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/GlobalVariable.h"
22 #include "llvm/Support/CFG.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Analysis/ConstantFolding.h"
25 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/ADT/SmallPtrSet.h"
28 #include "llvm/ADT/Statistic.h"
35 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
37 /// SafeToMergeTerminators - Return true if it is safe to merge these two
38 /// terminator instructions together.
40 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
41 if (SI1 == SI2) return false; // Can't merge with self!
43 // It is not safe to merge these two switch instructions if they have a common
44 // successor, and if that successor has a PHI node, and if *that* PHI node has
45 // conflicting incoming values from the two switch blocks.
46 BasicBlock *SI1BB = SI1->getParent();
47 BasicBlock *SI2BB = SI2->getParent();
48 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
50 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
51 if (SI1Succs.count(*I))
52 for (BasicBlock::iterator BBI = (*I)->begin();
53 isa<PHINode>(BBI); ++BBI) {
54 PHINode *PN = cast<PHINode>(BBI);
55 if (PN->getIncomingValueForBlock(SI1BB) !=
56 PN->getIncomingValueForBlock(SI2BB))
63 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
64 /// now be entries in it from the 'NewPred' block. The values that will be
65 /// flowing into the PHI nodes will be the same as those coming in from
66 /// ExistPred, an existing predecessor of Succ.
67 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
68 BasicBlock *ExistPred) {
69 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
70 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
71 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
74 for (BasicBlock::iterator I = Succ->begin();
75 (PN = dyn_cast<PHINode>(I)); ++I)
76 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
79 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
80 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
82 /// Assumption: Succ is the single successor for BB.
84 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
85 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
87 DOUT << "Looking to fold " << BB->getNameStart() << " into "
88 << Succ->getNameStart() << "\n";
89 // Shortcut, if there is only a single predecessor it must be BB and merging
91 if (Succ->getSinglePredecessor()) return true;
93 typedef SmallPtrSet<Instruction*, 16> InstrSet;
96 // Make a list of all phi nodes in BB
97 BasicBlock::iterator BBI = BB->begin();
98 while (isa<PHINode>(*BBI)) BBPHIs.insert(BBI++);
100 // Make a list of the predecessors of BB
101 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
102 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
104 // Use that list to make another list of common predecessors of BB and Succ
105 BlockSet CommonPreds;
106 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
108 if (BBPreds.count(*PI))
109 CommonPreds.insert(*PI);
111 // Shortcut, if there are no common predecessors, merging is always safe
112 if (CommonPreds.empty())
115 // Look at all the phi nodes in Succ, to see if they present a conflict when
116 // merging these blocks
117 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
118 PHINode *PN = cast<PHINode>(I);
120 // If the incoming value from BB is again a PHINode in
121 // BB which has the same incoming value for *PI as PN does, we can
122 // merge the phi nodes and then the blocks can still be merged
123 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
124 if (BBPN && BBPN->getParent() == BB) {
125 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
127 if (BBPN->getIncomingValueForBlock(*PI)
128 != PN->getIncomingValueForBlock(*PI)) {
129 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
130 << Succ->getNameStart() << " is conflicting with "
131 << BBPN->getNameStart() << " with regard to common predecessor "
132 << (*PI)->getNameStart() << "\n";
136 // Remove this phinode from the list of phis in BB, since it has been
140 Value* Val = PN->getIncomingValueForBlock(BB);
141 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
143 // See if the incoming value for the common predecessor is equal to the
144 // one for BB, in which case this phi node will not prevent the merging
146 if (Val != PN->getIncomingValueForBlock(*PI)) {
147 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
148 << Succ->getNameStart() << " is conflicting with regard to common "
149 << "predecessor " << (*PI)->getNameStart() << "\n";
156 // If there are any other phi nodes in BB that don't have a phi node in Succ
157 // to merge with, they must be moved to Succ completely. However, for any
158 // predecessors of Succ, branches will be added to the phi node that just
159 // point to itself. So, for any common predecessors, this must not cause
161 for (InstrSet::iterator I = BBPHIs.begin(), E = BBPHIs.end();
163 PHINode *PN = cast<PHINode>(*I);
164 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
166 if (PN->getIncomingValueForBlock(*PI) != PN) {
167 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
168 << BB->getNameStart() << " is conflicting with regard to common "
169 << "predecessor " << (*PI)->getNameStart() << "\n";
177 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
178 /// branch to Succ, and contains no instructions other than PHI nodes and the
179 /// branch. If possible, eliminate BB.
180 static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
182 // Check to see if merging these blocks would cause conflicts for any of the
183 // phi nodes in BB or Succ. If not, we can safely merge.
184 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
186 DOUT << "Killing Trivial BB: \n" << *BB;
188 if (isa<PHINode>(Succ->begin())) {
189 // If there is more than one pred of succ, and there are PHI nodes in
190 // the successor, then we need to add incoming edges for the PHI nodes
192 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
194 // Loop over all of the PHI nodes in the successor of BB.
195 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
196 PHINode *PN = cast<PHINode>(I);
197 Value *OldVal = PN->removeIncomingValue(BB, false);
198 assert(OldVal && "No entry in PHI for Pred BB!");
200 // If this incoming value is one of the PHI nodes in BB, the new entries
201 // in the PHI node are the entries from the old PHI.
202 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
203 PHINode *OldValPN = cast<PHINode>(OldVal);
204 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
205 // Note that, since we are merging phi nodes and BB and Succ might
206 // have common predecessors, we could end up with a phi node with
207 // identical incoming branches. This will be cleaned up later (and
208 // will trigger asserts if we try to clean it up now, without also
209 // simplifying the corresponding conditional branch).
210 PN->addIncoming(OldValPN->getIncomingValue(i),
211 OldValPN->getIncomingBlock(i));
213 // Add an incoming value for each of the new incoming values.
214 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
215 PN->addIncoming(OldVal, BBPreds[i]);
220 if (isa<PHINode>(&BB->front())) {
221 SmallVector<BasicBlock*, 16>
222 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
224 // Move all PHI nodes in BB to Succ if they are alive, otherwise
226 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
227 if (PN->use_empty()) {
228 // Just remove the dead phi. This happens if Succ's PHIs were the only
229 // users of the PHI nodes.
230 PN->eraseFromParent();
234 // The instruction is alive, so this means that BB must dominate all
235 // predecessors of Succ (Since all uses of the PN are after its
236 // definition, so in Succ or a block dominated by Succ. If a predecessor
237 // of Succ would not be dominated by BB, PN would violate the def before
238 // use SSA demand). Therefore, we can simply move the phi node to the
240 Succ->getInstList().splice(Succ->begin(),
241 BB->getInstList(), BB->begin());
243 // We need to add new entries for the PHI node to account for
244 // predecessors of Succ that the PHI node does not take into
245 // account. At this point, since we know that BB dominated succ and all
246 // of its predecessors, this means that we should any newly added
247 // incoming edges should use the PHI node itself as the value for these
248 // edges, because they are loop back edges.
249 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
250 if (OldSuccPreds[i] != BB)
251 PN->addIncoming(PN, OldSuccPreds[i]);
255 // Everything that jumped to BB now goes to Succ.
256 BB->replaceAllUsesWith(Succ);
257 if (!Succ->hasName()) Succ->takeName(BB);
258 BB->eraseFromParent(); // Delete the old basic block.
262 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
263 /// presumably PHI nodes in it), check to see if the merge at this block is due
264 /// to an "if condition". If so, return the boolean condition that determines
265 /// which entry into BB will be taken. Also, return by references the block
266 /// that will be entered from if the condition is true, and the block that will
267 /// be entered if the condition is false.
270 static Value *GetIfCondition(BasicBlock *BB,
271 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
272 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
273 "Function can only handle blocks with 2 predecessors!");
274 BasicBlock *Pred1 = *pred_begin(BB);
275 BasicBlock *Pred2 = *++pred_begin(BB);
277 // We can only handle branches. Other control flow will be lowered to
278 // branches if possible anyway.
279 if (!isa<BranchInst>(Pred1->getTerminator()) ||
280 !isa<BranchInst>(Pred2->getTerminator()))
282 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
283 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
285 // Eliminate code duplication by ensuring that Pred1Br is conditional if
287 if (Pred2Br->isConditional()) {
288 // If both branches are conditional, we don't have an "if statement". In
289 // reality, we could transform this case, but since the condition will be
290 // required anyway, we stand no chance of eliminating it, so the xform is
291 // probably not profitable.
292 if (Pred1Br->isConditional())
295 std::swap(Pred1, Pred2);
296 std::swap(Pred1Br, Pred2Br);
299 if (Pred1Br->isConditional()) {
300 // If we found a conditional branch predecessor, make sure that it branches
301 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
302 if (Pred1Br->getSuccessor(0) == BB &&
303 Pred1Br->getSuccessor(1) == Pred2) {
306 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
307 Pred1Br->getSuccessor(1) == BB) {
311 // We know that one arm of the conditional goes to BB, so the other must
312 // go somewhere unrelated, and this must not be an "if statement".
316 // The only thing we have to watch out for here is to make sure that Pred2
317 // doesn't have incoming edges from other blocks. If it does, the condition
318 // doesn't dominate BB.
319 if (++pred_begin(Pred2) != pred_end(Pred2))
322 return Pred1Br->getCondition();
325 // Ok, if we got here, both predecessors end with an unconditional branch to
326 // BB. Don't panic! If both blocks only have a single (identical)
327 // predecessor, and THAT is a conditional branch, then we're all ok!
328 if (pred_begin(Pred1) == pred_end(Pred1) ||
329 ++pred_begin(Pred1) != pred_end(Pred1) ||
330 pred_begin(Pred2) == pred_end(Pred2) ||
331 ++pred_begin(Pred2) != pred_end(Pred2) ||
332 *pred_begin(Pred1) != *pred_begin(Pred2))
335 // Otherwise, if this is a conditional branch, then we can use it!
336 BasicBlock *CommonPred = *pred_begin(Pred1);
337 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
338 assert(BI->isConditional() && "Two successors but not conditional?");
339 if (BI->getSuccessor(0) == Pred1) {
346 return BI->getCondition();
351 /// DominatesMergePoint - If we have a merge point of an "if condition" as
352 /// accepted above, return true if the specified value dominates the block. We
353 /// don't handle the true generality of domination here, just a special case
354 /// which works well enough for us.
356 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
357 /// see if V (which must be an instruction) is cheap to compute and is
358 /// non-trapping. If both are true, the instruction is inserted into the set
359 /// and true is returned.
360 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
361 std::set<Instruction*> *AggressiveInsts) {
362 Instruction *I = dyn_cast<Instruction>(V);
364 // Non-instructions all dominate instructions, but not all constantexprs
365 // can be executed unconditionally.
366 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
371 BasicBlock *PBB = I->getParent();
373 // We don't want to allow weird loops that might have the "if condition" in
374 // the bottom of this block.
375 if (PBB == BB) return false;
377 // If this instruction is defined in a block that contains an unconditional
378 // branch to BB, then it must be in the 'conditional' part of the "if
380 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
381 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
382 if (!AggressiveInsts) return false;
383 // Okay, it looks like the instruction IS in the "condition". Check to
384 // see if its a cheap instruction to unconditionally compute, and if it
385 // only uses stuff defined outside of the condition. If so, hoist it out.
386 switch (I->getOpcode()) {
387 default: return false; // Cannot hoist this out safely.
388 case Instruction::Load: {
389 // We can hoist loads that are non-volatile and obviously cannot trap.
390 if (cast<LoadInst>(I)->isVolatile())
392 // FIXME: A computation of a constant can trap!
393 if (!isa<AllocaInst>(I->getOperand(0)) &&
394 !isa<Constant>(I->getOperand(0)))
396 // External weak globals may have address 0, so we can't load them.
397 Value *V2 = I->getOperand(0)->getUnderlyingObject();
399 GlobalVariable* GV = dyn_cast<GlobalVariable>(V2);
400 if (GV && GV->hasExternalWeakLinkage())
403 // Finally, we have to check to make sure there are no instructions
404 // before the load in its basic block, as we are going to hoist the loop
405 // out to its predecessor.
406 BasicBlock::iterator IP = PBB->begin();
407 while (isa<DbgInfoIntrinsic>(IP))
409 if (IP != BasicBlock::iterator(I))
413 case Instruction::Add:
414 case Instruction::Sub:
415 case Instruction::And:
416 case Instruction::Or:
417 case Instruction::Xor:
418 case Instruction::Shl:
419 case Instruction::LShr:
420 case Instruction::AShr:
421 case Instruction::ICmp:
422 break; // These are all cheap and non-trapping instructions.
425 // Okay, we can only really hoist these out if their operands are not
426 // defined in the conditional region.
427 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
428 if (!DominatesMergePoint(*i, BB, 0))
430 // Okay, it's safe to do this! Remember this instruction.
431 AggressiveInsts->insert(I);
437 /// GatherConstantSetEQs - Given a potentially 'or'd together collection of
438 /// icmp_eq instructions that compare a value against a constant, return the
439 /// value being compared, and stick the constant into the Values vector.
440 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
441 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
442 if (Inst->getOpcode() == Instruction::ICmp &&
443 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
444 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
446 return Inst->getOperand(0);
447 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
449 return Inst->getOperand(1);
451 } else if (Inst->getOpcode() == Instruction::Or) {
452 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
453 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
461 /// GatherConstantSetNEs - Given a potentially 'and'd together collection of
462 /// setne instructions that compare a value against a constant, return the value
463 /// being compared, and stick the constant into the Values vector.
464 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
465 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
466 if (Inst->getOpcode() == Instruction::ICmp &&
467 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
468 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
470 return Inst->getOperand(0);
471 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
473 return Inst->getOperand(1);
475 } else if (Inst->getOpcode() == Instruction::And) {
476 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
477 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
485 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
486 /// bunch of comparisons of one value against constants, return the value and
487 /// the constants being compared.
488 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
489 std::vector<ConstantInt*> &Values) {
490 if (Cond->getOpcode() == Instruction::Or) {
491 CompVal = GatherConstantSetEQs(Cond, Values);
493 // Return true to indicate that the condition is true if the CompVal is
494 // equal to one of the constants.
496 } else if (Cond->getOpcode() == Instruction::And) {
497 CompVal = GatherConstantSetNEs(Cond, Values);
499 // Return false to indicate that the condition is false if the CompVal is
500 // equal to one of the constants.
506 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
507 Instruction* Cond = 0;
508 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
509 Cond = dyn_cast<Instruction>(SI->getCondition());
510 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
511 if (BI->isConditional())
512 Cond = dyn_cast<Instruction>(BI->getCondition());
515 TI->eraseFromParent();
516 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
519 /// isValueEqualityComparison - Return true if the specified terminator checks
520 /// to see if a value is equal to constant integer value.
521 static Value *isValueEqualityComparison(TerminatorInst *TI) {
522 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
523 // Do not permit merging of large switch instructions into their
524 // predecessors unless there is only one predecessor.
525 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
526 pred_end(SI->getParent())) > 128)
529 return SI->getCondition();
531 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
532 if (BI->isConditional() && BI->getCondition()->hasOneUse())
533 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
534 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
535 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
536 isa<ConstantInt>(ICI->getOperand(1)))
537 return ICI->getOperand(0);
541 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
542 /// decode all of the 'cases' that it represents and return the 'default' block.
544 GetValueEqualityComparisonCases(TerminatorInst *TI,
545 std::vector<std::pair<ConstantInt*,
546 BasicBlock*> > &Cases) {
547 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
548 Cases.reserve(SI->getNumCases());
549 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
550 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
551 return SI->getDefaultDest();
554 BranchInst *BI = cast<BranchInst>(TI);
555 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
556 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
557 BI->getSuccessor(ICI->getPredicate() ==
558 ICmpInst::ICMP_NE)));
559 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
563 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
564 /// in the list that match the specified block.
565 static void EliminateBlockCases(BasicBlock *BB,
566 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
567 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
568 if (Cases[i].second == BB) {
569 Cases.erase(Cases.begin()+i);
574 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
577 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
578 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
579 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
581 // Make V1 be smaller than V2.
582 if (V1->size() > V2->size())
585 if (V1->size() == 0) return false;
586 if (V1->size() == 1) {
588 ConstantInt *TheVal = (*V1)[0].first;
589 for (unsigned i = 0, e = V2->size(); i != e; ++i)
590 if (TheVal == (*V2)[i].first)
594 // Otherwise, just sort both lists and compare element by element.
595 std::sort(V1->begin(), V1->end());
596 std::sort(V2->begin(), V2->end());
597 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
598 while (i1 != e1 && i2 != e2) {
599 if ((*V1)[i1].first == (*V2)[i2].first)
601 if ((*V1)[i1].first < (*V2)[i2].first)
609 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
610 /// terminator instruction and its block is known to only have a single
611 /// predecessor block, check to see if that predecessor is also a value
612 /// comparison with the same value, and if that comparison determines the
613 /// outcome of this comparison. If so, simplify TI. This does a very limited
614 /// form of jump threading.
615 static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
617 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
618 if (!PredVal) return false; // Not a value comparison in predecessor.
620 Value *ThisVal = isValueEqualityComparison(TI);
621 assert(ThisVal && "This isn't a value comparison!!");
622 if (ThisVal != PredVal) return false; // Different predicates.
624 // Find out information about when control will move from Pred to TI's block.
625 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
626 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
628 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
630 // Find information about how control leaves this block.
631 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
632 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
633 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
635 // If TI's block is the default block from Pred's comparison, potentially
636 // simplify TI based on this knowledge.
637 if (PredDef == TI->getParent()) {
638 // If we are here, we know that the value is none of those cases listed in
639 // PredCases. If there are any cases in ThisCases that are in PredCases, we
641 if (ValuesOverlap(PredCases, ThisCases)) {
642 if (isa<BranchInst>(TI)) {
643 // Okay, one of the successors of this condbr is dead. Convert it to a
645 assert(ThisCases.size() == 1 && "Branch can only have one case!");
646 // Insert the new branch.
647 Instruction *NI = BranchInst::Create(ThisDef, TI);
649 // Remove PHI node entries for the dead edge.
650 ThisCases[0].second->removePredecessor(TI->getParent());
652 DOUT << "Threading pred instr: " << *Pred->getTerminator()
653 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
655 EraseTerminatorInstAndDCECond(TI);
659 SwitchInst *SI = cast<SwitchInst>(TI);
660 // Okay, TI has cases that are statically dead, prune them away.
661 SmallPtrSet<Constant*, 16> DeadCases;
662 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
663 DeadCases.insert(PredCases[i].first);
665 DOUT << "Threading pred instr: " << *Pred->getTerminator()
666 << "Through successor TI: " << *TI;
668 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
669 if (DeadCases.count(SI->getCaseValue(i))) {
670 SI->getSuccessor(i)->removePredecessor(TI->getParent());
674 DOUT << "Leaving: " << *TI << "\n";
680 // Otherwise, TI's block must correspond to some matched value. Find out
681 // which value (or set of values) this is.
682 ConstantInt *TIV = 0;
683 BasicBlock *TIBB = TI->getParent();
684 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
685 if (PredCases[i].second == TIBB) {
687 TIV = PredCases[i].first;
689 return false; // Cannot handle multiple values coming to this block.
691 assert(TIV && "No edge from pred to succ?");
693 // Okay, we found the one constant that our value can be if we get into TI's
694 // BB. Find out which successor will unconditionally be branched to.
695 BasicBlock *TheRealDest = 0;
696 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
697 if (ThisCases[i].first == TIV) {
698 TheRealDest = ThisCases[i].second;
702 // If not handled by any explicit cases, it is handled by the default case.
703 if (TheRealDest == 0) TheRealDest = ThisDef;
705 // Remove PHI node entries for dead edges.
706 BasicBlock *CheckEdge = TheRealDest;
707 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
708 if (*SI != CheckEdge)
709 (*SI)->removePredecessor(TIBB);
713 // Insert the new branch.
714 Instruction *NI = BranchInst::Create(TheRealDest, TI);
716 DOUT << "Threading pred instr: " << *Pred->getTerminator()
717 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
719 EraseTerminatorInstAndDCECond(TI);
726 /// ConstantIntOrdering - This class implements a stable ordering of constant
727 /// integers that does not depend on their address. This is important for
728 /// applications that sort ConstantInt's to ensure uniqueness.
729 struct ConstantIntOrdering {
730 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
731 return LHS->getValue().ult(RHS->getValue());
736 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
737 /// equality comparison instruction (either a switch or a branch on "X == c").
738 /// See if any of the predecessors of the terminator block are value comparisons
739 /// on the same value. If so, and if safe to do so, fold them together.
740 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
741 BasicBlock *BB = TI->getParent();
742 Value *CV = isValueEqualityComparison(TI); // CondVal
743 assert(CV && "Not a comparison?");
744 bool Changed = false;
746 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
747 while (!Preds.empty()) {
748 BasicBlock *Pred = Preds.pop_back_val();
750 // See if the predecessor is a comparison with the same value.
751 TerminatorInst *PTI = Pred->getTerminator();
752 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
754 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
755 // Figure out which 'cases' to copy from SI to PSI.
756 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
757 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
759 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
760 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
762 // Based on whether the default edge from PTI goes to BB or not, fill in
763 // PredCases and PredDefault with the new switch cases we would like to
765 SmallVector<BasicBlock*, 8> NewSuccessors;
767 if (PredDefault == BB) {
768 // If this is the default destination from PTI, only the edges in TI
769 // that don't occur in PTI, or that branch to BB will be activated.
770 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
771 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
772 if (PredCases[i].second != BB)
773 PTIHandled.insert(PredCases[i].first);
775 // The default destination is BB, we don't need explicit targets.
776 std::swap(PredCases[i], PredCases.back());
777 PredCases.pop_back();
781 // Reconstruct the new switch statement we will be building.
782 if (PredDefault != BBDefault) {
783 PredDefault->removePredecessor(Pred);
784 PredDefault = BBDefault;
785 NewSuccessors.push_back(BBDefault);
787 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
788 if (!PTIHandled.count(BBCases[i].first) &&
789 BBCases[i].second != BBDefault) {
790 PredCases.push_back(BBCases[i]);
791 NewSuccessors.push_back(BBCases[i].second);
795 // If this is not the default destination from PSI, only the edges
796 // in SI that occur in PSI with a destination of BB will be
798 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
799 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
800 if (PredCases[i].second == BB) {
801 PTIHandled.insert(PredCases[i].first);
802 std::swap(PredCases[i], PredCases.back());
803 PredCases.pop_back();
807 // Okay, now we know which constants were sent to BB from the
808 // predecessor. Figure out where they will all go now.
809 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
810 if (PTIHandled.count(BBCases[i].first)) {
811 // If this is one we are capable of getting...
812 PredCases.push_back(BBCases[i]);
813 NewSuccessors.push_back(BBCases[i].second);
814 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
817 // If there are any constants vectored to BB that TI doesn't handle,
818 // they must go to the default destination of TI.
819 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
821 E = PTIHandled.end(); I != E; ++I) {
822 PredCases.push_back(std::make_pair(*I, BBDefault));
823 NewSuccessors.push_back(BBDefault);
827 // Okay, at this point, we know which new successor Pred will get. Make
828 // sure we update the number of entries in the PHI nodes for these
830 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
831 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
833 // Now that the successors are updated, create the new Switch instruction.
834 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
835 PredCases.size(), PTI);
836 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
837 NewSI->addCase(PredCases[i].first, PredCases[i].second);
839 EraseTerminatorInstAndDCECond(PTI);
841 // Okay, last check. If BB is still a successor of PSI, then we must
842 // have an infinite loop case. If so, add an infinitely looping block
843 // to handle the case to preserve the behavior of the code.
844 BasicBlock *InfLoopBlock = 0;
845 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
846 if (NewSI->getSuccessor(i) == BB) {
847 if (InfLoopBlock == 0) {
848 // Insert it at the end of the function, because it's either code,
849 // or it won't matter if it's hot. :)
850 InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
851 BranchInst::Create(InfLoopBlock, InfLoopBlock);
853 NewSI->setSuccessor(i, InfLoopBlock);
862 // isSafeToHoistInvoke - If we would need to insert a select that uses the
863 // value of this invoke (comments in HoistThenElseCodeToIf explain why we
864 // would need to do this), we can't hoist the invoke, as there is nowhere
865 // to put the select in this case.
866 static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
867 Instruction *I1, Instruction *I2) {
868 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
870 for (BasicBlock::iterator BBI = SI->begin();
871 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
872 Value *BB1V = PN->getIncomingValueForBlock(BB1);
873 Value *BB2V = PN->getIncomingValueForBlock(BB2);
874 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
882 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
883 /// BB2, hoist any common code in the two blocks up into the branch block. The
884 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
885 static bool HoistThenElseCodeToIf(BranchInst *BI) {
886 // This does very trivial matching, with limited scanning, to find identical
887 // instructions in the two blocks. In particular, we don't want to get into
888 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
889 // such, we currently just scan for obviously identical instructions in an
891 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
892 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
894 BasicBlock::iterator BB1_Itr = BB1->begin();
895 BasicBlock::iterator BB2_Itr = BB2->begin();
897 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
898 while (isa<DbgInfoIntrinsic>(I1))
900 while (isa<DbgInfoIntrinsic>(I2))
902 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
903 !I1->isIdenticalTo(I2) ||
904 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
907 // If we get here, we can hoist at least one instruction.
908 BasicBlock *BIParent = BI->getParent();
911 // If we are hoisting the terminator instruction, don't move one (making a
912 // broken BB), instead clone it, and remove BI.
913 if (isa<TerminatorInst>(I1))
914 goto HoistTerminator;
916 // For a normal instruction, we just move one to right before the branch,
917 // then replace all uses of the other with the first. Finally, we remove
918 // the now redundant second instruction.
919 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
920 if (!I2->use_empty())
921 I2->replaceAllUsesWith(I1);
922 BB2->getInstList().erase(I2);
925 while (isa<DbgInfoIntrinsic>(I1))
928 while (isa<DbgInfoIntrinsic>(I2))
930 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
935 // It may not be possible to hoist an invoke.
936 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
939 // Okay, it is safe to hoist the terminator.
940 Instruction *NT = I1->clone();
941 BIParent->getInstList().insert(BI, NT);
942 if (NT->getType() != Type::VoidTy) {
943 I1->replaceAllUsesWith(NT);
944 I2->replaceAllUsesWith(NT);
948 // Hoisting one of the terminators from our successor is a great thing.
949 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
950 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
951 // nodes, so we insert select instruction to compute the final result.
952 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
953 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
955 for (BasicBlock::iterator BBI = SI->begin();
956 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
957 Value *BB1V = PN->getIncomingValueForBlock(BB1);
958 Value *BB2V = PN->getIncomingValueForBlock(BB2);
960 // These values do not agree. Insert a select instruction before NT
961 // that determines the right value.
962 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
964 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
965 BB1V->getName()+"."+BB2V->getName(), NT);
966 // Make the PHI node use the select for all incoming values for BB1/BB2
967 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
968 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
969 PN->setIncomingValue(i, SI);
974 // Update any PHI nodes in our new successors.
975 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
976 AddPredecessorToBlock(*SI, BIParent, BB1);
978 EraseTerminatorInstAndDCECond(BI);
982 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
983 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
984 /// (for now, restricted to a single instruction that's side effect free) from
985 /// the BB1 into the branch block to speculatively execute it.
986 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
987 // Only speculatively execution a single instruction (not counting the
988 // terminator) for now.
989 Instruction *HInst = NULL;
990 Instruction *Term = BB1->getTerminator();
991 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
993 Instruction *I = BBI;
995 if (isa<DbgInfoIntrinsic>(I)) continue;
996 if (I == Term) break;
1006 // Be conservative for now. FP select instruction can often be expensive.
1007 Value *BrCond = BI->getCondition();
1008 if (isa<Instruction>(BrCond) &&
1009 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
1012 // If BB1 is actually on the false edge of the conditional branch, remember
1013 // to swap the select operands later.
1014 bool Invert = false;
1015 if (BB1 != BI->getSuccessor(0)) {
1016 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
1023 // br i1 %t1, label %BB1, label %BB2
1032 // %t3 = select i1 %t1, %t2, %t3
1033 switch (HInst->getOpcode()) {
1034 default: return false; // Not safe / profitable to hoist.
1035 case Instruction::Add:
1036 case Instruction::Sub:
1037 // Not worth doing for vector ops.
1038 if (isa<VectorType>(HInst->getType()))
1041 case Instruction::And:
1042 case Instruction::Or:
1043 case Instruction::Xor:
1044 case Instruction::Shl:
1045 case Instruction::LShr:
1046 case Instruction::AShr:
1047 // Don't mess with vector operations.
1048 if (isa<VectorType>(HInst->getType()))
1050 break; // These are all cheap and non-trapping instructions.
1053 // If the instruction is obviously dead, don't try to predicate it.
1054 if (HInst->use_empty()) {
1055 HInst->eraseFromParent();
1059 // Can we speculatively execute the instruction? And what is the value
1060 // if the condition is false? Consider the phi uses, if the incoming value
1061 // from the "if" block are all the same V, then V is the value of the
1062 // select if the condition is false.
1063 BasicBlock *BIParent = BI->getParent();
1064 SmallVector<PHINode*, 4> PHIUses;
1065 Value *FalseV = NULL;
1067 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1068 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
1070 // Ignore any user that is not a PHI node in BB2. These can only occur in
1071 // unreachable blocks, because they would not be dominated by the instr.
1072 PHINode *PN = dyn_cast<PHINode>(UI);
1073 if (!PN || PN->getParent() != BB2)
1075 PHIUses.push_back(PN);
1077 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1080 else if (FalseV != PHIV)
1081 return false; // Inconsistent value when condition is false.
1084 assert(FalseV && "Must have at least one user, and it must be a PHI");
1086 // Do not hoist the instruction if any of its operands are defined but not
1087 // used in this BB. The transformation will prevent the operand from
1088 // being sunk into the use block.
1089 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1091 Instruction *OpI = dyn_cast<Instruction>(*i);
1092 if (OpI && OpI->getParent() == BIParent &&
1093 !OpI->isUsedInBasicBlock(BIParent))
1097 // If we get here, we can hoist the instruction. Try to place it
1098 // before the icmp instruction preceding the conditional branch.
1099 BasicBlock::iterator InsertPos = BI;
1100 if (InsertPos != BIParent->begin())
1102 // Skip debug info between condition and branch.
1103 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1105 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1106 SmallPtrSet<Instruction *, 4> BB1Insns;
1107 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1108 BB1I != BB1E; ++BB1I)
1109 BB1Insns.insert(BB1I);
1110 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1112 Instruction *Use = cast<Instruction>(*UI);
1113 if (BB1Insns.count(Use)) {
1114 // If BrCond uses the instruction that place it just before
1115 // branch instruction.
1122 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1124 // Create a select whose true value is the speculatively executed value and
1125 // false value is the previously determined FalseV.
1128 SI = SelectInst::Create(BrCond, FalseV, HInst,
1129 FalseV->getName() + "." + HInst->getName(), BI);
1131 SI = SelectInst::Create(BrCond, HInst, FalseV,
1132 HInst->getName() + "." + FalseV->getName(), BI);
1134 // Make the PHI node use the select for all incoming values for "then" and
1136 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1137 PHINode *PN = PHIUses[i];
1138 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1139 if (PN->getIncomingBlock(j) == BB1 ||
1140 PN->getIncomingBlock(j) == BIParent)
1141 PN->setIncomingValue(j, SI);
1148 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1149 /// across this block.
1150 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1151 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1154 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1155 if (isa<DbgInfoIntrinsic>(BBI))
1157 if (Size > 10) return false; // Don't clone large BB's.
1160 // We can only support instructions that do not define values that are
1161 // live outside of the current basic block.
1162 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1164 Instruction *U = cast<Instruction>(*UI);
1165 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1168 // Looks ok, continue checking.
1174 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1175 /// that is defined in the same block as the branch and if any PHI entries are
1176 /// constants, thread edges corresponding to that entry to be branches to their
1177 /// ultimate destination.
1178 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1179 BasicBlock *BB = BI->getParent();
1180 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1181 // NOTE: we currently cannot transform this case if the PHI node is used
1182 // outside of the block.
1183 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1186 // Degenerate case of a single entry PHI.
1187 if (PN->getNumIncomingValues() == 1) {
1188 FoldSingleEntryPHINodes(PN->getParent());
1192 // Now we know that this block has multiple preds and two succs.
1193 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1195 // Okay, this is a simple enough basic block. See if any phi values are
1197 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1199 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1200 CB->getType() == Type::Int1Ty) {
1201 // Okay, we now know that all edges from PredBB should be revectored to
1202 // branch to RealDest.
1203 BasicBlock *PredBB = PN->getIncomingBlock(i);
1204 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1206 if (RealDest == BB) continue; // Skip self loops.
1208 // The dest block might have PHI nodes, other predecessors and other
1209 // difficult cases. Instead of being smart about this, just insert a new
1210 // block that jumps to the destination block, effectively splitting
1211 // the edge we are about to create.
1212 BasicBlock *EdgeBB = BasicBlock::Create(RealDest->getName()+".critedge",
1213 RealDest->getParent(), RealDest);
1214 BranchInst::Create(RealDest, EdgeBB);
1216 for (BasicBlock::iterator BBI = RealDest->begin();
1217 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1218 Value *V = PN->getIncomingValueForBlock(BB);
1219 PN->addIncoming(V, EdgeBB);
1222 // BB may have instructions that are being threaded over. Clone these
1223 // instructions into EdgeBB. We know that there will be no uses of the
1224 // cloned instructions outside of EdgeBB.
1225 BasicBlock::iterator InsertPt = EdgeBB->begin();
1226 std::map<Value*, Value*> TranslateMap; // Track translated values.
1227 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1228 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1229 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1231 // Clone the instruction.
1232 Instruction *N = BBI->clone();
1233 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1235 // Update operands due to translation.
1236 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1238 std::map<Value*, Value*>::iterator PI =
1239 TranslateMap.find(*i);
1240 if (PI != TranslateMap.end())
1244 // Check for trivial simplification.
1245 if (Constant *C = ConstantFoldInstruction(N)) {
1246 TranslateMap[BBI] = C;
1247 delete N; // Constant folded away, don't need actual inst
1249 // Insert the new instruction into its new home.
1250 EdgeBB->getInstList().insert(InsertPt, N);
1251 if (!BBI->use_empty())
1252 TranslateMap[BBI] = N;
1257 // Loop over all of the edges from PredBB to BB, changing them to branch
1258 // to EdgeBB instead.
1259 TerminatorInst *PredBBTI = PredBB->getTerminator();
1260 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1261 if (PredBBTI->getSuccessor(i) == BB) {
1262 BB->removePredecessor(PredBB);
1263 PredBBTI->setSuccessor(i, EdgeBB);
1266 // Recurse, simplifying any other constants.
1267 return FoldCondBranchOnPHI(BI) | true;
1274 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1275 /// PHI node, see if we can eliminate it.
1276 static bool FoldTwoEntryPHINode(PHINode *PN) {
1277 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1278 // statement", which has a very simple dominance structure. Basically, we
1279 // are trying to find the condition that is being branched on, which
1280 // subsequently causes this merge to happen. We really want control
1281 // dependence information for this check, but simplifycfg can't keep it up
1282 // to date, and this catches most of the cases we care about anyway.
1284 BasicBlock *BB = PN->getParent();
1285 BasicBlock *IfTrue, *IfFalse;
1286 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1287 if (!IfCond) return false;
1289 // Okay, we found that we can merge this two-entry phi node into a select.
1290 // Doing so would require us to fold *all* two entry phi nodes in this block.
1291 // At some point this becomes non-profitable (particularly if the target
1292 // doesn't support cmov's). Only do this transformation if there are two or
1293 // fewer PHI nodes in this block.
1294 unsigned NumPhis = 0;
1295 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1299 DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
1300 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
1302 // Loop over the PHI's seeing if we can promote them all to select
1303 // instructions. While we are at it, keep track of the instructions
1304 // that need to be moved to the dominating block.
1305 std::set<Instruction*> AggressiveInsts;
1307 BasicBlock::iterator AfterPHIIt = BB->begin();
1308 while (isa<PHINode>(AfterPHIIt)) {
1309 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1310 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1311 if (PN->getIncomingValue(0) != PN)
1312 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1314 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1315 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1316 &AggressiveInsts) ||
1317 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1318 &AggressiveInsts)) {
1323 // If we all PHI nodes are promotable, check to make sure that all
1324 // instructions in the predecessor blocks can be promoted as well. If
1325 // not, we won't be able to get rid of the control flow, so it's not
1326 // worth promoting to select instructions.
1327 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1328 PN = cast<PHINode>(BB->begin());
1329 BasicBlock *Pred = PN->getIncomingBlock(0);
1330 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1332 DomBlock = *pred_begin(Pred);
1333 for (BasicBlock::iterator I = Pred->begin();
1334 !isa<TerminatorInst>(I); ++I)
1335 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1336 // This is not an aggressive instruction that we can promote.
1337 // Because of this, we won't be able to get rid of the control
1338 // flow, so the xform is not worth it.
1343 Pred = PN->getIncomingBlock(1);
1344 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1346 DomBlock = *pred_begin(Pred);
1347 for (BasicBlock::iterator I = Pred->begin();
1348 !isa<TerminatorInst>(I); ++I)
1349 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1350 // This is not an aggressive instruction that we can promote.
1351 // Because of this, we won't be able to get rid of the control
1352 // flow, so the xform is not worth it.
1357 // If we can still promote the PHI nodes after this gauntlet of tests,
1358 // do all of the PHI's now.
1360 // Move all 'aggressive' instructions, which are defined in the
1361 // conditional parts of the if's up to the dominating block.
1363 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1364 IfBlock1->getInstList(),
1366 IfBlock1->getTerminator());
1369 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1370 IfBlock2->getInstList(),
1372 IfBlock2->getTerminator());
1375 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1376 // Change the PHI node into a select instruction.
1378 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1380 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1382 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1383 PN->replaceAllUsesWith(NV);
1386 BB->getInstList().erase(PN);
1391 /// isTerminatorFirstRelevantInsn - Return true if Term is very first
1392 /// instruction ignoring Phi nodes and dbg intrinsics.
1393 static bool isTerminatorFirstRelevantInsn(BasicBlock *BB, Instruction *Term) {
1394 BasicBlock::iterator BBI = Term;
1395 while (BBI != BB->begin()) {
1397 if (!isa<DbgInfoIntrinsic>(BBI))
1401 if (isa<PHINode>(BBI) || &*BBI == Term || isa<DbgInfoIntrinsic>(BBI))
1406 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1407 /// to two returning blocks, try to merge them together into one return,
1408 /// introducing a select if the return values disagree.
1409 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1410 assert(BI->isConditional() && "Must be a conditional branch");
1411 BasicBlock *TrueSucc = BI->getSuccessor(0);
1412 BasicBlock *FalseSucc = BI->getSuccessor(1);
1413 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1414 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1416 // Check to ensure both blocks are empty (just a return) or optionally empty
1417 // with PHI nodes. If there are other instructions, merging would cause extra
1418 // computation on one path or the other.
1419 if (!isTerminatorFirstRelevantInsn(TrueSucc, TrueRet))
1421 if (!isTerminatorFirstRelevantInsn(FalseSucc, FalseRet))
1424 // Okay, we found a branch that is going to two return nodes. If
1425 // there is no return value for this function, just change the
1426 // branch into a return.
1427 if (FalseRet->getNumOperands() == 0) {
1428 TrueSucc->removePredecessor(BI->getParent());
1429 FalseSucc->removePredecessor(BI->getParent());
1430 ReturnInst::Create(0, BI);
1431 EraseTerminatorInstAndDCECond(BI);
1435 // Otherwise, figure out what the true and false return values are
1436 // so we can insert a new select instruction.
1437 Value *TrueValue = TrueRet->getReturnValue();
1438 Value *FalseValue = FalseRet->getReturnValue();
1440 // Unwrap any PHI nodes in the return blocks.
1441 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1442 if (TVPN->getParent() == TrueSucc)
1443 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1444 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1445 if (FVPN->getParent() == FalseSucc)
1446 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1448 // In order for this transformation to be safe, we must be able to
1449 // unconditionally execute both operands to the return. This is
1450 // normally the case, but we could have a potentially-trapping
1451 // constant expression that prevents this transformation from being
1453 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1456 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1460 // Okay, we collected all the mapped values and checked them for sanity, and
1461 // defined to really do this transformation. First, update the CFG.
1462 TrueSucc->removePredecessor(BI->getParent());
1463 FalseSucc->removePredecessor(BI->getParent());
1465 // Insert select instructions where needed.
1466 Value *BrCond = BI->getCondition();
1468 // Insert a select if the results differ.
1469 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1470 } else if (isa<UndefValue>(TrueValue)) {
1471 TrueValue = FalseValue;
1473 TrueValue = SelectInst::Create(BrCond, TrueValue,
1474 FalseValue, "retval", BI);
1478 Value *RI = !TrueValue ?
1479 ReturnInst::Create(BI) :
1480 ReturnInst::Create(TrueValue, BI);
1482 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1483 << "\n " << *BI << "NewRet = " << *RI
1484 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
1486 EraseTerminatorInstAndDCECond(BI);
1491 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1492 /// and if a predecessor branches to us and one of our successors, fold the
1493 /// setcc into the predecessor and use logical operations to pick the right
1495 bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1496 BasicBlock *BB = BI->getParent();
1497 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1498 if (Cond == 0) return false;
1501 // Only allow this if the condition is a simple instruction that can be
1502 // executed unconditionally. It must be in the same block as the branch, and
1503 // must be at the front of the block.
1504 BasicBlock::iterator FrontIt = BB->front();
1505 // Ignore dbg intrinsics.
1506 while(isa<DbgInfoIntrinsic>(FrontIt))
1508 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1509 Cond->getParent() != BB || &*FrontIt != Cond || !Cond->hasOneUse()) {
1513 // Make sure the instruction after the condition is the cond branch.
1514 BasicBlock::iterator CondIt = Cond; ++CondIt;
1515 // Ingore dbg intrinsics.
1516 while(isa<DbgInfoIntrinsic>(CondIt))
1518 if (&*CondIt != BI) {
1519 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1523 // Cond is known to be a compare or binary operator. Check to make sure that
1524 // neither operand is a potentially-trapping constant expression.
1525 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1528 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1533 // Finally, don't infinitely unroll conditional loops.
1534 BasicBlock *TrueDest = BI->getSuccessor(0);
1535 BasicBlock *FalseDest = BI->getSuccessor(1);
1536 if (TrueDest == BB || FalseDest == BB)
1539 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1540 BasicBlock *PredBlock = *PI;
1541 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1543 // Check that we have two conditional branches. If there is a PHI node in
1544 // the common successor, verify that the same value flows in from both
1546 if (PBI == 0 || PBI->isUnconditional() ||
1547 !SafeToMergeTerminators(BI, PBI))
1550 Instruction::BinaryOps Opc;
1551 bool InvertPredCond = false;
1553 if (PBI->getSuccessor(0) == TrueDest)
1554 Opc = Instruction::Or;
1555 else if (PBI->getSuccessor(1) == FalseDest)
1556 Opc = Instruction::And;
1557 else if (PBI->getSuccessor(0) == FalseDest)
1558 Opc = Instruction::And, InvertPredCond = true;
1559 else if (PBI->getSuccessor(1) == TrueDest)
1560 Opc = Instruction::Or, InvertPredCond = true;
1564 DOUT << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB;
1566 // If we need to invert the condition in the pred block to match, do so now.
1567 if (InvertPredCond) {
1569 BinaryOperator::CreateNot(PBI->getCondition(),
1570 PBI->getCondition()->getName()+".not", PBI);
1571 PBI->setCondition(NewCond);
1572 BasicBlock *OldTrue = PBI->getSuccessor(0);
1573 BasicBlock *OldFalse = PBI->getSuccessor(1);
1574 PBI->setSuccessor(0, OldFalse);
1575 PBI->setSuccessor(1, OldTrue);
1578 // Clone Cond into the predecessor basic block, and or/and the
1579 // two conditions together.
1580 Instruction *New = Cond->clone();
1581 PredBlock->getInstList().insert(PBI, New);
1582 New->takeName(Cond);
1583 Cond->setName(New->getName()+".old");
1585 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1586 New, "or.cond", PBI);
1587 PBI->setCondition(NewCond);
1588 if (PBI->getSuccessor(0) == BB) {
1589 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1590 PBI->setSuccessor(0, TrueDest);
1592 if (PBI->getSuccessor(1) == BB) {
1593 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1594 PBI->setSuccessor(1, FalseDest);
1601 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1602 /// predecessor of another block, this function tries to simplify it. We know
1603 /// that PBI and BI are both conditional branches, and BI is in one of the
1604 /// successor blocks of PBI - PBI branches to BI.
1605 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1606 assert(PBI->isConditional() && BI->isConditional());
1607 BasicBlock *BB = BI->getParent();
1609 // If this block ends with a branch instruction, and if there is a
1610 // predecessor that ends on a branch of the same condition, make
1611 // this conditional branch redundant.
1612 if (PBI->getCondition() == BI->getCondition() &&
1613 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1614 // Okay, the outcome of this conditional branch is statically
1615 // knowable. If this block had a single pred, handle specially.
1616 if (BB->getSinglePredecessor()) {
1617 // Turn this into a branch on constant.
1618 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1619 BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
1620 return true; // Nuke the branch on constant.
1623 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1624 // in the constant and simplify the block result. Subsequent passes of
1625 // simplifycfg will thread the block.
1626 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1627 PHINode *NewPN = PHINode::Create(Type::Int1Ty,
1628 BI->getCondition()->getName() + ".pr",
1630 // Okay, we're going to insert the PHI node. Since PBI is not the only
1631 // predecessor, compute the PHI'd conditional value for all of the preds.
1632 // Any predecessor where the condition is not computable we keep symbolic.
1633 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1634 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1635 PBI != BI && PBI->isConditional() &&
1636 PBI->getCondition() == BI->getCondition() &&
1637 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1638 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1639 NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
1642 NewPN->addIncoming(BI->getCondition(), *PI);
1645 BI->setCondition(NewPN);
1650 // If this is a conditional branch in an empty block, and if any
1651 // predecessors is a conditional branch to one of our destinations,
1652 // fold the conditions into logical ops and one cond br.
1653 BasicBlock::iterator BBI = BB->begin();
1654 // Ignore dbg intrinsics.
1655 while (isa<DbgInfoIntrinsic>(BBI))
1661 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1666 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1668 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1669 PBIOp = 0, BIOp = 1;
1670 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1671 PBIOp = 1, BIOp = 0;
1672 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1677 // Check to make sure that the other destination of this branch
1678 // isn't BB itself. If so, this is an infinite loop that will
1679 // keep getting unwound.
1680 if (PBI->getSuccessor(PBIOp) == BB)
1683 // Do not perform this transformation if it would require
1684 // insertion of a large number of select instructions. For targets
1685 // without predication/cmovs, this is a big pessimization.
1686 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1688 unsigned NumPhis = 0;
1689 for (BasicBlock::iterator II = CommonDest->begin();
1690 isa<PHINode>(II); ++II, ++NumPhis)
1691 if (NumPhis > 2) // Disable this xform.
1694 // Finally, if everything is ok, fold the branches to logical ops.
1695 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1697 DOUT << "FOLDING BRs:" << *PBI->getParent()
1698 << "AND: " << *BI->getParent();
1701 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1702 // branch in it, where one edge (OtherDest) goes back to itself but the other
1703 // exits. We don't *know* that the program avoids the infinite loop
1704 // (even though that seems likely). If we do this xform naively, we'll end up
1705 // recursively unpeeling the loop. Since we know that (after the xform is
1706 // done) that the block *is* infinite if reached, we just make it an obviously
1707 // infinite loop with no cond branch.
1708 if (OtherDest == BB) {
1709 // Insert it at the end of the function, because it's either code,
1710 // or it won't matter if it's hot. :)
1711 BasicBlock *InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
1712 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1713 OtherDest = InfLoopBlock;
1716 DOUT << *PBI->getParent()->getParent();
1718 // BI may have other predecessors. Because of this, we leave
1719 // it alone, but modify PBI.
1721 // Make sure we get to CommonDest on True&True directions.
1722 Value *PBICond = PBI->getCondition();
1724 PBICond = BinaryOperator::CreateNot(PBICond,
1725 PBICond->getName()+".not",
1727 Value *BICond = BI->getCondition();
1729 BICond = BinaryOperator::CreateNot(BICond,
1730 BICond->getName()+".not",
1732 // Merge the conditions.
1733 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1735 // Modify PBI to branch on the new condition to the new dests.
1736 PBI->setCondition(Cond);
1737 PBI->setSuccessor(0, CommonDest);
1738 PBI->setSuccessor(1, OtherDest);
1740 // OtherDest may have phi nodes. If so, add an entry from PBI's
1741 // block that are identical to the entries for BI's block.
1743 for (BasicBlock::iterator II = OtherDest->begin();
1744 (PN = dyn_cast<PHINode>(II)); ++II) {
1745 Value *V = PN->getIncomingValueForBlock(BB);
1746 PN->addIncoming(V, PBI->getParent());
1749 // We know that the CommonDest already had an edge from PBI to
1750 // it. If it has PHIs though, the PHIs may have different
1751 // entries for BB and PBI's BB. If so, insert a select to make
1753 for (BasicBlock::iterator II = CommonDest->begin();
1754 (PN = dyn_cast<PHINode>(II)); ++II) {
1755 Value *BIV = PN->getIncomingValueForBlock(BB);
1756 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1757 Value *PBIV = PN->getIncomingValue(PBBIdx);
1759 // Insert a select in PBI to pick the right value.
1760 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1761 PBIV->getName()+".mux", PBI);
1762 PN->setIncomingValue(PBBIdx, NV);
1766 DOUT << "INTO: " << *PBI->getParent();
1768 DOUT << *PBI->getParent()->getParent();
1770 // This basic block is probably dead. We know it has at least
1771 // one fewer predecessor.
1776 /// SimplifyCFG - This function is used to do simplification of a CFG. For
1777 /// example, it adjusts branches to branches to eliminate the extra hop, it
1778 /// eliminates unreachable basic blocks, and does other "peephole" optimization
1779 /// of the CFG. It returns true if a modification was made.
1781 /// WARNING: The entry node of a function may not be simplified.
1783 bool llvm::SimplifyCFG(BasicBlock *BB) {
1784 bool Changed = false;
1785 Function *M = BB->getParent();
1787 assert(BB && BB->getParent() && "Block not embedded in function!");
1788 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1789 assert(&BB->getParent()->getEntryBlock() != BB &&
1790 "Can't Simplify entry block!");
1792 // Remove basic blocks that have no predecessors... or that just have themself
1793 // as a predecessor. These are unreachable.
1794 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1795 DOUT << "Removing BB: \n" << *BB;
1796 DeleteDeadBlock(BB);
1800 // Check to see if we can constant propagate this terminator instruction
1802 Changed |= ConstantFoldTerminator(BB);
1804 // If there is a trivial two-entry PHI node in this basic block, and we can
1805 // eliminate it, do so now.
1806 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1807 if (PN->getNumIncomingValues() == 2)
1808 Changed |= FoldTwoEntryPHINode(PN);
1810 // If this is a returning block with only PHI nodes in it, fold the return
1811 // instruction into any unconditional branch predecessors.
1813 // If any predecessor is a conditional branch that just selects among
1814 // different return values, fold the replace the branch/return with a select
1816 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1817 if (isTerminatorFirstRelevantInsn(BB, BB->getTerminator())) {
1818 // Find predecessors that end with branches.
1819 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1820 SmallVector<BranchInst*, 8> CondBranchPreds;
1821 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1822 TerminatorInst *PTI = (*PI)->getTerminator();
1823 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1824 if (BI->isUnconditional())
1825 UncondBranchPreds.push_back(*PI);
1827 CondBranchPreds.push_back(BI);
1831 // If we found some, do the transformation!
1832 if (!UncondBranchPreds.empty()) {
1833 while (!UncondBranchPreds.empty()) {
1834 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
1835 DOUT << "FOLDING: " << *BB
1836 << "INTO UNCOND BRANCH PRED: " << *Pred;
1837 Instruction *UncondBranch = Pred->getTerminator();
1838 // Clone the return and add it to the end of the predecessor.
1839 Instruction *NewRet = RI->clone();
1840 Pred->getInstList().push_back(NewRet);
1842 BasicBlock::iterator BBI = RI;
1843 if (BBI != BB->begin()) {
1844 // Move region end info into the predecessor.
1845 if (DbgRegionEndInst *DREI = dyn_cast<DbgRegionEndInst>(--BBI))
1846 DREI->moveBefore(NewRet);
1849 // If the return instruction returns a value, and if the value was a
1850 // PHI node in "BB", propagate the right value into the return.
1851 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1853 if (PHINode *PN = dyn_cast<PHINode>(*i))
1854 if (PN->getParent() == BB)
1855 *i = PN->getIncomingValueForBlock(Pred);
1857 // Update any PHI nodes in the returning block to realize that we no
1858 // longer branch to them.
1859 BB->removePredecessor(Pred);
1860 Pred->getInstList().erase(UncondBranch);
1863 // If we eliminated all predecessors of the block, delete the block now.
1864 if (pred_begin(BB) == pred_end(BB))
1865 // We know there are no successors, so just nuke the block.
1866 M->getBasicBlockList().erase(BB);
1871 // Check out all of the conditional branches going to this return
1872 // instruction. If any of them just select between returns, change the
1873 // branch itself into a select/return pair.
1874 while (!CondBranchPreds.empty()) {
1875 BranchInst *BI = CondBranchPreds.pop_back_val();
1877 // Check to see if the non-BB successor is also a return block.
1878 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1879 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1880 SimplifyCondBranchToTwoReturns(BI))
1884 } else if (isa<UnwindInst>(BB->begin())) {
1885 // Check to see if the first instruction in this block is just an unwind.
1886 // If so, replace any invoke instructions which use this as an exception
1887 // destination with call instructions, and any unconditional branch
1888 // predecessor with an unwind.
1890 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1891 while (!Preds.empty()) {
1892 BasicBlock *Pred = Preds.back();
1893 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1894 if (BI->isUnconditional()) {
1895 Pred->getInstList().pop_back(); // nuke uncond branch
1896 new UnwindInst(Pred); // Use unwind.
1899 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1900 if (II->getUnwindDest() == BB) {
1901 // Insert a new branch instruction before the invoke, because this
1902 // is now a fall through...
1903 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1904 Pred->getInstList().remove(II); // Take out of symbol table
1906 // Insert the call now...
1907 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1908 CallInst *CI = CallInst::Create(II->getCalledValue(),
1909 Args.begin(), Args.end(),
1911 CI->setCallingConv(II->getCallingConv());
1912 CI->setAttributes(II->getAttributes());
1913 // If the invoke produced a value, the Call now does instead
1914 II->replaceAllUsesWith(CI);
1922 // If this block is now dead, remove it.
1923 if (pred_begin(BB) == pred_end(BB)) {
1924 // We know there are no successors, so just nuke the block.
1925 M->getBasicBlockList().erase(BB);
1929 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1930 if (isValueEqualityComparison(SI)) {
1931 // If we only have one predecessor, and if it is a branch on this value,
1932 // see if that predecessor totally determines the outcome of this switch.
1933 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1934 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1935 return SimplifyCFG(BB) || 1;
1937 // If the block only contains the switch, see if we can fold the block
1938 // away into any preds.
1939 BasicBlock::iterator BBI = BB->begin();
1940 // Ignore dbg intrinsics.
1941 while (isa<DbgInfoIntrinsic>(BBI))
1944 if (FoldValueComparisonIntoPredecessors(SI))
1945 return SimplifyCFG(BB) || 1;
1947 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1948 if (BI->isUnconditional()) {
1949 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1951 BasicBlock *Succ = BI->getSuccessor(0);
1952 // Ignore dbg intrinsics.
1953 while (isa<DbgInfoIntrinsic>(BBI))
1955 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1956 Succ != BB) // Don't hurt infinite loops!
1957 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1960 } else { // Conditional branch
1961 if (isValueEqualityComparison(BI)) {
1962 // If we only have one predecessor, and if it is a branch on this value,
1963 // see if that predecessor totally determines the outcome of this
1965 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1966 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1967 return SimplifyCFG(BB) || 1;
1969 // This block must be empty, except for the setcond inst, if it exists.
1970 // Ignore dbg intrinsics.
1971 BasicBlock::iterator I = BB->begin();
1972 // Ignore dbg intrinsics.
1973 while (isa<DbgInfoIntrinsic>(I))
1976 if (FoldValueComparisonIntoPredecessors(BI))
1977 return SimplifyCFG(BB) | true;
1978 } else if (&*I == cast<Instruction>(BI->getCondition())){
1980 // Ignore dbg intrinsics.
1981 while (isa<DbgInfoIntrinsic>(I))
1984 if (FoldValueComparisonIntoPredecessors(BI))
1985 return SimplifyCFG(BB) | true;
1990 // If this is a branch on a phi node in the current block, thread control
1991 // through this block if any PHI node entries are constants.
1992 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1993 if (PN->getParent() == BI->getParent())
1994 if (FoldCondBranchOnPHI(BI))
1995 return SimplifyCFG(BB) | true;
1997 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1998 // branches to us and one of our successors, fold the setcc into the
1999 // predecessor and use logical operations to pick the right destination.
2000 if (FoldBranchToCommonDest(BI))
2001 return SimplifyCFG(BB) | 1;
2004 // Scan predecessor blocks for conditional branches.
2005 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2006 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2007 if (PBI != BI && PBI->isConditional())
2008 if (SimplifyCondBranchToCondBranch(PBI, BI))
2009 return SimplifyCFG(BB) | true;
2011 } else if (isa<UnreachableInst>(BB->getTerminator())) {
2012 // If there are any instructions immediately before the unreachable that can
2013 // be removed, do so.
2014 Instruction *Unreachable = BB->getTerminator();
2015 while (Unreachable != BB->begin()) {
2016 BasicBlock::iterator BBI = Unreachable;
2018 // Do not delete instructions that can have side effects, like calls
2019 // (which may never return) and volatile loads and stores.
2020 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2022 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2023 if (SI->isVolatile())
2026 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2027 if (LI->isVolatile())
2030 // Delete this instruction
2031 BB->getInstList().erase(BBI);
2035 // If the unreachable instruction is the first in the block, take a gander
2036 // at all of the predecessors of this instruction, and simplify them.
2037 if (&BB->front() == Unreachable) {
2038 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2039 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2040 TerminatorInst *TI = Preds[i]->getTerminator();
2042 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2043 if (BI->isUnconditional()) {
2044 if (BI->getSuccessor(0) == BB) {
2045 new UnreachableInst(TI);
2046 TI->eraseFromParent();
2050 if (BI->getSuccessor(0) == BB) {
2051 BranchInst::Create(BI->getSuccessor(1), BI);
2052 EraseTerminatorInstAndDCECond(BI);
2053 } else if (BI->getSuccessor(1) == BB) {
2054 BranchInst::Create(BI->getSuccessor(0), BI);
2055 EraseTerminatorInstAndDCECond(BI);
2059 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2060 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2061 if (SI->getSuccessor(i) == BB) {
2062 BB->removePredecessor(SI->getParent());
2067 // If the default value is unreachable, figure out the most popular
2068 // destination and make it the default.
2069 if (SI->getSuccessor(0) == BB) {
2070 std::map<BasicBlock*, unsigned> Popularity;
2071 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2072 Popularity[SI->getSuccessor(i)]++;
2074 // Find the most popular block.
2075 unsigned MaxPop = 0;
2076 BasicBlock *MaxBlock = 0;
2077 for (std::map<BasicBlock*, unsigned>::iterator
2078 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2079 if (I->second > MaxPop) {
2081 MaxBlock = I->first;
2085 // Make this the new default, allowing us to delete any explicit
2087 SI->setSuccessor(0, MaxBlock);
2090 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2092 if (isa<PHINode>(MaxBlock->begin()))
2093 for (unsigned i = 0; i != MaxPop-1; ++i)
2094 MaxBlock->removePredecessor(SI->getParent());
2096 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2097 if (SI->getSuccessor(i) == MaxBlock) {
2103 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2104 if (II->getUnwindDest() == BB) {
2105 // Convert the invoke to a call instruction. This would be a good
2106 // place to note that the call does not throw though.
2107 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2108 II->removeFromParent(); // Take out of symbol table
2110 // Insert the call now...
2111 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
2112 CallInst *CI = CallInst::Create(II->getCalledValue(),
2113 Args.begin(), Args.end(),
2115 CI->setCallingConv(II->getCallingConv());
2116 CI->setAttributes(II->getAttributes());
2117 // If the invoke produced a value, the Call does now instead.
2118 II->replaceAllUsesWith(CI);
2125 // If this block is now dead, remove it.
2126 if (pred_begin(BB) == pred_end(BB)) {
2127 // We know there are no successors, so just nuke the block.
2128 M->getBasicBlockList().erase(BB);
2134 // Merge basic blocks into their predecessor if there is only one distinct
2135 // pred, and if there is only one distinct successor of the predecessor, and
2136 // if there are no PHI nodes.
2138 if (MergeBlockIntoPredecessor(BB))
2141 // Otherwise, if this block only has a single predecessor, and if that block
2142 // is a conditional branch, see if we can hoist any code from this block up
2143 // into our predecessor.
2144 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2145 BasicBlock *OnlyPred = *PI++;
2146 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2147 if (*PI != OnlyPred) {
2148 OnlyPred = 0; // There are multiple different predecessors...
2153 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2154 if (BI->isConditional()) {
2155 // Get the other block.
2156 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2157 PI = pred_begin(OtherBB);
2160 if (PI == pred_end(OtherBB)) {
2161 // We have a conditional branch to two blocks that are only reachable
2162 // from the condbr. We know that the condbr dominates the two blocks,
2163 // so see if there is any identical code in the "then" and "else"
2164 // blocks. If so, we can hoist it up to the branching block.
2165 Changed |= HoistThenElseCodeToIf(BI);
2167 BasicBlock* OnlySucc = NULL;
2168 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2172 else if (*SI != OnlySucc) {
2173 OnlySucc = 0; // There are multiple distinct successors!
2178 if (OnlySucc == OtherBB) {
2179 // If BB's only successor is the other successor of the predecessor,
2180 // i.e. a triangle, see if we can hoist any code from this block up
2181 // to the "if" block.
2182 Changed |= SpeculativelyExecuteBB(BI, BB);
2187 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2188 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2189 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2190 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2191 Instruction *Cond = cast<Instruction>(BI->getCondition());
2192 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2193 // 'setne's and'ed together, collect them.
2195 std::vector<ConstantInt*> Values;
2196 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2197 if (CompVal && CompVal->getType()->isInteger()) {
2198 // There might be duplicate constants in the list, which the switch
2199 // instruction can't handle, remove them now.
2200 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2201 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2203 // Figure out which block is which destination.
2204 BasicBlock *DefaultBB = BI->getSuccessor(1);
2205 BasicBlock *EdgeBB = BI->getSuccessor(0);
2206 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2208 // Create the new switch instruction now.
2209 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2212 // Add all of the 'cases' to the switch instruction.
2213 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2214 New->addCase(Values[i], EdgeBB);
2216 // We added edges from PI to the EdgeBB. As such, if there were any
2217 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2218 // the number of edges added.
2219 for (BasicBlock::iterator BBI = EdgeBB->begin();
2220 isa<PHINode>(BBI); ++BBI) {
2221 PHINode *PN = cast<PHINode>(BBI);
2222 Value *InVal = PN->getIncomingValueForBlock(*PI);
2223 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2224 PN->addIncoming(InVal, *PI);
2227 // Erase the old branch instruction.
2228 EraseTerminatorInstAndDCECond(BI);