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;
75 DominanceFrontier *DF;
77 BasicBlock *loopHeader;
78 BasicBlock *loopPreheader;
80 /// LoopDF - Loop's dominance frontier. This set is a collection of
81 /// loop exiting blocks' DF member blocks. However this does set does not
82 /// includes basic blocks that are inside loop.
83 SmallPtrSet<BasicBlock *, 8> LoopDF;
85 /// OrigLoopExitMap - This is used to map loop exiting block with
86 /// corresponding loop exit block, before updating CFG.
87 DenseMap<BasicBlock *, BasicBlock *> OrigLoopExitMap;
89 static char ID; // Pass ID, replacement for typeid
90 explicit LoopUnswitch(bool Os = false) :
91 LoopPass((intptr_t)&ID), OptimizeForSize(Os), redoLoop(false),
92 currentLoop(NULL), DF(NULL), DT(NULL), loopHeader(NULL),
93 loopPreheader(NULL) {}
95 bool runOnLoop(Loop *L, LPPassManager &LPM);
96 bool processCurrentLoop();
98 /// This transformation requires natural loop information & requires that
99 /// loop preheaders be inserted into the CFG...
101 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
102 AU.addRequiredID(LoopSimplifyID);
103 AU.addPreservedID(LoopSimplifyID);
104 AU.addRequired<LoopInfo>();
105 AU.addPreserved<LoopInfo>();
106 AU.addRequiredID(LCSSAID);
107 AU.addPreservedID(LCSSAID);
108 AU.addPreserved<DominatorTree>();
109 AU.addPreserved<DominanceFrontier>();
114 /// RemoveLoopFromWorklist - If the specified loop is on the loop worklist,
116 void RemoveLoopFromWorklist(Loop *L) {
117 std::vector<Loop*>::iterator I = std::find(LoopProcessWorklist.begin(),
118 LoopProcessWorklist.end(), L);
119 if (I != LoopProcessWorklist.end())
120 LoopProcessWorklist.erase(I);
123 void initLoopData() {
124 loopHeader = currentLoop->getHeader();
125 loopPreheader = currentLoop->getLoopPreheader();
128 /// Split all of the edges from inside the loop to their exit blocks.
129 /// Update the appropriate Phi nodes as we do so.
130 void SplitExitEdges(Loop *L, const SmallVector<BasicBlock *, 8> &ExitBlocks,
131 SmallVector<BasicBlock *, 8> &MiddleBlocks);
133 /// If BB's dominance frontier has a member that is not part of loop L then
134 /// remove it. Add NewDFMember in BB's dominance frontier.
135 void ReplaceLoopExternalDFMember(Loop *L, BasicBlock *BB,
136 BasicBlock *NewDFMember);
138 bool UnswitchIfProfitable(Value *LoopCond, Constant *Val);
139 unsigned getLoopUnswitchCost(Value *LIC);
140 void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
141 BasicBlock *ExitBlock);
142 void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
144 void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
145 Constant *Val, bool isEqual);
147 void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
148 BasicBlock *TrueDest,
149 BasicBlock *FalseDest,
150 Instruction *InsertPt);
152 void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
153 void RemoveBlockIfDead(BasicBlock *BB,
154 std::vector<Instruction*> &Worklist, Loop *l);
155 void RemoveLoopFromHierarchy(Loop *L);
156 bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = 0,
157 BasicBlock **LoopExit = 0);
161 char LoopUnswitch::ID = 0;
162 static RegisterPass<LoopUnswitch> X("loop-unswitch", "Unswitch loops");
164 LoopPass *llvm::createLoopUnswitchPass(bool Os) {
165 return new LoopUnswitch(Os);
168 /// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
169 /// invariant in the loop, or has an invariant piece, return the invariant.
170 /// Otherwise, return null.
171 static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
172 // Constants should be folded, not unswitched on!
173 if (isa<Constant>(Cond)) return false;
175 // TODO: Handle: br (VARIANT|INVARIANT).
176 // TODO: Hoist simple expressions out of loops.
177 if (L->isLoopInvariant(Cond)) return Cond;
179 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond))
180 if (BO->getOpcode() == Instruction::And ||
181 BO->getOpcode() == Instruction::Or) {
182 // If either the left or right side is invariant, we can unswitch on this,
183 // which will cause the branch to go away in one loop and the condition to
184 // simplify in the other one.
185 if (Value *LHS = FindLIVLoopCondition(BO->getOperand(0), L, Changed))
187 if (Value *RHS = FindLIVLoopCondition(BO->getOperand(1), L, Changed))
194 bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
195 LI = &getAnalysis<LoopInfo>();
197 DF = getAnalysisToUpdate<DominanceFrontier>();
198 DT = getAnalysisToUpdate<DominatorTree>();
200 bool Changed = false;
203 assert(currentLoop->isLCSSAForm());
205 Changed |= processCurrentLoop();
211 /// processCurrentLoop - Do actual work and unswitch loop if possible
213 bool LoopUnswitch::processCurrentLoop() {
214 bool Changed = false;
216 // Loop over all of the basic blocks in the loop. If we find an interior
217 // block that is branching on a loop-invariant condition, we can unswitch this
219 for (Loop::block_iterator I = currentLoop->block_begin(),
220 E = currentLoop->block_end();
222 TerminatorInst *TI = (*I)->getTerminator();
223 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
224 // If this isn't branching on an invariant condition, we can't unswitch
226 if (BI->isConditional()) {
227 // See if this, or some part of it, is loop invariant. If so, we can
228 // unswitch on it if we desire.
229 Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
230 currentLoop, Changed);
231 if (LoopCond && UnswitchIfProfitable(LoopCond,
232 ConstantInt::getTrue())) {
237 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
238 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
239 currentLoop, Changed);
240 if (LoopCond && SI->getNumCases() > 1) {
241 // Find a value to unswitch on:
242 // FIXME: this should chose the most expensive case!
243 Constant *UnswitchVal = SI->getCaseValue(1);
244 // Do not process same value again and again.
245 if (!UnswitchedVals.insert(UnswitchVal))
248 if (UnswitchIfProfitable(LoopCond, UnswitchVal)) {
255 // Scan the instructions to check for unswitchable values.
256 for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
258 if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
259 Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
260 currentLoop, Changed);
261 if (LoopCond && UnswitchIfProfitable(LoopCond,
262 ConstantInt::getTrue())) {
271 /// isTrivialLoopExitBlock - Check to see if all paths from BB either:
272 /// 1. Exit the loop with no side effects.
273 /// 2. Branch to the latch block with no side-effects.
275 /// If these conditions are true, we return true and set ExitBB to the block we
278 static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
280 std::set<BasicBlock*> &Visited) {
281 if (!Visited.insert(BB).second) {
282 // Already visited and Ok, end of recursion.
284 } else if (!L->contains(BB)) {
285 // Otherwise, this is a loop exit, this is fine so long as this is the
287 if (ExitBB != 0) return false;
292 // Otherwise, this is an unvisited intra-loop node. Check all successors.
293 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
294 // Check to see if the successor is a trivial loop exit.
295 if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
299 // Okay, everything after this looks good, check to make sure that this block
300 // doesn't include any side effects.
301 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
302 if (I->mayWriteToMemory())
308 /// isTrivialLoopExitBlock - Return true if the specified block unconditionally
309 /// leads to an exit from the specified loop, and has no side-effects in the
310 /// process. If so, return the block that is exited to, otherwise return null.
311 static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
312 std::set<BasicBlock*> Visited;
313 Visited.insert(L->getHeader()); // Branches to header are ok.
314 BasicBlock *ExitBB = 0;
315 if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
320 /// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
321 /// trivial: that is, that the condition controls whether or not the loop does
322 /// anything at all. If this is a trivial condition, unswitching produces no
323 /// code duplications (equivalently, it produces a simpler loop and a new empty
324 /// loop, which gets deleted).
326 /// If this is a trivial condition, return true, otherwise return false. When
327 /// returning true, this sets Cond and Val to the condition that controls the
328 /// trivial condition: when Cond dynamically equals Val, the loop is known to
329 /// exit. Finally, this sets LoopExit to the BB that the loop exits to when
332 bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
333 BasicBlock **LoopExit) {
334 BasicBlock *Header = currentLoop->getHeader();
335 TerminatorInst *HeaderTerm = Header->getTerminator();
337 BasicBlock *LoopExitBB = 0;
338 if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
339 // If the header block doesn't end with a conditional branch on Cond, we
341 if (!BI->isConditional() || BI->getCondition() != Cond)
344 // Check to see if a successor of the branch is guaranteed to go to the
345 // latch block or exit through a one exit block without having any
346 // side-effects. If so, determine the value of Cond that causes it to do
348 if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
349 BI->getSuccessor(0)))) {
350 if (Val) *Val = ConstantInt::getTrue();
351 } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
352 BI->getSuccessor(1)))) {
353 if (Val) *Val = ConstantInt::getFalse();
355 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
356 // If this isn't a switch on Cond, we can't handle it.
357 if (SI->getCondition() != Cond) return false;
359 // Check to see if a successor of the switch is guaranteed to go to the
360 // latch block or exit through a one exit block without having any
361 // side-effects. If so, determine the value of Cond that causes it to do
362 // this. Note that we can't trivially unswitch on the default case.
363 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i)
364 if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
365 SI->getSuccessor(i)))) {
366 // Okay, we found a trivial case, remember the value that is trivial.
367 if (Val) *Val = SI->getCaseValue(i);
372 // If we didn't find a single unique LoopExit block, or if the loop exit block
373 // contains phi nodes, this isn't trivial.
374 if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
375 return false; // Can't handle this.
377 if (LoopExit) *LoopExit = LoopExitBB;
379 // We already know that nothing uses any scalar values defined inside of this
380 // loop. As such, we just have to check to see if this loop will execute any
381 // side-effecting instructions (e.g. stores, calls, volatile loads) in the
382 // part of the loop that the code *would* execute. We already checked the
383 // tail, check the header now.
384 for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
385 if (I->mayWriteToMemory())
390 /// getLoopUnswitchCost - Return the cost (code size growth) that will happen if
391 /// we choose to unswitch current loop on the specified value.
393 unsigned LoopUnswitch::getLoopUnswitchCost(Value *LIC) {
394 // If the condition is trivial, always unswitch. There is no code growth for
396 if (IsTrivialUnswitchCondition(LIC))
399 // FIXME: This is really overly conservative. However, more liberal
400 // estimations have thus far resulted in excessive unswitching, which is bad
401 // both in compile time and in code size. This should be replaced once
402 // someone figures out how a good estimation.
403 return currentLoop->getBlocks().size();
406 // FIXME: this is brain dead. It should take into consideration code
408 for (Loop::block_iterator I = currentLoop->block_begin(),
409 E = currentLoop->block_end();
412 // Do not include empty blocks in the cost calculation. This happen due to
413 // loop canonicalization and will be removed.
414 if (BB->begin() == BasicBlock::iterator(BB->getTerminator()))
417 // Count basic blocks.
424 /// UnswitchIfProfitable - We have found that we can unswitch currentLoop when
425 /// LoopCond == Val to simplify the loop. If we decide that this is profitable,
426 /// unswitch the loop, reprocess the pieces, then return true.
427 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val){
428 // Check to see if it would be profitable to unswitch current loop.
429 unsigned Cost = getLoopUnswitchCost(LoopCond);
431 // Do not do non-trivial unswitch while optimizing for size.
432 if (Cost && OptimizeForSize)
435 if (Cost > Threshold) {
436 // FIXME: this should estimate growth by the amount of code shared by the
437 // resultant unswitched loops.
439 DOUT << "NOT unswitching loop %"
440 << currentLoop->getHeader()->getName() << ", cost too high: "
441 << currentLoop->getBlocks().size() << "\n";
448 BasicBlock *ExitBlock;
449 if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
450 UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock);
452 UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
458 // RemapInstruction - Convert the instruction operands from referencing the
459 // current values into those specified by ValueMap.
461 static inline void RemapInstruction(Instruction *I,
462 DenseMap<const Value *, Value*> &ValueMap) {
463 for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
464 Value *Op = I->getOperand(op);
465 DenseMap<const Value *, Value*>::iterator It = ValueMap.find(Op);
466 if (It != ValueMap.end()) Op = It->second;
467 I->setOperand(op, Op);
471 // CloneDomInfo - NewBB is cloned from Orig basic block. Now clone Dominator
474 // If Orig block's immediate dominator is mapped in VM then use corresponding
475 // immediate dominator from the map. Otherwise Orig block's dominator is also
476 // NewBB's dominator.
478 // OrigPreheader is loop pre-header before this pass started
479 // updating CFG. NewPrehader is loops new pre-header. However, after CFG
480 // manipulation, loop L may not exist. So rely on input parameter NewPreheader.
481 static void CloneDomInfo(BasicBlock *NewBB, BasicBlock *Orig,
482 BasicBlock *NewPreheader, BasicBlock *OrigPreheader,
483 BasicBlock *OrigHeader,
484 DominatorTree *DT, DominanceFrontier *DF,
485 DenseMap<const Value*, Value*> &VM) {
487 // If NewBB alreay has found its place in domiantor tree then no need to do
489 if (DT->getNode(NewBB))
492 // If Orig does not have any immediate domiantor then its clone, NewBB, does
493 // not need any immediate dominator.
494 DomTreeNode *OrigNode = DT->getNode(Orig);
497 DomTreeNode *OrigIDomNode = OrigNode->getIDom();
501 BasicBlock *OrigIDom = NULL;
503 // If Orig is original loop header then its immediate dominator is
505 if (Orig == OrigHeader)
506 OrigIDom = NewPreheader;
508 // If Orig is new pre-header then its immediate dominator is
509 // original pre-header.
510 else if (Orig == NewPreheader)
511 OrigIDom = OrigPreheader;
513 // Otherwise ask DT to find Orig's immediate dominator.
515 OrigIDom = OrigIDomNode->getBlock();
517 // Initially use Orig's immediate dominator as NewBB's immediate dominator.
518 BasicBlock *NewIDom = OrigIDom;
519 DenseMap<const Value*, Value*>::iterator I = VM.find(OrigIDom);
521 NewIDom = cast<BasicBlock>(I->second);
523 // If NewIDom does not have corresponding dominatore tree node then
525 if (!DT->getNode(NewIDom))
526 CloneDomInfo(NewIDom, OrigIDom, NewPreheader, OrigPreheader,
527 OrigHeader, DT, DF, VM);
530 DT->addNewBlock(NewBB, NewIDom);
532 // Copy cloned dominance frontiner set
533 DominanceFrontier::DomSetType NewDFSet;
535 DominanceFrontier::iterator DFI = DF->find(Orig);
536 if ( DFI != DF->end()) {
537 DominanceFrontier::DomSetType S = DFI->second;
538 for (DominanceFrontier::DomSetType::iterator I = S.begin(), E = S.end();
541 DenseMap<const Value*, Value*>::iterator IDM = VM.find(BB);
543 NewDFSet.insert(cast<BasicBlock>(IDM->second));
548 DF->addBasicBlock(NewBB, NewDFSet);
552 /// CloneLoop - Recursively clone the specified loop and all of its children,
553 /// mapping the blocks with the specified map.
554 static Loop *CloneLoop(Loop *L, Loop *PL, DenseMap<const Value*, Value*> &VM,
555 LoopInfo *LI, LPPassManager *LPM) {
556 Loop *New = new Loop();
558 LPM->insertLoop(New, PL);
560 // Add all of the blocks in L to the new loop.
561 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
563 if (LI->getLoopFor(*I) == L)
564 New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), LI->getBase());
566 // Add all of the subloops to the new loop.
567 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
568 CloneLoop(*I, New, VM, LI, LPM);
573 /// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
574 /// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
575 /// code immediately before InsertPt.
576 void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
577 BasicBlock *TrueDest,
578 BasicBlock *FalseDest,
579 Instruction *InsertPt) {
580 // Insert a conditional branch on LIC to the two preheaders. The original
581 // code is the true version and the new code is the false version.
582 Value *BranchVal = LIC;
583 if (!isa<ConstantInt>(Val) || Val->getType() != Type::Int1Ty)
584 BranchVal = new ICmpInst(ICmpInst::ICMP_EQ, LIC, Val, "tmp", InsertPt);
585 else if (Val != ConstantInt::getTrue())
586 // We want to enter the new loop when the condition is true.
587 std::swap(TrueDest, FalseDest);
589 // Insert the new branch.
590 BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt);
594 /// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
595 /// condition in it (a cond branch from its header block to its latch block,
596 /// where the path through the loop that doesn't execute its body has no
597 /// side-effects), unswitch it. This doesn't involve any code duplication, just
598 /// moving the conditional branch outside of the loop and updating loop info.
599 void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
601 BasicBlock *ExitBlock) {
602 DOUT << "loop-unswitch: Trivial-Unswitch loop %"
603 << loopHeader->getName() << " [" << L->getBlocks().size()
604 << " blocks] in Function " << L->getHeader()->getParent()->getName()
605 << " on cond: " << *Val << " == " << *Cond << "\n";
607 // First step, split the preheader, so that we know that there is a safe place
608 // to insert the conditional branch. We will change loopPreheader to have a
609 // conditional branch on Cond.
610 BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, this);
612 // Now that we have a place to insert the conditional branch, create a place
613 // to branch to: this is the exit block out of the loop that we should
616 // Split this block now, so that the loop maintains its exit block, and so
617 // that the jump from the preheader can execute the contents of the exit block
618 // without actually branching to it (the exit block should be dominated by the
619 // loop header, not the preheader).
620 assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
621 BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this);
623 // Okay, now we have a position to branch from and a position to branch to,
624 // insert the new conditional branch.
625 EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
626 loopPreheader->getTerminator());
628 DT->changeImmediateDominator(NewExit, loopPreheader);
629 DT->changeImmediateDominator(NewPH, loopPreheader);
633 // NewExit is now part of NewPH and Loop Header's dominance
635 DominanceFrontier::iterator DFI = DF->find(NewPH);
636 if (DFI != DF->end())
637 DF->addToFrontier(DFI, NewExit);
638 DFI = DF->find(loopHeader);
639 DF->addToFrontier(DFI, NewExit);
641 // ExitBlock does not have successors then NewExit is part of
642 // its dominance frontier.
643 if (succ_begin(ExitBlock) == succ_end(ExitBlock)) {
644 DFI = DF->find(ExitBlock);
645 DF->addToFrontier(DFI, NewExit);
648 LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L);
649 loopPreheader->getTerminator()->eraseFromParent();
651 // We need to reprocess this loop, it could be unswitched again.
654 // Now that we know that the loop is never entered when this condition is a
655 // particular value, rewrite the loop with this info. We know that this will
656 // at least eliminate the old branch.
657 RewriteLoopBodyWithConditionConstant(L, Cond, Val, false);
661 /// ReplaceLoopExternalDFMember -
662 /// If BB's dominance frontier has a member that is not part of loop L then
663 /// remove it. Add NewDFMember in BB's dominance frontier.
664 void LoopUnswitch::ReplaceLoopExternalDFMember(Loop *L, BasicBlock *BB,
665 BasicBlock *NewDFMember) {
667 DominanceFrontier::iterator DFI = DF->find(BB);
668 if (DFI == DF->end())
671 DominanceFrontier::DomSetType &DFSet = DFI->second;
672 for (DominanceFrontier::DomSetType::iterator DI = DFSet.begin(),
673 DE = DFSet.end(); DI != DE;) {
674 BasicBlock *B = *DI++;
678 DF->removeFromFrontier(DFI, B);
682 DF->addToFrontier(DFI, NewDFMember);
685 /// SplitExitEdges - Split all of the edges from inside the loop to their exit
686 /// blocks. Update the appropriate Phi nodes as we do so.
687 void LoopUnswitch::SplitExitEdges(Loop *L,
688 const SmallVector<BasicBlock *, 8> &ExitBlocks,
689 SmallVector<BasicBlock *, 8> &MiddleBlocks) {
691 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
692 BasicBlock *ExitBlock = ExitBlocks[i];
693 std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock));
695 for (unsigned j = 0, e = Preds.size(); j != e; ++j) {
696 BasicBlock* MiddleBlock = SplitEdge(Preds[j], ExitBlock, this);
697 MiddleBlocks.push_back(MiddleBlock);
698 BasicBlock* StartBlock = Preds[j];
699 BasicBlock* EndBlock;
700 if (MiddleBlock->getSinglePredecessor() == ExitBlock) {
701 EndBlock = MiddleBlock;
702 MiddleBlock = EndBlock->getSinglePredecessor();;
704 EndBlock = ExitBlock;
707 OrigLoopExitMap[StartBlock] = EndBlock;
709 std::set<PHINode*> InsertedPHIs;
710 PHINode* OldLCSSA = 0;
711 for (BasicBlock::iterator I = EndBlock->begin();
712 (OldLCSSA = dyn_cast<PHINode>(I)); ++I) {
713 Value* OldValue = OldLCSSA->getIncomingValueForBlock(MiddleBlock);
714 PHINode* NewLCSSA = PHINode::Create(OldLCSSA->getType(),
715 OldLCSSA->getName() + ".us-lcssa",
716 MiddleBlock->getTerminator());
717 NewLCSSA->addIncoming(OldValue, StartBlock);
718 OldLCSSA->setIncomingValue(OldLCSSA->getBasicBlockIndex(MiddleBlock),
720 InsertedPHIs.insert(NewLCSSA);
723 BasicBlock::iterator InsertPt = EndBlock->getFirstNonPHI();
724 for (BasicBlock::iterator I = MiddleBlock->begin();
725 (OldLCSSA = dyn_cast<PHINode>(I)) && InsertedPHIs.count(OldLCSSA) == 0;
727 PHINode *NewLCSSA = PHINode::Create(OldLCSSA->getType(),
728 OldLCSSA->getName() + ".us-lcssa",
730 OldLCSSA->replaceAllUsesWith(NewLCSSA);
731 NewLCSSA->addIncoming(OldLCSSA, MiddleBlock);
735 // StartBlock -- > MiddleBlock -- > EndBlock
736 // StartBlock is loop exiting block. EndBlock will become merge point
737 // of two loop exits after loop unswitch.
739 // If StartBlock's DF member includes a block that is not loop member
740 // then replace that DF member with EndBlock.
742 // If MiddleBlock's DF member includes a block that is not loop member
743 // tnen replace that DF member with EndBlock.
745 ReplaceLoopExternalDFMember(L, StartBlock, EndBlock);
746 ReplaceLoopExternalDFMember(L, MiddleBlock, EndBlock);
753 /// UnswitchNontrivialCondition - We determined that the loop is profitable
754 /// to unswitch when LIC equal Val. Split it into loop versions and test the
755 /// condition outside of either loop. Return the loops created as Out1/Out2.
756 void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
758 Function *F = loopHeader->getParent();
759 DOUT << "loop-unswitch: Unswitching loop %"
760 << loopHeader->getName() << " [" << L->getBlocks().size()
761 << " blocks] in Function " << F->getName()
762 << " when '" << *Val << "' == " << *LIC << "\n";
764 // LoopBlocks contains all of the basic blocks of the loop, including the
765 // preheader of the loop, the body of the loop, and the exit blocks of the
766 // loop, in that order.
767 std::vector<BasicBlock*> LoopBlocks;
769 // First step, split the preheader and exit blocks, and add these blocks to
770 // the LoopBlocks list.
771 BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, this);
772 LoopBlocks.push_back(NewPreheader);
774 // We want the loop to come after the preheader, but before the exit blocks.
775 LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
777 SmallVector<BasicBlock*, 8> ExitBlocks;
778 L->getUniqueExitBlocks(ExitBlocks);
780 // Split all of the edges from inside the loop to their exit blocks. Update
781 // the appropriate Phi nodes as we do so.
782 SmallVector<BasicBlock *,8> MiddleBlocks;
783 SplitExitEdges(L, ExitBlocks, MiddleBlocks);
785 // The exit blocks may have been changed due to edge splitting, recompute.
787 L->getUniqueExitBlocks(ExitBlocks);
789 // Add exit blocks to the loop blocks.
790 LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
792 // Next step, clone all of the basic blocks that make up the loop (including
793 // the loop preheader and exit blocks), keeping track of the mapping between
794 // the instructions and blocks.
795 std::vector<BasicBlock*> NewBlocks;
796 NewBlocks.reserve(LoopBlocks.size());
797 DenseMap<const Value*, Value*> ValueMap;
798 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
799 BasicBlock *New = CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F);
800 NewBlocks.push_back(New);
801 ValueMap[LoopBlocks[i]] = New; // Keep the BB mapping.
802 LPM->cloneBasicBlockSimpleAnalysis(LoopBlocks[i], New, L);
805 // OutSiders are basic block that are dominated by original header and
806 // at the same time they are not part of loop.
807 SmallPtrSet<BasicBlock *, 8> OutSiders;
809 DomTreeNode *OrigHeaderNode = DT->getNode(loopHeader);
810 for(std::vector<DomTreeNode*>::iterator DI = OrigHeaderNode->begin(),
811 DE = OrigHeaderNode->end(); DI != DE; ++DI) {
812 BasicBlock *B = (*DI)->getBlock();
814 DenseMap<const Value*, Value*>::iterator VI = ValueMap.find(B);
815 if (VI == ValueMap.end())
820 // Splice the newly inserted blocks into the function right before the
821 // original preheader.
822 F->getBasicBlockList().splice(LoopBlocks[0], F->getBasicBlockList(),
823 NewBlocks[0], F->end());
825 // Now we create the new Loop object for the versioned loop.
826 Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI, LPM);
827 Loop *ParentLoop = L->getParentLoop();
829 // Make sure to add the cloned preheader and exit blocks to the parent loop
831 ParentLoop->addBasicBlockToLoop(NewBlocks[0], LI->getBase());
834 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
835 BasicBlock *NewExit = cast<BasicBlock>(ValueMap[ExitBlocks[i]]);
836 // The new exit block should be in the same loop as the old one.
837 if (Loop *ExitBBLoop = LI->getLoopFor(ExitBlocks[i]))
838 ExitBBLoop->addBasicBlockToLoop(NewExit, LI->getBase());
840 assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
841 "Exit block should have been split to have one successor!");
842 BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
844 // If the successor of the exit block had PHI nodes, add an entry for
847 for (BasicBlock::iterator I = ExitSucc->begin();
848 (PN = dyn_cast<PHINode>(I)); ++I) {
849 Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
850 DenseMap<const Value *, Value*>::iterator It = ValueMap.find(V);
851 if (It != ValueMap.end()) V = It->second;
852 PN->addIncoming(V, NewExit);
856 // Rewrite the code to refer to itself.
857 for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
858 for (BasicBlock::iterator I = NewBlocks[i]->begin(),
859 E = NewBlocks[i]->end(); I != E; ++I)
860 RemapInstruction(I, ValueMap);
862 // Rewrite the original preheader to select between versions of the loop.
863 BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator());
864 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
865 "Preheader splitting did not work correctly!");
867 // Emit the new branch that selects between the two versions of this loop.
868 EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
869 LPM->deleteSimpleAnalysisValue(OldBR, L);
870 OldBR->eraseFromParent();
872 // Update dominator info
875 SmallVector<BasicBlock *,4> ExitingBlocks;
876 L->getExitingBlocks(ExitingBlocks);
878 // Clone dominator info for all cloned basic block.
879 for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
880 BasicBlock *LBB = LoopBlocks[i];
881 BasicBlock *NBB = NewBlocks[i];
882 CloneDomInfo(NBB, LBB, NewPreheader, loopPreheader,
883 loopHeader, DT, DF, ValueMap);
885 // If LBB's dominance frontier includes DFMember
886 // such that DFMember is also a member of LoopDF then
887 // - Remove DFMember from LBB's dominance frontier
888 // - Copy loop exiting blocks', that are dominated by BB,
889 // dominance frontier member in BB's dominance frontier
891 DominanceFrontier::iterator LBBI = DF->find(LBB);
892 DominanceFrontier::iterator NBBI = DF->find(NBB);
893 if (LBBI == DF->end())
896 DominanceFrontier::DomSetType &LBSet = LBBI->second;
897 for (DominanceFrontier::DomSetType::iterator LI = LBSet.begin(),
898 LE = LBSet.end(); LI != LE; /* NULL */) {
899 BasicBlock *B = *LI++;
900 if (B == LBB && B == loopHeader)
902 bool removeB = false;
903 if (!LoopDF.count(B))
906 // If LBB dominates loop exits then insert loop exit block's DF
908 for(SmallVector<BasicBlock *, 4>::iterator
909 LExitI = ExitingBlocks.begin(),
910 LExitE = ExitingBlocks.end(); LExitI != LExitE; ++LExitI) {
911 BasicBlock *E = *LExitI;
913 if (!DT->dominates(LBB,E))
916 DenseMap<BasicBlock *, BasicBlock *>::iterator DFBI =
917 OrigLoopExitMap.find(E);
918 if (DFBI == OrigLoopExitMap.end())
921 BasicBlock *DFB = DFBI->second;
922 DF->addToFrontier(LBBI, DFB);
923 DF->addToFrontier(NBBI, DFB);
927 // If B's replacement is inserted in DF then now is the time to remove
930 DF->removeFromFrontier(LBBI, B);
932 DF->removeFromFrontier(NBBI, cast<BasicBlock>(ValueMap[B]));
934 DF->removeFromFrontier(NBBI, B);
940 // MiddleBlocks are dominated by original pre header. SplitEdge updated
941 // MiddleBlocks' dominance frontier appropriately.
942 for (unsigned i = 0, e = MiddleBlocks.size(); i != e; ++i) {
943 BasicBlock *MBB = MiddleBlocks[i];
944 if (!MBB->getSinglePredecessor())
945 DT->changeImmediateDominator(MBB, loopPreheader);
948 // All Outsiders are now dominated by original pre header.
949 for (SmallPtrSet<BasicBlock *, 8>::iterator OI = OutSiders.begin(),
950 OE = OutSiders.end(); OI != OE; ++OI) {
951 BasicBlock *OB = *OI;
952 DT->changeImmediateDominator(OB, loopPreheader);
955 // New loop headers are dominated by original preheader
956 DT->changeImmediateDominator(NewBlocks[0], loopPreheader);
957 DT->changeImmediateDominator(LoopBlocks[0], loopPreheader);
960 LoopProcessWorklist.push_back(NewLoop);
963 // Now we rewrite the original code to know that the condition is true and the
964 // new code to know that the condition is false.
965 RewriteLoopBodyWithConditionConstant(L , LIC, Val, false);
967 // It's possible that simplifying one loop could cause the other to be
968 // deleted. If so, don't simplify it.
969 if (!LoopProcessWorklist.empty() && LoopProcessWorklist.back() == NewLoop)
970 RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true);
973 /// RemoveFromWorklist - Remove all instances of I from the worklist vector
975 static void RemoveFromWorklist(Instruction *I,
976 std::vector<Instruction*> &Worklist) {
977 std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(),
979 while (WI != Worklist.end()) {
980 unsigned Offset = WI-Worklist.begin();
982 WI = std::find(Worklist.begin()+Offset, Worklist.end(), I);
986 /// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
987 /// program, replacing all uses with V and update the worklist.
988 static void ReplaceUsesOfWith(Instruction *I, Value *V,
989 std::vector<Instruction*> &Worklist,
990 Loop *L, LPPassManager *LPM) {
991 DOUT << "Replace with '" << *V << "': " << *I;
993 // Add uses to the worklist, which may be dead now.
994 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
995 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
996 Worklist.push_back(Use);
998 // Add users to the worklist which may be simplified now.
999 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
1001 Worklist.push_back(cast<Instruction>(*UI));
1002 LPM->deleteSimpleAnalysisValue(I, L);
1003 RemoveFromWorklist(I, Worklist);
1004 I->replaceAllUsesWith(V);
1005 I->eraseFromParent();
1009 /// RemoveBlockIfDead - If the specified block is dead, remove it, update loop
1010 /// information, and remove any dead successors it has.
1012 void LoopUnswitch::RemoveBlockIfDead(BasicBlock *BB,
1013 std::vector<Instruction*> &Worklist,
1015 if (pred_begin(BB) != pred_end(BB)) {
1016 // This block isn't dead, since an edge to BB was just removed, see if there
1017 // are any easy simplifications we can do now.
1018 if (BasicBlock *Pred = BB->getSinglePredecessor()) {
1019 // If it has one pred, fold phi nodes in BB.
1020 while (isa<PHINode>(BB->begin()))
1021 ReplaceUsesOfWith(BB->begin(),
1022 cast<PHINode>(BB->begin())->getIncomingValue(0),
1025 // If this is the header of a loop and the only pred is the latch, we now
1026 // have an unreachable loop.
1027 if (Loop *L = LI->getLoopFor(BB))
1028 if (loopHeader == BB && L->contains(Pred)) {
1029 // Remove the branch from the latch to the header block, this makes
1030 // the header dead, which will make the latch dead (because the header
1031 // dominates the latch).
1032 LPM->deleteSimpleAnalysisValue(Pred->getTerminator(), L);
1033 Pred->getTerminator()->eraseFromParent();
1034 new UnreachableInst(Pred);
1036 // The loop is now broken, remove it from LI.
1037 RemoveLoopFromHierarchy(L);
1039 // Reprocess the header, which now IS dead.
1040 RemoveBlockIfDead(BB, Worklist, L);
1044 // If pred ends in a uncond branch, add uncond branch to worklist so that
1045 // the two blocks will get merged.
1046 if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator()))
1047 if (BI->isUnconditional())
1048 Worklist.push_back(BI);
1053 DOUT << "Nuking dead block: " << *BB;
1055 // Remove the instructions in the basic block from the worklist.
1056 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
1057 RemoveFromWorklist(I, Worklist);
1059 // Anything that uses the instructions in this basic block should have their
1060 // uses replaced with undefs.
1061 if (!I->use_empty())
1062 I->replaceAllUsesWith(UndefValue::get(I->getType()));
1065 // If this is the edge to the header block for a loop, remove the loop and
1066 // promote all subloops.
1067 if (Loop *BBLoop = LI->getLoopFor(BB)) {
1068 if (BBLoop->getLoopLatch() == BB)
1069 RemoveLoopFromHierarchy(BBLoop);
1072 // Remove the block from the loop info, which removes it from any loops it
1074 LI->removeBlock(BB);
1077 // Remove phi node entries in successors for this block.
1078 TerminatorInst *TI = BB->getTerminator();
1079 std::vector<BasicBlock*> Succs;
1080 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
1081 Succs.push_back(TI->getSuccessor(i));
1082 TI->getSuccessor(i)->removePredecessor(BB);
1085 // Unique the successors, remove anything with multiple uses.
1086 std::sort(Succs.begin(), Succs.end());
1087 Succs.erase(std::unique(Succs.begin(), Succs.end()), Succs.end());
1089 // Remove the basic block, including all of the instructions contained in it.
1090 LPM->deleteSimpleAnalysisValue(BB, L);
1091 BB->eraseFromParent();
1092 // Remove successor blocks here that are not dead, so that we know we only
1093 // have dead blocks in this list. Nondead blocks have a way of becoming dead,
1094 // then getting removed before we revisit them, which is badness.
1096 for (unsigned i = 0; i != Succs.size(); ++i)
1097 if (pred_begin(Succs[i]) != pred_end(Succs[i])) {
1098 // One exception is loop headers. If this block was the preheader for a
1099 // loop, then we DO want to visit the loop so the loop gets deleted.
1100 // We know that if the successor is a loop header, that this loop had to
1101 // be the preheader: the case where this was the latch block was handled
1102 // above and headers can only have two predecessors.
1103 if (!LI->isLoopHeader(Succs[i])) {
1104 Succs.erase(Succs.begin()+i);
1109 for (unsigned i = 0, e = Succs.size(); i != e; ++i)
1110 RemoveBlockIfDead(Succs[i], Worklist, L);
1113 /// RemoveLoopFromHierarchy - We have discovered that the specified loop has
1114 /// become unwrapped, either because the backedge was deleted, or because the
1115 /// edge into the header was removed. If the edge into the header from the
1116 /// latch block was removed, the loop is unwrapped but subloops are still alive,
1117 /// so they just reparent loops. If the loops are actually dead, they will be
1119 void LoopUnswitch::RemoveLoopFromHierarchy(Loop *L) {
1120 LPM->deleteLoopFromQueue(L);
1121 RemoveLoopFromWorklist(L);
1126 // RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
1127 // the value specified by Val in the specified loop, or we know it does NOT have
1128 // that value. Rewrite any uses of LIC or of properties correlated to it.
1129 void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
1132 assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
1134 // FIXME: Support correlated properties, like:
1141 // FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
1142 // selects, switches.
1143 std::vector<User*> Users(LIC->use_begin(), LIC->use_end());
1144 std::vector<Instruction*> Worklist;
1146 // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
1147 // in the loop with the appropriate one directly.
1148 if (IsEqual || (isa<ConstantInt>(Val) && Val->getType() == Type::Int1Ty)) {
1153 Replacement = ConstantInt::get(Type::Int1Ty,
1154 !cast<ConstantInt>(Val)->getZExtValue());
1156 for (unsigned i = 0, e = Users.size(); i != e; ++i)
1157 if (Instruction *U = cast<Instruction>(Users[i])) {
1158 if (!L->contains(U->getParent()))
1160 U->replaceUsesOfWith(LIC, Replacement);
1161 Worklist.push_back(U);
1164 // Otherwise, we don't know the precise value of LIC, but we do know that it
1165 // is certainly NOT "Val". As such, simplify any uses in the loop that we
1166 // can. This case occurs when we unswitch switch statements.
1167 for (unsigned i = 0, e = Users.size(); i != e; ++i)
1168 if (Instruction *U = cast<Instruction>(Users[i])) {
1169 if (!L->contains(U->getParent()))
1172 Worklist.push_back(U);
1174 // If we know that LIC is not Val, use this info to simplify code.
1175 if (SwitchInst *SI = dyn_cast<SwitchInst>(U)) {
1176 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
1177 if (SI->getCaseValue(i) == Val) {
1178 // Found a dead case value. Don't remove PHI nodes in the
1179 // successor if they become single-entry, those PHI nodes may
1180 // be in the Users list.
1182 // FIXME: This is a hack. We need to keep the successor around
1183 // and hooked up so as to preserve the loop structure, because
1184 // trying to update it is complicated. So instead we preserve the
1185 // loop structure and put the block on an dead code path.
1187 BasicBlock* Old = SI->getParent();
1188 BasicBlock* Split = SplitBlock(Old, SI, this);
1190 Instruction* OldTerm = Old->getTerminator();
1191 BranchInst::Create(Split, SI->getSuccessor(i),
1192 ConstantInt::getTrue(), OldTerm);
1194 LPM->deleteSimpleAnalysisValue(Old->getTerminator(), L);
1195 Old->getTerminator()->eraseFromParent();
1198 for (BasicBlock::iterator II = SI->getSuccessor(i)->begin();
1199 (PN = dyn_cast<PHINode>(II)); ++II) {
1200 Value *InVal = PN->removeIncomingValue(Split, false);
1201 PN->addIncoming(InVal, Old);
1210 // TODO: We could do other simplifications, for example, turning
1211 // LIC == Val -> false.
1215 SimplifyCode(Worklist, L);
1218 /// SimplifyCode - Okay, now that we have simplified some instructions in the
1219 /// loop, walk over it and constant prop, dce, and fold control flow where
1220 /// possible. Note that this is effectively a very simple loop-structure-aware
1221 /// optimizer. During processing of this loop, L could very well be deleted, so
1222 /// it must not be used.
1224 /// FIXME: When the loop optimizer is more mature, separate this out to a new
1227 void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
1228 while (!Worklist.empty()) {
1229 Instruction *I = Worklist.back();
1230 Worklist.pop_back();
1232 // Simple constant folding.
1233 if (Constant *C = ConstantFoldInstruction(I)) {
1234 ReplaceUsesOfWith(I, C, Worklist, L, LPM);
1239 if (isInstructionTriviallyDead(I)) {
1240 DOUT << "Remove dead instruction '" << *I;
1242 // Add uses to the worklist, which may be dead now.
1243 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1244 if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
1245 Worklist.push_back(Use);
1246 LPM->deleteSimpleAnalysisValue(I, L);
1247 RemoveFromWorklist(I, Worklist);
1248 I->eraseFromParent();
1253 // Special case hacks that appear commonly in unswitched code.
1254 switch (I->getOpcode()) {
1255 case Instruction::Select:
1256 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(0))) {
1257 ReplaceUsesOfWith(I, I->getOperand(!CB->getZExtValue()+1), Worklist, L,
1262 case Instruction::And:
1263 if (isa<ConstantInt>(I->getOperand(0)) &&
1264 I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS
1265 cast<BinaryOperator>(I)->swapOperands();
1266 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1)))
1267 if (CB->getType() == Type::Int1Ty) {
1268 if (CB->isOne()) // X & 1 -> X
1269 ReplaceUsesOfWith(I, I->getOperand(0), Worklist, L, LPM);
1271 ReplaceUsesOfWith(I, I->getOperand(1), Worklist, L, LPM);
1275 case Instruction::Or:
1276 if (isa<ConstantInt>(I->getOperand(0)) &&
1277 I->getOperand(0)->getType() == Type::Int1Ty) // constant -> RHS
1278 cast<BinaryOperator>(I)->swapOperands();
1279 if (ConstantInt *CB = dyn_cast<ConstantInt>(I->getOperand(1)))
1280 if (CB->getType() == Type::Int1Ty) {
1281 if (CB->isOne()) // X | 1 -> 1
1282 ReplaceUsesOfWith(I, I->getOperand(1), Worklist, L, LPM);
1284 ReplaceUsesOfWith(I, I->getOperand(0), Worklist, L, LPM);
1288 case Instruction::Br: {
1289 BranchInst *BI = cast<BranchInst>(I);
1290 if (BI->isUnconditional()) {
1291 // If BI's parent is the only pred of the successor, fold the two blocks
1293 BasicBlock *Pred = BI->getParent();
1294 BasicBlock *Succ = BI->getSuccessor(0);
1295 BasicBlock *SinglePred = Succ->getSinglePredecessor();
1296 if (!SinglePred) continue; // Nothing to do.
1297 assert(SinglePred == Pred && "CFG broken");
1299 DOUT << "Merging blocks: " << Pred->getName() << " <- "
1300 << Succ->getName() << "\n";
1302 // Resolve any single entry PHI nodes in Succ.
1303 while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
1304 ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist, L, LPM);
1306 // Move all of the successor contents from Succ to Pred.
1307 Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
1309 LPM->deleteSimpleAnalysisValue(BI, L);
1310 BI->eraseFromParent();
1311 RemoveFromWorklist(BI, Worklist);
1313 // If Succ has any successors with PHI nodes, update them to have
1314 // entries coming from Pred instead of Succ.
1315 Succ->replaceAllUsesWith(Pred);
1317 // Remove Succ from the loop tree.
1318 LI->removeBlock(Succ);
1319 LPM->deleteSimpleAnalysisValue(Succ, L);
1320 Succ->eraseFromParent();
1322 } else if (ConstantInt *CB = dyn_cast<ConstantInt>(BI->getCondition())){
1323 // Conditional branch. Turn it into an unconditional branch, then
1324 // remove dead blocks.
1325 break; // FIXME: Enable.
1327 DOUT << "Folded branch: " << *BI;
1328 BasicBlock *DeadSucc = BI->getSuccessor(CB->getZExtValue());
1329 BasicBlock *LiveSucc = BI->getSuccessor(!CB->getZExtValue());
1330 DeadSucc->removePredecessor(BI->getParent(), true);
1331 Worklist.push_back(BranchInst::Create(LiveSucc, BI));
1332 LPM->deleteSimpleAnalysisValue(BI, L);
1333 BI->eraseFromParent();
1334 RemoveFromWorklist(BI, Worklist);
1337 RemoveBlockIfDead(DeadSucc, Worklist, L);