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Diffstat (limited to 'contrib/llvm/lib/Transforms/Utils/Local.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Utils/Local.cpp | 1279 |
1 files changed, 1279 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/Utils/Local.cpp b/contrib/llvm/lib/Transforms/Utils/Local.cpp new file mode 100644 index 0000000..a5e443f --- /dev/null +++ b/contrib/llvm/lib/Transforms/Utils/Local.cpp @@ -0,0 +1,1279 @@ +//===-- Local.cpp - Functions to perform local transformations ------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// This family of functions perform various local transformations to the +// program. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/MemoryBuiltins.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/IR/CFG.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DIBuilder.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DebugInfo.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/GetElementPtrTypeIterator.h" +#include "llvm/IR/GlobalAlias.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Intrinsics.h" +#include "llvm/IR/MDBuilder.h" +#include "llvm/IR/Metadata.h" +#include "llvm/IR/Operator.h" +#include "llvm/IR/ValueHandle.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/MathExtras.h" +#include "llvm/Support/raw_ostream.h" +using namespace llvm; + +#define DEBUG_TYPE "local" + +STATISTIC(NumRemoved, "Number of unreachable basic blocks removed"); + +//===----------------------------------------------------------------------===// +// Local constant propagation. +// + +/// ConstantFoldTerminator - If a terminator instruction is predicated on a +/// constant value, convert it into an unconditional branch to the constant +/// destination. This is a nontrivial operation because the successors of this +/// basic block must have their PHI nodes updated. +/// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch +/// conditions and indirectbr addresses this might make dead if +/// DeleteDeadConditions is true. +bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions, + const TargetLibraryInfo *TLI) { + TerminatorInst *T = BB->getTerminator(); + IRBuilder<> Builder(T); + + // Branch - See if we are conditional jumping on constant + if (BranchInst *BI = dyn_cast<BranchInst>(T)) { + if (BI->isUnconditional()) return false; // Can't optimize uncond branch + BasicBlock *Dest1 = BI->getSuccessor(0); + BasicBlock *Dest2 = BI->getSuccessor(1); + + if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) { + // Are we branching on constant? + // YES. Change to unconditional branch... + BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2; + BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1; + + //cerr << "Function: " << T->getParent()->getParent() + // << "\nRemoving branch from " << T->getParent() + // << "\n\nTo: " << OldDest << endl; + + // Let the basic block know that we are letting go of it. Based on this, + // it will adjust it's PHI nodes. + OldDest->removePredecessor(BB); + + // Replace the conditional branch with an unconditional one. + Builder.CreateBr(Destination); + BI->eraseFromParent(); + return true; + } + + if (Dest2 == Dest1) { // Conditional branch to same location? + // This branch matches something like this: + // br bool %cond, label %Dest, label %Dest + // and changes it into: br label %Dest + + // Let the basic block know that we are letting go of one copy of it. + assert(BI->getParent() && "Terminator not inserted in block!"); + Dest1->removePredecessor(BI->getParent()); + + // Replace the conditional branch with an unconditional one. + Builder.CreateBr(Dest1); + Value *Cond = BI->getCondition(); + BI->eraseFromParent(); + if (DeleteDeadConditions) + RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI); + return true; + } + return false; + } + + if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) { + // If we are switching on a constant, we can convert the switch into a + // single branch instruction! + ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition()); + BasicBlock *TheOnlyDest = SI->getDefaultDest(); + BasicBlock *DefaultDest = TheOnlyDest; + + // Figure out which case it goes to. + for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); + i != e; ++i) { + // Found case matching a constant operand? + if (i.getCaseValue() == CI) { + TheOnlyDest = i.getCaseSuccessor(); + break; + } + + // Check to see if this branch is going to the same place as the default + // dest. If so, eliminate it as an explicit compare. + if (i.getCaseSuccessor() == DefaultDest) { + MDNode* MD = SI->getMetadata(LLVMContext::MD_prof); + unsigned NCases = SI->getNumCases(); + // Fold the case metadata into the default if there will be any branches + // left, unless the metadata doesn't match the switch. + if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) { + // Collect branch weights into a vector. + SmallVector<uint32_t, 8> Weights; + for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e; + ++MD_i) { + ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i)); + assert(CI); + Weights.push_back(CI->getValue().getZExtValue()); + } + // Merge weight of this case to the default weight. + unsigned idx = i.getCaseIndex(); + Weights[0] += Weights[idx+1]; + // Remove weight for this case. + std::swap(Weights[idx+1], Weights.back()); + Weights.pop_back(); + SI->setMetadata(LLVMContext::MD_prof, + MDBuilder(BB->getContext()). + createBranchWeights(Weights)); + } + // Remove this entry. + DefaultDest->removePredecessor(SI->getParent()); + SI->removeCase(i); + --i; --e; + continue; + } + + // Otherwise, check to see if the switch only branches to one destination. + // We do this by reseting "TheOnlyDest" to null when we find two non-equal + // destinations. + if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = nullptr; + } + + if (CI && !TheOnlyDest) { + // Branching on a constant, but not any of the cases, go to the default + // successor. + TheOnlyDest = SI->getDefaultDest(); + } + + // If we found a single destination that we can fold the switch into, do so + // now. + if (TheOnlyDest) { + // Insert the new branch. + Builder.CreateBr(TheOnlyDest); + BasicBlock *BB = SI->getParent(); + + // Remove entries from PHI nodes which we no longer branch to... + for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) { + // Found case matching a constant operand? + BasicBlock *Succ = SI->getSuccessor(i); + if (Succ == TheOnlyDest) + TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest + else + Succ->removePredecessor(BB); + } + + // Delete the old switch. + Value *Cond = SI->getCondition(); + SI->eraseFromParent(); + if (DeleteDeadConditions) + RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI); + return true; + } + + if (SI->getNumCases() == 1) { + // Otherwise, we can fold this switch into a conditional branch + // instruction if it has only one non-default destination. + SwitchInst::CaseIt FirstCase = SI->case_begin(); + Value *Cond = Builder.CreateICmpEQ(SI->getCondition(), + FirstCase.getCaseValue(), "cond"); + + // Insert the new branch. + BranchInst *NewBr = Builder.CreateCondBr(Cond, + FirstCase.getCaseSuccessor(), + SI->getDefaultDest()); + MDNode* MD = SI->getMetadata(LLVMContext::MD_prof); + if (MD && MD->getNumOperands() == 3) { + ConstantInt *SICase = dyn_cast<ConstantInt>(MD->getOperand(2)); + ConstantInt *SIDef = dyn_cast<ConstantInt>(MD->getOperand(1)); + assert(SICase && SIDef); + // The TrueWeight should be the weight for the single case of SI. + NewBr->setMetadata(LLVMContext::MD_prof, + MDBuilder(BB->getContext()). + createBranchWeights(SICase->getValue().getZExtValue(), + SIDef->getValue().getZExtValue())); + } + + // Delete the old switch. + SI->eraseFromParent(); + return true; + } + return false; + } + + if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) { + // indirectbr blockaddress(@F, @BB) -> br label @BB + if (BlockAddress *BA = + dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) { + BasicBlock *TheOnlyDest = BA->getBasicBlock(); + // Insert the new branch. + Builder.CreateBr(TheOnlyDest); + + for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { + if (IBI->getDestination(i) == TheOnlyDest) + TheOnlyDest = nullptr; + else + IBI->getDestination(i)->removePredecessor(IBI->getParent()); + } + Value *Address = IBI->getAddress(); + IBI->eraseFromParent(); + if (DeleteDeadConditions) + RecursivelyDeleteTriviallyDeadInstructions(Address, TLI); + + // If we didn't find our destination in the IBI successor list, then we + // have undefined behavior. Replace the unconditional branch with an + // 'unreachable' instruction. + if (TheOnlyDest) { + BB->getTerminator()->eraseFromParent(); + new UnreachableInst(BB->getContext(), BB); + } + + return true; + } + } + + return false; +} + + +//===----------------------------------------------------------------------===// +// Local dead code elimination. +// + +/// isInstructionTriviallyDead - Return true if the result produced by the +/// instruction is not used, and the instruction has no side effects. +/// +bool llvm::isInstructionTriviallyDead(Instruction *I, + const TargetLibraryInfo *TLI) { + if (!I->use_empty() || isa<TerminatorInst>(I)) return false; + + // We don't want the landingpad instruction removed by anything this general. + if (isa<LandingPadInst>(I)) + return false; + + // We don't want debug info removed by anything this general, unless + // debug info is empty. + if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) { + if (DDI->getAddress()) + return false; + return true; + } + if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) { + if (DVI->getValue()) + return false; + return true; + } + + if (!I->mayHaveSideEffects()) return true; + + // Special case intrinsics that "may have side effects" but can be deleted + // when dead. + if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { + // Safe to delete llvm.stacksave if dead. + if (II->getIntrinsicID() == Intrinsic::stacksave) + return true; + + // Lifetime intrinsics are dead when their right-hand is undef. + if (II->getIntrinsicID() == Intrinsic::lifetime_start || + II->getIntrinsicID() == Intrinsic::lifetime_end) + return isa<UndefValue>(II->getArgOperand(1)); + } + + if (isAllocLikeFn(I, TLI)) return true; + + if (CallInst *CI = isFreeCall(I, TLI)) + if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0))) + return C->isNullValue() || isa<UndefValue>(C); + + return false; +} + +/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a +/// trivially dead instruction, delete it. If that makes any of its operands +/// trivially dead, delete them too, recursively. Return true if any +/// instructions were deleted. +bool +llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V, + const TargetLibraryInfo *TLI) { + Instruction *I = dyn_cast<Instruction>(V); + if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI)) + return false; + + SmallVector<Instruction*, 16> DeadInsts; + DeadInsts.push_back(I); + + do { + I = DeadInsts.pop_back_val(); + + // Null out all of the instruction's operands to see if any operand becomes + // dead as we go. + for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) { + Value *OpV = I->getOperand(i); + I->setOperand(i, nullptr); + + if (!OpV->use_empty()) continue; + + // If the operand is an instruction that became dead as we nulled out the + // operand, and if it is 'trivially' dead, delete it in a future loop + // iteration. + if (Instruction *OpI = dyn_cast<Instruction>(OpV)) + if (isInstructionTriviallyDead(OpI, TLI)) + DeadInsts.push_back(OpI); + } + + I->eraseFromParent(); + } while (!DeadInsts.empty()); + + return true; +} + +/// areAllUsesEqual - Check whether the uses of a value are all the same. +/// This is similar to Instruction::hasOneUse() except this will also return +/// true when there are no uses or multiple uses that all refer to the same +/// value. +static bool areAllUsesEqual(Instruction *I) { + Value::user_iterator UI = I->user_begin(); + Value::user_iterator UE = I->user_end(); + if (UI == UE) + return true; + + User *TheUse = *UI; + for (++UI; UI != UE; ++UI) { + if (*UI != TheUse) + return false; + } + return true; +} + +/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively +/// dead PHI node, due to being a def-use chain of single-use nodes that +/// either forms a cycle or is terminated by a trivially dead instruction, +/// delete it. If that makes any of its operands trivially dead, delete them +/// too, recursively. Return true if a change was made. +bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN, + const TargetLibraryInfo *TLI) { + SmallPtrSet<Instruction*, 4> Visited; + for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects(); + I = cast<Instruction>(*I->user_begin())) { + if (I->use_empty()) + return RecursivelyDeleteTriviallyDeadInstructions(I, TLI); + + // If we find an instruction more than once, we're on a cycle that + // won't prove fruitful. + if (!Visited.insert(I)) { + // Break the cycle and delete the instruction and its operands. + I->replaceAllUsesWith(UndefValue::get(I->getType())); + (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI); + return true; + } + } + return false; +} + +/// SimplifyInstructionsInBlock - Scan the specified basic block and try to +/// simplify any instructions in it and recursively delete dead instructions. +/// +/// This returns true if it changed the code, note that it can delete +/// instructions in other blocks as well in this block. +bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const DataLayout *TD, + const TargetLibraryInfo *TLI) { + bool MadeChange = false; + +#ifndef NDEBUG + // In debug builds, ensure that the terminator of the block is never replaced + // or deleted by these simplifications. The idea of simplification is that it + // cannot introduce new instructions, and there is no way to replace the + // terminator of a block without introducing a new instruction. + AssertingVH<Instruction> TerminatorVH(--BB->end()); +#endif + + for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) { + assert(!BI->isTerminator()); + Instruction *Inst = BI++; + + WeakVH BIHandle(BI); + if (recursivelySimplifyInstruction(Inst, TD, TLI)) { + MadeChange = true; + if (BIHandle != BI) + BI = BB->begin(); + continue; + } + + MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI); + if (BIHandle != BI) + BI = BB->begin(); + } + return MadeChange; +} + +//===----------------------------------------------------------------------===// +// Control Flow Graph Restructuring. +// + + +/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this +/// method is called when we're about to delete Pred as a predecessor of BB. If +/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred. +/// +/// Unlike the removePredecessor method, this attempts to simplify uses of PHI +/// nodes that collapse into identity values. For example, if we have: +/// x = phi(1, 0, 0, 0) +/// y = and x, z +/// +/// .. and delete the predecessor corresponding to the '1', this will attempt to +/// recursively fold the and to 0. +void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred, + DataLayout *TD) { + // This only adjusts blocks with PHI nodes. + if (!isa<PHINode>(BB->begin())) + return; + + // Remove the entries for Pred from the PHI nodes in BB, but do not simplify + // them down. This will leave us with single entry phi nodes and other phis + // that can be removed. + BB->removePredecessor(Pred, true); + + WeakVH PhiIt = &BB->front(); + while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) { + PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt)); + Value *OldPhiIt = PhiIt; + + if (!recursivelySimplifyInstruction(PN, TD)) + continue; + + // If recursive simplification ended up deleting the next PHI node we would + // iterate to, then our iterator is invalid, restart scanning from the top + // of the block. + if (PhiIt != OldPhiIt) PhiIt = &BB->front(); + } +} + + +/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its +/// predecessor is known to have one successor (DestBB!). Eliminate the edge +/// between them, moving the instructions in the predecessor into DestBB and +/// deleting the predecessor block. +/// +void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) { + // If BB has single-entry PHI nodes, fold them. + while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) { + Value *NewVal = PN->getIncomingValue(0); + // Replace self referencing PHI with undef, it must be dead. + if (NewVal == PN) NewVal = UndefValue::get(PN->getType()); + PN->replaceAllUsesWith(NewVal); + PN->eraseFromParent(); + } + + BasicBlock *PredBB = DestBB->getSinglePredecessor(); + assert(PredBB && "Block doesn't have a single predecessor!"); + + // Zap anything that took the address of DestBB. Not doing this will give the + // address an invalid value. + if (DestBB->hasAddressTaken()) { + BlockAddress *BA = BlockAddress::get(DestBB); + Constant *Replacement = + ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1); + BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement, + BA->getType())); + BA->destroyConstant(); + } + + // Anything that branched to PredBB now branches to DestBB. + PredBB->replaceAllUsesWith(DestBB); + + // Splice all the instructions from PredBB to DestBB. + PredBB->getTerminator()->eraseFromParent(); + DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList()); + + // If the PredBB is the entry block of the function, move DestBB up to + // become the entry block after we erase PredBB. + if (PredBB == &DestBB->getParent()->getEntryBlock()) + DestBB->moveAfter(PredBB); + + if (P) { + if (DominatorTreeWrapperPass *DTWP = + P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) { + DominatorTree &DT = DTWP->getDomTree(); + BasicBlock *PredBBIDom = DT.getNode(PredBB)->getIDom()->getBlock(); + DT.changeImmediateDominator(DestBB, PredBBIDom); + DT.eraseNode(PredBB); + } + } + // Nuke BB. + PredBB->eraseFromParent(); +} + +/// CanMergeValues - Return true if we can choose one of these values to use +/// in place of the other. Note that we will always choose the non-undef +/// value to keep. +static bool CanMergeValues(Value *First, Value *Second) { + return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second); +} + +/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an +/// almost-empty BB ending in an unconditional branch to Succ, into Succ. +/// +/// Assumption: Succ is the single successor for BB. +/// +static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { + assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); + + DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into " + << Succ->getName() << "\n"); + // Shortcut, if there is only a single predecessor it must be BB and merging + // is always safe + if (Succ->getSinglePredecessor()) return true; + + // Make a list of the predecessors of BB + SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB)); + + // Look at all the phi nodes in Succ, to see if they present a conflict when + // merging these blocks + for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { + PHINode *PN = cast<PHINode>(I); + + // If the incoming value from BB is again a PHINode in + // BB which has the same incoming value for *PI as PN does, we can + // merge the phi nodes and then the blocks can still be merged + PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB)); + if (BBPN && BBPN->getParent() == BB) { + for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { + BasicBlock *IBB = PN->getIncomingBlock(PI); + if (BBPreds.count(IBB) && + !CanMergeValues(BBPN->getIncomingValueForBlock(IBB), + PN->getIncomingValue(PI))) { + DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " + << Succ->getName() << " is conflicting with " + << BBPN->getName() << " with regard to common predecessor " + << IBB->getName() << "\n"); + return false; + } + } + } else { + Value* Val = PN->getIncomingValueForBlock(BB); + for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) { + // See if the incoming value for the common predecessor is equal to the + // one for BB, in which case this phi node will not prevent the merging + // of the block. + BasicBlock *IBB = PN->getIncomingBlock(PI); + if (BBPreds.count(IBB) && + !CanMergeValues(Val, PN->getIncomingValue(PI))) { + DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in " + << Succ->getName() << " is conflicting with regard to common " + << "predecessor " << IBB->getName() << "\n"); + return false; + } + } + } + } + + return true; +} + +typedef SmallVector<BasicBlock *, 16> PredBlockVector; +typedef DenseMap<BasicBlock *, Value *> IncomingValueMap; + +/// \brief Determines the value to use as the phi node input for a block. +/// +/// Select between \p OldVal any value that we know flows from \p BB +/// to a particular phi on the basis of which one (if either) is not +/// undef. Update IncomingValues based on the selected value. +/// +/// \param OldVal The value we are considering selecting. +/// \param BB The block that the value flows in from. +/// \param IncomingValues A map from block-to-value for other phi inputs +/// that we have examined. +/// +/// \returns the selected value. +static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB, + IncomingValueMap &IncomingValues) { + if (!isa<UndefValue>(OldVal)) { + assert((!IncomingValues.count(BB) || + IncomingValues.find(BB)->second == OldVal) && + "Expected OldVal to match incoming value from BB!"); + + IncomingValues.insert(std::make_pair(BB, OldVal)); + return OldVal; + } + + IncomingValueMap::const_iterator It = IncomingValues.find(BB); + if (It != IncomingValues.end()) return It->second; + + return OldVal; +} + +/// \brief Create a map from block to value for the operands of a +/// given phi. +/// +/// Create a map from block to value for each non-undef value flowing +/// into \p PN. +/// +/// \param PN The phi we are collecting the map for. +/// \param IncomingValues [out] The map from block to value for this phi. +static void gatherIncomingValuesToPhi(PHINode *PN, + IncomingValueMap &IncomingValues) { + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + BasicBlock *BB = PN->getIncomingBlock(i); + Value *V = PN->getIncomingValue(i); + + if (!isa<UndefValue>(V)) + IncomingValues.insert(std::make_pair(BB, V)); + } +} + +/// \brief Replace the incoming undef values to a phi with the values +/// from a block-to-value map. +/// +/// \param PN The phi we are replacing the undefs in. +/// \param IncomingValues A map from block to value. +static void replaceUndefValuesInPhi(PHINode *PN, + const IncomingValueMap &IncomingValues) { + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + Value *V = PN->getIncomingValue(i); + + if (!isa<UndefValue>(V)) continue; + + BasicBlock *BB = PN->getIncomingBlock(i); + IncomingValueMap::const_iterator It = IncomingValues.find(BB); + if (It == IncomingValues.end()) continue; + + PN->setIncomingValue(i, It->second); + } +} + +/// \brief Replace a value flowing from a block to a phi with +/// potentially multiple instances of that value flowing from the +/// block's predecessors to the phi. +/// +/// \param BB The block with the value flowing into the phi. +/// \param BBPreds The predecessors of BB. +/// \param PN The phi that we are updating. +static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB, + const PredBlockVector &BBPreds, + PHINode *PN) { + Value *OldVal = PN->removeIncomingValue(BB, false); + assert(OldVal && "No entry in PHI for Pred BB!"); + + IncomingValueMap IncomingValues; + + // We are merging two blocks - BB, and the block containing PN - and + // as a result we need to redirect edges from the predecessors of BB + // to go to the block containing PN, and update PN + // accordingly. Since we allow merging blocks in the case where the + // predecessor and successor blocks both share some predecessors, + // and where some of those common predecessors might have undef + // values flowing into PN, we want to rewrite those values to be + // consistent with the non-undef values. + + gatherIncomingValuesToPhi(PN, IncomingValues); + + // If this incoming value is one of the PHI nodes in BB, the new entries + // in the PHI node are the entries from the old PHI. + if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { + PHINode *OldValPN = cast<PHINode>(OldVal); + for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) { + // Note that, since we are merging phi nodes and BB and Succ might + // have common predecessors, we could end up with a phi node with + // identical incoming branches. This will be cleaned up later (and + // will trigger asserts if we try to clean it up now, without also + // simplifying the corresponding conditional branch). + BasicBlock *PredBB = OldValPN->getIncomingBlock(i); + Value *PredVal = OldValPN->getIncomingValue(i); + Value *Selected = selectIncomingValueForBlock(PredVal, PredBB, + IncomingValues); + + // And add a new incoming value for this predecessor for the + // newly retargeted branch. + PN->addIncoming(Selected, PredBB); + } + } else { + for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) { + // Update existing incoming values in PN for this + // predecessor of BB. + BasicBlock *PredBB = BBPreds[i]; + Value *Selected = selectIncomingValueForBlock(OldVal, PredBB, + IncomingValues); + + // And add a new incoming value for this predecessor for the + // newly retargeted branch. + PN->addIncoming(Selected, PredBB); + } + } + + replaceUndefValuesInPhi(PN, IncomingValues); +} + +/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an +/// unconditional branch, and contains no instructions other than PHI nodes, +/// potential side-effect free intrinsics and the branch. If possible, +/// eliminate BB by rewriting all the predecessors to branch to the successor +/// block and return true. If we can't transform, return false. +bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) { + assert(BB != &BB->getParent()->getEntryBlock() && + "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!"); + + // We can't eliminate infinite loops. + BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0); + if (BB == Succ) return false; + + // Check to see if merging these blocks would cause conflicts for any of the + // phi nodes in BB or Succ. If not, we can safely merge. + if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; + + // Check for cases where Succ has multiple predecessors and a PHI node in BB + // has uses which will not disappear when the PHI nodes are merged. It is + // possible to handle such cases, but difficult: it requires checking whether + // BB dominates Succ, which is non-trivial to calculate in the case where + // Succ has multiple predecessors. Also, it requires checking whether + // constructing the necessary self-referential PHI node doesn't introduce any + // conflicts; this isn't too difficult, but the previous code for doing this + // was incorrect. + // + // Note that if this check finds a live use, BB dominates Succ, so BB is + // something like a loop pre-header (or rarely, a part of an irreducible CFG); + // folding the branch isn't profitable in that case anyway. + if (!Succ->getSinglePredecessor()) { + BasicBlock::iterator BBI = BB->begin(); + while (isa<PHINode>(*BBI)) { + for (Use &U : BBI->uses()) { + if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) { + if (PN->getIncomingBlock(U) != BB) + return false; + } else { + return false; + } + } + ++BBI; + } + } + + DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB); + + if (isa<PHINode>(Succ->begin())) { + // If there is more than one pred of succ, and there are PHI nodes in + // the successor, then we need to add incoming edges for the PHI nodes + // + const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB)); + + // Loop over all of the PHI nodes in the successor of BB. + for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { + PHINode *PN = cast<PHINode>(I); + + redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN); + } + } + + if (Succ->getSinglePredecessor()) { + // BB is the only predecessor of Succ, so Succ will end up with exactly + // the same predecessors BB had. + + // Copy over any phi, debug or lifetime instruction. + BB->getTerminator()->eraseFromParent(); + Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList()); + } else { + while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { + // We explicitly check for such uses in CanPropagatePredecessorsForPHIs. + assert(PN->use_empty() && "There shouldn't be any uses here!"); + PN->eraseFromParent(); + } + } + + // Everything that jumped to BB now goes to Succ. + BB->replaceAllUsesWith(Succ); + if (!Succ->hasName()) Succ->takeName(BB); + BB->eraseFromParent(); // Delete the old basic block. + return true; +} + +/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI +/// nodes in this block. This doesn't try to be clever about PHI nodes +/// which differ only in the order of the incoming values, but instcombine +/// orders them so it usually won't matter. +/// +bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) { + bool Changed = false; + + // This implementation doesn't currently consider undef operands + // specially. Theoretically, two phis which are identical except for + // one having an undef where the other doesn't could be collapsed. + + // Map from PHI hash values to PHI nodes. If multiple PHIs have + // the same hash value, the element is the first PHI in the + // linked list in CollisionMap. + DenseMap<uintptr_t, PHINode *> HashMap; + + // Maintain linked lists of PHI nodes with common hash values. + DenseMap<PHINode *, PHINode *> CollisionMap; + + // Examine each PHI. + for (BasicBlock::iterator I = BB->begin(); + PHINode *PN = dyn_cast<PHINode>(I++); ) { + // Compute a hash value on the operands. Instcombine will likely have sorted + // them, which helps expose duplicates, but we have to check all the + // operands to be safe in case instcombine hasn't run. + uintptr_t Hash = 0; + // This hash algorithm is quite weak as hash functions go, but it seems + // to do a good enough job for this particular purpose, and is very quick. + for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) { + Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I)); + Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); + } + for (PHINode::block_iterator I = PN->block_begin(), E = PN->block_end(); + I != E; ++I) { + Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock *>(*I)); + Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7)); + } + // Avoid colliding with the DenseMap sentinels ~0 and ~0-1. + Hash >>= 1; + // If we've never seen this hash value before, it's a unique PHI. + std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair = + HashMap.insert(std::make_pair(Hash, PN)); + if (Pair.second) continue; + // Otherwise it's either a duplicate or a hash collision. + for (PHINode *OtherPN = Pair.first->second; ; ) { + if (OtherPN->isIdenticalTo(PN)) { + // A duplicate. Replace this PHI with its duplicate. + PN->replaceAllUsesWith(OtherPN); + PN->eraseFromParent(); + Changed = true; + break; + } + // A non-duplicate hash collision. + DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN); + if (I == CollisionMap.end()) { + // Set this PHI to be the head of the linked list of colliding PHIs. + PHINode *Old = Pair.first->second; + Pair.first->second = PN; + CollisionMap[PN] = Old; + break; + } + // Proceed to the next PHI in the list. + OtherPN = I->second; + } + } + + return Changed; +} + +/// enforceKnownAlignment - If the specified pointer points to an object that +/// we control, modify the object's alignment to PrefAlign. This isn't +/// often possible though. If alignment is important, a more reliable approach +/// is to simply align all global variables and allocation instructions to +/// their preferred alignment from the beginning. +/// +static unsigned enforceKnownAlignment(Value *V, unsigned Align, + unsigned PrefAlign, const DataLayout *TD) { + V = V->stripPointerCasts(); + + if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) { + // If the preferred alignment is greater than the natural stack alignment + // then don't round up. This avoids dynamic stack realignment. + if (TD && TD->exceedsNaturalStackAlignment(PrefAlign)) + return Align; + // If there is a requested alignment and if this is an alloca, round up. + if (AI->getAlignment() >= PrefAlign) + return AI->getAlignment(); + AI->setAlignment(PrefAlign); + return PrefAlign; + } + + if (auto *GO = dyn_cast<GlobalObject>(V)) { + // If there is a large requested alignment and we can, bump up the alignment + // of the global. + if (GO->isDeclaration()) + return Align; + // If the memory we set aside for the global may not be the memory used by + // the final program then it is impossible for us to reliably enforce the + // preferred alignment. + if (GO->isWeakForLinker()) + return Align; + + if (GO->getAlignment() >= PrefAlign) + return GO->getAlignment(); + // We can only increase the alignment of the global if it has no alignment + // specified or if it is not assigned a section. If it is assigned a + // section, the global could be densely packed with other objects in the + // section, increasing the alignment could cause padding issues. + if (!GO->hasSection() || GO->getAlignment() == 0) + GO->setAlignment(PrefAlign); + return GO->getAlignment(); + } + + return Align; +} + +/// getOrEnforceKnownAlignment - If the specified pointer has an alignment that +/// we can determine, return it, otherwise return 0. If PrefAlign is specified, +/// and it is more than the alignment of the ultimate object, see if we can +/// increase the alignment of the ultimate object, making this check succeed. +unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign, + const DataLayout *DL) { + assert(V->getType()->isPointerTy() && + "getOrEnforceKnownAlignment expects a pointer!"); + unsigned BitWidth = DL ? DL->getPointerTypeSizeInBits(V->getType()) : 64; + + APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); + computeKnownBits(V, KnownZero, KnownOne, DL); + unsigned TrailZ = KnownZero.countTrailingOnes(); + + // Avoid trouble with ridiculously large TrailZ values, such as + // those computed from a null pointer. + TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1)); + + unsigned Align = 1u << std::min(BitWidth - 1, TrailZ); + + // LLVM doesn't support alignments larger than this currently. + Align = std::min(Align, +Value::MaximumAlignment); + + if (PrefAlign > Align) + Align = enforceKnownAlignment(V, Align, PrefAlign, DL); + + // We don't need to make any adjustment. + return Align; +} + +///===---------------------------------------------------------------------===// +/// Dbg Intrinsic utilities +/// + +/// See if there is a dbg.value intrinsic for DIVar before I. +static bool LdStHasDebugValue(DIVariable &DIVar, Instruction *I) { + // Since we can't guarantee that the original dbg.declare instrinsic + // is removed by LowerDbgDeclare(), we need to make sure that we are + // not inserting the same dbg.value intrinsic over and over. + llvm::BasicBlock::InstListType::iterator PrevI(I); + if (PrevI != I->getParent()->getInstList().begin()) { + --PrevI; + if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI)) + if (DVI->getValue() == I->getOperand(0) && + DVI->getOffset() == 0 && + DVI->getVariable() == DIVar) + return true; + } + return false; +} + +/// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value +/// that has an associated llvm.dbg.decl intrinsic. +bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, + StoreInst *SI, DIBuilder &Builder) { + DIVariable DIVar(DDI->getVariable()); + assert((!DIVar || DIVar.isVariable()) && + "Variable in DbgDeclareInst should be either null or a DIVariable."); + if (!DIVar) + return false; + + if (LdStHasDebugValue(DIVar, SI)) + return true; + + Instruction *DbgVal = nullptr; + // If an argument is zero extended then use argument directly. The ZExt + // may be zapped by an optimization pass in future. + Argument *ExtendedArg = nullptr; + if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0))) + ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0)); + if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0))) + ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0)); + if (ExtendedArg) + DbgVal = Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, SI); + else + DbgVal = Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, SI); + DbgVal->setDebugLoc(DDI->getDebugLoc()); + return true; +} + +/// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value +/// that has an associated llvm.dbg.decl intrinsic. +bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI, + LoadInst *LI, DIBuilder &Builder) { + DIVariable DIVar(DDI->getVariable()); + assert((!DIVar || DIVar.isVariable()) && + "Variable in DbgDeclareInst should be either null or a DIVariable."); + if (!DIVar) + return false; + + if (LdStHasDebugValue(DIVar, LI)) + return true; + + Instruction *DbgVal = + Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, + DIVar, LI); + DbgVal->setDebugLoc(DDI->getDebugLoc()); + return true; +} + +/// Determine whether this alloca is either a VLA or an array. +static bool isArray(AllocaInst *AI) { + return AI->isArrayAllocation() || + AI->getType()->getElementType()->isArrayTy(); +} + +/// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set +/// of llvm.dbg.value intrinsics. +bool llvm::LowerDbgDeclare(Function &F) { + DIBuilder DIB(*F.getParent()); + SmallVector<DbgDeclareInst *, 4> Dbgs; + for (auto &FI : F) + for (BasicBlock::iterator BI : FI) + if (auto DDI = dyn_cast<DbgDeclareInst>(BI)) + Dbgs.push_back(DDI); + + if (Dbgs.empty()) + return false; + + for (auto &I : Dbgs) { + DbgDeclareInst *DDI = I; + AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress()); + // If this is an alloca for a scalar variable, insert a dbg.value + // at each load and store to the alloca and erase the dbg.declare. + // The dbg.values allow tracking a variable even if it is not + // stored on the stack, while the dbg.declare can only describe + // the stack slot (and at a lexical-scope granularity). Later + // passes will attempt to elide the stack slot. + if (AI && !isArray(AI)) { + for (User *U : AI->users()) + if (StoreInst *SI = dyn_cast<StoreInst>(U)) + ConvertDebugDeclareToDebugValue(DDI, SI, DIB); + else if (LoadInst *LI = dyn_cast<LoadInst>(U)) + ConvertDebugDeclareToDebugValue(DDI, LI, DIB); + else if (CallInst *CI = dyn_cast<CallInst>(U)) { + // This is a call by-value or some other instruction that + // takes a pointer to the variable. Insert a *value* + // intrinsic that describes the alloca. + auto DbgVal = + DIB.insertDbgValueIntrinsic(AI, 0, + DIVariable(DDI->getVariable()), CI); + DbgVal->setDebugLoc(DDI->getDebugLoc()); + } + DDI->eraseFromParent(); + } + } + return true; +} + +/// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the +/// alloca 'V', if any. +DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) { + if (MDNode *DebugNode = MDNode::getIfExists(V->getContext(), V)) + for (User *U : DebugNode->users()) + if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U)) + return DDI; + + return nullptr; +} + +bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress, + DIBuilder &Builder) { + DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI); + if (!DDI) + return false; + DIVariable DIVar(DDI->getVariable()); + assert((!DIVar || DIVar.isVariable()) && + "Variable in DbgDeclareInst should be either null or a DIVariable."); + if (!DIVar) + return false; + + // Create a copy of the original DIDescriptor for user variable, appending + // "deref" operation to a list of address elements, as new llvm.dbg.declare + // will take a value storing address of the memory for variable, not + // alloca itself. + Type *Int64Ty = Type::getInt64Ty(AI->getContext()); + SmallVector<Value*, 4> NewDIVarAddress; + if (DIVar.hasComplexAddress()) { + for (unsigned i = 0, n = DIVar.getNumAddrElements(); i < n; ++i) { + NewDIVarAddress.push_back( + ConstantInt::get(Int64Ty, DIVar.getAddrElement(i))); + } + } + NewDIVarAddress.push_back(ConstantInt::get(Int64Ty, DIBuilder::OpDeref)); + DIVariable NewDIVar = Builder.createComplexVariable( + DIVar.getTag(), DIVar.getContext(), DIVar.getName(), + DIVar.getFile(), DIVar.getLineNumber(), DIVar.getType(), + NewDIVarAddress, DIVar.getArgNumber()); + + // Insert llvm.dbg.declare in the same basic block as the original alloca, + // and remove old llvm.dbg.declare. + BasicBlock *BB = AI->getParent(); + Builder.insertDeclare(NewAllocaAddress, NewDIVar, BB); + DDI->eraseFromParent(); + return true; +} + +/// changeToUnreachable - Insert an unreachable instruction before the specified +/// instruction, making it and the rest of the code in the block dead. +static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) { + BasicBlock *BB = I->getParent(); + // Loop over all of the successors, removing BB's entry from any PHI + // nodes. + for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) + (*SI)->removePredecessor(BB); + + // Insert a call to llvm.trap right before this. This turns the undefined + // behavior into a hard fail instead of falling through into random code. + if (UseLLVMTrap) { + Function *TrapFn = + Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap); + CallInst *CallTrap = CallInst::Create(TrapFn, "", I); + CallTrap->setDebugLoc(I->getDebugLoc()); + } + new UnreachableInst(I->getContext(), I); + + // All instructions after this are dead. + BasicBlock::iterator BBI = I, BBE = BB->end(); + while (BBI != BBE) { + if (!BBI->use_empty()) + BBI->replaceAllUsesWith(UndefValue::get(BBI->getType())); + BB->getInstList().erase(BBI++); + } +} + +/// changeToCall - Convert the specified invoke into a normal call. +static void changeToCall(InvokeInst *II) { + SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3); + CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II); + NewCall->takeName(II); + NewCall->setCallingConv(II->getCallingConv()); + NewCall->setAttributes(II->getAttributes()); + NewCall->setDebugLoc(II->getDebugLoc()); + II->replaceAllUsesWith(NewCall); + + // Follow the call by a branch to the normal destination. + BranchInst::Create(II->getNormalDest(), II); + + // Update PHI nodes in the unwind destination + II->getUnwindDest()->removePredecessor(II->getParent()); + II->eraseFromParent(); +} + +static bool markAliveBlocks(BasicBlock *BB, + SmallPtrSet<BasicBlock*, 128> &Reachable) { + + SmallVector<BasicBlock*, 128> Worklist; + Worklist.push_back(BB); + Reachable.insert(BB); + bool Changed = false; + do { + BB = Worklist.pop_back_val(); + + // Do a quick scan of the basic block, turning any obviously unreachable + // instructions into LLVM unreachable insts. The instruction combining pass + // canonicalizes unreachable insts into stores to null or undef. + for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){ + if (CallInst *CI = dyn_cast<CallInst>(BBI)) { + if (CI->doesNotReturn()) { + // If we found a call to a no-return function, insert an unreachable + // instruction after it. Make sure there isn't *already* one there + // though. + ++BBI; + if (!isa<UnreachableInst>(BBI)) { + // Don't insert a call to llvm.trap right before the unreachable. + changeToUnreachable(BBI, false); + Changed = true; + } + break; + } + } + + // Store to undef and store to null are undefined and used to signal that + // they should be changed to unreachable by passes that can't modify the + // CFG. + if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) { + // Don't touch volatile stores. + if (SI->isVolatile()) continue; + + Value *Ptr = SI->getOperand(1); + + if (isa<UndefValue>(Ptr) || + (isa<ConstantPointerNull>(Ptr) && + SI->getPointerAddressSpace() == 0)) { + changeToUnreachable(SI, true); + Changed = true; + break; + } + } + } + + // Turn invokes that call 'nounwind' functions into ordinary calls. + if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) { + Value *Callee = II->getCalledValue(); + if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) { + changeToUnreachable(II, true); + Changed = true; + } else if (II->doesNotThrow()) { + if (II->use_empty() && II->onlyReadsMemory()) { + // jump to the normal destination branch. + BranchInst::Create(II->getNormalDest(), II); + II->getUnwindDest()->removePredecessor(II->getParent()); + II->eraseFromParent(); + } else + changeToCall(II); + Changed = true; + } + } + + Changed |= ConstantFoldTerminator(BB, true); + for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) + if (Reachable.insert(*SI)) + Worklist.push_back(*SI); + } while (!Worklist.empty()); + return Changed; +} + +/// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even +/// if they are in a dead cycle. Return true if a change was made, false +/// otherwise. +bool llvm::removeUnreachableBlocks(Function &F) { + SmallPtrSet<BasicBlock*, 128> Reachable; + bool Changed = markAliveBlocks(F.begin(), Reachable); + + // If there are unreachable blocks in the CFG... + if (Reachable.size() == F.size()) + return Changed; + + assert(Reachable.size() < F.size()); + NumRemoved += F.size()-Reachable.size(); + + // Loop over all of the basic blocks that are not reachable, dropping all of + // their internal references... + for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) { + if (Reachable.count(BB)) + continue; + + for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) + if (Reachable.count(*SI)) + (*SI)->removePredecessor(BB); + BB->dropAllReferences(); + } + + for (Function::iterator I = ++F.begin(); I != F.end();) + if (!Reachable.count(I)) + I = F.getBasicBlockList().erase(I); + else + ++I; + + return true; +} |
