1 //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // 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/DerivedTypes.h"
20 #include "llvm/Support/CFG.h"
21 #include "llvm/Support/Debug.h"
22 #include "llvm/Analysis/ConstantFolding.h"
23 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
24 #include "llvm/ADT/SmallVector.h"
25 #include "llvm/ADT/SmallPtrSet.h"
26 #include "llvm/ADT/Statistic.h"
33 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
35 /// SafeToMergeTerminators - Return true if it is safe to merge these two
36 /// terminator instructions together.
38 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
39 if (SI1 == SI2) return false; // Can't merge with self!
41 // It is not safe to merge these two switch instructions if they have a common
42 // successor, and if that successor has a PHI node, and if *that* PHI node has
43 // conflicting incoming values from the two switch blocks.
44 BasicBlock *SI1BB = SI1->getParent();
45 BasicBlock *SI2BB = SI2->getParent();
46 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
48 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
49 if (SI1Succs.count(*I))
50 for (BasicBlock::iterator BBI = (*I)->begin();
51 isa<PHINode>(BBI); ++BBI) {
52 PHINode *PN = cast<PHINode>(BBI);
53 if (PN->getIncomingValueForBlock(SI1BB) !=
54 PN->getIncomingValueForBlock(SI2BB))
61 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
62 /// now be entries in it from the 'NewPred' block. The values that will be
63 /// flowing into the PHI nodes will be the same as those coming in from
64 /// ExistPred, an existing predecessor of Succ.
65 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
66 BasicBlock *ExistPred) {
67 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
68 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
69 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
72 for (BasicBlock::iterator I = Succ->begin();
73 (PN = dyn_cast<PHINode>(I)); ++I)
74 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
77 // CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
78 // almost-empty BB ending in an unconditional branch to Succ, into succ.
80 // Assumption: Succ is the single successor for BB.
82 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
83 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
85 DOUT << "Looking to fold " << BB->getNameStart() << " into "
86 << Succ->getNameStart() << "\n";
87 // Shortcut, if there is only a single predecessor is must be BB and merging
89 if (Succ->getSinglePredecessor()) return true;
91 typedef SmallPtrSet<Instruction*, 16> InstrSet;
94 // Make a list of all phi nodes in BB
95 BasicBlock::iterator BBI = BB->begin();
96 while (isa<PHINode>(*BBI)) BBPHIs.insert(BBI++);
98 // Make a list of the predecessors of BB
99 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
100 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
102 // Use that list to make another list of common predecessors of BB and Succ
103 BlockSet CommonPreds;
104 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
106 if (BBPreds.count(*PI))
107 CommonPreds.insert(*PI);
109 // Shortcut, if there are no common predecessors, merging is always safe
110 if (CommonPreds.empty())
113 // Look at all the phi nodes in Succ, to see if they present a conflict when
114 // merging these blocks
115 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
116 PHINode *PN = cast<PHINode>(I);
118 // If the incoming value from BB is again a PHINode in
119 // BB which has the same incoming value for *PI as PN does, we can
120 // merge the phi nodes and then the blocks can still be merged
121 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
122 if (BBPN && BBPN->getParent() == BB) {
123 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
125 if (BBPN->getIncomingValueForBlock(*PI)
126 != PN->getIncomingValueForBlock(*PI)) {
127 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
128 << Succ->getNameStart() << " is conflicting with "
129 << BBPN->getNameStart() << " with regard to common predecessor "
130 << (*PI)->getNameStart() << "\n";
134 // Remove this phinode from the list of phis in BB, since it has been
138 Value* Val = PN->getIncomingValueForBlock(BB);
139 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
141 // See if the incoming value for the common predecessor is equal to the
142 // one for BB, in which case this phi node will not prevent the merging
144 if (Val != PN->getIncomingValueForBlock(*PI)) {
145 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
146 << Succ->getNameStart() << " is conflicting with regard to common "
147 << "predecessor " << (*PI)->getNameStart() << "\n";
154 // If there are any other phi nodes in BB that don't have a phi node in Succ
155 // to merge with, they must be moved to Succ completely. However, for any
156 // predecessors of Succ, branches will be added to the phi node that just
157 // point to itself. So, for any common predecessors, this must not cause
159 for (InstrSet::iterator I = BBPHIs.begin(), E = BBPHIs.end();
161 PHINode *PN = cast<PHINode>(*I);
162 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
164 if (PN->getIncomingValueForBlock(*PI) != PN) {
165 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
166 << BB->getNameStart() << " is conflicting with regard to common "
167 << "predecessor " << (*PI)->getNameStart() << "\n";
175 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
176 /// branch to Succ, and contains no instructions other than PHI nodes and the
177 /// branch. If possible, eliminate BB.
178 static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
180 // Check to see if merging these blocks would cause conflicts for any of the
181 // phi nodes in BB or Succ. If not, we can safely merge.
182 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
184 DOUT << "Killing Trivial BB: \n" << *BB;
186 if (isa<PHINode>(Succ->begin())) {
187 // If there is more than one pred of succ, and there are PHI nodes in
188 // the successor, then we need to add incoming edges for the PHI nodes
190 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
192 // Loop over all of the PHI nodes in the successor of BB.
193 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
194 PHINode *PN = cast<PHINode>(I);
195 Value *OldVal = PN->removeIncomingValue(BB, false);
196 assert(OldVal && "No entry in PHI for Pred BB!");
198 // If this incoming value is one of the PHI nodes in BB, the new entries
199 // in the PHI node are the entries from the old PHI.
200 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
201 PHINode *OldValPN = cast<PHINode>(OldVal);
202 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
203 // Note that, since we are merging phi nodes and BB and Succ might
204 // have common predecessors, we could end up with a phi node with
205 // identical incoming branches. This will be cleaned up later (and
206 // will trigger asserts if we try to clean it up now, without also
207 // simplifying the corresponding conditional branch).
208 PN->addIncoming(OldValPN->getIncomingValue(i),
209 OldValPN->getIncomingBlock(i));
211 // Add an incoming value for each of the new incoming values.
212 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
213 PN->addIncoming(OldVal, BBPreds[i]);
218 if (isa<PHINode>(&BB->front())) {
219 SmallVector<BasicBlock*, 16>
220 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
222 // Move all PHI nodes in BB to Succ if they are alive, otherwise
224 while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
225 if (PN->use_empty()) {
226 // Just remove the dead phi. This happens if Succ's PHIs were the only
227 // users of the PHI nodes.
228 PN->eraseFromParent();
230 // The instruction is alive, so this means that BB must dominate all
231 // predecessors of Succ (Since all uses of the PN are after its
232 // definition, so in Succ or a block dominated by Succ. If a predecessor
233 // of Succ would not be dominated by BB, PN would violate the def before
234 // use SSA demand). Therefore, we can simply move the phi node to the
236 Succ->getInstList().splice(Succ->begin(),
237 BB->getInstList(), BB->begin());
239 // We need to add new entries for the PHI node to account for
240 // predecessors of Succ that the PHI node does not take into
241 // account. At this point, since we know that BB dominated succ and all
242 // of its predecessors, this means that we should any newly added
243 // incoming edges should use the PHI node itself as the value for these
244 // edges, because they are loop back edges.
245 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
246 if (OldSuccPreds[i] != BB)
247 PN->addIncoming(PN, OldSuccPreds[i]);
251 // Everything that jumped to BB now goes to Succ.
252 BB->replaceAllUsesWith(Succ);
253 if (!Succ->hasName()) Succ->takeName(BB);
254 BB->eraseFromParent(); // Delete the old basic block.
258 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
259 /// presumably PHI nodes in it), check to see if the merge at this block is due
260 /// to an "if condition". If so, return the boolean condition that determines
261 /// which entry into BB will be taken. Also, return by references the block
262 /// that will be entered from if the condition is true, and the block that will
263 /// be entered if the condition is false.
266 static Value *GetIfCondition(BasicBlock *BB,
267 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
268 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
269 "Function can only handle blocks with 2 predecessors!");
270 BasicBlock *Pred1 = *pred_begin(BB);
271 BasicBlock *Pred2 = *++pred_begin(BB);
273 // We can only handle branches. Other control flow will be lowered to
274 // branches if possible anyway.
275 if (!isa<BranchInst>(Pred1->getTerminator()) ||
276 !isa<BranchInst>(Pred2->getTerminator()))
278 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
279 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
281 // Eliminate code duplication by ensuring that Pred1Br is conditional if
283 if (Pred2Br->isConditional()) {
284 // If both branches are conditional, we don't have an "if statement". In
285 // reality, we could transform this case, but since the condition will be
286 // required anyway, we stand no chance of eliminating it, so the xform is
287 // probably not profitable.
288 if (Pred1Br->isConditional())
291 std::swap(Pred1, Pred2);
292 std::swap(Pred1Br, Pred2Br);
295 if (Pred1Br->isConditional()) {
296 // If we found a conditional branch predecessor, make sure that it branches
297 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
298 if (Pred1Br->getSuccessor(0) == BB &&
299 Pred1Br->getSuccessor(1) == Pred2) {
302 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
303 Pred1Br->getSuccessor(1) == BB) {
307 // We know that one arm of the conditional goes to BB, so the other must
308 // go somewhere unrelated, and this must not be an "if statement".
312 // The only thing we have to watch out for here is to make sure that Pred2
313 // doesn't have incoming edges from other blocks. If it does, the condition
314 // doesn't dominate BB.
315 if (++pred_begin(Pred2) != pred_end(Pred2))
318 return Pred1Br->getCondition();
321 // Ok, if we got here, both predecessors end with an unconditional branch to
322 // BB. Don't panic! If both blocks only have a single (identical)
323 // predecessor, and THAT is a conditional branch, then we're all ok!
324 if (pred_begin(Pred1) == pred_end(Pred1) ||
325 ++pred_begin(Pred1) != pred_end(Pred1) ||
326 pred_begin(Pred2) == pred_end(Pred2) ||
327 ++pred_begin(Pred2) != pred_end(Pred2) ||
328 *pred_begin(Pred1) != *pred_begin(Pred2))
331 // Otherwise, if this is a conditional branch, then we can use it!
332 BasicBlock *CommonPred = *pred_begin(Pred1);
333 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
334 assert(BI->isConditional() && "Two successors but not conditional?");
335 if (BI->getSuccessor(0) == Pred1) {
342 return BI->getCondition();
348 // If we have a merge point of an "if condition" as accepted above, return true
349 // if the specified value dominates the block. We don't handle the true
350 // generality of domination here, just a special case which works well enough
353 // If AggressiveInsts is non-null, and if V does not dominate BB, we check to
354 // see if V (which must be an instruction) is cheap to compute and is
355 // non-trapping. If both are true, the instruction is inserted into the set and
357 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
358 std::set<Instruction*> *AggressiveInsts) {
359 Instruction *I = dyn_cast<Instruction>(V);
361 // Non-instructions all dominate instructions, but not all constantexprs
362 // can be executed unconditionally.
363 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
368 BasicBlock *PBB = I->getParent();
370 // We don't want to allow weird loops that might have the "if condition" in
371 // the bottom of this block.
372 if (PBB == BB) return false;
374 // If this instruction is defined in a block that contains an unconditional
375 // branch to BB, then it must be in the 'conditional' part of the "if
377 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
378 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
379 if (!AggressiveInsts) return false;
380 // Okay, it looks like the instruction IS in the "condition". Check to
381 // see if its a cheap instruction to unconditionally compute, and if it
382 // only uses stuff defined outside of the condition. If so, hoist it out.
383 switch (I->getOpcode()) {
384 default: return false; // Cannot hoist this out safely.
385 case Instruction::Load:
386 // We can hoist loads that are non-volatile and obviously cannot trap.
387 if (cast<LoadInst>(I)->isVolatile())
389 if (!isa<AllocaInst>(I->getOperand(0)) &&
390 !isa<Constant>(I->getOperand(0)))
393 // Finally, we have to check to make sure there are no instructions
394 // before the load in its basic block, as we are going to hoist the loop
395 // out to its predecessor.
396 if (PBB->begin() != BasicBlock::iterator(I))
399 case Instruction::Add:
400 case Instruction::Sub:
401 case Instruction::And:
402 case Instruction::Or:
403 case Instruction::Xor:
404 case Instruction::Shl:
405 case Instruction::LShr:
406 case Instruction::AShr:
407 case Instruction::ICmp:
408 case Instruction::FCmp:
409 if (I->getOperand(0)->getType()->isFPOrFPVector())
410 return false; // FP arithmetic might trap.
411 break; // These are all cheap and non-trapping instructions.
414 // Okay, we can only really hoist these out if their operands are not
415 // defined in the conditional region.
416 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
417 if (!DominatesMergePoint(*i, BB, 0))
419 // Okay, it's safe to do this! Remember this instruction.
420 AggressiveInsts->insert(I);
426 // GatherConstantSetEQs - Given a potentially 'or'd together collection of
427 // icmp_eq instructions that compare a value against a constant, return the
428 // value being compared, and stick the constant into the Values vector.
429 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
430 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
431 if (Inst->getOpcode() == Instruction::ICmp &&
432 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
433 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
435 return Inst->getOperand(0);
436 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
438 return Inst->getOperand(1);
440 } else if (Inst->getOpcode() == Instruction::Or) {
441 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
442 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
450 // GatherConstantSetNEs - Given a potentially 'and'd together collection of
451 // setne instructions that compare a value against a constant, return the value
452 // being compared, and stick the constant into the Values vector.
453 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
454 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
455 if (Inst->getOpcode() == Instruction::ICmp &&
456 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
457 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
459 return Inst->getOperand(0);
460 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
462 return Inst->getOperand(1);
464 } else if (Inst->getOpcode() == Instruction::And) {
465 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
466 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
476 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
477 /// bunch of comparisons of one value against constants, return the value and
478 /// the constants being compared.
479 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
480 std::vector<ConstantInt*> &Values) {
481 if (Cond->getOpcode() == Instruction::Or) {
482 CompVal = GatherConstantSetEQs(Cond, Values);
484 // Return true to indicate that the condition is true if the CompVal is
485 // equal to one of the constants.
487 } else if (Cond->getOpcode() == Instruction::And) {
488 CompVal = GatherConstantSetNEs(Cond, Values);
490 // Return false to indicate that the condition is false if the CompVal is
491 // equal to one of the constants.
497 /// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
498 /// has no side effects, nuke it. If it uses any instructions that become dead
499 /// because the instruction is now gone, nuke them too.
500 static void ErasePossiblyDeadInstructionTree(Instruction *I) {
501 if (!isInstructionTriviallyDead(I)) return;
503 SmallVector<Instruction*, 16> InstrsToInspect;
504 InstrsToInspect.push_back(I);
506 while (!InstrsToInspect.empty()) {
507 I = InstrsToInspect.back();
508 InstrsToInspect.pop_back();
510 if (!isInstructionTriviallyDead(I)) continue;
512 // If I is in the work list multiple times, remove previous instances.
513 for (unsigned i = 0, e = InstrsToInspect.size(); i != e; ++i)
514 if (InstrsToInspect[i] == I) {
515 InstrsToInspect.erase(InstrsToInspect.begin()+i);
519 // Add operands of dead instruction to worklist.
520 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
521 if (Instruction *OpI = dyn_cast<Instruction>(*i))
522 InstrsToInspect.push_back(OpI);
524 // Remove dead instruction.
525 I->eraseFromParent();
529 // isValueEqualityComparison - Return true if the specified terminator checks to
530 // see if a value is equal to constant integer value.
531 static Value *isValueEqualityComparison(TerminatorInst *TI) {
532 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
533 // Do not permit merging of large switch instructions into their
534 // predecessors unless there is only one predecessor.
535 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
536 pred_end(SI->getParent())) > 128)
539 return SI->getCondition();
541 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
542 if (BI->isConditional() && BI->getCondition()->hasOneUse())
543 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
544 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
545 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
546 isa<ConstantInt>(ICI->getOperand(1)))
547 return ICI->getOperand(0);
551 // Given a value comparison instruction, decode all of the 'cases' that it
552 // represents and return the 'default' block.
554 GetValueEqualityComparisonCases(TerminatorInst *TI,
555 std::vector<std::pair<ConstantInt*,
556 BasicBlock*> > &Cases) {
557 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
558 Cases.reserve(SI->getNumCases());
559 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
560 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
561 return SI->getDefaultDest();
564 BranchInst *BI = cast<BranchInst>(TI);
565 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
566 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
567 BI->getSuccessor(ICI->getPredicate() ==
568 ICmpInst::ICMP_NE)));
569 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
573 // EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
574 // in the list that match the specified block.
575 static void EliminateBlockCases(BasicBlock *BB,
576 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
577 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
578 if (Cases[i].second == BB) {
579 Cases.erase(Cases.begin()+i);
584 // ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
587 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
588 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
589 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
591 // Make V1 be smaller than V2.
592 if (V1->size() > V2->size())
595 if (V1->size() == 0) return false;
596 if (V1->size() == 1) {
598 ConstantInt *TheVal = (*V1)[0].first;
599 for (unsigned i = 0, e = V2->size(); i != e; ++i)
600 if (TheVal == (*V2)[i].first)
604 // Otherwise, just sort both lists and compare element by element.
605 std::sort(V1->begin(), V1->end());
606 std::sort(V2->begin(), V2->end());
607 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
608 while (i1 != e1 && i2 != e2) {
609 if ((*V1)[i1].first == (*V2)[i2].first)
611 if ((*V1)[i1].first < (*V2)[i2].first)
619 // SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
620 // terminator instruction and its block is known to only have a single
621 // predecessor block, check to see if that predecessor is also a value
622 // comparison with the same value, and if that comparison determines the outcome
623 // of this comparison. If so, simplify TI. This does a very limited form of
625 static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
627 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
628 if (!PredVal) return false; // Not a value comparison in predecessor.
630 Value *ThisVal = isValueEqualityComparison(TI);
631 assert(ThisVal && "This isn't a value comparison!!");
632 if (ThisVal != PredVal) return false; // Different predicates.
634 // Find out information about when control will move from Pred to TI's block.
635 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
636 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
638 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
640 // Find information about how control leaves this block.
641 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
642 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
643 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
645 // If TI's block is the default block from Pred's comparison, potentially
646 // simplify TI based on this knowledge.
647 if (PredDef == TI->getParent()) {
648 // If we are here, we know that the value is none of those cases listed in
649 // PredCases. If there are any cases in ThisCases that are in PredCases, we
651 if (ValuesOverlap(PredCases, ThisCases)) {
652 if (BranchInst *BTI = dyn_cast<BranchInst>(TI)) {
653 // Okay, one of the successors of this condbr is dead. Convert it to a
655 assert(ThisCases.size() == 1 && "Branch can only have one case!");
656 Value *Cond = BTI->getCondition();
657 // Insert the new branch.
658 Instruction *NI = BranchInst::Create(ThisDef, TI);
660 // Remove PHI node entries for the dead edge.
661 ThisCases[0].second->removePredecessor(TI->getParent());
663 DOUT << "Threading pred instr: " << *Pred->getTerminator()
664 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
666 TI->eraseFromParent(); // Nuke the old one.
667 // If condition is now dead, nuke it.
668 if (Instruction *CondI = dyn_cast<Instruction>(Cond))
669 ErasePossiblyDeadInstructionTree(CondI);
673 SwitchInst *SI = cast<SwitchInst>(TI);
674 // Okay, TI has cases that are statically dead, prune them away.
675 SmallPtrSet<Constant*, 16> DeadCases;
676 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
677 DeadCases.insert(PredCases[i].first);
679 DOUT << "Threading pred instr: " << *Pred->getTerminator()
680 << "Through successor TI: " << *TI;
682 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
683 if (DeadCases.count(SI->getCaseValue(i))) {
684 SI->getSuccessor(i)->removePredecessor(TI->getParent());
688 DOUT << "Leaving: " << *TI << "\n";
694 // Otherwise, TI's block must correspond to some matched value. Find out
695 // which value (or set of values) this is.
696 ConstantInt *TIV = 0;
697 BasicBlock *TIBB = TI->getParent();
698 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
699 if (PredCases[i].second == TIBB) {
701 TIV = PredCases[i].first;
703 return false; // Cannot handle multiple values coming to this block.
705 assert(TIV && "No edge from pred to succ?");
707 // Okay, we found the one constant that our value can be if we get into TI's
708 // BB. Find out which successor will unconditionally be branched to.
709 BasicBlock *TheRealDest = 0;
710 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
711 if (ThisCases[i].first == TIV) {
712 TheRealDest = ThisCases[i].second;
716 // If not handled by any explicit cases, it is handled by the default case.
717 if (TheRealDest == 0) TheRealDest = ThisDef;
719 // Remove PHI node entries for dead edges.
720 BasicBlock *CheckEdge = TheRealDest;
721 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
722 if (*SI != CheckEdge)
723 (*SI)->removePredecessor(TIBB);
727 // Insert the new branch.
728 Instruction *NI = BranchInst::Create(TheRealDest, TI);
730 DOUT << "Threading pred instr: " << *Pred->getTerminator()
731 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
732 Instruction *Cond = 0;
733 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
734 Cond = dyn_cast<Instruction>(BI->getCondition());
735 TI->eraseFromParent(); // Nuke the old one.
737 if (Cond) ErasePossiblyDeadInstructionTree(Cond);
743 // FoldValueComparisonIntoPredecessors - The specified terminator is a value
744 // equality comparison instruction (either a switch or a branch on "X == c").
745 // See if any of the predecessors of the terminator block are value comparisons
746 // on the same value. If so, and if safe to do so, fold them together.
747 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
748 BasicBlock *BB = TI->getParent();
749 Value *CV = isValueEqualityComparison(TI); // CondVal
750 assert(CV && "Not a comparison?");
751 bool Changed = false;
753 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
754 while (!Preds.empty()) {
755 BasicBlock *Pred = Preds.back();
758 // See if the predecessor is a comparison with the same value.
759 TerminatorInst *PTI = Pred->getTerminator();
760 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
762 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
763 // Figure out which 'cases' to copy from SI to PSI.
764 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
765 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
767 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
768 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
770 // Based on whether the default edge from PTI goes to BB or not, fill in
771 // PredCases and PredDefault with the new switch cases we would like to
773 SmallVector<BasicBlock*, 8> NewSuccessors;
775 if (PredDefault == BB) {
776 // If this is the default destination from PTI, only the edges in TI
777 // that don't occur in PTI, or that branch to BB will be activated.
778 std::set<ConstantInt*> PTIHandled;
779 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
780 if (PredCases[i].second != BB)
781 PTIHandled.insert(PredCases[i].first);
783 // The default destination is BB, we don't need explicit targets.
784 std::swap(PredCases[i], PredCases.back());
785 PredCases.pop_back();
789 // Reconstruct the new switch statement we will be building.
790 if (PredDefault != BBDefault) {
791 PredDefault->removePredecessor(Pred);
792 PredDefault = BBDefault;
793 NewSuccessors.push_back(BBDefault);
795 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
796 if (!PTIHandled.count(BBCases[i].first) &&
797 BBCases[i].second != BBDefault) {
798 PredCases.push_back(BBCases[i]);
799 NewSuccessors.push_back(BBCases[i].second);
803 // If this is not the default destination from PSI, only the edges
804 // in SI that occur in PSI with a destination of BB will be
806 std::set<ConstantInt*> PTIHandled;
807 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
808 if (PredCases[i].second == BB) {
809 PTIHandled.insert(PredCases[i].first);
810 std::swap(PredCases[i], PredCases.back());
811 PredCases.pop_back();
815 // Okay, now we know which constants were sent to BB from the
816 // predecessor. Figure out where they will all go now.
817 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
818 if (PTIHandled.count(BBCases[i].first)) {
819 // If this is one we are capable of getting...
820 PredCases.push_back(BBCases[i]);
821 NewSuccessors.push_back(BBCases[i].second);
822 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
825 // If there are any constants vectored to BB that TI doesn't handle,
826 // they must go to the default destination of TI.
827 for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
828 E = PTIHandled.end(); I != E; ++I) {
829 PredCases.push_back(std::make_pair(*I, BBDefault));
830 NewSuccessors.push_back(BBDefault);
834 // Okay, at this point, we know which new successor Pred will get. Make
835 // sure we update the number of entries in the PHI nodes for these
837 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
838 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
840 // Now that the successors are updated, create the new Switch instruction.
841 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
842 PredCases.size(), PTI);
843 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
844 NewSI->addCase(PredCases[i].first, PredCases[i].second);
846 Instruction *DeadCond = 0;
847 if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
848 // If PTI is a branch, remember the condition.
849 DeadCond = dyn_cast<Instruction>(BI->getCondition());
850 Pred->getInstList().erase(PTI);
852 // If the condition is dead now, remove the instruction tree.
853 if (DeadCond) ErasePossiblyDeadInstructionTree(DeadCond);
855 // Okay, last check. If BB is still a successor of PSI, then we must
856 // have an infinite loop case. If so, add an infinitely looping block
857 // to handle the case to preserve the behavior of the code.
858 BasicBlock *InfLoopBlock = 0;
859 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
860 if (NewSI->getSuccessor(i) == BB) {
861 if (InfLoopBlock == 0) {
862 // Insert it at the end of the function, because it's either code,
863 // or it won't matter if it's hot. :)
864 InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
865 BranchInst::Create(InfLoopBlock, InfLoopBlock);
867 NewSI->setSuccessor(i, InfLoopBlock);
876 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
877 /// BB2, hoist any common code in the two blocks up into the branch block. The
878 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
879 static bool HoistThenElseCodeToIf(BranchInst *BI) {
880 // This does very trivial matching, with limited scanning, to find identical
881 // instructions in the two blocks. In particular, we don't want to get into
882 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
883 // such, we currently just scan for obviously identical instructions in an
885 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
886 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
888 Instruction *I1 = BB1->begin(), *I2 = BB2->begin();
889 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
890 isa<InvokeInst>(I1) || !I1->isIdenticalTo(I2))
893 // If we get here, we can hoist at least one instruction.
894 BasicBlock *BIParent = BI->getParent();
897 // If we are hoisting the terminator instruction, don't move one (making a
898 // broken BB), instead clone it, and remove BI.
899 if (isa<TerminatorInst>(I1))
900 goto HoistTerminator;
902 // For a normal instruction, we just move one to right before the branch,
903 // then replace all uses of the other with the first. Finally, we remove
904 // the now redundant second instruction.
905 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
906 if (!I2->use_empty())
907 I2->replaceAllUsesWith(I1);
908 BB2->getInstList().erase(I2);
912 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
917 // Okay, it is safe to hoist the terminator.
918 Instruction *NT = I1->clone();
919 BIParent->getInstList().insert(BI, NT);
920 if (NT->getType() != Type::VoidTy) {
921 I1->replaceAllUsesWith(NT);
922 I2->replaceAllUsesWith(NT);
926 // Hoisting one of the terminators from our successor is a great thing.
927 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
928 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
929 // nodes, so we insert select instruction to compute the final result.
930 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
931 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
933 for (BasicBlock::iterator BBI = SI->begin();
934 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
935 Value *BB1V = PN->getIncomingValueForBlock(BB1);
936 Value *BB2V = PN->getIncomingValueForBlock(BB2);
938 // These values do not agree. Insert a select instruction before NT
939 // that determines the right value.
940 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
942 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
943 BB1V->getName()+"."+BB2V->getName(), NT);
944 // Make the PHI node use the select for all incoming values for BB1/BB2
945 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
946 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
947 PN->setIncomingValue(i, SI);
952 // Update any PHI nodes in our new successors.
953 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
954 AddPredecessorToBlock(*SI, BIParent, BB1);
956 BI->eraseFromParent();
960 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
961 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
962 /// (for now, restricted to a single instruction that's side effect free) from
963 /// the BB1 into the branch block to speculatively execute it.
964 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
965 // Only speculatively execution a single instruction (not counting the
966 // terminator) for now.
967 BasicBlock::iterator BBI = BB1->begin();
968 ++BBI; // must have at least a terminator
969 if (BBI == BB1->end()) return false; // only one inst
971 if (BBI != BB1->end()) return false; // more than 2 insts.
973 // Be conservative for now. FP select instruction can often be expensive.
974 Value *BrCond = BI->getCondition();
975 if (isa<Instruction>(BrCond) &&
976 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
979 // If BB1 is actually on the false edge of the conditional branch, remember
980 // to swap the select operands later.
982 if (BB1 != BI->getSuccessor(0)) {
983 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
990 // br i1 %t1, label %BB1, label %BB2
999 // %t3 = select i1 %t1, %t2, %t3
1000 Instruction *I = BB1->begin();
1001 switch (I->getOpcode()) {
1002 default: return false; // Not safe / profitable to hoist.
1003 case Instruction::Add:
1004 case Instruction::Sub:
1005 case Instruction::And:
1006 case Instruction::Or:
1007 case Instruction::Xor:
1008 case Instruction::Shl:
1009 case Instruction::LShr:
1010 case Instruction::AShr:
1011 if (!I->getOperand(0)->getType()->isInteger())
1012 // FP arithmetic might trap. Not worth doing for vector ops.
1014 break; // These are all cheap and non-trapping instructions.
1017 // Can we speculatively execute the instruction? And what is the value
1018 // if the condition is false? Consider the phi uses, if the incoming value
1019 // from the "if" block are all the same V, then V is the value of the
1020 // select if the condition is false.
1021 BasicBlock *BIParent = BI->getParent();
1022 SmallVector<PHINode*, 4> PHIUses;
1023 Value *FalseV = NULL;
1024 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1026 PHINode *PN = dyn_cast<PHINode>(UI);
1029 PHIUses.push_back(PN);
1030 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1033 else if (FalseV != PHIV)
1034 return false; // Don't know the value when condition is false.
1036 if (!FalseV) // Can this happen?
1039 // Do not hoist the instruction if any of its operands are defined but not
1040 // used in this BB. The transformation will prevent the operand from
1041 // being sunk into the use block.
1042 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
1043 Instruction *OpI = dyn_cast<Instruction>(*i);
1044 if (OpI && OpI->getParent() == BIParent &&
1045 !OpI->isUsedInBasicBlock(BIParent))
1049 // If we get here, we can hoist the instruction. Try to place it
1050 // before the icmp instruction preceeding the conditional branch.
1051 BasicBlock::iterator InsertPos = BI;
1052 if (InsertPos != BIParent->begin())
1054 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1055 SmallPtrSet<Instruction *, 4> BB1Insns;
1056 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1057 BB1I != BB1E; ++BB1I)
1058 BB1Insns.insert(BB1I);
1059 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1061 Instruction *Use = cast<Instruction>(*UI);
1062 if (BB1Insns.count(Use)) {
1063 // If BrCond uses the instruction that place it just before
1064 // branch instruction.
1071 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), I);
1073 // Create a select whose true value is the speculatively executed value and
1074 // false value is the previously determined FalseV.
1077 SI = SelectInst::Create(BrCond, FalseV, I,
1078 FalseV->getName() + "." + I->getName(), BI);
1080 SI = SelectInst::Create(BrCond, I, FalseV,
1081 I->getName() + "." + FalseV->getName(), BI);
1083 // Make the PHI node use the select for all incoming values for "then" and
1085 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1086 PHINode *PN = PHIUses[i];
1087 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1088 if (PN->getIncomingBlock(j) == BB1 ||
1089 PN->getIncomingBlock(j) == BIParent)
1090 PN->setIncomingValue(j, SI);
1097 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1098 /// across this block.
1099 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1100 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1103 // If this basic block contains anything other than a PHI (which controls the
1104 // branch) and branch itself, bail out. FIXME: improve this in the future.
1105 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) {
1106 if (Size > 10) return false; // Don't clone large BB's.
1108 // We can only support instructions that are do not define values that are
1109 // live outside of the current basic block.
1110 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1112 Instruction *U = cast<Instruction>(*UI);
1113 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1116 // Looks ok, continue checking.
1122 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1123 /// that is defined in the same block as the branch and if any PHI entries are
1124 /// constants, thread edges corresponding to that entry to be branches to their
1125 /// ultimate destination.
1126 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1127 BasicBlock *BB = BI->getParent();
1128 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1129 // NOTE: we currently cannot transform this case if the PHI node is used
1130 // outside of the block.
1131 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1134 // Degenerate case of a single entry PHI.
1135 if (PN->getNumIncomingValues() == 1) {
1136 if (PN->getIncomingValue(0) != PN)
1137 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1139 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1140 PN->eraseFromParent();
1144 // Now we know that this block has multiple preds and two succs.
1145 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1147 // Okay, this is a simple enough basic block. See if any phi values are
1149 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1151 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1152 CB->getType() == Type::Int1Ty) {
1153 // Okay, we now know that all edges from PredBB should be revectored to
1154 // branch to RealDest.
1155 BasicBlock *PredBB = PN->getIncomingBlock(i);
1156 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1158 if (RealDest == BB) continue; // Skip self loops.
1160 // The dest block might have PHI nodes, other predecessors and other
1161 // difficult cases. Instead of being smart about this, just insert a new
1162 // block that jumps to the destination block, effectively splitting
1163 // the edge we are about to create.
1164 BasicBlock *EdgeBB = BasicBlock::Create(RealDest->getName()+".critedge",
1165 RealDest->getParent(), RealDest);
1166 BranchInst::Create(RealDest, EdgeBB);
1168 for (BasicBlock::iterator BBI = RealDest->begin();
1169 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1170 Value *V = PN->getIncomingValueForBlock(BB);
1171 PN->addIncoming(V, EdgeBB);
1174 // BB may have instructions that are being threaded over. Clone these
1175 // instructions into EdgeBB. We know that there will be no uses of the
1176 // cloned instructions outside of EdgeBB.
1177 BasicBlock::iterator InsertPt = EdgeBB->begin();
1178 std::map<Value*, Value*> TranslateMap; // Track translated values.
1179 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1180 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1181 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1183 // Clone the instruction.
1184 Instruction *N = BBI->clone();
1185 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1187 // Update operands due to translation.
1188 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1190 std::map<Value*, Value*>::iterator PI =
1191 TranslateMap.find(*i);
1192 if (PI != TranslateMap.end())
1196 // Check for trivial simplification.
1197 if (Constant *C = ConstantFoldInstruction(N)) {
1198 TranslateMap[BBI] = C;
1199 delete N; // Constant folded away, don't need actual inst
1201 // Insert the new instruction into its new home.
1202 EdgeBB->getInstList().insert(InsertPt, N);
1203 if (!BBI->use_empty())
1204 TranslateMap[BBI] = N;
1209 // Loop over all of the edges from PredBB to BB, changing them to branch
1210 // to EdgeBB instead.
1211 TerminatorInst *PredBBTI = PredBB->getTerminator();
1212 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1213 if (PredBBTI->getSuccessor(i) == BB) {
1214 BB->removePredecessor(PredBB);
1215 PredBBTI->setSuccessor(i, EdgeBB);
1218 // Recurse, simplifying any other constants.
1219 return FoldCondBranchOnPHI(BI) | true;
1226 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1227 /// PHI node, see if we can eliminate it.
1228 static bool FoldTwoEntryPHINode(PHINode *PN) {
1229 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1230 // statement", which has a very simple dominance structure. Basically, we
1231 // are trying to find the condition that is being branched on, which
1232 // subsequently causes this merge to happen. We really want control
1233 // dependence information for this check, but simplifycfg can't keep it up
1234 // to date, and this catches most of the cases we care about anyway.
1236 BasicBlock *BB = PN->getParent();
1237 BasicBlock *IfTrue, *IfFalse;
1238 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1239 if (!IfCond) return false;
1241 // Okay, we found that we can merge this two-entry phi node into a select.
1242 // Doing so would require us to fold *all* two entry phi nodes in this block.
1243 // At some point this becomes non-profitable (particularly if the target
1244 // doesn't support cmov's). Only do this transformation if there are two or
1245 // fewer PHI nodes in this block.
1246 unsigned NumPhis = 0;
1247 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1251 DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
1252 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
1254 // Loop over the PHI's seeing if we can promote them all to select
1255 // instructions. While we are at it, keep track of the instructions
1256 // that need to be moved to the dominating block.
1257 std::set<Instruction*> AggressiveInsts;
1259 BasicBlock::iterator AfterPHIIt = BB->begin();
1260 while (isa<PHINode>(AfterPHIIt)) {
1261 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1262 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1263 if (PN->getIncomingValue(0) != PN)
1264 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1266 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1267 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1268 &AggressiveInsts) ||
1269 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1270 &AggressiveInsts)) {
1275 // If we all PHI nodes are promotable, check to make sure that all
1276 // instructions in the predecessor blocks can be promoted as well. If
1277 // not, we won't be able to get rid of the control flow, so it's not
1278 // worth promoting to select instructions.
1279 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1280 PN = cast<PHINode>(BB->begin());
1281 BasicBlock *Pred = PN->getIncomingBlock(0);
1282 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1284 DomBlock = *pred_begin(Pred);
1285 for (BasicBlock::iterator I = Pred->begin();
1286 !isa<TerminatorInst>(I); ++I)
1287 if (!AggressiveInsts.count(I)) {
1288 // This is not an aggressive instruction that we can promote.
1289 // Because of this, we won't be able to get rid of the control
1290 // flow, so the xform is not worth it.
1295 Pred = PN->getIncomingBlock(1);
1296 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1298 DomBlock = *pred_begin(Pred);
1299 for (BasicBlock::iterator I = Pred->begin();
1300 !isa<TerminatorInst>(I); ++I)
1301 if (!AggressiveInsts.count(I)) {
1302 // This is not an aggressive instruction that we can promote.
1303 // Because of this, we won't be able to get rid of the control
1304 // flow, so the xform is not worth it.
1309 // If we can still promote the PHI nodes after this gauntlet of tests,
1310 // do all of the PHI's now.
1312 // Move all 'aggressive' instructions, which are defined in the
1313 // conditional parts of the if's up to the dominating block.
1315 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1316 IfBlock1->getInstList(),
1318 IfBlock1->getTerminator());
1321 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1322 IfBlock2->getInstList(),
1324 IfBlock2->getTerminator());
1327 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1328 // Change the PHI node into a select instruction.
1330 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1332 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1334 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1335 PN->replaceAllUsesWith(NV);
1338 BB->getInstList().erase(PN);
1343 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1344 /// to two returning blocks, try to merge them together into one return,
1345 /// introducing a select if the return values disagree.
1346 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1347 assert(BI->isConditional() && "Must be a conditional branch");
1348 BasicBlock *TrueSucc = BI->getSuccessor(0);
1349 BasicBlock *FalseSucc = BI->getSuccessor(1);
1350 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1351 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1353 // Check to ensure both blocks are empty (just a return) or optionally empty
1354 // with PHI nodes. If there are other instructions, merging would cause extra
1355 // computation on one path or the other.
1356 BasicBlock::iterator BBI = TrueRet;
1357 if (BBI != TrueSucc->begin() && !isa<PHINode>(--BBI))
1358 return false; // Not empty with optional phi nodes.
1360 if (BBI != FalseSucc->begin() && !isa<PHINode>(--BBI))
1361 return false; // Not empty with optional phi nodes.
1363 // Okay, we found a branch that is going to two return nodes. If
1364 // there is no return value for this function, just change the
1365 // branch into a return.
1366 if (FalseRet->getNumOperands() == 0) {
1367 TrueSucc->removePredecessor(BI->getParent());
1368 FalseSucc->removePredecessor(BI->getParent());
1369 ReturnInst::Create(0, BI);
1370 BI->eraseFromParent();
1374 // Otherwise, figure out what the true and false return values are
1375 // so we can insert a new select instruction.
1376 Value *TrueValue = TrueRet->getReturnValue();
1377 Value *FalseValue = FalseRet->getReturnValue();
1379 // Unwrap any PHI nodes in the return blocks.
1380 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1381 if (TVPN->getParent() == TrueSucc)
1382 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1383 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1384 if (FVPN->getParent() == FalseSucc)
1385 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1387 // In order for this transformation to be safe, we must be able to
1388 // unconditionally execute both operands to the return. This is
1389 // normally the case, but we could have a potentially-trapping
1390 // constant expression that prevents this transformation from being
1392 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1395 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1399 // Okay, we collected all the mapped values and checked them for sanity, and
1400 // defined to really do this transformation. First, update the CFG.
1401 TrueSucc->removePredecessor(BI->getParent());
1402 FalseSucc->removePredecessor(BI->getParent());
1404 // Insert select instructions where needed.
1405 Value *BrCond = BI->getCondition();
1407 // Insert a select if the results differ.
1408 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1409 } else if (isa<UndefValue>(TrueValue)) {
1410 TrueValue = FalseValue;
1412 TrueValue = SelectInst::Create(BrCond, TrueValue,
1413 FalseValue, "retval", BI);
1417 Value *RI = !TrueValue ?
1418 ReturnInst::Create(BI) :
1419 ReturnInst::Create(TrueValue, BI);
1421 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1422 << "\n " << *BI << "NewRet = " << *RI
1423 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
1425 BI->eraseFromParent();
1427 if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
1428 ErasePossiblyDeadInstructionTree(BrCondI);
1432 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1433 /// and if a predecessor branches to us and one of our successors, fold the
1434 /// setcc into the predecessor and use logical operations to pick the right
1436 static bool FoldBranchToCommonDest(BranchInst *BI) {
1437 BasicBlock *BB = BI->getParent();
1438 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1439 if (Cond == 0) return false;
1442 // Only allow this if the condition is a simple instruction that can be
1443 // executed unconditionally. It must be in the same block as the branch, and
1444 // must be at the front of the block.
1445 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1446 Cond->getParent() != BB || &BB->front() != Cond || !Cond->hasOneUse())
1449 // Make sure the instruction after the condition is the cond branch.
1450 BasicBlock::iterator CondIt = Cond; ++CondIt;
1454 // Finally, don't infinitely unroll conditional loops.
1455 BasicBlock *TrueDest = BI->getSuccessor(0);
1456 BasicBlock *FalseDest = BI->getSuccessor(1);
1457 if (TrueDest == BB || FalseDest == BB)
1460 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1461 BasicBlock *PredBlock = *PI;
1462 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1463 // Check that we have two conditional branches. If there is a PHI node in
1464 // the common successor, verify that the same value flows in from both
1466 if (PBI == 0 || PBI->isUnconditional() ||
1467 !SafeToMergeTerminators(BI, PBI))
1470 Instruction::BinaryOps Opc;
1471 bool InvertPredCond = false;
1473 if (PBI->getSuccessor(0) == TrueDest)
1474 Opc = Instruction::Or;
1475 else if (PBI->getSuccessor(1) == FalseDest)
1476 Opc = Instruction::And;
1477 else if (PBI->getSuccessor(0) == FalseDest)
1478 Opc = Instruction::And, InvertPredCond = true;
1479 else if (PBI->getSuccessor(1) == TrueDest)
1480 Opc = Instruction::Or, InvertPredCond = true;
1484 // If we need to invert the condition in the pred block to match, do so now.
1485 if (InvertPredCond) {
1487 BinaryOperator::CreateNot(PBI->getCondition(),
1488 PBI->getCondition()->getName()+".not", PBI);
1489 PBI->setCondition(NewCond);
1490 BasicBlock *OldTrue = PBI->getSuccessor(0);
1491 BasicBlock *OldFalse = PBI->getSuccessor(1);
1492 PBI->setSuccessor(0, OldFalse);
1493 PBI->setSuccessor(1, OldTrue);
1496 // Clone Cond into the predecessor basic block, and or/and the
1497 // two conditions together.
1498 Instruction *New = Cond->clone();
1499 PredBlock->getInstList().insert(PBI, New);
1500 New->takeName(Cond);
1501 Cond->setName(New->getName()+".old");
1503 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1504 New, "or.cond", PBI);
1505 PBI->setCondition(NewCond);
1506 if (PBI->getSuccessor(0) == BB) {
1507 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1508 PBI->setSuccessor(0, TrueDest);
1510 if (PBI->getSuccessor(1) == BB) {
1511 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1512 PBI->setSuccessor(1, FalseDest);
1519 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1520 /// predecessor of another block, this function tries to simplify it. We know
1521 /// that PBI and BI are both conditional branches, and BI is in one of the
1522 /// successor blocks of PBI - PBI branches to BI.
1523 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1524 assert(PBI->isConditional() && BI->isConditional());
1525 BasicBlock *BB = BI->getParent();
1527 // If this block ends with a branch instruction, and if there is a
1528 // predecessor that ends on a branch of the same condition, make
1529 // this conditional branch redundant.
1530 if (PBI->getCondition() == BI->getCondition() &&
1531 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1532 // Okay, the outcome of this conditional branch is statically
1533 // knowable. If this block had a single pred, handle specially.
1534 if (BB->getSinglePredecessor()) {
1535 // Turn this into a branch on constant.
1536 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1537 BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
1538 return true; // Nuke the branch on constant.
1541 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1542 // in the constant and simplify the block result. Subsequent passes of
1543 // simplifycfg will thread the block.
1544 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1545 PHINode *NewPN = PHINode::Create(Type::Int1Ty,
1546 BI->getCondition()->getName() + ".pr",
1548 // Okay, we're going to insert the PHI node. Since PBI is not the only
1549 // predecessor, compute the PHI'd conditional value for all of the preds.
1550 // Any predecessor where the condition is not computable we keep symbolic.
1551 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1552 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1553 PBI != BI && PBI->isConditional() &&
1554 PBI->getCondition() == BI->getCondition() &&
1555 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1556 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1557 NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
1560 NewPN->addIncoming(BI->getCondition(), *PI);
1563 BI->setCondition(NewPN);
1568 // If this is a conditional branch in an empty block, and if any
1569 // predecessors is a conditional branch to one of our destinations,
1570 // fold the conditions into logical ops and one cond br.
1571 if (&BB->front() != BI)
1575 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1577 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1578 PBIOp = 0, BIOp = 1;
1579 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1580 PBIOp = 1, BIOp = 0;
1581 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1586 // Check to make sure that the other destination of this branch
1587 // isn't BB itself. If so, this is an infinite loop that will
1588 // keep getting unwound.
1589 if (PBI->getSuccessor(PBIOp) == BB)
1592 // Do not perform this transformation if it would require
1593 // insertion of a large number of select instructions. For targets
1594 // without predication/cmovs, this is a big pessimization.
1595 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1597 unsigned NumPhis = 0;
1598 for (BasicBlock::iterator II = CommonDest->begin();
1599 isa<PHINode>(II); ++II, ++NumPhis)
1600 if (NumPhis > 2) // Disable this xform.
1603 // Finally, if everything is ok, fold the branches to logical ops.
1604 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1606 DOUT << "FOLDING BRs:" << *PBI->getParent()
1607 << "AND: " << *BI->getParent();
1610 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1611 // branch in it, where one edge (OtherDest) goes back to itself but the other
1612 // exits. We don't *know* that the program avoids the infinite loop
1613 // (even though that seems likely). If we do this xform naively, we'll end up
1614 // recursively unpeeling the loop. Since we know that (after the xform is
1615 // done) that the block *is* infinite if reached, we just make it an obviously
1616 // infinite loop with no cond branch.
1617 if (OtherDest == BB) {
1618 // Insert it at the end of the function, because it's either code,
1619 // or it won't matter if it's hot. :)
1620 BasicBlock *InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
1621 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1622 OtherDest = InfLoopBlock;
1625 DOUT << *PBI->getParent()->getParent();
1627 // BI may have other predecessors. Because of this, we leave
1628 // it alone, but modify PBI.
1630 // Make sure we get to CommonDest on True&True directions.
1631 Value *PBICond = PBI->getCondition();
1633 PBICond = BinaryOperator::CreateNot(PBICond,
1634 PBICond->getName()+".not",
1636 Value *BICond = BI->getCondition();
1638 BICond = BinaryOperator::CreateNot(BICond,
1639 BICond->getName()+".not",
1641 // Merge the conditions.
1642 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1644 // Modify PBI to branch on the new condition to the new dests.
1645 PBI->setCondition(Cond);
1646 PBI->setSuccessor(0, CommonDest);
1647 PBI->setSuccessor(1, OtherDest);
1649 // OtherDest may have phi nodes. If so, add an entry from PBI's
1650 // block that are identical to the entries for BI's block.
1652 for (BasicBlock::iterator II = OtherDest->begin();
1653 (PN = dyn_cast<PHINode>(II)); ++II) {
1654 Value *V = PN->getIncomingValueForBlock(BB);
1655 PN->addIncoming(V, PBI->getParent());
1658 // We know that the CommonDest already had an edge from PBI to
1659 // it. If it has PHIs though, the PHIs may have different
1660 // entries for BB and PBI's BB. If so, insert a select to make
1662 for (BasicBlock::iterator II = CommonDest->begin();
1663 (PN = dyn_cast<PHINode>(II)); ++II) {
1664 Value *BIV = PN->getIncomingValueForBlock(BB);
1665 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1666 Value *PBIV = PN->getIncomingValue(PBBIdx);
1668 // Insert a select in PBI to pick the right value.
1669 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1670 PBIV->getName()+".mux", PBI);
1671 PN->setIncomingValue(PBBIdx, NV);
1675 DOUT << "INTO: " << *PBI->getParent();
1677 DOUT << *PBI->getParent()->getParent();
1679 // This basic block is probably dead. We know it has at least
1680 // one fewer predecessor.
1686 /// ConstantIntOrdering - This class implements a stable ordering of constant
1687 /// integers that does not depend on their address. This is important for
1688 /// applications that sort ConstantInt's to ensure uniqueness.
1689 struct ConstantIntOrdering {
1690 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
1691 return LHS->getValue().ult(RHS->getValue());
1696 // SimplifyCFG - This function is used to do simplification of a CFG. For
1697 // example, it adjusts branches to branches to eliminate the extra hop, it
1698 // eliminates unreachable basic blocks, and does other "peephole" optimization
1699 // of the CFG. It returns true if a modification was made.
1701 // WARNING: The entry node of a function may not be simplified.
1703 bool llvm::SimplifyCFG(BasicBlock *BB) {
1704 bool Changed = false;
1705 Function *M = BB->getParent();
1707 assert(BB && BB->getParent() && "Block not embedded in function!");
1708 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1709 assert(&BB->getParent()->getEntryBlock() != BB &&
1710 "Can't Simplify entry block!");
1712 // Remove basic blocks that have no predecessors... or that just have themself
1713 // as a predecessor. These are unreachable.
1714 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1715 DOUT << "Removing BB: \n" << *BB;
1717 // Loop through all of our successors and make sure they know that one
1718 // of their predecessors is going away.
1719 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
1720 SI->removePredecessor(BB);
1722 while (!BB->empty()) {
1723 Instruction &I = BB->back();
1724 // If this instruction is used, replace uses with an arbitrary
1725 // value. Because control flow can't get here, we don't care
1726 // what we replace the value with. Note that since this block is
1727 // unreachable, and all values contained within it must dominate their
1728 // uses, that all uses will eventually be removed.
1730 // Make all users of this instruction use undef instead
1731 I.replaceAllUsesWith(UndefValue::get(I.getType()));
1733 // Remove the instruction from the basic block
1734 BB->getInstList().pop_back();
1736 BB->eraseFromParent();
1740 // Check to see if we can constant propagate this terminator instruction
1742 Changed |= ConstantFoldTerminator(BB);
1744 // If there is a trivial two-entry PHI node in this basic block, and we can
1745 // eliminate it, do so now.
1746 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1747 if (PN->getNumIncomingValues() == 2)
1748 Changed |= FoldTwoEntryPHINode(PN);
1750 // If this is a returning block with only PHI nodes in it, fold the return
1751 // instruction into any unconditional branch predecessors.
1753 // If any predecessor is a conditional branch that just selects among
1754 // different return values, fold the replace the branch/return with a select
1756 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1757 BasicBlock::iterator BBI = BB->getTerminator();
1758 if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
1759 // Find predecessors that end with branches.
1760 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1761 SmallVector<BranchInst*, 8> CondBranchPreds;
1762 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1763 TerminatorInst *PTI = (*PI)->getTerminator();
1764 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1765 if (BI->isUnconditional())
1766 UncondBranchPreds.push_back(*PI);
1768 CondBranchPreds.push_back(BI);
1772 // If we found some, do the transformation!
1773 if (!UncondBranchPreds.empty()) {
1774 while (!UncondBranchPreds.empty()) {
1775 BasicBlock *Pred = UncondBranchPreds.back();
1776 DOUT << "FOLDING: " << *BB
1777 << "INTO UNCOND BRANCH PRED: " << *Pred;
1778 UncondBranchPreds.pop_back();
1779 Instruction *UncondBranch = Pred->getTerminator();
1780 // Clone the return and add it to the end of the predecessor.
1781 Instruction *NewRet = RI->clone();
1782 Pred->getInstList().push_back(NewRet);
1784 // If the return instruction returns a value, and if the value was a
1785 // PHI node in "BB", propagate the right value into the return.
1786 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1788 if (PHINode *PN = dyn_cast<PHINode>(*i))
1789 if (PN->getParent() == BB)
1790 *i = PN->getIncomingValueForBlock(Pred);
1792 // Update any PHI nodes in the returning block to realize that we no
1793 // longer branch to them.
1794 BB->removePredecessor(Pred);
1795 Pred->getInstList().erase(UncondBranch);
1798 // If we eliminated all predecessors of the block, delete the block now.
1799 if (pred_begin(BB) == pred_end(BB))
1800 // We know there are no successors, so just nuke the block.
1801 M->getBasicBlockList().erase(BB);
1806 // Check out all of the conditional branches going to this return
1807 // instruction. If any of them just select between returns, change the
1808 // branch itself into a select/return pair.
1809 while (!CondBranchPreds.empty()) {
1810 BranchInst *BI = CondBranchPreds.back();
1811 CondBranchPreds.pop_back();
1813 // Check to see if the non-BB successor is also a return block.
1814 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1815 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1816 SimplifyCondBranchToTwoReturns(BI))
1820 } else if (isa<UnwindInst>(BB->begin())) {
1821 // Check to see if the first instruction in this block is just an unwind.
1822 // If so, replace any invoke instructions which use this as an exception
1823 // destination with call instructions, and any unconditional branch
1824 // predecessor with an unwind.
1826 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1827 while (!Preds.empty()) {
1828 BasicBlock *Pred = Preds.back();
1829 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1830 if (BI->isUnconditional()) {
1831 Pred->getInstList().pop_back(); // nuke uncond branch
1832 new UnwindInst(Pred); // Use unwind.
1835 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1836 if (II->getUnwindDest() == BB) {
1837 // Insert a new branch instruction before the invoke, because this
1838 // is now a fall through...
1839 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1840 Pred->getInstList().remove(II); // Take out of symbol table
1842 // Insert the call now...
1843 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1844 CallInst *CI = CallInst::Create(II->getCalledValue(),
1845 Args.begin(), Args.end(),
1847 CI->setCallingConv(II->getCallingConv());
1848 CI->setAttributes(II->getAttributes());
1849 // If the invoke produced a value, the Call now does instead
1850 II->replaceAllUsesWith(CI);
1858 // If this block is now dead, remove it.
1859 if (pred_begin(BB) == pred_end(BB)) {
1860 // We know there are no successors, so just nuke the block.
1861 M->getBasicBlockList().erase(BB);
1865 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1866 if (isValueEqualityComparison(SI)) {
1867 // If we only have one predecessor, and if it is a branch on this value,
1868 // see if that predecessor totally determines the outcome of this switch.
1869 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1870 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1871 return SimplifyCFG(BB) || 1;
1873 // If the block only contains the switch, see if we can fold the block
1874 // away into any preds.
1875 if (SI == &BB->front())
1876 if (FoldValueComparisonIntoPredecessors(SI))
1877 return SimplifyCFG(BB) || 1;
1879 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1880 if (BI->isUnconditional()) {
1881 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1883 BasicBlock *Succ = BI->getSuccessor(0);
1884 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1885 Succ != BB) // Don't hurt infinite loops!
1886 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1889 } else { // Conditional branch
1890 if (isValueEqualityComparison(BI)) {
1891 // If we only have one predecessor, and if it is a branch on this value,
1892 // see if that predecessor totally determines the outcome of this
1894 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1895 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1896 return SimplifyCFG(BB) || 1;
1898 // This block must be empty, except for the setcond inst, if it exists.
1899 BasicBlock::iterator I = BB->begin();
1901 (&*I == cast<Instruction>(BI->getCondition()) &&
1903 if (FoldValueComparisonIntoPredecessors(BI))
1904 return SimplifyCFG(BB) | true;
1907 // If this is a branch on a phi node in the current block, thread control
1908 // through this block if any PHI node entries are constants.
1909 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1910 if (PN->getParent() == BI->getParent())
1911 if (FoldCondBranchOnPHI(BI))
1912 return SimplifyCFG(BB) | true;
1914 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1915 // branches to us and one of our successors, fold the setcc into the
1916 // predecessor and use logical operations to pick the right destination.
1917 if (FoldBranchToCommonDest(BI))
1918 return SimplifyCFG(BB) | 1;
1921 // Scan predecessor blocks for conditional branches.
1922 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1923 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1924 if (PBI != BI && PBI->isConditional())
1925 if (SimplifyCondBranchToCondBranch(PBI, BI))
1926 return SimplifyCFG(BB) | true;
1928 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1929 // If there are any instructions immediately before the unreachable that can
1930 // be removed, do so.
1931 Instruction *Unreachable = BB->getTerminator();
1932 while (Unreachable != BB->begin()) {
1933 BasicBlock::iterator BBI = Unreachable;
1935 // Do not delete instructions that can have side effects, like calls
1936 // (which may never return) and volatile loads and stores.
1937 if (isa<CallInst>(BBI)) break;
1939 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
1940 if (SI->isVolatile())
1943 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
1944 if (LI->isVolatile())
1947 // Delete this instruction
1948 BB->getInstList().erase(BBI);
1952 // If the unreachable instruction is the first in the block, take a gander
1953 // at all of the predecessors of this instruction, and simplify them.
1954 if (&BB->front() == Unreachable) {
1955 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1956 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1957 TerminatorInst *TI = Preds[i]->getTerminator();
1959 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1960 if (BI->isUnconditional()) {
1961 if (BI->getSuccessor(0) == BB) {
1962 new UnreachableInst(TI);
1963 TI->eraseFromParent();
1967 if (BI->getSuccessor(0) == BB) {
1968 BranchInst::Create(BI->getSuccessor(1), BI);
1969 BI->eraseFromParent();
1970 } else if (BI->getSuccessor(1) == BB) {
1971 BranchInst::Create(BI->getSuccessor(0), BI);
1972 BI->eraseFromParent();
1976 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1977 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1978 if (SI->getSuccessor(i) == BB) {
1979 BB->removePredecessor(SI->getParent());
1984 // If the default value is unreachable, figure out the most popular
1985 // destination and make it the default.
1986 if (SI->getSuccessor(0) == BB) {
1987 std::map<BasicBlock*, unsigned> Popularity;
1988 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1989 Popularity[SI->getSuccessor(i)]++;
1991 // Find the most popular block.
1992 unsigned MaxPop = 0;
1993 BasicBlock *MaxBlock = 0;
1994 for (std::map<BasicBlock*, unsigned>::iterator
1995 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
1996 if (I->second > MaxPop) {
1998 MaxBlock = I->first;
2002 // Make this the new default, allowing us to delete any explicit
2004 SI->setSuccessor(0, MaxBlock);
2007 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2009 if (isa<PHINode>(MaxBlock->begin()))
2010 for (unsigned i = 0; i != MaxPop-1; ++i)
2011 MaxBlock->removePredecessor(SI->getParent());
2013 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2014 if (SI->getSuccessor(i) == MaxBlock) {
2020 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2021 if (II->getUnwindDest() == BB) {
2022 // Convert the invoke to a call instruction. This would be a good
2023 // place to note that the call does not throw though.
2024 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2025 II->removeFromParent(); // Take out of symbol table
2027 // Insert the call now...
2028 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
2029 CallInst *CI = CallInst::Create(II->getCalledValue(),
2030 Args.begin(), Args.end(),
2032 CI->setCallingConv(II->getCallingConv());
2033 CI->setAttributes(II->getAttributes());
2034 // If the invoke produced a value, the Call does now instead.
2035 II->replaceAllUsesWith(CI);
2042 // If this block is now dead, remove it.
2043 if (pred_begin(BB) == pred_end(BB)) {
2044 // We know there are no successors, so just nuke the block.
2045 M->getBasicBlockList().erase(BB);
2051 // Merge basic blocks into their predecessor if there is only one distinct
2052 // pred, and if there is only one distinct successor of the predecessor, and
2053 // if there are no PHI nodes.
2055 if (MergeBlockIntoPredecessor(BB))
2058 // Otherwise, if this block only has a single predecessor, and if that block
2059 // is a conditional branch, see if we can hoist any code from this block up
2060 // into our predecessor.
2061 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2062 BasicBlock *OnlyPred = *PI++;
2063 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2064 if (*PI != OnlyPred) {
2065 OnlyPred = 0; // There are multiple different predecessors...
2070 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2071 if (BI->isConditional()) {
2072 // Get the other block.
2073 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2074 PI = pred_begin(OtherBB);
2077 if (PI == pred_end(OtherBB)) {
2078 // We have a conditional branch to two blocks that are only reachable
2079 // from the condbr. We know that the condbr dominates the two blocks,
2080 // so see if there is any identical code in the "then" and "else"
2081 // blocks. If so, we can hoist it up to the branching block.
2082 Changed |= HoistThenElseCodeToIf(BI);
2084 BasicBlock* OnlySucc = NULL;
2085 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2089 else if (*SI != OnlySucc) {
2090 OnlySucc = 0; // There are multiple distinct successors!
2095 if (OnlySucc == OtherBB) {
2096 // If BB's only successor is the other successor of the predecessor,
2097 // i.e. a triangle, see if we can hoist any code from this block up
2098 // to the "if" block.
2099 Changed |= SpeculativelyExecuteBB(BI, BB);
2104 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2105 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2106 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2107 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2108 Instruction *Cond = cast<Instruction>(BI->getCondition());
2109 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2110 // 'setne's and'ed together, collect them.
2112 std::vector<ConstantInt*> Values;
2113 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2114 if (CompVal && CompVal->getType()->isInteger()) {
2115 // There might be duplicate constants in the list, which the switch
2116 // instruction can't handle, remove them now.
2117 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2118 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2120 // Figure out which block is which destination.
2121 BasicBlock *DefaultBB = BI->getSuccessor(1);
2122 BasicBlock *EdgeBB = BI->getSuccessor(0);
2123 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2125 // Create the new switch instruction now.
2126 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2129 // Add all of the 'cases' to the switch instruction.
2130 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2131 New->addCase(Values[i], EdgeBB);
2133 // We added edges from PI to the EdgeBB. As such, if there were any
2134 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2135 // the number of edges added.
2136 for (BasicBlock::iterator BBI = EdgeBB->begin();
2137 isa<PHINode>(BBI); ++BBI) {
2138 PHINode *PN = cast<PHINode>(BBI);
2139 Value *InVal = PN->getIncomingValueForBlock(*PI);
2140 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2141 PN->addIncoming(InVal, *PI);
2144 // Erase the old branch instruction.
2145 (*PI)->getInstList().erase(BI);
2147 // Erase the potentially condition tree that was used to computed the
2148 // branch condition.
2149 ErasePossiblyDeadInstructionTree(Cond);