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/Pass.h"
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/ADT/Statistic.h"
20 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
21 #include "llvm/Transforms/Utils/Local.h"
22 #include "llvm/Support/CommandLine.h"
23 #include "llvm/Support/Compiler.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/ADT/SmallPtrSet.h"
28 STATISTIC(NumThreads, "Number of jumps threaded");
29 STATISTIC(NumFolds, "Number of terminators folded");
31 static cl::opt<unsigned>
32 Threshold("jump-threading-threshold",
33 cl::desc("Max block size to duplicate for jump threading"),
34 cl::init(6), cl::Hidden);
37 /// This pass performs 'jump threading', which looks at blocks that have
38 /// multiple predecessors and multiple successors. If one or more of the
39 /// predecessors of the block can be proven to always jump to one of the
40 /// successors, we forward the edge from the predecessor to the successor by
41 /// duplicating the contents of this block.
43 /// An example of when this can occur is code like this:
50 /// In this case, the unconditional branch at the end of the first if can be
51 /// revectored to the false side of the second if.
53 class VISIBILITY_HIDDEN JumpThreading : public FunctionPass {
55 static char ID; // Pass identification
56 JumpThreading() : FunctionPass(&ID) {}
58 bool runOnFunction(Function &F);
59 bool ProcessBlock(BasicBlock *BB);
60 void ThreadEdge(BasicBlock *BB, BasicBlock *PredBB, BasicBlock *SuccBB);
61 BasicBlock *FactorCommonPHIPreds(PHINode *PN, Constant *CstVal);
63 bool ProcessJumpOnPHI(PHINode *PN);
64 bool ProcessBranchOnLogical(Value *V, BasicBlock *BB, bool isAnd);
65 bool ProcessBranchOnCompare(CmpInst *Cmp, BasicBlock *BB);
67 bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
71 char JumpThreading::ID = 0;
72 static RegisterPass<JumpThreading>
73 X("jump-threading", "Jump Threading");
75 // Public interface to the Jump Threading pass
76 FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); }
78 /// runOnFunction - Top level algorithm.
80 bool JumpThreading::runOnFunction(Function &F) {
81 DOUT << "Jump threading on function '" << F.getNameStart() << "'\n";
83 bool AnotherIteration = true, EverChanged = false;
84 while (AnotherIteration) {
85 AnotherIteration = false;
87 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
88 while (ProcessBlock(I))
90 AnotherIteration = Changed;
91 EverChanged |= Changed;
96 /// FactorCommonPHIPreds - If there are multiple preds with the same incoming
97 /// value for the PHI, factor them together so we get one block to thread for
99 /// This is important for things like "phi i1 [true, true, false, true, x]"
100 /// where we only need to clone the block for the true blocks once.
102 BasicBlock *JumpThreading::FactorCommonPHIPreds(PHINode *PN, Constant *CstVal) {
103 SmallVector<BasicBlock*, 16> CommonPreds;
104 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
105 if (PN->getIncomingValue(i) == CstVal)
106 CommonPreds.push_back(PN->getIncomingBlock(i));
108 if (CommonPreds.size() == 1)
109 return CommonPreds[0];
111 DOUT << " Factoring out " << CommonPreds.size()
112 << " common predecessors.\n";
113 return SplitBlockPredecessors(PN->getParent(),
114 &CommonPreds[0], CommonPreds.size(),
119 /// getJumpThreadDuplicationCost - Return the cost of duplicating this block to
120 /// thread across it.
121 static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) {
122 /// Ignore PHI nodes, these will be flattened when duplication happens.
123 BasicBlock::const_iterator I = BB->getFirstNonPHI();
125 // Sum up the cost of each instruction until we get to the terminator. Don't
126 // include the terminator because the copy won't include it.
128 for (; !isa<TerminatorInst>(I); ++I) {
129 // Debugger intrinsics don't incur code size.
130 if (isa<DbgInfoIntrinsic>(I)) continue;
132 // If this is a pointer->pointer bitcast, it is free.
133 if (isa<BitCastInst>(I) && isa<PointerType>(I->getType()))
136 // All other instructions count for at least one unit.
139 // Calls are more expensive. If they are non-intrinsic calls, we model them
140 // as having cost of 4. If they are a non-vector intrinsic, we model them
141 // as having cost of 2 total, and if they are a vector intrinsic, we model
142 // them as having cost 1.
143 if (const CallInst *CI = dyn_cast<CallInst>(I)) {
144 if (!isa<IntrinsicInst>(CI))
146 else if (isa<VectorType>(CI->getType()))
151 // Threading through a switch statement is particularly profitable. If this
152 // block ends in a switch, decrease its cost to make it more likely to happen.
153 if (isa<SwitchInst>(I))
154 Size = Size > 6 ? Size-6 : 0;
159 /// ProcessBlock - If there are any predecessors whose control can be threaded
160 /// through to a successor, transform them now.
161 bool JumpThreading::ProcessBlock(BasicBlock *BB) {
162 // If this block has a single predecessor, and if that pred has a single
163 // successor, merge the blocks. This encourages recursive jump threading
164 // because now the condition in this block can be threaded through
165 // predecessors of our predecessor block.
166 if (BasicBlock *SinglePred = BB->getSinglePredecessor())
167 if (SinglePred->getTerminator()->getNumSuccessors() == 1 &&
169 // Remember if SinglePred was the entry block of the function. If so, we
170 // will need to move BB back to the entry position.
171 bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
172 MergeBasicBlockIntoOnlyPred(BB);
174 if (isEntry && BB != &BB->getParent()->getEntryBlock())
175 BB->moveBefore(&BB->getParent()->getEntryBlock());
179 // See if this block ends with a branch or switch. If so, see if the
180 // condition is a phi node. If so, and if an entry of the phi node is a
181 // constant, we can thread the block.
183 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
184 // Can't thread an unconditional jump.
185 if (BI->isUnconditional()) return false;
186 Condition = BI->getCondition();
187 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator()))
188 Condition = SI->getCondition();
190 return false; // Must be an invoke.
192 // If the terminator of this block is branching on a constant, simplify the
193 // terminator to an unconditional branch. This can occur due to threading in
195 if (isa<ConstantInt>(Condition)) {
196 DOUT << " In block '" << BB->getNameStart()
197 << "' folding terminator: " << *BB->getTerminator();
199 ConstantFoldTerminator(BB);
203 // If there is only a single predecessor of this block, nothing to fold.
204 if (BB->getSinglePredecessor())
207 // See if this is a phi node in the current block.
208 PHINode *PN = dyn_cast<PHINode>(Condition);
209 if (PN && PN->getParent() == BB)
210 return ProcessJumpOnPHI(PN);
212 // If this is a conditional branch whose condition is and/or of a phi, try to
214 if (BinaryOperator *CondI = dyn_cast<BinaryOperator>(Condition)) {
215 if ((CondI->getOpcode() == Instruction::And ||
216 CondI->getOpcode() == Instruction::Or) &&
217 isa<BranchInst>(BB->getTerminator()) &&
218 ProcessBranchOnLogical(CondI, BB,
219 CondI->getOpcode() == Instruction::And))
223 // If we have "br (phi != 42)" and the phi node has any constant values as
224 // operands, we can thread through this block.
225 if (CmpInst *CondCmp = dyn_cast<CmpInst>(Condition))
226 if (isa<PHINode>(CondCmp->getOperand(0)) &&
227 isa<Constant>(CondCmp->getOperand(1)) &&
228 ProcessBranchOnCompare(CondCmp, BB))
231 // Check for some cases that are worth simplifying. Right now we want to look
232 // for loads that are used by a switch or by the condition for the branch. If
233 // we see one, check to see if it's partially redundant. If so, insert a PHI
234 // which can then be used to thread the values.
236 // This is particularly important because reg2mem inserts loads and stores all
237 // over the place, and this blocks jump threading if we don't zap them.
238 Value *SimplifyValue = Condition;
239 if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue))
240 if (isa<Constant>(CondCmp->getOperand(1)))
241 SimplifyValue = CondCmp->getOperand(0);
243 if (LoadInst *LI = dyn_cast<LoadInst>(SimplifyValue))
244 if (SimplifyPartiallyRedundantLoad(LI))
247 // TODO: If we have: "br (X > 0)" and we have a predecessor where we know
248 // "(X == 4)" thread through this block.
253 /// SimplifyPartiallyRedundantLoad - If LI is an obviously partially redundant
254 /// load instruction, eliminate it by replacing it with a PHI node. This is an
255 /// important optimization that encourages jump threading, and needs to be run
256 /// interlaced with other jump threading tasks.
257 bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
258 // Don't hack volatile loads.
259 if (LI->isVolatile()) return false;
261 // If the load is defined in a block with exactly one predecessor, it can't be
262 // partially redundant.
263 BasicBlock *LoadBB = LI->getParent();
264 if (LoadBB->getSinglePredecessor())
267 Value *LoadedPtr = LI->getOperand(0);
269 // If the loaded operand is defined in the LoadBB, it can't be available.
270 // FIXME: Could do PHI translation, that would be fun :)
271 if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr))
272 if (PtrOp->getParent() == LoadBB)
275 // Scan a few instructions up from the load, to see if it is obviously live at
276 // the entry to its block.
277 BasicBlock::iterator BBIt = LI;
279 if (Value *AvailableVal = FindAvailableLoadedValue(LoadedPtr, LoadBB,
281 // If the value if the load is locally available within the block, just use
282 // it. This frequently occurs for reg2mem'd allocas.
283 //cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n";
284 LI->replaceAllUsesWith(AvailableVal);
285 LI->eraseFromParent();
289 // Otherwise, if we scanned the whole block and got to the top of the block,
290 // we know the block is locally transparent to the load. If not, something
291 // might clobber its value.
292 if (BBIt != LoadBB->begin())
296 SmallPtrSet<BasicBlock*, 8> PredsScanned;
297 typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy;
298 AvailablePredsTy AvailablePreds;
299 BasicBlock *OneUnavailablePred = 0;
301 // If we got here, the loaded value is transparent through to the start of the
302 // block. Check to see if it is available in any of the predecessor blocks.
303 for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
305 BasicBlock *PredBB = *PI;
307 // If we already scanned this predecessor, skip it.
308 if (!PredsScanned.insert(PredBB))
311 // Scan the predecessor to see if the value is available in the pred.
312 BBIt = PredBB->end();
313 Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6);
314 if (!PredAvailable) {
315 OneUnavailablePred = PredBB;
319 // If so, this load is partially redundant. Remember this info so that we
320 // can create a PHI node.
321 AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable));
324 // If the loaded value isn't available in any predecessor, it isn't partially
326 if (AvailablePreds.empty()) return false;
328 // Okay, the loaded value is available in at least one (and maybe all!)
329 // predecessors. If the value is unavailable in more than one unique
330 // predecessor, we want to insert a merge block for those common predecessors.
331 // This ensures that we only have to insert one reload, thus not increasing
333 BasicBlock *UnavailablePred = 0;
335 // If there is exactly one predecessor where the value is unavailable, the
336 // already computed 'OneUnavailablePred' block is it. If it ends in an
337 // unconditional branch, we know that it isn't a critical edge.
338 if (PredsScanned.size() == AvailablePreds.size()+1 &&
339 OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) {
340 UnavailablePred = OneUnavailablePred;
341 } else if (PredsScanned.size() != AvailablePreds.size()) {
342 // Otherwise, we had multiple unavailable predecessors or we had a critical
343 // edge from the one.
344 SmallVector<BasicBlock*, 8> PredsToSplit;
345 SmallPtrSet<BasicBlock*, 8> AvailablePredSet;
347 for (unsigned i = 0, e = AvailablePreds.size(); i != e; ++i)
348 AvailablePredSet.insert(AvailablePreds[i].first);
350 // Add all the unavailable predecessors to the PredsToSplit list.
351 for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
353 if (!AvailablePredSet.count(*PI))
354 PredsToSplit.push_back(*PI);
356 // Split them out to their own block.
358 SplitBlockPredecessors(LoadBB, &PredsToSplit[0], PredsToSplit.size(),
359 "thread-split", this);
362 // If the value isn't available in all predecessors, then there will be
363 // exactly one where it isn't available. Insert a load on that edge and add
364 // it to the AvailablePreds list.
365 if (UnavailablePred) {
366 assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&
367 "Can't handle critical edge here!");
368 Value *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr",
369 UnavailablePred->getTerminator());
370 AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
373 // Now we know that each predecessor of this block has a value in
374 // AvailablePreds, sort them for efficient access as we're walking the preds.
375 std::sort(AvailablePreds.begin(), AvailablePreds.end());
377 // Create a PHI node at the start of the block for the PRE'd load value.
378 PHINode *PN = PHINode::Create(LI->getType(), "", LoadBB->begin());
381 // Insert new entries into the PHI for each predecessor. A single block may
382 // have multiple entries here.
383 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); PI != E;
385 AvailablePredsTy::iterator I =
386 std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(),
387 std::make_pair(*PI, (Value*)0));
389 assert(I != AvailablePreds.end() && I->first == *PI &&
390 "Didn't find entry for predecessor!");
392 PN->addIncoming(I->second, I->first);
395 //cerr << "PRE: " << *LI << *PN << "\n";
397 LI->replaceAllUsesWith(PN);
398 LI->eraseFromParent();
404 /// ProcessJumpOnPHI - We have a conditional branch of switch on a PHI node in
405 /// the current block. See if there are any simplifications we can do based on
406 /// inputs to the phi node.
408 bool JumpThreading::ProcessJumpOnPHI(PHINode *PN) {
409 // See if the phi node has any constant values. If so, we can determine where
410 // the corresponding predecessor will branch.
411 ConstantInt *PredCst = 0;
412 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
413 if ((PredCst = dyn_cast<ConstantInt>(PN->getIncomingValue(i))))
416 // If no incoming value has a constant, we don't know the destination of any
421 // See if the cost of duplicating this block is low enough.
422 BasicBlock *BB = PN->getParent();
423 unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
424 if (JumpThreadCost > Threshold) {
425 DOUT << " Not threading BB '" << BB->getNameStart()
426 << "' - Cost is too high: " << JumpThreadCost << "\n";
430 // If so, we can actually do this threading. Merge any common predecessors
431 // that will act the same.
432 BasicBlock *PredBB = FactorCommonPHIPreds(PN, PredCst);
434 // Next, figure out which successor we are threading to.
436 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
437 SuccBB = BI->getSuccessor(PredCst == ConstantInt::getFalse());
439 SwitchInst *SI = cast<SwitchInst>(BB->getTerminator());
440 SuccBB = SI->getSuccessor(SI->findCaseValue(PredCst));
443 // If threading to the same block as we come from, we would infinite loop.
445 DOUT << " Not threading BB '" << BB->getNameStart()
446 << "' - would thread to self!\n";
450 // And finally, do it!
451 DOUT << " Threading edge from '" << PredBB->getNameStart() << "' to '"
452 << SuccBB->getNameStart() << "' with cost: " << JumpThreadCost
453 << ", across block:\n "
456 ThreadEdge(BB, PredBB, SuccBB);
461 /// ProcessJumpOnLogicalPHI - PN's basic block contains a conditional branch
462 /// whose condition is an AND/OR where one side is PN. If PN has constant
463 /// operands that permit us to evaluate the condition for some operand, thread
464 /// through the block. For example with:
465 /// br (and X, phi(Y, Z, false))
466 /// the predecessor corresponding to the 'false' will always jump to the false
467 /// destination of the branch.
469 bool JumpThreading::ProcessBranchOnLogical(Value *V, BasicBlock *BB,
471 // If this is a binary operator tree of the same AND/OR opcode, check the
473 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V))
474 if ((isAnd && BO->getOpcode() == Instruction::And) ||
475 (!isAnd && BO->getOpcode() == Instruction::Or)) {
476 if (ProcessBranchOnLogical(BO->getOperand(0), BB, isAnd))
478 if (ProcessBranchOnLogical(BO->getOperand(1), BB, isAnd))
482 // If this isn't a PHI node, we can't handle it.
483 PHINode *PN = dyn_cast<PHINode>(V);
484 if (!PN || PN->getParent() != BB) return false;
486 // We can only do the simplification for phi nodes of 'false' with AND or
487 // 'true' with OR. See if we have any entries in the phi for this.
488 unsigned PredNo = ~0U;
489 ConstantInt *PredCst = ConstantInt::get(Type::Int1Ty, !isAnd);
490 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
491 if (PN->getIncomingValue(i) == PredCst) {
497 // If no match, bail out.
501 // See if the cost of duplicating this block is low enough.
502 unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
503 if (JumpThreadCost > Threshold) {
504 DOUT << " Not threading BB '" << BB->getNameStart()
505 << "' - Cost is too high: " << JumpThreadCost << "\n";
509 // If so, we can actually do this threading. Merge any common predecessors
510 // that will act the same.
511 BasicBlock *PredBB = FactorCommonPHIPreds(PN, PredCst);
513 // Next, figure out which successor we are threading to. If this was an AND,
514 // the constant must be FALSE, and we must be targeting the 'false' block.
515 // If this is an OR, the constant must be TRUE, and we must be targeting the
517 BasicBlock *SuccBB = BB->getTerminator()->getSuccessor(isAnd);
519 // If threading to the same block as we come from, we would infinite loop.
521 DOUT << " Not threading BB '" << BB->getNameStart()
522 << "' - would thread to self!\n";
526 // And finally, do it!
527 DOUT << " Threading edge through bool from '" << PredBB->getNameStart()
528 << "' to '" << SuccBB->getNameStart() << "' with cost: "
529 << JumpThreadCost << ", across block:\n "
532 ThreadEdge(BB, PredBB, SuccBB);
537 /// ProcessBranchOnCompare - We found a branch on a comparison between a phi
538 /// node and a constant. If the PHI node contains any constants as inputs, we
539 /// can fold the compare for that edge and thread through it.
540 bool JumpThreading::ProcessBranchOnCompare(CmpInst *Cmp, BasicBlock *BB) {
541 PHINode *PN = cast<PHINode>(Cmp->getOperand(0));
542 Constant *RHS = cast<Constant>(Cmp->getOperand(1));
544 // If the phi isn't in the current block, an incoming edge to this block
545 // doesn't control the destination.
546 if (PN->getParent() != BB)
549 // We can do this simplification if any comparisons fold to true or false.
551 Constant *PredCst = 0;
552 bool TrueDirection = false;
553 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
554 PredCst = dyn_cast<Constant>(PN->getIncomingValue(i));
555 if (PredCst == 0) continue;
558 if (ICmpInst *ICI = dyn_cast<ICmpInst>(Cmp))
559 Res = ConstantExpr::getICmp(ICI->getPredicate(), PredCst, RHS);
561 Res = ConstantExpr::getFCmp(cast<FCmpInst>(Cmp)->getPredicate(),
563 // If this folded to a constant expr, we can't do anything.
564 if (ConstantInt *ResC = dyn_cast<ConstantInt>(Res)) {
565 TrueDirection = ResC->getZExtValue();
568 // If this folded to undef, just go the false way.
569 if (isa<UndefValue>(Res)) {
570 TrueDirection = false;
574 // Otherwise, we can't fold this input.
578 // If no match, bail out.
582 // See if the cost of duplicating this block is low enough.
583 unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
584 if (JumpThreadCost > Threshold) {
585 DOUT << " Not threading BB '" << BB->getNameStart()
586 << "' - Cost is too high: " << JumpThreadCost << "\n";
590 // If so, we can actually do this threading. Merge any common predecessors
591 // that will act the same.
592 BasicBlock *PredBB = FactorCommonPHIPreds(PN, PredCst);
594 // Next, get our successor.
595 BasicBlock *SuccBB = BB->getTerminator()->getSuccessor(!TrueDirection);
597 // If threading to the same block as we come from, we would infinite loop.
599 DOUT << " Not threading BB '" << BB->getNameStart()
600 << "' - would thread to self!\n";
605 // And finally, do it!
606 DOUT << " Threading edge through bool from '" << PredBB->getNameStart()
607 << "' to '" << SuccBB->getNameStart() << "' with cost: "
608 << JumpThreadCost << ", across block:\n "
611 ThreadEdge(BB, PredBB, SuccBB);
617 /// ThreadEdge - We have decided that it is safe and profitable to thread an
618 /// edge from PredBB to SuccBB across BB. Transform the IR to reflect this
620 void JumpThreading::ThreadEdge(BasicBlock *BB, BasicBlock *PredBB,
621 BasicBlock *SuccBB) {
623 // Jump Threading can not update SSA properties correctly if the values
624 // defined in the duplicated block are used outside of the block itself. For
625 // this reason, we spill all values that are used outside of BB to the stack.
626 for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
627 if (!I->isUsedOutsideOfBlock(BB))
630 // We found a use of I outside of BB. Create a new stack slot to
631 // break this inter-block usage pattern.
632 DemoteRegToStack(*I);
635 // We are going to have to map operands from the original BB block to the new
636 // copy of the block 'NewBB'. If there are PHI nodes in BB, evaluate them to
637 // account for entry from PredBB.
638 DenseMap<Instruction*, Value*> ValueMapping;
641 BasicBlock::Create(BB->getName()+".thread", BB->getParent(), BB);
642 NewBB->moveAfter(PredBB);
644 BasicBlock::iterator BI = BB->begin();
645 for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
646 ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
648 // Clone the non-phi instructions of BB into NewBB, keeping track of the
649 // mapping and using it to remap operands in the cloned instructions.
650 for (; !isa<TerminatorInst>(BI); ++BI) {
651 Instruction *New = BI->clone();
652 New->setName(BI->getNameStart());
653 NewBB->getInstList().push_back(New);
654 ValueMapping[BI] = New;
656 // Remap operands to patch up intra-block references.
657 for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
658 if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i)))
659 if (Value *Remapped = ValueMapping[Inst])
660 New->setOperand(i, Remapped);
663 // We didn't copy the terminator from BB over to NewBB, because there is now
664 // an unconditional jump to SuccBB. Insert the unconditional jump.
665 BranchInst::Create(SuccBB, NewBB);
667 // Check to see if SuccBB has PHI nodes. If so, we need to add entries to the
668 // PHI nodes for NewBB now.
669 for (BasicBlock::iterator PNI = SuccBB->begin(); isa<PHINode>(PNI); ++PNI) {
670 PHINode *PN = cast<PHINode>(PNI);
671 // Ok, we have a PHI node. Figure out what the incoming value was for the
673 Value *IV = PN->getIncomingValueForBlock(BB);
675 // Remap the value if necessary.
676 if (Instruction *Inst = dyn_cast<Instruction>(IV))
677 if (Value *MappedIV = ValueMapping[Inst])
679 PN->addIncoming(IV, NewBB);
682 // Finally, NewBB is good to go. Update the terminator of PredBB to jump to
683 // NewBB instead of BB. This eliminates predecessors from BB, which requires
684 // us to simplify any PHI nodes in BB.
685 TerminatorInst *PredTerm = PredBB->getTerminator();
686 for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i)
687 if (PredTerm->getSuccessor(i) == BB) {
688 BB->removePredecessor(PredBB);
689 PredTerm->setSuccessor(i, NewBB);