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/IntrinsicInst.h"
19 #include "llvm/LLVMContext.h"
20 #include "llvm/Type.h"
21 #include "llvm/DerivedTypes.h"
22 #include "llvm/GlobalVariable.h"
23 #include "llvm/Support/CFG.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Support/raw_ostream.h"
26 #include "llvm/Analysis/ConstantFolding.h"
27 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
28 #include "llvm/ADT/SmallVector.h"
29 #include "llvm/ADT/SmallPtrSet.h"
30 #include "llvm/ADT/Statistic.h"
37 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
39 /// SafeToMergeTerminators - Return true if it is safe to merge these two
40 /// terminator instructions together.
42 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
43 if (SI1 == SI2) return false; // Can't merge with self!
45 // It is not safe to merge these two switch instructions if they have a common
46 // successor, and if that successor has a PHI node, and if *that* PHI node has
47 // conflicting incoming values from the two switch blocks.
48 BasicBlock *SI1BB = SI1->getParent();
49 BasicBlock *SI2BB = SI2->getParent();
50 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
52 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
53 if (SI1Succs.count(*I))
54 for (BasicBlock::iterator BBI = (*I)->begin();
55 isa<PHINode>(BBI); ++BBI) {
56 PHINode *PN = cast<PHINode>(BBI);
57 if (PN->getIncomingValueForBlock(SI1BB) !=
58 PN->getIncomingValueForBlock(SI2BB))
65 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
66 /// now be entries in it from the 'NewPred' block. The values that will be
67 /// flowing into the PHI nodes will be the same as those coming in from
68 /// ExistPred, an existing predecessor of Succ.
69 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
70 BasicBlock *ExistPred) {
71 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
72 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
73 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
76 for (BasicBlock::iterator I = Succ->begin();
77 (PN = dyn_cast<PHINode>(I)); ++I)
78 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
81 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
82 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
84 /// Assumption: Succ is the single successor for BB.
86 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
87 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
89 DEBUG(errs() << "Looking to fold " << BB->getName() << " into "
90 << Succ->getName() << "\n");
91 // Shortcut, if there is only a single predecessor it must be BB and merging
93 if (Succ->getSinglePredecessor()) return true;
95 // Make a list of the predecessors of BB
96 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
97 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
99 // Use that list to make another list of common predecessors of BB and Succ
100 BlockSet CommonPreds;
101 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
103 if (BBPreds.count(*PI))
104 CommonPreds.insert(*PI);
106 // Shortcut, if there are no common predecessors, merging is always safe
107 if (CommonPreds.empty())
110 // Look at all the phi nodes in Succ, to see if they present a conflict when
111 // merging these blocks
112 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
113 PHINode *PN = cast<PHINode>(I);
115 // If the incoming value from BB is again a PHINode in
116 // BB which has the same incoming value for *PI as PN does, we can
117 // merge the phi nodes and then the blocks can still be merged
118 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
119 if (BBPN && BBPN->getParent() == BB) {
120 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
122 if (BBPN->getIncomingValueForBlock(*PI)
123 != PN->getIncomingValueForBlock(*PI)) {
124 DEBUG(errs() << "Can't fold, phi node " << PN->getName() << " in "
125 << Succ->getName() << " is conflicting with "
126 << BBPN->getName() << " with regard to common predecessor "
127 << (*PI)->getName() << "\n");
132 Value* Val = PN->getIncomingValueForBlock(BB);
133 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
135 // See if the incoming value for the common predecessor is equal to the
136 // one for BB, in which case this phi node will not prevent the merging
138 if (Val != PN->getIncomingValueForBlock(*PI)) {
139 DEBUG(errs() << "Can't fold, phi node " << PN->getName() << " in "
140 << Succ->getName() << " is conflicting with regard to common "
141 << "predecessor " << (*PI)->getName() << "\n");
151 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
152 /// branch to Succ, and contains no instructions other than PHI nodes and the
153 /// branch. If possible, eliminate BB.
154 static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
156 // Check to see if merging these blocks would cause conflicts for any of the
157 // phi nodes in BB or Succ. If not, we can safely merge.
158 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
160 // Check for cases where Succ has multiple predecessors and a PHI node in BB
161 // has uses which will not disappear when the PHI nodes are merged. It is
162 // possible to handle such cases, but difficult: it requires checking whether
163 // BB dominates Succ, which is non-trivial to calculate in the case where
164 // Succ has multiple predecessors. Also, it requires checking whether
165 // constructing the necessary self-referential PHI node doesn't intoduce any
166 // conflicts; this isn't too difficult, but the previous code for doing this
169 // Note that if this check finds a live use, BB dominates Succ, so BB is
170 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
171 // folding the branch isn't profitable in that case anyway.
172 if (!Succ->getSinglePredecessor()) {
173 BasicBlock::iterator BBI = BB->begin();
174 while (isa<PHINode>(*BBI)) {
175 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
177 if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
178 if (PN->getIncomingBlock(UI) != BB)
188 DOUT << "Killing Trivial BB: \n" << *BB;
190 if (isa<PHINode>(Succ->begin())) {
191 // If there is more than one pred of succ, and there are PHI nodes in
192 // the successor, then we need to add incoming edges for the PHI nodes
194 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
196 // Loop over all of the PHI nodes in the successor of BB.
197 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
198 PHINode *PN = cast<PHINode>(I);
199 Value *OldVal = PN->removeIncomingValue(BB, false);
200 assert(OldVal && "No entry in PHI for Pred BB!");
202 // If this incoming value is one of the PHI nodes in BB, the new entries
203 // in the PHI node are the entries from the old PHI.
204 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
205 PHINode *OldValPN = cast<PHINode>(OldVal);
206 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
207 // Note that, since we are merging phi nodes and BB and Succ might
208 // have common predecessors, we could end up with a phi node with
209 // identical incoming branches. This will be cleaned up later (and
210 // will trigger asserts if we try to clean it up now, without also
211 // simplifying the corresponding conditional branch).
212 PN->addIncoming(OldValPN->getIncomingValue(i),
213 OldValPN->getIncomingBlock(i));
215 // Add an incoming value for each of the new incoming values.
216 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
217 PN->addIncoming(OldVal, BBPreds[i]);
222 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
223 if (Succ->getSinglePredecessor()) {
224 // BB is the only predecessor of Succ, so Succ will end up with exactly
225 // the same predecessors BB had.
226 Succ->getInstList().splice(Succ->begin(),
227 BB->getInstList(), BB->begin());
229 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
230 assert(PN->use_empty() && "There shouldn't be any uses here!");
231 PN->eraseFromParent();
235 // Everything that jumped to BB now goes to Succ.
236 BB->replaceAllUsesWith(Succ);
237 if (!Succ->hasName()) Succ->takeName(BB);
238 BB->eraseFromParent(); // Delete the old basic block.
242 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
243 /// presumably PHI nodes in it), check to see if the merge at this block is due
244 /// to an "if condition". If so, return the boolean condition that determines
245 /// which entry into BB will be taken. Also, return by references the block
246 /// that will be entered from if the condition is true, and the block that will
247 /// be entered if the condition is false.
250 static Value *GetIfCondition(BasicBlock *BB,
251 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
252 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
253 "Function can only handle blocks with 2 predecessors!");
254 BasicBlock *Pred1 = *pred_begin(BB);
255 BasicBlock *Pred2 = *++pred_begin(BB);
257 // We can only handle branches. Other control flow will be lowered to
258 // branches if possible anyway.
259 if (!isa<BranchInst>(Pred1->getTerminator()) ||
260 !isa<BranchInst>(Pred2->getTerminator()))
262 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
263 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
265 // Eliminate code duplication by ensuring that Pred1Br is conditional if
267 if (Pred2Br->isConditional()) {
268 // If both branches are conditional, we don't have an "if statement". In
269 // reality, we could transform this case, but since the condition will be
270 // required anyway, we stand no chance of eliminating it, so the xform is
271 // probably not profitable.
272 if (Pred1Br->isConditional())
275 std::swap(Pred1, Pred2);
276 std::swap(Pred1Br, Pred2Br);
279 if (Pred1Br->isConditional()) {
280 // If we found a conditional branch predecessor, make sure that it branches
281 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
282 if (Pred1Br->getSuccessor(0) == BB &&
283 Pred1Br->getSuccessor(1) == Pred2) {
286 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
287 Pred1Br->getSuccessor(1) == BB) {
291 // We know that one arm of the conditional goes to BB, so the other must
292 // go somewhere unrelated, and this must not be an "if statement".
296 // The only thing we have to watch out for here is to make sure that Pred2
297 // doesn't have incoming edges from other blocks. If it does, the condition
298 // doesn't dominate BB.
299 if (++pred_begin(Pred2) != pred_end(Pred2))
302 return Pred1Br->getCondition();
305 // Ok, if we got here, both predecessors end with an unconditional branch to
306 // BB. Don't panic! If both blocks only have a single (identical)
307 // predecessor, and THAT is a conditional branch, then we're all ok!
308 if (pred_begin(Pred1) == pred_end(Pred1) ||
309 ++pred_begin(Pred1) != pred_end(Pred1) ||
310 pred_begin(Pred2) == pred_end(Pred2) ||
311 ++pred_begin(Pred2) != pred_end(Pred2) ||
312 *pred_begin(Pred1) != *pred_begin(Pred2))
315 // Otherwise, if this is a conditional branch, then we can use it!
316 BasicBlock *CommonPred = *pred_begin(Pred1);
317 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
318 assert(BI->isConditional() && "Two successors but not conditional?");
319 if (BI->getSuccessor(0) == Pred1) {
326 return BI->getCondition();
331 /// DominatesMergePoint - If we have a merge point of an "if condition" as
332 /// accepted above, return true if the specified value dominates the block. We
333 /// don't handle the true generality of domination here, just a special case
334 /// which works well enough for us.
336 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
337 /// see if V (which must be an instruction) is cheap to compute and is
338 /// non-trapping. If both are true, the instruction is inserted into the set
339 /// and true is returned.
340 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
341 std::set<Instruction*> *AggressiveInsts) {
342 Instruction *I = dyn_cast<Instruction>(V);
344 // Non-instructions all dominate instructions, but not all constantexprs
345 // can be executed unconditionally.
346 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
351 BasicBlock *PBB = I->getParent();
353 // We don't want to allow weird loops that might have the "if condition" in
354 // the bottom of this block.
355 if (PBB == BB) return false;
357 // If this instruction is defined in a block that contains an unconditional
358 // branch to BB, then it must be in the 'conditional' part of the "if
360 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
361 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
362 if (!AggressiveInsts) return false;
363 // Okay, it looks like the instruction IS in the "condition". Check to
364 // see if its a cheap instruction to unconditionally compute, and if it
365 // only uses stuff defined outside of the condition. If so, hoist it out.
366 if (!I->isSafeToSpeculativelyExecute())
369 switch (I->getOpcode()) {
370 default: return false; // Cannot hoist this out safely.
371 case Instruction::Load: {
372 // We have to check to make sure there are no instructions before the
373 // load in its basic block, as we are going to hoist the loop out to
375 BasicBlock::iterator IP = PBB->begin();
376 while (isa<DbgInfoIntrinsic>(IP))
378 if (IP != BasicBlock::iterator(I))
382 case Instruction::Add:
383 case Instruction::Sub:
384 case Instruction::And:
385 case Instruction::Or:
386 case Instruction::Xor:
387 case Instruction::Shl:
388 case Instruction::LShr:
389 case Instruction::AShr:
390 case Instruction::ICmp:
391 break; // These are all cheap and non-trapping instructions.
394 // Okay, we can only really hoist these out if their operands are not
395 // defined in the conditional region.
396 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
397 if (!DominatesMergePoint(*i, BB, 0))
399 // Okay, it's safe to do this! Remember this instruction.
400 AggressiveInsts->insert(I);
406 /// GatherConstantSetEQs - Given a potentially 'or'd together collection of
407 /// icmp_eq instructions that compare a value against a constant, return the
408 /// value being compared, and stick the constant into the Values vector.
409 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
410 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
411 if (Inst->getOpcode() == Instruction::ICmp &&
412 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
413 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
415 return Inst->getOperand(0);
416 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
418 return Inst->getOperand(1);
420 } else if (Inst->getOpcode() == Instruction::Or) {
421 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
422 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
430 /// GatherConstantSetNEs - Given a potentially 'and'd together collection of
431 /// setne instructions that compare a value against a constant, return the value
432 /// being compared, and stick the constant into the Values vector.
433 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
434 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
435 if (Inst->getOpcode() == Instruction::ICmp &&
436 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
437 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
439 return Inst->getOperand(0);
440 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
442 return Inst->getOperand(1);
444 } else if (Inst->getOpcode() == Instruction::And) {
445 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
446 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
454 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
455 /// bunch of comparisons of one value against constants, return the value and
456 /// the constants being compared.
457 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
458 std::vector<ConstantInt*> &Values) {
459 if (Cond->getOpcode() == Instruction::Or) {
460 CompVal = GatherConstantSetEQs(Cond, Values);
462 // Return true to indicate that the condition is true if the CompVal is
463 // equal to one of the constants.
465 } else if (Cond->getOpcode() == Instruction::And) {
466 CompVal = GatherConstantSetNEs(Cond, Values);
468 // Return false to indicate that the condition is false if the CompVal is
469 // equal to one of the constants.
475 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
476 Instruction* Cond = 0;
477 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
478 Cond = dyn_cast<Instruction>(SI->getCondition());
479 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
480 if (BI->isConditional())
481 Cond = dyn_cast<Instruction>(BI->getCondition());
484 TI->eraseFromParent();
485 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
488 /// isValueEqualityComparison - Return true if the specified terminator checks
489 /// to see if a value is equal to constant integer value.
490 static Value *isValueEqualityComparison(TerminatorInst *TI) {
491 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
492 // Do not permit merging of large switch instructions into their
493 // predecessors unless there is only one predecessor.
494 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
495 pred_end(SI->getParent())) > 128)
498 return SI->getCondition();
500 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
501 if (BI->isConditional() && BI->getCondition()->hasOneUse())
502 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
503 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
504 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
505 isa<ConstantInt>(ICI->getOperand(1)))
506 return ICI->getOperand(0);
510 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
511 /// decode all of the 'cases' that it represents and return the 'default' block.
513 GetValueEqualityComparisonCases(TerminatorInst *TI,
514 std::vector<std::pair<ConstantInt*,
515 BasicBlock*> > &Cases) {
516 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
517 Cases.reserve(SI->getNumCases());
518 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
519 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
520 return SI->getDefaultDest();
523 BranchInst *BI = cast<BranchInst>(TI);
524 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
525 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
526 BI->getSuccessor(ICI->getPredicate() ==
527 ICmpInst::ICMP_NE)));
528 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
532 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
533 /// in the list that match the specified block.
534 static void EliminateBlockCases(BasicBlock *BB,
535 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
536 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
537 if (Cases[i].second == BB) {
538 Cases.erase(Cases.begin()+i);
543 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
546 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
547 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
548 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
550 // Make V1 be smaller than V2.
551 if (V1->size() > V2->size())
554 if (V1->size() == 0) return false;
555 if (V1->size() == 1) {
557 ConstantInt *TheVal = (*V1)[0].first;
558 for (unsigned i = 0, e = V2->size(); i != e; ++i)
559 if (TheVal == (*V2)[i].first)
563 // Otherwise, just sort both lists and compare element by element.
564 std::sort(V1->begin(), V1->end());
565 std::sort(V2->begin(), V2->end());
566 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
567 while (i1 != e1 && i2 != e2) {
568 if ((*V1)[i1].first == (*V2)[i2].first)
570 if ((*V1)[i1].first < (*V2)[i2].first)
578 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
579 /// terminator instruction and its block is known to only have a single
580 /// predecessor block, check to see if that predecessor is also a value
581 /// comparison with the same value, and if that comparison determines the
582 /// outcome of this comparison. If so, simplify TI. This does a very limited
583 /// form of jump threading.
584 static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
586 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
587 if (!PredVal) return false; // Not a value comparison in predecessor.
589 Value *ThisVal = isValueEqualityComparison(TI);
590 assert(ThisVal && "This isn't a value comparison!!");
591 if (ThisVal != PredVal) return false; // Different predicates.
593 // Find out information about when control will move from Pred to TI's block.
594 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
595 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
597 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
599 // Find information about how control leaves this block.
600 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
601 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
602 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
604 // If TI's block is the default block from Pred's comparison, potentially
605 // simplify TI based on this knowledge.
606 if (PredDef == TI->getParent()) {
607 // If we are here, we know that the value is none of those cases listed in
608 // PredCases. If there are any cases in ThisCases that are in PredCases, we
610 if (ValuesOverlap(PredCases, ThisCases)) {
611 if (isa<BranchInst>(TI)) {
612 // Okay, one of the successors of this condbr is dead. Convert it to a
614 assert(ThisCases.size() == 1 && "Branch can only have one case!");
615 // Insert the new branch.
616 Instruction *NI = BranchInst::Create(ThisDef, TI);
618 // Remove PHI node entries for the dead edge.
619 ThisCases[0].second->removePredecessor(TI->getParent());
621 DOUT << "Threading pred instr: " << *Pred->getTerminator()
622 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
624 EraseTerminatorInstAndDCECond(TI);
628 SwitchInst *SI = cast<SwitchInst>(TI);
629 // Okay, TI has cases that are statically dead, prune them away.
630 SmallPtrSet<Constant*, 16> DeadCases;
631 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
632 DeadCases.insert(PredCases[i].first);
634 DOUT << "Threading pred instr: " << *Pred->getTerminator()
635 << "Through successor TI: " << *TI;
637 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
638 if (DeadCases.count(SI->getCaseValue(i))) {
639 SI->getSuccessor(i)->removePredecessor(TI->getParent());
643 DOUT << "Leaving: " << *TI << "\n";
649 // Otherwise, TI's block must correspond to some matched value. Find out
650 // which value (or set of values) this is.
651 ConstantInt *TIV = 0;
652 BasicBlock *TIBB = TI->getParent();
653 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
654 if (PredCases[i].second == TIBB) {
656 TIV = PredCases[i].first;
658 return false; // Cannot handle multiple values coming to this block.
660 assert(TIV && "No edge from pred to succ?");
662 // Okay, we found the one constant that our value can be if we get into TI's
663 // BB. Find out which successor will unconditionally be branched to.
664 BasicBlock *TheRealDest = 0;
665 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
666 if (ThisCases[i].first == TIV) {
667 TheRealDest = ThisCases[i].second;
671 // If not handled by any explicit cases, it is handled by the default case.
672 if (TheRealDest == 0) TheRealDest = ThisDef;
674 // Remove PHI node entries for dead edges.
675 BasicBlock *CheckEdge = TheRealDest;
676 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
677 if (*SI != CheckEdge)
678 (*SI)->removePredecessor(TIBB);
682 // Insert the new branch.
683 Instruction *NI = BranchInst::Create(TheRealDest, TI);
685 DOUT << "Threading pred instr: " << *Pred->getTerminator()
686 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
688 EraseTerminatorInstAndDCECond(TI);
695 /// ConstantIntOrdering - This class implements a stable ordering of constant
696 /// integers that does not depend on their address. This is important for
697 /// applications that sort ConstantInt's to ensure uniqueness.
698 struct ConstantIntOrdering {
699 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
700 return LHS->getValue().ult(RHS->getValue());
705 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
706 /// equality comparison instruction (either a switch or a branch on "X == c").
707 /// See if any of the predecessors of the terminator block are value comparisons
708 /// on the same value. If so, and if safe to do so, fold them together.
709 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
710 BasicBlock *BB = TI->getParent();
711 Value *CV = isValueEqualityComparison(TI); // CondVal
712 assert(CV && "Not a comparison?");
713 bool Changed = false;
715 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
716 while (!Preds.empty()) {
717 BasicBlock *Pred = Preds.pop_back_val();
719 // See if the predecessor is a comparison with the same value.
720 TerminatorInst *PTI = Pred->getTerminator();
721 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
723 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
724 // Figure out which 'cases' to copy from SI to PSI.
725 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
726 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
728 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
729 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
731 // Based on whether the default edge from PTI goes to BB or not, fill in
732 // PredCases and PredDefault with the new switch cases we would like to
734 SmallVector<BasicBlock*, 8> NewSuccessors;
736 if (PredDefault == BB) {
737 // If this is the default destination from PTI, only the edges in TI
738 // that don't occur in PTI, or that branch to BB will be activated.
739 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
740 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
741 if (PredCases[i].second != BB)
742 PTIHandled.insert(PredCases[i].first);
744 // The default destination is BB, we don't need explicit targets.
745 std::swap(PredCases[i], PredCases.back());
746 PredCases.pop_back();
750 // Reconstruct the new switch statement we will be building.
751 if (PredDefault != BBDefault) {
752 PredDefault->removePredecessor(Pred);
753 PredDefault = BBDefault;
754 NewSuccessors.push_back(BBDefault);
756 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
757 if (!PTIHandled.count(BBCases[i].first) &&
758 BBCases[i].second != BBDefault) {
759 PredCases.push_back(BBCases[i]);
760 NewSuccessors.push_back(BBCases[i].second);
764 // If this is not the default destination from PSI, only the edges
765 // in SI that occur in PSI with a destination of BB will be
767 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
768 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
769 if (PredCases[i].second == BB) {
770 PTIHandled.insert(PredCases[i].first);
771 std::swap(PredCases[i], PredCases.back());
772 PredCases.pop_back();
776 // Okay, now we know which constants were sent to BB from the
777 // predecessor. Figure out where they will all go now.
778 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
779 if (PTIHandled.count(BBCases[i].first)) {
780 // If this is one we are capable of getting...
781 PredCases.push_back(BBCases[i]);
782 NewSuccessors.push_back(BBCases[i].second);
783 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
786 // If there are any constants vectored to BB that TI doesn't handle,
787 // they must go to the default destination of TI.
788 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
790 E = PTIHandled.end(); I != E; ++I) {
791 PredCases.push_back(std::make_pair(*I, BBDefault));
792 NewSuccessors.push_back(BBDefault);
796 // Okay, at this point, we know which new successor Pred will get. Make
797 // sure we update the number of entries in the PHI nodes for these
799 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
800 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
802 // Now that the successors are updated, create the new Switch instruction.
803 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
804 PredCases.size(), PTI);
805 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
806 NewSI->addCase(PredCases[i].first, PredCases[i].second);
808 EraseTerminatorInstAndDCECond(PTI);
810 // Okay, last check. If BB is still a successor of PSI, then we must
811 // have an infinite loop case. If so, add an infinitely looping block
812 // to handle the case to preserve the behavior of the code.
813 BasicBlock *InfLoopBlock = 0;
814 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
815 if (NewSI->getSuccessor(i) == BB) {
816 if (InfLoopBlock == 0) {
817 // Insert it at the end of the function, because it's either code,
818 // or it won't matter if it's hot. :)
819 InfLoopBlock = BasicBlock::Create(BB->getContext(),
820 "infloop", BB->getParent());
821 BranchInst::Create(InfLoopBlock, InfLoopBlock);
823 NewSI->setSuccessor(i, InfLoopBlock);
832 // isSafeToHoistInvoke - If we would need to insert a select that uses the
833 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
834 // would need to do this), we can't hoist the invoke, as there is nowhere
835 // to put the select in this case.
836 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
837 Instruction *I1, Instruction *I2) {
838 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
840 for (BasicBlock::iterator BBI = SI->begin();
841 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
842 Value *BB1V = PN->getIncomingValueForBlock(BB1);
843 Value *BB2V = PN->getIncomingValueForBlock(BB2);
844 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
852 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
853 /// BB2, hoist any common code in the two blocks up into the branch block. The
854 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
855 static bool HoistThenElseCodeToIf(BranchInst *BI) {
856 // This does very trivial matching, with limited scanning, to find identical
857 // instructions in the two blocks. In particular, we don't want to get into
858 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
859 // such, we currently just scan for obviously identical instructions in an
861 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
862 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
864 BasicBlock::iterator BB1_Itr = BB1->begin();
865 BasicBlock::iterator BB2_Itr = BB2->begin();
867 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
868 while (isa<DbgInfoIntrinsic>(I1))
870 while (isa<DbgInfoIntrinsic>(I2))
872 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
873 !I1->isIdenticalTo(I2) ||
874 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
877 // If we get here, we can hoist at least one instruction.
878 BasicBlock *BIParent = BI->getParent();
881 // If we are hoisting the terminator instruction, don't move one (making a
882 // broken BB), instead clone it, and remove BI.
883 if (isa<TerminatorInst>(I1))
884 goto HoistTerminator;
886 // For a normal instruction, we just move one to right before the branch,
887 // then replace all uses of the other with the first. Finally, we remove
888 // the now redundant second instruction.
889 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
890 if (!I2->use_empty())
891 I2->replaceAllUsesWith(I1);
892 BB2->getInstList().erase(I2);
895 while (isa<DbgInfoIntrinsic>(I1))
898 while (isa<DbgInfoIntrinsic>(I2))
900 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
905 // It may not be possible to hoist an invoke.
906 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
909 // Okay, it is safe to hoist the terminator.
910 Instruction *NT = I1->clone(BB1->getContext());
911 BIParent->getInstList().insert(BI, NT);
912 if (NT->getType() != Type::getVoidTy(BB1->getContext())) {
913 I1->replaceAllUsesWith(NT);
914 I2->replaceAllUsesWith(NT);
918 // Hoisting one of the terminators from our successor is a great thing.
919 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
920 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
921 // nodes, so we insert select instruction to compute the final result.
922 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
923 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
925 for (BasicBlock::iterator BBI = SI->begin();
926 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
927 Value *BB1V = PN->getIncomingValueForBlock(BB1);
928 Value *BB2V = PN->getIncomingValueForBlock(BB2);
930 // These values do not agree. Insert a select instruction before NT
931 // that determines the right value.
932 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
934 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
935 BB1V->getName()+"."+BB2V->getName(), NT);
936 // Make the PHI node use the select for all incoming values for BB1/BB2
937 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
938 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
939 PN->setIncomingValue(i, SI);
944 // Update any PHI nodes in our new successors.
945 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
946 AddPredecessorToBlock(*SI, BIParent, BB1);
948 EraseTerminatorInstAndDCECond(BI);
952 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
953 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
954 /// (for now, restricted to a single instruction that's side effect free) from
955 /// the BB1 into the branch block to speculatively execute it.
956 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
957 // Only speculatively execution a single instruction (not counting the
958 // terminator) for now.
959 Instruction *HInst = NULL;
960 Instruction *Term = BB1->getTerminator();
961 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
963 Instruction *I = BBI;
965 if (isa<DbgInfoIntrinsic>(I)) continue;
966 if (I == Term) break;
976 // Be conservative for now. FP select instruction can often be expensive.
977 Value *BrCond = BI->getCondition();
978 if (isa<Instruction>(BrCond) &&
979 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
982 // If BB1 is actually on the false edge of the conditional branch, remember
983 // to swap the select operands later.
985 if (BB1 != BI->getSuccessor(0)) {
986 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
993 // br i1 %t1, label %BB1, label %BB2
1002 // %t3 = select i1 %t1, %t2, %t3
1003 switch (HInst->getOpcode()) {
1004 default: return false; // Not safe / profitable to hoist.
1005 case Instruction::Add:
1006 case Instruction::Sub:
1007 // Not worth doing for vector ops.
1008 if (isa<VectorType>(HInst->getType()))
1011 case Instruction::And:
1012 case Instruction::Or:
1013 case Instruction::Xor:
1014 case Instruction::Shl:
1015 case Instruction::LShr:
1016 case Instruction::AShr:
1017 // Don't mess with vector operations.
1018 if (isa<VectorType>(HInst->getType()))
1020 break; // These are all cheap and non-trapping instructions.
1023 // If the instruction is obviously dead, don't try to predicate it.
1024 if (HInst->use_empty()) {
1025 HInst->eraseFromParent();
1029 // Can we speculatively execute the instruction? And what is the value
1030 // if the condition is false? Consider the phi uses, if the incoming value
1031 // from the "if" block are all the same V, then V is the value of the
1032 // select if the condition is false.
1033 BasicBlock *BIParent = BI->getParent();
1034 SmallVector<PHINode*, 4> PHIUses;
1035 Value *FalseV = NULL;
1037 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1038 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
1040 // Ignore any user that is not a PHI node in BB2. These can only occur in
1041 // unreachable blocks, because they would not be dominated by the instr.
1042 PHINode *PN = dyn_cast<PHINode>(UI);
1043 if (!PN || PN->getParent() != BB2)
1045 PHIUses.push_back(PN);
1047 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1050 else if (FalseV != PHIV)
1051 return false; // Inconsistent value when condition is false.
1054 assert(FalseV && "Must have at least one user, and it must be a PHI");
1056 // Do not hoist the instruction if any of its operands are defined but not
1057 // used in this BB. The transformation will prevent the operand from
1058 // being sunk into the use block.
1059 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1061 Instruction *OpI = dyn_cast<Instruction>(*i);
1062 if (OpI && OpI->getParent() == BIParent &&
1063 !OpI->isUsedInBasicBlock(BIParent))
1067 // If we get here, we can hoist the instruction. Try to place it
1068 // before the icmp instruction preceding the conditional branch.
1069 BasicBlock::iterator InsertPos = BI;
1070 if (InsertPos != BIParent->begin())
1072 // Skip debug info between condition and branch.
1073 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1075 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1076 SmallPtrSet<Instruction *, 4> BB1Insns;
1077 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1078 BB1I != BB1E; ++BB1I)
1079 BB1Insns.insert(BB1I);
1080 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1082 Instruction *Use = cast<Instruction>(*UI);
1083 if (BB1Insns.count(Use)) {
1084 // If BrCond uses the instruction that place it just before
1085 // branch instruction.
1092 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1094 // Create a select whose true value is the speculatively executed value and
1095 // false value is the previously determined FalseV.
1098 SI = SelectInst::Create(BrCond, FalseV, HInst,
1099 FalseV->getName() + "." + HInst->getName(), BI);
1101 SI = SelectInst::Create(BrCond, HInst, FalseV,
1102 HInst->getName() + "." + FalseV->getName(), BI);
1104 // Make the PHI node use the select for all incoming values for "then" and
1106 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1107 PHINode *PN = PHIUses[i];
1108 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1109 if (PN->getIncomingBlock(j) == BB1 ||
1110 PN->getIncomingBlock(j) == BIParent)
1111 PN->setIncomingValue(j, SI);
1118 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1119 /// across this block.
1120 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1121 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1124 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1125 if (isa<DbgInfoIntrinsic>(BBI))
1127 if (Size > 10) return false; // Don't clone large BB's.
1130 // We can only support instructions that do not define values that are
1131 // live outside of the current basic block.
1132 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1134 Instruction *U = cast<Instruction>(*UI);
1135 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1138 // Looks ok, continue checking.
1144 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1145 /// that is defined in the same block as the branch and if any PHI entries are
1146 /// constants, thread edges corresponding to that entry to be branches to their
1147 /// ultimate destination.
1148 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1149 BasicBlock *BB = BI->getParent();
1150 LLVMContext &Context = BB->getContext();
1151 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1152 // NOTE: we currently cannot transform this case if the PHI node is used
1153 // outside of the block.
1154 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1157 // Degenerate case of a single entry PHI.
1158 if (PN->getNumIncomingValues() == 1) {
1159 FoldSingleEntryPHINodes(PN->getParent());
1163 // Now we know that this block has multiple preds and two succs.
1164 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1166 // Okay, this is a simple enough basic block. See if any phi values are
1168 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1170 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1171 CB->getType() == Type::getInt1Ty(BB->getContext())) {
1172 // Okay, we now know that all edges from PredBB should be revectored to
1173 // branch to RealDest.
1174 BasicBlock *PredBB = PN->getIncomingBlock(i);
1175 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1177 if (RealDest == BB) continue; // Skip self loops.
1179 // The dest block might have PHI nodes, other predecessors and other
1180 // difficult cases. Instead of being smart about this, just insert a new
1181 // block that jumps to the destination block, effectively splitting
1182 // the edge we are about to create.
1183 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1184 RealDest->getName()+".critedge",
1185 RealDest->getParent(), RealDest);
1186 BranchInst::Create(RealDest, EdgeBB);
1188 for (BasicBlock::iterator BBI = RealDest->begin();
1189 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1190 Value *V = PN->getIncomingValueForBlock(BB);
1191 PN->addIncoming(V, EdgeBB);
1194 // BB may have instructions that are being threaded over. Clone these
1195 // instructions into EdgeBB. We know that there will be no uses of the
1196 // cloned instructions outside of EdgeBB.
1197 BasicBlock::iterator InsertPt = EdgeBB->begin();
1198 std::map<Value*, Value*> TranslateMap; // Track translated values.
1199 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1200 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1201 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1203 // Clone the instruction.
1204 Instruction *N = BBI->clone(Context);
1205 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1207 // Update operands due to translation.
1208 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1210 std::map<Value*, Value*>::iterator PI =
1211 TranslateMap.find(*i);
1212 if (PI != TranslateMap.end())
1216 // Check for trivial simplification.
1217 if (Constant *C = ConstantFoldInstruction(N, Context)) {
1218 TranslateMap[BBI] = C;
1219 delete N; // Constant folded away, don't need actual inst
1221 // Insert the new instruction into its new home.
1222 EdgeBB->getInstList().insert(InsertPt, N);
1223 if (!BBI->use_empty())
1224 TranslateMap[BBI] = N;
1229 // Loop over all of the edges from PredBB to BB, changing them to branch
1230 // to EdgeBB instead.
1231 TerminatorInst *PredBBTI = PredBB->getTerminator();
1232 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1233 if (PredBBTI->getSuccessor(i) == BB) {
1234 BB->removePredecessor(PredBB);
1235 PredBBTI->setSuccessor(i, EdgeBB);
1238 // Recurse, simplifying any other constants.
1239 return FoldCondBranchOnPHI(BI) | true;
1246 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1247 /// PHI node, see if we can eliminate it.
1248 static bool FoldTwoEntryPHINode(PHINode *PN) {
1249 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1250 // statement", which has a very simple dominance structure. Basically, we
1251 // are trying to find the condition that is being branched on, which
1252 // subsequently causes this merge to happen. We really want control
1253 // dependence information for this check, but simplifycfg can't keep it up
1254 // to date, and this catches most of the cases we care about anyway.
1256 BasicBlock *BB = PN->getParent();
1257 BasicBlock *IfTrue, *IfFalse;
1258 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1259 if (!IfCond) return false;
1261 // Okay, we found that we can merge this two-entry phi node into a select.
1262 // Doing so would require us to fold *all* two entry phi nodes in this block.
1263 // At some point this becomes non-profitable (particularly if the target
1264 // doesn't support cmov's). Only do this transformation if there are two or
1265 // fewer PHI nodes in this block.
1266 unsigned NumPhis = 0;
1267 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1271 DEBUG(errs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1272 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1274 // Loop over the PHI's seeing if we can promote them all to select
1275 // instructions. While we are at it, keep track of the instructions
1276 // that need to be moved to the dominating block.
1277 std::set<Instruction*> AggressiveInsts;
1279 BasicBlock::iterator AfterPHIIt = BB->begin();
1280 while (isa<PHINode>(AfterPHIIt)) {
1281 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1282 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1283 if (PN->getIncomingValue(0) != PN)
1284 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1286 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1287 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1288 &AggressiveInsts) ||
1289 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1290 &AggressiveInsts)) {
1295 // If we all PHI nodes are promotable, check to make sure that all
1296 // instructions in the predecessor blocks can be promoted as well. If
1297 // not, we won't be able to get rid of the control flow, so it's not
1298 // worth promoting to select instructions.
1299 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1300 PN = cast<PHINode>(BB->begin());
1301 BasicBlock *Pred = PN->getIncomingBlock(0);
1302 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1304 DomBlock = *pred_begin(Pred);
1305 for (BasicBlock::iterator I = Pred->begin();
1306 !isa<TerminatorInst>(I); ++I)
1307 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1308 // This is not an aggressive instruction that we can promote.
1309 // Because of this, we won't be able to get rid of the control
1310 // flow, so the xform is not worth it.
1315 Pred = PN->getIncomingBlock(1);
1316 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1318 DomBlock = *pred_begin(Pred);
1319 for (BasicBlock::iterator I = Pred->begin();
1320 !isa<TerminatorInst>(I); ++I)
1321 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1322 // This is not an aggressive instruction that we can promote.
1323 // Because of this, we won't be able to get rid of the control
1324 // flow, so the xform is not worth it.
1329 // If we can still promote the PHI nodes after this gauntlet of tests,
1330 // do all of the PHI's now.
1332 // Move all 'aggressive' instructions, which are defined in the
1333 // conditional parts of the if's up to the dominating block.
1335 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1336 IfBlock1->getInstList(),
1338 IfBlock1->getTerminator());
1341 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1342 IfBlock2->getInstList(),
1344 IfBlock2->getTerminator());
1347 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1348 // Change the PHI node into a select instruction.
1350 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1352 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1354 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1355 PN->replaceAllUsesWith(NV);
1358 BB->getInstList().erase(PN);
1363 /// isTerminatorFirstRelevantInsn - Return true if Term is very first
1364 /// instruction ignoring Phi nodes and dbg intrinsics.
1365 static bool isTerminatorFirstRelevantInsn(BasicBlock *BB, Instruction *Term) {
1366 BasicBlock::iterator BBI = Term;
1367 while (BBI != BB->begin()) {
1369 if (!isa<DbgInfoIntrinsic>(BBI))
1373 if (isa<PHINode>(BBI) || &*BBI == Term || isa<DbgInfoIntrinsic>(BBI))
1378 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1379 /// to two returning blocks, try to merge them together into one return,
1380 /// introducing a select if the return values disagree.
1381 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1382 assert(BI->isConditional() && "Must be a conditional branch");
1383 BasicBlock *TrueSucc = BI->getSuccessor(0);
1384 BasicBlock *FalseSucc = BI->getSuccessor(1);
1385 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1386 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1388 // Check to ensure both blocks are empty (just a return) or optionally empty
1389 // with PHI nodes. If there are other instructions, merging would cause extra
1390 // computation on one path or the other.
1391 if (!isTerminatorFirstRelevantInsn(TrueSucc, TrueRet))
1393 if (!isTerminatorFirstRelevantInsn(FalseSucc, FalseRet))
1396 // Okay, we found a branch that is going to two return nodes. If
1397 // there is no return value for this function, just change the
1398 // branch into a return.
1399 if (FalseRet->getNumOperands() == 0) {
1400 TrueSucc->removePredecessor(BI->getParent());
1401 FalseSucc->removePredecessor(BI->getParent());
1402 ReturnInst::Create(BI->getContext(), 0, BI);
1403 EraseTerminatorInstAndDCECond(BI);
1407 // Otherwise, figure out what the true and false return values are
1408 // so we can insert a new select instruction.
1409 Value *TrueValue = TrueRet->getReturnValue();
1410 Value *FalseValue = FalseRet->getReturnValue();
1412 // Unwrap any PHI nodes in the return blocks.
1413 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1414 if (TVPN->getParent() == TrueSucc)
1415 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1416 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1417 if (FVPN->getParent() == FalseSucc)
1418 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1420 // In order for this transformation to be safe, we must be able to
1421 // unconditionally execute both operands to the return. This is
1422 // normally the case, but we could have a potentially-trapping
1423 // constant expression that prevents this transformation from being
1425 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1428 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1432 // Okay, we collected all the mapped values and checked them for sanity, and
1433 // defined to really do this transformation. First, update the CFG.
1434 TrueSucc->removePredecessor(BI->getParent());
1435 FalseSucc->removePredecessor(BI->getParent());
1437 // Insert select instructions where needed.
1438 Value *BrCond = BI->getCondition();
1440 // Insert a select if the results differ.
1441 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1442 } else if (isa<UndefValue>(TrueValue)) {
1443 TrueValue = FalseValue;
1445 TrueValue = SelectInst::Create(BrCond, TrueValue,
1446 FalseValue, "retval", BI);
1450 Value *RI = !TrueValue ?
1451 ReturnInst::Create(BI->getContext(), BI) :
1452 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1454 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1455 << "\n " << *BI << "NewRet = " << *RI
1456 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
1458 EraseTerminatorInstAndDCECond(BI);
1463 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1464 /// and if a predecessor branches to us and one of our successors, fold the
1465 /// setcc into the predecessor and use logical operations to pick the right
1467 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1468 BasicBlock *BB = BI->getParent();
1469 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1470 if (Cond == 0) return false;
1473 // Only allow this if the condition is a simple instruction that can be
1474 // executed unconditionally. It must be in the same block as the branch, and
1475 // must be at the front of the block.
1476 BasicBlock::iterator FrontIt = BB->front();
1477 // Ignore dbg intrinsics.
1478 while(isa<DbgInfoIntrinsic>(FrontIt))
1480 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1481 Cond->getParent() != BB || &*FrontIt != Cond || !Cond->hasOneUse()) {
1485 // Make sure the instruction after the condition is the cond branch.
1486 BasicBlock::iterator CondIt = Cond; ++CondIt;
1487 // Ingore dbg intrinsics.
1488 while(isa<DbgInfoIntrinsic>(CondIt))
1490 if (&*CondIt != BI) {
1491 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1495 // Cond is known to be a compare or binary operator. Check to make sure that
1496 // neither operand is a potentially-trapping constant expression.
1497 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1500 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1505 // Finally, don't infinitely unroll conditional loops.
1506 BasicBlock *TrueDest = BI->getSuccessor(0);
1507 BasicBlock *FalseDest = BI->getSuccessor(1);
1508 if (TrueDest == BB || FalseDest == BB)
1511 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1512 BasicBlock *PredBlock = *PI;
1513 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1515 // Check that we have two conditional branches. If there is a PHI node in
1516 // the common successor, verify that the same value flows in from both
1518 if (PBI == 0 || PBI->isUnconditional() ||
1519 !SafeToMergeTerminators(BI, PBI))
1522 Instruction::BinaryOps Opc;
1523 bool InvertPredCond = false;
1525 if (PBI->getSuccessor(0) == TrueDest)
1526 Opc = Instruction::Or;
1527 else if (PBI->getSuccessor(1) == FalseDest)
1528 Opc = Instruction::And;
1529 else if (PBI->getSuccessor(0) == FalseDest)
1530 Opc = Instruction::And, InvertPredCond = true;
1531 else if (PBI->getSuccessor(1) == TrueDest)
1532 Opc = Instruction::Or, InvertPredCond = true;
1536 DOUT << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB;
1538 // If we need to invert the condition in the pred block to match, do so now.
1539 if (InvertPredCond) {
1541 BinaryOperator::CreateNot(PBI->getCondition(),
1542 PBI->getCondition()->getName()+".not", PBI);
1543 PBI->setCondition(NewCond);
1544 BasicBlock *OldTrue = PBI->getSuccessor(0);
1545 BasicBlock *OldFalse = PBI->getSuccessor(1);
1546 PBI->setSuccessor(0, OldFalse);
1547 PBI->setSuccessor(1, OldTrue);
1550 // Clone Cond into the predecessor basic block, and or/and the
1551 // two conditions together.
1552 Instruction *New = Cond->clone(BB->getContext());
1553 PredBlock->getInstList().insert(PBI, New);
1554 New->takeName(Cond);
1555 Cond->setName(New->getName()+".old");
1557 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1558 New, "or.cond", PBI);
1559 PBI->setCondition(NewCond);
1560 if (PBI->getSuccessor(0) == BB) {
1561 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1562 PBI->setSuccessor(0, TrueDest);
1564 if (PBI->getSuccessor(1) == BB) {
1565 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1566 PBI->setSuccessor(1, FalseDest);
1573 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1574 /// predecessor of another block, this function tries to simplify it. We know
1575 /// that PBI and BI are both conditional branches, and BI is in one of the
1576 /// successor blocks of PBI - PBI branches to BI.
1577 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1578 assert(PBI->isConditional() && BI->isConditional());
1579 BasicBlock *BB = BI->getParent();
1581 // If this block ends with a branch instruction, and if there is a
1582 // predecessor that ends on a branch of the same condition, make
1583 // this conditional branch redundant.
1584 if (PBI->getCondition() == BI->getCondition() &&
1585 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1586 // Okay, the outcome of this conditional branch is statically
1587 // knowable. If this block had a single pred, handle specially.
1588 if (BB->getSinglePredecessor()) {
1589 // Turn this into a branch on constant.
1590 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1591 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1593 return true; // Nuke the branch on constant.
1596 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1597 // in the constant and simplify the block result. Subsequent passes of
1598 // simplifycfg will thread the block.
1599 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1600 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1601 BI->getCondition()->getName() + ".pr",
1603 // Okay, we're going to insert the PHI node. Since PBI is not the only
1604 // predecessor, compute the PHI'd conditional value for all of the preds.
1605 // Any predecessor where the condition is not computable we keep symbolic.
1606 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1607 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1608 PBI != BI && PBI->isConditional() &&
1609 PBI->getCondition() == BI->getCondition() &&
1610 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1611 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1612 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1615 NewPN->addIncoming(BI->getCondition(), *PI);
1618 BI->setCondition(NewPN);
1623 // If this is a conditional branch in an empty block, and if any
1624 // predecessors is a conditional branch to one of our destinations,
1625 // fold the conditions into logical ops and one cond br.
1626 BasicBlock::iterator BBI = BB->begin();
1627 // Ignore dbg intrinsics.
1628 while (isa<DbgInfoIntrinsic>(BBI))
1634 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1639 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1641 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1642 PBIOp = 0, BIOp = 1;
1643 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1644 PBIOp = 1, BIOp = 0;
1645 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1650 // Check to make sure that the other destination of this branch
1651 // isn't BB itself. If so, this is an infinite loop that will
1652 // keep getting unwound.
1653 if (PBI->getSuccessor(PBIOp) == BB)
1656 // Do not perform this transformation if it would require
1657 // insertion of a large number of select instructions. For targets
1658 // without predication/cmovs, this is a big pessimization.
1659 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1661 unsigned NumPhis = 0;
1662 for (BasicBlock::iterator II = CommonDest->begin();
1663 isa<PHINode>(II); ++II, ++NumPhis)
1664 if (NumPhis > 2) // Disable this xform.
1667 // Finally, if everything is ok, fold the branches to logical ops.
1668 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1670 DOUT << "FOLDING BRs:" << *PBI->getParent()
1671 << "AND: " << *BI->getParent();
1674 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1675 // branch in it, where one edge (OtherDest) goes back to itself but the other
1676 // exits. We don't *know* that the program avoids the infinite loop
1677 // (even though that seems likely). If we do this xform naively, we'll end up
1678 // recursively unpeeling the loop. Since we know that (after the xform is
1679 // done) that the block *is* infinite if reached, we just make it an obviously
1680 // infinite loop with no cond branch.
1681 if (OtherDest == BB) {
1682 // Insert it at the end of the function, because it's either code,
1683 // or it won't matter if it's hot. :)
1684 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1685 "infloop", BB->getParent());
1686 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1687 OtherDest = InfLoopBlock;
1690 DOUT << *PBI->getParent()->getParent();
1692 // BI may have other predecessors. Because of this, we leave
1693 // it alone, but modify PBI.
1695 // Make sure we get to CommonDest on True&True directions.
1696 Value *PBICond = PBI->getCondition();
1698 PBICond = BinaryOperator::CreateNot(PBICond,
1699 PBICond->getName()+".not",
1701 Value *BICond = BI->getCondition();
1703 BICond = BinaryOperator::CreateNot(BICond,
1704 BICond->getName()+".not",
1706 // Merge the conditions.
1707 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1709 // Modify PBI to branch on the new condition to the new dests.
1710 PBI->setCondition(Cond);
1711 PBI->setSuccessor(0, CommonDest);
1712 PBI->setSuccessor(1, OtherDest);
1714 // OtherDest may have phi nodes. If so, add an entry from PBI's
1715 // block that are identical to the entries for BI's block.
1717 for (BasicBlock::iterator II = OtherDest->begin();
1718 (PN = dyn_cast<PHINode>(II)); ++II) {
1719 Value *V = PN->getIncomingValueForBlock(BB);
1720 PN->addIncoming(V, PBI->getParent());
1723 // We know that the CommonDest already had an edge from PBI to
1724 // it. If it has PHIs though, the PHIs may have different
1725 // entries for BB and PBI's BB. If so, insert a select to make
1727 for (BasicBlock::iterator II = CommonDest->begin();
1728 (PN = dyn_cast<PHINode>(II)); ++II) {
1729 Value *BIV = PN->getIncomingValueForBlock(BB);
1730 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1731 Value *PBIV = PN->getIncomingValue(PBBIdx);
1733 // Insert a select in PBI to pick the right value.
1734 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1735 PBIV->getName()+".mux", PBI);
1736 PN->setIncomingValue(PBBIdx, NV);
1740 DOUT << "INTO: " << *PBI->getParent();
1742 DOUT << *PBI->getParent()->getParent();
1744 // This basic block is probably dead. We know it has at least
1745 // one fewer predecessor.
1750 /// SimplifyCFG - This function is used to do simplification of a CFG. For
1751 /// example, it adjusts branches to branches to eliminate the extra hop, it
1752 /// eliminates unreachable basic blocks, and does other "peephole" optimization
1753 /// of the CFG. It returns true if a modification was made.
1755 /// WARNING: The entry node of a function may not be simplified.
1757 bool llvm::SimplifyCFG(BasicBlock *BB) {
1758 bool Changed = false;
1759 Function *M = BB->getParent();
1761 assert(BB && BB->getParent() && "Block not embedded in function!");
1762 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1763 assert(&BB->getParent()->getEntryBlock() != BB &&
1764 "Can't Simplify entry block!");
1766 // Remove basic blocks that have no predecessors... or that just have themself
1767 // as a predecessor. These are unreachable.
1768 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1769 DOUT << "Removing BB: \n" << *BB;
1770 DeleteDeadBlock(BB);
1774 // Check to see if we can constant propagate this terminator instruction
1776 Changed |= ConstantFoldTerminator(BB);
1778 // If there is a trivial two-entry PHI node in this basic block, and we can
1779 // eliminate it, do so now.
1780 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1781 if (PN->getNumIncomingValues() == 2)
1782 Changed |= FoldTwoEntryPHINode(PN);
1784 // If this is a returning block with only PHI nodes in it, fold the return
1785 // instruction into any unconditional branch predecessors.
1787 // If any predecessor is a conditional branch that just selects among
1788 // different return values, fold the replace the branch/return with a select
1790 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1791 if (isTerminatorFirstRelevantInsn(BB, BB->getTerminator())) {
1792 // Find predecessors that end with branches.
1793 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1794 SmallVector<BranchInst*, 8> CondBranchPreds;
1795 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1796 TerminatorInst *PTI = (*PI)->getTerminator();
1797 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1798 if (BI->isUnconditional())
1799 UncondBranchPreds.push_back(*PI);
1801 CondBranchPreds.push_back(BI);
1805 // If we found some, do the transformation!
1806 if (!UncondBranchPreds.empty()) {
1807 while (!UncondBranchPreds.empty()) {
1808 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
1809 DOUT << "FOLDING: " << *BB
1810 << "INTO UNCOND BRANCH PRED: " << *Pred;
1811 Instruction *UncondBranch = Pred->getTerminator();
1812 // Clone the return and add it to the end of the predecessor.
1813 Instruction *NewRet = RI->clone(BB->getContext());
1814 Pred->getInstList().push_back(NewRet);
1816 BasicBlock::iterator BBI = RI;
1817 if (BBI != BB->begin()) {
1818 // Move region end info into the predecessor.
1819 if (DbgRegionEndInst *DREI = dyn_cast<DbgRegionEndInst>(--BBI))
1820 DREI->moveBefore(NewRet);
1823 // If the return instruction returns a value, and if the value was a
1824 // PHI node in "BB", propagate the right value into the return.
1825 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1827 if (PHINode *PN = dyn_cast<PHINode>(*i))
1828 if (PN->getParent() == BB)
1829 *i = PN->getIncomingValueForBlock(Pred);
1831 // Update any PHI nodes in the returning block to realize that we no
1832 // longer branch to them.
1833 BB->removePredecessor(Pred);
1834 Pred->getInstList().erase(UncondBranch);
1837 // If we eliminated all predecessors of the block, delete the block now.
1838 if (pred_begin(BB) == pred_end(BB))
1839 // We know there are no successors, so just nuke the block.
1840 M->getBasicBlockList().erase(BB);
1845 // Check out all of the conditional branches going to this return
1846 // instruction. If any of them just select between returns, change the
1847 // branch itself into a select/return pair.
1848 while (!CondBranchPreds.empty()) {
1849 BranchInst *BI = CondBranchPreds.pop_back_val();
1851 // Check to see if the non-BB successor is also a return block.
1852 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1853 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1854 SimplifyCondBranchToTwoReturns(BI))
1858 } else if (isa<UnwindInst>(BB->begin())) {
1859 // Check to see if the first instruction in this block is just an unwind.
1860 // If so, replace any invoke instructions which use this as an exception
1861 // destination with call instructions, and any unconditional branch
1862 // predecessor with an unwind.
1864 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1865 while (!Preds.empty()) {
1866 BasicBlock *Pred = Preds.back();
1867 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1868 if (BI->isUnconditional()) {
1869 Pred->getInstList().pop_back(); // nuke uncond branch
1870 new UnwindInst(Pred->getContext(), Pred); // Use unwind.
1873 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1874 if (II->getUnwindDest() == BB) {
1875 // Insert a new branch instruction before the invoke, because this
1876 // is now a fall through...
1877 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1878 Pred->getInstList().remove(II); // Take out of symbol table
1880 // Insert the call now...
1881 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1882 CallInst *CI = CallInst::Create(II->getCalledValue(),
1883 Args.begin(), Args.end(),
1885 CI->setCallingConv(II->getCallingConv());
1886 CI->setAttributes(II->getAttributes());
1887 // If the invoke produced a value, the Call now does instead
1888 II->replaceAllUsesWith(CI);
1896 // If this block is now dead, remove it.
1897 if (pred_begin(BB) == pred_end(BB)) {
1898 // We know there are no successors, so just nuke the block.
1899 M->getBasicBlockList().erase(BB);
1903 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1904 if (isValueEqualityComparison(SI)) {
1905 // If we only have one predecessor, and if it is a branch on this value,
1906 // see if that predecessor totally determines the outcome of this switch.
1907 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1908 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1909 return SimplifyCFG(BB) || 1;
1911 // If the block only contains the switch, see if we can fold the block
1912 // away into any preds.
1913 BasicBlock::iterator BBI = BB->begin();
1914 // Ignore dbg intrinsics.
1915 while (isa<DbgInfoIntrinsic>(BBI))
1918 if (FoldValueComparisonIntoPredecessors(SI))
1919 return SimplifyCFG(BB) || 1;
1921 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1922 if (BI->isUnconditional()) {
1923 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1925 BasicBlock *Succ = BI->getSuccessor(0);
1926 // Ignore dbg intrinsics.
1927 while (isa<DbgInfoIntrinsic>(BBI))
1929 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1930 Succ != BB) // Don't hurt infinite loops!
1931 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1934 } else { // Conditional branch
1935 if (isValueEqualityComparison(BI)) {
1936 // If we only have one predecessor, and if it is a branch on this value,
1937 // see if that predecessor totally determines the outcome of this
1939 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1940 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1941 return SimplifyCFG(BB) || 1;
1943 // This block must be empty, except for the setcond inst, if it exists.
1944 // Ignore dbg intrinsics.
1945 BasicBlock::iterator I = BB->begin();
1946 // Ignore dbg intrinsics.
1947 while (isa<DbgInfoIntrinsic>(I))
1950 if (FoldValueComparisonIntoPredecessors(BI))
1951 return SimplifyCFG(BB) | true;
1952 } else if (&*I == cast<Instruction>(BI->getCondition())){
1954 // Ignore dbg intrinsics.
1955 while (isa<DbgInfoIntrinsic>(I))
1958 if (FoldValueComparisonIntoPredecessors(BI))
1959 return SimplifyCFG(BB) | true;
1964 // If this is a branch on a phi node in the current block, thread control
1965 // through this block if any PHI node entries are constants.
1966 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1967 if (PN->getParent() == BI->getParent())
1968 if (FoldCondBranchOnPHI(BI))
1969 return SimplifyCFG(BB) | true;
1971 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1972 // branches to us and one of our successors, fold the setcc into the
1973 // predecessor and use logical operations to pick the right destination.
1974 if (FoldBranchToCommonDest(BI))
1975 return SimplifyCFG(BB) | 1;
1978 // Scan predecessor blocks for conditional branches.
1979 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1980 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1981 if (PBI != BI && PBI->isConditional())
1982 if (SimplifyCondBranchToCondBranch(PBI, BI))
1983 return SimplifyCFG(BB) | true;
1985 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1986 // If there are any instructions immediately before the unreachable that can
1987 // be removed, do so.
1988 Instruction *Unreachable = BB->getTerminator();
1989 while (Unreachable != BB->begin()) {
1990 BasicBlock::iterator BBI = Unreachable;
1992 // Do not delete instructions that can have side effects, like calls
1993 // (which may never return) and volatile loads and stores.
1994 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
1996 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
1997 if (SI->isVolatile())
2000 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2001 if (LI->isVolatile())
2004 // Delete this instruction
2005 BB->getInstList().erase(BBI);
2009 // If the unreachable instruction is the first in the block, take a gander
2010 // at all of the predecessors of this instruction, and simplify them.
2011 if (&BB->front() == Unreachable) {
2012 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2013 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2014 TerminatorInst *TI = Preds[i]->getTerminator();
2016 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2017 if (BI->isUnconditional()) {
2018 if (BI->getSuccessor(0) == BB) {
2019 new UnreachableInst(TI->getContext(), TI);
2020 TI->eraseFromParent();
2024 if (BI->getSuccessor(0) == BB) {
2025 BranchInst::Create(BI->getSuccessor(1), BI);
2026 EraseTerminatorInstAndDCECond(BI);
2027 } else if (BI->getSuccessor(1) == BB) {
2028 BranchInst::Create(BI->getSuccessor(0), BI);
2029 EraseTerminatorInstAndDCECond(BI);
2033 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2034 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2035 if (SI->getSuccessor(i) == BB) {
2036 BB->removePredecessor(SI->getParent());
2041 // If the default value is unreachable, figure out the most popular
2042 // destination and make it the default.
2043 if (SI->getSuccessor(0) == BB) {
2044 std::map<BasicBlock*, unsigned> Popularity;
2045 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2046 Popularity[SI->getSuccessor(i)]++;
2048 // Find the most popular block.
2049 unsigned MaxPop = 0;
2050 BasicBlock *MaxBlock = 0;
2051 for (std::map<BasicBlock*, unsigned>::iterator
2052 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2053 if (I->second > MaxPop) {
2055 MaxBlock = I->first;
2059 // Make this the new default, allowing us to delete any explicit
2061 SI->setSuccessor(0, MaxBlock);
2064 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2066 if (isa<PHINode>(MaxBlock->begin()))
2067 for (unsigned i = 0; i != MaxPop-1; ++i)
2068 MaxBlock->removePredecessor(SI->getParent());
2070 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2071 if (SI->getSuccessor(i) == MaxBlock) {
2077 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2078 if (II->getUnwindDest() == BB) {
2079 // Convert the invoke to a call instruction. This would be a good
2080 // place to note that the call does not throw though.
2081 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2082 II->removeFromParent(); // Take out of symbol table
2084 // Insert the call now...
2085 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
2086 CallInst *CI = CallInst::Create(II->getCalledValue(),
2087 Args.begin(), Args.end(),
2089 CI->setCallingConv(II->getCallingConv());
2090 CI->setAttributes(II->getAttributes());
2091 // If the invoke produced a value, the Call does now instead.
2092 II->replaceAllUsesWith(CI);
2099 // If this block is now dead, remove it.
2100 if (pred_begin(BB) == pred_end(BB)) {
2101 // We know there are no successors, so just nuke the block.
2102 M->getBasicBlockList().erase(BB);
2108 // Merge basic blocks into their predecessor if there is only one distinct
2109 // pred, and if there is only one distinct successor of the predecessor, and
2110 // if there are no PHI nodes.
2112 if (MergeBlockIntoPredecessor(BB))
2115 // Otherwise, if this block only has a single predecessor, and if that block
2116 // is a conditional branch, see if we can hoist any code from this block up
2117 // into our predecessor.
2118 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2119 BasicBlock *OnlyPred = *PI++;
2120 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2121 if (*PI != OnlyPred) {
2122 OnlyPred = 0; // There are multiple different predecessors...
2127 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2128 if (BI->isConditional()) {
2129 // Get the other block.
2130 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2131 PI = pred_begin(OtherBB);
2134 if (PI == pred_end(OtherBB)) {
2135 // We have a conditional branch to two blocks that are only reachable
2136 // from the condbr. We know that the condbr dominates the two blocks,
2137 // so see if there is any identical code in the "then" and "else"
2138 // blocks. If so, we can hoist it up to the branching block.
2139 Changed |= HoistThenElseCodeToIf(BI);
2141 BasicBlock* OnlySucc = NULL;
2142 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2146 else if (*SI != OnlySucc) {
2147 OnlySucc = 0; // There are multiple distinct successors!
2152 if (OnlySucc == OtherBB) {
2153 // If BB's only successor is the other successor of the predecessor,
2154 // i.e. a triangle, see if we can hoist any code from this block up
2155 // to the "if" block.
2156 Changed |= SpeculativelyExecuteBB(BI, BB);
2161 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2162 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2163 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2164 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2165 Instruction *Cond = cast<Instruction>(BI->getCondition());
2166 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2167 // 'setne's and'ed together, collect them.
2169 std::vector<ConstantInt*> Values;
2170 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2171 if (CompVal && CompVal->getType()->isInteger()) {
2172 // There might be duplicate constants in the list, which the switch
2173 // instruction can't handle, remove them now.
2174 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2175 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2177 // Figure out which block is which destination.
2178 BasicBlock *DefaultBB = BI->getSuccessor(1);
2179 BasicBlock *EdgeBB = BI->getSuccessor(0);
2180 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2182 // Create the new switch instruction now.
2183 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2186 // Add all of the 'cases' to the switch instruction.
2187 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2188 New->addCase(Values[i], EdgeBB);
2190 // We added edges from PI to the EdgeBB. As such, if there were any
2191 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2192 // the number of edges added.
2193 for (BasicBlock::iterator BBI = EdgeBB->begin();
2194 isa<PHINode>(BBI); ++BBI) {
2195 PHINode *PN = cast<PHINode>(BBI);
2196 Value *InVal = PN->getIncomingValueForBlock(*PI);
2197 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2198 PN->addIncoming(InVal, *PI);
2201 // Erase the old branch instruction.
2202 EraseTerminatorInstAndDCECond(BI);