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 BasicBlock::iterator BBI = BB1->begin();
969 ++BBI; // must have at least a terminator
970 if (BBI == BB1->end()) return false; // only one inst
972 if (BBI != BB1->end()) return false; // more than 2 insts.
974 // Be conservative for now. FP select instruction can often be expensive.
975 Value *BrCond = BI->getCondition();
976 if (isa<Instruction>(BrCond) &&
977 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
980 // If BB1 is actually on the false edge of the conditional branch, remember
981 // to swap the select operands later.
983 if (BB1 != BI->getSuccessor(0)) {
984 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
991 // br i1 %t1, label %BB1, label %BB2
1000 // %t3 = select i1 %t1, %t2, %t3
1001 Instruction *I = BB1->begin();
1002 switch (I->getOpcode()) {
1003 default: return false; // Not safe / profitable to hoist.
1004 case Instruction::Add:
1005 case Instruction::Sub:
1006 case Instruction::And:
1007 case Instruction::Or:
1008 case Instruction::Xor:
1009 case Instruction::Shl:
1010 case Instruction::LShr:
1011 case Instruction::AShr:
1012 if (!I->getOperand(0)->getType()->isInteger())
1013 // FP arithmetic might trap. Not worth doing for vector ops.
1015 break; // These are all cheap and non-trapping instructions.
1018 // Can we speculatively execute the instruction? And what is the value
1019 // if the condition is false? Consider the phi uses, if the incoming value
1020 // from the "if" block are all the same V, then V is the value of the
1021 // select if the condition is false.
1022 BasicBlock *BIParent = BI->getParent();
1023 SmallVector<PHINode*, 4> PHIUses;
1024 Value *FalseV = NULL;
1025 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1027 PHINode *PN = dyn_cast<PHINode>(UI);
1030 PHIUses.push_back(PN);
1031 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1034 else if (FalseV != PHIV)
1035 return false; // Don't know the value when condition is false.
1037 if (!FalseV) // Can this happen?
1040 // Do not hoist the instruction if any of its operands are defined but not
1041 // used in this BB. The transformation will prevent the operand from
1042 // being sunk into the use block.
1043 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
1044 Instruction *OpI = dyn_cast<Instruction>(*i);
1045 if (OpI && OpI->getParent() == BIParent &&
1046 !OpI->isUsedInBasicBlock(BIParent))
1050 // If we get here, we can hoist the instruction. Try to place it before the
1051 // icmp instruction preceeding the conditional branch.
1052 BasicBlock::iterator InsertPos = BI;
1053 if (InsertPos != BIParent->begin())
1055 if (InsertPos == BrCond && !isa<PHINode>(BrCond))
1056 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), I);
1058 BIParent->getInstList().splice(BI, BB1->getInstList(), I);
1060 // Create a select whose true value is the speculatively executed value and
1061 // false value is the previously determined FalseV.
1064 SI = SelectInst::Create(BrCond, FalseV, I,
1065 FalseV->getName() + "." + I->getName(), BI);
1067 SI = SelectInst::Create(BrCond, I, FalseV,
1068 I->getName() + "." + FalseV->getName(), BI);
1070 // Make the PHI node use the select for all incoming values for "then" and
1072 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1073 PHINode *PN = PHIUses[i];
1074 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1075 if (PN->getIncomingBlock(j) == BB1 ||
1076 PN->getIncomingBlock(j) == BIParent)
1077 PN->setIncomingValue(j, SI);
1084 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1085 /// across this block.
1086 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1087 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1090 // If this basic block contains anything other than a PHI (which controls the
1091 // branch) and branch itself, bail out. FIXME: improve this in the future.
1092 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) {
1093 if (Size > 10) return false; // Don't clone large BB's.
1095 // We can only support instructions that are do not define values that are
1096 // live outside of the current basic block.
1097 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1099 Instruction *U = cast<Instruction>(*UI);
1100 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1103 // Looks ok, continue checking.
1109 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1110 /// that is defined in the same block as the branch and if any PHI entries are
1111 /// constants, thread edges corresponding to that entry to be branches to their
1112 /// ultimate destination.
1113 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1114 BasicBlock *BB = BI->getParent();
1115 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1116 // NOTE: we currently cannot transform this case if the PHI node is used
1117 // outside of the block.
1118 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1121 // Degenerate case of a single entry PHI.
1122 if (PN->getNumIncomingValues() == 1) {
1123 if (PN->getIncomingValue(0) != PN)
1124 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1126 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1127 PN->eraseFromParent();
1131 // Now we know that this block has multiple preds and two succs.
1132 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1134 // Okay, this is a simple enough basic block. See if any phi values are
1136 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1138 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1139 CB->getType() == Type::Int1Ty) {
1140 // Okay, we now know that all edges from PredBB should be revectored to
1141 // branch to RealDest.
1142 BasicBlock *PredBB = PN->getIncomingBlock(i);
1143 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1145 if (RealDest == BB) continue; // Skip self loops.
1147 // The dest block might have PHI nodes, other predecessors and other
1148 // difficult cases. Instead of being smart about this, just insert a new
1149 // block that jumps to the destination block, effectively splitting
1150 // the edge we are about to create.
1151 BasicBlock *EdgeBB = BasicBlock::Create(RealDest->getName()+".critedge",
1152 RealDest->getParent(), RealDest);
1153 BranchInst::Create(RealDest, EdgeBB);
1155 for (BasicBlock::iterator BBI = RealDest->begin();
1156 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1157 Value *V = PN->getIncomingValueForBlock(BB);
1158 PN->addIncoming(V, EdgeBB);
1161 // BB may have instructions that are being threaded over. Clone these
1162 // instructions into EdgeBB. We know that there will be no uses of the
1163 // cloned instructions outside of EdgeBB.
1164 BasicBlock::iterator InsertPt = EdgeBB->begin();
1165 std::map<Value*, Value*> TranslateMap; // Track translated values.
1166 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1167 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1168 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1170 // Clone the instruction.
1171 Instruction *N = BBI->clone();
1172 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1174 // Update operands due to translation.
1175 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1177 std::map<Value*, Value*>::iterator PI =
1178 TranslateMap.find(*i);
1179 if (PI != TranslateMap.end())
1183 // Check for trivial simplification.
1184 if (Constant *C = ConstantFoldInstruction(N)) {
1185 TranslateMap[BBI] = C;
1186 delete N; // Constant folded away, don't need actual inst
1188 // Insert the new instruction into its new home.
1189 EdgeBB->getInstList().insert(InsertPt, N);
1190 if (!BBI->use_empty())
1191 TranslateMap[BBI] = N;
1196 // Loop over all of the edges from PredBB to BB, changing them to branch
1197 // to EdgeBB instead.
1198 TerminatorInst *PredBBTI = PredBB->getTerminator();
1199 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1200 if (PredBBTI->getSuccessor(i) == BB) {
1201 BB->removePredecessor(PredBB);
1202 PredBBTI->setSuccessor(i, EdgeBB);
1205 // Recurse, simplifying any other constants.
1206 return FoldCondBranchOnPHI(BI) | true;
1213 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1214 /// PHI node, see if we can eliminate it.
1215 static bool FoldTwoEntryPHINode(PHINode *PN) {
1216 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1217 // statement", which has a very simple dominance structure. Basically, we
1218 // are trying to find the condition that is being branched on, which
1219 // subsequently causes this merge to happen. We really want control
1220 // dependence information for this check, but simplifycfg can't keep it up
1221 // to date, and this catches most of the cases we care about anyway.
1223 BasicBlock *BB = PN->getParent();
1224 BasicBlock *IfTrue, *IfFalse;
1225 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1226 if (!IfCond) return false;
1228 // Okay, we found that we can merge this two-entry phi node into a select.
1229 // Doing so would require us to fold *all* two entry phi nodes in this block.
1230 // At some point this becomes non-profitable (particularly if the target
1231 // doesn't support cmov's). Only do this transformation if there are two or
1232 // fewer PHI nodes in this block.
1233 unsigned NumPhis = 0;
1234 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1238 DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
1239 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
1241 // Loop over the PHI's seeing if we can promote them all to select
1242 // instructions. While we are at it, keep track of the instructions
1243 // that need to be moved to the dominating block.
1244 std::set<Instruction*> AggressiveInsts;
1246 BasicBlock::iterator AfterPHIIt = BB->begin();
1247 while (isa<PHINode>(AfterPHIIt)) {
1248 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1249 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1250 if (PN->getIncomingValue(0) != PN)
1251 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1253 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1254 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1255 &AggressiveInsts) ||
1256 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1257 &AggressiveInsts)) {
1262 // If we all PHI nodes are promotable, check to make sure that all
1263 // instructions in the predecessor blocks can be promoted as well. If
1264 // not, we won't be able to get rid of the control flow, so it's not
1265 // worth promoting to select instructions.
1266 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1267 PN = cast<PHINode>(BB->begin());
1268 BasicBlock *Pred = PN->getIncomingBlock(0);
1269 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1271 DomBlock = *pred_begin(Pred);
1272 for (BasicBlock::iterator I = Pred->begin();
1273 !isa<TerminatorInst>(I); ++I)
1274 if (!AggressiveInsts.count(I)) {
1275 // This is not an aggressive instruction that we can promote.
1276 // Because of this, we won't be able to get rid of the control
1277 // flow, so the xform is not worth it.
1282 Pred = PN->getIncomingBlock(1);
1283 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1285 DomBlock = *pred_begin(Pred);
1286 for (BasicBlock::iterator I = Pred->begin();
1287 !isa<TerminatorInst>(I); ++I)
1288 if (!AggressiveInsts.count(I)) {
1289 // This is not an aggressive instruction that we can promote.
1290 // Because of this, we won't be able to get rid of the control
1291 // flow, so the xform is not worth it.
1296 // If we can still promote the PHI nodes after this gauntlet of tests,
1297 // do all of the PHI's now.
1299 // Move all 'aggressive' instructions, which are defined in the
1300 // conditional parts of the if's up to the dominating block.
1302 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1303 IfBlock1->getInstList(),
1305 IfBlock1->getTerminator());
1308 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1309 IfBlock2->getInstList(),
1311 IfBlock2->getTerminator());
1314 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1315 // Change the PHI node into a select instruction.
1317 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1319 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1321 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1322 PN->replaceAllUsesWith(NV);
1325 BB->getInstList().erase(PN);
1330 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1331 /// to two returning blocks, try to merge them together into one return,
1332 /// introducing a select if the return values disagree.
1333 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1334 assert(BI->isConditional() && "Must be a conditional branch");
1335 BasicBlock *TrueSucc = BI->getSuccessor(0);
1336 BasicBlock *FalseSucc = BI->getSuccessor(1);
1337 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1338 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1340 // Check to ensure both blocks are empty (just a return) or optionally empty
1341 // with PHI nodes. If there are other instructions, merging would cause extra
1342 // computation on one path or the other.
1343 BasicBlock::iterator BBI = TrueRet;
1344 if (BBI != TrueSucc->begin() && !isa<PHINode>(--BBI))
1345 return false; // Not empty with optional phi nodes.
1347 if (BBI != FalseSucc->begin() && !isa<PHINode>(--BBI))
1348 return false; // Not empty with optional phi nodes.
1350 // Okay, we found a branch that is going to two return nodes. If
1351 // there is no return value for this function, just change the
1352 // branch into a return.
1353 if (FalseRet->getNumOperands() == 0) {
1354 TrueSucc->removePredecessor(BI->getParent());
1355 FalseSucc->removePredecessor(BI->getParent());
1356 ReturnInst::Create(0, BI);
1357 BI->eraseFromParent();
1361 // Otherwise, build up the result values for the new return.
1362 SmallVector<Value*, 4> TrueResult;
1363 SmallVector<Value*, 4> FalseResult;
1365 for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
1366 // Otherwise, figure out what the true and false return values are
1367 // so we can insert a new select instruction.
1368 Value *TrueValue = TrueRet->getOperand(i);
1369 Value *FalseValue = FalseRet->getOperand(i);
1371 // Unwrap any PHI nodes in the return blocks.
1372 if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue))
1373 if (TVPN->getParent() == TrueSucc)
1374 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1375 if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue))
1376 if (FVPN->getParent() == FalseSucc)
1377 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1379 // In order for this transformation to be safe, we must be able to
1380 // unconditionally execute both operands to the return. This is
1381 // normally the case, but we could have a potentially-trapping
1382 // constant expression that prevents this transformation from being
1384 if (ConstantExpr *TCV = dyn_cast<ConstantExpr>(TrueValue))
1387 if (ConstantExpr *FCV = dyn_cast<ConstantExpr>(FalseValue))
1391 TrueResult.push_back(TrueValue);
1392 FalseResult.push_back(FalseValue);
1395 // Okay, we collected all the mapped values and checked them for sanity, and
1396 // defined to really do this transformation. First, update the CFG.
1397 TrueSucc->removePredecessor(BI->getParent());
1398 FalseSucc->removePredecessor(BI->getParent());
1400 // Insert select instructions where needed.
1401 Value *BrCond = BI->getCondition();
1402 for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
1403 // Insert a select if the results differ.
1404 if (TrueResult[i] == FalseResult[i] || isa<UndefValue>(FalseResult[i]))
1406 if (isa<UndefValue>(TrueResult[i])) {
1407 TrueResult[i] = FalseResult[i];
1411 TrueResult[i] = SelectInst::Create(BrCond, TrueResult[i],
1412 FalseResult[i], "retval", BI);
1415 Value *RI = ReturnInst::Create(&TrueResult[0], TrueResult.size(), BI);
1417 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1418 << "\n " << *BI << "NewRet = " << *RI
1419 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
1421 BI->eraseFromParent();
1423 if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
1424 ErasePossiblyDeadInstructionTree(BrCondI);
1428 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1429 /// and if a predecessor branches to us and one of our successors, fold the
1430 /// setcc into the predecessor and use logical operations to pick the right
1432 static bool FoldBranchToCommonDest(BranchInst *BI) {
1433 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1434 if (Cond == 0) return false;
1436 BasicBlock *BB = BI->getParent();
1438 // Only allow this if the condition is a simple instruction that can be
1439 // executed unconditionally. It must be in the same block as the branch, and
1440 // must be at the front of the block.
1441 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1442 Cond->getParent() != BB || &BB->front() != Cond || !Cond->hasOneUse())
1445 // Make sure the instruction after the condition is the cond branch.
1446 BasicBlock::iterator CondIt = Cond; ++CondIt;
1450 // Finally, don't infinitely unroll conditional loops.
1451 BasicBlock *TrueDest = BI->getSuccessor(0);
1452 BasicBlock *FalseDest = BI->getSuccessor(1);
1453 if (TrueDest == BB || FalseDest == BB)
1456 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1457 BasicBlock *PredBlock = *PI;
1458 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1459 if (PBI == 0 || PBI->isUnconditional() ||
1460 !SafeToMergeTerminators(BI, PBI))
1463 Instruction::BinaryOps Opc;
1464 bool InvertPredCond = false;
1466 if (PBI->getSuccessor(0) == TrueDest)
1467 Opc = Instruction::Or;
1468 else if (PBI->getSuccessor(1) == FalseDest)
1469 Opc = Instruction::And;
1470 else if (PBI->getSuccessor(0) == FalseDest)
1471 Opc = Instruction::And, InvertPredCond = true;
1472 else if (PBI->getSuccessor(1) == TrueDest)
1473 Opc = Instruction::Or, InvertPredCond = true;
1477 // If we need to invert the condition in the pred block to match, do so now.
1478 if (InvertPredCond) {
1480 BinaryOperator::CreateNot(PBI->getCondition(),
1481 PBI->getCondition()->getName()+".not", PBI);
1482 PBI->setCondition(NewCond);
1483 BasicBlock *OldTrue = PBI->getSuccessor(0);
1484 BasicBlock *OldFalse = PBI->getSuccessor(1);
1485 PBI->setSuccessor(0, OldFalse);
1486 PBI->setSuccessor(1, OldTrue);
1489 // Clone Cond into the predecessor basic block, and or/and the
1490 // two conditions together.
1491 Instruction *New = Cond->clone();
1492 PredBlock->getInstList().insert(PBI, New);
1493 New->takeName(Cond);
1494 Cond->setName(New->getName()+".old");
1496 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1497 New, "or.cond", PBI);
1498 PBI->setCondition(NewCond);
1499 if (PBI->getSuccessor(0) == BB) {
1500 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1501 PBI->setSuccessor(0, TrueDest);
1503 if (PBI->getSuccessor(1) == BB) {
1504 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1505 PBI->setSuccessor(1, FalseDest);
1512 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1513 /// predecessor of another block, this function tries to simplify it. We know
1514 /// that PBI and BI are both conditional branches, and BI is in one of the
1515 /// successor blocks of PBI - PBI branches to BI.
1516 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1517 assert(PBI->isConditional() && BI->isConditional());
1518 BasicBlock *BB = BI->getParent();
1520 // If this block ends with a branch instruction, and if there is a
1521 // predecessor that ends on a branch of the same condition, make
1522 // this conditional branch redundant.
1523 if (PBI->getCondition() == BI->getCondition() &&
1524 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1525 // Okay, the outcome of this conditional branch is statically
1526 // knowable. If this block had a single pred, handle specially.
1527 if (BB->getSinglePredecessor()) {
1528 // Turn this into a branch on constant.
1529 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1530 BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
1531 return true; // Nuke the branch on constant.
1534 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1535 // in the constant and simplify the block result. Subsequent passes of
1536 // simplifycfg will thread the block.
1537 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1538 PHINode *NewPN = PHINode::Create(Type::Int1Ty,
1539 BI->getCondition()->getName() + ".pr",
1541 // Okay, we're going to insert the PHI node. Since PBI is not the only
1542 // predecessor, compute the PHI'd conditional value for all of the preds.
1543 // Any predecessor where the condition is not computable we keep symbolic.
1544 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1545 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1546 PBI != BI && PBI->isConditional() &&
1547 PBI->getCondition() == BI->getCondition() &&
1548 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1549 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1550 NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
1553 NewPN->addIncoming(BI->getCondition(), *PI);
1556 BI->setCondition(NewPN);
1561 // If this is a conditional branch in an empty block, and if any
1562 // predecessors is a conditional branch to one of our destinations,
1563 // fold the conditions into logical ops and one cond br.
1564 if (&BB->front() != BI)
1568 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1570 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1571 PBIOp = 0, BIOp = 1;
1572 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1573 PBIOp = 1, BIOp = 0;
1574 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1579 // Check to make sure that the other destination of this branch
1580 // isn't BB itself. If so, this is an infinite loop that will
1581 // keep getting unwound.
1582 if (PBI->getSuccessor(PBIOp) == BB)
1585 // Do not perform this transformation if it would require
1586 // insertion of a large number of select instructions. For targets
1587 // without predication/cmovs, this is a big pessimization.
1588 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1590 unsigned NumPhis = 0;
1591 for (BasicBlock::iterator II = CommonDest->begin();
1592 isa<PHINode>(II); ++II, ++NumPhis)
1593 if (NumPhis > 2) // Disable this xform.
1596 // Finally, if everything is ok, fold the branches to logical ops.
1597 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1599 // If OtherDest *is* BB, then this is a basic block with just
1600 // a conditional branch in it, where one edge (OtherDesg) goes
1601 // back to the block. We know that the program doesn't get
1602 // stuck in the infinite loop, so the condition must be such
1603 // that OtherDest isn't branched through. Forward to CommonDest,
1604 // and avoid an infinite loop at optimizer time.
1605 if (OtherDest == BB)
1606 OtherDest = CommonDest;
1608 DOUT << "FOLDING BRs:" << *PBI->getParent()
1609 << "AND: " << *BI->getParent();
1611 DOUT << *PBI->getParent()->getParent();
1613 // BI may have other predecessors. Because of this, we leave
1614 // it alone, but modify PBI.
1616 // Make sure we get to CommonDest on True&True directions.
1617 Value *PBICond = PBI->getCondition();
1619 PBICond = BinaryOperator::CreateNot(PBICond,
1620 PBICond->getName()+".not",
1622 Value *BICond = BI->getCondition();
1624 BICond = BinaryOperator::CreateNot(BICond,
1625 BICond->getName()+".not",
1627 // Merge the conditions.
1628 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1630 // Modify PBI to branch on the new condition to the new dests.
1631 PBI->setCondition(Cond);
1632 PBI->setSuccessor(0, CommonDest);
1633 PBI->setSuccessor(1, OtherDest);
1635 // OtherDest may have phi nodes. If so, add an entry from PBI's
1636 // block that are identical to the entries for BI's block.
1638 for (BasicBlock::iterator II = OtherDest->begin();
1639 (PN = dyn_cast<PHINode>(II)); ++II) {
1640 Value *V = PN->getIncomingValueForBlock(BB);
1641 PN->addIncoming(V, PBI->getParent());
1644 // We know that the CommonDest already had an edge from PBI to
1645 // it. If it has PHIs though, the PHIs may have different
1646 // entries for BB and PBI's BB. If so, insert a select to make
1648 for (BasicBlock::iterator II = CommonDest->begin();
1649 (PN = dyn_cast<PHINode>(II)); ++II) {
1650 Value *BIV = PN->getIncomingValueForBlock(BB);
1651 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1652 Value *PBIV = PN->getIncomingValue(PBBIdx);
1654 // Insert a select in PBI to pick the right value.
1655 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1656 PBIV->getName()+".mux", PBI);
1657 PN->setIncomingValue(PBBIdx, NV);
1661 DOUT << "INTO: " << *PBI->getParent();
1663 DOUT << *PBI->getParent()->getParent();
1665 // This basic block is probably dead. We know it has at least
1666 // one fewer predecessor.
1672 /// ConstantIntOrdering - This class implements a stable ordering of constant
1673 /// integers that does not depend on their address. This is important for
1674 /// applications that sort ConstantInt's to ensure uniqueness.
1675 struct ConstantIntOrdering {
1676 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
1677 return LHS->getValue().ult(RHS->getValue());
1682 // SimplifyCFG - This function is used to do simplification of a CFG. For
1683 // example, it adjusts branches to branches to eliminate the extra hop, it
1684 // eliminates unreachable basic blocks, and does other "peephole" optimization
1685 // of the CFG. It returns true if a modification was made.
1687 // WARNING: The entry node of a function may not be simplified.
1689 bool llvm::SimplifyCFG(BasicBlock *BB) {
1690 bool Changed = false;
1691 Function *M = BB->getParent();
1693 assert(BB && BB->getParent() && "Block not embedded in function!");
1694 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1695 assert(&BB->getParent()->getEntryBlock() != BB &&
1696 "Can't Simplify entry block!");
1698 // Remove basic blocks that have no predecessors... which are unreachable.
1699 if ((pred_begin(BB) == pred_end(BB)) ||
1700 (*pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB))) {
1701 DOUT << "Removing BB: \n" << *BB;
1703 // Loop through all of our successors and make sure they know that one
1704 // of their predecessors is going away.
1705 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
1706 SI->removePredecessor(BB);
1708 while (!BB->empty()) {
1709 Instruction &I = BB->back();
1710 // If this instruction is used, replace uses with an arbitrary
1711 // value. Because control flow can't get here, we don't care
1712 // what we replace the value with. Note that since this block is
1713 // unreachable, and all values contained within it must dominate their
1714 // uses, that all uses will eventually be removed.
1716 // Make all users of this instruction use undef instead
1717 I.replaceAllUsesWith(UndefValue::get(I.getType()));
1719 // Remove the instruction from the basic block
1720 BB->getInstList().pop_back();
1722 M->getBasicBlockList().erase(BB);
1726 // Check to see if we can constant propagate this terminator instruction
1728 Changed |= ConstantFoldTerminator(BB);
1730 // If there is a trivial two-entry PHI node in this basic block, and we can
1731 // eliminate it, do so now.
1732 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1733 if (PN->getNumIncomingValues() == 2)
1734 Changed |= FoldTwoEntryPHINode(PN);
1736 // If this is a returning block with only PHI nodes in it, fold the return
1737 // instruction into any unconditional branch predecessors.
1739 // If any predecessor is a conditional branch that just selects among
1740 // different return values, fold the replace the branch/return with a select
1742 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1743 BasicBlock::iterator BBI = BB->getTerminator();
1744 if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
1745 // Find predecessors that end with branches.
1746 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1747 SmallVector<BranchInst*, 8> CondBranchPreds;
1748 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1749 TerminatorInst *PTI = (*PI)->getTerminator();
1750 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1751 if (BI->isUnconditional())
1752 UncondBranchPreds.push_back(*PI);
1754 CondBranchPreds.push_back(BI);
1758 // If we found some, do the transformation!
1759 if (!UncondBranchPreds.empty()) {
1760 while (!UncondBranchPreds.empty()) {
1761 BasicBlock *Pred = UncondBranchPreds.back();
1762 DOUT << "FOLDING: " << *BB
1763 << "INTO UNCOND BRANCH PRED: " << *Pred;
1764 UncondBranchPreds.pop_back();
1765 Instruction *UncondBranch = Pred->getTerminator();
1766 // Clone the return and add it to the end of the predecessor.
1767 Instruction *NewRet = RI->clone();
1768 Pred->getInstList().push_back(NewRet);
1770 // If the return instruction returns a value, and if the value was a
1771 // PHI node in "BB", propagate the right value into the return.
1772 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1774 if (PHINode *PN = dyn_cast<PHINode>(*i))
1775 if (PN->getParent() == BB)
1776 *i = PN->getIncomingValueForBlock(Pred);
1778 // Update any PHI nodes in the returning block to realize that we no
1779 // longer branch to them.
1780 BB->removePredecessor(Pred);
1781 Pred->getInstList().erase(UncondBranch);
1784 // If we eliminated all predecessors of the block, delete the block now.
1785 if (pred_begin(BB) == pred_end(BB))
1786 // We know there are no successors, so just nuke the block.
1787 M->getBasicBlockList().erase(BB);
1792 // Check out all of the conditional branches going to this return
1793 // instruction. If any of them just select between returns, change the
1794 // branch itself into a select/return pair.
1795 while (!CondBranchPreds.empty()) {
1796 BranchInst *BI = CondBranchPreds.back();
1797 CondBranchPreds.pop_back();
1799 // Check to see if the non-BB successor is also a return block.
1800 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1801 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1802 SimplifyCondBranchToTwoReturns(BI))
1806 } else if (isa<UnwindInst>(BB->begin())) {
1807 // Check to see if the first instruction in this block is just an unwind.
1808 // If so, replace any invoke instructions which use this as an exception
1809 // destination with call instructions, and any unconditional branch
1810 // predecessor with an unwind.
1812 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1813 while (!Preds.empty()) {
1814 BasicBlock *Pred = Preds.back();
1815 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1816 if (BI->isUnconditional()) {
1817 Pred->getInstList().pop_back(); // nuke uncond branch
1818 new UnwindInst(Pred); // Use unwind.
1821 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1822 if (II->getUnwindDest() == BB) {
1823 // Insert a new branch instruction before the invoke, because this
1824 // is now a fall through...
1825 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1826 Pred->getInstList().remove(II); // Take out of symbol table
1828 // Insert the call now...
1829 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1830 CallInst *CI = CallInst::Create(II->getCalledValue(),
1831 Args.begin(), Args.end(),
1833 CI->setCallingConv(II->getCallingConv());
1834 CI->setParamAttrs(II->getParamAttrs());
1835 // If the invoke produced a value, the Call now does instead
1836 II->replaceAllUsesWith(CI);
1844 // If this block is now dead, remove it.
1845 if (pred_begin(BB) == pred_end(BB)) {
1846 // We know there are no successors, so just nuke the block.
1847 M->getBasicBlockList().erase(BB);
1851 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1852 if (isValueEqualityComparison(SI)) {
1853 // If we only have one predecessor, and if it is a branch on this value,
1854 // see if that predecessor totally determines the outcome of this switch.
1855 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1856 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1857 return SimplifyCFG(BB) || 1;
1859 // If the block only contains the switch, see if we can fold the block
1860 // away into any preds.
1861 if (SI == &BB->front())
1862 if (FoldValueComparisonIntoPredecessors(SI))
1863 return SimplifyCFG(BB) || 1;
1865 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1866 if (BI->isUnconditional()) {
1867 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1869 BasicBlock *Succ = BI->getSuccessor(0);
1870 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1871 Succ != BB) // Don't hurt infinite loops!
1872 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1875 } else { // Conditional branch
1876 if (isValueEqualityComparison(BI)) {
1877 // If we only have one predecessor, and if it is a branch on this value,
1878 // see if that predecessor totally determines the outcome of this
1880 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1881 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1882 return SimplifyCFG(BB) || 1;
1884 // This block must be empty, except for the setcond inst, if it exists.
1885 BasicBlock::iterator I = BB->begin();
1887 (&*I == cast<Instruction>(BI->getCondition()) &&
1889 if (FoldValueComparisonIntoPredecessors(BI))
1890 return SimplifyCFG(BB) | true;
1893 // If this is a branch on a phi node in the current block, thread control
1894 // through this block if any PHI node entries are constants.
1895 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1896 if (PN->getParent() == BI->getParent())
1897 if (FoldCondBranchOnPHI(BI))
1898 return SimplifyCFG(BB) | true;
1900 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1901 // branches to us and one of our successors, fold the setcc into the
1902 // predecessor and use logical operations to pick the right destination.
1903 if (FoldBranchToCommonDest(BI))
1904 return SimplifyCFG(BB) | 1;
1907 // Scan predecessor blocks for conditional branches.
1908 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1909 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1910 if (PBI != BI && PBI->isConditional())
1911 if (SimplifyCondBranchToCondBranch(PBI, BI))
1912 return SimplifyCFG(BB) | true;
1914 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1915 // If there are any instructions immediately before the unreachable that can
1916 // be removed, do so.
1917 Instruction *Unreachable = BB->getTerminator();
1918 while (Unreachable != BB->begin()) {
1919 BasicBlock::iterator BBI = Unreachable;
1921 if (isa<CallInst>(BBI)) break;
1922 // Delete this instruction
1923 BB->getInstList().erase(BBI);
1927 // If the unreachable instruction is the first in the block, take a gander
1928 // at all of the predecessors of this instruction, and simplify them.
1929 if (&BB->front() == Unreachable) {
1930 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1931 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1932 TerminatorInst *TI = Preds[i]->getTerminator();
1934 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1935 if (BI->isUnconditional()) {
1936 if (BI->getSuccessor(0) == BB) {
1937 new UnreachableInst(TI);
1938 TI->eraseFromParent();
1942 if (BI->getSuccessor(0) == BB) {
1943 BranchInst::Create(BI->getSuccessor(1), BI);
1944 BI->eraseFromParent();
1945 } else if (BI->getSuccessor(1) == BB) {
1946 BranchInst::Create(BI->getSuccessor(0), BI);
1947 BI->eraseFromParent();
1951 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1952 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1953 if (SI->getSuccessor(i) == BB) {
1954 BB->removePredecessor(SI->getParent());
1959 // If the default value is unreachable, figure out the most popular
1960 // destination and make it the default.
1961 if (SI->getSuccessor(0) == BB) {
1962 std::map<BasicBlock*, unsigned> Popularity;
1963 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1964 Popularity[SI->getSuccessor(i)]++;
1966 // Find the most popular block.
1967 unsigned MaxPop = 0;
1968 BasicBlock *MaxBlock = 0;
1969 for (std::map<BasicBlock*, unsigned>::iterator
1970 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
1971 if (I->second > MaxPop) {
1973 MaxBlock = I->first;
1977 // Make this the new default, allowing us to delete any explicit
1979 SI->setSuccessor(0, MaxBlock);
1982 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
1984 if (isa<PHINode>(MaxBlock->begin()))
1985 for (unsigned i = 0; i != MaxPop-1; ++i)
1986 MaxBlock->removePredecessor(SI->getParent());
1988 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1989 if (SI->getSuccessor(i) == MaxBlock) {
1995 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
1996 if (II->getUnwindDest() == BB) {
1997 // Convert the invoke to a call instruction. This would be a good
1998 // place to note that the call does not throw though.
1999 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2000 II->removeFromParent(); // Take out of symbol table
2002 // Insert the call now...
2003 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
2004 CallInst *CI = CallInst::Create(II->getCalledValue(),
2005 Args.begin(), Args.end(),
2007 CI->setCallingConv(II->getCallingConv());
2008 CI->setParamAttrs(II->getParamAttrs());
2009 // If the invoke produced a value, the Call does now instead.
2010 II->replaceAllUsesWith(CI);
2017 // If this block is now dead, remove it.
2018 if (pred_begin(BB) == pred_end(BB)) {
2019 // We know there are no successors, so just nuke the block.
2020 M->getBasicBlockList().erase(BB);
2026 // Merge basic blocks into their predecessor if there is only one distinct
2027 // pred, and if there is only one distinct successor of the predecessor, and
2028 // if there are no PHI nodes.
2030 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2031 BasicBlock *OnlyPred = *PI++;
2032 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2033 if (*PI != OnlyPred) {
2034 OnlyPred = 0; // There are multiple different predecessors...
2038 BasicBlock *OnlySucc = 0;
2039 if (OnlyPred && OnlyPred != BB && // Don't break self loops
2040 OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) {
2041 // Check to see if there is only one distinct successor...
2042 succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred));
2044 for (; SI != SE; ++SI)
2045 if (*SI != OnlySucc) {
2046 OnlySucc = 0; // There are multiple distinct successors!
2052 DOUT << "Merging: " << *BB << "into: " << *OnlyPred;
2054 // Resolve any PHI nodes at the start of the block. They are all
2055 // guaranteed to have exactly one entry if they exist, unless there are
2056 // multiple duplicate (but guaranteed to be equal) entries for the
2057 // incoming edges. This occurs when there are multiple edges from
2058 // OnlyPred to OnlySucc.
2060 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
2061 PN->replaceAllUsesWith(PN->getIncomingValue(0));
2062 BB->getInstList().pop_front(); // Delete the phi node.
2065 // Delete the unconditional branch from the predecessor.
2066 OnlyPred->getInstList().pop_back();
2068 // Move all definitions in the successor to the predecessor.
2069 OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
2071 // Make all PHI nodes that referred to BB now refer to Pred as their
2073 BB->replaceAllUsesWith(OnlyPred);
2075 // Inherit predecessors name if it exists.
2076 if (!OnlyPred->hasName())
2077 OnlyPred->takeName(BB);
2079 // Erase basic block from the function.
2080 M->getBasicBlockList().erase(BB);
2085 // Otherwise, if this block only has a single predecessor, and if that block
2086 // is a conditional branch, see if we can hoist any code from this block up
2087 // into our predecessor.
2089 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2090 if (BI->isConditional()) {
2091 // Get the other block.
2092 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2093 PI = pred_begin(OtherBB);
2095 if (PI == pred_end(OtherBB)) {
2096 // We have a conditional branch to two blocks that are only reachable
2097 // from the condbr. We know that the condbr dominates the two blocks,
2098 // so see if there is any identical code in the "then" and "else"
2099 // blocks. If so, we can hoist it up to the branching block.
2100 Changed |= HoistThenElseCodeToIf(BI);
2103 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2107 else if (*SI != OnlySucc) {
2108 OnlySucc = 0; // There are multiple distinct successors!
2113 if (OnlySucc == OtherBB) {
2114 // If BB's only successor is the other successor of the predecessor,
2115 // i.e. a triangle, see if we can hoist any code from this block up
2116 // to the "if" block.
2117 Changed |= SpeculativelyExecuteBB(BI, BB);
2122 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2123 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2124 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2125 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2126 Instruction *Cond = cast<Instruction>(BI->getCondition());
2127 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2128 // 'setne's and'ed together, collect them.
2130 std::vector<ConstantInt*> Values;
2131 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2132 if (CompVal && CompVal->getType()->isInteger()) {
2133 // There might be duplicate constants in the list, which the switch
2134 // instruction can't handle, remove them now.
2135 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2136 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2138 // Figure out which block is which destination.
2139 BasicBlock *DefaultBB = BI->getSuccessor(1);
2140 BasicBlock *EdgeBB = BI->getSuccessor(0);
2141 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2143 // Create the new switch instruction now.
2144 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2147 // Add all of the 'cases' to the switch instruction.
2148 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2149 New->addCase(Values[i], EdgeBB);
2151 // We added edges from PI to the EdgeBB. As such, if there were any
2152 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2153 // the number of edges added.
2154 for (BasicBlock::iterator BBI = EdgeBB->begin();
2155 isa<PHINode>(BBI); ++BBI) {
2156 PHINode *PN = cast<PHINode>(BBI);
2157 Value *InVal = PN->getIncomingValueForBlock(*PI);
2158 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2159 PN->addIncoming(InVal, *PI);
2162 // Erase the old branch instruction.
2163 (*PI)->getInstList().erase(BI);
2165 // Erase the potentially condition tree that was used to computed the
2166 // branch condition.
2167 ErasePossiblyDeadInstructionTree(Cond);