any PHI entries are
928 /// constants, thread edges corresponding to that entry to be branches to their
929 /// ultimate destination.
930 static bool FoldCondBranchOnPHI(BranchInst *BI) {
931 BasicBlock *BB = BI->getParent();
932 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
933 // NOTE: we currently cannot transform this case if the PHI node is used
934 // outside of the block.
935 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
938 // Degenerate case of a single entry PHI.
939 if (PN->getNumIncomingValues() == 1) {
940 if (PN->getIncomingValue(0) != PN)
941 PN->replaceAllUsesWith(PN->getIncomingValue(0));
943 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
944 PN->eraseFromParent();
948 // Now we know that this block has multiple preds and two succs.
949 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
951 // Okay, this is a simple enough basic block. See if any phi values are
953 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
954 if (ConstantBool *CB = dyn_cast<ConstantBool>(PN->getIncomingValue(i))) {
955 // Okay, we now know that all edges from PredBB should be revectored to
956 // branch to RealDest.
957 BasicBlock *PredBB = PN->getIncomingBlock(i);
958 BasicBlock *RealDest = BI->getSuccessor(!CB->getValue());
960 if (RealDest == BB) continue; // Skip self loops.
962 // The dest block might have PHI nodes, other predecessors and other
963 // difficult cases. Instead of being smart about this, just insert a new
964 // block that jumps to the destination block, effectively splitting
965 // the edge we are about to create.
966 BasicBlock *EdgeBB = new BasicBlock(RealDest->getName()+".critedge",
967 RealDest->getParent(), RealDest);
968 new BranchInst(RealDest, EdgeBB);
970 for (BasicBlock::iterator BBI = RealDest->begin();
971 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
972 Value *V = PN->getIncomingValueForBlock(BB);
973 PN->addIncoming(V, EdgeBB);
976 // BB may have instructions that are being threaded over. Clone these
977 // instructions into EdgeBB. We know that there will be no uses of the
978 // cloned instructions outside of EdgeBB.
979 BasicBlock::iterator InsertPt = EdgeBB->begin();
980 std::map<Value*, Value*> TranslateMap; // Track translated values.
981 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
982 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
983 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
985 // Clone the instruction.
986 Instruction *N = BBI->clone();
987 if (BBI->hasName()) N->setName(BBI->getName()+".c");
989 // Update operands due to translation.
990 for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
991 std::map<Value*, Value*>::iterator PI =
992 TranslateMap.find(N->getOperand(i));
993 if (PI != TranslateMap.end())
994 N->setOperand(i, PI->second);
997 // Check for trivial simplification.
998 if (Constant *C = ConstantFoldInstruction(N)) {
999 TranslateMap[BBI] = C;
1000 delete N; // Constant folded away, don't need actual inst
1002 // Insert the new instruction into its new home.
1003 EdgeBB->getInstList().insert(InsertPt, N);
1004 if (!BBI->use_empty())
1005 TranslateMap[BBI] = N;
1010 // Loop over all of the edges from PredBB to BB, changing them to branch
1011 // to EdgeBB instead.
1012 TerminatorInst *PredBBTI = PredBB->getTerminator();
1013 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1014 if (PredBBTI->getSuccessor(i) == BB) {
1015 BB->removePredecessor(PredBB);
1016 PredBBTI->setSuccessor(i, EdgeBB);
1019 // Recurse, simplifying any other constants.
1020 return FoldCondBranchOnPHI(BI) | true;
1026 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1027 /// PHI node, see if we can eliminate it.
1028 static bool FoldTwoEntryPHINode(PHINode *PN) {
1029 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1030 // statement", which has a very simple dominance structure. Basically, we
1031 // are trying to find the condition that is being branched on, which
1032 // subsequently causes this merge to happen. We really want control
1033 // dependence information for this check, but simplifycfg can't keep it up
1034 // to date, and this catches most of the cases we care about anyway.
1036 BasicBlock *BB = PN->getParent();
1037 BasicBlock *IfTrue, *IfFalse;
1038 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1039 if (!IfCond) return false;
1041 DEBUG(std::cerr << "FOUND IF CONDITION! " << *IfCond << " T: "
1042 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1044 // Loop over the PHI's seeing if we can promote them all to select
1045 // instructions. While we are at it, keep track of the instructions
1046 // that need to be moved to the dominating block.
1047 std::set<Instruction*> AggressiveInsts;
1049 BasicBlock::iterator AfterPHIIt = BB->begin();
1050 while (isa<PHINode>(AfterPHIIt)) {
1051 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1052 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1053 if (PN->getIncomingValue(0) != PN)
1054 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1056 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1057 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1058 &AggressiveInsts) ||
1059 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1060 &AggressiveInsts)) {
1065 // If we all PHI nodes are promotable, check to make sure that all
1066 // instructions in the predecessor blocks can be promoted as well. If
1067 // not, we won't be able to get rid of the control flow, so it's not
1068 // worth promoting to select instructions.
1069 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1070 PN = cast<PHINode>(BB->begin());
1071 BasicBlock *Pred = PN->getIncomingBlock(0);
1072 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1074 DomBlock = *pred_begin(Pred);
1075 for (BasicBlock::iterator I = Pred->begin();
1076 !isa<TerminatorInst>(I); ++I)
1077 if (!AggressiveInsts.count(I)) {
1078 // This is not an aggressive instruction that we can promote.
1079 // Because of this, we won't be able to get rid of the control
1080 // flow, so the xform is not worth it.
1085 Pred = PN->getIncomingBlock(1);
1086 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1088 DomBlock = *pred_begin(Pred);
1089 for (BasicBlock::iterator I = Pred->begin();
1090 !isa<TerminatorInst>(I); ++I)
1091 if (!AggressiveInsts.count(I)) {
1092 // This is not an aggressive instruction that we can promote.
1093 // Because of this, we won't be able to get rid of the control
1094 // flow, so the xform is not worth it.
1099 // If we can still promote the PHI nodes after this gauntlet of tests,
1100 // do all of the PHI's now.
1102 // Move all 'aggressive' instructions, which are defined in the
1103 // conditional parts of the if's up to the dominating block.
1105 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1106 IfBlock1->getInstList(),
1108 IfBlock1->getTerminator());
1111 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1112 IfBlock2->getInstList(),
1114 IfBlock2->getTerminator());
1117 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1118 // Change the PHI node into a select instruction.
1120 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1122 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1124 std::string Name = PN->getName(); PN->setName("");
1125 PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal,
1127 BB->getInstList().erase(PN);
1133 /// ConstantIntOrdering - This class implements a stable ordering of constant
1134 /// integers that does not depend on their address. This is important for
1135 /// applications that sort ConstantInt's to ensure uniqueness.
1136 struct ConstantIntOrdering {
1137 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
1138 return LHS->getRawValue() < RHS->getRawValue();
1143 // SimplifyCFG - This function is used to do simplification of a CFG. For
1144 // example, it adjusts branches to branches to eliminate the extra hop, it
1145 // eliminates unreachable basic blocks, and does other "peephole" optimization
1146 // of the CFG. It returns true if a modification was made.
1148 // WARNING: The entry node of a function may not be simplified.
1150 bool llvm::SimplifyCFG(BasicBlock *BB) {
1151 bool Changed = false;
1152 Function *M = BB->getParent();
1154 assert(BB && BB->getParent() && "Block not embedded in function!");
1155 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1156 assert(&BB->getParent()->front() != BB && "Can't Simplify entry block!");
1158 // Remove basic blocks that have no predecessors... which are unreachable.
1159 if (pred_begin(BB) == pred_end(BB) ||
1160 *pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB)) {
1161 DEBUG(std::cerr << "Removing BB: \n" << *BB);
1163 // Loop through all of our successors and make sure they know that one
1164 // of their predecessors is going away.
1165 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
1166 SI->removePredecessor(BB);
1168 while (!BB->empty()) {
1169 Instruction &I = BB->back();
1170 // If this instruction is used, replace uses with an arbitrary
1171 // value. Because control flow can't get here, we don't care
1172 // what we replace the value with. Note that since this block is
1173 // unreachable, and all values contained within it must dominate their
1174 // uses, that all uses will eventually be removed.
1176 // Make all users of this instruction use undef instead
1177 I.replaceAllUsesWith(UndefValue::get(I.getType()));
1179 // Remove the instruction from the basic block
1180 BB->getInstList().pop_back();
1182 M->getBasicBlockList().erase(BB);
1186 // Check to see if we can constant propagate this terminator instruction
1188 Changed |= ConstantFoldTerminator(BB);
1190 // If this is a returning block with only PHI nodes in it, fold the return
1191 // instruction into any unconditional branch predecessors.
1193 // If any predecessor is a conditional branch that just selects among
1194 // different return values, fold the replace the branch/return with a select
1196 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1197 BasicBlock::iterator BBI = BB->getTerminator();
1198 if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
1199 // Find predecessors that end with branches.
1200 std::vector<BasicBlock*> UncondBranchPreds;
1201 std::vector<BranchInst*> CondBranchPreds;
1202 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1203 TerminatorInst *PTI = (*PI)->getTerminator();
1204 if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
1205 if (BI->isUnconditional())
1206 UncondBranchPreds.push_back(*PI);
1208 CondBranchPreds.push_back(BI);
1211 // If we found some, do the transformation!
1212 if (!UncondBranchPreds.empty()) {
1213 while (!UncondBranchPreds.empty()) {
1214 BasicBlock *Pred = UncondBranchPreds.back();
1215 DEBUG(std::cerr << "FOLDING: " << *BB
1216 << "INTO UNCOND BRANCH PRED: " << *Pred);
1217 UncondBranchPreds.pop_back();
1218 Instruction *UncondBranch = Pred->getTerminator();
1219 // Clone the return and add it to the end of the predecessor.
1220 Instruction *NewRet = RI->clone();
1221 Pred->getInstList().push_back(NewRet);
1223 // If the return instruction returns a value, and if the value was a
1224 // PHI node in "BB", propagate the right value into the return.
1225 if (NewRet->getNumOperands() == 1)
1226 if (PHINode *PN = dyn_cast<PHINode>(NewRet->getOperand(0)))
1227 if (PN->getParent() == BB)
1228 NewRet->setOperand(0, PN->getIncomingValueForBlock(Pred));
1229 // Update any PHI nodes in the returning block to realize that we no
1230 // longer branch to them.
1231 BB->removePredecessor(Pred);
1232 Pred->getInstList().erase(UncondBranch);
1235 // If we eliminated all predecessors of the block, delete the block now.
1236 if (pred_begin(BB) == pred_end(BB))
1237 // We know there are no successors, so just nuke the block.
1238 M->getBasicBlockList().erase(BB);
1243 // Check out all of the conditional branches going to this return
1244 // instruction. If any of them just select between returns, change the
1245 // branch itself into a select/return pair.
1246 while (!CondBranchPreds.empty()) {
1247 BranchInst *BI = CondBranchPreds.back();
1248 CondBranchPreds.pop_back();
1249 BasicBlock *TrueSucc = BI->getSuccessor(0);
1250 BasicBlock *FalseSucc = BI->getSuccessor(1);
1251 BasicBlock *OtherSucc = TrueSucc == BB ? FalseSucc : TrueSucc;
1253 // Check to see if the non-BB successor is also a return block.
1254 if (isa<ReturnInst>(OtherSucc->getTerminator())) {
1255 // Check to see if there are only PHI instructions in this block.
1256 BasicBlock::iterator OSI = OtherSucc->getTerminator();
1257 if (OSI == OtherSucc->begin() || isa<PHINode>(--OSI)) {
1258 // Okay, we found a branch that is going to two return nodes. If
1259 // there is no return value for this function, just change the
1260 // branch into a return.
1261 if (RI->getNumOperands() == 0) {
1262 TrueSucc->removePredecessor(BI->getParent());
1263 FalseSucc->removePredecessor(BI->getParent());
1264 new ReturnInst(0, BI);
1265 BI->getParent()->getInstList().erase(BI);
1269 // Otherwise, figure out what the true and false return values are
1270 // so we can insert a new select instruction.
1271 Value *TrueValue = TrueSucc->getTerminator()->getOperand(0);
1272 Value *FalseValue = FalseSucc->getTerminator()->getOperand(0);
1274 // Unwrap any PHI nodes in the return blocks.
1275 if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue))
1276 if (TVPN->getParent() == TrueSucc)
1277 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1278 if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue))
1279 if (FVPN->getParent() == FalseSucc)
1280 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1282 TrueSucc->removePredecessor(BI->getParent());
1283 FalseSucc->removePredecessor(BI->getParent());
1285 // Insert a new select instruction.
1287 Value *BrCond = BI->getCondition();
1288 if (TrueValue != FalseValue)
1289 NewRetVal = new SelectInst(BrCond, TrueValue,
1290 FalseValue, "retval", BI);
1292 NewRetVal = TrueValue;
1294 DEBUG(std::cerr << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1295 << "\n " << *BI << "Select = " << *NewRetVal
1296 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1298 new ReturnInst(NewRetVal, BI);
1299 BI->eraseFromParent();
1300 if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
1301 if (isInstructionTriviallyDead(BrCondI))
1302 BrCondI->eraseFromParent();
1308 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->begin())) {
1309 // Check to see if the first instruction in this block is just an unwind.
1310 // If so, replace any invoke instructions which use this as an exception
1311 // destination with call instructions, and any unconditional branch
1312 // predecessor with an unwind.
1314 std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
1315 while (!Preds.empty()) {
1316 BasicBlock *Pred = Preds.back();
1317 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1318 if (BI->isUnconditional()) {
1319 Pred->getInstList().pop_back(); // nuke uncond branch
1320 new UnwindInst(Pred); // Use unwind.
1323 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1324 if (II->getUnwindDest() == BB) {
1325 // Insert a new branch instruction before the invoke, because this
1326 // is now a fall through...
1327 BranchInst *BI = new BranchInst(II->getNormalDest(), II);
1328 Pred->getInstList().remove(II); // Take out of symbol table
1330 // Insert the call now...
1331 std::vector<Value*> Args(II->op_begin()+3, II->op_end());
1332 CallInst *CI = new CallInst(II->getCalledValue(), Args,
1334 CI->setCallingConv(II->getCallingConv());
1335 // If the invoke produced a value, the Call now does instead
1336 II->replaceAllUsesWith(CI);
1344 // If this block is now dead, remove it.
1345 if (pred_begin(BB) == pred_end(BB)) {
1346 // We know there are no successors, so just nuke the block.
1347 M->getBasicBlockList().erase(BB);
1351 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1352 if (isValueEqualityComparison(SI)) {
1353 // If we only have one predecessor, and if it is a branch on this value,
1354 // see if that predecessor totally determines the outcome of this switch.
1355 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1356 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1357 return SimplifyCFG(BB) || 1;
1359 // If the block only contains the switch, see if we can fold the block
1360 // away into any preds.
1361 if (SI == &BB->front())
1362 if (FoldValueComparisonIntoPredecessors(SI))
1363 return SimplifyCFG(BB) || 1;
1365 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1366 if (BI->isUnconditional()) {
1367 BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes...
1368 while (isa<PHINode>(*BBI)) ++BBI;
1370 BasicBlock *Succ = BI->getSuccessor(0);
1371 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1372 Succ != BB) // Don't hurt infinite loops!
1373 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1376 } else { // Conditional branch
1377 if (Value *CompVal = isValueEqualityComparison(BI)) {
1378 // If we only have one predecessor, and if it is a branch on this value,
1379 // see if that predecessor totally determines the outcome of this
1381 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1382 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1383 return SimplifyCFG(BB) || 1;
1385 // This block must be empty, except for the setcond inst, if it exists.
1386 BasicBlock::iterator I = BB->begin();
1388 (&*I == cast<Instruction>(BI->getCondition()) &&
1390 if (FoldValueComparisonIntoPredecessors(BI))
1391 return SimplifyCFG(BB) | true;
1394 // If this is a branch on a phi node in the current block, thread control
1395 // through this block if any PHI node entries are constants.
1396 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1397 if (PN->getParent() == BI->getParent())
1398 if (FoldCondBranchOnPHI(BI))
1399 return SimplifyCFG(BB) | true;
1401 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1402 // branches to us and one of our successors, fold the setcc into the
1403 // predecessor and use logical operations to pick the right destination.
1404 BasicBlock *TrueDest = BI->getSuccessor(0);
1405 BasicBlock *FalseDest = BI->getSuccessor(1);
1406 if (BinaryOperator *Cond = dyn_cast<BinaryOperator>(BI->getCondition()))
1407 if (Cond->getParent() == BB && &BB->front() == Cond &&
1408 Cond->getNext() == BI && Cond->hasOneUse() &&
1409 TrueDest != BB && FalseDest != BB)
1410 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI)
1411 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1412 if (PBI->isConditional() && SafeToMergeTerminators(BI, PBI)) {
1413 BasicBlock *PredBlock = *PI;
1414 if (PBI->getSuccessor(0) == FalseDest ||
1415 PBI->getSuccessor(1) == TrueDest) {
1416 // Invert the predecessors condition test (xor it with true),
1417 // which allows us to write this code once.
1419 BinaryOperator::createNot(PBI->getCondition(),
1420 PBI->getCondition()->getName()+".not", PBI);
1421 PBI->setCondition(NewCond);
1422 BasicBlock *OldTrue = PBI->getSuccessor(0);
1423 BasicBlock *OldFalse = PBI->getSuccessor(1);
1424 PBI->setSuccessor(0, OldFalse);
1425 PBI->setSuccessor(1, OldTrue);
1428 if (PBI->getSuccessor(0) == TrueDest ||
1429 PBI->getSuccessor(1) == FalseDest) {
1430 // Clone Cond into the predecessor basic block, and or/and the
1431 // two conditions together.
1432 Instruction *New = Cond->clone();
1433 New->setName(Cond->getName());
1434 Cond->setName(Cond->getName()+".old");
1435 PredBlock->getInstList().insert(PBI, New);
1436 Instruction::BinaryOps Opcode =
1437 PBI->getSuccessor(0) == TrueDest ?
1438 Instruction::Or : Instruction::And;
1440 BinaryOperator::create(Opcode, PBI->getCondition(),
1441 New, "bothcond", PBI);
1442 PBI->setCondition(NewCond);
1443 if (PBI->getSuccessor(0) == BB) {
1444 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1445 PBI->setSuccessor(0, TrueDest);
1447 if (PBI->getSuccessor(1) == BB) {
1448 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1449 PBI->setSuccessor(1, FalseDest);
1451 return SimplifyCFG(BB) | 1;
1455 // Scan predessor blocks for conditional branchs.
1456 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1457 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1458 if (PBI != BI && PBI->isConditional()) {
1460 // If this block ends with a branch instruction, and if there is a
1461 // predecessor that ends on a branch of the same condition, make this
1462 // conditional branch redundant.
1463 if (PBI->getCondition() == BI->getCondition() &&
1464 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1465 // Okay, the outcome of this conditional branch is statically
1466 // knowable. If this block had a single pred, handle specially.
1467 if (BB->getSinglePredecessor()) {
1468 // Turn this into a branch on constant.
1469 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1470 BI->setCondition(ConstantBool::get(CondIsTrue));
1471 return SimplifyCFG(BB); // Nuke the branch on constant.
1474 // Otherwise, if there are multiple predecessors, insert a PHI that
1475 // merges in the constant and simplify the block result.
1476 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1477 PHINode *NewPN = new PHINode(Type::BoolTy,
1478 BI->getCondition()->getName()+".pr",
1480 for (PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1481 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1482 PBI != BI && PBI->isConditional() &&
1483 PBI->getCondition() == BI->getCondition() &&
1484 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1485 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1486 NewPN->addIncoming(ConstantBool::get(CondIsTrue), *PI);
1488 NewPN->addIncoming(BI->getCondition(), *PI);
1491 BI->setCondition(NewPN);
1492 // This will thread the branch.
1493 return SimplifyCFG(BB) | true;
1497 // If this is a conditional branch in an empty block, and if any
1498 // predecessors is a conditional branch to one of our destinations,
1499 // fold the conditions into logical ops and one cond br.
1500 if (&BB->front() == BI) {
1502 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
1504 } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
1505 PBIOp = 0; BIOp = 1;
1506 } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
1507 PBIOp = 1; BIOp = 0;
1508 } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
1514 // Finally, if everything is ok, fold the branches to logical ops.
1516 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1517 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1519 DEBUG(std::cerr << "FOLDING BRs:" << *PBI->getParent()
1520 << "AND: " << *BI->getParent());
1522 // BI may have other predecessors. Because of this, we leave
1523 // it alone, but modify PBI.
1525 // Make sure we get to CommonDest on True&True directions.
1526 Value *PBICond = PBI->getCondition();
1528 PBICond = BinaryOperator::createNot(PBICond,
1529 PBICond->getName()+".not",
1531 Value *BICond = BI->getCondition();
1533 BICond = BinaryOperator::createNot(BICond,
1534 BICond->getName()+".not",
1536 // Merge the conditions.
1538 BinaryOperator::createOr(PBICond, BICond, "brmerge", PBI);
1540 // Modify PBI to branch on the new condition to the new dests.
1541 PBI->setCondition(Cond);
1542 PBI->setSuccessor(0, CommonDest);
1543 PBI->setSuccessor(1, OtherDest);
1545 // OtherDest may have phi nodes. If so, add an entry from PBI's
1546 // block that are identical to the entries for BI's block.
1548 for (BasicBlock::iterator II = OtherDest->begin();
1549 (PN = dyn_cast<PHINode>(II)); ++II) {
1550 Value *V = PN->getIncomingValueForBlock(BB);
1551 PN->addIncoming(V, PBI->getParent());
1554 // We know that the CommonDest already had an edge from PBI to
1555 // it. If it has PHIs though, the PHIs may have different
1556 // entries for BB and PBI's BB. If so, insert a select to make
1558 for (BasicBlock::iterator II = CommonDest->begin();
1559 (PN = dyn_cast<PHINode>(II)); ++II) {
1560 Value * BIV = PN->getIncomingValueForBlock(BB);
1561 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1562 Value *PBIV = PN->getIncomingValue(PBBIdx);
1564 // Insert a select in PBI to pick the right value.
1565 Value *NV = new SelectInst(PBICond, PBIV, BIV,
1566 PBIV->getName()+".mux", PBI);
1567 PN->setIncomingValue(PBBIdx, NV);
1571 DEBUG(std::cerr << "INTO: " << *PBI->getParent());
1573 // This basic block is probably dead. We know it has at least
1574 // one fewer predecessor.
1575 return SimplifyCFG(BB) | true;
1580 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1581 // If there are any instructions immediately before the unreachable that can
1582 // be removed, do so.
1583 Instruction *Unreachable = BB->getTerminator();
1584 while (Unreachable != BB->begin()) {
1585 BasicBlock::iterator BBI = Unreachable;
1587 if (isa<CallInst>(BBI)) break;
1588 // Delete this instruction
1589 BB->getInstList().erase(BBI);
1593 // If the unreachable instruction is the first in the block, take a gander
1594 // at all of the predecessors of this instruction, and simplify them.
1595 if (&BB->front() == Unreachable) {
1596 std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
1597 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1598 TerminatorInst *TI = Preds[i]->getTerminator();
1600 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1601 if (BI->isUnconditional()) {
1602 if (BI->getSuccessor(0) == BB) {
1603 new UnreachableInst(TI);
1604 TI->eraseFromParent();
1608 if (BI->getSuccessor(0) == BB) {
1609 new BranchInst(BI->getSuccessor(1), BI);
1610 BI->eraseFromParent();
1611 } else if (BI->getSuccessor(1) == BB) {
1612 new BranchInst(BI->getSuccessor(0), BI);
1613 BI->eraseFromParent();
1617 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1618 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1619 if (SI->getSuccessor(i) == BB) {
1620 BB->removePredecessor(SI->getParent());
1625 // If the default value is unreachable, figure out the most popular
1626 // destination and make it the default.
1627 if (SI->getSuccessor(0) == BB) {
1628 std::map<BasicBlock*, unsigned> Popularity;
1629 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1630 Popularity[SI->getSuccessor(i)]++;
1632 // Find the most popular block.
1633 unsigned MaxPop = 0;
1634 BasicBlock *MaxBlock = 0;
1635 for (std::map<BasicBlock*, unsigned>::iterator
1636 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
1637 if (I->second > MaxPop) {
1639 MaxBlock = I->first;
1643 // Make this the new default, allowing us to delete any explicit
1645 SI->setSuccessor(0, MaxBlock);
1648 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
1650 if (isa<PHINode>(MaxBlock->begin()))
1651 for (unsigned i = 0; i != MaxPop-1; ++i)
1652 MaxBlock->removePredecessor(SI->getParent());
1654 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1655 if (SI->getSuccessor(i) == MaxBlock) {
1661 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
1662 if (II->getUnwindDest() == BB) {
1663 // Convert the invoke to a call instruction. This would be a good
1664 // place to note that the call does not throw though.
1665 BranchInst *BI = new BranchInst(II->getNormalDest(), II);
1666 II->removeFromParent(); // Take out of symbol table
1668 // Insert the call now...
1669 std::vector<Value*> Args(II->op_begin()+3, II->op_end());
1670 CallInst *CI = new CallInst(II->getCalledValue(), Args,
1672 CI->setCallingConv(II->getCallingConv());
1673 // If the invoke produced a value, the Call does now instead.
1674 II->replaceAllUsesWith(CI);
1681 // If this block is now dead, remove it.
1682 if (pred_begin(BB) == pred_end(BB)) {
1683 // We know there are no successors, so just nuke the block.
1684 M->getBasicBlockList().erase(BB);
1690 // Merge basic blocks into their predecessor if there is only one distinct
1691 // pred, and if there is only one distinct successor of the predecessor, and
1692 // if there are no PHI nodes.
1694 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
1695 BasicBlock *OnlyPred = *PI++;
1696 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
1697 if (*PI != OnlyPred) {
1698 OnlyPred = 0; // There are multiple different predecessors...
1702 BasicBlock *OnlySucc = 0;
1703 if (OnlyPred && OnlyPred != BB && // Don't break self loops
1704 OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) {
1705 // Check to see if there is only one distinct successor...
1706 succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred));
1708 for (; SI != SE; ++SI)
1709 if (*SI != OnlySucc) {
1710 OnlySucc = 0; // There are multiple distinct successors!
1716 DEBUG(std::cerr << "Merging: " << *BB << "into: " << *OnlyPred);
1717 TerminatorInst *Term = OnlyPred->getTerminator();
1719 // Resolve any PHI nodes at the start of the block. They are all
1720 // guaranteed to have exactly one entry if they exist, unless there are
1721 // multiple duplicate (but guaranteed to be equal) entries for the
1722 // incoming edges. This occurs when there are multiple edges from
1723 // OnlyPred to OnlySucc.
1725 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
1726 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1727 BB->getInstList().pop_front(); // Delete the phi node...
1730 // Delete the unconditional branch from the predecessor...
1731 OnlyPred->getInstList().pop_back();
1733 // Move all definitions in the successor to the predecessor...
1734 OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
1736 // Make all PHI nodes that referred to BB now refer to Pred as their
1738 BB->replaceAllUsesWith(OnlyPred);
1740 std::string OldName = BB->getName();
1742 // Erase basic block from the function...
1743 M->getBasicBlockList().erase(BB);
1745 // Inherit predecessors name if it exists...
1746 if (!OldName.empty() && !OnlyPred->hasName())
1747 OnlyPred->setName(OldName);
1752 // Otherwise, if this block only has a single predecessor, and if that block
1753 // is a conditional branch, see if we can hoist any code from this block up
1754 // into our predecessor.
1756 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
1757 if (BI->isConditional()) {
1758 // Get the other block.
1759 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
1760 PI = pred_begin(OtherBB);
1762 if (PI == pred_end(OtherBB)) {
1763 // We have a conditional branch to two blocks that are only reachable
1764 // from the condbr. We know that the condbr dominates the two blocks,
1765 // so see if there is any identical code in the "then" and "else"
1766 // blocks. If so, we can hoist it up to the branching block.
1767 Changed |= HoistThenElseCodeToIf(BI);
1771 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1772 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1773 // Change br (X == 0 | X == 1), T, F into a switch instruction.
1774 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
1775 Instruction *Cond = cast<Instruction>(BI->getCondition());
1776 // If this is a bunch of seteq's or'd together, or if it's a bunch of
1777 // 'setne's and'ed together, collect them.
1779 std::vector<ConstantInt*> Values;
1780 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
1781 if (CompVal && CompVal->getType()->isInteger()) {
1782 // There might be duplicate constants in the list, which the switch
1783 // instruction can't handle, remove them now.
1784 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
1785 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
1787 // Figure out which block is which destination.
1788 BasicBlock *DefaultBB = BI->getSuccessor(1);
1789 BasicBlock *EdgeBB = BI->getSuccessor(0);
1790 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
1792 // Create the new switch instruction now.
1793 SwitchInst *New = new SwitchInst(CompVal, DefaultBB,Values.size(),BI);
1795 // Add all of the 'cases' to the switch instruction.
1796 for (unsigned i = 0, e = Values.size(); i != e; ++i)
1797 New->addCase(Values[i], EdgeBB);
1799 // We added edges from PI to the EdgeBB. As such, if there were any
1800 // PHI nodes in EdgeBB, they need entries to be added corresponding to
1801 // the number of edges added.
1802 for (BasicBlock::iterator BBI = EdgeBB->begin();
1803 isa<PHINode>(BBI); ++BBI) {
1804 PHINode *PN = cast<PHINode>(BBI);
1805 Value *InVal = PN->getIncomingValueForBlock(*PI);
1806 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
1807 PN->addIncoming(InVal, *PI);
1810 // Erase the old branch instruction.
1811 (*PI)->getInstList().erase(BI);
1813 // Erase the potentially condition tree that was used to computed the
1814 // branch condition.
1815 ErasePossiblyDeadInstructionTree(Cond);
1820 // If there is a trivial two-entry PHI node in this basic block, and we can
1821 // eliminate it, do so now.
1822 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1823 if (PN->getNumIncomingValues() == 2)
1824 Changed |= FoldTwoEntryPHINode(PN);