1 //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Peephole optimize the CFG.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "simplifycfg"
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/Constants.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/Type.h"
19 #include "llvm/Support/CFG.h"
20 #include "llvm/Support/Debug.h"
27 // PropagatePredecessorsForPHIs - This gets "Succ" ready to have the
28 // predecessors from "BB". This is a little tricky because "Succ" has PHI
29 // nodes, which need to have extra slots added to them to hold the merge edges
30 // from BB's predecessors, and BB itself might have had PHI nodes in it. This
31 // function returns true (failure) if the Succ BB already has a predecessor that
32 // is a predecessor of BB and incoming PHI arguments would not be discernible.
34 // Assumption: Succ is the single successor for BB.
36 static bool PropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
37 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
39 if (!isa<PHINode>(Succ->front()))
40 return false; // We can make the transformation, no problem.
42 // If there is more than one predecessor, and there are PHI nodes in
43 // the successor, then we need to add incoming edges for the PHI nodes
45 const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
47 // Check to see if one of the predecessors of BB is already a predecessor of
48 // Succ. If so, we cannot do the transformation if there are any PHI nodes
49 // with incompatible values coming in from the two edges!
51 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); PI != PE; ++PI)
52 if (std::find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) {
53 // Loop over all of the PHI nodes checking to see if there are
54 // incompatible values coming in.
55 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
56 PHINode *PN = cast<PHINode>(I);
57 // Loop up the entries in the PHI node for BB and for *PI if the values
58 // coming in are non-equal, we cannot merge these two blocks (instead we
59 // should insert a conditional move or something, then merge the
61 int Idx1 = PN->getBasicBlockIndex(BB);
62 int Idx2 = PN->getBasicBlockIndex(*PI);
63 assert(Idx1 != -1 && Idx2 != -1 &&
64 "Didn't have entries for my predecessors??");
65 if (PN->getIncomingValue(Idx1) != PN->getIncomingValue(Idx2))
66 return true; // Values are not equal...
70 // Loop over all of the PHI nodes in the successor BB.
71 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
72 PHINode *PN = cast<PHINode>(I);
73 Value *OldVal = PN->removeIncomingValue(BB, false);
74 assert(OldVal && "No entry in PHI for Pred BB!");
76 // If this incoming value is one of the PHI nodes in BB, the new entries in
77 // the PHI node are the entries from the old PHI.
78 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
79 PHINode *OldValPN = cast<PHINode>(OldVal);
80 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
81 PN->addIncoming(OldValPN->getIncomingValue(i),
82 OldValPN->getIncomingBlock(i));
84 for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
85 End = BBPreds.end(); PredI != End; ++PredI) {
86 // Add an incoming value for each of the new incoming values...
87 PN->addIncoming(OldVal, *PredI);
94 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
95 /// presumably PHI nodes in it), check to see if the merge at this block is due
96 /// to an "if condition". If so, return the boolean condition that determines
97 /// which entry into BB will be taken. Also, return by references the block
98 /// that will be entered from if the condition is true, and the block that will
99 /// be entered if the condition is false.
102 static Value *GetIfCondition(BasicBlock *BB,
103 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
104 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
105 "Function can only handle blocks with 2 predecessors!");
106 BasicBlock *Pred1 = *pred_begin(BB);
107 BasicBlock *Pred2 = *++pred_begin(BB);
109 // We can only handle branches. Other control flow will be lowered to
110 // branches if possible anyway.
111 if (!isa<BranchInst>(Pred1->getTerminator()) ||
112 !isa<BranchInst>(Pred2->getTerminator()))
114 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
115 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
117 // Eliminate code duplication by ensuring that Pred1Br is conditional if
119 if (Pred2Br->isConditional()) {
120 // If both branches are conditional, we don't have an "if statement". In
121 // reality, we could transform this case, but since the condition will be
122 // required anyway, we stand no chance of eliminating it, so the xform is
123 // probably not profitable.
124 if (Pred1Br->isConditional())
127 std::swap(Pred1, Pred2);
128 std::swap(Pred1Br, Pred2Br);
131 if (Pred1Br->isConditional()) {
132 // If we found a conditional branch predecessor, make sure that it branches
133 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
134 if (Pred1Br->getSuccessor(0) == BB &&
135 Pred1Br->getSuccessor(1) == Pred2) {
138 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
139 Pred1Br->getSuccessor(1) == BB) {
143 // We know that one arm of the conditional goes to BB, so the other must
144 // go somewhere unrelated, and this must not be an "if statement".
148 // The only thing we have to watch out for here is to make sure that Pred2
149 // doesn't have incoming edges from other blocks. If it does, the condition
150 // doesn't dominate BB.
151 if (++pred_begin(Pred2) != pred_end(Pred2))
154 return Pred1Br->getCondition();
157 // Ok, if we got here, both predecessors end with an unconditional branch to
158 // BB. Don't panic! If both blocks only have a single (identical)
159 // predecessor, and THAT is a conditional branch, then we're all ok!
160 if (pred_begin(Pred1) == pred_end(Pred1) ||
161 ++pred_begin(Pred1) != pred_end(Pred1) ||
162 pred_begin(Pred2) == pred_end(Pred2) ||
163 ++pred_begin(Pred2) != pred_end(Pred2) ||
164 *pred_begin(Pred1) != *pred_begin(Pred2))
167 // Otherwise, if this is a conditional branch, then we can use it!
168 BasicBlock *CommonPred = *pred_begin(Pred1);
169 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
170 assert(BI->isConditional() && "Two successors but not conditional?");
171 if (BI->getSuccessor(0) == Pred1) {
178 return BI->getCondition();
184 // If we have a merge point of an "if condition" as accepted above, return true
185 // if the specified value dominates the block. We don't handle the true
186 // generality of domination here, just a special case which works well enough
189 // If AggressiveInsts is non-null, and if V does not dominate BB, we check to
190 // see if V (which must be an instruction) is cheap to compute and is
191 // non-trapping. If both are true, the instruction is inserted into the set and
193 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
194 std::set<Instruction*> *AggressiveInsts) {
195 Instruction *I = dyn_cast<Instruction>(V);
196 if (!I) return true; // Non-instructions all dominate instructions.
197 BasicBlock *PBB = I->getParent();
199 // We don't want to allow wierd loops that might have the "if condition" in
200 // the bottom of this block.
201 if (PBB == BB) return false;
203 // If this instruction is defined in a block that contains an unconditional
204 // branch to BB, then it must be in the 'conditional' part of the "if
206 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
207 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
208 if (!AggressiveInsts) return false;
209 // Okay, it looks like the instruction IS in the "condition". Check to
210 // see if its a cheap instruction to unconditionally compute, and if it
211 // only uses stuff defined outside of the condition. If so, hoist it out.
212 switch (I->getOpcode()) {
213 default: return false; // Cannot hoist this out safely.
214 case Instruction::Load:
215 // We can hoist loads that are non-volatile and obviously cannot trap.
216 if (cast<LoadInst>(I)->isVolatile())
218 if (!isa<AllocaInst>(I->getOperand(0)) &&
219 !isa<Constant>(I->getOperand(0)))
222 // Finally, we have to check to make sure there are no instructions
223 // before the load in its basic block, as we are going to hoist the loop
224 // out to its predecessor.
225 if (PBB->begin() != BasicBlock::iterator(I))
228 case Instruction::Add:
229 case Instruction::Sub:
230 case Instruction::And:
231 case Instruction::Or:
232 case Instruction::Xor:
233 case Instruction::Shl:
234 case Instruction::Shr:
235 break; // These are all cheap and non-trapping instructions.
238 // Okay, we can only really hoist these out if their operands are not
239 // defined in the conditional region.
240 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
241 if (!DominatesMergePoint(I->getOperand(i), BB, 0))
243 // Okay, it's safe to do this! Remember this instruction.
244 AggressiveInsts->insert(I);
250 // GatherConstantSetEQs - Given a potentially 'or'd together collection of seteq
251 // instructions that compare a value against a constant, return the value being
252 // compared, and stick the constant into the Values vector.
253 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
254 if (Instruction *Inst = dyn_cast<Instruction>(V))
255 if (Inst->getOpcode() == Instruction::SetEQ) {
256 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
258 return Inst->getOperand(0);
259 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
261 return Inst->getOperand(1);
263 } else if (Inst->getOpcode() == Instruction::Or) {
264 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
265 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
272 // GatherConstantSetNEs - Given a potentially 'and'd together collection of
273 // setne instructions that compare a value against a constant, return the value
274 // being compared, and stick the constant into the Values vector.
275 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
276 if (Instruction *Inst = dyn_cast<Instruction>(V))
277 if (Inst->getOpcode() == Instruction::SetNE) {
278 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
280 return Inst->getOperand(0);
281 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
283 return Inst->getOperand(1);
285 } else if (Inst->getOpcode() == Instruction::Cast) {
286 // Cast of X to bool is really a comparison against zero.
287 assert(Inst->getType() == Type::BoolTy && "Can only handle bool values!");
288 Values.push_back(ConstantInt::get(Inst->getOperand(0)->getType(), 0));
289 return Inst->getOperand(0);
290 } else if (Inst->getOpcode() == Instruction::And) {
291 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
292 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
301 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
302 /// bunch of comparisons of one value against constants, return the value and
303 /// the constants being compared.
304 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
305 std::vector<ConstantInt*> &Values) {
306 if (Cond->getOpcode() == Instruction::Or) {
307 CompVal = GatherConstantSetEQs(Cond, Values);
309 // Return true to indicate that the condition is true if the CompVal is
310 // equal to one of the constants.
312 } else if (Cond->getOpcode() == Instruction::And) {
313 CompVal = GatherConstantSetNEs(Cond, Values);
315 // Return false to indicate that the condition is false if the CompVal is
316 // equal to one of the constants.
322 /// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
323 /// has no side effects, nuke it. If it uses any instructions that become dead
324 /// because the instruction is now gone, nuke them too.
325 static void ErasePossiblyDeadInstructionTree(Instruction *I) {
326 if (isInstructionTriviallyDead(I)) {
327 std::vector<Value*> Operands(I->op_begin(), I->op_end());
328 I->getParent()->getInstList().erase(I);
329 for (unsigned i = 0, e = Operands.size(); i != e; ++i)
330 if (Instruction *OpI = dyn_cast<Instruction>(Operands[i]))
331 ErasePossiblyDeadInstructionTree(OpI);
335 /// SafeToMergeTerminators - Return true if it is safe to merge these two
336 /// terminator instructions together.
338 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
339 if (SI1 == SI2) return false; // Can't merge with self!
341 // It is not safe to merge these two switch instructions if they have a common
342 // successor, and if that successor has a PHI node, and if *that* PHI node has
343 // conflicting incoming values from the two switch blocks.
344 BasicBlock *SI1BB = SI1->getParent();
345 BasicBlock *SI2BB = SI2->getParent();
346 std::set<BasicBlock*> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
348 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
349 if (SI1Succs.count(*I))
350 for (BasicBlock::iterator BBI = (*I)->begin();
351 isa<PHINode>(BBI); ++BBI) {
352 PHINode *PN = cast<PHINode>(BBI);
353 if (PN->getIncomingValueForBlock(SI1BB) !=
354 PN->getIncomingValueForBlock(SI2BB))
361 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
362 /// now be entries in it from the 'NewPred' block. The values that will be
363 /// flowing into the PHI nodes will be the same as those coming in from
364 /// ExistPred, an existing predecessor of Succ.
365 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
366 BasicBlock *ExistPred) {
367 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
368 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
369 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
371 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
372 PHINode *PN = cast<PHINode>(I);
373 Value *V = PN->getIncomingValueForBlock(ExistPred);
374 PN->addIncoming(V, NewPred);
378 // isValueEqualityComparison - Return true if the specified terminator checks to
379 // see if a value is equal to constant integer value.
380 static Value *isValueEqualityComparison(TerminatorInst *TI) {
381 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
382 // Do not permit merging of large switch instructions into their
383 // predecessors unless there is only one predecessor.
384 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
385 pred_end(SI->getParent())) > 128)
388 return SI->getCondition();
390 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
391 if (BI->isConditional() && BI->getCondition()->hasOneUse())
392 if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))
393 if ((SCI->getOpcode() == Instruction::SetEQ ||
394 SCI->getOpcode() == Instruction::SetNE) &&
395 isa<ConstantInt>(SCI->getOperand(1)))
396 return SCI->getOperand(0);
400 // Given a value comparison instruction, decode all of the 'cases' that it
401 // represents and return the 'default' block.
403 GetValueEqualityComparisonCases(TerminatorInst *TI,
404 std::vector<std::pair<ConstantInt*,
405 BasicBlock*> > &Cases) {
406 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
407 Cases.reserve(SI->getNumCases());
408 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
409 Cases.push_back(std::make_pair(cast<ConstantInt>(SI->getCaseValue(i)),
410 SI->getSuccessor(i)));
411 return SI->getDefaultDest();
414 BranchInst *BI = cast<BranchInst>(TI);
415 SetCondInst *SCI = cast<SetCondInst>(BI->getCondition());
416 Cases.push_back(std::make_pair(cast<ConstantInt>(SCI->getOperand(1)),
417 BI->getSuccessor(SCI->getOpcode() ==
418 Instruction::SetNE)));
419 return BI->getSuccessor(SCI->getOpcode() == Instruction::SetEQ);
423 // FoldValueComparisonIntoPredecessors - The specified terminator is a value
424 // equality comparison instruction (either a switch or a branch on "X == c").
425 // See if any of the predecessors of the terminator block are value comparisons
426 // on the same value. If so, and if safe to do so, fold them together.
427 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
428 BasicBlock *BB = TI->getParent();
429 Value *CV = isValueEqualityComparison(TI); // CondVal
430 assert(CV && "Not a comparison?");
431 bool Changed = false;
433 std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
434 while (!Preds.empty()) {
435 BasicBlock *Pred = Preds.back();
438 // See if the predecessor is a comparison with the same value.
439 TerminatorInst *PTI = Pred->getTerminator();
440 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
442 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
443 // Figure out which 'cases' to copy from SI to PSI.
444 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
445 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
447 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
448 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
450 // Based on whether the default edge from PTI goes to BB or not, fill in
451 // PredCases and PredDefault with the new switch cases we would like to
453 std::vector<BasicBlock*> NewSuccessors;
455 if (PredDefault == BB) {
456 // If this is the default destination from PTI, only the edges in TI
457 // that don't occur in PTI, or that branch to BB will be activated.
458 std::set<ConstantInt*> PTIHandled;
459 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
460 if (PredCases[i].second != BB)
461 PTIHandled.insert(PredCases[i].first);
463 // The default destination is BB, we don't need explicit targets.
464 std::swap(PredCases[i], PredCases.back());
465 PredCases.pop_back();
469 // Reconstruct the new switch statement we will be building.
470 if (PredDefault != BBDefault) {
471 PredDefault->removePredecessor(Pred);
472 PredDefault = BBDefault;
473 NewSuccessors.push_back(BBDefault);
475 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
476 if (!PTIHandled.count(BBCases[i].first) &&
477 BBCases[i].second != BBDefault) {
478 PredCases.push_back(BBCases[i]);
479 NewSuccessors.push_back(BBCases[i].second);
483 // If this is not the default destination from PSI, only the edges
484 // in SI that occur in PSI with a destination of BB will be
486 std::set<ConstantInt*> PTIHandled;
487 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
488 if (PredCases[i].second == BB) {
489 PTIHandled.insert(PredCases[i].first);
490 std::swap(PredCases[i], PredCases.back());
491 PredCases.pop_back();
495 // Okay, now we know which constants were sent to BB from the
496 // predecessor. Figure out where they will all go now.
497 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
498 if (PTIHandled.count(BBCases[i].first)) {
499 // If this is one we are capable of getting...
500 PredCases.push_back(BBCases[i]);
501 NewSuccessors.push_back(BBCases[i].second);
502 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
505 // If there are any constants vectored to BB that TI doesn't handle,
506 // they must go to the default destination of TI.
507 for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
508 E = PTIHandled.end(); I != E; ++I) {
509 PredCases.push_back(std::make_pair(*I, BBDefault));
510 NewSuccessors.push_back(BBDefault);
514 // Okay, at this point, we know which new successor Pred will get. Make
515 // sure we update the number of entries in the PHI nodes for these
517 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
518 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
520 // Now that the successors are updated, create the new Switch instruction.
521 SwitchInst *NewSI = new SwitchInst(CV, PredDefault, PTI);
522 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
523 NewSI->addCase(PredCases[i].first, PredCases[i].second);
524 Pred->getInstList().erase(PTI);
526 // Okay, last check. If BB is still a successor of PSI, then we must
527 // have an infinite loop case. If so, add an infinitely looping block
528 // to handle the case to preserve the behavior of the code.
529 BasicBlock *InfLoopBlock = 0;
530 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
531 if (NewSI->getSuccessor(i) == BB) {
532 if (InfLoopBlock == 0) {
533 // Insert it at the end of the loop, because it's either code,
534 // or it won't matter if it's hot. :)
535 InfLoopBlock = new BasicBlock("infloop", BB->getParent());
536 new BranchInst(InfLoopBlock, InfLoopBlock);
538 NewSI->setSuccessor(i, InfLoopBlock);
548 /// ConstantIntOrdering - This class implements a stable ordering of constant
549 /// integers that does not depend on their address. This is important for
550 /// applications that sort ConstantInt's to ensure uniqueness.
551 struct ConstantIntOrdering {
552 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
553 return LHS->getRawValue() < RHS->getRawValue();
559 // SimplifyCFG - This function is used to do simplification of a CFG. For
560 // example, it adjusts branches to branches to eliminate the extra hop, it
561 // eliminates unreachable basic blocks, and does other "peephole" optimization
562 // of the CFG. It returns true if a modification was made.
564 // WARNING: The entry node of a function may not be simplified.
566 bool llvm::SimplifyCFG(BasicBlock *BB) {
567 bool Changed = false;
568 Function *M = BB->getParent();
570 assert(BB && BB->getParent() && "Block not embedded in function!");
571 assert(BB->getTerminator() && "Degenerate basic block encountered!");
572 assert(&BB->getParent()->front() != BB && "Can't Simplify entry block!");
574 // Remove basic blocks that have no predecessors... which are unreachable.
575 if (pred_begin(BB) == pred_end(BB) ||
576 *pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB)) {
577 DEBUG(std::cerr << "Removing BB: \n" << *BB);
579 // Loop through all of our successors and make sure they know that one
580 // of their predecessors is going away.
581 for_each(succ_begin(BB), succ_end(BB),
582 std::bind2nd(std::mem_fun(&BasicBlock::removePredecessor), BB));
584 while (!BB->empty()) {
585 Instruction &I = BB->back();
586 // If this instruction is used, replace uses with an arbitrary
587 // constant value. Because control flow can't get here, we don't care
588 // what we replace the value with. Note that since this block is
589 // unreachable, and all values contained within it must dominate their
590 // uses, that all uses will eventually be removed.
592 // Make all users of this instruction reference the constant instead
593 I.replaceAllUsesWith(Constant::getNullValue(I.getType()));
595 // Remove the instruction from the basic block
596 BB->getInstList().pop_back();
598 M->getBasicBlockList().erase(BB);
602 // Check to see if we can constant propagate this terminator instruction
604 Changed |= ConstantFoldTerminator(BB);
606 // Check to see if this block has no non-phi instructions and only a single
607 // successor. If so, replace references to this basic block with references
609 succ_iterator SI(succ_begin(BB));
610 if (SI != succ_end(BB) && ++SI == succ_end(BB)) { // One succ?
612 BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes...
613 while (isa<PHINode>(*BBI)) ++BBI;
615 if (BBI->isTerminator()) { // Terminator is the only non-phi instruction!
616 BasicBlock *Succ = *succ_begin(BB); // There is exactly one successor
618 if (Succ != BB) { // Arg, don't hurt infinite loops!
619 // If our successor has PHI nodes, then we need to update them to
620 // include entries for BB's predecessors, not for BB itself.
621 // Be careful though, if this transformation fails (returns true) then
622 // we cannot do this transformation!
624 if (!PropagatePredecessorsForPHIs(BB, Succ)) {
625 DEBUG(std::cerr << "Killing Trivial BB: \n" << *BB);
626 std::string OldName = BB->getName();
628 std::vector<BasicBlock*>
629 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
631 // Move all PHI nodes in BB to Succ if they are alive, otherwise
633 while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
635 BB->getInstList().erase(BB->begin()); // Nuke instruction...
637 // The instruction is alive, so this means that Succ must have
638 // *ONLY* had BB as a predecessor, and the PHI node is still valid
639 // now. Simply move it into Succ, because we know that BB
640 // strictly dominated Succ.
641 BB->getInstList().remove(BB->begin());
642 Succ->getInstList().push_front(PN);
644 // We need to add new entries for the PHI node to account for
645 // predecessors of Succ that the PHI node does not take into
646 // account. At this point, since we know that BB dominated succ,
647 // this means that we should any newly added incoming edges should
648 // use the PHI node as the value for these edges, because they are
650 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
651 if (OldSuccPreds[i] != BB)
652 PN->addIncoming(PN, OldSuccPreds[i]);
655 // Everything that jumped to BB now goes to Succ...
656 BB->replaceAllUsesWith(Succ);
658 // Delete the old basic block...
659 M->getBasicBlockList().erase(BB);
661 if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can
662 Succ->setName(OldName);
669 // If this is a returning block with only PHI nodes in it, fold the return
670 // instruction into any unconditional branch predecessors.
672 // If any predecessor is a conditional branch that just selects among
673 // different return values, fold the replace the branch/return with a select
675 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
676 BasicBlock::iterator BBI = BB->getTerminator();
677 if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
678 // Find predecessors that end with branches.
679 std::vector<BasicBlock*> UncondBranchPreds;
680 std::vector<BranchInst*> CondBranchPreds;
681 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
682 TerminatorInst *PTI = (*PI)->getTerminator();
683 if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
684 if (BI->isUnconditional())
685 UncondBranchPreds.push_back(*PI);
687 CondBranchPreds.push_back(BI);
690 // If we found some, do the transformation!
691 if (!UncondBranchPreds.empty()) {
692 while (!UncondBranchPreds.empty()) {
693 BasicBlock *Pred = UncondBranchPreds.back();
694 UncondBranchPreds.pop_back();
695 Instruction *UncondBranch = Pred->getTerminator();
696 // Clone the return and add it to the end of the predecessor.
697 Instruction *NewRet = RI->clone();
698 Pred->getInstList().push_back(NewRet);
700 // If the return instruction returns a value, and if the value was a
701 // PHI node in "BB", propagate the right value into the return.
702 if (NewRet->getNumOperands() == 1)
703 if (PHINode *PN = dyn_cast<PHINode>(NewRet->getOperand(0)))
704 if (PN->getParent() == BB)
705 NewRet->setOperand(0, PN->getIncomingValueForBlock(Pred));
706 // Update any PHI nodes in the returning block to realize that we no
707 // longer branch to them.
708 BB->removePredecessor(Pred);
709 Pred->getInstList().erase(UncondBranch);
712 // If we eliminated all predecessors of the block, delete the block now.
713 if (pred_begin(BB) == pred_end(BB))
714 // We know there are no successors, so just nuke the block.
715 M->getBasicBlockList().erase(BB);
720 // Check out all of the conditional branches going to this return
721 // instruction. If any of them just select between returns, change the
722 // branch itself into a select/return pair.
723 while (!CondBranchPreds.empty()) {
724 BranchInst *BI = CondBranchPreds.back();
725 CondBranchPreds.pop_back();
726 BasicBlock *TrueSucc = BI->getSuccessor(0);
727 BasicBlock *FalseSucc = BI->getSuccessor(1);
728 BasicBlock *OtherSucc = TrueSucc == BB ? FalseSucc : TrueSucc;
730 // Check to see if the non-BB successor is also a return block.
731 if (isa<ReturnInst>(OtherSucc->getTerminator())) {
732 // Check to see if there are only PHI instructions in this block.
733 BasicBlock::iterator OSI = OtherSucc->getTerminator();
734 if (OSI == OtherSucc->begin() || isa<PHINode>(--OSI)) {
735 // Okay, we found a branch that is going to two return nodes. If
736 // there is no return value for this function, just change the
737 // branch into a return.
738 if (RI->getNumOperands() == 0) {
739 TrueSucc->removePredecessor(BI->getParent());
740 FalseSucc->removePredecessor(BI->getParent());
741 new ReturnInst(0, BI);
742 BI->getParent()->getInstList().erase(BI);
746 // Otherwise, figure out what the true and false return values are
747 // so we can insert a new select instruction.
748 Value *TrueValue = TrueSucc->getTerminator()->getOperand(0);
749 Value *FalseValue = FalseSucc->getTerminator()->getOperand(0);
751 // Unwrap any PHI nodes in the return blocks.
752 if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue))
753 if (TVPN->getParent() == TrueSucc)
754 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
755 if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue))
756 if (FVPN->getParent() == FalseSucc)
757 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
759 TrueSucc->removePredecessor(BI->getParent());
760 FalseSucc->removePredecessor(BI->getParent());
762 // Insert a new select instruction.
764 Value *BrCond = BI->getCondition();
765 if (TrueValue != FalseValue)
766 NewRetVal = new SelectInst(BrCond, TrueValue,
767 FalseValue, "retval", BI);
769 NewRetVal = TrueValue;
771 new ReturnInst(NewRetVal, BI);
772 BI->getParent()->getInstList().erase(BI);
773 if (BrCond->use_empty())
774 if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
775 BrCondI->getParent()->getInstList().erase(BrCondI);
781 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->begin())) {
782 // Check to see if the first instruction in this block is just an unwind.
783 // If so, replace any invoke instructions which use this as an exception
784 // destination with call instructions, and any unconditional branch
785 // predecessor with an unwind.
787 std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
788 while (!Preds.empty()) {
789 BasicBlock *Pred = Preds.back();
790 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
791 if (BI->isUnconditional()) {
792 Pred->getInstList().pop_back(); // nuke uncond branch
793 new UnwindInst(Pred); // Use unwind.
796 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
797 if (II->getUnwindDest() == BB) {
798 // Insert a new branch instruction before the invoke, because this
799 // is now a fall through...
800 BranchInst *BI = new BranchInst(II->getNormalDest(), II);
801 Pred->getInstList().remove(II); // Take out of symbol table
803 // Insert the call now...
804 std::vector<Value*> Args(II->op_begin()+3, II->op_end());
805 CallInst *CI = new CallInst(II->getCalledValue(), Args,
807 // If the invoke produced a value, the Call now does instead
808 II->replaceAllUsesWith(CI);
816 // If this block is now dead, remove it.
817 if (pred_begin(BB) == pred_end(BB)) {
818 // We know there are no successors, so just nuke the block.
819 M->getBasicBlockList().erase(BB);
823 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->begin())) {
824 if (isValueEqualityComparison(SI))
825 if (FoldValueComparisonIntoPredecessors(SI))
826 return SimplifyCFG(BB) || 1;
827 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
828 if (BI->isConditional()) {
829 if (Value *CompVal = isValueEqualityComparison(BI)) {
830 // This block must be empty, except for the setcond inst, if it exists.
831 BasicBlock::iterator I = BB->begin();
833 (&*I == cast<Instruction>(BI->getCondition()) &&
835 if (FoldValueComparisonIntoPredecessors(BI))
836 return SimplifyCFG(BB) | true;
839 // If this basic block is ONLY a setcc and a branch, and if a predecessor
840 // branches to us and one of our successors, fold the setcc into the
841 // predecessor and use logical operations to pick the right destination.
842 BasicBlock *TrueDest = BI->getSuccessor(0);
843 BasicBlock *FalseDest = BI->getSuccessor(1);
844 if (BinaryOperator *Cond = dyn_cast<BinaryOperator>(BI->getCondition()))
845 if (Cond->getParent() == BB && &BB->front() == Cond &&
846 Cond->getNext() == BI && Cond->hasOneUse() &&
847 TrueDest != BB && FalseDest != BB)
848 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI)
849 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
850 if (PBI->isConditional() && SafeToMergeTerminators(BI, PBI)) {
851 BasicBlock *PredBlock = *PI;
852 if (PBI->getSuccessor(0) == FalseDest ||
853 PBI->getSuccessor(1) == TrueDest) {
854 // Invert the predecessors condition test (xor it with true),
855 // which allows us to write this code once.
857 BinaryOperator::createNot(PBI->getCondition(),
858 PBI->getCondition()->getName()+".not", PBI);
859 PBI->setCondition(NewCond);
860 BasicBlock *OldTrue = PBI->getSuccessor(0);
861 BasicBlock *OldFalse = PBI->getSuccessor(1);
862 PBI->setSuccessor(0, OldFalse);
863 PBI->setSuccessor(1, OldTrue);
866 if (PBI->getSuccessor(0) == TrueDest ||
867 PBI->getSuccessor(1) == FalseDest) {
868 // Clone Cond into the predecessor basic block, and or/and the
869 // two conditions together.
870 Instruction *New = Cond->clone();
871 New->setName(Cond->getName());
872 Cond->setName(Cond->getName()+".old");
873 PredBlock->getInstList().insert(PBI, New);
874 Instruction::BinaryOps Opcode =
875 PBI->getSuccessor(0) == TrueDest ?
876 Instruction::Or : Instruction::And;
878 BinaryOperator::create(Opcode, PBI->getCondition(),
879 New, "bothcond", PBI);
880 PBI->setCondition(NewCond);
881 if (PBI->getSuccessor(0) == BB) {
882 AddPredecessorToBlock(TrueDest, PredBlock, BB);
883 PBI->setSuccessor(0, TrueDest);
885 if (PBI->getSuccessor(1) == BB) {
886 AddPredecessorToBlock(FalseDest, PredBlock, BB);
887 PBI->setSuccessor(1, FalseDest);
889 return SimplifyCFG(BB) | 1;
893 // If this block ends with a branch instruction, and if there is one
894 // predecessor, see if the previous block ended with a branch on the same
895 // condition, which makes this conditional branch redundant.
896 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
897 BasicBlock *OnlyPred = *PI++;
898 for (; PI != PE; ++PI)// Search all predecessors, see if they are all same
899 if (*PI != OnlyPred) {
900 OnlyPred = 0; // There are multiple different predecessors...
905 if (BranchInst *PBI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
906 if (PBI->isConditional() &&
907 PBI->getCondition() == BI->getCondition() &&
908 (PBI->getSuccessor(0) != BB || PBI->getSuccessor(1) != BB)) {
909 // Okay, the outcome of this conditional branch is statically
910 // knowable. Delete the outgoing CFG edge that is impossible to
912 bool CondIsTrue = PBI->getSuccessor(0) == BB;
913 BI->getSuccessor(CondIsTrue)->removePredecessor(BB);
914 new BranchInst(BI->getSuccessor(!CondIsTrue), BB);
915 BB->getInstList().erase(BI);
916 return SimplifyCFG(BB) | true;
919 } else if (isa<UnreachableInst>(BB->getTerminator())) {
920 // If there are any instructions immediately before the unreachable that can
921 // be removed, do so.
922 Instruction *Unreachable = BB->getTerminator();
923 while (Unreachable != BB->begin()) {
924 BasicBlock::iterator BBI = Unreachable;
926 if (isa<CallInst>(BBI)) break;
927 // Delete this instruction
928 BB->getInstList().erase(BBI);
932 // If the unreachable instruction is the first in the block, take a gander
933 // at all of the predecessors of this instruction, and simplify them.
934 if (&BB->front() == Unreachable) {
935 std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
936 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
937 TerminatorInst *TI = Preds[i]->getTerminator();
939 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
940 if (BI->isUnconditional()) {
941 if (BI->getSuccessor(0) == BB) {
942 new UnreachableInst(TI);
943 TI->eraseFromParent();
947 if (BI->getSuccessor(0) == BB) {
948 new BranchInst(BI->getSuccessor(1), BI);
949 BI->eraseFromParent();
950 } else if (BI->getSuccessor(1) == BB) {
951 new BranchInst(BI->getSuccessor(0), BI);
952 BI->eraseFromParent();
956 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
957 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
958 if (SI->getSuccessor(i) == BB) {
963 // If the default value is unreachable, figure out the most popular
964 // destination and make it the default.
965 if (SI->getSuccessor(0) == BB) {
966 std::map<BasicBlock*, unsigned> Popularity;
967 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
968 Popularity[SI->getSuccessor(i)]++;
970 // Find the most popular block.
972 BasicBlock *MaxBlock = 0;
973 for (std::map<BasicBlock*, unsigned>::iterator
974 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
975 if (I->second > MaxPop) {
981 // Make this the new default, allowing us to delete any explicit
983 SI->setSuccessor(0, MaxBlock);
986 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
987 if (SI->getSuccessor(i) == MaxBlock) {
993 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
994 if (II->getUnwindDest() == BB) {
995 // Convert the invoke to a call instruction. This would be a good
996 // place to note that the call does not throw though.
997 BranchInst *BI = new BranchInst(II->getNormalDest(), II);
998 II->removeFromParent(); // Take out of symbol table
1000 // Insert the call now...
1001 std::vector<Value*> Args(II->op_begin()+3, II->op_end());
1002 CallInst *CI = new CallInst(II->getCalledValue(), Args,
1004 // If the invoke produced a value, the Call does now instead.
1005 II->replaceAllUsesWith(CI);
1012 // If this block is now dead, remove it.
1013 if (pred_begin(BB) == pred_end(BB)) {
1014 // We know there are no successors, so just nuke the block.
1015 M->getBasicBlockList().erase(BB);
1021 // Merge basic blocks into their predecessor if there is only one distinct
1022 // pred, and if there is only one distinct successor of the predecessor, and
1023 // if there are no PHI nodes.
1025 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
1026 BasicBlock *OnlyPred = *PI++;
1027 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
1028 if (*PI != OnlyPred) {
1029 OnlyPred = 0; // There are multiple different predecessors...
1033 BasicBlock *OnlySucc = 0;
1034 if (OnlyPred && OnlyPred != BB && // Don't break self loops
1035 OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) {
1036 // Check to see if there is only one distinct successor...
1037 succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred));
1039 for (; SI != SE; ++SI)
1040 if (*SI != OnlySucc) {
1041 OnlySucc = 0; // There are multiple distinct successors!
1047 DEBUG(std::cerr << "Merging: " << *BB << "into: " << *OnlyPred);
1048 TerminatorInst *Term = OnlyPred->getTerminator();
1050 // Resolve any PHI nodes at the start of the block. They are all
1051 // guaranteed to have exactly one entry if they exist, unless there are
1052 // multiple duplicate (but guaranteed to be equal) entries for the
1053 // incoming edges. This occurs when there are multiple edges from
1054 // OnlyPred to OnlySucc.
1056 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
1057 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1058 BB->getInstList().pop_front(); // Delete the phi node...
1061 // Delete the unconditional branch from the predecessor...
1062 OnlyPred->getInstList().pop_back();
1064 // Move all definitions in the successor to the predecessor...
1065 OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
1067 // Make all PHI nodes that referred to BB now refer to Pred as their
1069 BB->replaceAllUsesWith(OnlyPred);
1071 std::string OldName = BB->getName();
1073 // Erase basic block from the function...
1074 M->getBasicBlockList().erase(BB);
1076 // Inherit predecessors name if it exists...
1077 if (!OldName.empty() && !OnlyPred->hasName())
1078 OnlyPred->setName(OldName);
1083 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1084 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1085 // Change br (X == 0 | X == 1), T, F into a switch instruction.
1086 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
1087 Instruction *Cond = cast<Instruction>(BI->getCondition());
1088 // If this is a bunch of seteq's or'd together, or if it's a bunch of
1089 // 'setne's and'ed together, collect them.
1091 std::vector<ConstantInt*> Values;
1092 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
1093 if (CompVal && CompVal->getType()->isInteger()) {
1094 // There might be duplicate constants in the list, which the switch
1095 // instruction can't handle, remove them now.
1096 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
1097 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
1099 // Figure out which block is which destination.
1100 BasicBlock *DefaultBB = BI->getSuccessor(1);
1101 BasicBlock *EdgeBB = BI->getSuccessor(0);
1102 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
1104 // Create the new switch instruction now.
1105 SwitchInst *New = new SwitchInst(CompVal, DefaultBB, BI);
1107 // Add all of the 'cases' to the switch instruction.
1108 for (unsigned i = 0, e = Values.size(); i != e; ++i)
1109 New->addCase(Values[i], EdgeBB);
1111 // We added edges from PI to the EdgeBB. As such, if there were any
1112 // PHI nodes in EdgeBB, they need entries to be added corresponding to
1113 // the number of edges added.
1114 for (BasicBlock::iterator BBI = EdgeBB->begin();
1115 isa<PHINode>(BBI); ++BBI) {
1116 PHINode *PN = cast<PHINode>(BBI);
1117 Value *InVal = PN->getIncomingValueForBlock(*PI);
1118 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
1119 PN->addIncoming(InVal, *PI);
1122 // Erase the old branch instruction.
1123 (*PI)->getInstList().erase(BI);
1125 // Erase the potentially condition tree that was used to computed the
1126 // branch condition.
1127 ErasePossiblyDeadInstructionTree(Cond);
1132 // If there is a trivial two-entry PHI node in this basic block, and we can
1133 // eliminate it, do so now.
1134 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1135 if (PN->getNumIncomingValues() == 2) {
1136 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1137 // statement", which has a very simple dominance structure. Basically, we
1138 // are trying to find the condition that is being branched on, which
1139 // subsequently causes this merge to happen. We really want control
1140 // dependence information for this check, but simplifycfg can't keep it up
1141 // to date, and this catches most of the cases we care about anyway.
1143 BasicBlock *IfTrue, *IfFalse;
1144 if (Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse)) {
1145 DEBUG(std::cerr << "FOUND IF CONDITION! " << *IfCond << " T: "
1146 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1148 // Loop over the PHI's seeing if we can promote them all to select
1149 // instructions. While we are at it, keep track of the instructions
1150 // that need to be moved to the dominating block.
1151 std::set<Instruction*> AggressiveInsts;
1152 bool CanPromote = true;
1154 BasicBlock::iterator AfterPHIIt = BB->begin();
1155 while (isa<PHINode>(AfterPHIIt)) {
1156 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1157 if (PN->getIncomingValue(0) == PN->getIncomingValue(1))
1158 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1159 else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1160 &AggressiveInsts) ||
1161 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1162 &AggressiveInsts)) {
1168 // Did we eliminate all PHI's?
1169 CanPromote |= AfterPHIIt == BB->begin();
1171 // If we all PHI nodes are promotable, check to make sure that all
1172 // instructions in the predecessor blocks can be promoted as well. If
1173 // not, we won't be able to get rid of the control flow, so it's not
1174 // worth promoting to select instructions.
1175 BasicBlock *DomBlock, *IfBlock1 = 0, *IfBlock2 = 0;
1177 PN = cast<PHINode>(BB->begin());
1178 BasicBlock *Pred = PN->getIncomingBlock(0);
1179 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1181 DomBlock = *pred_begin(Pred);
1182 for (BasicBlock::iterator I = Pred->begin();
1183 !isa<TerminatorInst>(I); ++I)
1184 if (!AggressiveInsts.count(I)) {
1185 // This is not an aggressive instruction that we can promote.
1186 // Because of this, we won't be able to get rid of the control
1187 // flow, so the xform is not worth it.
1193 Pred = PN->getIncomingBlock(1);
1195 cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1197 DomBlock = *pred_begin(Pred);
1198 for (BasicBlock::iterator I = Pred->begin();
1199 !isa<TerminatorInst>(I); ++I)
1200 if (!AggressiveInsts.count(I)) {
1201 // This is not an aggressive instruction that we can promote.
1202 // Because of this, we won't be able to get rid of the control
1203 // flow, so the xform is not worth it.
1210 // If we can still promote the PHI nodes after this gauntlet of tests,
1211 // do all of the PHI's now.
1213 // Move all 'aggressive' instructions, which are defined in the
1214 // conditional parts of the if's up to the dominating block.
1216 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1217 IfBlock1->getInstList(),
1219 IfBlock1->getTerminator());
1222 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1223 IfBlock2->getInstList(),
1225 IfBlock2->getTerminator());
1228 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1229 // Change the PHI node into a select instruction.
1231 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1233 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1235 std::string Name = PN->getName(); PN->setName("");
1236 PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal,
1238 BB->getInstList().erase(PN);