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 DEBUG(errs() << "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);
619 // Remove PHI node entries for the dead edge.
620 ThisCases[0].second->removePredecessor(TI->getParent());
622 DEBUG(errs() << "Threading pred instr: " << *Pred->getTerminator()
623 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
625 EraseTerminatorInstAndDCECond(TI);
629 SwitchInst *SI = cast<SwitchInst>(TI);
630 // Okay, TI has cases that are statically dead, prune them away.
631 SmallPtrSet<Constant*, 16> DeadCases;
632 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
633 DeadCases.insert(PredCases[i].first);
635 DEBUG(errs() << "Threading pred instr: " << *Pred->getTerminator()
636 << "Through successor TI: " << *TI);
638 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
639 if (DeadCases.count(SI->getCaseValue(i))) {
640 SI->getSuccessor(i)->removePredecessor(TI->getParent());
644 DEBUG(errs() << "Leaving: " << *TI << "\n");
650 // Otherwise, TI's block must correspond to some matched value. Find out
651 // which value (or set of values) this is.
652 ConstantInt *TIV = 0;
653 BasicBlock *TIBB = TI->getParent();
654 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
655 if (PredCases[i].second == TIBB) {
657 TIV = PredCases[i].first;
659 return false; // Cannot handle multiple values coming to this block.
661 assert(TIV && "No edge from pred to succ?");
663 // Okay, we found the one constant that our value can be if we get into TI's
664 // BB. Find out which successor will unconditionally be branched to.
665 BasicBlock *TheRealDest = 0;
666 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
667 if (ThisCases[i].first == TIV) {
668 TheRealDest = ThisCases[i].second;
672 // If not handled by any explicit cases, it is handled by the default case.
673 if (TheRealDest == 0) TheRealDest = ThisDef;
675 // Remove PHI node entries for dead edges.
676 BasicBlock *CheckEdge = TheRealDest;
677 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
678 if (*SI != CheckEdge)
679 (*SI)->removePredecessor(TIBB);
683 // Insert the new branch.
684 Instruction *NI = BranchInst::Create(TheRealDest, TI);
687 DEBUG(errs() << "Threading pred instr: " << *Pred->getTerminator()
688 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
690 EraseTerminatorInstAndDCECond(TI);
697 /// ConstantIntOrdering - This class implements a stable ordering of constant
698 /// integers that does not depend on their address. This is important for
699 /// applications that sort ConstantInt's to ensure uniqueness.
700 struct ConstantIntOrdering {
701 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
702 return LHS->getValue().ult(RHS->getValue());
707 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
708 /// equality comparison instruction (either a switch or a branch on "X == c").
709 /// See if any of the predecessors of the terminator block are value comparisons
710 /// on the same value. If so, and if safe to do so, fold them together.
711 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
712 BasicBlock *BB = TI->getParent();
713 Value *CV = isValueEqualityComparison(TI); // CondVal
714 assert(CV && "Not a comparison?");
715 bool Changed = false;
717 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
718 while (!Preds.empty()) {
719 BasicBlock *Pred = Preds.pop_back_val();
721 // See if the predecessor is a comparison with the same value.
722 TerminatorInst *PTI = Pred->getTerminator();
723 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
725 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
726 // Figure out which 'cases' to copy from SI to PSI.
727 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
728 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
730 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
731 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
733 // Based on whether the default edge from PTI goes to BB or not, fill in
734 // PredCases and PredDefault with the new switch cases we would like to
736 SmallVector<BasicBlock*, 8> NewSuccessors;
738 if (PredDefault == BB) {
739 // If this is the default destination from PTI, only the edges in TI
740 // that don't occur in PTI, or that branch to BB will be activated.
741 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
742 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
743 if (PredCases[i].second != BB)
744 PTIHandled.insert(PredCases[i].first);
746 // The default destination is BB, we don't need explicit targets.
747 std::swap(PredCases[i], PredCases.back());
748 PredCases.pop_back();
752 // Reconstruct the new switch statement we will be building.
753 if (PredDefault != BBDefault) {
754 PredDefault->removePredecessor(Pred);
755 PredDefault = BBDefault;
756 NewSuccessors.push_back(BBDefault);
758 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
759 if (!PTIHandled.count(BBCases[i].first) &&
760 BBCases[i].second != BBDefault) {
761 PredCases.push_back(BBCases[i]);
762 NewSuccessors.push_back(BBCases[i].second);
766 // If this is not the default destination from PSI, only the edges
767 // in SI that occur in PSI with a destination of BB will be
769 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
770 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
771 if (PredCases[i].second == BB) {
772 PTIHandled.insert(PredCases[i].first);
773 std::swap(PredCases[i], PredCases.back());
774 PredCases.pop_back();
778 // Okay, now we know which constants were sent to BB from the
779 // predecessor. Figure out where they will all go now.
780 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
781 if (PTIHandled.count(BBCases[i].first)) {
782 // If this is one we are capable of getting...
783 PredCases.push_back(BBCases[i]);
784 NewSuccessors.push_back(BBCases[i].second);
785 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
788 // If there are any constants vectored to BB that TI doesn't handle,
789 // they must go to the default destination of TI.
790 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
792 E = PTIHandled.end(); I != E; ++I) {
793 PredCases.push_back(std::make_pair(*I, BBDefault));
794 NewSuccessors.push_back(BBDefault);
798 // Okay, at this point, we know which new successor Pred will get. Make
799 // sure we update the number of entries in the PHI nodes for these
801 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
802 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
804 // Now that the successors are updated, create the new Switch instruction.
805 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
806 PredCases.size(), PTI);
807 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
808 NewSI->addCase(PredCases[i].first, PredCases[i].second);
810 EraseTerminatorInstAndDCECond(PTI);
812 // Okay, last check. If BB is still a successor of PSI, then we must
813 // have an infinite loop case. If so, add an infinitely looping block
814 // to handle the case to preserve the behavior of the code.
815 BasicBlock *InfLoopBlock = 0;
816 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
817 if (NewSI->getSuccessor(i) == BB) {
818 if (InfLoopBlock == 0) {
819 // Insert it at the end of the function, because it's either code,
820 // or it won't matter if it's hot. :)
821 InfLoopBlock = BasicBlock::Create(BB->getContext(),
822 "infloop", BB->getParent());
823 BranchInst::Create(InfLoopBlock, InfLoopBlock);
825 NewSI->setSuccessor(i, InfLoopBlock);
834 // isSafeToHoistInvoke - If we would need to insert a select that uses the
835 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
836 // would need to do this), we can't hoist the invoke, as there is nowhere
837 // to put the select in this case.
838 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
839 Instruction *I1, Instruction *I2) {
840 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
842 for (BasicBlock::iterator BBI = SI->begin();
843 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
844 Value *BB1V = PN->getIncomingValueForBlock(BB1);
845 Value *BB2V = PN->getIncomingValueForBlock(BB2);
846 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
854 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
855 /// BB2, hoist any common code in the two blocks up into the branch block. The
856 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
857 static bool HoistThenElseCodeToIf(BranchInst *BI) {
858 // This does very trivial matching, with limited scanning, to find identical
859 // instructions in the two blocks. In particular, we don't want to get into
860 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
861 // such, we currently just scan for obviously identical instructions in an
863 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
864 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
866 BasicBlock::iterator BB1_Itr = BB1->begin();
867 BasicBlock::iterator BB2_Itr = BB2->begin();
869 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
870 while (isa<DbgInfoIntrinsic>(I1))
872 while (isa<DbgInfoIntrinsic>(I2))
874 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
875 !I1->isIdenticalTo(I2) ||
876 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
879 // If we get here, we can hoist at least one instruction.
880 BasicBlock *BIParent = BI->getParent();
883 // If we are hoisting the terminator instruction, don't move one (making a
884 // broken BB), instead clone it, and remove BI.
885 if (isa<TerminatorInst>(I1))
886 goto HoistTerminator;
888 // For a normal instruction, we just move one to right before the branch,
889 // then replace all uses of the other with the first. Finally, we remove
890 // the now redundant second instruction.
891 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
892 if (!I2->use_empty())
893 I2->replaceAllUsesWith(I1);
894 BB2->getInstList().erase(I2);
897 while (isa<DbgInfoIntrinsic>(I1))
900 while (isa<DbgInfoIntrinsic>(I2))
902 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
907 // It may not be possible to hoist an invoke.
908 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
911 // Okay, it is safe to hoist the terminator.
912 Instruction *NT = I1->clone(BB1->getContext());
913 BIParent->getInstList().insert(BI, NT);
914 if (NT->getType() != Type::getVoidTy(BB1->getContext())) {
915 I1->replaceAllUsesWith(NT);
916 I2->replaceAllUsesWith(NT);
920 // Hoisting one of the terminators from our successor is a great thing.
921 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
922 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
923 // nodes, so we insert select instruction to compute the final result.
924 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
925 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
927 for (BasicBlock::iterator BBI = SI->begin();
928 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
929 Value *BB1V = PN->getIncomingValueForBlock(BB1);
930 Value *BB2V = PN->getIncomingValueForBlock(BB2);
932 // These values do not agree. Insert a select instruction before NT
933 // that determines the right value.
934 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
936 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
937 BB1V->getName()+"."+BB2V->getName(), NT);
938 // Make the PHI node use the select for all incoming values for BB1/BB2
939 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
940 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
941 PN->setIncomingValue(i, SI);
946 // Update any PHI nodes in our new successors.
947 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
948 AddPredecessorToBlock(*SI, BIParent, BB1);
950 EraseTerminatorInstAndDCECond(BI);
954 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
955 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
956 /// (for now, restricted to a single instruction that's side effect free) from
957 /// the BB1 into the branch block to speculatively execute it.
958 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
959 // Only speculatively execution a single instruction (not counting the
960 // terminator) for now.
961 Instruction *HInst = NULL;
962 Instruction *Term = BB1->getTerminator();
963 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
965 Instruction *I = BBI;
967 if (isa<DbgInfoIntrinsic>(I)) continue;
968 if (I == Term) break;
978 // Be conservative for now. FP select instruction can often be expensive.
979 Value *BrCond = BI->getCondition();
980 if (isa<Instruction>(BrCond) &&
981 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
984 // If BB1 is actually on the false edge of the conditional branch, remember
985 // to swap the select operands later.
987 if (BB1 != BI->getSuccessor(0)) {
988 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
995 // br i1 %t1, label %BB1, label %BB2
1004 // %t3 = select i1 %t1, %t2, %t3
1005 switch (HInst->getOpcode()) {
1006 default: return false; // Not safe / profitable to hoist.
1007 case Instruction::Add:
1008 case Instruction::Sub:
1009 // Not worth doing for vector ops.
1010 if (isa<VectorType>(HInst->getType()))
1013 case Instruction::And:
1014 case Instruction::Or:
1015 case Instruction::Xor:
1016 case Instruction::Shl:
1017 case Instruction::LShr:
1018 case Instruction::AShr:
1019 // Don't mess with vector operations.
1020 if (isa<VectorType>(HInst->getType()))
1022 break; // These are all cheap and non-trapping instructions.
1025 // If the instruction is obviously dead, don't try to predicate it.
1026 if (HInst->use_empty()) {
1027 HInst->eraseFromParent();
1031 // Can we speculatively execute the instruction? And what is the value
1032 // if the condition is false? Consider the phi uses, if the incoming value
1033 // from the "if" block are all the same V, then V is the value of the
1034 // select if the condition is false.
1035 BasicBlock *BIParent = BI->getParent();
1036 SmallVector<PHINode*, 4> PHIUses;
1037 Value *FalseV = NULL;
1039 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1040 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
1042 // Ignore any user that is not a PHI node in BB2. These can only occur in
1043 // unreachable blocks, because they would not be dominated by the instr.
1044 PHINode *PN = dyn_cast<PHINode>(UI);
1045 if (!PN || PN->getParent() != BB2)
1047 PHIUses.push_back(PN);
1049 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1052 else if (FalseV != PHIV)
1053 return false; // Inconsistent value when condition is false.
1056 assert(FalseV && "Must have at least one user, and it must be a PHI");
1058 // Do not hoist the instruction if any of its operands are defined but not
1059 // used in this BB. The transformation will prevent the operand from
1060 // being sunk into the use block.
1061 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1063 Instruction *OpI = dyn_cast<Instruction>(*i);
1064 if (OpI && OpI->getParent() == BIParent &&
1065 !OpI->isUsedInBasicBlock(BIParent))
1069 // If we get here, we can hoist the instruction. Try to place it
1070 // before the icmp instruction preceding the conditional branch.
1071 BasicBlock::iterator InsertPos = BI;
1072 if (InsertPos != BIParent->begin())
1074 // Skip debug info between condition and branch.
1075 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1077 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1078 SmallPtrSet<Instruction *, 4> BB1Insns;
1079 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1080 BB1I != BB1E; ++BB1I)
1081 BB1Insns.insert(BB1I);
1082 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1084 Instruction *Use = cast<Instruction>(*UI);
1085 if (BB1Insns.count(Use)) {
1086 // If BrCond uses the instruction that place it just before
1087 // branch instruction.
1094 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1096 // Create a select whose true value is the speculatively executed value and
1097 // false value is the previously determined FalseV.
1100 SI = SelectInst::Create(BrCond, FalseV, HInst,
1101 FalseV->getName() + "." + HInst->getName(), BI);
1103 SI = SelectInst::Create(BrCond, HInst, FalseV,
1104 HInst->getName() + "." + FalseV->getName(), BI);
1106 // Make the PHI node use the select for all incoming values for "then" and
1108 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1109 PHINode *PN = PHIUses[i];
1110 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1111 if (PN->getIncomingBlock(j) == BB1 ||
1112 PN->getIncomingBlock(j) == BIParent)
1113 PN->setIncomingValue(j, SI);
1120 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1121 /// across this block.
1122 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1123 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1126 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1127 if (isa<DbgInfoIntrinsic>(BBI))
1129 if (Size > 10) return false; // Don't clone large BB's.
1132 // We can only support instructions that do not define values that are
1133 // live outside of the current basic block.
1134 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1136 Instruction *U = cast<Instruction>(*UI);
1137 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1140 // Looks ok, continue checking.
1146 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1147 /// that is defined in the same block as the branch and if any PHI entries are
1148 /// constants, thread edges corresponding to that entry to be branches to their
1149 /// ultimate destination.
1150 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1151 BasicBlock *BB = BI->getParent();
1152 LLVMContext &Context = BB->getContext();
1153 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1154 // NOTE: we currently cannot transform this case if the PHI node is used
1155 // outside of the block.
1156 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1159 // Degenerate case of a single entry PHI.
1160 if (PN->getNumIncomingValues() == 1) {
1161 FoldSingleEntryPHINodes(PN->getParent());
1165 // Now we know that this block has multiple preds and two succs.
1166 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1168 // Okay, this is a simple enough basic block. See if any phi values are
1170 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1172 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1173 CB->getType() == Type::getInt1Ty(BB->getContext())) {
1174 // Okay, we now know that all edges from PredBB should be revectored to
1175 // branch to RealDest.
1176 BasicBlock *PredBB = PN->getIncomingBlock(i);
1177 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1179 if (RealDest == BB) continue; // Skip self loops.
1181 // The dest block might have PHI nodes, other predecessors and other
1182 // difficult cases. Instead of being smart about this, just insert a new
1183 // block that jumps to the destination block, effectively splitting
1184 // the edge we are about to create.
1185 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1186 RealDest->getName()+".critedge",
1187 RealDest->getParent(), RealDest);
1188 BranchInst::Create(RealDest, EdgeBB);
1190 for (BasicBlock::iterator BBI = RealDest->begin();
1191 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1192 Value *V = PN->getIncomingValueForBlock(BB);
1193 PN->addIncoming(V, EdgeBB);
1196 // BB may have instructions that are being threaded over. Clone these
1197 // instructions into EdgeBB. We know that there will be no uses of the
1198 // cloned instructions outside of EdgeBB.
1199 BasicBlock::iterator InsertPt = EdgeBB->begin();
1200 std::map<Value*, Value*> TranslateMap; // Track translated values.
1201 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1202 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1203 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1205 // Clone the instruction.
1206 Instruction *N = BBI->clone(Context);
1207 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1209 // Update operands due to translation.
1210 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1212 std::map<Value*, Value*>::iterator PI =
1213 TranslateMap.find(*i);
1214 if (PI != TranslateMap.end())
1218 // Check for trivial simplification.
1219 if (Constant *C = ConstantFoldInstruction(N, Context)) {
1220 TranslateMap[BBI] = C;
1221 delete N; // Constant folded away, don't need actual inst
1223 // Insert the new instruction into its new home.
1224 EdgeBB->getInstList().insert(InsertPt, N);
1225 if (!BBI->use_empty())
1226 TranslateMap[BBI] = N;
1231 // Loop over all of the edges from PredBB to BB, changing them to branch
1232 // to EdgeBB instead.
1233 TerminatorInst *PredBBTI = PredBB->getTerminator();
1234 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1235 if (PredBBTI->getSuccessor(i) == BB) {
1236 BB->removePredecessor(PredBB);
1237 PredBBTI->setSuccessor(i, EdgeBB);
1240 // Recurse, simplifying any other constants.
1241 return FoldCondBranchOnPHI(BI) | true;
1248 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1249 /// PHI node, see if we can eliminate it.
1250 static bool FoldTwoEntryPHINode(PHINode *PN) {
1251 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1252 // statement", which has a very simple dominance structure. Basically, we
1253 // are trying to find the condition that is being branched on, which
1254 // subsequently causes this merge to happen. We really want control
1255 // dependence information for this check, but simplifycfg can't keep it up
1256 // to date, and this catches most of the cases we care about anyway.
1258 BasicBlock *BB = PN->getParent();
1259 BasicBlock *IfTrue, *IfFalse;
1260 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1261 if (!IfCond) return false;
1263 // Okay, we found that we can merge this two-entry phi node into a select.
1264 // Doing so would require us to fold *all* two entry phi nodes in this block.
1265 // At some point this becomes non-profitable (particularly if the target
1266 // doesn't support cmov's). Only do this transformation if there are two or
1267 // fewer PHI nodes in this block.
1268 unsigned NumPhis = 0;
1269 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1273 DEBUG(errs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1274 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1276 // Loop over the PHI's seeing if we can promote them all to select
1277 // instructions. While we are at it, keep track of the instructions
1278 // that need to be moved to the dominating block.
1279 std::set<Instruction*> AggressiveInsts;
1281 BasicBlock::iterator AfterPHIIt = BB->begin();
1282 while (isa<PHINode>(AfterPHIIt)) {
1283 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1284 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1285 if (PN->getIncomingValue(0) != PN)
1286 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1288 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1289 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1290 &AggressiveInsts) ||
1291 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1292 &AggressiveInsts)) {
1297 // If we all PHI nodes are promotable, check to make sure that all
1298 // instructions in the predecessor blocks can be promoted as well. If
1299 // not, we won't be able to get rid of the control flow, so it's not
1300 // worth promoting to select instructions.
1301 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1302 PN = cast<PHINode>(BB->begin());
1303 BasicBlock *Pred = PN->getIncomingBlock(0);
1304 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1306 DomBlock = *pred_begin(Pred);
1307 for (BasicBlock::iterator I = Pred->begin();
1308 !isa<TerminatorInst>(I); ++I)
1309 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1310 // This is not an aggressive instruction that we can promote.
1311 // Because of this, we won't be able to get rid of the control
1312 // flow, so the xform is not worth it.
1317 Pred = PN->getIncomingBlock(1);
1318 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1320 DomBlock = *pred_begin(Pred);
1321 for (BasicBlock::iterator I = Pred->begin();
1322 !isa<TerminatorInst>(I); ++I)
1323 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1324 // This is not an aggressive instruction that we can promote.
1325 // Because of this, we won't be able to get rid of the control
1326 // flow, so the xform is not worth it.
1331 // If we can still promote the PHI nodes after this gauntlet of tests,
1332 // do all of the PHI's now.
1334 // Move all 'aggressive' instructions, which are defined in the
1335 // conditional parts of the if's up to the dominating block.
1337 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1338 IfBlock1->getInstList(),
1340 IfBlock1->getTerminator());
1343 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1344 IfBlock2->getInstList(),
1346 IfBlock2->getTerminator());
1349 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1350 // Change the PHI node into a select instruction.
1352 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1354 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1356 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1357 PN->replaceAllUsesWith(NV);
1360 BB->getInstList().erase(PN);
1365 /// isTerminatorFirstRelevantInsn - Return true if Term is very first
1366 /// instruction ignoring Phi nodes and dbg intrinsics.
1367 static bool isTerminatorFirstRelevantInsn(BasicBlock *BB, Instruction *Term) {
1368 BasicBlock::iterator BBI = Term;
1369 while (BBI != BB->begin()) {
1371 if (!isa<DbgInfoIntrinsic>(BBI))
1375 if (isa<PHINode>(BBI) || &*BBI == Term || isa<DbgInfoIntrinsic>(BBI))
1380 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1381 /// to two returning blocks, try to merge them together into one return,
1382 /// introducing a select if the return values disagree.
1383 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1384 assert(BI->isConditional() && "Must be a conditional branch");
1385 BasicBlock *TrueSucc = BI->getSuccessor(0);
1386 BasicBlock *FalseSucc = BI->getSuccessor(1);
1387 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1388 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1390 // Check to ensure both blocks are empty (just a return) or optionally empty
1391 // with PHI nodes. If there are other instructions, merging would cause extra
1392 // computation on one path or the other.
1393 if (!isTerminatorFirstRelevantInsn(TrueSucc, TrueRet))
1395 if (!isTerminatorFirstRelevantInsn(FalseSucc, FalseRet))
1398 // Okay, we found a branch that is going to two return nodes. If
1399 // there is no return value for this function, just change the
1400 // branch into a return.
1401 if (FalseRet->getNumOperands() == 0) {
1402 TrueSucc->removePredecessor(BI->getParent());
1403 FalseSucc->removePredecessor(BI->getParent());
1404 ReturnInst::Create(BI->getContext(), 0, BI);
1405 EraseTerminatorInstAndDCECond(BI);
1409 // Otherwise, figure out what the true and false return values are
1410 // so we can insert a new select instruction.
1411 Value *TrueValue = TrueRet->getReturnValue();
1412 Value *FalseValue = FalseRet->getReturnValue();
1414 // Unwrap any PHI nodes in the return blocks.
1415 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1416 if (TVPN->getParent() == TrueSucc)
1417 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1418 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1419 if (FVPN->getParent() == FalseSucc)
1420 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1422 // In order for this transformation to be safe, we must be able to
1423 // unconditionally execute both operands to the return. This is
1424 // normally the case, but we could have a potentially-trapping
1425 // constant expression that prevents this transformation from being
1427 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1430 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1434 // Okay, we collected all the mapped values and checked them for sanity, and
1435 // defined to really do this transformation. First, update the CFG.
1436 TrueSucc->removePredecessor(BI->getParent());
1437 FalseSucc->removePredecessor(BI->getParent());
1439 // Insert select instructions where needed.
1440 Value *BrCond = BI->getCondition();
1442 // Insert a select if the results differ.
1443 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1444 } else if (isa<UndefValue>(TrueValue)) {
1445 TrueValue = FalseValue;
1447 TrueValue = SelectInst::Create(BrCond, TrueValue,
1448 FalseValue, "retval", BI);
1452 Value *RI = !TrueValue ?
1453 ReturnInst::Create(BI->getContext(), BI) :
1454 ReturnInst::Create(BI->getContext(), TrueValue, BI);
1457 DEBUG(errs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1458 << "\n " << *BI << "NewRet = " << *RI
1459 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1461 EraseTerminatorInstAndDCECond(BI);
1466 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1467 /// and if a predecessor branches to us and one of our successors, fold the
1468 /// setcc into the predecessor and use logical operations to pick the right
1470 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1471 BasicBlock *BB = BI->getParent();
1472 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1473 if (Cond == 0) return false;
1476 // Only allow this if the condition is a simple instruction that can be
1477 // executed unconditionally. It must be in the same block as the branch, and
1478 // must be at the front of the block.
1479 BasicBlock::iterator FrontIt = BB->front();
1480 // Ignore dbg intrinsics.
1481 while(isa<DbgInfoIntrinsic>(FrontIt))
1483 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1484 Cond->getParent() != BB || &*FrontIt != Cond || !Cond->hasOneUse()) {
1488 // Make sure the instruction after the condition is the cond branch.
1489 BasicBlock::iterator CondIt = Cond; ++CondIt;
1490 // Ingore dbg intrinsics.
1491 while(isa<DbgInfoIntrinsic>(CondIt))
1493 if (&*CondIt != BI) {
1494 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1498 // Cond is known to be a compare or binary operator. Check to make sure that
1499 // neither operand is a potentially-trapping constant expression.
1500 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1503 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1508 // Finally, don't infinitely unroll conditional loops.
1509 BasicBlock *TrueDest = BI->getSuccessor(0);
1510 BasicBlock *FalseDest = BI->getSuccessor(1);
1511 if (TrueDest == BB || FalseDest == BB)
1514 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1515 BasicBlock *PredBlock = *PI;
1516 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1518 // Check that we have two conditional branches. If there is a PHI node in
1519 // the common successor, verify that the same value flows in from both
1521 if (PBI == 0 || PBI->isUnconditional() ||
1522 !SafeToMergeTerminators(BI, PBI))
1525 Instruction::BinaryOps Opc;
1526 bool InvertPredCond = false;
1528 if (PBI->getSuccessor(0) == TrueDest)
1529 Opc = Instruction::Or;
1530 else if (PBI->getSuccessor(1) == FalseDest)
1531 Opc = Instruction::And;
1532 else if (PBI->getSuccessor(0) == FalseDest)
1533 Opc = Instruction::And, InvertPredCond = true;
1534 else if (PBI->getSuccessor(1) == TrueDest)
1535 Opc = Instruction::Or, InvertPredCond = true;
1539 DEBUG(errs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1541 // If we need to invert the condition in the pred block to match, do so now.
1542 if (InvertPredCond) {
1544 BinaryOperator::CreateNot(PBI->getCondition(),
1545 PBI->getCondition()->getName()+".not", PBI);
1546 PBI->setCondition(NewCond);
1547 BasicBlock *OldTrue = PBI->getSuccessor(0);
1548 BasicBlock *OldFalse = PBI->getSuccessor(1);
1549 PBI->setSuccessor(0, OldFalse);
1550 PBI->setSuccessor(1, OldTrue);
1553 // Clone Cond into the predecessor basic block, and or/and the
1554 // two conditions together.
1555 Instruction *New = Cond->clone(BB->getContext());
1556 PredBlock->getInstList().insert(PBI, New);
1557 New->takeName(Cond);
1558 Cond->setName(New->getName()+".old");
1560 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1561 New, "or.cond", PBI);
1562 PBI->setCondition(NewCond);
1563 if (PBI->getSuccessor(0) == BB) {
1564 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1565 PBI->setSuccessor(0, TrueDest);
1567 if (PBI->getSuccessor(1) == BB) {
1568 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1569 PBI->setSuccessor(1, FalseDest);
1576 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1577 /// predecessor of another block, this function tries to simplify it. We know
1578 /// that PBI and BI are both conditional branches, and BI is in one of the
1579 /// successor blocks of PBI - PBI branches to BI.
1580 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1581 assert(PBI->isConditional() && BI->isConditional());
1582 BasicBlock *BB = BI->getParent();
1584 // If this block ends with a branch instruction, and if there is a
1585 // predecessor that ends on a branch of the same condition, make
1586 // this conditional branch redundant.
1587 if (PBI->getCondition() == BI->getCondition() &&
1588 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1589 // Okay, the outcome of this conditional branch is statically
1590 // knowable. If this block had a single pred, handle specially.
1591 if (BB->getSinglePredecessor()) {
1592 // Turn this into a branch on constant.
1593 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1594 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1596 return true; // Nuke the branch on constant.
1599 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1600 // in the constant and simplify the block result. Subsequent passes of
1601 // simplifycfg will thread the block.
1602 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1603 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1604 BI->getCondition()->getName() + ".pr",
1606 // Okay, we're going to insert the PHI node. Since PBI is not the only
1607 // predecessor, compute the PHI'd conditional value for all of the preds.
1608 // Any predecessor where the condition is not computable we keep symbolic.
1609 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1610 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1611 PBI != BI && PBI->isConditional() &&
1612 PBI->getCondition() == BI->getCondition() &&
1613 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1614 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1615 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1618 NewPN->addIncoming(BI->getCondition(), *PI);
1621 BI->setCondition(NewPN);
1626 // If this is a conditional branch in an empty block, and if any
1627 // predecessors is a conditional branch to one of our destinations,
1628 // fold the conditions into logical ops and one cond br.
1629 BasicBlock::iterator BBI = BB->begin();
1630 // Ignore dbg intrinsics.
1631 while (isa<DbgInfoIntrinsic>(BBI))
1637 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1642 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1644 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1645 PBIOp = 0, BIOp = 1;
1646 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1647 PBIOp = 1, BIOp = 0;
1648 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1653 // Check to make sure that the other destination of this branch
1654 // isn't BB itself. If so, this is an infinite loop that will
1655 // keep getting unwound.
1656 if (PBI->getSuccessor(PBIOp) == BB)
1659 // Do not perform this transformation if it would require
1660 // insertion of a large number of select instructions. For targets
1661 // without predication/cmovs, this is a big pessimization.
1662 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1664 unsigned NumPhis = 0;
1665 for (BasicBlock::iterator II = CommonDest->begin();
1666 isa<PHINode>(II); ++II, ++NumPhis)
1667 if (NumPhis > 2) // Disable this xform.
1670 // Finally, if everything is ok, fold the branches to logical ops.
1671 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1673 DEBUG(errs() << "FOLDING BRs:" << *PBI->getParent()
1674 << "AND: " << *BI->getParent());
1677 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1678 // branch in it, where one edge (OtherDest) goes back to itself but the other
1679 // exits. We don't *know* that the program avoids the infinite loop
1680 // (even though that seems likely). If we do this xform naively, we'll end up
1681 // recursively unpeeling the loop. Since we know that (after the xform is
1682 // done) that the block *is* infinite if reached, we just make it an obviously
1683 // infinite loop with no cond branch.
1684 if (OtherDest == BB) {
1685 // Insert it at the end of the function, because it's either code,
1686 // or it won't matter if it's hot. :)
1687 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1688 "infloop", BB->getParent());
1689 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1690 OtherDest = InfLoopBlock;
1693 DEBUG(errs() << *PBI->getParent()->getParent());
1695 // BI may have other predecessors. Because of this, we leave
1696 // it alone, but modify PBI.
1698 // Make sure we get to CommonDest on True&True directions.
1699 Value *PBICond = PBI->getCondition();
1701 PBICond = BinaryOperator::CreateNot(PBICond,
1702 PBICond->getName()+".not",
1704 Value *BICond = BI->getCondition();
1706 BICond = BinaryOperator::CreateNot(BICond,
1707 BICond->getName()+".not",
1709 // Merge the conditions.
1710 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1712 // Modify PBI to branch on the new condition to the new dests.
1713 PBI->setCondition(Cond);
1714 PBI->setSuccessor(0, CommonDest);
1715 PBI->setSuccessor(1, OtherDest);
1717 // OtherDest may have phi nodes. If so, add an entry from PBI's
1718 // block that are identical to the entries for BI's block.
1720 for (BasicBlock::iterator II = OtherDest->begin();
1721 (PN = dyn_cast<PHINode>(II)); ++II) {
1722 Value *V = PN->getIncomingValueForBlock(BB);
1723 PN->addIncoming(V, PBI->getParent());
1726 // We know that the CommonDest already had an edge from PBI to
1727 // it. If it has PHIs though, the PHIs may have different
1728 // entries for BB and PBI's BB. If so, insert a select to make
1730 for (BasicBlock::iterator II = CommonDest->begin();
1731 (PN = dyn_cast<PHINode>(II)); ++II) {
1732 Value *BIV = PN->getIncomingValueForBlock(BB);
1733 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1734 Value *PBIV = PN->getIncomingValue(PBBIdx);
1736 // Insert a select in PBI to pick the right value.
1737 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1738 PBIV->getName()+".mux", PBI);
1739 PN->setIncomingValue(PBBIdx, NV);
1743 DEBUG(errs() << "INTO: " << *PBI->getParent());
1744 DEBUG(errs() << *PBI->getParent()->getParent());
1746 // This basic block is probably dead. We know it has at least
1747 // one fewer predecessor.
1752 /// SimplifyCFG - This function is used to do simplification of a CFG. For
1753 /// example, it adjusts branches to branches to eliminate the extra hop, it
1754 /// eliminates unreachable basic blocks, and does other "peephole" optimization
1755 /// of the CFG. It returns true if a modification was made.
1757 /// WARNING: The entry node of a function may not be simplified.
1759 bool llvm::SimplifyCFG(BasicBlock *BB) {
1760 bool Changed = false;
1761 Function *M = BB->getParent();
1763 assert(BB && BB->getParent() && "Block not embedded in function!");
1764 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1765 assert(&BB->getParent()->getEntryBlock() != BB &&
1766 "Can't Simplify entry block!");
1768 // Remove basic blocks that have no predecessors... or that just have themself
1769 // as a predecessor. These are unreachable.
1770 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1771 DEBUG(errs() << "Removing BB: \n" << *BB);
1772 DeleteDeadBlock(BB);
1776 // Check to see if we can constant propagate this terminator instruction
1778 Changed |= ConstantFoldTerminator(BB);
1780 // If there is a trivial two-entry PHI node in this basic block, and we can
1781 // eliminate it, do so now.
1782 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1783 if (PN->getNumIncomingValues() == 2)
1784 Changed |= FoldTwoEntryPHINode(PN);
1786 // If this is a returning block with only PHI nodes in it, fold the return
1787 // instruction into any unconditional branch predecessors.
1789 // If any predecessor is a conditional branch that just selects among
1790 // different return values, fold the replace the branch/return with a select
1792 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1793 if (isTerminatorFirstRelevantInsn(BB, BB->getTerminator())) {
1794 // Find predecessors that end with branches.
1795 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1796 SmallVector<BranchInst*, 8> CondBranchPreds;
1797 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1798 TerminatorInst *PTI = (*PI)->getTerminator();
1799 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1800 if (BI->isUnconditional())
1801 UncondBranchPreds.push_back(*PI);
1803 CondBranchPreds.push_back(BI);
1807 // If we found some, do the transformation!
1808 if (!UncondBranchPreds.empty()) {
1809 while (!UncondBranchPreds.empty()) {
1810 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
1811 DEBUG(errs() << "FOLDING: " << *BB
1812 << "INTO UNCOND BRANCH PRED: " << *Pred);
1813 Instruction *UncondBranch = Pred->getTerminator();
1814 // Clone the return and add it to the end of the predecessor.
1815 Instruction *NewRet = RI->clone(BB->getContext());
1816 Pred->getInstList().push_back(NewRet);
1818 BasicBlock::iterator BBI = RI;
1819 if (BBI != BB->begin()) {
1820 // Move region end info into the predecessor.
1821 if (DbgRegionEndInst *DREI = dyn_cast<DbgRegionEndInst>(--BBI))
1822 DREI->moveBefore(NewRet);
1825 // If the return instruction returns a value, and if the value was a
1826 // PHI node in "BB", propagate the right value into the return.
1827 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1829 if (PHINode *PN = dyn_cast<PHINode>(*i))
1830 if (PN->getParent() == BB)
1831 *i = PN->getIncomingValueForBlock(Pred);
1833 // Update any PHI nodes in the returning block to realize that we no
1834 // longer branch to them.
1835 BB->removePredecessor(Pred);
1836 Pred->getInstList().erase(UncondBranch);
1839 // If we eliminated all predecessors of the block, delete the block now.
1840 if (pred_begin(BB) == pred_end(BB))
1841 // We know there are no successors, so just nuke the block.
1842 M->getBasicBlockList().erase(BB);
1847 // Check out all of the conditional branches going to this return
1848 // instruction. If any of them just select between returns, change the
1849 // branch itself into a select/return pair.
1850 while (!CondBranchPreds.empty()) {
1851 BranchInst *BI = CondBranchPreds.pop_back_val();
1853 // Check to see if the non-BB successor is also a return block.
1854 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1855 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1856 SimplifyCondBranchToTwoReturns(BI))
1860 } else if (isa<UnwindInst>(BB->begin())) {
1861 // Check to see if the first instruction in this block is just an unwind.
1862 // If so, replace any invoke instructions which use this as an exception
1863 // destination with call instructions, and any unconditional branch
1864 // predecessor with an unwind.
1866 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1867 while (!Preds.empty()) {
1868 BasicBlock *Pred = Preds.back();
1869 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1870 if (BI->isUnconditional()) {
1871 Pred->getInstList().pop_back(); // nuke uncond branch
1872 new UnwindInst(Pred->getContext(), Pred); // Use unwind.
1875 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1876 if (II->getUnwindDest() == BB) {
1877 // Insert a new branch instruction before the invoke, because this
1878 // is now a fall through...
1879 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1880 Pred->getInstList().remove(II); // Take out of symbol table
1882 // Insert the call now...
1883 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1884 CallInst *CI = CallInst::Create(II->getCalledValue(),
1885 Args.begin(), Args.end(),
1887 CI->setCallingConv(II->getCallingConv());
1888 CI->setAttributes(II->getAttributes());
1889 // If the invoke produced a value, the Call now does instead
1890 II->replaceAllUsesWith(CI);
1898 // If this block is now dead, remove it.
1899 if (pred_begin(BB) == pred_end(BB)) {
1900 // We know there are no successors, so just nuke the block.
1901 M->getBasicBlockList().erase(BB);
1905 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1906 if (isValueEqualityComparison(SI)) {
1907 // If we only have one predecessor, and if it is a branch on this value,
1908 // see if that predecessor totally determines the outcome of this switch.
1909 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1910 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1911 return SimplifyCFG(BB) || 1;
1913 // If the block only contains the switch, see if we can fold the block
1914 // away into any preds.
1915 BasicBlock::iterator BBI = BB->begin();
1916 // Ignore dbg intrinsics.
1917 while (isa<DbgInfoIntrinsic>(BBI))
1920 if (FoldValueComparisonIntoPredecessors(SI))
1921 return SimplifyCFG(BB) || 1;
1923 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1924 if (BI->isUnconditional()) {
1925 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1927 BasicBlock *Succ = BI->getSuccessor(0);
1928 // Ignore dbg intrinsics.
1929 while (isa<DbgInfoIntrinsic>(BBI))
1931 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1932 Succ != BB) // Don't hurt infinite loops!
1933 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1936 } else { // Conditional branch
1937 if (isValueEqualityComparison(BI)) {
1938 // If we only have one predecessor, and if it is a branch on this value,
1939 // see if that predecessor totally determines the outcome of this
1941 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1942 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1943 return SimplifyCFG(BB) || 1;
1945 // This block must be empty, except for the setcond inst, if it exists.
1946 // Ignore dbg intrinsics.
1947 BasicBlock::iterator I = BB->begin();
1948 // Ignore dbg intrinsics.
1949 while (isa<DbgInfoIntrinsic>(I))
1952 if (FoldValueComparisonIntoPredecessors(BI))
1953 return SimplifyCFG(BB) | true;
1954 } else if (&*I == cast<Instruction>(BI->getCondition())){
1956 // Ignore dbg intrinsics.
1957 while (isa<DbgInfoIntrinsic>(I))
1960 if (FoldValueComparisonIntoPredecessors(BI))
1961 return SimplifyCFG(BB) | true;
1966 // If this is a branch on a phi node in the current block, thread control
1967 // through this block if any PHI node entries are constants.
1968 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1969 if (PN->getParent() == BI->getParent())
1970 if (FoldCondBranchOnPHI(BI))
1971 return SimplifyCFG(BB) | true;
1973 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1974 // branches to us and one of our successors, fold the setcc into the
1975 // predecessor and use logical operations to pick the right destination.
1976 if (FoldBranchToCommonDest(BI))
1977 return SimplifyCFG(BB) | 1;
1980 // Scan predecessor blocks for conditional branches.
1981 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1982 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1983 if (PBI != BI && PBI->isConditional())
1984 if (SimplifyCondBranchToCondBranch(PBI, BI))
1985 return SimplifyCFG(BB) | true;
1987 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1988 // If there are any instructions immediately before the unreachable that can
1989 // be removed, do so.
1990 Instruction *Unreachable = BB->getTerminator();
1991 while (Unreachable != BB->begin()) {
1992 BasicBlock::iterator BBI = Unreachable;
1994 // Do not delete instructions that can have side effects, like calls
1995 // (which may never return) and volatile loads and stores.
1996 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
1998 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
1999 if (SI->isVolatile())
2002 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2003 if (LI->isVolatile())
2006 // Delete this instruction
2007 BB->getInstList().erase(BBI);
2011 // If the unreachable instruction is the first in the block, take a gander
2012 // at all of the predecessors of this instruction, and simplify them.
2013 if (&BB->front() == Unreachable) {
2014 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2015 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2016 TerminatorInst *TI = Preds[i]->getTerminator();
2018 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2019 if (BI->isUnconditional()) {
2020 if (BI->getSuccessor(0) == BB) {
2021 new UnreachableInst(TI->getContext(), TI);
2022 TI->eraseFromParent();
2026 if (BI->getSuccessor(0) == BB) {
2027 BranchInst::Create(BI->getSuccessor(1), BI);
2028 EraseTerminatorInstAndDCECond(BI);
2029 } else if (BI->getSuccessor(1) == BB) {
2030 BranchInst::Create(BI->getSuccessor(0), BI);
2031 EraseTerminatorInstAndDCECond(BI);
2035 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2036 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2037 if (SI->getSuccessor(i) == BB) {
2038 BB->removePredecessor(SI->getParent());
2043 // If the default value is unreachable, figure out the most popular
2044 // destination and make it the default.
2045 if (SI->getSuccessor(0) == BB) {
2046 std::map<BasicBlock*, unsigned> Popularity;
2047 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2048 Popularity[SI->getSuccessor(i)]++;
2050 // Find the most popular block.
2051 unsigned MaxPop = 0;
2052 BasicBlock *MaxBlock = 0;
2053 for (std::map<BasicBlock*, unsigned>::iterator
2054 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2055 if (I->second > MaxPop) {
2057 MaxBlock = I->first;
2061 // Make this the new default, allowing us to delete any explicit
2063 SI->setSuccessor(0, MaxBlock);
2066 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2068 if (isa<PHINode>(MaxBlock->begin()))
2069 for (unsigned i = 0; i != MaxPop-1; ++i)
2070 MaxBlock->removePredecessor(SI->getParent());
2072 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2073 if (SI->getSuccessor(i) == MaxBlock) {
2079 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2080 if (II->getUnwindDest() == BB) {
2081 // Convert the invoke to a call instruction. This would be a good
2082 // place to note that the call does not throw though.
2083 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2084 II->removeFromParent(); // Take out of symbol table
2086 // Insert the call now...
2087 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
2088 CallInst *CI = CallInst::Create(II->getCalledValue(),
2089 Args.begin(), Args.end(),
2091 CI->setCallingConv(II->getCallingConv());
2092 CI->setAttributes(II->getAttributes());
2093 // If the invoke produced a value, the Call does now instead.
2094 II->replaceAllUsesWith(CI);
2101 // If this block is now dead, remove it.
2102 if (pred_begin(BB) == pred_end(BB)) {
2103 // We know there are no successors, so just nuke the block.
2104 M->getBasicBlockList().erase(BB);
2110 // Merge basic blocks into their predecessor if there is only one distinct
2111 // pred, and if there is only one distinct successor of the predecessor, and
2112 // if there are no PHI nodes.
2114 if (MergeBlockIntoPredecessor(BB))
2117 // Otherwise, if this block only has a single predecessor, and if that block
2118 // is a conditional branch, see if we can hoist any code from this block up
2119 // into our predecessor.
2120 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2121 BasicBlock *OnlyPred = *PI++;
2122 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2123 if (*PI != OnlyPred) {
2124 OnlyPred = 0; // There are multiple different predecessors...
2129 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2130 if (BI->isConditional()) {
2131 // Get the other block.
2132 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2133 PI = pred_begin(OtherBB);
2136 if (PI == pred_end(OtherBB)) {
2137 // We have a conditional branch to two blocks that are only reachable
2138 // from the condbr. We know that the condbr dominates the two blocks,
2139 // so see if there is any identical code in the "then" and "else"
2140 // blocks. If so, we can hoist it up to the branching block.
2141 Changed |= HoistThenElseCodeToIf(BI);
2143 BasicBlock* OnlySucc = NULL;
2144 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2148 else if (*SI != OnlySucc) {
2149 OnlySucc = 0; // There are multiple distinct successors!
2154 if (OnlySucc == OtherBB) {
2155 // If BB's only successor is the other successor of the predecessor,
2156 // i.e. a triangle, see if we can hoist any code from this block up
2157 // to the "if" block.
2158 Changed |= SpeculativelyExecuteBB(BI, BB);
2163 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2164 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2165 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2166 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2167 Instruction *Cond = cast<Instruction>(BI->getCondition());
2168 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2169 // 'setne's and'ed together, collect them.
2171 std::vector<ConstantInt*> Values;
2172 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2173 if (CompVal && CompVal->getType()->isInteger()) {
2174 // There might be duplicate constants in the list, which the switch
2175 // instruction can't handle, remove them now.
2176 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2177 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2179 // Figure out which block is which destination.
2180 BasicBlock *DefaultBB = BI->getSuccessor(1);
2181 BasicBlock *EdgeBB = BI->getSuccessor(0);
2182 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2184 // Create the new switch instruction now.
2185 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2188 // Add all of the 'cases' to the switch instruction.
2189 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2190 New->addCase(Values[i], EdgeBB);
2192 // We added edges from PI to the EdgeBB. As such, if there were any
2193 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2194 // the number of edges added.
2195 for (BasicBlock::iterator BBI = EdgeBB->begin();
2196 isa<PHINode>(BBI); ++BBI) {
2197 PHINode *PN = cast<PHINode>(BBI);
2198 Value *InVal = PN->getIncomingValueForBlock(*PI);
2199 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2200 PN->addIncoming(InVal, *PI);
2203 // Erase the old branch instruction.
2204 EraseTerminatorInstAndDCECond(BI);