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/ConstantFolding.h"
36 #include "llvm/Analysis/LoopInfo.h"
37 #include "llvm/Analysis/LoopPass.h"
38 #include "llvm/Analysis/Dominators.h"
39 #include "llvm/Transforms/Utils/Cloning.h"
40 #include "llvm/Transforms/Utils/Local.h"
41 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
42 #include "llvm/ADT/Statistic.h"
43 #include "llvm/ADT/SmallPtrSet.h"
44 #include "llvm/Support/CommandLine.h"
45 #include "llvm/Support/Compiler.h"
46 #include "llvm/Support/Debug.h"
51 STATISTIC(NumBranches, "Number of branches unswitched");
52 STATISTIC(NumSwitches, "Number of switches unswitched");
53 STATISTIC(NumSelects , "Number of selects unswitched");
54 STATISTIC(NumTrivial , "Number of unswitches that are trivial");
55 STATISTIC(NumSimplify, "Number of simplifications of unswitched code");
57 static cl::opt<unsigned>
58 Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
59 cl::init(10), cl::Hidden);
62 class VISIBILITY_HIDDEN LoopUnswitch : public LoopPass {
63 LoopInfo *LI; // Loop information
66 // LoopProcessWorklist - Used to check if second loop needs processing
67 // after RewriteLoopBodyWithConditionConstant rewrites first loop.
68 std::vector<Loop*> LoopProcessWorklist;
69 SmallPtrSet<Value *,8> UnswitchedVals;
74 DominanceFrontier *DF;
77 /// LoopDF - Loop's dominance frontier. This set is a collection of
78 /// loop exiting blocks' DF member blocks. However this does set does not
79 /// includes basic blocks that are inside loop.
80 SmallPtrSet<BasicBlock *, 8> LoopDF;
82 /// OrigLoopExitMap - This is used to map loop exiting block with
83 /// corresponding loop exit block, before updating CFG.
84 DenseMap<BasicBlock *, BasicBlock *> OrigLoopExitMap;
86 static char ID; // Pass ID, replacement for typeid
87 explicit LoopUnswitch(bool Os = false) :
88 LoopPass((intptr_t)&ID), OptimizeForSize(Os), redoLoop(false) {}
90 bool runOnLoop(Loop *L, LPPassManager &LPM);
91 bool processLoop(Loop *L);
93 /// This transformation requires natural loop information & requires that
94 /// loop preheaders be inserted into the CFG...
96 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
97 AU.addRequiredID(LoopSimplifyID);
98 AU.addPreservedID(LoopSimplifyID);
99 AU.addRequired<LoopInfo>();
100 AU.addPreserved<LoopInfo>();
101 AU.addRequiredID(LCSSAID);
102 AU.addPreservedID(LCSSAID);
103 AU.addPreserved<DominatorTree>();
104 AU.addPreserved<DominanceFrontier>();
109 /// RemoveLoopFromWorklist - If the specified loop is on the loop worklist,
111 void RemoveLoopFromWorklist(Loop *L) {
112 std::vector<Loop*>::iterator I = std::find(LoopProcessWorklist.begin(),
113 LoopProcessWorklist.end(), L);
114 if (I != LoopProcessWorklist.end())
115 LoopProcessWorklist.erase(I);
118 /// Split all of the edges from inside the loop to their exit blocks.
119 /// Update the appropriate Phi nodes as we do so.
120 void SplitExitEdges(Loop *L, const SmallVector<BasicBlock *, 8> &ExitBlocks,
121 SmallVector<BasicBlock *, 8> &MiddleBlocks);
123 /// If BB's dominance frontier has a member that is not part of loop L then
124 /// remove it. Add NewDFMember in BB's dominance frontier.
125 void ReplaceLoopExternalDFMember(Loop *L, BasicBlock *BB,
126 BasicBlock *NewDFMember);
128 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L);
129 unsigned getLoopUnswitchCost(Loop *L, Value *LIC);
130 void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
131 BasicBlock *ExitBlock);
132 void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
134 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
135 Constant *Val, bool isEqual);
137 void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
138 BasicBlock *TrueDest,
139 BasicBlock *FalseDest,
140 Instruction *InsertPt);
142 void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
143 void RemoveBlockIfDead(BasicBlock *BB,
144 std::vector<Instruction*> &Worklist, Loop *l);
145 void RemoveLoopFromHierarchy(Loop *L);
148 char LoopUnswitch::ID = 0;
149 static RegisterPass<LoopUnswitch> X("loop-unswitch", "Unswitch loops");
151 LoopPass *llvm::createLoopUnswitchPass(bool Os) {
152 return new LoopUnswitch(Os);
155 /// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
156 /// invariant in the loop, or has an invariant piece, return the invariant.
157 /// Otherwise, return null.
158 static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
159 // Constants should be folded, not unswitched on!
160 if (isa<Constant>(Cond)) return false;
162 // TODO: Handle: br (VARIANT|INVARIANT).
163 // TODO: Hoist simple expressions out of loops.
164 if (L->isLoopInvariant(Cond)) return Cond;
166 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
167 if (BO->getOpcode() == Instruction::And ||
168 BO->getOpcode() == Instruction::Or) {
169 // If either the left or right side is invariant, we can unswitch on this,
170 // which will cause the branch to go away in one loop and the condition to
171 // simplify in the other one.
172 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
174 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
181 bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
182 LI = &getAnalysis<LoopInfo>();
184 DF = getAnalysisToUpdate<DominanceFrontier>();
185 DT = getAnalysisToUpdate<DominatorTree>();
187 bool Changed = false;
191 Changed |= processLoop(L);
197 /// processLoop - Do actual work and unswitch loop if possible and profitable.
198 bool LoopUnswitch::processLoop(Loop *L) {
199 assert(L->isLCSSAForm());
200 bool Changed = false;
202 // Loop over all of the basic blocks in the loop. If we find an interior
203 // block that is branching on a loop-invariant condition, we can unswitch this
205 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
207 TerminatorInst *TI = (*I)->getTerminator();
208 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
209 // If this isn't branching on an invariant condition, we can't unswitch
211 if (BI->isConditional()) {
212 // See if this, or some part of it, is loop invariant. If so, we can
213 // unswitch on it if we desire.
214 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), L, Changed);
215 if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(),
221 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
222 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
223 if (LoopCond && SI->getNumCases() > 1) {
224 // Find a value to unswitch on:
225 // FIXME: this should chose the most expensive case!
226 Constant *UnswitchVal = SI->getCaseValue(1);
227 // Do not process same value again and again.
228 if (!UnswitchedVals.insert(UnswitchVal))
231 if (UnswitchIfProfitable(LoopCond, UnswitchVal, L)) {
238 // Scan the instructions to check for unswitchable values.
239 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
241 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
242 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
243 if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(),
251 assert(L->isLCSSAForm());
256 /// isTrivialLoopExitBlock - Check to see if all paths from BB either:
257 /// 1. Exit the loop with no side effects.
258 /// 2. Branch to the latch block with no side-effects.
260 /// If these conditions are true, we return true and set ExitBB to the block we
263 static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
265 std::set<BasicBlock*> &Visited) {
266 if (!Visited.insert(BB).second) {
267 // Already visited and Ok, end of recursion.
269 } else if (!L->contains(BB)) {
270 // Otherwise, this is a loop exit, this is fine so long as this is the
272 if (ExitBB != 0) return false;
277 // Otherwise, this is an unvisited intra-loop node. Check all successors.
278 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
279 // Check to see if the successor is a trivial loop exit.
280 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
284 // Okay, everything after this looks good, check to make sure that this block
285 // doesn't include any side effects.
286 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
287 if (I->mayWriteToMemory())
293 /// isTrivialLoopExitBlock - Return true if the specified block unconditionally
294 /// leads to an exit from the specified loop, and has no side-effects in the
295 /// process. If so, return the block that is exited to, otherwise return null.
296 static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
297 std::set<BasicBlock*> Visited;
298 Visited.insert(L->getHeader()); // Branches to header are ok.
299 BasicBlock *ExitBB = 0;
300 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
305 /// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
306 /// trivial: that is, that the condition controls whether or not the loop does
307 /// anything at all. If this is a trivial condition, unswitching produces no
308 /// code duplications (equivalently, it produces a simpler loop and a new empty
309 /// loop, which gets deleted).
311 /// If this is a trivial condition, return true, otherwise return false. When
312 /// returning true, this sets Cond and Val to the condition that controls the
313 /// trivial condition: when Cond dynamically equals Val, the loop is known to
314 /// exit. Finally, this sets LoopExit to the BB that the loop exits to when
317 static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond, Constant **Val = 0,
318 BasicBlock **LoopExit = 0) {
319 BasicBlock *Header = L->getHeader();
320 TerminatorInst *HeaderTerm = Header->getTerminator();
322 BasicBlock *LoopExitBB = 0;
323 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
324 // If the header block doesn't end with a conditional branch on Cond, we
326 if (!BI->isConditional() || BI->getCondition() != Cond)
329 // Check to see if a successor of the branch is guaranteed to go to the
330 // latch block or exit through a one exit block without having any
331 // side-effects. If so, determine the value of Cond that causes it to do
333 if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(0)))) {
334 if (Val) *Val = ConstantInt::getTrue();
335 } else if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(1)))) {
336 if (Val) *Val = ConstantInt::getFalse();
338 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
339 // If this isn't a switch on Cond, we can't handle it.
340 if (SI->getCondition() != Cond) return false;
342 // Check to see if a successor of the switch is guaranteed to go to the
343 // latch block or exit through a one exit block without having any
344 // side-effects. If so, determine the value of Cond that causes it to do
345 // this. Note that we can't trivially unswitch on the default case.
346 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i)
347 if ((LoopExitBB = isTrivialLoopExitBlock(L, SI->getSuccessor(i)))) {
348 // Okay, we found a trivial case, remember the value that is trivial.
349 if (Val) *Val = SI->getCaseValue(i);
354 // If we didn't find a single unique LoopExit block, or if the loop exit block
355 // contains phi nodes, this isn't trivial.
356 if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
357 return false; // Can't handle this.
359 if (LoopExit) *LoopExit = LoopExitBB;
361 // We already know that nothing uses any scalar values defined inside of this
362 // loop. As such, we just have to check to see if this loop will execute any
363 // side-effecting instructions (e.g. stores, calls, volatile loads) in the
364 // part of the loop that the code *would* execute. We already checked the
365 // tail, check the header now.
366 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
367 if (I->mayWriteToMemory())
372 /// getLoopUnswitchCost - Return the cost (code size growth) that will happen if
373 /// we choose to unswitch the specified loop on the specified value.
375 unsigned LoopUnswitch::getLoopUnswitchCost(Loop *L, Value *LIC) {
376 // If the condition is trivial, always unswitch. There is no code growth for
378 if (IsTrivialUnswitchCondition(L, LIC))
381 // FIXME: This is really overly conservative. However, more liberal
382 // estimations have thus far resulted in excessive unswitching, which is bad
383 // both in compile time and in code size. This should be replaced once
384 // someone figures out how a good estimation.
385 return L->getBlocks().size();
388 // FIXME: this is brain dead. It should take into consideration code
390 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
393 // Do not include empty blocks in the cost calculation. This happen due to
394 // loop canonicalization and will be removed.
395 if (BB->begin() == BasicBlock::iterator(BB->getTerminator()))
398 // Count basic blocks.
405 /// UnswitchIfProfitable - We have found that we can unswitch L when
406 /// LoopCond == Val to simplify the loop. If we decide that this is profitable,
407 /// unswitch the loop, reprocess the pieces, then return true.
408 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L){
409 // Check to see if it would be profitable to unswitch this loop.
410 unsigned Cost = getLoopUnswitchCost(L, LoopCond);
412 // Do not do non-trivial unswitch while optimizing for size.
413 if (Cost && OptimizeForSize)
416 if (Cost > Threshold) {
417 // FIXME: this should estimate growth by the amount of code shared by the
418 // resultant unswitched loops.
420 DOUT << "NOT unswitching loop %"
421 << L->getHeader()->getName() << ", cost too high: "
422 << L->getBlocks().size() << "\n";
426 // If this is a trivial condition to unswitch (which results in no code
427 // duplication), do it now.
429 BasicBlock *ExitBlock;
430 if (IsTrivialUnswitchCondition(L, LoopCond, &CondVal, &ExitBlock)) {
431 UnswitchTrivialCondition(L, LoopCond, CondVal, ExitBlock);
433 UnswitchNontrivialCondition(LoopCond, Val, L);
439 // RemapInstruction - Convert the instruction operands from referencing the
440 // current values into those specified by ValueMap.
442 static inline void RemapInstruction(Instruction *I,
443 DenseMap<const Value *, Value*> &ValueMap) {
444 for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
445 Value *Op = I->getOperand(op);
446 DenseMap<const Value *, Value*>::iterator It = ValueMap.find(Op);
447 if (It != ValueMap.end()) Op = It->second;
448 I->setOperand(op, Op);
452 // CloneDomInfo - NewBB is cloned from Orig basic block. Now clone Dominator
455 // If Orig block's immediate dominator is mapped in VM then use corresponding
456 // immediate dominator from the map. Otherwise Orig block's dominator is also
457 // NewBB's dominator.
459 // OrigPreheader is loop pre-header before this pass started
460 // updating CFG. NewPrehader is loops new pre-header. However, after CFG
461 // manipulation, loop L may not exist. So rely on input parameter NewPreheader.
462 static void CloneDomInfo(BasicBlock *NewBB, BasicBlock *Orig,
463 BasicBlock *NewPreheader, BasicBlock *OrigPreheader,
464 BasicBlock *OrigHeader,
465 DominatorTree *DT, DominanceFrontier *DF,
466 DenseMap<const Value*, Value*> &VM) {
468 // If NewBB alreay has found its place in domiantor tree then no need to do
470 if (DT->getNode(NewBB))
473 // If Orig does not have any immediate domiantor then its clone, NewBB, does
474 // not need any immediate dominator.
475 DomTreeNode *OrigNode = DT->getNode(Orig);
478 DomTreeNode *OrigIDomNode = OrigNode->getIDom();
482 BasicBlock *OrigIDom = NULL;
484 // If Orig is original loop header then its immediate dominator is
486 if (Orig == OrigHeader)
487 OrigIDom = NewPreheader;
489 // If Orig is new pre-header then its immediate dominator is
490 // original pre-header.
491 else if (Orig == NewPreheader)
492 OrigIDom = OrigPreheader;
494 // Other as DT to find Orig's immediate dominator.
496 OrigIDom = OrigIDomNode->getBlock();
498 // Initially use Orig's immediate dominator as NewBB's immediate dominator.
499 BasicBlock *NewIDom = OrigIDom;
500 DenseMap<const Value*, Value*>::iterator I = VM.find(OrigIDom);
502 NewIDom = cast<BasicBlock>(I->second);
504 // If NewIDom does not have corresponding dominatore tree node then
506 if (!DT->getNode(NewIDom))
507 CloneDomInfo(NewIDom, OrigIDom, NewPreheader, OrigPreheader,
508 OrigHeader, DT, DF, VM);
511 DT->addNewBlock(NewBB, NewIDom);
513 // Copy cloned dominance frontiner set
514 DominanceFrontier::DomSetType NewDFSet;
516 DominanceFrontier::iterator DFI = DF->find(Orig);
517 if ( DFI != DF->end()) {
518 DominanceFrontier::DomSetType S = DFI->second;
519 for (DominanceFrontier::DomSetType::iterator I = S.begin(), E = S.end();
522 DenseMap<const Value*, Value*>::iterator IDM = VM.find(BB);
524 NewDFSet.insert(cast<BasicBlock>(IDM->second));
529 DF->addBasicBlock(NewBB, NewDFSet);
533 /// CloneLoop - Recursively clone the specified loop and all of its children,
534 /// mapping the blocks with the specified map.
535 static Loop *CloneLoop(Loop *L, Loop *PL, DenseMap<const Value*, Value*> &VM,
536 LoopInfo *LI, LPPassManager *LPM) {
537 Loop *New = new Loop();
539 LPM->insertLoop(New, PL);
541 // Add all of the blocks in L to the new loop.
542 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
544 if (LI->getLoopFor(*I) == L)
545 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), LI->getBase());
547 // Add all of the subloops to the new loop.
548 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
549 CloneLoop(*I, New, VM, LI, LPM);
554 /// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
555 /// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
556 /// code immediately before InsertPt.
557 void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
558 BasicBlock *TrueDest,
559 BasicBlock *FalseDest,
560 Instruction *InsertPt) {
561 // Insert a conditional branch on LIC to the two preheaders. The original
562 // code is the true version and the new code is the false version.
563 Value *BranchVal = LIC;
564 if (!isa<ConstantInt>(Val) || Val->getType() != Type::Int1Ty)
565 BranchVal = new ICmpInst(ICmpInst::ICMP_EQ, LIC, Val, "tmp", InsertPt);
566 else if (Val != ConstantInt::getTrue())
567 // We want to enter the new loop when the condition is true.
568 std::swap(TrueDest, FalseDest);
570 // Insert the new branch.
571 BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt);
576 /// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
577 /// condition in it (a cond branch from its header block to its latch block,
578 /// where the path through the loop that doesn't execute its body has no
579 /// side-effects), unswitch it. This doesn't involve any code duplication, just
580 /// moving the conditional branch outside of the loop and updating loop info.
581 void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
583 BasicBlock *ExitBlock) {
584 DOUT << "loop-unswitch: Trivial-Unswitch loop %"
585 << L->getHeader()->getName() << " [" << L->getBlocks().size()
586 << " blocks] in Function " << L->getHeader()->getParent()->getName()
587 << " on cond: " << *Val << " == " << *Cond << "\n";
589 // First step, split the preheader, so that we know that there is a safe place
590 // to insert the conditional branch. We will change 'OrigPH' to have a
591 // conditional branch on Cond.
592 BasicBlock *OrigPH = L->getLoopPreheader();
593 BasicBlock *NewPH = SplitEdge(OrigPH, L->getHeader(), this);
595 // Now that we have a place to insert the conditional branch, create a place
596 // to branch to: this is the exit block out of the loop that we should
599 // Split this block now, so that the loop maintains its exit block, and so
600 // that the jump from the preheader can execute the contents of the exit block
601 // without actually branching to it (the exit block should be dominated by the
602 // loop header, not the preheader).
603 assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
604 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this);
606 // Okay, now we have a position to branch from and a position to branch to,
607 // insert the new conditional branch.
608 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
609 OrigPH->getTerminator());
610 LPM->deleteSimpleAnalysisValue(OrigPH->getTerminator(), L);
611 OrigPH->getTerminator()->eraseFromParent();
613 // We need to reprocess this loop, it could be unswitched again.
616 // Now that we know that the loop is never entered when this condition is a
617 // particular value, rewrite the loop with this info. We know that this will
618 // at least eliminate the old branch.
619 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
623 /// ReplaceLoopExternalDFMember -
624 /// If BB's dominance frontier has a member that is not part of loop L then
625 /// remove it. Add NewDFMember in BB's dominance frontier.
626 void LoopUnswitch::ReplaceLoopExternalDFMember(Loop *L, BasicBlock *BB,
627 BasicBlock *NewDFMember) {
629 DominanceFrontier::iterator DFI = DF->find(BB);
630 if (DFI == DF->end())
633 DominanceFrontier::DomSetType &DFSet = DFI->second;
634 for (DominanceFrontier::DomSetType::iterator DI = DFSet.begin(),
635 DE = DFSet.end(); DI != DE;) {
636 BasicBlock *B = *DI++;
640 DF->removeFromFrontier(DFI, B);
644 DF->addToFrontier(DFI, NewDFMember);
647 /// SplitExitEdges - Split all of the edges from inside the loop to their exit
648 /// blocks. Update the appropriate Phi nodes as we do so.
649 void LoopUnswitch::SplitExitEdges(Loop *L,
650 const SmallVector<BasicBlock *, 8> &ExitBlocks,
651 SmallVector<BasicBlock *, 8> &MiddleBlocks) {
653 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
654 BasicBlock *ExitBlock = ExitBlocks[i];
655 std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock));
657 for (unsigned j = 0, e = Preds.size(); j != e; ++j) {
658 BasicBlock* MiddleBlock = SplitEdge(Preds[j], ExitBlock, this);
659 MiddleBlocks.push_back(MiddleBlock);
660 BasicBlock* StartBlock = Preds[j];
661 BasicBlock* EndBlock;
662 if (MiddleBlock->getSinglePredecessor() == ExitBlock) {
663 EndBlock = MiddleBlock;
664 MiddleBlock = EndBlock->getSinglePredecessor();;
666 EndBlock = ExitBlock;
669 OrigLoopExitMap[StartBlock] = EndBlock;
671 std::set<PHINode*> InsertedPHIs;
672 PHINode* OldLCSSA = 0;
673 for (BasicBlock::iterator I = EndBlock->begin();
674 (OldLCSSA = dyn_cast<PHINode>(I)); ++I) {
675 Value* OldValue = OldLCSSA->getIncomingValueForBlock(MiddleBlock);
676 PHINode* NewLCSSA = PHINode::Create(OldLCSSA->getType(),
677 OldLCSSA->getName() + ".us-lcssa",
678 MiddleBlock->getTerminator());
679 NewLCSSA->addIncoming(OldValue, StartBlock);
680 OldLCSSA->setIncomingValue(OldLCSSA->getBasicBlockIndex(MiddleBlock),
682 InsertedPHIs.insert(NewLCSSA);
685 BasicBlock::iterator InsertPt = EndBlock->getFirstNonPHI();
686 for (BasicBlock::iterator I = MiddleBlock->begin();
687 (OldLCSSA = dyn_cast<PHINode>(I)) && InsertedPHIs.count(OldLCSSA) == 0;
689 PHINode *NewLCSSA = PHINode::Create(OldLCSSA->getType(),
690 OldLCSSA->getName() + ".us-lcssa",
692 OldLCSSA->replaceAllUsesWith(NewLCSSA);
693 NewLCSSA->addIncoming(OldLCSSA, MiddleBlock);
697 // StartBlock -- > MiddleBlock -- > EndBlock
698 // StartBlock is loop exiting block. EndBlock will become merge point
699 // of two loop exits after loop unswitch.
701 // If StartBlock's DF member includes a block that is not loop member
702 // then replace that DF member with EndBlock.
704 // If MiddleBlock's DF member includes a block that is not loop member
705 // tnen replace that DF member with EndBlock.
707 ReplaceLoopExternalDFMember(L, StartBlock, EndBlock);
708 ReplaceLoopExternalDFMember(L, MiddleBlock, EndBlock);
715 /// UnswitchNontrivialCondition - We determined that the loop is profitable
716 /// to unswitch when LIC equal Val. Split it into loop versions and test the
717 /// condition outside of either loop. Return the loops created as Out1/Out2.
718 void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
720 Function *F = L->getHeader()->getParent();
721 DOUT << "loop-unswitch: Unswitching loop %"
722 << L->getHeader()->getName() << " [" << L->getBlocks().size()
723 << " blocks] in Function " << F->getName()
724 << " when '" << *Val << "' == " << *LIC << "\n";
726 // LoopBlocks contains all of the basic blocks of the loop, including the
727 // preheader of the loop, the body of the loop, and the exit blocks of the
728 // loop, in that order.
729 std::vector<BasicBlock*> LoopBlocks;
731 // First step, split the preheader and exit blocks, and add these blocks to
732 // the LoopBlocks list.
733 BasicBlock *OrigHeader = L->getHeader();
734 BasicBlock *OrigPreheader = L->getLoopPreheader();
735 BasicBlock *NewPreheader = SplitEdge(OrigPreheader, L->getHeader(), this);
736 LoopBlocks.push_back(NewPreheader);
738 // We want the loop to come after the preheader, but before the exit blocks.
739 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
741 SmallVector<BasicBlock*, 8> ExitBlocks;
742 L->getUniqueExitBlocks(ExitBlocks);
744 // Split all of the edges from inside the loop to their exit blocks. Update
745 // the appropriate Phi nodes as we do so.
746 SmallVector<BasicBlock *,8> MiddleBlocks;
747 SplitExitEdges(L, ExitBlocks, MiddleBlocks);
749 // The exit blocks may have been changed due to edge splitting, recompute.
751 L->getUniqueExitBlocks(ExitBlocks);
753 // Add exit blocks to the loop blocks.
754 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
756 // Next step, clone all of the basic blocks that make up the loop (including
757 // the loop preheader and exit blocks), keeping track of the mapping between
758 // the instructions and blocks.
759 std::vector<BasicBlock*> NewBlocks;
760 NewBlocks.reserve(LoopBlocks.size());
761 DenseMap<const Value*, Value*> ValueMap;
762 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
763 BasicBlock *New = CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F);
764 NewBlocks.push_back(New);
765 ValueMap[LoopBlocks[i]] = New; // Keep the BB mapping.
766 LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], New, L);
769 // OutSiders are basic block that are dominated by original header and
770 // at the same time they are not part of loop.
771 SmallPtrSet<BasicBlock *, 8> OutSiders;
773 DomTreeNode *OrigHeaderNode = DT->getNode(OrigHeader);
774 for(std::vector<DomTreeNode*>::iterator DI = OrigHeaderNode->begin(),
775 DE = OrigHeaderNode->end(); DI != DE; ++DI) {
776 BasicBlock *B = (*DI)->getBlock();
778 DenseMap<const Value*, Value*>::iterator VI = ValueMap.find(B);
779 if (VI == ValueMap.end())
784 // Splice the newly inserted blocks into the function right before the
785 // original preheader.
786 F->getBasicBlockList().splice(LoopBlocks[0], F->getBasicBlockList(),
787 NewBlocks[0], F->end());
789 // Now we create the new Loop object for the versioned loop.
790 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI, LPM);
791 Loop *ParentLoop = L->getParentLoop();
793 // Make sure to add the cloned preheader and exit blocks to the parent loop
795 ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase());
798 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
799 BasicBlock *NewExit = cast<BasicBlock>(ValueMap[ExitBlocks[i]]);
800 // The new exit block should be in the same loop as the old one.
801 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
802 ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase());
804 assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
805 "Exit block should have been split to have one successor!");
806 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
808 // If the successor of the exit block had PHI nodes, add an entry for
811 for (BasicBlock::iterator I = ExitSucc->begin();
812 (PN = dyn_cast<PHINode>(I)); ++I) {
813 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
814 DenseMap<const Value *, Value*>::iterator It = ValueMap.find(V);
815 if (It != ValueMap.end()) V = It->second;
816 PN->addIncoming(V, NewExit);
820 // Rewrite the code to refer to itself.
821 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
822 for (BasicBlock::iterator I = NewBlocks[i]->begin(),
823 E = NewBlocks[i]->end(); I != E; ++I)
824 RemapInstruction(I, ValueMap);
826 // Rewrite the original preheader to select between versions of the loop.
827 BranchInst *OldBR = cast<BranchInst>(OrigPreheader->getTerminator());
828 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
829 "Preheader splitting did not work correctly!");
831 // Emit the new branch that selects between the two versions of this loop.
832 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
833 LPM->deleteSimpleAnalysisValue(OldBR, L);
834 OldBR->eraseFromParent();
836 // Update dominator info
839 SmallVector<BasicBlock *,4> ExitingBlocks;
840 L->getExitingBlocks(ExitingBlocks);
842 // Clone dominator info for all cloned basic block.
843 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
844 BasicBlock *LBB = LoopBlocks[i];
845 BasicBlock *NBB = NewBlocks[i];
846 CloneDomInfo(NBB, LBB, NewPreheader, OrigPreheader,
847 OrigHeader, DT, DF, ValueMap);
849 // If LBB's dominance frontier includes DFMember
850 // such that DFMember is also a member of LoopDF then
851 // - Remove DFMember from LBB's dominance frontier
852 // - Copy loop exiting blocks', that are dominated by BB,
853 // dominance frontier member in BB's dominance frontier
855 DominanceFrontier::iterator LBBI = DF->find(LBB);
856 DominanceFrontier::iterator NBBI = DF->find(NBB);
857 if (LBBI == DF->end())
860 DominanceFrontier::DomSetType &LBSet = LBBI->second;
861 for (DominanceFrontier::DomSetType::iterator LI = LBSet.begin(),
862 LE = LBSet.end(); LI != LE; /* NULL */) {
863 BasicBlock *B = *LI++;
864 if (B == LBB && B == L->getHeader())
866 bool removeB = false;
867 if (!LoopDF.count(B))
870 // If LBB dominates loop exits then insert loop exit block's DF
872 for(SmallVector<BasicBlock *, 4>::iterator
873 LExitI = ExitingBlocks.begin(),
874 LExitE = ExitingBlocks.end(); LExitI != LExitE; ++LExitI) {
875 BasicBlock *E = *LExitI;
877 if (!DT->dominates(LBB,E))
880 DenseMap<BasicBlock *, BasicBlock *>::iterator DFBI =
881 OrigLoopExitMap.find(E);
882 if (DFBI == OrigLoopExitMap.end())
885 BasicBlock *DFB = DFBI->second;
886 DF->addToFrontier(LBBI, DFB);
887 DF->addToFrontier(NBBI, DFB);
891 // If B's replacement is inserted in DF then now is the time to remove
894 DF->removeFromFrontier(LBBI, B);
896 DF->removeFromFrontier(NBBI, cast<BasicBlock>(ValueMap[B]));
898 DF->removeFromFrontier(NBBI, B);
904 // MiddleBlocks are dominated by original pre header. SplitEdge updated
905 // MiddleBlocks' dominance frontier appropriately.
906 for (unsigned i = 0, e = MiddleBlocks.size(); i != e; ++i) {
907 BasicBlock *MBB = MiddleBlocks[i];
908 if (!MBB->getSinglePredecessor())
909 DT->changeImmediateDominator(MBB, OrigPreheader);
912 // All Outsiders are now dominated by original pre header.
913 for (SmallPtrSet<BasicBlock *, 8>::iterator OI = OutSiders.begin(),
914 OE = OutSiders.end(); OI != OE; ++OI) {
915 BasicBlock *OB = *OI;
916 DT->changeImmediateDominator(OB, OrigPreheader);
919 // New loop headers are dominated by original preheader
920 DT->changeImmediateDominator(NewBlocks[0], OrigPreheader);
921 DT->changeImmediateDominator(LoopBlocks[0], OrigPreheader);
924 LoopProcessWorklist.push_back(NewLoop);
927 // Now we rewrite the original code to know that the condition is true and the
928 // new code to know that the condition is false.
929 RewriteLoopBodyWithConditionConstant(L , LIC, Val, false);
931 // It's possible that simplifying one loop could cause the other to be
932 // deleted. If so, don't simplify it.
933 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop)
934 RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true);
937 /// RemoveFromWorklist - Remove all instances of I from the worklist vector
939 static void RemoveFromWorklist(Instruction *I,
940 std::vector<Instruction*> &Worklist) {
941 std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(),
943 while (WI != Worklist.end()) {
944 unsigned Offset = WI-Worklist.begin();
946 WI = std::find(Worklist.begin()+Offset, Worklist.end(), I);
950 /// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
951 /// program, replacing all uses with V and update the worklist.
952 static void ReplaceUsesOfWith(Instruction *I, Value *V,
953 std::vector<Instruction*> &Worklist,
954 Loop *L, LPPassManager *LPM) {
955 DOUT << "Replace with '" << *V << "': " << *I;
957 // Add uses to the worklist, which may be dead now.
958 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
959 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
960 Worklist.push_back(Use);
962 // Add users to the worklist which may be simplified now.
963 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
965 Worklist.push_back(cast<Instruction>(*UI));
966 LPM->deleteSimpleAnalysisValue(I, L);
967 RemoveFromWorklist(I, Worklist);
968 I->replaceAllUsesWith(V);
969 I->eraseFromParent();
973 /// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
974 /// information, and remove any dead successors it has.
976 void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
977 std::vector<Instruction*> &Worklist,
979 if (pred_begin(BB) != pred_end(BB)) {
980 // This block isn't dead, since an edge to BB was just removed, see if there
981 // are any easy simplifications we can do now.
982 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
983 // If it has one pred, fold phi nodes in BB.
984 while (isa<PHINode>(BB->begin()))
985 ReplaceUsesOfWith(BB->begin(),
986 cast<PHINode>(BB->begin())->getIncomingValue(0),
989 // If this is the header of a loop and the only pred is the latch, we now
990 // have an unreachable loop.
991 if (Loop *L = LI->getLoopFor(BB))
992 if (L->getHeader() == BB && L->contains(Pred)) {
993 // Remove the branch from the latch to the header block, this makes
994 // the header dead, which will make the latch dead (because the header
995 // dominates the latch).
996 LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L);
997 Pred->getTerminator()->eraseFromParent();
998 new UnreachableInst(Pred);
1000 // The loop is now broken, remove it from LI.
1001 RemoveLoopFromHierarchy(L);
1003 // Reprocess the header, which now IS dead.
1004 RemoveBlockIfDead(BB, Worklist, L);
1008 // If pred ends in a uncond branch, add uncond branch to worklist so that
1009 // the two blocks will get merged.
1010 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
1011 if (BI->isUnconditional())
1012 Worklist.push_back(BI);
1017 DOUT << "Nuking dead block: " << *BB;
1019 // Remove the instructions in the basic block from the worklist.
1020 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1021 RemoveFromWorklist(I, Worklist);
1023 // Anything that uses the instructions in this basic block should have their
1024 // uses replaced with undefs.
1025 if (!I->use_empty())
1026 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1029 // If this is the edge to the header block for a loop, remove the loop and
1030 // promote all subloops.
1031 if (Loop *BBLoop = LI->getLoopFor(BB)) {
1032 if (BBLoop->getLoopLatch() == BB)
1033 RemoveLoopFromHierarchy(BBLoop);
1036 // Remove the block from the loop info, which removes it from any loops it
1038 LI->removeBlock(BB);
1041 // Remove phi node entries in successors for this block.
1042 TerminatorInst *TI = BB->getTerminator();
1043 std::vector<BasicBlock*> Succs;
1044 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1045 Succs.push_back(TI->getSuccessor(i));
1046 TI->getSuccessor(i)->removePredecessor(BB);
1049 // Unique the successors, remove anything with multiple uses.
1050 std::sort(Succs.begin(), Succs.end());
1051 Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
1053 // Remove the basic block, including all of the instructions contained in it.
1054 LPM->deleteSimpleAnalysisValue(BB, L);
1055 BB->eraseFromParent();
1056 // Remove successor blocks here that are not dead, so that we know we only
1057 // have dead blocks in this list. Nondead blocks have a way of becoming dead,
1058 // then getting removed before we revisit them, which is badness.
1060 for (unsigned i = 0; i != Succs.size(); ++i)
1061 if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
1062 // One exception is loop headers. If this block was the preheader for a
1063 // loop, then we DO want to visit the loop so the loop gets deleted.
1064 // We know that if the successor is a loop header, that this loop had to
1065 // be the preheader: the case where this was the latch block was handled
1066 // above and headers can only have two predecessors.
1067 if (!LI->isLoopHeader(Succs[i])) {
1068 Succs.erase(Succs.begin()+i);
1073 for (unsigned i = 0, e = Succs.size(); i != e; ++i)
1074 RemoveBlockIfDead(Succs[i], Worklist, L);
1077 /// RemoveLoopFromHierarchy - We have discovered that the specified loop has
1078 /// become unwrapped, either because the backedge was deleted, or because the
1079 /// edge into the header was removed. If the edge into the header from the
1080 /// latch block was removed, the loop is unwrapped but subloops are still alive,
1081 /// so they just reparent loops. If the loops are actually dead, they will be
1083 void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) {
1084 LPM->deleteLoopFromQueue(L);
1085 RemoveLoopFromWorklist(L);
1090 // RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
1091 // the value specified by Val in the specified loop, or we know it does NOT have
1092 // that value. Rewrite any uses of LIC or of properties correlated to it.
1093 void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
1096 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
1098 // FIXME: Support correlated properties, like:
1105 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
1106 // selects, switches.
1107 std::vector<User*> Users(LIC->use_begin(), LIC->use_end());
1108 std::vector<Instruction*> Worklist;
1110 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
1111 // in the loop with the appropriate one directly.
1112 if (IsEqual || (isa<ConstantInt>(Val) && Val->getType() == Type::Int1Ty)) {
1117 Replacement = ConstantInt::get(Type::Int1Ty,
1118 !cast<ConstantInt>(Val)->getZExtValue());
1120 for (unsigned i = 0, e = Users.size(); i != e; ++i)
1121 if (Instruction *U = cast<Instruction>(Users[i])) {
1122 if (!L->contains(U->getParent()))
1124 U->replaceUsesOfWith(LIC, Replacement);
1125 Worklist.push_back(U);
1128 // Otherwise, we don't know the precise value of LIC, but we do know that it
1129 // is certainly NOT "Val". As such, simplify any uses in the loop that we
1130 // can. This case occurs when we unswitch switch statements.
1131 for (unsigned i = 0, e = Users.size(); i != e; ++i)
1132 if (Instruction *U = cast<Instruction>(Users[i])) {
1133 if (!L->contains(U->getParent()))
1136 Worklist.push_back(U);
1138 // If we know that LIC is not Val, use this info to simplify code.
1139 if (SwitchInst *SI = dyn_cast<SwitchInst>(U)) {
1140 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
1141 if (SI->getCaseValue(i) == Val) {
1142 // Found a dead case value. Don't remove PHI nodes in the
1143 // successor if they become single-entry, those PHI nodes may
1144 // be in the Users list.
1146 // FIXME: This is a hack. We need to keep the successor around
1147 // and hooked up so as to preserve the loop structure, because
1148 // trying to update it is complicated. So instead we preserve the
1149 // loop structure and put the block on an dead code path.
1151 BasicBlock* Old = SI->getParent();
1152 BasicBlock* Split = SplitBlock(Old, SI, this);
1154 Instruction* OldTerm = Old->getTerminator();
1155 BranchInst::Create(Split, SI->getSuccessor(i),
1156 ConstantInt::getTrue(), OldTerm);
1158 LPM->deleteSimpleAnalysisValue(Old->getTerminator(), L);
1159 Old->getTerminator()->eraseFromParent();
1162 for (BasicBlock::iterator II = SI->getSuccessor(i)->begin();
1163 (PN = dyn_cast<PHINode>(II)); ++II) {
1164 Value *InVal = PN->removeIncomingValue(Split, false);
1165 PN->addIncoming(InVal, Old);
1174 // TODO: We could do other simplifications, for example, turning
1175 // LIC == Val -> false.
1179 SimplifyCode(Worklist, L);
1182 /// SimplifyCode - Okay, now that we have simplified some instructions in the
1183 /// loop, walk over it and constant prop, dce, and fold control flow where
1184 /// possible. Note that this is effectively a very simple loop-structure-aware
1185 /// optimizer. During processing of this loop, L could very well be deleted, so
1186 /// it must not be used.
1188 /// FIXME: When the loop optimizer is more mature, separate this out to a new
1191 void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
1192 while (!Worklist.empty()) {
1193 Instruction *I = Worklist.back();
1194 Worklist.pop_back();
1196 // Simple constant folding.
1197 if (Constant *C = ConstantFoldInstruction(I)) {
1198 ReplaceUsesOfWith(I, C, Worklist, L, LPM);
1203 if (isInstructionTriviallyDead(I)) {
1204 DOUT << "Remove dead instruction '" << *I;
1206 // Add uses to the worklist, which may be dead now.
1207 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1208 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
1209 Worklist.push_back(Use);
1210 LPM->deleteSimpleAnalysisValue(I, L);
1211 RemoveFromWorklist(I, Worklist);
1212 I->eraseFromParent();
1217 // Special case hacks that appear commonly in unswitched code.
1218 switch (I->getOpcode()) {
1219 case Instruction::Select:
1220 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(0))) {
1221 ReplaceUsesOfWith(I, I->getOperand(!CB->getZExtValue()+1), Worklist, L,
1226 case Instruction::And:
1227 if (isa<ConstantInt>(I->getOperand(0)) &&
1228 I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS
1229 cast<BinaryOperator>(I)->swapOperands();
1230 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1)))
1231 if (CB->getType() == Type::Int1Ty) {
1232 if (CB->isOne()) // X & 1 -> X
1233 ReplaceUsesOfWith(I, I->getOperand(0), Worklist, L, LPM);
1235 ReplaceUsesOfWith(I, I->getOperand(1), Worklist, L, LPM);
1239 case Instruction::Or:
1240 if (isa<ConstantInt>(I->getOperand(0)) &&
1241 I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS
1242 cast<BinaryOperator>(I)->swapOperands();
1243 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1)))
1244 if (CB->getType() == Type::Int1Ty) {
1245 if (CB->isOne()) // X | 1 -> 1
1246 ReplaceUsesOfWith(I, I->getOperand(1), Worklist, L, LPM);
1248 ReplaceUsesOfWith(I, I->getOperand(0), Worklist, L, LPM);
1252 case Instruction::Br: {
1253 BranchInst *BI = cast<BranchInst>(I);
1254 if (BI->isUnconditional()) {
1255 // If BI's parent is the only pred of the successor, fold the two blocks
1257 BasicBlock *Pred = BI->getParent();
1258 BasicBlock *Succ = BI->getSuccessor(0);
1259 BasicBlock *SinglePred = Succ->getSinglePredecessor();
1260 if (!SinglePred) continue; // Nothing to do.
1261 assert(SinglePred == Pred && "CFG broken");
1263 DOUT << "Merging blocks: " << Pred->getName() << " <- "
1264 << Succ->getName() << "\n";
1266 // Resolve any single entry PHI nodes in Succ.
1267 while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
1268 ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM);
1270 // Move all of the successor contents from Succ to Pred.
1271 Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
1273 LPM->deleteSimpleAnalysisValue(BI, L);
1274 BI->eraseFromParent();
1275 RemoveFromWorklist(BI, Worklist);
1277 // If Succ has any successors with PHI nodes, update them to have
1278 // entries coming from Pred instead of Succ.
1279 Succ->replaceAllUsesWith(Pred);
1281 // Remove Succ from the loop tree.
1282 LI->removeBlock(Succ);
1283 LPM->deleteSimpleAnalysisValue(Succ, L);
1284 Succ->eraseFromParent();
1286 } else if (ConstantInt *CB = dyn_cast<ConstantInt>(BI->getCondition())){
1287 // Conditional branch. Turn it into an unconditional branch, then
1288 // remove dead blocks.
1289 break; // FIXME: Enable.
1291 DOUT << "Folded branch: " << *BI;
1292 BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue());
1293 BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue());
1294 DeadSucc->removePredecessor(BI->getParent(), true);
1295 Worklist.push_back(BranchInst::Create(LiveSucc, BI));
1296 LPM->deleteSimpleAnalysisValue(BI, L);
1297 BI->eraseFromParent();
1298 RemoveFromWorklist(BI, Worklist);
1301 RemoveBlockIfDead(DeadSucc, Worklist, L);