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/CodeMetrics.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"
55 STATISTIC(NumBranches, "Number of branches unswitched");
56 STATISTIC(NumSwitches, "Number of switches unswitched");
57 STATISTIC(NumSelects , "Number of selects unswitched");
58 STATISTIC(NumTrivial , "Number of unswitches that are trivial");
59 STATISTIC(NumSimplify, "Number of simplifications of unswitched code");
60 STATISTIC(TotalInsts, "Total number of instructions analyzed");
62 // The specific value of 100 here was chosen based only on intuition and a
63 // few specific examples.
64 static cl::opt<unsigned>
65 Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
66 cl::init(100), cl::Hidden);
70 class LUAnalysisCache {
72 typedef DenseMap<const SwitchInst*, SmallPtrSet<const Value *, 8> >
75 typedef UnswitchedValsMap::iterator UnswitchedValsIt;
77 struct LoopProperties {
78 unsigned CanBeUnswitchedCount;
79 unsigned SizeEstimation;
80 UnswitchedValsMap UnswitchedVals;
83 // Here we use std::map instead of DenseMap, since we need to keep valid
84 // LoopProperties pointer for current loop for better performance.
85 typedef std::map<const Loop*, LoopProperties> LoopPropsMap;
86 typedef LoopPropsMap::iterator LoopPropsMapIt;
88 LoopPropsMap LoopsProperties;
89 UnswitchedValsMap* CurLoopInstructions;
90 LoopProperties* CurrentLoopProperties;
92 // Max size of code we can produce on remained iterations.
98 CurLoopInstructions(NULL), CurrentLoopProperties(NULL),
102 // Analyze loop. Check its size, calculate is it possible to unswitch
103 // it. Returns true if we can unswitch this loop.
104 bool countLoop(const Loop* L);
106 // Clean all data related to given loop.
107 void forgetLoop(const Loop* L);
109 // Mark case value as unswitched.
110 // Since SI instruction can be partly unswitched, in order to avoid
111 // extra unswitching in cloned loops keep track all unswitched values.
112 void setUnswitched(const SwitchInst* SI, const Value* V);
114 // Check was this case value unswitched before or not.
115 bool isUnswitched(const SwitchInst* SI, const Value* V);
117 // Clone all loop-unswitch related loop properties.
118 // Redistribute unswitching quotas.
119 // Note, that new loop data is stored inside the VMap.
120 void cloneData(const Loop* NewLoop, const Loop* OldLoop,
121 const ValueToValueMapTy& VMap);
124 class LoopUnswitch : public LoopPass {
125 LoopInfo *LI; // Loop information
128 // LoopProcessWorklist - Used to check if second loop needs processing
129 // after RewriteLoopBodyWithConditionConstant rewrites first loop.
130 std::vector<Loop*> LoopProcessWorklist;
132 LUAnalysisCache BranchesInfo;
134 bool OptimizeForSize;
139 BasicBlock *loopHeader;
140 BasicBlock *loopPreheader;
142 // LoopBlocks contains all of the basic blocks of the loop, including the
143 // preheader of the loop, the body of the loop, and the exit blocks of the
144 // loop, in that order.
145 std::vector<BasicBlock*> LoopBlocks;
146 // NewBlocks contained cloned copy of basic blocks from LoopBlocks.
147 std::vector<BasicBlock*> NewBlocks;
150 static char ID; // Pass ID, replacement for typeid
151 explicit LoopUnswitch(bool Os = false) :
152 LoopPass(ID), OptimizeForSize(Os), redoLoop(false),
153 currentLoop(NULL), DT(NULL), loopHeader(NULL),
154 loopPreheader(NULL) {
155 initializeLoopUnswitchPass(*PassRegistry::getPassRegistry());
158 bool runOnLoop(Loop *L, LPPassManager &LPM);
159 bool processCurrentLoop();
161 /// This transformation requires natural loop information & requires that
162 /// loop preheaders be inserted into the CFG.
164 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
165 AU.addRequiredID(LoopSimplifyID);
166 AU.addPreservedID(LoopSimplifyID);
167 AU.addRequired<LoopInfo>();
168 AU.addPreserved<LoopInfo>();
169 AU.addRequiredID(LCSSAID);
170 AU.addPreservedID(LCSSAID);
171 AU.addPreserved<DominatorTree>();
172 AU.addPreserved<ScalarEvolution>();
177 virtual void releaseMemory() {
178 BranchesInfo.forgetLoop(currentLoop);
181 /// RemoveLoopFromWorklist - If the specified loop is on the loop worklist,
183 void RemoveLoopFromWorklist(Loop *L) {
184 std::vector<Loop*>::iterator I = std::find(LoopProcessWorklist.begin(),
185 LoopProcessWorklist.end(), L);
186 if (I != LoopProcessWorklist.end())
187 LoopProcessWorklist.erase(I);
190 void initLoopData() {
191 loopHeader = currentLoop->getHeader();
192 loopPreheader = currentLoop->getLoopPreheader();
195 /// Split all of the edges from inside the loop to their exit blocks.
196 /// Update the appropriate Phi nodes as we do so.
197 void SplitExitEdges(Loop *L, const SmallVector<BasicBlock *, 8> &ExitBlocks);
199 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val);
200 void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
201 BasicBlock *ExitBlock);
202 void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
204 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
205 Constant *Val, bool isEqual);
207 void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
208 BasicBlock *TrueDest,
209 BasicBlock *FalseDest,
210 Instruction *InsertPt);
212 void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
213 void RemoveBlockIfDead(BasicBlock *BB,
214 std::vector<Instruction*> &Worklist, Loop *l);
215 void RemoveLoopFromHierarchy(Loop *L);
216 bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = 0,
217 BasicBlock **LoopExit = 0);
222 // Analyze loop. Check its size, calculate is it possible to unswitch
223 // it. Returns true if we can unswitch this loop.
224 bool LUAnalysisCache::countLoop(const Loop* L) {
226 std::pair<LoopPropsMapIt, bool> InsertRes =
227 LoopsProperties.insert(std::make_pair(L, LoopProperties()));
229 LoopProperties& Props = InsertRes.first->second;
231 if (InsertRes.second) {
234 // Limit the number of instructions to avoid causing significant code
235 // expansion, and the number of basic blocks, to avoid loops with
236 // large numbers of branches which cause loop unswitching to go crazy.
237 // This is a very ad-hoc heuristic.
239 // FIXME: This is overly conservative because it does not take into
240 // consideration code simplification opportunities and code that can
241 // be shared by the resultant unswitched loops.
243 for (Loop::block_iterator I = L->block_begin(),
246 Metrics.analyzeBasicBlock(*I);
248 Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5);
249 Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation);
250 MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount;
253 if (!Props.CanBeUnswitchedCount) {
254 DEBUG(dbgs() << "NOT unswitching loop %"
255 << L->getHeader()->getName() << ", cost too high: "
256 << L->getBlocks().size() << "\n");
261 // Be careful. This links are good only before new loop addition.
262 CurrentLoopProperties = &Props;
263 CurLoopInstructions = &Props.UnswitchedVals;
268 // Clean all data related to given loop.
269 void LUAnalysisCache::forgetLoop(const Loop* L) {
271 LoopPropsMapIt LIt = LoopsProperties.find(L);
273 if (LIt != LoopsProperties.end()) {
274 LoopProperties& Props = LIt->second;
275 MaxSize += Props.CanBeUnswitchedCount * Props.SizeEstimation;
276 LoopsProperties.erase(LIt);
279 CurrentLoopProperties = NULL;
280 CurLoopInstructions = NULL;
283 // Mark case value as unswitched.
284 // Since SI instruction can be partly unswitched, in order to avoid
285 // extra unswitching in cloned loops keep track all unswitched values.
286 void LUAnalysisCache::setUnswitched(const SwitchInst* SI, const Value* V) {
287 (*CurLoopInstructions)[SI].insert(V);
290 // Check was this case value unswitched before or not.
291 bool LUAnalysisCache::isUnswitched(const SwitchInst* SI, const Value* V) {
292 return (*CurLoopInstructions)[SI].count(V);
295 // Clone all loop-unswitch related loop properties.
296 // Redistribute unswitching quotas.
297 // Note, that new loop data is stored inside the VMap.
298 void LUAnalysisCache::cloneData(const Loop* NewLoop, const Loop* OldLoop,
299 const ValueToValueMapTy& VMap) {
301 LoopProperties& NewLoopProps = LoopsProperties[NewLoop];
302 LoopProperties& OldLoopProps = *CurrentLoopProperties;
303 UnswitchedValsMap& Insts = OldLoopProps.UnswitchedVals;
305 // Reallocate "can-be-unswitched quota"
307 --OldLoopProps.CanBeUnswitchedCount;
308 unsigned Quota = OldLoopProps.CanBeUnswitchedCount;
309 NewLoopProps.CanBeUnswitchedCount = Quota / 2;
310 OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2;
312 NewLoopProps.SizeEstimation = OldLoopProps.SizeEstimation;
314 // Clone unswitched values info:
315 // for new loop switches we clone info about values that was
316 // already unswitched and has redundant successors.
317 for (UnswitchedValsIt I = Insts.begin(); I != Insts.end(); ++I) {
318 const SwitchInst* OldInst = I->first;
319 Value* NewI = VMap.lookup(OldInst);
320 const SwitchInst* NewInst = cast_or_null<SwitchInst>(NewI);
321 assert(NewInst && "All instructions that are in SrcBB must be in VMap.");
323 NewLoopProps.UnswitchedVals[NewInst] = OldLoopProps.UnswitchedVals[OldInst];
327 char LoopUnswitch::ID = 0;
328 INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops",
330 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
331 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
332 INITIALIZE_PASS_DEPENDENCY(LCSSA)
333 INITIALIZE_PASS_END(LoopUnswitch, "loop-unswitch", "Unswitch loops",
336 Pass *llvm::createLoopUnswitchPass(bool Os) {
337 return new LoopUnswitch(Os);
340 /// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
341 /// invariant in the loop, or has an invariant piece, return the invariant.
342 /// Otherwise, return null.
343 static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
345 // We started analyze new instruction, increment scanned instructions counter.
348 // We can never unswitch on vector conditions.
349 if (Cond->getType()->isVectorTy())
352 // Constants should be folded, not unswitched on!
353 if (isa<Constant>(Cond)) return 0;
355 // TODO: Handle: br (VARIANT|INVARIANT).
357 // Hoist simple values out.
358 if (L->makeLoopInvariant(Cond, Changed))
361 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
362 if (BO->getOpcode() == Instruction::And ||
363 BO->getOpcode() == Instruction::Or) {
364 // If either the left or right side is invariant, we can unswitch on this,
365 // which will cause the branch to go away in one loop and the condition to
366 // simplify in the other one.
367 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
369 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
376 bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
377 LI = &getAnalysis<LoopInfo>();
379 DT = getAnalysisIfAvailable<DominatorTree>();
381 Function *F = currentLoop->getHeader()->getParent();
382 bool Changed = false;
384 assert(currentLoop->isLCSSAForm(*DT));
386 Changed |= processCurrentLoop();
390 // FIXME: Reconstruct dom info, because it is not preserved properly.
392 DT->runOnFunction(*F);
397 /// processCurrentLoop - Do actual work and unswitch loop if possible
399 bool LoopUnswitch::processCurrentLoop() {
400 bool Changed = false;
404 // If LoopSimplify was unable to form a preheader, don't do any unswitching.
408 // Loops with indirectbr cannot be cloned.
409 if (!currentLoop->isSafeToClone())
412 // Without dedicated exits, splitting the exit edge may fail.
413 if (!currentLoop->hasDedicatedExits())
416 LLVMContext &Context = loopHeader->getContext();
418 // Probably we reach the quota of branches for this loop. If so
420 if (!BranchesInfo.countLoop(currentLoop))
423 // Loop over all of the basic blocks in the loop. If we find an interior
424 // block that is branching on a loop-invariant condition, we can unswitch this
426 for (Loop::block_iterator I = currentLoop->block_begin(),
427 E = currentLoop->block_end(); I != E; ++I) {
428 TerminatorInst *TI = (*I)->getTerminator();
429 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
430 // If this isn't branching on an invariant condition, we can't unswitch
432 if (BI->isConditional()) {
433 // See if this, or some part of it, is loop invariant. If so, we can
434 // unswitch on it if we desire.
435 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
436 currentLoop, Changed);
437 if (LoopCond && UnswitchIfProfitable(LoopCond,
438 ConstantInt::getTrue(Context))) {
443 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
444 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
445 currentLoop, Changed);
446 unsigned NumCases = SI->getNumCases();
447 if (LoopCond && NumCases) {
448 // Find a value to unswitch on:
449 // FIXME: this should chose the most expensive case!
450 // FIXME: scan for a case with a non-critical edge?
451 Constant *UnswitchVal = NULL;
453 // Do not process same value again and again.
454 // At this point we have some cases already unswitched and
455 // some not yet unswitched. Let's find the first not yet unswitched one.
456 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
458 Constant* UnswitchValCandidate = i.getCaseValue();
459 if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) {
460 UnswitchVal = UnswitchValCandidate;
468 if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
475 // Scan the instructions to check for unswitchable values.
476 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
478 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
479 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
480 currentLoop, Changed);
481 if (LoopCond && UnswitchIfProfitable(LoopCond,
482 ConstantInt::getTrue(Context))) {
491 /// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
492 /// loop with no side effects (including infinite loops).
494 /// If true, we return true and set ExitBB to the block we
497 static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
499 std::set<BasicBlock*> &Visited) {
500 if (!Visited.insert(BB).second) {
501 // Already visited. Without more analysis, this could indicate an infinite
504 } else if (!L->contains(BB)) {
505 // Otherwise, this is a loop exit, this is fine so long as this is the
507 if (ExitBB != 0) return false;
512 // Otherwise, this is an unvisited intra-loop node. Check all successors.
513 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
514 // Check to see if the successor is a trivial loop exit.
515 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
519 // Okay, everything after this looks good, check to make sure that this block
520 // doesn't include any side effects.
521 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
522 if (I->mayHaveSideEffects())
528 /// isTrivialLoopExitBlock - Return true if the specified block unconditionally
529 /// leads to an exit from the specified loop, and has no side-effects in the
530 /// process. If so, return the block that is exited to, otherwise return null.
531 static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
532 std::set<BasicBlock*> Visited;
533 Visited.insert(L->getHeader()); // Branches to header make infinite loops.
534 BasicBlock *ExitBB = 0;
535 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
540 /// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
541 /// trivial: that is, that the condition controls whether or not the loop does
542 /// anything at all. If this is a trivial condition, unswitching produces no
543 /// code duplications (equivalently, it produces a simpler loop and a new empty
544 /// loop, which gets deleted).
546 /// If this is a trivial condition, return true, otherwise return false. When
547 /// returning true, this sets Cond and Val to the condition that controls the
548 /// trivial condition: when Cond dynamically equals Val, the loop is known to
549 /// exit. Finally, this sets LoopExit to the BB that the loop exits to when
552 bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
553 BasicBlock **LoopExit) {
554 BasicBlock *Header = currentLoop->getHeader();
555 TerminatorInst *HeaderTerm = Header->getTerminator();
556 LLVMContext &Context = Header->getContext();
558 BasicBlock *LoopExitBB = 0;
559 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
560 // If the header block doesn't end with a conditional branch on Cond, we
562 if (!BI->isConditional() || BI->getCondition() != Cond)
565 // Check to see if a successor of the branch is guaranteed to
566 // exit through a unique exit block without having any
567 // side-effects. If so, determine the value of Cond that causes it to do
569 if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
570 BI->getSuccessor(0)))) {
571 if (Val) *Val = ConstantInt::getTrue(Context);
572 } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
573 BI->getSuccessor(1)))) {
574 if (Val) *Val = ConstantInt::getFalse(Context);
576 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
577 // If this isn't a switch on Cond, we can't handle it.
578 if (SI->getCondition() != Cond) return false;
580 // Check to see if a successor of the switch is guaranteed to go to the
581 // latch block or exit through a one exit block without having any
582 // side-effects. If so, determine the value of Cond that causes it to do
584 // Note that we can't trivially unswitch on the default case or
585 // on already unswitched cases.
586 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
588 BasicBlock* LoopExitCandidate;
589 if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
590 i.getCaseSuccessor()))) {
591 // Okay, we found a trivial case, remember the value that is trivial.
592 ConstantInt* CaseVal = i.getCaseValue();
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) {
627 Function *F = loopHeader->getParent();
628 Constant *CondVal = 0;
629 BasicBlock *ExitBlock = 0;
631 if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
632 // If the condition is trivial, always unswitch. There is no code growth
634 UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock);
638 // Check to see if it would be profitable to unswitch current loop.
640 // Do not do non-trivial unswitch while optimizing for size.
641 if (OptimizeForSize || F->hasFnAttr(Attribute::OptimizeForSize))
644 UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
648 /// CloneLoop - Recursively clone the specified loop and all of its children,
649 /// mapping the blocks with the specified map.
650 static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
651 LoopInfo *LI, LPPassManager *LPM) {
652 Loop *New = new Loop();
653 LPM->insertLoop(New, PL);
655 // Add all of the blocks in L to the new loop.
656 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
658 if (LI->getLoopFor(*I) == L)
659 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), LI->getBase());
661 // Add all of the subloops to the new loop.
662 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
663 CloneLoop(*I, New, VM, LI, LPM);
668 /// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
669 /// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
670 /// code immediately before InsertPt.
671 void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
672 BasicBlock *TrueDest,
673 BasicBlock *FalseDest,
674 Instruction *InsertPt) {
675 // Insert a conditional branch on LIC to the two preheaders. The original
676 // code is the true version and the new code is the false version.
677 Value *BranchVal = LIC;
678 if (!isa<ConstantInt>(Val) ||
679 Val->getType() != Type::getInt1Ty(LIC->getContext()))
680 BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val);
681 else if (Val != ConstantInt::getTrue(Val->getContext()))
682 // We want to enter the new loop when the condition is true.
683 std::swap(TrueDest, FalseDest);
685 // Insert the new branch.
686 BranchInst *BI = BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt);
688 // If either edge is critical, split it. This helps preserve LoopSimplify
689 // form for enclosing loops.
690 SplitCriticalEdge(BI, 0, this, false, false, true);
691 SplitCriticalEdge(BI, 1, this, false, false, true);
694 /// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
695 /// condition in it (a cond branch from its header block to its latch block,
696 /// where the path through the loop that doesn't execute its body has no
697 /// side-effects), unswitch it. This doesn't involve any code duplication, just
698 /// moving the conditional branch outside of the loop and updating loop info.
699 void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
701 BasicBlock *ExitBlock) {
702 DEBUG(dbgs() << "loop-unswitch: Trivial-Unswitch loop %"
703 << loopHeader->getName() << " [" << L->getBlocks().size()
704 << " blocks] in Function " << L->getHeader()->getParent()->getName()
705 << " on cond: " << *Val << " == " << *Cond << "\n");
707 // First step, split the preheader, so that we know that there is a safe place
708 // to insert the conditional branch. We will change loopPreheader to have a
709 // conditional branch on Cond.
710 BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, this);
712 // Now that we have a place to insert the conditional branch, create a place
713 // to branch to: this is the exit block out of the loop that we should
716 // Split this block now, so that the loop maintains its exit block, and so
717 // that the jump from the preheader can execute the contents of the exit block
718 // without actually branching to it (the exit block should be dominated by the
719 // loop header, not the preheader).
720 assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
721 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this);
723 // Okay, now we have a position to branch from and a position to branch to,
724 // insert the new conditional branch.
725 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
726 loopPreheader->getTerminator());
727 LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L);
728 loopPreheader->getTerminator()->eraseFromParent();
730 // We need to reprocess this loop, it could be unswitched again.
733 // Now that we know that the loop is never entered when this condition is a
734 // particular value, rewrite the loop with this info. We know that this will
735 // at least eliminate the old branch.
736 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
740 /// SplitExitEdges - Split all of the edges from inside the loop to their exit
741 /// blocks. Update the appropriate Phi nodes as we do so.
742 void LoopUnswitch::SplitExitEdges(Loop *L,
743 const SmallVector<BasicBlock *, 8> &ExitBlocks){
745 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
746 BasicBlock *ExitBlock = ExitBlocks[i];
747 SmallVector<BasicBlock *, 4> Preds(pred_begin(ExitBlock),
748 pred_end(ExitBlock));
750 // Although SplitBlockPredecessors doesn't preserve loop-simplify in
751 // general, if we call it on all predecessors of all exits then it does.
752 if (!ExitBlock->isLandingPad()) {
753 SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", this);
755 SmallVector<BasicBlock*, 2> NewBBs;
756 SplitLandingPadPredecessors(ExitBlock, Preds, ".us-lcssa", ".us-lcssa",
762 /// UnswitchNontrivialCondition - We determined that the loop is profitable
763 /// to unswitch when LIC equal Val. Split it into loop versions and test the
764 /// condition outside of either loop. Return the loops created as Out1/Out2.
765 void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
767 Function *F = loopHeader->getParent();
768 DEBUG(dbgs() << "loop-unswitch: Unswitching loop %"
769 << loopHeader->getName() << " [" << L->getBlocks().size()
770 << " blocks] in Function " << F->getName()
771 << " when '" << *Val << "' == " << *LIC << "\n");
773 if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>())
779 // First step, split the preheader and exit blocks, and add these blocks to
780 // the LoopBlocks list.
781 BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, this);
782 LoopBlocks.push_back(NewPreheader);
784 // We want the loop to come after the preheader, but before the exit blocks.
785 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
787 SmallVector<BasicBlock*, 8> ExitBlocks;
788 L->getUniqueExitBlocks(ExitBlocks);
790 // Split all of the edges from inside the loop to their exit blocks. Update
791 // the appropriate Phi nodes as we do so.
792 SplitExitEdges(L, ExitBlocks);
794 // The exit blocks may have been changed due to edge splitting, recompute.
796 L->getUniqueExitBlocks(ExitBlocks);
798 // Add exit blocks to the loop blocks.
799 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
801 // Next step, clone all of the basic blocks that make up the loop (including
802 // the loop preheader and exit blocks), keeping track of the mapping between
803 // the instructions and blocks.
804 NewBlocks.reserve(LoopBlocks.size());
805 ValueToValueMapTy VMap;
806 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
807 BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F);
809 NewBlocks.push_back(NewBB);
810 VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping.
811 LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L);
814 // Splice the newly inserted blocks into the function right before the
815 // original preheader.
816 F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(),
817 NewBlocks[0], F->end());
819 // Now we create the new Loop object for the versioned loop.
820 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM);
822 // Recalculate unswitching quota, inherit simplified switches info for NewBB,
823 // Probably clone more loop-unswitch related loop properties.
824 BranchesInfo.cloneData(NewLoop, L, VMap);
826 Loop *ParentLoop = L->getParentLoop();
828 // Make sure to add the cloned preheader and exit blocks to the parent loop
830 ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase());
833 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
834 BasicBlock *NewExit = cast<BasicBlock>(VMap[ExitBlocks[i]]);
835 // The new exit block should be in the same loop as the old one.
836 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
837 ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase());
839 assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
840 "Exit block should have been split to have one successor!");
841 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
843 // If the successor of the exit block had PHI nodes, add an entry for
846 for (BasicBlock::iterator I = ExitSucc->begin(); isa<PHINode>(I); ++I) {
847 PN = cast<PHINode>(I);
848 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
849 ValueToValueMapTy::iterator It = VMap.find(V);
850 if (It != VMap.end()) V = It->second;
851 PN->addIncoming(V, NewExit);
854 if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
855 PN = PHINode::Create(LPad->getType(), 0, "",
856 ExitSucc->getFirstInsertionPt());
858 for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
861 LandingPadInst *LPI = BB->getLandingPadInst();
862 LPI->replaceAllUsesWith(PN);
863 PN->addIncoming(LPI, BB);
868 // Rewrite the code to refer to itself.
869 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
870 for (BasicBlock::iterator I = NewBlocks[i]->begin(),
871 E = NewBlocks[i]->end(); I != E; ++I)
872 RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
874 // Rewrite the original preheader to select between versions of the loop.
875 BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator());
876 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
877 "Preheader splitting did not work correctly!");
879 // Emit the new branch that selects between the two versions of this loop.
880 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
881 LPM->deleteSimpleAnalysisValue(OldBR, L);
882 OldBR->eraseFromParent();
884 LoopProcessWorklist.push_back(NewLoop);
887 // Keep a WeakVH holding onto LIC. If the first call to RewriteLoopBody
888 // deletes the instruction (for example by simplifying a PHI that feeds into
889 // the condition that we're unswitching on), we don't rewrite the second
891 WeakVH LICHandle(LIC);
893 // Now we rewrite the original code to know that the condition is true and the
894 // new code to know that the condition is false.
895 RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
897 // It's possible that simplifying one loop could cause the other to be
898 // changed to another value or a constant. If its a constant, don't simplify
900 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop &&
901 LICHandle && !isa<Constant>(LICHandle))
902 RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
905 /// RemoveFromWorklist - Remove all instances of I from the worklist vector
907 static void RemoveFromWorklist(Instruction *I,
908 std::vector<Instruction*> &Worklist) {
909 std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(),
911 while (WI != Worklist.end()) {
912 unsigned Offset = WI-Worklist.begin();
914 WI = std::find(Worklist.begin()+Offset, Worklist.end(), I);
918 /// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
919 /// program, replacing all uses with V and update the worklist.
920 static void ReplaceUsesOfWith(Instruction *I, Value *V,
921 std::vector<Instruction*> &Worklist,
922 Loop *L, LPPassManager *LPM) {
923 DEBUG(dbgs() << "Replace with '" << *V << "': " << *I);
925 // Add uses to the worklist, which may be dead now.
926 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
927 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
928 Worklist.push_back(Use);
930 // Add users to the worklist which may be simplified now.
931 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
933 Worklist.push_back(cast<Instruction>(*UI));
934 LPM->deleteSimpleAnalysisValue(I, L);
935 RemoveFromWorklist(I, Worklist);
936 I->replaceAllUsesWith(V);
937 I->eraseFromParent();
941 /// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
942 /// information, and remove any dead successors it has.
944 void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
945 std::vector<Instruction*> &Worklist,
947 if (pred_begin(BB) != pred_end(BB)) {
948 // This block isn't dead, since an edge to BB was just removed, see if there
949 // are any easy simplifications we can do now.
950 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
951 // If it has one pred, fold phi nodes in BB.
952 while (isa<PHINode>(BB->begin()))
953 ReplaceUsesOfWith(BB->begin(),
954 cast<PHINode>(BB->begin())->getIncomingValue(0),
957 // If this is the header of a loop and the only pred is the latch, we now
958 // have an unreachable loop.
959 if (Loop *L = LI->getLoopFor(BB))
960 if (loopHeader == BB && L->contains(Pred)) {
961 // Remove the branch from the latch to the header block, this makes
962 // the header dead, which will make the latch dead (because the header
963 // dominates the latch).
964 LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L);
965 Pred->getTerminator()->eraseFromParent();
966 new UnreachableInst(BB->getContext(), Pred);
968 // The loop is now broken, remove it from LI.
969 RemoveLoopFromHierarchy(L);
971 // Reprocess the header, which now IS dead.
972 RemoveBlockIfDead(BB, Worklist, L);
976 // If pred ends in a uncond branch, add uncond branch to worklist so that
977 // the two blocks will get merged.
978 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
979 if (BI->isUnconditional())
980 Worklist.push_back(BI);
985 DEBUG(dbgs() << "Nuking dead block: " << *BB);
987 // Remove the instructions in the basic block from the worklist.
988 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
989 RemoveFromWorklist(I, Worklist);
991 // Anything that uses the instructions in this basic block should have their
992 // uses replaced with undefs.
993 // If I is not void type then replaceAllUsesWith undef.
994 // This allows ValueHandlers and custom metadata to adjust itself.
995 if (!I->getType()->isVoidTy())
996 I->replaceAllUsesWith(UndefValue::get(I->getType()));
999 // If this is the edge to the header block for a loop, remove the loop and
1000 // promote all subloops.
1001 if (Loop *BBLoop = LI->getLoopFor(BB)) {
1002 if (BBLoop->getLoopLatch() == BB) {
1003 RemoveLoopFromHierarchy(BBLoop);
1004 if (currentLoop == BBLoop) {
1011 // Remove the block from the loop info, which removes it from any loops it
1013 LI->removeBlock(BB);
1016 // Remove phi node entries in successors for this block.
1017 TerminatorInst *TI = BB->getTerminator();
1018 SmallVector<BasicBlock*, 4> Succs;
1019 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1020 Succs.push_back(TI->getSuccessor(i));
1021 TI->getSuccessor(i)->removePredecessor(BB);
1024 // Unique the successors, remove anything with multiple uses.
1025 array_pod_sort(Succs.begin(), Succs.end());
1026 Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
1028 // Remove the basic block, including all of the instructions contained in it.
1029 LPM->deleteSimpleAnalysisValue(BB, L);
1030 BB->eraseFromParent();
1031 // Remove successor blocks here that are not dead, so that we know we only
1032 // have dead blocks in this list. Nondead blocks have a way of becoming dead,
1033 // then getting removed before we revisit them, which is badness.
1035 for (unsigned i = 0; i != Succs.size(); ++i)
1036 if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
1037 // One exception is loop headers. If this block was the preheader for a
1038 // loop, then we DO want to visit the loop so the loop gets deleted.
1039 // We know that if the successor is a loop header, that this loop had to
1040 // be the preheader: the case where this was the latch block was handled
1041 // above and headers can only have two predecessors.
1042 if (!LI->isLoopHeader(Succs[i])) {
1043 Succs.erase(Succs.begin()+i);
1048 for (unsigned i = 0, e = Succs.size(); i != e; ++i)
1049 RemoveBlockIfDead(Succs[i], Worklist, L);
1052 /// RemoveLoopFromHierarchy - We have discovered that the specified loop has
1053 /// become unwrapped, either because the backedge was deleted, or because the
1054 /// edge into the header was removed. If the edge into the header from the
1055 /// latch block was removed, the loop is unwrapped but subloops are still alive,
1056 /// so they just reparent loops. If the loops are actually dead, they will be
1058 void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) {
1059 LPM->deleteLoopFromQueue(L);
1060 RemoveLoopFromWorklist(L);
1063 // RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
1064 // the value specified by Val in the specified loop, or we know it does NOT have
1065 // that value. Rewrite any uses of LIC or of properties correlated to it.
1066 void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
1069 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
1071 // FIXME: Support correlated properties, like:
1078 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
1079 // selects, switches.
1080 std::vector<Instruction*> Worklist;
1081 LLVMContext &Context = Val->getContext();
1084 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
1085 // in the loop with the appropriate one directly.
1086 if (IsEqual || (isa<ConstantInt>(Val) &&
1087 Val->getType()->isIntegerTy(1))) {
1092 Replacement = ConstantInt::get(Type::getInt1Ty(Val->getContext()),
1093 !cast<ConstantInt>(Val)->getZExtValue());
1095 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
1097 Instruction *U = dyn_cast<Instruction>(*UI);
1098 if (!U || !L->contains(U))
1100 Worklist.push_back(U);
1103 for (std::vector<Instruction*>::iterator UI = Worklist.begin();
1104 UI != Worklist.end(); ++UI)
1105 (*UI)->replaceUsesOfWith(LIC, Replacement);
1107 SimplifyCode(Worklist, L);
1111 // Otherwise, we don't know the precise value of LIC, but we do know that it
1112 // is certainly NOT "Val". As such, simplify any uses in the loop that we
1113 // can. This case occurs when we unswitch switch statements.
1114 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
1116 Instruction *U = dyn_cast<Instruction>(*UI);
1117 if (!U || !L->contains(U))
1120 Worklist.push_back(U);
1122 // TODO: We could do other simplifications, for example, turning
1123 // 'icmp eq LIC, Val' -> false.
1125 // If we know that LIC is not Val, use this info to simplify code.
1126 SwitchInst *SI = dyn_cast<SwitchInst>(U);
1127 if (SI == 0 || !isa<ConstantInt>(Val)) continue;
1129 SwitchInst::CaseIt DeadCase = SI->findCaseValue(cast<ConstantInt>(Val));
1130 // Default case is live for multiple values.
1131 if (DeadCase == SI->case_default()) continue;
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 = DeadCase.getCaseSuccessor();
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 = DeadCase.getCaseSuccessor();
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
1217 // 'false'. TODO: update the domtree properly so we can pass it here.
1218 if (Value *V = SimplifyInstruction(I))
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);