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"
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 LLVMContext &Context = loopHeader->getContext();
410 // Probably we reach the quota of branches for this loop. If so
412 if (!BranchesInfo.countLoop(currentLoop))
415 // Loop over all of the basic blocks in the loop. If we find an interior
416 // block that is branching on a loop-invariant condition, we can unswitch this
418 for (Loop::block_iterator I = currentLoop->block_begin(),
419 E = currentLoop->block_end(); I != E; ++I) {
420 TerminatorInst *TI = (*I)->getTerminator();
421 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
422 // If this isn't branching on an invariant condition, we can't unswitch
424 if (BI->isConditional()) {
425 // See if this, or some part of it, is loop invariant. If so, we can
426 // unswitch on it if we desire.
427 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
428 currentLoop, Changed);
429 if (LoopCond && UnswitchIfProfitable(LoopCond,
430 ConstantInt::getTrue(Context))) {
435 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
436 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
437 currentLoop, Changed);
438 unsigned NumCases = SI->getNumCases();
439 if (LoopCond && NumCases) {
440 // Find a value to unswitch on:
441 // FIXME: this should chose the most expensive case!
442 // FIXME: scan for a case with a non-critical edge?
443 Constant *UnswitchVal = NULL;
445 // Do not process same value again and again.
446 // At this point we have some cases already unswitched and
447 // some not yet unswitched. Let's find the first not yet unswitched one.
448 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
450 Constant* UnswitchValCandidate = i.getCaseValue();
451 if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) {
452 UnswitchVal = UnswitchValCandidate;
460 if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
467 // Scan the instructions to check for unswitchable values.
468 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
470 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
471 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
472 currentLoop, Changed);
473 if (LoopCond && UnswitchIfProfitable(LoopCond,
474 ConstantInt::getTrue(Context))) {
483 /// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
484 /// loop with no side effects (including infinite loops).
486 /// If true, we return true and set ExitBB to the block we
489 static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
491 std::set<BasicBlock*> &Visited) {
492 if (!Visited.insert(BB).second) {
493 // Already visited. Without more analysis, this could indicate an infinite
496 } else if (!L->contains(BB)) {
497 // Otherwise, this is a loop exit, this is fine so long as this is the
499 if (ExitBB != 0) return false;
504 // Otherwise, this is an unvisited intra-loop node. Check all successors.
505 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
506 // Check to see if the successor is a trivial loop exit.
507 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
511 // Okay, everything after this looks good, check to make sure that this block
512 // doesn't include any side effects.
513 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
514 if (I->mayHaveSideEffects())
520 /// isTrivialLoopExitBlock - Return true if the specified block unconditionally
521 /// leads to an exit from the specified loop, and has no side-effects in the
522 /// process. If so, return the block that is exited to, otherwise return null.
523 static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
524 std::set<BasicBlock*> Visited;
525 Visited.insert(L->getHeader()); // Branches to header make infinite loops.
526 BasicBlock *ExitBB = 0;
527 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
532 /// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
533 /// trivial: that is, that the condition controls whether or not the loop does
534 /// anything at all. If this is a trivial condition, unswitching produces no
535 /// code duplications (equivalently, it produces a simpler loop and a new empty
536 /// loop, which gets deleted).
538 /// If this is a trivial condition, return true, otherwise return false. When
539 /// returning true, this sets Cond and Val to the condition that controls the
540 /// trivial condition: when Cond dynamically equals Val, the loop is known to
541 /// exit. Finally, this sets LoopExit to the BB that the loop exits to when
544 bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
545 BasicBlock **LoopExit) {
546 BasicBlock *Header = currentLoop->getHeader();
547 TerminatorInst *HeaderTerm = Header->getTerminator();
548 LLVMContext &Context = Header->getContext();
550 BasicBlock *LoopExitBB = 0;
551 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
552 // If the header block doesn't end with a conditional branch on Cond, we
554 if (!BI->isConditional() || BI->getCondition() != Cond)
557 // Check to see if a successor of the branch is guaranteed to
558 // exit through a unique exit block without having any
559 // side-effects. If so, determine the value of Cond that causes it to do
561 if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
562 BI->getSuccessor(0)))) {
563 if (Val) *Val = ConstantInt::getTrue(Context);
564 } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
565 BI->getSuccessor(1)))) {
566 if (Val) *Val = ConstantInt::getFalse(Context);
568 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
569 // If this isn't a switch on Cond, we can't handle it.
570 if (SI->getCondition() != Cond) return false;
572 // Check to see if a successor of the switch is guaranteed to go to the
573 // latch block or exit through a one exit block without having any
574 // side-effects. If so, determine the value of Cond that causes it to do
576 // Note that we can't trivially unswitch on the default case or
577 // on already unswitched cases.
578 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
580 BasicBlock* LoopExitCandidate;
581 if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
582 i.getCaseSuccessor()))) {
583 // Okay, we found a trivial case, remember the value that is trivial.
584 ConstantInt* CaseVal = i.getCaseValue();
586 // Check that it was not unswitched before, since already unswitched
587 // trivial vals are looks trivial too.
588 if (BranchesInfo.isUnswitched(SI, CaseVal))
590 LoopExitBB = LoopExitCandidate;
591 if (Val) *Val = CaseVal;
597 // If we didn't find a single unique LoopExit block, or if the loop exit block
598 // contains phi nodes, this isn't trivial.
599 if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
600 return false; // Can't handle this.
602 if (LoopExit) *LoopExit = LoopExitBB;
604 // We already know that nothing uses any scalar values defined inside of this
605 // loop. As such, we just have to check to see if this loop will execute any
606 // side-effecting instructions (e.g. stores, calls, volatile loads) in the
607 // part of the loop that the code *would* execute. We already checked the
608 // tail, check the header now.
609 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
610 if (I->mayHaveSideEffects())
615 /// UnswitchIfProfitable - We have found that we can unswitch currentLoop when
616 /// LoopCond == Val to simplify the loop. If we decide that this is profitable,
617 /// unswitch the loop, reprocess the pieces, then return true.
618 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
620 Function *F = loopHeader->getParent();
622 Constant *CondVal = 0;
623 BasicBlock *ExitBlock = 0;
624 if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
625 // If the condition is trivial, always unswitch. There is no code growth
627 UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock);
631 // Check to see if it would be profitable to unswitch current loop.
633 // Do not do non-trivial unswitch while optimizing for size.
634 if (OptimizeForSize || F->hasFnAttr(Attribute::OptimizeForSize))
637 UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
641 /// CloneLoop - Recursively clone the specified loop and all of its children,
642 /// mapping the blocks with the specified map.
643 static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
644 LoopInfo *LI, LPPassManager *LPM) {
645 Loop *New = new Loop();
646 LPM->insertLoop(New, PL);
648 // Add all of the blocks in L to the new loop.
649 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
651 if (LI->getLoopFor(*I) == L)
652 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), LI->getBase());
654 // Add all of the subloops to the new loop.
655 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
656 CloneLoop(*I, New, VM, LI, LPM);
661 /// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
662 /// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
663 /// code immediately before InsertPt.
664 void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
665 BasicBlock *TrueDest,
666 BasicBlock *FalseDest,
667 Instruction *InsertPt) {
668 // Insert a conditional branch on LIC to the two preheaders. The original
669 // code is the true version and the new code is the false version.
670 Value *BranchVal = LIC;
671 if (!isa<ConstantInt>(Val) ||
672 Val->getType() != Type::getInt1Ty(LIC->getContext()))
673 BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val);
674 else if (Val != ConstantInt::getTrue(Val->getContext()))
675 // We want to enter the new loop when the condition is true.
676 std::swap(TrueDest, FalseDest);
678 // Insert the new branch.
679 BranchInst *BI = BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt);
681 // If either edge is critical, split it. This helps preserve LoopSimplify
682 // form for enclosing loops.
683 SplitCriticalEdge(BI, 0, this);
684 SplitCriticalEdge(BI, 1, this);
687 /// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
688 /// condition in it (a cond branch from its header block to its latch block,
689 /// where the path through the loop that doesn't execute its body has no
690 /// side-effects), unswitch it. This doesn't involve any code duplication, just
691 /// moving the conditional branch outside of the loop and updating loop info.
692 void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
694 BasicBlock *ExitBlock) {
695 DEBUG(dbgs() << "loop-unswitch: Trivial-Unswitch loop %"
696 << loopHeader->getName() << " [" << L->getBlocks().size()
697 << " blocks] in Function " << L->getHeader()->getParent()->getName()
698 << " on cond: " << *Val << " == " << *Cond << "\n");
700 // First step, split the preheader, so that we know that there is a safe place
701 // to insert the conditional branch. We will change loopPreheader to have a
702 // conditional branch on Cond.
703 BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, this);
705 // Now that we have a place to insert the conditional branch, create a place
706 // to branch to: this is the exit block out of the loop that we should
709 // Split this block now, so that the loop maintains its exit block, and so
710 // that the jump from the preheader can execute the contents of the exit block
711 // without actually branching to it (the exit block should be dominated by the
712 // loop header, not the preheader).
713 assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
714 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this);
716 // Okay, now we have a position to branch from and a position to branch to,
717 // insert the new conditional branch.
718 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
719 loopPreheader->getTerminator());
720 LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L);
721 loopPreheader->getTerminator()->eraseFromParent();
723 // We need to reprocess this loop, it could be unswitched again.
726 // Now that we know that the loop is never entered when this condition is a
727 // particular value, rewrite the loop with this info. We know that this will
728 // at least eliminate the old branch.
729 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
733 /// SplitExitEdges - Split all of the edges from inside the loop to their exit
734 /// blocks. Update the appropriate Phi nodes as we do so.
735 void LoopUnswitch::SplitExitEdges(Loop *L,
736 const SmallVector<BasicBlock *, 8> &ExitBlocks){
738 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
739 BasicBlock *ExitBlock = ExitBlocks[i];
740 SmallVector<BasicBlock *, 4> Preds(pred_begin(ExitBlock),
741 pred_end(ExitBlock));
743 // Although SplitBlockPredecessors doesn't preserve loop-simplify in
744 // general, if we call it on all predecessors of all exits then it does.
745 if (!ExitBlock->isLandingPad()) {
746 SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", this);
748 SmallVector<BasicBlock*, 2> NewBBs;
749 SplitLandingPadPredecessors(ExitBlock, Preds, ".us-lcssa", ".us-lcssa",
755 /// UnswitchNontrivialCondition - We determined that the loop is profitable
756 /// to unswitch when LIC equal Val. Split it into loop versions and test the
757 /// condition outside of either loop. Return the loops created as Out1/Out2.
758 void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
760 Function *F = loopHeader->getParent();
761 DEBUG(dbgs() << "loop-unswitch: Unswitching loop %"
762 << loopHeader->getName() << " [" << L->getBlocks().size()
763 << " blocks] in Function " << F->getName()
764 << " when '" << *Val << "' == " << *LIC << "\n");
766 if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>())
772 // First step, split the preheader and exit blocks, and add these blocks to
773 // the LoopBlocks list.
774 BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, this);
775 LoopBlocks.push_back(NewPreheader);
777 // We want the loop to come after the preheader, but before the exit blocks.
778 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
780 SmallVector<BasicBlock*, 8> ExitBlocks;
781 L->getUniqueExitBlocks(ExitBlocks);
783 // Split all of the edges from inside the loop to their exit blocks. Update
784 // the appropriate Phi nodes as we do so.
785 SplitExitEdges(L, ExitBlocks);
787 // The exit blocks may have been changed due to edge splitting, recompute.
789 L->getUniqueExitBlocks(ExitBlocks);
791 // Add exit blocks to the loop blocks.
792 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
794 // Next step, clone all of the basic blocks that make up the loop (including
795 // the loop preheader and exit blocks), keeping track of the mapping between
796 // the instructions and blocks.
797 NewBlocks.reserve(LoopBlocks.size());
798 ValueToValueMapTy VMap;
799 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
800 BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F);
802 NewBlocks.push_back(NewBB);
803 VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping.
804 LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L);
807 // Splice the newly inserted blocks into the function right before the
808 // original preheader.
809 F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(),
810 NewBlocks[0], F->end());
812 // Now we create the new Loop object for the versioned loop.
813 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM);
815 // Recalculate unswitching quota, inherit simplified switches info for NewBB,
816 // Probably clone more loop-unswitch related loop properties.
817 BranchesInfo.cloneData(NewLoop, L, VMap);
819 Loop *ParentLoop = L->getParentLoop();
821 // Make sure to add the cloned preheader and exit blocks to the parent loop
823 ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase());
826 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
827 BasicBlock *NewExit = cast<BasicBlock>(VMap[ExitBlocks[i]]);
828 // The new exit block should be in the same loop as the old one.
829 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
830 ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase());
832 assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
833 "Exit block should have been split to have one successor!");
834 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
836 // If the successor of the exit block had PHI nodes, add an entry for
839 for (BasicBlock::iterator I = ExitSucc->begin(); isa<PHINode>(I); ++I) {
840 PN = cast<PHINode>(I);
841 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
842 ValueToValueMapTy::iterator It = VMap.find(V);
843 if (It != VMap.end()) V = It->second;
844 PN->addIncoming(V, NewExit);
847 if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
848 PN = PHINode::Create(LPad->getType(), 0, "",
849 ExitSucc->getFirstInsertionPt());
851 for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
854 LandingPadInst *LPI = BB->getLandingPadInst();
855 LPI->replaceAllUsesWith(PN);
856 PN->addIncoming(LPI, BB);
861 // Rewrite the code to refer to itself.
862 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
863 for (BasicBlock::iterator I = NewBlocks[i]->begin(),
864 E = NewBlocks[i]->end(); I != E; ++I)
865 RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
867 // Rewrite the original preheader to select between versions of the loop.
868 BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator());
869 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
870 "Preheader splitting did not work correctly!");
872 // Emit the new branch that selects between the two versions of this loop.
873 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
874 LPM->deleteSimpleAnalysisValue(OldBR, L);
875 OldBR->eraseFromParent();
877 LoopProcessWorklist.push_back(NewLoop);
880 // Keep a WeakVH holding onto LIC. If the first call to RewriteLoopBody
881 // deletes the instruction (for example by simplifying a PHI that feeds into
882 // the condition that we're unswitching on), we don't rewrite the second
884 WeakVH LICHandle(LIC);
886 // Now we rewrite the original code to know that the condition is true and the
887 // new code to know that the condition is false.
888 RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
890 // It's possible that simplifying one loop could cause the other to be
891 // changed to another value or a constant. If its a constant, don't simplify
893 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop &&
894 LICHandle && !isa<Constant>(LICHandle))
895 RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
898 /// RemoveFromWorklist - Remove all instances of I from the worklist vector
900 static void RemoveFromWorklist(Instruction *I,
901 std::vector<Instruction*> &Worklist) {
902 std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(),
904 while (WI != Worklist.end()) {
905 unsigned Offset = WI-Worklist.begin();
907 WI = std::find(Worklist.begin()+Offset, Worklist.end(), I);
911 /// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
912 /// program, replacing all uses with V and update the worklist.
913 static void ReplaceUsesOfWith(Instruction *I, Value *V,
914 std::vector<Instruction*> &Worklist,
915 Loop *L, LPPassManager *LPM) {
916 DEBUG(dbgs() << "Replace with '" << *V << "': " << *I);
918 // Add uses to the worklist, which may be dead now.
919 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
920 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
921 Worklist.push_back(Use);
923 // Add users to the worklist which may be simplified now.
924 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
926 Worklist.push_back(cast<Instruction>(*UI));
927 LPM->deleteSimpleAnalysisValue(I, L);
928 RemoveFromWorklist(I, Worklist);
929 I->replaceAllUsesWith(V);
930 I->eraseFromParent();
934 /// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
935 /// information, and remove any dead successors it has.
937 void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
938 std::vector<Instruction*> &Worklist,
940 if (pred_begin(BB) != pred_end(BB)) {
941 // This block isn't dead, since an edge to BB was just removed, see if there
942 // are any easy simplifications we can do now.
943 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
944 // If it has one pred, fold phi nodes in BB.
945 while (isa<PHINode>(BB->begin()))
946 ReplaceUsesOfWith(BB->begin(),
947 cast<PHINode>(BB->begin())->getIncomingValue(0),
950 // If this is the header of a loop and the only pred is the latch, we now
951 // have an unreachable loop.
952 if (Loop *L = LI->getLoopFor(BB))
953 if (loopHeader == BB && L->contains(Pred)) {
954 // Remove the branch from the latch to the header block, this makes
955 // the header dead, which will make the latch dead (because the header
956 // dominates the latch).
957 LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L);
958 Pred->getTerminator()->eraseFromParent();
959 new UnreachableInst(BB->getContext(), Pred);
961 // The loop is now broken, remove it from LI.
962 RemoveLoopFromHierarchy(L);
964 // Reprocess the header, which now IS dead.
965 RemoveBlockIfDead(BB, Worklist, L);
969 // If pred ends in a uncond branch, add uncond branch to worklist so that
970 // the two blocks will get merged.
971 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
972 if (BI->isUnconditional())
973 Worklist.push_back(BI);
978 DEBUG(dbgs() << "Nuking dead block: " << *BB);
980 // Remove the instructions in the basic block from the worklist.
981 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
982 RemoveFromWorklist(I, Worklist);
984 // Anything that uses the instructions in this basic block should have their
985 // uses replaced with undefs.
986 // If I is not void type then replaceAllUsesWith undef.
987 // This allows ValueHandlers and custom metadata to adjust itself.
988 if (!I->getType()->isVoidTy())
989 I->replaceAllUsesWith(UndefValue::get(I->getType()));
992 // If this is the edge to the header block for a loop, remove the loop and
993 // promote all subloops.
994 if (Loop *BBLoop = LI->getLoopFor(BB)) {
995 if (BBLoop->getLoopLatch() == BB) {
996 RemoveLoopFromHierarchy(BBLoop);
997 if (currentLoop == BBLoop) {
1004 // Remove the block from the loop info, which removes it from any loops it
1006 LI->removeBlock(BB);
1009 // Remove phi node entries in successors for this block.
1010 TerminatorInst *TI = BB->getTerminator();
1011 SmallVector<BasicBlock*, 4> Succs;
1012 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1013 Succs.push_back(TI->getSuccessor(i));
1014 TI->getSuccessor(i)->removePredecessor(BB);
1017 // Unique the successors, remove anything with multiple uses.
1018 array_pod_sort(Succs.begin(), Succs.end());
1019 Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
1021 // Remove the basic block, including all of the instructions contained in it.
1022 LPM->deleteSimpleAnalysisValue(BB, L);
1023 BB->eraseFromParent();
1024 // Remove successor blocks here that are not dead, so that we know we only
1025 // have dead blocks in this list. Nondead blocks have a way of becoming dead,
1026 // then getting removed before we revisit them, which is badness.
1028 for (unsigned i = 0; i != Succs.size(); ++i)
1029 if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
1030 // One exception is loop headers. If this block was the preheader for a
1031 // loop, then we DO want to visit the loop so the loop gets deleted.
1032 // We know that if the successor is a loop header, that this loop had to
1033 // be the preheader: the case where this was the latch block was handled
1034 // above and headers can only have two predecessors.
1035 if (!LI->isLoopHeader(Succs[i])) {
1036 Succs.erase(Succs.begin()+i);
1041 for (unsigned i = 0, e = Succs.size(); i != e; ++i)
1042 RemoveBlockIfDead(Succs[i], Worklist, L);
1045 /// RemoveLoopFromHierarchy - We have discovered that the specified loop has
1046 /// become unwrapped, either because the backedge was deleted, or because the
1047 /// edge into the header was removed. If the edge into the header from the
1048 /// latch block was removed, the loop is unwrapped but subloops are still alive,
1049 /// so they just reparent loops. If the loops are actually dead, they will be
1051 void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) {
1052 LPM->deleteLoopFromQueue(L);
1053 RemoveLoopFromWorklist(L);
1056 // RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
1057 // the value specified by Val in the specified loop, or we know it does NOT have
1058 // that value. Rewrite any uses of LIC or of properties correlated to it.
1059 void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
1062 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
1064 // FIXME: Support correlated properties, like:
1071 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
1072 // selects, switches.
1073 std::vector<Instruction*> Worklist;
1074 LLVMContext &Context = Val->getContext();
1077 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
1078 // in the loop with the appropriate one directly.
1079 if (IsEqual || (isa<ConstantInt>(Val) &&
1080 Val->getType()->isIntegerTy(1))) {
1085 Replacement = ConstantInt::get(Type::getInt1Ty(Val->getContext()),
1086 !cast<ConstantInt>(Val)->getZExtValue());
1088 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
1090 Instruction *U = dyn_cast<Instruction>(*UI);
1091 if (!U || !L->contains(U))
1093 Worklist.push_back(U);
1096 for (std::vector<Instruction*>::iterator UI = Worklist.begin();
1097 UI != Worklist.end(); ++UI)
1098 (*UI)->replaceUsesOfWith(LIC, Replacement);
1100 SimplifyCode(Worklist, L);
1104 // Otherwise, we don't know the precise value of LIC, but we do know that it
1105 // is certainly NOT "Val". As such, simplify any uses in the loop that we
1106 // can. This case occurs when we unswitch switch statements.
1107 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
1109 Instruction *U = dyn_cast<Instruction>(*UI);
1110 if (!U || !L->contains(U))
1113 Worklist.push_back(U);
1115 // TODO: We could do other simplifications, for example, turning
1116 // 'icmp eq LIC, Val' -> false.
1118 // If we know that LIC is not Val, use this info to simplify code.
1119 SwitchInst *SI = dyn_cast<SwitchInst>(U);
1120 if (SI == 0 || !isa<ConstantInt>(Val)) continue;
1122 SwitchInst::CaseIt DeadCase = SI->findCaseValue(cast<ConstantInt>(Val));
1123 // Default case is live for multiple values.
1124 if (DeadCase == SI->case_default()) continue;
1126 // Found a dead case value. Don't remove PHI nodes in the
1127 // successor if they become single-entry, those PHI nodes may
1128 // be in the Users list.
1130 BasicBlock *Switch = SI->getParent();
1131 BasicBlock *SISucc = DeadCase.getCaseSuccessor();
1132 BasicBlock *Latch = L->getLoopLatch();
1134 BranchesInfo.setUnswitched(SI, Val);
1136 if (!SI->findCaseDest(SISucc)) continue; // Edge is critical.
1137 // If the DeadCase successor dominates the loop latch, then the
1138 // transformation isn't safe since it will delete the sole predecessor edge
1140 if (Latch && DT->dominates(SISucc, Latch))
1143 // FIXME: This is a hack. We need to keep the successor around
1144 // and hooked up so as to preserve the loop structure, because
1145 // trying to update it is complicated. So instead we preserve the
1146 // loop structure and put the block on a dead code path.
1147 SplitEdge(Switch, SISucc, this);
1148 // Compute the successors instead of relying on the return value
1149 // of SplitEdge, since it may have split the switch successor
1151 BasicBlock *NewSISucc = DeadCase.getCaseSuccessor();
1152 BasicBlock *OldSISucc = *succ_begin(NewSISucc);
1153 // Create an "unreachable" destination.
1154 BasicBlock *Abort = BasicBlock::Create(Context, "us-unreachable",
1155 Switch->getParent(),
1157 new UnreachableInst(Context, Abort);
1158 // Force the new case destination to branch to the "unreachable"
1159 // block while maintaining a (dead) CFG edge to the old block.
1160 NewSISucc->getTerminator()->eraseFromParent();
1161 BranchInst::Create(Abort, OldSISucc,
1162 ConstantInt::getTrue(Context), NewSISucc);
1163 // Release the PHI operands for this edge.
1164 for (BasicBlock::iterator II = NewSISucc->begin();
1165 PHINode *PN = dyn_cast<PHINode>(II); ++II)
1166 PN->setIncomingValue(PN->getBasicBlockIndex(Switch),
1167 UndefValue::get(PN->getType()));
1168 // Tell the domtree about the new block. We don't fully update the
1169 // domtree here -- instead we force it to do a full recomputation
1170 // after the pass is complete -- but we do need to inform it of
1173 DT->addNewBlock(Abort, NewSISucc);
1176 SimplifyCode(Worklist, L);
1179 /// SimplifyCode - Okay, now that we have simplified some instructions in the
1180 /// loop, walk over it and constant prop, dce, and fold control flow where
1181 /// possible. Note that this is effectively a very simple loop-structure-aware
1182 /// optimizer. During processing of this loop, L could very well be deleted, so
1183 /// it must not be used.
1185 /// FIXME: When the loop optimizer is more mature, separate this out to a new
1188 void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
1189 while (!Worklist.empty()) {
1190 Instruction *I = Worklist.back();
1191 Worklist.pop_back();
1194 if (isInstructionTriviallyDead(I)) {
1195 DEBUG(dbgs() << "Remove dead instruction '" << *I);
1197 // Add uses to the worklist, which may be dead now.
1198 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1199 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
1200 Worklist.push_back(Use);
1201 LPM->deleteSimpleAnalysisValue(I, L);
1202 RemoveFromWorklist(I, Worklist);
1203 I->eraseFromParent();
1208 // See if instruction simplification can hack this up. This is common for
1209 // things like "select false, X, Y" after unswitching made the condition be
1211 if (Value *V = SimplifyInstruction(I, 0, 0, DT))
1212 if (LI->replacementPreservesLCSSAForm(I, V)) {
1213 ReplaceUsesOfWith(I, V, Worklist, L, LPM);
1217 // Special case hacks that appear commonly in unswitched code.
1218 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1219 if (BI->isUnconditional()) {
1220 // If BI's parent is the only pred of the successor, fold the two blocks
1222 BasicBlock *Pred = BI->getParent();
1223 BasicBlock *Succ = BI->getSuccessor(0);
1224 BasicBlock *SinglePred = Succ->getSinglePredecessor();
1225 if (!SinglePred) continue; // Nothing to do.
1226 assert(SinglePred == Pred && "CFG broken");
1228 DEBUG(dbgs() << "Merging blocks: " << Pred->getName() << " <- "
1229 << Succ->getName() << "\n");
1231 // Resolve any single entry PHI nodes in Succ.
1232 while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
1233 ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM);
1235 // If Succ has any successors with PHI nodes, update them to have
1236 // entries coming from Pred instead of Succ.
1237 Succ->replaceAllUsesWith(Pred);
1239 // Move all of the successor contents from Succ to Pred.
1240 Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
1242 LPM->deleteSimpleAnalysisValue(BI, L);
1243 BI->eraseFromParent();
1244 RemoveFromWorklist(BI, Worklist);
1246 // Remove Succ from the loop tree.
1247 LI->removeBlock(Succ);
1248 LPM->deleteSimpleAnalysisValue(Succ, L);
1249 Succ->eraseFromParent();
1254 if (ConstantInt *CB = dyn_cast<ConstantInt>(BI->getCondition())){
1255 // Conditional branch. Turn it into an unconditional branch, then
1256 // remove dead blocks.
1257 continue; // FIXME: Enable.
1259 DEBUG(dbgs() << "Folded branch: " << *BI);
1260 BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue());
1261 BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue());
1262 DeadSucc->removePredecessor(BI->getParent(), true);
1263 Worklist.push_back(BranchInst::Create(LiveSucc, BI));
1264 LPM->deleteSimpleAnalysisValue(BI, L);
1265 BI->eraseFromParent();
1266 RemoveFromWorklist(BI, Worklist);
1269 RemoveBlockIfDead(DeadSucc, Worklist, L);