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Local.cpp
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00001 //===-- Local.cpp - Functions to perform local transformations ------------===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file is distributed under the University of Illinois Open Source
00006 // License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This family of functions perform various local transformations to the
00011 // program.
00012 //
00013 //===----------------------------------------------------------------------===//
00014 
00015 #include "llvm/Transforms/Utils/Local.h"
00016 #include "llvm/ADT/DenseMap.h"
00017 #include "llvm/ADT/STLExtras.h"
00018 #include "llvm/ADT/SmallPtrSet.h"
00019 #include "llvm/ADT/Statistic.h"
00020 #include "llvm/Analysis/InstructionSimplify.h"
00021 #include "llvm/Analysis/MemoryBuiltins.h"
00022 #include "llvm/Analysis/ValueTracking.h"
00023 #include "llvm/IR/CFG.h"
00024 #include "llvm/IR/Constants.h"
00025 #include "llvm/IR/DIBuilder.h"
00026 #include "llvm/IR/DataLayout.h"
00027 #include "llvm/IR/DebugInfo.h"
00028 #include "llvm/IR/DerivedTypes.h"
00029 #include "llvm/IR/Dominators.h"
00030 #include "llvm/IR/GetElementPtrTypeIterator.h"
00031 #include "llvm/IR/GlobalAlias.h"
00032 #include "llvm/IR/GlobalVariable.h"
00033 #include "llvm/IR/IRBuilder.h"
00034 #include "llvm/IR/Instructions.h"
00035 #include "llvm/IR/IntrinsicInst.h"
00036 #include "llvm/IR/Intrinsics.h"
00037 #include "llvm/IR/MDBuilder.h"
00038 #include "llvm/IR/Metadata.h"
00039 #include "llvm/IR/Operator.h"
00040 #include "llvm/IR/ValueHandle.h"
00041 #include "llvm/Support/Debug.h"
00042 #include "llvm/Support/MathExtras.h"
00043 #include "llvm/Support/raw_ostream.h"
00044 using namespace llvm;
00045 
00046 #define DEBUG_TYPE "local"
00047 
00048 STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
00049 
00050 //===----------------------------------------------------------------------===//
00051 //  Local constant propagation.
00052 //
00053 
00054 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
00055 /// constant value, convert it into an unconditional branch to the constant
00056 /// destination.  This is a nontrivial operation because the successors of this
00057 /// basic block must have their PHI nodes updated.
00058 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
00059 /// conditions and indirectbr addresses this might make dead if
00060 /// DeleteDeadConditions is true.
00061 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
00062                                   const TargetLibraryInfo *TLI) {
00063   TerminatorInst *T = BB->getTerminator();
00064   IRBuilder<> Builder(T);
00065 
00066   // Branch - See if we are conditional jumping on constant
00067   if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
00068     if (BI->isUnconditional()) return false;  // Can't optimize uncond branch
00069     BasicBlock *Dest1 = BI->getSuccessor(0);
00070     BasicBlock *Dest2 = BI->getSuccessor(1);
00071 
00072     if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
00073       // Are we branching on constant?
00074       // YES.  Change to unconditional branch...
00075       BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
00076       BasicBlock *OldDest     = Cond->getZExtValue() ? Dest2 : Dest1;
00077 
00078       //cerr << "Function: " << T->getParent()->getParent()
00079       //     << "\nRemoving branch from " << T->getParent()
00080       //     << "\n\nTo: " << OldDest << endl;
00081 
00082       // Let the basic block know that we are letting go of it.  Based on this,
00083       // it will adjust it's PHI nodes.
00084       OldDest->removePredecessor(BB);
00085 
00086       // Replace the conditional branch with an unconditional one.
00087       Builder.CreateBr(Destination);
00088       BI->eraseFromParent();
00089       return true;
00090     }
00091 
00092     if (Dest2 == Dest1) {       // Conditional branch to same location?
00093       // This branch matches something like this:
00094       //     br bool %cond, label %Dest, label %Dest
00095       // and changes it into:  br label %Dest
00096 
00097       // Let the basic block know that we are letting go of one copy of it.
00098       assert(BI->getParent() && "Terminator not inserted in block!");
00099       Dest1->removePredecessor(BI->getParent());
00100 
00101       // Replace the conditional branch with an unconditional one.
00102       Builder.CreateBr(Dest1);
00103       Value *Cond = BI->getCondition();
00104       BI->eraseFromParent();
00105       if (DeleteDeadConditions)
00106         RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
00107       return true;
00108     }
00109     return false;
00110   }
00111 
00112   if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
00113     // If we are switching on a constant, we can convert the switch into a
00114     // single branch instruction!
00115     ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
00116     BasicBlock *TheOnlyDest = SI->getDefaultDest();
00117     BasicBlock *DefaultDest = TheOnlyDest;
00118 
00119     // Figure out which case it goes to.
00120     for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
00121          i != e; ++i) {
00122       // Found case matching a constant operand?
00123       if (i.getCaseValue() == CI) {
00124         TheOnlyDest = i.getCaseSuccessor();
00125         break;
00126       }
00127 
00128       // Check to see if this branch is going to the same place as the default
00129       // dest.  If so, eliminate it as an explicit compare.
00130       if (i.getCaseSuccessor() == DefaultDest) {
00131         MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
00132         unsigned NCases = SI->getNumCases();
00133         // Fold the case metadata into the default if there will be any branches
00134         // left, unless the metadata doesn't match the switch.
00135         if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) {
00136           // Collect branch weights into a vector.
00137           SmallVector<uint32_t, 8> Weights;
00138           for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
00139                ++MD_i) {
00140             ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
00141             assert(CI);
00142             Weights.push_back(CI->getValue().getZExtValue());
00143           }
00144           // Merge weight of this case to the default weight.
00145           unsigned idx = i.getCaseIndex();
00146           Weights[0] += Weights[idx+1];
00147           // Remove weight for this case.
00148           std::swap(Weights[idx+1], Weights.back());
00149           Weights.pop_back();
00150           SI->setMetadata(LLVMContext::MD_prof,
00151                           MDBuilder(BB->getContext()).
00152                           createBranchWeights(Weights));
00153         }
00154         // Remove this entry.
00155         DefaultDest->removePredecessor(SI->getParent());
00156         SI->removeCase(i);
00157         --i; --e;
00158         continue;
00159       }
00160 
00161       // Otherwise, check to see if the switch only branches to one destination.
00162       // We do this by reseting "TheOnlyDest" to null when we find two non-equal
00163       // destinations.
00164       if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = nullptr;
00165     }
00166 
00167     if (CI && !TheOnlyDest) {
00168       // Branching on a constant, but not any of the cases, go to the default
00169       // successor.
00170       TheOnlyDest = SI->getDefaultDest();
00171     }
00172 
00173     // If we found a single destination that we can fold the switch into, do so
00174     // now.
00175     if (TheOnlyDest) {
00176       // Insert the new branch.
00177       Builder.CreateBr(TheOnlyDest);
00178       BasicBlock *BB = SI->getParent();
00179 
00180       // Remove entries from PHI nodes which we no longer branch to...
00181       for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
00182         // Found case matching a constant operand?
00183         BasicBlock *Succ = SI->getSuccessor(i);
00184         if (Succ == TheOnlyDest)
00185           TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest
00186         else
00187           Succ->removePredecessor(BB);
00188       }
00189 
00190       // Delete the old switch.
00191       Value *Cond = SI->getCondition();
00192       SI->eraseFromParent();
00193       if (DeleteDeadConditions)
00194         RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
00195       return true;
00196     }
00197 
00198     if (SI->getNumCases() == 1) {
00199       // Otherwise, we can fold this switch into a conditional branch
00200       // instruction if it has only one non-default destination.
00201       SwitchInst::CaseIt FirstCase = SI->case_begin();
00202       Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
00203           FirstCase.getCaseValue(), "cond");
00204 
00205       // Insert the new branch.
00206       BranchInst *NewBr = Builder.CreateCondBr(Cond,
00207                                                FirstCase.getCaseSuccessor(),
00208                                                SI->getDefaultDest());
00209       MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
00210       if (MD && MD->getNumOperands() == 3) {
00211         ConstantInt *SICase = dyn_cast<ConstantInt>(MD->getOperand(2));
00212         ConstantInt *SIDef = dyn_cast<ConstantInt>(MD->getOperand(1));
00213         assert(SICase && SIDef);
00214         // The TrueWeight should be the weight for the single case of SI.
00215         NewBr->setMetadata(LLVMContext::MD_prof,
00216                         MDBuilder(BB->getContext()).
00217                         createBranchWeights(SICase->getValue().getZExtValue(),
00218                                             SIDef->getValue().getZExtValue()));
00219       }
00220 
00221       // Delete the old switch.
00222       SI->eraseFromParent();
00223       return true;
00224     }
00225     return false;
00226   }
00227 
00228   if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
00229     // indirectbr blockaddress(@F, @BB) -> br label @BB
00230     if (BlockAddress *BA =
00231           dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
00232       BasicBlock *TheOnlyDest = BA->getBasicBlock();
00233       // Insert the new branch.
00234       Builder.CreateBr(TheOnlyDest);
00235 
00236       for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
00237         if (IBI->getDestination(i) == TheOnlyDest)
00238           TheOnlyDest = nullptr;
00239         else
00240           IBI->getDestination(i)->removePredecessor(IBI->getParent());
00241       }
00242       Value *Address = IBI->getAddress();
00243       IBI->eraseFromParent();
00244       if (DeleteDeadConditions)
00245         RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
00246 
00247       // If we didn't find our destination in the IBI successor list, then we
00248       // have undefined behavior.  Replace the unconditional branch with an
00249       // 'unreachable' instruction.
00250       if (TheOnlyDest) {
00251         BB->getTerminator()->eraseFromParent();
00252         new UnreachableInst(BB->getContext(), BB);
00253       }
00254 
00255       return true;
00256     }
00257   }
00258 
00259   return false;
00260 }
00261 
00262 
00263 //===----------------------------------------------------------------------===//
00264 //  Local dead code elimination.
00265 //
00266 
00267 /// isInstructionTriviallyDead - Return true if the result produced by the
00268 /// instruction is not used, and the instruction has no side effects.
00269 ///
00270 bool llvm::isInstructionTriviallyDead(Instruction *I,
00271                                       const TargetLibraryInfo *TLI) {
00272   if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
00273 
00274   // We don't want the landingpad instruction removed by anything this general.
00275   if (isa<LandingPadInst>(I))
00276     return false;
00277 
00278   // We don't want debug info removed by anything this general, unless
00279   // debug info is empty.
00280   if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
00281     if (DDI->getAddress())
00282       return false;
00283     return true;
00284   }
00285   if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
00286     if (DVI->getValue())
00287       return false;
00288     return true;
00289   }
00290 
00291   if (!I->mayHaveSideEffects()) return true;
00292 
00293   // Special case intrinsics that "may have side effects" but can be deleted
00294   // when dead.
00295   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
00296     // Safe to delete llvm.stacksave if dead.
00297     if (II->getIntrinsicID() == Intrinsic::stacksave)
00298       return true;
00299 
00300     // Lifetime intrinsics are dead when their right-hand is undef.
00301     if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
00302         II->getIntrinsicID() == Intrinsic::lifetime_end)
00303       return isa<UndefValue>(II->getArgOperand(1));
00304 
00305     // Assumptions are dead if their condition is trivially true.
00306     if (II->getIntrinsicID() == Intrinsic::assume) {
00307       if (ConstantInt *Cond = dyn_cast<ConstantInt>(II->getArgOperand(0)))
00308         return !Cond->isZero();
00309 
00310       return false;
00311     }
00312   }
00313 
00314   if (isAllocLikeFn(I, TLI)) return true;
00315 
00316   if (CallInst *CI = isFreeCall(I, TLI))
00317     if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
00318       return C->isNullValue() || isa<UndefValue>(C);
00319 
00320   return false;
00321 }
00322 
00323 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
00324 /// trivially dead instruction, delete it.  If that makes any of its operands
00325 /// trivially dead, delete them too, recursively.  Return true if any
00326 /// instructions were deleted.
00327 bool
00328 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
00329                                                  const TargetLibraryInfo *TLI) {
00330   Instruction *I = dyn_cast<Instruction>(V);
00331   if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
00332     return false;
00333 
00334   SmallVector<Instruction*, 16> DeadInsts;
00335   DeadInsts.push_back(I);
00336 
00337   do {
00338     I = DeadInsts.pop_back_val();
00339 
00340     // Null out all of the instruction's operands to see if any operand becomes
00341     // dead as we go.
00342     for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
00343       Value *OpV = I->getOperand(i);
00344       I->setOperand(i, nullptr);
00345 
00346       if (!OpV->use_empty()) continue;
00347 
00348       // If the operand is an instruction that became dead as we nulled out the
00349       // operand, and if it is 'trivially' dead, delete it in a future loop
00350       // iteration.
00351       if (Instruction *OpI = dyn_cast<Instruction>(OpV))
00352         if (isInstructionTriviallyDead(OpI, TLI))
00353           DeadInsts.push_back(OpI);
00354     }
00355 
00356     I->eraseFromParent();
00357   } while (!DeadInsts.empty());
00358 
00359   return true;
00360 }
00361 
00362 /// areAllUsesEqual - Check whether the uses of a value are all the same.
00363 /// This is similar to Instruction::hasOneUse() except this will also return
00364 /// true when there are no uses or multiple uses that all refer to the same
00365 /// value.
00366 static bool areAllUsesEqual(Instruction *I) {
00367   Value::user_iterator UI = I->user_begin();
00368   Value::user_iterator UE = I->user_end();
00369   if (UI == UE)
00370     return true;
00371 
00372   User *TheUse = *UI;
00373   for (++UI; UI != UE; ++UI) {
00374     if (*UI != TheUse)
00375       return false;
00376   }
00377   return true;
00378 }
00379 
00380 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
00381 /// dead PHI node, due to being a def-use chain of single-use nodes that
00382 /// either forms a cycle or is terminated by a trivially dead instruction,
00383 /// delete it.  If that makes any of its operands trivially dead, delete them
00384 /// too, recursively.  Return true if a change was made.
00385 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
00386                                         const TargetLibraryInfo *TLI) {
00387   SmallPtrSet<Instruction*, 4> Visited;
00388   for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
00389        I = cast<Instruction>(*I->user_begin())) {
00390     if (I->use_empty())
00391       return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
00392 
00393     // If we find an instruction more than once, we're on a cycle that
00394     // won't prove fruitful.
00395     if (!Visited.insert(I)) {
00396       // Break the cycle and delete the instruction and its operands.
00397       I->replaceAllUsesWith(UndefValue::get(I->getType()));
00398       (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
00399       return true;
00400     }
00401   }
00402   return false;
00403 }
00404 
00405 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
00406 /// simplify any instructions in it and recursively delete dead instructions.
00407 ///
00408 /// This returns true if it changed the code, note that it can delete
00409 /// instructions in other blocks as well in this block.
00410 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const DataLayout *TD,
00411                                        const TargetLibraryInfo *TLI) {
00412   bool MadeChange = false;
00413 
00414 #ifndef NDEBUG
00415   // In debug builds, ensure that the terminator of the block is never replaced
00416   // or deleted by these simplifications. The idea of simplification is that it
00417   // cannot introduce new instructions, and there is no way to replace the
00418   // terminator of a block without introducing a new instruction.
00419   AssertingVH<Instruction> TerminatorVH(--BB->end());
00420 #endif
00421 
00422   for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) {
00423     assert(!BI->isTerminator());
00424     Instruction *Inst = BI++;
00425 
00426     WeakVH BIHandle(BI);
00427     if (recursivelySimplifyInstruction(Inst, TD, TLI)) {
00428       MadeChange = true;
00429       if (BIHandle != BI)
00430         BI = BB->begin();
00431       continue;
00432     }
00433 
00434     MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
00435     if (BIHandle != BI)
00436       BI = BB->begin();
00437   }
00438   return MadeChange;
00439 }
00440 
00441 //===----------------------------------------------------------------------===//
00442 //  Control Flow Graph Restructuring.
00443 //
00444 
00445 
00446 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
00447 /// method is called when we're about to delete Pred as a predecessor of BB.  If
00448 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
00449 ///
00450 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
00451 /// nodes that collapse into identity values.  For example, if we have:
00452 ///   x = phi(1, 0, 0, 0)
00453 ///   y = and x, z
00454 ///
00455 /// .. and delete the predecessor corresponding to the '1', this will attempt to
00456 /// recursively fold the and to 0.
00457 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
00458                                         DataLayout *TD) {
00459   // This only adjusts blocks with PHI nodes.
00460   if (!isa<PHINode>(BB->begin()))
00461     return;
00462 
00463   // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
00464   // them down.  This will leave us with single entry phi nodes and other phis
00465   // that can be removed.
00466   BB->removePredecessor(Pred, true);
00467 
00468   WeakVH PhiIt = &BB->front();
00469   while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
00470     PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
00471     Value *OldPhiIt = PhiIt;
00472 
00473     if (!recursivelySimplifyInstruction(PN, TD))
00474       continue;
00475 
00476     // If recursive simplification ended up deleting the next PHI node we would
00477     // iterate to, then our iterator is invalid, restart scanning from the top
00478     // of the block.
00479     if (PhiIt != OldPhiIt) PhiIt = &BB->front();
00480   }
00481 }
00482 
00483 
00484 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
00485 /// predecessor is known to have one successor (DestBB!).  Eliminate the edge
00486 /// between them, moving the instructions in the predecessor into DestBB and
00487 /// deleting the predecessor block.
00488 ///
00489 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
00490   // If BB has single-entry PHI nodes, fold them.
00491   while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
00492     Value *NewVal = PN->getIncomingValue(0);
00493     // Replace self referencing PHI with undef, it must be dead.
00494     if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
00495     PN->replaceAllUsesWith(NewVal);
00496     PN->eraseFromParent();
00497   }
00498 
00499   BasicBlock *PredBB = DestBB->getSinglePredecessor();
00500   assert(PredBB && "Block doesn't have a single predecessor!");
00501 
00502   // Zap anything that took the address of DestBB.  Not doing this will give the
00503   // address an invalid value.
00504   if (DestBB->hasAddressTaken()) {
00505     BlockAddress *BA = BlockAddress::get(DestBB);
00506     Constant *Replacement =
00507       ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
00508     BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
00509                                                      BA->getType()));
00510     BA->destroyConstant();
00511   }
00512 
00513   // Anything that branched to PredBB now branches to DestBB.
00514   PredBB->replaceAllUsesWith(DestBB);
00515 
00516   // Splice all the instructions from PredBB to DestBB.
00517   PredBB->getTerminator()->eraseFromParent();
00518   DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
00519 
00520   // If the PredBB is the entry block of the function, move DestBB up to
00521   // become the entry block after we erase PredBB.
00522   if (PredBB == &DestBB->getParent()->getEntryBlock())
00523     DestBB->moveAfter(PredBB);
00524 
00525   if (P) {
00526     if (DominatorTreeWrapperPass *DTWP =
00527             P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
00528       DominatorTree &DT = DTWP->getDomTree();
00529       BasicBlock *PredBBIDom = DT.getNode(PredBB)->getIDom()->getBlock();
00530       DT.changeImmediateDominator(DestBB, PredBBIDom);
00531       DT.eraseNode(PredBB);
00532     }
00533   }
00534   // Nuke BB.
00535   PredBB->eraseFromParent();
00536 }
00537 
00538 /// CanMergeValues - Return true if we can choose one of these values to use
00539 /// in place of the other. Note that we will always choose the non-undef
00540 /// value to keep.
00541 static bool CanMergeValues(Value *First, Value *Second) {
00542   return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
00543 }
00544 
00545 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
00546 /// almost-empty BB ending in an unconditional branch to Succ, into Succ.
00547 ///
00548 /// Assumption: Succ is the single successor for BB.
00549 ///
00550 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
00551   assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
00552 
00553   DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
00554         << Succ->getName() << "\n");
00555   // Shortcut, if there is only a single predecessor it must be BB and merging
00556   // is always safe
00557   if (Succ->getSinglePredecessor()) return true;
00558 
00559   // Make a list of the predecessors of BB
00560   SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
00561 
00562   // Look at all the phi nodes in Succ, to see if they present a conflict when
00563   // merging these blocks
00564   for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
00565     PHINode *PN = cast<PHINode>(I);
00566 
00567     // If the incoming value from BB is again a PHINode in
00568     // BB which has the same incoming value for *PI as PN does, we can
00569     // merge the phi nodes and then the blocks can still be merged
00570     PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
00571     if (BBPN && BBPN->getParent() == BB) {
00572       for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
00573         BasicBlock *IBB = PN->getIncomingBlock(PI);
00574         if (BBPreds.count(IBB) &&
00575             !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
00576                             PN->getIncomingValue(PI))) {
00577           DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
00578                 << Succ->getName() << " is conflicting with "
00579                 << BBPN->getName() << " with regard to common predecessor "
00580                 << IBB->getName() << "\n");
00581           return false;
00582         }
00583       }
00584     } else {
00585       Value* Val = PN->getIncomingValueForBlock(BB);
00586       for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
00587         // See if the incoming value for the common predecessor is equal to the
00588         // one for BB, in which case this phi node will not prevent the merging
00589         // of the block.
00590         BasicBlock *IBB = PN->getIncomingBlock(PI);
00591         if (BBPreds.count(IBB) &&
00592             !CanMergeValues(Val, PN->getIncomingValue(PI))) {
00593           DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
00594                 << Succ->getName() << " is conflicting with regard to common "
00595                 << "predecessor " << IBB->getName() << "\n");
00596           return false;
00597         }
00598       }
00599     }
00600   }
00601 
00602   return true;
00603 }
00604 
00605 typedef SmallVector<BasicBlock *, 16> PredBlockVector;
00606 typedef DenseMap<BasicBlock *, Value *> IncomingValueMap;
00607 
00608 /// \brief Determines the value to use as the phi node input for a block.
00609 ///
00610 /// Select between \p OldVal any value that we know flows from \p BB
00611 /// to a particular phi on the basis of which one (if either) is not
00612 /// undef. Update IncomingValues based on the selected value.
00613 ///
00614 /// \param OldVal The value we are considering selecting.
00615 /// \param BB The block that the value flows in from.
00616 /// \param IncomingValues A map from block-to-value for other phi inputs
00617 /// that we have examined.
00618 ///
00619 /// \returns the selected value.
00620 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
00621                                           IncomingValueMap &IncomingValues) {
00622   if (!isa<UndefValue>(OldVal)) {
00623     assert((!IncomingValues.count(BB) ||
00624             IncomingValues.find(BB)->second == OldVal) &&
00625            "Expected OldVal to match incoming value from BB!");
00626 
00627     IncomingValues.insert(std::make_pair(BB, OldVal));
00628     return OldVal;
00629   }
00630 
00631   IncomingValueMap::const_iterator It = IncomingValues.find(BB);
00632   if (It != IncomingValues.end()) return It->second;
00633 
00634   return OldVal;
00635 }
00636 
00637 /// \brief Create a map from block to value for the operands of a
00638 /// given phi.
00639 ///
00640 /// Create a map from block to value for each non-undef value flowing
00641 /// into \p PN.
00642 ///
00643 /// \param PN The phi we are collecting the map for.
00644 /// \param IncomingValues [out] The map from block to value for this phi.
00645 static void gatherIncomingValuesToPhi(PHINode *PN,
00646                                       IncomingValueMap &IncomingValues) {
00647   for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
00648     BasicBlock *BB = PN->getIncomingBlock(i);
00649     Value *V = PN->getIncomingValue(i);
00650 
00651     if (!isa<UndefValue>(V))
00652       IncomingValues.insert(std::make_pair(BB, V));
00653   }
00654 }
00655 
00656 /// \brief Replace the incoming undef values to a phi with the values
00657 /// from a block-to-value map.
00658 ///
00659 /// \param PN The phi we are replacing the undefs in.
00660 /// \param IncomingValues A map from block to value.
00661 static void replaceUndefValuesInPhi(PHINode *PN,
00662                                     const IncomingValueMap &IncomingValues) {
00663   for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
00664     Value *V = PN->getIncomingValue(i);
00665 
00666     if (!isa<UndefValue>(V)) continue;
00667 
00668     BasicBlock *BB = PN->getIncomingBlock(i);
00669     IncomingValueMap::const_iterator It = IncomingValues.find(BB);
00670     if (It == IncomingValues.end()) continue;
00671 
00672     PN->setIncomingValue(i, It->second);
00673   }
00674 }
00675 
00676 /// \brief Replace a value flowing from a block to a phi with
00677 /// potentially multiple instances of that value flowing from the
00678 /// block's predecessors to the phi.
00679 ///
00680 /// \param BB The block with the value flowing into the phi.
00681 /// \param BBPreds The predecessors of BB.
00682 /// \param PN The phi that we are updating.
00683 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
00684                                                 const PredBlockVector &BBPreds,
00685                                                 PHINode *PN) {
00686   Value *OldVal = PN->removeIncomingValue(BB, false);
00687   assert(OldVal && "No entry in PHI for Pred BB!");
00688 
00689   IncomingValueMap IncomingValues;
00690 
00691   // We are merging two blocks - BB, and the block containing PN - and
00692   // as a result we need to redirect edges from the predecessors of BB
00693   // to go to the block containing PN, and update PN
00694   // accordingly. Since we allow merging blocks in the case where the
00695   // predecessor and successor blocks both share some predecessors,
00696   // and where some of those common predecessors might have undef
00697   // values flowing into PN, we want to rewrite those values to be
00698   // consistent with the non-undef values.
00699 
00700   gatherIncomingValuesToPhi(PN, IncomingValues);
00701 
00702   // If this incoming value is one of the PHI nodes in BB, the new entries
00703   // in the PHI node are the entries from the old PHI.
00704   if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
00705     PHINode *OldValPN = cast<PHINode>(OldVal);
00706     for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
00707       // Note that, since we are merging phi nodes and BB and Succ might
00708       // have common predecessors, we could end up with a phi node with
00709       // identical incoming branches. This will be cleaned up later (and
00710       // will trigger asserts if we try to clean it up now, without also
00711       // simplifying the corresponding conditional branch).
00712       BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
00713       Value *PredVal = OldValPN->getIncomingValue(i);
00714       Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
00715                                                     IncomingValues);
00716 
00717       // And add a new incoming value for this predecessor for the
00718       // newly retargeted branch.
00719       PN->addIncoming(Selected, PredBB);
00720     }
00721   } else {
00722     for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
00723       // Update existing incoming values in PN for this
00724       // predecessor of BB.
00725       BasicBlock *PredBB = BBPreds[i];
00726       Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
00727                                                     IncomingValues);
00728 
00729       // And add a new incoming value for this predecessor for the
00730       // newly retargeted branch.
00731       PN->addIncoming(Selected, PredBB);
00732     }
00733   }
00734 
00735   replaceUndefValuesInPhi(PN, IncomingValues);
00736 }
00737 
00738 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
00739 /// unconditional branch, and contains no instructions other than PHI nodes,
00740 /// potential side-effect free intrinsics and the branch.  If possible,
00741 /// eliminate BB by rewriting all the predecessors to branch to the successor
00742 /// block and return true.  If we can't transform, return false.
00743 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
00744   assert(BB != &BB->getParent()->getEntryBlock() &&
00745          "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
00746 
00747   // We can't eliminate infinite loops.
00748   BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
00749   if (BB == Succ) return false;
00750 
00751   // Check to see if merging these blocks would cause conflicts for any of the
00752   // phi nodes in BB or Succ. If not, we can safely merge.
00753   if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
00754 
00755   // Check for cases where Succ has multiple predecessors and a PHI node in BB
00756   // has uses which will not disappear when the PHI nodes are merged.  It is
00757   // possible to handle such cases, but difficult: it requires checking whether
00758   // BB dominates Succ, which is non-trivial to calculate in the case where
00759   // Succ has multiple predecessors.  Also, it requires checking whether
00760   // constructing the necessary self-referential PHI node doesn't introduce any
00761   // conflicts; this isn't too difficult, but the previous code for doing this
00762   // was incorrect.
00763   //
00764   // Note that if this check finds a live use, BB dominates Succ, so BB is
00765   // something like a loop pre-header (or rarely, a part of an irreducible CFG);
00766   // folding the branch isn't profitable in that case anyway.
00767   if (!Succ->getSinglePredecessor()) {
00768     BasicBlock::iterator BBI = BB->begin();
00769     while (isa<PHINode>(*BBI)) {
00770       for (Use &U : BBI->uses()) {
00771         if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
00772           if (PN->getIncomingBlock(U) != BB)
00773             return false;
00774         } else {
00775           return false;
00776         }
00777       }
00778       ++BBI;
00779     }
00780   }
00781 
00782   DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
00783 
00784   if (isa<PHINode>(Succ->begin())) {
00785     // If there is more than one pred of succ, and there are PHI nodes in
00786     // the successor, then we need to add incoming edges for the PHI nodes
00787     //
00788     const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
00789 
00790     // Loop over all of the PHI nodes in the successor of BB.
00791     for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
00792       PHINode *PN = cast<PHINode>(I);
00793 
00794       redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
00795     }
00796   }
00797 
00798   if (Succ->getSinglePredecessor()) {
00799     // BB is the only predecessor of Succ, so Succ will end up with exactly
00800     // the same predecessors BB had.
00801 
00802     // Copy over any phi, debug or lifetime instruction.
00803     BB->getTerminator()->eraseFromParent();
00804     Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
00805   } else {
00806     while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
00807       // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
00808       assert(PN->use_empty() && "There shouldn't be any uses here!");
00809       PN->eraseFromParent();
00810     }
00811   }
00812 
00813   // Everything that jumped to BB now goes to Succ.
00814   BB->replaceAllUsesWith(Succ);
00815   if (!Succ->hasName()) Succ->takeName(BB);
00816   BB->eraseFromParent();              // Delete the old basic block.
00817   return true;
00818 }
00819 
00820 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
00821 /// nodes in this block. This doesn't try to be clever about PHI nodes
00822 /// which differ only in the order of the incoming values, but instcombine
00823 /// orders them so it usually won't matter.
00824 ///
00825 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
00826   bool Changed = false;
00827 
00828   // This implementation doesn't currently consider undef operands
00829   // specially. Theoretically, two phis which are identical except for
00830   // one having an undef where the other doesn't could be collapsed.
00831 
00832   // Map from PHI hash values to PHI nodes. If multiple PHIs have
00833   // the same hash value, the element is the first PHI in the
00834   // linked list in CollisionMap.
00835   DenseMap<uintptr_t, PHINode *> HashMap;
00836 
00837   // Maintain linked lists of PHI nodes with common hash values.
00838   DenseMap<PHINode *, PHINode *> CollisionMap;
00839 
00840   // Examine each PHI.
00841   for (BasicBlock::iterator I = BB->begin();
00842        PHINode *PN = dyn_cast<PHINode>(I++); ) {
00843     // Compute a hash value on the operands. Instcombine will likely have sorted
00844     // them, which helps expose duplicates, but we have to check all the
00845     // operands to be safe in case instcombine hasn't run.
00846     uintptr_t Hash = 0;
00847     // This hash algorithm is quite weak as hash functions go, but it seems
00848     // to do a good enough job for this particular purpose, and is very quick.
00849     for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
00850       Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
00851       Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
00852     }
00853     for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end();
00854          I != E; ++I) {
00855       Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I));
00856       Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
00857     }
00858     // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
00859     Hash >>= 1;
00860     // If we've never seen this hash value before, it's a unique PHI.
00861     std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
00862       HashMap.insert(std::make_pair(Hash, PN));
00863     if (Pair.second) continue;
00864     // Otherwise it's either a duplicate or a hash collision.
00865     for (PHINode *OtherPN = Pair.first->second; ; ) {
00866       if (OtherPN->isIdenticalTo(PN)) {
00867         // A duplicate. Replace this PHI with its duplicate.
00868         PN->replaceAllUsesWith(OtherPN);
00869         PN->eraseFromParent();
00870         Changed = true;
00871         break;
00872       }
00873       // A non-duplicate hash collision.
00874       DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
00875       if (I == CollisionMap.end()) {
00876         // Set this PHI to be the head of the linked list of colliding PHIs.
00877         PHINode *Old = Pair.first->second;
00878         Pair.first->second = PN;
00879         CollisionMap[PN] = Old;
00880         break;
00881       }
00882       // Proceed to the next PHI in the list.
00883       OtherPN = I->second;
00884     }
00885   }
00886 
00887   return Changed;
00888 }
00889 
00890 /// enforceKnownAlignment - If the specified pointer points to an object that
00891 /// we control, modify the object's alignment to PrefAlign. This isn't
00892 /// often possible though. If alignment is important, a more reliable approach
00893 /// is to simply align all global variables and allocation instructions to
00894 /// their preferred alignment from the beginning.
00895 ///
00896 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
00897                                       unsigned PrefAlign, const DataLayout *TD) {
00898   V = V->stripPointerCasts();
00899 
00900   if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
00901     // If the preferred alignment is greater than the natural stack alignment
00902     // then don't round up. This avoids dynamic stack realignment.
00903     if (TD && TD->exceedsNaturalStackAlignment(PrefAlign))
00904       return Align;
00905     // If there is a requested alignment and if this is an alloca, round up.
00906     if (AI->getAlignment() >= PrefAlign)
00907       return AI->getAlignment();
00908     AI->setAlignment(PrefAlign);
00909     return PrefAlign;
00910   }
00911 
00912   if (auto *GO = dyn_cast<GlobalObject>(V)) {
00913     // If there is a large requested alignment and we can, bump up the alignment
00914     // of the global.
00915     if (GO->isDeclaration())
00916       return Align;
00917     // If the memory we set aside for the global may not be the memory used by
00918     // the final program then it is impossible for us to reliably enforce the
00919     // preferred alignment.
00920     if (GO->isWeakForLinker())
00921       return Align;
00922 
00923     if (GO->getAlignment() >= PrefAlign)
00924       return GO->getAlignment();
00925     // We can only increase the alignment of the global if it has no alignment
00926     // specified or if it is not assigned a section.  If it is assigned a
00927     // section, the global could be densely packed with other objects in the
00928     // section, increasing the alignment could cause padding issues.
00929     if (!GO->hasSection() || GO->getAlignment() == 0)
00930       GO->setAlignment(PrefAlign);
00931     return GO->getAlignment();
00932   }
00933 
00934   return Align;
00935 }
00936 
00937 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
00938 /// we can determine, return it, otherwise return 0.  If PrefAlign is specified,
00939 /// and it is more than the alignment of the ultimate object, see if we can
00940 /// increase the alignment of the ultimate object, making this check succeed.
00941 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
00942                                           const DataLayout *DL) {
00943   assert(V->getType()->isPointerTy() &&
00944          "getOrEnforceKnownAlignment expects a pointer!");
00945   unsigned BitWidth = DL ? DL->getPointerTypeSizeInBits(V->getType()) : 64;
00946 
00947   APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
00948   computeKnownBits(V, KnownZero, KnownOne, DL);
00949   unsigned TrailZ = KnownZero.countTrailingOnes();
00950 
00951   // Avoid trouble with ridiculously large TrailZ values, such as
00952   // those computed from a null pointer.
00953   TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
00954 
00955   unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
00956 
00957   // LLVM doesn't support alignments larger than this currently.
00958   Align = std::min(Align, +Value::MaximumAlignment);
00959 
00960   if (PrefAlign > Align)
00961     Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
00962 
00963   // We don't need to make any adjustment.
00964   return Align;
00965 }
00966 
00967 ///===---------------------------------------------------------------------===//
00968 ///  Dbg Intrinsic utilities
00969 ///
00970 
00971 /// See if there is a dbg.value intrinsic for DIVar before I.
00972 static bool LdStHasDebugValue(DIVariable &DIVar, Instruction *I) {
00973   // Since we can't guarantee that the original dbg.declare instrinsic
00974   // is removed by LowerDbgDeclare(), we need to make sure that we are
00975   // not inserting the same dbg.value intrinsic over and over.
00976   llvm::BasicBlock::InstListType::iterator PrevI(I);
00977   if (PrevI != I->getParent()->getInstList().begin()) {
00978     --PrevI;
00979     if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
00980       if (DVI->getValue() == I->getOperand(0) &&
00981           DVI->getOffset() == 0 &&
00982           DVI->getVariable() == DIVar)
00983         return true;
00984   }
00985   return false;
00986 }
00987 
00988 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
00989 /// that has an associated llvm.dbg.decl intrinsic.
00990 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
00991                                            StoreInst *SI, DIBuilder &Builder) {
00992   DIVariable DIVar(DDI->getVariable());
00993   assert((!DIVar || DIVar.isVariable()) &&
00994          "Variable in DbgDeclareInst should be either null or a DIVariable.");
00995   if (!DIVar)
00996     return false;
00997 
00998   if (LdStHasDebugValue(DIVar, SI))
00999     return true;
01000 
01001   Instruction *DbgVal = nullptr;
01002   // If an argument is zero extended then use argument directly. The ZExt
01003   // may be zapped by an optimization pass in future.
01004   Argument *ExtendedArg = nullptr;
01005   if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
01006     ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
01007   if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
01008     ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
01009   if (ExtendedArg)
01010     DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI);
01011   else
01012     DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI);
01013   DbgVal->setDebugLoc(DDI->getDebugLoc());
01014   return true;
01015 }
01016 
01017 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
01018 /// that has an associated llvm.dbg.decl intrinsic.
01019 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
01020                                            LoadInst *LI, DIBuilder &Builder) {
01021   DIVariable DIVar(DDI->getVariable());
01022   assert((!DIVar || DIVar.isVariable()) &&
01023          "Variable in DbgDeclareInst should be either null or a DIVariable.");
01024   if (!DIVar)
01025     return false;
01026 
01027   if (LdStHasDebugValue(DIVar, LI))
01028     return true;
01029 
01030   Instruction *DbgVal =
01031     Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0,
01032                                     DIVar, LI);
01033   DbgVal->setDebugLoc(DDI->getDebugLoc());
01034   return true;
01035 }
01036 
01037 /// Determine whether this alloca is either a VLA or an array.
01038 static bool isArray(AllocaInst *AI) {
01039   return AI->isArrayAllocation() ||
01040     AI->getType()->getElementType()->isArrayTy();
01041 }
01042 
01043 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
01044 /// of llvm.dbg.value intrinsics.
01045 bool llvm::LowerDbgDeclare(Function &F) {
01046   DIBuilder DIB(*F.getParent());
01047   SmallVector<DbgDeclareInst *, 4> Dbgs;
01048   for (auto &FI : F)
01049     for (BasicBlock::iterator BI : FI)
01050       if (auto DDI = dyn_cast<DbgDeclareInst>(BI))
01051         Dbgs.push_back(DDI);
01052 
01053   if (Dbgs.empty())
01054     return false;
01055 
01056   for (auto &I : Dbgs) {
01057     DbgDeclareInst *DDI = I;
01058     AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
01059     // If this is an alloca for a scalar variable, insert a dbg.value
01060     // at each load and store to the alloca and erase the dbg.declare.
01061     // The dbg.values allow tracking a variable even if it is not
01062     // stored on the stack, while the dbg.declare can only describe
01063     // the stack slot (and at a lexical-scope granularity). Later
01064     // passes will attempt to elide the stack slot.
01065     if (AI && !isArray(AI)) {
01066       for (User *U : AI->users())
01067         if (StoreInst *SI = dyn_cast<StoreInst>(U))
01068           ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
01069         else if (LoadInst *LI = dyn_cast<LoadInst>(U))
01070           ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
01071         else if (CallInst *CI = dyn_cast<CallInst>(U)) {
01072     // This is a call by-value or some other instruction that
01073     // takes a pointer to the variable. Insert a *value*
01074     // intrinsic that describes the alloca.
01075     auto DbgVal =
01076       DIB.insertDbgValueIntrinsic(AI, 0,
01077           DIVariable(DDI->getVariable()), CI);
01078     DbgVal->setDebugLoc(DDI->getDebugLoc());
01079   }
01080       DDI->eraseFromParent();
01081     }
01082   }
01083   return true;
01084 }
01085 
01086 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
01087 /// alloca 'V', if any.
01088 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
01089   if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V))
01090     for (User *U : DebugNode->users())
01091       if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
01092         return DDI;
01093 
01094   return nullptr;
01095 }
01096 
01097 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
01098                                       DIBuilder &Builder) {
01099   DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI);
01100   if (!DDI)
01101     return false;
01102   DIVariable DIVar(DDI->getVariable());
01103   assert((!DIVar || DIVar.isVariable()) &&
01104          "Variable in DbgDeclareInst should be either null or a DIVariable.");
01105   if (!DIVar)
01106     return false;
01107 
01108   // Create a copy of the original DIDescriptor for user variable, appending
01109   // "deref" operation to a list of address elements, as new llvm.dbg.declare
01110   // will take a value storing address of the memory for variable, not
01111   // alloca itself.
01112   Type *Int64Ty = Type::getInt64Ty(AI->getContext());
01113   SmallVector<Value*, 4> NewDIVarAddress;
01114   if (DIVar.hasComplexAddress()) {
01115     for (unsigned i = 0, n = DIVar.getNumAddrElements(); i < n; ++i) {
01116       NewDIVarAddress.push_back(
01117           ConstantInt::get(Int64Ty, DIVar.getAddrElement(i)));
01118     }
01119   }
01120   NewDIVarAddress.push_back(ConstantInt::get(Int64Ty, DIBuilder::OpDeref));
01121   DIVariable NewDIVar = Builder.createComplexVariable(
01122       DIVar.getTag(), DIVar.getContext(), DIVar.getName(),
01123       DIVar.getFile(), DIVar.getLineNumber(), DIVar.getType(),
01124       NewDIVarAddress, DIVar.getArgNumber());
01125 
01126   // Insert llvm.dbg.declare in the same basic block as the original alloca,
01127   // and remove old llvm.dbg.declare.
01128   BasicBlock *BB = AI->getParent();
01129   Builder.insertDeclare(NewAllocaAddress, NewDIVar, BB);
01130   DDI->eraseFromParent();
01131   return true;
01132 }
01133 
01134 /// changeToUnreachable - Insert an unreachable instruction before the specified
01135 /// instruction, making it and the rest of the code in the block dead.
01136 static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
01137   BasicBlock *BB = I->getParent();
01138   // Loop over all of the successors, removing BB's entry from any PHI
01139   // nodes.
01140   for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
01141     (*SI)->removePredecessor(BB);
01142 
01143   // Insert a call to llvm.trap right before this.  This turns the undefined
01144   // behavior into a hard fail instead of falling through into random code.
01145   if (UseLLVMTrap) {
01146     Function *TrapFn =
01147       Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
01148     CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
01149     CallTrap->setDebugLoc(I->getDebugLoc());
01150   }
01151   new UnreachableInst(I->getContext(), I);
01152 
01153   // All instructions after this are dead.
01154   BasicBlock::iterator BBI = I, BBE = BB->end();
01155   while (BBI != BBE) {
01156     if (!BBI->use_empty())
01157       BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
01158     BB->getInstList().erase(BBI++);
01159   }
01160 }
01161 
01162 /// changeToCall - Convert the specified invoke into a normal call.
01163 static void changeToCall(InvokeInst *II) {
01164   SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
01165   CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
01166   NewCall->takeName(II);
01167   NewCall->setCallingConv(II->getCallingConv());
01168   NewCall->setAttributes(II->getAttributes());
01169   NewCall->setDebugLoc(II->getDebugLoc());
01170   II->replaceAllUsesWith(NewCall);
01171 
01172   // Follow the call by a branch to the normal destination.
01173   BranchInst::Create(II->getNormalDest(), II);
01174 
01175   // Update PHI nodes in the unwind destination
01176   II->getUnwindDest()->removePredecessor(II->getParent());
01177   II->eraseFromParent();
01178 }
01179 
01180 static bool markAliveBlocks(BasicBlock *BB,
01181                             SmallPtrSetImpl<BasicBlock*> &Reachable) {
01182 
01183   SmallVector<BasicBlock*, 128> Worklist;
01184   Worklist.push_back(BB);
01185   Reachable.insert(BB);
01186   bool Changed = false;
01187   do {
01188     BB = Worklist.pop_back_val();
01189 
01190     // Do a quick scan of the basic block, turning any obviously unreachable
01191     // instructions into LLVM unreachable insts.  The instruction combining pass
01192     // canonicalizes unreachable insts into stores to null or undef.
01193     for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
01194       // Assumptions that are known to be false are equivalent to unreachable.
01195       // Also, if the condition is undefined, then we make the choice most
01196       // beneficial to the optimizer, and choose that to also be unreachable.
01197       if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI))
01198         if (II->getIntrinsicID() == Intrinsic::assume) {
01199           bool MakeUnreachable = false;
01200           if (isa<UndefValue>(II->getArgOperand(0)))
01201             MakeUnreachable = true;
01202           else if (ConstantInt *Cond =
01203                    dyn_cast<ConstantInt>(II->getArgOperand(0)))
01204             MakeUnreachable = Cond->isZero();
01205 
01206           if (MakeUnreachable) { 
01207             // Don't insert a call to llvm.trap right before the unreachable.
01208             changeToUnreachable(BBI, false);
01209             Changed = true;
01210             break;
01211           }
01212         }
01213 
01214       if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
01215         if (CI->doesNotReturn()) {
01216           // If we found a call to a no-return function, insert an unreachable
01217           // instruction after it.  Make sure there isn't *already* one there
01218           // though.
01219           ++BBI;
01220           if (!isa<UnreachableInst>(BBI)) {
01221             // Don't insert a call to llvm.trap right before the unreachable.
01222             changeToUnreachable(BBI, false);
01223             Changed = true;
01224           }
01225           break;
01226         }
01227       }
01228 
01229       // Store to undef and store to null are undefined and used to signal that
01230       // they should be changed to unreachable by passes that can't modify the
01231       // CFG.
01232       if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
01233         // Don't touch volatile stores.
01234         if (SI->isVolatile()) continue;
01235 
01236         Value *Ptr = SI->getOperand(1);
01237 
01238         if (isa<UndefValue>(Ptr) ||
01239             (isa<ConstantPointerNull>(Ptr) &&
01240              SI->getPointerAddressSpace() == 0)) {
01241           changeToUnreachable(SI, true);
01242           Changed = true;
01243           break;
01244         }
01245       }
01246     }
01247 
01248     // Turn invokes that call 'nounwind' functions into ordinary calls.
01249     if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
01250       Value *Callee = II->getCalledValue();
01251       if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
01252         changeToUnreachable(II, true);
01253         Changed = true;
01254       } else if (II->doesNotThrow()) {
01255         if (II->use_empty() && II->onlyReadsMemory()) {
01256           // jump to the normal destination branch.
01257           BranchInst::Create(II->getNormalDest(), II);
01258           II->getUnwindDest()->removePredecessor(II->getParent());
01259           II->eraseFromParent();
01260         } else
01261           changeToCall(II);
01262         Changed = true;
01263       }
01264     }
01265 
01266     Changed |= ConstantFoldTerminator(BB, true);
01267     for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
01268       if (Reachable.insert(*SI))
01269         Worklist.push_back(*SI);
01270   } while (!Worklist.empty());
01271   return Changed;
01272 }
01273 
01274 /// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
01275 /// if they are in a dead cycle.  Return true if a change was made, false
01276 /// otherwise.
01277 bool llvm::removeUnreachableBlocks(Function &F) {
01278   SmallPtrSet<BasicBlock*, 128> Reachable;
01279   bool Changed = markAliveBlocks(F.begin(), Reachable);
01280 
01281   // If there are unreachable blocks in the CFG...
01282   if (Reachable.size() == F.size())
01283     return Changed;
01284 
01285   assert(Reachable.size() < F.size());
01286   NumRemoved += F.size()-Reachable.size();
01287 
01288   // Loop over all of the basic blocks that are not reachable, dropping all of
01289   // their internal references...
01290   for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
01291     if (Reachable.count(BB))
01292       continue;
01293 
01294     for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
01295       if (Reachable.count(*SI))
01296         (*SI)->removePredecessor(BB);
01297     BB->dropAllReferences();
01298   }
01299 
01300   for (Function::iterator I = ++F.begin(); I != F.end();)
01301     if (!Reachable.count(I))
01302       I = F.getBasicBlockList().erase(I);
01303     else
01304       ++I;
01305 
01306   return true;
01307 }
01308 
01309 void llvm::combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs) {
01310   SmallVector<std::pair<unsigned, MDNode*>, 4> Metadata;
01311   K->dropUnknownMetadata(KnownIDs);
01312   K->getAllMetadataOtherThanDebugLoc(Metadata);
01313   for (unsigned i = 0, n = Metadata.size(); i < n; ++i) {
01314     unsigned Kind = Metadata[i].first;
01315     MDNode *JMD = J->getMetadata(Kind);
01316     MDNode *KMD = Metadata[i].second;
01317 
01318     switch (Kind) {
01319       default:
01320         K->setMetadata(Kind, nullptr); // Remove unknown metadata
01321         break;
01322       case LLVMContext::MD_dbg:
01323         llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
01324       case LLVMContext::MD_tbaa:
01325         K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
01326         break;
01327       case LLVMContext::MD_alias_scope:
01328       case LLVMContext::MD_noalias:
01329         K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
01330         break;
01331       case LLVMContext::MD_range:
01332         K->setMetadata(Kind, MDNode::getMostGenericRange(JMD, KMD));
01333         break;
01334       case LLVMContext::MD_fpmath:
01335         K->setMetadata(Kind, MDNode::getMostGenericFPMath(JMD, KMD));
01336         break;
01337       case LLVMContext::MD_invariant_load:
01338         // Only set the !invariant.load if it is present in both instructions.
01339         K->setMetadata(Kind, JMD);
01340         break;
01341     }
01342   }
01343 }