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 50 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 // TODO: This few lines are here for cosmetic purposes only.
133 // Will be removed with the next commit.
134 struct LoopProperties {
135 unsigned CanBeUnswitchedCount;
136 unsigned SizeEstimation;
139 // TODO: This few lines are here for cosmetic purposes only.
140 // Will be removed with the next commit.
141 typedef DenseMap<const Loop*, LoopProperties> LoopPropsMap;
142 typedef LoopPropsMap::iterator LoopPropsMapIt;
143 LoopPropsMap LoopsProperties;
145 LUAnalysisCache BranchesInfo;
147 bool OptimizeForSize;
152 BasicBlock *loopHeader;
153 BasicBlock *loopPreheader;
155 // LoopBlocks contains all of the basic blocks of the loop, including the
156 // preheader of the loop, the body of the loop, and the exit blocks of the
157 // loop, in that order.
158 std::vector<BasicBlock*> LoopBlocks;
159 // NewBlocks contained cloned copy of basic blocks from LoopBlocks.
160 std::vector<BasicBlock*> NewBlocks;
163 static char ID; // Pass ID, replacement for typeid
164 explicit LoopUnswitch(bool Os = false) :
165 LoopPass(ID), OptimizeForSize(Os), redoLoop(false),
166 currentLoop(NULL), DT(NULL), loopHeader(NULL),
167 loopPreheader(NULL) {
168 initializeLoopUnswitchPass(*PassRegistry::getPassRegistry());
171 bool runOnLoop(Loop *L, LPPassManager &LPM);
172 bool processCurrentLoop();
174 /// This transformation requires natural loop information & requires that
175 /// loop preheaders be inserted into the CFG.
177 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
178 AU.addRequiredID(LoopSimplifyID);
179 AU.addPreservedID(LoopSimplifyID);
180 AU.addRequired<LoopInfo>();
181 AU.addPreserved<LoopInfo>();
182 AU.addRequiredID(LCSSAID);
183 AU.addPreservedID(LCSSAID);
184 AU.addPreserved<DominatorTree>();
185 AU.addPreserved<ScalarEvolution>();
190 virtual void releaseMemory() {
191 BranchesInfo.forgetLoop(currentLoop);
194 /// RemoveLoopFromWorklist - If the specified loop is on the loop worklist,
196 void RemoveLoopFromWorklist(Loop *L) {
197 std::vector<Loop*>::iterator I = std::find(LoopProcessWorklist.begin(),
198 LoopProcessWorklist.end(), L);
199 if (I != LoopProcessWorklist.end())
200 LoopProcessWorklist.erase(I);
203 void initLoopData() {
204 loopHeader = currentLoop->getHeader();
205 loopPreheader = currentLoop->getLoopPreheader();
208 /// Split all of the edges from inside the loop to their exit blocks.
209 /// Update the appropriate Phi nodes as we do so.
210 void SplitExitEdges(Loop *L, const SmallVector<BasicBlock *, 8> &ExitBlocks);
212 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val);
213 void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
214 BasicBlock *ExitBlock);
215 void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
217 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
218 Constant *Val, bool isEqual);
220 void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
221 BasicBlock *TrueDest,
222 BasicBlock *FalseDest,
223 Instruction *InsertPt);
225 void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
226 void RemoveBlockIfDead(BasicBlock *BB,
227 std::vector<Instruction*> &Worklist, Loop *l);
228 void RemoveLoopFromHierarchy(Loop *L);
229 bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = 0,
230 BasicBlock **LoopExit = 0);
235 // Analyze loop. Check its size, calculate is it possible to unswitch
236 // it. Returns true if we can unswitch this loop.
237 bool LUAnalysisCache::countLoop(const Loop* L) {
239 std::pair<LoopPropsMapIt, bool> InsertRes =
240 LoopsProperties.insert(std::make_pair(L, LoopProperties()));
242 LoopProperties& Props = InsertRes.first->second;
244 if (InsertRes.second) {
247 // Limit the number of instructions to avoid causing significant code
248 // expansion, and the number of basic blocks, to avoid loops with
249 // large numbers of branches which cause loop unswitching to go crazy.
250 // This is a very ad-hoc heuristic.
252 // FIXME: This is overly conservative because it does not take into
253 // consideration code simplification opportunities and code that can
254 // be shared by the resultant unswitched loops.
256 for (Loop::block_iterator I = L->block_begin(),
259 Metrics.analyzeBasicBlock(*I);
261 Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5);
262 Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation);
263 MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount;
266 if (!Props.CanBeUnswitchedCount) {
267 DEBUG(dbgs() << "NOT unswitching loop %"
268 << L->getHeader()->getName() << ", cost too high: "
269 << L->getBlocks().size() << "\n");
274 // Be careful. This links are good only before new loop addition.
275 CurrentLoopProperties = &Props;
276 CurLoopInstructions = &Props.UnswitchedVals;
281 // Clean all data related to given loop.
282 void LUAnalysisCache::forgetLoop(const Loop* L) {
284 LoopPropsMapIt LIt = LoopsProperties.find(L);
286 if (LIt != LoopsProperties.end()) {
287 LoopProperties& Props = LIt->second;
288 MaxSize += Props.CanBeUnswitchedCount * Props.SizeEstimation;
289 LoopsProperties.erase(LIt);
292 CurrentLoopProperties = NULL;
293 CurLoopInstructions = NULL;
296 // Mark case value as unswitched.
297 // Since SI instruction can be partly unswitched, in order to avoid
298 // extra unswitching in cloned loops keep track all unswitched values.
299 void LUAnalysisCache::setUnswitched(const SwitchInst* SI, const Value* V) {
300 (*CurLoopInstructions)[SI].insert(V);
303 // Check was this case value unswitched before or not.
304 bool LUAnalysisCache::isUnswitched(const SwitchInst* SI, const Value* V) {
305 return (*CurLoopInstructions)[SI].count(V);
308 // Clone all loop-unswitch related loop properties.
309 // Redistribute unswitching quotas.
310 // Note, that new loop data is stored inside the VMap.
311 void LUAnalysisCache::cloneData(const Loop* NewLoop, const Loop* OldLoop,
312 const ValueToValueMapTy& VMap) {
314 LoopProperties& NewLoopProps = LoopsProperties[NewLoop];
315 LoopProperties& OldLoopProps = *CurrentLoopProperties;
316 UnswitchedValsMap& Insts = OldLoopProps.UnswitchedVals;
318 // Reallocate "can-be-unswitched quota"
320 --OldLoopProps.CanBeUnswitchedCount;
321 unsigned Quota = OldLoopProps.CanBeUnswitchedCount;
322 NewLoopProps.CanBeUnswitchedCount = Quota / 2;
323 OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2;
325 NewLoopProps.SizeEstimation = OldLoopProps.SizeEstimation;
327 // Clone unswitched values info:
328 // for new loop switches we clone info about values that was
329 // already unswitched and has redundant successors.
330 for (UnswitchedValsIt I = Insts.begin(); I != Insts.end(); ++I) {
331 const SwitchInst* OldInst = I->first;
332 Value* NewI = VMap.lookup(OldInst);
333 const SwitchInst* NewInst = cast_or_null<SwitchInst>(NewI);
334 assert(NewInst && "All instructions that are in SrcBB must be in VMap.");
336 NewLoopProps.UnswitchedVals[NewInst] = OldLoopProps.UnswitchedVals[OldInst];
340 char LoopUnswitch::ID = 0;
341 INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops",
343 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
344 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
345 INITIALIZE_PASS_DEPENDENCY(LCSSA)
346 INITIALIZE_PASS_END(LoopUnswitch, "loop-unswitch", "Unswitch loops",
349 Pass *llvm::createLoopUnswitchPass(bool Os) {
350 return new LoopUnswitch(Os);
353 /// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
354 /// invariant in the loop, or has an invariant piece, return the invariant.
355 /// Otherwise, return null.
356 static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
358 // We started analyze new instruction, increment scanned instructions counter.
361 // We can never unswitch on vector conditions.
362 if (Cond->getType()->isVectorTy())
365 // Constants should be folded, not unswitched on!
366 if (isa<Constant>(Cond)) return 0;
368 // TODO: Handle: br (VARIANT|INVARIANT).
370 // Hoist simple values out.
371 if (L->makeLoopInvariant(Cond, Changed))
374 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
375 if (BO->getOpcode() == Instruction::And ||
376 BO->getOpcode() == Instruction::Or) {
377 // If either the left or right side is invariant, we can unswitch on this,
378 // which will cause the branch to go away in one loop and the condition to
379 // simplify in the other one.
380 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
382 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
389 bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
390 LI = &getAnalysis<LoopInfo>();
392 DT = getAnalysisIfAvailable<DominatorTree>();
394 Function *F = currentLoop->getHeader()->getParent();
395 bool Changed = false;
397 assert(currentLoop->isLCSSAForm(*DT));
399 Changed |= processCurrentLoop();
403 // FIXME: Reconstruct dom info, because it is not preserved properly.
405 DT->runOnFunction(*F);
410 /// processCurrentLoop - Do actual work and unswitch loop if possible
412 bool LoopUnswitch::processCurrentLoop() {
413 bool Changed = false;
417 // If LoopSimplify was unable to form a preheader, don't do any unswitching.
421 LLVMContext &Context = loopHeader->getContext();
423 // Probably we reach the quota of branches for this loop. If so
425 if (!BranchesInfo.countLoop(currentLoop))
428 // Loop over all of the basic blocks in the loop. If we find an interior
429 // block that is branching on a loop-invariant condition, we can unswitch this
431 for (Loop::block_iterator I = currentLoop->block_begin(),
432 E = currentLoop->block_end(); I != E; ++I) {
433 TerminatorInst *TI = (*I)->getTerminator();
434 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
435 // If this isn't branching on an invariant condition, we can't unswitch
437 if (BI->isConditional()) {
438 // See if this, or some part of it, is loop invariant. If so, we can
439 // unswitch on it if we desire.
440 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
441 currentLoop, Changed);
442 if (LoopCond && UnswitchIfProfitable(LoopCond,
443 ConstantInt::getTrue(Context))) {
448 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
449 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
450 currentLoop, Changed);
451 unsigned NumCases = SI->getNumCases();
452 if (LoopCond && NumCases > 1) {
453 // Find a value to unswitch on:
454 // FIXME: this should chose the most expensive case!
455 // FIXME: scan for a case with a non-critical edge?
456 Constant *UnswitchVal = NULL;
458 // Do not process same value again and again.
459 // At this point we have some cases already unswitched and
460 // some not yet unswitched. Let's find the first not yet unswitched one.
461 for (unsigned i = 1; i < NumCases; ++i) {
462 Constant* UnswitchValCandidate = SI->getCaseValue(i);
463 if (!BranchesInfo.isUnswitched(SI, UnswitchValCandidate)) {
464 UnswitchVal = UnswitchValCandidate;
472 if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
479 // Scan the instructions to check for unswitchable values.
480 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
482 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
483 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
484 currentLoop, Changed);
485 if (LoopCond && UnswitchIfProfitable(LoopCond,
486 ConstantInt::getTrue(Context))) {
495 /// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
496 /// loop with no side effects (including infinite loops).
498 /// If true, we return true and set ExitBB to the block we
501 static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
503 std::set<BasicBlock*> &Visited) {
504 if (!Visited.insert(BB).second) {
505 // Already visited. Without more analysis, this could indicate an infinite
508 } else if (!L->contains(BB)) {
509 // Otherwise, this is a loop exit, this is fine so long as this is the
511 if (ExitBB != 0) return false;
516 // Otherwise, this is an unvisited intra-loop node. Check all successors.
517 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
518 // Check to see if the successor is a trivial loop exit.
519 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
523 // Okay, everything after this looks good, check to make sure that this block
524 // doesn't include any side effects.
525 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
526 if (I->mayHaveSideEffects())
532 /// isTrivialLoopExitBlock - Return true if the specified block unconditionally
533 /// leads to an exit from the specified loop, and has no side-effects in the
534 /// process. If so, return the block that is exited to, otherwise return null.
535 static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
536 std::set<BasicBlock*> Visited;
537 Visited.insert(L->getHeader()); // Branches to header make infinite loops.
538 BasicBlock *ExitBB = 0;
539 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
544 /// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
545 /// trivial: that is, that the condition controls whether or not the loop does
546 /// anything at all. If this is a trivial condition, unswitching produces no
547 /// code duplications (equivalently, it produces a simpler loop and a new empty
548 /// loop, which gets deleted).
550 /// If this is a trivial condition, return true, otherwise return false. When
551 /// returning true, this sets Cond and Val to the condition that controls the
552 /// trivial condition: when Cond dynamically equals Val, the loop is known to
553 /// exit. Finally, this sets LoopExit to the BB that the loop exits to when
556 bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
557 BasicBlock **LoopExit) {
558 BasicBlock *Header = currentLoop->getHeader();
559 TerminatorInst *HeaderTerm = Header->getTerminator();
560 LLVMContext &Context = Header->getContext();
562 BasicBlock *LoopExitBB = 0;
563 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
564 // If the header block doesn't end with a conditional branch on Cond, we
566 if (!BI->isConditional() || BI->getCondition() != Cond)
569 // Check to see if a successor of the branch is guaranteed to
570 // exit through a unique exit block without having any
571 // side-effects. If so, determine the value of Cond that causes it to do
573 if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
574 BI->getSuccessor(0)))) {
575 if (Val) *Val = ConstantInt::getTrue(Context);
576 } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
577 BI->getSuccessor(1)))) {
578 if (Val) *Val = ConstantInt::getFalse(Context);
580 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
581 // If this isn't a switch on Cond, we can't handle it.
582 if (SI->getCondition() != Cond) return false;
584 // Check to see if a successor of the switch is guaranteed to go to the
585 // latch block or exit through a one exit block without having any
586 // side-effects. If so, determine the value of Cond that causes it to do
588 // Note that we can't trivially unswitch on the default case or
589 // on already unswitched cases.
590 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
591 BasicBlock* LoopExitCandidate;
592 if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
593 SI->getSuccessor(i)))) {
594 // Okay, we found a trivial case, remember the value that is trivial.
595 ConstantInt* CaseVal = SI->getCaseValue(i);
597 // Check that it was not unswitched before, since already unswitched
598 // trivial vals are looks trivial too.
599 if (BranchesInfo.isUnswitched(SI, CaseVal))
601 LoopExitBB = LoopExitCandidate;
602 if (Val) *Val = CaseVal;
608 // If we didn't find a single unique LoopExit block, or if the loop exit block
609 // contains phi nodes, this isn't trivial.
610 if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
611 return false; // Can't handle this.
613 if (LoopExit) *LoopExit = LoopExitBB;
615 // We already know that nothing uses any scalar values defined inside of this
616 // loop. As such, we just have to check to see if this loop will execute any
617 // side-effecting instructions (e.g. stores, calls, volatile loads) in the
618 // part of the loop that the code *would* execute. We already checked the
619 // tail, check the header now.
620 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
621 if (I->mayHaveSideEffects())
626 /// UnswitchIfProfitable - We have found that we can unswitch currentLoop when
627 /// LoopCond == Val to simplify the loop. If we decide that this is profitable,
628 /// unswitch the loop, reprocess the pieces, then return true.
629 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
631 Function *F = loopHeader->getParent();
633 Constant *CondVal = 0;
634 BasicBlock *ExitBlock = 0;
635 if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
636 // If the condition is trivial, always unswitch. There is no code growth
638 UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock);
642 // Check to see if it would be profitable to unswitch current loop.
644 // Do not do non-trivial unswitch while optimizing for size.
645 if (OptimizeForSize || F->hasFnAttr(Attribute::OptimizeForSize))
648 UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
652 /// CloneLoop - Recursively clone the specified loop and all of its children,
653 /// mapping the blocks with the specified map.
654 static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
655 LoopInfo *LI, LPPassManager *LPM) {
656 Loop *New = new Loop();
657 LPM->insertLoop(New, PL);
659 // Add all of the blocks in L to the new loop.
660 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
662 if (LI->getLoopFor(*I) == L)
663 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), LI->getBase());
665 // Add all of the subloops to the new loop.
666 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
667 CloneLoop(*I, New, VM, LI, LPM);
672 /// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
673 /// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
674 /// code immediately before InsertPt.
675 void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
676 BasicBlock *TrueDest,
677 BasicBlock *FalseDest,
678 Instruction *InsertPt) {
679 // Insert a conditional branch on LIC to the two preheaders. The original
680 // code is the true version and the new code is the false version.
681 Value *BranchVal = LIC;
682 if (!isa<ConstantInt>(Val) ||
683 Val->getType() != Type::getInt1Ty(LIC->getContext()))
684 BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val);
685 else if (Val != ConstantInt::getTrue(Val->getContext()))
686 // We want to enter the new loop when the condition is true.
687 std::swap(TrueDest, FalseDest);
689 // Insert the new branch.
690 BranchInst *BI = BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt);
692 // If either edge is critical, split it. This helps preserve LoopSimplify
693 // form for enclosing loops.
694 SplitCriticalEdge(BI, 0, this);
695 SplitCriticalEdge(BI, 1, this);
698 /// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
699 /// condition in it (a cond branch from its header block to its latch block,
700 /// where the path through the loop that doesn't execute its body has no
701 /// side-effects), unswitch it. This doesn't involve any code duplication, just
702 /// moving the conditional branch outside of the loop and updating loop info.
703 void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
705 BasicBlock *ExitBlock) {
706 DEBUG(dbgs() << "loop-unswitch: Trivial-Unswitch loop %"
707 << loopHeader->getName() << " [" << L->getBlocks().size()
708 << " blocks] in Function " << L->getHeader()->getParent()->getName()
709 << " on cond: " << *Val << " == " << *Cond << "\n");
711 // First step, split the preheader, so that we know that there is a safe place
712 // to insert the conditional branch. We will change loopPreheader to have a
713 // conditional branch on Cond.
714 BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, this);
716 // Now that we have a place to insert the conditional branch, create a place
717 // to branch to: this is the exit block out of the loop that we should
720 // Split this block now, so that the loop maintains its exit block, and so
721 // that the jump from the preheader can execute the contents of the exit block
722 // without actually branching to it (the exit block should be dominated by the
723 // loop header, not the preheader).
724 assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
725 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this);
727 // Okay, now we have a position to branch from and a position to branch to,
728 // insert the new conditional branch.
729 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
730 loopPreheader->getTerminator());
731 LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L);
732 loopPreheader->getTerminator()->eraseFromParent();
734 // We need to reprocess this loop, it could be unswitched again.
737 // Now that we know that the loop is never entered when this condition is a
738 // particular value, rewrite the loop with this info. We know that this will
739 // at least eliminate the old branch.
740 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
744 /// SplitExitEdges - Split all of the edges from inside the loop to their exit
745 /// blocks. Update the appropriate Phi nodes as we do so.
746 void LoopUnswitch::SplitExitEdges(Loop *L,
747 const SmallVector<BasicBlock *, 8> &ExitBlocks){
749 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
750 BasicBlock *ExitBlock = ExitBlocks[i];
751 SmallVector<BasicBlock *, 4> Preds(pred_begin(ExitBlock),
752 pred_end(ExitBlock));
754 // Although SplitBlockPredecessors doesn't preserve loop-simplify in
755 // general, if we call it on all predecessors of all exits then it does.
756 if (!ExitBlock->isLandingPad()) {
757 SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", this);
759 SmallVector<BasicBlock*, 2> NewBBs;
760 SplitLandingPadPredecessors(ExitBlock, Preds, ".us-lcssa", ".us-lcssa",
766 /// UnswitchNontrivialCondition - We determined that the loop is profitable
767 /// to unswitch when LIC equal Val. Split it into loop versions and test the
768 /// condition outside of either loop. Return the loops created as Out1/Out2.
769 void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
771 Function *F = loopHeader->getParent();
772 DEBUG(dbgs() << "loop-unswitch: Unswitching loop %"
773 << loopHeader->getName() << " [" << L->getBlocks().size()
774 << " blocks] in Function " << F->getName()
775 << " when '" << *Val << "' == " << *LIC << "\n");
777 if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>())
783 // First step, split the preheader and exit blocks, and add these blocks to
784 // the LoopBlocks list.
785 BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, this);
786 LoopBlocks.push_back(NewPreheader);
788 // We want the loop to come after the preheader, but before the exit blocks.
789 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
791 SmallVector<BasicBlock*, 8> ExitBlocks;
792 L->getUniqueExitBlocks(ExitBlocks);
794 // Split all of the edges from inside the loop to their exit blocks. Update
795 // the appropriate Phi nodes as we do so.
796 SplitExitEdges(L, ExitBlocks);
798 // The exit blocks may have been changed due to edge splitting, recompute.
800 L->getUniqueExitBlocks(ExitBlocks);
802 // Add exit blocks to the loop blocks.
803 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
805 // Next step, clone all of the basic blocks that make up the loop (including
806 // the loop preheader and exit blocks), keeping track of the mapping between
807 // the instructions and blocks.
808 NewBlocks.reserve(LoopBlocks.size());
809 ValueToValueMapTy VMap;
810 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
811 BasicBlock *NewBB = CloneBasicBlock(LoopBlocks[i], VMap, ".us", F);
813 NewBlocks.push_back(NewBB);
814 VMap[LoopBlocks[i]] = NewBB; // Keep the BB mapping.
815 LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], NewBB, L);
818 // Splice the newly inserted blocks into the function right before the
819 // original preheader.
820 F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(),
821 NewBlocks[0], F->end());
823 // Now we create the new Loop object for the versioned loop.
824 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), VMap, LI, LPM);
826 // Recalculate unswitching quota, inherit simplified switches info for NewBB,
827 // Probably clone more loop-unswitch related loop properties.
828 BranchesInfo.cloneData(NewLoop, L, VMap);
830 Loop *ParentLoop = L->getParentLoop();
832 // Make sure to add the cloned preheader and exit blocks to the parent loop
834 ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase());
837 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
838 BasicBlock *NewExit = cast<BasicBlock>(VMap[ExitBlocks[i]]);
839 // The new exit block should be in the same loop as the old one.
840 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
841 ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase());
843 assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
844 "Exit block should have been split to have one successor!");
845 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
847 // If the successor of the exit block had PHI nodes, add an entry for
850 for (BasicBlock::iterator I = ExitSucc->begin(); isa<PHINode>(I); ++I) {
851 PN = cast<PHINode>(I);
852 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
853 ValueToValueMapTy::iterator It = VMap.find(V);
854 if (It != VMap.end()) V = It->second;
855 PN->addIncoming(V, NewExit);
858 if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
859 PN = PHINode::Create(LPad->getType(), 0, "",
860 ExitSucc->getFirstInsertionPt());
862 for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
865 LandingPadInst *LPI = BB->getLandingPadInst();
866 LPI->replaceAllUsesWith(PN);
867 PN->addIncoming(LPI, BB);
872 // Rewrite the code to refer to itself.
873 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
874 for (BasicBlock::iterator I = NewBlocks[i]->begin(),
875 E = NewBlocks[i]->end(); I != E; ++I)
876 RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
878 // Rewrite the original preheader to select between versions of the loop.
879 BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator());
880 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
881 "Preheader splitting did not work correctly!");
883 // Emit the new branch that selects between the two versions of this loop.
884 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
885 LPM->deleteSimpleAnalysisValue(OldBR, L);
886 OldBR->eraseFromParent();
888 LoopProcessWorklist.push_back(NewLoop);
891 // Keep a WeakVH holding onto LIC. If the first call to RewriteLoopBody
892 // deletes the instruction (for example by simplifying a PHI that feeds into
893 // the condition that we're unswitching on), we don't rewrite the second
895 WeakVH LICHandle(LIC);
897 // Now we rewrite the original code to know that the condition is true and the
898 // new code to know that the condition is false.
899 RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
901 // It's possible that simplifying one loop could cause the other to be
902 // changed to another value or a constant. If its a constant, don't simplify
904 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop &&
905 LICHandle && !isa<Constant>(LICHandle))
906 RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
909 /// RemoveFromWorklist - Remove all instances of I from the worklist vector
911 static void RemoveFromWorklist(Instruction *I,
912 std::vector<Instruction*> &Worklist) {
913 std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(),
915 while (WI != Worklist.end()) {
916 unsigned Offset = WI-Worklist.begin();
918 WI = std::find(Worklist.begin()+Offset, Worklist.end(), I);
922 /// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
923 /// program, replacing all uses with V and update the worklist.
924 static void ReplaceUsesOfWith(Instruction *I, Value *V,
925 std::vector<Instruction*> &Worklist,
926 Loop *L, LPPassManager *LPM) {
927 DEBUG(dbgs() << "Replace with '" << *V << "': " << *I);
929 // Add uses to the worklist, which may be dead now.
930 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
931 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
932 Worklist.push_back(Use);
934 // Add users to the worklist which may be simplified now.
935 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
937 Worklist.push_back(cast<Instruction>(*UI));
938 LPM->deleteSimpleAnalysisValue(I, L);
939 RemoveFromWorklist(I, Worklist);
940 I->replaceAllUsesWith(V);
941 I->eraseFromParent();
945 /// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
946 /// information, and remove any dead successors it has.
948 void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
949 std::vector<Instruction*> &Worklist,
951 if (pred_begin(BB) != pred_end(BB)) {
952 // This block isn't dead, since an edge to BB was just removed, see if there
953 // are any easy simplifications we can do now.
954 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
955 // If it has one pred, fold phi nodes in BB.
956 while (isa<PHINode>(BB->begin()))
957 ReplaceUsesOfWith(BB->begin(),
958 cast<PHINode>(BB->begin())->getIncomingValue(0),
961 // If this is the header of a loop and the only pred is the latch, we now
962 // have an unreachable loop.
963 if (Loop *L = LI->getLoopFor(BB))
964 if (loopHeader == BB && L->contains(Pred)) {
965 // Remove the branch from the latch to the header block, this makes
966 // the header dead, which will make the latch dead (because the header
967 // dominates the latch).
968 LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L);
969 Pred->getTerminator()->eraseFromParent();
970 new UnreachableInst(BB->getContext(), Pred);
972 // The loop is now broken, remove it from LI.
973 RemoveLoopFromHierarchy(L);
975 // Reprocess the header, which now IS dead.
976 RemoveBlockIfDead(BB, Worklist, L);
980 // If pred ends in a uncond branch, add uncond branch to worklist so that
981 // the two blocks will get merged.
982 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
983 if (BI->isUnconditional())
984 Worklist.push_back(BI);
989 DEBUG(dbgs() << "Nuking dead block: " << *BB);
991 // Remove the instructions in the basic block from the worklist.
992 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
993 RemoveFromWorklist(I, Worklist);
995 // Anything that uses the instructions in this basic block should have their
996 // uses replaced with undefs.
997 // If I is not void type then replaceAllUsesWith undef.
998 // This allows ValueHandlers and custom metadata to adjust itself.
999 if (!I->getType()->isVoidTy())
1000 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1003 // If this is the edge to the header block for a loop, remove the loop and
1004 // promote all subloops.
1005 if (Loop *BBLoop = LI->getLoopFor(BB)) {
1006 if (BBLoop->getLoopLatch() == BB) {
1007 RemoveLoopFromHierarchy(BBLoop);
1008 if (currentLoop == BBLoop) {
1015 // Remove the block from the loop info, which removes it from any loops it
1017 LI->removeBlock(BB);
1020 // Remove phi node entries in successors for this block.
1021 TerminatorInst *TI = BB->getTerminator();
1022 SmallVector<BasicBlock*, 4> Succs;
1023 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1024 Succs.push_back(TI->getSuccessor(i));
1025 TI->getSuccessor(i)->removePredecessor(BB);
1028 // Unique the successors, remove anything with multiple uses.
1029 array_pod_sort(Succs.begin(), Succs.end());
1030 Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
1032 // Remove the basic block, including all of the instructions contained in it.
1033 LPM->deleteSimpleAnalysisValue(BB, L);
1034 BB->eraseFromParent();
1035 // Remove successor blocks here that are not dead, so that we know we only
1036 // have dead blocks in this list. Nondead blocks have a way of becoming dead,
1037 // then getting removed before we revisit them, which is badness.
1039 for (unsigned i = 0; i != Succs.size(); ++i)
1040 if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
1041 // One exception is loop headers. If this block was the preheader for a
1042 // loop, then we DO want to visit the loop so the loop gets deleted.
1043 // We know that if the successor is a loop header, that this loop had to
1044 // be the preheader: the case where this was the latch block was handled
1045 // above and headers can only have two predecessors.
1046 if (!LI->isLoopHeader(Succs[i])) {
1047 Succs.erase(Succs.begin()+i);
1052 for (unsigned i = 0, e = Succs.size(); i != e; ++i)
1053 RemoveBlockIfDead(Succs[i], Worklist, L);
1056 /// RemoveLoopFromHierarchy - We have discovered that the specified loop has
1057 /// become unwrapped, either because the backedge was deleted, or because the
1058 /// edge into the header was removed. If the edge into the header from the
1059 /// latch block was removed, the loop is unwrapped but subloops are still alive,
1060 /// so they just reparent loops. If the loops are actually dead, they will be
1062 void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) {
1063 LPM->deleteLoopFromQueue(L);
1064 RemoveLoopFromWorklist(L);
1067 // RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
1068 // the value specified by Val in the specified loop, or we know it does NOT have
1069 // that value. Rewrite any uses of LIC or of properties correlated to it.
1070 void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
1073 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
1075 // FIXME: Support correlated properties, like:
1082 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
1083 // selects, switches.
1084 std::vector<Instruction*> Worklist;
1085 LLVMContext &Context = Val->getContext();
1088 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
1089 // in the loop with the appropriate one directly.
1090 if (IsEqual || (isa<ConstantInt>(Val) &&
1091 Val->getType()->isIntegerTy(1))) {
1096 Replacement = ConstantInt::get(Type::getInt1Ty(Val->getContext()),
1097 !cast<ConstantInt>(Val)->getZExtValue());
1099 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
1101 Instruction *U = dyn_cast<Instruction>(*UI);
1102 if (!U || !L->contains(U))
1104 Worklist.push_back(U);
1107 for (std::vector<Instruction*>::iterator UI = Worklist.begin();
1108 UI != Worklist.end(); ++UI)
1109 (*UI)->replaceUsesOfWith(LIC, Replacement);
1111 SimplifyCode(Worklist, L);
1115 // Otherwise, we don't know the precise value of LIC, but we do know that it
1116 // is certainly NOT "Val". As such, simplify any uses in the loop that we
1117 // can. This case occurs when we unswitch switch statements.
1118 for (Value::use_iterator UI = LIC->use_begin(), E = LIC->use_end();
1120 Instruction *U = dyn_cast<Instruction>(*UI);
1121 if (!U || !L->contains(U))
1124 Worklist.push_back(U);
1126 // TODO: We could do other simplifications, for example, turning
1127 // 'icmp eq LIC, Val' -> false.
1129 // If we know that LIC is not Val, use this info to simplify code.
1130 SwitchInst *SI = dyn_cast<SwitchInst>(U);
1131 if (SI == 0 || !isa<ConstantInt>(Val)) continue;
1133 unsigned DeadCase = SI->findCaseValue(cast<ConstantInt>(Val));
1134 if (DeadCase == 0) continue; // Default case is live for multiple values.
1136 // Found a dead case value. Don't remove PHI nodes in the
1137 // successor if they become single-entry, those PHI nodes may
1138 // be in the Users list.
1140 BasicBlock *Switch = SI->getParent();
1141 BasicBlock *SISucc = SI->getSuccessor(DeadCase);
1142 BasicBlock *Latch = L->getLoopLatch();
1144 BranchesInfo.setUnswitched(SI, Val);
1146 if (!SI->findCaseDest(SISucc)) continue; // Edge is critical.
1147 // If the DeadCase successor dominates the loop latch, then the
1148 // transformation isn't safe since it will delete the sole predecessor edge
1150 if (Latch && DT->dominates(SISucc, Latch))
1153 // FIXME: This is a hack. We need to keep the successor around
1154 // and hooked up so as to preserve the loop structure, because
1155 // trying to update it is complicated. So instead we preserve the
1156 // loop structure and put the block on a dead code path.
1157 SplitEdge(Switch, SISucc, this);
1158 // Compute the successors instead of relying on the return value
1159 // of SplitEdge, since it may have split the switch successor
1161 BasicBlock *NewSISucc = SI->getSuccessor(DeadCase);
1162 BasicBlock *OldSISucc = *succ_begin(NewSISucc);
1163 // Create an "unreachable" destination.
1164 BasicBlock *Abort = BasicBlock::Create(Context, "us-unreachable",
1165 Switch->getParent(),
1167 new UnreachableInst(Context, Abort);
1168 // Force the new case destination to branch to the "unreachable"
1169 // block while maintaining a (dead) CFG edge to the old block.
1170 NewSISucc->getTerminator()->eraseFromParent();
1171 BranchInst::Create(Abort, OldSISucc,
1172 ConstantInt::getTrue(Context), NewSISucc);
1173 // Release the PHI operands for this edge.
1174 for (BasicBlock::iterator II = NewSISucc->begin();
1175 PHINode *PN = dyn_cast<PHINode>(II); ++II)
1176 PN->setIncomingValue(PN->getBasicBlockIndex(Switch),
1177 UndefValue::get(PN->getType()));
1178 // Tell the domtree about the new block. We don't fully update the
1179 // domtree here -- instead we force it to do a full recomputation
1180 // after the pass is complete -- but we do need to inform it of
1183 DT->addNewBlock(Abort, NewSISucc);
1186 SimplifyCode(Worklist, L);
1189 /// SimplifyCode - Okay, now that we have simplified some instructions in the
1190 /// loop, walk over it and constant prop, dce, and fold control flow where
1191 /// possible. Note that this is effectively a very simple loop-structure-aware
1192 /// optimizer. During processing of this loop, L could very well be deleted, so
1193 /// it must not be used.
1195 /// FIXME: When the loop optimizer is more mature, separate this out to a new
1198 void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
1199 while (!Worklist.empty()) {
1200 Instruction *I = Worklist.back();
1201 Worklist.pop_back();
1204 if (isInstructionTriviallyDead(I)) {
1205 DEBUG(dbgs() << "Remove dead instruction '" << *I);
1207 // Add uses to the worklist, which may be dead now.
1208 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1209 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
1210 Worklist.push_back(Use);
1211 LPM->deleteSimpleAnalysisValue(I, L);
1212 RemoveFromWorklist(I, Worklist);
1213 I->eraseFromParent();
1218 // See if instruction simplification can hack this up. This is common for
1219 // things like "select false, X, Y" after unswitching made the condition be
1221 if (Value *V = SimplifyInstruction(I, 0, 0, DT))
1222 if (LI->replacementPreservesLCSSAForm(I, V)) {
1223 ReplaceUsesOfWith(I, V, Worklist, L, LPM);
1227 // Special case hacks that appear commonly in unswitched code.
1228 if (BranchInst *BI = dyn_cast<BranchInst>(I)) {
1229 if (BI->isUnconditional()) {
1230 // If BI's parent is the only pred of the successor, fold the two blocks
1232 BasicBlock *Pred = BI->getParent();
1233 BasicBlock *Succ = BI->getSuccessor(0);
1234 BasicBlock *SinglePred = Succ->getSinglePredecessor();
1235 if (!SinglePred) continue; // Nothing to do.
1236 assert(SinglePred == Pred && "CFG broken");
1238 DEBUG(dbgs() << "Merging blocks: " << Pred->getName() << " <- "
1239 << Succ->getName() << "\n");
1241 // Resolve any single entry PHI nodes in Succ.
1242 while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
1243 ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM);
1245 // If Succ has any successors with PHI nodes, update them to have
1246 // entries coming from Pred instead of Succ.
1247 Succ->replaceAllUsesWith(Pred);
1249 // Move all of the successor contents from Succ to Pred.
1250 Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
1252 LPM->deleteSimpleAnalysisValue(BI, L);
1253 BI->eraseFromParent();
1254 RemoveFromWorklist(BI, Worklist);
1256 // Remove Succ from the loop tree.
1257 LI->removeBlock(Succ);
1258 LPM->deleteSimpleAnalysisValue(Succ, L);
1259 Succ->eraseFromParent();
1264 if (ConstantInt *CB = dyn_cast<ConstantInt>(BI->getCondition())){
1265 // Conditional branch. Turn it into an unconditional branch, then
1266 // remove dead blocks.
1267 continue; // FIXME: Enable.
1269 DEBUG(dbgs() << "Folded branch: " << *BI);
1270 BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue());
1271 BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue());
1272 DeadSucc->removePredecessor(BI->getParent(), true);
1273 Worklist.push_back(BranchInst::Create(LiveSucc, BI));
1274 LPM->deleteSimpleAnalysisValue(BI, L);
1275 BI->eraseFromParent();
1276 RemoveFromWorklist(BI, Worklist);
1279 RemoveBlockIfDead(DeadSucc, Worklist, L);