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 /// HasIndirectBrsInPreds - Returns true if there are predecessors, that are
196 /// terminated with indirect branch instruction.
197 bool HasIndirectBrsInPreds(const SmallVectorImpl<BasicBlock *> &ExitBlocks);
199 /// Split all of the edges from inside the loop to their exit blocks.
200 /// Update the appropriate Phi nodes as we do so.
201 void SplitExitEdges(Loop *L, const SmallVector<BasicBlock *, 8> &ExitBlocks);
203 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val);
204 void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
205 BasicBlock *ExitBlock);
206 bool UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
208 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
209 Constant *Val, bool isEqual);
211 void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
212 BasicBlock *TrueDest,
213 BasicBlock *FalseDest,
214 Instruction *InsertPt);
216 void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
217 void RemoveBlockIfDead(BasicBlock *BB,
218 std::vector<Instruction*> &Worklist, Loop *l);
219 void RemoveLoopFromHierarchy(Loop *L);
220 bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = 0,
221 BasicBlock **LoopExit = 0);
226 // Analyze loop. Check its size, calculate is it possible to unswitch
227 // it. Returns true if we can unswitch this loop.
228 bool LUAnalysisCache::countLoop(const Loop* L) {
230 std::pair<LoopPropsMapIt, bool> InsertRes =
231 LoopsProperties.insert(std::make_pair(L, LoopProperties()));
233 LoopProperties& Props = InsertRes.first->second;
235 if (InsertRes.second) {
238 // Limit the number of instructions to avoid causing significant code
239 // expansion, and the number of basic blocks, to avoid loops with
240 // large numbers of branches which cause loop unswitching to go crazy.
241 // This is a very ad-hoc heuristic.
243 // FIXME: This is overly conservative because it does not take into
244 // consideration code simplification opportunities and code that can
245 // be shared by the resultant unswitched loops.
247 for (Loop::block_iterator I = L->block_begin(),
250 Metrics.analyzeBasicBlock(*I);
252 Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5);
253 Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation);
254 MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount;
257 if (!Props.CanBeUnswitchedCount) {
258 DEBUG(dbgs() << "NOT unswitching loop %"
259 << L->getHeader()->getName() << ", cost too high: "
260 << L->getBlocks().size() << "\n");
265 // Be careful. This links are good only before new loop addition.
266 CurrentLoopProperties = &Props;
267 CurLoopInstructions = &Props.UnswitchedVals;
272 // Clean all data related to given loop.
273 void LUAnalysisCache::forgetLoop(const Loop* L) {
275 LoopPropsMapIt LIt = LoopsProperties.find(L);
277 if (LIt != LoopsProperties.end()) {
278 LoopProperties& Props = LIt->second;
279 MaxSize += Props.CanBeUnswitchedCount * Props.SizeEstimation;
280 LoopsProperties.erase(LIt);
283 CurrentLoopProperties = NULL;
284 CurLoopInstructions = NULL;
287 // Mark case value as unswitched.
288 // Since SI instruction can be partly unswitched, in order to avoid
289 // extra unswitching in cloned loops keep track all unswitched values.
290 void LUAnalysisCache::setUnswitched(const SwitchInst* SI, const Value* V) {
291 (*CurLoopInstructions)[SI].insert(V);
294 // Check was this case value unswitched before or not.
295 bool LUAnalysisCache::isUnswitched(const SwitchInst* SI, const Value* V) {
296 return (*CurLoopInstructions)[SI].count(V);
299 // Clone all loop-unswitch related loop properties.
300 // Redistribute unswitching quotas.
301 // Note, that new loop data is stored inside the VMap.
302 void LUAnalysisCache::cloneData(const Loop* NewLoop, const Loop* OldLoop,
303 const ValueToValueMapTy& VMap) {
305 LoopProperties& NewLoopProps = LoopsProperties[NewLoop];
306 LoopProperties& OldLoopProps = *CurrentLoopProperties;
307 UnswitchedValsMap& Insts = OldLoopProps.UnswitchedVals;
309 // Reallocate "can-be-unswitched quota"
311 --OldLoopProps.CanBeUnswitchedCount;
312 unsigned Quota = OldLoopProps.CanBeUnswitchedCount;
313 NewLoopProps.CanBeUnswitchedCount = Quota / 2;
314 OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2;
316 NewLoopProps.SizeEstimation = OldLoopProps.SizeEstimation;
318 // Clone unswitched values info:
319 // for new loop switches we clone info about values that was
320 // already unswitched and has redundant successors.
321 for (UnswitchedValsIt I = Insts.begin(); I != Insts.end(); ++I) {
322 const SwitchInst* OldInst = I->first;
323 Value* NewI = VMap.lookup(OldInst);
324 const SwitchInst* NewInst = cast_or_null<SwitchInst>(NewI);
325 assert(NewInst && "All instructions that are in SrcBB must be in VMap.");
327 NewLoopProps.UnswitchedVals[NewInst] = OldLoopProps.UnswitchedVals[OldInst];
331 char LoopUnswitch::ID = 0;
332 INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops",
334 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
335 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
336 INITIALIZE_PASS_DEPENDENCY(LCSSA)
337 INITIALIZE_PASS_END(LoopUnswitch, "loop-unswitch", "Unswitch loops",
340 Pass *llvm::createLoopUnswitchPass(bool Os) {
341 return new LoopUnswitch(Os);
344 /// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
345 /// invariant in the loop, or has an invariant piece, return the invariant.
346 /// Otherwise, return null.
347 static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
349 // We started analyze new instruction, increment scanned instructions counter.
352 // We can never unswitch on vector conditions.
353 if (Cond->getType()->isVectorTy())
356 // Constants should be folded, not unswitched on!
357 if (isa<Constant>(Cond)) return 0;
359 // TODO: Handle: br (VARIANT|INVARIANT).
361 // Hoist simple values out.
362 if (L->makeLoopInvariant(Cond, Changed))
365 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
366 if (BO->getOpcode() == Instruction::And ||
367 BO->getOpcode() == Instruction::Or) {
368 // If either the left or right side is invariant, we can unswitch on this,
369 // which will cause the branch to go away in one loop and the condition to
370 // simplify in the other one.
371 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
373 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
380 bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
381 LI = &getAnalysis<LoopInfo>();
383 DT = getAnalysisIfAvailable<DominatorTree>();
385 Function *F = currentLoop->getHeader()->getParent();
386 bool Changed = false;
388 assert(currentLoop->isLCSSAForm(*DT));
390 Changed |= processCurrentLoop();
394 // FIXME: Reconstruct dom info, because it is not preserved properly.
396 DT->runOnFunction(*F);
401 /// processCurrentLoop - Do actual work and unswitch loop if possible
403 bool LoopUnswitch::processCurrentLoop() {
404 bool Changed = false;
408 // If LoopSimplify was unable to form a preheader, don't do any unswitching.
412 LLVMContext &Context = loopHeader->getContext();
414 // Probably we reach the quota of branches for this loop. If so
416 if (!BranchesInfo.countLoop(currentLoop))
419 // Loop over all of the basic blocks in the loop. If we find an interior
420 // block that is branching on a loop-invariant condition, we can unswitch this
422 for (Loop::block_iterator I = currentLoop->block_begin(),
423 E = currentLoop->block_end(); I != E; ++I) {
424 TerminatorInst *TI = (*I)->getTerminator();
425 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
426 // If this isn't branching on an invariant condition, we can't unswitch
428 if (BI->isConditional()) {
429 // See if this, or some part of it, is loop invariant. If so, we can
430 // unswitch on it if we desire.
431 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
432 currentLoop, Changed);
433 if (LoopCond && UnswitchIfProfitable(LoopCond,
434 ConstantInt::getTrue(Context))) {
439 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
440 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
441 currentLoop, Changed);
442 unsigned NumCases = SI->getNumCases();
443 if (LoopCond && NumCases) {
444 // Find a value to unswitch on:
445 // FIXME: this should chose the most expensive case!
446 // FIXME: scan for a case with a non-critical edge?
447 Constant *UnswitchVal = NULL;
449 // Do not process same value again and again.
450 // At this point we have some cases already unswitched and
451 // some not yet unswitched. Let's find the first not yet unswitched one.
452 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
454 Constant* UnswitchValCandidate = i.getCaseValue();
455 if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) {
456 UnswitchVal = UnswitchValCandidate;
464 if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
471 // Scan the instructions to check for unswitchable values.
472 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
474 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
475 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
476 currentLoop, Changed);
477 if (LoopCond && UnswitchIfProfitable(LoopCond,
478 ConstantInt::getTrue(Context))) {
487 /// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
488 /// loop with no side effects (including infinite loops).
490 /// If true, we return true and set ExitBB to the block we
493 static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
495 std::set<BasicBlock*> &Visited) {
496 if (!Visited.insert(BB).second) {
497 // Already visited. Without more analysis, this could indicate an infinite
500 } else if (!L->contains(BB)) {
501 // Otherwise, this is a loop exit, this is fine so long as this is the
503 if (ExitBB != 0) return false;
508 // Otherwise, this is an unvisited intra-loop node. Check all successors.
509 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
510 // Check to see if the successor is a trivial loop exit.
511 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
515 // Okay, everything after this looks good, check to make sure that this block
516 // doesn't include any side effects.
517 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
518 if (I->mayHaveSideEffects())
524 /// isTrivialLoopExitBlock - Return true if the specified block unconditionally
525 /// leads to an exit from the specified loop, and has no side-effects in the
526 /// process. If so, return the block that is exited to, otherwise return null.
527 static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
528 std::set<BasicBlock*> Visited;
529 Visited.insert(L->getHeader()); // Branches to header make infinite loops.
530 BasicBlock *ExitBB = 0;
531 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
536 /// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
537 /// trivial: that is, that the condition controls whether or not the loop does
538 /// anything at all. If this is a trivial condition, unswitching produces no
539 /// code duplications (equivalently, it produces a simpler loop and a new empty
540 /// loop, which gets deleted).
542 /// If this is a trivial condition, return true, otherwise return false. When
543 /// returning true, this sets Cond and Val to the condition that controls the
544 /// trivial condition: when Cond dynamically equals Val, the loop is known to
545 /// exit. Finally, this sets LoopExit to the BB that the loop exits to when
548 bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
549 BasicBlock **LoopExit) {
550 BasicBlock *Header = currentLoop->getHeader();
551 TerminatorInst *HeaderTerm = Header->getTerminator();
552 LLVMContext &Context = Header->getContext();
554 BasicBlock *LoopExitBB = 0;
555 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
556 // If the header block doesn't end with a conditional branch on Cond, we
558 if (!BI->isConditional() || BI->getCondition() != Cond)
561 // Check to see if a successor of the branch is guaranteed to
562 // exit through a unique exit block without having any
563 // side-effects. If so, determine the value of Cond that causes it to do
565 if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
566 BI->getSuccessor(0)))) {
567 if (Val) *Val = ConstantInt::getTrue(Context);
568 } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
569 BI->getSuccessor(1)))) {
570 if (Val) *Val = ConstantInt::getFalse(Context);
572 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
573 // If this isn't a switch on Cond, we can't handle it.
574 if (SI->getCondition() != Cond) return false;
576 // Check to see if a successor of the switch is guaranteed to go to the
577 // latch block or exit through a one exit block without having any
578 // side-effects. If so, determine the value of Cond that causes it to do
580 // Note that we can't trivially unswitch on the default case or
581 // on already unswitched cases.
582 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
584 BasicBlock* LoopExitCandidate;
585 if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
586 i.getCaseSuccessor()))) {
587 // Okay, we found a trivial case, remember the value that is trivial.
588 ConstantInt* CaseVal = i.getCaseValue();
590 // Check that it was not unswitched before, since already unswitched
591 // trivial vals are looks trivial too.
592 if (BranchesInfo.isUnswitched(SI, CaseVal))
594 LoopExitBB = LoopExitCandidate;
595 if (Val) *Val = CaseVal;
601 // If we didn't find a single unique LoopExit block, or if the loop exit block
602 // contains phi nodes, this isn't trivial.
603 if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
604 return false; // Can't handle this.
606 if (LoopExit) *LoopExit = LoopExitBB;
608 // We already know that nothing uses any scalar values defined inside of this
609 // loop. As such, we just have to check to see if this loop will execute any
610 // side-effecting instructions (e.g. stores, calls, volatile loads) in the
611 // part of the loop that the code *would* execute. We already checked the
612 // tail, check the header now.
613 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
614 if (I->mayHaveSideEffects())
619 /// UnswitchIfProfitable - We have found that we can unswitch currentLoop when
620 /// LoopCond == Val to simplify the loop. If we decide that this is profitable,
621 /// unswitch the loop, reprocess the pieces, then return true.
622 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
624 Function *F = loopHeader->getParent();
626 Constant *CondVal = 0;
627 BasicBlock *ExitBlock = 0;
628 if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
629 // If the condition is trivial, always unswitch. There is no code growth
631 UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock);
635 // Check to see if it would be profitable to unswitch current loop.
637 // Do not do non-trivial unswitch while optimizing for size.
638 if (OptimizeForSize || F->hasFnAttr(Attribute::OptimizeForSize))
641 return UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
644 /// CloneLoop - Recursively clone the specified loop and all of its children,
645 /// mapping the blocks with the specified map.
646 static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
647 LoopInfo *LI, LPPassManager *LPM) {
648 Loop *New = new Loop();
649 LPM->insertLoop(New, PL);
651 // Add all of the blocks in L to the new loop.
652 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
654 if (LI->getLoopFor(*I) == L)
655 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), LI->getBase());
657 // Add all of the subloops to the new loop.
658 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
659 CloneLoop(*I, New, VM, LI, LPM);
664 /// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
665 /// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
666 /// code immediately before InsertPt.
667 void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
668 BasicBlock *TrueDest,
669 BasicBlock *FalseDest,
670 Instruction *InsertPt) {
671 // Insert a conditional branch on LIC to the two preheaders. The original
672 // code is the true version and the new code is the false version.
673 Value *BranchVal = LIC;
674 if (!isa<ConstantInt>(Val) ||
675 Val->getType() != Type::getInt1Ty(LIC->getContext()))
676 BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val);
677 else if (Val != ConstantInt::getTrue(Val->getContext()))
678 // We want to enter the new loop when the condition is true.
679 std::swap(TrueDest, FalseDest);
681 // Insert the new branch.
682 BranchInst *BI = BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt);
684 // If either edge is critical, split it. This helps preserve LoopSimplify
685 // form for enclosing loops.
686 SplitCriticalEdge(BI, 0, this);
687 SplitCriticalEdge(BI, 1, this);
690 /// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
691 /// condition in it (a cond branch from its header block to its latch block,
692 /// where the path through the loop that doesn't execute its body has no
693 /// side-effects), unswitch it. This doesn't involve any code duplication, just
694 /// moving the conditional branch outside of the loop and updating loop info.
695 void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
697 BasicBlock *ExitBlock) {
698 DEBUG(dbgs() << "loop-unswitch: Trivial-Unswitch loop %"
699 << loopHeader->getName() << " [" << L->getBlocks().size()
700 << " blocks] in Function " << L->getHeader()->getParent()->getName()
701 << " on cond: " << *Val << " == " << *Cond << "\n");
703 // First step, split the preheader, so that we know that there is a safe place
704 // to insert the conditional branch. We will change loopPreheader to have a
705 // conditional branch on Cond.
706 BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, this);
708 // Now that we have a place to insert the conditional branch, create a place
709 // to branch to: this is the exit block out of the loop that we should
712 // Split this block now, so that the loop maintains its exit block, and so
713 // that the jump from the preheader can execute the contents of the exit block
714 // without actually branching to it (the exit block should be dominated by the
715 // loop header, not the preheader).
716 assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
717 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this);
719 // Okay, now we have a position to branch from and a position to branch to,
720 // insert the new conditional branch.
721 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
722 loopPreheader->getTerminator());
723 LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L);
724 loopPreheader->getTerminator()->eraseFromParent();
726 // We need to reprocess this loop, it could be unswitched again.
729 // Now that we know that the loop is never entered when this condition is a
730 // particular value, rewrite the loop with this info. We know that this will
731 // at least eliminate the old branch.
732 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
736 /// HasIndirectBrsInPreds - Returns true if there are predecessors, that are
737 /// terminated with indirect branch instruction.
738 bool LoopUnswitch::HasIndirectBrsInPreds(
739 const SmallVectorImpl<BasicBlock *> &ExitBlocks){
741 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
742 const BasicBlock *ExitBlock = ExitBlocks[i];
743 for (const_pred_iterator p = pred_begin(ExitBlock), e = pred_end(ExitBlock);
745 // Cannot split an edge from an IndirectBrInst
746 if (isa<IndirectBrInst>((*p)->getTerminator()))
754 /// SplitExitEdges - Split all of the edges from inside the loop to their exit
755 /// blocks. Update the appropriate Phi nodes as we do so.
756 void LoopUnswitch::SplitExitEdges(Loop *L,
757 const SmallVector<BasicBlock *, 8> &ExitBlocks){
759 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
760 BasicBlock *ExitBlock = ExitBlocks[i];
761 SmallVector<BasicBlock *, 4> Preds(pred_begin(ExitBlock),
762 pred_end(ExitBlock));
764 // Although SplitBlockPredecessors doesn't preserve loop-simplify in
765 // general, if we call it on all predecessors of all exits then it does.
766 if (!ExitBlock->isLandingPad()) {
767 SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", this);
769 SmallVector<BasicBlock*, 2> NewBBs;
770 SplitLandingPadPredecessors(ExitBlock, Preds, ".us-lcssa", ".us-lcssa",
776 /// UnswitchNontrivialCondition - We determined that the loop is profitable
777 /// to unswitch when LIC equal Val. Split it into loop versions and test the
778 /// condition outside of either loop. Return the loops created as Out1/Out2.
779 bool LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
781 Function *F = loopHeader->getParent();
782 DEBUG(dbgs() << "loop-unswitch: Unswitching loop %"
783 << loopHeader->getName() << " [" << L->getBlocks().size()
784 << " blocks] in Function " << F->getName()
785 << " when '" << *Val << "' == " << *LIC << "\n");
787 if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>())
793 // First step, split the preheader and exit blocks, and add these blocks to
794 // the LoopBlocks list.
795 BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, this);
796 LoopBlocks.push_back(NewPreheader);
798 // We want the loop to come after the preheader, but before the exit blocks.
799 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
801 SmallVector<BasicBlock*, 8> ExitBlocks;
802 L->getUniqueExitBlocks(ExitBlocks);
803 if (HasIndirectBrsInPreds(ExitBlocks))
806 // Split all of the edges from inside the loop to their exit blocks. Update
807 // the appropriate Phi nodes as we do so.
808 SplitExitEdges(L, ExitBlocks);
810 // The exit blocks may have been changed due to edge splitting, recompute.
812 L->getUniqueExitBlocks(ExitBlocks);
814 // Add exit blocks to the loop blocks.
815 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
817 // Next step, clone all of the basic blocks that make up the loop (including
818 // the loop preheader and exit blocks), keeping track of the mapping between
819 // the instructions and blocks.
820 NewBlocks.reserve(LoopBlocks.size());
821 ValueToValueMapTy VMap;
822 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
823 BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F);
825 NewBlocks.push_back(NewBB);
826 VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping.
827 LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L);
830 // Splice the newly inserted blocks into the function right before the
831 // original preheader.
832 F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(),
833 NewBlocks[0], F->end());
835 // Now we create the new Loop object for the versioned loop.
836 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM);
838 // Recalculate unswitching quota, inherit simplified switches info for NewBB,
839 // Probably clone more loop-unswitch related loop properties.
840 BranchesInfo.cloneData(NewLoop, L, VMap);
842 Loop *ParentLoop = L->getParentLoop();
844 // Make sure to add the cloned preheader and exit blocks to the parent loop
846 ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase());
849 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
850 BasicBlock *NewExit = cast<BasicBlock>(VMap[ExitBlocks[i]]);
851 // The new exit block should be in the same loop as the old one.
852 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
853 ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase());
855 assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
856 "Exit block should have been split to have one successor!");
857 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
859 // If the successor of the exit block had PHI nodes, add an entry for
862 for (BasicBlock::iterator I = ExitSucc->begin(); isa<PHINode>(I); ++I) {
863 PN = cast<PHINode>(I);
864 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
865 ValueToValueMapTy::iterator It = VMap.find(V);
866 if (It != VMap.end()) V = It->second;
867 PN->addIncoming(V, NewExit);
870 if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
871 PN = PHINode::Create(LPad->getType(), 0, "",
872 ExitSucc->getFirstInsertionPt());
874 for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
877 LandingPadInst *LPI = BB->getLandingPadInst();
878 LPI->replaceAllUsesWith(PN);
879 PN->addIncoming(LPI, BB);
884 // Rewrite the code to refer to itself.
885 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
886 for (BasicBlock::iterator I = NewBlocks[i]->begin(),
887 E = NewBlocks[i]->end(); I != E; ++I)
888 RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
890 // Rewrite the original preheader to select between versions of the loop.
891 BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator());
892 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
893 "Preheader splitting did not work correctly!");
895 // Emit the new branch that selects between the two versions of this loop.
896 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
897 LPM->deleteSimpleAnalysisValue(OldBR, L);
898 OldBR->eraseFromParent();
900 LoopProcessWorklist.push_back(NewLoop);
903 // Keep a WeakVH holding onto LIC. If the first call to RewriteLoopBody
904 // deletes the instruction (for example by simplifying a PHI that feeds into
905 // the condition that we're unswitching on), we don't rewrite the second
907 WeakVH LICHandle(LIC);
909 // Now we rewrite the original code to know that the condition is true and the
910 // new code to know that the condition is false.
911 RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
913 // It's possible that simplifying one loop could cause the other to be
914 // changed to another value or a constant. If its a constant, don't simplify
916 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop &&
917 LICHandle && !isa<Constant>(LICHandle))
918 RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
923 /// RemoveFromWorklist - Remove all instances of I from the worklist vector
925 static void RemoveFromWorklist(Instruction *I,
926 std::vector<Instruction*> &Worklist) {
927 std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(),
929 while (WI != Worklist.end()) {
930 unsigned Offset = WI-Worklist.begin();
932 WI = std::find(Worklist.begin()+Offset, Worklist.end(), I);
936 /// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
937 /// program, replacing all uses with V and update the worklist.
938 static void ReplaceUsesOfWith(Instruction *I, Value *V,
939 std::vector<Instruction*> &Worklist,
940 Loop *L, LPPassManager *LPM) {
941 DEBUG(dbgs() << "Replace with '" << *V << "': " << *I);
943 // Add uses to the worklist, which may be dead now.
944 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
945 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
946 Worklist.push_back(Use);
948 // Add users to the worklist which may be simplified now.
949 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
951 Worklist.push_back(cast<Instruction>(*UI));
952 LPM->deleteSimpleAnalysisValue(I, L);
953 RemoveFromWorklist(I, Worklist);
954 I->replaceAllUsesWith(V);
955 I->eraseFromParent();
959 /// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
960 /// information, and remove any dead successors it has.
962 void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
963 std::vector<Instruction*> &Worklist,
965 if (pred_begin(BB) != pred_end(BB)) {
966 // This block isn't dead, since an edge to BB was just removed, see if there
967 // are any easy simplifications we can do now.
968 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
969 // If it has one pred, fold phi nodes in BB.
970 while (isa<PHINode>(BB->begin()))
971 ReplaceUsesOfWith(BB->begin(),
972 cast<PHINode>(BB->begin())->getIncomingValue(0),
975 // If this is the header of a loop and the only pred is the latch, we now
976 // have an unreachable loop.
977 if (Loop *L = LI->getLoopFor(BB))
978 if (loopHeader == BB && L->contains(Pred)) {
979 // Remove the branch from the latch to the header block, this makes
980 // the header dead, which will make the latch dead (because the header
981 // dominates the latch).
982 LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L);
983 Pred->getTerminator()->eraseFromParent();
984 new UnreachableInst(BB->getContext(), Pred);
986 // The loop is now broken, remove it from LI.
987 RemoveLoopFromHierarchy(L);
989 // Reprocess the header, which now IS dead.
990 RemoveBlockIfDead(BB, Worklist, L);
994 // If pred ends in a uncond branch, add uncond branch to worklist so that
995 // the two blocks will get merged.
996 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
997 if (BI->isUnconditional())
998 Worklist.push_back(BI);
1003 DEBUG(dbgs() << "Nuking dead block: " << *BB);
1005 // Remove the instructions in the basic block from the worklist.
1006 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1007 RemoveFromWorklist(I, Worklist);
1009 // Anything that uses the instructions in this basic block should have their
1010 // uses replaced with undefs.
1011 // If I is not void type then replaceAllUsesWith undef.
1012 // This allows ValueHandlers and custom metadata to adjust itself.
1013 if (!I->getType()->isVoidTy())
1014 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1017 // If this is the edge to the header block for a loop, remove the loop and
1018 // promote all subloops.
1019 if (Loop *BBLoop = LI->getLoopFor(BB)) {
1020 if (BBLoop->getLoopLatch() == BB) {
1021 RemoveLoopFromHierarchy(BBLoop);
1022 if (currentLoop == BBLoop) {
1029 // Remove the block from the loop info, which removes it from any loops it
1031 LI->removeBlock(BB);
1034 // Remove phi node entries in successors for this block.
1035 TerminatorInst *TI = BB->getTerminator();
1036 SmallVector<BasicBlock*, 4> Succs;
1037 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1038 Succs.push_back(TI->getSuccessor(i));
1039 TI->getSuccessor(i)->removePredecessor(BB);
1042 // Unique the successors, remove anything with multiple uses.
1043 array_pod_sort(Succs.begin(), Succs.end());
1044 Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
1046 // Remove the basic block, including all of the instructions contained in it.
1047 LPM->deleteSimpleAnalysisValue(BB, L);
1048 BB->eraseFromParent();
1049 // Remove successor blocks here that are not dead, so that we know we only
1050 // have dead blocks in this list. Nondead blocks have a way of becoming dead,
1051 // then getting removed before we revisit them, which is badness.
1053 for (unsigned i = 0; i != Succs.size(); ++i)
1054 if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
1055 // One exception is loop headers. If this block was the preheader for a
1056 // loop, then we DO want to visit the loop so the loop gets deleted.
1057 // We know that if the successor is a loop header, that this loop had to
1058 // be the preheader: the case where this was the latch block was handled
1059 // above and headers can only have two predecessors.
1060 if (!LI->isLoopHeader(Succs[i])) {
1061 Succs.erase(Succs.begin()+i);
1066 for (unsigned i = 0, e = Succs.size(); i != e; ++i)
1067 RemoveBlockIfDead(Succs[i], Worklist, L);
1070 /// RemoveLoopFromHierarchy - We have discovered that the specified loop has
1071 /// become unwrapped, either because the backedge was deleted, or because the
1072 /// edge into the header was removed. If the edge into the header from the
1073 /// latch block was removed, the loop is unwrapped but subloops are still alive,
1074 /// so they just reparent loops. If the loops are actually dead, they will be
1076 void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) {
1077 LPM->deleteLoopFromQueue(L);
1078 RemoveLoopFromWorklist(L);
1081 // RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
1082 // the value specified by Val in the specified loop, or we know it does NOT have
1083 // that value. Rewrite any uses of LIC or of properties correlated to it.
1084 void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
1087 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
1089 // FIXME: Support correlated properties, like:
1096 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
1097 // selects, switches.
1098 std::vector<Instruction*> Worklist;
1099 LLVMContext &Context = Val->getContext();
1102 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
1103 // in the loop with the appropriate one directly.
1104 if (IsEqual || (isa<ConstantInt>(Val) &&
1105 Val->getType()->isIntegerTy(1))) {
1110 Replacement = ConstantInt::get(Type::getInt1Ty(Val->getContext()),
1111 !cast<ConstantInt>(Val)->getZExtValue());
1113 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
1115 Instruction *U = dyn_cast<Instruction>(*UI);
1116 if (!U || !L->contains(U))
1118 Worklist.push_back(U);
1121 for (std::vector<Instruction*>::iterator UI = Worklist.begin();
1122 UI != Worklist.end(); ++UI)
1123 (*UI)->replaceUsesOfWith(LIC, Replacement);
1125 SimplifyCode(Worklist, L);
1129 // Otherwise, we don't know the precise value of LIC, but we do know that it
1130 // is certainly NOT "Val". As such, simplify any uses in the loop that we
1131 // can. This case occurs when we unswitch switch statements.
1132 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
1134 Instruction *U = dyn_cast<Instruction>(*UI);
1135 if (!U || !L->contains(U))
1138 Worklist.push_back(U);
1140 // TODO: We could do other simplifications, for example, turning
1141 // 'icmp eq LIC, Val' -> false.
1143 // If we know that LIC is not Val, use this info to simplify code.
1144 SwitchInst *SI = dyn_cast<SwitchInst>(U);
1145 if (SI == 0 || !isa<ConstantInt>(Val)) continue;
1147 SwitchInst::CaseIt DeadCase = SI->findCaseValue(cast<ConstantInt>(Val));
1148 // Default case is live for multiple values.
1149 if (DeadCase == SI->case_default()) continue;
1151 // Found a dead case value. Don't remove PHI nodes in the
1152 // successor if they become single-entry, those PHI nodes may
1153 // be in the Users list.
1155 BasicBlock *Switch = SI->getParent();
1156 BasicBlock *SISucc = DeadCase.getCaseSuccessor();
1157 BasicBlock *Latch = L->getLoopLatch();
1159 BranchesInfo.setUnswitched(SI, Val);
1161 if (!SI->findCaseDest(SISucc)) continue; // Edge is critical.
1162 // If the DeadCase successor dominates the loop latch, then the
1163 // transformation isn't safe since it will delete the sole predecessor edge
1165 if (Latch && DT->dominates(SISucc, Latch))
1168 // FIXME: This is a hack. We need to keep the successor around
1169 // and hooked up so as to preserve the loop structure, because
1170 // trying to update it is complicated. So instead we preserve the
1171 // loop structure and put the block on a dead code path.
1172 SplitEdge(Switch, SISucc, this);
1173 // Compute the successors instead of relying on the return value
1174 // of SplitEdge, since it may have split the switch successor
1176 BasicBlock *NewSISucc = DeadCase.getCaseSuccessor();
1177 BasicBlock *OldSISucc = *succ_begin(NewSISucc);
1178 // Create an "unreachable" destination.
1179 BasicBlock *Abort = BasicBlock::Create(Context, "us-unreachable",
1180 Switch->getParent(),
1182 new UnreachableInst(Context, Abort);
1183 // Force the new case destination to branch to the "unreachable"
1184 // block while maintaining a (dead) CFG edge to the old block.
1185 NewSISucc->getTerminator()->eraseFromParent();
1186 BranchInst::Create(Abort, OldSISucc,
1187 ConstantInt::getTrue(Context), NewSISucc);
1188 // Release the PHI operands for this edge.
1189 for (BasicBlock::iterator II = NewSISucc->begin();
1190 PHINode *PN = dyn_cast<PHINode>(II); ++II)
1191 PN->setIncomingValue(PN->getBasicBlockIndex(Switch),
1192 UndefValue::get(PN->getType()));
1193 // Tell the domtree about the new block. We don't fully update the
1194 // domtree here -- instead we force it to do a full recomputation
1195 // after the pass is complete -- but we do need to inform it of
1198 DT->addNewBlock(Abort, NewSISucc);
1201 SimplifyCode(Worklist, L);
1204 /// SimplifyCode - Okay, now that we have simplified some instructions in the
1205 /// loop, walk over it and constant prop, dce, and fold control flow where
1206 /// possible. Note that this is effectively a very simple loop-structure-aware
1207 /// optimizer. During processing of this loop, L could very well be deleted, so
1208 /// it must not be used.
1210 /// FIXME: When the loop optimizer is more mature, separate this out to a new
1213 void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
1214 while (!Worklist.empty()) {
1215 Instruction *I = Worklist.back();
1216 Worklist.pop_back();
1219 if (isInstructionTriviallyDead(I)) {
1220 DEBUG(dbgs() << "Remove dead instruction '" << *I);
1222 // Add uses to the worklist, which may be dead now.
1223 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1224 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
1225 Worklist.push_back(Use);
1226 LPM->deleteSimpleAnalysisValue(I, L);
1227 RemoveFromWorklist(I, Worklist);
1228 I->eraseFromParent();
1233 // See if instruction simplification can hack this up. This is common for
1234 // things like "select false, X, Y" after unswitching made the condition be
1236 if (Value *V = SimplifyInstruction(I, 0, 0, DT))
1237 if (LI->replacementPreservesLCSSAForm(I, V)) {
1238 ReplaceUsesOfWith(I, V, Worklist, L, LPM);
1242 // Special case hacks that appear commonly in unswitched code.
1243 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1244 if (BI->isUnconditional()) {
1245 // If BI's parent is the only pred of the successor, fold the two blocks
1247 BasicBlock *Pred = BI->getParent();
1248 BasicBlock *Succ = BI->getSuccessor(0);
1249 BasicBlock *SinglePred = Succ->getSinglePredecessor();
1250 if (!SinglePred) continue; // Nothing to do.
1251 assert(SinglePred == Pred && "CFG broken");
1253 DEBUG(dbgs() << "Merging blocks: " << Pred->getName() << " <- "
1254 << Succ->getName() << "\n");
1256 // Resolve any single entry PHI nodes in Succ.
1257 while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
1258 ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM);
1260 // If Succ has any successors with PHI nodes, update them to have
1261 // entries coming from Pred instead of Succ.
1262 Succ->replaceAllUsesWith(Pred);
1264 // Move all of the successor contents from Succ to Pred.
1265 Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
1267 LPM->deleteSimpleAnalysisValue(BI, L);
1268 BI->eraseFromParent();
1269 RemoveFromWorklist(BI, Worklist);
1271 // Remove Succ from the loop tree.
1272 LI->removeBlock(Succ);
1273 LPM->deleteSimpleAnalysisValue(Succ, L);
1274 Succ->eraseFromParent();
1279 if (ConstantInt *CB = dyn_cast<ConstantInt>(BI->getCondition())){
1280 // Conditional branch. Turn it into an unconditional branch, then
1281 // remove dead blocks.
1282 continue; // FIXME: Enable.
1284 DEBUG(dbgs() << "Folded branch: " << *BI);
1285 BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue());
1286 BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue());
1287 DeadSucc->removePredecessor(BI->getParent(), true);
1288 Worklist.push_back(BranchInst::Create(LiveSucc, BI));
1289 LPM->deleteSimpleAnalysisValue(BI, L);
1290 BI->eraseFromParent();
1291 RemoveFromWorklist(BI, Worklist);
1294 RemoveBlockIfDead(DeadSucc, Worklist, L);