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 // FIXME: THREADING will delete values that are just used to compute the
173 // branch, so they shouldn't count against the duplication cost.
176 // Sum up the cost of each instruction until we get to the terminator. Don't
177 // include the terminator because the copy won't include it.
179 for (; !isa<TerminatorInst>(I); ++I) {
180 // Debugger intrinsics don't incur code size.
181 if (isa<DbgInfoIntrinsic>(I)) continue;
183 // If this is a pointer->pointer bitcast, it is free.
184 if (isa<BitCastInst>(I) && isa<PointerType>(I->getType()))
187 // All other instructions count for at least one unit.
190 // Calls are more expensive. If they are non-intrinsic calls, we model them
191 // as having cost of 4. If they are a non-vector intrinsic, we model them
192 // as having cost of 2 total, and if they are a vector intrinsic, we model
193 // them as having cost 1.
194 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
195 if (!isa<IntrinsicInst>(CI))
197 else if (!isa<VectorType>(CI->getType()))
202 // Threading through a switch statement is particularly profitable. If this
203 // block ends in a switch, decrease its cost to make it more likely to happen.
204 if (isa<SwitchInst>(I))
205 Size = Size > 6 ? Size-6 : 0;
210 /// FindLoopHeaders - We do not want jump threading to turn proper loop
211 /// structures into irreducible loops. Doing this breaks up the loop nesting
212 /// hierarchy and pessimizes later transformations. To prevent this from
213 /// happening, we first have to find the loop headers. Here we approximate this
214 /// by finding targets of backedges in the CFG.
216 /// Note that there definitely are cases when we want to allow threading of
217 /// edges across a loop header. For example, threading a jump from outside the
218 /// loop (the preheader) to an exit block of the loop is definitely profitable.
219 /// It is also almost always profitable to thread backedges from within the loop
220 /// to exit blocks, and is often profitable to thread backedges to other blocks
221 /// within the loop (forming a nested loop). This simple analysis is not rich
222 /// enough to track all of these properties and keep it up-to-date as the CFG
223 /// mutates, so we don't allow any of these transformations.
225 void JumpThreading::FindLoopHeaders(Function &F) {
226 SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges;
227 FindFunctionBackedges(F, Edges);
229 for (unsigned i = 0, e = Edges.size(); i != e; ++i)
230 LoopHeaders.insert(const_cast<BasicBlock*>(Edges[i].second));
233 /// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see
234 /// if we can infer that the value is a known ConstantInt in any of our
235 /// predecessors. If so, return the known list of value and pred BB in the
236 /// result vector. If a value is known to be undef, it is returned as null.
238 /// The BB basic block is known to start with a PHI node.
240 /// This returns true if there were any known values.
243 /// TODO: Per PR2563, we could infer value range information about a predecessor
244 /// based on its terminator.
246 ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
247 PHINode *TheFirstPHI = cast<PHINode>(BB->begin());
249 // If V is a constantint, then it is known in all predecessors.
250 if (isa<ConstantInt>(V) || isa<UndefValue>(V)) {
251 ConstantInt *CI = dyn_cast<ConstantInt>(V);
252 Result.resize(TheFirstPHI->getNumIncomingValues());
253 for (unsigned i = 0, e = Result.size(); i != e; ++i)
254 Result[i] = std::make_pair(CI, TheFirstPHI->getIncomingBlock(i));
258 // If V is a non-instruction value, or an instruction in a different block,
259 // then it can't be derived from a PHI.
260 Instruction *I = dyn_cast<Instruction>(V);
261 if (I == 0 || I->getParent() != BB)
264 /// If I is a PHI node, then we know the incoming values for any constants.
265 if (PHINode *PN = dyn_cast<PHINode>(I)) {
266 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
267 Value *InVal = PN->getIncomingValue(i);
268 if (isa<ConstantInt>(InVal) || isa<UndefValue>(InVal)) {
269 ConstantInt *CI = dyn_cast<ConstantInt>(InVal);
270 Result.push_back(std::make_pair(CI, PN->getIncomingBlock(i)));
273 return !Result.empty();
276 SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals, RHSVals;
278 // Handle some boolean conditions.
279 if (I->getType()->getPrimitiveSizeInBits() == 1) {
281 // X & false -> false
282 if (I->getOpcode() == Instruction::Or ||
283 I->getOpcode() == Instruction::And) {
284 ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals);
285 ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals);
287 if (LHSVals.empty() && RHSVals.empty())
290 ConstantInt *InterestingVal;
291 if (I->getOpcode() == Instruction::Or)
292 InterestingVal = ConstantInt::getTrue(I->getContext());
294 InterestingVal = ConstantInt::getFalse(I->getContext());
296 // Scan for the sentinel.
297 for (unsigned i = 0, e = LHSVals.size(); i != e; ++i)
298 if (LHSVals[i].first == InterestingVal || LHSVals[i].first == 0)
299 Result.push_back(LHSVals[i]);
300 for (unsigned i = 0, e = RHSVals.size(); i != e; ++i)
301 if (RHSVals[i].first == InterestingVal || RHSVals[i].first == 0)
302 Result.push_back(RHSVals[i]);
303 return !Result.empty();
306 // Handle the NOT form of XOR.
307 if (I->getOpcode() == Instruction::Xor &&
308 isa<ConstantInt>(I->getOperand(1)) &&
309 cast<ConstantInt>(I->getOperand(1))->isOne()) {
310 ComputeValueKnownInPredecessors(I->getOperand(0), BB, Result);
314 // Invert the known values.
315 for (unsigned i = 0, e = Result.size(); i != e; ++i)
317 cast<ConstantInt>(ConstantExpr::getNot(Result[i].first));
322 // Handle compare with phi operand, where the PHI is defined in this block.
323 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
324 PHINode *PN = dyn_cast<PHINode>(Cmp->getOperand(0));
325 if (PN && PN->getParent() == BB) {
326 // We can do this simplification if any comparisons fold to true or false.
328 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
329 BasicBlock *PredBB = PN->getIncomingBlock(i);
330 Value *LHS = PN->getIncomingValue(i);
331 Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB);
333 Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS);
334 if (Res == 0) continue;
336 if (isa<UndefValue>(Res))
337 Result.push_back(std::make_pair((ConstantInt*)0, PredBB));
338 else if (ConstantInt *CI = dyn_cast<ConstantInt>(Res))
339 Result.push_back(std::make_pair(CI, PredBB));
342 return !Result.empty();
345 // TODO: We could also recurse to see if we can determine constants another
353 /// GetBestDestForBranchOnUndef - If we determine that the specified block ends
354 /// in an undefined jump, decide which block is best to revector to.
356 /// Since we can pick an arbitrary destination, we pick the successor with the
357 /// fewest predecessors. This should reduce the in-degree of the others.
359 static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) {
360 TerminatorInst *BBTerm = BB->getTerminator();
361 unsigned MinSucc = 0;
362 BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc);
363 // Compute the successor with the minimum number of predecessors.
364 unsigned MinNumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
365 for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) {
366 TestBB = BBTerm->getSuccessor(i);
367 unsigned NumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
368 if (NumPreds < MinNumPreds)
375 /// ProcessBlock - If there are any predecessors whose control can be threaded
376 /// through to a successor, transform them now.
377 bool JumpThreading::ProcessBlock(BasicBlock *BB) {
378 // If this block has a single predecessor, and if that pred has a single
379 // successor, merge the blocks. This encourages recursive jump threading
380 // because now the condition in this block can be threaded through
381 // predecessors of our predecessor block.
382 if (BasicBlock *SinglePred = BB->getSinglePredecessor()) {
383 if (SinglePred->getTerminator()->getNumSuccessors() == 1 &&
385 // If SinglePred was a loop header, BB becomes one.
386 if (LoopHeaders.erase(SinglePred))
387 LoopHeaders.insert(BB);
389 // Remember if SinglePred was the entry block of the function. If so, we
390 // will need to move BB back to the entry position.
391 bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
392 MergeBasicBlockIntoOnlyPred(BB);
394 if (isEntry && BB != &BB->getParent()->getEntryBlock())
395 BB->moveBefore(&BB->getParent()->getEntryBlock());
400 // Look to see if the terminator is a branch of switch, if not we can't thread
403 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
404 // Can't thread an unconditional jump.
405 if (BI->isUnconditional()) return false;
406 Condition = BI->getCondition();
407 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator()))
408 Condition = SI->getCondition();
410 return false; // Must be an invoke.
412 // If the terminator of this block is branching on a constant, simplify the
413 // terminator to an unconditional branch. This can occur due to threading in
415 if (isa<ConstantInt>(Condition)) {
416 DEBUG(errs() << " In block '" << BB->getName()
417 << "' folding terminator: " << *BB->getTerminator() << '\n');
419 ConstantFoldTerminator(BB);
423 // If the terminator is branching on an undef, we can pick any of the
424 // successors to branch to. Let GetBestDestForJumpOnUndef decide.
425 if (isa<UndefValue>(Condition)) {
426 unsigned BestSucc = GetBestDestForJumpOnUndef(BB);
428 // Fold the branch/switch.
429 TerminatorInst *BBTerm = BB->getTerminator();
430 for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) {
431 if (i == BestSucc) continue;
432 RemovePredecessorAndSimplify(BBTerm->getSuccessor(i), BB, TD);
435 DEBUG(errs() << " In block '" << BB->getName()
436 << "' folding undef terminator: " << *BBTerm << '\n');
437 BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm);
438 BBTerm->eraseFromParent();
442 Instruction *CondInst = dyn_cast<Instruction>(Condition);
444 // If the condition is an instruction defined in another block, see if a
445 // predecessor has the same condition:
449 if (!Condition->hasOneUse() && // Multiple uses.
450 (CondInst == 0 || CondInst->getParent() != BB)) { // Non-local definition.
451 pred_iterator PI = pred_begin(BB), E = pred_end(BB);
452 if (isa<BranchInst>(BB->getTerminator())) {
453 for (; PI != E; ++PI)
454 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
455 if (PBI->isConditional() && PBI->getCondition() == Condition &&
456 ProcessBranchOnDuplicateCond(*PI, BB))
459 assert(isa<SwitchInst>(BB->getTerminator()) && "Unknown jump terminator");
460 for (; PI != E; ++PI)
461 if (SwitchInst *PSI = dyn_cast<SwitchInst>((*PI)->getTerminator()))
462 if (PSI->getCondition() == Condition &&
463 ProcessSwitchOnDuplicateCond(*PI, BB))
468 // All the rest of our checks depend on the condition being an instruction.
472 // See if this is a phi node in the current block.
473 if (PHINode *PN = dyn_cast<PHINode>(CondInst))
474 if (PN->getParent() == BB)
475 return ProcessJumpOnPHI(PN);
477 if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
478 if (!isa<PHINode>(CondCmp->getOperand(0)) ||
479 cast<PHINode>(CondCmp->getOperand(0))->getParent() != BB) {
480 // If we have a comparison, loop over the predecessors to see if there is
481 // a condition with a lexically identical value.
482 pred_iterator PI = pred_begin(BB), E = pred_end(BB);
483 for (; PI != E; ++PI)
484 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
485 if (PBI->isConditional() && *PI != BB) {
486 if (CmpInst *CI = dyn_cast<CmpInst>(PBI->getCondition())) {
487 if (CI->getOperand(0) == CondCmp->getOperand(0) &&
488 CI->getOperand(1) == CondCmp->getOperand(1) &&
489 CI->getPredicate() == CondCmp->getPredicate()) {
490 // TODO: Could handle things like (x != 4) --> (x == 17)
491 if (ProcessBranchOnDuplicateCond(*PI, BB))
499 // Check for some cases that are worth simplifying. Right now we want to look
500 // for loads that are used by a switch or by the condition for the branch. If
501 // we see one, check to see if it's partially redundant. If so, insert a PHI
502 // which can then be used to thread the values.
504 // This is particularly important because reg2mem inserts loads and stores all
505 // over the place, and this blocks jump threading if we don't zap them.
506 Value *SimplifyValue = CondInst;
507 if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue))
508 if (isa<Constant>(CondCmp->getOperand(1)))
509 SimplifyValue = CondCmp->getOperand(0);
511 if (LoadInst *LI = dyn_cast<LoadInst>(SimplifyValue))
512 if (SimplifyPartiallyRedundantLoad(LI))
516 // Handle a variety of cases where we are branching on something derived from
517 // a PHI node in the current block. If we can prove that any predecessors
518 // compute a predictable value based on a PHI node, thread those predecessors.
520 // We only bother doing this if the current block has a PHI node and if the
521 // conditional instruction lives in the current block. If either condition
522 // fails, this won't be a computable value anyway.
523 if (CondInst->getParent() == BB && isa<PHINode>(BB->front()))
524 if (ProcessThreadableEdges(CondInst, BB))
528 // TODO: If we have: "br (X > 0)" and we have a predecessor where we know
529 // "(X == 4)" thread through this block.
534 /// ProcessBranchOnDuplicateCond - We found a block and a predecessor of that
535 /// block that jump on exactly the same condition. This means that we almost
536 /// always know the direction of the edge in the DESTBB:
538 /// br COND, DESTBB, BBY
540 /// br COND, BBZ, BBW
542 /// If DESTBB has multiple predecessors, we can't just constant fold the branch
543 /// in DESTBB, we have to thread over it.
544 bool JumpThreading::ProcessBranchOnDuplicateCond(BasicBlock *PredBB,
546 BranchInst *PredBI = cast<BranchInst>(PredBB->getTerminator());
548 // If both successors of PredBB go to DESTBB, we don't know anything. We can
549 // fold the branch to an unconditional one, which allows other recursive
552 if (PredBI->getSuccessor(1) != BB)
554 else if (PredBI->getSuccessor(0) != BB)
557 DEBUG(errs() << " In block '" << PredBB->getName()
558 << "' folding terminator: " << *PredBB->getTerminator() << '\n');
560 ConstantFoldTerminator(PredBB);
564 BranchInst *DestBI = cast<BranchInst>(BB->getTerminator());
566 // If the dest block has one predecessor, just fix the branch condition to a
567 // constant and fold it.
568 if (BB->getSinglePredecessor()) {
569 DEBUG(errs() << " In block '" << BB->getName()
570 << "' folding condition to '" << BranchDir << "': "
571 << *BB->getTerminator() << '\n');
573 Value *OldCond = DestBI->getCondition();
574 DestBI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
576 ConstantFoldTerminator(BB);
577 RecursivelyDeleteTriviallyDeadInstructions(OldCond);
582 // Next, figure out which successor we are threading to.
583 BasicBlock *SuccBB = DestBI->getSuccessor(!BranchDir);
585 SmallVector<BasicBlock*, 2> Preds;
586 Preds.push_back(PredBB);
588 // Ok, try to thread it!
589 return ThreadEdge(BB, Preds, SuccBB);
592 /// ProcessSwitchOnDuplicateCond - We found a block and a predecessor of that
593 /// block that switch on exactly the same condition. This means that we almost
594 /// always know the direction of the edge in the DESTBB:
596 /// switch COND [... DESTBB, BBY ... ]
598 /// switch COND [... BBZ, BBW ]
600 /// Optimizing switches like this is very important, because simplifycfg builds
601 /// switches out of repeated 'if' conditions.
602 bool JumpThreading::ProcessSwitchOnDuplicateCond(BasicBlock *PredBB,
603 BasicBlock *DestBB) {
604 // Can't thread edge to self.
605 if (PredBB == DestBB)
608 SwitchInst *PredSI = cast<SwitchInst>(PredBB->getTerminator());
609 SwitchInst *DestSI = cast<SwitchInst>(DestBB->getTerminator());
611 // There are a variety of optimizations that we can potentially do on these
612 // blocks: we order them from most to least preferable.
614 // If DESTBB *just* contains the switch, then we can forward edges from PREDBB
615 // directly to their destination. This does not introduce *any* code size
616 // growth. Skip debug info first.
617 BasicBlock::iterator BBI = DestBB->begin();
618 while (isa<DbgInfoIntrinsic>(BBI))
621 // FIXME: Thread if it just contains a PHI.
622 if (isa<SwitchInst>(BBI)) {
623 bool MadeChange = false;
624 // Ignore the default edge for now.
625 for (unsigned i = 1, e = DestSI->getNumSuccessors(); i != e; ++i) {
626 ConstantInt *DestVal = DestSI->getCaseValue(i);
627 BasicBlock *DestSucc = DestSI->getSuccessor(i);
629 // Okay, DestSI has a case for 'DestVal' that goes to 'DestSucc'. See if
630 // PredSI has an explicit case for it. If so, forward. If it is covered
631 // by the default case, we can't update PredSI.
632 unsigned PredCase = PredSI->findCaseValue(DestVal);
633 if (PredCase == 0) continue;
635 // If PredSI doesn't go to DestBB on this value, then it won't reach the
636 // case on this condition.
637 if (PredSI->getSuccessor(PredCase) != DestBB &&
638 DestSI->getSuccessor(i) != DestBB)
641 // Otherwise, we're safe to make the change. Make sure that the edge from
642 // DestSI to DestSucc is not critical and has no PHI nodes.
643 DEBUG(errs() << "FORWARDING EDGE " << *DestVal << " FROM: " << *PredSI);
644 DEBUG(errs() << "THROUGH: " << *DestSI);
646 // If the destination has PHI nodes, just split the edge for updating
648 if (isa<PHINode>(DestSucc->begin()) && !DestSucc->getSinglePredecessor()){
649 SplitCriticalEdge(DestSI, i, this);
650 DestSucc = DestSI->getSuccessor(i);
652 FoldSingleEntryPHINodes(DestSucc);
653 PredSI->setSuccessor(PredCase, DestSucc);
665 /// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant
666 /// load instruction, eliminate it by replacing it with a PHI node. This is an
667 /// important optimization that encourages jump threading, and needs to be run
668 /// interlaced with other jump threading tasks.
669 bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
670 // Don't hack volatile loads.
671 if (LI->isVolatile()) return false;
673 // If the load is defined in a block with exactly one predecessor, it can't be
674 // partially redundant.
675 BasicBlock *LoadBB = LI->getParent();
676 if (LoadBB->getSinglePredecessor())
679 Value *LoadedPtr = LI->getOperand(0);
681 // If the loaded operand is defined in the LoadBB, it can't be available.
682 // FIXME: Could do PHI translation, that would be fun :)
683 if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr))
684 if (PtrOp->getParent() == LoadBB)
687 // Scan a few instructions up from the load, to see if it is obviously live at
688 // the entry to its block.
689 BasicBlock::iterator BBIt = LI;
691 if (Value *AvailableVal = FindAvailableLoadedValue(LoadedPtr, LoadBB,
693 // If the value if the load is locally available within the block, just use
694 // it. This frequently occurs for reg2mem'd allocas.
695 //cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n";
697 // If the returned value is the load itself, replace with an undef. This can
698 // only happen in dead loops.
699 if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType());
700 LI->replaceAllUsesWith(AvailableVal);
701 LI->eraseFromParent();
705 // Otherwise, if we scanned the whole block and got to the top of the block,
706 // we know the block is locally transparent to the load. If not, something
707 // might clobber its value.
708 if (BBIt != LoadBB->begin())
712 SmallPtrSet<BasicBlock*, 8> PredsScanned;
713 typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy;
714 AvailablePredsTy AvailablePreds;
715 BasicBlock *OneUnavailablePred = 0;
717 // If we got here, the loaded value is transparent through to the start of the
718 // block. Check to see if it is available in any of the predecessor blocks.
719 for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
721 BasicBlock *PredBB = *PI;
723 // If we already scanned this predecessor, skip it.
724 if (!PredsScanned.insert(PredBB))
727 // Scan the predecessor to see if the value is available in the pred.
728 BBIt = PredBB->end();
729 Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6);
730 if (!PredAvailable) {
731 OneUnavailablePred = PredBB;
735 // If so, this load is partially redundant. Remember this info so that we
736 // can create a PHI node.
737 AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable));
740 // If the loaded value isn't available in any predecessor, it isn't partially
742 if (AvailablePreds.empty()) return false;
744 // Okay, the loaded value is available in at least one (and maybe all!)
745 // predecessors. If the value is unavailable in more than one unique
746 // predecessor, we want to insert a merge block for those common predecessors.
747 // This ensures that we only have to insert one reload, thus not increasing
749 BasicBlock *UnavailablePred = 0;
751 // If there is exactly one predecessor where the value is unavailable, the
752 // already computed 'OneUnavailablePred' block is it. If it ends in an
753 // unconditional branch, we know that it isn't a critical edge.
754 if (PredsScanned.size() == AvailablePreds.size()+1 &&
755 OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) {
756 UnavailablePred = OneUnavailablePred;
757 } else if (PredsScanned.size() != AvailablePreds.size()) {
758 // Otherwise, we had multiple unavailable predecessors or we had a critical
759 // edge from the one.
760 SmallVector<BasicBlock*, 8> PredsToSplit;
761 SmallPtrSet<BasicBlock*, 8> AvailablePredSet;
763 for (unsigned i = 0, e = AvailablePreds.size(); i != e; ++i)
764 AvailablePredSet.insert(AvailablePreds[i].first);
766 // Add all the unavailable predecessors to the PredsToSplit list.
767 for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
769 if (!AvailablePredSet.count(*PI))
770 PredsToSplit.push_back(*PI);
772 // Split them out to their own block.
774 SplitBlockPredecessors(LoadBB, &PredsToSplit[0], PredsToSplit.size(),
775 "thread-split", this);
778 // If the value isn't available in all predecessors, then there will be
779 // exactly one where it isn't available. Insert a load on that edge and add
780 // it to the AvailablePreds list.
781 if (UnavailablePred) {
782 assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&
783 "Can't handle critical edge here!");
784 Value *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr",
785 UnavailablePred->getTerminator());
786 AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
789 // Now we know that each predecessor of this block has a value in
790 // AvailablePreds, sort them for efficient access as we're walking the preds.
791 array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
793 // Create a PHI node at the start of the block for the PRE'd load value.
794 PHINode *PN = PHINode::Create(LI->getType(), "", LoadBB->begin());
797 // Insert new entries into the PHI for each predecessor. A single block may
798 // have multiple entries here.
799 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); PI != E;
801 AvailablePredsTy::iterator I =
802 std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(),
803 std::make_pair(*PI, (Value*)0));
805 assert(I != AvailablePreds.end() && I->first == *PI &&
806 "Didn't find entry for predecessor!");
808 PN->addIncoming(I->second, I->first);
811 //cerr << "PRE: " << *LI << *PN << "\n";
813 LI->replaceAllUsesWith(PN);
814 LI->eraseFromParent();
819 /// FindMostPopularDest - The specified list contains multiple possible
820 /// threadable destinations. Pick the one that occurs the most frequently in
823 FindMostPopularDest(BasicBlock *BB,
824 const SmallVectorImpl<std::pair<BasicBlock*,
825 BasicBlock*> > &PredToDestList) {
826 assert(!PredToDestList.empty());
828 // Determine popularity. If there are multiple possible destinations, we
829 // explicitly choose to ignore 'undef' destinations. We prefer to thread
830 // blocks with known and real destinations to threading undef. We'll handle
831 // them later if interesting.
832 DenseMap<BasicBlock*, unsigned> DestPopularity;
833 for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
834 if (PredToDestList[i].second)
835 DestPopularity[PredToDestList[i].second]++;
837 // Find the most popular dest.
838 DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin();
839 BasicBlock *MostPopularDest = DPI->first;
840 unsigned Popularity = DPI->second;
841 SmallVector<BasicBlock*, 4> SamePopularity;
843 for (++DPI; DPI != DestPopularity.end(); ++DPI) {
844 // If the popularity of this entry isn't higher than the popularity we've
845 // seen so far, ignore it.
846 if (DPI->second < Popularity)
848 else if (DPI->second == Popularity) {
849 // If it is the same as what we've seen so far, keep track of it.
850 SamePopularity.push_back(DPI->first);
852 // If it is more popular, remember it.
853 SamePopularity.clear();
854 MostPopularDest = DPI->first;
855 Popularity = DPI->second;
859 // Okay, now we know the most popular destination. If there is more than
860 // destination, we need to determine one. This is arbitrary, but we need
861 // to make a deterministic decision. Pick the first one that appears in the
863 if (!SamePopularity.empty()) {
864 SamePopularity.push_back(MostPopularDest);
865 TerminatorInst *TI = BB->getTerminator();
866 for (unsigned i = 0; ; ++i) {
867 assert(i != TI->getNumSuccessors() && "Didn't find any successor!");
869 if (std::find(SamePopularity.begin(), SamePopularity.end(),
870 TI->getSuccessor(i)) == SamePopularity.end())
873 MostPopularDest = TI->getSuccessor(i);
878 // Okay, we have finally picked the most popular destination.
879 return MostPopularDest;
882 bool JumpThreading::ProcessThreadableEdges(Instruction *CondInst,
884 // If threading this would thread across a loop header, don't even try to
886 if (LoopHeaders.count(BB))
889 SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> PredValues;
890 if (!ComputeValueKnownInPredecessors(CondInst, BB, PredValues))
892 assert(!PredValues.empty() &&
893 "ComputeValueKnownInPredecessors returned true with no values");
895 DEBUG(errs() << "IN BB: " << *BB;
896 for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
897 errs() << " BB '" << BB->getName() << "': FOUND condition = ";
898 if (PredValues[i].first)
899 errs() << *PredValues[i].first;
902 errs() << " for pred '" << PredValues[i].second->getName()
906 // Decide what we want to thread through. Convert our list of known values to
907 // a list of known destinations for each pred. This also discards duplicate
908 // predecessors and keeps track of the undefined inputs (which are represented
909 // as a null dest in the PredToDestList).
910 SmallPtrSet<BasicBlock*, 16> SeenPreds;
911 SmallVector<std::pair<BasicBlock*, BasicBlock*>, 16> PredToDestList;
913 BasicBlock *OnlyDest = 0;
914 BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL;
916 for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
917 BasicBlock *Pred = PredValues[i].second;
918 if (!SeenPreds.insert(Pred))
919 continue; // Duplicate predecessor entry.
921 // If the predecessor ends with an indirect goto, we can't change its
923 if (isa<IndirectBrInst>(Pred->getTerminator()))
926 ConstantInt *Val = PredValues[i].first;
929 if (Val == 0) // Undef.
931 else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
932 DestBB = BI->getSuccessor(Val->isZero());
934 SwitchInst *SI = cast<SwitchInst>(BB->getTerminator());
935 DestBB = SI->getSuccessor(SI->findCaseValue(Val));
938 // If we have exactly one destination, remember it for efficiency below.
941 else if (OnlyDest != DestBB)
942 OnlyDest = MultipleDestSentinel;
944 PredToDestList.push_back(std::make_pair(Pred, DestBB));
947 // If all edges were unthreadable, we fail.
948 if (PredToDestList.empty())
951 // Determine which is the most common successor. If we have many inputs and
952 // this block is a switch, we want to start by threading the batch that goes
953 // to the most popular destination first. If we only know about one
954 // threadable destination (the common case) we can avoid this.
955 BasicBlock *MostPopularDest = OnlyDest;
957 if (MostPopularDest == MultipleDestSentinel)
958 MostPopularDest = FindMostPopularDest(BB, PredToDestList);
960 // Now that we know what the most popular destination is, factor all
961 // predecessors that will jump to it into a single predecessor.
962 SmallVector<BasicBlock*, 16> PredsToFactor;
963 for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
964 if (PredToDestList[i].second == MostPopularDest) {
965 BasicBlock *Pred = PredToDestList[i].first;
967 // This predecessor may be a switch or something else that has multiple
968 // edges to the block. Factor each of these edges by listing them
969 // according to # occurrences in PredsToFactor.
970 TerminatorInst *PredTI = Pred->getTerminator();
971 for (unsigned i = 0, e = PredTI->getNumSuccessors(); i != e; ++i)
972 if (PredTI->getSuccessor(i) == BB)
973 PredsToFactor.push_back(Pred);
976 // If the threadable edges are branching on an undefined value, we get to pick
977 // the destination that these predecessors should get to.
978 if (MostPopularDest == 0)
979 MostPopularDest = BB->getTerminator()->
980 getSuccessor(GetBestDestForJumpOnUndef(BB));
982 // Ok, try to thread it!
983 return ThreadEdge(BB, PredsToFactor, MostPopularDest);
986 /// ProcessJumpOnPHI - We have a conditional branch or switch on a PHI node in
987 /// the current block. See if there are any simplifications we can do based on
988 /// inputs to the phi node.
990 bool JumpThreading::ProcessJumpOnPHI(PHINode *PN) {
991 BasicBlock *BB = PN->getParent();
993 // If any of the predecessor blocks end in an unconditional branch, we can
994 // *duplicate* the jump into that block in order to further encourage jump
995 // threading and to eliminate cases where we have branch on a phi of an icmp
996 // (branch on icmp is much better).
998 // We don't want to do this tranformation for switches, because we don't
999 // really want to duplicate a switch.
1000 if (isa<SwitchInst>(BB->getTerminator()))
1003 // Look for unconditional branch predecessors.
1004 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1005 BasicBlock *PredBB = PN->getIncomingBlock(i);
1006 if (BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator()))
1007 if (PredBr->isUnconditional() &&
1008 // Try to duplicate BB into PredBB.
1009 DuplicateCondBranchOnPHIIntoPred(BB, PredBB))
1017 /// AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new
1018 /// predecessor to the PHIBB block. If it has PHI nodes, add entries for
1019 /// NewPred using the entries from OldPred (suitably mapped).
1020 static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB,
1021 BasicBlock *OldPred,
1022 BasicBlock *NewPred,
1023 DenseMap<Instruction*, Value*> &ValueMap) {
1024 for (BasicBlock::iterator PNI = PHIBB->begin();
1025 PHINode *PN = dyn_cast<PHINode>(PNI); ++PNI) {
1026 // Ok, we have a PHI node. Figure out what the incoming value was for the
1028 Value *IV = PN->getIncomingValueForBlock(OldPred);
1030 // Remap the value if necessary.
1031 if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
1032 DenseMap<Instruction*, Value*>::iterator I = ValueMap.find(Inst);
1033 if (I != ValueMap.end())
1037 PN->addIncoming(IV, NewPred);
1041 /// ThreadEdge - We have decided that it is safe and profitable to factor the
1042 /// blocks in PredBBs to one predecessor, then thread an edge from it to SuccBB
1043 /// across BB. Transform the IR to reflect this change.
1044 bool JumpThreading::ThreadEdge(BasicBlock *BB,
1045 const SmallVectorImpl<BasicBlock*> &PredBBs,
1046 BasicBlock *SuccBB) {
1047 // If threading to the same block as we come from, we would infinite loop.
1049 DEBUG(errs() << " Not threading across BB '" << BB->getName()
1050 << "' - would thread to self!\n");
1054 // If threading this would thread across a loop header, don't thread the edge.
1055 // See the comments above FindLoopHeaders for justifications and caveats.
1056 if (LoopHeaders.count(BB)) {
1057 DEBUG(errs() << " Not threading across loop header BB '" << BB->getName()
1058 << "' to dest BB '" << SuccBB->getName()
1059 << "' - it might create an irreducible loop!\n");
1063 unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
1064 if (JumpThreadCost > Threshold) {
1065 DEBUG(errs() << " Not threading BB '" << BB->getName()
1066 << "' - Cost is too high: " << JumpThreadCost << "\n");
1070 // And finally, do it! Start by factoring the predecessors is needed.
1072 if (PredBBs.size() == 1)
1073 PredBB = PredBBs[0];
1075 DEBUG(errs() << " Factoring out " << PredBBs.size()
1076 << " common predecessors.\n");
1077 PredBB = SplitBlockPredecessors(BB, &PredBBs[0], PredBBs.size(),
1081 // And finally, do it!
1082 DEBUG(errs() << " Threading edge from '" << PredBB->getName() << "' to '"
1083 << SuccBB->getName() << "' with cost: " << JumpThreadCost
1084 << ", across block:\n "
1087 // We are going to have to map operands from the original BB block to the new
1088 // copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to
1089 // account for entry from PredBB.
1090 DenseMap<Instruction*, Value*> ValueMapping;
1092 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(),
1093 BB->getName()+".thread",
1094 BB->getParent(), BB);
1095 NewBB->moveAfter(PredBB);
1097 BasicBlock::iterator BI = BB->begin();
1098 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
1099 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
1101 // Clone the non-phi instructions of BB into NewBB, keeping track of the
1102 // mapping and using it to remap operands in the cloned instructions.
1103 for (; !isa<TerminatorInst>(BI); ++BI) {
1104 Instruction *New = BI->clone();
1105 New->setName(BI->getName());
1106 NewBB->getInstList().push_back(New);
1107 ValueMapping[BI] = New;
1109 // Remap operands to patch up intra-block references.
1110 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
1111 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
1112 DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
1113 if (I != ValueMapping.end())
1114 New->setOperand(i, I->second);
1118 // We didn't copy the terminator from BB over to NewBB, because there is now
1119 // an unconditional jump to SuccBB. Insert the unconditional jump.
1120 BranchInst::Create(SuccBB, NewBB);
1122 // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the
1123 // PHI nodes for NewBB now.
1124 AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping);
1126 // If there were values defined in BB that are used outside the block, then we
1127 // now have to update all uses of the value to use either the original value,
1128 // the cloned value, or some PHI derived value. This can require arbitrary
1129 // PHI insertion, of which we are prepared to do, clean these up now.
1130 SSAUpdater SSAUpdate;
1131 SmallVector<Use*, 16> UsesToRename;
1132 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
1133 // Scan all uses of this instruction to see if it is used outside of its
1134 // block, and if so, record them in UsesToRename.
1135 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
1137 Instruction *User = cast<Instruction>(*UI);
1138 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
1139 if (UserPN->getIncomingBlock(UI) == BB)
1141 } else if (User->getParent() == BB)
1144 UsesToRename.push_back(&UI.getUse());
1147 // If there are no uses outside the block, we're done with this instruction.
1148 if (UsesToRename.empty())
1151 DEBUG(errs() << "JT: Renaming non-local uses of: " << *I << "\n");
1153 // We found a use of I outside of BB. Rename all uses of I that are outside
1154 // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
1155 // with the two values we know.
1156 SSAUpdate.Initialize(I);
1157 SSAUpdate.AddAvailableValue(BB, I);
1158 SSAUpdate.AddAvailableValue(NewBB, ValueMapping[I]);
1160 while (!UsesToRename.empty())
1161 SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
1162 DEBUG(errs() << "\n");
1166 // Ok, NewBB is good to go. Update the terminator of PredBB to jump to
1167 // NewBB instead of BB. This eliminates predecessors from BB, which requires
1168 // us to simplify any PHI nodes in BB.
1169 TerminatorInst *PredTerm = PredBB->getTerminator();
1170 for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i)
1171 if (PredTerm->getSuccessor(i) == BB) {
1172 RemovePredecessorAndSimplify(BB, PredBB, TD);
1173 PredTerm->setSuccessor(i, NewBB);
1176 // At this point, the IR is fully up to date and consistent. Do a quick scan
1177 // over the new instructions and zap any that are constants or dead. This
1178 // frequently happens because of phi translation.
1179 BI = NewBB->begin();
1180 for (BasicBlock::iterator E = NewBB->end(); BI != E; ) {
1181 Instruction *Inst = BI++;
1183 if (Value *V = SimplifyInstruction(Inst, TD)) {
1184 WeakVH BIHandle(BI);
1185 ReplaceAndSimplifyAllUses(Inst, V, TD);
1187 BI = NewBB->begin();
1191 RecursivelyDeleteTriviallyDeadInstructions(Inst);
1194 // Threaded an edge!
1199 /// DuplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch
1200 /// to BB which contains an i1 PHI node and a conditional branch on that PHI.
1201 /// If we can duplicate the contents of BB up into PredBB do so now, this
1202 /// improves the odds that the branch will be on an analyzable instruction like
1204 bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
1205 BasicBlock *PredBB) {
1206 // If BB is a loop header, then duplicating this block outside the loop would
1207 // cause us to transform this into an irreducible loop, don't do this.
1208 // See the comments above FindLoopHeaders for justifications and caveats.
1209 if (LoopHeaders.count(BB)) {
1210 DEBUG(errs() << " Not duplicating loop header '" << BB->getName()
1211 << "' into predecessor block '" << PredBB->getName()
1212 << "' - it might create an irreducible loop!\n");
1216 unsigned DuplicationCost = getJumpThreadDuplicationCost(BB);
1217 if (DuplicationCost > Threshold) {
1218 DEBUG(errs() << " Not duplicating BB '" << BB->getName()
1219 << "' - Cost is too high: " << DuplicationCost << "\n");
1223 // Okay, we decided to do this! Clone all the instructions in BB onto the end
1225 DEBUG(errs() << " Duplicating block '" << BB->getName() << "' into end of '"
1226 << PredBB->getName() << "' to eliminate branch on phi. Cost: "
1227 << DuplicationCost << " block is:" << *BB << "\n");
1229 // We are going to have to map operands from the original BB block into the
1230 // PredBB block. Evaluate PHI nodes in BB.
1231 DenseMap<Instruction*, Value*> ValueMapping;
1233 BasicBlock::iterator BI = BB->begin();
1234 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
1235 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
1237 BranchInst *OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
1239 // Clone the non-phi instructions of BB into PredBB, keeping track of the
1240 // mapping and using it to remap operands in the cloned instructions.
1241 for (; BI != BB->end(); ++BI) {
1242 Instruction *New = BI->clone();
1243 New->setName(BI->getName());
1244 PredBB->getInstList().insert(OldPredBranch, New);
1245 ValueMapping[BI] = New;
1247 // Remap operands to patch up intra-block references.
1248 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
1249 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
1250 DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
1251 if (I != ValueMapping.end())
1252 New->setOperand(i, I->second);
1256 // Check to see if the targets of the branch had PHI nodes. If so, we need to
1257 // add entries to the PHI nodes for branch from PredBB now.
1258 BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator());
1259 AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB,
1261 AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
1264 // If there were values defined in BB that are used outside the block, then we
1265 // now have to update all uses of the value to use either the original value,
1266 // the cloned value, or some PHI derived value. This can require arbitrary
1267 // PHI insertion, of which we are prepared to do, clean these up now.
1268 SSAUpdater SSAUpdate;
1269 SmallVector<Use*, 16> UsesToRename;
1270 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
1271 // Scan all uses of this instruction to see if it is used outside of its
1272 // block, and if so, record them in UsesToRename.
1273 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
1275 Instruction *User = cast<Instruction>(*UI);
1276 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
1277 if (UserPN->getIncomingBlock(UI) == BB)
1279 } else if (User->getParent() == BB)
1282 UsesToRename.push_back(&UI.getUse());
1285 // If there are no uses outside the block, we're done with this instruction.
1286 if (UsesToRename.empty())
1289 DEBUG(errs() << "JT: Renaming non-local uses of: " << *I << "\n");
1291 // We found a use of I outside of BB. Rename all uses of I that are outside
1292 // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
1293 // with the two values we know.
1294 SSAUpdate.Initialize(I);
1295 SSAUpdate.AddAvailableValue(BB, I);
1296 SSAUpdate.AddAvailableValue(PredBB, ValueMapping[I]);
1298 while (!UsesToRename.empty())
1299 SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
1300 DEBUG(errs() << "\n");
1303 // PredBB no longer jumps to BB, remove entries in the PHI node for the edge
1305 RemovePredecessorAndSimplify(BB, PredBB, TD);
1307 // Remove the unconditional branch at the end of the PredBB block.
1308 OldPredBranch->eraseFromParent();