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 /// SafeToMergeTerminators - Return true if it is safe to merge these two
37 /// terminator instructions together.
39 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
40 if (SI1 == SI2) return false; // Can't merge with self!
42 // It is not safe to merge these two switch instructions if they have a common
43 // successor, and if that successor has a PHI node, and if *that* PHI node has
44 // conflicting incoming values from the two switch blocks.
45 BasicBlock *SI1BB = SI1->getParent();
46 BasicBlock *SI2BB = SI2->getParent();
47 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
49 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
50 if (SI1Succs.count(*I))
51 for (BasicBlock::iterator BBI = (*I)->begin();
52 isa<PHINode>(BBI); ++BBI) {
53 PHINode *PN = cast<PHINode>(BBI);
54 if (PN->getIncomingValueForBlock(SI1BB) !=
55 PN->getIncomingValueForBlock(SI2BB))
62 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
63 /// now be entries in it from the 'NewPred' block. The values that will be
64 /// flowing into the PHI nodes will be the same as those coming in from
65 /// ExistPred, an existing predecessor of Succ.
66 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
67 BasicBlock *ExistPred) {
68 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
69 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
70 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
73 for (BasicBlock::iterator I = Succ->begin();
74 (PN = dyn_cast<PHINode>(I)); ++I)
75 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
78 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
79 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
81 /// Assumption: Succ is the single successor for BB.
83 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
84 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
86 DOUT << "Looking to fold " << BB->getNameStart() << " into "
87 << Succ->getNameStart() << "\n";
88 // Shortcut, if there is only a single predecessor is must be BB and merging
90 if (Succ->getSinglePredecessor()) return true;
92 typedef SmallPtrSet<Instruction*, 16> InstrSet;
95 // Make a list of all phi nodes in BB
96 BasicBlock::iterator BBI = BB->begin();
97 while (isa<PHINode>(*BBI)) BBPHIs.insert(BBI++);
99 // Make a list of the predecessors of BB
100 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
101 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
103 // Use that list to make another list of common predecessors of BB and Succ
104 BlockSet CommonPreds;
105 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
107 if (BBPreds.count(*PI))
108 CommonPreds.insert(*PI);
110 // Shortcut, if there are no common predecessors, merging is always safe
111 if (CommonPreds.empty())
114 // Look at all the phi nodes in Succ, to see if they present a conflict when
115 // merging these blocks
116 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
117 PHINode *PN = cast<PHINode>(I);
119 // If the incoming value from BB is again a PHINode in
120 // BB which has the same incoming value for *PI as PN does, we can
121 // merge the phi nodes and then the blocks can still be merged
122 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
123 if (BBPN && BBPN->getParent() == BB) {
124 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
126 if (BBPN->getIncomingValueForBlock(*PI)
127 != PN->getIncomingValueForBlock(*PI)) {
128 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
129 << Succ->getNameStart() << " is conflicting with "
130 << BBPN->getNameStart() << " with regard to common predecessor "
131 << (*PI)->getNameStart() << "\n";
135 // Remove this phinode from the list of phis in BB, since it has been
139 Value* Val = PN->getIncomingValueForBlock(BB);
140 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
142 // See if the incoming value for the common predecessor is equal to the
143 // one for BB, in which case this phi node will not prevent the merging
145 if (Val != PN->getIncomingValueForBlock(*PI)) {
146 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
147 << Succ->getNameStart() << " is conflicting with regard to common "
148 << "predecessor " << (*PI)->getNameStart() << "\n";
155 // If there are any other phi nodes in BB that don't have a phi node in Succ
156 // to merge with, they must be moved to Succ completely. However, for any
157 // predecessors of Succ, branches will be added to the phi node that just
158 // point to itself. So, for any common predecessors, this must not cause
160 for (InstrSet::iterator I = BBPHIs.begin(), E = BBPHIs.end();
162 PHINode *PN = cast<PHINode>(*I);
163 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
165 if (PN->getIncomingValueForBlock(*PI) != PN) {
166 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
167 << BB->getNameStart() << " is conflicting with regard to common "
168 << "predecessor " << (*PI)->getNameStart() << "\n";
176 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
177 /// branch to Succ, and contains no instructions other than PHI nodes and the
178 /// branch. If possible, eliminate BB.
179 static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
181 // Check to see if merging these blocks would cause conflicts for any of the
182 // phi nodes in BB or Succ. If not, we can safely merge.
183 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
185 DOUT << "Killing Trivial BB: \n" << *BB;
187 if (isa<PHINode>(Succ->begin())) {
188 // If there is more than one pred of succ, and there are PHI nodes in
189 // the successor, then we need to add incoming edges for the PHI nodes
191 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
193 // Loop over all of the PHI nodes in the successor of BB.
194 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
195 PHINode *PN = cast<PHINode>(I);
196 Value *OldVal = PN->removeIncomingValue(BB, false);
197 assert(OldVal && "No entry in PHI for Pred BB!");
199 // If this incoming value is one of the PHI nodes in BB, the new entries
200 // in the PHI node are the entries from the old PHI.
201 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
202 PHINode *OldValPN = cast<PHINode>(OldVal);
203 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
204 // Note that, since we are merging phi nodes and BB and Succ might
205 // have common predecessors, we could end up with a phi node with
206 // identical incoming branches. This will be cleaned up later (and
207 // will trigger asserts if we try to clean it up now, without also
208 // simplifying the corresponding conditional branch).
209 PN->addIncoming(OldValPN->getIncomingValue(i),
210 OldValPN->getIncomingBlock(i));
212 // Add an incoming value for each of the new incoming values.
213 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
214 PN->addIncoming(OldVal, BBPreds[i]);
219 if (isa<PHINode>(&BB->front())) {
220 SmallVector<BasicBlock*, 16>
221 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
223 // Move all PHI nodes in BB to Succ if they are alive, otherwise
225 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
226 if (PN->use_empty()) {
227 // Just remove the dead phi. This happens if Succ's PHIs were the only
228 // users of the PHI nodes.
229 PN->eraseFromParent();
233 // The instruction is alive, so this means that BB must dominate all
234 // predecessors of Succ (Since all uses of the PN are after its
235 // definition, so in Succ or a block dominated by Succ. If a predecessor
236 // of Succ would not be dominated by BB, PN would violate the def before
237 // use SSA demand). Therefore, we can simply move the phi node to the
239 Succ->getInstList().splice(Succ->begin(),
240 BB->getInstList(), BB->begin());
242 // We need to add new entries for the PHI node to account for
243 // predecessors of Succ that the PHI node does not take into
244 // account. At this point, since we know that BB dominated succ and all
245 // of its predecessors, this means that we should any newly added
246 // incoming edges should use the PHI node itself as the value for these
247 // edges, because they are loop back edges.
248 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
249 if (OldSuccPreds[i] != BB)
250 PN->addIncoming(PN, OldSuccPreds[i]);
254 // Everything that jumped to BB now goes to Succ.
255 BB->replaceAllUsesWith(Succ);
256 if (!Succ->hasName()) Succ->takeName(BB);
257 BB->eraseFromParent(); // Delete the old basic block.
261 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
262 /// presumably PHI nodes in it), check to see if the merge at this block is due
263 /// to an "if condition". If so, return the boolean condition that determines
264 /// which entry into BB will be taken. Also, return by references the block
265 /// that will be entered from if the condition is true, and the block that will
266 /// be entered if the condition is false.
269 static Value *GetIfCondition(BasicBlock *BB,
270 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
271 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
272 "Function can only handle blocks with 2 predecessors!");
273 BasicBlock *Pred1 = *pred_begin(BB);
274 BasicBlock *Pred2 = *++pred_begin(BB);
276 // We can only handle branches. Other control flow will be lowered to
277 // branches if possible anyway.
278 if (!isa<BranchInst>(Pred1->getTerminator()) ||
279 !isa<BranchInst>(Pred2->getTerminator()))
281 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
282 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
284 // Eliminate code duplication by ensuring that Pred1Br is conditional if
286 if (Pred2Br->isConditional()) {
287 // If both branches are conditional, we don't have an "if statement". In
288 // reality, we could transform this case, but since the condition will be
289 // required anyway, we stand no chance of eliminating it, so the xform is
290 // probably not profitable.
291 if (Pred1Br->isConditional())
294 std::swap(Pred1, Pred2);
295 std::swap(Pred1Br, Pred2Br);
298 if (Pred1Br->isConditional()) {
299 // If we found a conditional branch predecessor, make sure that it branches
300 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
301 if (Pred1Br->getSuccessor(0) == BB &&
302 Pred1Br->getSuccessor(1) == Pred2) {
305 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
306 Pred1Br->getSuccessor(1) == BB) {
310 // We know that one arm of the conditional goes to BB, so the other must
311 // go somewhere unrelated, and this must not be an "if statement".
315 // The only thing we have to watch out for here is to make sure that Pred2
316 // doesn't have incoming edges from other blocks. If it does, the condition
317 // doesn't dominate BB.
318 if (++pred_begin(Pred2) != pred_end(Pred2))
321 return Pred1Br->getCondition();
324 // Ok, if we got here, both predecessors end with an unconditional branch to
325 // BB. Don't panic! If both blocks only have a single (identical)
326 // predecessor, and THAT is a conditional branch, then we're all ok!
327 if (pred_begin(Pred1) == pred_end(Pred1) ||
328 ++pred_begin(Pred1) != pred_end(Pred1) ||
329 pred_begin(Pred2) == pred_end(Pred2) ||
330 ++pred_begin(Pred2) != pred_end(Pred2) ||
331 *pred_begin(Pred1) != *pred_begin(Pred2))
334 // Otherwise, if this is a conditional branch, then we can use it!
335 BasicBlock *CommonPred = *pred_begin(Pred1);
336 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
337 assert(BI->isConditional() && "Two successors but not conditional?");
338 if (BI->getSuccessor(0) == Pred1) {
345 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)))
397 // Finally, we have to check to make sure there are no instructions
398 // before the load in its basic block, as we are going to hoist the loop
399 // out to its predecessor.
400 if (PBB->begin() != BasicBlock::iterator(I))
403 case Instruction::Add:
404 case Instruction::Sub:
405 case Instruction::And:
406 case Instruction::Or:
407 case Instruction::Xor:
408 case Instruction::Shl:
409 case Instruction::LShr:
410 case Instruction::AShr:
411 case Instruction::ICmp:
412 case Instruction::FCmp:
413 if (I->getOperand(0)->getType()->isFPOrFPVector())
414 return false; // FP arithmetic might trap.
415 break; // These are all cheap and non-trapping instructions.
418 // Okay, we can only really hoist these out if their operands are not
419 // defined in the conditional region.
420 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
421 if (!DominatesMergePoint(*i, BB, 0))
423 // Okay, it's safe to do this! Remember this instruction.
424 AggressiveInsts->insert(I);
430 /// GatherConstantSetEQs - Given a potentially 'or'd together collection of
431 /// icmp_eq instructions that compare a value against a constant, return the
432 /// value being compared, and stick the constant into the Values vector.
433 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
434 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
435 if (Inst->getOpcode() == Instruction::ICmp &&
436 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
437 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
439 return Inst->getOperand(0);
440 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
442 return Inst->getOperand(1);
444 } else if (Inst->getOpcode() == Instruction::Or) {
445 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
446 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
454 /// GatherConstantSetNEs - Given a potentially 'and'd together collection of
455 /// setne instructions that compare a value against a constant, return the value
456 /// being compared, and stick the constant into the Values vector.
457 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
458 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
459 if (Inst->getOpcode() == Instruction::ICmp &&
460 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
461 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
463 return Inst->getOperand(0);
464 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
466 return Inst->getOperand(1);
468 } else if (Inst->getOpcode() == Instruction::And) {
469 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
470 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
478 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
479 /// bunch of comparisons of one value against constants, return the value and
480 /// the constants being compared.
481 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
482 std::vector<ConstantInt*> &Values) {
483 if (Cond->getOpcode() == Instruction::Or) {
484 CompVal = GatherConstantSetEQs(Cond, Values);
486 // Return true to indicate that the condition is true if the CompVal is
487 // equal to one of the constants.
489 } else if (Cond->getOpcode() == Instruction::And) {
490 CompVal = GatherConstantSetNEs(Cond, Values);
492 // Return false to indicate that the condition is false if the CompVal is
493 // equal to one of the constants.
499 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
500 Instruction* Cond = 0;
501 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
502 Cond = dyn_cast<Instruction>(SI->getCondition());
503 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
504 if (BI->isConditional())
505 Cond = dyn_cast<Instruction>(BI->getCondition());
508 TI->eraseFromParent();
509 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
512 /// isValueEqualityComparison - Return true if the specified terminator checks
513 /// to see if a value is equal to constant integer value.
514 static Value *isValueEqualityComparison(TerminatorInst *TI) {
515 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
516 // Do not permit merging of large switch instructions into their
517 // predecessors unless there is only one predecessor.
518 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
519 pred_end(SI->getParent())) > 128)
522 return SI->getCondition();
524 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
525 if (BI->isConditional() && BI->getCondition()->hasOneUse())
526 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
527 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
528 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
529 isa<ConstantInt>(ICI->getOperand(1)))
530 return ICI->getOperand(0);
534 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
535 /// decode all of the 'cases' that it represents and return the 'default' block.
537 GetValueEqualityComparisonCases(TerminatorInst *TI,
538 std::vector<std::pair<ConstantInt*,
539 BasicBlock*> > &Cases) {
540 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
541 Cases.reserve(SI->getNumCases());
542 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
543 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
544 return SI->getDefaultDest();
547 BranchInst *BI = cast<BranchInst>(TI);
548 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
549 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
550 BI->getSuccessor(ICI->getPredicate() ==
551 ICmpInst::ICMP_NE)));
552 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
556 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
557 /// in the list that match the specified block.
558 static void EliminateBlockCases(BasicBlock *BB,
559 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
560 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
561 if (Cases[i].second == BB) {
562 Cases.erase(Cases.begin()+i);
567 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
570 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
571 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
572 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
574 // Make V1 be smaller than V2.
575 if (V1->size() > V2->size())
578 if (V1->size() == 0) return false;
579 if (V1->size() == 1) {
581 ConstantInt *TheVal = (*V1)[0].first;
582 for (unsigned i = 0, e = V2->size(); i != e; ++i)
583 if (TheVal == (*V2)[i].first)
587 // Otherwise, just sort both lists and compare element by element.
588 std::sort(V1->begin(), V1->end());
589 std::sort(V2->begin(), V2->end());
590 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
591 while (i1 != e1 && i2 != e2) {
592 if ((*V1)[i1].first == (*V2)[i2].first)
594 if ((*V1)[i1].first < (*V2)[i2].first)
602 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
603 /// terminator instruction and its block is known to only have a single
604 /// predecessor block, check to see if that predecessor is also a value
605 /// comparison with the same value, and if that comparison determines the
606 /// outcome of this comparison. If so, simplify TI. This does a very limited
607 /// form of jump threading.
608 static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
610 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
611 if (!PredVal) return false; // Not a value comparison in predecessor.
613 Value *ThisVal = isValueEqualityComparison(TI);
614 assert(ThisVal && "This isn't a value comparison!!");
615 if (ThisVal != PredVal) return false; // Different predicates.
617 // Find out information about when control will move from Pred to TI's block.
618 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
619 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
621 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
623 // Find information about how control leaves this block.
624 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
625 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
626 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
628 // If TI's block is the default block from Pred's comparison, potentially
629 // simplify TI based on this knowledge.
630 if (PredDef == TI->getParent()) {
631 // If we are here, we know that the value is none of those cases listed in
632 // PredCases. If there are any cases in ThisCases that are in PredCases, we
634 if (ValuesOverlap(PredCases, ThisCases)) {
635 if (isa<BranchInst>(TI)) {
636 // Okay, one of the successors of this condbr is dead. Convert it to a
638 assert(ThisCases.size() == 1 && "Branch can only have one case!");
639 // Insert the new branch.
640 Instruction *NI = BranchInst::Create(ThisDef, TI);
642 // Remove PHI node entries for the dead edge.
643 ThisCases[0].second->removePredecessor(TI->getParent());
645 DOUT << "Threading pred instr: " << *Pred->getTerminator()
646 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
648 EraseTerminatorInstAndDCECond(TI);
652 SwitchInst *SI = cast<SwitchInst>(TI);
653 // Okay, TI has cases that are statically dead, prune them away.
654 SmallPtrSet<Constant*, 16> DeadCases;
655 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
656 DeadCases.insert(PredCases[i].first);
658 DOUT << "Threading pred instr: " << *Pred->getTerminator()
659 << "Through successor TI: " << *TI;
661 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
662 if (DeadCases.count(SI->getCaseValue(i))) {
663 SI->getSuccessor(i)->removePredecessor(TI->getParent());
667 DOUT << "Leaving: " << *TI << "\n";
673 // Otherwise, TI's block must correspond to some matched value. Find out
674 // which value (or set of values) this is.
675 ConstantInt *TIV = 0;
676 BasicBlock *TIBB = TI->getParent();
677 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
678 if (PredCases[i].second == TIBB) {
680 TIV = PredCases[i].first;
682 return false; // Cannot handle multiple values coming to this block.
684 assert(TIV && "No edge from pred to succ?");
686 // Okay, we found the one constant that our value can be if we get into TI's
687 // BB. Find out which successor will unconditionally be branched to.
688 BasicBlock *TheRealDest = 0;
689 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
690 if (ThisCases[i].first == TIV) {
691 TheRealDest = ThisCases[i].second;
695 // If not handled by any explicit cases, it is handled by the default case.
696 if (TheRealDest == 0) TheRealDest = ThisDef;
698 // Remove PHI node entries for dead edges.
699 BasicBlock *CheckEdge = TheRealDest;
700 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
701 if (*SI != CheckEdge)
702 (*SI)->removePredecessor(TIBB);
706 // Insert the new branch.
707 Instruction *NI = BranchInst::Create(TheRealDest, TI);
709 DOUT << "Threading pred instr: " << *Pred->getTerminator()
710 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
712 EraseTerminatorInstAndDCECond(TI);
718 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
719 /// equality comparison instruction (either a switch or a branch on "X == c").
720 /// See if any of the predecessors of the terminator block are value comparisons
721 /// on the same value. If so, and if safe to do so, fold them together.
722 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
723 BasicBlock *BB = TI->getParent();
724 Value *CV = isValueEqualityComparison(TI); // CondVal
725 assert(CV && "Not a comparison?");
726 bool Changed = false;
728 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
729 while (!Preds.empty()) {
730 BasicBlock *Pred = Preds.back();
733 // See if the predecessor is a comparison with the same value.
734 TerminatorInst *PTI = Pred->getTerminator();
735 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
737 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
738 // Figure out which 'cases' to copy from SI to PSI.
739 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
740 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
742 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
743 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
745 // Based on whether the default edge from PTI goes to BB or not, fill in
746 // PredCases and PredDefault with the new switch cases we would like to
748 SmallVector<BasicBlock*, 8> NewSuccessors;
750 if (PredDefault == BB) {
751 // If this is the default destination from PTI, only the edges in TI
752 // that don't occur in PTI, or that branch to BB will be activated.
753 std::set<ConstantInt*> PTIHandled;
754 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
755 if (PredCases[i].second != BB)
756 PTIHandled.insert(PredCases[i].first);
758 // The default destination is BB, we don't need explicit targets.
759 std::swap(PredCases[i], PredCases.back());
760 PredCases.pop_back();
764 // Reconstruct the new switch statement we will be building.
765 if (PredDefault != BBDefault) {
766 PredDefault->removePredecessor(Pred);
767 PredDefault = BBDefault;
768 NewSuccessors.push_back(BBDefault);
770 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
771 if (!PTIHandled.count(BBCases[i].first) &&
772 BBCases[i].second != BBDefault) {
773 PredCases.push_back(BBCases[i]);
774 NewSuccessors.push_back(BBCases[i].second);
778 // If this is not the default destination from PSI, only the edges
779 // in SI that occur in PSI with a destination of BB will be
781 std::set<ConstantInt*> PTIHandled;
782 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
783 if (PredCases[i].second == BB) {
784 PTIHandled.insert(PredCases[i].first);
785 std::swap(PredCases[i], PredCases.back());
786 PredCases.pop_back();
790 // Okay, now we know which constants were sent to BB from the
791 // predecessor. Figure out where they will all go now.
792 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
793 if (PTIHandled.count(BBCases[i].first)) {
794 // If this is one we are capable of getting...
795 PredCases.push_back(BBCases[i]);
796 NewSuccessors.push_back(BBCases[i].second);
797 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
800 // If there are any constants vectored to BB that TI doesn't handle,
801 // they must go to the default destination of TI.
802 for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
803 E = PTIHandled.end(); I != E; ++I) {
804 PredCases.push_back(std::make_pair(*I, BBDefault));
805 NewSuccessors.push_back(BBDefault);
809 // Okay, at this point, we know which new successor Pred will get. Make
810 // sure we update the number of entries in the PHI nodes for these
812 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
813 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
815 // Now that the successors are updated, create the new Switch instruction.
816 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
817 PredCases.size(), PTI);
818 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
819 NewSI->addCase(PredCases[i].first, PredCases[i].second);
821 EraseTerminatorInstAndDCECond(PTI);
823 // Okay, last check. If BB is still a successor of PSI, then we must
824 // have an infinite loop case. If so, add an infinitely looping block
825 // to handle the case to preserve the behavior of the code.
826 BasicBlock *InfLoopBlock = 0;
827 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
828 if (NewSI->getSuccessor(i) == BB) {
829 if (InfLoopBlock == 0) {
830 // Insert it at the end of the function, because it's either code,
831 // or it won't matter if it's hot. :)
832 InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
833 BranchInst::Create(InfLoopBlock, InfLoopBlock);
835 NewSI->setSuccessor(i, InfLoopBlock);
844 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
845 /// BB2, hoist any common code in the two blocks up into the branch block. The
846 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
847 static bool HoistThenElseCodeToIf(BranchInst *BI) {
848 // This does very trivial matching, with limited scanning, to find identical
849 // instructions in the two blocks. In particular, we don't want to get into
850 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
851 // such, we currently just scan for obviously identical instructions in an
853 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
854 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
856 BasicBlock::iterator BB1_Itr = BB1->begin();
857 BasicBlock::iterator BB2_Itr = BB2->begin();
859 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
860 while (isa<DbgInfoIntrinsic>(I1))
862 while (isa<DbgInfoIntrinsic>(I2))
864 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
865 isa<InvokeInst>(I1) || !I1->isIdenticalTo(I2))
868 // If we get here, we can hoist at least one instruction.
869 BasicBlock *BIParent = BI->getParent();
872 // If we are hoisting the terminator instruction, don't move one (making a
873 // broken BB), instead clone it, and remove BI.
874 if (isa<TerminatorInst>(I1))
875 goto HoistTerminator;
877 // For a normal instruction, we just move one to right before the branch,
878 // then replace all uses of the other with the first. Finally, we remove
879 // the now redundant second instruction.
880 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
881 if (!I2->use_empty())
882 I2->replaceAllUsesWith(I1);
883 BB2->getInstList().erase(I2);
886 while (isa<DbgInfoIntrinsic>(I1))
889 while (isa<DbgInfoIntrinsic>(I2))
891 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
896 // Okay, it is safe to hoist the terminator.
897 Instruction *NT = I1->clone();
898 BIParent->getInstList().insert(BI, NT);
899 if (NT->getType() != Type::VoidTy) {
900 I1->replaceAllUsesWith(NT);
901 I2->replaceAllUsesWith(NT);
905 // Hoisting one of the terminators from our successor is a great thing.
906 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
907 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
908 // nodes, so we insert select instruction to compute the final result.
909 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
910 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
912 for (BasicBlock::iterator BBI = SI->begin();
913 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
914 Value *BB1V = PN->getIncomingValueForBlock(BB1);
915 Value *BB2V = PN->getIncomingValueForBlock(BB2);
917 // These values do not agree. Insert a select instruction before NT
918 // that determines the right value.
919 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
921 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
922 BB1V->getName()+"."+BB2V->getName(), NT);
923 // Make the PHI node use the select for all incoming values for BB1/BB2
924 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
925 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
926 PN->setIncomingValue(i, SI);
931 // Update any PHI nodes in our new successors.
932 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
933 AddPredecessorToBlock(*SI, BIParent, BB1);
935 EraseTerminatorInstAndDCECond(BI);
939 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
940 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
941 /// (for now, restricted to a single instruction that's side effect free) from
942 /// the BB1 into the branch block to speculatively execute it.
943 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
944 // Only speculatively execution a single instruction (not counting the
945 // terminator) for now.
946 BasicBlock::iterator BBI = BB1->begin();
947 ++BBI; // must have at least a terminator
948 if (BBI == BB1->end()) return false; // only one inst
950 if (BBI != BB1->end()) return false; // more than 2 insts.
952 // Be conservative for now. FP select instruction can often be expensive.
953 Value *BrCond = BI->getCondition();
954 if (isa<Instruction>(BrCond) &&
955 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
958 // If BB1 is actually on the false edge of the conditional branch, remember
959 // to swap the select operands later.
961 if (BB1 != BI->getSuccessor(0)) {
962 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
969 // br i1 %t1, label %BB1, label %BB2
978 // %t3 = select i1 %t1, %t2, %t3
979 Instruction *I = BB1->begin();
980 switch (I->getOpcode()) {
981 default: return false; // Not safe / profitable to hoist.
982 case Instruction::Add:
983 case Instruction::Sub:
984 // FP arithmetic might trap. Not worth doing for vector ops.
985 if (I->getType()->isFloatingPoint() || isa<VectorType>(I->getType()))
988 case Instruction::And:
989 case Instruction::Or:
990 case Instruction::Xor:
991 case Instruction::Shl:
992 case Instruction::LShr:
993 case Instruction::AShr:
994 // Don't mess with vector operations.
995 if (isa<VectorType>(I->getType()))
997 break; // These are all cheap and non-trapping instructions.
1000 // If the instruction is obviously dead, don't try to predicate it.
1001 if (I->use_empty()) {
1002 I->eraseFromParent();
1006 // Can we speculatively execute the instruction? And what is the value
1007 // if the condition is false? Consider the phi uses, if the incoming value
1008 // from the "if" block are all the same V, then V is the value of the
1009 // select if the condition is false.
1010 BasicBlock *BIParent = BI->getParent();
1011 SmallVector<PHINode*, 4> PHIUses;
1012 Value *FalseV = NULL;
1014 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1015 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1017 // Ignore any user that is not a PHI node in BB2. These can only occur in
1018 // unreachable blocks, because they would not be dominated by the instr.
1019 PHINode *PN = dyn_cast<PHINode>(UI);
1020 if (!PN || PN->getParent() != BB2)
1022 PHIUses.push_back(PN);
1024 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1027 else if (FalseV != PHIV)
1028 return false; // Inconsistent value when condition is false.
1031 assert(FalseV && "Must have at least one user, and it must be a PHI");
1033 // Do not hoist the instruction if any of its operands are defined but not
1034 // used in this BB. The transformation will prevent the operand from
1035 // being sunk into the use block.
1036 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) {
1037 Instruction *OpI = dyn_cast<Instruction>(*i);
1038 if (OpI && OpI->getParent() == BIParent &&
1039 !OpI->isUsedInBasicBlock(BIParent))
1043 // If we get here, we can hoist the instruction. Try to place it
1044 // before the icmp instruction preceeding the conditional branch.
1045 BasicBlock::iterator InsertPos = BI;
1046 if (InsertPos != BIParent->begin())
1048 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1049 SmallPtrSet<Instruction *, 4> BB1Insns;
1050 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1051 BB1I != BB1E; ++BB1I)
1052 BB1Insns.insert(BB1I);
1053 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1055 Instruction *Use = cast<Instruction>(*UI);
1056 if (BB1Insns.count(Use)) {
1057 // If BrCond uses the instruction that place it just before
1058 // branch instruction.
1065 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), I);
1067 // Create a select whose true value is the speculatively executed value and
1068 // false value is the previously determined FalseV.
1071 SI = SelectInst::Create(BrCond, FalseV, I,
1072 FalseV->getName() + "." + I->getName(), BI);
1074 SI = SelectInst::Create(BrCond, I, FalseV,
1075 I->getName() + "." + FalseV->getName(), BI);
1077 // Make the PHI node use the select for all incoming values for "then" and
1079 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1080 PHINode *PN = PHIUses[i];
1081 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1082 if (PN->getIncomingBlock(j) == BB1 ||
1083 PN->getIncomingBlock(j) == BIParent)
1084 PN->setIncomingValue(j, SI);
1091 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1092 /// across this block.
1093 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1094 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1097 // If this basic block contains anything other than a PHI (which controls the
1098 // branch) and branch itself, bail out. FIXME: improve this in the future.
1099 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) {
1100 if (Size > 10) return false; // Don't clone large BB's.
1102 // We can only support instructions that are do not define values that are
1103 // live outside of the current basic block.
1104 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1106 Instruction *U = cast<Instruction>(*UI);
1107 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1110 // Looks ok, continue checking.
1116 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1117 /// that is defined in the same block as the branch and if any PHI entries are
1118 /// constants, thread edges corresponding to that entry to be branches to their
1119 /// ultimate destination.
1120 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1121 BasicBlock *BB = BI->getParent();
1122 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1123 // NOTE: we currently cannot transform this case if the PHI node is used
1124 // outside of the block.
1125 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1128 // Degenerate case of a single entry PHI.
1129 if (PN->getNumIncomingValues() == 1) {
1130 FoldSingleEntryPHINodes(PN->getParent());
1134 // Now we know that this block has multiple preds and two succs.
1135 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1137 // Okay, this is a simple enough basic block. See if any phi values are
1139 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1141 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1142 CB->getType() == Type::Int1Ty) {
1143 // Okay, we now know that all edges from PredBB should be revectored to
1144 // branch to RealDest.
1145 BasicBlock *PredBB = PN->getIncomingBlock(i);
1146 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1148 if (RealDest == BB) continue; // Skip self loops.
1150 // The dest block might have PHI nodes, other predecessors and other
1151 // difficult cases. Instead of being smart about this, just insert a new
1152 // block that jumps to the destination block, effectively splitting
1153 // the edge we are about to create.
1154 BasicBlock *EdgeBB = BasicBlock::Create(RealDest->getName()+".critedge",
1155 RealDest->getParent(), RealDest);
1156 BranchInst::Create(RealDest, EdgeBB);
1158 for (BasicBlock::iterator BBI = RealDest->begin();
1159 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1160 Value *V = PN->getIncomingValueForBlock(BB);
1161 PN->addIncoming(V, EdgeBB);
1164 // BB may have instructions that are being threaded over. Clone these
1165 // instructions into EdgeBB. We know that there will be no uses of the
1166 // cloned instructions outside of EdgeBB.
1167 BasicBlock::iterator InsertPt = EdgeBB->begin();
1168 std::map<Value*, Value*> TranslateMap; // Track translated values.
1169 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1170 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1171 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1173 // Clone the instruction.
1174 Instruction *N = BBI->clone();
1175 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1177 // Update operands due to translation.
1178 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1180 std::map<Value*, Value*>::iterator PI =
1181 TranslateMap.find(*i);
1182 if (PI != TranslateMap.end())
1186 // Check for trivial simplification.
1187 if (Constant *C = ConstantFoldInstruction(N)) {
1188 TranslateMap[BBI] = C;
1189 delete N; // Constant folded away, don't need actual inst
1191 // Insert the new instruction into its new home.
1192 EdgeBB->getInstList().insert(InsertPt, N);
1193 if (!BBI->use_empty())
1194 TranslateMap[BBI] = N;
1199 // Loop over all of the edges from PredBB to BB, changing them to branch
1200 // to EdgeBB instead.
1201 TerminatorInst *PredBBTI = PredBB->getTerminator();
1202 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1203 if (PredBBTI->getSuccessor(i) == BB) {
1204 BB->removePredecessor(PredBB);
1205 PredBBTI->setSuccessor(i, EdgeBB);
1208 // Recurse, simplifying any other constants.
1209 return FoldCondBranchOnPHI(BI) | true;
1216 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1217 /// PHI node, see if we can eliminate it.
1218 static bool FoldTwoEntryPHINode(PHINode *PN) {
1219 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1220 // statement", which has a very simple dominance structure. Basically, we
1221 // are trying to find the condition that is being branched on, which
1222 // subsequently causes this merge to happen. We really want control
1223 // dependence information for this check, but simplifycfg can't keep it up
1224 // to date, and this catches most of the cases we care about anyway.
1226 BasicBlock *BB = PN->getParent();
1227 BasicBlock *IfTrue, *IfFalse;
1228 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1229 if (!IfCond) return false;
1231 // Okay, we found that we can merge this two-entry phi node into a select.
1232 // Doing so would require us to fold *all* two entry phi nodes in this block.
1233 // At some point this becomes non-profitable (particularly if the target
1234 // doesn't support cmov's). Only do this transformation if there are two or
1235 // fewer PHI nodes in this block.
1236 unsigned NumPhis = 0;
1237 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1241 DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
1242 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
1244 // Loop over the PHI's seeing if we can promote them all to select
1245 // instructions. While we are at it, keep track of the instructions
1246 // that need to be moved to the dominating block.
1247 std::set<Instruction*> AggressiveInsts;
1249 BasicBlock::iterator AfterPHIIt = BB->begin();
1250 while (isa<PHINode>(AfterPHIIt)) {
1251 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1252 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1253 if (PN->getIncomingValue(0) != PN)
1254 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1256 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1257 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1258 &AggressiveInsts) ||
1259 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1260 &AggressiveInsts)) {
1265 // If we all PHI nodes are promotable, check to make sure that all
1266 // instructions in the predecessor blocks can be promoted as well. If
1267 // not, we won't be able to get rid of the control flow, so it's not
1268 // worth promoting to select instructions.
1269 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1270 PN = cast<PHINode>(BB->begin());
1271 BasicBlock *Pred = PN->getIncomingBlock(0);
1272 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1274 DomBlock = *pred_begin(Pred);
1275 for (BasicBlock::iterator I = Pred->begin();
1276 !isa<TerminatorInst>(I); ++I)
1277 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1278 // This is not an aggressive instruction that we can promote.
1279 // Because of this, we won't be able to get rid of the control
1280 // flow, so the xform is not worth it.
1285 Pred = PN->getIncomingBlock(1);
1286 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1288 DomBlock = *pred_begin(Pred);
1289 for (BasicBlock::iterator I = Pred->begin();
1290 !isa<TerminatorInst>(I); ++I)
1291 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1292 // This is not an aggressive instruction that we can promote.
1293 // Because of this, we won't be able to get rid of the control
1294 // flow, so the xform is not worth it.
1299 // If we can still promote the PHI nodes after this gauntlet of tests,
1300 // do all of the PHI's now.
1302 // Move all 'aggressive' instructions, which are defined in the
1303 // conditional parts of the if's up to the dominating block.
1305 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1306 IfBlock1->getInstList(),
1308 IfBlock1->getTerminator());
1311 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1312 IfBlock2->getInstList(),
1314 IfBlock2->getTerminator());
1317 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1318 // Change the PHI node into a select instruction.
1320 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1322 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1324 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1325 PN->replaceAllUsesWith(NV);
1328 BB->getInstList().erase(PN);
1333 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1334 /// to two returning blocks, try to merge them together into one return,
1335 /// introducing a select if the return values disagree.
1336 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1337 assert(BI->isConditional() && "Must be a conditional branch");
1338 BasicBlock *TrueSucc = BI->getSuccessor(0);
1339 BasicBlock *FalseSucc = BI->getSuccessor(1);
1340 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1341 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1343 // Check to ensure both blocks are empty (just a return) or optionally empty
1344 // with PHI nodes. If there are other instructions, merging would cause extra
1345 // computation on one path or the other.
1346 BasicBlock::iterator BBI = TrueRet;
1347 if (BBI != TrueSucc->begin() && !isa<PHINode>(--BBI))
1348 return false; // Not empty with optional phi nodes.
1350 if (BBI != FalseSucc->begin() && !isa<PHINode>(--BBI))
1351 return false; // Not empty with optional phi nodes.
1353 // Okay, we found a branch that is going to two return nodes. If
1354 // there is no return value for this function, just change the
1355 // branch into a return.
1356 if (FalseRet->getNumOperands() == 0) {
1357 TrueSucc->removePredecessor(BI->getParent());
1358 FalseSucc->removePredecessor(BI->getParent());
1359 ReturnInst::Create(0, BI);
1360 EraseTerminatorInstAndDCECond(BI);
1364 // Otherwise, figure out what the true and false return values are
1365 // so we can insert a new select instruction.
1366 Value *TrueValue = TrueRet->getReturnValue();
1367 Value *FalseValue = FalseRet->getReturnValue();
1369 // Unwrap any PHI nodes in the return blocks.
1370 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1371 if (TVPN->getParent() == TrueSucc)
1372 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1373 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1374 if (FVPN->getParent() == FalseSucc)
1375 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1377 // In order for this transformation to be safe, we must be able to
1378 // unconditionally execute both operands to the return. This is
1379 // normally the case, but we could have a potentially-trapping
1380 // constant expression that prevents this transformation from being
1382 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1385 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1389 // Okay, we collected all the mapped values and checked them for sanity, and
1390 // defined to really do this transformation. First, update the CFG.
1391 TrueSucc->removePredecessor(BI->getParent());
1392 FalseSucc->removePredecessor(BI->getParent());
1394 // Insert select instructions where needed.
1395 Value *BrCond = BI->getCondition();
1397 // Insert a select if the results differ.
1398 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1399 } else if (isa<UndefValue>(TrueValue)) {
1400 TrueValue = FalseValue;
1402 TrueValue = SelectInst::Create(BrCond, TrueValue,
1403 FalseValue, "retval", BI);
1407 Value *RI = !TrueValue ?
1408 ReturnInst::Create(BI) :
1409 ReturnInst::Create(TrueValue, BI);
1411 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1412 << "\n " << *BI << "NewRet = " << *RI
1413 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
1415 EraseTerminatorInstAndDCECond(BI);
1420 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1421 /// and if a predecessor branches to us and one of our successors, fold the
1422 /// setcc into the predecessor and use logical operations to pick the right
1424 static bool FoldBranchToCommonDest(BranchInst *BI) {
1425 BasicBlock *BB = BI->getParent();
1426 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1427 if (Cond == 0) return false;
1430 // Only allow this if the condition is a simple instruction that can be
1431 // executed unconditionally. It must be in the same block as the branch, and
1432 // must be at the front of the block.
1433 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1434 Cond->getParent() != BB || &BB->front() != Cond || !Cond->hasOneUse())
1437 // Make sure the instruction after the condition is the cond branch.
1438 BasicBlock::iterator CondIt = Cond; ++CondIt;
1442 // Cond is known to be a compare or binary operator. Check to make sure that
1443 // neither operand is a potentially-trapping constant expression.
1444 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1447 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1452 // Finally, don't infinitely unroll conditional loops.
1453 BasicBlock *TrueDest = BI->getSuccessor(0);
1454 BasicBlock *FalseDest = BI->getSuccessor(1);
1455 if (TrueDest == BB || FalseDest == BB)
1458 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1459 BasicBlock *PredBlock = *PI;
1460 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1462 // Check that we have two conditional branches. If there is a PHI node in
1463 // the common successor, verify that the same value flows in from both
1465 if (PBI == 0 || PBI->isUnconditional() ||
1466 !SafeToMergeTerminators(BI, PBI))
1469 Instruction::BinaryOps Opc;
1470 bool InvertPredCond = false;
1472 if (PBI->getSuccessor(0) == TrueDest)
1473 Opc = Instruction::Or;
1474 else if (PBI->getSuccessor(1) == FalseDest)
1475 Opc = Instruction::And;
1476 else if (PBI->getSuccessor(0) == FalseDest)
1477 Opc = Instruction::And, InvertPredCond = true;
1478 else if (PBI->getSuccessor(1) == TrueDest)
1479 Opc = Instruction::Or, InvertPredCond = true;
1483 DOUT << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB;
1485 // If we need to invert the condition in the pred block to match, do so now.
1486 if (InvertPredCond) {
1488 BinaryOperator::CreateNot(PBI->getCondition(),
1489 PBI->getCondition()->getName()+".not", PBI);
1490 PBI->setCondition(NewCond);
1491 BasicBlock *OldTrue = PBI->getSuccessor(0);
1492 BasicBlock *OldFalse = PBI->getSuccessor(1);
1493 PBI->setSuccessor(0, OldFalse);
1494 PBI->setSuccessor(1, OldTrue);
1497 // Clone Cond into the predecessor basic block, and or/and the
1498 // two conditions together.
1499 Instruction *New = Cond->clone();
1500 PredBlock->getInstList().insert(PBI, New);
1501 New->takeName(Cond);
1502 Cond->setName(New->getName()+".old");
1504 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1505 New, "or.cond", PBI);
1506 PBI->setCondition(NewCond);
1507 if (PBI->getSuccessor(0) == BB) {
1508 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1509 PBI->setSuccessor(0, TrueDest);
1511 if (PBI->getSuccessor(1) == BB) {
1512 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1513 PBI->setSuccessor(1, FalseDest);
1520 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1521 /// predecessor of another block, this function tries to simplify it. We know
1522 /// that PBI and BI are both conditional branches, and BI is in one of the
1523 /// successor blocks of PBI - PBI branches to BI.
1524 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1525 assert(PBI->isConditional() && BI->isConditional());
1526 BasicBlock *BB = BI->getParent();
1528 // If this block ends with a branch instruction, and if there is a
1529 // predecessor that ends on a branch of the same condition, make
1530 // this conditional branch redundant.
1531 if (PBI->getCondition() == BI->getCondition() &&
1532 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1533 // Okay, the outcome of this conditional branch is statically
1534 // knowable. If this block had a single pred, handle specially.
1535 if (BB->getSinglePredecessor()) {
1536 // Turn this into a branch on constant.
1537 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1538 BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
1539 return true; // Nuke the branch on constant.
1542 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1543 // in the constant and simplify the block result. Subsequent passes of
1544 // simplifycfg will thread the block.
1545 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1546 PHINode *NewPN = PHINode::Create(Type::Int1Ty,
1547 BI->getCondition()->getName() + ".pr",
1549 // Okay, we're going to insert the PHI node. Since PBI is not the only
1550 // predecessor, compute the PHI'd conditional value for all of the preds.
1551 // Any predecessor where the condition is not computable we keep symbolic.
1552 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1553 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1554 PBI != BI && PBI->isConditional() &&
1555 PBI->getCondition() == BI->getCondition() &&
1556 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1557 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1558 NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
1561 NewPN->addIncoming(BI->getCondition(), *PI);
1564 BI->setCondition(NewPN);
1569 // If this is a conditional branch in an empty block, and if any
1570 // predecessors is a conditional branch to one of our destinations,
1571 // fold the conditions into logical ops and one cond br.
1572 if (&BB->front() != BI)
1576 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1581 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1583 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1584 PBIOp = 0, BIOp = 1;
1585 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1586 PBIOp = 1, BIOp = 0;
1587 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1592 // Check to make sure that the other destination of this branch
1593 // isn't BB itself. If so, this is an infinite loop that will
1594 // keep getting unwound.
1595 if (PBI->getSuccessor(PBIOp) == BB)
1598 // Do not perform this transformation if it would require
1599 // insertion of a large number of select instructions. For targets
1600 // without predication/cmovs, this is a big pessimization.
1601 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1603 unsigned NumPhis = 0;
1604 for (BasicBlock::iterator II = CommonDest->begin();
1605 isa<PHINode>(II); ++II, ++NumPhis)
1606 if (NumPhis > 2) // Disable this xform.
1609 // Finally, if everything is ok, fold the branches to logical ops.
1610 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1612 DOUT << "FOLDING BRs:" << *PBI->getParent()
1613 << "AND: " << *BI->getParent();
1616 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1617 // branch in it, where one edge (OtherDest) goes back to itself but the other
1618 // exits. We don't *know* that the program avoids the infinite loop
1619 // (even though that seems likely). If we do this xform naively, we'll end up
1620 // recursively unpeeling the loop. Since we know that (after the xform is
1621 // done) that the block *is* infinite if reached, we just make it an obviously
1622 // infinite loop with no cond branch.
1623 if (OtherDest == BB) {
1624 // Insert it at the end of the function, because it's either code,
1625 // or it won't matter if it's hot. :)
1626 BasicBlock *InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
1627 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1628 OtherDest = InfLoopBlock;
1631 DOUT << *PBI->getParent()->getParent();
1633 // BI may have other predecessors. Because of this, we leave
1634 // it alone, but modify PBI.
1636 // Make sure we get to CommonDest on True&True directions.
1637 Value *PBICond = PBI->getCondition();
1639 PBICond = BinaryOperator::CreateNot(PBICond,
1640 PBICond->getName()+".not",
1642 Value *BICond = BI->getCondition();
1644 BICond = BinaryOperator::CreateNot(BICond,
1645 BICond->getName()+".not",
1647 // Merge the conditions.
1648 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1650 // Modify PBI to branch on the new condition to the new dests.
1651 PBI->setCondition(Cond);
1652 PBI->setSuccessor(0, CommonDest);
1653 PBI->setSuccessor(1, OtherDest);
1655 // OtherDest may have phi nodes. If so, add an entry from PBI's
1656 // block that are identical to the entries for BI's block.
1658 for (BasicBlock::iterator II = OtherDest->begin();
1659 (PN = dyn_cast<PHINode>(II)); ++II) {
1660 Value *V = PN->getIncomingValueForBlock(BB);
1661 PN->addIncoming(V, PBI->getParent());
1664 // We know that the CommonDest already had an edge from PBI to
1665 // it. If it has PHIs though, the PHIs may have different
1666 // entries for BB and PBI's BB. If so, insert a select to make
1668 for (BasicBlock::iterator II = CommonDest->begin();
1669 (PN = dyn_cast<PHINode>(II)); ++II) {
1670 Value *BIV = PN->getIncomingValueForBlock(BB);
1671 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1672 Value *PBIV = PN->getIncomingValue(PBBIdx);
1674 // Insert a select in PBI to pick the right value.
1675 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1676 PBIV->getName()+".mux", PBI);
1677 PN->setIncomingValue(PBBIdx, NV);
1681 DOUT << "INTO: " << *PBI->getParent();
1683 DOUT << *PBI->getParent()->getParent();
1685 // This basic block is probably dead. We know it has at least
1686 // one fewer predecessor.
1692 /// ConstantIntOrdering - This class implements a stable ordering of constant
1693 /// integers that does not depend on their address. This is important for
1694 /// applications that sort ConstantInt's to ensure uniqueness.
1695 struct ConstantIntOrdering {
1696 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
1697 return LHS->getValue().ult(RHS->getValue());
1702 /// SimplifyCFG - This function is used to do simplification of a CFG. For
1703 /// example, it adjusts branches to branches to eliminate the extra hop, it
1704 /// eliminates unreachable basic blocks, and does other "peephole" optimization
1705 /// of the CFG. It returns true if a modification was made.
1707 /// WARNING: The entry node of a function may not be simplified.
1709 bool llvm::SimplifyCFG(BasicBlock *BB) {
1710 bool Changed = false;
1711 Function *M = BB->getParent();
1713 assert(BB && BB->getParent() && "Block not embedded in function!");
1714 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1715 assert(&BB->getParent()->getEntryBlock() != BB &&
1716 "Can't Simplify entry block!");
1718 // Remove basic blocks that have no predecessors... or that just have themself
1719 // as a predecessor. These are unreachable.
1720 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1721 DOUT << "Removing BB: \n" << *BB;
1722 DeleteDeadBlock(BB);
1726 // Check to see if we can constant propagate this terminator instruction
1728 Changed |= ConstantFoldTerminator(BB);
1730 // If there is a trivial two-entry PHI node in this basic block, and we can
1731 // eliminate it, do so now.
1732 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1733 if (PN->getNumIncomingValues() == 2)
1734 Changed |= FoldTwoEntryPHINode(PN);
1736 // If this is a returning block with only PHI nodes in it, fold the return
1737 // instruction into any unconditional branch predecessors.
1739 // If any predecessor is a conditional branch that just selects among
1740 // different return values, fold the replace the branch/return with a select
1742 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1743 BasicBlock::iterator BBI = BB->getTerminator();
1744 if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
1745 // Find predecessors that end with branches.
1746 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1747 SmallVector<BranchInst*, 8> CondBranchPreds;
1748 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1749 TerminatorInst *PTI = (*PI)->getTerminator();
1750 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1751 if (BI->isUnconditional())
1752 UncondBranchPreds.push_back(*PI);
1754 CondBranchPreds.push_back(BI);
1758 // If we found some, do the transformation!
1759 if (!UncondBranchPreds.empty()) {
1760 while (!UncondBranchPreds.empty()) {
1761 BasicBlock *Pred = UncondBranchPreds.back();
1762 DOUT << "FOLDING: " << *BB
1763 << "INTO UNCOND BRANCH PRED: " << *Pred;
1764 UncondBranchPreds.pop_back();
1765 Instruction *UncondBranch = Pred->getTerminator();
1766 // Clone the return and add it to the end of the predecessor.
1767 Instruction *NewRet = RI->clone();
1768 Pred->getInstList().push_back(NewRet);
1770 // If the return instruction returns a value, and if the value was a
1771 // PHI node in "BB", propagate the right value into the return.
1772 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1774 if (PHINode *PN = dyn_cast<PHINode>(*i))
1775 if (PN->getParent() == BB)
1776 *i = PN->getIncomingValueForBlock(Pred);
1778 // Update any PHI nodes in the returning block to realize that we no
1779 // longer branch to them.
1780 BB->removePredecessor(Pred);
1781 Pred->getInstList().erase(UncondBranch);
1784 // If we eliminated all predecessors of the block, delete the block now.
1785 if (pred_begin(BB) == pred_end(BB))
1786 // We know there are no successors, so just nuke the block.
1787 M->getBasicBlockList().erase(BB);
1792 // Check out all of the conditional branches going to this return
1793 // instruction. If any of them just select between returns, change the
1794 // branch itself into a select/return pair.
1795 while (!CondBranchPreds.empty()) {
1796 BranchInst *BI = CondBranchPreds.back();
1797 CondBranchPreds.pop_back();
1799 // Check to see if the non-BB successor is also a return block.
1800 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1801 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1802 SimplifyCondBranchToTwoReturns(BI))
1806 } else if (isa<UnwindInst>(BB->begin())) {
1807 // Check to see if the first instruction in this block is just an unwind.
1808 // If so, replace any invoke instructions which use this as an exception
1809 // destination with call instructions, and any unconditional branch
1810 // predecessor with an unwind.
1812 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1813 while (!Preds.empty()) {
1814 BasicBlock *Pred = Preds.back();
1815 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1816 if (BI->isUnconditional()) {
1817 Pred->getInstList().pop_back(); // nuke uncond branch
1818 new UnwindInst(Pred); // Use unwind.
1821 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1822 if (II->getUnwindDest() == BB) {
1823 // Insert a new branch instruction before the invoke, because this
1824 // is now a fall through...
1825 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1826 Pred->getInstList().remove(II); // Take out of symbol table
1828 // Insert the call now...
1829 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1830 CallInst *CI = CallInst::Create(II->getCalledValue(),
1831 Args.begin(), Args.end(),
1833 CI->setCallingConv(II->getCallingConv());
1834 CI->setAttributes(II->getAttributes());
1835 // If the invoke produced a value, the Call now does instead
1836 II->replaceAllUsesWith(CI);
1844 // If this block is now dead, remove it.
1845 if (pred_begin(BB) == pred_end(BB)) {
1846 // We know there are no successors, so just nuke the block.
1847 M->getBasicBlockList().erase(BB);
1851 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1852 if (isValueEqualityComparison(SI)) {
1853 // If we only have one predecessor, and if it is a branch on this value,
1854 // see if that predecessor totally determines the outcome of this switch.
1855 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1856 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1857 return SimplifyCFG(BB) || 1;
1859 // If the block only contains the switch, see if we can fold the block
1860 // away into any preds.
1861 if (SI == &BB->front())
1862 if (FoldValueComparisonIntoPredecessors(SI))
1863 return SimplifyCFG(BB) || 1;
1865 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1866 if (BI->isUnconditional()) {
1867 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1869 BasicBlock *Succ = BI->getSuccessor(0);
1870 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1871 Succ != BB) // Don't hurt infinite loops!
1872 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1875 } else { // Conditional branch
1876 if (isValueEqualityComparison(BI)) {
1877 // If we only have one predecessor, and if it is a branch on this value,
1878 // see if that predecessor totally determines the outcome of this
1880 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1881 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1882 return SimplifyCFG(BB) || 1;
1884 // This block must be empty, except for the setcond inst, if it exists.
1885 BasicBlock::iterator I = BB->begin();
1887 (&*I == cast<Instruction>(BI->getCondition()) &&
1889 if (FoldValueComparisonIntoPredecessors(BI))
1890 return SimplifyCFG(BB) | true;
1893 // If this is a branch on a phi node in the current block, thread control
1894 // through this block if any PHI node entries are constants.
1895 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1896 if (PN->getParent() == BI->getParent())
1897 if (FoldCondBranchOnPHI(BI))
1898 return SimplifyCFG(BB) | true;
1900 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1901 // branches to us and one of our successors, fold the setcc into the
1902 // predecessor and use logical operations to pick the right destination.
1903 if (FoldBranchToCommonDest(BI))
1904 return SimplifyCFG(BB) | 1;
1907 // Scan predecessor blocks for conditional branches.
1908 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1909 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1910 if (PBI != BI && PBI->isConditional())
1911 if (SimplifyCondBranchToCondBranch(PBI, BI))
1912 return SimplifyCFG(BB) | true;
1914 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1915 // If there are any instructions immediately before the unreachable that can
1916 // be removed, do so.
1917 Instruction *Unreachable = BB->getTerminator();
1918 while (Unreachable != BB->begin()) {
1919 BasicBlock::iterator BBI = Unreachable;
1921 // Do not delete instructions that can have side effects, like calls
1922 // (which may never return) and volatile loads and stores.
1923 if (isa<CallInst>(BBI)) break;
1925 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
1926 if (SI->isVolatile())
1929 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
1930 if (LI->isVolatile())
1933 // Delete this instruction
1934 BB->getInstList().erase(BBI);
1938 // If the unreachable instruction is the first in the block, take a gander
1939 // at all of the predecessors of this instruction, and simplify them.
1940 if (&BB->front() == Unreachable) {
1941 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1942 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1943 TerminatorInst *TI = Preds[i]->getTerminator();
1945 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1946 if (BI->isUnconditional()) {
1947 if (BI->getSuccessor(0) == BB) {
1948 new UnreachableInst(TI);
1949 TI->eraseFromParent();
1953 if (BI->getSuccessor(0) == BB) {
1954 BranchInst::Create(BI->getSuccessor(1), BI);
1955 EraseTerminatorInstAndDCECond(BI);
1956 } else if (BI->getSuccessor(1) == BB) {
1957 BranchInst::Create(BI->getSuccessor(0), BI);
1958 EraseTerminatorInstAndDCECond(BI);
1962 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1963 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1964 if (SI->getSuccessor(i) == BB) {
1965 BB->removePredecessor(SI->getParent());
1970 // If the default value is unreachable, figure out the most popular
1971 // destination and make it the default.
1972 if (SI->getSuccessor(0) == BB) {
1973 std::map<BasicBlock*, unsigned> Popularity;
1974 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1975 Popularity[SI->getSuccessor(i)]++;
1977 // Find the most popular block.
1978 unsigned MaxPop = 0;
1979 BasicBlock *MaxBlock = 0;
1980 for (std::map<BasicBlock*, unsigned>::iterator
1981 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
1982 if (I->second > MaxPop) {
1984 MaxBlock = I->first;
1988 // Make this the new default, allowing us to delete any explicit
1990 SI->setSuccessor(0, MaxBlock);
1993 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
1995 if (isa<PHINode>(MaxBlock->begin()))
1996 for (unsigned i = 0; i != MaxPop-1; ++i)
1997 MaxBlock->removePredecessor(SI->getParent());
1999 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2000 if (SI->getSuccessor(i) == MaxBlock) {
2006 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2007 if (II->getUnwindDest() == BB) {
2008 // Convert the invoke to a call instruction. This would be a good
2009 // place to note that the call does not throw though.
2010 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2011 II->removeFromParent(); // Take out of symbol table
2013 // Insert the call now...
2014 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
2015 CallInst *CI = CallInst::Create(II->getCalledValue(),
2016 Args.begin(), Args.end(),
2018 CI->setCallingConv(II->getCallingConv());
2019 CI->setAttributes(II->getAttributes());
2020 // If the invoke produced a value, the Call does now instead.
2021 II->replaceAllUsesWith(CI);
2028 // If this block is now dead, remove it.
2029 if (pred_begin(BB) == pred_end(BB)) {
2030 // We know there are no successors, so just nuke the block.
2031 M->getBasicBlockList().erase(BB);
2037 // Merge basic blocks into their predecessor if there is only one distinct
2038 // pred, and if there is only one distinct successor of the predecessor, and
2039 // if there are no PHI nodes.
2041 if (MergeBlockIntoPredecessor(BB))
2044 // Otherwise, if this block only has a single predecessor, and if that block
2045 // is a conditional branch, see if we can hoist any code from this block up
2046 // into our predecessor.
2047 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2048 BasicBlock *OnlyPred = *PI++;
2049 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2050 if (*PI != OnlyPred) {
2051 OnlyPred = 0; // There are multiple different predecessors...
2056 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2057 if (BI->isConditional()) {
2058 // Get the other block.
2059 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2060 PI = pred_begin(OtherBB);
2063 if (PI == pred_end(OtherBB)) {
2064 // We have a conditional branch to two blocks that are only reachable
2065 // from the condbr. We know that the condbr dominates the two blocks,
2066 // so see if there is any identical code in the "then" and "else"
2067 // blocks. If so, we can hoist it up to the branching block.
2068 Changed |= HoistThenElseCodeToIf(BI);
2070 BasicBlock* OnlySucc = NULL;
2071 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2075 else if (*SI != OnlySucc) {
2076 OnlySucc = 0; // There are multiple distinct successors!
2081 if (OnlySucc == OtherBB) {
2082 // If BB's only successor is the other successor of the predecessor,
2083 // i.e. a triangle, see if we can hoist any code from this block up
2084 // to the "if" block.
2085 Changed |= SpeculativelyExecuteBB(BI, BB);
2090 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2091 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2092 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2093 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2094 Instruction *Cond = cast<Instruction>(BI->getCondition());
2095 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2096 // 'setne's and'ed together, collect them.
2098 std::vector<ConstantInt*> Values;
2099 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2100 if (CompVal && CompVal->getType()->isInteger()) {
2101 // There might be duplicate constants in the list, which the switch
2102 // instruction can't handle, remove them now.
2103 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2104 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2106 // Figure out which block is which destination.
2107 BasicBlock *DefaultBB = BI->getSuccessor(1);
2108 BasicBlock *EdgeBB = BI->getSuccessor(0);
2109 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2111 // Create the new switch instruction now.
2112 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2115 // Add all of the 'cases' to the switch instruction.
2116 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2117 New->addCase(Values[i], EdgeBB);
2119 // We added edges from PI to the EdgeBB. As such, if there were any
2120 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2121 // the number of edges added.
2122 for (BasicBlock::iterator BBI = EdgeBB->begin();
2123 isa<PHINode>(BBI); ++BBI) {
2124 PHINode *PN = cast<PHINode>(BBI);
2125 Value *InVal = PN->getIncomingValueForBlock(*PI);
2126 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2127 PN->addIncoming(InVal, *PI);
2130 // Erase the old branch instruction.
2131 EraseTerminatorInstAndDCECond(BI);