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/Type.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/Support/CFG.h"
21 #include "llvm/Support/Debug.h"
22 #include "llvm/Analysis/ConstantFolding.h"
23 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
24 #include "llvm/ADT/SmallVector.h"
25 #include "llvm/ADT/SmallPtrSet.h"
32 /// SafeToMergeTerminators - Return true if it is safe to merge these two
33 /// terminator instructions together.
35 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
36 if (SI1 == SI2) return false; // Can't merge with self!
38 // It is not safe to merge these two switch instructions if they have a common
39 // successor, and if that successor has a PHI node, and if *that* PHI node has
40 // conflicting incoming values from the two switch blocks.
41 BasicBlock *SI1BB = SI1->getParent();
42 BasicBlock *SI2BB = SI2->getParent();
43 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
45 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
46 if (SI1Succs.count(*I))
47 for (BasicBlock::iterator BBI = (*I)->begin();
48 isa<PHINode>(BBI); ++BBI) {
49 PHINode *PN = cast<PHINode>(BBI);
50 if (PN->getIncomingValueForBlock(SI1BB) !=
51 PN->getIncomingValueForBlock(SI2BB))
58 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
59 /// now be entries in it from the 'NewPred' block. The values that will be
60 /// flowing into the PHI nodes will be the same as those coming in from
61 /// ExistPred, an existing predecessor of Succ.
62 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
63 BasicBlock *ExistPred) {
64 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
65 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
66 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
68 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
69 PHINode *PN = cast<PHINode>(I);
70 Value *V = PN->getIncomingValueForBlock(ExistPred);
71 PN->addIncoming(V, NewPred);
75 // CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
76 // almost-empty BB ending in an unconditional branch to Succ, into succ.
78 // Assumption: Succ is the single successor for BB.
80 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
81 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
83 DOUT << "Looking to fold " << BB->getNameStart() << " into "
84 << Succ->getNameStart() << "\n";
85 // Shortcut, if there is only a single predecessor is must be BB and merging
87 if (Succ->getSinglePredecessor()) return true;
89 typedef SmallPtrSet<Instruction*, 16> InstrSet;
92 // Make a list of all phi nodes in BB
93 BasicBlock::iterator BBI = BB->begin();
94 while (isa<PHINode>(*BBI)) BBPHIs.insert(BBI++);
96 // Make a list of the predecessors of BB
97 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
98 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
100 // Use that list to make another list of common predecessors of BB and Succ
101 BlockSet CommonPreds;
102 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
104 if (BBPreds.count(*PI))
105 CommonPreds.insert(*PI);
107 // Shortcut, if there are no common predecessors, merging is always safe
108 if (CommonPreds.begin() == CommonPreds.end())
111 // Look at all the phi nodes in Succ, to see if they present a conflict when
112 // merging these blocks
113 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
114 PHINode *PN = cast<PHINode>(I);
116 // If the incoming value from BB is again a PHINode in
117 // BB which has the same incoming value for *PI as PN does, we can
118 // merge the phi nodes and then the blocks can still be merged
119 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
120 if (BBPN && BBPN->getParent() == BB) {
121 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
123 if (BBPN->getIncomingValueForBlock(*PI)
124 != PN->getIncomingValueForBlock(*PI)) {
125 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
126 << Succ->getNameStart() << " is conflicting with "
127 << BBPN->getNameStart() << " with regard to common predecessor "
128 << (*PI)->getNameStart() << "\n";
132 // Remove this phinode from the list of phis in BB, since it has been
136 Value* Val = PN->getIncomingValueForBlock(BB);
137 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
139 // See if the incoming value for the common predecessor is equal to the
140 // one for BB, in which case this phi node will not prevent the merging
142 if (Val != PN->getIncomingValueForBlock(*PI)) {
143 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
144 << Succ->getNameStart() << " is conflicting with regard to common "
145 << "predecessor " << (*PI)->getNameStart() << "\n";
152 // If there are any other phi nodes in BB that don't have a phi node in Succ
153 // to merge with, they must be moved to Succ completely. However, for any
154 // predecessors of Succ, branches will be added to the phi node that just
155 // point to itself. So, for any common predecessors, this must not cause
157 for (InstrSet::iterator I = BBPHIs.begin(), E = BBPHIs.end();
159 PHINode *PN = cast<PHINode>(*I);
160 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
162 if (PN->getIncomingValueForBlock(*PI) != PN) {
163 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
164 << BB->getNameStart() << " is conflicting with regard to common "
165 << "predecessor " << (*PI)->getNameStart() << "\n";
173 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
174 /// branch to Succ, and contains no instructions other than PHI nodes and the
175 /// branch. If possible, eliminate BB.
176 static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
178 // Check to see if merging these blocks would cause conflicts for any of the
179 // phi nodes in BB or Succ. If not, we can safely merge.
180 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
182 DOUT << "Killing Trivial BB: \n" << *BB;
184 if (isa<PHINode>(Succ->begin())) {
185 // If there is more than one pred of succ, and there are PHI nodes in
186 // the successor, then we need to add incoming edges for the PHI nodes
188 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
190 // Loop over all of the PHI nodes in the successor of BB.
191 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
192 PHINode *PN = cast<PHINode>(I);
193 Value *OldVal = PN->removeIncomingValue(BB, false);
194 assert(OldVal && "No entry in PHI for Pred BB!");
196 // If this incoming value is one of the PHI nodes in BB, the new entries
197 // in the PHI node are the entries from the old PHI.
198 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
199 PHINode *OldValPN = cast<PHINode>(OldVal);
200 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
201 // Note that, since we are merging phi nodes and BB and Succ might
202 // have common predecessors, we could end up with a phi node with
203 // identical incoming branches. This will be cleaned up later (and
204 // will trigger asserts if we try to clean it up now, without also
205 // simplifying the corresponding conditional branch).
206 PN->addIncoming(OldValPN->getIncomingValue(i),
207 OldValPN->getIncomingBlock(i));
209 // Add an incoming value for each of the new incoming values.
210 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
211 PN->addIncoming(OldVal, BBPreds[i]);
216 if (isa<PHINode>(&BB->front())) {
217 SmallVector<BasicBlock*, 16>
218 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
220 // Move all PHI nodes in BB to Succ if they are alive, otherwise
222 while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
223 if (PN->use_empty()) {
224 // Just remove the dead phi. This happens if Succ's PHIs were the only
225 // users of the PHI nodes.
226 PN->eraseFromParent();
228 // The instruction is alive, so this means that BB must dominate all
229 // predecessors of Succ (Since all uses of the PN are after its
230 // definition, so in Succ or a block dominated by Succ. If a predecessor
231 // of Succ would not be dominated by BB, PN would violate the def before
232 // use SSA demand). Therefore, we can simply move the phi node to the
234 Succ->getInstList().splice(Succ->begin(),
235 BB->getInstList(), BB->begin());
237 // We need to add new entries for the PHI node to account for
238 // predecessors of Succ that the PHI node does not take into
239 // account. At this point, since we know that BB dominated succ and all
240 // of its predecessors, this means that we should any newly added
241 // incoming edges should use the PHI node itself as the value for these
242 // edges, because they are loop back edges.
243 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
244 if (OldSuccPreds[i] != BB)
245 PN->addIncoming(PN, OldSuccPreds[i]);
249 // Everything that jumped to BB now goes to Succ.
250 BB->replaceAllUsesWith(Succ);
251 if (!Succ->hasName()) Succ->takeName(BB);
252 BB->eraseFromParent(); // Delete the old basic block.
256 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
257 /// presumably PHI nodes in it), check to see if the merge at this block is due
258 /// to an "if condition". If so, return the boolean condition that determines
259 /// which entry into BB will be taken. Also, return by references the block
260 /// that will be entered from if the condition is true, and the block that will
261 /// be entered if the condition is false.
264 static Value *GetIfCondition(BasicBlock *BB,
265 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
266 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
267 "Function can only handle blocks with 2 predecessors!");
268 BasicBlock *Pred1 = *pred_begin(BB);
269 BasicBlock *Pred2 = *++pred_begin(BB);
271 // We can only handle branches. Other control flow will be lowered to
272 // branches if possible anyway.
273 if (!isa<BranchInst>(Pred1->getTerminator()) ||
274 !isa<BranchInst>(Pred2->getTerminator()))
276 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
277 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
279 // Eliminate code duplication by ensuring that Pred1Br is conditional if
281 if (Pred2Br->isConditional()) {
282 // If both branches are conditional, we don't have an "if statement". In
283 // reality, we could transform this case, but since the condition will be
284 // required anyway, we stand no chance of eliminating it, so the xform is
285 // probably not profitable.
286 if (Pred1Br->isConditional())
289 std::swap(Pred1, Pred2);
290 std::swap(Pred1Br, Pred2Br);
293 if (Pred1Br->isConditional()) {
294 // If we found a conditional branch predecessor, make sure that it branches
295 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
296 if (Pred1Br->getSuccessor(0) == BB &&
297 Pred1Br->getSuccessor(1) == Pred2) {
300 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
301 Pred1Br->getSuccessor(1) == BB) {
305 // We know that one arm of the conditional goes to BB, so the other must
306 // go somewhere unrelated, and this must not be an "if statement".
310 // The only thing we have to watch out for here is to make sure that Pred2
311 // doesn't have incoming edges from other blocks. If it does, the condition
312 // doesn't dominate BB.
313 if (++pred_begin(Pred2) != pred_end(Pred2))
316 return Pred1Br->getCondition();
319 // Ok, if we got here, both predecessors end with an unconditional branch to
320 // BB. Don't panic! If both blocks only have a single (identical)
321 // predecessor, and THAT is a conditional branch, then we're all ok!
322 if (pred_begin(Pred1) == pred_end(Pred1) ||
323 ++pred_begin(Pred1) != pred_end(Pred1) ||
324 pred_begin(Pred2) == pred_end(Pred2) ||
325 ++pred_begin(Pred2) != pred_end(Pred2) ||
326 *pred_begin(Pred1) != *pred_begin(Pred2))
329 // Otherwise, if this is a conditional branch, then we can use it!
330 BasicBlock *CommonPred = *pred_begin(Pred1);
331 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
332 assert(BI->isConditional() && "Two successors but not conditional?");
333 if (BI->getSuccessor(0) == Pred1) {
340 return BI->getCondition();
346 // If we have a merge point of an "if condition" as accepted above, return true
347 // if the specified value dominates the block. We don't handle the true
348 // generality of domination here, just a special case which works well enough
351 // If AggressiveInsts is non-null, and if V does not dominate BB, we check to
352 // see if V (which must be an instruction) is cheap to compute and is
353 // non-trapping. If both are true, the instruction is inserted into the set and
355 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
356 std::set<Instruction*> *AggressiveInsts) {
357 Instruction *I = dyn_cast<Instruction>(V);
359 // Non-instructions all dominate instructions, but not all constantexprs
360 // can be executed unconditionally.
361 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
366 BasicBlock *PBB = I->getParent();
368 // We don't want to allow weird loops that might have the "if condition" in
369 // the bottom of this block.
370 if (PBB == BB) return false;
372 // If this instruction is defined in a block that contains an unconditional
373 // branch to BB, then it must be in the 'conditional' part of the "if
375 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
376 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
377 if (!AggressiveInsts) return false;
378 // Okay, it looks like the instruction IS in the "condition". Check to
379 // see if its a cheap instruction to unconditionally compute, and if it
380 // only uses stuff defined outside of the condition. If so, hoist it out.
381 switch (I->getOpcode()) {
382 default: return false; // Cannot hoist this out safely.
383 case Instruction::Load:
384 // We can hoist loads that are non-volatile and obviously cannot trap.
385 if (cast<LoadInst>(I)->isVolatile())
387 if (!isa<AllocaInst>(I->getOperand(0)) &&
388 !isa<Constant>(I->getOperand(0)))
391 // Finally, we have to check to make sure there are no instructions
392 // before the load in its basic block, as we are going to hoist the loop
393 // out to its predecessor.
394 if (PBB->begin() != BasicBlock::iterator(I))
397 case Instruction::Add:
398 case Instruction::Sub:
399 case Instruction::And:
400 case Instruction::Or:
401 case Instruction::Xor:
402 case Instruction::Shl:
403 case Instruction::LShr:
404 case Instruction::AShr:
405 case Instruction::ICmp:
406 case Instruction::FCmp:
407 if (I->getOperand(0)->getType()->isFPOrFPVector())
408 return false; // FP arithmetic might trap.
409 break; // These are all cheap and non-trapping instructions.
412 // Okay, we can only really hoist these out if their operands are not
413 // defined in the conditional region.
414 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
415 if (!DominatesMergePoint(*i, BB, 0))
417 // Okay, it's safe to do this! Remember this instruction.
418 AggressiveInsts->insert(I);
424 // GatherConstantSetEQs - Given a potentially 'or'd together collection of
425 // icmp_eq instructions that compare a value against a constant, return the
426 // value being compared, and stick the constant into the Values vector.
427 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
428 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
429 if (Inst->getOpcode() == Instruction::ICmp &&
430 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
431 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
433 return Inst->getOperand(0);
434 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
436 return Inst->getOperand(1);
438 } else if (Inst->getOpcode() == Instruction::Or) {
439 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
440 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
448 // GatherConstantSetNEs - Given a potentially 'and'd together collection of
449 // setne instructions that compare a value against a constant, return the value
450 // being compared, and stick the constant into the Values vector.
451 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
452 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
453 if (Inst->getOpcode() == Instruction::ICmp &&
454 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
455 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
457 return Inst->getOperand(0);
458 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
460 return Inst->getOperand(1);
462 } else if (Inst->getOpcode() == Instruction::And) {
463 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
464 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
474 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
475 /// bunch of comparisons of one value against constants, return the value and
476 /// the constants being compared.
477 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
478 std::vector<ConstantInt*> &Values) {
479 if (Cond->getOpcode() == Instruction::Or) {
480 CompVal = GatherConstantSetEQs(Cond, Values);
482 // Return true to indicate that the condition is true if the CompVal is
483 // equal to one of the constants.
485 } else if (Cond->getOpcode() == Instruction::And) {
486 CompVal = GatherConstantSetNEs(Cond, Values);
488 // Return false to indicate that the condition is false if the CompVal is
489 // equal to one of the constants.
495 /// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
496 /// has no side effects, nuke it. If it uses any instructions that become dead
497 /// because the instruction is now gone, nuke them too.
498 static void ErasePossiblyDeadInstructionTree(Instruction *I) {
499 if (!isInstructionTriviallyDead(I)) return;
501 SmallVector<Instruction*, 16> InstrsToInspect;
502 InstrsToInspect.push_back(I);
504 while (!InstrsToInspect.empty()) {
505 I = InstrsToInspect.back();
506 InstrsToInspect.pop_back();
508 if (!isInstructionTriviallyDead(I)) continue;
510 // If I is in the work list multiple times, remove previous instances.
511 for (unsigned i = 0, e = InstrsToInspect.size(); i != e; ++i)
512 if (InstrsToInspect[i] == I) {
513 InstrsToInspect.erase(InstrsToInspect.begin()+i);
517 // Add operands of dead instruction to worklist.
518 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
519 if (Instruction *OpI = dyn_cast<Instruction>(*i))
520 InstrsToInspect.push_back(OpI);
522 // Remove dead instruction.
523 I->eraseFromParent();
527 // isValueEqualityComparison - Return true if the specified terminator checks to
528 // see if a value is equal to constant integer value.
529 static Value *isValueEqualityComparison(TerminatorInst *TI) {
530 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
531 // Do not permit merging of large switch instructions into their
532 // predecessors unless there is only one predecessor.
533 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
534 pred_end(SI->getParent())) > 128)
537 return SI->getCondition();
539 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
540 if (BI->isConditional() && BI->getCondition()->hasOneUse())
541 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
542 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
543 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
544 isa<ConstantInt>(ICI->getOperand(1)))
545 return ICI->getOperand(0);
549 // Given a value comparison instruction, decode all of the 'cases' that it
550 // represents and return the 'default' block.
552 GetValueEqualityComparisonCases(TerminatorInst *TI,
553 std::vector<std::pair<ConstantInt*,
554 BasicBlock*> > &Cases) {
555 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
556 Cases.reserve(SI->getNumCases());
557 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
558 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
559 return SI->getDefaultDest();
562 BranchInst *BI = cast<BranchInst>(TI);
563 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
564 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
565 BI->getSuccessor(ICI->getPredicate() ==
566 ICmpInst::ICMP_NE)));
567 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
571 // EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
572 // in the list that match the specified block.
573 static void EliminateBlockCases(BasicBlock *BB,
574 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
575 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
576 if (Cases[i].second == BB) {
577 Cases.erase(Cases.begin()+i);
582 // ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
585 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
586 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
587 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
589 // Make V1 be smaller than V2.
590 if (V1->size() > V2->size())
593 if (V1->size() == 0) return false;
594 if (V1->size() == 1) {
596 ConstantInt *TheVal = (*V1)[0].first;
597 for (unsigned i = 0, e = V2->size(); i != e; ++i)
598 if (TheVal == (*V2)[i].first)
602 // Otherwise, just sort both lists and compare element by element.
603 std::sort(V1->begin(), V1->end());
604 std::sort(V2->begin(), V2->end());
605 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
606 while (i1 != e1 && i2 != e2) {
607 if ((*V1)[i1].first == (*V2)[i2].first)
609 if ((*V1)[i1].first < (*V2)[i2].first)
617 // SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
618 // terminator instruction and its block is known to only have a single
619 // predecessor block, check to see if that predecessor is also a value
620 // comparison with the same value, and if that comparison determines the outcome
621 // of this comparison. If so, simplify TI. This does a very limited form of
623 static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
625 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
626 if (!PredVal) return false; // Not a value comparison in predecessor.
628 Value *ThisVal = isValueEqualityComparison(TI);
629 assert(ThisVal && "This isn't a value comparison!!");
630 if (ThisVal != PredVal) return false; // Different predicates.
632 // Find out information about when control will move from Pred to TI's block.
633 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
634 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
636 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
638 // Find information about how control leaves this block.
639 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
640 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
641 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
643 // If TI's block is the default block from Pred's comparison, potentially
644 // simplify TI based on this knowledge.
645 if (PredDef == TI->getParent()) {
646 // If we are here, we know that the value is none of those cases listed in
647 // PredCases. If there are any cases in ThisCases that are in PredCases, we
649 if (ValuesOverlap(PredCases, ThisCases)) {
650 if (BranchInst *BTI = dyn_cast<BranchInst>(TI)) {
651 // Okay, one of the successors of this condbr is dead. Convert it to a
653 assert(ThisCases.size() == 1 && "Branch can only have one case!");
654 Value *Cond = BTI->getCondition();
655 // Insert the new branch.
656 Instruction *NI = BranchInst::Create(ThisDef, TI);
658 // Remove PHI node entries for the dead edge.
659 ThisCases[0].second->removePredecessor(TI->getParent());
661 DOUT << "Threading pred instr: " << *Pred->getTerminator()
662 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
664 TI->eraseFromParent(); // Nuke the old one.
665 // If condition is now dead, nuke it.
666 if (Instruction *CondI = dyn_cast<Instruction>(Cond))
667 ErasePossiblyDeadInstructionTree(CondI);
671 SwitchInst *SI = cast<SwitchInst>(TI);
672 // Okay, TI has cases that are statically dead, prune them away.
673 SmallPtrSet<Constant*, 16> DeadCases;
674 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
675 DeadCases.insert(PredCases[i].first);
677 DOUT << "Threading pred instr: " << *Pred->getTerminator()
678 << "Through successor TI: " << *TI;
680 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
681 if (DeadCases.count(SI->getCaseValue(i))) {
682 SI->getSuccessor(i)->removePredecessor(TI->getParent());
686 DOUT << "Leaving: " << *TI << "\n";
692 // Otherwise, TI's block must correspond to some matched value. Find out
693 // which value (or set of values) this is.
694 ConstantInt *TIV = 0;
695 BasicBlock *TIBB = TI->getParent();
696 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
697 if (PredCases[i].second == TIBB) {
699 TIV = PredCases[i].first;
701 return false; // Cannot handle multiple values coming to this block.
703 assert(TIV && "No edge from pred to succ?");
705 // Okay, we found the one constant that our value can be if we get into TI's
706 // BB. Find out which successor will unconditionally be branched to.
707 BasicBlock *TheRealDest = 0;
708 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
709 if (ThisCases[i].first == TIV) {
710 TheRealDest = ThisCases[i].second;
714 // If not handled by any explicit cases, it is handled by the default case.
715 if (TheRealDest == 0) TheRealDest = ThisDef;
717 // Remove PHI node entries for dead edges.
718 BasicBlock *CheckEdge = TheRealDest;
719 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
720 if (*SI != CheckEdge)
721 (*SI)->removePredecessor(TIBB);
725 // Insert the new branch.
726 Instruction *NI = BranchInst::Create(TheRealDest, TI);
728 DOUT << "Threading pred instr: " << *Pred->getTerminator()
729 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
730 Instruction *Cond = 0;
731 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
732 Cond = dyn_cast<Instruction>(BI->getCondition());
733 TI->eraseFromParent(); // Nuke the old one.
735 if (Cond) ErasePossiblyDeadInstructionTree(Cond);
741 // FoldValueComparisonIntoPredecessors - The specified terminator is a value
742 // equality comparison instruction (either a switch or a branch on "X == c").
743 // See if any of the predecessors of the terminator block are value comparisons
744 // on the same value. If so, and if safe to do so, fold them together.
745 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
746 BasicBlock *BB = TI->getParent();
747 Value *CV = isValueEqualityComparison(TI); // CondVal
748 assert(CV && "Not a comparison?");
749 bool Changed = false;
751 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
752 while (!Preds.empty()) {
753 BasicBlock *Pred = Preds.back();
756 // See if the predecessor is a comparison with the same value.
757 TerminatorInst *PTI = Pred->getTerminator();
758 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
760 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
761 // Figure out which 'cases' to copy from SI to PSI.
762 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
763 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
765 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
766 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
768 // Based on whether the default edge from PTI goes to BB or not, fill in
769 // PredCases and PredDefault with the new switch cases we would like to
771 SmallVector<BasicBlock*, 8> NewSuccessors;
773 if (PredDefault == BB) {
774 // If this is the default destination from PTI, only the edges in TI
775 // that don't occur in PTI, or that branch to BB will be activated.
776 std::set<ConstantInt*> PTIHandled;
777 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
778 if (PredCases[i].second != BB)
779 PTIHandled.insert(PredCases[i].first);
781 // The default destination is BB, we don't need explicit targets.
782 std::swap(PredCases[i], PredCases.back());
783 PredCases.pop_back();
787 // Reconstruct the new switch statement we will be building.
788 if (PredDefault != BBDefault) {
789 PredDefault->removePredecessor(Pred);
790 PredDefault = BBDefault;
791 NewSuccessors.push_back(BBDefault);
793 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
794 if (!PTIHandled.count(BBCases[i].first) &&
795 BBCases[i].second != BBDefault) {
796 PredCases.push_back(BBCases[i]);
797 NewSuccessors.push_back(BBCases[i].second);
801 // If this is not the default destination from PSI, only the edges
802 // in SI that occur in PSI with a destination of BB will be
804 std::set<ConstantInt*> PTIHandled;
805 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
806 if (PredCases[i].second == BB) {
807 PTIHandled.insert(PredCases[i].first);
808 std::swap(PredCases[i], PredCases.back());
809 PredCases.pop_back();
813 // Okay, now we know which constants were sent to BB from the
814 // predecessor. Figure out where they will all go now.
815 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
816 if (PTIHandled.count(BBCases[i].first)) {
817 // If this is one we are capable of getting...
818 PredCases.push_back(BBCases[i]);
819 NewSuccessors.push_back(BBCases[i].second);
820 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
823 // If there are any constants vectored to BB that TI doesn't handle,
824 // they must go to the default destination of TI.
825 for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
826 E = PTIHandled.end(); I != E; ++I) {
827 PredCases.push_back(std::make_pair(*I, BBDefault));
828 NewSuccessors.push_back(BBDefault);
832 // Okay, at this point, we know which new successor Pred will get. Make
833 // sure we update the number of entries in the PHI nodes for these
835 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
836 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
838 // Now that the successors are updated, create the new Switch instruction.
839 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
840 PredCases.size(), PTI);
841 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
842 NewSI->addCase(PredCases[i].first, PredCases[i].second);
844 Instruction *DeadCond = 0;
845 if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
846 // If PTI is a branch, remember the condition.
847 DeadCond = dyn_cast<Instruction>(BI->getCondition());
848 Pred->getInstList().erase(PTI);
850 // If the condition is dead now, remove the instruction tree.
851 if (DeadCond) ErasePossiblyDeadInstructionTree(DeadCond);
853 // Okay, last check. If BB is still a successor of PSI, then we must
854 // have an infinite loop case. If so, add an infinitely looping block
855 // to handle the case to preserve the behavior of the code.
856 BasicBlock *InfLoopBlock = 0;
857 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
858 if (NewSI->getSuccessor(i) == BB) {
859 if (InfLoopBlock == 0) {
860 // Insert it at the end of the loop, because it's either code,
861 // or it won't matter if it's hot. :)
862 InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
863 BranchInst::Create(InfLoopBlock, InfLoopBlock);
865 NewSI->setSuccessor(i, InfLoopBlock);
874 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
875 /// BB2, hoist any common code in the two blocks up into the branch block. The
876 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
877 static bool HoistThenElseCodeToIf(BranchInst *BI) {
878 // This does very trivial matching, with limited scanning, to find identical
879 // instructions in the two blocks. In particular, we don't want to get into
880 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
881 // such, we currently just scan for obviously identical instructions in an
883 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
884 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
886 Instruction *I1 = BB1->begin(), *I2 = BB2->begin();
887 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
888 isa<InvokeInst>(I1) || !I1->isIdenticalTo(I2))
891 // If we get here, we can hoist at least one instruction.
892 BasicBlock *BIParent = BI->getParent();
895 // If we are hoisting the terminator instruction, don't move one (making a
896 // broken BB), instead clone it, and remove BI.
897 if (isa<TerminatorInst>(I1))
898 goto HoistTerminator;
900 // For a normal instruction, we just move one to right before the branch,
901 // then replace all uses of the other with the first. Finally, we remove
902 // the now redundant second instruction.
903 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
904 if (!I2->use_empty())
905 I2->replaceAllUsesWith(I1);
906 BB2->getInstList().erase(I2);
910 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
915 // Okay, it is safe to hoist the terminator.
916 Instruction *NT = I1->clone();
917 BIParent->getInstList().insert(BI, NT);
918 if (NT->getType() != Type::VoidTy) {
919 I1->replaceAllUsesWith(NT);
920 I2->replaceAllUsesWith(NT);
924 // Hoisting one of the terminators from our successor is a great thing.
925 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
926 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
927 // nodes, so we insert select instruction to compute the final result.
928 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
929 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
931 for (BasicBlock::iterator BBI = SI->begin();
932 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
933 Value *BB1V = PN->getIncomingValueForBlock(BB1);
934 Value *BB2V = PN->getIncomingValueForBlock(BB2);
936 // These values do not agree. Insert a select instruction before NT
937 // that determines the right value.
938 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
940 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
941 BB1V->getName()+"."+BB2V->getName(), NT);
942 // Make the PHI node use the select for all incoming values for BB1/BB2
943 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
944 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
945 PN->setIncomingValue(i, SI);
950 // Update any PHI nodes in our new successors.
951 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
952 AddPredecessorToBlock(*SI, BIParent, BB1);
954 BI->eraseFromParent();
958 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
959 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
960 /// (for now, restricted to a single instruction that's side effect free) from
961 /// the BB1 into the branch block to speculatively execute it.
962 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
963 // Only speculatively execution a single instruction (not counting the
964 // terminator) for now.
965 if (BB1->size() != 2)
968 // If BB1 is actually on the false edge of the conditional branch, remember
969 // to swap the select operands later.
971 if (BB1 != BI->getSuccessor(0)) {
972 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
979 // br i1 %t1, label %BB1, label %BB2
988 // %t3 = select i1 %t1, %t2, %t3
989 Instruction *I = BB1->begin();
990 switch (I->getOpcode()) {
991 default: return false; // Not safe / profitable to hoist.
992 case Instruction::Add:
993 case Instruction::Sub:
994 case Instruction::And:
995 case Instruction::Or:
996 case Instruction::Xor:
997 case Instruction::Shl:
998 case Instruction::LShr:
999 case Instruction::AShr:
1000 if (I->getOperand(0)->getType()->isFPOrFPVector())
1001 return false; // FP arithmetic might trap.
1002 break; // These are all cheap and non-trapping instructions.
1005 // Can we speculatively execute the instruction? And what is the value
1006 // if the condition is false? Consider the phi uses, if the incoming value
1007 // from the "if" block are all the same V, then V is the value of the
1008 // select if the condition is false.
1009 BasicBlock *BIParent = BI->getParent();
1010 SmallVector<PHINode*, 4> PHIUses;
1011 Value *FalseV = NULL;
1012 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1014 PHINode *PN = dyn_cast<PHINode>(UI);
1017 PHIUses.push_back(PN);
1018 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1021 else if (FalseV != PHIV)
1022 return false; // Don't know the value when condition is false.
1024 if (!FalseV) // Can this happen?
1027 // If we get here, we can hoist the instruction. Try to place it before the
1028 // icmp / fcmp instruction preceeding the conditional branch.
1029 BasicBlock::iterator InsertPos = BI;
1030 if (InsertPos != BIParent->begin())
1032 if (InsertPos->getOpcode() == Instruction::ICmp ||
1033 InsertPos->getOpcode() == Instruction::FCmp)
1034 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), I);
1036 BIParent->getInstList().splice(BI, BB1->getInstList(), I);
1038 // Create a select whose true value is the speculatively executed value and
1039 // false value is the previously determined FalseV.
1042 SI = SelectInst::Create(BI->getCondition(), FalseV, I,
1043 FalseV->getName() + "." + I->getName(), BI);
1045 SI = SelectInst::Create(BI->getCondition(), I, FalseV,
1046 I->getName() + "." + FalseV->getName(), BI);
1048 // Make the PHI node use the select for all incoming values for "then" and
1050 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1051 PHINode *PN = PHIUses[i];
1052 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1053 if (PN->getIncomingBlock(j) == BB1 ||
1054 PN->getIncomingBlock(j) == BIParent)
1055 PN->setIncomingValue(j, SI);
1061 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1062 /// across this block.
1063 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1064 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1067 // If this basic block contains anything other than a PHI (which controls the
1068 // branch) and branch itself, bail out. FIXME: improve this in the future.
1069 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) {
1070 if (Size > 10) return false; // Don't clone large BB's.
1072 // We can only support instructions that are do not define values that are
1073 // live outside of the current basic block.
1074 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1076 Instruction *U = cast<Instruction>(*UI);
1077 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1080 // Looks ok, continue checking.
1086 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1087 /// that is defined in the same block as the branch and if any PHI entries are
1088 /// constants, thread edges corresponding to that entry to be branches to their
1089 /// ultimate destination.
1090 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1091 BasicBlock *BB = BI->getParent();
1092 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1093 // NOTE: we currently cannot transform this case if the PHI node is used
1094 // outside of the block.
1095 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1098 // Degenerate case of a single entry PHI.
1099 if (PN->getNumIncomingValues() == 1) {
1100 if (PN->getIncomingValue(0) != PN)
1101 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1103 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1104 PN->eraseFromParent();
1108 // Now we know that this block has multiple preds and two succs.
1109 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1111 // Okay, this is a simple enough basic block. See if any phi values are
1113 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1115 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1116 CB->getType() == Type::Int1Ty) {
1117 // Okay, we now know that all edges from PredBB should be revectored to
1118 // branch to RealDest.
1119 BasicBlock *PredBB = PN->getIncomingBlock(i);
1120 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1122 if (RealDest == BB) continue; // Skip self loops.
1124 // The dest block might have PHI nodes, other predecessors and other
1125 // difficult cases. Instead of being smart about this, just insert a new
1126 // block that jumps to the destination block, effectively splitting
1127 // the edge we are about to create.
1128 BasicBlock *EdgeBB = BasicBlock::Create(RealDest->getName()+".critedge",
1129 RealDest->getParent(), RealDest);
1130 BranchInst::Create(RealDest, EdgeBB);
1132 for (BasicBlock::iterator BBI = RealDest->begin();
1133 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1134 Value *V = PN->getIncomingValueForBlock(BB);
1135 PN->addIncoming(V, EdgeBB);
1138 // BB may have instructions that are being threaded over. Clone these
1139 // instructions into EdgeBB. We know that there will be no uses of the
1140 // cloned instructions outside of EdgeBB.
1141 BasicBlock::iterator InsertPt = EdgeBB->begin();
1142 std::map<Value*, Value*> TranslateMap; // Track translated values.
1143 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1144 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1145 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1147 // Clone the instruction.
1148 Instruction *N = BBI->clone();
1149 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1151 // Update operands due to translation.
1152 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1154 std::map<Value*, Value*>::iterator PI =
1155 TranslateMap.find(*i);
1156 if (PI != TranslateMap.end())
1160 // Check for trivial simplification.
1161 if (Constant *C = ConstantFoldInstruction(N)) {
1162 TranslateMap[BBI] = C;
1163 delete N; // Constant folded away, don't need actual inst
1165 // Insert the new instruction into its new home.
1166 EdgeBB->getInstList().insert(InsertPt, N);
1167 if (!BBI->use_empty())
1168 TranslateMap[BBI] = N;
1173 // Loop over all of the edges from PredBB to BB, changing them to branch
1174 // to EdgeBB instead.
1175 TerminatorInst *PredBBTI = PredBB->getTerminator();
1176 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1177 if (PredBBTI->getSuccessor(i) == BB) {
1178 BB->removePredecessor(PredBB);
1179 PredBBTI->setSuccessor(i, EdgeBB);
1182 // Recurse, simplifying any other constants.
1183 return FoldCondBranchOnPHI(BI) | true;
1190 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1191 /// PHI node, see if we can eliminate it.
1192 static bool FoldTwoEntryPHINode(PHINode *PN) {
1193 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1194 // statement", which has a very simple dominance structure. Basically, we
1195 // are trying to find the condition that is being branched on, which
1196 // subsequently causes this merge to happen. We really want control
1197 // dependence information for this check, but simplifycfg can't keep it up
1198 // to date, and this catches most of the cases we care about anyway.
1200 BasicBlock *BB = PN->getParent();
1201 BasicBlock *IfTrue, *IfFalse;
1202 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1203 if (!IfCond) return false;
1205 // Okay, we found that we can merge this two-entry phi node into a select.
1206 // Doing so would require us to fold *all* two entry phi nodes in this block.
1207 // At some point this becomes non-profitable (particularly if the target
1208 // doesn't support cmov's). Only do this transformation if there are two or
1209 // fewer PHI nodes in this block.
1210 unsigned NumPhis = 0;
1211 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1215 DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
1216 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
1218 // Loop over the PHI's seeing if we can promote them all to select
1219 // instructions. While we are at it, keep track of the instructions
1220 // that need to be moved to the dominating block.
1221 std::set<Instruction*> AggressiveInsts;
1223 BasicBlock::iterator AfterPHIIt = BB->begin();
1224 while (isa<PHINode>(AfterPHIIt)) {
1225 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1226 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1227 if (PN->getIncomingValue(0) != PN)
1228 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1230 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1231 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1232 &AggressiveInsts) ||
1233 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1234 &AggressiveInsts)) {
1239 // If we all PHI nodes are promotable, check to make sure that all
1240 // instructions in the predecessor blocks can be promoted as well. If
1241 // not, we won't be able to get rid of the control flow, so it's not
1242 // worth promoting to select instructions.
1243 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1244 PN = cast<PHINode>(BB->begin());
1245 BasicBlock *Pred = PN->getIncomingBlock(0);
1246 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1248 DomBlock = *pred_begin(Pred);
1249 for (BasicBlock::iterator I = Pred->begin();
1250 !isa<TerminatorInst>(I); ++I)
1251 if (!AggressiveInsts.count(I)) {
1252 // This is not an aggressive instruction that we can promote.
1253 // Because of this, we won't be able to get rid of the control
1254 // flow, so the xform is not worth it.
1259 Pred = PN->getIncomingBlock(1);
1260 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1262 DomBlock = *pred_begin(Pred);
1263 for (BasicBlock::iterator I = Pred->begin();
1264 !isa<TerminatorInst>(I); ++I)
1265 if (!AggressiveInsts.count(I)) {
1266 // This is not an aggressive instruction that we can promote.
1267 // Because of this, we won't be able to get rid of the control
1268 // flow, so the xform is not worth it.
1273 // If we can still promote the PHI nodes after this gauntlet of tests,
1274 // do all of the PHI's now.
1276 // Move all 'aggressive' instructions, which are defined in the
1277 // conditional parts of the if's up to the dominating block.
1279 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1280 IfBlock1->getInstList(),
1282 IfBlock1->getTerminator());
1285 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1286 IfBlock2->getInstList(),
1288 IfBlock2->getTerminator());
1291 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1292 // Change the PHI node into a select instruction.
1294 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1296 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1298 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1299 PN->replaceAllUsesWith(NV);
1302 BB->getInstList().erase(PN);
1307 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1308 /// to two returning blocks, try to merge them together into one return,
1309 /// introducing a select if the return values disagree.
1310 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1311 assert(BI->isConditional() && "Must be a conditional branch");
1312 BasicBlock *TrueSucc = BI->getSuccessor(0);
1313 BasicBlock *FalseSucc = BI->getSuccessor(1);
1314 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1315 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1317 // Check to ensure both blocks are empty (just a return) or optionally empty
1318 // with PHI nodes. If there are other instructions, merging would cause extra
1319 // computation on one path or the other.
1320 BasicBlock::iterator BBI = TrueRet;
1321 if (BBI != TrueSucc->begin() && !isa<PHINode>(--BBI))
1322 return false; // Not empty with optional phi nodes.
1324 if (BBI != FalseSucc->begin() && !isa<PHINode>(--BBI))
1325 return false; // Not empty with optional phi nodes.
1327 // Okay, we found a branch that is going to two return nodes. If
1328 // there is no return value for this function, just change the
1329 // branch into a return.
1330 if (FalseRet->getNumOperands() == 0) {
1331 TrueSucc->removePredecessor(BI->getParent());
1332 FalseSucc->removePredecessor(BI->getParent());
1333 ReturnInst::Create(0, BI);
1334 BI->eraseFromParent();
1338 // Otherwise, build up the result values for the new return.
1339 SmallVector<Value*, 4> TrueResult;
1340 SmallVector<Value*, 4> FalseResult;
1342 for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
1343 // Otherwise, figure out what the true and false return values are
1344 // so we can insert a new select instruction.
1345 Value *TrueValue = TrueRet->getOperand(i);
1346 Value *FalseValue = FalseRet->getOperand(i);
1348 // Unwrap any PHI nodes in the return blocks.
1349 if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue))
1350 if (TVPN->getParent() == TrueSucc)
1351 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1352 if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue))
1353 if (FVPN->getParent() == FalseSucc)
1354 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1356 // In order for this transformation to be safe, we must be able to
1357 // unconditionally execute both operands to the return. This is
1358 // normally the case, but we could have a potentially-trapping
1359 // constant expression that prevents this transformation from being
1361 if (ConstantExpr *TCV = dyn_cast<ConstantExpr>(TrueValue))
1364 if (ConstantExpr *FCV = dyn_cast<ConstantExpr>(FalseValue))
1368 TrueResult.push_back(TrueValue);
1369 FalseResult.push_back(FalseValue);
1372 // Okay, we collected all the mapped values and checked them for sanity, and
1373 // defined to really do this transformation. First, update the CFG.
1374 TrueSucc->removePredecessor(BI->getParent());
1375 FalseSucc->removePredecessor(BI->getParent());
1377 // Insert select instructions where needed.
1378 Value *BrCond = BI->getCondition();
1379 for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
1380 // Insert a select if the results differ.
1381 if (TrueResult[i] == FalseResult[i] || isa<UndefValue>(FalseResult[i]))
1383 if (isa<UndefValue>(TrueResult[i])) {
1384 TrueResult[i] = FalseResult[i];
1388 TrueResult[i] = SelectInst::Create(BrCond, TrueResult[i],
1389 FalseResult[i], "retval", BI);
1392 Value *RI = ReturnInst::Create(&TrueResult[0], TrueResult.size(), BI);
1394 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1395 << "\n " << *BI << "NewRet = " << *RI
1396 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
1398 BI->eraseFromParent();
1400 if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
1401 ErasePossiblyDeadInstructionTree(BrCondI);
1407 /// ConstantIntOrdering - This class implements a stable ordering of constant
1408 /// integers that does not depend on their address. This is important for
1409 /// applications that sort ConstantInt's to ensure uniqueness.
1410 struct ConstantIntOrdering {
1411 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
1412 return LHS->getValue().ult(RHS->getValue());
1417 // SimplifyCFG - This function is used to do simplification of a CFG. For
1418 // example, it adjusts branches to branches to eliminate the extra hop, it
1419 // eliminates unreachable basic blocks, and does other "peephole" optimization
1420 // of the CFG. It returns true if a modification was made.
1422 // WARNING: The entry node of a function may not be simplified.
1424 bool llvm::SimplifyCFG(BasicBlock *BB) {
1425 bool Changed = false;
1426 Function *M = BB->getParent();
1428 assert(BB && BB->getParent() && "Block not embedded in function!");
1429 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1430 assert(&BB->getParent()->getEntryBlock() != BB &&
1431 "Can't Simplify entry block!");
1433 // Remove basic blocks that have no predecessors... which are unreachable.
1434 if ((pred_begin(BB) == pred_end(BB)) ||
1435 (*pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB))) {
1436 DOUT << "Removing BB: \n" << *BB;
1438 // Loop through all of our successors and make sure they know that one
1439 // of their predecessors is going away.
1440 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
1441 SI->removePredecessor(BB);
1443 while (!BB->empty()) {
1444 Instruction &I = BB->back();
1445 // If this instruction is used, replace uses with an arbitrary
1446 // value. Because control flow can't get here, we don't care
1447 // what we replace the value with. Note that since this block is
1448 // unreachable, and all values contained within it must dominate their
1449 // uses, that all uses will eventually be removed.
1451 // Make all users of this instruction use undef instead
1452 I.replaceAllUsesWith(UndefValue::get(I.getType()));
1454 // Remove the instruction from the basic block
1455 BB->getInstList().pop_back();
1457 M->getBasicBlockList().erase(BB);
1461 // Check to see if we can constant propagate this terminator instruction
1463 Changed |= ConstantFoldTerminator(BB);
1465 // If there is a trivial two-entry PHI node in this basic block, and we can
1466 // eliminate it, do so now.
1467 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1468 if (PN->getNumIncomingValues() == 2)
1469 Changed |= FoldTwoEntryPHINode(PN);
1471 // If this is a returning block with only PHI nodes in it, fold the return
1472 // instruction into any unconditional branch predecessors.
1474 // If any predecessor is a conditional branch that just selects among
1475 // different return values, fold the replace the branch/return with a select
1477 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1478 BasicBlock::iterator BBI = BB->getTerminator();
1479 if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
1480 // Find predecessors that end with branches.
1481 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1482 SmallVector<BranchInst*, 8> CondBranchPreds;
1483 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1484 TerminatorInst *PTI = (*PI)->getTerminator();
1485 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1486 if (BI->isUnconditional())
1487 UncondBranchPreds.push_back(*PI);
1489 CondBranchPreds.push_back(BI);
1493 // If we found some, do the transformation!
1494 if (!UncondBranchPreds.empty()) {
1495 while (!UncondBranchPreds.empty()) {
1496 BasicBlock *Pred = UncondBranchPreds.back();
1497 DOUT << "FOLDING: " << *BB
1498 << "INTO UNCOND BRANCH PRED: " << *Pred;
1499 UncondBranchPreds.pop_back();
1500 Instruction *UncondBranch = Pred->getTerminator();
1501 // Clone the return and add it to the end of the predecessor.
1502 Instruction *NewRet = RI->clone();
1503 Pred->getInstList().push_back(NewRet);
1505 // If the return instruction returns a value, and if the value was a
1506 // PHI node in "BB", propagate the right value into the return.
1507 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1509 if (PHINode *PN = dyn_cast<PHINode>(*i))
1510 if (PN->getParent() == BB)
1511 *i = PN->getIncomingValueForBlock(Pred);
1513 // Update any PHI nodes in the returning block to realize that we no
1514 // longer branch to them.
1515 BB->removePredecessor(Pred);
1516 Pred->getInstList().erase(UncondBranch);
1519 // If we eliminated all predecessors of the block, delete the block now.
1520 if (pred_begin(BB) == pred_end(BB))
1521 // We know there are no successors, so just nuke the block.
1522 M->getBasicBlockList().erase(BB);
1527 // Check out all of the conditional branches going to this return
1528 // instruction. If any of them just select between returns, change the
1529 // branch itself into a select/return pair.
1530 while (!CondBranchPreds.empty()) {
1531 BranchInst *BI = CondBranchPreds.back();
1532 CondBranchPreds.pop_back();
1534 // Check to see if the non-BB successor is also a return block.
1535 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1536 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1537 SimplifyCondBranchToTwoReturns(BI))
1541 } else if (isa<UnwindInst>(BB->begin())) {
1542 // Check to see if the first instruction in this block is just an unwind.
1543 // If so, replace any invoke instructions which use this as an exception
1544 // destination with call instructions, and any unconditional branch
1545 // predecessor with an unwind.
1547 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1548 while (!Preds.empty()) {
1549 BasicBlock *Pred = Preds.back();
1550 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1551 if (BI->isUnconditional()) {
1552 Pred->getInstList().pop_back(); // nuke uncond branch
1553 new UnwindInst(Pred); // Use unwind.
1556 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1557 if (II->getUnwindDest() == BB) {
1558 // Insert a new branch instruction before the invoke, because this
1559 // is now a fall through...
1560 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1561 Pred->getInstList().remove(II); // Take out of symbol table
1563 // Insert the call now...
1564 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1565 CallInst *CI = CallInst::Create(II->getCalledValue(),
1566 Args.begin(), Args.end(),
1568 CI->setCallingConv(II->getCallingConv());
1569 CI->setParamAttrs(II->getParamAttrs());
1570 // If the invoke produced a value, the Call now does instead
1571 II->replaceAllUsesWith(CI);
1579 // If this block is now dead, remove it.
1580 if (pred_begin(BB) == pred_end(BB)) {
1581 // We know there are no successors, so just nuke the block.
1582 M->getBasicBlockList().erase(BB);
1586 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1587 if (isValueEqualityComparison(SI)) {
1588 // If we only have one predecessor, and if it is a branch on this value,
1589 // see if that predecessor totally determines the outcome of this switch.
1590 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1591 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1592 return SimplifyCFG(BB) || 1;
1594 // If the block only contains the switch, see if we can fold the block
1595 // away into any preds.
1596 if (SI == &BB->front())
1597 if (FoldValueComparisonIntoPredecessors(SI))
1598 return SimplifyCFG(BB) || 1;
1600 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1601 if (BI->isUnconditional()) {
1602 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1604 BasicBlock *Succ = BI->getSuccessor(0);
1605 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1606 Succ != BB) // Don't hurt infinite loops!
1607 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1610 } else { // Conditional branch
1611 if (isValueEqualityComparison(BI)) {
1612 // If we only have one predecessor, and if it is a branch on this value,
1613 // see if that predecessor totally determines the outcome of this
1615 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1616 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1617 return SimplifyCFG(BB) || 1;
1619 // This block must be empty, except for the setcond inst, if it exists.
1620 BasicBlock::iterator I = BB->begin();
1622 (&*I == cast<Instruction>(BI->getCondition()) &&
1624 if (FoldValueComparisonIntoPredecessors(BI))
1625 return SimplifyCFG(BB) | true;
1628 // If this is a branch on a phi node in the current block, thread control
1629 // through this block if any PHI node entries are constants.
1630 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1631 if (PN->getParent() == BI->getParent())
1632 if (FoldCondBranchOnPHI(BI))
1633 return SimplifyCFG(BB) | true;
1635 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1636 // branches to us and one of our successors, fold the setcc into the
1637 // predecessor and use logical operations to pick the right destination.
1638 BasicBlock *TrueDest = BI->getSuccessor(0);
1639 BasicBlock *FalseDest = BI->getSuccessor(1);
1640 if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition())) {
1641 BasicBlock::iterator CondIt = Cond;
1642 if ((isa<CmpInst>(Cond) || isa<BinaryOperator>(Cond)) &&
1643 Cond->getParent() == BB && &BB->front() == Cond &&
1644 &*++CondIt == BI && Cond->hasOneUse() &&
1645 TrueDest != BB && FalseDest != BB)
1646 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI)
1647 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1648 if (PBI->isConditional() && SafeToMergeTerminators(BI, PBI)) {
1649 BasicBlock *PredBlock = *PI;
1650 if (PBI->getSuccessor(0) == FalseDest ||
1651 PBI->getSuccessor(1) == TrueDest) {
1652 // Invert the predecessors condition test (xor it with true),
1653 // which allows us to write this code once.
1655 BinaryOperator::CreateNot(PBI->getCondition(),
1656 PBI->getCondition()->getName()+".not", PBI);
1657 PBI->setCondition(NewCond);
1658 BasicBlock *OldTrue = PBI->getSuccessor(0);
1659 BasicBlock *OldFalse = PBI->getSuccessor(1);
1660 PBI->setSuccessor(0, OldFalse);
1661 PBI->setSuccessor(1, OldTrue);
1664 if ((PBI->getSuccessor(0) == TrueDest && FalseDest != BB) ||
1665 (PBI->getSuccessor(1) == FalseDest && TrueDest != BB)) {
1666 // Clone Cond into the predecessor basic block, and or/and the
1667 // two conditions together.
1668 Instruction *New = Cond->clone();
1669 PredBlock->getInstList().insert(PBI, New);
1670 New->takeName(Cond);
1671 Cond->setName(New->getName()+".old");
1672 Instruction::BinaryOps Opcode =
1673 PBI->getSuccessor(0) == TrueDest ?
1674 Instruction::Or : Instruction::And;
1676 BinaryOperator::Create(Opcode, PBI->getCondition(),
1677 New, "bothcond", PBI);
1678 PBI->setCondition(NewCond);
1679 if (PBI->getSuccessor(0) == BB) {
1680 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1681 PBI->setSuccessor(0, TrueDest);
1683 if (PBI->getSuccessor(1) == BB) {
1684 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1685 PBI->setSuccessor(1, FalseDest);
1687 return SimplifyCFG(BB) | 1;
1692 // Scan predessor blocks for conditional branches.
1693 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1694 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1695 if (PBI != BI && PBI->isConditional()) {
1697 // If this block ends with a branch instruction, and if there is a
1698 // predecessor that ends on a branch of the same condition, make
1699 // this conditional branch redundant.
1700 if (PBI->getCondition() == BI->getCondition() &&
1701 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1702 // Okay, the outcome of this conditional branch is statically
1703 // knowable. If this block had a single pred, handle specially.
1704 if (BB->getSinglePredecessor()) {
1705 // Turn this into a branch on constant.
1706 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1707 BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
1708 return SimplifyCFG(BB); // Nuke the branch on constant.
1711 // Otherwise, if there are multiple predecessors, insert a PHI
1712 // that merges in the constant and simplify the block result.
1713 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1714 PHINode *NewPN = PHINode::Create(Type::Int1Ty,
1715 BI->getCondition()->getName()
1716 + ".pr", BB->begin());
1717 for (PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1718 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1719 PBI != BI && PBI->isConditional() &&
1720 PBI->getCondition() == BI->getCondition() &&
1721 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1722 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1723 NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
1726 NewPN->addIncoming(BI->getCondition(), *PI);
1729 BI->setCondition(NewPN);
1730 // This will thread the branch.
1731 return SimplifyCFG(BB) | true;
1735 // If this is a conditional branch in an empty block, and if any
1736 // predecessors is a conditional branch to one of our destinations,
1737 // fold the conditions into logical ops and one cond br.
1738 if (&BB->front() == BI) {
1740 if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
1742 } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
1743 PBIOp = 0; BIOp = 1;
1744 } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
1745 PBIOp = 1; BIOp = 0;
1746 } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
1752 // Check to make sure that the other destination of this branch
1753 // isn't BB itself. If so, this is an infinite loop that will
1754 // keep getting unwound.
1755 if (PBIOp != -1 && PBI->getSuccessor(PBIOp) == BB)
1758 // Do not perform this transformation if it would require
1759 // insertion of a large number of select instructions. For targets
1760 // without predication/cmovs, this is a big pessimization.
1762 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1764 unsigned NumPhis = 0;
1765 for (BasicBlock::iterator II = CommonDest->begin();
1766 isa<PHINode>(II); ++II, ++NumPhis) {
1768 // Disable this xform.
1775 // Finally, if everything is ok, fold the branches to logical ops.
1777 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1778 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1780 // If OtherDest *is* BB, then this is a basic block with just
1781 // a conditional branch in it, where one edge (OtherDesg) goes
1782 // back to the block. We know that the program doesn't get
1783 // stuck in the infinite loop, so the condition must be such
1784 // that OtherDest isn't branched through. Forward to CommonDest,
1785 // and avoid an infinite loop at optimizer time.
1786 if (OtherDest == BB)
1787 OtherDest = CommonDest;
1789 DOUT << "FOLDING BRs:" << *PBI->getParent()
1790 << "AND: " << *BI->getParent();
1792 // BI may have other predecessors. Because of this, we leave
1793 // it alone, but modify PBI.
1795 // Make sure we get to CommonDest on True&True directions.
1796 Value *PBICond = PBI->getCondition();
1798 PBICond = BinaryOperator::CreateNot(PBICond,
1799 PBICond->getName()+".not",
1801 Value *BICond = BI->getCondition();
1803 BICond = BinaryOperator::CreateNot(BICond,
1804 BICond->getName()+".not",
1806 // Merge the conditions.
1808 BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1810 // Modify PBI to branch on the new condition to the new dests.
1811 PBI->setCondition(Cond);
1812 PBI->setSuccessor(0, CommonDest);
1813 PBI->setSuccessor(1, OtherDest);
1815 // OtherDest may have phi nodes. If so, add an entry from PBI's
1816 // block that are identical to the entries for BI's block.
1818 for (BasicBlock::iterator II = OtherDest->begin();
1819 (PN = dyn_cast<PHINode>(II)); ++II) {
1820 Value *V = PN->getIncomingValueForBlock(BB);
1821 PN->addIncoming(V, PBI->getParent());
1824 // We know that the CommonDest already had an edge from PBI to
1825 // it. If it has PHIs though, the PHIs may have different
1826 // entries for BB and PBI's BB. If so, insert a select to make
1828 for (BasicBlock::iterator II = CommonDest->begin();
1829 (PN = dyn_cast<PHINode>(II)); ++II) {
1830 Value * BIV = PN->getIncomingValueForBlock(BB);
1831 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1832 Value *PBIV = PN->getIncomingValue(PBBIdx);
1834 // Insert a select in PBI to pick the right value.
1835 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1836 PBIV->getName()+".mux", PBI);
1837 PN->setIncomingValue(PBBIdx, NV);
1841 DOUT << "INTO: " << *PBI->getParent();
1843 // This basic block is probably dead. We know it has at least
1844 // one fewer predecessor.
1845 return SimplifyCFG(BB) | true;
1850 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1851 // If there are any instructions immediately before the unreachable that can
1852 // be removed, do so.
1853 Instruction *Unreachable = BB->getTerminator();
1854 while (Unreachable != BB->begin()) {
1855 BasicBlock::iterator BBI = Unreachable;
1857 if (isa<CallInst>(BBI)) break;
1858 // Delete this instruction
1859 BB->getInstList().erase(BBI);
1863 // If the unreachable instruction is the first in the block, take a gander
1864 // at all of the predecessors of this instruction, and simplify them.
1865 if (&BB->front() == Unreachable) {
1866 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1867 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1868 TerminatorInst *TI = Preds[i]->getTerminator();
1870 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1871 if (BI->isUnconditional()) {
1872 if (BI->getSuccessor(0) == BB) {
1873 new UnreachableInst(TI);
1874 TI->eraseFromParent();
1878 if (BI->getSuccessor(0) == BB) {
1879 BranchInst::Create(BI->getSuccessor(1), BI);
1880 BI->eraseFromParent();
1881 } else if (BI->getSuccessor(1) == BB) {
1882 BranchInst::Create(BI->getSuccessor(0), BI);
1883 BI->eraseFromParent();
1887 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1888 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1889 if (SI->getSuccessor(i) == BB) {
1890 BB->removePredecessor(SI->getParent());
1895 // If the default value is unreachable, figure out the most popular
1896 // destination and make it the default.
1897 if (SI->getSuccessor(0) == BB) {
1898 std::map<BasicBlock*, unsigned> Popularity;
1899 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1900 Popularity[SI->getSuccessor(i)]++;
1902 // Find the most popular block.
1903 unsigned MaxPop = 0;
1904 BasicBlock *MaxBlock = 0;
1905 for (std::map<BasicBlock*, unsigned>::iterator
1906 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
1907 if (I->second > MaxPop) {
1909 MaxBlock = I->first;
1913 // Make this the new default, allowing us to delete any explicit
1915 SI->setSuccessor(0, MaxBlock);
1918 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
1920 if (isa<PHINode>(MaxBlock->begin()))
1921 for (unsigned i = 0; i != MaxPop-1; ++i)
1922 MaxBlock->removePredecessor(SI->getParent());
1924 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1925 if (SI->getSuccessor(i) == MaxBlock) {
1931 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
1932 if (II->getUnwindDest() == BB) {
1933 // Convert the invoke to a call instruction. This would be a good
1934 // place to note that the call does not throw though.
1935 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1936 II->removeFromParent(); // Take out of symbol table
1938 // Insert the call now...
1939 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
1940 CallInst *CI = CallInst::Create(II->getCalledValue(),
1941 Args.begin(), Args.end(),
1943 CI->setCallingConv(II->getCallingConv());
1944 CI->setParamAttrs(II->getParamAttrs());
1945 // If the invoke produced a value, the Call does now instead.
1946 II->replaceAllUsesWith(CI);
1953 // If this block is now dead, remove it.
1954 if (pred_begin(BB) == pred_end(BB)) {
1955 // We know there are no successors, so just nuke the block.
1956 M->getBasicBlockList().erase(BB);
1962 // Merge basic blocks into their predecessor if there is only one distinct
1963 // pred, and if there is only one distinct successor of the predecessor, and
1964 // if there are no PHI nodes.
1966 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
1967 BasicBlock *OnlyPred = *PI++;
1968 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
1969 if (*PI != OnlyPred) {
1970 OnlyPred = 0; // There are multiple different predecessors...
1974 BasicBlock *OnlySucc = 0;
1975 if (OnlyPred && OnlyPred != BB && // Don't break self loops
1976 OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) {
1977 // Check to see if there is only one distinct successor...
1978 succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred));
1980 for (; SI != SE; ++SI)
1981 if (*SI != OnlySucc) {
1982 OnlySucc = 0; // There are multiple distinct successors!
1988 DOUT << "Merging: " << *BB << "into: " << *OnlyPred;
1990 // Resolve any PHI nodes at the start of the block. They are all
1991 // guaranteed to have exactly one entry if they exist, unless there are
1992 // multiple duplicate (but guaranteed to be equal) entries for the
1993 // incoming edges. This occurs when there are multiple edges from
1994 // OnlyPred to OnlySucc.
1996 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
1997 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1998 BB->getInstList().pop_front(); // Delete the phi node.
2001 // Delete the unconditional branch from the predecessor.
2002 OnlyPred->getInstList().pop_back();
2004 // Move all definitions in the successor to the predecessor.
2005 OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
2007 // Make all PHI nodes that referred to BB now refer to Pred as their
2009 BB->replaceAllUsesWith(OnlyPred);
2011 // Inherit predecessors name if it exists.
2012 if (!OnlyPred->hasName())
2013 OnlyPred->takeName(BB);
2015 // Erase basic block from the function.
2016 M->getBasicBlockList().erase(BB);
2021 // Otherwise, if this block only has a single predecessor, and if that block
2022 // is a conditional branch, see if we can hoist any code from this block up
2023 // into our predecessor.
2025 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2026 if (BI->isConditional()) {
2027 // Get the other block.
2028 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2029 PI = pred_begin(OtherBB);
2031 if (PI == pred_end(OtherBB)) {
2032 // We have a conditional branch to two blocks that are only reachable
2033 // from the condbr. We know that the condbr dominates the two blocks,
2034 // so see if there is any identical code in the "then" and "else"
2035 // blocks. If so, we can hoist it up to the branching block.
2036 Changed |= HoistThenElseCodeToIf(BI);
2039 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2043 else if (*SI != OnlySucc) {
2044 OnlySucc = 0; // There are multiple distinct successors!
2049 if (OnlySucc == OtherBB) {
2050 // If BB's only successor is the other successor of the predecessor,
2051 // i.e. a triangle, see if we can hoist any code from this block up
2052 // to the "if" block.
2053 Changed |= SpeculativelyExecuteBB(BI, BB);
2058 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2059 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2060 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2061 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2062 Instruction *Cond = cast<Instruction>(BI->getCondition());
2063 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2064 // 'setne's and'ed together, collect them.
2066 std::vector<ConstantInt*> Values;
2067 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2068 if (CompVal && CompVal->getType()->isInteger()) {
2069 // There might be duplicate constants in the list, which the switch
2070 // instruction can't handle, remove them now.
2071 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2072 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2074 // Figure out which block is which destination.
2075 BasicBlock *DefaultBB = BI->getSuccessor(1);
2076 BasicBlock *EdgeBB = BI->getSuccessor(0);
2077 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2079 // Create the new switch instruction now.
2080 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2083 // Add all of the 'cases' to the switch instruction.
2084 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2085 New->addCase(Values[i], EdgeBB);
2087 // We added edges from PI to the EdgeBB. As such, if there were any
2088 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2089 // the number of edges added.
2090 for (BasicBlock::iterator BBI = EdgeBB->begin();
2091 isa<PHINode>(BBI); ++BBI) {
2092 PHINode *PN = cast<PHINode>(BBI);
2093 Value *InVal = PN->getIncomingValueForBlock(*PI);
2094 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2095 PN->addIncoming(InVal, *PI);
2098 // Erase the old branch instruction.
2099 (*PI)->getInstList().erase(BI);
2101 // Erase the potentially condition tree that was used to computed the
2102 // branch condition.
2103 ErasePossiblyDeadInstructionTree(Cond);