1 //===-- LoopUnswitch.cpp - Hoist loop-invariant conditionals in loop ------===//
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 // This pass transforms loops that contain branches on loop-invariant conditions
11 // to have multiple loops. For example, it turns the left into the right code:
20 // This can increase the size of the code exponentially (doubling it every time
21 // a loop is unswitched) so we only unswitch if the resultant code will be
22 // smaller than a threshold.
24 // This pass expects LICM to be run before it to hoist invariant conditions out
25 // of the loop, to make the unswitching opportunity obvious.
27 //===----------------------------------------------------------------------===//
29 #define DEBUG_TYPE "loop-unswitch"
30 #include "llvm/Transforms/Scalar.h"
31 #include "llvm/Constants.h"
32 #include "llvm/DerivedTypes.h"
33 #include "llvm/Function.h"
34 #include "llvm/Instructions.h"
35 #include "llvm/Analysis/InlineCost.h"
36 #include "llvm/Analysis/InstructionSimplify.h"
37 #include "llvm/Analysis/LoopInfo.h"
38 #include "llvm/Analysis/LoopPass.h"
39 #include "llvm/Analysis/Dominators.h"
40 #include "llvm/Analysis/ScalarEvolution.h"
41 #include "llvm/Transforms/Utils/Cloning.h"
42 #include "llvm/Transforms/Utils/Local.h"
43 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
44 #include "llvm/ADT/Statistic.h"
45 #include "llvm/ADT/SmallPtrSet.h"
46 #include "llvm/ADT/STLExtras.h"
47 #include "llvm/Support/CommandLine.h"
48 #include "llvm/Support/Debug.h"
49 #include "llvm/Support/raw_ostream.h"
54 STATISTIC(NumBranches, "Number of branches unswitched");
55 STATISTIC(NumSwitches, "Number of switches unswitched");
56 STATISTIC(NumSelects , "Number of selects unswitched");
57 STATISTIC(NumTrivial , "Number of unswitches that are trivial");
58 STATISTIC(NumSimplify, "Number of simplifications of unswitched code");
59 STATISTIC(TotalInsts, "Total number of instructions analyzed");
61 // The specific value of 50 here was chosen based only on intuition and a
62 // few specific examples.
63 static cl::opt<unsigned>
64 Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
65 cl::init(100), cl::Hidden);
69 class LUAnalysisCache {
71 typedef DenseMap<const SwitchInst*, SmallPtrSet<const Value *,8> >
74 typedef UnswitchedValsMap::iterator UnswitchedValsIt;
76 struct LoopProperties {
77 unsigned CanBeUnswitchedCount;
78 unsigned SizeEstimation;
79 UnswitchedValsMap UnswitchedVals;
82 typedef DenseMap<const Loop*, LoopProperties> LoopPropsMap;
83 typedef LoopPropsMap::iterator LoopPropsMapIt;
85 LoopPropsMap LoopsProperties;
86 UnswitchedValsMap* CurLoopInstructions;
87 LoopProperties* CurrentLoopProperties;
94 CurLoopInstructions(NULL), CurrentLoopProperties(NULL),
98 // Analyze loop. Check its size, calculate is it possible to unswitch
99 // it. Returns true if we can unswitch this loop.
100 bool countLoop(const Loop* L);
102 // Clean all data related to given loop.
103 void forgetLoop(const Loop* L);
105 // Mark case value as unswitched.
106 // Since SI instruction can be partly unswitched, in order to avoid
107 // extra unswitching in cloned loops keep track all unswitched values.
108 void setUnswitched(const SwitchInst* SI, const Value* V);
110 // Check was this case value unswitched before or not.
111 bool isUnswitched(const SwitchInst* SI, const Value* V);
113 // Clone all loop-unswitch related loop properties.
114 // Redistribute unswitching quotas.
115 // Note, that new loop data is stored inside the VMap.
116 void cloneData(const Loop* NewLoop, const Loop* OldLoop,
117 const ValueToValueMapTy& VMap);
120 class LoopUnswitch : public LoopPass {
121 LoopInfo *LI; // Loop information
124 // LoopProcessWorklist - Used to check if second loop needs processing
125 // after RewriteLoopBodyWithConditionConstant rewrites first loop.
126 std::vector<Loop*> LoopProcessWorklist;
128 // TODO: This few lines are here for cosmetic purposes only.
129 // Will be removed with the next commit.
130 struct LoopProperties {
131 unsigned CanBeUnswitchedCount;
132 unsigned SizeEstimation;
135 // TODO: This few lines are here for cosmetic purposes only.
136 // Will be removed with the next commit.
137 typedef DenseMap<const Loop*, LoopProperties> LoopPropsMap;
138 typedef LoopPropsMap::iterator LoopPropsMapIt;
139 LoopPropsMap LoopsProperties;
141 LUAnalysisCache BranchesInfo;
143 bool OptimizeForSize;
148 BasicBlock *loopHeader;
149 BasicBlock *loopPreheader;
151 // LoopBlocks contains all of the basic blocks of the loop, including the
152 // preheader of the loop, the body of the loop, and the exit blocks of the
153 // loop, in that order.
154 std::vector<BasicBlock*> LoopBlocks;
155 // NewBlocks contained cloned copy of basic blocks from LoopBlocks.
156 std::vector<BasicBlock*> NewBlocks;
159 static char ID; // Pass ID, replacement for typeid
160 explicit LoopUnswitch(bool Os = false) :
161 LoopPass(ID), OptimizeForSize(Os), redoLoop(false),
162 currentLoop(NULL), DT(NULL), loopHeader(NULL),
163 loopPreheader(NULL) {
164 initializeLoopUnswitchPass(*PassRegistry::getPassRegistry());
167 bool runOnLoop(Loop *L, LPPassManager &LPM);
168 bool processCurrentLoop();
170 /// This transformation requires natural loop information & requires that
171 /// loop preheaders be inserted into the CFG.
173 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
174 AU.addRequiredID(LoopSimplifyID);
175 AU.addPreservedID(LoopSimplifyID);
176 AU.addRequired<LoopInfo>();
177 AU.addPreserved<LoopInfo>();
178 AU.addRequiredID(LCSSAID);
179 AU.addPreservedID(LCSSAID);
180 AU.addPreserved<DominatorTree>();
181 AU.addPreserved<ScalarEvolution>();
186 virtual void releaseMemory() {
187 BranchesInfo.forgetLoop(currentLoop);
190 /// RemoveLoopFromWorklist - If the specified loop is on the loop worklist,
192 void RemoveLoopFromWorklist(Loop *L) {
193 std::vector<Loop*>::iterator I = std::find(LoopProcessWorklist.begin(),
194 LoopProcessWorklist.end(), L);
195 if (I != LoopProcessWorklist.end())
196 LoopProcessWorklist.erase(I);
199 void initLoopData() {
200 loopHeader = currentLoop->getHeader();
201 loopPreheader = currentLoop->getLoopPreheader();
204 /// Split all of the edges from inside the loop to their exit blocks.
205 /// Update the appropriate Phi nodes as we do so.
206 void SplitExitEdges(Loop *L, const SmallVector<BasicBlock *, 8> &ExitBlocks);
208 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val);
209 void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
210 BasicBlock *ExitBlock);
211 void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
213 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
214 Constant *Val, bool isEqual);
216 void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
217 BasicBlock *TrueDest,
218 BasicBlock *FalseDest,
219 Instruction *InsertPt);
221 void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
222 void RemoveBlockIfDead(BasicBlock *BB,
223 std::vector<Instruction*> &Worklist, Loop *l);
224 void RemoveLoopFromHierarchy(Loop *L);
225 bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = 0,
226 BasicBlock **LoopExit = 0);
231 // Analyze loop. Check its size, calculate is it possible to unswitch
232 // it. Returns true if we can unswitch this loop.
233 bool LUAnalysisCache::countLoop(const Loop* L) {
235 std::pair<LoopPropsMapIt, bool> InsertRes =
236 LoopsProperties.insert(std::make_pair(L, LoopProperties()));
238 LoopProperties& Props = InsertRes.first->second;
240 if (InsertRes.second) {
243 // Limit the number of instructions to avoid causing significant code
244 // expansion, and the number of basic blocks, to avoid loops with
245 // large numbers of branches which cause loop unswitching to go crazy.
246 // This is a very ad-hoc heuristic.
248 // FIXME: This is overly conservative because it does not take into
249 // consideration code simplification opportunities and code that can
250 // be shared by the resultant unswitched loops.
252 for (Loop::block_iterator I = L->block_begin(),
255 Metrics.analyzeBasicBlock(*I);
257 Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5);
258 Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation);
259 MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount;
262 if (!Props.CanBeUnswitchedCount) {
263 DEBUG(dbgs() << "NOT unswitching loop %"
264 << L->getHeader()->getName() << ", cost too high: "
265 << L->getBlocks().size() << "\n");
270 // Be careful. This links are good only before new loop addition.
271 CurrentLoopProperties = &Props;
272 CurLoopInstructions = &Props.UnswitchedVals;
277 // Clean all data related to given loop.
278 void LUAnalysisCache::forgetLoop(const Loop* L) {
280 LoopPropsMapIt LIt = LoopsProperties.find(L);
282 if (LIt != LoopsProperties.end()) {
283 LoopProperties& Props = LIt->second;
284 MaxSize += Props.CanBeUnswitchedCount * Props.SizeEstimation;
285 LoopsProperties.erase(LIt);
288 CurrentLoopProperties = NULL;
289 CurLoopInstructions = NULL;
292 // Mark case value as unswitched.
293 // Since SI instruction can be partly unswitched, in order to avoid
294 // extra unswitching in cloned loops keep track all unswitched values.
295 void LUAnalysisCache::setUnswitched(const SwitchInst* SI, const Value* V) {
297 (*CurLoopInstructions)[SI].insert(V);
300 // Check was this case value unswitched before or not.
301 bool LUAnalysisCache::isUnswitched(const SwitchInst* SI, const Value* V) {
302 return (*CurLoopInstructions)[SI].count(V);
305 // Clone all loop-unswitch related loop properties.
306 // Redistribute unswitching quotas.
307 // Note, that new loop data is stored inside the VMap.
308 void LUAnalysisCache::cloneData(const Loop* NewLoop, const Loop* OldLoop,
309 const ValueToValueMapTy& VMap) {
311 LoopProperties& NewLoopProps = LoopsProperties[NewLoop];
312 LoopProperties& OldLoopProps = *CurrentLoopProperties;
313 UnswitchedValsMap& Insts = OldLoopProps.UnswitchedVals;
315 // Reallocate "can-be-unswitched quota"
317 --OldLoopProps.CanBeUnswitchedCount;
318 unsigned Quota = OldLoopProps.CanBeUnswitchedCount;
319 NewLoopProps.CanBeUnswitchedCount = Quota / 2;
320 OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2;
322 NewLoopProps.SizeEstimation = OldLoopProps.SizeEstimation;
324 // Clone unswitched values info:
325 // for new loop switches we clone info about values that was
326 // already unswitched and has redundant successors.
327 for (UnswitchedValsIt I = Insts.begin(); I != Insts.end(); ++I) {
328 const SwitchInst* OldInst = I->first;
329 Value* NewI = VMap.lookup(OldInst);
330 const SwitchInst* NewInst = cast_or_null<SwitchInst>(NewI);
331 assert(NewInst && "All instructions that are in SrcBB must be in VMap.");
333 NewLoopProps.UnswitchedVals[NewInst] = OldLoopProps.UnswitchedVals[OldInst];
337 char LoopUnswitch::ID = 0;
338 INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops",
340 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
341 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
342 INITIALIZE_PASS_DEPENDENCY(LCSSA)
343 INITIALIZE_PASS_END(LoopUnswitch, "loop-unswitch", "Unswitch loops",
346 Pass *llvm::createLoopUnswitchPass(bool Os) {
347 return new LoopUnswitch(Os);
350 /// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
351 /// invariant in the loop, or has an invariant piece, return the invariant.
352 /// Otherwise, return null.
353 static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
355 // We started analyze new instruction, increment scanned instructions counter.
358 // We can never unswitch on vector conditions.
359 if (Cond->getType()->isVectorTy())
362 // Constants should be folded, not unswitched on!
363 if (isa<Constant>(Cond)) return 0;
365 // TODO: Handle: br (VARIANT|INVARIANT).
367 // Hoist simple values out.
368 if (L->makeLoopInvariant(Cond, Changed))
371 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
372 if (BO->getOpcode() == Instruction::And ||
373 BO->getOpcode() == Instruction::Or) {
374 // If either the left or right side is invariant, we can unswitch on this,
375 // which will cause the branch to go away in one loop and the condition to
376 // simplify in the other one.
377 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
379 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
386 bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
387 LI = &getAnalysis<LoopInfo>();
389 DT = getAnalysisIfAvailable<DominatorTree>();
391 Function *F = currentLoop->getHeader()->getParent();
392 bool Changed = false;
394 assert(currentLoop->isLCSSAForm(*DT));
396 Changed |= processCurrentLoop();
400 // FIXME: Reconstruct dom info, because it is not preserved properly.
402 DT->runOnFunction(*F);
407 /// processCurrentLoop - Do actual work and unswitch loop if possible
409 bool LoopUnswitch::processCurrentLoop() {
410 bool Changed = false;
414 // If LoopSimplify was unable to form a preheader, don't do any unswitching.
418 LLVMContext &Context = loopHeader->getContext();
420 // Probably we reach the quota of branches for this loop. If so
422 if (!BranchesInfo.countLoop(currentLoop))
425 // Loop over all of the basic blocks in the loop. If we find an interior
426 // block that is branching on a loop-invariant condition, we can unswitch this
428 for (Loop::block_iterator I = currentLoop->block_begin(),
429 E = currentLoop->block_end(); I != E; ++I) {
430 TerminatorInst *TI = (*I)->getTerminator();
431 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
432 // If this isn't branching on an invariant condition, we can't unswitch
434 if (BI->isConditional()) {
435 // See if this, or some part of it, is loop invariant. If so, we can
436 // unswitch on it if we desire.
437 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
438 currentLoop, Changed);
439 if (LoopCond && UnswitchIfProfitable(LoopCond,
440 ConstantInt::getTrue(Context))) {
445 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
446 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
447 currentLoop, Changed);
448 unsigned NumCases = SI->getNumCases();
449 if (LoopCond && NumCases > 1) {
450 // Find a value to unswitch on:
451 // FIXME: this should chose the most expensive case!
452 // FIXME: scan for a case with a non-critical edge?
453 Constant *UnswitchVal = NULL;
455 // Do not process same value again and again.
456 // At this point we have some cases already unswitched and
457 // some not yet unswitched. Let's find the first not yet unswitched one.
458 for (unsigned i = 1; i < NumCases; ++i) {
459 Constant* UnswitchValCandidate = SI->getCaseValue(i);
460 if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) {
461 UnswitchVal = UnswitchValCandidate;
469 if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
476 // Scan the instructions to check for unswitchable values.
477 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
479 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
480 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
481 currentLoop, Changed);
482 if (LoopCond && UnswitchIfProfitable(LoopCond,
483 ConstantInt::getTrue(Context))) {
492 /// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
493 /// loop with no side effects (including infinite loops).
495 /// If true, we return true and set ExitBB to the block we
498 static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
500 std::set<BasicBlock*> &Visited) {
501 if (!Visited.insert(BB).second) {
502 // Already visited. Without more analysis, this could indicate an infinite
505 } else if (!L->contains(BB)) {
506 // Otherwise, this is a loop exit, this is fine so long as this is the
508 if (ExitBB != 0) return false;
513 // Otherwise, this is an unvisited intra-loop node. Check all successors.
514 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
515 // Check to see if the successor is a trivial loop exit.
516 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
520 // Okay, everything after this looks good, check to make sure that this block
521 // doesn't include any side effects.
522 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
523 if (I->mayHaveSideEffects())
529 /// isTrivialLoopExitBlock - Return true if the specified block unconditionally
530 /// leads to an exit from the specified loop, and has no side-effects in the
531 /// process. If so, return the block that is exited to, otherwise return null.
532 static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
533 std::set<BasicBlock*> Visited;
534 Visited.insert(L->getHeader()); // Branches to header make infinite loops.
535 BasicBlock *ExitBB = 0;
536 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
541 /// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
542 /// trivial: that is, that the condition controls whether or not the loop does
543 /// anything at all. If this is a trivial condition, unswitching produces no
544 /// code duplications (equivalently, it produces a simpler loop and a new empty
545 /// loop, which gets deleted).
547 /// If this is a trivial condition, return true, otherwise return false. When
548 /// returning true, this sets Cond and Val to the condition that controls the
549 /// trivial condition: when Cond dynamically equals Val, the loop is known to
550 /// exit. Finally, this sets LoopExit to the BB that the loop exits to when
553 bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
554 BasicBlock **LoopExit) {
555 BasicBlock *Header = currentLoop->getHeader();
556 TerminatorInst *HeaderTerm = Header->getTerminator();
557 LLVMContext &Context = Header->getContext();
559 BasicBlock *LoopExitBB = 0;
560 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
561 // If the header block doesn't end with a conditional branch on Cond, we
563 if (!BI->isConditional() || BI->getCondition() != Cond)
566 // Check to see if a successor of the branch is guaranteed to
567 // exit through a unique exit block without having any
568 // side-effects. If so, determine the value of Cond that causes it to do
570 if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
571 BI->getSuccessor(0)))) {
572 if (Val) *Val = ConstantInt::getTrue(Context);
573 } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
574 BI->getSuccessor(1)))) {
575 if (Val) *Val = ConstantInt::getFalse(Context);
577 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
578 // If this isn't a switch on Cond, we can't handle it.
579 if (SI->getCondition() != Cond) return false;
581 // Check to see if a successor of the switch is guaranteed to go to the
582 // latch block or exit through a one exit block without having any
583 // side-effects. If so, determine the value of Cond that causes it to do
585 // Note that we can't trivially unswitch on the default case or
586 // on already unswitched cases.
587 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
588 BasicBlock* LoopExitCandidate;
589 if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
590 SI->getSuccessor(i)))) {
591 // Okay, we found a trivial case, remember the value that is trivial.
592 ConstantInt* CaseVal = SI->getCaseValue(i);
594 // Check that it was not unswitched before, since already unswitched
595 // trivial vals are looks trivial too.
596 if (BranchesInfo.isUnswitched(SI, CaseVal))
598 LoopExitBB = LoopExitCandidate;
599 if (Val) *Val = CaseVal;
605 // If we didn't find a single unique LoopExit block, or if the loop exit block
606 // contains phi nodes, this isn't trivial.
607 if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
608 return false; // Can't handle this.
610 if (LoopExit) *LoopExit = LoopExitBB;
612 // We already know that nothing uses any scalar values defined inside of this
613 // loop. As such, we just have to check to see if this loop will execute any
614 // side-effecting instructions (e.g. stores, calls, volatile loads) in the
615 // part of the loop that the code *would* execute. We already checked the
616 // tail, check the header now.
617 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
618 if (I->mayHaveSideEffects())
623 /// UnswitchIfProfitable - We have found that we can unswitch currentLoop when
624 /// LoopCond == Val to simplify the loop. If we decide that this is profitable,
625 /// unswitch the loop, reprocess the pieces, then return true.
626 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
628 Function *F = loopHeader->getParent();
630 Constant *CondVal = 0;
631 BasicBlock *ExitBlock = 0;
632 if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
633 // If the condition is trivial, always unswitch. There is no code growth
635 UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock);
639 // Check to see if it would be profitable to unswitch current loop.
641 // Do not do non-trivial unswitch while optimizing for size.
642 if (OptimizeForSize || F->hasFnAttr(Attribute::OptimizeForSize))
645 UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
649 /// CloneLoop - Recursively clone the specified loop and all of its children,
650 /// mapping the blocks with the specified map.
651 static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
652 LoopInfo *LI, LPPassManager *LPM) {
653 Loop *New = new Loop();
654 LPM->insertLoop(New, PL);
656 // Add all of the blocks in L to the new loop.
657 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
659 if (LI->getLoopFor(*I) == L)
660 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), LI->getBase());
662 // Add all of the subloops to the new loop.
663 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
664 CloneLoop(*I, New, VM, LI, LPM);
669 /// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
670 /// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
671 /// code immediately before InsertPt.
672 void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
673 BasicBlock *TrueDest,
674 BasicBlock *FalseDest,
675 Instruction *InsertPt) {
676 // Insert a conditional branch on LIC to the two preheaders. The original
677 // code is the true version and the new code is the false version.
678 Value *BranchVal = LIC;
679 if (!isa<ConstantInt>(Val) ||
680 Val->getType() != Type::getInt1Ty(LIC->getContext()))
681 BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val);
682 else if (Val != ConstantInt::getTrue(Val->getContext()))
683 // We want to enter the new loop when the condition is true.
684 std::swap(TrueDest, FalseDest);
686 // Insert the new branch.
687 BranchInst *BI = BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt);
689 // If either edge is critical, split it. This helps preserve LoopSimplify
690 // form for enclosing loops.
691 SplitCriticalEdge(BI, 0, this);
692 SplitCriticalEdge(BI, 1, this);
695 /// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
696 /// condition in it (a cond branch from its header block to its latch block,
697 /// where the path through the loop that doesn't execute its body has no
698 /// side-effects), unswitch it. This doesn't involve any code duplication, just
699 /// moving the conditional branch outside of the loop and updating loop info.
700 void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
702 BasicBlock *ExitBlock) {
703 DEBUG(dbgs() << "loop-unswitch: Trivial-Unswitch loop %"
704 << loopHeader->getName() << " [" << L->getBlocks().size()
705 << " blocks] in Function " << L->getHeader()->getParent()->getName()
706 << " on cond: " << *Val << " == " << *Cond << "\n");
708 // First step, split the preheader, so that we know that there is a safe place
709 // to insert the conditional branch. We will change loopPreheader to have a
710 // conditional branch on Cond.
711 BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, this);
713 // Now that we have a place to insert the conditional branch, create a place
714 // to branch to: this is the exit block out of the loop that we should
717 // Split this block now, so that the loop maintains its exit block, and so
718 // that the jump from the preheader can execute the contents of the exit block
719 // without actually branching to it (the exit block should be dominated by the
720 // loop header, not the preheader).
721 assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
722 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this);
724 // Okay, now we have a position to branch from and a position to branch to,
725 // insert the new conditional branch.
726 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
727 loopPreheader->getTerminator());
728 LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L);
729 loopPreheader->getTerminator()->eraseFromParent();
731 // We need to reprocess this loop, it could be unswitched again.
734 // Now that we know that the loop is never entered when this condition is a
735 // particular value, rewrite the loop with this info. We know that this will
736 // at least eliminate the old branch.
737 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
741 /// SplitExitEdges - Split all of the edges from inside the loop to their exit
742 /// blocks. Update the appropriate Phi nodes as we do so.
743 void LoopUnswitch::SplitExitEdges(Loop *L,
744 const SmallVector<BasicBlock *, 8> &ExitBlocks){
746 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
747 BasicBlock *ExitBlock = ExitBlocks[i];
748 SmallVector<BasicBlock *, 4> Preds(pred_begin(ExitBlock),
749 pred_end(ExitBlock));
751 // Although SplitBlockPredecessors doesn't preserve loop-simplify in
752 // general, if we call it on all predecessors of all exits then it does.
753 if (!ExitBlock->isLandingPad()) {
754 SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", this);
756 SmallVector<BasicBlock*, 2> NewBBs;
757 SplitLandingPadPredecessors(ExitBlock, Preds, ".us-lcssa", ".us-lcssa",
763 /// UnswitchNontrivialCondition - We determined that the loop is profitable
764 /// to unswitch when LIC equal Val. Split it into loop versions and test the
765 /// condition outside of either loop. Return the loops created as Out1/Out2.
766 void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
768 Function *F = loopHeader->getParent();
769 DEBUG(dbgs() << "loop-unswitch: Unswitching loop %"
770 << loopHeader->getName() << " [" << L->getBlocks().size()
771 << " blocks] in Function " << F->getName()
772 << " when '" << *Val << "' == " << *LIC << "\n");
774 if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>())
780 // First step, split the preheader and exit blocks, and add these blocks to
781 // the LoopBlocks list.
782 BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, this);
783 LoopBlocks.push_back(NewPreheader);
785 // We want the loop to come after the preheader, but before the exit blocks.
786 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
788 SmallVector<BasicBlock*, 8> ExitBlocks;
789 L->getUniqueExitBlocks(ExitBlocks);
791 // Split all of the edges from inside the loop to their exit blocks. Update
792 // the appropriate Phi nodes as we do so.
793 SplitExitEdges(L, ExitBlocks);
795 // The exit blocks may have been changed due to edge splitting, recompute.
797 L->getUniqueExitBlocks(ExitBlocks);
799 // Add exit blocks to the loop blocks.
800 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
802 // Next step, clone all of the basic blocks that make up the loop (including
803 // the loop preheader and exit blocks), keeping track of the mapping between
804 // the instructions and blocks.
805 NewBlocks.reserve(LoopBlocks.size());
806 ValueToValueMapTy VMap;
807 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
808 BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F);
810 NewBlocks.push_back(NewBB);
811 VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping.
812 LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L);
815 // Splice the newly inserted blocks into the function right before the
816 // original preheader.
817 F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(),
818 NewBlocks[0], F->end());
820 // Now we create the new Loop object for the versioned loop.
821 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM);
823 // Recalculate unswitching quota, inherit simplified switches info for NewBB,
824 // Probably clone more loop-unswitch related loop properties.
825 BranchesInfo.cloneData(NewLoop, L, VMap);
827 Loop *ParentLoop = L->getParentLoop();
829 // Make sure to add the cloned preheader and exit blocks to the parent loop
831 ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase());
834 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
835 BasicBlock *NewExit = cast<BasicBlock>(VMap[ExitBlocks[i]]);
836 // The new exit block should be in the same loop as the old one.
837 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
838 ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase());
840 assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
841 "Exit block should have been split to have one successor!");
842 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
844 // If the successor of the exit block had PHI nodes, add an entry for
847 for (BasicBlock::iterator I = ExitSucc->begin(); isa<PHINode>(I); ++I) {
848 PN = cast<PHINode>(I);
849 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
850 ValueToValueMapTy::iterator It = VMap.find(V);
851 if (It != VMap.end()) V = It->second;
852 PN->addIncoming(V, NewExit);
855 if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
856 PN = PHINode::Create(LPad->getType(), 0, "",
857 ExitSucc->getFirstInsertionPt());
859 for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
862 LandingPadInst *LPI = BB->getLandingPadInst();
863 LPI->replaceAllUsesWith(PN);
864 PN->addIncoming(LPI, BB);
869 // Rewrite the code to refer to itself.
870 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
871 for (BasicBlock::iterator I = NewBlocks[i]->begin(),
872 E = NewBlocks[i]->end(); I != E; ++I)
873 RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
875 // Rewrite the original preheader to select between versions of the loop.
876 BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator());
877 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
878 "Preheader splitting did not work correctly!");
880 // Emit the new branch that selects between the two versions of this loop.
881 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
882 LPM->deleteSimpleAnalysisValue(OldBR, L);
883 OldBR->eraseFromParent();
885 LoopProcessWorklist.push_back(NewLoop);
888 // Keep a WeakVH holding onto LIC. If the first call to RewriteLoopBody
889 // deletes the instruction (for example by simplifying a PHI that feeds into
890 // the condition that we're unswitching on), we don't rewrite the second
892 WeakVH LICHandle(LIC);
894 // Now we rewrite the original code to know that the condition is true and the
895 // new code to know that the condition is false.
896 RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
898 // It's possible that simplifying one loop could cause the other to be
899 // changed to another value or a constant. If its a constant, don't simplify
901 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop &&
902 LICHandle && !isa<Constant>(LICHandle))
903 RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
906 /// RemoveFromWorklist - Remove all instances of I from the worklist vector
908 static void RemoveFromWorklist(Instruction *I,
909 std::vector<Instruction*> &Worklist) {
910 std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(),
912 while (WI != Worklist.end()) {
913 unsigned Offset = WI-Worklist.begin();
915 WI = std::find(Worklist.begin()+Offset, Worklist.end(), I);
919 /// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
920 /// program, replacing all uses with V and update the worklist.
921 static void ReplaceUsesOfWith(Instruction *I, Value *V,
922 std::vector<Instruction*> &Worklist,
923 Loop *L, LPPassManager *LPM) {
924 DEBUG(dbgs() << "Replace with '" << *V << "': " << *I);
926 // Add uses to the worklist, which may be dead now.
927 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
928 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
929 Worklist.push_back(Use);
931 // Add users to the worklist which may be simplified now.
932 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
934 Worklist.push_back(cast<Instruction>(*UI));
935 LPM->deleteSimpleAnalysisValue(I, L);
936 RemoveFromWorklist(I, Worklist);
937 I->replaceAllUsesWith(V);
938 I->eraseFromParent();
942 /// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
943 /// information, and remove any dead successors it has.
945 void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
946 std::vector<Instruction*> &Worklist,
948 if (pred_begin(BB) != pred_end(BB)) {
949 // This block isn't dead, since an edge to BB was just removed, see if there
950 // are any easy simplifications we can do now.
951 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
952 // If it has one pred, fold phi nodes in BB.
953 while (isa<PHINode>(BB->begin()))
954 ReplaceUsesOfWith(BB->begin(),
955 cast<PHINode>(BB->begin())->getIncomingValue(0),
958 // If this is the header of a loop and the only pred is the latch, we now
959 // have an unreachable loop.
960 if (Loop *L = LI->getLoopFor(BB))
961 if (loopHeader == BB && L->contains(Pred)) {
962 // Remove the branch from the latch to the header block, this makes
963 // the header dead, which will make the latch dead (because the header
964 // dominates the latch).
965 LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L);
966 Pred->getTerminator()->eraseFromParent();
967 new UnreachableInst(BB->getContext(), Pred);
969 // The loop is now broken, remove it from LI.
970 RemoveLoopFromHierarchy(L);
972 // Reprocess the header, which now IS dead.
973 RemoveBlockIfDead(BB, Worklist, L);
977 // If pred ends in a uncond branch, add uncond branch to worklist so that
978 // the two blocks will get merged.
979 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
980 if (BI->isUnconditional())
981 Worklist.push_back(BI);
986 DEBUG(dbgs() << "Nuking dead block: " << *BB);
988 // Remove the instructions in the basic block from the worklist.
989 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
990 RemoveFromWorklist(I, Worklist);
992 // Anything that uses the instructions in this basic block should have their
993 // uses replaced with undefs.
994 // If I is not void type then replaceAllUsesWith undef.
995 // This allows ValueHandlers and custom metadata to adjust itself.
996 if (!I->getType()->isVoidTy())
997 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1000 // If this is the edge to the header block for a loop, remove the loop and
1001 // promote all subloops.
1002 if (Loop *BBLoop = LI->getLoopFor(BB)) {
1003 if (BBLoop->getLoopLatch() == BB) {
1004 RemoveLoopFromHierarchy(BBLoop);
1005 if (currentLoop == BBLoop) {
1012 // Remove the block from the loop info, which removes it from any loops it
1014 LI->removeBlock(BB);
1017 // Remove phi node entries in successors for this block.
1018 TerminatorInst *TI = BB->getTerminator();
1019 SmallVector<BasicBlock*, 4> Succs;
1020 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1021 Succs.push_back(TI->getSuccessor(i));
1022 TI->getSuccessor(i)->removePredecessor(BB);
1025 // Unique the successors, remove anything with multiple uses.
1026 array_pod_sort(Succs.begin(), Succs.end());
1027 Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
1029 // Remove the basic block, including all of the instructions contained in it.
1030 LPM->deleteSimpleAnalysisValue(BB, L);
1031 BB->eraseFromParent();
1032 // Remove successor blocks here that are not dead, so that we know we only
1033 // have dead blocks in this list. Nondead blocks have a way of becoming dead,
1034 // then getting removed before we revisit them, which is badness.
1036 for (unsigned i = 0; i != Succs.size(); ++i)
1037 if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
1038 // One exception is loop headers. If this block was the preheader for a
1039 // loop, then we DO want to visit the loop so the loop gets deleted.
1040 // We know that if the successor is a loop header, that this loop had to
1041 // be the preheader: the case where this was the latch block was handled
1042 // above and headers can only have two predecessors.
1043 if (!LI->isLoopHeader(Succs[i])) {
1044 Succs.erase(Succs.begin()+i);
1049 for (unsigned i = 0, e = Succs.size(); i != e; ++i)
1050 RemoveBlockIfDead(Succs[i], Worklist, L);
1053 /// RemoveLoopFromHierarchy - We have discovered that the specified loop has
1054 /// become unwrapped, either because the backedge was deleted, or because the
1055 /// edge into the header was removed. If the edge into the header from the
1056 /// latch block was removed, the loop is unwrapped but subloops are still alive,
1057 /// so they just reparent loops. If the loops are actually dead, they will be
1059 void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) {
1060 LPM->deleteLoopFromQueue(L);
1061 RemoveLoopFromWorklist(L);
1064 // RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
1065 // the value specified by Val in the specified loop, or we know it does NOT have
1066 // that value. Rewrite any uses of LIC or of properties correlated to it.
1067 void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
1070 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
1072 // FIXME: Support correlated properties, like:
1079 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
1080 // selects, switches.
1081 std::vector<Instruction*> Worklist;
1082 LLVMContext &Context = Val->getContext();
1085 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
1086 // in the loop with the appropriate one directly.
1087 if (IsEqual || (isa<ConstantInt>(Val) &&
1088 Val->getType()->isIntegerTy(1))) {
1093 Replacement = ConstantInt::get(Type::getInt1Ty(Val->getContext()),
1094 !cast<ConstantInt>(Val)->getZExtValue());
1096 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
1098 Instruction *U = dyn_cast<Instruction>(*UI);
1099 if (!U || !L->contains(U))
1101 Worklist.push_back(U);
1104 for (std::vector<Instruction*>::iterator UI = Worklist.begin();
1105 UI != Worklist.end(); ++UI)
1106 (*UI)->replaceUsesOfWith(LIC, Replacement);
1108 SimplifyCode(Worklist, L);
1112 // Otherwise, we don't know the precise value of LIC, but we do know that it
1113 // is certainly NOT "Val". As such, simplify any uses in the loop that we
1114 // can. This case occurs when we unswitch switch statements.
1115 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
1117 Instruction *U = dyn_cast<Instruction>(*UI);
1118 if (!U || !L->contains(U))
1121 Worklist.push_back(U);
1123 // TODO: We could do other simplifications, for example, turning
1124 // 'icmp eq LIC, Val' -> false.
1126 // If we know that LIC is not Val, use this info to simplify code.
1127 SwitchInst *SI = dyn_cast<SwitchInst>(U);
1128 if (SI == 0 || !isa<ConstantInt>(Val)) continue;
1130 unsigned DeadCase = SI->findCaseValue(cast<ConstantInt>(Val));
1131 if (DeadCase == 0) continue; // Default case is live for multiple values.
1133 // Found a dead case value. Don't remove PHI nodes in the
1134 // successor if they become single-entry, those PHI nodes may
1135 // be in the Users list.
1137 BasicBlock *Switch = SI->getParent();
1138 BasicBlock *SISucc = SI->getSuccessor(DeadCase);
1139 BasicBlock *Latch = L->getLoopLatch();
1141 BranchesInfo.setUnswitched(SI, Val);
1143 if (!SI->findCaseDest(SISucc)) continue; // Edge is critical.
1144 // If the DeadCase successor dominates the loop latch, then the
1145 // transformation isn't safe since it will delete the sole predecessor edge
1147 if (Latch && DT->dominates(SISucc, Latch))
1150 // FIXME: This is a hack. We need to keep the successor around
1151 // and hooked up so as to preserve the loop structure, because
1152 // trying to update it is complicated. So instead we preserve the
1153 // loop structure and put the block on a dead code path.
1154 SplitEdge(Switch, SISucc, this);
1155 // Compute the successors instead of relying on the return value
1156 // of SplitEdge, since it may have split the switch successor
1158 BasicBlock *NewSISucc = SI->getSuccessor(DeadCase);
1159 BasicBlock *OldSISucc = *succ_begin(NewSISucc);
1160 // Create an "unreachable" destination.
1161 BasicBlock *Abort = BasicBlock::Create(Context, "us-unreachable",
1162 Switch->getParent(),
1164 new UnreachableInst(Context, Abort);
1165 // Force the new case destination to branch to the "unreachable"
1166 // block while maintaining a (dead) CFG edge to the old block.
1167 NewSISucc->getTerminator()->eraseFromParent();
1168 BranchInst::Create(Abort, OldSISucc,
1169 ConstantInt::getTrue(Context), NewSISucc);
1170 // Release the PHI operands for this edge.
1171 for (BasicBlock::iterator II = NewSISucc->begin();
1172 PHINode *PN = dyn_cast<PHINode>(II); ++II)
1173 PN->setIncomingValue(PN->getBasicBlockIndex(Switch),
1174 UndefValue::get(PN->getType()));
1175 // Tell the domtree about the new block. We don't fully update the
1176 // domtree here -- instead we force it to do a full recomputation
1177 // after the pass is complete -- but we do need to inform it of
1180 DT->addNewBlock(Abort, NewSISucc);
1183 SimplifyCode(Worklist, L);
1186 /// SimplifyCode - Okay, now that we have simplified some instructions in the
1187 /// loop, walk over it and constant prop, dce, and fold control flow where
1188 /// possible. Note that this is effectively a very simple loop-structure-aware
1189 /// optimizer. During processing of this loop, L could very well be deleted, so
1190 /// it must not be used.
1192 /// FIXME: When the loop optimizer is more mature, separate this out to a new
1195 void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
1196 while (!Worklist.empty()) {
1197 Instruction *I = Worklist.back();
1198 Worklist.pop_back();
1201 if (isInstructionTriviallyDead(I)) {
1202 DEBUG(dbgs() << "Remove dead instruction '" << *I);
1204 // Add uses to the worklist, which may be dead now.
1205 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1206 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
1207 Worklist.push_back(Use);
1208 LPM->deleteSimpleAnalysisValue(I, L);
1209 RemoveFromWorklist(I, Worklist);
1210 I->eraseFromParent();
1215 // See if instruction simplification can hack this up. This is common for
1216 // things like "select false, X, Y" after unswitching made the condition be
1218 if (Value *V = SimplifyInstruction(I, 0, 0, DT))
1219 if (LI->replacementPreservesLCSSAForm(I, V)) {
1220 ReplaceUsesOfWith(I, V, Worklist, L, LPM);
1224 // Special case hacks that appear commonly in unswitched code.
1225 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1226 if (BI->isUnconditional()) {
1227 // If BI's parent is the only pred of the successor, fold the two blocks
1229 BasicBlock *Pred = BI->getParent();
1230 BasicBlock *Succ = BI->getSuccessor(0);
1231 BasicBlock *SinglePred = Succ->getSinglePredecessor();
1232 if (!SinglePred) continue; // Nothing to do.
1233 assert(SinglePred == Pred && "CFG broken");
1235 DEBUG(dbgs() << "Merging blocks: " << Pred->getName() << " <- "
1236 << Succ->getName() << "\n");
1238 // Resolve any single entry PHI nodes in Succ.
1239 while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
1240 ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM);
1242 // If Succ has any successors with PHI nodes, update them to have
1243 // entries coming from Pred instead of Succ.
1244 Succ->replaceAllUsesWith(Pred);
1246 // Move all of the successor contents from Succ to Pred.
1247 Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
1249 LPM->deleteSimpleAnalysisValue(BI, L);
1250 BI->eraseFromParent();
1251 RemoveFromWorklist(BI, Worklist);
1253 // Remove Succ from the loop tree.
1254 LI->removeBlock(Succ);
1255 LPM->deleteSimpleAnalysisValue(Succ, L);
1256 Succ->eraseFromParent();
1261 if (ConstantInt *CB = dyn_cast<ConstantInt>(BI->getCondition())){
1262 // Conditional branch. Turn it into an unconditional branch, then
1263 // remove dead blocks.
1264 continue; // FIXME: Enable.
1266 DEBUG(dbgs() << "Folded branch: " << *BI);
1267 BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue());
1268 BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue());
1269 DeadSucc->removePredecessor(BI->getParent(), true);
1270 Worklist.push_back(BranchInst::Create(LiveSucc, BI));
1271 LPM->deleteSimpleAnalysisValue(BI, L);
1272 BI->eraseFromParent();
1273 RemoveFromWorklist(BI, Worklist);
1276 RemoveBlockIfDead(DeadSucc, Worklist, L);