1 //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Peephole optimize the CFG.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "simplifycfg"
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/Constants.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/IntrinsicInst.h"
19 #include "llvm/Type.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/GlobalVariable.h"
22 #include "llvm/Support/CFG.h"
23 #include "llvm/Support/Debug.h"
24 #include "llvm/Analysis/ConstantFolding.h"
25 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/ADT/SmallPtrSet.h"
28 #include "llvm/ADT/Statistic.h"
35 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
37 /// SafeToMergeTerminators - Return true if it is safe to merge these two
38 /// terminator instructions together.
40 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
41 if (SI1 == SI2) return false; // Can't merge with self!
43 // It is not safe to merge these two switch instructions if they have a common
44 // successor, and if that successor has a PHI node, and if *that* PHI node has
45 // conflicting incoming values from the two switch blocks.
46 BasicBlock *SI1BB = SI1->getParent();
47 BasicBlock *SI2BB = SI2->getParent();
48 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
50 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
51 if (SI1Succs.count(*I))
52 for (BasicBlock::iterator BBI = (*I)->begin();
53 isa<PHINode>(BBI); ++BBI) {
54 PHINode *PN = cast<PHINode>(BBI);
55 if (PN->getIncomingValueForBlock(SI1BB) !=
56 PN->getIncomingValueForBlock(SI2BB))
63 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
64 /// now be entries in it from the 'NewPred' block. The values that will be
65 /// flowing into the PHI nodes will be the same as those coming in from
66 /// ExistPred, an existing predecessor of Succ.
67 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
68 BasicBlock *ExistPred) {
69 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
70 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
71 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
74 for (BasicBlock::iterator I = Succ->begin();
75 (PN = dyn_cast<PHINode>(I)); ++I)
76 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
79 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
80 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
82 /// Assumption: Succ is the single successor for BB.
84 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
85 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
87 DOUT << "Looking to fold " << BB->getNameStart() << " into "
88 << Succ->getNameStart() << "\n";
89 // Shortcut, if there is only a single predecessor it must be BB and merging
91 if (Succ->getSinglePredecessor()) return true;
93 typedef SmallPtrSet<Instruction*, 16> InstrSet;
96 // Make a list of all phi nodes in BB
97 BasicBlock::iterator BBI = BB->begin();
98 while (isa<PHINode>(*BBI)) BBPHIs.insert(BBI++);
100 // Make a list of the predecessors of BB
101 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
102 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
104 // Use that list to make another list of common predecessors of BB and Succ
105 BlockSet CommonPreds;
106 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
108 if (BBPreds.count(*PI))
109 CommonPreds.insert(*PI);
111 // Shortcut, if there are no common predecessors, merging is always safe
112 if (CommonPreds.empty())
115 // Look at all the phi nodes in Succ, to see if they present a conflict when
116 // merging these blocks
117 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
118 PHINode *PN = cast<PHINode>(I);
120 // If the incoming value from BB is again a PHINode in
121 // BB which has the same incoming value for *PI as PN does, we can
122 // merge the phi nodes and then the blocks can still be merged
123 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
124 if (BBPN && BBPN->getParent() == BB) {
125 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
127 if (BBPN->getIncomingValueForBlock(*PI)
128 != PN->getIncomingValueForBlock(*PI)) {
129 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
130 << Succ->getNameStart() << " is conflicting with "
131 << BBPN->getNameStart() << " with regard to common predecessor "
132 << (*PI)->getNameStart() << "\n";
136 // Remove this phinode from the list of phis in BB, since it has been
140 Value* Val = PN->getIncomingValueForBlock(BB);
141 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
143 // See if the incoming value for the common predecessor is equal to the
144 // one for BB, in which case this phi node will not prevent the merging
146 if (Val != PN->getIncomingValueForBlock(*PI)) {
147 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
148 << Succ->getNameStart() << " is conflicting with regard to common "
149 << "predecessor " << (*PI)->getNameStart() << "\n";
156 // If there are any other phi nodes in BB that don't have a phi node in Succ
157 // to merge with, they must be moved to Succ completely. However, for any
158 // predecessors of Succ, branches will be added to the phi node that just
159 // point to itself. So, for any common predecessors, this must not cause
161 for (InstrSet::iterator I = BBPHIs.begin(), E = BBPHIs.end();
163 PHINode *PN = cast<PHINode>(*I);
164 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
166 if (PN->getIncomingValueForBlock(*PI) != PN) {
167 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
168 << BB->getNameStart() << " is conflicting with regard to common "
169 << "predecessor " << (*PI)->getNameStart() << "\n";
177 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
178 /// branch to Succ, and contains no instructions other than PHI nodes and the
179 /// branch. If possible, eliminate BB.
180 static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
182 // Check to see if merging these blocks would cause conflicts for any of the
183 // phi nodes in BB or Succ. If not, we can safely merge.
184 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
186 DOUT << "Killing Trivial BB: \n" << *BB;
188 if (isa<PHINode>(Succ->begin())) {
189 // If there is more than one pred of succ, and there are PHI nodes in
190 // the successor, then we need to add incoming edges for the PHI nodes
192 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
194 // Loop over all of the PHI nodes in the successor of BB.
195 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
196 PHINode *PN = cast<PHINode>(I);
197 Value *OldVal = PN->removeIncomingValue(BB, false);
198 assert(OldVal && "No entry in PHI for Pred BB!");
200 // If this incoming value is one of the PHI nodes in BB, the new entries
201 // in the PHI node are the entries from the old PHI.
202 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
203 PHINode *OldValPN = cast<PHINode>(OldVal);
204 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
205 // Note that, since we are merging phi nodes and BB and Succ might
206 // have common predecessors, we could end up with a phi node with
207 // identical incoming branches. This will be cleaned up later (and
208 // will trigger asserts if we try to clean it up now, without also
209 // simplifying the corresponding conditional branch).
210 PN->addIncoming(OldValPN->getIncomingValue(i),
211 OldValPN->getIncomingBlock(i));
213 // Add an incoming value for each of the new incoming values.
214 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
215 PN->addIncoming(OldVal, BBPreds[i]);
220 if (isa<PHINode>(&BB->front())) {
221 SmallVector<BasicBlock*, 16>
222 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
224 // Move all PHI nodes in BB to Succ if they are alive, otherwise
226 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
227 if (PN->use_empty()) {
228 // Just remove the dead phi. This happens if Succ's PHIs were the only
229 // users of the PHI nodes.
230 PN->eraseFromParent();
234 // The instruction is alive, so this means that BB must dominate all
235 // predecessors of Succ (Since all uses of the PN are after its
236 // definition, so in Succ or a block dominated by Succ. If a predecessor
237 // of Succ would not be dominated by BB, PN would violate the def before
238 // use SSA demand). Therefore, we can simply move the phi node to the
240 Succ->getInstList().splice(Succ->begin(),
241 BB->getInstList(), BB->begin());
243 // We need to add new entries for the PHI node to account for
244 // predecessors of Succ that the PHI node does not take into
245 // account. At this point, since we know that BB dominated succ and all
246 // of its predecessors, this means that we should any newly added
247 // incoming edges should use the PHI node itself as the value for these
248 // edges, because they are loop back edges.
249 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
250 if (OldSuccPreds[i] != BB)
251 PN->addIncoming(PN, OldSuccPreds[i]);
255 // Everything that jumped to BB now goes to Succ.
256 BB->replaceAllUsesWith(Succ);
257 if (!Succ->hasName()) Succ->takeName(BB);
258 BB->eraseFromParent(); // Delete the old basic block.
262 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
263 /// presumably PHI nodes in it), check to see if the merge at this block is due
264 /// to an "if condition". If so, return the boolean condition that determines
265 /// which entry into BB will be taken. Also, return by references the block
266 /// that will be entered from if the condition is true, and the block that will
267 /// be entered if the condition is false.
270 static Value *GetIfCondition(BasicBlock *BB,
271 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
272 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
273 "Function can only handle blocks with 2 predecessors!");
274 BasicBlock *Pred1 = *pred_begin(BB);
275 BasicBlock *Pred2 = *++pred_begin(BB);
277 // We can only handle branches. Other control flow will be lowered to
278 // branches if possible anyway.
279 if (!isa<BranchInst>(Pred1->getTerminator()) ||
280 !isa<BranchInst>(Pred2->getTerminator()))
282 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
283 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
285 // Eliminate code duplication by ensuring that Pred1Br is conditional if
287 if (Pred2Br->isConditional()) {
288 // If both branches are conditional, we don't have an "if statement". In
289 // reality, we could transform this case, but since the condition will be
290 // required anyway, we stand no chance of eliminating it, so the xform is
291 // probably not profitable.
292 if (Pred1Br->isConditional())
295 std::swap(Pred1, Pred2);
296 std::swap(Pred1Br, Pred2Br);
299 if (Pred1Br->isConditional()) {
300 // If we found a conditional branch predecessor, make sure that it branches
301 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
302 if (Pred1Br->getSuccessor(0) == BB &&
303 Pred1Br->getSuccessor(1) == Pred2) {
306 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
307 Pred1Br->getSuccessor(1) == BB) {
311 // We know that one arm of the conditional goes to BB, so the other must
312 // go somewhere unrelated, and this must not be an "if statement".
316 // The only thing we have to watch out for here is to make sure that Pred2
317 // doesn't have incoming edges from other blocks. If it does, the condition
318 // doesn't dominate BB.
319 if (++pred_begin(Pred2) != pred_end(Pred2))
322 return Pred1Br->getCondition();
325 // Ok, if we got here, both predecessors end with an unconditional branch to
326 // BB. Don't panic! If both blocks only have a single (identical)
327 // predecessor, and THAT is a conditional branch, then we're all ok!
328 if (pred_begin(Pred1) == pred_end(Pred1) ||
329 ++pred_begin(Pred1) != pred_end(Pred1) ||
330 pred_begin(Pred2) == pred_end(Pred2) ||
331 ++pred_begin(Pred2) != pred_end(Pred2) ||
332 *pred_begin(Pred1) != *pred_begin(Pred2))
335 // Otherwise, if this is a conditional branch, then we can use it!
336 BasicBlock *CommonPred = *pred_begin(Pred1);
337 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
338 assert(BI->isConditional() && "Two successors but not conditional?");
339 if (BI->getSuccessor(0) == Pred1) {
346 return BI->getCondition();
351 /// findGlobalVariableBase - Recurse into a ConstantExpr to find the underlying
352 /// GlobalVariable, if there is one.
353 static GlobalVariable* findGlobalVariableBase(ConstantExpr* CE) {
354 if (isa<GlobalVariable>(CE))
355 return dyn_cast<GlobalVariable>(CE);
356 if (CE->getOpcode()==Instruction::GetElementPtr ||
357 CE->getOpcode()==Instruction::BitCast) {
358 if (isa<GlobalVariable>(CE->getOperand(0)))
359 return dyn_cast<GlobalVariable>(CE->getOperand(0));
360 if (ConstantExpr *CE2 = dyn_cast<ConstantExpr>(CE->getOperand(0)))
361 return findGlobalVariableBase(CE2);
366 /// DominatesMergePoint - If we have a merge point of an "if condition" as
367 /// accepted above, return true if the specified value dominates the block. We
368 /// don't handle the true generality of domination here, just a special case
369 /// which works well enough for us.
371 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
372 /// see if V (which must be an instruction) is cheap to compute and is
373 /// non-trapping. If both are true, the instruction is inserted into the set
374 /// and true is returned.
375 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
376 std::set<Instruction*> *AggressiveInsts) {
377 Instruction *I = dyn_cast<Instruction>(V);
379 // Non-instructions all dominate instructions, but not all constantexprs
380 // can be executed unconditionally.
381 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
386 BasicBlock *PBB = I->getParent();
388 // We don't want to allow weird loops that might have the "if condition" in
389 // the bottom of this block.
390 if (PBB == BB) return false;
392 // If this instruction is defined in a block that contains an unconditional
393 // branch to BB, then it must be in the 'conditional' part of the "if
395 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
396 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
397 if (!AggressiveInsts) return false;
398 // Okay, it looks like the instruction IS in the "condition". Check to
399 // see if its a cheap instruction to unconditionally compute, and if it
400 // only uses stuff defined outside of the condition. If so, hoist it out.
401 switch (I->getOpcode()) {
402 default: return false; // Cannot hoist this out safely.
403 case Instruction::Load: {
404 // We can hoist loads that are non-volatile and obviously cannot trap.
405 if (cast<LoadInst>(I)->isVolatile())
407 // FIXME: A computation of a constant can trap!
408 if (!isa<AllocaInst>(I->getOperand(0)) &&
409 !isa<Constant>(I->getOperand(0)))
411 // External weak globals may have address 0, so we can't load them.
412 GlobalVariable* GV = dyn_cast<GlobalVariable>(I->getOperand(0));
413 if (GV && GV->hasExternalWeakLinkage())
415 // The global may be buried within a ConstantExpr.
416 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(I->getOperand(0)))
417 GV = findGlobalVariableBase(CE);
418 if (GV && GV->hasExternalWeakLinkage())
421 // Finally, we have to check to make sure there are no instructions
422 // before the load in its basic block, as we are going to hoist the loop
423 // out to its predecessor.
424 BasicBlock::iterator IP = PBB->begin();
425 while (isa<DbgInfoIntrinsic>(IP))
427 if (IP != BasicBlock::iterator(I))
431 case Instruction::Add:
432 case Instruction::Sub:
433 case Instruction::And:
434 case Instruction::Or:
435 case Instruction::Xor:
436 case Instruction::Shl:
437 case Instruction::LShr:
438 case Instruction::AShr:
439 case Instruction::ICmp:
440 case Instruction::FCmp:
441 if (I->getOperand(0)->getType()->isFPOrFPVector())
442 return false; // FP arithmetic might trap.
443 break; // These are all cheap and non-trapping instructions.
446 // Okay, we can only really hoist these out if their operands are not
447 // defined in the conditional region.
448 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
449 if (!DominatesMergePoint(*i, BB, 0))
451 // Okay, it's safe to do this! Remember this instruction.
452 AggressiveInsts->insert(I);
458 /// GatherConstantSetEQs - Given a potentially 'or'd together collection of
459 /// icmp_eq instructions that compare a value against a constant, return the
460 /// value being compared, and stick the constant into the Values vector.
461 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
462 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
463 if (Inst->getOpcode() == Instruction::ICmp &&
464 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
465 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
467 return Inst->getOperand(0);
468 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
470 return Inst->getOperand(1);
472 } else if (Inst->getOpcode() == Instruction::Or) {
473 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
474 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
482 /// GatherConstantSetNEs - Given a potentially 'and'd together collection of
483 /// setne instructions that compare a value against a constant, return the value
484 /// being compared, and stick the constant into the Values vector.
485 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
486 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
487 if (Inst->getOpcode() == Instruction::ICmp &&
488 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
489 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
491 return Inst->getOperand(0);
492 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
494 return Inst->getOperand(1);
496 } else if (Inst->getOpcode() == Instruction::And) {
497 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
498 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
506 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
507 /// bunch of comparisons of one value against constants, return the value and
508 /// the constants being compared.
509 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
510 std::vector<ConstantInt*> &Values) {
511 if (Cond->getOpcode() == Instruction::Or) {
512 CompVal = GatherConstantSetEQs(Cond, Values);
514 // Return true to indicate that the condition is true if the CompVal is
515 // equal to one of the constants.
517 } else if (Cond->getOpcode() == Instruction::And) {
518 CompVal = GatherConstantSetNEs(Cond, Values);
520 // Return false to indicate that the condition is false if the CompVal is
521 // equal to one of the constants.
527 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
528 Instruction* Cond = 0;
529 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
530 Cond = dyn_cast<Instruction>(SI->getCondition());
531 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
532 if (BI->isConditional())
533 Cond = dyn_cast<Instruction>(BI->getCondition());
536 TI->eraseFromParent();
537 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
540 /// isValueEqualityComparison - Return true if the specified terminator checks
541 /// to see if a value is equal to constant integer value.
542 static Value *isValueEqualityComparison(TerminatorInst *TI) {
543 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
544 // Do not permit merging of large switch instructions into their
545 // predecessors unless there is only one predecessor.
546 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
547 pred_end(SI->getParent())) > 128)
550 return SI->getCondition();
552 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
553 if (BI->isConditional() && BI->getCondition()->hasOneUse())
554 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
555 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
556 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
557 isa<ConstantInt>(ICI->getOperand(1)))
558 return ICI->getOperand(0);
562 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
563 /// decode all of the 'cases' that it represents and return the 'default' block.
565 GetValueEqualityComparisonCases(TerminatorInst *TI,
566 std::vector<std::pair<ConstantInt*,
567 BasicBlock*> > &Cases) {
568 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
569 Cases.reserve(SI->getNumCases());
570 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
571 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
572 return SI->getDefaultDest();
575 BranchInst *BI = cast<BranchInst>(TI);
576 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
577 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
578 BI->getSuccessor(ICI->getPredicate() ==
579 ICmpInst::ICMP_NE)));
580 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
584 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
585 /// in the list that match the specified block.
586 static void EliminateBlockCases(BasicBlock *BB,
587 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
588 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
589 if (Cases[i].second == BB) {
590 Cases.erase(Cases.begin()+i);
595 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
598 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
599 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
600 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
602 // Make V1 be smaller than V2.
603 if (V1->size() > V2->size())
606 if (V1->size() == 0) return false;
607 if (V1->size() == 1) {
609 ConstantInt *TheVal = (*V1)[0].first;
610 for (unsigned i = 0, e = V2->size(); i != e; ++i)
611 if (TheVal == (*V2)[i].first)
615 // Otherwise, just sort both lists and compare element by element.
616 std::sort(V1->begin(), V1->end());
617 std::sort(V2->begin(), V2->end());
618 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
619 while (i1 != e1 && i2 != e2) {
620 if ((*V1)[i1].first == (*V2)[i2].first)
622 if ((*V1)[i1].first < (*V2)[i2].first)
630 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
631 /// terminator instruction and its block is known to only have a single
632 /// predecessor block, check to see if that predecessor is also a value
633 /// comparison with the same value, and if that comparison determines the
634 /// outcome of this comparison. If so, simplify TI. This does a very limited
635 /// form of jump threading.
636 static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
638 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
639 if (!PredVal) return false; // Not a value comparison in predecessor.
641 Value *ThisVal = isValueEqualityComparison(TI);
642 assert(ThisVal && "This isn't a value comparison!!");
643 if (ThisVal != PredVal) return false; // Different predicates.
645 // Find out information about when control will move from Pred to TI's block.
646 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
647 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
649 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
651 // Find information about how control leaves this block.
652 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
653 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
654 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
656 // If TI's block is the default block from Pred's comparison, potentially
657 // simplify TI based on this knowledge.
658 if (PredDef == TI->getParent()) {
659 // If we are here, we know that the value is none of those cases listed in
660 // PredCases. If there are any cases in ThisCases that are in PredCases, we
662 if (ValuesOverlap(PredCases, ThisCases)) {
663 if (isa<BranchInst>(TI)) {
664 // Okay, one of the successors of this condbr is dead. Convert it to a
666 assert(ThisCases.size() == 1 && "Branch can only have one case!");
667 // Insert the new branch.
668 Instruction *NI = BranchInst::Create(ThisDef, TI);
670 // Remove PHI node entries for the dead edge.
671 ThisCases[0].second->removePredecessor(TI->getParent());
673 DOUT << "Threading pred instr: " << *Pred->getTerminator()
674 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
676 EraseTerminatorInstAndDCECond(TI);
680 SwitchInst *SI = cast<SwitchInst>(TI);
681 // Okay, TI has cases that are statically dead, prune them away.
682 SmallPtrSet<Constant*, 16> DeadCases;
683 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
684 DeadCases.insert(PredCases[i].first);
686 DOUT << "Threading pred instr: " << *Pred->getTerminator()
687 << "Through successor TI: " << *TI;
689 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
690 if (DeadCases.count(SI->getCaseValue(i))) {
691 SI->getSuccessor(i)->removePredecessor(TI->getParent());
695 DOUT << "Leaving: " << *TI << "\n";
701 // Otherwise, TI's block must correspond to some matched value. Find out
702 // which value (or set of values) this is.
703 ConstantInt *TIV = 0;
704 BasicBlock *TIBB = TI->getParent();
705 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
706 if (PredCases[i].second == TIBB) {
708 TIV = PredCases[i].first;
710 return false; // Cannot handle multiple values coming to this block.
712 assert(TIV && "No edge from pred to succ?");
714 // Okay, we found the one constant that our value can be if we get into TI's
715 // BB. Find out which successor will unconditionally be branched to.
716 BasicBlock *TheRealDest = 0;
717 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
718 if (ThisCases[i].first == TIV) {
719 TheRealDest = ThisCases[i].second;
723 // If not handled by any explicit cases, it is handled by the default case.
724 if (TheRealDest == 0) TheRealDest = ThisDef;
726 // Remove PHI node entries for dead edges.
727 BasicBlock *CheckEdge = TheRealDest;
728 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
729 if (*SI != CheckEdge)
730 (*SI)->removePredecessor(TIBB);
734 // Insert the new branch.
735 Instruction *NI = BranchInst::Create(TheRealDest, TI);
737 DOUT << "Threading pred instr: " << *Pred->getTerminator()
738 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
740 EraseTerminatorInstAndDCECond(TI);
747 /// ConstantIntOrdering - This class implements a stable ordering of constant
748 /// integers that does not depend on their address. This is important for
749 /// applications that sort ConstantInt's to ensure uniqueness.
750 struct ConstantIntOrdering {
751 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
752 return LHS->getValue().ult(RHS->getValue());
757 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
758 /// equality comparison instruction (either a switch or a branch on "X == c").
759 /// See if any of the predecessors of the terminator block are value comparisons
760 /// on the same value. If so, and if safe to do so, fold them together.
761 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
762 BasicBlock *BB = TI->getParent();
763 Value *CV = isValueEqualityComparison(TI); // CondVal
764 assert(CV && "Not a comparison?");
765 bool Changed = false;
767 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
768 while (!Preds.empty()) {
769 BasicBlock *Pred = Preds.pop_back_val();
771 // See if the predecessor is a comparison with the same value.
772 TerminatorInst *PTI = Pred->getTerminator();
773 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
775 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
776 // Figure out which 'cases' to copy from SI to PSI.
777 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
778 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
780 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
781 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
783 // Based on whether the default edge from PTI goes to BB or not, fill in
784 // PredCases and PredDefault with the new switch cases we would like to
786 SmallVector<BasicBlock*, 8> NewSuccessors;
788 if (PredDefault == BB) {
789 // If this is the default destination from PTI, only the edges in TI
790 // that don't occur in PTI, or that branch to BB will be activated.
791 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
792 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
793 if (PredCases[i].second != BB)
794 PTIHandled.insert(PredCases[i].first);
796 // The default destination is BB, we don't need explicit targets.
797 std::swap(PredCases[i], PredCases.back());
798 PredCases.pop_back();
802 // Reconstruct the new switch statement we will be building.
803 if (PredDefault != BBDefault) {
804 PredDefault->removePredecessor(Pred);
805 PredDefault = BBDefault;
806 NewSuccessors.push_back(BBDefault);
808 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
809 if (!PTIHandled.count(BBCases[i].first) &&
810 BBCases[i].second != BBDefault) {
811 PredCases.push_back(BBCases[i]);
812 NewSuccessors.push_back(BBCases[i].second);
816 // If this is not the default destination from PSI, only the edges
817 // in SI that occur in PSI with a destination of BB will be
819 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
820 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
821 if (PredCases[i].second == BB) {
822 PTIHandled.insert(PredCases[i].first);
823 std::swap(PredCases[i], PredCases.back());
824 PredCases.pop_back();
828 // Okay, now we know which constants were sent to BB from the
829 // predecessor. Figure out where they will all go now.
830 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
831 if (PTIHandled.count(BBCases[i].first)) {
832 // If this is one we are capable of getting...
833 PredCases.push_back(BBCases[i]);
834 NewSuccessors.push_back(BBCases[i].second);
835 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
838 // If there are any constants vectored to BB that TI doesn't handle,
839 // they must go to the default destination of TI.
840 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
842 E = PTIHandled.end(); I != E; ++I) {
843 PredCases.push_back(std::make_pair(*I, BBDefault));
844 NewSuccessors.push_back(BBDefault);
848 // Okay, at this point, we know which new successor Pred will get. Make
849 // sure we update the number of entries in the PHI nodes for these
851 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
852 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
854 // Now that the successors are updated, create the new Switch instruction.
855 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
856 PredCases.size(), PTI);
857 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
858 NewSI->addCase(PredCases[i].first, PredCases[i].second);
860 EraseTerminatorInstAndDCECond(PTI);
862 // Okay, last check. If BB is still a successor of PSI, then we must
863 // have an infinite loop case. If so, add an infinitely looping block
864 // to handle the case to preserve the behavior of the code.
865 BasicBlock *InfLoopBlock = 0;
866 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
867 if (NewSI->getSuccessor(i) == BB) {
868 if (InfLoopBlock == 0) {
869 // Insert it at the end of the function, because it's either code,
870 // or it won't matter if it's hot. :)
871 InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
872 BranchInst::Create(InfLoopBlock, InfLoopBlock);
874 NewSI->setSuccessor(i, InfLoopBlock);
883 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
884 /// BB2, hoist any common code in the two blocks up into the branch block. The
885 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
886 static bool HoistThenElseCodeToIf(BranchInst *BI) {
887 // This does very trivial matching, with limited scanning, to find identical
888 // instructions in the two blocks. In particular, we don't want to get into
889 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
890 // such, we currently just scan for obviously identical instructions in an
892 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
893 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
895 BasicBlock::iterator BB1_Itr = BB1->begin();
896 BasicBlock::iterator BB2_Itr = BB2->begin();
898 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
899 while (isa<DbgInfoIntrinsic>(I1))
901 while (isa<DbgInfoIntrinsic>(I2))
903 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
904 isa<InvokeInst>(I1) || !I1->isIdenticalTo(I2))
907 // If we get here, we can hoist at least one instruction.
908 BasicBlock *BIParent = BI->getParent();
911 // If we are hoisting the terminator instruction, don't move one (making a
912 // broken BB), instead clone it, and remove BI.
913 if (isa<TerminatorInst>(I1))
914 goto HoistTerminator;
916 // For a normal instruction, we just move one to right before the branch,
917 // then replace all uses of the other with the first. Finally, we remove
918 // the now redundant second instruction.
919 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
920 if (!I2->use_empty())
921 I2->replaceAllUsesWith(I1);
922 BB2->getInstList().erase(I2);
925 while (isa<DbgInfoIntrinsic>(I1))
928 while (isa<DbgInfoIntrinsic>(I2))
930 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
935 // Okay, it is safe to hoist the terminator.
936 Instruction *NT = I1->clone();
937 BIParent->getInstList().insert(BI, NT);
938 if (NT->getType() != Type::VoidTy) {
939 I1->replaceAllUsesWith(NT);
940 I2->replaceAllUsesWith(NT);
944 // Hoisting one of the terminators from our successor is a great thing.
945 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
946 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
947 // nodes, so we insert select instruction to compute the final result.
948 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
949 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
951 for (BasicBlock::iterator BBI = SI->begin();
952 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
953 Value *BB1V = PN->getIncomingValueForBlock(BB1);
954 Value *BB2V = PN->getIncomingValueForBlock(BB2);
956 // These values do not agree. Insert a select instruction before NT
957 // that determines the right value.
958 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
960 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
961 BB1V->getName()+"."+BB2V->getName(), NT);
962 // Make the PHI node use the select for all incoming values for BB1/BB2
963 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
964 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
965 PN->setIncomingValue(i, SI);
970 // Update any PHI nodes in our new successors.
971 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
972 AddPredecessorToBlock(*SI, BIParent, BB1);
974 EraseTerminatorInstAndDCECond(BI);
978 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
979 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
980 /// (for now, restricted to a single instruction that's side effect free) from
981 /// the BB1 into the branch block to speculatively execute it.
982 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
983 // Only speculatively execution a single instruction (not counting the
984 // terminator) for now.
985 Instruction *HInst = NULL;
986 Instruction *Term = BB1->getTerminator();
987 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
989 Instruction *I = BBI;
991 if (isa<DbgInfoIntrinsic>(I)) continue;
992 if (I == Term) break;
1002 // Be conservative for now. FP select instruction can often be expensive.
1003 Value *BrCond = BI->getCondition();
1004 if (isa<Instruction>(BrCond) &&
1005 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
1008 // If BB1 is actually on the false edge of the conditional branch, remember
1009 // to swap the select operands later.
1010 bool Invert = false;
1011 if (BB1 != BI->getSuccessor(0)) {
1012 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
1019 // br i1 %t1, label %BB1, label %BB2
1028 // %t3 = select i1 %t1, %t2, %t3
1029 switch (HInst->getOpcode()) {
1030 default: return false; // Not safe / profitable to hoist.
1031 case Instruction::Add:
1032 case Instruction::Sub:
1033 // FP arithmetic might trap. Not worth doing for vector ops.
1034 if (HInst->getType()->isFloatingPoint()
1035 || isa<VectorType>(HInst->getType()))
1038 case Instruction::And:
1039 case Instruction::Or:
1040 case Instruction::Xor:
1041 case Instruction::Shl:
1042 case Instruction::LShr:
1043 case Instruction::AShr:
1044 // Don't mess with vector operations.
1045 if (isa<VectorType>(HInst->getType()))
1047 break; // These are all cheap and non-trapping instructions.
1050 // If the instruction is obviously dead, don't try to predicate it.
1051 if (HInst->use_empty()) {
1052 HInst->eraseFromParent();
1056 // Can we speculatively execute the instruction? And what is the value
1057 // if the condition is false? Consider the phi uses, if the incoming value
1058 // from the "if" block are all the same V, then V is the value of the
1059 // select if the condition is false.
1060 BasicBlock *BIParent = BI->getParent();
1061 SmallVector<PHINode*, 4> PHIUses;
1062 Value *FalseV = NULL;
1064 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1065 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
1067 // Ignore any user that is not a PHI node in BB2. These can only occur in
1068 // unreachable blocks, because they would not be dominated by the instr.
1069 PHINode *PN = dyn_cast<PHINode>(UI);
1070 if (!PN || PN->getParent() != BB2)
1072 PHIUses.push_back(PN);
1074 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1077 else if (FalseV != PHIV)
1078 return false; // Inconsistent value when condition is false.
1081 assert(FalseV && "Must have at least one user, and it must be a PHI");
1083 // Do not hoist the instruction if any of its operands are defined but not
1084 // used in this BB. The transformation will prevent the operand from
1085 // being sunk into the use block.
1086 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1088 Instruction *OpI = dyn_cast<Instruction>(*i);
1089 if (OpI && OpI->getParent() == BIParent &&
1090 !OpI->isUsedInBasicBlock(BIParent))
1094 // If we get here, we can hoist the instruction. Try to place it
1095 // before the icmp instruction preceding the conditional branch.
1096 BasicBlock::iterator InsertPos = BI;
1097 if (InsertPos != BIParent->begin())
1099 // Skip debug info between condition and branch.
1100 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
1102 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1103 SmallPtrSet<Instruction *, 4> BB1Insns;
1104 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1105 BB1I != BB1E; ++BB1I)
1106 BB1Insns.insert(BB1I);
1107 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1109 Instruction *Use = cast<Instruction>(*UI);
1110 if (BB1Insns.count(Use)) {
1111 // If BrCond uses the instruction that place it just before
1112 // branch instruction.
1119 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1121 // Create a select whose true value is the speculatively executed value and
1122 // false value is the previously determined FalseV.
1125 SI = SelectInst::Create(BrCond, FalseV, HInst,
1126 FalseV->getName() + "." + HInst->getName(), BI);
1128 SI = SelectInst::Create(BrCond, HInst, FalseV,
1129 HInst->getName() + "." + FalseV->getName(), BI);
1131 // Make the PHI node use the select for all incoming values for "then" and
1133 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1134 PHINode *PN = PHIUses[i];
1135 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1136 if (PN->getIncomingBlock(j) == BB1 ||
1137 PN->getIncomingBlock(j) == BIParent)
1138 PN->setIncomingValue(j, SI);
1145 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1146 /// across this block.
1147 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1148 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1151 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1152 if (isa<DbgInfoIntrinsic>(BBI))
1154 if (Size > 10) return false; // Don't clone large BB's.
1157 // We can only support instructions that do not define values that are
1158 // live outside of the current basic block.
1159 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1161 Instruction *U = cast<Instruction>(*UI);
1162 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1165 // Looks ok, continue checking.
1171 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1172 /// that is defined in the same block as the branch and if any PHI entries are
1173 /// constants, thread edges corresponding to that entry to be branches to their
1174 /// ultimate destination.
1175 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1176 BasicBlock *BB = BI->getParent();
1177 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1178 // NOTE: we currently cannot transform this case if the PHI node is used
1179 // outside of the block.
1180 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1183 // Degenerate case of a single entry PHI.
1184 if (PN->getNumIncomingValues() == 1) {
1185 FoldSingleEntryPHINodes(PN->getParent());
1189 // Now we know that this block has multiple preds and two succs.
1190 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1192 // Okay, this is a simple enough basic block. See if any phi values are
1194 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1196 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1197 CB->getType() == Type::Int1Ty) {
1198 // Okay, we now know that all edges from PredBB should be revectored to
1199 // branch to RealDest.
1200 BasicBlock *PredBB = PN->getIncomingBlock(i);
1201 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1203 if (RealDest == BB) continue; // Skip self loops.
1205 // The dest block might have PHI nodes, other predecessors and other
1206 // difficult cases. Instead of being smart about this, just insert a new
1207 // block that jumps to the destination block, effectively splitting
1208 // the edge we are about to create.
1209 BasicBlock *EdgeBB = BasicBlock::Create(RealDest->getName()+".critedge",
1210 RealDest->getParent(), RealDest);
1211 BranchInst::Create(RealDest, EdgeBB);
1213 for (BasicBlock::iterator BBI = RealDest->begin();
1214 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1215 Value *V = PN->getIncomingValueForBlock(BB);
1216 PN->addIncoming(V, EdgeBB);
1219 // BB may have instructions that are being threaded over. Clone these
1220 // instructions into EdgeBB. We know that there will be no uses of the
1221 // cloned instructions outside of EdgeBB.
1222 BasicBlock::iterator InsertPt = EdgeBB->begin();
1223 std::map<Value*, Value*> TranslateMap; // Track translated values.
1224 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1225 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1226 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1228 // Clone the instruction.
1229 Instruction *N = BBI->clone();
1230 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1232 // Update operands due to translation.
1233 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1235 std::map<Value*, Value*>::iterator PI =
1236 TranslateMap.find(*i);
1237 if (PI != TranslateMap.end())
1241 // Check for trivial simplification.
1242 if (Constant *C = ConstantFoldInstruction(N)) {
1243 TranslateMap[BBI] = C;
1244 delete N; // Constant folded away, don't need actual inst
1246 // Insert the new instruction into its new home.
1247 EdgeBB->getInstList().insert(InsertPt, N);
1248 if (!BBI->use_empty())
1249 TranslateMap[BBI] = N;
1254 // Loop over all of the edges from PredBB to BB, changing them to branch
1255 // to EdgeBB instead.
1256 TerminatorInst *PredBBTI = PredBB->getTerminator();
1257 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1258 if (PredBBTI->getSuccessor(i) == BB) {
1259 BB->removePredecessor(PredBB);
1260 PredBBTI->setSuccessor(i, EdgeBB);
1263 // Recurse, simplifying any other constants.
1264 return FoldCondBranchOnPHI(BI) | true;
1271 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1272 /// PHI node, see if we can eliminate it.
1273 static bool FoldTwoEntryPHINode(PHINode *PN) {
1274 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1275 // statement", which has a very simple dominance structure. Basically, we
1276 // are trying to find the condition that is being branched on, which
1277 // subsequently causes this merge to happen. We really want control
1278 // dependence information for this check, but simplifycfg can't keep it up
1279 // to date, and this catches most of the cases we care about anyway.
1281 BasicBlock *BB = PN->getParent();
1282 BasicBlock *IfTrue, *IfFalse;
1283 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1284 if (!IfCond) return false;
1286 // Okay, we found that we can merge this two-entry phi node into a select.
1287 // Doing so would require us to fold *all* two entry phi nodes in this block.
1288 // At some point this becomes non-profitable (particularly if the target
1289 // doesn't support cmov's). Only do this transformation if there are two or
1290 // fewer PHI nodes in this block.
1291 unsigned NumPhis = 0;
1292 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1296 DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
1297 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
1299 // Loop over the PHI's seeing if we can promote them all to select
1300 // instructions. While we are at it, keep track of the instructions
1301 // that need to be moved to the dominating block.
1302 std::set<Instruction*> AggressiveInsts;
1304 BasicBlock::iterator AfterPHIIt = BB->begin();
1305 while (isa<PHINode>(AfterPHIIt)) {
1306 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1307 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1308 if (PN->getIncomingValue(0) != PN)
1309 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1311 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1312 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1313 &AggressiveInsts) ||
1314 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1315 &AggressiveInsts)) {
1320 // If we all PHI nodes are promotable, check to make sure that all
1321 // instructions in the predecessor blocks can be promoted as well. If
1322 // not, we won't be able to get rid of the control flow, so it's not
1323 // worth promoting to select instructions.
1324 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1325 PN = cast<PHINode>(BB->begin());
1326 BasicBlock *Pred = PN->getIncomingBlock(0);
1327 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1329 DomBlock = *pred_begin(Pred);
1330 for (BasicBlock::iterator I = Pred->begin();
1331 !isa<TerminatorInst>(I); ++I)
1332 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1333 // This is not an aggressive instruction that we can promote.
1334 // Because of this, we won't be able to get rid of the control
1335 // flow, so the xform is not worth it.
1340 Pred = PN->getIncomingBlock(1);
1341 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1343 DomBlock = *pred_begin(Pred);
1344 for (BasicBlock::iterator I = Pred->begin();
1345 !isa<TerminatorInst>(I); ++I)
1346 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1347 // This is not an aggressive instruction that we can promote.
1348 // Because of this, we won't be able to get rid of the control
1349 // flow, so the xform is not worth it.
1354 // If we can still promote the PHI nodes after this gauntlet of tests,
1355 // do all of the PHI's now.
1357 // Move all 'aggressive' instructions, which are defined in the
1358 // conditional parts of the if's up to the dominating block.
1360 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1361 IfBlock1->getInstList(),
1363 IfBlock1->getTerminator());
1366 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1367 IfBlock2->getInstList(),
1369 IfBlock2->getTerminator());
1372 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1373 // Change the PHI node into a select instruction.
1375 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1377 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1379 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1380 PN->replaceAllUsesWith(NV);
1383 BB->getInstList().erase(PN);
1388 /// isTerminatorFirstRelevantInsn - Return true if Term is very first
1389 /// instruction ignoring Phi nodes and dbg intrinsics.
1390 static bool isTerminatorFirstRelevantInsn(BasicBlock *BB, Instruction *Term) {
1391 BasicBlock::iterator BBI = Term;
1392 while (BBI != BB->begin()) {
1394 if (!isa<DbgInfoIntrinsic>(BBI))
1398 if (isa<PHINode>(BBI) || &*BBI == Term || isa<DbgInfoIntrinsic>(BBI))
1403 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1404 /// to two returning blocks, try to merge them together into one return,
1405 /// introducing a select if the return values disagree.
1406 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1407 assert(BI->isConditional() && "Must be a conditional branch");
1408 BasicBlock *TrueSucc = BI->getSuccessor(0);
1409 BasicBlock *FalseSucc = BI->getSuccessor(1);
1410 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1411 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1413 // Check to ensure both blocks are empty (just a return) or optionally empty
1414 // with PHI nodes. If there are other instructions, merging would cause extra
1415 // computation on one path or the other.
1416 if (!isTerminatorFirstRelevantInsn(TrueSucc, TrueRet))
1418 if (!isTerminatorFirstRelevantInsn(FalseSucc, FalseRet))
1421 // Okay, we found a branch that is going to two return nodes. If
1422 // there is no return value for this function, just change the
1423 // branch into a return.
1424 if (FalseRet->getNumOperands() == 0) {
1425 TrueSucc->removePredecessor(BI->getParent());
1426 FalseSucc->removePredecessor(BI->getParent());
1427 ReturnInst::Create(0, BI);
1428 EraseTerminatorInstAndDCECond(BI);
1432 // Otherwise, figure out what the true and false return values are
1433 // so we can insert a new select instruction.
1434 Value *TrueValue = TrueRet->getReturnValue();
1435 Value *FalseValue = FalseRet->getReturnValue();
1437 // Unwrap any PHI nodes in the return blocks.
1438 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1439 if (TVPN->getParent() == TrueSucc)
1440 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1441 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1442 if (FVPN->getParent() == FalseSucc)
1443 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1445 // In order for this transformation to be safe, we must be able to
1446 // unconditionally execute both operands to the return. This is
1447 // normally the case, but we could have a potentially-trapping
1448 // constant expression that prevents this transformation from being
1450 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1453 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1457 // Okay, we collected all the mapped values and checked them for sanity, and
1458 // defined to really do this transformation. First, update the CFG.
1459 TrueSucc->removePredecessor(BI->getParent());
1460 FalseSucc->removePredecessor(BI->getParent());
1462 // Insert select instructions where needed.
1463 Value *BrCond = BI->getCondition();
1465 // Insert a select if the results differ.
1466 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1467 } else if (isa<UndefValue>(TrueValue)) {
1468 TrueValue = FalseValue;
1470 TrueValue = SelectInst::Create(BrCond, TrueValue,
1471 FalseValue, "retval", BI);
1475 Value *RI = !TrueValue ?
1476 ReturnInst::Create(BI) :
1477 ReturnInst::Create(TrueValue, BI);
1479 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1480 << "\n " << *BI << "NewRet = " << *RI
1481 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
1483 EraseTerminatorInstAndDCECond(BI);
1488 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1489 /// and if a predecessor branches to us and one of our successors, fold the
1490 /// setcc into the predecessor and use logical operations to pick the right
1492 static bool FoldBranchToCommonDest(BranchInst *BI) {
1493 BasicBlock *BB = BI->getParent();
1494 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1495 if (Cond == 0) return false;
1498 // Only allow this if the condition is a simple instruction that can be
1499 // executed unconditionally. It must be in the same block as the branch, and
1500 // must be at the front of the block.
1501 BasicBlock::iterator FrontIt = BB->front();
1502 // Ignore dbg intrinsics.
1503 while(isa<DbgInfoIntrinsic>(FrontIt))
1505 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1506 Cond->getParent() != BB || &*FrontIt != Cond || !Cond->hasOneUse()) {
1510 // Make sure the instruction after the condition is the cond branch.
1511 BasicBlock::iterator CondIt = Cond; ++CondIt;
1512 // Ingore dbg intrinsics.
1513 while(isa<DbgInfoIntrinsic>(CondIt))
1515 if (&*CondIt != BI) {
1516 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1520 // Cond is known to be a compare or binary operator. Check to make sure that
1521 // neither operand is a potentially-trapping constant expression.
1522 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1525 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1530 // Finally, don't infinitely unroll conditional loops.
1531 BasicBlock *TrueDest = BI->getSuccessor(0);
1532 BasicBlock *FalseDest = BI->getSuccessor(1);
1533 if (TrueDest == BB || FalseDest == BB)
1536 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1537 BasicBlock *PredBlock = *PI;
1538 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1540 // Check that we have two conditional branches. If there is a PHI node in
1541 // the common successor, verify that the same value flows in from both
1543 if (PBI == 0 || PBI->isUnconditional() ||
1544 !SafeToMergeTerminators(BI, PBI))
1547 Instruction::BinaryOps Opc;
1548 bool InvertPredCond = false;
1550 if (PBI->getSuccessor(0) == TrueDest)
1551 Opc = Instruction::Or;
1552 else if (PBI->getSuccessor(1) == FalseDest)
1553 Opc = Instruction::And;
1554 else if (PBI->getSuccessor(0) == FalseDest)
1555 Opc = Instruction::And, InvertPredCond = true;
1556 else if (PBI->getSuccessor(1) == TrueDest)
1557 Opc = Instruction::Or, InvertPredCond = true;
1561 DOUT << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB;
1563 // If we need to invert the condition in the pred block to match, do so now.
1564 if (InvertPredCond) {
1566 BinaryOperator::CreateNot(PBI->getCondition(),
1567 PBI->getCondition()->getName()+".not", PBI);
1568 PBI->setCondition(NewCond);
1569 BasicBlock *OldTrue = PBI->getSuccessor(0);
1570 BasicBlock *OldFalse = PBI->getSuccessor(1);
1571 PBI->setSuccessor(0, OldFalse);
1572 PBI->setSuccessor(1, OldTrue);
1575 // Clone Cond into the predecessor basic block, and or/and the
1576 // two conditions together.
1577 Instruction *New = Cond->clone();
1578 PredBlock->getInstList().insert(PBI, New);
1579 New->takeName(Cond);
1580 Cond->setName(New->getName()+".old");
1582 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1583 New, "or.cond", PBI);
1584 PBI->setCondition(NewCond);
1585 if (PBI->getSuccessor(0) == BB) {
1586 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1587 PBI->setSuccessor(0, TrueDest);
1589 if (PBI->getSuccessor(1) == BB) {
1590 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1591 PBI->setSuccessor(1, FalseDest);
1598 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1599 /// predecessor of another block, this function tries to simplify it. We know
1600 /// that PBI and BI are both conditional branches, and BI is in one of the
1601 /// successor blocks of PBI - PBI branches to BI.
1602 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1603 assert(PBI->isConditional() && BI->isConditional());
1604 BasicBlock *BB = BI->getParent();
1606 // If this block ends with a branch instruction, and if there is a
1607 // predecessor that ends on a branch of the same condition, make
1608 // this conditional branch redundant.
1609 if (PBI->getCondition() == BI->getCondition() &&
1610 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1611 // Okay, the outcome of this conditional branch is statically
1612 // knowable. If this block had a single pred, handle specially.
1613 if (BB->getSinglePredecessor()) {
1614 // Turn this into a branch on constant.
1615 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1616 BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
1617 return true; // Nuke the branch on constant.
1620 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1621 // in the constant and simplify the block result. Subsequent passes of
1622 // simplifycfg will thread the block.
1623 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1624 PHINode *NewPN = PHINode::Create(Type::Int1Ty,
1625 BI->getCondition()->getName() + ".pr",
1627 // Okay, we're going to insert the PHI node. Since PBI is not the only
1628 // predecessor, compute the PHI'd conditional value for all of the preds.
1629 // Any predecessor where the condition is not computable we keep symbolic.
1630 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1631 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1632 PBI != BI && PBI->isConditional() &&
1633 PBI->getCondition() == BI->getCondition() &&
1634 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1635 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1636 NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
1639 NewPN->addIncoming(BI->getCondition(), *PI);
1642 BI->setCondition(NewPN);
1647 // If this is a conditional branch in an empty block, and if any
1648 // predecessors is a conditional branch to one of our destinations,
1649 // fold the conditions into logical ops and one cond br.
1650 BasicBlock::iterator BBI = BB->begin();
1651 // Ignore dbg intrinsics.
1652 while (isa<DbgInfoIntrinsic>(BBI))
1658 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1663 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1665 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1666 PBIOp = 0, BIOp = 1;
1667 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1668 PBIOp = 1, BIOp = 0;
1669 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1674 // Check to make sure that the other destination of this branch
1675 // isn't BB itself. If so, this is an infinite loop that will
1676 // keep getting unwound.
1677 if (PBI->getSuccessor(PBIOp) == BB)
1680 // Do not perform this transformation if it would require
1681 // insertion of a large number of select instructions. For targets
1682 // without predication/cmovs, this is a big pessimization.
1683 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1685 unsigned NumPhis = 0;
1686 for (BasicBlock::iterator II = CommonDest->begin();
1687 isa<PHINode>(II); ++II, ++NumPhis)
1688 if (NumPhis > 2) // Disable this xform.
1691 // Finally, if everything is ok, fold the branches to logical ops.
1692 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1694 DOUT << "FOLDING BRs:" << *PBI->getParent()
1695 << "AND: " << *BI->getParent();
1698 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1699 // branch in it, where one edge (OtherDest) goes back to itself but the other
1700 // exits. We don't *know* that the program avoids the infinite loop
1701 // (even though that seems likely). If we do this xform naively, we'll end up
1702 // recursively unpeeling the loop. Since we know that (after the xform is
1703 // done) that the block *is* infinite if reached, we just make it an obviously
1704 // infinite loop with no cond branch.
1705 if (OtherDest == BB) {
1706 // Insert it at the end of the function, because it's either code,
1707 // or it won't matter if it's hot. :)
1708 BasicBlock *InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
1709 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1710 OtherDest = InfLoopBlock;
1713 DOUT << *PBI->getParent()->getParent();
1715 // BI may have other predecessors. Because of this, we leave
1716 // it alone, but modify PBI.
1718 // Make sure we get to CommonDest on True&True directions.
1719 Value *PBICond = PBI->getCondition();
1721 PBICond = BinaryOperator::CreateNot(PBICond,
1722 PBICond->getName()+".not",
1724 Value *BICond = BI->getCondition();
1726 BICond = BinaryOperator::CreateNot(BICond,
1727 BICond->getName()+".not",
1729 // Merge the conditions.
1730 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1732 // Modify PBI to branch on the new condition to the new dests.
1733 PBI->setCondition(Cond);
1734 PBI->setSuccessor(0, CommonDest);
1735 PBI->setSuccessor(1, OtherDest);
1737 // OtherDest may have phi nodes. If so, add an entry from PBI's
1738 // block that are identical to the entries for BI's block.
1740 for (BasicBlock::iterator II = OtherDest->begin();
1741 (PN = dyn_cast<PHINode>(II)); ++II) {
1742 Value *V = PN->getIncomingValueForBlock(BB);
1743 PN->addIncoming(V, PBI->getParent());
1746 // We know that the CommonDest already had an edge from PBI to
1747 // it. If it has PHIs though, the PHIs may have different
1748 // entries for BB and PBI's BB. If so, insert a select to make
1750 for (BasicBlock::iterator II = CommonDest->begin();
1751 (PN = dyn_cast<PHINode>(II)); ++II) {
1752 Value *BIV = PN->getIncomingValueForBlock(BB);
1753 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1754 Value *PBIV = PN->getIncomingValue(PBBIdx);
1756 // Insert a select in PBI to pick the right value.
1757 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1758 PBIV->getName()+".mux", PBI);
1759 PN->setIncomingValue(PBBIdx, NV);
1763 DOUT << "INTO: " << *PBI->getParent();
1765 DOUT << *PBI->getParent()->getParent();
1767 // This basic block is probably dead. We know it has at least
1768 // one fewer predecessor.
1773 /// SimplifyCFG - This function is used to do simplification of a CFG. For
1774 /// example, it adjusts branches to branches to eliminate the extra hop, it
1775 /// eliminates unreachable basic blocks, and does other "peephole" optimization
1776 /// of the CFG. It returns true if a modification was made.
1778 /// WARNING: The entry node of a function may not be simplified.
1780 bool llvm::SimplifyCFG(BasicBlock *BB) {
1781 bool Changed = false;
1782 Function *M = BB->getParent();
1784 assert(BB && BB->getParent() && "Block not embedded in function!");
1785 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1786 assert(&BB->getParent()->getEntryBlock() != BB &&
1787 "Can't Simplify entry block!");
1789 // Remove basic blocks that have no predecessors... or that just have themself
1790 // as a predecessor. These are unreachable.
1791 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1792 DOUT << "Removing BB: \n" << *BB;
1793 DeleteDeadBlock(BB);
1797 // Check to see if we can constant propagate this terminator instruction
1799 Changed |= ConstantFoldTerminator(BB);
1801 // If there is a trivial two-entry PHI node in this basic block, and we can
1802 // eliminate it, do so now.
1803 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1804 if (PN->getNumIncomingValues() == 2)
1805 Changed |= FoldTwoEntryPHINode(PN);
1807 // If this is a returning block with only PHI nodes in it, fold the return
1808 // instruction into any unconditional branch predecessors.
1810 // If any predecessor is a conditional branch that just selects among
1811 // different return values, fold the replace the branch/return with a select
1813 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1814 if (isTerminatorFirstRelevantInsn(BB, BB->getTerminator())) {
1815 // Find predecessors that end with branches.
1816 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1817 SmallVector<BranchInst*, 8> CondBranchPreds;
1818 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1819 TerminatorInst *PTI = (*PI)->getTerminator();
1820 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1821 if (BI->isUnconditional())
1822 UncondBranchPreds.push_back(*PI);
1824 CondBranchPreds.push_back(BI);
1828 // If we found some, do the transformation!
1829 if (!UncondBranchPreds.empty()) {
1830 while (!UncondBranchPreds.empty()) {
1831 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
1832 DOUT << "FOLDING: " << *BB
1833 << "INTO UNCOND BRANCH PRED: " << *Pred;
1834 Instruction *UncondBranch = Pred->getTerminator();
1835 // Clone the return and add it to the end of the predecessor.
1836 Instruction *NewRet = RI->clone();
1837 Pred->getInstList().push_back(NewRet);
1839 BasicBlock::iterator BBI = RI;
1840 if (BBI != BB->begin()) {
1841 // Move region end info into the predecessor.
1842 if (DbgRegionEndInst *DREI = dyn_cast<DbgRegionEndInst>(--BBI))
1843 DREI->moveBefore(NewRet);
1846 // If the return instruction returns a value, and if the value was a
1847 // PHI node in "BB", propagate the right value into the return.
1848 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1850 if (PHINode *PN = dyn_cast<PHINode>(*i))
1851 if (PN->getParent() == BB)
1852 *i = PN->getIncomingValueForBlock(Pred);
1854 // Update any PHI nodes in the returning block to realize that we no
1855 // longer branch to them.
1856 BB->removePredecessor(Pred);
1857 Pred->getInstList().erase(UncondBranch);
1860 // If we eliminated all predecessors of the block, delete the block now.
1861 if (pred_begin(BB) == pred_end(BB))
1862 // We know there are no successors, so just nuke the block.
1863 M->getBasicBlockList().erase(BB);
1868 // Check out all of the conditional branches going to this return
1869 // instruction. If any of them just select between returns, change the
1870 // branch itself into a select/return pair.
1871 while (!CondBranchPreds.empty()) {
1872 BranchInst *BI = CondBranchPreds.pop_back_val();
1874 // Check to see if the non-BB successor is also a return block.
1875 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1876 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1877 SimplifyCondBranchToTwoReturns(BI))
1881 } else if (isa<UnwindInst>(BB->begin())) {
1882 // Check to see if the first instruction in this block is just an unwind.
1883 // If so, replace any invoke instructions which use this as an exception
1884 // destination with call instructions, and any unconditional branch
1885 // predecessor with an unwind.
1887 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1888 while (!Preds.empty()) {
1889 BasicBlock *Pred = Preds.back();
1890 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1891 if (BI->isUnconditional()) {
1892 Pred->getInstList().pop_back(); // nuke uncond branch
1893 new UnwindInst(Pred); // Use unwind.
1896 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1897 if (II->getUnwindDest() == BB) {
1898 // Insert a new branch instruction before the invoke, because this
1899 // is now a fall through...
1900 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1901 Pred->getInstList().remove(II); // Take out of symbol table
1903 // Insert the call now...
1904 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1905 CallInst *CI = CallInst::Create(II->getCalledValue(),
1906 Args.begin(), Args.end(),
1908 CI->setCallingConv(II->getCallingConv());
1909 CI->setAttributes(II->getAttributes());
1910 // If the invoke produced a value, the Call now does instead
1911 II->replaceAllUsesWith(CI);
1919 // If this block is now dead, remove it.
1920 if (pred_begin(BB) == pred_end(BB)) {
1921 // We know there are no successors, so just nuke the block.
1922 M->getBasicBlockList().erase(BB);
1926 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1927 if (isValueEqualityComparison(SI)) {
1928 // If we only have one predecessor, and if it is a branch on this value,
1929 // see if that predecessor totally determines the outcome of this switch.
1930 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1931 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1932 return SimplifyCFG(BB) || 1;
1934 // If the block only contains the switch, see if we can fold the block
1935 // away into any preds.
1936 BasicBlock::iterator BBI = BB->begin();
1937 // Ignore dbg intrinsics.
1938 while (isa<DbgInfoIntrinsic>(BBI))
1941 if (FoldValueComparisonIntoPredecessors(SI))
1942 return SimplifyCFG(BB) || 1;
1944 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1945 if (BI->isUnconditional()) {
1946 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1948 BasicBlock *Succ = BI->getSuccessor(0);
1949 // Ignore dbg intrinsics.
1950 while (isa<DbgInfoIntrinsic>(BBI))
1952 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1953 Succ != BB) // Don't hurt infinite loops!
1954 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1957 } else { // Conditional branch
1958 if (isValueEqualityComparison(BI)) {
1959 // If we only have one predecessor, and if it is a branch on this value,
1960 // see if that predecessor totally determines the outcome of this
1962 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1963 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1964 return SimplifyCFG(BB) || 1;
1966 // This block must be empty, except for the setcond inst, if it exists.
1967 // Ignore dbg intrinsics.
1968 BasicBlock::iterator I = BB->begin();
1969 // Ignore dbg intrinsics.
1970 while (isa<DbgInfoIntrinsic>(I))
1973 if (FoldValueComparisonIntoPredecessors(BI))
1974 return SimplifyCFG(BB) | true;
1975 } else if (&*I == cast<Instruction>(BI->getCondition())){
1977 // Ignore dbg intrinsics.
1978 while (isa<DbgInfoIntrinsic>(I))
1981 if (FoldValueComparisonIntoPredecessors(BI))
1982 return SimplifyCFG(BB) | true;
1987 // If this is a branch on a phi node in the current block, thread control
1988 // through this block if any PHI node entries are constants.
1989 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1990 if (PN->getParent() == BI->getParent())
1991 if (FoldCondBranchOnPHI(BI))
1992 return SimplifyCFG(BB) | true;
1994 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1995 // branches to us and one of our successors, fold the setcc into the
1996 // predecessor and use logical operations to pick the right destination.
1997 if (FoldBranchToCommonDest(BI))
1998 return SimplifyCFG(BB) | 1;
2001 // Scan predecessor blocks for conditional branches.
2002 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2003 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2004 if (PBI != BI && PBI->isConditional())
2005 if (SimplifyCondBranchToCondBranch(PBI, BI))
2006 return SimplifyCFG(BB) | true;
2008 } else if (isa<UnreachableInst>(BB->getTerminator())) {
2009 // If there are any instructions immediately before the unreachable that can
2010 // be removed, do so.
2011 Instruction *Unreachable = BB->getTerminator();
2012 while (Unreachable != BB->begin()) {
2013 BasicBlock::iterator BBI = Unreachable;
2015 // Do not delete instructions that can have side effects, like calls
2016 // (which may never return) and volatile loads and stores.
2017 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2019 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2020 if (SI->isVolatile())
2023 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2024 if (LI->isVolatile())
2027 // Delete this instruction
2028 BB->getInstList().erase(BBI);
2032 // If the unreachable instruction is the first in the block, take a gander
2033 // at all of the predecessors of this instruction, and simplify them.
2034 if (&BB->front() == Unreachable) {
2035 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2036 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2037 TerminatorInst *TI = Preds[i]->getTerminator();
2039 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2040 if (BI->isUnconditional()) {
2041 if (BI->getSuccessor(0) == BB) {
2042 new UnreachableInst(TI);
2043 TI->eraseFromParent();
2047 if (BI->getSuccessor(0) == BB) {
2048 BranchInst::Create(BI->getSuccessor(1), BI);
2049 EraseTerminatorInstAndDCECond(BI);
2050 } else if (BI->getSuccessor(1) == BB) {
2051 BranchInst::Create(BI->getSuccessor(0), BI);
2052 EraseTerminatorInstAndDCECond(BI);
2056 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2057 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2058 if (SI->getSuccessor(i) == BB) {
2059 BB->removePredecessor(SI->getParent());
2064 // If the default value is unreachable, figure out the most popular
2065 // destination and make it the default.
2066 if (SI->getSuccessor(0) == BB) {
2067 std::map<BasicBlock*, unsigned> Popularity;
2068 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2069 Popularity[SI->getSuccessor(i)]++;
2071 // Find the most popular block.
2072 unsigned MaxPop = 0;
2073 BasicBlock *MaxBlock = 0;
2074 for (std::map<BasicBlock*, unsigned>::iterator
2075 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2076 if (I->second > MaxPop) {
2078 MaxBlock = I->first;
2082 // Make this the new default, allowing us to delete any explicit
2084 SI->setSuccessor(0, MaxBlock);
2087 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2089 if (isa<PHINode>(MaxBlock->begin()))
2090 for (unsigned i = 0; i != MaxPop-1; ++i)
2091 MaxBlock->removePredecessor(SI->getParent());
2093 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2094 if (SI->getSuccessor(i) == MaxBlock) {
2100 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2101 if (II->getUnwindDest() == BB) {
2102 // Convert the invoke to a call instruction. This would be a good
2103 // place to note that the call does not throw though.
2104 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2105 II->removeFromParent(); // Take out of symbol table
2107 // Insert the call now...
2108 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
2109 CallInst *CI = CallInst::Create(II->getCalledValue(),
2110 Args.begin(), Args.end(),
2112 CI->setCallingConv(II->getCallingConv());
2113 CI->setAttributes(II->getAttributes());
2114 // If the invoke produced a value, the Call does now instead.
2115 II->replaceAllUsesWith(CI);
2122 // If this block is now dead, remove it.
2123 if (pred_begin(BB) == pred_end(BB)) {
2124 // We know there are no successors, so just nuke the block.
2125 M->getBasicBlockList().erase(BB);
2131 // Merge basic blocks into their predecessor if there is only one distinct
2132 // pred, and if there is only one distinct successor of the predecessor, and
2133 // if there are no PHI nodes.
2135 if (MergeBlockIntoPredecessor(BB))
2138 // Otherwise, if this block only has a single predecessor, and if that block
2139 // is a conditional branch, see if we can hoist any code from this block up
2140 // into our predecessor.
2141 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2142 BasicBlock *OnlyPred = *PI++;
2143 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2144 if (*PI != OnlyPred) {
2145 OnlyPred = 0; // There are multiple different predecessors...
2150 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2151 if (BI->isConditional()) {
2152 // Get the other block.
2153 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2154 PI = pred_begin(OtherBB);
2157 if (PI == pred_end(OtherBB)) {
2158 // We have a conditional branch to two blocks that are only reachable
2159 // from the condbr. We know that the condbr dominates the two blocks,
2160 // so see if there is any identical code in the "then" and "else"
2161 // blocks. If so, we can hoist it up to the branching block.
2162 Changed |= HoistThenElseCodeToIf(BI);
2164 BasicBlock* OnlySucc = NULL;
2165 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2169 else if (*SI != OnlySucc) {
2170 OnlySucc = 0; // There are multiple distinct successors!
2175 if (OnlySucc == OtherBB) {
2176 // If BB's only successor is the other successor of the predecessor,
2177 // i.e. a triangle, see if we can hoist any code from this block up
2178 // to the "if" block.
2179 Changed |= SpeculativelyExecuteBB(BI, BB);
2184 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2185 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2186 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2187 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2188 Instruction *Cond = cast<Instruction>(BI->getCondition());
2189 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2190 // 'setne's and'ed together, collect them.
2192 std::vector<ConstantInt*> Values;
2193 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2194 if (CompVal && CompVal->getType()->isInteger()) {
2195 // There might be duplicate constants in the list, which the switch
2196 // instruction can't handle, remove them now.
2197 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2198 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2200 // Figure out which block is which destination.
2201 BasicBlock *DefaultBB = BI->getSuccessor(1);
2202 BasicBlock *EdgeBB = BI->getSuccessor(0);
2203 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2205 // Create the new switch instruction now.
2206 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2209 // Add all of the 'cases' to the switch instruction.
2210 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2211 New->addCase(Values[i], EdgeBB);
2213 // We added edges from PI to the EdgeBB. As such, if there were any
2214 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2215 // the number of edges added.
2216 for (BasicBlock::iterator BBI = EdgeBB->begin();
2217 isa<PHINode>(BBI); ++BBI) {
2218 PHINode *PN = cast<PHINode>(BBI);
2219 Value *InVal = PN->getIncomingValueForBlock(*PI);
2220 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2221 PN->addIncoming(InVal, *PI);
2224 // Erase the old branch instruction.
2225 EraseTerminatorInstAndDCECond(BI);