1 //===- JumpThreading.cpp - Thread control through conditional blocks ------===//
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 file implements the Jump Threading pass.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "jump-threading"
15 #include "llvm/Transforms/Scalar.h"
16 #include "llvm/IntrinsicInst.h"
17 #include "llvm/LLVMContext.h"
18 #include "llvm/Pass.h"
19 #include "llvm/Analysis/InstructionSimplify.h"
20 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
21 #include "llvm/Transforms/Utils/Local.h"
22 #include "llvm/Transforms/Utils/SSAUpdater.h"
23 #include "llvm/Target/TargetData.h"
24 #include "llvm/ADT/DenseMap.h"
25 #include "llvm/ADT/Statistic.h"
26 #include "llvm/ADT/STLExtras.h"
27 #include "llvm/ADT/SmallPtrSet.h"
28 #include "llvm/ADT/SmallSet.h"
29 #include "llvm/Support/CommandLine.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/Support/raw_ostream.h"
34 STATISTIC(NumThreads, "Number of jumps threaded");
35 STATISTIC(NumFolds, "Number of terminators folded");
36 STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi");
38 static cl::opt<unsigned>
39 Threshold("jump-threading-threshold",
40 cl::desc("Max block size to duplicate for jump threading"),
41 cl::init(6), cl::Hidden);
44 /// This pass performs 'jump threading', which looks at blocks that have
45 /// multiple predecessors and multiple successors. If one or more of the
46 /// predecessors of the block can be proven to always jump to one of the
47 /// successors, we forward the edge from the predecessor to the successor by
48 /// duplicating the contents of this block.
50 /// An example of when this can occur is code like this:
57 /// In this case, the unconditional branch at the end of the first if can be
58 /// revectored to the false side of the second if.
60 class JumpThreading : public FunctionPass {
63 SmallPtrSet<BasicBlock*, 16> LoopHeaders;
65 SmallSet<AssertingVH<BasicBlock>, 16> LoopHeaders;
68 static char ID; // Pass identification
69 JumpThreading() : FunctionPass(&ID) {}
71 bool runOnFunction(Function &F);
72 void FindLoopHeaders(Function &F);
74 bool ProcessBlock(BasicBlock *BB);
75 bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock*> &PredBBs,
77 bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
80 typedef SmallVectorImpl<std::pair<ConstantInt*,
81 BasicBlock*> > PredValueInfo;
83 bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,
84 PredValueInfo &Result);
85 bool ProcessThreadableEdges(Instruction *CondInst, BasicBlock *BB);
88 bool ProcessBranchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
89 bool ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
91 bool ProcessJumpOnPHI(PHINode *PN);
93 bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
97 char JumpThreading::ID = 0;
98 static RegisterPass<JumpThreading>
99 X("jump-threading", "Jump Threading");
101 // Public interface to the Jump Threading pass
102 FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); }
104 /// runOnFunction - Top level algorithm.
106 bool JumpThreading::runOnFunction(Function &F) {
107 DEBUG(errs() << "Jump threading on function '" << F.getName() << "'\n");
108 TD = getAnalysisIfAvailable<TargetData>();
112 bool AnotherIteration = true, EverChanged = false;
113 while (AnotherIteration) {
114 AnotherIteration = false;
115 bool Changed = false;
116 for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
118 // Thread all of the branches we can over this block.
119 while (ProcessBlock(BB))
124 // If the block is trivially dead, zap it. This eliminates the successor
125 // edges which simplifies the CFG.
126 if (pred_begin(BB) == pred_end(BB) &&
127 BB != &BB->getParent()->getEntryBlock()) {
128 DEBUG(errs() << " JT: Deleting dead block '" << BB->getName()
129 << "' with terminator: " << *BB->getTerminator() << '\n');
130 LoopHeaders.erase(BB);
133 } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
134 // Can't thread an unconditional jump, but if the block is "almost
135 // empty", we can replace uses of it with uses of the successor and make
137 if (BI->isUnconditional() &&
138 BB != &BB->getParent()->getEntryBlock()) {
139 BasicBlock::iterator BBI = BB->getFirstNonPHI();
140 // Ignore dbg intrinsics.
141 while (isa<DbgInfoIntrinsic>(BBI))
143 // If the terminator is the only non-phi instruction, try to nuke it.
144 if (BBI->isTerminator()) {
145 // Since TryToSimplifyUncondBranchFromEmptyBlock may delete the
146 // block, we have to make sure it isn't in the LoopHeaders set. We
147 // reinsert afterward in the rare case when the block isn't deleted.
148 bool ErasedFromLoopHeaders = LoopHeaders.erase(BB);
150 if (TryToSimplifyUncondBranchFromEmptyBlock(BB))
152 else if (ErasedFromLoopHeaders)
153 LoopHeaders.insert(BB);
158 AnotherIteration = Changed;
159 EverChanged |= Changed;
166 /// getJumpThreadDuplicationCost - Return the cost of duplicating this block to
167 /// thread across it.
168 static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) {
169 /// Ignore PHI nodes, these will be flattened when duplication happens.
170 BasicBlock::const_iterator I = BB->getFirstNonPHI();
172 // Sum up the cost of each instruction until we get to the terminator. Don't
173 // include the terminator because the copy won't include it.
175 for (; !isa<TerminatorInst>(I); ++I) {
176 // Debugger intrinsics don't incur code size.
177 if (isa<DbgInfoIntrinsic>(I)) continue;
179 // If this is a pointer->pointer bitcast, it is free.
180 if (isa<BitCastInst>(I) && isa<PointerType>(I->getType()))
183 // All other instructions count for at least one unit.
186 // Calls are more expensive. If they are non-intrinsic calls, we model them
187 // as having cost of 4. If they are a non-vector intrinsic, we model them
188 // as having cost of 2 total, and if they are a vector intrinsic, we model
189 // them as having cost 1.
190 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
191 if (!isa<IntrinsicInst>(CI))
193 else if (!isa<VectorType>(CI->getType()))
198 // Threading through a switch statement is particularly profitable. If this
199 // block ends in a switch, decrease its cost to make it more likely to happen.
200 if (isa<SwitchInst>(I))
201 Size = Size > 6 ? Size-6 : 0;
206 /// FindLoopHeaders - We do not want jump threading to turn proper loop
207 /// structures into irreducible loops. Doing this breaks up the loop nesting
208 /// hierarchy and pessimizes later transformations. To prevent this from
209 /// happening, we first have to find the loop headers. Here we approximate this
210 /// by finding targets of backedges in the CFG.
212 /// Note that there definitely are cases when we want to allow threading of
213 /// edges across a loop header. For example, threading a jump from outside the
214 /// loop (the preheader) to an exit block of the loop is definitely profitable.
215 /// It is also almost always profitable to thread backedges from within the loop
216 /// to exit blocks, and is often profitable to thread backedges to other blocks
217 /// within the loop (forming a nested loop). This simple analysis is not rich
218 /// enough to track all of these properties and keep it up-to-date as the CFG
219 /// mutates, so we don't allow any of these transformations.
221 void JumpThreading::FindLoopHeaders(Function &F) {
222 SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges;
223 FindFunctionBackedges(F, Edges);
225 for (unsigned i = 0, e = Edges.size(); i != e; ++i)
226 LoopHeaders.insert(const_cast<BasicBlock*>(Edges[i].second));
229 /// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see
230 /// if we can infer that the value is a known ConstantInt in any of our
231 /// predecessors. If so, return the known list of value and pred BB in the
232 /// result vector. If a value is known to be undef, it is returned as null.
234 /// The BB basic block is known to start with a PHI node.
236 /// This returns true if there were any known values.
239 /// TODO: Per PR2563, we could infer value range information about a predecessor
240 /// based on its terminator.
242 ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
243 PHINode *TheFirstPHI = cast<PHINode>(BB->begin());
245 // If V is a constantint, then it is known in all predecessors.
246 if (isa<ConstantInt>(V) || isa<UndefValue>(V)) {
247 ConstantInt *CI = dyn_cast<ConstantInt>(V);
248 Result.resize(TheFirstPHI->getNumIncomingValues());
249 for (unsigned i = 0, e = Result.size(); i != e; ++i)
250 Result[i] = std::make_pair(CI, TheFirstPHI->getIncomingBlock(i));
254 // If V is a non-instruction value, or an instruction in a different block,
255 // then it can't be derived from a PHI.
256 Instruction *I = dyn_cast<Instruction>(V);
257 if (I == 0 || I->getParent() != BB)
260 /// If I is a PHI node, then we know the incoming values for any constants.
261 if (PHINode *PN = dyn_cast<PHINode>(I)) {
262 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
263 Value *InVal = PN->getIncomingValue(i);
264 if (isa<ConstantInt>(InVal) || isa<UndefValue>(InVal)) {
265 ConstantInt *CI = dyn_cast<ConstantInt>(InVal);
266 Result.push_back(std::make_pair(CI, PN->getIncomingBlock(i)));
269 return !Result.empty();
272 SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals, RHSVals;
274 // Handle some boolean conditions.
275 if (I->getType()->getPrimitiveSizeInBits() == 1) {
277 // X & false -> false
278 if (I->getOpcode() == Instruction::Or ||
279 I->getOpcode() == Instruction::And) {
280 ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals);
281 ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals);
283 if (LHSVals.empty() && RHSVals.empty())
286 ConstantInt *InterestingVal;
287 if (I->getOpcode() == Instruction::Or)
288 InterestingVal = ConstantInt::getTrue(I->getContext());
290 InterestingVal = ConstantInt::getFalse(I->getContext());
292 // Scan for the sentinel.
293 for (unsigned i = 0, e = LHSVals.size(); i != e; ++i)
294 if (LHSVals[i].first == InterestingVal || LHSVals[i].first == 0)
295 Result.push_back(LHSVals[i]);
296 for (unsigned i = 0, e = RHSVals.size(); i != e; ++i)
297 if (RHSVals[i].first == InterestingVal || RHSVals[i].first == 0)
298 Result.push_back(RHSVals[i]);
299 return !Result.empty();
302 // TODO: Should handle the NOT form of XOR.
306 // Handle compare with phi operand, where the PHI is defined in this block.
307 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
308 PHINode *PN = dyn_cast<PHINode>(Cmp->getOperand(0));
309 if (PN && PN->getParent() == BB) {
310 // We can do this simplification if any comparisons fold to true or false.
312 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
313 BasicBlock *PredBB = PN->getIncomingBlock(i);
314 Value *LHS = PN->getIncomingValue(i);
315 Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB);
317 Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS);
318 if (Res == 0) continue;
320 if (isa<UndefValue>(Res))
321 Result.push_back(std::make_pair((ConstantInt*)0, PredBB));
322 else if (ConstantInt *CI = dyn_cast<ConstantInt>(Res))
323 Result.push_back(std::make_pair(CI, PredBB));
326 return !Result.empty();
329 // TODO: We could also recurse to see if we can determine constants another
337 /// GetBestDestForBranchOnUndef - If we determine that the specified block ends
338 /// in an undefined jump, decide which block is best to revector to.
340 /// Since we can pick an arbitrary destination, we pick the successor with the
341 /// fewest predecessors. This should reduce the in-degree of the others.
343 static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) {
344 TerminatorInst *BBTerm = BB->getTerminator();
345 unsigned MinSucc = 0;
346 BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc);
347 // Compute the successor with the minimum number of predecessors.
348 unsigned MinNumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
349 for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) {
350 TestBB = BBTerm->getSuccessor(i);
351 unsigned NumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
352 if (NumPreds < MinNumPreds)
359 /// ProcessBlock - If there are any predecessors whose control can be threaded
360 /// through to a successor, transform them now.
361 bool JumpThreading::ProcessBlock(BasicBlock *BB) {
362 // If this block has a single predecessor, and if that pred has a single
363 // successor, merge the blocks. This encourages recursive jump threading
364 // because now the condition in this block can be threaded through
365 // predecessors of our predecessor block.
366 if (BasicBlock *SinglePred = BB->getSinglePredecessor()) {
367 if (SinglePred->getTerminator()->getNumSuccessors() == 1 &&
369 // If SinglePred was a loop header, BB becomes one.
370 if (LoopHeaders.erase(SinglePred))
371 LoopHeaders.insert(BB);
373 // Remember if SinglePred was the entry block of the function. If so, we
374 // will need to move BB back to the entry position.
375 bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
376 MergeBasicBlockIntoOnlyPred(BB);
378 if (isEntry && BB != &BB->getParent()->getEntryBlock())
379 BB->moveBefore(&BB->getParent()->getEntryBlock());
384 // Look to see if the terminator is a branch of switch, if not we can't thread
387 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
388 // Can't thread an unconditional jump.
389 if (BI->isUnconditional()) return false;
390 Condition = BI->getCondition();
391 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator()))
392 Condition = SI->getCondition();
394 return false; // Must be an invoke.
396 // If the terminator of this block is branching on a constant, simplify the
397 // terminator to an unconditional branch. This can occur due to threading in
399 if (isa<ConstantInt>(Condition)) {
400 DEBUG(errs() << " In block '" << BB->getName()
401 << "' folding terminator: " << *BB->getTerminator() << '\n');
403 ConstantFoldTerminator(BB);
407 // If the terminator is branching on an undef, we can pick any of the
408 // successors to branch to. Let GetBestDestForJumpOnUndef decide.
409 if (isa<UndefValue>(Condition)) {
410 unsigned BestSucc = GetBestDestForJumpOnUndef(BB);
412 // Fold the branch/switch.
413 TerminatorInst *BBTerm = BB->getTerminator();
414 for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) {
415 if (i == BestSucc) continue;
416 RemovePredecessorAndSimplify(BBTerm->getSuccessor(i), BB, TD);
419 DEBUG(errs() << " In block '" << BB->getName()
420 << "' folding undef terminator: " << *BBTerm << '\n');
421 BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm);
422 BBTerm->eraseFromParent();
426 Instruction *CondInst = dyn_cast<Instruction>(Condition);
428 // If the condition is an instruction defined in another block, see if a
429 // predecessor has the same condition:
433 if (!Condition->hasOneUse() && // Multiple uses.
434 (CondInst == 0 || CondInst->getParent() != BB)) { // Non-local definition.
435 pred_iterator PI = pred_begin(BB), E = pred_end(BB);
436 if (isa<BranchInst>(BB->getTerminator())) {
437 for (; PI != E; ++PI)
438 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
439 if (PBI->isConditional() && PBI->getCondition() == Condition &&
440 ProcessBranchOnDuplicateCond(*PI, BB))
443 assert(isa<SwitchInst>(BB->getTerminator()) && "Unknown jump terminator");
444 for (; PI != E; ++PI)
445 if (SwitchInst *PSI = dyn_cast<SwitchInst>((*PI)->getTerminator()))
446 if (PSI->getCondition() == Condition &&
447 ProcessSwitchOnDuplicateCond(*PI, BB))
452 // All the rest of our checks depend on the condition being an instruction.
456 // See if this is a phi node in the current block.
457 if (PHINode *PN = dyn_cast<PHINode>(CondInst))
458 if (PN->getParent() == BB)
459 return ProcessJumpOnPHI(PN);
461 if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
462 if (!isa<PHINode>(CondCmp->getOperand(0)) ||
463 cast<PHINode>(CondCmp->getOperand(0))->getParent() != BB) {
464 // If we have a comparison, loop over the predecessors to see if there is
465 // a condition with a lexically identical value.
466 pred_iterator PI = pred_begin(BB), E = pred_end(BB);
467 for (; PI != E; ++PI)
468 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
469 if (PBI->isConditional() && *PI != BB) {
470 if (CmpInst *CI = dyn_cast<CmpInst>(PBI->getCondition())) {
471 if (CI->getOperand(0) == CondCmp->getOperand(0) &&
472 CI->getOperand(1) == CondCmp->getOperand(1) &&
473 CI->getPredicate() == CondCmp->getPredicate()) {
474 // TODO: Could handle things like (x != 4) --> (x == 17)
475 if (ProcessBranchOnDuplicateCond(*PI, BB))
483 // Check for some cases that are worth simplifying. Right now we want to look
484 // for loads that are used by a switch or by the condition for the branch. If
485 // we see one, check to see if it's partially redundant. If so, insert a PHI
486 // which can then be used to thread the values.
488 // This is particularly important because reg2mem inserts loads and stores all
489 // over the place, and this blocks jump threading if we don't zap them.
490 Value *SimplifyValue = CondInst;
491 if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue))
492 if (isa<Constant>(CondCmp->getOperand(1)))
493 SimplifyValue = CondCmp->getOperand(0);
495 if (LoadInst *LI = dyn_cast<LoadInst>(SimplifyValue))
496 if (SimplifyPartiallyRedundantLoad(LI))
500 // Handle a variety of cases where we are branching on something derived from
501 // a PHI node in the current block. If we can prove that any predecessors
502 // compute a predictable value based on a PHI node, thread those predecessors.
504 // We only bother doing this if the current block has a PHI node and if the
505 // conditional instruction lives in the current block. If either condition
506 // fails, this won't be a computable value anyway.
507 if (CondInst->getParent() == BB && isa<PHINode>(BB->front()))
508 if (ProcessThreadableEdges(CondInst, BB))
512 // TODO: If we have: "br (X > 0)" and we have a predecessor where we know
513 // "(X == 4)" thread through this block.
518 /// ProcessBranchOnDuplicateCond - We found a block and a predecessor of that
519 /// block that jump on exactly the same condition. This means that we almost
520 /// always know the direction of the edge in the DESTBB:
522 /// br COND, DESTBB, BBY
524 /// br COND, BBZ, BBW
526 /// If DESTBB has multiple predecessors, we can't just constant fold the branch
527 /// in DESTBB, we have to thread over it.
528 bool JumpThreading::ProcessBranchOnDuplicateCond(BasicBlock *PredBB,
530 BranchInst *PredBI = cast<BranchInst>(PredBB->getTerminator());
532 // If both successors of PredBB go to DESTBB, we don't know anything. We can
533 // fold the branch to an unconditional one, which allows other recursive
536 if (PredBI->getSuccessor(1) != BB)
538 else if (PredBI->getSuccessor(0) != BB)
541 DEBUG(errs() << " In block '" << PredBB->getName()
542 << "' folding terminator: " << *PredBB->getTerminator() << '\n');
544 ConstantFoldTerminator(PredBB);
548 BranchInst *DestBI = cast<BranchInst>(BB->getTerminator());
550 // If the dest block has one predecessor, just fix the branch condition to a
551 // constant and fold it.
552 if (BB->getSinglePredecessor()) {
553 DEBUG(errs() << " In block '" << BB->getName()
554 << "' folding condition to '" << BranchDir << "': "
555 << *BB->getTerminator() << '\n');
557 Value *OldCond = DestBI->getCondition();
558 DestBI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
560 ConstantFoldTerminator(BB);
561 RecursivelyDeleteTriviallyDeadInstructions(OldCond);
566 // Next, figure out which successor we are threading to.
567 BasicBlock *SuccBB = DestBI->getSuccessor(!BranchDir);
569 SmallVector<BasicBlock*, 2> Preds;
570 Preds.push_back(PredBB);
572 // Ok, try to thread it!
573 return ThreadEdge(BB, Preds, SuccBB);
576 /// ProcessSwitchOnDuplicateCond - We found a block and a predecessor of that
577 /// block that switch on exactly the same condition. This means that we almost
578 /// always know the direction of the edge in the DESTBB:
580 /// switch COND [... DESTBB, BBY ... ]
582 /// switch COND [... BBZ, BBW ]
584 /// Optimizing switches like this is very important, because simplifycfg builds
585 /// switches out of repeated 'if' conditions.
586 bool JumpThreading::ProcessSwitchOnDuplicateCond(BasicBlock *PredBB,
587 BasicBlock *DestBB) {
588 // Can't thread edge to self.
589 if (PredBB == DestBB)
592 SwitchInst *PredSI = cast<SwitchInst>(PredBB->getTerminator());
593 SwitchInst *DestSI = cast<SwitchInst>(DestBB->getTerminator());
595 // There are a variety of optimizations that we can potentially do on these
596 // blocks: we order them from most to least preferable.
598 // If DESTBB *just* contains the switch, then we can forward edges from PREDBB
599 // directly to their destination. This does not introduce *any* code size
600 // growth. Skip debug info first.
601 BasicBlock::iterator BBI = DestBB->begin();
602 while (isa<DbgInfoIntrinsic>(BBI))
605 // FIXME: Thread if it just contains a PHI.
606 if (isa<SwitchInst>(BBI)) {
607 bool MadeChange = false;
608 // Ignore the default edge for now.
609 for (unsigned i = 1, e = DestSI->getNumSuccessors(); i != e; ++i) {
610 ConstantInt *DestVal = DestSI->getCaseValue(i);
611 BasicBlock *DestSucc = DestSI->getSuccessor(i);
613 // Okay, DestSI has a case for 'DestVal' that goes to 'DestSucc'. See if
614 // PredSI has an explicit case for it. If so, forward. If it is covered
615 // by the default case, we can't update PredSI.
616 unsigned PredCase = PredSI->findCaseValue(DestVal);
617 if (PredCase == 0) continue;
619 // If PredSI doesn't go to DestBB on this value, then it won't reach the
620 // case on this condition.
621 if (PredSI->getSuccessor(PredCase) != DestBB &&
622 DestSI->getSuccessor(i) != DestBB)
625 // Otherwise, we're safe to make the change. Make sure that the edge from
626 // DestSI to DestSucc is not critical and has no PHI nodes.
627 DEBUG(errs() << "FORWARDING EDGE " << *DestVal << " FROM: " << *PredSI);
628 DEBUG(errs() << "THROUGH: " << *DestSI);
630 // If the destination has PHI nodes, just split the edge for updating
632 if (isa<PHINode>(DestSucc->begin()) && !DestSucc->getSinglePredecessor()){
633 SplitCriticalEdge(DestSI, i, this);
634 DestSucc = DestSI->getSuccessor(i);
636 FoldSingleEntryPHINodes(DestSucc);
637 PredSI->setSuccessor(PredCase, DestSucc);
649 /// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant
650 /// load instruction, eliminate it by replacing it with a PHI node. This is an
651 /// important optimization that encourages jump threading, and needs to be run
652 /// interlaced with other jump threading tasks.
653 bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
654 // Don't hack volatile loads.
655 if (LI->isVolatile()) return false;
657 // If the load is defined in a block with exactly one predecessor, it can't be
658 // partially redundant.
659 BasicBlock *LoadBB = LI->getParent();
660 if (LoadBB->getSinglePredecessor())
663 Value *LoadedPtr = LI->getOperand(0);
665 // If the loaded operand is defined in the LoadBB, it can't be available.
666 // FIXME: Could do PHI translation, that would be fun :)
667 if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr))
668 if (PtrOp->getParent() == LoadBB)
671 // Scan a few instructions up from the load, to see if it is obviously live at
672 // the entry to its block.
673 BasicBlock::iterator BBIt = LI;
675 if (Value *AvailableVal = FindAvailableLoadedValue(LoadedPtr, LoadBB,
677 // If the value if the load is locally available within the block, just use
678 // it. This frequently occurs for reg2mem'd allocas.
679 //cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n";
681 // If the returned value is the load itself, replace with an undef. This can
682 // only happen in dead loops.
683 if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType());
684 LI->replaceAllUsesWith(AvailableVal);
685 LI->eraseFromParent();
689 // Otherwise, if we scanned the whole block and got to the top of the block,
690 // we know the block is locally transparent to the load. If not, something
691 // might clobber its value.
692 if (BBIt != LoadBB->begin())
696 SmallPtrSet<BasicBlock*, 8> PredsScanned;
697 typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy;
698 AvailablePredsTy AvailablePreds;
699 BasicBlock *OneUnavailablePred = 0;
701 // If we got here, the loaded value is transparent through to the start of the
702 // block. Check to see if it is available in any of the predecessor blocks.
703 for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
705 BasicBlock *PredBB = *PI;
707 // If we already scanned this predecessor, skip it.
708 if (!PredsScanned.insert(PredBB))
711 // Scan the predecessor to see if the value is available in the pred.
712 BBIt = PredBB->end();
713 Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6);
714 if (!PredAvailable) {
715 OneUnavailablePred = PredBB;
719 // If so, this load is partially redundant. Remember this info so that we
720 // can create a PHI node.
721 AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable));
724 // If the loaded value isn't available in any predecessor, it isn't partially
726 if (AvailablePreds.empty()) return false;
728 // Okay, the loaded value is available in at least one (and maybe all!)
729 // predecessors. If the value is unavailable in more than one unique
730 // predecessor, we want to insert a merge block for those common predecessors.
731 // This ensures that we only have to insert one reload, thus not increasing
733 BasicBlock *UnavailablePred = 0;
735 // If there is exactly one predecessor where the value is unavailable, the
736 // already computed 'OneUnavailablePred' block is it. If it ends in an
737 // unconditional branch, we know that it isn't a critical edge.
738 if (PredsScanned.size() == AvailablePreds.size()+1 &&
739 OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) {
740 UnavailablePred = OneUnavailablePred;
741 } else if (PredsScanned.size() != AvailablePreds.size()) {
742 // Otherwise, we had multiple unavailable predecessors or we had a critical
743 // edge from the one.
744 SmallVector<BasicBlock*, 8> PredsToSplit;
745 SmallPtrSet<BasicBlock*, 8> AvailablePredSet;
747 for (unsigned i = 0, e = AvailablePreds.size(); i != e; ++i)
748 AvailablePredSet.insert(AvailablePreds[i].first);
750 // Add all the unavailable predecessors to the PredsToSplit list.
751 for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
753 if (!AvailablePredSet.count(*PI))
754 PredsToSplit.push_back(*PI);
756 // Split them out to their own block.
758 SplitBlockPredecessors(LoadBB, &PredsToSplit[0], PredsToSplit.size(),
759 "thread-split", this);
762 // If the value isn't available in all predecessors, then there will be
763 // exactly one where it isn't available. Insert a load on that edge and add
764 // it to the AvailablePreds list.
765 if (UnavailablePred) {
766 assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&
767 "Can't handle critical edge here!");
768 Value *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr",
769 UnavailablePred->getTerminator());
770 AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
773 // Now we know that each predecessor of this block has a value in
774 // AvailablePreds, sort them for efficient access as we're walking the preds.
775 array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
777 // Create a PHI node at the start of the block for the PRE'd load value.
778 PHINode *PN = PHINode::Create(LI->getType(), "", LoadBB->begin());
781 // Insert new entries into the PHI for each predecessor. A single block may
782 // have multiple entries here.
783 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); PI != E;
785 AvailablePredsTy::iterator I =
786 std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(),
787 std::make_pair(*PI, (Value*)0));
789 assert(I != AvailablePreds.end() && I->first == *PI &&
790 "Didn't find entry for predecessor!");
792 PN->addIncoming(I->second, I->first);
795 //cerr << "PRE: " << *LI << *PN << "\n";
797 LI->replaceAllUsesWith(PN);
798 LI->eraseFromParent();
803 /// FindMostPopularDest - The specified list contains multiple possible
804 /// threadable destinations. Pick the one that occurs the most frequently in
807 FindMostPopularDest(BasicBlock *BB,
808 const SmallVectorImpl<std::pair<BasicBlock*,
809 BasicBlock*> > &PredToDestList) {
810 assert(!PredToDestList.empty());
812 // Determine popularity. If there are multiple possible destinations, we
813 // explicitly choose to ignore 'undef' destinations. We prefer to thread
814 // blocks with known and real destinations to threading undef. We'll handle
815 // them later if interesting.
816 DenseMap<BasicBlock*, unsigned> DestPopularity;
817 for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
818 if (PredToDestList[i].second)
819 DestPopularity[PredToDestList[i].second]++;
821 // Find the most popular dest.
822 DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin();
823 BasicBlock *MostPopularDest = DPI->first;
824 unsigned Popularity = DPI->second;
825 SmallVector<BasicBlock*, 4> SamePopularity;
827 for (++DPI; DPI != DestPopularity.end(); ++DPI) {
828 // If the popularity of this entry isn't higher than the popularity we've
829 // seen so far, ignore it.
830 if (DPI->second < Popularity)
832 else if (DPI->second == Popularity) {
833 // If it is the same as what we've seen so far, keep track of it.
834 SamePopularity.push_back(DPI->first);
836 // If it is more popular, remember it.
837 SamePopularity.clear();
838 MostPopularDest = DPI->first;
839 Popularity = DPI->second;
843 // Okay, now we know the most popular destination. If there is more than
844 // destination, we need to determine one. This is arbitrary, but we need
845 // to make a deterministic decision. Pick the first one that appears in the
847 if (!SamePopularity.empty()) {
848 SamePopularity.push_back(MostPopularDest);
849 TerminatorInst *TI = BB->getTerminator();
850 for (unsigned i = 0; ; ++i) {
851 assert(i != TI->getNumSuccessors() && "Didn't find any successor!");
853 if (std::find(SamePopularity.begin(), SamePopularity.end(),
854 TI->getSuccessor(i)) == SamePopularity.end())
857 MostPopularDest = TI->getSuccessor(i);
862 // Okay, we have finally picked the most popular destination.
863 return MostPopularDest;
866 bool JumpThreading::ProcessThreadableEdges(Instruction *CondInst,
868 // If threading this would thread across a loop header, don't even try to
870 if (LoopHeaders.count(BB))
873 SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> PredValues;
874 if (!ComputeValueKnownInPredecessors(CondInst, BB, PredValues))
876 assert(!PredValues.empty() &&
877 "ComputeValueKnownInPredecessors returned true with no values");
879 DEBUG(errs() << "IN BB: " << *BB;
880 for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
881 errs() << " BB '" << BB->getName() << "': FOUND condition = ";
882 if (PredValues[i].first)
883 errs() << *PredValues[i].first;
886 errs() << " for pred '" << PredValues[i].second->getName()
890 // Decide what we want to thread through. Convert our list of known values to
891 // a list of known destinations for each pred. This also discards duplicate
892 // predecessors and keeps track of the undefined inputs (which are represented
893 // as a null dest in the PredToDestList).
894 SmallPtrSet<BasicBlock*, 16> SeenPreds;
895 SmallVector<std::pair<BasicBlock*, BasicBlock*>, 16> PredToDestList;
897 BasicBlock *OnlyDest = 0;
898 BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL;
900 for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
901 BasicBlock *Pred = PredValues[i].second;
902 if (!SeenPreds.insert(Pred))
903 continue; // Duplicate predecessor entry.
905 // If the predecessor ends with an indirect goto, we can't change its
907 if (isa<IndirectBrInst>(Pred->getTerminator()))
910 ConstantInt *Val = PredValues[i].first;
913 if (Val == 0) // Undef.
915 else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
916 DestBB = BI->getSuccessor(Val->isZero());
918 SwitchInst *SI = cast<SwitchInst>(BB->getTerminator());
919 DestBB = SI->getSuccessor(SI->findCaseValue(Val));
922 // If we have exactly one destination, remember it for efficiency below.
925 else if (OnlyDest != DestBB)
926 OnlyDest = MultipleDestSentinel;
928 PredToDestList.push_back(std::make_pair(Pred, DestBB));
931 // If all edges were unthreadable, we fail.
932 if (PredToDestList.empty())
935 // Determine which is the most common successor. If we have many inputs and
936 // this block is a switch, we want to start by threading the batch that goes
937 // to the most popular destination first. If we only know about one
938 // threadable destination (the common case) we can avoid this.
939 BasicBlock *MostPopularDest = OnlyDest;
941 if (MostPopularDest == MultipleDestSentinel)
942 MostPopularDest = FindMostPopularDest(BB, PredToDestList);
944 // Now that we know what the most popular destination is, factor all
945 // predecessors that will jump to it into a single predecessor.
946 SmallVector<BasicBlock*, 16> PredsToFactor;
947 for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
948 if (PredToDestList[i].second == MostPopularDest) {
949 BasicBlock *Pred = PredToDestList[i].first;
951 // This predecessor may be a switch or something else that has multiple
952 // edges to the block. Factor each of these edges by listing them
953 // according to # occurrences in PredsToFactor.
954 TerminatorInst *PredTI = Pred->getTerminator();
955 for (unsigned i = 0, e = PredTI->getNumSuccessors(); i != e; ++i)
956 if (PredTI->getSuccessor(i) == BB)
957 PredsToFactor.push_back(Pred);
960 // If the threadable edges are branching on an undefined value, we get to pick
961 // the destination that these predecessors should get to.
962 if (MostPopularDest == 0)
963 MostPopularDest = BB->getTerminator()->
964 getSuccessor(GetBestDestForJumpOnUndef(BB));
966 // Ok, try to thread it!
967 return ThreadEdge(BB, PredsToFactor, MostPopularDest);
970 /// ProcessJumpOnPHI - We have a conditional branch or switch on a PHI node in
971 /// the current block. See if there are any simplifications we can do based on
972 /// inputs to the phi node.
974 bool JumpThreading::ProcessJumpOnPHI(PHINode *PN) {
975 BasicBlock *BB = PN->getParent();
977 // If any of the predecessor blocks end in an unconditional branch, we can
978 // *duplicate* the jump into that block in order to further encourage jump
979 // threading and to eliminate cases where we have branch on a phi of an icmp
980 // (branch on icmp is much better).
982 // We don't want to do this tranformation for switches, because we don't
983 // really want to duplicate a switch.
984 if (isa<SwitchInst>(BB->getTerminator()))
987 // Look for unconditional branch predecessors.
988 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
989 BasicBlock *PredBB = PN->getIncomingBlock(i);
990 if (BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator()))
991 if (PredBr->isUnconditional() &&
992 // Try to duplicate BB into PredBB.
993 DuplicateCondBranchOnPHIIntoPred(BB, PredBB))
1001 /// AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new
1002 /// predecessor to the PHIBB block. If it has PHI nodes, add entries for
1003 /// NewPred using the entries from OldPred (suitably mapped).
1004 static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB,
1005 BasicBlock *OldPred,
1006 BasicBlock *NewPred,
1007 DenseMap<Instruction*, Value*> &ValueMap) {
1008 for (BasicBlock::iterator PNI = PHIBB->begin();
1009 PHINode *PN = dyn_cast<PHINode>(PNI); ++PNI) {
1010 // Ok, we have a PHI node. Figure out what the incoming value was for the
1012 Value *IV = PN->getIncomingValueForBlock(OldPred);
1014 // Remap the value if necessary.
1015 if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
1016 DenseMap<Instruction*, Value*>::iterator I = ValueMap.find(Inst);
1017 if (I != ValueMap.end())
1021 PN->addIncoming(IV, NewPred);
1025 /// ThreadEdge - We have decided that it is safe and profitable to factor the
1026 /// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB
1027 /// across BB. Transform the IR to reflect this change.
1028 bool JumpThreading::ThreadEdge(BasicBlock *BB,
1029 const SmallVectorImpl<BasicBlock*> &PredBBs,
1030 BasicBlock *SuccBB) {
1031 // If threading to the same block as we come from, we would infinite loop.
1033 DEBUG(errs() << " Not threading across BB '" << BB->getName()
1034 << "' - would thread to self!\n");
1038 // If threading this would thread across a loop header, don't thread the edge.
1039 // See the comments above FindLoopHeaders for justifications and caveats.
1040 if (LoopHeaders.count(BB)) {
1041 DEBUG(errs() << " Not threading across loop header BB '" << BB->getName()
1042 << "' to dest BB '" << SuccBB->getName()
1043 << "' - it might create an irreducible loop!\n");
1047 unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
1048 if (JumpThreadCost > Threshold) {
1049 DEBUG(errs() << " Not threading BB '" << BB->getName()
1050 << "' - Cost is too high: " << JumpThreadCost << "\n");
1054 // And finally, do it! Start by factoring the predecessors is needed.
1056 if (PredBBs.size() == 1)
1057 PredBB = PredBBs[0];
1059 DEBUG(errs() << " Factoring out " << PredBBs.size()
1060 << " common predecessors.\n");
1061 PredBB = SplitBlockPredecessors(BB, &PredBBs[0], PredBBs.size(),
1065 // And finally, do it!
1066 DEBUG(errs() << " Threading edge from '" << PredBB->getName() << "' to '"
1067 << SuccBB->getName() << "' with cost: " << JumpThreadCost
1068 << ", across block:\n "
1071 // We are going to have to map operands from the original BB block to the new
1072 // copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to
1073 // account for entry from PredBB.
1074 DenseMap<Instruction*, Value*> ValueMapping;
1076 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(),
1077 BB->getName()+".thread",
1078 BB->getParent(), BB);
1079 NewBB->moveAfter(PredBB);
1081 BasicBlock::iterator BI = BB->begin();
1082 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
1083 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
1085 // Clone the non-phi instructions of BB into NewBB, keeping track of the
1086 // mapping and using it to remap operands in the cloned instructions.
1087 for (; !isa<TerminatorInst>(BI); ++BI) {
1088 Instruction *New = BI->clone();
1089 New->setName(BI->getName());
1090 NewBB->getInstList().push_back(New);
1091 ValueMapping[BI] = New;
1093 // Remap operands to patch up intra-block references.
1094 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
1095 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
1096 DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
1097 if (I != ValueMapping.end())
1098 New->setOperand(i, I->second);
1102 // We didn't copy the terminator from BB over to NewBB, because there is now
1103 // an unconditional jump to SuccBB. Insert the unconditional jump.
1104 BranchInst::Create(SuccBB, NewBB);
1106 // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the
1107 // PHI nodes for NewBB now.
1108 AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping);
1110 // If there were values defined in BB that are used outside the block, then we
1111 // now have to update all uses of the value to use either the original value,
1112 // the cloned value, or some PHI derived value. This can require arbitrary
1113 // PHI insertion, of which we are prepared to do, clean these up now.
1114 SSAUpdater SSAUpdate;
1115 SmallVector<Use*, 16> UsesToRename;
1116 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
1117 // Scan all uses of this instruction to see if it is used outside of its
1118 // block, and if so, record them in UsesToRename.
1119 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
1121 Instruction *User = cast<Instruction>(*UI);
1122 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
1123 if (UserPN->getIncomingBlock(UI) == BB)
1125 } else if (User->getParent() == BB)
1128 UsesToRename.push_back(&UI.getUse());
1131 // If there are no uses outside the block, we're done with this instruction.
1132 if (UsesToRename.empty())
1135 DEBUG(errs() << "JT: Renaming non-local uses of: " << *I << "\n");
1137 // We found a use of I outside of BB. Rename all uses of I that are outside
1138 // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
1139 // with the two values we know.
1140 SSAUpdate.Initialize(I);
1141 SSAUpdate.AddAvailableValue(BB, I);
1142 SSAUpdate.AddAvailableValue(NewBB, ValueMapping[I]);
1144 while (!UsesToRename.empty())
1145 SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
1146 DEBUG(errs() << "\n");
1150 // Ok, NewBB is good to go. Update the terminator of PredBB to jump to
1151 // NewBB instead of BB. This eliminates predecessors from BB, which requires
1152 // us to simplify any PHI nodes in BB.
1153 TerminatorInst *PredTerm = PredBB->getTerminator();
1154 for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i)
1155 if (PredTerm->getSuccessor(i) == BB) {
1156 RemovePredecessorAndSimplify(BB, PredBB, TD);
1157 PredTerm->setSuccessor(i, NewBB);
1160 // At this point, the IR is fully up to date and consistent. Do a quick scan
1161 // over the new instructions and zap any that are constants or dead. This
1162 // frequently happens because of phi translation.
1163 BI = NewBB->begin();
1164 for (BasicBlock::iterator E = NewBB->end(); BI != E; ) {
1165 Instruction *Inst = BI++;
1167 if (Value *V = SimplifyInstruction(Inst, TD)) {
1168 WeakVH BIHandle(BI);
1169 ReplaceAndSimplifyAllUses(Inst, V, TD);
1171 BI = NewBB->begin();
1175 RecursivelyDeleteTriviallyDeadInstructions(Inst);
1178 // Threaded an edge!
1183 /// DuplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch
1184 /// to BB which contains an i1 PHI node and a conditional branch on that PHI.
1185 /// If we can duplicate the contents of BB up into PredBB do so now, this
1186 /// improves the odds that the branch will be on an analyzable instruction like
1188 bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
1189 BasicBlock *PredBB) {
1190 // If BB is a loop header, then duplicating this block outside the loop would
1191 // cause us to transform this into an irreducible loop, don't do this.
1192 // See the comments above FindLoopHeaders for justifications and caveats.
1193 if (LoopHeaders.count(BB)) {
1194 DEBUG(errs() << " Not duplicating loop header '" << BB->getName()
1195 << "' into predecessor block '" << PredBB->getName()
1196 << "' - it might create an irreducible loop!\n");
1200 unsigned DuplicationCost = getJumpThreadDuplicationCost(BB);
1201 if (DuplicationCost > Threshold) {
1202 DEBUG(errs() << " Not duplicating BB '" << BB->getName()
1203 << "' - Cost is too high: " << DuplicationCost << "\n");
1207 // Okay, we decided to do this! Clone all the instructions in BB onto the end
1209 DEBUG(errs() << " Duplicating block '" << BB->getName() << "' into end of '"
1210 << PredBB->getName() << "' to eliminate branch on phi. Cost: "
1211 << DuplicationCost << " block is:" << *BB << "\n");
1213 // We are going to have to map operands from the original BB block into the
1214 // PredBB block. Evaluate PHI nodes in BB.
1215 DenseMap<Instruction*, Value*> ValueMapping;
1217 BasicBlock::iterator BI = BB->begin();
1218 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
1219 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
1221 BranchInst *OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
1223 // Clone the non-phi instructions of BB into PredBB, keeping track of the
1224 // mapping and using it to remap operands in the cloned instructions.
1225 for (; BI != BB->end(); ++BI) {
1226 Instruction *New = BI->clone();
1227 New->setName(BI->getName());
1228 PredBB->getInstList().insert(OldPredBranch, New);
1229 ValueMapping[BI] = New;
1231 // Remap operands to patch up intra-block references.
1232 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
1233 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
1234 DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
1235 if (I != ValueMapping.end())
1236 New->setOperand(i, I->second);
1240 // Check to see if the targets of the branch had PHI nodes. If so, we need to
1241 // add entries to the PHI nodes for branch from PredBB now.
1242 BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator());
1243 AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB,
1245 AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
1248 // If there were values defined in BB that are used outside the block, then we
1249 // now have to update all uses of the value to use either the original value,
1250 // the cloned value, or some PHI derived value. This can require arbitrary
1251 // PHI insertion, of which we are prepared to do, clean these up now.
1252 SSAUpdater SSAUpdate;
1253 SmallVector<Use*, 16> UsesToRename;
1254 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
1255 // Scan all uses of this instruction to see if it is used outside of its
1256 // block, and if so, record them in UsesToRename.
1257 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
1259 Instruction *User = cast<Instruction>(*UI);
1260 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
1261 if (UserPN->getIncomingBlock(UI) == BB)
1263 } else if (User->getParent() == BB)
1266 UsesToRename.push_back(&UI.getUse());
1269 // If there are no uses outside the block, we're done with this instruction.
1270 if (UsesToRename.empty())
1273 DEBUG(errs() << "JT: Renaming non-local uses of: " << *I << "\n");
1275 // We found a use of I outside of BB. Rename all uses of I that are outside
1276 // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
1277 // with the two values we know.
1278 SSAUpdate.Initialize(I);
1279 SSAUpdate.AddAvailableValue(BB, I);
1280 SSAUpdate.AddAvailableValue(PredBB, ValueMapping[I]);
1282 while (!UsesToRename.empty())
1283 SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
1284 DEBUG(errs() << "\n");
1287 // PredBB no longer jumps to BB, remove entries in the PHI node for the edge
1289 RemovePredecessorAndSimplify(BB, PredBB, TD);
1291 // Remove the unconditional branch at the end of the PredBB block.
1292 OldPredBranch->eraseFromParent();