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/ConstantFolding.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, BasicBlock *PredBB, BasicBlock *SuccBB);
76 bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
78 BasicBlock *FactorCommonPHIPreds(PHINode *PN, Value *Val);
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 while (ProcessBlock(BB))
123 // If the block is trivially dead, zap it. This eliminates the successor
124 // edges which simplifies the CFG.
125 if (pred_begin(BB) == pred_end(BB) &&
126 BB != &BB->getParent()->getEntryBlock()) {
127 DEBUG(errs() << " JT: Deleting dead block '" << BB->getName()
128 << "' with terminator: " << *BB->getTerminator() << '\n');
129 LoopHeaders.erase(BB);
134 AnotherIteration = Changed;
135 EverChanged |= Changed;
142 /// getJumpThreadDuplicationCost - Return the cost of duplicating this block to
143 /// thread across it.
144 static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) {
145 /// Ignore PHI nodes, these will be flattened when duplication happens.
146 BasicBlock::const_iterator I = BB->getFirstNonPHI();
148 // Sum up the cost of each instruction until we get to the terminator. Don't
149 // include the terminator because the copy won't include it.
151 for (; !isa<TerminatorInst>(I); ++I) {
152 // Debugger intrinsics don't incur code size.
153 if (isa<DbgInfoIntrinsic>(I)) continue;
155 // If this is a pointer->pointer bitcast, it is free.
156 if (isa<BitCastInst>(I) && isa<PointerType>(I->getType()))
159 // All other instructions count for at least one unit.
162 // Calls are more expensive. If they are non-intrinsic calls, we model them
163 // as having cost of 4. If they are a non-vector intrinsic, we model them
164 // as having cost of 2 total, and if they are a vector intrinsic, we model
165 // them as having cost 1.
166 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
167 if (!isa<IntrinsicInst>(CI))
169 else if (!isa<VectorType>(CI->getType()))
174 // Threading through a switch statement is particularly profitable. If this
175 // block ends in a switch, decrease its cost to make it more likely to happen.
176 if (isa<SwitchInst>(I))
177 Size = Size > 6 ? Size-6 : 0;
184 /// FindLoopHeaders - We do not want jump threading to turn proper loop
185 /// structures into irreducible loops. Doing this breaks up the loop nesting
186 /// hierarchy and pessimizes later transformations. To prevent this from
187 /// happening, we first have to find the loop headers. Here we approximate this
188 /// by finding targets of backedges in the CFG.
190 /// Note that there definitely are cases when we want to allow threading of
191 /// edges across a loop header. For example, threading a jump from outside the
192 /// loop (the preheader) to an exit block of the loop is definitely profitable.
193 /// It is also almost always profitable to thread backedges from within the loop
194 /// to exit blocks, and is often profitable to thread backedges to other blocks
195 /// within the loop (forming a nested loop). This simple analysis is not rich
196 /// enough to track all of these properties and keep it up-to-date as the CFG
197 /// mutates, so we don't allow any of these transformations.
199 void JumpThreading::FindLoopHeaders(Function &F) {
200 SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges;
201 FindFunctionBackedges(F, Edges);
203 for (unsigned i = 0, e = Edges.size(); i != e; ++i)
204 LoopHeaders.insert(const_cast<BasicBlock*>(Edges[i].second));
208 /// FactorCommonPHIPreds - If there are multiple preds with the same incoming
209 /// value for the PHI, factor them together so we get one block to thread for
211 /// This is important for things like "phi i1 [true, true, false, true, x]"
212 /// where we only need to clone the block for the true blocks once.
214 BasicBlock *JumpThreading::FactorCommonPHIPreds(PHINode *PN, Value *Val) {
215 SmallVector<BasicBlock*, 16> CommonPreds;
216 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
217 if (PN->getIncomingValue(i) == Val)
218 CommonPreds.push_back(PN->getIncomingBlock(i));
220 if (CommonPreds.size() == 1)
221 return CommonPreds[0];
223 DEBUG(errs() << " Factoring out " << CommonPreds.size()
224 << " common predecessors.\n");
225 return SplitBlockPredecessors(PN->getParent(),
226 &CommonPreds[0], CommonPreds.size(),
230 /// GetResultOfComparison - Given an icmp/fcmp predicate and the left and right
231 /// hand sides of the compare instruction, try to determine the result. If the
232 /// result can not be determined, a null pointer is returned.
233 static Constant *GetResultOfComparison(CmpInst::Predicate pred,
234 Value *LHS, Value *RHS) {
235 if (Constant *CLHS = dyn_cast<Constant>(LHS))
236 if (Constant *CRHS = dyn_cast<Constant>(RHS))
237 return ConstantExpr::getCompare(pred, CLHS, CRHS);
240 if (isa<IntegerType>(LHS->getType()) || isa<PointerType>(LHS->getType()))
241 if (ICmpInst::isTrueWhenEqual(pred))
242 return ConstantInt::getTrue(LHS->getContext());
244 return ConstantInt::getFalse(LHS->getContext());
249 /// ComputeValueKnownInPredecessors - Given a basic block BB and a value V, see
250 /// if we can infer that the value is a known ConstantInt in any of our
251 /// predecessors. If so, return the known the list of value and pred BB in the
252 /// result vector. If a value is known to be undef, it is returned as null.
254 /// The BB basic block is known to start with a PHI node.
256 /// This returns true if there were any known values.
259 /// TODO: Per PR2563, we could infer value range information about a predecessor
260 /// based on its terminator.
262 ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
263 PHINode *TheFirstPHI = cast<PHINode>(BB->begin());
265 // If V is a constantint, then it is known in all predecessors.
266 if (isa<ConstantInt>(V) || isa<UndefValue>(V)) {
267 ConstantInt *CI = dyn_cast<ConstantInt>(V);
268 Result.resize(TheFirstPHI->getNumIncomingValues());
269 for (unsigned i = 0, e = Result.size(); i != e; ++i)
270 Result.push_back(std::make_pair(CI, TheFirstPHI->getIncomingBlock(i)));
274 // If V is a non-instruction value, or an instruction in a different block,
275 // then it can't be derived from a PHI.
276 Instruction *I = dyn_cast<Instruction>(V);
277 if (I == 0 || I->getParent() != BB)
280 /// If I is a PHI node, then we know the incoming values for any constants.
281 if (PHINode *PN = dyn_cast<PHINode>(I)) {
282 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
283 Value *InVal = PN->getIncomingValue(i);
284 if (isa<ConstantInt>(InVal) || isa<UndefValue>(InVal)) {
285 ConstantInt *CI = dyn_cast<ConstantInt>(InVal);
286 Result.push_back(std::make_pair(CI, PN->getIncomingBlock(i)));
289 return !Result.empty();
292 SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals, RHSVals;
294 // Handle some boolean conditions.
295 if (I->getType()->getPrimitiveSizeInBits() == 1) {
297 // X & false -> false
298 if (I->getOpcode() == Instruction::Or ||
299 I->getOpcode() == Instruction::And) {
300 ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals);
301 ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals);
303 if (LHSVals.empty() && RHSVals.empty())
306 ConstantInt *InterestingVal;
307 if (I->getOpcode() == Instruction::Or)
308 InterestingVal = ConstantInt::getTrue(I->getContext());
310 InterestingVal = ConstantInt::getFalse(I->getContext());
312 // Scan for the sentinel.
313 for (unsigned i = 0, e = LHSVals.size(); i != e; ++i)
314 if (LHSVals[i].first == InterestingVal || LHSVals[i].first == 0)
315 Result.push_back(LHSVals[i]);
316 for (unsigned i = 0, e = RHSVals.size(); i != e; ++i)
317 if (RHSVals[i].first == InterestingVal || RHSVals[i].first == 0)
318 Result.push_back(RHSVals[i]);
319 return !Result.empty();
322 // TODO: Should handle the NOT form of XOR.
326 // Handle compare with phi operand, where the PHI is defined in this block.
327 if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
328 PHINode *PN = dyn_cast<PHINode>(Cmp->getOperand(0));
329 if (PN && PN->getParent() == BB) {
330 // We can do this simplification if any comparisons fold to true or false.
332 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
333 BasicBlock *PredBB = PN->getIncomingBlock(i);
334 Value *LHS = PN->getIncomingValue(i);
335 Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB);
337 Constant *Res = GetResultOfComparison(Cmp->getPredicate(), LHS, RHS);
338 if (Res == 0) continue;
340 if (isa<UndefValue>(Res))
341 Result.push_back(std::make_pair((ConstantInt*)0, PredBB));
342 else if (ConstantInt *CI = dyn_cast<ConstantInt>(Res))
343 Result.push_back(std::make_pair(CI, PredBB));
346 return !Result.empty();
349 // TODO: We could also recurse to see if we can determine constants another
357 /// GetBestDestForBranchOnUndef - If we determine that the specified block ends
358 /// in an undefined jump, decide which block is best to revector to.
360 /// Since we can pick an arbitrary destination, we pick the successor with the
361 /// fewest predecessors. This should reduce the in-degree of the others.
363 static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) {
364 TerminatorInst *BBTerm = BB->getTerminator();
365 unsigned MinSucc = 0;
366 BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc);
367 // Compute the successor with the minimum number of predecessors.
368 unsigned MinNumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
369 for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) {
370 TestBB = BBTerm->getSuccessor(i);
371 unsigned NumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
372 if (NumPreds < MinNumPreds)
379 /// ProcessBlock - If there are any predecessors whose control can be threaded
380 /// through to a successor, transform them now.
381 bool JumpThreading::ProcessBlock(BasicBlock *BB) {
382 // If this block has a single predecessor, and if that pred has a single
383 // successor, merge the blocks. This encourages recursive jump threading
384 // because now the condition in this block can be threaded through
385 // predecessors of our predecessor block.
386 if (BasicBlock *SinglePred = BB->getSinglePredecessor()) {
387 if (SinglePred->getTerminator()->getNumSuccessors() == 1 &&
389 // If SinglePred was a loop header, BB becomes one.
390 if (LoopHeaders.erase(SinglePred))
391 LoopHeaders.insert(BB);
393 // Remember if SinglePred was the entry block of the function. If so, we
394 // will need to move BB back to the entry position.
395 bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
396 MergeBasicBlockIntoOnlyPred(BB);
398 if (isEntry && BB != &BB->getParent()->getEntryBlock())
399 BB->moveBefore(&BB->getParent()->getEntryBlock());
404 // Look to see if the terminator is a branch of switch, if not we can't thread
407 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
408 // Can't thread an unconditional jump.
409 if (BI->isUnconditional()) return false;
410 Condition = BI->getCondition();
411 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator()))
412 Condition = SI->getCondition();
414 return false; // Must be an invoke.
416 // If the terminator of this block is branching on a constant, simplify the
417 // terminator to an unconditional branch. This can occur due to threading in
419 if (isa<ConstantInt>(Condition)) {
420 DEBUG(errs() << " In block '" << BB->getName()
421 << "' folding terminator: " << *BB->getTerminator() << '\n');
423 ConstantFoldTerminator(BB);
427 // If the terminator is branching on an undef, we can pick any of the
428 // successors to branch to. Let GetBestDestForJumpOnUndef decide.
429 if (isa<UndefValue>(Condition)) {
430 unsigned BestSucc = GetBestDestForJumpOnUndef(BB);
432 // Fold the branch/switch.
433 TerminatorInst *BBTerm = BB->getTerminator();
434 for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) {
435 if (i == BestSucc) continue;
436 BBTerm->getSuccessor(i)->removePredecessor(BB);
439 DEBUG(errs() << " In block '" << BB->getName()
440 << "' folding undef terminator: " << *BBTerm << '\n');
441 BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm);
442 BBTerm->eraseFromParent();
446 Instruction *CondInst = dyn_cast<Instruction>(Condition);
448 // If the condition is an instruction defined in another block, see if a
449 // predecessor has the same condition:
453 if (!Condition->hasOneUse() && // Multiple uses.
454 (CondInst == 0 || CondInst->getParent() != BB)) { // Non-local definition.
455 pred_iterator PI = pred_begin(BB), E = pred_end(BB);
456 if (isa<BranchInst>(BB->getTerminator())) {
457 for (; PI != E; ++PI)
458 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
459 if (PBI->isConditional() && PBI->getCondition() == Condition &&
460 ProcessBranchOnDuplicateCond(*PI, BB))
463 assert(isa<SwitchInst>(BB->getTerminator()) && "Unknown jump terminator");
464 for (; PI != E; ++PI)
465 if (SwitchInst *PSI = dyn_cast<SwitchInst>((*PI)->getTerminator()))
466 if (PSI->getCondition() == Condition &&
467 ProcessSwitchOnDuplicateCond(*PI, BB))
472 // All the rest of our checks depend on the condition being an instruction.
476 // See if this is a phi node in the current block.
477 if (PHINode *PN = dyn_cast<PHINode>(CondInst))
478 if (PN->getParent() == BB)
479 return ProcessJumpOnPHI(PN);
481 if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
482 if (!isa<PHINode>(CondCmp->getOperand(0)) ||
483 cast<PHINode>(CondCmp->getOperand(0))->getParent() != BB) {
484 // If we have a comparison, loop over the predecessors to see if there is
485 // a condition with a lexically identical value.
486 pred_iterator PI = pred_begin(BB), E = pred_end(BB);
487 for (; PI != E; ++PI)
488 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
489 if (PBI->isConditional() && *PI != BB) {
490 if (CmpInst *CI = dyn_cast<CmpInst>(PBI->getCondition())) {
491 if (CI->getOperand(0) == CondCmp->getOperand(0) &&
492 CI->getOperand(1) == CondCmp->getOperand(1) &&
493 CI->getPredicate() == CondCmp->getPredicate()) {
494 // TODO: Could handle things like (x != 4) --> (x == 17)
495 if (ProcessBranchOnDuplicateCond(*PI, BB))
503 // Check for some cases that are worth simplifying. Right now we want to look
504 // for loads that are used by a switch or by the condition for the branch. If
505 // we see one, check to see if it's partially redundant. If so, insert a PHI
506 // which can then be used to thread the values.
508 // This is particularly important because reg2mem inserts loads and stores all
509 // over the place, and this blocks jump threading if we don't zap them.
510 Value *SimplifyValue = CondInst;
511 if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue))
512 if (isa<Constant>(CondCmp->getOperand(1)))
513 SimplifyValue = CondCmp->getOperand(0);
515 if (LoadInst *LI = dyn_cast<LoadInst>(SimplifyValue))
516 if (SimplifyPartiallyRedundantLoad(LI))
520 // Handle a variety of cases where we are branching on something derived from
521 // a PHI node in the current block. If we can prove that any predecessors
522 // compute a predictable value based on a PHI node, thread those predecessors.
524 // We only bother doing this if the current block has a PHI node and if the
525 // conditional instruction lives in the current block. If either condition
526 // fail, this won't be a computable value anyway.
527 if (CondInst->getParent() == BB && isa<PHINode>(BB->front()))
528 if (ProcessThreadableEdges(CondInst, BB))
532 // TODO: If we have: "br (X > 0)" and we have a predecessor where we know
533 // "(X == 4)" thread through this block.
538 /// ProcessBranchOnDuplicateCond - We found a block and a predecessor of that
539 /// block that jump on exactly the same condition. This means that we almost
540 /// always know the direction of the edge in the DESTBB:
542 /// br COND, DESTBB, BBY
544 /// br COND, BBZ, BBW
546 /// If DESTBB has multiple predecessors, we can't just constant fold the branch
547 /// in DESTBB, we have to thread over it.
548 bool JumpThreading::ProcessBranchOnDuplicateCond(BasicBlock *PredBB,
550 BranchInst *PredBI = cast<BranchInst>(PredBB->getTerminator());
552 // If both successors of PredBB go to DESTBB, we don't know anything. We can
553 // fold the branch to an unconditional one, which allows other recursive
556 if (PredBI->getSuccessor(1) != BB)
558 else if (PredBI->getSuccessor(0) != BB)
561 DEBUG(errs() << " In block '" << PredBB->getName()
562 << "' folding terminator: " << *PredBB->getTerminator() << '\n');
564 ConstantFoldTerminator(PredBB);
568 BranchInst *DestBI = cast<BranchInst>(BB->getTerminator());
570 // If the dest block has one predecessor, just fix the branch condition to a
571 // constant and fold it.
572 if (BB->getSinglePredecessor()) {
573 DEBUG(errs() << " In block '" << BB->getName()
574 << "' folding condition to '" << BranchDir << "': "
575 << *BB->getTerminator() << '\n');
577 Value *OldCond = DestBI->getCondition();
578 DestBI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
580 ConstantFoldTerminator(BB);
581 RecursivelyDeleteTriviallyDeadInstructions(OldCond);
586 // Next, figure out which successor we are threading to.
587 BasicBlock *SuccBB = DestBI->getSuccessor(!BranchDir);
589 // Ok, try to thread it!
590 return ThreadEdge(BB, PredBB, SuccBB);
593 /// ProcessSwitchOnDuplicateCond - We found a block and a predecessor of that
594 /// block that switch on exactly the same condition. This means that we almost
595 /// always know the direction of the edge in the DESTBB:
597 /// switch COND [... DESTBB, BBY ... ]
599 /// switch COND [... BBZ, BBW ]
601 /// Optimizing switches like this is very important, because simplifycfg builds
602 /// switches out of repeated 'if' conditions.
603 bool JumpThreading::ProcessSwitchOnDuplicateCond(BasicBlock *PredBB,
604 BasicBlock *DestBB) {
605 // Can't thread edge to self.
606 if (PredBB == DestBB)
609 SwitchInst *PredSI = cast<SwitchInst>(PredBB->getTerminator());
610 SwitchInst *DestSI = cast<SwitchInst>(DestBB->getTerminator());
612 // There are a variety of optimizations that we can potentially do on these
613 // blocks: we order them from most to least preferable.
615 // If DESTBB *just* contains the switch, then we can forward edges from PREDBB
616 // directly to their destination. This does not introduce *any* code size
617 // growth. Skip debug info first.
618 BasicBlock::iterator BBI = DestBB->begin();
619 while (isa<DbgInfoIntrinsic>(BBI))
622 // FIXME: Thread if it just contains a PHI.
623 if (isa<SwitchInst>(BBI)) {
624 bool MadeChange = false;
625 // Ignore the default edge for now.
626 for (unsigned i = 1, e = DestSI->getNumSuccessors(); i != e; ++i) {
627 ConstantInt *DestVal = DestSI->getCaseValue(i);
628 BasicBlock *DestSucc = DestSI->getSuccessor(i);
630 // Okay, DestSI has a case for 'DestVal' that goes to 'DestSucc'. See if
631 // PredSI has an explicit case for it. If so, forward. If it is covered
632 // by the default case, we can't update PredSI.
633 unsigned PredCase = PredSI->findCaseValue(DestVal);
634 if (PredCase == 0) continue;
636 // If PredSI doesn't go to DestBB on this value, then it won't reach the
637 // case on this condition.
638 if (PredSI->getSuccessor(PredCase) != DestBB &&
639 DestSI->getSuccessor(i) != DestBB)
642 // Otherwise, we're safe to make the change. Make sure that the edge from
643 // DestSI to DestSucc is not critical and has no PHI nodes.
644 DEBUG(errs() << "FORWARDING EDGE " << *DestVal << " FROM: " << *PredSI);
645 DEBUG(errs() << "THROUGH: " << *DestSI);
647 // If the destination has PHI nodes, just split the edge for updating
649 if (isa<PHINode>(DestSucc->begin()) && !DestSucc->getSinglePredecessor()){
650 SplitCriticalEdge(DestSI, i, this);
651 DestSucc = DestSI->getSuccessor(i);
653 FoldSingleEntryPHINodes(DestSucc);
654 PredSI->setSuccessor(PredCase, DestSucc);
666 /// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant
667 /// load instruction, eliminate it by replacing it with a PHI node. This is an
668 /// important optimization that encourages jump threading, and needs to be run
669 /// interlaced with other jump threading tasks.
670 bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
671 // Don't hack volatile loads.
672 if (LI->isVolatile()) return false;
674 // If the load is defined in a block with exactly one predecessor, it can't be
675 // partially redundant.
676 BasicBlock *LoadBB = LI->getParent();
677 if (LoadBB->getSinglePredecessor())
680 Value *LoadedPtr = LI->getOperand(0);
682 // If the loaded operand is defined in the LoadBB, it can't be available.
683 // FIXME: Could do PHI translation, that would be fun :)
684 if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr))
685 if (PtrOp->getParent() == LoadBB)
688 // Scan a few instructions up from the load, to see if it is obviously live at
689 // the entry to its block.
690 BasicBlock::iterator BBIt = LI;
692 if (Value *AvailableVal = FindAvailableLoadedValue(LoadedPtr, LoadBB,
694 // If the value if the load is locally available within the block, just use
695 // it. This frequently occurs for reg2mem'd allocas.
696 //cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n";
698 // If the returned value is the load itself, replace with an undef. This can
699 // only happen in dead loops.
700 if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType());
701 LI->replaceAllUsesWith(AvailableVal);
702 LI->eraseFromParent();
706 // Otherwise, if we scanned the whole block and got to the top of the block,
707 // we know the block is locally transparent to the load. If not, something
708 // might clobber its value.
709 if (BBIt != LoadBB->begin())
713 SmallPtrSet<BasicBlock*, 8> PredsScanned;
714 typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy;
715 AvailablePredsTy AvailablePreds;
716 BasicBlock *OneUnavailablePred = 0;
718 // If we got here, the loaded value is transparent through to the start of the
719 // block. Check to see if it is available in any of the predecessor blocks.
720 for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
722 BasicBlock *PredBB = *PI;
724 // If we already scanned this predecessor, skip it.
725 if (!PredsScanned.insert(PredBB))
728 // Scan the predecessor to see if the value is available in the pred.
729 BBIt = PredBB->end();
730 Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6);
731 if (!PredAvailable) {
732 OneUnavailablePred = PredBB;
736 // If so, this load is partially redundant. Remember this info so that we
737 // can create a PHI node.
738 AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable));
741 // If the loaded value isn't available in any predecessor, it isn't partially
743 if (AvailablePreds.empty()) return false;
745 // Okay, the loaded value is available in at least one (and maybe all!)
746 // predecessors. If the value is unavailable in more than one unique
747 // predecessor, we want to insert a merge block for those common predecessors.
748 // This ensures that we only have to insert one reload, thus not increasing
750 BasicBlock *UnavailablePred = 0;
752 // If there is exactly one predecessor where the value is unavailable, the
753 // already computed 'OneUnavailablePred' block is it. If it ends in an
754 // unconditional branch, we know that it isn't a critical edge.
755 if (PredsScanned.size() == AvailablePreds.size()+1 &&
756 OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) {
757 UnavailablePred = OneUnavailablePred;
758 } else if (PredsScanned.size() != AvailablePreds.size()) {
759 // Otherwise, we had multiple unavailable predecessors or we had a critical
760 // edge from the one.
761 SmallVector<BasicBlock*, 8> PredsToSplit;
762 SmallPtrSet<BasicBlock*, 8> AvailablePredSet;
764 for (unsigned i = 0, e = AvailablePreds.size(); i != e; ++i)
765 AvailablePredSet.insert(AvailablePreds[i].first);
767 // Add all the unavailable predecessors to the PredsToSplit list.
768 for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
770 if (!AvailablePredSet.count(*PI))
771 PredsToSplit.push_back(*PI);
773 // Split them out to their own block.
775 SplitBlockPredecessors(LoadBB, &PredsToSplit[0], PredsToSplit.size(),
776 "thread-split", this);
779 // If the value isn't available in all predecessors, then there will be
780 // exactly one where it isn't available. Insert a load on that edge and add
781 // it to the AvailablePreds list.
782 if (UnavailablePred) {
783 assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&
784 "Can't handle critical edge here!");
785 Value *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr",
786 UnavailablePred->getTerminator());
787 AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
790 // Now we know that each predecessor of this block has a value in
791 // AvailablePreds, sort them for efficient access as we're walking the preds.
792 array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
794 // Create a PHI node at the start of the block for the PRE'd load value.
795 PHINode *PN = PHINode::Create(LI->getType(), "", LoadBB->begin());
798 // Insert new entries into the PHI for each predecessor. A single block may
799 // have multiple entries here.
800 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); PI != E;
802 AvailablePredsTy::iterator I =
803 std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(),
804 std::make_pair(*PI, (Value*)0));
806 assert(I != AvailablePreds.end() && I->first == *PI &&
807 "Didn't find entry for predecessor!");
809 PN->addIncoming(I->second, I->first);
812 //cerr << "PRE: " << *LI << *PN << "\n";
814 LI->replaceAllUsesWith(PN);
815 LI->eraseFromParent();
820 /// FindMostPopularDest - The specified list contains multiple possible
821 /// threadable destinations. Pick the one that occurs the most frequently in
824 FindMostPopularDest(BasicBlock *BB,
825 const SmallVectorImpl<std::pair<BasicBlock*,
826 BasicBlock*> > &PredToDestList) {
827 assert(!PredToDestList.empty());
829 // Determine popularity. If there are multiple possible destinations, we
830 // explicitly choose to ignore 'undef' destinations. We prefer to thread
831 // blocks with known and real destinations to threading undef. We'll handle
832 // them later if interesting.
833 DenseMap<BasicBlock*, unsigned> DestPopularity;
834 for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
835 if (PredToDestList[i].second)
836 DestPopularity[PredToDestList[i].second]++;
838 // Find the most popular dest.
839 DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin();
840 BasicBlock *MostPopularDest = DPI->first;
841 unsigned Popularity = DPI->second;
842 SmallVector<BasicBlock*, 4> SamePopularity;
844 for (++DPI; DPI != DestPopularity.end(); ++DPI) {
845 // If the popularity of this entry isn't higher than the popularity we've
846 // seen so far, ignore it.
847 if (DPI->second < Popularity)
849 else if (DPI->second == Popularity) {
850 // If it is the same as what we've seen so far, keep track of it.
851 SamePopularity.push_back(DPI->first);
853 // If it is more popular, remember it.
854 SamePopularity.clear();
855 MostPopularDest = DPI->first;
856 Popularity = DPI->second;
860 // Okay, now we know the most popular destination. If there is more than
861 // destination, we need to determine one. This is arbitrary, but we need
862 // to make a deterministic decision. Pick the first one that appears in the
864 if (!SamePopularity.empty()) {
865 SamePopularity.push_back(MostPopularDest);
866 TerminatorInst *TI = BB->getTerminator();
867 for (unsigned i = 0; ; ++i) {
868 assert(i != TI->getNumSuccessors() && "Didn't find any successor!");
870 if (std::find(SamePopularity.begin(), SamePopularity.end(),
871 TI->getSuccessor(i)) == SamePopularity.end())
874 MostPopularDest = TI->getSuccessor(i);
879 // Okay, we have finally picked the most popular destination.
880 return MostPopularDest;
883 bool JumpThreading::ProcessThreadableEdges(Instruction *CondInst,
885 // If threading this would thread across a loop header, don't even try to
887 if (LoopHeaders.count(BB))
892 SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> PredValues;
893 if (!ComputeValueKnownInPredecessors(CondInst, BB, PredValues))
895 assert(!PredValues.empty() &&
896 "ComputeValueKnownInPredecessors returned true with no values");
898 DEBUG(errs() << "IN BB: " << *BB;
899 for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
900 errs() << " BB '" << BB->getName() << "': FOUND condition = ";
901 if (PredValues[i].first)
902 errs() << *PredValues[i].first;
905 errs() << " for pred '" << PredValues[i].second->getName()
909 // Decide what we want to thread through. Convert our list of known values to
910 // a list of known destinations for each pred. This also discards duplicate
911 // predecessors and keeps track of the undefined inputs (which are represented
912 // as a null dest in the PredToDestList.
913 SmallPtrSet<BasicBlock*, 16> SeenPreds;
914 SmallVector<std::pair<BasicBlock*, BasicBlock*>, 16> PredToDestList;
916 BasicBlock *OnlyDest = 0;
917 BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL;
919 for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
920 BasicBlock *Pred = PredValues[i].second;
921 if (!SeenPreds.insert(Pred))
922 continue; // Duplicate predecessor entry.
924 // If the predecessor ends with an indirect goto, we can't change its
926 if (isa<IndirectBrInst>(Pred->getTerminator()))
929 ConstantInt *Val = PredValues[i].first;
932 if (Val == 0) // Undef.
934 else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
935 DestBB = BI->getSuccessor(Val->isZero());
937 SwitchInst *SI = cast<SwitchInst>(BB->getTerminator());
938 DestBB = SI->getSuccessor(SI->findCaseValue(Val));
941 // If we have exactly one destination, remember it for efficiency below.
944 else if (OnlyDest != DestBB)
945 OnlyDest = MultipleDestSentinel;
947 PredToDestList.push_back(std::make_pair(Pred, DestBB));
950 // If all edges were unthreadable, we fail.
951 if (PredToDestList.empty())
954 // Determine which is the most common successor. If we have many inputs and
955 // this block is a switch, we want to start by threading the batch that goes
956 // to the most popular destination first. If we only know about one
957 // threadable destination (the common case) we can avoid this.
958 BasicBlock *MostPopularDest = OnlyDest;
960 if (MostPopularDest == MultipleDestSentinel)
961 MostPopularDest = FindMostPopularDest(BB, PredToDestList);
963 // Now that we know what the most popular destination is, factor all
964 // predecessors that will jump to it into a single predecessor.
965 SmallVector<BasicBlock*, 16> PredsToFactor;
966 for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
967 if (PredToDestList[i].second == MostPopularDest)
968 PredsToFactor.push_back(PredToDestList[i].first);
970 BasicBlock *PredToThread;
971 if (PredsToFactor.size() == 1)
972 PredToThread = PredsToFactor[0];
974 DEBUG(errs() << " Factoring out " << PredsToFactor.size()
975 << " common predecessors.\n");
976 PredToThread = SplitBlockPredecessors(BB, &PredsToFactor[0],
977 PredsToFactor.size(),
981 // If the threadable edges are branching on an undefined value, we get to pick
982 // the destination that these predecessors should get to.
983 if (MostPopularDest == 0)
984 MostPopularDest = BB->getTerminator()->
985 getSuccessor(GetBestDestForJumpOnUndef(BB));
987 // Ok, try to thread it!
988 return ThreadEdge(BB, PredToThread, MostPopularDest);
991 /// ProcessJumpOnPHI - We have a conditional branch or switch on a PHI node in
992 /// the current block. See if there are any simplifications we can do based on
993 /// inputs to the phi node.
995 bool JumpThreading::ProcessJumpOnPHI(PHINode *PN) {
996 BasicBlock *BB = PN->getParent();
998 // If any of the predecessor blocks end in an unconditional branch, we can
999 // *duplicate* the jump into that block in order to further encourage jump
1000 // threading and to eliminate cases where we have branch on a phi of an icmp
1001 // (branch on icmp is much better).
1003 // We don't want to do this tranformation for switches, because we don't
1004 // really want to duplicate a switch.
1005 if (isa<SwitchInst>(BB->getTerminator()))
1008 // Look for unconditional branch predecessors.
1009 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1010 BasicBlock *PredBB = PN->getIncomingBlock(i);
1011 if (BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator()))
1012 if (PredBr->isUnconditional() &&
1013 // Try to duplicate BB into PredBB.
1014 DuplicateCondBranchOnPHIIntoPred(BB, PredBB))
1022 /// AddPHINodeEntriesForMappedBlock - We're adding 'NewPred' as a new
1023 /// predecessor to the PHIBB block. If it has PHI nodes, add entries for
1024 /// NewPred using the entries from OldPred (suitably mapped).
1025 static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB,
1026 BasicBlock *OldPred,
1027 BasicBlock *NewPred,
1028 DenseMap<Instruction*, Value*> &ValueMap) {
1029 for (BasicBlock::iterator PNI = PHIBB->begin();
1030 PHINode *PN = dyn_cast<PHINode>(PNI); ++PNI) {
1031 // Ok, we have a PHI node. Figure out what the incoming value was for the
1033 Value *IV = PN->getIncomingValueForBlock(OldPred);
1035 // Remap the value if necessary.
1036 if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
1037 DenseMap<Instruction*, Value*>::iterator I = ValueMap.find(Inst);
1038 if (I != ValueMap.end())
1042 PN->addIncoming(IV, NewPred);
1046 /// ThreadEdge - We have decided that it is safe and profitable to thread an
1047 /// edge from PredBB to SuccBB across BB. Transform the IR to reflect this
1049 bool JumpThreading::ThreadEdge(BasicBlock *BB, BasicBlock *PredBB,
1050 BasicBlock *SuccBB) {
1051 // If threading to the same block as we come from, we would infinite loop.
1053 DEBUG(errs() << " Not threading across BB '" << BB->getName()
1054 << "' - would thread to self!\n");
1058 // If threading this would thread across a loop header, don't thread the edge.
1059 // See the comments above FindLoopHeaders for justifications and caveats.
1060 if (LoopHeaders.count(BB)) {
1061 DEBUG(errs() << " Not threading from '" << PredBB->getName()
1062 << "' across loop header BB '" << BB->getName()
1063 << "' to dest BB '" << SuccBB->getName()
1064 << "' - it might create an irreducible loop!\n");
1068 unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
1069 if (JumpThreadCost > Threshold) {
1070 DEBUG(errs() << " Not threading BB '" << BB->getName()
1071 << "' - Cost is too high: " << JumpThreadCost << "\n");
1075 // And finally, do it!
1076 DEBUG(errs() << " Threading edge from '" << PredBB->getName() << "' to '"
1077 << SuccBB->getName() << "' with cost: " << JumpThreadCost
1078 << ", across block:\n "
1081 // We are going to have to map operands from the original BB block to the new
1082 // copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to
1083 // account for entry from PredBB.
1084 DenseMap<Instruction*, Value*> ValueMapping;
1086 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(),
1087 BB->getName()+".thread",
1088 BB->getParent(), BB);
1089 NewBB->moveAfter(PredBB);
1091 BasicBlock::iterator BI = BB->begin();
1092 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
1093 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
1095 // Clone the non-phi instructions of BB into NewBB, keeping track of the
1096 // mapping and using it to remap operands in the cloned instructions.
1097 for (; !isa<TerminatorInst>(BI); ++BI) {
1098 Instruction *New = BI->clone();
1099 New->setName(BI->getName());
1100 NewBB->getInstList().push_back(New);
1101 ValueMapping[BI] = New;
1103 // Remap operands to patch up intra-block references.
1104 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
1105 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
1106 DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
1107 if (I != ValueMapping.end())
1108 New->setOperand(i, I->second);
1112 // We didn't copy the terminator from BB over to NewBB, because there is now
1113 // an unconditional jump to SuccBB. Insert the unconditional jump.
1114 BranchInst::Create(SuccBB, NewBB);
1116 // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the
1117 // PHI nodes for NewBB now.
1118 AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping);
1120 // If there were values defined in BB that are used outside the block, then we
1121 // now have to update all uses of the value to use either the original value,
1122 // the cloned value, or some PHI derived value. This can require arbitrary
1123 // PHI insertion, of which we are prepared to do, clean these up now.
1124 SSAUpdater SSAUpdate;
1125 SmallVector<Use*, 16> UsesToRename;
1126 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
1127 // Scan all uses of this instruction to see if it is used outside of its
1128 // block, and if so, record them in UsesToRename.
1129 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
1131 Instruction *User = cast<Instruction>(*UI);
1132 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
1133 if (UserPN->getIncomingBlock(UI) == BB)
1135 } else if (User->getParent() == BB)
1138 UsesToRename.push_back(&UI.getUse());
1141 // If there are no uses outside the block, we're done with this instruction.
1142 if (UsesToRename.empty())
1145 DEBUG(errs() << "JT: Renaming non-local uses of: " << *I << "\n");
1147 // We found a use of I outside of BB. Rename all uses of I that are outside
1148 // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
1149 // with the two values we know.
1150 SSAUpdate.Initialize(I);
1151 SSAUpdate.AddAvailableValue(BB, I);
1152 SSAUpdate.AddAvailableValue(NewBB, ValueMapping[I]);
1154 while (!UsesToRename.empty())
1155 SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
1156 DEBUG(errs() << "\n");
1160 // Ok, NewBB is good to go. Update the terminator of PredBB to jump to
1161 // NewBB instead of BB. This eliminates predecessors from BB, which requires
1162 // us to simplify any PHI nodes in BB.
1163 TerminatorInst *PredTerm = PredBB->getTerminator();
1164 for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i)
1165 if (PredTerm->getSuccessor(i) == BB) {
1166 BB->removePredecessor(PredBB);
1167 PredTerm->setSuccessor(i, NewBB);
1170 // At this point, the IR is fully up to date and consistent. Do a quick scan
1171 // over the new instructions and zap any that are constants or dead. This
1172 // frequently happens because of phi translation.
1173 BI = NewBB->begin();
1174 for (BasicBlock::iterator E = NewBB->end(); BI != E; ) {
1175 Instruction *Inst = BI++;
1176 if (Constant *C = ConstantFoldInstruction(Inst, TD)) {
1177 Inst->replaceAllUsesWith(C);
1178 Inst->eraseFromParent();
1182 RecursivelyDeleteTriviallyDeadInstructions(Inst);
1185 // Threaded an edge!
1190 /// DuplicateCondBranchOnPHIIntoPred - PredBB contains an unconditional branch
1191 /// to BB which contains an i1 PHI node and a conditional branch on that PHI.
1192 /// If we can duplicate the contents of BB up into PredBB do so now, this
1193 /// improves the odds that the branch will be on an analyzable instruction like
1195 bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
1196 BasicBlock *PredBB) {
1197 // If BB is a loop header, then duplicating this block outside the loop would
1198 // cause us to transform this into an irreducible loop, don't do this.
1199 // See the comments above FindLoopHeaders for justifications and caveats.
1200 if (LoopHeaders.count(BB)) {
1201 DEBUG(errs() << " Not duplicating loop header '" << BB->getName()
1202 << "' into predecessor block '" << PredBB->getName()
1203 << "' - it might create an irreducible loop!\n");
1207 unsigned DuplicationCost = getJumpThreadDuplicationCost(BB);
1208 if (DuplicationCost > Threshold) {
1209 DEBUG(errs() << " Not duplicating BB '" << BB->getName()
1210 << "' - Cost is too high: " << DuplicationCost << "\n");
1214 // Okay, we decided to do this! Clone all the instructions in BB onto the end
1216 DEBUG(errs() << " Duplicating block '" << BB->getName() << "' into end of '"
1217 << PredBB->getName() << "' to eliminate branch on phi. Cost: "
1218 << DuplicationCost << " block is:" << *BB << "\n");
1220 // We are going to have to map operands from the original BB block into the
1221 // PredBB block. Evaluate PHI nodes in BB.
1222 DenseMap<Instruction*, Value*> ValueMapping;
1224 BasicBlock::iterator BI = BB->begin();
1225 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
1226 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
1228 BranchInst *OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
1230 // Clone the non-phi instructions of BB into PredBB, keeping track of the
1231 // mapping and using it to remap operands in the cloned instructions.
1232 for (; BI != BB->end(); ++BI) {
1233 Instruction *New = BI->clone();
1234 New->setName(BI->getName());
1235 PredBB->getInstList().insert(OldPredBranch, New);
1236 ValueMapping[BI] = New;
1238 // Remap operands to patch up intra-block references.
1239 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
1240 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
1241 DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
1242 if (I != ValueMapping.end())
1243 New->setOperand(i, I->second);
1247 // Check to see if the targets of the branch had PHI nodes. If so, we need to
1248 // add entries to the PHI nodes for branch from PredBB now.
1249 BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator());
1250 AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB,
1252 AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
1255 // If there were values defined in BB that are used outside the block, then we
1256 // now have to update all uses of the value to use either the original value,
1257 // the cloned value, or some PHI derived value. This can require arbitrary
1258 // PHI insertion, of which we are prepared to do, clean these up now.
1259 SSAUpdater SSAUpdate;
1260 SmallVector<Use*, 16> UsesToRename;
1261 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
1262 // Scan all uses of this instruction to see if it is used outside of its
1263 // block, and if so, record them in UsesToRename.
1264 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
1266 Instruction *User = cast<Instruction>(*UI);
1267 if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
1268 if (UserPN->getIncomingBlock(UI) == BB)
1270 } else if (User->getParent() == BB)
1273 UsesToRename.push_back(&UI.getUse());
1276 // If there are no uses outside the block, we're done with this instruction.
1277 if (UsesToRename.empty())
1280 DEBUG(errs() << "JT: Renaming non-local uses of: " << *I << "\n");
1282 // We found a use of I outside of BB. Rename all uses of I that are outside
1283 // its block to be uses of the appropriate PHI node etc. See ValuesInBlocks
1284 // with the two values we know.
1285 SSAUpdate.Initialize(I);
1286 SSAUpdate.AddAvailableValue(BB, I);
1287 SSAUpdate.AddAvailableValue(PredBB, ValueMapping[I]);
1289 while (!UsesToRename.empty())
1290 SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
1291 DEBUG(errs() << "\n");
1294 // PredBB no longer jumps to BB, remove entries in the PHI node for the edge
1296 BB->removePredecessor(PredBB);
1298 // Remove the unconditional branch at the end of the PredBB block.
1299 OldPredBranch->eraseFromParent();