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"
32 /// SafeToMergeTerminators - Return true if it is safe to merge these two
33 /// terminator instructions together.
35 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
36 if (SI1 == SI2) return false; // Can't merge with self!
38 // It is not safe to merge these two switch instructions if they have a common
39 // successor, and if that successor has a PHI node, and if *that* PHI node has
40 // conflicting incoming values from the two switch blocks.
41 BasicBlock *SI1BB = SI1->getParent();
42 BasicBlock *SI2BB = SI2->getParent();
43 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
45 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
46 if (SI1Succs.count(*I))
47 for (BasicBlock::iterator BBI = (*I)->begin();
48 isa<PHINode>(BBI); ++BBI) {
49 PHINode *PN = cast<PHINode>(BBI);
50 if (PN->getIncomingValueForBlock(SI1BB) !=
51 PN->getIncomingValueForBlock(SI2BB))
58 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
59 /// now be entries in it from the 'NewPred' block. The values that will be
60 /// flowing into the PHI nodes will be the same as those coming in from
61 /// ExistPred, an existing predecessor of Succ.
62 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
63 BasicBlock *ExistPred) {
64 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
65 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
66 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
68 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
69 PHINode *PN = cast<PHINode>(I);
70 Value *V = PN->getIncomingValueForBlock(ExistPred);
71 PN->addIncoming(V, NewPred);
75 // CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
76 // almost-empty BB ending in an unconditional branch to Succ, into succ.
78 // Assumption: Succ is the single successor for BB.
80 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
81 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
83 DOUT << "Looking to fold " << BB->getNameStart() << " into "
84 << Succ->getNameStart() << "\n";
85 // Shortcut, if there is only a single predecessor is must be BB and merging
87 if (Succ->getSinglePredecessor()) return true;
89 typedef SmallPtrSet<Instruction*, 16> InstrSet;
92 // Make a list of all phi nodes in BB
93 BasicBlock::iterator BBI = BB->begin();
94 while (isa<PHINode>(*BBI)) BBPHIs.insert(BBI++);
96 // Make a list of the predecessors of BB
97 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
98 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
100 // Use that list to make another list of common predecessors of BB and Succ
101 BlockSet CommonPreds;
102 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
104 if (BBPreds.count(*PI))
105 CommonPreds.insert(*PI);
107 // Shortcut, if there are no common predecessors, merging is always safe
108 if (CommonPreds.begin() == CommonPreds.end())
111 // Look at all the phi nodes in Succ, to see if they present a conflict when
112 // merging these blocks
113 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
114 PHINode *PN = cast<PHINode>(I);
116 // If the incoming value from BB is again a PHINode in
117 // BB which has the same incoming value for *PI as PN does, we can
118 // merge the phi nodes and then the blocks can still be merged
119 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
120 if (BBPN && BBPN->getParent() == BB) {
121 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
123 if (BBPN->getIncomingValueForBlock(*PI)
124 != PN->getIncomingValueForBlock(*PI)) {
125 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
126 << Succ->getNameStart() << " is conflicting with "
127 << BBPN->getNameStart() << " with regard to common predecessor "
128 << (*PI)->getNameStart() << "\n";
132 // Remove this phinode from the list of phis in BB, since it has been
136 Value* Val = PN->getIncomingValueForBlock(BB);
137 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
139 // See if the incoming value for the common predecessor is equal to the
140 // one for BB, in which case this phi node will not prevent the merging
142 if (Val != PN->getIncomingValueForBlock(*PI)) {
143 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
144 << Succ->getNameStart() << " is conflicting with regard to common "
145 << "predecessor " << (*PI)->getNameStart() << "\n";
152 // If there are any other phi nodes in BB that don't have a phi node in Succ
153 // to merge with, they must be moved to Succ completely. However, for any
154 // predecessors of Succ, branches will be added to the phi node that just
155 // point to itself. So, for any common predecessors, this must not cause
157 for (InstrSet::iterator I = BBPHIs.begin(), E = BBPHIs.end();
159 PHINode *PN = cast<PHINode>(*I);
160 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
162 if (PN->getIncomingValueForBlock(*PI) != PN) {
163 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
164 << BB->getNameStart() << " is conflicting with regard to common "
165 << "predecessor " << (*PI)->getNameStart() << "\n";
173 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
174 /// branch to Succ, and contains no instructions other than PHI nodes and the
175 /// branch. If possible, eliminate BB.
176 static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
178 // Check to see if merging these blocks would cause conflicts for any of the
179 // phi nodes in BB or Succ. If not, we can safely merge.
180 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
182 DOUT << "Killing Trivial BB: \n" << *BB;
184 if (isa<PHINode>(Succ->begin())) {
185 // If there is more than one pred of succ, and there are PHI nodes in
186 // the successor, then we need to add incoming edges for the PHI nodes
188 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
190 // Loop over all of the PHI nodes in the successor of BB.
191 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
192 PHINode *PN = cast<PHINode>(I);
193 Value *OldVal = PN->removeIncomingValue(BB, false);
194 assert(OldVal && "No entry in PHI for Pred BB!");
196 // If this incoming value is one of the PHI nodes in BB, the new entries
197 // in the PHI node are the entries from the old PHI.
198 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
199 PHINode *OldValPN = cast<PHINode>(OldVal);
200 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
201 // Note that, since we are merging phi nodes and BB and Succ might
202 // have common predecessors, we could end up with a phi node with
203 // identical incoming branches. This will be cleaned up later (and
204 // will trigger asserts if we try to clean it up now, without also
205 // simplifying the corresponding conditional branch).
206 PN->addIncoming(OldValPN->getIncomingValue(i),
207 OldValPN->getIncomingBlock(i));
209 // Add an incoming value for each of the new incoming values.
210 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
211 PN->addIncoming(OldVal, BBPreds[i]);
216 if (isa<PHINode>(&BB->front())) {
217 SmallVector<BasicBlock*, 16>
218 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
220 // Move all PHI nodes in BB to Succ if they are alive, otherwise
222 while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
223 if (PN->use_empty()) {
224 // Just remove the dead phi. This happens if Succ's PHIs were the only
225 // users of the PHI nodes.
226 PN->eraseFromParent();
228 // The instruction is alive, so this means that BB must dominate all
229 // predecessors of Succ (Since all uses of the PN are after its
230 // definition, so in Succ or a block dominated by Succ. If a predecessor
231 // of Succ would not be dominated by BB, PN would violate the def before
232 // use SSA demand). Therefore, we can simply move the phi node to the
234 Succ->getInstList().splice(Succ->begin(),
235 BB->getInstList(), BB->begin());
237 // We need to add new entries for the PHI node to account for
238 // predecessors of Succ that the PHI node does not take into
239 // account. At this point, since we know that BB dominated succ and all
240 // of its predecessors, this means that we should any newly added
241 // incoming edges should use the PHI node itself as the value for these
242 // edges, because they are loop back edges.
243 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
244 if (OldSuccPreds[i] != BB)
245 PN->addIncoming(PN, OldSuccPreds[i]);
249 // Everything that jumped to BB now goes to Succ.
250 BB->replaceAllUsesWith(Succ);
251 if (!Succ->hasName()) Succ->takeName(BB);
252 BB->eraseFromParent(); // Delete the old basic block.
256 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
257 /// presumably PHI nodes in it), check to see if the merge at this block is due
258 /// to an "if condition". If so, return the boolean condition that determines
259 /// which entry into BB will be taken. Also, return by references the block
260 /// that will be entered from if the condition is true, and the block that will
261 /// be entered if the condition is false.
264 static Value *GetIfCondition(BasicBlock *BB,
265 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
266 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
267 "Function can only handle blocks with 2 predecessors!");
268 BasicBlock *Pred1 = *pred_begin(BB);
269 BasicBlock *Pred2 = *++pred_begin(BB);
271 // We can only handle branches. Other control flow will be lowered to
272 // branches if possible anyway.
273 if (!isa<BranchInst>(Pred1->getTerminator()) ||
274 !isa<BranchInst>(Pred2->getTerminator()))
276 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
277 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
279 // Eliminate code duplication by ensuring that Pred1Br is conditional if
281 if (Pred2Br->isConditional()) {
282 // If both branches are conditional, we don't have an "if statement". In
283 // reality, we could transform this case, but since the condition will be
284 // required anyway, we stand no chance of eliminating it, so the xform is
285 // probably not profitable.
286 if (Pred1Br->isConditional())
289 std::swap(Pred1, Pred2);
290 std::swap(Pred1Br, Pred2Br);
293 if (Pred1Br->isConditional()) {
294 // If we found a conditional branch predecessor, make sure that it branches
295 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
296 if (Pred1Br->getSuccessor(0) == BB &&
297 Pred1Br->getSuccessor(1) == Pred2) {
300 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
301 Pred1Br->getSuccessor(1) == BB) {
305 // We know that one arm of the conditional goes to BB, so the other must
306 // go somewhere unrelated, and this must not be an "if statement".
310 // The only thing we have to watch out for here is to make sure that Pred2
311 // doesn't have incoming edges from other blocks. If it does, the condition
312 // doesn't dominate BB.
313 if (++pred_begin(Pred2) != pred_end(Pred2))
316 return Pred1Br->getCondition();
319 // Ok, if we got here, both predecessors end with an unconditional branch to
320 // BB. Don't panic! If both blocks only have a single (identical)
321 // predecessor, and THAT is a conditional branch, then we're all ok!
322 if (pred_begin(Pred1) == pred_end(Pred1) ||
323 ++pred_begin(Pred1) != pred_end(Pred1) ||
324 pred_begin(Pred2) == pred_end(Pred2) ||
325 ++pred_begin(Pred2) != pred_end(Pred2) ||
326 *pred_begin(Pred1) != *pred_begin(Pred2))
329 // Otherwise, if this is a conditional branch, then we can use it!
330 BasicBlock *CommonPred = *pred_begin(Pred1);
331 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
332 assert(BI->isConditional() && "Two successors but not conditional?");
333 if (BI->getSuccessor(0) == Pred1) {
340 return BI->getCondition();
346 // If we have a merge point of an "if condition" as accepted above, return true
347 // if the specified value dominates the block. We don't handle the true
348 // generality of domination here, just a special case which works well enough
351 // If AggressiveInsts is non-null, and if V does not dominate BB, we check to
352 // see if V (which must be an instruction) is cheap to compute and is
353 // non-trapping. If both are true, the instruction is inserted into the set and
355 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
356 std::set<Instruction*> *AggressiveInsts) {
357 Instruction *I = dyn_cast<Instruction>(V);
359 // Non-instructions all dominate instructions, but not all constantexprs
360 // can be executed unconditionally.
361 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
366 BasicBlock *PBB = I->getParent();
368 // We don't want to allow weird loops that might have the "if condition" in
369 // the bottom of this block.
370 if (PBB == BB) return false;
372 // If this instruction is defined in a block that contains an unconditional
373 // branch to BB, then it must be in the 'conditional' part of the "if
375 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
376 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
377 if (!AggressiveInsts) return false;
378 // Okay, it looks like the instruction IS in the "condition". Check to
379 // see if its a cheap instruction to unconditionally compute, and if it
380 // only uses stuff defined outside of the condition. If so, hoist it out.
381 switch (I->getOpcode()) {
382 default: return false; // Cannot hoist this out safely.
383 case Instruction::Load:
384 // We can hoist loads that are non-volatile and obviously cannot trap.
385 if (cast<LoadInst>(I)->isVolatile())
387 if (!isa<AllocaInst>(I->getOperand(0)) &&
388 !isa<Constant>(I->getOperand(0)))
391 // Finally, we have to check to make sure there are no instructions
392 // before the load in its basic block, as we are going to hoist the loop
393 // out to its predecessor.
394 if (PBB->begin() != BasicBlock::iterator(I))
397 case Instruction::Add:
398 case Instruction::Sub:
399 case Instruction::And:
400 case Instruction::Or:
401 case Instruction::Xor:
402 case Instruction::Shl:
403 case Instruction::LShr:
404 case Instruction::AShr:
405 case Instruction::ICmp:
406 case Instruction::FCmp:
407 if (I->getOperand(0)->getType()->isFPOrFPVector())
408 return false; // FP arithmetic might trap.
409 break; // These are all cheap and non-trapping instructions.
412 // Okay, we can only really hoist these out if their operands are not
413 // defined in the conditional region.
414 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
415 if (!DominatesMergePoint(I->getOperand(i), BB, 0))
417 // Okay, it's safe to do this! Remember this instruction.
418 AggressiveInsts->insert(I);
424 // GatherConstantSetEQs - Given a potentially 'or'd together collection of
425 // icmp_eq instructions that compare a value against a constant, return the
426 // value being compared, and stick the constant into the Values vector.
427 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
428 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
429 if (Inst->getOpcode() == Instruction::ICmp &&
430 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
431 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
433 return Inst->getOperand(0);
434 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
436 return Inst->getOperand(1);
438 } else if (Inst->getOpcode() == Instruction::Or) {
439 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
440 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
448 // GatherConstantSetNEs - Given a potentially 'and'd together collection of
449 // setne instructions that compare a value against a constant, return the value
450 // being compared, and stick the constant into the Values vector.
451 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
452 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
453 if (Inst->getOpcode() == Instruction::ICmp &&
454 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
455 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
457 return Inst->getOperand(0);
458 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
460 return Inst->getOperand(1);
462 } else if (Inst->getOpcode() == Instruction::And) {
463 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
464 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
474 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
475 /// bunch of comparisons of one value against constants, return the value and
476 /// the constants being compared.
477 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
478 std::vector<ConstantInt*> &Values) {
479 if (Cond->getOpcode() == Instruction::Or) {
480 CompVal = GatherConstantSetEQs(Cond, Values);
482 // Return true to indicate that the condition is true if the CompVal is
483 // equal to one of the constants.
485 } else if (Cond->getOpcode() == Instruction::And) {
486 CompVal = GatherConstantSetNEs(Cond, Values);
488 // Return false to indicate that the condition is false if the CompVal is
489 // equal to one of the constants.
495 /// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
496 /// has no side effects, nuke it. If it uses any instructions that become dead
497 /// because the instruction is now gone, nuke them too.
498 static void ErasePossiblyDeadInstructionTree(Instruction *I) {
499 if (!isInstructionTriviallyDead(I)) return;
501 SmallVector<Instruction*, 16> InstrsToInspect;
502 InstrsToInspect.push_back(I);
504 while (!InstrsToInspect.empty()) {
505 I = InstrsToInspect.back();
506 InstrsToInspect.pop_back();
508 if (!isInstructionTriviallyDead(I)) continue;
510 // If I is in the work list multiple times, remove previous instances.
511 for (unsigned i = 0, e = InstrsToInspect.size(); i != e; ++i)
512 if (InstrsToInspect[i] == I) {
513 InstrsToInspect.erase(InstrsToInspect.begin()+i);
517 // Add operands of dead instruction to worklist.
518 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
519 if (Instruction *OpI = dyn_cast<Instruction>(I->getOperand(i)))
520 InstrsToInspect.push_back(OpI);
522 // Remove dead instruction.
523 I->eraseFromParent();
527 // isValueEqualityComparison - Return true if the specified terminator checks to
528 // see if a value is equal to constant integer value.
529 static Value *isValueEqualityComparison(TerminatorInst *TI) {
530 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
531 // Do not permit merging of large switch instructions into their
532 // predecessors unless there is only one predecessor.
533 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
534 pred_end(SI->getParent())) > 128)
537 return SI->getCondition();
539 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
540 if (BI->isConditional() && BI->getCondition()->hasOneUse())
541 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
542 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
543 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
544 isa<ConstantInt>(ICI->getOperand(1)))
545 return ICI->getOperand(0);
549 // Given a value comparison instruction, decode all of the 'cases' that it
550 // represents and return the 'default' block.
552 GetValueEqualityComparisonCases(TerminatorInst *TI,
553 std::vector<std::pair<ConstantInt*,
554 BasicBlock*> > &Cases) {
555 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
556 Cases.reserve(SI->getNumCases());
557 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
558 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
559 return SI->getDefaultDest();
562 BranchInst *BI = cast<BranchInst>(TI);
563 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
564 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
565 BI->getSuccessor(ICI->getPredicate() ==
566 ICmpInst::ICMP_NE)));
567 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
571 // EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
572 // in the list that match the specified block.
573 static void EliminateBlockCases(BasicBlock *BB,
574 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
575 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
576 if (Cases[i].second == BB) {
577 Cases.erase(Cases.begin()+i);
582 // ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
585 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
586 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
587 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
589 // Make V1 be smaller than V2.
590 if (V1->size() > V2->size())
593 if (V1->size() == 0) return false;
594 if (V1->size() == 1) {
596 ConstantInt *TheVal = (*V1)[0].first;
597 for (unsigned i = 0, e = V2->size(); i != e; ++i)
598 if (TheVal == (*V2)[i].first)
602 // Otherwise, just sort both lists and compare element by element.
603 std::sort(V1->begin(), V1->end());
604 std::sort(V2->begin(), V2->end());
605 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
606 while (i1 != e1 && i2 != e2) {
607 if ((*V1)[i1].first == (*V2)[i2].first)
609 if ((*V1)[i1].first < (*V2)[i2].first)
617 // SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
618 // terminator instruction and its block is known to only have a single
619 // predecessor block, check to see if that predecessor is also a value
620 // comparison with the same value, and if that comparison determines the outcome
621 // of this comparison. If so, simplify TI. This does a very limited form of
623 static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
625 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
626 if (!PredVal) return false; // Not a value comparison in predecessor.
628 Value *ThisVal = isValueEqualityComparison(TI);
629 assert(ThisVal && "This isn't a value comparison!!");
630 if (ThisVal != PredVal) return false; // Different predicates.
632 // Find out information about when control will move from Pred to TI's block.
633 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
634 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
636 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
638 // Find information about how control leaves this block.
639 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
640 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
641 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
643 // If TI's block is the default block from Pred's comparison, potentially
644 // simplify TI based on this knowledge.
645 if (PredDef == TI->getParent()) {
646 // If we are here, we know that the value is none of those cases listed in
647 // PredCases. If there are any cases in ThisCases that are in PredCases, we
649 if (ValuesOverlap(PredCases, ThisCases)) {
650 if (BranchInst *BTI = dyn_cast<BranchInst>(TI)) {
651 // Okay, one of the successors of this condbr is dead. Convert it to a
653 assert(ThisCases.size() == 1 && "Branch can only have one case!");
654 Value *Cond = BTI->getCondition();
655 // Insert the new branch.
656 Instruction *NI = BranchInst::Create(ThisDef, TI);
658 // Remove PHI node entries for the dead edge.
659 ThisCases[0].second->removePredecessor(TI->getParent());
661 DOUT << "Threading pred instr: " << *Pred->getTerminator()
662 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
664 TI->eraseFromParent(); // Nuke the old one.
665 // If condition is now dead, nuke it.
666 if (Instruction *CondI = dyn_cast<Instruction>(Cond))
667 ErasePossiblyDeadInstructionTree(CondI);
671 SwitchInst *SI = cast<SwitchInst>(TI);
672 // Okay, TI has cases that are statically dead, prune them away.
673 SmallPtrSet<Constant*, 16> DeadCases;
674 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
675 DeadCases.insert(PredCases[i].first);
677 DOUT << "Threading pred instr: " << *Pred->getTerminator()
678 << "Through successor TI: " << *TI;
680 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
681 if (DeadCases.count(SI->getCaseValue(i))) {
682 SI->getSuccessor(i)->removePredecessor(TI->getParent());
686 DOUT << "Leaving: " << *TI << "\n";
692 // Otherwise, TI's block must correspond to some matched value. Find out
693 // which value (or set of values) this is.
694 ConstantInt *TIV = 0;
695 BasicBlock *TIBB = TI->getParent();
696 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
697 if (PredCases[i].second == TIBB) {
699 TIV = PredCases[i].first;
701 return false; // Cannot handle multiple values coming to this block.
703 assert(TIV && "No edge from pred to succ?");
705 // Okay, we found the one constant that our value can be if we get into TI's
706 // BB. Find out which successor will unconditionally be branched to.
707 BasicBlock *TheRealDest = 0;
708 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
709 if (ThisCases[i].first == TIV) {
710 TheRealDest = ThisCases[i].second;
714 // If not handled by any explicit cases, it is handled by the default case.
715 if (TheRealDest == 0) TheRealDest = ThisDef;
717 // Remove PHI node entries for dead edges.
718 BasicBlock *CheckEdge = TheRealDest;
719 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
720 if (*SI != CheckEdge)
721 (*SI)->removePredecessor(TIBB);
725 // Insert the new branch.
726 Instruction *NI = BranchInst::Create(TheRealDest, TI);
728 DOUT << "Threading pred instr: " << *Pred->getTerminator()
729 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
730 Instruction *Cond = 0;
731 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
732 Cond = dyn_cast<Instruction>(BI->getCondition());
733 TI->eraseFromParent(); // Nuke the old one.
735 if (Cond) ErasePossiblyDeadInstructionTree(Cond);
741 // FoldValueComparisonIntoPredecessors - The specified terminator is a value
742 // equality comparison instruction (either a switch or a branch on "X == c").
743 // See if any of the predecessors of the terminator block are value comparisons
744 // on the same value. If so, and if safe to do so, fold them together.
745 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
746 BasicBlock *BB = TI->getParent();
747 Value *CV = isValueEqualityComparison(TI); // CondVal
748 assert(CV && "Not a comparison?");
749 bool Changed = false;
751 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
752 while (!Preds.empty()) {
753 BasicBlock *Pred = Preds.back();
756 // See if the predecessor is a comparison with the same value.
757 TerminatorInst *PTI = Pred->getTerminator();
758 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
760 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
761 // Figure out which 'cases' to copy from SI to PSI.
762 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
763 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
765 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
766 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
768 // Based on whether the default edge from PTI goes to BB or not, fill in
769 // PredCases and PredDefault with the new switch cases we would like to
771 SmallVector<BasicBlock*, 8> NewSuccessors;
773 if (PredDefault == BB) {
774 // If this is the default destination from PTI, only the edges in TI
775 // that don't occur in PTI, or that branch to BB will be activated.
776 std::set<ConstantInt*> PTIHandled;
777 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
778 if (PredCases[i].second != BB)
779 PTIHandled.insert(PredCases[i].first);
781 // The default destination is BB, we don't need explicit targets.
782 std::swap(PredCases[i], PredCases.back());
783 PredCases.pop_back();
787 // Reconstruct the new switch statement we will be building.
788 if (PredDefault != BBDefault) {
789 PredDefault->removePredecessor(Pred);
790 PredDefault = BBDefault;
791 NewSuccessors.push_back(BBDefault);
793 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
794 if (!PTIHandled.count(BBCases[i].first) &&
795 BBCases[i].second != BBDefault) {
796 PredCases.push_back(BBCases[i]);
797 NewSuccessors.push_back(BBCases[i].second);
801 // If this is not the default destination from PSI, only the edges
802 // in SI that occur in PSI with a destination of BB will be
804 std::set<ConstantInt*> PTIHandled;
805 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
806 if (PredCases[i].second == BB) {
807 PTIHandled.insert(PredCases[i].first);
808 std::swap(PredCases[i], PredCases.back());
809 PredCases.pop_back();
813 // Okay, now we know which constants were sent to BB from the
814 // predecessor. Figure out where they will all go now.
815 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
816 if (PTIHandled.count(BBCases[i].first)) {
817 // If this is one we are capable of getting...
818 PredCases.push_back(BBCases[i]);
819 NewSuccessors.push_back(BBCases[i].second);
820 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
823 // If there are any constants vectored to BB that TI doesn't handle,
824 // they must go to the default destination of TI.
825 for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
826 E = PTIHandled.end(); I != E; ++I) {
827 PredCases.push_back(std::make_pair(*I, BBDefault));
828 NewSuccessors.push_back(BBDefault);
832 // Okay, at this point, we know which new successor Pred will get. Make
833 // sure we update the number of entries in the PHI nodes for these
835 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
836 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
838 // Now that the successors are updated, create the new Switch instruction.
839 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
840 PredCases.size(), PTI);
841 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
842 NewSI->addCase(PredCases[i].first, PredCases[i].second);
844 Instruction *DeadCond = 0;
845 if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
846 // If PTI is a branch, remember the condition.
847 DeadCond = dyn_cast<Instruction>(BI->getCondition());
848 Pred->getInstList().erase(PTI);
850 // If the condition is dead now, remove the instruction tree.
851 if (DeadCond) ErasePossiblyDeadInstructionTree(DeadCond);
853 // Okay, last check. If BB is still a successor of PSI, then we must
854 // have an infinite loop case. If so, add an infinitely looping block
855 // to handle the case to preserve the behavior of the code.
856 BasicBlock *InfLoopBlock = 0;
857 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
858 if (NewSI->getSuccessor(i) == BB) {
859 if (InfLoopBlock == 0) {
860 // Insert it at the end of the loop, because it's either code,
861 // or it won't matter if it's hot. :)
862 InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
863 BranchInst::Create(InfLoopBlock, InfLoopBlock);
865 NewSI->setSuccessor(i, InfLoopBlock);
874 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
875 /// BB2, hoist any common code in the two blocks up into the branch block. The
876 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
877 static bool HoistThenElseCodeToIf(BranchInst *BI) {
878 // This does very trivial matching, with limited scanning, to find identical
879 // instructions in the two blocks. In particular, we don't want to get into
880 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
881 // such, we currently just scan for obviously identical instructions in an
883 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
884 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
886 Instruction *I1 = BB1->begin(), *I2 = BB2->begin();
887 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
888 isa<InvokeInst>(I1) || !I1->isIdenticalTo(I2))
891 // If we get here, we can hoist at least one instruction.
892 BasicBlock *BIParent = BI->getParent();
895 // If we are hoisting the terminator instruction, don't move one (making a
896 // broken BB), instead clone it, and remove BI.
897 if (isa<TerminatorInst>(I1))
898 goto HoistTerminator;
900 // For a normal instruction, we just move one to right before the branch,
901 // then replace all uses of the other with the first. Finally, we remove
902 // the now redundant second instruction.
903 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
904 if (!I2->use_empty())
905 I2->replaceAllUsesWith(I1);
906 BB2->getInstList().erase(I2);
910 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
915 // Okay, it is safe to hoist the terminator.
916 Instruction *NT = I1->clone();
917 BIParent->getInstList().insert(BI, NT);
918 if (NT->getType() != Type::VoidTy) {
919 I1->replaceAllUsesWith(NT);
920 I2->replaceAllUsesWith(NT);
924 // Hoisting one of the terminators from our successor is a great thing.
925 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
926 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
927 // nodes, so we insert select instruction to compute the final result.
928 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
929 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
931 for (BasicBlock::iterator BBI = SI->begin();
932 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
933 Value *BB1V = PN->getIncomingValueForBlock(BB1);
934 Value *BB2V = PN->getIncomingValueForBlock(BB2);
936 // These values do not agree. Insert a select instruction before NT
937 // that determines the right value.
938 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
940 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
941 BB1V->getName()+"."+BB2V->getName(), NT);
942 // Make the PHI node use the select for all incoming values for BB1/BB2
943 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
944 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
945 PN->setIncomingValue(i, SI);
950 // Update any PHI nodes in our new successors.
951 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
952 AddPredecessorToBlock(*SI, BIParent, BB1);
954 BI->eraseFromParent();
958 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
959 /// across this block.
960 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
961 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
964 // If this basic block contains anything other than a PHI (which controls the
965 // branch) and branch itself, bail out. FIXME: improve this in the future.
966 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) {
967 if (Size > 10) return false; // Don't clone large BB's.
969 // We can only support instructions that are do not define values that are
970 // live outside of the current basic block.
971 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
973 Instruction *U = cast<Instruction>(*UI);
974 if (U->getParent() != BB || isa<PHINode>(U)) return false;
977 // Looks ok, continue checking.
983 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
984 /// that is defined in the same block as the branch and if any PHI entries are
985 /// constants, thread edges corresponding to that entry to be branches to their
986 /// ultimate destination.
987 static bool FoldCondBranchOnPHI(BranchInst *BI) {
988 BasicBlock *BB = BI->getParent();
989 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
990 // NOTE: we currently cannot transform this case if the PHI node is used
991 // outside of the block.
992 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
995 // Degenerate case of a single entry PHI.
996 if (PN->getNumIncomingValues() == 1) {
997 if (PN->getIncomingValue(0) != PN)
998 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1000 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1001 PN->eraseFromParent();
1005 // Now we know that this block has multiple preds and two succs.
1006 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1008 // Okay, this is a simple enough basic block. See if any phi values are
1010 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1012 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1013 CB->getType() == Type::Int1Ty) {
1014 // Okay, we now know that all edges from PredBB should be revectored to
1015 // branch to RealDest.
1016 BasicBlock *PredBB = PN->getIncomingBlock(i);
1017 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1019 if (RealDest == BB) continue; // Skip self loops.
1021 // The dest block might have PHI nodes, other predecessors and other
1022 // difficult cases. Instead of being smart about this, just insert a new
1023 // block that jumps to the destination block, effectively splitting
1024 // the edge we are about to create.
1025 BasicBlock *EdgeBB = BasicBlock::Create(RealDest->getName()+".critedge",
1026 RealDest->getParent(), RealDest);
1027 BranchInst::Create(RealDest, EdgeBB);
1029 for (BasicBlock::iterator BBI = RealDest->begin();
1030 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1031 Value *V = PN->getIncomingValueForBlock(BB);
1032 PN->addIncoming(V, EdgeBB);
1035 // BB may have instructions that are being threaded over. Clone these
1036 // instructions into EdgeBB. We know that there will be no uses of the
1037 // cloned instructions outside of EdgeBB.
1038 BasicBlock::iterator InsertPt = EdgeBB->begin();
1039 std::map<Value*, Value*> TranslateMap; // Track translated values.
1040 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1041 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1042 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1044 // Clone the instruction.
1045 Instruction *N = BBI->clone();
1046 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1048 // Update operands due to translation.
1049 for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
1050 std::map<Value*, Value*>::iterator PI =
1051 TranslateMap.find(N->getOperand(i));
1052 if (PI != TranslateMap.end())
1053 N->setOperand(i, PI->second);
1056 // Check for trivial simplification.
1057 if (Constant *C = ConstantFoldInstruction(N)) {
1058 TranslateMap[BBI] = C;
1059 delete N; // Constant folded away, don't need actual inst
1061 // Insert the new instruction into its new home.
1062 EdgeBB->getInstList().insert(InsertPt, N);
1063 if (!BBI->use_empty())
1064 TranslateMap[BBI] = N;
1069 // Loop over all of the edges from PredBB to BB, changing them to branch
1070 // to EdgeBB instead.
1071 TerminatorInst *PredBBTI = PredBB->getTerminator();
1072 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1073 if (PredBBTI->getSuccessor(i) == BB) {
1074 BB->removePredecessor(PredBB);
1075 PredBBTI->setSuccessor(i, EdgeBB);
1078 // Recurse, simplifying any other constants.
1079 return FoldCondBranchOnPHI(BI) | true;
1086 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1087 /// PHI node, see if we can eliminate it.
1088 static bool FoldTwoEntryPHINode(PHINode *PN) {
1089 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1090 // statement", which has a very simple dominance structure. Basically, we
1091 // are trying to find the condition that is being branched on, which
1092 // subsequently causes this merge to happen. We really want control
1093 // dependence information for this check, but simplifycfg can't keep it up
1094 // to date, and this catches most of the cases we care about anyway.
1096 BasicBlock *BB = PN->getParent();
1097 BasicBlock *IfTrue, *IfFalse;
1098 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1099 if (!IfCond) return false;
1101 // Okay, we found that we can merge this two-entry phi node into a select.
1102 // Doing so would require us to fold *all* two entry phi nodes in this block.
1103 // At some point this becomes non-profitable (particularly if the target
1104 // doesn't support cmov's). Only do this transformation if there are two or
1105 // fewer PHI nodes in this block.
1106 unsigned NumPhis = 0;
1107 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1111 DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
1112 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
1114 // Loop over the PHI's seeing if we can promote them all to select
1115 // instructions. While we are at it, keep track of the instructions
1116 // that need to be moved to the dominating block.
1117 std::set<Instruction*> AggressiveInsts;
1119 BasicBlock::iterator AfterPHIIt = BB->begin();
1120 while (isa<PHINode>(AfterPHIIt)) {
1121 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1122 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1123 if (PN->getIncomingValue(0) != PN)
1124 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1126 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1127 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1128 &AggressiveInsts) ||
1129 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1130 &AggressiveInsts)) {
1135 // If we all PHI nodes are promotable, check to make sure that all
1136 // instructions in the predecessor blocks can be promoted as well. If
1137 // not, we won't be able to get rid of the control flow, so it's not
1138 // worth promoting to select instructions.
1139 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1140 PN = cast<PHINode>(BB->begin());
1141 BasicBlock *Pred = PN->getIncomingBlock(0);
1142 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1144 DomBlock = *pred_begin(Pred);
1145 for (BasicBlock::iterator I = Pred->begin();
1146 !isa<TerminatorInst>(I); ++I)
1147 if (!AggressiveInsts.count(I)) {
1148 // This is not an aggressive instruction that we can promote.
1149 // Because of this, we won't be able to get rid of the control
1150 // flow, so the xform is not worth it.
1155 Pred = PN->getIncomingBlock(1);
1156 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1158 DomBlock = *pred_begin(Pred);
1159 for (BasicBlock::iterator I = Pred->begin();
1160 !isa<TerminatorInst>(I); ++I)
1161 if (!AggressiveInsts.count(I)) {
1162 // This is not an aggressive instruction that we can promote.
1163 // Because of this, we won't be able to get rid of the control
1164 // flow, so the xform is not worth it.
1169 // If we can still promote the PHI nodes after this gauntlet of tests,
1170 // do all of the PHI's now.
1172 // Move all 'aggressive' instructions, which are defined in the
1173 // conditional parts of the if's up to the dominating block.
1175 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1176 IfBlock1->getInstList(),
1178 IfBlock1->getTerminator());
1181 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1182 IfBlock2->getInstList(),
1184 IfBlock2->getTerminator());
1187 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1188 // Change the PHI node into a select instruction.
1190 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1192 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1194 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1195 PN->replaceAllUsesWith(NV);
1198 BB->getInstList().erase(PN);
1203 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1204 /// to two returning blocks, try to merge them together into one return,
1205 /// introducing a select if the return values disagree.
1206 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1207 assert(BI->isConditional() && "Must be a conditional branch");
1208 BasicBlock *TrueSucc = BI->getSuccessor(0);
1209 BasicBlock *FalseSucc = BI->getSuccessor(1);
1210 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1211 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1213 // Check to ensure both blocks are empty (just a return) or optionally empty
1214 // with PHI nodes. If there are other instructions, merging would cause extra
1215 // computation on one path or the other.
1216 BasicBlock::iterator BBI = TrueRet;
1217 if (BBI != TrueSucc->begin() && !isa<PHINode>(--BBI))
1218 return false; // Not empty with optional phi nodes.
1220 if (BBI != FalseSucc->begin() && !isa<PHINode>(--BBI))
1221 return false; // Not empty with optional phi nodes.
1223 // Okay, we found a branch that is going to two return nodes. If
1224 // there is no return value for this function, just change the
1225 // branch into a return.
1226 if (FalseRet->getNumOperands() == 0) {
1227 TrueSucc->removePredecessor(BI->getParent());
1228 FalseSucc->removePredecessor(BI->getParent());
1229 ReturnInst::Create(0, BI);
1230 BI->eraseFromParent();
1234 // Otherwise, build up the result values for the new return.
1235 SmallVector<Value*, 4> TrueResult;
1236 SmallVector<Value*, 4> FalseResult;
1238 for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
1239 // Otherwise, figure out what the true and false return values are
1240 // so we can insert a new select instruction.
1241 Value *TrueValue = TrueRet->getOperand(i);
1242 Value *FalseValue = FalseRet->getOperand(i);
1244 // Unwrap any PHI nodes in the return blocks.
1245 if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue))
1246 if (TVPN->getParent() == TrueSucc)
1247 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1248 if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue))
1249 if (FVPN->getParent() == FalseSucc)
1250 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1252 // In order for this transformation to be safe, we must be able to
1253 // unconditionally execute both operands to the return. This is
1254 // normally the case, but we could have a potentially-trapping
1255 // constant expression that prevents this transformation from being
1257 if (ConstantExpr *TCV = dyn_cast<ConstantExpr>(TrueValue))
1260 if (ConstantExpr *FCV = dyn_cast<ConstantExpr>(FalseValue))
1264 TrueResult.push_back(TrueValue);
1265 FalseResult.push_back(FalseValue);
1268 // Okay, we collected all the mapped values and checked them for sanity, and
1269 // defined to really do this transformation. First, update the CFG.
1270 TrueSucc->removePredecessor(BI->getParent());
1271 FalseSucc->removePredecessor(BI->getParent());
1273 // Insert select instructions where needed.
1274 Value *BrCond = BI->getCondition();
1275 for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
1276 // Insert a select if the results differ.
1277 if (TrueResult[i] == FalseResult[i] || isa<UndefValue>(FalseResult[i]))
1279 if (isa<UndefValue>(TrueResult[i])) {
1280 TrueResult[i] = FalseResult[i];
1284 TrueResult[i] = SelectInst::Create(BrCond, TrueResult[i],
1285 FalseResult[i], "retval", BI);
1288 Value *RI = ReturnInst::Create(&TrueResult[0], TrueResult.size(), BI);
1290 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1291 << "\n " << *BI << "NewRet = " << *RI
1292 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
1294 BI->eraseFromParent();
1296 if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
1297 ErasePossiblyDeadInstructionTree(BrCondI);
1303 /// ConstantIntOrdering - This class implements a stable ordering of constant
1304 /// integers that does not depend on their address. This is important for
1305 /// applications that sort ConstantInt's to ensure uniqueness.
1306 struct ConstantIntOrdering {
1307 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
1308 return LHS->getValue().ult(RHS->getValue());
1313 // SimplifyCFG - This function is used to do simplification of a CFG. For
1314 // example, it adjusts branches to branches to eliminate the extra hop, it
1315 // eliminates unreachable basic blocks, and does other "peephole" optimization
1316 // of the CFG. It returns true if a modification was made.
1318 // WARNING: The entry node of a function may not be simplified.
1320 bool llvm::SimplifyCFG(BasicBlock *BB) {
1321 bool Changed = false;
1322 Function *M = BB->getParent();
1324 assert(BB && BB->getParent() && "Block not embedded in function!");
1325 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1326 assert(&BB->getParent()->getEntryBlock() != BB &&
1327 "Can't Simplify entry block!");
1329 // Remove basic blocks that have no predecessors... which are unreachable.
1330 if ((pred_begin(BB) == pred_end(BB)) ||
1331 (*pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB))) {
1332 DOUT << "Removing BB: \n" << *BB;
1334 // Loop through all of our successors and make sure they know that one
1335 // of their predecessors is going away.
1336 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
1337 SI->removePredecessor(BB);
1339 while (!BB->empty()) {
1340 Instruction &I = BB->back();
1341 // If this instruction is used, replace uses with an arbitrary
1342 // value. Because control flow can't get here, we don't care
1343 // what we replace the value with. Note that since this block is
1344 // unreachable, and all values contained within it must dominate their
1345 // uses, that all uses will eventually be removed.
1347 // Make all users of this instruction use undef instead
1348 I.replaceAllUsesWith(UndefValue::get(I.getType()));
1350 // Remove the instruction from the basic block
1351 BB->getInstList().pop_back();
1353 M->getBasicBlockList().erase(BB);
1357 // Check to see if we can constant propagate this terminator instruction
1359 Changed |= ConstantFoldTerminator(BB);
1361 // If there is a trivial two-entry PHI node in this basic block, and we can
1362 // eliminate it, do so now.
1363 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1364 if (PN->getNumIncomingValues() == 2)
1365 Changed |= FoldTwoEntryPHINode(PN);
1367 // If this is a returning block with only PHI nodes in it, fold the return
1368 // instruction into any unconditional branch predecessors.
1370 // If any predecessor is a conditional branch that just selects among
1371 // different return values, fold the replace the branch/return with a select
1373 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1374 BasicBlock::iterator BBI = BB->getTerminator();
1375 if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
1376 // Find predecessors that end with branches.
1377 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1378 SmallVector<BranchInst*, 8> CondBranchPreds;
1379 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1380 TerminatorInst *PTI = (*PI)->getTerminator();
1381 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1382 if (BI->isUnconditional())
1383 UncondBranchPreds.push_back(*PI);
1385 CondBranchPreds.push_back(BI);
1389 // If we found some, do the transformation!
1390 if (!UncondBranchPreds.empty()) {
1391 while (!UncondBranchPreds.empty()) {
1392 BasicBlock *Pred = UncondBranchPreds.back();
1393 DOUT << "FOLDING: " << *BB
1394 << "INTO UNCOND BRANCH PRED: " << *Pred;
1395 UncondBranchPreds.pop_back();
1396 Instruction *UncondBranch = Pred->getTerminator();
1397 // Clone the return and add it to the end of the predecessor.
1398 Instruction *NewRet = RI->clone();
1399 Pred->getInstList().push_back(NewRet);
1401 // If the return instruction returns a value, and if the value was a
1402 // PHI node in "BB", propagate the right value into the return.
1403 for (unsigned i = 0, e = NewRet->getNumOperands(); i != e; ++i)
1404 if (PHINode *PN = dyn_cast<PHINode>(NewRet->getOperand(i)))
1405 if (PN->getParent() == BB)
1406 NewRet->setOperand(i, PN->getIncomingValueForBlock(Pred));
1408 // Update any PHI nodes in the returning block to realize that we no
1409 // longer branch to them.
1410 BB->removePredecessor(Pred);
1411 Pred->getInstList().erase(UncondBranch);
1414 // If we eliminated all predecessors of the block, delete the block now.
1415 if (pred_begin(BB) == pred_end(BB))
1416 // We know there are no successors, so just nuke the block.
1417 M->getBasicBlockList().erase(BB);
1422 // Check out all of the conditional branches going to this return
1423 // instruction. If any of them just select between returns, change the
1424 // branch itself into a select/return pair.
1425 while (!CondBranchPreds.empty()) {
1426 BranchInst *BI = CondBranchPreds.back();
1427 CondBranchPreds.pop_back();
1429 // Check to see if the non-BB successor is also a return block.
1430 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1431 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1432 SimplifyCondBranchToTwoReturns(BI))
1436 } else if (isa<UnwindInst>(BB->begin())) {
1437 // Check to see if the first instruction in this block is just an unwind.
1438 // If so, replace any invoke instructions which use this as an exception
1439 // destination with call instructions, and any unconditional branch
1440 // predecessor with an unwind.
1442 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1443 while (!Preds.empty()) {
1444 BasicBlock *Pred = Preds.back();
1445 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1446 if (BI->isUnconditional()) {
1447 Pred->getInstList().pop_back(); // nuke uncond branch
1448 new UnwindInst(Pred); // Use unwind.
1451 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1452 if (II->getUnwindDest() == BB) {
1453 // Insert a new branch instruction before the invoke, because this
1454 // is now a fall through...
1455 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1456 Pred->getInstList().remove(II); // Take out of symbol table
1458 // Insert the call now...
1459 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1460 CallInst *CI = CallInst::Create(II->getCalledValue(),
1461 Args.begin(), Args.end(), II->getName(), BI);
1462 CI->setCallingConv(II->getCallingConv());
1463 CI->setParamAttrs(II->getParamAttrs());
1464 // If the invoke produced a value, the Call now does instead
1465 II->replaceAllUsesWith(CI);
1473 // If this block is now dead, remove it.
1474 if (pred_begin(BB) == pred_end(BB)) {
1475 // We know there are no successors, so just nuke the block.
1476 M->getBasicBlockList().erase(BB);
1480 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1481 if (isValueEqualityComparison(SI)) {
1482 // If we only have one predecessor, and if it is a branch on this value,
1483 // see if that predecessor totally determines the outcome of this switch.
1484 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1485 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1486 return SimplifyCFG(BB) || 1;
1488 // If the block only contains the switch, see if we can fold the block
1489 // away into any preds.
1490 if (SI == &BB->front())
1491 if (FoldValueComparisonIntoPredecessors(SI))
1492 return SimplifyCFG(BB) || 1;
1494 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1495 if (BI->isUnconditional()) {
1496 BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes...
1497 while (isa<PHINode>(*BBI)) ++BBI;
1499 BasicBlock *Succ = BI->getSuccessor(0);
1500 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1501 Succ != BB) // Don't hurt infinite loops!
1502 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1505 } else { // Conditional branch
1506 if (isValueEqualityComparison(BI)) {
1507 // If we only have one predecessor, and if it is a branch on this value,
1508 // see if that predecessor totally determines the outcome of this
1510 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1511 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1512 return SimplifyCFG(BB) || 1;
1514 // This block must be empty, except for the setcond inst, if it exists.
1515 BasicBlock::iterator I = BB->begin();
1517 (&*I == cast<Instruction>(BI->getCondition()) &&
1519 if (FoldValueComparisonIntoPredecessors(BI))
1520 return SimplifyCFG(BB) | true;
1523 // If this is a branch on a phi node in the current block, thread control
1524 // through this block if any PHI node entries are constants.
1525 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1526 if (PN->getParent() == BI->getParent())
1527 if (FoldCondBranchOnPHI(BI))
1528 return SimplifyCFG(BB) | true;
1530 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1531 // branches to us and one of our successors, fold the setcc into the
1532 // predecessor and use logical operations to pick the right destination.
1533 BasicBlock *TrueDest = BI->getSuccessor(0);
1534 BasicBlock *FalseDest = BI->getSuccessor(1);
1535 if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition())) {
1536 BasicBlock::iterator CondIt = Cond;
1537 if ((isa<CmpInst>(Cond) || isa<BinaryOperator>(Cond)) &&
1538 Cond->getParent() == BB && &BB->front() == Cond &&
1539 &*++CondIt == BI && Cond->hasOneUse() &&
1540 TrueDest != BB && FalseDest != BB)
1541 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI)
1542 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1543 if (PBI->isConditional() && SafeToMergeTerminators(BI, PBI)) {
1544 BasicBlock *PredBlock = *PI;
1545 if (PBI->getSuccessor(0) == FalseDest ||
1546 PBI->getSuccessor(1) == TrueDest) {
1547 // Invert the predecessors condition test (xor it with true),
1548 // which allows us to write this code once.
1550 BinaryOperator::CreateNot(PBI->getCondition(),
1551 PBI->getCondition()->getName()+".not", PBI);
1552 PBI->setCondition(NewCond);
1553 BasicBlock *OldTrue = PBI->getSuccessor(0);
1554 BasicBlock *OldFalse = PBI->getSuccessor(1);
1555 PBI->setSuccessor(0, OldFalse);
1556 PBI->setSuccessor(1, OldTrue);
1559 if ((PBI->getSuccessor(0) == TrueDest && FalseDest != BB) ||
1560 (PBI->getSuccessor(1) == FalseDest && TrueDest != BB)) {
1561 // Clone Cond into the predecessor basic block, and or/and the
1562 // two conditions together.
1563 Instruction *New = Cond->clone();
1564 PredBlock->getInstList().insert(PBI, New);
1565 New->takeName(Cond);
1566 Cond->setName(New->getName()+".old");
1567 Instruction::BinaryOps Opcode =
1568 PBI->getSuccessor(0) == TrueDest ?
1569 Instruction::Or : Instruction::And;
1571 BinaryOperator::Create(Opcode, PBI->getCondition(),
1572 New, "bothcond", PBI);
1573 PBI->setCondition(NewCond);
1574 if (PBI->getSuccessor(0) == BB) {
1575 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1576 PBI->setSuccessor(0, TrueDest);
1578 if (PBI->getSuccessor(1) == BB) {
1579 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1580 PBI->setSuccessor(1, FalseDest);
1582 return SimplifyCFG(BB) | 1;
1587 // Scan predessor blocks for conditional branches.
1588 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1589 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1590 if (PBI != BI && PBI->isConditional()) {
1592 // If this block ends with a branch instruction, and if there is a
1593 // predecessor that ends on a branch of the same condition, make
1594 // this conditional branch redundant.
1595 if (PBI->getCondition() == BI->getCondition() &&
1596 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1597 // Okay, the outcome of this conditional branch is statically
1598 // knowable. If this block had a single pred, handle specially.
1599 if (BB->getSinglePredecessor()) {
1600 // Turn this into a branch on constant.
1601 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1602 BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
1603 return SimplifyCFG(BB); // Nuke the branch on constant.
1606 // Otherwise, if there are multiple predecessors, insert a PHI
1607 // that merges in the constant and simplify the block result.
1608 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1609 PHINode *NewPN = PHINode::Create(Type::Int1Ty,
1610 BI->getCondition()->getName()+".pr",
1612 for (PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1613 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1614 PBI != BI && PBI->isConditional() &&
1615 PBI->getCondition() == BI->getCondition() &&
1616 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1617 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1618 NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
1621 NewPN->addIncoming(BI->getCondition(), *PI);
1624 BI->setCondition(NewPN);
1625 // This will thread the branch.
1626 return SimplifyCFG(BB) | true;
1630 // If this is a conditional branch in an empty block, and if any
1631 // predecessors is a conditional branch to one of our destinations,
1632 // fold the conditions into logical ops and one cond br.
1633 if (&BB->front() == BI) {
1635 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
1637 } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
1638 PBIOp = 0; BIOp = 1;
1639 } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
1640 PBIOp = 1; BIOp = 0;
1641 } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
1647 // Check to make sure that the other destination of this branch
1648 // isn't BB itself. If so, this is an infinite loop that will
1649 // keep getting unwound.
1650 if (PBIOp != -1 && PBI->getSuccessor(PBIOp) == BB)
1653 // Do not perform this transformation if it would require
1654 // insertion of a large number of select instructions. For targets
1655 // without predication/cmovs, this is a big pessimization.
1657 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1659 unsigned NumPhis = 0;
1660 for (BasicBlock::iterator II = CommonDest->begin();
1661 isa<PHINode>(II); ++II, ++NumPhis) {
1663 // Disable this xform.
1670 // Finally, if everything is ok, fold the branches to logical ops.
1672 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1673 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1675 // If OtherDest *is* BB, then this is a basic block with just
1676 // a conditional branch in it, where one edge (OtherDesg) goes
1677 // back to the block. We know that the program doesn't get
1678 // stuck in the infinite loop, so the condition must be such
1679 // that OtherDest isn't branched through. Forward to CommonDest,
1680 // and avoid an infinite loop at optimizer time.
1681 if (OtherDest == BB)
1682 OtherDest = CommonDest;
1684 DOUT << "FOLDING BRs:" << *PBI->getParent()
1685 << "AND: " << *BI->getParent();
1687 // BI may have other predecessors. Because of this, we leave
1688 // it alone, but modify PBI.
1690 // Make sure we get to CommonDest on True&True directions.
1691 Value *PBICond = PBI->getCondition();
1693 PBICond = BinaryOperator::CreateNot(PBICond,
1694 PBICond->getName()+".not",
1696 Value *BICond = BI->getCondition();
1698 BICond = BinaryOperator::CreateNot(BICond,
1699 BICond->getName()+".not",
1701 // Merge the conditions.
1703 BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1705 // Modify PBI to branch on the new condition to the new dests.
1706 PBI->setCondition(Cond);
1707 PBI->setSuccessor(0, CommonDest);
1708 PBI->setSuccessor(1, OtherDest);
1710 // OtherDest may have phi nodes. If so, add an entry from PBI's
1711 // block that are identical to the entries for BI's block.
1713 for (BasicBlock::iterator II = OtherDest->begin();
1714 (PN = dyn_cast<PHINode>(II)); ++II) {
1715 Value *V = PN->getIncomingValueForBlock(BB);
1716 PN->addIncoming(V, PBI->getParent());
1719 // We know that the CommonDest already had an edge from PBI to
1720 // it. If it has PHIs though, the PHIs may have different
1721 // entries for BB and PBI's BB. If so, insert a select to make
1723 for (BasicBlock::iterator II = CommonDest->begin();
1724 (PN = dyn_cast<PHINode>(II)); ++II) {
1725 Value * BIV = PN->getIncomingValueForBlock(BB);
1726 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1727 Value *PBIV = PN->getIncomingValue(PBBIdx);
1729 // Insert a select in PBI to pick the right value.
1730 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1731 PBIV->getName()+".mux", PBI);
1732 PN->setIncomingValue(PBBIdx, NV);
1736 DOUT << "INTO: " << *PBI->getParent();
1738 // This basic block is probably dead. We know it has at least
1739 // one fewer predecessor.
1740 return SimplifyCFG(BB) | true;
1745 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1746 // If there are any instructions immediately before the unreachable that can
1747 // be removed, do so.
1748 Instruction *Unreachable = BB->getTerminator();
1749 while (Unreachable != BB->begin()) {
1750 BasicBlock::iterator BBI = Unreachable;
1752 if (isa<CallInst>(BBI)) break;
1753 // Delete this instruction
1754 BB->getInstList().erase(BBI);
1758 // If the unreachable instruction is the first in the block, take a gander
1759 // at all of the predecessors of this instruction, and simplify them.
1760 if (&BB->front() == Unreachable) {
1761 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1762 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1763 TerminatorInst *TI = Preds[i]->getTerminator();
1765 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1766 if (BI->isUnconditional()) {
1767 if (BI->getSuccessor(0) == BB) {
1768 new UnreachableInst(TI);
1769 TI->eraseFromParent();
1773 if (BI->getSuccessor(0) == BB) {
1774 BranchInst::Create(BI->getSuccessor(1), BI);
1775 BI->eraseFromParent();
1776 } else if (BI->getSuccessor(1) == BB) {
1777 BranchInst::Create(BI->getSuccessor(0), BI);
1778 BI->eraseFromParent();
1782 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1783 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1784 if (SI->getSuccessor(i) == BB) {
1785 BB->removePredecessor(SI->getParent());
1790 // If the default value is unreachable, figure out the most popular
1791 // destination and make it the default.
1792 if (SI->getSuccessor(0) == BB) {
1793 std::map<BasicBlock*, unsigned> Popularity;
1794 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1795 Popularity[SI->getSuccessor(i)]++;
1797 // Find the most popular block.
1798 unsigned MaxPop = 0;
1799 BasicBlock *MaxBlock = 0;
1800 for (std::map<BasicBlock*, unsigned>::iterator
1801 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
1802 if (I->second > MaxPop) {
1804 MaxBlock = I->first;
1808 // Make this the new default, allowing us to delete any explicit
1810 SI->setSuccessor(0, MaxBlock);
1813 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
1815 if (isa<PHINode>(MaxBlock->begin()))
1816 for (unsigned i = 0; i != MaxPop-1; ++i)
1817 MaxBlock->removePredecessor(SI->getParent());
1819 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1820 if (SI->getSuccessor(i) == MaxBlock) {
1826 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
1827 if (II->getUnwindDest() == BB) {
1828 // Convert the invoke to a call instruction. This would be a good
1829 // place to note that the call does not throw though.
1830 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1831 II->removeFromParent(); // Take out of symbol table
1833 // Insert the call now...
1834 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
1835 CallInst *CI = CallInst::Create(II->getCalledValue(),
1836 Args.begin(), Args.end(),
1838 CI->setCallingConv(II->getCallingConv());
1839 CI->setParamAttrs(II->getParamAttrs());
1840 // If the invoke produced a value, the Call does now instead.
1841 II->replaceAllUsesWith(CI);
1848 // If this block is now dead, remove it.
1849 if (pred_begin(BB) == pred_end(BB)) {
1850 // We know there are no successors, so just nuke the block.
1851 M->getBasicBlockList().erase(BB);
1857 // Merge basic blocks into their predecessor if there is only one distinct
1858 // pred, and if there is only one distinct successor of the predecessor, and
1859 // if there are no PHI nodes.
1861 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
1862 BasicBlock *OnlyPred = *PI++;
1863 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
1864 if (*PI != OnlyPred) {
1865 OnlyPred = 0; // There are multiple different predecessors...
1869 BasicBlock *OnlySucc = 0;
1870 if (OnlyPred && OnlyPred != BB && // Don't break self loops
1871 OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) {
1872 // Check to see if there is only one distinct successor...
1873 succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred));
1875 for (; SI != SE; ++SI)
1876 if (*SI != OnlySucc) {
1877 OnlySucc = 0; // There are multiple distinct successors!
1883 DOUT << "Merging: " << *BB << "into: " << *OnlyPred;
1885 // Resolve any PHI nodes at the start of the block. They are all
1886 // guaranteed to have exactly one entry if they exist, unless there are
1887 // multiple duplicate (but guaranteed to be equal) entries for the
1888 // incoming edges. This occurs when there are multiple edges from
1889 // OnlyPred to OnlySucc.
1891 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
1892 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1893 BB->getInstList().pop_front(); // Delete the phi node.
1896 // Delete the unconditional branch from the predecessor.
1897 OnlyPred->getInstList().pop_back();
1899 // Move all definitions in the successor to the predecessor.
1900 OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
1902 // Make all PHI nodes that referred to BB now refer to Pred as their
1904 BB->replaceAllUsesWith(OnlyPred);
1906 // Inherit predecessors name if it exists.
1907 if (!OnlyPred->hasName())
1908 OnlyPred->takeName(BB);
1910 // Erase basic block from the function.
1911 M->getBasicBlockList().erase(BB);
1916 // Otherwise, if this block only has a single predecessor, and if that block
1917 // is a conditional branch, see if we can hoist any code from this block up
1918 // into our predecessor.
1920 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
1921 if (BI->isConditional()) {
1922 // Get the other block.
1923 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
1924 PI = pred_begin(OtherBB);
1926 if (PI == pred_end(OtherBB)) {
1927 // We have a conditional branch to two blocks that are only reachable
1928 // from the condbr. We know that the condbr dominates the two blocks,
1929 // so see if there is any identical code in the "then" and "else"
1930 // blocks. If so, we can hoist it up to the branching block.
1931 Changed |= HoistThenElseCodeToIf(BI);
1935 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1936 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1937 // Change br (X == 0 | X == 1), T, F into a switch instruction.
1938 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
1939 Instruction *Cond = cast<Instruction>(BI->getCondition());
1940 // If this is a bunch of seteq's or'd together, or if it's a bunch of
1941 // 'setne's and'ed together, collect them.
1943 std::vector<ConstantInt*> Values;
1944 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
1945 if (CompVal && CompVal->getType()->isInteger()) {
1946 // There might be duplicate constants in the list, which the switch
1947 // instruction can't handle, remove them now.
1948 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
1949 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
1951 // Figure out which block is which destination.
1952 BasicBlock *DefaultBB = BI->getSuccessor(1);
1953 BasicBlock *EdgeBB = BI->getSuccessor(0);
1954 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
1956 // Create the new switch instruction now.
1957 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
1960 // Add all of the 'cases' to the switch instruction.
1961 for (unsigned i = 0, e = Values.size(); i != e; ++i)
1962 New->addCase(Values[i], EdgeBB);
1964 // We added edges from PI to the EdgeBB. As such, if there were any
1965 // PHI nodes in EdgeBB, they need entries to be added corresponding to
1966 // the number of edges added.
1967 for (BasicBlock::iterator BBI = EdgeBB->begin();
1968 isa<PHINode>(BBI); ++BBI) {
1969 PHINode *PN = cast<PHINode>(BBI);
1970 Value *InVal = PN->getIncomingValueForBlock(*PI);
1971 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
1972 PN->addIncoming(InVal, *PI);
1975 // Erase the old branch instruction.
1976 (*PI)->getInstList().erase(BI);
1978 // Erase the potentially condition tree that was used to computed the
1979 // branch condition.
1980 ErasePossiblyDeadInstructionTree(Cond);