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
71 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
72 PHINode *PN = cast<PHINode>(I);
73 Value *V = PN->getIncomingValueForBlock(ExistPred);
74 PN->addIncoming(V, NewPred);
78 // CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
79 // almost-empty BB ending in an unconditional branch to Succ, into succ.
81 // Assumption: Succ is the single successor for BB.
83 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
84 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
86 DOUT << "Looking to fold " << BB->getNameStart() << " into "
87 << Succ->getNameStart() << "\n";
88 // Shortcut, if there is only a single predecessor is must be BB and merging
90 if (Succ->getSinglePredecessor()) return true;
92 typedef SmallPtrSet<Instruction*, 16> InstrSet;
95 // Make a list of all phi nodes in BB
96 BasicBlock::iterator BBI = BB->begin();
97 while (isa<PHINode>(*BBI)) BBPHIs.insert(BBI++);
99 // Make a list of the predecessors of BB
100 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
101 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
103 // Use that list to make another list of common predecessors of BB and Succ
104 BlockSet CommonPreds;
105 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
107 if (BBPreds.count(*PI))
108 CommonPreds.insert(*PI);
110 // Shortcut, if there are no common predecessors, merging is always safe
111 if (CommonPreds.begin() == CommonPreds.end())
114 // Look at all the phi nodes in Succ, to see if they present a conflict when
115 // merging these blocks
116 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
117 PHINode *PN = cast<PHINode>(I);
119 // If the incoming value from BB is again a PHINode in
120 // BB which has the same incoming value for *PI as PN does, we can
121 // merge the phi nodes and then the blocks can still be merged
122 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
123 if (BBPN && BBPN->getParent() == BB) {
124 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
126 if (BBPN->getIncomingValueForBlock(*PI)
127 != PN->getIncomingValueForBlock(*PI)) {
128 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
129 << Succ->getNameStart() << " is conflicting with "
130 << BBPN->getNameStart() << " with regard to common predecessor "
131 << (*PI)->getNameStart() << "\n";
135 // Remove this phinode from the list of phis in BB, since it has been
139 Value* Val = PN->getIncomingValueForBlock(BB);
140 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
142 // See if the incoming value for the common predecessor is equal to the
143 // one for BB, in which case this phi node will not prevent the merging
145 if (Val != PN->getIncomingValueForBlock(*PI)) {
146 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
147 << Succ->getNameStart() << " is conflicting with regard to common "
148 << "predecessor " << (*PI)->getNameStart() << "\n";
155 // If there are any other phi nodes in BB that don't have a phi node in Succ
156 // to merge with, they must be moved to Succ completely. However, for any
157 // predecessors of Succ, branches will be added to the phi node that just
158 // point to itself. So, for any common predecessors, this must not cause
160 for (InstrSet::iterator I = BBPHIs.begin(), E = BBPHIs.end();
162 PHINode *PN = cast<PHINode>(*I);
163 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
165 if (PN->getIncomingValueForBlock(*PI) != PN) {
166 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
167 << BB->getNameStart() << " is conflicting with regard to common "
168 << "predecessor " << (*PI)->getNameStart() << "\n";
176 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
177 /// branch to Succ, and contains no instructions other than PHI nodes and the
178 /// branch. If possible, eliminate BB.
179 static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
181 // Check to see if merging these blocks would cause conflicts for any of the
182 // phi nodes in BB or Succ. If not, we can safely merge.
183 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
185 DOUT << "Killing Trivial BB: \n" << *BB;
187 if (isa<PHINode>(Succ->begin())) {
188 // If there is more than one pred of succ, and there are PHI nodes in
189 // the successor, then we need to add incoming edges for the PHI nodes
191 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
193 // Loop over all of the PHI nodes in the successor of BB.
194 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
195 PHINode *PN = cast<PHINode>(I);
196 Value *OldVal = PN->removeIncomingValue(BB, false);
197 assert(OldVal && "No entry in PHI for Pred BB!");
199 // If this incoming value is one of the PHI nodes in BB, the new entries
200 // in the PHI node are the entries from the old PHI.
201 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
202 PHINode *OldValPN = cast<PHINode>(OldVal);
203 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
204 // Note that, since we are merging phi nodes and BB and Succ might
205 // have common predecessors, we could end up with a phi node with
206 // identical incoming branches. This will be cleaned up later (and
207 // will trigger asserts if we try to clean it up now, without also
208 // simplifying the corresponding conditional branch).
209 PN->addIncoming(OldValPN->getIncomingValue(i),
210 OldValPN->getIncomingBlock(i));
212 // Add an incoming value for each of the new incoming values.
213 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
214 PN->addIncoming(OldVal, BBPreds[i]);
219 if (isa<PHINode>(&BB->front())) {
220 SmallVector<BasicBlock*, 16>
221 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
223 // Move all PHI nodes in BB to Succ if they are alive, otherwise
225 while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
226 if (PN->use_empty()) {
227 // Just remove the dead phi. This happens if Succ's PHIs were the only
228 // users of the PHI nodes.
229 PN->eraseFromParent();
231 // The instruction is alive, so this means that BB must dominate all
232 // predecessors of Succ (Since all uses of the PN are after its
233 // definition, so in Succ or a block dominated by Succ. If a predecessor
234 // of Succ would not be dominated by BB, PN would violate the def before
235 // use SSA demand). Therefore, we can simply move the phi node to the
237 Succ->getInstList().splice(Succ->begin(),
238 BB->getInstList(), BB->begin());
240 // We need to add new entries for the PHI node to account for
241 // predecessors of Succ that the PHI node does not take into
242 // account. At this point, since we know that BB dominated succ and all
243 // of its predecessors, this means that we should any newly added
244 // incoming edges should use the PHI node itself as the value for these
245 // edges, because they are loop back edges.
246 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
247 if (OldSuccPreds[i] != BB)
248 PN->addIncoming(PN, OldSuccPreds[i]);
252 // Everything that jumped to BB now goes to Succ.
253 BB->replaceAllUsesWith(Succ);
254 if (!Succ->hasName()) Succ->takeName(BB);
255 BB->eraseFromParent(); // Delete the old basic block.
259 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
260 /// presumably PHI nodes in it), check to see if the merge at this block is due
261 /// to an "if condition". If so, return the boolean condition that determines
262 /// which entry into BB will be taken. Also, return by references the block
263 /// that will be entered from if the condition is true, and the block that will
264 /// be entered if the condition is false.
267 static Value *GetIfCondition(BasicBlock *BB,
268 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
269 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
270 "Function can only handle blocks with 2 predecessors!");
271 BasicBlock *Pred1 = *pred_begin(BB);
272 BasicBlock *Pred2 = *++pred_begin(BB);
274 // We can only handle branches. Other control flow will be lowered to
275 // branches if possible anyway.
276 if (!isa<BranchInst>(Pred1->getTerminator()) ||
277 !isa<BranchInst>(Pred2->getTerminator()))
279 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
280 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
282 // Eliminate code duplication by ensuring that Pred1Br is conditional if
284 if (Pred2Br->isConditional()) {
285 // If both branches are conditional, we don't have an "if statement". In
286 // reality, we could transform this case, but since the condition will be
287 // required anyway, we stand no chance of eliminating it, so the xform is
288 // probably not profitable.
289 if (Pred1Br->isConditional())
292 std::swap(Pred1, Pred2);
293 std::swap(Pred1Br, Pred2Br);
296 if (Pred1Br->isConditional()) {
297 // If we found a conditional branch predecessor, make sure that it branches
298 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
299 if (Pred1Br->getSuccessor(0) == BB &&
300 Pred1Br->getSuccessor(1) == Pred2) {
303 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
304 Pred1Br->getSuccessor(1) == BB) {
308 // We know that one arm of the conditional goes to BB, so the other must
309 // go somewhere unrelated, and this must not be an "if statement".
313 // The only thing we have to watch out for here is to make sure that Pred2
314 // doesn't have incoming edges from other blocks. If it does, the condition
315 // doesn't dominate BB.
316 if (++pred_begin(Pred2) != pred_end(Pred2))
319 return Pred1Br->getCondition();
322 // Ok, if we got here, both predecessors end with an unconditional branch to
323 // BB. Don't panic! If both blocks only have a single (identical)
324 // predecessor, and THAT is a conditional branch, then we're all ok!
325 if (pred_begin(Pred1) == pred_end(Pred1) ||
326 ++pred_begin(Pred1) != pred_end(Pred1) ||
327 pred_begin(Pred2) == pred_end(Pred2) ||
328 ++pred_begin(Pred2) != pred_end(Pred2) ||
329 *pred_begin(Pred1) != *pred_begin(Pred2))
332 // Otherwise, if this is a conditional branch, then we can use it!
333 BasicBlock *CommonPred = *pred_begin(Pred1);
334 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
335 assert(BI->isConditional() && "Two successors but not conditional?");
336 if (BI->getSuccessor(0) == Pred1) {
343 return BI->getCondition();
349 // If we have a merge point of an "if condition" as accepted above, return true
350 // if the specified value dominates the block. We don't handle the true
351 // generality of domination here, just a special case which works well enough
354 // If AggressiveInsts is non-null, and if V does not dominate BB, we check to
355 // see if V (which must be an instruction) is cheap to compute and is
356 // non-trapping. If both are true, the instruction is inserted into the set and
358 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
359 std::set<Instruction*> *AggressiveInsts) {
360 Instruction *I = dyn_cast<Instruction>(V);
362 // Non-instructions all dominate instructions, but not all constantexprs
363 // can be executed unconditionally.
364 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
369 BasicBlock *PBB = I->getParent();
371 // We don't want to allow weird loops that might have the "if condition" in
372 // the bottom of this block.
373 if (PBB == BB) return false;
375 // If this instruction is defined in a block that contains an unconditional
376 // branch to BB, then it must be in the 'conditional' part of the "if
378 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
379 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
380 if (!AggressiveInsts) return false;
381 // Okay, it looks like the instruction IS in the "condition". Check to
382 // see if its a cheap instruction to unconditionally compute, and if it
383 // only uses stuff defined outside of the condition. If so, hoist it out.
384 switch (I->getOpcode()) {
385 default: return false; // Cannot hoist this out safely.
386 case Instruction::Load:
387 // We can hoist loads that are non-volatile and obviously cannot trap.
388 if (cast<LoadInst>(I)->isVolatile())
390 if (!isa<AllocaInst>(I->getOperand(0)) &&
391 !isa<Constant>(I->getOperand(0)))
394 // Finally, we have to check to make sure there are no instructions
395 // before the load in its basic block, as we are going to hoist the loop
396 // out to its predecessor.
397 if (PBB->begin() != BasicBlock::iterator(I))
400 case Instruction::Add:
401 case Instruction::Sub:
402 case Instruction::And:
403 case Instruction::Or:
404 case Instruction::Xor:
405 case Instruction::Shl:
406 case Instruction::LShr:
407 case Instruction::AShr:
408 case Instruction::ICmp:
409 case Instruction::FCmp:
410 if (I->getOperand(0)->getType()->isFPOrFPVector())
411 return false; // FP arithmetic might trap.
412 break; // These are all cheap and non-trapping instructions.
415 // Okay, we can only really hoist these out if their operands are not
416 // defined in the conditional region.
417 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
418 if (!DominatesMergePoint(*i, BB, 0))
420 // Okay, it's safe to do this! Remember this instruction.
421 AggressiveInsts->insert(I);
427 // GatherConstantSetEQs - Given a potentially 'or'd together collection of
428 // icmp_eq instructions that compare a value against a constant, return the
429 // value being compared, and stick the constant into the Values vector.
430 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
431 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
432 if (Inst->getOpcode() == Instruction::ICmp &&
433 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
434 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
436 return Inst->getOperand(0);
437 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
439 return Inst->getOperand(1);
441 } else if (Inst->getOpcode() == Instruction::Or) {
442 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
443 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
451 // GatherConstantSetNEs - Given a potentially 'and'd together collection of
452 // setne instructions that compare a value against a constant, return the value
453 // being compared, and stick the constant into the Values vector.
454 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
455 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
456 if (Inst->getOpcode() == Instruction::ICmp &&
457 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
458 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
460 return Inst->getOperand(0);
461 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
463 return Inst->getOperand(1);
465 } else if (Inst->getOpcode() == Instruction::And) {
466 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
467 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
477 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
478 /// bunch of comparisons of one value against constants, return the value and
479 /// the constants being compared.
480 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
481 std::vector<ConstantInt*> &Values) {
482 if (Cond->getOpcode() == Instruction::Or) {
483 CompVal = GatherConstantSetEQs(Cond, Values);
485 // Return true to indicate that the condition is true if the CompVal is
486 // equal to one of the constants.
488 } else if (Cond->getOpcode() == Instruction::And) {
489 CompVal = GatherConstantSetNEs(Cond, Values);
491 // Return false to indicate that the condition is false if the CompVal is
492 // equal to one of the constants.
498 /// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
499 /// has no side effects, nuke it. If it uses any instructions that become dead
500 /// because the instruction is now gone, nuke them too.
501 static void ErasePossiblyDeadInstructionTree(Instruction *I) {
502 if (!isInstructionTriviallyDead(I)) return;
504 SmallVector<Instruction*, 16> InstrsToInspect;
505 InstrsToInspect.push_back(I);
507 while (!InstrsToInspect.empty()) {
508 I = InstrsToInspect.back();
509 InstrsToInspect.pop_back();
511 if (!isInstructionTriviallyDead(I)) continue;
513 // If I is in the work list multiple times, remove previous instances.
514 for (unsigned i = 0, e = InstrsToInspect.size(); i != e; ++i)
515 if (InstrsToInspect[i] == I) {
516 InstrsToInspect.erase(InstrsToInspect.begin()+i);
520 // Add operands of dead instruction to worklist.
521 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
522 if (Instruction *OpI = dyn_cast<Instruction>(*i))
523 InstrsToInspect.push_back(OpI);
525 // Remove dead instruction.
526 I->eraseFromParent();
530 // isValueEqualityComparison - Return true if the specified terminator checks to
531 // see if a value is equal to constant integer value.
532 static Value *isValueEqualityComparison(TerminatorInst *TI) {
533 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
534 // Do not permit merging of large switch instructions into their
535 // predecessors unless there is only one predecessor.
536 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
537 pred_end(SI->getParent())) > 128)
540 return SI->getCondition();
542 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
543 if (BI->isConditional() && BI->getCondition()->hasOneUse())
544 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
545 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
546 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
547 isa<ConstantInt>(ICI->getOperand(1)))
548 return ICI->getOperand(0);
552 // Given a value comparison instruction, decode all of the 'cases' that it
553 // represents and return the 'default' block.
555 GetValueEqualityComparisonCases(TerminatorInst *TI,
556 std::vector<std::pair<ConstantInt*,
557 BasicBlock*> > &Cases) {
558 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
559 Cases.reserve(SI->getNumCases());
560 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
561 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
562 return SI->getDefaultDest();
565 BranchInst *BI = cast<BranchInst>(TI);
566 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
567 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
568 BI->getSuccessor(ICI->getPredicate() ==
569 ICmpInst::ICMP_NE)));
570 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
574 // EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
575 // in the list that match the specified block.
576 static void EliminateBlockCases(BasicBlock *BB,
577 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
578 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
579 if (Cases[i].second == BB) {
580 Cases.erase(Cases.begin()+i);
585 // ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
588 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
589 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
590 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
592 // Make V1 be smaller than V2.
593 if (V1->size() > V2->size())
596 if (V1->size() == 0) return false;
597 if (V1->size() == 1) {
599 ConstantInt *TheVal = (*V1)[0].first;
600 for (unsigned i = 0, e = V2->size(); i != e; ++i)
601 if (TheVal == (*V2)[i].first)
605 // Otherwise, just sort both lists and compare element by element.
606 std::sort(V1->begin(), V1->end());
607 std::sort(V2->begin(), V2->end());
608 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
609 while (i1 != e1 && i2 != e2) {
610 if ((*V1)[i1].first == (*V2)[i2].first)
612 if ((*V1)[i1].first < (*V2)[i2].first)
620 // SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
621 // terminator instruction and its block is known to only have a single
622 // predecessor block, check to see if that predecessor is also a value
623 // comparison with the same value, and if that comparison determines the outcome
624 // of this comparison. If so, simplify TI. This does a very limited form of
626 static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
628 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
629 if (!PredVal) return false; // Not a value comparison in predecessor.
631 Value *ThisVal = isValueEqualityComparison(TI);
632 assert(ThisVal && "This isn't a value comparison!!");
633 if (ThisVal != PredVal) return false; // Different predicates.
635 // Find out information about when control will move from Pred to TI's block.
636 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
637 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
639 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
641 // Find information about how control leaves this block.
642 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
643 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
644 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
646 // If TI's block is the default block from Pred's comparison, potentially
647 // simplify TI based on this knowledge.
648 if (PredDef == TI->getParent()) {
649 // If we are here, we know that the value is none of those cases listed in
650 // PredCases. If there are any cases in ThisCases that are in PredCases, we
652 if (ValuesOverlap(PredCases, ThisCases)) {
653 if (BranchInst *BTI = dyn_cast<BranchInst>(TI)) {
654 // Okay, one of the successors of this condbr is dead. Convert it to a
656 assert(ThisCases.size() == 1 && "Branch can only have one case!");
657 Value *Cond = BTI->getCondition();
658 // Insert the new branch.
659 Instruction *NI = BranchInst::Create(ThisDef, TI);
661 // Remove PHI node entries for the dead edge.
662 ThisCases[0].second->removePredecessor(TI->getParent());
664 DOUT << "Threading pred instr: " << *Pred->getTerminator()
665 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
667 TI->eraseFromParent(); // Nuke the old one.
668 // If condition is now dead, nuke it.
669 if (Instruction *CondI = dyn_cast<Instruction>(Cond))
670 ErasePossiblyDeadInstructionTree(CondI);
674 SwitchInst *SI = cast<SwitchInst>(TI);
675 // Okay, TI has cases that are statically dead, prune them away.
676 SmallPtrSet<Constant*, 16> DeadCases;
677 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
678 DeadCases.insert(PredCases[i].first);
680 DOUT << "Threading pred instr: " << *Pred->getTerminator()
681 << "Through successor TI: " << *TI;
683 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
684 if (DeadCases.count(SI->getCaseValue(i))) {
685 SI->getSuccessor(i)->removePredecessor(TI->getParent());
689 DOUT << "Leaving: " << *TI << "\n";
695 // Otherwise, TI's block must correspond to some matched value. Find out
696 // which value (or set of values) this is.
697 ConstantInt *TIV = 0;
698 BasicBlock *TIBB = TI->getParent();
699 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
700 if (PredCases[i].second == TIBB) {
702 TIV = PredCases[i].first;
704 return false; // Cannot handle multiple values coming to this block.
706 assert(TIV && "No edge from pred to succ?");
708 // Okay, we found the one constant that our value can be if we get into TI's
709 // BB. Find out which successor will unconditionally be branched to.
710 BasicBlock *TheRealDest = 0;
711 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
712 if (ThisCases[i].first == TIV) {
713 TheRealDest = ThisCases[i].second;
717 // If not handled by any explicit cases, it is handled by the default case.
718 if (TheRealDest == 0) TheRealDest = ThisDef;
720 // Remove PHI node entries for dead edges.
721 BasicBlock *CheckEdge = TheRealDest;
722 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
723 if (*SI != CheckEdge)
724 (*SI)->removePredecessor(TIBB);
728 // Insert the new branch.
729 Instruction *NI = BranchInst::Create(TheRealDest, TI);
731 DOUT << "Threading pred instr: " << *Pred->getTerminator()
732 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
733 Instruction *Cond = 0;
734 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
735 Cond = dyn_cast<Instruction>(BI->getCondition());
736 TI->eraseFromParent(); // Nuke the old one.
738 if (Cond) ErasePossiblyDeadInstructionTree(Cond);
744 // FoldValueComparisonIntoPredecessors - The specified terminator is a value
745 // equality comparison instruction (either a switch or a branch on "X == c").
746 // See if any of the predecessors of the terminator block are value comparisons
747 // on the same value. If so, and if safe to do so, fold them together.
748 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
749 BasicBlock *BB = TI->getParent();
750 Value *CV = isValueEqualityComparison(TI); // CondVal
751 assert(CV && "Not a comparison?");
752 bool Changed = false;
754 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
755 while (!Preds.empty()) {
756 BasicBlock *Pred = Preds.back();
759 // See if the predecessor is a comparison with the same value.
760 TerminatorInst *PTI = Pred->getTerminator();
761 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
763 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
764 // Figure out which 'cases' to copy from SI to PSI.
765 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
766 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
768 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
769 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
771 // Based on whether the default edge from PTI goes to BB or not, fill in
772 // PredCases and PredDefault with the new switch cases we would like to
774 SmallVector<BasicBlock*, 8> NewSuccessors;
776 if (PredDefault == BB) {
777 // If this is the default destination from PTI, only the edges in TI
778 // that don't occur in PTI, or that branch to BB will be activated.
779 std::set<ConstantInt*> PTIHandled;
780 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
781 if (PredCases[i].second != BB)
782 PTIHandled.insert(PredCases[i].first);
784 // The default destination is BB, we don't need explicit targets.
785 std::swap(PredCases[i], PredCases.back());
786 PredCases.pop_back();
790 // Reconstruct the new switch statement we will be building.
791 if (PredDefault != BBDefault) {
792 PredDefault->removePredecessor(Pred);
793 PredDefault = BBDefault;
794 NewSuccessors.push_back(BBDefault);
796 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
797 if (!PTIHandled.count(BBCases[i].first) &&
798 BBCases[i].second != BBDefault) {
799 PredCases.push_back(BBCases[i]);
800 NewSuccessors.push_back(BBCases[i].second);
804 // If this is not the default destination from PSI, only the edges
805 // in SI that occur in PSI with a destination of BB will be
807 std::set<ConstantInt*> PTIHandled;
808 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
809 if (PredCases[i].second == BB) {
810 PTIHandled.insert(PredCases[i].first);
811 std::swap(PredCases[i], PredCases.back());
812 PredCases.pop_back();
816 // Okay, now we know which constants were sent to BB from the
817 // predecessor. Figure out where they will all go now.
818 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
819 if (PTIHandled.count(BBCases[i].first)) {
820 // If this is one we are capable of getting...
821 PredCases.push_back(BBCases[i]);
822 NewSuccessors.push_back(BBCases[i].second);
823 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
826 // If there are any constants vectored to BB that TI doesn't handle,
827 // they must go to the default destination of TI.
828 for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
829 E = PTIHandled.end(); I != E; ++I) {
830 PredCases.push_back(std::make_pair(*I, BBDefault));
831 NewSuccessors.push_back(BBDefault);
835 // Okay, at this point, we know which new successor Pred will get. Make
836 // sure we update the number of entries in the PHI nodes for these
838 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
839 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
841 // Now that the successors are updated, create the new Switch instruction.
842 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
843 PredCases.size(), PTI);
844 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
845 NewSI->addCase(PredCases[i].first, PredCases[i].second);
847 Instruction *DeadCond = 0;
848 if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
849 // If PTI is a branch, remember the condition.
850 DeadCond = dyn_cast<Instruction>(BI->getCondition());
851 Pred->getInstList().erase(PTI);
853 // If the condition is dead now, remove the instruction tree.
854 if (DeadCond) ErasePossiblyDeadInstructionTree(DeadCond);
856 // Okay, last check. If BB is still a successor of PSI, then we must
857 // have an infinite loop case. If so, add an infinitely looping block
858 // to handle the case to preserve the behavior of the code.
859 BasicBlock *InfLoopBlock = 0;
860 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
861 if (NewSI->getSuccessor(i) == BB) {
862 if (InfLoopBlock == 0) {
863 // Insert it at the end of the loop, because it's either code,
864 // or it won't matter if it's hot. :)
865 InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
866 BranchInst::Create(InfLoopBlock, InfLoopBlock);
868 NewSI->setSuccessor(i, InfLoopBlock);
877 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
878 /// BB2, hoist any common code in the two blocks up into the branch block. The
879 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
880 static bool HoistThenElseCodeToIf(BranchInst *BI) {
881 // This does very trivial matching, with limited scanning, to find identical
882 // instructions in the two blocks. In particular, we don't want to get into
883 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
884 // such, we currently just scan for obviously identical instructions in an
886 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
887 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
889 Instruction *I1 = BB1->begin(), *I2 = BB2->begin();
890 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
891 isa<InvokeInst>(I1) || !I1->isIdenticalTo(I2))
894 // If we get here, we can hoist at least one instruction.
895 BasicBlock *BIParent = BI->getParent();
898 // If we are hoisting the terminator instruction, don't move one (making a
899 // broken BB), instead clone it, and remove BI.
900 if (isa<TerminatorInst>(I1))
901 goto HoistTerminator;
903 // For a normal instruction, we just move one to right before the branch,
904 // then replace all uses of the other with the first. Finally, we remove
905 // the now redundant second instruction.
906 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
907 if (!I2->use_empty())
908 I2->replaceAllUsesWith(I1);
909 BB2->getInstList().erase(I2);
913 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
918 // Okay, it is safe to hoist the terminator.
919 Instruction *NT = I1->clone();
920 BIParent->getInstList().insert(BI, NT);
921 if (NT->getType() != Type::VoidTy) {
922 I1->replaceAllUsesWith(NT);
923 I2->replaceAllUsesWith(NT);
927 // Hoisting one of the terminators from our successor is a great thing.
928 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
929 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
930 // nodes, so we insert select instruction to compute the final result.
931 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
932 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
934 for (BasicBlock::iterator BBI = SI->begin();
935 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
936 Value *BB1V = PN->getIncomingValueForBlock(BB1);
937 Value *BB2V = PN->getIncomingValueForBlock(BB2);
939 // These values do not agree. Insert a select instruction before NT
940 // that determines the right value.
941 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
943 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
944 BB1V->getName()+"."+BB2V->getName(), NT);
945 // Make the PHI node use the select for all incoming values for BB1/BB2
946 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
947 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
948 PN->setIncomingValue(i, SI);
953 // Update any PHI nodes in our new successors.
954 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
955 AddPredecessorToBlock(*SI, BIParent, BB1);
957 BI->eraseFromParent();
961 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
962 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
963 /// (for now, restricted to a single instruction that's side effect free) from
964 /// the BB1 into the branch block to speculatively execute it.
965 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
966 // Only speculatively execution a single instruction (not counting the
967 // terminator) for now.
968 if (BB1->size() != 2)
971 // Be conservative for now. FP select instruction can often be expensive.
972 Value *BrCond = BI->getCondition();
973 if (isa<Instruction>(BrCond) &&
974 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
977 // If BB1 is actually on the false edge of the conditional branch, remember
978 // to swap the select operands later.
980 if (BB1 != BI->getSuccessor(0)) {
981 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
988 // br i1 %t1, label %BB1, label %BB2
997 // %t3 = select i1 %t1, %t2, %t3
998 Instruction *I = BB1->begin();
999 switch (I->getOpcode()) {
1000 default: return false; // Not safe / profitable to hoist.
1001 case Instruction::Add:
1002 case Instruction::Sub:
1003 case Instruction::And:
1004 case Instruction::Or:
1005 case Instruction::Xor:
1006 case Instruction::Shl:
1007 case Instruction::LShr:
1008 case Instruction::AShr:
1009 if (I->getOperand(0)->getType()->isFPOrFPVector())
1010 return false; // FP arithmetic might trap.
1011 break; // These are all cheap and non-trapping instructions.
1014 // Can we speculatively execute the instruction? And what is the value
1015 // if the condition is false? Consider the phi uses, if the incoming value
1016 // from the "if" block are all the same V, then V is the value of the
1017 // select if the condition is false.
1018 BasicBlock *BIParent = BI->getParent();
1019 SmallVector<PHINode*, 4> PHIUses;
1020 Value *FalseV = NULL;
1021 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1023 PHINode *PN = dyn_cast<PHINode>(UI);
1026 PHIUses.push_back(PN);
1027 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1030 else if (FalseV != PHIV)
1031 return false; // Don't know the value when condition is false.
1033 if (!FalseV) // Can this happen?
1036 // Do not hoist the instruction if any of its operands are defined but not
1037 // used in this BB. The transformation will prevent the operand from
1038 // being sunk into the use block.
1039 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
1040 Instruction *OpI = dyn_cast<Instruction>(*i);
1041 if (OpI && OpI->getParent() == BIParent &&
1042 !OpI->isUsedInBasicBlock(BIParent))
1046 // If we get here, we can hoist the instruction. Try to place it before the
1047 // icmp instruction preceeding the conditional branch.
1048 BasicBlock::iterator InsertPos = BI;
1049 if (InsertPos != BIParent->begin())
1051 if (InsertPos == BrCond && !isa<PHINode>(BrCond))
1052 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), I);
1054 BIParent->getInstList().splice(BI, BB1->getInstList(), I);
1056 // Create a select whose true value is the speculatively executed value and
1057 // false value is the previously determined FalseV.
1060 SI = SelectInst::Create(BrCond, FalseV, I,
1061 FalseV->getName() + "." + I->getName(), BI);
1063 SI = SelectInst::Create(BrCond, I, FalseV,
1064 I->getName() + "." + FalseV->getName(), BI);
1066 // Make the PHI node use the select for all incoming values for "then" and
1068 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1069 PHINode *PN = PHIUses[i];
1070 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1071 if (PN->getIncomingBlock(j) == BB1 ||
1072 PN->getIncomingBlock(j) == BIParent)
1073 PN->setIncomingValue(j, SI);
1080 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1081 /// across this block.
1082 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1083 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1086 // If this basic block contains anything other than a PHI (which controls the
1087 // branch) and branch itself, bail out. FIXME: improve this in the future.
1088 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) {
1089 if (Size > 10) return false; // Don't clone large BB's.
1091 // We can only support instructions that are do not define values that are
1092 // live outside of the current basic block.
1093 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1095 Instruction *U = cast<Instruction>(*UI);
1096 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1099 // Looks ok, continue checking.
1105 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1106 /// that is defined in the same block as the branch and if any PHI entries are
1107 /// constants, thread edges corresponding to that entry to be branches to their
1108 /// ultimate destination.
1109 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1110 BasicBlock *BB = BI->getParent();
1111 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1112 // NOTE: we currently cannot transform this case if the PHI node is used
1113 // outside of the block.
1114 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1117 // Degenerate case of a single entry PHI.
1118 if (PN->getNumIncomingValues() == 1) {
1119 if (PN->getIncomingValue(0) != PN)
1120 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1122 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1123 PN->eraseFromParent();
1127 // Now we know that this block has multiple preds and two succs.
1128 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1130 // Okay, this is a simple enough basic block. See if any phi values are
1132 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1134 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1135 CB->getType() == Type::Int1Ty) {
1136 // Okay, we now know that all edges from PredBB should be revectored to
1137 // branch to RealDest.
1138 BasicBlock *PredBB = PN->getIncomingBlock(i);
1139 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1141 if (RealDest == BB) continue; // Skip self loops.
1143 // The dest block might have PHI nodes, other predecessors and other
1144 // difficult cases. Instead of being smart about this, just insert a new
1145 // block that jumps to the destination block, effectively splitting
1146 // the edge we are about to create.
1147 BasicBlock *EdgeBB = BasicBlock::Create(RealDest->getName()+".critedge",
1148 RealDest->getParent(), RealDest);
1149 BranchInst::Create(RealDest, EdgeBB);
1151 for (BasicBlock::iterator BBI = RealDest->begin();
1152 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1153 Value *V = PN->getIncomingValueForBlock(BB);
1154 PN->addIncoming(V, EdgeBB);
1157 // BB may have instructions that are being threaded over. Clone these
1158 // instructions into EdgeBB. We know that there will be no uses of the
1159 // cloned instructions outside of EdgeBB.
1160 BasicBlock::iterator InsertPt = EdgeBB->begin();
1161 std::map<Value*, Value*> TranslateMap; // Track translated values.
1162 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1163 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1164 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1166 // Clone the instruction.
1167 Instruction *N = BBI->clone();
1168 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1170 // Update operands due to translation.
1171 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1173 std::map<Value*, Value*>::iterator PI =
1174 TranslateMap.find(*i);
1175 if (PI != TranslateMap.end())
1179 // Check for trivial simplification.
1180 if (Constant *C = ConstantFoldInstruction(N)) {
1181 TranslateMap[BBI] = C;
1182 delete N; // Constant folded away, don't need actual inst
1184 // Insert the new instruction into its new home.
1185 EdgeBB->getInstList().insert(InsertPt, N);
1186 if (!BBI->use_empty())
1187 TranslateMap[BBI] = N;
1192 // Loop over all of the edges from PredBB to BB, changing them to branch
1193 // to EdgeBB instead.
1194 TerminatorInst *PredBBTI = PredBB->getTerminator();
1195 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1196 if (PredBBTI->getSuccessor(i) == BB) {
1197 BB->removePredecessor(PredBB);
1198 PredBBTI->setSuccessor(i, EdgeBB);
1201 // Recurse, simplifying any other constants.
1202 return FoldCondBranchOnPHI(BI) | true;
1209 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1210 /// PHI node, see if we can eliminate it.
1211 static bool FoldTwoEntryPHINode(PHINode *PN) {
1212 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1213 // statement", which has a very simple dominance structure. Basically, we
1214 // are trying to find the condition that is being branched on, which
1215 // subsequently causes this merge to happen. We really want control
1216 // dependence information for this check, but simplifycfg can't keep it up
1217 // to date, and this catches most of the cases we care about anyway.
1219 BasicBlock *BB = PN->getParent();
1220 BasicBlock *IfTrue, *IfFalse;
1221 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1222 if (!IfCond) return false;
1224 // Okay, we found that we can merge this two-entry phi node into a select.
1225 // Doing so would require us to fold *all* two entry phi nodes in this block.
1226 // At some point this becomes non-profitable (particularly if the target
1227 // doesn't support cmov's). Only do this transformation if there are two or
1228 // fewer PHI nodes in this block.
1229 unsigned NumPhis = 0;
1230 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1234 DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
1235 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
1237 // Loop over the PHI's seeing if we can promote them all to select
1238 // instructions. While we are at it, keep track of the instructions
1239 // that need to be moved to the dominating block.
1240 std::set<Instruction*> AggressiveInsts;
1242 BasicBlock::iterator AfterPHIIt = BB->begin();
1243 while (isa<PHINode>(AfterPHIIt)) {
1244 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1245 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1246 if (PN->getIncomingValue(0) != PN)
1247 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1249 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1250 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1251 &AggressiveInsts) ||
1252 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1253 &AggressiveInsts)) {
1258 // If we all PHI nodes are promotable, check to make sure that all
1259 // instructions in the predecessor blocks can be promoted as well. If
1260 // not, we won't be able to get rid of the control flow, so it's not
1261 // worth promoting to select instructions.
1262 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1263 PN = cast<PHINode>(BB->begin());
1264 BasicBlock *Pred = PN->getIncomingBlock(0);
1265 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1267 DomBlock = *pred_begin(Pred);
1268 for (BasicBlock::iterator I = Pred->begin();
1269 !isa<TerminatorInst>(I); ++I)
1270 if (!AggressiveInsts.count(I)) {
1271 // This is not an aggressive instruction that we can promote.
1272 // Because of this, we won't be able to get rid of the control
1273 // flow, so the xform is not worth it.
1278 Pred = PN->getIncomingBlock(1);
1279 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1281 DomBlock = *pred_begin(Pred);
1282 for (BasicBlock::iterator I = Pred->begin();
1283 !isa<TerminatorInst>(I); ++I)
1284 if (!AggressiveInsts.count(I)) {
1285 // This is not an aggressive instruction that we can promote.
1286 // Because of this, we won't be able to get rid of the control
1287 // flow, so the xform is not worth it.
1292 // If we can still promote the PHI nodes after this gauntlet of tests,
1293 // do all of the PHI's now.
1295 // Move all 'aggressive' instructions, which are defined in the
1296 // conditional parts of the if's up to the dominating block.
1298 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1299 IfBlock1->getInstList(),
1301 IfBlock1->getTerminator());
1304 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1305 IfBlock2->getInstList(),
1307 IfBlock2->getTerminator());
1310 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1311 // Change the PHI node into a select instruction.
1313 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1315 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1317 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1318 PN->replaceAllUsesWith(NV);
1321 BB->getInstList().erase(PN);
1326 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1327 /// to two returning blocks, try to merge them together into one return,
1328 /// introducing a select if the return values disagree.
1329 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1330 assert(BI->isConditional() && "Must be a conditional branch");
1331 BasicBlock *TrueSucc = BI->getSuccessor(0);
1332 BasicBlock *FalseSucc = BI->getSuccessor(1);
1333 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1334 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1336 // Check to ensure both blocks are empty (just a return) or optionally empty
1337 // with PHI nodes. If there are other instructions, merging would cause extra
1338 // computation on one path or the other.
1339 BasicBlock::iterator BBI = TrueRet;
1340 if (BBI != TrueSucc->begin() && !isa<PHINode>(--BBI))
1341 return false; // Not empty with optional phi nodes.
1343 if (BBI != FalseSucc->begin() && !isa<PHINode>(--BBI))
1344 return false; // Not empty with optional phi nodes.
1346 // Okay, we found a branch that is going to two return nodes. If
1347 // there is no return value for this function, just change the
1348 // branch into a return.
1349 if (FalseRet->getNumOperands() == 0) {
1350 TrueSucc->removePredecessor(BI->getParent());
1351 FalseSucc->removePredecessor(BI->getParent());
1352 ReturnInst::Create(0, BI);
1353 BI->eraseFromParent();
1357 // Otherwise, build up the result values for the new return.
1358 SmallVector<Value*, 4> TrueResult;
1359 SmallVector<Value*, 4> FalseResult;
1361 for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
1362 // Otherwise, figure out what the true and false return values are
1363 // so we can insert a new select instruction.
1364 Value *TrueValue = TrueRet->getOperand(i);
1365 Value *FalseValue = FalseRet->getOperand(i);
1367 // Unwrap any PHI nodes in the return blocks.
1368 if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue))
1369 if (TVPN->getParent() == TrueSucc)
1370 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1371 if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue))
1372 if (FVPN->getParent() == FalseSucc)
1373 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1375 // In order for this transformation to be safe, we must be able to
1376 // unconditionally execute both operands to the return. This is
1377 // normally the case, but we could have a potentially-trapping
1378 // constant expression that prevents this transformation from being
1380 if (ConstantExpr *TCV = dyn_cast<ConstantExpr>(TrueValue))
1383 if (ConstantExpr *FCV = dyn_cast<ConstantExpr>(FalseValue))
1387 TrueResult.push_back(TrueValue);
1388 FalseResult.push_back(FalseValue);
1391 // Okay, we collected all the mapped values and checked them for sanity, and
1392 // defined to really do this transformation. First, update the CFG.
1393 TrueSucc->removePredecessor(BI->getParent());
1394 FalseSucc->removePredecessor(BI->getParent());
1396 // Insert select instructions where needed.
1397 Value *BrCond = BI->getCondition();
1398 for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
1399 // Insert a select if the results differ.
1400 if (TrueResult[i] == FalseResult[i] || isa<UndefValue>(FalseResult[i]))
1402 if (isa<UndefValue>(TrueResult[i])) {
1403 TrueResult[i] = FalseResult[i];
1407 TrueResult[i] = SelectInst::Create(BrCond, TrueResult[i],
1408 FalseResult[i], "retval", BI);
1411 Value *RI = ReturnInst::Create(&TrueResult[0], TrueResult.size(), BI);
1413 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1414 << "\n " << *BI << "NewRet = " << *RI
1415 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
1417 BI->eraseFromParent();
1419 if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
1420 ErasePossiblyDeadInstructionTree(BrCondI);
1426 /// ConstantIntOrdering - This class implements a stable ordering of constant
1427 /// integers that does not depend on their address. This is important for
1428 /// applications that sort ConstantInt's to ensure uniqueness.
1429 struct ConstantIntOrdering {
1430 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
1431 return LHS->getValue().ult(RHS->getValue());
1436 // SimplifyCFG - This function is used to do simplification of a CFG. For
1437 // example, it adjusts branches to branches to eliminate the extra hop, it
1438 // eliminates unreachable basic blocks, and does other "peephole" optimization
1439 // of the CFG. It returns true if a modification was made.
1441 // WARNING: The entry node of a function may not be simplified.
1443 bool llvm::SimplifyCFG(BasicBlock *BB) {
1444 bool Changed = false;
1445 Function *M = BB->getParent();
1447 assert(BB && BB->getParent() && "Block not embedded in function!");
1448 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1449 assert(&BB->getParent()->getEntryBlock() != BB &&
1450 "Can't Simplify entry block!");
1452 // Remove basic blocks that have no predecessors... which are unreachable.
1453 if ((pred_begin(BB) == pred_end(BB)) ||
1454 (*pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB))) {
1455 DOUT << "Removing BB: \n" << *BB;
1457 // Loop through all of our successors and make sure they know that one
1458 // of their predecessors is going away.
1459 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
1460 SI->removePredecessor(BB);
1462 while (!BB->empty()) {
1463 Instruction &I = BB->back();
1464 // If this instruction is used, replace uses with an arbitrary
1465 // value. Because control flow can't get here, we don't care
1466 // what we replace the value with. Note that since this block is
1467 // unreachable, and all values contained within it must dominate their
1468 // uses, that all uses will eventually be removed.
1470 // Make all users of this instruction use undef instead
1471 I.replaceAllUsesWith(UndefValue::get(I.getType()));
1473 // Remove the instruction from the basic block
1474 BB->getInstList().pop_back();
1476 M->getBasicBlockList().erase(BB);
1480 // Check to see if we can constant propagate this terminator instruction
1482 Changed |= ConstantFoldTerminator(BB);
1484 // If there is a trivial two-entry PHI node in this basic block, and we can
1485 // eliminate it, do so now.
1486 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1487 if (PN->getNumIncomingValues() == 2)
1488 Changed |= FoldTwoEntryPHINode(PN);
1490 // If this is a returning block with only PHI nodes in it, fold the return
1491 // instruction into any unconditional branch predecessors.
1493 // If any predecessor is a conditional branch that just selects among
1494 // different return values, fold the replace the branch/return with a select
1496 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1497 BasicBlock::iterator BBI = BB->getTerminator();
1498 if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
1499 // Find predecessors that end with branches.
1500 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1501 SmallVector<BranchInst*, 8> CondBranchPreds;
1502 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1503 TerminatorInst *PTI = (*PI)->getTerminator();
1504 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1505 if (BI->isUnconditional())
1506 UncondBranchPreds.push_back(*PI);
1508 CondBranchPreds.push_back(BI);
1512 // If we found some, do the transformation!
1513 if (!UncondBranchPreds.empty()) {
1514 while (!UncondBranchPreds.empty()) {
1515 BasicBlock *Pred = UncondBranchPreds.back();
1516 DOUT << "FOLDING: " << *BB
1517 << "INTO UNCOND BRANCH PRED: " << *Pred;
1518 UncondBranchPreds.pop_back();
1519 Instruction *UncondBranch = Pred->getTerminator();
1520 // Clone the return and add it to the end of the predecessor.
1521 Instruction *NewRet = RI->clone();
1522 Pred->getInstList().push_back(NewRet);
1524 // If the return instruction returns a value, and if the value was a
1525 // PHI node in "BB", propagate the right value into the return.
1526 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1528 if (PHINode *PN = dyn_cast<PHINode>(*i))
1529 if (PN->getParent() == BB)
1530 *i = PN->getIncomingValueForBlock(Pred);
1532 // Update any PHI nodes in the returning block to realize that we no
1533 // longer branch to them.
1534 BB->removePredecessor(Pred);
1535 Pred->getInstList().erase(UncondBranch);
1538 // If we eliminated all predecessors of the block, delete the block now.
1539 if (pred_begin(BB) == pred_end(BB))
1540 // We know there are no successors, so just nuke the block.
1541 M->getBasicBlockList().erase(BB);
1546 // Check out all of the conditional branches going to this return
1547 // instruction. If any of them just select between returns, change the
1548 // branch itself into a select/return pair.
1549 while (!CondBranchPreds.empty()) {
1550 BranchInst *BI = CondBranchPreds.back();
1551 CondBranchPreds.pop_back();
1553 // Check to see if the non-BB successor is also a return block.
1554 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1555 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1556 SimplifyCondBranchToTwoReturns(BI))
1560 } else if (isa<UnwindInst>(BB->begin())) {
1561 // Check to see if the first instruction in this block is just an unwind.
1562 // If so, replace any invoke instructions which use this as an exception
1563 // destination with call instructions, and any unconditional branch
1564 // predecessor with an unwind.
1566 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1567 while (!Preds.empty()) {
1568 BasicBlock *Pred = Preds.back();
1569 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1570 if (BI->isUnconditional()) {
1571 Pred->getInstList().pop_back(); // nuke uncond branch
1572 new UnwindInst(Pred); // Use unwind.
1575 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1576 if (II->getUnwindDest() == BB) {
1577 // Insert a new branch instruction before the invoke, because this
1578 // is now a fall through...
1579 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1580 Pred->getInstList().remove(II); // Take out of symbol table
1582 // Insert the call now...
1583 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1584 CallInst *CI = CallInst::Create(II->getCalledValue(),
1585 Args.begin(), Args.end(),
1587 CI->setCallingConv(II->getCallingConv());
1588 CI->setParamAttrs(II->getParamAttrs());
1589 // If the invoke produced a value, the Call now does instead
1590 II->replaceAllUsesWith(CI);
1598 // If this block is now dead, remove it.
1599 if (pred_begin(BB) == pred_end(BB)) {
1600 // We know there are no successors, so just nuke the block.
1601 M->getBasicBlockList().erase(BB);
1605 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1606 if (isValueEqualityComparison(SI)) {
1607 // If we only have one predecessor, and if it is a branch on this value,
1608 // see if that predecessor totally determines the outcome of this switch.
1609 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1610 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1611 return SimplifyCFG(BB) || 1;
1613 // If the block only contains the switch, see if we can fold the block
1614 // away into any preds.
1615 if (SI == &BB->front())
1616 if (FoldValueComparisonIntoPredecessors(SI))
1617 return SimplifyCFG(BB) || 1;
1619 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1620 if (BI->isUnconditional()) {
1621 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1623 BasicBlock *Succ = BI->getSuccessor(0);
1624 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1625 Succ != BB) // Don't hurt infinite loops!
1626 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1629 } else { // Conditional branch
1630 if (isValueEqualityComparison(BI)) {
1631 // If we only have one predecessor, and if it is a branch on this value,
1632 // see if that predecessor totally determines the outcome of this
1634 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1635 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1636 return SimplifyCFG(BB) || 1;
1638 // This block must be empty, except for the setcond inst, if it exists.
1639 BasicBlock::iterator I = BB->begin();
1641 (&*I == cast<Instruction>(BI->getCondition()) &&
1643 if (FoldValueComparisonIntoPredecessors(BI))
1644 return SimplifyCFG(BB) | true;
1647 // If this is a branch on a phi node in the current block, thread control
1648 // through this block if any PHI node entries are constants.
1649 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1650 if (PN->getParent() == BI->getParent())
1651 if (FoldCondBranchOnPHI(BI))
1652 return SimplifyCFG(BB) | true;
1654 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1655 // branches to us and one of our successors, fold the setcc into the
1656 // predecessor and use logical operations to pick the right destination.
1657 BasicBlock *TrueDest = BI->getSuccessor(0);
1658 BasicBlock *FalseDest = BI->getSuccessor(1);
1659 if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition())) {
1660 BasicBlock::iterator CondIt = Cond;
1661 if ((isa<CmpInst>(Cond) || isa<BinaryOperator>(Cond)) &&
1662 Cond->getParent() == BB && &BB->front() == Cond &&
1663 &*++CondIt == BI && Cond->hasOneUse() &&
1664 TrueDest != BB && FalseDest != BB)
1665 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI)
1666 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1667 if (PBI->isConditional() && SafeToMergeTerminators(BI, PBI)) {
1668 BasicBlock *PredBlock = *PI;
1669 if (PBI->getSuccessor(0) == FalseDest ||
1670 PBI->getSuccessor(1) == TrueDest) {
1671 // Invert the predecessors condition test (xor it with true),
1672 // which allows us to write this code once.
1674 BinaryOperator::CreateNot(PBI->getCondition(),
1675 PBI->getCondition()->getName()+".not", PBI);
1676 PBI->setCondition(NewCond);
1677 BasicBlock *OldTrue = PBI->getSuccessor(0);
1678 BasicBlock *OldFalse = PBI->getSuccessor(1);
1679 PBI->setSuccessor(0, OldFalse);
1680 PBI->setSuccessor(1, OldTrue);
1683 if ((PBI->getSuccessor(0) == TrueDest && FalseDest != BB) ||
1684 (PBI->getSuccessor(1) == FalseDest && TrueDest != BB)) {
1685 // Clone Cond into the predecessor basic block, and or/and the
1686 // two conditions together.
1687 Instruction *New = Cond->clone();
1688 PredBlock->getInstList().insert(PBI, New);
1689 New->takeName(Cond);
1690 Cond->setName(New->getName()+".old");
1691 Instruction::BinaryOps Opcode =
1692 PBI->getSuccessor(0) == TrueDest ?
1693 Instruction::Or : Instruction::And;
1695 BinaryOperator::Create(Opcode, PBI->getCondition(),
1696 New, "bothcond", PBI);
1697 PBI->setCondition(NewCond);
1698 if (PBI->getSuccessor(0) == BB) {
1699 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1700 PBI->setSuccessor(0, TrueDest);
1702 if (PBI->getSuccessor(1) == BB) {
1703 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1704 PBI->setSuccessor(1, FalseDest);
1706 return SimplifyCFG(BB) | 1;
1711 // Scan predessor blocks for conditional branches.
1712 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1713 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1714 if (PBI != BI && PBI->isConditional()) {
1716 // If this block ends with a branch instruction, and if there is a
1717 // predecessor that ends on a branch of the same condition, make
1718 // this conditional branch redundant.
1719 if (PBI->getCondition() == BI->getCondition() &&
1720 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1721 // Okay, the outcome of this conditional branch is statically
1722 // knowable. If this block had a single pred, handle specially.
1723 if (BB->getSinglePredecessor()) {
1724 // Turn this into a branch on constant.
1725 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1726 BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
1727 return SimplifyCFG(BB); // Nuke the branch on constant.
1730 // Otherwise, if there are multiple predecessors, insert a PHI
1731 // that merges in the constant and simplify the block result.
1732 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1733 PHINode *NewPN = PHINode::Create(Type::Int1Ty,
1734 BI->getCondition()->getName()
1735 + ".pr", BB->begin());
1736 for (PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1737 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1738 PBI != BI && PBI->isConditional() &&
1739 PBI->getCondition() == BI->getCondition() &&
1740 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1741 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1742 NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
1745 NewPN->addIncoming(BI->getCondition(), *PI);
1748 BI->setCondition(NewPN);
1749 // This will thread the branch.
1750 return SimplifyCFG(BB) | true;
1754 // If this is a conditional branch in an empty block, and if any
1755 // predecessors is a conditional branch to one of our destinations,
1756 // fold the conditions into logical ops and one cond br.
1757 if (&BB->front() == BI) {
1759 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
1761 } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
1762 PBIOp = 0; BIOp = 1;
1763 } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
1764 PBIOp = 1; BIOp = 0;
1765 } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
1771 // Check to make sure that the other destination of this branch
1772 // isn't BB itself. If so, this is an infinite loop that will
1773 // keep getting unwound.
1774 if (PBIOp != -1 && PBI->getSuccessor(PBIOp) == BB)
1777 // Do not perform this transformation if it would require
1778 // insertion of a large number of select instructions. For targets
1779 // without predication/cmovs, this is a big pessimization.
1781 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1783 unsigned NumPhis = 0;
1784 for (BasicBlock::iterator II = CommonDest->begin();
1785 isa<PHINode>(II); ++II, ++NumPhis) {
1787 // Disable this xform.
1794 // Finally, if everything is ok, fold the branches to logical ops.
1796 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1797 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1799 // If OtherDest *is* BB, then this is a basic block with just
1800 // a conditional branch in it, where one edge (OtherDesg) goes
1801 // back to the block. We know that the program doesn't get
1802 // stuck in the infinite loop, so the condition must be such
1803 // that OtherDest isn't branched through. Forward to CommonDest,
1804 // and avoid an infinite loop at optimizer time.
1805 if (OtherDest == BB)
1806 OtherDest = CommonDest;
1808 DOUT << "FOLDING BRs:" << *PBI->getParent()
1809 << "AND: " << *BI->getParent();
1811 // BI may have other predecessors. Because of this, we leave
1812 // it alone, but modify PBI.
1814 // Make sure we get to CommonDest on True&True directions.
1815 Value *PBICond = PBI->getCondition();
1817 PBICond = BinaryOperator::CreateNot(PBICond,
1818 PBICond->getName()+".not",
1820 Value *BICond = BI->getCondition();
1822 BICond = BinaryOperator::CreateNot(BICond,
1823 BICond->getName()+".not",
1825 // Merge the conditions.
1827 BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1829 // Modify PBI to branch on the new condition to the new dests.
1830 PBI->setCondition(Cond);
1831 PBI->setSuccessor(0, CommonDest);
1832 PBI->setSuccessor(1, OtherDest);
1834 // OtherDest may have phi nodes. If so, add an entry from PBI's
1835 // block that are identical to the entries for BI's block.
1837 for (BasicBlock::iterator II = OtherDest->begin();
1838 (PN = dyn_cast<PHINode>(II)); ++II) {
1839 Value *V = PN->getIncomingValueForBlock(BB);
1840 PN->addIncoming(V, PBI->getParent());
1843 // We know that the CommonDest already had an edge from PBI to
1844 // it. If it has PHIs though, the PHIs may have different
1845 // entries for BB and PBI's BB. If so, insert a select to make
1847 for (BasicBlock::iterator II = CommonDest->begin();
1848 (PN = dyn_cast<PHINode>(II)); ++II) {
1849 Value * BIV = PN->getIncomingValueForBlock(BB);
1850 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1851 Value *PBIV = PN->getIncomingValue(PBBIdx);
1853 // Insert a select in PBI to pick the right value.
1854 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1855 PBIV->getName()+".mux", PBI);
1856 PN->setIncomingValue(PBBIdx, NV);
1860 DOUT << "INTO: " << *PBI->getParent();
1862 // This basic block is probably dead. We know it has at least
1863 // one fewer predecessor.
1864 return SimplifyCFG(BB) | true;
1869 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1870 // If there are any instructions immediately before the unreachable that can
1871 // be removed, do so.
1872 Instruction *Unreachable = BB->getTerminator();
1873 while (Unreachable != BB->begin()) {
1874 BasicBlock::iterator BBI = Unreachable;
1876 if (isa<CallInst>(BBI)) break;
1877 // Delete this instruction
1878 BB->getInstList().erase(BBI);
1882 // If the unreachable instruction is the first in the block, take a gander
1883 // at all of the predecessors of this instruction, and simplify them.
1884 if (&BB->front() == Unreachable) {
1885 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1886 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1887 TerminatorInst *TI = Preds[i]->getTerminator();
1889 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1890 if (BI->isUnconditional()) {
1891 if (BI->getSuccessor(0) == BB) {
1892 new UnreachableInst(TI);
1893 TI->eraseFromParent();
1897 if (BI->getSuccessor(0) == BB) {
1898 BranchInst::Create(BI->getSuccessor(1), BI);
1899 BI->eraseFromParent();
1900 } else if (BI->getSuccessor(1) == BB) {
1901 BranchInst::Create(BI->getSuccessor(0), BI);
1902 BI->eraseFromParent();
1906 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1907 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1908 if (SI->getSuccessor(i) == BB) {
1909 BB->removePredecessor(SI->getParent());
1914 // If the default value is unreachable, figure out the most popular
1915 // destination and make it the default.
1916 if (SI->getSuccessor(0) == BB) {
1917 std::map<BasicBlock*, unsigned> Popularity;
1918 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1919 Popularity[SI->getSuccessor(i)]++;
1921 // Find the most popular block.
1922 unsigned MaxPop = 0;
1923 BasicBlock *MaxBlock = 0;
1924 for (std::map<BasicBlock*, unsigned>::iterator
1925 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
1926 if (I->second > MaxPop) {
1928 MaxBlock = I->first;
1932 // Make this the new default, allowing us to delete any explicit
1934 SI->setSuccessor(0, MaxBlock);
1937 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
1939 if (isa<PHINode>(MaxBlock->begin()))
1940 for (unsigned i = 0; i != MaxPop-1; ++i)
1941 MaxBlock->removePredecessor(SI->getParent());
1943 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1944 if (SI->getSuccessor(i) == MaxBlock) {
1950 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
1951 if (II->getUnwindDest() == BB) {
1952 // Convert the invoke to a call instruction. This would be a good
1953 // place to note that the call does not throw though.
1954 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1955 II->removeFromParent(); // Take out of symbol table
1957 // Insert the call now...
1958 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
1959 CallInst *CI = CallInst::Create(II->getCalledValue(),
1960 Args.begin(), Args.end(),
1962 CI->setCallingConv(II->getCallingConv());
1963 CI->setParamAttrs(II->getParamAttrs());
1964 // If the invoke produced a value, the Call does now instead.
1965 II->replaceAllUsesWith(CI);
1972 // If this block is now dead, remove it.
1973 if (pred_begin(BB) == pred_end(BB)) {
1974 // We know there are no successors, so just nuke the block.
1975 M->getBasicBlockList().erase(BB);
1981 // Merge basic blocks into their predecessor if there is only one distinct
1982 // pred, and if there is only one distinct successor of the predecessor, and
1983 // if there are no PHI nodes.
1985 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
1986 BasicBlock *OnlyPred = *PI++;
1987 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
1988 if (*PI != OnlyPred) {
1989 OnlyPred = 0; // There are multiple different predecessors...
1993 BasicBlock *OnlySucc = 0;
1994 if (OnlyPred && OnlyPred != BB && // Don't break self loops
1995 OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) {
1996 // Check to see if there is only one distinct successor...
1997 succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred));
1999 for (; SI != SE; ++SI)
2000 if (*SI != OnlySucc) {
2001 OnlySucc = 0; // There are multiple distinct successors!
2007 DOUT << "Merging: " << *BB << "into: " << *OnlyPred;
2009 // Resolve any PHI nodes at the start of the block. They are all
2010 // guaranteed to have exactly one entry if they exist, unless there are
2011 // multiple duplicate (but guaranteed to be equal) entries for the
2012 // incoming edges. This occurs when there are multiple edges from
2013 // OnlyPred to OnlySucc.
2015 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
2016 PN->replaceAllUsesWith(PN->getIncomingValue(0));
2017 BB->getInstList().pop_front(); // Delete the phi node.
2020 // Delete the unconditional branch from the predecessor.
2021 OnlyPred->getInstList().pop_back();
2023 // Move all definitions in the successor to the predecessor.
2024 OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
2026 // Make all PHI nodes that referred to BB now refer to Pred as their
2028 BB->replaceAllUsesWith(OnlyPred);
2030 // Inherit predecessors name if it exists.
2031 if (!OnlyPred->hasName())
2032 OnlyPred->takeName(BB);
2034 // Erase basic block from the function.
2035 M->getBasicBlockList().erase(BB);
2040 // Otherwise, if this block only has a single predecessor, and if that block
2041 // is a conditional branch, see if we can hoist any code from this block up
2042 // into our predecessor.
2044 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2045 if (BI->isConditional()) {
2046 // Get the other block.
2047 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2048 PI = pred_begin(OtherBB);
2050 if (PI == pred_end(OtherBB)) {
2051 // We have a conditional branch to two blocks that are only reachable
2052 // from the condbr. We know that the condbr dominates the two blocks,
2053 // so see if there is any identical code in the "then" and "else"
2054 // blocks. If so, we can hoist it up to the branching block.
2055 Changed |= HoistThenElseCodeToIf(BI);
2058 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2062 else if (*SI != OnlySucc) {
2063 OnlySucc = 0; // There are multiple distinct successors!
2068 if (OnlySucc == OtherBB) {
2069 // If BB's only successor is the other successor of the predecessor,
2070 // i.e. a triangle, see if we can hoist any code from this block up
2071 // to the "if" block.
2072 Changed |= SpeculativelyExecuteBB(BI, BB);
2077 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2078 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2079 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2080 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2081 Instruction *Cond = cast<Instruction>(BI->getCondition());
2082 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2083 // 'setne's and'ed together, collect them.
2085 std::vector<ConstantInt*> Values;
2086 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2087 if (CompVal && CompVal->getType()->isInteger()) {
2088 // There might be duplicate constants in the list, which the switch
2089 // instruction can't handle, remove them now.
2090 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2091 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2093 // Figure out which block is which destination.
2094 BasicBlock *DefaultBB = BI->getSuccessor(1);
2095 BasicBlock *EdgeBB = BI->getSuccessor(0);
2096 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2098 // Create the new switch instruction now.
2099 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2102 // Add all of the 'cases' to the switch instruction.
2103 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2104 New->addCase(Values[i], EdgeBB);
2106 // We added edges from PI to the EdgeBB. As such, if there were any
2107 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2108 // the number of edges added.
2109 for (BasicBlock::iterator BBI = EdgeBB->begin();
2110 isa<PHINode>(BBI); ++BBI) {
2111 PHINode *PN = cast<PHINode>(BBI);
2112 Value *InVal = PN->getIncomingValueForBlock(*PI);
2113 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2114 PN->addIncoming(InVal, *PI);
2117 // Erase the old branch instruction.
2118 (*PI)->getInstList().erase(BI);
2120 // Erase the potentially condition tree that was used to computed the
2121 // branch condition.
2122 ErasePossiblyDeadInstructionTree(Cond);