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/Type.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/Support/CFG.h"
22 #include "llvm/Support/Debug.h"
23 #include "llvm/Analysis/ConstantFolding.h"
24 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
25 #include "llvm/ADT/SmallVector.h"
26 #include "llvm/ADT/SmallPtrSet.h"
27 #include "llvm/ADT/Statistic.h"
34 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
36 #include "llvm/Support/CommandLine.h"
38 DisableXForm("disable-xform", cl::Hidden, cl::init(false));
40 /// SafeToMergeTerminators - Return true if it is safe to merge these two
41 /// terminator instructions together.
43 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
44 if (SI1 == SI2) return false; // Can't merge with self!
46 // It is not safe to merge these two switch instructions if they have a common
47 // successor, and if that successor has a PHI node, and if *that* PHI node has
48 // conflicting incoming values from the two switch blocks.
49 BasicBlock *SI1BB = SI1->getParent();
50 BasicBlock *SI2BB = SI2->getParent();
51 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
53 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
54 if (SI1Succs.count(*I))
55 for (BasicBlock::iterator BBI = (*I)->begin();
56 isa<PHINode>(BBI); ++BBI) {
57 PHINode *PN = cast<PHINode>(BBI);
58 if (PN->getIncomingValueForBlock(SI1BB) !=
59 PN->getIncomingValueForBlock(SI2BB))
66 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
67 /// now be entries in it from the 'NewPred' block. The values that will be
68 /// flowing into the PHI nodes will be the same as those coming in from
69 /// ExistPred, an existing predecessor of Succ.
70 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
71 BasicBlock *ExistPred) {
72 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
73 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
74 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
77 for (BasicBlock::iterator I = Succ->begin();
78 (PN = dyn_cast<PHINode>(I)); ++I)
79 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
82 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
83 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
85 /// Assumption: Succ is the single successor for BB.
87 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
88 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
90 DOUT << "Looking to fold " << BB->getNameStart() << " into "
91 << Succ->getNameStart() << "\n";
92 // Shortcut, if there is only a single predecessor is must be BB and merging
94 if (Succ->getSinglePredecessor()) return true;
96 typedef SmallPtrSet<Instruction*, 16> InstrSet;
99 // Make a list of all phi nodes in BB
100 BasicBlock::iterator BBI = BB->begin();
101 while (isa<PHINode>(*BBI)) BBPHIs.insert(BBI++);
103 // Make a list of the predecessors of BB
104 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
105 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
107 // Use that list to make another list of common predecessors of BB and Succ
108 BlockSet CommonPreds;
109 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
111 if (BBPreds.count(*PI))
112 CommonPreds.insert(*PI);
114 // Shortcut, if there are no common predecessors, merging is always safe
115 if (CommonPreds.empty())
118 // Look at all the phi nodes in Succ, to see if they present a conflict when
119 // merging these blocks
120 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
121 PHINode *PN = cast<PHINode>(I);
123 // If the incoming value from BB is again a PHINode in
124 // BB which has the same incoming value for *PI as PN does, we can
125 // merge the phi nodes and then the blocks can still be merged
126 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
127 if (BBPN && BBPN->getParent() == BB) {
128 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
130 if (BBPN->getIncomingValueForBlock(*PI)
131 != PN->getIncomingValueForBlock(*PI)) {
132 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
133 << Succ->getNameStart() << " is conflicting with "
134 << BBPN->getNameStart() << " with regard to common predecessor "
135 << (*PI)->getNameStart() << "\n";
139 // Remove this phinode from the list of phis in BB, since it has been
143 Value* Val = PN->getIncomingValueForBlock(BB);
144 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
146 // See if the incoming value for the common predecessor is equal to the
147 // one for BB, in which case this phi node will not prevent the merging
149 if (Val != PN->getIncomingValueForBlock(*PI)) {
150 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
151 << Succ->getNameStart() << " is conflicting with regard to common "
152 << "predecessor " << (*PI)->getNameStart() << "\n";
159 // If there are any other phi nodes in BB that don't have a phi node in Succ
160 // to merge with, they must be moved to Succ completely. However, for any
161 // predecessors of Succ, branches will be added to the phi node that just
162 // point to itself. So, for any common predecessors, this must not cause
164 for (InstrSet::iterator I = BBPHIs.begin(), E = BBPHIs.end();
166 PHINode *PN = cast<PHINode>(*I);
167 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
169 if (PN->getIncomingValueForBlock(*PI) != PN) {
170 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
171 << BB->getNameStart() << " is conflicting with regard to common "
172 << "predecessor " << (*PI)->getNameStart() << "\n";
180 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
181 /// branch to Succ, and contains no instructions other than PHI nodes and the
182 /// branch. If possible, eliminate BB.
183 static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
185 // Check to see if merging these blocks would cause conflicts for any of the
186 // phi nodes in BB or Succ. If not, we can safely merge.
187 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
189 DOUT << "Killing Trivial BB: \n" << *BB;
191 if (isa<PHINode>(Succ->begin())) {
192 // If there is more than one pred of succ, and there are PHI nodes in
193 // the successor, then we need to add incoming edges for the PHI nodes
195 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
197 // Loop over all of the PHI nodes in the successor of BB.
198 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
199 PHINode *PN = cast<PHINode>(I);
200 Value *OldVal = PN->removeIncomingValue(BB, false);
201 assert(OldVal && "No entry in PHI for Pred BB!");
203 // If this incoming value is one of the PHI nodes in BB, the new entries
204 // in the PHI node are the entries from the old PHI.
205 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
206 PHINode *OldValPN = cast<PHINode>(OldVal);
207 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
208 // Note that, since we are merging phi nodes and BB and Succ might
209 // have common predecessors, we could end up with a phi node with
210 // identical incoming branches. This will be cleaned up later (and
211 // will trigger asserts if we try to clean it up now, without also
212 // simplifying the corresponding conditional branch).
213 PN->addIncoming(OldValPN->getIncomingValue(i),
214 OldValPN->getIncomingBlock(i));
216 // Add an incoming value for each of the new incoming values.
217 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
218 PN->addIncoming(OldVal, BBPreds[i]);
223 if (isa<PHINode>(&BB->front())) {
224 SmallVector<BasicBlock*, 16>
225 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
227 // Move all PHI nodes in BB to Succ if they are alive, otherwise
229 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
230 if (PN->use_empty()) {
231 // Just remove the dead phi. This happens if Succ's PHIs were the only
232 // users of the PHI nodes.
233 PN->eraseFromParent();
237 // The instruction is alive, so this means that BB must dominate all
238 // predecessors of Succ (Since all uses of the PN are after its
239 // definition, so in Succ or a block dominated by Succ. If a predecessor
240 // of Succ would not be dominated by BB, PN would violate the def before
241 // use SSA demand). Therefore, we can simply move the phi node to the
243 Succ->getInstList().splice(Succ->begin(),
244 BB->getInstList(), BB->begin());
246 // We need to add new entries for the PHI node to account for
247 // predecessors of Succ that the PHI node does not take into
248 // account. At this point, since we know that BB dominated succ and all
249 // of its predecessors, this means that we should any newly added
250 // incoming edges should use the PHI node itself as the value for these
251 // edges, because they are loop back edges.
252 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
253 if (OldSuccPreds[i] != BB)
254 PN->addIncoming(PN, OldSuccPreds[i]);
258 // Everything that jumped to BB now goes to Succ.
259 BB->replaceAllUsesWith(Succ);
260 if (!Succ->hasName()) Succ->takeName(BB);
261 BB->eraseFromParent(); // Delete the old basic block.
265 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
266 /// presumably PHI nodes in it), check to see if the merge at this block is due
267 /// to an "if condition". If so, return the boolean condition that determines
268 /// which entry into BB will be taken. Also, return by references the block
269 /// that will be entered from if the condition is true, and the block that will
270 /// be entered if the condition is false.
273 static Value *GetIfCondition(BasicBlock *BB,
274 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
275 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
276 "Function can only handle blocks with 2 predecessors!");
277 BasicBlock *Pred1 = *pred_begin(BB);
278 BasicBlock *Pred2 = *++pred_begin(BB);
280 // We can only handle branches. Other control flow will be lowered to
281 // branches if possible anyway.
282 if (!isa<BranchInst>(Pred1->getTerminator()) ||
283 !isa<BranchInst>(Pred2->getTerminator()))
285 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
286 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
288 // Eliminate code duplication by ensuring that Pred1Br is conditional if
290 if (Pred2Br->isConditional()) {
291 // If both branches are conditional, we don't have an "if statement". In
292 // reality, we could transform this case, but since the condition will be
293 // required anyway, we stand no chance of eliminating it, so the xform is
294 // probably not profitable.
295 if (Pred1Br->isConditional())
298 std::swap(Pred1, Pred2);
299 std::swap(Pred1Br, Pred2Br);
302 if (Pred1Br->isConditional()) {
303 // If we found a conditional branch predecessor, make sure that it branches
304 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
305 if (Pred1Br->getSuccessor(0) == BB &&
306 Pred1Br->getSuccessor(1) == Pred2) {
309 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
310 Pred1Br->getSuccessor(1) == BB) {
314 // We know that one arm of the conditional goes to BB, so the other must
315 // go somewhere unrelated, and this must not be an "if statement".
319 // The only thing we have to watch out for here is to make sure that Pred2
320 // doesn't have incoming edges from other blocks. If it does, the condition
321 // doesn't dominate BB.
322 if (++pred_begin(Pred2) != pred_end(Pred2))
325 return Pred1Br->getCondition();
328 // Ok, if we got here, both predecessors end with an unconditional branch to
329 // BB. Don't panic! If both blocks only have a single (identical)
330 // predecessor, and THAT is a conditional branch, then we're all ok!
331 if (pred_begin(Pred1) == pred_end(Pred1) ||
332 ++pred_begin(Pred1) != pred_end(Pred1) ||
333 pred_begin(Pred2) == pred_end(Pred2) ||
334 ++pred_begin(Pred2) != pred_end(Pred2) ||
335 *pred_begin(Pred1) != *pred_begin(Pred2))
338 // Otherwise, if this is a conditional branch, then we can use it!
339 BasicBlock *CommonPred = *pred_begin(Pred1);
340 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
341 assert(BI->isConditional() && "Two successors but not conditional?");
342 if (BI->getSuccessor(0) == Pred1) {
349 return BI->getCondition();
355 /// DominatesMergePoint - If we have a merge point of an "if condition" as
356 /// accepted above, return true if the specified value dominates the block. We
357 /// don't handle the true generality of domination here, just a special case
358 /// which works well enough for us.
360 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
361 /// see if V (which must be an instruction) is cheap to compute and is
362 /// non-trapping. If both are true, the instruction is inserted into the set
363 /// and true is returned.
364 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
365 std::set<Instruction*> *AggressiveInsts) {
366 Instruction *I = dyn_cast<Instruction>(V);
368 // Non-instructions all dominate instructions, but not all constantexprs
369 // can be executed unconditionally.
370 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
375 BasicBlock *PBB = I->getParent();
377 // We don't want to allow weird loops that might have the "if condition" in
378 // the bottom of this block.
379 if (PBB == BB) return false;
381 // If this instruction is defined in a block that contains an unconditional
382 // branch to BB, then it must be in the 'conditional' part of the "if
384 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
385 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
386 if (!AggressiveInsts) return false;
387 // Okay, it looks like the instruction IS in the "condition". Check to
388 // see if its a cheap instruction to unconditionally compute, and if it
389 // only uses stuff defined outside of the condition. If so, hoist it out.
390 switch (I->getOpcode()) {
391 default: return false; // Cannot hoist this out safely.
392 case Instruction::Load:
393 // We can hoist loads that are non-volatile and obviously cannot trap.
394 if (cast<LoadInst>(I)->isVolatile())
396 // FIXME: A computation of a constant can trap!
397 if (!isa<AllocaInst>(I->getOperand(0)) &&
398 !isa<Constant>(I->getOperand(0)))
401 // Finally, we have to check to make sure there are no instructions
402 // before the load in its basic block, as we are going to hoist the loop
403 // out to its predecessor.
404 if (PBB->begin() != BasicBlock::iterator(I))
407 case Instruction::Add:
408 case Instruction::Sub:
409 case Instruction::And:
410 case Instruction::Or:
411 case Instruction::Xor:
412 case Instruction::Shl:
413 case Instruction::LShr:
414 case Instruction::AShr:
415 case Instruction::ICmp:
416 case Instruction::FCmp:
417 if (I->getOperand(0)->getType()->isFPOrFPVector())
418 return false; // FP arithmetic might trap.
419 break; // These are all cheap and non-trapping instructions.
422 // Okay, we can only really hoist these out if their operands are not
423 // defined in the conditional region.
424 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
425 if (!DominatesMergePoint(*i, BB, 0))
427 // Okay, it's safe to do this! Remember this instruction.
428 AggressiveInsts->insert(I);
434 /// GatherConstantSetEQs - Given a potentially 'or'd together collection of
435 /// icmp_eq instructions that compare a value against a constant, return the
436 /// value being compared, and stick the constant into the Values vector.
437 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
438 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
439 if (Inst->getOpcode() == Instruction::ICmp &&
440 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
441 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
443 return Inst->getOperand(0);
444 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
446 return Inst->getOperand(1);
448 } else if (Inst->getOpcode() == Instruction::Or) {
449 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
450 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
458 /// GatherConstantSetNEs - Given a potentially 'and'd together collection of
459 /// setne instructions that compare a value against a constant, return the value
460 /// being compared, and stick the constant into the Values vector.
461 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
462 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
463 if (Inst->getOpcode() == Instruction::ICmp &&
464 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
465 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
467 return Inst->getOperand(0);
468 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
470 return Inst->getOperand(1);
472 } else if (Inst->getOpcode() == Instruction::And) {
473 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
474 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
482 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
483 /// bunch of comparisons of one value against constants, return the value and
484 /// the constants being compared.
485 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
486 std::vector<ConstantInt*> &Values) {
487 if (Cond->getOpcode() == Instruction::Or) {
488 CompVal = GatherConstantSetEQs(Cond, Values);
490 // Return true to indicate that the condition is true if the CompVal is
491 // equal to one of the constants.
493 } else if (Cond->getOpcode() == Instruction::And) {
494 CompVal = GatherConstantSetNEs(Cond, Values);
496 // Return false to indicate that the condition is false if the CompVal is
497 // equal to one of the constants.
503 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
504 Instruction* Cond = 0;
505 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
506 Cond = dyn_cast<Instruction>(SI->getCondition());
507 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
508 if (BI->isConditional())
509 Cond = dyn_cast<Instruction>(BI->getCondition());
512 TI->eraseFromParent();
513 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
516 /// isValueEqualityComparison - Return true if the specified terminator checks
517 /// to see if a value is equal to constant integer value.
518 static Value *isValueEqualityComparison(TerminatorInst *TI) {
519 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
520 // Do not permit merging of large switch instructions into their
521 // predecessors unless there is only one predecessor.
522 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
523 pred_end(SI->getParent())) > 128)
526 return SI->getCondition();
528 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
529 if (BI->isConditional() && BI->getCondition()->hasOneUse())
530 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
531 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
532 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
533 isa<ConstantInt>(ICI->getOperand(1)))
534 return ICI->getOperand(0);
538 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
539 /// decode all of the 'cases' that it represents and return the 'default' block.
541 GetValueEqualityComparisonCases(TerminatorInst *TI,
542 std::vector<std::pair<ConstantInt*,
543 BasicBlock*> > &Cases) {
544 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
545 Cases.reserve(SI->getNumCases());
546 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
547 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
548 return SI->getDefaultDest();
551 BranchInst *BI = cast<BranchInst>(TI);
552 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
553 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
554 BI->getSuccessor(ICI->getPredicate() ==
555 ICmpInst::ICMP_NE)));
556 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
560 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
561 /// in the list that match the specified block.
562 static void EliminateBlockCases(BasicBlock *BB,
563 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
564 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
565 if (Cases[i].second == BB) {
566 Cases.erase(Cases.begin()+i);
571 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
574 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
575 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
576 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
578 // Make V1 be smaller than V2.
579 if (V1->size() > V2->size())
582 if (V1->size() == 0) return false;
583 if (V1->size() == 1) {
585 ConstantInt *TheVal = (*V1)[0].first;
586 for (unsigned i = 0, e = V2->size(); i != e; ++i)
587 if (TheVal == (*V2)[i].first)
591 // Otherwise, just sort both lists and compare element by element.
592 std::sort(V1->begin(), V1->end());
593 std::sort(V2->begin(), V2->end());
594 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
595 while (i1 != e1 && i2 != e2) {
596 if ((*V1)[i1].first == (*V2)[i2].first)
598 if ((*V1)[i1].first < (*V2)[i2].first)
606 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
607 /// terminator instruction and its block is known to only have a single
608 /// predecessor block, check to see if that predecessor is also a value
609 /// comparison with the same value, and if that comparison determines the
610 /// outcome of this comparison. If so, simplify TI. This does a very limited
611 /// form of jump threading.
612 static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
614 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
615 if (!PredVal) return false; // Not a value comparison in predecessor.
617 Value *ThisVal = isValueEqualityComparison(TI);
618 assert(ThisVal && "This isn't a value comparison!!");
619 if (ThisVal != PredVal) return false; // Different predicates.
621 // Find out information about when control will move from Pred to TI's block.
622 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
623 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
625 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
627 // Find information about how control leaves this block.
628 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
629 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
630 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
632 // If TI's block is the default block from Pred's comparison, potentially
633 // simplify TI based on this knowledge.
634 if (PredDef == TI->getParent()) {
635 // If we are here, we know that the value is none of those cases listed in
636 // PredCases. If there are any cases in ThisCases that are in PredCases, we
638 if (ValuesOverlap(PredCases, ThisCases)) {
639 if (isa<BranchInst>(TI)) {
640 // Okay, one of the successors of this condbr is dead. Convert it to a
642 assert(ThisCases.size() == 1 && "Branch can only have one case!");
643 // Insert the new branch.
644 Instruction *NI = BranchInst::Create(ThisDef, TI);
646 // Remove PHI node entries for the dead edge.
647 ThisCases[0].second->removePredecessor(TI->getParent());
649 DOUT << "Threading pred instr: " << *Pred->getTerminator()
650 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
652 EraseTerminatorInstAndDCECond(TI);
656 SwitchInst *SI = cast<SwitchInst>(TI);
657 // Okay, TI has cases that are statically dead, prune them away.
658 SmallPtrSet<Constant*, 16> DeadCases;
659 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
660 DeadCases.insert(PredCases[i].first);
662 DOUT << "Threading pred instr: " << *Pred->getTerminator()
663 << "Through successor TI: " << *TI;
665 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
666 if (DeadCases.count(SI->getCaseValue(i))) {
667 SI->getSuccessor(i)->removePredecessor(TI->getParent());
671 DOUT << "Leaving: " << *TI << "\n";
677 // Otherwise, TI's block must correspond to some matched value. Find out
678 // which value (or set of values) this is.
679 ConstantInt *TIV = 0;
680 BasicBlock *TIBB = TI->getParent();
681 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
682 if (PredCases[i].second == TIBB) {
684 TIV = PredCases[i].first;
686 return false; // Cannot handle multiple values coming to this block.
688 assert(TIV && "No edge from pred to succ?");
690 // Okay, we found the one constant that our value can be if we get into TI's
691 // BB. Find out which successor will unconditionally be branched to.
692 BasicBlock *TheRealDest = 0;
693 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
694 if (ThisCases[i].first == TIV) {
695 TheRealDest = ThisCases[i].second;
699 // If not handled by any explicit cases, it is handled by the default case.
700 if (TheRealDest == 0) TheRealDest = ThisDef;
702 // Remove PHI node entries for dead edges.
703 BasicBlock *CheckEdge = TheRealDest;
704 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
705 if (*SI != CheckEdge)
706 (*SI)->removePredecessor(TIBB);
710 // Insert the new branch.
711 Instruction *NI = BranchInst::Create(TheRealDest, TI);
713 DOUT << "Threading pred instr: " << *Pred->getTerminator()
714 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
716 EraseTerminatorInstAndDCECond(TI);
722 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
723 /// equality comparison instruction (either a switch or a branch on "X == c").
724 /// See if any of the predecessors of the terminator block are value comparisons
725 /// on the same value. If so, and if safe to do so, fold them together.
726 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
727 BasicBlock *BB = TI->getParent();
728 Value *CV = isValueEqualityComparison(TI); // CondVal
729 assert(CV && "Not a comparison?");
730 bool Changed = false;
732 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
733 while (!Preds.empty()) {
734 BasicBlock *Pred = Preds.back();
737 // See if the predecessor is a comparison with the same value.
738 TerminatorInst *PTI = Pred->getTerminator();
739 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
741 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
742 // Figure out which 'cases' to copy from SI to PSI.
743 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
744 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
746 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
747 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
749 // Based on whether the default edge from PTI goes to BB or not, fill in
750 // PredCases and PredDefault with the new switch cases we would like to
752 SmallVector<BasicBlock*, 8> NewSuccessors;
754 if (PredDefault == BB) {
755 // If this is the default destination from PTI, only the edges in TI
756 // that don't occur in PTI, or that branch to BB will be activated.
757 std::set<ConstantInt*> PTIHandled;
758 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
759 if (PredCases[i].second != BB)
760 PTIHandled.insert(PredCases[i].first);
762 // The default destination is BB, we don't need explicit targets.
763 std::swap(PredCases[i], PredCases.back());
764 PredCases.pop_back();
768 // Reconstruct the new switch statement we will be building.
769 if (PredDefault != BBDefault) {
770 PredDefault->removePredecessor(Pred);
771 PredDefault = BBDefault;
772 NewSuccessors.push_back(BBDefault);
774 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
775 if (!PTIHandled.count(BBCases[i].first) &&
776 BBCases[i].second != BBDefault) {
777 PredCases.push_back(BBCases[i]);
778 NewSuccessors.push_back(BBCases[i].second);
782 // If this is not the default destination from PSI, only the edges
783 // in SI that occur in PSI with a destination of BB will be
785 std::set<ConstantInt*> PTIHandled;
786 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
787 if (PredCases[i].second == BB) {
788 PTIHandled.insert(PredCases[i].first);
789 std::swap(PredCases[i], PredCases.back());
790 PredCases.pop_back();
794 // Okay, now we know which constants were sent to BB from the
795 // predecessor. Figure out where they will all go now.
796 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
797 if (PTIHandled.count(BBCases[i].first)) {
798 // If this is one we are capable of getting...
799 PredCases.push_back(BBCases[i]);
800 NewSuccessors.push_back(BBCases[i].second);
801 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
804 // If there are any constants vectored to BB that TI doesn't handle,
805 // they must go to the default destination of TI.
806 for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
807 E = PTIHandled.end(); I != E; ++I) {
808 PredCases.push_back(std::make_pair(*I, BBDefault));
809 NewSuccessors.push_back(BBDefault);
813 // Okay, at this point, we know which new successor Pred will get. Make
814 // sure we update the number of entries in the PHI nodes for these
816 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
817 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
819 // Now that the successors are updated, create the new Switch instruction.
820 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
821 PredCases.size(), PTI);
822 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
823 NewSI->addCase(PredCases[i].first, PredCases[i].second);
825 EraseTerminatorInstAndDCECond(PTI);
827 // Okay, last check. If BB is still a successor of PSI, then we must
828 // have an infinite loop case. If so, add an infinitely looping block
829 // to handle the case to preserve the behavior of the code.
830 BasicBlock *InfLoopBlock = 0;
831 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
832 if (NewSI->getSuccessor(i) == BB) {
833 if (InfLoopBlock == 0) {
834 // Insert it at the end of the function, because it's either code,
835 // or it won't matter if it's hot. :)
836 InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
837 BranchInst::Create(InfLoopBlock, InfLoopBlock);
839 NewSI->setSuccessor(i, InfLoopBlock);
848 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
849 /// BB2, hoist any common code in the two blocks up into the branch block. The
850 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
851 static bool HoistThenElseCodeToIf(BranchInst *BI) {
852 // This does very trivial matching, with limited scanning, to find identical
853 // instructions in the two blocks. In particular, we don't want to get into
854 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
855 // such, we currently just scan for obviously identical instructions in an
857 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
858 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
860 BasicBlock::iterator BB1_Itr = BB1->begin();
861 BasicBlock::iterator BB2_Itr = BB2->begin();
863 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
864 while (isa<DbgInfoIntrinsic>(I1))
866 while (isa<DbgInfoIntrinsic>(I2))
868 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
869 isa<InvokeInst>(I1) || !I1->isIdenticalTo(I2))
872 // If we get here, we can hoist at least one instruction.
873 BasicBlock *BIParent = BI->getParent();
876 // If we are hoisting the terminator instruction, don't move one (making a
877 // broken BB), instead clone it, and remove BI.
878 if (isa<TerminatorInst>(I1))
879 goto HoistTerminator;
881 // For a normal instruction, we just move one to right before the branch,
882 // then replace all uses of the other with the first. Finally, we remove
883 // the now redundant second instruction.
884 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
885 if (!I2->use_empty())
886 I2->replaceAllUsesWith(I1);
887 BB2->getInstList().erase(I2);
890 while (isa<DbgInfoIntrinsic>(I1))
893 while (isa<DbgInfoIntrinsic>(I2))
895 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
900 // Okay, it is safe to hoist the terminator.
901 Instruction *NT = I1->clone();
902 BIParent->getInstList().insert(BI, NT);
903 if (NT->getType() != Type::VoidTy) {
904 I1->replaceAllUsesWith(NT);
905 I2->replaceAllUsesWith(NT);
909 // Hoisting one of the terminators from our successor is a great thing.
910 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
911 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
912 // nodes, so we insert select instruction to compute the final result.
913 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
914 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
916 for (BasicBlock::iterator BBI = SI->begin();
917 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
918 Value *BB1V = PN->getIncomingValueForBlock(BB1);
919 Value *BB2V = PN->getIncomingValueForBlock(BB2);
921 // These values do not agree. Insert a select instruction before NT
922 // that determines the right value.
923 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
925 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
926 BB1V->getName()+"."+BB2V->getName(), NT);
927 // Make the PHI node use the select for all incoming values for BB1/BB2
928 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
929 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
930 PN->setIncomingValue(i, SI);
935 // Update any PHI nodes in our new successors.
936 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
937 AddPredecessorToBlock(*SI, BIParent, BB1);
939 EraseTerminatorInstAndDCECond(BI);
943 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
944 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
945 /// (for now, restricted to a single instruction that's side effect free) from
946 /// the BB1 into the branch block to speculatively execute it.
947 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
948 // Only speculatively execution a single instruction (not counting the
949 // terminator) for now.
950 BasicBlock::iterator BBI = BB1->begin();
951 ++BBI; // must have at least a terminator
952 if (BBI == BB1->end()) return false; // only one inst
954 if (BBI != BB1->end()) return false; // more than 2 insts.
956 // Be conservative for now. FP select instruction can often be expensive.
957 Value *BrCond = BI->getCondition();
958 if (isa<Instruction>(BrCond) &&
959 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
962 // If BB1 is actually on the false edge of the conditional branch, remember
963 // to swap the select operands later.
965 if (BB1 != BI->getSuccessor(0)) {
966 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
973 // br i1 %t1, label %BB1, label %BB2
982 // %t3 = select i1 %t1, %t2, %t3
983 Instruction *I = BB1->begin();
984 switch (I->getOpcode()) {
985 default: return false; // Not safe / profitable to hoist.
986 case Instruction::Add:
987 case Instruction::Sub:
988 // FP arithmetic might trap. Not worth doing for vector ops.
989 if (I->getType()->isFloatingPoint() || isa<VectorType>(I->getType()))
992 case Instruction::And:
993 case Instruction::Or:
994 case Instruction::Xor:
995 case Instruction::Shl:
996 case Instruction::LShr:
997 case Instruction::AShr:
998 // Don't mess with vector operations.
999 if (isa<VectorType>(I->getType()))
1001 break; // These are all cheap and non-trapping instructions.
1004 // If the instruction is obviously dead, don't try to predicate it.
1005 if (I->use_empty()) {
1006 I->eraseFromParent();
1010 // Can we speculatively execute the instruction? And what is the value
1011 // if the condition is false? Consider the phi uses, if the incoming value
1012 // from the "if" block are all the same V, then V is the value of the
1013 // select if the condition is false.
1014 BasicBlock *BIParent = BI->getParent();
1015 SmallVector<PHINode*, 4> PHIUses;
1016 Value *FalseV = NULL;
1018 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1019 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1021 // Ignore any user that is not a PHI node in BB2. These can only occur in
1022 // unreachable blocks, because they would not be dominated by the instr.
1023 PHINode *PN = dyn_cast<PHINode>(UI);
1024 if (!PN || PN->getParent() != BB2)
1026 PHIUses.push_back(PN);
1028 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1031 else if (FalseV != PHIV)
1032 return false; // Inconsistent value when condition is false.
1035 assert(FalseV && "Must have at least one user, and it must be a PHI");
1037 // Do not hoist the instruction if any of its operands are defined but not
1038 // used in this BB. The transformation will prevent the operand from
1039 // being sunk into the use block.
1040 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
1041 Instruction *OpI = dyn_cast<Instruction>(*i);
1042 if (OpI && OpI->getParent() == BIParent &&
1043 !OpI->isUsedInBasicBlock(BIParent))
1047 // If we get here, we can hoist the instruction. Try to place it
1048 // before the icmp instruction preceeding the conditional branch.
1049 BasicBlock::iterator InsertPos = BI;
1050 if (InsertPos != BIParent->begin())
1052 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1053 SmallPtrSet<Instruction *, 4> BB1Insns;
1054 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1055 BB1I != BB1E; ++BB1I)
1056 BB1Insns.insert(BB1I);
1057 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1059 Instruction *Use = cast<Instruction>(*UI);
1060 if (BB1Insns.count(Use)) {
1061 // If BrCond uses the instruction that place it just before
1062 // branch instruction.
1069 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), I);
1071 // Create a select whose true value is the speculatively executed value and
1072 // false value is the previously determined FalseV.
1075 SI = SelectInst::Create(BrCond, FalseV, I,
1076 FalseV->getName() + "." + I->getName(), BI);
1078 SI = SelectInst::Create(BrCond, I, FalseV,
1079 I->getName() + "." + FalseV->getName(), BI);
1081 // Make the PHI node use the select for all incoming values for "then" and
1083 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1084 PHINode *PN = PHIUses[i];
1085 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1086 if (PN->getIncomingBlock(j) == BB1 ||
1087 PN->getIncomingBlock(j) == BIParent)
1088 PN->setIncomingValue(j, SI);
1095 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1096 /// across this block.
1097 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1098 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1101 // If this basic block contains anything other than a PHI (which controls the
1102 // branch) and branch itself, bail out. FIXME: improve this in the future.
1103 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) {
1104 if (Size > 10) return false; // Don't clone large BB's.
1106 // We can only support instructions that are do not define values that are
1107 // live outside of the current basic block.
1108 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1110 Instruction *U = cast<Instruction>(*UI);
1111 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1114 // Looks ok, continue checking.
1120 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1121 /// that is defined in the same block as the branch and if any PHI entries are
1122 /// constants, thread edges corresponding to that entry to be branches to their
1123 /// ultimate destination.
1124 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1125 BasicBlock *BB = BI->getParent();
1126 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1127 // NOTE: we currently cannot transform this case if the PHI node is used
1128 // outside of the block.
1129 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1132 // Degenerate case of a single entry PHI.
1133 if (PN->getNumIncomingValues() == 1) {
1134 FoldSingleEntryPHINodes(PN->getParent());
1138 // Now we know that this block has multiple preds and two succs.
1139 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1141 // Okay, this is a simple enough basic block. See if any phi values are
1143 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1145 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1146 CB->getType() == Type::Int1Ty) {
1147 // Okay, we now know that all edges from PredBB should be revectored to
1148 // branch to RealDest.
1149 BasicBlock *PredBB = PN->getIncomingBlock(i);
1150 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1152 if (RealDest == BB) continue; // Skip self loops.
1154 // The dest block might have PHI nodes, other predecessors and other
1155 // difficult cases. Instead of being smart about this, just insert a new
1156 // block that jumps to the destination block, effectively splitting
1157 // the edge we are about to create.
1158 BasicBlock *EdgeBB = BasicBlock::Create(RealDest->getName()+".critedge",
1159 RealDest->getParent(), RealDest);
1160 BranchInst::Create(RealDest, EdgeBB);
1162 for (BasicBlock::iterator BBI = RealDest->begin();
1163 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1164 Value *V = PN->getIncomingValueForBlock(BB);
1165 PN->addIncoming(V, EdgeBB);
1168 // BB may have instructions that are being threaded over. Clone these
1169 // instructions into EdgeBB. We know that there will be no uses of the
1170 // cloned instructions outside of EdgeBB.
1171 BasicBlock::iterator InsertPt = EdgeBB->begin();
1172 std::map<Value*, Value*> TranslateMap; // Track translated values.
1173 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1174 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1175 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1177 // Clone the instruction.
1178 Instruction *N = BBI->clone();
1179 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1181 // Update operands due to translation.
1182 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1184 std::map<Value*, Value*>::iterator PI =
1185 TranslateMap.find(*i);
1186 if (PI != TranslateMap.end())
1190 // Check for trivial simplification.
1191 if (Constant *C = ConstantFoldInstruction(N)) {
1192 TranslateMap[BBI] = C;
1193 delete N; // Constant folded away, don't need actual inst
1195 // Insert the new instruction into its new home.
1196 EdgeBB->getInstList().insert(InsertPt, N);
1197 if (!BBI->use_empty())
1198 TranslateMap[BBI] = N;
1203 // Loop over all of the edges from PredBB to BB, changing them to branch
1204 // to EdgeBB instead.
1205 TerminatorInst *PredBBTI = PredBB->getTerminator();
1206 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1207 if (PredBBTI->getSuccessor(i) == BB) {
1208 BB->removePredecessor(PredBB);
1209 PredBBTI->setSuccessor(i, EdgeBB);
1212 // Recurse, simplifying any other constants.
1213 return FoldCondBranchOnPHI(BI) | true;
1220 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1221 /// PHI node, see if we can eliminate it.
1222 static bool FoldTwoEntryPHINode(PHINode *PN) {
1223 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1224 // statement", which has a very simple dominance structure. Basically, we
1225 // are trying to find the condition that is being branched on, which
1226 // subsequently causes this merge to happen. We really want control
1227 // dependence information for this check, but simplifycfg can't keep it up
1228 // to date, and this catches most of the cases we care about anyway.
1230 BasicBlock *BB = PN->getParent();
1231 BasicBlock *IfTrue, *IfFalse;
1232 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1233 if (!IfCond) return false;
1235 // Okay, we found that we can merge this two-entry phi node into a select.
1236 // Doing so would require us to fold *all* two entry phi nodes in this block.
1237 // At some point this becomes non-profitable (particularly if the target
1238 // doesn't support cmov's). Only do this transformation if there are two or
1239 // fewer PHI nodes in this block.
1240 unsigned NumPhis = 0;
1241 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1245 DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
1246 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
1248 // Loop over the PHI's seeing if we can promote them all to select
1249 // instructions. While we are at it, keep track of the instructions
1250 // that need to be moved to the dominating block.
1251 std::set<Instruction*> AggressiveInsts;
1253 BasicBlock::iterator AfterPHIIt = BB->begin();
1254 while (isa<PHINode>(AfterPHIIt)) {
1255 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1256 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1257 if (PN->getIncomingValue(0) != PN)
1258 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1260 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1261 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1262 &AggressiveInsts) ||
1263 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1264 &AggressiveInsts)) {
1269 // If we all PHI nodes are promotable, check to make sure that all
1270 // instructions in the predecessor blocks can be promoted as well. If
1271 // not, we won't be able to get rid of the control flow, so it's not
1272 // worth promoting to select instructions.
1273 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1274 PN = cast<PHINode>(BB->begin());
1275 BasicBlock *Pred = PN->getIncomingBlock(0);
1276 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1278 DomBlock = *pred_begin(Pred);
1279 for (BasicBlock::iterator I = Pred->begin();
1280 !isa<TerminatorInst>(I); ++I)
1281 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1282 // This is not an aggressive instruction that we can promote.
1283 // Because of this, we won't be able to get rid of the control
1284 // flow, so the xform is not worth it.
1289 Pred = PN->getIncomingBlock(1);
1290 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1292 DomBlock = *pred_begin(Pred);
1293 for (BasicBlock::iterator I = Pred->begin();
1294 !isa<TerminatorInst>(I); ++I)
1295 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1296 // This is not an aggressive instruction that we can promote.
1297 // Because of this, we won't be able to get rid of the control
1298 // flow, so the xform is not worth it.
1303 // If we can still promote the PHI nodes after this gauntlet of tests,
1304 // do all of the PHI's now.
1306 // Move all 'aggressive' instructions, which are defined in the
1307 // conditional parts of the if's up to the dominating block.
1309 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1310 IfBlock1->getInstList(),
1312 IfBlock1->getTerminator());
1315 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1316 IfBlock2->getInstList(),
1318 IfBlock2->getTerminator());
1321 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1322 // Change the PHI node into a select instruction.
1324 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1326 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1328 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1329 PN->replaceAllUsesWith(NV);
1332 BB->getInstList().erase(PN);
1337 /// isTerminatorFirstRelevantInsn - Return true if Term is very first
1338 /// instruction ignoring Phi nodes and dbg intrinsics.
1339 static bool isTerminatorFirstRelevantInsn(BasicBlock *BB, Instruction *Term) {
1340 BasicBlock::iterator BBI = Term;
1341 while (BBI != BB->begin()) {
1343 if (!isa<DbgInfoIntrinsic>(BBI))
1347 if (isa<PHINode>(BBI) || &*BBI == Term || isa<DbgInfoIntrinsic>(BBI))
1352 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1353 /// to two returning blocks, try to merge them together into one return,
1354 /// introducing a select if the return values disagree.
1355 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1356 assert(BI->isConditional() && "Must be a conditional branch");
1357 BasicBlock *TrueSucc = BI->getSuccessor(0);
1358 BasicBlock *FalseSucc = BI->getSuccessor(1);
1359 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1360 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1362 // Check to ensure both blocks are empty (just a return) or optionally empty
1363 // with PHI nodes. If there are other instructions, merging would cause extra
1364 // computation on one path or the other.
1365 if (!isTerminatorFirstRelevantInsn(TrueSucc, TrueRet))
1367 if (!isTerminatorFirstRelevantInsn(FalseSucc, FalseRet))
1370 // Okay, we found a branch that is going to two return nodes. If
1371 // there is no return value for this function, just change the
1372 // branch into a return.
1373 if (FalseRet->getNumOperands() == 0) {
1374 TrueSucc->removePredecessor(BI->getParent());
1375 FalseSucc->removePredecessor(BI->getParent());
1376 ReturnInst::Create(0, BI);
1377 EraseTerminatorInstAndDCECond(BI);
1381 // Otherwise, figure out what the true and false return values are
1382 // so we can insert a new select instruction.
1383 Value *TrueValue = TrueRet->getReturnValue();
1384 Value *FalseValue = FalseRet->getReturnValue();
1386 // Unwrap any PHI nodes in the return blocks.
1387 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1388 if (TVPN->getParent() == TrueSucc)
1389 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1390 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1391 if (FVPN->getParent() == FalseSucc)
1392 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1394 // In order for this transformation to be safe, we must be able to
1395 // unconditionally execute both operands to the return. This is
1396 // normally the case, but we could have a potentially-trapping
1397 // constant expression that prevents this transformation from being
1399 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1402 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1406 // Okay, we collected all the mapped values and checked them for sanity, and
1407 // defined to really do this transformation. First, update the CFG.
1408 TrueSucc->removePredecessor(BI->getParent());
1409 FalseSucc->removePredecessor(BI->getParent());
1411 // Insert select instructions where needed.
1412 Value *BrCond = BI->getCondition();
1414 // Insert a select if the results differ.
1415 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1416 } else if (isa<UndefValue>(TrueValue)) {
1417 TrueValue = FalseValue;
1419 TrueValue = SelectInst::Create(BrCond, TrueValue,
1420 FalseValue, "retval", BI);
1424 Value *RI = !TrueValue ?
1425 ReturnInst::Create(BI) :
1426 ReturnInst::Create(TrueValue, BI);
1428 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1429 << "\n " << *BI << "NewRet = " << *RI
1430 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
1432 EraseTerminatorInstAndDCECond(BI);
1437 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1438 /// and if a predecessor branches to us and one of our successors, fold the
1439 /// setcc into the predecessor and use logical operations to pick the right
1441 static bool FoldBranchToCommonDest(BranchInst *BI) {
1442 BasicBlock *BB = BI->getParent();
1443 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1444 if (Cond == 0) return false;
1447 // Only allow this if the condition is a simple instruction that can be
1448 // executed unconditionally. It must be in the same block as the branch, and
1449 // must be at the front of the block.
1450 BasicBlock::iterator FrontIt = BB->front();
1451 // Ignore dbg intrinsics.
1452 while(isa<DbgInfoIntrinsic>(FrontIt))
1454 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1455 Cond->getParent() != BB || &*FrontIt != Cond || !Cond->hasOneUse()) {
1459 // Make sure the instruction after the condition is the cond branch.
1460 BasicBlock::iterator CondIt = Cond; ++CondIt;
1461 // Ingore dbg intrinsics.
1462 while(isa<DbgInfoIntrinsic>(CondIt))
1464 if (&*CondIt != BI) {
1465 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1469 // Cond is known to be a compare or binary operator. Check to make sure that
1470 // neither operand is a potentially-trapping constant expression.
1471 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1474 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1479 // Finally, don't infinitely unroll conditional loops.
1480 BasicBlock *TrueDest = BI->getSuccessor(0);
1481 BasicBlock *FalseDest = BI->getSuccessor(1);
1482 if (TrueDest == BB || FalseDest == BB)
1485 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1486 BasicBlock *PredBlock = *PI;
1487 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1489 // Check that we have two conditional branches. If there is a PHI node in
1490 // the common successor, verify that the same value flows in from both
1492 if (PBI == 0 || PBI->isUnconditional() ||
1493 !SafeToMergeTerminators(BI, PBI))
1496 Instruction::BinaryOps Opc;
1497 bool InvertPredCond = false;
1499 if (PBI->getSuccessor(0) == TrueDest)
1500 Opc = Instruction::Or;
1501 else if (PBI->getSuccessor(1) == FalseDest)
1502 Opc = Instruction::And;
1503 else if (PBI->getSuccessor(0) == FalseDest)
1504 Opc = Instruction::And, InvertPredCond = true;
1505 else if (PBI->getSuccessor(1) == TrueDest)
1506 Opc = Instruction::Or, InvertPredCond = true;
1510 DOUT << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB;
1512 // If we need to invert the condition in the pred block to match, do so now.
1513 if (InvertPredCond) {
1515 BinaryOperator::CreateNot(PBI->getCondition(),
1516 PBI->getCondition()->getName()+".not", PBI);
1517 PBI->setCondition(NewCond);
1518 BasicBlock *OldTrue = PBI->getSuccessor(0);
1519 BasicBlock *OldFalse = PBI->getSuccessor(1);
1520 PBI->setSuccessor(0, OldFalse);
1521 PBI->setSuccessor(1, OldTrue);
1524 // Clone Cond into the predecessor basic block, and or/and the
1525 // two conditions together.
1526 Instruction *New = Cond->clone();
1527 PredBlock->getInstList().insert(PBI, New);
1528 New->takeName(Cond);
1529 Cond->setName(New->getName()+".old");
1531 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1532 New, "or.cond", PBI);
1533 PBI->setCondition(NewCond);
1534 if (PBI->getSuccessor(0) == BB) {
1535 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1536 PBI->setSuccessor(0, TrueDest);
1538 if (PBI->getSuccessor(1) == BB) {
1539 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1540 PBI->setSuccessor(1, FalseDest);
1547 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1548 /// predecessor of another block, this function tries to simplify it. We know
1549 /// that PBI and BI are both conditional branches, and BI is in one of the
1550 /// successor blocks of PBI - PBI branches to BI.
1551 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1552 assert(PBI->isConditional() && BI->isConditional());
1553 BasicBlock *BB = BI->getParent();
1555 // If this block ends with a branch instruction, and if there is a
1556 // predecessor that ends on a branch of the same condition, make
1557 // this conditional branch redundant.
1558 if (PBI->getCondition() == BI->getCondition() &&
1559 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1560 // Okay, the outcome of this conditional branch is statically
1561 // knowable. If this block had a single pred, handle specially.
1562 if (BB->getSinglePredecessor()) {
1563 // Turn this into a branch on constant.
1564 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1565 BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
1566 return true; // Nuke the branch on constant.
1569 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1570 // in the constant and simplify the block result. Subsequent passes of
1571 // simplifycfg will thread the block.
1572 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1573 PHINode *NewPN = PHINode::Create(Type::Int1Ty,
1574 BI->getCondition()->getName() + ".pr",
1576 // Okay, we're going to insert the PHI node. Since PBI is not the only
1577 // predecessor, compute the PHI'd conditional value for all of the preds.
1578 // Any predecessor where the condition is not computable we keep symbolic.
1579 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1580 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1581 PBI != BI && PBI->isConditional() &&
1582 PBI->getCondition() == BI->getCondition() &&
1583 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1584 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1585 NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
1588 NewPN->addIncoming(BI->getCondition(), *PI);
1591 BI->setCondition(NewPN);
1596 // If this is a conditional branch in an empty block, and if any
1597 // predecessors is a conditional branch to one of our destinations,
1598 // fold the conditions into logical ops and one cond br.
1599 BasicBlock::iterator BBI = BB->begin();
1600 // Ignore dbg intrinsics.
1601 while (isa<DbgInfoIntrinsic>(BBI))
1607 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1612 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1614 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1615 PBIOp = 0, BIOp = 1;
1616 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1617 PBIOp = 1, BIOp = 0;
1618 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1623 // Check to make sure that the other destination of this branch
1624 // isn't BB itself. If so, this is an infinite loop that will
1625 // keep getting unwound.
1626 if (PBI->getSuccessor(PBIOp) == BB)
1629 // Do not perform this transformation if it would require
1630 // insertion of a large number of select instructions. For targets
1631 // without predication/cmovs, this is a big pessimization.
1632 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1634 unsigned NumPhis = 0;
1635 for (BasicBlock::iterator II = CommonDest->begin();
1636 isa<PHINode>(II); ++II, ++NumPhis)
1637 if (NumPhis > 2) // Disable this xform.
1640 // Finally, if everything is ok, fold the branches to logical ops.
1641 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1643 DOUT << "FOLDING BRs:" << *PBI->getParent()
1644 << "AND: " << *BI->getParent();
1647 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1648 // branch in it, where one edge (OtherDest) goes back to itself but the other
1649 // exits. We don't *know* that the program avoids the infinite loop
1650 // (even though that seems likely). If we do this xform naively, we'll end up
1651 // recursively unpeeling the loop. Since we know that (after the xform is
1652 // done) that the block *is* infinite if reached, we just make it an obviously
1653 // infinite loop with no cond branch.
1654 if (OtherDest == BB) {
1655 // Insert it at the end of the function, because it's either code,
1656 // or it won't matter if it's hot. :)
1657 BasicBlock *InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
1658 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1659 OtherDest = InfLoopBlock;
1662 DOUT << *PBI->getParent()->getParent();
1664 // BI may have other predecessors. Because of this, we leave
1665 // it alone, but modify PBI.
1667 // Make sure we get to CommonDest on True&True directions.
1668 Value *PBICond = PBI->getCondition();
1670 PBICond = BinaryOperator::CreateNot(PBICond,
1671 PBICond->getName()+".not",
1673 Value *BICond = BI->getCondition();
1675 BICond = BinaryOperator::CreateNot(BICond,
1676 BICond->getName()+".not",
1678 // Merge the conditions.
1679 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1681 // Modify PBI to branch on the new condition to the new dests.
1682 PBI->setCondition(Cond);
1683 PBI->setSuccessor(0, CommonDest);
1684 PBI->setSuccessor(1, OtherDest);
1686 // OtherDest may have phi nodes. If so, add an entry from PBI's
1687 // block that are identical to the entries for BI's block.
1689 for (BasicBlock::iterator II = OtherDest->begin();
1690 (PN = dyn_cast<PHINode>(II)); ++II) {
1691 Value *V = PN->getIncomingValueForBlock(BB);
1692 PN->addIncoming(V, PBI->getParent());
1695 // We know that the CommonDest already had an edge from PBI to
1696 // it. If it has PHIs though, the PHIs may have different
1697 // entries for BB and PBI's BB. If so, insert a select to make
1699 for (BasicBlock::iterator II = CommonDest->begin();
1700 (PN = dyn_cast<PHINode>(II)); ++II) {
1701 Value *BIV = PN->getIncomingValueForBlock(BB);
1702 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1703 Value *PBIV = PN->getIncomingValue(PBBIdx);
1705 // Insert a select in PBI to pick the right value.
1706 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1707 PBIV->getName()+".mux", PBI);
1708 PN->setIncomingValue(PBBIdx, NV);
1712 DOUT << "INTO: " << *PBI->getParent();
1714 DOUT << *PBI->getParent()->getParent();
1716 // This basic block is probably dead. We know it has at least
1717 // one fewer predecessor.
1723 /// ConstantIntOrdering - This class implements a stable ordering of constant
1724 /// integers that does not depend on their address. This is important for
1725 /// applications that sort ConstantInt's to ensure uniqueness.
1726 struct ConstantIntOrdering {
1727 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
1728 return LHS->getValue().ult(RHS->getValue());
1733 /// SimplifyCFG - This function is used to do simplification of a CFG. For
1734 /// example, it adjusts branches to branches to eliminate the extra hop, it
1735 /// eliminates unreachable basic blocks, and does other "peephole" optimization
1736 /// of the CFG. It returns true if a modification was made.
1738 /// WARNING: The entry node of a function may not be simplified.
1740 bool llvm::SimplifyCFG(BasicBlock *BB) {
1741 bool Changed = false;
1742 Function *M = BB->getParent();
1744 assert(BB && BB->getParent() && "Block not embedded in function!");
1745 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1746 assert(&BB->getParent()->getEntryBlock() != BB &&
1747 "Can't Simplify entry block!");
1749 // Remove basic blocks that have no predecessors... or that just have themself
1750 // as a predecessor. These are unreachable.
1751 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1752 DOUT << "Removing BB: \n" << *BB;
1753 DeleteDeadBlock(BB);
1757 // Check to see if we can constant propagate this terminator instruction
1759 Changed |= ConstantFoldTerminator(BB);
1761 // If there is a trivial two-entry PHI node in this basic block, and we can
1762 // eliminate it, do so now.
1763 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1764 if (PN->getNumIncomingValues() == 2)
1765 Changed |= FoldTwoEntryPHINode(PN);
1767 // If this is a returning block with only PHI nodes in it, fold the return
1768 // instruction into any unconditional branch predecessors.
1770 // If any predecessor is a conditional branch that just selects among
1771 // different return values, fold the replace the branch/return with a select
1773 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1774 if (isTerminatorFirstRelevantInsn(BB, BB->getTerminator())) {
1775 // Find predecessors that end with branches.
1776 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1777 SmallVector<BranchInst*, 8> CondBranchPreds;
1778 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1779 TerminatorInst *PTI = (*PI)->getTerminator();
1780 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1781 if (BI->isUnconditional())
1782 UncondBranchPreds.push_back(*PI);
1784 CondBranchPreds.push_back(BI);
1788 // If we found some, do the transformation!
1789 if (!UncondBranchPreds.empty() && !DisableXForm) {
1790 while (!UncondBranchPreds.empty()) {
1791 BasicBlock *Pred = UncondBranchPreds.back();
1792 DOUT << "FOLDING: " << *BB
1793 << "INTO UNCOND BRANCH PRED: " << *Pred;
1794 UncondBranchPreds.pop_back();
1795 Instruction *UncondBranch = Pred->getTerminator();
1796 // Clone the return and add it to the end of the predecessor.
1797 Instruction *NewRet = RI->clone();
1798 Pred->getInstList().push_back(NewRet);
1800 BasicBlock::iterator BBI = RI;
1801 if (BBI != BB->begin()) {
1802 // Move region end info into the predecessor.
1803 if (DbgRegionEndInst *DREI = dyn_cast<DbgRegionEndInst>(--BBI))
1804 DREI->moveBefore(NewRet);
1807 // If the return instruction returns a value, and if the value was a
1808 // PHI node in "BB", propagate the right value into the return.
1809 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1811 if (PHINode *PN = dyn_cast<PHINode>(*i))
1812 if (PN->getParent() == BB)
1813 *i = PN->getIncomingValueForBlock(Pred);
1815 // Update any PHI nodes in the returning block to realize that we no
1816 // longer branch to them.
1817 BB->removePredecessor(Pred);
1818 Pred->getInstList().erase(UncondBranch);
1821 // If we eliminated all predecessors of the block, delete the block now.
1822 if (pred_begin(BB) == pred_end(BB))
1823 // We know there are no successors, so just nuke the block.
1824 M->getBasicBlockList().erase(BB);
1829 // Check out all of the conditional branches going to this return
1830 // instruction. If any of them just select between returns, change the
1831 // branch itself into a select/return pair.
1832 while (!CondBranchPreds.empty()) {
1833 BranchInst *BI = CondBranchPreds.back();
1834 CondBranchPreds.pop_back();
1836 // Check to see if the non-BB successor is also a return block.
1837 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1838 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1839 SimplifyCondBranchToTwoReturns(BI))
1843 } else if (isa<UnwindInst>(BB->begin())) {
1844 // Check to see if the first instruction in this block is just an unwind.
1845 // If so, replace any invoke instructions which use this as an exception
1846 // destination with call instructions, and any unconditional branch
1847 // predecessor with an unwind.
1849 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1850 while (!Preds.empty()) {
1851 BasicBlock *Pred = Preds.back();
1852 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1853 if (BI->isUnconditional()) {
1854 Pred->getInstList().pop_back(); // nuke uncond branch
1855 new UnwindInst(Pred); // Use unwind.
1858 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1859 if (II->getUnwindDest() == BB) {
1860 // Insert a new branch instruction before the invoke, because this
1861 // is now a fall through...
1862 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1863 Pred->getInstList().remove(II); // Take out of symbol table
1865 // Insert the call now...
1866 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1867 CallInst *CI = CallInst::Create(II->getCalledValue(),
1868 Args.begin(), Args.end(),
1870 CI->setCallingConv(II->getCallingConv());
1871 CI->setAttributes(II->getAttributes());
1872 // If the invoke produced a value, the Call now does instead
1873 II->replaceAllUsesWith(CI);
1881 // If this block is now dead, remove it.
1882 if (pred_begin(BB) == pred_end(BB)) {
1883 // We know there are no successors, so just nuke the block.
1884 M->getBasicBlockList().erase(BB);
1888 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1889 if (isValueEqualityComparison(SI)) {
1890 // If we only have one predecessor, and if it is a branch on this value,
1891 // see if that predecessor totally determines the outcome of this switch.
1892 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1893 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1894 return SimplifyCFG(BB) || 1;
1896 // If the block only contains the switch, see if we can fold the block
1897 // away into any preds.
1898 BasicBlock::iterator BBI = BB->begin();
1899 // Ignore dbg intrinsics.
1900 while (isa<DbgInfoIntrinsic>(BBI))
1903 if (FoldValueComparisonIntoPredecessors(SI))
1904 return SimplifyCFG(BB) || 1;
1906 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1907 if (BI->isUnconditional()) {
1908 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1910 BasicBlock *Succ = BI->getSuccessor(0);
1911 // Ignore dbg intrinsics.
1912 while (isa<DbgInfoIntrinsic>(BBI))
1914 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1915 Succ != BB) // Don't hurt infinite loops!
1916 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1919 } else { // Conditional branch
1920 if (isValueEqualityComparison(BI)) {
1921 // If we only have one predecessor, and if it is a branch on this value,
1922 // see if that predecessor totally determines the outcome of this
1924 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1925 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1926 return SimplifyCFG(BB) || 1;
1928 // This block must be empty, except for the setcond inst, if it exists.
1929 // Ignore dbg intrinsics.
1930 BasicBlock::iterator I = BB->begin();
1931 // Ignore dbg intrinsics.
1932 while (isa<DbgInfoIntrinsic>(I))
1935 if (FoldValueComparisonIntoPredecessors(BI))
1936 return SimplifyCFG(BB) | true;
1937 } else if (&*I == cast<Instruction>(BI->getCondition())){
1939 // Ignore dbg intrinsics.
1940 while (isa<DbgInfoIntrinsic>(I))
1943 if (FoldValueComparisonIntoPredecessors(BI))
1944 return SimplifyCFG(BB) | true;
1949 // If this is a branch on a phi node in the current block, thread control
1950 // through this block if any PHI node entries are constants.
1951 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1952 if (PN->getParent() == BI->getParent())
1953 if (FoldCondBranchOnPHI(BI))
1954 return SimplifyCFG(BB) | true;
1956 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1957 // branches to us and one of our successors, fold the setcc into the
1958 // predecessor and use logical operations to pick the right destination.
1959 if (FoldBranchToCommonDest(BI))
1960 return SimplifyCFG(BB) | 1;
1963 // Scan predecessor blocks for conditional branches.
1964 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1965 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1966 if (PBI != BI && PBI->isConditional())
1967 if (SimplifyCondBranchToCondBranch(PBI, BI))
1968 return SimplifyCFG(BB) | true;
1970 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1971 // If there are any instructions immediately before the unreachable that can
1972 // be removed, do so.
1973 Instruction *Unreachable = BB->getTerminator();
1974 while (Unreachable != BB->begin()) {
1975 BasicBlock::iterator BBI = Unreachable;
1977 // Do not delete instructions that can have side effects, like calls
1978 // (which may never return) and volatile loads and stores.
1979 if (isa<CallInst>(BBI)) break;
1981 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
1982 if (SI->isVolatile())
1985 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
1986 if (LI->isVolatile())
1989 // Delete this instruction
1990 BB->getInstList().erase(BBI);
1994 // If the unreachable instruction is the first in the block, take a gander
1995 // at all of the predecessors of this instruction, and simplify them.
1996 if (&BB->front() == Unreachable) {
1997 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1998 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1999 TerminatorInst *TI = Preds[i]->getTerminator();
2001 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2002 if (BI->isUnconditional()) {
2003 if (BI->getSuccessor(0) == BB) {
2004 new UnreachableInst(TI);
2005 TI->eraseFromParent();
2009 if (BI->getSuccessor(0) == BB) {
2010 BranchInst::Create(BI->getSuccessor(1), BI);
2011 EraseTerminatorInstAndDCECond(BI);
2012 } else if (BI->getSuccessor(1) == BB) {
2013 BranchInst::Create(BI->getSuccessor(0), BI);
2014 EraseTerminatorInstAndDCECond(BI);
2018 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2019 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2020 if (SI->getSuccessor(i) == BB) {
2021 BB->removePredecessor(SI->getParent());
2026 // If the default value is unreachable, figure out the most popular
2027 // destination and make it the default.
2028 if (SI->getSuccessor(0) == BB) {
2029 std::map<BasicBlock*, unsigned> Popularity;
2030 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2031 Popularity[SI->getSuccessor(i)]++;
2033 // Find the most popular block.
2034 unsigned MaxPop = 0;
2035 BasicBlock *MaxBlock = 0;
2036 for (std::map<BasicBlock*, unsigned>::iterator
2037 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2038 if (I->second > MaxPop) {
2040 MaxBlock = I->first;
2044 // Make this the new default, allowing us to delete any explicit
2046 SI->setSuccessor(0, MaxBlock);
2049 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2051 if (isa<PHINode>(MaxBlock->begin()))
2052 for (unsigned i = 0; i != MaxPop-1; ++i)
2053 MaxBlock->removePredecessor(SI->getParent());
2055 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2056 if (SI->getSuccessor(i) == MaxBlock) {
2062 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2063 if (II->getUnwindDest() == BB) {
2064 // Convert the invoke to a call instruction. This would be a good
2065 // place to note that the call does not throw though.
2066 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2067 II->removeFromParent(); // Take out of symbol table
2069 // Insert the call now...
2070 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
2071 CallInst *CI = CallInst::Create(II->getCalledValue(),
2072 Args.begin(), Args.end(),
2074 CI->setCallingConv(II->getCallingConv());
2075 CI->setAttributes(II->getAttributes());
2076 // If the invoke produced a value, the Call does now instead.
2077 II->replaceAllUsesWith(CI);
2084 // If this block is now dead, remove it.
2085 if (pred_begin(BB) == pred_end(BB)) {
2086 // We know there are no successors, so just nuke the block.
2087 M->getBasicBlockList().erase(BB);
2093 // Merge basic blocks into their predecessor if there is only one distinct
2094 // pred, and if there is only one distinct successor of the predecessor, and
2095 // if there are no PHI nodes.
2097 if (MergeBlockIntoPredecessor(BB))
2100 // Otherwise, if this block only has a single predecessor, and if that block
2101 // is a conditional branch, see if we can hoist any code from this block up
2102 // into our predecessor.
2103 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2104 BasicBlock *OnlyPred = *PI++;
2105 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2106 if (*PI != OnlyPred) {
2107 OnlyPred = 0; // There are multiple different predecessors...
2112 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2113 if (BI->isConditional()) {
2114 // Get the other block.
2115 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2116 PI = pred_begin(OtherBB);
2119 if (PI == pred_end(OtherBB)) {
2120 // We have a conditional branch to two blocks that are only reachable
2121 // from the condbr. We know that the condbr dominates the two blocks,
2122 // so see if there is any identical code in the "then" and "else"
2123 // blocks. If so, we can hoist it up to the branching block.
2124 Changed |= HoistThenElseCodeToIf(BI);
2126 BasicBlock* OnlySucc = NULL;
2127 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2131 else if (*SI != OnlySucc) {
2132 OnlySucc = 0; // There are multiple distinct successors!
2137 if (OnlySucc == OtherBB) {
2138 // If BB's only successor is the other successor of the predecessor,
2139 // i.e. a triangle, see if we can hoist any code from this block up
2140 // to the "if" block.
2141 Changed |= SpeculativelyExecuteBB(BI, BB);
2146 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2147 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2148 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2149 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2150 Instruction *Cond = cast<Instruction>(BI->getCondition());
2151 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2152 // 'setne's and'ed together, collect them.
2154 std::vector<ConstantInt*> Values;
2155 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2156 if (CompVal && CompVal->getType()->isInteger()) {
2157 // There might be duplicate constants in the list, which the switch
2158 // instruction can't handle, remove them now.
2159 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2160 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2162 // Figure out which block is which destination.
2163 BasicBlock *DefaultBB = BI->getSuccessor(1);
2164 BasicBlock *EdgeBB = BI->getSuccessor(0);
2165 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2167 // Create the new switch instruction now.
2168 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2171 // Add all of the 'cases' to the switch instruction.
2172 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2173 New->addCase(Values[i], EdgeBB);
2175 // We added edges from PI to the EdgeBB. As such, if there were any
2176 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2177 // the number of edges added.
2178 for (BasicBlock::iterator BBI = EdgeBB->begin();
2179 isa<PHINode>(BBI); ++BBI) {
2180 PHINode *PN = cast<PHINode>(BBI);
2181 Value *InVal = PN->getIncomingValueForBlock(*PI);
2182 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2183 PN->addIncoming(InVal, *PI);
2186 // Erase the old branch instruction.
2187 EraseTerminatorInstAndDCECond(BI);