1//===- CloneFunction.cpp - Clone a function into another function ---------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the CloneFunctionInto interface, which is used as the
11// low-level function cloner.  This is used by the CloneFunction and function
12// inliner to do the dirty work of copying the body of a function around.
13//
14//===----------------------------------------------------------------------===//
15
16#include "llvm/Transforms/Utils/Cloning.h"
17#include "llvm/ADT/SmallVector.h"
18#include "llvm/Analysis/ConstantFolding.h"
19#include "llvm/Analysis/InstructionSimplify.h"
20#include "llvm/DebugInfo.h"
21#include "llvm/IR/Constants.h"
22#include "llvm/IR/DerivedTypes.h"
23#include "llvm/IR/Function.h"
24#include "llvm/IR/GlobalVariable.h"
25#include "llvm/IR/Instructions.h"
26#include "llvm/IR/IntrinsicInst.h"
27#include "llvm/IR/LLVMContext.h"
28#include "llvm/IR/Metadata.h"
29#include "llvm/Support/CFG.h"
30#include "llvm/Transforms/Utils/BasicBlockUtils.h"
31#include "llvm/Transforms/Utils/Local.h"
32#include "llvm/Transforms/Utils/ValueMapper.h"
33#include <map>
34using namespace llvm;
35
36// CloneBasicBlock - See comments in Cloning.h
37BasicBlock *llvm::CloneBasicBlock(const BasicBlock *BB,
38                                  ValueToValueMapTy &VMap,
39                                  const Twine &NameSuffix, Function *F,
40                                  ClonedCodeInfo *CodeInfo) {
41  BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "", F);
42  if (BB->hasName()) NewBB->setName(BB->getName()+NameSuffix);
43
44  bool hasCalls = false, hasDynamicAllocas = false, hasStaticAllocas = false;
45
46  // Loop over all instructions, and copy them over.
47  for (BasicBlock::const_iterator II = BB->begin(), IE = BB->end();
48       II != IE; ++II) {
49    Instruction *NewInst = II->clone();
50    if (II->hasName())
51      NewInst->setName(II->getName()+NameSuffix);
52    NewBB->getInstList().push_back(NewInst);
53    VMap[II] = NewInst;                // Add instruction map to value.
54
55    hasCalls |= (isa<CallInst>(II) && !isa<DbgInfoIntrinsic>(II));
56    if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
57      if (isa<ConstantInt>(AI->getArraySize()))
58        hasStaticAllocas = true;
59      else
60        hasDynamicAllocas = true;
61    }
62  }
63
64  if (CodeInfo) {
65    CodeInfo->ContainsCalls          |= hasCalls;
66    CodeInfo->ContainsDynamicAllocas |= hasDynamicAllocas;
67    CodeInfo->ContainsDynamicAllocas |= hasStaticAllocas &&
68                                        BB != &BB->getParent()->getEntryBlock();
69  }
70  return NewBB;
71}
72
73// Clone OldFunc into NewFunc, transforming the old arguments into references to
74// VMap values.
75//
76void llvm::CloneFunctionInto(Function *NewFunc, const Function *OldFunc,
77                             ValueToValueMapTy &VMap,
78                             bool ModuleLevelChanges,
79                             SmallVectorImpl<ReturnInst*> &Returns,
80                             const char *NameSuffix, ClonedCodeInfo *CodeInfo,
81                             ValueMapTypeRemapper *TypeMapper,
82                             ValueMaterializer *Materializer) {
83  assert(NameSuffix && "NameSuffix cannot be null!");
84
85#ifndef NDEBUG
86  for (Function::const_arg_iterator I = OldFunc->arg_begin(),
87       E = OldFunc->arg_end(); I != E; ++I)
88    assert(VMap.count(I) && "No mapping from source argument specified!");
89#endif
90
91  AttributeSet OldAttrs = OldFunc->getAttributes();
92  // Clone any argument attributes that are present in the VMap.
93  for (Function::const_arg_iterator I = OldFunc->arg_begin(),
94                                    E = OldFunc->arg_end();
95       I != E; ++I)
96    if (Argument *Anew = dyn_cast<Argument>(VMap[I])) {
97      AttributeSet attrs =
98          OldAttrs.getParamAttributes(I->getArgNo() + 1);
99      if (attrs.getNumSlots() > 0)
100        Anew->addAttr(attrs);
101    }
102
103  NewFunc->setAttributes(NewFunc->getAttributes()
104                         .addAttributes(NewFunc->getContext(),
105                                        AttributeSet::ReturnIndex,
106                                        OldAttrs.getRetAttributes()));
107  NewFunc->setAttributes(NewFunc->getAttributes()
108                         .addAttributes(NewFunc->getContext(),
109                                        AttributeSet::FunctionIndex,
110                                        OldAttrs.getFnAttributes()));
111
112  // Loop over all of the basic blocks in the function, cloning them as
113  // appropriate.  Note that we save BE this way in order to handle cloning of
114  // recursive functions into themselves.
115  //
116  for (Function::const_iterator BI = OldFunc->begin(), BE = OldFunc->end();
117       BI != BE; ++BI) {
118    const BasicBlock &BB = *BI;
119
120    // Create a new basic block and copy instructions into it!
121    BasicBlock *CBB = CloneBasicBlock(&BB, VMap, NameSuffix, NewFunc, CodeInfo);
122
123    // Add basic block mapping.
124    VMap[&BB] = CBB;
125
126    // It is only legal to clone a function if a block address within that
127    // function is never referenced outside of the function.  Given that, we
128    // want to map block addresses from the old function to block addresses in
129    // the clone. (This is different from the generic ValueMapper
130    // implementation, which generates an invalid blockaddress when
131    // cloning a function.)
132    if (BB.hasAddressTaken()) {
133      Constant *OldBBAddr = BlockAddress::get(const_cast<Function*>(OldFunc),
134                                              const_cast<BasicBlock*>(&BB));
135      VMap[OldBBAddr] = BlockAddress::get(NewFunc, CBB);
136    }
137
138    // Note return instructions for the caller.
139    if (ReturnInst *RI = dyn_cast<ReturnInst>(CBB->getTerminator()))
140      Returns.push_back(RI);
141  }
142
143  // Loop over all of the instructions in the function, fixing up operand
144  // references as we go.  This uses VMap to do all the hard work.
145  for (Function::iterator BB = cast<BasicBlock>(VMap[OldFunc->begin()]),
146         BE = NewFunc->end(); BB != BE; ++BB)
147    // Loop over all instructions, fixing each one as we find it...
148    for (BasicBlock::iterator II = BB->begin(); II != BB->end(); ++II)
149      RemapInstruction(II, VMap,
150                       ModuleLevelChanges ? RF_None : RF_NoModuleLevelChanges,
151                       TypeMapper, Materializer);
152}
153
154/// CloneFunction - Return a copy of the specified function, but without
155/// embedding the function into another module.  Also, any references specified
156/// in the VMap are changed to refer to their mapped value instead of the
157/// original one.  If any of the arguments to the function are in the VMap,
158/// the arguments are deleted from the resultant function.  The VMap is
159/// updated to include mappings from all of the instructions and basicblocks in
160/// the function from their old to new values.
161///
162Function *llvm::CloneFunction(const Function *F, ValueToValueMapTy &VMap,
163                              bool ModuleLevelChanges,
164                              ClonedCodeInfo *CodeInfo) {
165  std::vector<Type*> ArgTypes;
166
167  // The user might be deleting arguments to the function by specifying them in
168  // the VMap.  If so, we need to not add the arguments to the arg ty vector
169  //
170  for (Function::const_arg_iterator I = F->arg_begin(), E = F->arg_end();
171       I != E; ++I)
172    if (VMap.count(I) == 0)  // Haven't mapped the argument to anything yet?
173      ArgTypes.push_back(I->getType());
174
175  // Create a new function type...
176  FunctionType *FTy = FunctionType::get(F->getFunctionType()->getReturnType(),
177                                    ArgTypes, F->getFunctionType()->isVarArg());
178
179  // Create the new function...
180  Function *NewF = Function::Create(FTy, F->getLinkage(), F->getName());
181
182  // Loop over the arguments, copying the names of the mapped arguments over...
183  Function::arg_iterator DestI = NewF->arg_begin();
184  for (Function::const_arg_iterator I = F->arg_begin(), E = F->arg_end();
185       I != E; ++I)
186    if (VMap.count(I) == 0) {   // Is this argument preserved?
187      DestI->setName(I->getName()); // Copy the name over...
188      VMap[I] = DestI++;        // Add mapping to VMap
189    }
190
191  SmallVector<ReturnInst*, 8> Returns;  // Ignore returns cloned.
192  CloneFunctionInto(NewF, F, VMap, ModuleLevelChanges, Returns, "", CodeInfo);
193  return NewF;
194}
195
196
197
198namespace {
199  /// PruningFunctionCloner - This class is a private class used to implement
200  /// the CloneAndPruneFunctionInto method.
201  struct PruningFunctionCloner {
202    Function *NewFunc;
203    const Function *OldFunc;
204    ValueToValueMapTy &VMap;
205    bool ModuleLevelChanges;
206    const char *NameSuffix;
207    ClonedCodeInfo *CodeInfo;
208    const DataLayout *TD;
209  public:
210    PruningFunctionCloner(Function *newFunc, const Function *oldFunc,
211                          ValueToValueMapTy &valueMap,
212                          bool moduleLevelChanges,
213                          const char *nameSuffix,
214                          ClonedCodeInfo *codeInfo,
215                          const DataLayout *td)
216    : NewFunc(newFunc), OldFunc(oldFunc),
217      VMap(valueMap), ModuleLevelChanges(moduleLevelChanges),
218      NameSuffix(nameSuffix), CodeInfo(codeInfo), TD(td) {
219    }
220
221    /// CloneBlock - The specified block is found to be reachable, clone it and
222    /// anything that it can reach.
223    void CloneBlock(const BasicBlock *BB,
224                    std::vector<const BasicBlock*> &ToClone);
225  };
226}
227
228/// CloneBlock - The specified block is found to be reachable, clone it and
229/// anything that it can reach.
230void PruningFunctionCloner::CloneBlock(const BasicBlock *BB,
231                                       std::vector<const BasicBlock*> &ToClone){
232  WeakVH &BBEntry = VMap[BB];
233
234  // Have we already cloned this block?
235  if (BBEntry) return;
236
237  // Nope, clone it now.
238  BasicBlock *NewBB;
239  BBEntry = NewBB = BasicBlock::Create(BB->getContext());
240  if (BB->hasName()) NewBB->setName(BB->getName()+NameSuffix);
241
242  // It is only legal to clone a function if a block address within that
243  // function is never referenced outside of the function.  Given that, we
244  // want to map block addresses from the old function to block addresses in
245  // the clone. (This is different from the generic ValueMapper
246  // implementation, which generates an invalid blockaddress when
247  // cloning a function.)
248  //
249  // Note that we don't need to fix the mapping for unreachable blocks;
250  // the default mapping there is safe.
251  if (BB->hasAddressTaken()) {
252    Constant *OldBBAddr = BlockAddress::get(const_cast<Function*>(OldFunc),
253                                            const_cast<BasicBlock*>(BB));
254    VMap[OldBBAddr] = BlockAddress::get(NewFunc, NewBB);
255  }
256
257
258  bool hasCalls = false, hasDynamicAllocas = false, hasStaticAllocas = false;
259
260  // Loop over all instructions, and copy them over, DCE'ing as we go.  This
261  // loop doesn't include the terminator.
262  for (BasicBlock::const_iterator II = BB->begin(), IE = --BB->end();
263       II != IE; ++II) {
264    Instruction *NewInst = II->clone();
265
266    // Eagerly remap operands to the newly cloned instruction, except for PHI
267    // nodes for which we defer processing until we update the CFG.
268    if (!isa<PHINode>(NewInst)) {
269      RemapInstruction(NewInst, VMap,
270                       ModuleLevelChanges ? RF_None : RF_NoModuleLevelChanges);
271
272      // If we can simplify this instruction to some other value, simply add
273      // a mapping to that value rather than inserting a new instruction into
274      // the basic block.
275      if (Value *V = SimplifyInstruction(NewInst, TD)) {
276        // On the off-chance that this simplifies to an instruction in the old
277        // function, map it back into the new function.
278        if (Value *MappedV = VMap.lookup(V))
279          V = MappedV;
280
281        VMap[II] = V;
282        delete NewInst;
283        continue;
284      }
285    }
286
287    if (II->hasName())
288      NewInst->setName(II->getName()+NameSuffix);
289    VMap[II] = NewInst;                // Add instruction map to value.
290    NewBB->getInstList().push_back(NewInst);
291    hasCalls |= (isa<CallInst>(II) && !isa<DbgInfoIntrinsic>(II));
292    if (const AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
293      if (isa<ConstantInt>(AI->getArraySize()))
294        hasStaticAllocas = true;
295      else
296        hasDynamicAllocas = true;
297    }
298  }
299
300  // Finally, clone over the terminator.
301  const TerminatorInst *OldTI = BB->getTerminator();
302  bool TerminatorDone = false;
303  if (const BranchInst *BI = dyn_cast<BranchInst>(OldTI)) {
304    if (BI->isConditional()) {
305      // If the condition was a known constant in the callee...
306      ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition());
307      // Or is a known constant in the caller...
308      if (Cond == 0) {
309        Value *V = VMap[BI->getCondition()];
310        Cond = dyn_cast_or_null<ConstantInt>(V);
311      }
312
313      // Constant fold to uncond branch!
314      if (Cond) {
315        BasicBlock *Dest = BI->getSuccessor(!Cond->getZExtValue());
316        VMap[OldTI] = BranchInst::Create(Dest, NewBB);
317        ToClone.push_back(Dest);
318        TerminatorDone = true;
319      }
320    }
321  } else if (const SwitchInst *SI = dyn_cast<SwitchInst>(OldTI)) {
322    // If switching on a value known constant in the caller.
323    ConstantInt *Cond = dyn_cast<ConstantInt>(SI->getCondition());
324    if (Cond == 0) { // Or known constant after constant prop in the callee...
325      Value *V = VMap[SI->getCondition()];
326      Cond = dyn_cast_or_null<ConstantInt>(V);
327    }
328    if (Cond) {     // Constant fold to uncond branch!
329      SwitchInst::ConstCaseIt Case = SI->findCaseValue(Cond);
330      BasicBlock *Dest = const_cast<BasicBlock*>(Case.getCaseSuccessor());
331      VMap[OldTI] = BranchInst::Create(Dest, NewBB);
332      ToClone.push_back(Dest);
333      TerminatorDone = true;
334    }
335  }
336
337  if (!TerminatorDone) {
338    Instruction *NewInst = OldTI->clone();
339    if (OldTI->hasName())
340      NewInst->setName(OldTI->getName()+NameSuffix);
341    NewBB->getInstList().push_back(NewInst);
342    VMap[OldTI] = NewInst;             // Add instruction map to value.
343
344    // Recursively clone any reachable successor blocks.
345    const TerminatorInst *TI = BB->getTerminator();
346    for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
347      ToClone.push_back(TI->getSuccessor(i));
348  }
349
350  if (CodeInfo) {
351    CodeInfo->ContainsCalls          |= hasCalls;
352    CodeInfo->ContainsDynamicAllocas |= hasDynamicAllocas;
353    CodeInfo->ContainsDynamicAllocas |= hasStaticAllocas &&
354      BB != &BB->getParent()->front();
355  }
356}
357
358/// CloneAndPruneFunctionInto - This works exactly like CloneFunctionInto,
359/// except that it does some simple constant prop and DCE on the fly.  The
360/// effect of this is to copy significantly less code in cases where (for
361/// example) a function call with constant arguments is inlined, and those
362/// constant arguments cause a significant amount of code in the callee to be
363/// dead.  Since this doesn't produce an exact copy of the input, it can't be
364/// used for things like CloneFunction or CloneModule.
365void llvm::CloneAndPruneFunctionInto(Function *NewFunc, const Function *OldFunc,
366                                     ValueToValueMapTy &VMap,
367                                     bool ModuleLevelChanges,
368                                     SmallVectorImpl<ReturnInst*> &Returns,
369                                     const char *NameSuffix,
370                                     ClonedCodeInfo *CodeInfo,
371                                     const DataLayout *TD,
372                                     Instruction *TheCall) {
373  assert(NameSuffix && "NameSuffix cannot be null!");
374
375#ifndef NDEBUG
376  for (Function::const_arg_iterator II = OldFunc->arg_begin(),
377       E = OldFunc->arg_end(); II != E; ++II)
378    assert(VMap.count(II) && "No mapping from source argument specified!");
379#endif
380
381  PruningFunctionCloner PFC(NewFunc, OldFunc, VMap, ModuleLevelChanges,
382                            NameSuffix, CodeInfo, TD);
383
384  // Clone the entry block, and anything recursively reachable from it.
385  std::vector<const BasicBlock*> CloneWorklist;
386  CloneWorklist.push_back(&OldFunc->getEntryBlock());
387  while (!CloneWorklist.empty()) {
388    const BasicBlock *BB = CloneWorklist.back();
389    CloneWorklist.pop_back();
390    PFC.CloneBlock(BB, CloneWorklist);
391  }
392
393  // Loop over all of the basic blocks in the old function.  If the block was
394  // reachable, we have cloned it and the old block is now in the value map:
395  // insert it into the new function in the right order.  If not, ignore it.
396  //
397  // Defer PHI resolution until rest of function is resolved.
398  SmallVector<const PHINode*, 16> PHIToResolve;
399  for (Function::const_iterator BI = OldFunc->begin(), BE = OldFunc->end();
400       BI != BE; ++BI) {
401    Value *V = VMap[BI];
402    BasicBlock *NewBB = cast_or_null<BasicBlock>(V);
403    if (NewBB == 0) continue;  // Dead block.
404
405    // Add the new block to the new function.
406    NewFunc->getBasicBlockList().push_back(NewBB);
407
408    // Handle PHI nodes specially, as we have to remove references to dead
409    // blocks.
410    for (BasicBlock::const_iterator I = BI->begin(), E = BI->end(); I != E; ++I)
411      if (const PHINode *PN = dyn_cast<PHINode>(I))
412        PHIToResolve.push_back(PN);
413      else
414        break;
415
416    // Finally, remap the terminator instructions, as those can't be remapped
417    // until all BBs are mapped.
418    RemapInstruction(NewBB->getTerminator(), VMap,
419                     ModuleLevelChanges ? RF_None : RF_NoModuleLevelChanges);
420  }
421
422  // Defer PHI resolution until rest of function is resolved, PHI resolution
423  // requires the CFG to be up-to-date.
424  for (unsigned phino = 0, e = PHIToResolve.size(); phino != e; ) {
425    const PHINode *OPN = PHIToResolve[phino];
426    unsigned NumPreds = OPN->getNumIncomingValues();
427    const BasicBlock *OldBB = OPN->getParent();
428    BasicBlock *NewBB = cast<BasicBlock>(VMap[OldBB]);
429
430    // Map operands for blocks that are live and remove operands for blocks
431    // that are dead.
432    for (; phino != PHIToResolve.size() &&
433         PHIToResolve[phino]->getParent() == OldBB; ++phino) {
434      OPN = PHIToResolve[phino];
435      PHINode *PN = cast<PHINode>(VMap[OPN]);
436      for (unsigned pred = 0, e = NumPreds; pred != e; ++pred) {
437        Value *V = VMap[PN->getIncomingBlock(pred)];
438        if (BasicBlock *MappedBlock = cast_or_null<BasicBlock>(V)) {
439          Value *InVal = MapValue(PN->getIncomingValue(pred),
440                                  VMap,
441                        ModuleLevelChanges ? RF_None : RF_NoModuleLevelChanges);
442          assert(InVal && "Unknown input value?");
443          PN->setIncomingValue(pred, InVal);
444          PN->setIncomingBlock(pred, MappedBlock);
445        } else {
446          PN->removeIncomingValue(pred, false);
447          --pred, --e;  // Revisit the next entry.
448        }
449      }
450    }
451
452    // The loop above has removed PHI entries for those blocks that are dead
453    // and has updated others.  However, if a block is live (i.e. copied over)
454    // but its terminator has been changed to not go to this block, then our
455    // phi nodes will have invalid entries.  Update the PHI nodes in this
456    // case.
457    PHINode *PN = cast<PHINode>(NewBB->begin());
458    NumPreds = std::distance(pred_begin(NewBB), pred_end(NewBB));
459    if (NumPreds != PN->getNumIncomingValues()) {
460      assert(NumPreds < PN->getNumIncomingValues());
461      // Count how many times each predecessor comes to this block.
462      std::map<BasicBlock*, unsigned> PredCount;
463      for (pred_iterator PI = pred_begin(NewBB), E = pred_end(NewBB);
464           PI != E; ++PI)
465        --PredCount[*PI];
466
467      // Figure out how many entries to remove from each PHI.
468      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
469        ++PredCount[PN->getIncomingBlock(i)];
470
471      // At this point, the excess predecessor entries are positive in the
472      // map.  Loop over all of the PHIs and remove excess predecessor
473      // entries.
474      BasicBlock::iterator I = NewBB->begin();
475      for (; (PN = dyn_cast<PHINode>(I)); ++I) {
476        for (std::map<BasicBlock*, unsigned>::iterator PCI =PredCount.begin(),
477             E = PredCount.end(); PCI != E; ++PCI) {
478          BasicBlock *Pred     = PCI->first;
479          for (unsigned NumToRemove = PCI->second; NumToRemove; --NumToRemove)
480            PN->removeIncomingValue(Pred, false);
481        }
482      }
483    }
484
485    // If the loops above have made these phi nodes have 0 or 1 operand,
486    // replace them with undef or the input value.  We must do this for
487    // correctness, because 0-operand phis are not valid.
488    PN = cast<PHINode>(NewBB->begin());
489    if (PN->getNumIncomingValues() == 0) {
490      BasicBlock::iterator I = NewBB->begin();
491      BasicBlock::const_iterator OldI = OldBB->begin();
492      while ((PN = dyn_cast<PHINode>(I++))) {
493        Value *NV = UndefValue::get(PN->getType());
494        PN->replaceAllUsesWith(NV);
495        assert(VMap[OldI] == PN && "VMap mismatch");
496        VMap[OldI] = NV;
497        PN->eraseFromParent();
498        ++OldI;
499      }
500    }
501  }
502
503  // Make a second pass over the PHINodes now that all of them have been
504  // remapped into the new function, simplifying the PHINode and performing any
505  // recursive simplifications exposed. This will transparently update the
506  // WeakVH in the VMap. Notably, we rely on that so that if we coalesce
507  // two PHINodes, the iteration over the old PHIs remains valid, and the
508  // mapping will just map us to the new node (which may not even be a PHI
509  // node).
510  for (unsigned Idx = 0, Size = PHIToResolve.size(); Idx != Size; ++Idx)
511    if (PHINode *PN = dyn_cast<PHINode>(VMap[PHIToResolve[Idx]]))
512      recursivelySimplifyInstruction(PN, TD);
513
514  // Now that the inlined function body has been fully constructed, go through
515  // and zap unconditional fall-through branches.  This happen all the time when
516  // specializing code: code specialization turns conditional branches into
517  // uncond branches, and this code folds them.
518  Function::iterator Begin = cast<BasicBlock>(VMap[&OldFunc->getEntryBlock()]);
519  Function::iterator I = Begin;
520  while (I != NewFunc->end()) {
521    // Check if this block has become dead during inlining or other
522    // simplifications. Note that the first block will appear dead, as it has
523    // not yet been wired up properly.
524    if (I != Begin && (pred_begin(I) == pred_end(I) ||
525                       I->getSinglePredecessor() == I)) {
526      BasicBlock *DeadBB = I++;
527      DeleteDeadBlock(DeadBB);
528      continue;
529    }
530
531    // We need to simplify conditional branches and switches with a constant
532    // operand. We try to prune these out when cloning, but if the
533    // simplification required looking through PHI nodes, those are only
534    // available after forming the full basic block. That may leave some here,
535    // and we still want to prune the dead code as early as possible.
536    ConstantFoldTerminator(I);
537
538    BranchInst *BI = dyn_cast<BranchInst>(I->getTerminator());
539    if (!BI || BI->isConditional()) { ++I; continue; }
540
541    BasicBlock *Dest = BI->getSuccessor(0);
542    if (!Dest->getSinglePredecessor()) {
543      ++I; continue;
544    }
545
546    // We shouldn't be able to get single-entry PHI nodes here, as instsimplify
547    // above should have zapped all of them..
548    assert(!isa<PHINode>(Dest->begin()));
549
550    // We know all single-entry PHI nodes in the inlined function have been
551    // removed, so we just need to splice the blocks.
552    BI->eraseFromParent();
553
554    // Make all PHI nodes that referred to Dest now refer to I as their source.
555    Dest->replaceAllUsesWith(I);
556
557    // Move all the instructions in the succ to the pred.
558    I->getInstList().splice(I->end(), Dest->getInstList());
559
560    // Remove the dest block.
561    Dest->eraseFromParent();
562
563    // Do not increment I, iteratively merge all things this block branches to.
564  }
565
566  // Make a final pass over the basic blocks from theh old function to gather
567  // any return instructions which survived folding. We have to do this here
568  // because we can iteratively remove and merge returns above.
569  for (Function::iterator I = cast<BasicBlock>(VMap[&OldFunc->getEntryBlock()]),
570                          E = NewFunc->end();
571       I != E; ++I)
572    if (ReturnInst *RI = dyn_cast<ReturnInst>(I->getTerminator()))
573      Returns.push_back(RI);
574}
575