1 //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Peephole optimize the CFG.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "simplifycfg"
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/Constants.h"
17 #include "llvm/Instructions.h"
18 #include "llvm/IntrinsicInst.h"
19 #include "llvm/Type.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/Support/CFG.h"
22 #include "llvm/Support/Debug.h"
23 #include "llvm/Analysis/ConstantFolding.h"
24 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
25 #include "llvm/ADT/SmallVector.h"
26 #include "llvm/ADT/SmallPtrSet.h"
27 #include "llvm/ADT/Statistic.h"
34 STATISTIC(NumSpeculations, "Number of speculative executed instructions");
36 /// SafeToMergeTerminators - Return true if it is safe to merge these two
37 /// terminator instructions together.
39 static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
40 if (SI1 == SI2) return false; // Can't merge with self!
42 // It is not safe to merge these two switch instructions if they have a common
43 // successor, and if that successor has a PHI node, and if *that* PHI node has
44 // conflicting incoming values from the two switch blocks.
45 BasicBlock *SI1BB = SI1->getParent();
46 BasicBlock *SI2BB = SI2->getParent();
47 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
49 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
50 if (SI1Succs.count(*I))
51 for (BasicBlock::iterator BBI = (*I)->begin();
52 isa<PHINode>(BBI); ++BBI) {
53 PHINode *PN = cast<PHINode>(BBI);
54 if (PN->getIncomingValueForBlock(SI1BB) !=
55 PN->getIncomingValueForBlock(SI2BB))
62 /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
63 /// now be entries in it from the 'NewPred' block. The values that will be
64 /// flowing into the PHI nodes will be the same as those coming in from
65 /// ExistPred, an existing predecessor of Succ.
66 static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
67 BasicBlock *ExistPred) {
68 assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
69 succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
70 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
73 for (BasicBlock::iterator I = Succ->begin();
74 (PN = dyn_cast<PHINode>(I)); ++I)
75 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
78 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
79 /// almost-empty BB ending in an unconditional branch to Succ, into succ.
81 /// Assumption: Succ is the single successor for BB.
83 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
84 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
86 DOUT << "Looking to fold " << BB->getNameStart() << " into "
87 << Succ->getNameStart() << "\n";
88 // Shortcut, if there is only a single predecessor is must be BB and merging
90 if (Succ->getSinglePredecessor()) return true;
92 typedef SmallPtrSet<Instruction*, 16> InstrSet;
95 // Make a list of all phi nodes in BB
96 BasicBlock::iterator BBI = BB->begin();
97 while (isa<PHINode>(*BBI)) BBPHIs.insert(BBI++);
99 // Make a list of the predecessors of BB
100 typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
101 BlockSet BBPreds(pred_begin(BB), pred_end(BB));
103 // Use that list to make another list of common predecessors of BB and Succ
104 BlockSet CommonPreds;
105 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
107 if (BBPreds.count(*PI))
108 CommonPreds.insert(*PI);
110 // Shortcut, if there are no common predecessors, merging is always safe
111 if (CommonPreds.empty())
114 // Look at all the phi nodes in Succ, to see if they present a conflict when
115 // merging these blocks
116 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
117 PHINode *PN = cast<PHINode>(I);
119 // If the incoming value from BB is again a PHINode in
120 // BB which has the same incoming value for *PI as PN does, we can
121 // merge the phi nodes and then the blocks can still be merged
122 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
123 if (BBPN && BBPN->getParent() == BB) {
124 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
126 if (BBPN->getIncomingValueForBlock(*PI)
127 != PN->getIncomingValueForBlock(*PI)) {
128 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
129 << Succ->getNameStart() << " is conflicting with "
130 << BBPN->getNameStart() << " with regard to common predecessor "
131 << (*PI)->getNameStart() << "\n";
135 // Remove this phinode from the list of phis in BB, since it has been
139 Value* Val = PN->getIncomingValueForBlock(BB);
140 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
142 // See if the incoming value for the common predecessor is equal to the
143 // one for BB, in which case this phi node will not prevent the merging
145 if (Val != PN->getIncomingValueForBlock(*PI)) {
146 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
147 << Succ->getNameStart() << " is conflicting with regard to common "
148 << "predecessor " << (*PI)->getNameStart() << "\n";
155 // If there are any other phi nodes in BB that don't have a phi node in Succ
156 // to merge with, they must be moved to Succ completely. However, for any
157 // predecessors of Succ, branches will be added to the phi node that just
158 // point to itself. So, for any common predecessors, this must not cause
160 for (InstrSet::iterator I = BBPHIs.begin(), E = BBPHIs.end();
162 PHINode *PN = cast<PHINode>(*I);
163 for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
165 if (PN->getIncomingValueForBlock(*PI) != PN) {
166 DOUT << "Can't fold, phi node " << *PN->getNameStart() << " in "
167 << BB->getNameStart() << " is conflicting with regard to common "
168 << "predecessor " << (*PI)->getNameStart() << "\n";
176 /// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
177 /// branch to Succ, and contains no instructions other than PHI nodes and the
178 /// branch. If possible, eliminate BB.
179 static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
181 // Check to see if merging these blocks would cause conflicts for any of the
182 // phi nodes in BB or Succ. If not, we can safely merge.
183 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
185 DOUT << "Killing Trivial BB: \n" << *BB;
187 if (isa<PHINode>(Succ->begin())) {
188 // If there is more than one pred of succ, and there are PHI nodes in
189 // the successor, then we need to add incoming edges for the PHI nodes
191 const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
193 // Loop over all of the PHI nodes in the successor of BB.
194 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
195 PHINode *PN = cast<PHINode>(I);
196 Value *OldVal = PN->removeIncomingValue(BB, false);
197 assert(OldVal && "No entry in PHI for Pred BB!");
199 // If this incoming value is one of the PHI nodes in BB, the new entries
200 // in the PHI node are the entries from the old PHI.
201 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
202 PHINode *OldValPN = cast<PHINode>(OldVal);
203 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
204 // Note that, since we are merging phi nodes and BB and Succ might
205 // have common predecessors, we could end up with a phi node with
206 // identical incoming branches. This will be cleaned up later (and
207 // will trigger asserts if we try to clean it up now, without also
208 // simplifying the corresponding conditional branch).
209 PN->addIncoming(OldValPN->getIncomingValue(i),
210 OldValPN->getIncomingBlock(i));
212 // Add an incoming value for each of the new incoming values.
213 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
214 PN->addIncoming(OldVal, BBPreds[i]);
219 if (isa<PHINode>(&BB->front())) {
220 SmallVector<BasicBlock*, 16>
221 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
223 // Move all PHI nodes in BB to Succ if they are alive, otherwise
225 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
226 if (PN->use_empty()) {
227 // Just remove the dead phi. This happens if Succ's PHIs were the only
228 // users of the PHI nodes.
229 PN->eraseFromParent();
233 // The instruction is alive, so this means that BB must dominate all
234 // predecessors of Succ (Since all uses of the PN are after its
235 // definition, so in Succ or a block dominated by Succ. If a predecessor
236 // of Succ would not be dominated by BB, PN would violate the def before
237 // use SSA demand). Therefore, we can simply move the phi node to the
239 Succ->getInstList().splice(Succ->begin(),
240 BB->getInstList(), BB->begin());
242 // We need to add new entries for the PHI node to account for
243 // predecessors of Succ that the PHI node does not take into
244 // account. At this point, since we know that BB dominated succ and all
245 // of its predecessors, this means that we should any newly added
246 // incoming edges should use the PHI node itself as the value for these
247 // edges, because they are loop back edges.
248 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
249 if (OldSuccPreds[i] != BB)
250 PN->addIncoming(PN, OldSuccPreds[i]);
254 // Everything that jumped to BB now goes to Succ.
255 BB->replaceAllUsesWith(Succ);
256 if (!Succ->hasName()) Succ->takeName(BB);
257 BB->eraseFromParent(); // Delete the old basic block.
261 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
262 /// presumably PHI nodes in it), check to see if the merge at this block is due
263 /// to an "if condition". If so, return the boolean condition that determines
264 /// which entry into BB will be taken. Also, return by references the block
265 /// that will be entered from if the condition is true, and the block that will
266 /// be entered if the condition is false.
269 static Value *GetIfCondition(BasicBlock *BB,
270 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
271 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
272 "Function can only handle blocks with 2 predecessors!");
273 BasicBlock *Pred1 = *pred_begin(BB);
274 BasicBlock *Pred2 = *++pred_begin(BB);
276 // We can only handle branches. Other control flow will be lowered to
277 // branches if possible anyway.
278 if (!isa<BranchInst>(Pred1->getTerminator()) ||
279 !isa<BranchInst>(Pred2->getTerminator()))
281 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
282 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
284 // Eliminate code duplication by ensuring that Pred1Br is conditional if
286 if (Pred2Br->isConditional()) {
287 // If both branches are conditional, we don't have an "if statement". In
288 // reality, we could transform this case, but since the condition will be
289 // required anyway, we stand no chance of eliminating it, so the xform is
290 // probably not profitable.
291 if (Pred1Br->isConditional())
294 std::swap(Pred1, Pred2);
295 std::swap(Pred1Br, Pred2Br);
298 if (Pred1Br->isConditional()) {
299 // If we found a conditional branch predecessor, make sure that it branches
300 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
301 if (Pred1Br->getSuccessor(0) == BB &&
302 Pred1Br->getSuccessor(1) == Pred2) {
305 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
306 Pred1Br->getSuccessor(1) == BB) {
310 // We know that one arm of the conditional goes to BB, so the other must
311 // go somewhere unrelated, and this must not be an "if statement".
315 // The only thing we have to watch out for here is to make sure that Pred2
316 // doesn't have incoming edges from other blocks. If it does, the condition
317 // doesn't dominate BB.
318 if (++pred_begin(Pred2) != pred_end(Pred2))
321 return Pred1Br->getCondition();
324 // Ok, if we got here, both predecessors end with an unconditional branch to
325 // BB. Don't panic! If both blocks only have a single (identical)
326 // predecessor, and THAT is a conditional branch, then we're all ok!
327 if (pred_begin(Pred1) == pred_end(Pred1) ||
328 ++pred_begin(Pred1) != pred_end(Pred1) ||
329 pred_begin(Pred2) == pred_end(Pred2) ||
330 ++pred_begin(Pred2) != pred_end(Pred2) ||
331 *pred_begin(Pred1) != *pred_begin(Pred2))
334 // Otherwise, if this is a conditional branch, then we can use it!
335 BasicBlock *CommonPred = *pred_begin(Pred1);
336 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
337 assert(BI->isConditional() && "Two successors but not conditional?");
338 if (BI->getSuccessor(0) == Pred1) {
345 return BI->getCondition();
351 /// DominatesMergePoint - If we have a merge point of an "if condition" as
352 /// accepted above, return true if the specified value dominates the block. We
353 /// don't handle the true generality of domination here, just a special case
354 /// which works well enough for us.
356 /// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
357 /// see if V (which must be an instruction) is cheap to compute and is
358 /// non-trapping. If both are true, the instruction is inserted into the set
359 /// and true is returned.
360 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
361 std::set<Instruction*> *AggressiveInsts) {
362 Instruction *I = dyn_cast<Instruction>(V);
364 // Non-instructions all dominate instructions, but not all constantexprs
365 // can be executed unconditionally.
366 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
371 BasicBlock *PBB = I->getParent();
373 // We don't want to allow weird loops that might have the "if condition" in
374 // the bottom of this block.
375 if (PBB == BB) return false;
377 // If this instruction is defined in a block that contains an unconditional
378 // branch to BB, then it must be in the 'conditional' part of the "if
380 if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
381 if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
382 if (!AggressiveInsts) return false;
383 // Okay, it looks like the instruction IS in the "condition". Check to
384 // see if its a cheap instruction to unconditionally compute, and if it
385 // only uses stuff defined outside of the condition. If so, hoist it out.
386 switch (I->getOpcode()) {
387 default: return false; // Cannot hoist this out safely.
388 case Instruction::Load:
389 // We can hoist loads that are non-volatile and obviously cannot trap.
390 if (cast<LoadInst>(I)->isVolatile())
392 // FIXME: A computation of a constant can trap!
393 if (!isa<AllocaInst>(I->getOperand(0)) &&
394 !isa<Constant>(I->getOperand(0)))
397 // Finally, we have to check to make sure there are no instructions
398 // before the load in its basic block, as we are going to hoist the loop
399 // out to its predecessor.
400 if (PBB->begin() != BasicBlock::iterator(I))
403 case Instruction::Add:
404 case Instruction::Sub:
405 case Instruction::And:
406 case Instruction::Or:
407 case Instruction::Xor:
408 case Instruction::Shl:
409 case Instruction::LShr:
410 case Instruction::AShr:
411 case Instruction::ICmp:
412 case Instruction::FCmp:
413 if (I->getOperand(0)->getType()->isFPOrFPVector())
414 return false; // FP arithmetic might trap.
415 break; // These are all cheap and non-trapping instructions.
418 // Okay, we can only really hoist these out if their operands are not
419 // defined in the conditional region.
420 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
421 if (!DominatesMergePoint(*i, BB, 0))
423 // Okay, it's safe to do this! Remember this instruction.
424 AggressiveInsts->insert(I);
430 /// GatherConstantSetEQs - Given a potentially 'or'd together collection of
431 /// icmp_eq instructions that compare a value against a constant, return the
432 /// value being compared, and stick the constant into the Values vector.
433 static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
434 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
435 if (Inst->getOpcode() == Instruction::ICmp &&
436 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
437 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
439 return Inst->getOperand(0);
440 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
442 return Inst->getOperand(1);
444 } else if (Inst->getOpcode() == Instruction::Or) {
445 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
446 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
454 /// GatherConstantSetNEs - Given a potentially 'and'd together collection of
455 /// setne instructions that compare a value against a constant, return the value
456 /// being compared, and stick the constant into the Values vector.
457 static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
458 if (Instruction *Inst = dyn_cast<Instruction>(V)) {
459 if (Inst->getOpcode() == Instruction::ICmp &&
460 cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
461 if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
463 return Inst->getOperand(0);
464 } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
466 return Inst->getOperand(1);
468 } else if (Inst->getOpcode() == Instruction::And) {
469 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
470 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
478 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
479 /// bunch of comparisons of one value against constants, return the value and
480 /// the constants being compared.
481 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
482 std::vector<ConstantInt*> &Values) {
483 if (Cond->getOpcode() == Instruction::Or) {
484 CompVal = GatherConstantSetEQs(Cond, Values);
486 // Return true to indicate that the condition is true if the CompVal is
487 // equal to one of the constants.
489 } else if (Cond->getOpcode() == Instruction::And) {
490 CompVal = GatherConstantSetNEs(Cond, Values);
492 // Return false to indicate that the condition is false if the CompVal is
493 // equal to one of the constants.
499 static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
500 Instruction* Cond = 0;
501 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
502 Cond = dyn_cast<Instruction>(SI->getCondition());
503 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
504 if (BI->isConditional())
505 Cond = dyn_cast<Instruction>(BI->getCondition());
508 TI->eraseFromParent();
509 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
512 /// isValueEqualityComparison - Return true if the specified terminator checks
513 /// to see if a value is equal to constant integer value.
514 static Value *isValueEqualityComparison(TerminatorInst *TI) {
515 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
516 // Do not permit merging of large switch instructions into their
517 // predecessors unless there is only one predecessor.
518 if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
519 pred_end(SI->getParent())) > 128)
522 return SI->getCondition();
524 if (BranchInst *BI = dyn_cast<BranchInst>(TI))
525 if (BI->isConditional() && BI->getCondition()->hasOneUse())
526 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
527 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
528 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
529 isa<ConstantInt>(ICI->getOperand(1)))
530 return ICI->getOperand(0);
534 /// GetValueEqualityComparisonCases - Given a value comparison instruction,
535 /// decode all of the 'cases' that it represents and return the 'default' block.
537 GetValueEqualityComparisonCases(TerminatorInst *TI,
538 std::vector<std::pair<ConstantInt*,
539 BasicBlock*> > &Cases) {
540 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
541 Cases.reserve(SI->getNumCases());
542 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
543 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
544 return SI->getDefaultDest();
547 BranchInst *BI = cast<BranchInst>(TI);
548 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
549 Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
550 BI->getSuccessor(ICI->getPredicate() ==
551 ICmpInst::ICMP_NE)));
552 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
556 /// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
557 /// in the list that match the specified block.
558 static void EliminateBlockCases(BasicBlock *BB,
559 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
560 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
561 if (Cases[i].second == BB) {
562 Cases.erase(Cases.begin()+i);
567 /// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
570 ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
571 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
572 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
574 // Make V1 be smaller than V2.
575 if (V1->size() > V2->size())
578 if (V1->size() == 0) return false;
579 if (V1->size() == 1) {
581 ConstantInt *TheVal = (*V1)[0].first;
582 for (unsigned i = 0, e = V2->size(); i != e; ++i)
583 if (TheVal == (*V2)[i].first)
587 // Otherwise, just sort both lists and compare element by element.
588 std::sort(V1->begin(), V1->end());
589 std::sort(V2->begin(), V2->end());
590 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
591 while (i1 != e1 && i2 != e2) {
592 if ((*V1)[i1].first == (*V2)[i2].first)
594 if ((*V1)[i1].first < (*V2)[i2].first)
602 /// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
603 /// terminator instruction and its block is known to only have a single
604 /// predecessor block, check to see if that predecessor is also a value
605 /// comparison with the same value, and if that comparison determines the
606 /// outcome of this comparison. If so, simplify TI. This does a very limited
607 /// form of jump threading.
608 static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
610 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
611 if (!PredVal) return false; // Not a value comparison in predecessor.
613 Value *ThisVal = isValueEqualityComparison(TI);
614 assert(ThisVal && "This isn't a value comparison!!");
615 if (ThisVal != PredVal) return false; // Different predicates.
617 // Find out information about when control will move from Pred to TI's block.
618 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
619 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
621 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
623 // Find information about how control leaves this block.
624 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
625 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
626 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
628 // If TI's block is the default block from Pred's comparison, potentially
629 // simplify TI based on this knowledge.
630 if (PredDef == TI->getParent()) {
631 // If we are here, we know that the value is none of those cases listed in
632 // PredCases. If there are any cases in ThisCases that are in PredCases, we
634 if (ValuesOverlap(PredCases, ThisCases)) {
635 if (isa<BranchInst>(TI)) {
636 // Okay, one of the successors of this condbr is dead. Convert it to a
638 assert(ThisCases.size() == 1 && "Branch can only have one case!");
639 // Insert the new branch.
640 Instruction *NI = BranchInst::Create(ThisDef, TI);
642 // Remove PHI node entries for the dead edge.
643 ThisCases[0].second->removePredecessor(TI->getParent());
645 DOUT << "Threading pred instr: " << *Pred->getTerminator()
646 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
648 EraseTerminatorInstAndDCECond(TI);
652 SwitchInst *SI = cast<SwitchInst>(TI);
653 // Okay, TI has cases that are statically dead, prune them away.
654 SmallPtrSet<Constant*, 16> DeadCases;
655 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
656 DeadCases.insert(PredCases[i].first);
658 DOUT << "Threading pred instr: " << *Pred->getTerminator()
659 << "Through successor TI: " << *TI;
661 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
662 if (DeadCases.count(SI->getCaseValue(i))) {
663 SI->getSuccessor(i)->removePredecessor(TI->getParent());
667 DOUT << "Leaving: " << *TI << "\n";
673 // Otherwise, TI's block must correspond to some matched value. Find out
674 // which value (or set of values) this is.
675 ConstantInt *TIV = 0;
676 BasicBlock *TIBB = TI->getParent();
677 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
678 if (PredCases[i].second == TIBB) {
680 TIV = PredCases[i].first;
682 return false; // Cannot handle multiple values coming to this block.
684 assert(TIV && "No edge from pred to succ?");
686 // Okay, we found the one constant that our value can be if we get into TI's
687 // BB. Find out which successor will unconditionally be branched to.
688 BasicBlock *TheRealDest = 0;
689 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
690 if (ThisCases[i].first == TIV) {
691 TheRealDest = ThisCases[i].second;
695 // If not handled by any explicit cases, it is handled by the default case.
696 if (TheRealDest == 0) TheRealDest = ThisDef;
698 // Remove PHI node entries for dead edges.
699 BasicBlock *CheckEdge = TheRealDest;
700 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
701 if (*SI != CheckEdge)
702 (*SI)->removePredecessor(TIBB);
706 // Insert the new branch.
707 Instruction *NI = BranchInst::Create(TheRealDest, TI);
709 DOUT << "Threading pred instr: " << *Pred->getTerminator()
710 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
712 EraseTerminatorInstAndDCECond(TI);
718 /// FoldValueComparisonIntoPredecessors - The specified terminator is a value
719 /// equality comparison instruction (either a switch or a branch on "X == c").
720 /// See if any of the predecessors of the terminator block are value comparisons
721 /// on the same value. If so, and if safe to do so, fold them together.
722 static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
723 BasicBlock *BB = TI->getParent();
724 Value *CV = isValueEqualityComparison(TI); // CondVal
725 assert(CV && "Not a comparison?");
726 bool Changed = false;
728 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
729 while (!Preds.empty()) {
730 BasicBlock *Pred = Preds.back();
733 // See if the predecessor is a comparison with the same value.
734 TerminatorInst *PTI = Pred->getTerminator();
735 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
737 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
738 // Figure out which 'cases' to copy from SI to PSI.
739 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
740 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
742 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
743 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
745 // Based on whether the default edge from PTI goes to BB or not, fill in
746 // PredCases and PredDefault with the new switch cases we would like to
748 SmallVector<BasicBlock*, 8> NewSuccessors;
750 if (PredDefault == BB) {
751 // If this is the default destination from PTI, only the edges in TI
752 // that don't occur in PTI, or that branch to BB will be activated.
753 std::set<ConstantInt*> PTIHandled;
754 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
755 if (PredCases[i].second != BB)
756 PTIHandled.insert(PredCases[i].first);
758 // The default destination is BB, we don't need explicit targets.
759 std::swap(PredCases[i], PredCases.back());
760 PredCases.pop_back();
764 // Reconstruct the new switch statement we will be building.
765 if (PredDefault != BBDefault) {
766 PredDefault->removePredecessor(Pred);
767 PredDefault = BBDefault;
768 NewSuccessors.push_back(BBDefault);
770 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
771 if (!PTIHandled.count(BBCases[i].first) &&
772 BBCases[i].second != BBDefault) {
773 PredCases.push_back(BBCases[i]);
774 NewSuccessors.push_back(BBCases[i].second);
778 // If this is not the default destination from PSI, only the edges
779 // in SI that occur in PSI with a destination of BB will be
781 std::set<ConstantInt*> PTIHandled;
782 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
783 if (PredCases[i].second == BB) {
784 PTIHandled.insert(PredCases[i].first);
785 std::swap(PredCases[i], PredCases.back());
786 PredCases.pop_back();
790 // Okay, now we know which constants were sent to BB from the
791 // predecessor. Figure out where they will all go now.
792 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
793 if (PTIHandled.count(BBCases[i].first)) {
794 // If this is one we are capable of getting...
795 PredCases.push_back(BBCases[i]);
796 NewSuccessors.push_back(BBCases[i].second);
797 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
800 // If there are any constants vectored to BB that TI doesn't handle,
801 // they must go to the default destination of TI.
802 for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
803 E = PTIHandled.end(); I != E; ++I) {
804 PredCases.push_back(std::make_pair(*I, BBDefault));
805 NewSuccessors.push_back(BBDefault);
809 // Okay, at this point, we know which new successor Pred will get. Make
810 // sure we update the number of entries in the PHI nodes for these
812 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
813 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
815 // Now that the successors are updated, create the new Switch instruction.
816 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
817 PredCases.size(), PTI);
818 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
819 NewSI->addCase(PredCases[i].first, PredCases[i].second);
821 EraseTerminatorInstAndDCECond(PTI);
823 // Okay, last check. If BB is still a successor of PSI, then we must
824 // have an infinite loop case. If so, add an infinitely looping block
825 // to handle the case to preserve the behavior of the code.
826 BasicBlock *InfLoopBlock = 0;
827 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
828 if (NewSI->getSuccessor(i) == BB) {
829 if (InfLoopBlock == 0) {
830 // Insert it at the end of the function, because it's either code,
831 // or it won't matter if it's hot. :)
832 InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
833 BranchInst::Create(InfLoopBlock, InfLoopBlock);
835 NewSI->setSuccessor(i, InfLoopBlock);
844 /// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
845 /// BB2, hoist any common code in the two blocks up into the branch block. The
846 /// caller of this function guarantees that BI's block dominates BB1 and BB2.
847 static bool HoistThenElseCodeToIf(BranchInst *BI) {
848 // This does very trivial matching, with limited scanning, to find identical
849 // instructions in the two blocks. In particular, we don't want to get into
850 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
851 // such, we currently just scan for obviously identical instructions in an
853 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
854 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
856 BasicBlock::iterator BB1_Itr = BB1->begin();
857 BasicBlock::iterator BB2_Itr = BB2->begin();
859 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
860 while (isa<DbgInfoIntrinsic>(I1))
862 while (isa<DbgInfoIntrinsic>(I2))
864 if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
865 isa<InvokeInst>(I1) || !I1->isIdenticalTo(I2))
868 // If we get here, we can hoist at least one instruction.
869 BasicBlock *BIParent = BI->getParent();
872 // If we are hoisting the terminator instruction, don't move one (making a
873 // broken BB), instead clone it, and remove BI.
874 if (isa<TerminatorInst>(I1))
875 goto HoistTerminator;
877 // For a normal instruction, we just move one to right before the branch,
878 // then replace all uses of the other with the first. Finally, we remove
879 // the now redundant second instruction.
880 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
881 if (!I2->use_empty())
882 I2->replaceAllUsesWith(I1);
883 BB2->getInstList().erase(I2);
886 while (isa<DbgInfoIntrinsic>(I1))
889 while (isa<DbgInfoIntrinsic>(I2))
891 } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
896 // Okay, it is safe to hoist the terminator.
897 Instruction *NT = I1->clone();
898 BIParent->getInstList().insert(BI, NT);
899 if (NT->getType() != Type::VoidTy) {
900 I1->replaceAllUsesWith(NT);
901 I2->replaceAllUsesWith(NT);
905 // Hoisting one of the terminators from our successor is a great thing.
906 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
907 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
908 // nodes, so we insert select instruction to compute the final result.
909 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
910 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
912 for (BasicBlock::iterator BBI = SI->begin();
913 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
914 Value *BB1V = PN->getIncomingValueForBlock(BB1);
915 Value *BB2V = PN->getIncomingValueForBlock(BB2);
917 // These values do not agree. Insert a select instruction before NT
918 // that determines the right value.
919 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
921 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
922 BB1V->getName()+"."+BB2V->getName(), NT);
923 // Make the PHI node use the select for all incoming values for BB1/BB2
924 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
925 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
926 PN->setIncomingValue(i, SI);
931 // Update any PHI nodes in our new successors.
932 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
933 AddPredecessorToBlock(*SI, BIParent, BB1);
935 EraseTerminatorInstAndDCECond(BI);
939 /// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
940 /// and an BB2 and the only successor of BB1 is BB2, hoist simple code
941 /// (for now, restricted to a single instruction that's side effect free) from
942 /// the BB1 into the branch block to speculatively execute it.
943 static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
944 // Only speculatively execution a single instruction (not counting the
945 // terminator) for now.
946 Instruction *HInst = NULL;
947 Instruction *Term = BB1->getTerminator();
948 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
950 Instruction *I = BBI;
952 if (isa<DbgInfoIntrinsic>(I)) continue;
953 if (I == Term) break;
963 // Be conservative for now. FP select instruction can often be expensive.
964 Value *BrCond = BI->getCondition();
965 if (isa<Instruction>(BrCond) &&
966 cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
969 // If BB1 is actually on the false edge of the conditional branch, remember
970 // to swap the select operands later.
972 if (BB1 != BI->getSuccessor(0)) {
973 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
980 // br i1 %t1, label %BB1, label %BB2
989 // %t3 = select i1 %t1, %t2, %t3
990 switch (HInst->getOpcode()) {
991 default: return false; // Not safe / profitable to hoist.
992 case Instruction::Add:
993 case Instruction::Sub:
994 // FP arithmetic might trap. Not worth doing for vector ops.
995 if (HInst->getType()->isFloatingPoint()
996 || isa<VectorType>(HInst->getType()))
999 case Instruction::And:
1000 case Instruction::Or:
1001 case Instruction::Xor:
1002 case Instruction::Shl:
1003 case Instruction::LShr:
1004 case Instruction::AShr:
1005 // Don't mess with vector operations.
1006 if (isa<VectorType>(HInst->getType()))
1008 break; // These are all cheap and non-trapping instructions.
1011 // If the instruction is obviously dead, don't try to predicate it.
1012 if (HInst->use_empty()) {
1013 HInst->eraseFromParent();
1017 // Can we speculatively execute the instruction? And what is the value
1018 // if the condition is false? Consider the phi uses, if the incoming value
1019 // from the "if" block are all the same V, then V is the value of the
1020 // select if the condition is false.
1021 BasicBlock *BIParent = BI->getParent();
1022 SmallVector<PHINode*, 4> PHIUses;
1023 Value *FalseV = NULL;
1025 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
1026 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
1028 // Ignore any user that is not a PHI node in BB2. These can only occur in
1029 // unreachable blocks, because they would not be dominated by the instr.
1030 PHINode *PN = dyn_cast<PHINode>(UI);
1031 if (!PN || PN->getParent() != BB2)
1033 PHIUses.push_back(PN);
1035 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1038 else if (FalseV != PHIV)
1039 return false; // Inconsistent value when condition is false.
1042 assert(FalseV && "Must have at least one user, and it must be a PHI");
1044 // Do not hoist the instruction if any of its operands are defined but not
1045 // used in this BB. The transformation will prevent the operand from
1046 // being sunk into the use block.
1047 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1049 Instruction *OpI = dyn_cast<Instruction>(*i);
1050 if (OpI && OpI->getParent() == BIParent &&
1051 !OpI->isUsedInBasicBlock(BIParent))
1055 // If we get here, we can hoist the instruction. Try to place it
1056 // before the icmp instruction preceeding the conditional branch.
1057 BasicBlock::iterator InsertPos = BI;
1058 if (InsertPos != BIParent->begin())
1060 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
1061 SmallPtrSet<Instruction *, 4> BB1Insns;
1062 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1063 BB1I != BB1E; ++BB1I)
1064 BB1Insns.insert(BB1I);
1065 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1067 Instruction *Use = cast<Instruction>(*UI);
1068 if (BB1Insns.count(Use)) {
1069 // If BrCond uses the instruction that place it just before
1070 // branch instruction.
1077 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1079 // Create a select whose true value is the speculatively executed value and
1080 // false value is the previously determined FalseV.
1083 SI = SelectInst::Create(BrCond, FalseV, HInst,
1084 FalseV->getName() + "." + HInst->getName(), BI);
1086 SI = SelectInst::Create(BrCond, HInst, FalseV,
1087 HInst->getName() + "." + FalseV->getName(), BI);
1089 // Make the PHI node use the select for all incoming values for "then" and
1091 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1092 PHINode *PN = PHIUses[i];
1093 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1094 if (PN->getIncomingBlock(j) == BB1 ||
1095 PN->getIncomingBlock(j) == BIParent)
1096 PN->setIncomingValue(j, SI);
1103 /// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1104 /// across this block.
1105 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1106 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1109 // If this basic block contains anything other than a PHI (which controls the
1110 // branch) and branch itself, bail out. FIXME: improve this in the future.
1111 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) {
1112 if (Size > 10) return false; // Don't clone large BB's.
1114 // We can only support instructions that are do not define values that are
1115 // live outside of the current basic block.
1116 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1118 Instruction *U = cast<Instruction>(*UI);
1119 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1122 // Looks ok, continue checking.
1128 /// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1129 /// that is defined in the same block as the branch and if any PHI entries are
1130 /// constants, thread edges corresponding to that entry to be branches to their
1131 /// ultimate destination.
1132 static bool FoldCondBranchOnPHI(BranchInst *BI) {
1133 BasicBlock *BB = BI->getParent();
1134 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1135 // NOTE: we currently cannot transform this case if the PHI node is used
1136 // outside of the block.
1137 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1140 // Degenerate case of a single entry PHI.
1141 if (PN->getNumIncomingValues() == 1) {
1142 FoldSingleEntryPHINodes(PN->getParent());
1146 // Now we know that this block has multiple preds and two succs.
1147 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1149 // Okay, this is a simple enough basic block. See if any phi values are
1151 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1153 if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1154 CB->getType() == Type::Int1Ty) {
1155 // Okay, we now know that all edges from PredBB should be revectored to
1156 // branch to RealDest.
1157 BasicBlock *PredBB = PN->getIncomingBlock(i);
1158 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1160 if (RealDest == BB) continue; // Skip self loops.
1162 // The dest block might have PHI nodes, other predecessors and other
1163 // difficult cases. Instead of being smart about this, just insert a new
1164 // block that jumps to the destination block, effectively splitting
1165 // the edge we are about to create.
1166 BasicBlock *EdgeBB = BasicBlock::Create(RealDest->getName()+".critedge",
1167 RealDest->getParent(), RealDest);
1168 BranchInst::Create(RealDest, EdgeBB);
1170 for (BasicBlock::iterator BBI = RealDest->begin();
1171 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1172 Value *V = PN->getIncomingValueForBlock(BB);
1173 PN->addIncoming(V, EdgeBB);
1176 // BB may have instructions that are being threaded over. Clone these
1177 // instructions into EdgeBB. We know that there will be no uses of the
1178 // cloned instructions outside of EdgeBB.
1179 BasicBlock::iterator InsertPt = EdgeBB->begin();
1180 std::map<Value*, Value*> TranslateMap; // Track translated values.
1181 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1182 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1183 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1185 // Clone the instruction.
1186 Instruction *N = BBI->clone();
1187 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1189 // Update operands due to translation.
1190 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1192 std::map<Value*, Value*>::iterator PI =
1193 TranslateMap.find(*i);
1194 if (PI != TranslateMap.end())
1198 // Check for trivial simplification.
1199 if (Constant *C = ConstantFoldInstruction(N)) {
1200 TranslateMap[BBI] = C;
1201 delete N; // Constant folded away, don't need actual inst
1203 // Insert the new instruction into its new home.
1204 EdgeBB->getInstList().insert(InsertPt, N);
1205 if (!BBI->use_empty())
1206 TranslateMap[BBI] = N;
1211 // Loop over all of the edges from PredBB to BB, changing them to branch
1212 // to EdgeBB instead.
1213 TerminatorInst *PredBBTI = PredBB->getTerminator();
1214 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1215 if (PredBBTI->getSuccessor(i) == BB) {
1216 BB->removePredecessor(PredBB);
1217 PredBBTI->setSuccessor(i, EdgeBB);
1220 // Recurse, simplifying any other constants.
1221 return FoldCondBranchOnPHI(BI) | true;
1228 /// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1229 /// PHI node, see if we can eliminate it.
1230 static bool FoldTwoEntryPHINode(PHINode *PN) {
1231 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1232 // statement", which has a very simple dominance structure. Basically, we
1233 // are trying to find the condition that is being branched on, which
1234 // subsequently causes this merge to happen. We really want control
1235 // dependence information for this check, but simplifycfg can't keep it up
1236 // to date, and this catches most of the cases we care about anyway.
1238 BasicBlock *BB = PN->getParent();
1239 BasicBlock *IfTrue, *IfFalse;
1240 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1241 if (!IfCond) return false;
1243 // Okay, we found that we can merge this two-entry phi node into a select.
1244 // Doing so would require us to fold *all* two entry phi nodes in this block.
1245 // At some point this becomes non-profitable (particularly if the target
1246 // doesn't support cmov's). Only do this transformation if there are two or
1247 // fewer PHI nodes in this block.
1248 unsigned NumPhis = 0;
1249 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1253 DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
1254 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
1256 // Loop over the PHI's seeing if we can promote them all to select
1257 // instructions. While we are at it, keep track of the instructions
1258 // that need to be moved to the dominating block.
1259 std::set<Instruction*> AggressiveInsts;
1261 BasicBlock::iterator AfterPHIIt = BB->begin();
1262 while (isa<PHINode>(AfterPHIIt)) {
1263 PHINode *PN = cast<PHINode>(AfterPHIIt++);
1264 if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1265 if (PN->getIncomingValue(0) != PN)
1266 PN->replaceAllUsesWith(PN->getIncomingValue(0));
1268 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1269 } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1270 &AggressiveInsts) ||
1271 !DominatesMergePoint(PN->getIncomingValue(1), BB,
1272 &AggressiveInsts)) {
1277 // If we all PHI nodes are promotable, check to make sure that all
1278 // instructions in the predecessor blocks can be promoted as well. If
1279 // not, we won't be able to get rid of the control flow, so it's not
1280 // worth promoting to select instructions.
1281 BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1282 PN = cast<PHINode>(BB->begin());
1283 BasicBlock *Pred = PN->getIncomingBlock(0);
1284 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1286 DomBlock = *pred_begin(Pred);
1287 for (BasicBlock::iterator I = Pred->begin();
1288 !isa<TerminatorInst>(I); ++I)
1289 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1290 // This is not an aggressive instruction that we can promote.
1291 // Because of this, we won't be able to get rid of the control
1292 // flow, so the xform is not worth it.
1297 Pred = PN->getIncomingBlock(1);
1298 if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1300 DomBlock = *pred_begin(Pred);
1301 for (BasicBlock::iterator I = Pred->begin();
1302 !isa<TerminatorInst>(I); ++I)
1303 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1304 // This is not an aggressive instruction that we can promote.
1305 // Because of this, we won't be able to get rid of the control
1306 // flow, so the xform is not worth it.
1311 // If we can still promote the PHI nodes after this gauntlet of tests,
1312 // do all of the PHI's now.
1314 // Move all 'aggressive' instructions, which are defined in the
1315 // conditional parts of the if's up to the dominating block.
1317 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1318 IfBlock1->getInstList(),
1320 IfBlock1->getTerminator());
1323 DomBlock->getInstList().splice(DomBlock->getTerminator(),
1324 IfBlock2->getInstList(),
1326 IfBlock2->getTerminator());
1329 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1330 // Change the PHI node into a select instruction.
1332 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1334 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1336 Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1337 PN->replaceAllUsesWith(NV);
1340 BB->getInstList().erase(PN);
1345 /// isTerminatorFirstRelevantInsn - Return true if Term is very first
1346 /// instruction ignoring Phi nodes and dbg intrinsics.
1347 static bool isTerminatorFirstRelevantInsn(BasicBlock *BB, Instruction *Term) {
1348 BasicBlock::iterator BBI = Term;
1349 while (BBI != BB->begin()) {
1351 if (!isa<DbgInfoIntrinsic>(BBI))
1355 if (isa<PHINode>(BBI) || &*BBI == Term || isa<DbgInfoIntrinsic>(BBI))
1360 /// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1361 /// to two returning blocks, try to merge them together into one return,
1362 /// introducing a select if the return values disagree.
1363 static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1364 assert(BI->isConditional() && "Must be a conditional branch");
1365 BasicBlock *TrueSucc = BI->getSuccessor(0);
1366 BasicBlock *FalseSucc = BI->getSuccessor(1);
1367 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1368 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1370 // Check to ensure both blocks are empty (just a return) or optionally empty
1371 // with PHI nodes. If there are other instructions, merging would cause extra
1372 // computation on one path or the other.
1373 if (!isTerminatorFirstRelevantInsn(TrueSucc, TrueRet))
1375 if (!isTerminatorFirstRelevantInsn(FalseSucc, FalseRet))
1378 // Okay, we found a branch that is going to two return nodes. If
1379 // there is no return value for this function, just change the
1380 // branch into a return.
1381 if (FalseRet->getNumOperands() == 0) {
1382 TrueSucc->removePredecessor(BI->getParent());
1383 FalseSucc->removePredecessor(BI->getParent());
1384 ReturnInst::Create(0, BI);
1385 EraseTerminatorInstAndDCECond(BI);
1389 // Otherwise, figure out what the true and false return values are
1390 // so we can insert a new select instruction.
1391 Value *TrueValue = TrueRet->getReturnValue();
1392 Value *FalseValue = FalseRet->getReturnValue();
1394 // Unwrap any PHI nodes in the return blocks.
1395 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1396 if (TVPN->getParent() == TrueSucc)
1397 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1398 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1399 if (FVPN->getParent() == FalseSucc)
1400 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1402 // In order for this transformation to be safe, we must be able to
1403 // unconditionally execute both operands to the return. This is
1404 // normally the case, but we could have a potentially-trapping
1405 // constant expression that prevents this transformation from being
1407 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1410 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1414 // Okay, we collected all the mapped values and checked them for sanity, and
1415 // defined to really do this transformation. First, update the CFG.
1416 TrueSucc->removePredecessor(BI->getParent());
1417 FalseSucc->removePredecessor(BI->getParent());
1419 // Insert select instructions where needed.
1420 Value *BrCond = BI->getCondition();
1422 // Insert a select if the results differ.
1423 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1424 } else if (isa<UndefValue>(TrueValue)) {
1425 TrueValue = FalseValue;
1427 TrueValue = SelectInst::Create(BrCond, TrueValue,
1428 FalseValue, "retval", BI);
1432 Value *RI = !TrueValue ?
1433 ReturnInst::Create(BI) :
1434 ReturnInst::Create(TrueValue, BI);
1436 DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1437 << "\n " << *BI << "NewRet = " << *RI
1438 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
1440 EraseTerminatorInstAndDCECond(BI);
1445 /// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1446 /// and if a predecessor branches to us and one of our successors, fold the
1447 /// setcc into the predecessor and use logical operations to pick the right
1449 static bool FoldBranchToCommonDest(BranchInst *BI) {
1450 BasicBlock *BB = BI->getParent();
1451 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1452 if (Cond == 0) return false;
1455 // Only allow this if the condition is a simple instruction that can be
1456 // executed unconditionally. It must be in the same block as the branch, and
1457 // must be at the front of the block.
1458 BasicBlock::iterator FrontIt = BB->front();
1459 // Ignore dbg intrinsics.
1460 while(isa<DbgInfoIntrinsic>(FrontIt))
1462 if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1463 Cond->getParent() != BB || &*FrontIt != Cond || !Cond->hasOneUse()) {
1467 // Make sure the instruction after the condition is the cond branch.
1468 BasicBlock::iterator CondIt = Cond; ++CondIt;
1469 // Ingore dbg intrinsics.
1470 while(isa<DbgInfoIntrinsic>(CondIt))
1472 if (&*CondIt != BI) {
1473 assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1477 // Cond is known to be a compare or binary operator. Check to make sure that
1478 // neither operand is a potentially-trapping constant expression.
1479 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1482 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1487 // Finally, don't infinitely unroll conditional loops.
1488 BasicBlock *TrueDest = BI->getSuccessor(0);
1489 BasicBlock *FalseDest = BI->getSuccessor(1);
1490 if (TrueDest == BB || FalseDest == BB)
1493 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1494 BasicBlock *PredBlock = *PI;
1495 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1497 // Check that we have two conditional branches. If there is a PHI node in
1498 // the common successor, verify that the same value flows in from both
1500 if (PBI == 0 || PBI->isUnconditional() ||
1501 !SafeToMergeTerminators(BI, PBI))
1504 Instruction::BinaryOps Opc;
1505 bool InvertPredCond = false;
1507 if (PBI->getSuccessor(0) == TrueDest)
1508 Opc = Instruction::Or;
1509 else if (PBI->getSuccessor(1) == FalseDest)
1510 Opc = Instruction::And;
1511 else if (PBI->getSuccessor(0) == FalseDest)
1512 Opc = Instruction::And, InvertPredCond = true;
1513 else if (PBI->getSuccessor(1) == TrueDest)
1514 Opc = Instruction::Or, InvertPredCond = true;
1518 DOUT << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB;
1520 // If we need to invert the condition in the pred block to match, do so now.
1521 if (InvertPredCond) {
1523 BinaryOperator::CreateNot(PBI->getCondition(),
1524 PBI->getCondition()->getName()+".not", PBI);
1525 PBI->setCondition(NewCond);
1526 BasicBlock *OldTrue = PBI->getSuccessor(0);
1527 BasicBlock *OldFalse = PBI->getSuccessor(1);
1528 PBI->setSuccessor(0, OldFalse);
1529 PBI->setSuccessor(1, OldTrue);
1532 // Clone Cond into the predecessor basic block, and or/and the
1533 // two conditions together.
1534 Instruction *New = Cond->clone();
1535 PredBlock->getInstList().insert(PBI, New);
1536 New->takeName(Cond);
1537 Cond->setName(New->getName()+".old");
1539 Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1540 New, "or.cond", PBI);
1541 PBI->setCondition(NewCond);
1542 if (PBI->getSuccessor(0) == BB) {
1543 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1544 PBI->setSuccessor(0, TrueDest);
1546 if (PBI->getSuccessor(1) == BB) {
1547 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1548 PBI->setSuccessor(1, FalseDest);
1555 /// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1556 /// predecessor of another block, this function tries to simplify it. We know
1557 /// that PBI and BI are both conditional branches, and BI is in one of the
1558 /// successor blocks of PBI - PBI branches to BI.
1559 static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1560 assert(PBI->isConditional() && BI->isConditional());
1561 BasicBlock *BB = BI->getParent();
1563 // If this block ends with a branch instruction, and if there is a
1564 // predecessor that ends on a branch of the same condition, make
1565 // this conditional branch redundant.
1566 if (PBI->getCondition() == BI->getCondition() &&
1567 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1568 // Okay, the outcome of this conditional branch is statically
1569 // knowable. If this block had a single pred, handle specially.
1570 if (BB->getSinglePredecessor()) {
1571 // Turn this into a branch on constant.
1572 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1573 BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
1574 return true; // Nuke the branch on constant.
1577 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1578 // in the constant and simplify the block result. Subsequent passes of
1579 // simplifycfg will thread the block.
1580 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1581 PHINode *NewPN = PHINode::Create(Type::Int1Ty,
1582 BI->getCondition()->getName() + ".pr",
1584 // Okay, we're going to insert the PHI node. Since PBI is not the only
1585 // predecessor, compute the PHI'd conditional value for all of the preds.
1586 // Any predecessor where the condition is not computable we keep symbolic.
1587 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1588 if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1589 PBI != BI && PBI->isConditional() &&
1590 PBI->getCondition() == BI->getCondition() &&
1591 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1592 bool CondIsTrue = PBI->getSuccessor(0) == BB;
1593 NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
1596 NewPN->addIncoming(BI->getCondition(), *PI);
1599 BI->setCondition(NewPN);
1604 // If this is a conditional branch in an empty block, and if any
1605 // predecessors is a conditional branch to one of our destinations,
1606 // fold the conditions into logical ops and one cond br.
1607 BasicBlock::iterator BBI = BB->begin();
1608 // Ignore dbg intrinsics.
1609 while (isa<DbgInfoIntrinsic>(BBI))
1615 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1620 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1622 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1623 PBIOp = 0, BIOp = 1;
1624 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1625 PBIOp = 1, BIOp = 0;
1626 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1631 // Check to make sure that the other destination of this branch
1632 // isn't BB itself. If so, this is an infinite loop that will
1633 // keep getting unwound.
1634 if (PBI->getSuccessor(PBIOp) == BB)
1637 // Do not perform this transformation if it would require
1638 // insertion of a large number of select instructions. For targets
1639 // without predication/cmovs, this is a big pessimization.
1640 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1642 unsigned NumPhis = 0;
1643 for (BasicBlock::iterator II = CommonDest->begin();
1644 isa<PHINode>(II); ++II, ++NumPhis)
1645 if (NumPhis > 2) // Disable this xform.
1648 // Finally, if everything is ok, fold the branches to logical ops.
1649 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1651 DOUT << "FOLDING BRs:" << *PBI->getParent()
1652 << "AND: " << *BI->getParent();
1655 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1656 // branch in it, where one edge (OtherDest) goes back to itself but the other
1657 // exits. We don't *know* that the program avoids the infinite loop
1658 // (even though that seems likely). If we do this xform naively, we'll end up
1659 // recursively unpeeling the loop. Since we know that (after the xform is
1660 // done) that the block *is* infinite if reached, we just make it an obviously
1661 // infinite loop with no cond branch.
1662 if (OtherDest == BB) {
1663 // Insert it at the end of the function, because it's either code,
1664 // or it won't matter if it's hot. :)
1665 BasicBlock *InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
1666 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1667 OtherDest = InfLoopBlock;
1670 DOUT << *PBI->getParent()->getParent();
1672 // BI may have other predecessors. Because of this, we leave
1673 // it alone, but modify PBI.
1675 // Make sure we get to CommonDest on True&True directions.
1676 Value *PBICond = PBI->getCondition();
1678 PBICond = BinaryOperator::CreateNot(PBICond,
1679 PBICond->getName()+".not",
1681 Value *BICond = BI->getCondition();
1683 BICond = BinaryOperator::CreateNot(BICond,
1684 BICond->getName()+".not",
1686 // Merge the conditions.
1687 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1689 // Modify PBI to branch on the new condition to the new dests.
1690 PBI->setCondition(Cond);
1691 PBI->setSuccessor(0, CommonDest);
1692 PBI->setSuccessor(1, OtherDest);
1694 // OtherDest may have phi nodes. If so, add an entry from PBI's
1695 // block that are identical to the entries for BI's block.
1697 for (BasicBlock::iterator II = OtherDest->begin();
1698 (PN = dyn_cast<PHINode>(II)); ++II) {
1699 Value *V = PN->getIncomingValueForBlock(BB);
1700 PN->addIncoming(V, PBI->getParent());
1703 // We know that the CommonDest already had an edge from PBI to
1704 // it. If it has PHIs though, the PHIs may have different
1705 // entries for BB and PBI's BB. If so, insert a select to make
1707 for (BasicBlock::iterator II = CommonDest->begin();
1708 (PN = dyn_cast<PHINode>(II)); ++II) {
1709 Value *BIV = PN->getIncomingValueForBlock(BB);
1710 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1711 Value *PBIV = PN->getIncomingValue(PBBIdx);
1713 // Insert a select in PBI to pick the right value.
1714 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1715 PBIV->getName()+".mux", PBI);
1716 PN->setIncomingValue(PBBIdx, NV);
1720 DOUT << "INTO: " << *PBI->getParent();
1722 DOUT << *PBI->getParent()->getParent();
1724 // This basic block is probably dead. We know it has at least
1725 // one fewer predecessor.
1731 /// ConstantIntOrdering - This class implements a stable ordering of constant
1732 /// integers that does not depend on their address. This is important for
1733 /// applications that sort ConstantInt's to ensure uniqueness.
1734 struct ConstantIntOrdering {
1735 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
1736 return LHS->getValue().ult(RHS->getValue());
1741 /// SimplifyCFG - This function is used to do simplification of a CFG. For
1742 /// example, it adjusts branches to branches to eliminate the extra hop, it
1743 /// eliminates unreachable basic blocks, and does other "peephole" optimization
1744 /// of the CFG. It returns true if a modification was made.
1746 /// WARNING: The entry node of a function may not be simplified.
1748 bool llvm::SimplifyCFG(BasicBlock *BB) {
1749 bool Changed = false;
1750 Function *M = BB->getParent();
1752 assert(BB && BB->getParent() && "Block not embedded in function!");
1753 assert(BB->getTerminator() && "Degenerate basic block encountered!");
1754 assert(&BB->getParent()->getEntryBlock() != BB &&
1755 "Can't Simplify entry block!");
1757 // Remove basic blocks that have no predecessors... or that just have themself
1758 // as a predecessor. These are unreachable.
1759 if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1760 DOUT << "Removing BB: \n" << *BB;
1761 DeleteDeadBlock(BB);
1765 // Check to see if we can constant propagate this terminator instruction
1767 Changed |= ConstantFoldTerminator(BB);
1769 // If there is a trivial two-entry PHI node in this basic block, and we can
1770 // eliminate it, do so now.
1771 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1772 if (PN->getNumIncomingValues() == 2)
1773 Changed |= FoldTwoEntryPHINode(PN);
1775 // If this is a returning block with only PHI nodes in it, fold the return
1776 // instruction into any unconditional branch predecessors.
1778 // If any predecessor is a conditional branch that just selects among
1779 // different return values, fold the replace the branch/return with a select
1781 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1782 if (isTerminatorFirstRelevantInsn(BB, BB->getTerminator())) {
1783 // Find predecessors that end with branches.
1784 SmallVector<BasicBlock*, 8> UncondBranchPreds;
1785 SmallVector<BranchInst*, 8> CondBranchPreds;
1786 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1787 TerminatorInst *PTI = (*PI)->getTerminator();
1788 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1789 if (BI->isUnconditional())
1790 UncondBranchPreds.push_back(*PI);
1792 CondBranchPreds.push_back(BI);
1796 // If we found some, do the transformation!
1797 if (!UncondBranchPreds.empty()) {
1798 while (!UncondBranchPreds.empty()) {
1799 BasicBlock *Pred = UncondBranchPreds.back();
1800 DOUT << "FOLDING: " << *BB
1801 << "INTO UNCOND BRANCH PRED: " << *Pred;
1802 UncondBranchPreds.pop_back();
1803 Instruction *UncondBranch = Pred->getTerminator();
1804 // Clone the return and add it to the end of the predecessor.
1805 Instruction *NewRet = RI->clone();
1806 Pred->getInstList().push_back(NewRet);
1808 BasicBlock::iterator BBI = RI;
1809 if (BBI != BB->begin()) {
1810 // Move region end info into the predecessor.
1811 if (DbgRegionEndInst *DREI = dyn_cast<DbgRegionEndInst>(--BBI))
1812 DREI->moveBefore(NewRet);
1815 // If the return instruction returns a value, and if the value was a
1816 // PHI node in "BB", propagate the right value into the return.
1817 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1819 if (PHINode *PN = dyn_cast<PHINode>(*i))
1820 if (PN->getParent() == BB)
1821 *i = PN->getIncomingValueForBlock(Pred);
1823 // Update any PHI nodes in the returning block to realize that we no
1824 // longer branch to them.
1825 BB->removePredecessor(Pred);
1826 Pred->getInstList().erase(UncondBranch);
1829 // If we eliminated all predecessors of the block, delete the block now.
1830 if (pred_begin(BB) == pred_end(BB))
1831 // We know there are no successors, so just nuke the block.
1832 M->getBasicBlockList().erase(BB);
1837 // Check out all of the conditional branches going to this return
1838 // instruction. If any of them just select between returns, change the
1839 // branch itself into a select/return pair.
1840 while (!CondBranchPreds.empty()) {
1841 BranchInst *BI = CondBranchPreds.back();
1842 CondBranchPreds.pop_back();
1844 // Check to see if the non-BB successor is also a return block.
1845 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1846 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1847 SimplifyCondBranchToTwoReturns(BI))
1851 } else if (isa<UnwindInst>(BB->begin())) {
1852 // Check to see if the first instruction in this block is just an unwind.
1853 // If so, replace any invoke instructions which use this as an exception
1854 // destination with call instructions, and any unconditional branch
1855 // predecessor with an unwind.
1857 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1858 while (!Preds.empty()) {
1859 BasicBlock *Pred = Preds.back();
1860 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
1861 if (BI->isUnconditional()) {
1862 Pred->getInstList().pop_back(); // nuke uncond branch
1863 new UnwindInst(Pred); // Use unwind.
1866 } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1867 if (II->getUnwindDest() == BB) {
1868 // Insert a new branch instruction before the invoke, because this
1869 // is now a fall through...
1870 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1871 Pred->getInstList().remove(II); // Take out of symbol table
1873 // Insert the call now...
1874 SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1875 CallInst *CI = CallInst::Create(II->getCalledValue(),
1876 Args.begin(), Args.end(),
1878 CI->setCallingConv(II->getCallingConv());
1879 CI->setAttributes(II->getAttributes());
1880 // If the invoke produced a value, the Call now does instead
1881 II->replaceAllUsesWith(CI);
1889 // If this block is now dead, remove it.
1890 if (pred_begin(BB) == pred_end(BB)) {
1891 // We know there are no successors, so just nuke the block.
1892 M->getBasicBlockList().erase(BB);
1896 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1897 if (isValueEqualityComparison(SI)) {
1898 // If we only have one predecessor, and if it is a branch on this value,
1899 // see if that predecessor totally determines the outcome of this switch.
1900 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1901 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1902 return SimplifyCFG(BB) || 1;
1904 // If the block only contains the switch, see if we can fold the block
1905 // away into any preds.
1906 BasicBlock::iterator BBI = BB->begin();
1907 // Ignore dbg intrinsics.
1908 while (isa<DbgInfoIntrinsic>(BBI))
1911 if (FoldValueComparisonIntoPredecessors(SI))
1912 return SimplifyCFG(BB) || 1;
1914 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1915 if (BI->isUnconditional()) {
1916 BasicBlock::iterator BBI = BB->getFirstNonPHI();
1918 BasicBlock *Succ = BI->getSuccessor(0);
1919 // Ignore dbg intrinsics.
1920 while (isa<DbgInfoIntrinsic>(BBI))
1922 if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
1923 Succ != BB) // Don't hurt infinite loops!
1924 if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
1927 } else { // Conditional branch
1928 if (isValueEqualityComparison(BI)) {
1929 // If we only have one predecessor, and if it is a branch on this value,
1930 // see if that predecessor totally determines the outcome of this
1932 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1933 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1934 return SimplifyCFG(BB) || 1;
1936 // This block must be empty, except for the setcond inst, if it exists.
1937 // Ignore dbg intrinsics.
1938 BasicBlock::iterator I = BB->begin();
1939 // Ignore dbg intrinsics.
1940 while (isa<DbgInfoIntrinsic>(I))
1943 if (FoldValueComparisonIntoPredecessors(BI))
1944 return SimplifyCFG(BB) | true;
1945 } else if (&*I == cast<Instruction>(BI->getCondition())){
1947 // Ignore dbg intrinsics.
1948 while (isa<DbgInfoIntrinsic>(I))
1951 if (FoldValueComparisonIntoPredecessors(BI))
1952 return SimplifyCFG(BB) | true;
1957 // If this is a branch on a phi node in the current block, thread control
1958 // through this block if any PHI node entries are constants.
1959 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1960 if (PN->getParent() == BI->getParent())
1961 if (FoldCondBranchOnPHI(BI))
1962 return SimplifyCFG(BB) | true;
1964 // If this basic block is ONLY a setcc and a branch, and if a predecessor
1965 // branches to us and one of our successors, fold the setcc into the
1966 // predecessor and use logical operations to pick the right destination.
1967 if (FoldBranchToCommonDest(BI))
1968 return SimplifyCFG(BB) | 1;
1971 // Scan predecessor blocks for conditional branches.
1972 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1973 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1974 if (PBI != BI && PBI->isConditional())
1975 if (SimplifyCondBranchToCondBranch(PBI, BI))
1976 return SimplifyCFG(BB) | true;
1978 } else if (isa<UnreachableInst>(BB->getTerminator())) {
1979 // If there are any instructions immediately before the unreachable that can
1980 // be removed, do so.
1981 Instruction *Unreachable = BB->getTerminator();
1982 while (Unreachable != BB->begin()) {
1983 BasicBlock::iterator BBI = Unreachable;
1985 // Do not delete instructions that can have side effects, like calls
1986 // (which may never return) and volatile loads and stores.
1987 if (isa<CallInst>(BBI)) break;
1989 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
1990 if (SI->isVolatile())
1993 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
1994 if (LI->isVolatile())
1997 // Delete this instruction
1998 BB->getInstList().erase(BBI);
2002 // If the unreachable instruction is the first in the block, take a gander
2003 // at all of the predecessors of this instruction, and simplify them.
2004 if (&BB->front() == Unreachable) {
2005 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2006 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2007 TerminatorInst *TI = Preds[i]->getTerminator();
2009 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2010 if (BI->isUnconditional()) {
2011 if (BI->getSuccessor(0) == BB) {
2012 new UnreachableInst(TI);
2013 TI->eraseFromParent();
2017 if (BI->getSuccessor(0) == BB) {
2018 BranchInst::Create(BI->getSuccessor(1), BI);
2019 EraseTerminatorInstAndDCECond(BI);
2020 } else if (BI->getSuccessor(1) == BB) {
2021 BranchInst::Create(BI->getSuccessor(0), BI);
2022 EraseTerminatorInstAndDCECond(BI);
2026 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2027 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2028 if (SI->getSuccessor(i) == BB) {
2029 BB->removePredecessor(SI->getParent());
2034 // If the default value is unreachable, figure out the most popular
2035 // destination and make it the default.
2036 if (SI->getSuccessor(0) == BB) {
2037 std::map<BasicBlock*, unsigned> Popularity;
2038 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2039 Popularity[SI->getSuccessor(i)]++;
2041 // Find the most popular block.
2042 unsigned MaxPop = 0;
2043 BasicBlock *MaxBlock = 0;
2044 for (std::map<BasicBlock*, unsigned>::iterator
2045 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
2046 if (I->second > MaxPop) {
2048 MaxBlock = I->first;
2052 // Make this the new default, allowing us to delete any explicit
2054 SI->setSuccessor(0, MaxBlock);
2057 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2059 if (isa<PHINode>(MaxBlock->begin()))
2060 for (unsigned i = 0; i != MaxPop-1; ++i)
2061 MaxBlock->removePredecessor(SI->getParent());
2063 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2064 if (SI->getSuccessor(i) == MaxBlock) {
2070 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2071 if (II->getUnwindDest() == BB) {
2072 // Convert the invoke to a call instruction. This would be a good
2073 // place to note that the call does not throw though.
2074 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2075 II->removeFromParent(); // Take out of symbol table
2077 // Insert the call now...
2078 SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
2079 CallInst *CI = CallInst::Create(II->getCalledValue(),
2080 Args.begin(), Args.end(),
2082 CI->setCallingConv(II->getCallingConv());
2083 CI->setAttributes(II->getAttributes());
2084 // If the invoke produced a value, the Call does now instead.
2085 II->replaceAllUsesWith(CI);
2092 // If this block is now dead, remove it.
2093 if (pred_begin(BB) == pred_end(BB)) {
2094 // We know there are no successors, so just nuke the block.
2095 M->getBasicBlockList().erase(BB);
2101 // Merge basic blocks into their predecessor if there is only one distinct
2102 // pred, and if there is only one distinct successor of the predecessor, and
2103 // if there are no PHI nodes.
2105 if (MergeBlockIntoPredecessor(BB))
2108 // Otherwise, if this block only has a single predecessor, and if that block
2109 // is a conditional branch, see if we can hoist any code from this block up
2110 // into our predecessor.
2111 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2112 BasicBlock *OnlyPred = *PI++;
2113 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2114 if (*PI != OnlyPred) {
2115 OnlyPred = 0; // There are multiple different predecessors...
2120 if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2121 if (BI->isConditional()) {
2122 // Get the other block.
2123 BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2124 PI = pred_begin(OtherBB);
2127 if (PI == pred_end(OtherBB)) {
2128 // We have a conditional branch to two blocks that are only reachable
2129 // from the condbr. We know that the condbr dominates the two blocks,
2130 // so see if there is any identical code in the "then" and "else"
2131 // blocks. If so, we can hoist it up to the branching block.
2132 Changed |= HoistThenElseCodeToIf(BI);
2134 BasicBlock* OnlySucc = NULL;
2135 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2139 else if (*SI != OnlySucc) {
2140 OnlySucc = 0; // There are multiple distinct successors!
2145 if (OnlySucc == OtherBB) {
2146 // If BB's only successor is the other successor of the predecessor,
2147 // i.e. a triangle, see if we can hoist any code from this block up
2148 // to the "if" block.
2149 Changed |= SpeculativelyExecuteBB(BI, BB);
2154 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2155 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2156 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2157 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2158 Instruction *Cond = cast<Instruction>(BI->getCondition());
2159 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2160 // 'setne's and'ed together, collect them.
2162 std::vector<ConstantInt*> Values;
2163 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2164 if (CompVal && CompVal->getType()->isInteger()) {
2165 // There might be duplicate constants in the list, which the switch
2166 // instruction can't handle, remove them now.
2167 std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2168 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2170 // Figure out which block is which destination.
2171 BasicBlock *DefaultBB = BI->getSuccessor(1);
2172 BasicBlock *EdgeBB = BI->getSuccessor(0);
2173 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2175 // Create the new switch instruction now.
2176 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2179 // Add all of the 'cases' to the switch instruction.
2180 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2181 New->addCase(Values[i], EdgeBB);
2183 // We added edges from PI to the EdgeBB. As such, if there were any
2184 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2185 // the number of edges added.
2186 for (BasicBlock::iterator BBI = EdgeBB->begin();
2187 isa<PHINode>(BBI); ++BBI) {
2188 PHINode *PN = cast<PHINode>(BBI);
2189 Value *InVal = PN->getIncomingValueForBlock(*PI);
2190 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2191 PN->addIncoming(InVal, *PI);
2194 // Erase the old branch instruction.
2195 EraseTerminatorInstAndDCECond(BI);