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Diffstat (limited to 'lib/Transforms/Utils/SimplifyCFG.cpp')
| -rw-r--r-- | lib/Transforms/Utils/SimplifyCFG.cpp | 1821 |
1 files changed, 1821 insertions, 0 deletions
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp new file mode 100644 index 0000000000..6b5914365b --- /dev/null +++ b/lib/Transforms/Utils/SimplifyCFG.cpp @@ -0,0 +1,1821 @@ +//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===// +// +// The LLVM Compiler Infrastructure +// +// This file was developed by the LLVM research group and is distributed under +// the University of Illinois Open Source License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// +// +// Peephole optimize the CFG. +// +//===----------------------------------------------------------------------===// + +#define DEBUG_TYPE "simplifycfg" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/Constants.h" +#include "llvm/Instructions.h" +#include "llvm/Type.h" +#include "llvm/Support/CFG.h" +#include "llvm/Support/Debug.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include <algorithm> +#include <functional> +#include <set> +#include <map> +using namespace llvm; + +/// SafeToMergeTerminators - Return true if it is safe to merge these two +/// terminator instructions together. +/// +static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) { + if (SI1 == SI2) return false; // Can't merge with self! + + // It is not safe to merge these two switch instructions if they have a common + // successor, and if that successor has a PHI node, and if *that* PHI node has + // conflicting incoming values from the two switch blocks. + BasicBlock *SI1BB = SI1->getParent(); + BasicBlock *SI2BB = SI2->getParent(); + std::set<BasicBlock*> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB)); + + for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I) + if (SI1Succs.count(*I)) + for (BasicBlock::iterator BBI = (*I)->begin(); + isa<PHINode>(BBI); ++BBI) { + PHINode *PN = cast<PHINode>(BBI); + if (PN->getIncomingValueForBlock(SI1BB) != + PN->getIncomingValueForBlock(SI2BB)) + return false; + } + + return true; +} + +/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will +/// now be entries in it from the 'NewPred' block. The values that will be +/// flowing into the PHI nodes will be the same as those coming in from +/// ExistPred, an existing predecessor of Succ. +static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred, + BasicBlock *ExistPred) { + assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) != + succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!"); + if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do + + for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { + PHINode *PN = cast<PHINode>(I); + Value *V = PN->getIncomingValueForBlock(ExistPred); + PN->addIncoming(V, NewPred); + } +} + +// 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!"); + + // Check to see if one of the predecessors of BB is already a predecessor of + // Succ. If so, we cannot do the transformation if there are any PHI nodes + // with incompatible values coming in from the two edges! + // + if (isa<PHINode>(Succ->front())) { + std::set<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB)); + for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);\ + PI != PE; ++PI) + if (std::find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) { + // Loop over all of the PHI nodes checking to see if there are + // incompatible values coming in. + for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { + PHINode *PN = cast<PHINode>(I); + // Loop up the entries in the PHI node for BB and for *PI if the + // values coming in are non-equal, we cannot merge these two blocks + // (instead we should insert a conditional move or something, then + // merge the blocks). + if (PN->getIncomingValueForBlock(BB) != + PN->getIncomingValueForBlock(*PI)) + return false; // Values are not equal... + } + } + } + + // Finally, if BB has PHI nodes that are used by things other than the PHIs in + // Succ and Succ has predecessors that are not Succ and not Pred, we cannot + // fold these blocks, as we don't know whether BB dominates Succ or not to + // update the PHI nodes correctly. + if (!isa<PHINode>(BB->begin()) || Succ->getSinglePredecessor()) return true; + + // If the predecessors of Succ are only BB and Succ itself, we can handle this. + bool IsSafe = true; + for (pred_iterator PI = pred_begin(Succ), E = pred_end(Succ); PI != E; ++PI) + if (*PI != Succ && *PI != BB) { + IsSafe = false; + break; + } + if (IsSafe) return true; + + // If the PHI nodes in BB are only used by instructions in Succ, we are ok. + IsSafe = true; + for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I) && IsSafe; ++I) { + PHINode *PN = cast<PHINode>(I); + for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; + ++UI) + if (cast<Instruction>(*UI)->getParent() != Succ) { + IsSafe = false; + break; + } + } + + return IsSafe; +} + +/// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional +/// branch to Succ, and contains no instructions other than PHI nodes and the +/// branch. If possible, eliminate BB. +static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB, + BasicBlock *Succ) { + // If our successor has PHI nodes, then we need to update them to include + // entries for BB's predecessors, not for BB itself. Be careful though, + // if this transformation fails (returns true) then we cannot do this + // transformation! + // + if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false; + + DEBUG(std::cerr << "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 std::vector<BasicBlock*> 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); + Value *OldVal = PN->removeIncomingValue(BB, false); + assert(OldVal && "No entry in PHI for Pred BB!"); + + // 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) + PN->addIncoming(OldValPN->getIncomingValue(i), + OldValPN->getIncomingBlock(i)); + } else { + for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(), + End = BBPreds.end(); PredI != End; ++PredI) { + // Add an incoming value for each of the new incoming values... + PN->addIncoming(OldVal, *PredI); + } + } + } + } + + if (isa<PHINode>(&BB->front())) { + std::vector<BasicBlock*> + OldSuccPreds(pred_begin(Succ), pred_end(Succ)); + + // Move all PHI nodes in BB to Succ if they are alive, otherwise + // delete them. + while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) + if (PN->use_empty()) { + // Just remove the dead phi. This happens if Succ's PHIs were the only + // users of the PHI nodes. + PN->eraseFromParent(); + } else { + // The instruction is alive, so this means that Succ must have + // *ONLY* had BB as a predecessor, and the PHI node is still valid + // now. Simply move it into Succ, because we know that BB + // strictly dominated Succ. + Succ->getInstList().splice(Succ->begin(), + BB->getInstList(), BB->begin()); + + // We need to add new entries for the PHI node to account for + // predecessors of Succ that the PHI node does not take into + // account. At this point, since we know that BB dominated succ, + // this means that we should any newly added incoming edges should + // use the PHI node as the value for these edges, because they are + // loop back edges. + for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i) + if (OldSuccPreds[i] != BB) + PN->addIncoming(PN, OldSuccPreds[i]); + } + } + + // Everything that jumped to BB now goes to Succ. + std::string OldName = BB->getName(); + BB->replaceAllUsesWith(Succ); + BB->eraseFromParent(); // Delete the old basic block. + + if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can + Succ->setName(OldName); + return true; +} + +/// GetIfCondition - Given a basic block (BB) with two predecessors (and +/// presumably PHI nodes in it), check to see if the merge at this block is due +/// to an "if condition". If so, return the boolean condition that determines +/// which entry into BB will be taken. Also, return by references the block +/// that will be entered from if the condition is true, and the block that will +/// be entered if the condition is false. +/// +/// +static Value *GetIfCondition(BasicBlock *BB, + BasicBlock *&IfTrue, BasicBlock *&IfFalse) { + assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 && + "Function can only handle blocks with 2 predecessors!"); + BasicBlock *Pred1 = *pred_begin(BB); + BasicBlock *Pred2 = *++pred_begin(BB); + + // We can only handle branches. Other control flow will be lowered to + // branches if possible anyway. + if (!isa<BranchInst>(Pred1->getTerminator()) || + !isa<BranchInst>(Pred2->getTerminator())) + return 0; + BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator()); + BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator()); + + // Eliminate code duplication by ensuring that Pred1Br is conditional if + // either are. + if (Pred2Br->isConditional()) { + // If both branches are conditional, we don't have an "if statement". In + // reality, we could transform this case, but since the condition will be + // required anyway, we stand no chance of eliminating it, so the xform is + // probably not profitable. + if (Pred1Br->isConditional()) + return 0; + + std::swap(Pred1, Pred2); + std::swap(Pred1Br, Pred2Br); + } + + if (Pred1Br->isConditional()) { + // If we found a conditional branch predecessor, make sure that it branches + // to BB and Pred2Br. If it doesn't, this isn't an "if statement". + if (Pred1Br->getSuccessor(0) == BB && + Pred1Br->getSuccessor(1) == Pred2) { + IfTrue = Pred1; + IfFalse = Pred2; + } else if (Pred1Br->getSuccessor(0) == Pred2 && + Pred1Br->getSuccessor(1) == BB) { + IfTrue = Pred2; + IfFalse = Pred1; + } else { + // We know that one arm of the conditional goes to BB, so the other must + // go somewhere unrelated, and this must not be an "if statement". + return 0; + } + + // The only thing we have to watch out for here is to make sure that Pred2 + // doesn't have incoming edges from other blocks. If it does, the condition + // doesn't dominate BB. + if (++pred_begin(Pred2) != pred_end(Pred2)) + return 0; + + return Pred1Br->getCondition(); + } + + // Ok, if we got here, both predecessors end with an unconditional branch to + // BB. Don't panic! If both blocks only have a single (identical) + // predecessor, and THAT is a conditional branch, then we're all ok! + if (pred_begin(Pred1) == pred_end(Pred1) || + ++pred_begin(Pred1) != pred_end(Pred1) || + pred_begin(Pred2) == pred_end(Pred2) || + ++pred_begin(Pred2) != pred_end(Pred2) || + *pred_begin(Pred1) != *pred_begin(Pred2)) + return 0; + + // Otherwise, if this is a conditional branch, then we can use it! + BasicBlock *CommonPred = *pred_begin(Pred1); + if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) { + assert(BI->isConditional() && "Two successors but not conditional?"); + if (BI->getSuccessor(0) == Pred1) { + IfTrue = Pred1; + IfFalse = Pred2; + } else { + IfTrue = Pred2; + IfFalse = Pred1; + } + return BI->getCondition(); + } + return 0; +} + + +// If we have a merge point of an "if condition" as accepted above, return true +// if the specified value dominates the block. We don't handle the true +// generality of domination here, just a special case which works well enough +// for us. +// +// If AggressiveInsts is non-null, and if V does not dominate BB, we check to +// see if V (which must be an instruction) is cheap to compute and is +// non-trapping. If both are true, the instruction is inserted into the set and +// true is returned. +static bool DominatesMergePoint(Value *V, BasicBlock *BB, + std::set<Instruction*> *AggressiveInsts) { + Instruction *I = dyn_cast<Instruction>(V); + if (!I) return true; // Non-instructions all dominate instructions. + BasicBlock *PBB = I->getParent(); + + // We don't want to allow weird loops that might have the "if condition" in + // the bottom of this block. + if (PBB == BB) return false; + + // If this instruction is defined in a block that contains an unconditional + // branch to BB, then it must be in the 'conditional' part of the "if + // statement". + if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator())) + if (BI->isUnconditional() && BI->getSuccessor(0) == BB) { + if (!AggressiveInsts) return false; + // Okay, it looks like the instruction IS in the "condition". Check to + // see if its a cheap instruction to unconditionally compute, and if it + // only uses stuff defined outside of the condition. If so, hoist it out. + switch (I->getOpcode()) { + default: return false; // Cannot hoist this out safely. + case Instruction::Load: + // We can hoist loads that are non-volatile and obviously cannot trap. + if (cast<LoadInst>(I)->isVolatile()) + return false; + if (!isa<AllocaInst>(I->getOperand(0)) && + !isa<Constant>(I->getOperand(0))) + return false; + + // Finally, we have to check to make sure there are no instructions + // before the load in its basic block, as we are going to hoist the loop + // out to its predecessor. + if (PBB->begin() != BasicBlock::iterator(I)) + return false; + break; + case Instruction::Add: + case Instruction::Sub: + case Instruction::And: + case Instruction::Or: + case Instruction::Xor: + case Instruction::Shl: + case Instruction::Shr: + case Instruction::SetEQ: + case Instruction::SetNE: + case Instruction::SetLT: + case Instruction::SetGT: + case Instruction::SetLE: + case Instruction::SetGE: + break; // These are all cheap and non-trapping instructions. + } + + // Okay, we can only really hoist these out if their operands are not + // defined in the conditional region. + for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) + if (!DominatesMergePoint(I->getOperand(i), BB, 0)) + return false; + // Okay, it's safe to do this! Remember this instruction. + AggressiveInsts->insert(I); + } + + return true; +} + +// GatherConstantSetEQs - Given a potentially 'or'd together collection of seteq +// instructions that compare a value against a constant, return the value being +// compared, and stick the constant into the Values vector. +static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){ + if (Instruction *Inst = dyn_cast<Instruction>(V)) + if (Inst->getOpcode() == Instruction::SetEQ) { + if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) { + Values.push_back(C); + return Inst->getOperand(0); + } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) { + Values.push_back(C); + return Inst->getOperand(1); + } + } else if (Inst->getOpcode() == Instruction::Or) { + if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values)) + if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values)) + if (LHS == RHS) + return LHS; + } + return 0; +} + +// GatherConstantSetNEs - Given a potentially 'and'd together collection of +// setne instructions that compare a value against a constant, return the value +// being compared, and stick the constant into the Values vector. +static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){ + if (Instruction *Inst = dyn_cast<Instruction>(V)) + if (Inst->getOpcode() == Instruction::SetNE) { + if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) { + Values.push_back(C); + return Inst->getOperand(0); + } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) { + Values.push_back(C); + return Inst->getOperand(1); + } + } else if (Inst->getOpcode() == Instruction::Cast) { + // Cast of X to bool is really a comparison against zero. + assert(Inst->getType() == Type::BoolTy && "Can only handle bool values!"); + Values.push_back(ConstantInt::get(Inst->getOperand(0)->getType(), 0)); + return Inst->getOperand(0); + } else if (Inst->getOpcode() == Instruction::And) { + if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values)) + if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values)) + if (LHS == RHS) + return LHS; + } + return 0; +} + + + +/// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a +/// bunch of comparisons of one value against constants, return the value and +/// the constants being compared. +static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal, + std::vector<ConstantInt*> &Values) { + if (Cond->getOpcode() == Instruction::Or) { + CompVal = GatherConstantSetEQs(Cond, Values); + + // Return true to indicate that the condition is true if the CompVal is + // equal to one of the constants. + return true; + } else if (Cond->getOpcode() == Instruction::And) { + CompVal = GatherConstantSetNEs(Cond, Values); + + // Return false to indicate that the condition is false if the CompVal is + // equal to one of the constants. + return false; + } + return false; +} + +/// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and +/// has no side effects, nuke it. If it uses any instructions that become dead +/// because the instruction is now gone, nuke them too. +static void ErasePossiblyDeadInstructionTree(Instruction *I) { + if (isInstructionTriviallyDead(I)) { + std::vector<Value*> Operands(I->op_begin(), I->op_end()); + I->getParent()->getInstList().erase(I); + for (unsigned i = 0, e = Operands.size(); i != e; ++i) + if (Instruction *OpI = dyn_cast<Instruction>(Operands[i])) + ErasePossiblyDeadInstructionTree(OpI); + } +} + +// isValueEqualityComparison - Return true if the specified terminator checks to +// see if a value is equal to constant integer value. +static Value *isValueEqualityComparison(TerminatorInst *TI) { + if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { + // Do not permit merging of large switch instructions into their + // predecessors unless there is only one predecessor. + if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()), + pred_end(SI->getParent())) > 128) + return 0; + + return SI->getCondition(); + } + if (BranchInst *BI = dyn_cast<BranchInst>(TI)) + if (BI->isConditional() && BI->getCondition()->hasOneUse()) + if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition())) + if ((SCI->getOpcode() == Instruction::SetEQ || + SCI->getOpcode() == Instruction::SetNE) && + isa<ConstantInt>(SCI->getOperand(1))) + return SCI->getOperand(0); + return 0; +} + +// Given a value comparison instruction, decode all of the 'cases' that it +// represents and return the 'default' block. +static BasicBlock * +GetValueEqualityComparisonCases(TerminatorInst *TI, + std::vector<std::pair<ConstantInt*, + BasicBlock*> > &Cases) { + if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { + Cases.reserve(SI->getNumCases()); + for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) + Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i))); + return SI->getDefaultDest(); + } + + BranchInst *BI = cast<BranchInst>(TI); + SetCondInst *SCI = cast<SetCondInst>(BI->getCondition()); + Cases.push_back(std::make_pair(cast<ConstantInt>(SCI->getOperand(1)), + BI->getSuccessor(SCI->getOpcode() == + Instruction::SetNE))); + return BI->getSuccessor(SCI->getOpcode() == Instruction::SetEQ); +} + + +// EliminateBlockCases - Given an vector of bb/value pairs, remove any entries +// in the list that match the specified block. +static void EliminateBlockCases(BasicBlock *BB, + std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) { + for (unsigned i = 0, e = Cases.size(); i != e; ++i) + if (Cases[i].second == BB) { + Cases.erase(Cases.begin()+i); + --i; --e; + } +} + +// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as +// well. +static bool +ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1, + std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) { + std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2; + + // Make V1 be smaller than V2. + if (V1->size() > V2->size()) + std::swap(V1, V2); + + if (V1->size() == 0) return false; + if (V1->size() == 1) { + // Just scan V2. + ConstantInt *TheVal = (*V1)[0].first; + for (unsigned i = 0, e = V2->size(); i != e; ++i) + if (TheVal == (*V2)[i].first) + return true; + } + + // Otherwise, just sort both lists and compare element by element. + std::sort(V1->begin(), V1->end()); + std::sort(V2->begin(), V2->end()); + unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size(); + while (i1 != e1 && i2 != e2) { + if ((*V1)[i1].first == (*V2)[i2].first) + return true; + if ((*V1)[i1].first < (*V2)[i2].first) + ++i1; + else + ++i2; + } + return false; +} + +// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a +// terminator instruction and its block is known to only have a single +// predecessor block, check to see if that predecessor is also a value +// comparison with the same value, and if that comparison determines the outcome +// of this comparison. If so, simplify TI. This does a very limited form of +// jump threading. +static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, + BasicBlock *Pred) { + Value *PredVal = isValueEqualityComparison(Pred->getTerminator()); + if (!PredVal) return false; // Not a value comparison in predecessor. + + Value *ThisVal = isValueEqualityComparison(TI); + assert(ThisVal && "This isn't a value comparison!!"); + if (ThisVal != PredVal) return false; // Different predicates. + + // Find out information about when control will move from Pred to TI's block. + std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; + BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(), + PredCases); + EliminateBlockCases(PredDef, PredCases); // Remove default from cases. + + // Find information about how control leaves this block. + std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases; + BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases); + EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases. + + // If TI's block is the default block from Pred's comparison, potentially + // simplify TI based on this knowledge. + if (PredDef == TI->getParent()) { + // If we are here, we know that the value is none of those cases listed in + // PredCases. If there are any cases in ThisCases that are in PredCases, we + // can simplify TI. + if (ValuesOverlap(PredCases, ThisCases)) { + if (BranchInst *BTI = dyn_cast<BranchInst>(TI)) { + // Okay, one of the successors of this condbr is dead. Convert it to a + // uncond br. + assert(ThisCases.size() == 1 && "Branch can only have one case!"); + Value *Cond = BTI->getCondition(); + // Insert the new branch. + Instruction *NI = new BranchInst(ThisDef, TI); + + // Remove PHI node entries for the dead edge. + ThisCases[0].second->removePredecessor(TI->getParent()); + + DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator() + << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); + + TI->eraseFromParent(); // Nuke the old one. + // If condition is now dead, nuke it. + if (Instruction *CondI = dyn_cast<Instruction>(Cond)) + ErasePossiblyDeadInstructionTree(CondI); + return true; + + } else { + SwitchInst *SI = cast<SwitchInst>(TI); + // Okay, TI has cases that are statically dead, prune them away. + std::set<Constant*> DeadCases; + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + DeadCases.insert(PredCases[i].first); + + DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator() + << "Through successor TI: " << *TI); + + for (unsigned i = SI->getNumCases()-1; i != 0; --i) + if (DeadCases.count(SI->getCaseValue(i))) { + SI->getSuccessor(i)->removePredecessor(TI->getParent()); + SI->removeCase(i); + } + + DEBUG(std::cerr << "Leaving: " << *TI << "\n"); + return true; + } + } + + } else { + // Otherwise, TI's block must correspond to some matched value. Find out + // which value (or set of values) this is. + ConstantInt *TIV = 0; + BasicBlock *TIBB = TI->getParent(); + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + if (PredCases[i].second == TIBB) + if (TIV == 0) + TIV = PredCases[i].first; + else + return false; // Cannot handle multiple values coming to this block. + assert(TIV && "No edge from pred to succ?"); + + // Okay, we found the one constant that our value can be if we get into TI's + // BB. Find out which successor will unconditionally be branched to. + BasicBlock *TheRealDest = 0; + for (unsigned i = 0, e = ThisCases.size(); i != e; ++i) + if (ThisCases[i].first == TIV) { + TheRealDest = ThisCases[i].second; + break; + } + + // If not handled by any explicit cases, it is handled by the default case. + if (TheRealDest == 0) TheRealDest = ThisDef; + + // Remove PHI node entries for dead edges. + BasicBlock *CheckEdge = TheRealDest; + for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI) + if (*SI != CheckEdge) + (*SI)->removePredecessor(TIBB); + else + CheckEdge = 0; + + // Insert the new branch. + Instruction *NI = new BranchInst(TheRealDest, TI); + + DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator() + << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); + Instruction *Cond = 0; + if (BranchInst *BI = dyn_cast<BranchInst>(TI)) + Cond = dyn_cast<Instruction>(BI->getCondition()); + TI->eraseFromParent(); // Nuke the old one. + + if (Cond) ErasePossiblyDeadInstructionTree(Cond); + return true; + } + return false; +} + +// FoldValueComparisonIntoPredecessors - The specified terminator is a value +// equality comparison instruction (either a switch or a branch on "X == c"). +// See if any of the predecessors of the terminator block are value comparisons +// on the same value. If so, and if safe to do so, fold them together. +static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) { + BasicBlock *BB = TI->getParent(); + Value *CV = isValueEqualityComparison(TI); // CondVal + assert(CV && "Not a comparison?"); + bool Changed = false; + + std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB)); + while (!Preds.empty()) { + BasicBlock *Pred = Preds.back(); + Preds.pop_back(); + + // See if the predecessor is a comparison with the same value. + TerminatorInst *PTI = Pred->getTerminator(); + Value *PCV = isValueEqualityComparison(PTI); // PredCondVal + + if (PCV == CV && SafeToMergeTerminators(TI, PTI)) { + // Figure out which 'cases' to copy from SI to PSI. + std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases; + BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases); + + std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; + BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases); + + // Based on whether the default edge from PTI goes to BB or not, fill in + // PredCases and PredDefault with the new switch cases we would like to + // build. + std::vector<BasicBlock*> NewSuccessors; + + if (PredDefault == BB) { + // If this is the default destination from PTI, only the edges in TI + // that don't occur in PTI, or that branch to BB will be activated. + std::set<ConstantInt*> PTIHandled; + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + if (PredCases[i].second != BB) + PTIHandled.insert(PredCases[i].first); + else { + // The default destination is BB, we don't need explicit targets. + std::swap(PredCases[i], PredCases.back()); + PredCases.pop_back(); + --i; --e; + } + + // Reconstruct the new switch statement we will be building. + if (PredDefault != BBDefault) { + PredDefault->removePredecessor(Pred); + PredDefault = BBDefault; + NewSuccessors.push_back(BBDefault); + } + for (unsigned i = 0, e = BBCases.size(); i != e; ++i) + if (!PTIHandled.count(BBCases[i].first) && + BBCases[i].second != BBDefault) { + PredCases.push_back(BBCases[i]); + NewSuccessors.push_back(BBCases[i].second); + } + + } else { + // If this is not the default destination from PSI, only the edges + // in SI that occur in PSI with a destination of BB will be + // activated. + std::set<ConstantInt*> PTIHandled; + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + if (PredCases[i].second == BB) { + PTIHandled.insert(PredCases[i].first); + std::swap(PredCases[i], PredCases.back()); + PredCases.pop_back(); + --i; --e; + } + + // Okay, now we know which constants were sent to BB from the + // predecessor. Figure out where they will all go now. + for (unsigned i = 0, e = BBCases.size(); i != e; ++i) + if (PTIHandled.count(BBCases[i].first)) { + // If this is one we are capable of getting... + PredCases.push_back(BBCases[i]); + NewSuccessors.push_back(BBCases[i].second); + PTIHandled.erase(BBCases[i].first);// This constant is taken care of + } + + // If there are any constants vectored to BB that TI doesn't handle, + // they must go to the default destination of TI. + for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(), + E = PTIHandled.end(); I != E; ++I) { + PredCases.push_back(std::make_pair(*I, BBDefault)); + NewSuccessors.push_back(BBDefault); + } + } + + // Okay, at this point, we know which new successor Pred will get. Make + // sure we update the number of entries in the PHI nodes for these + // successors. + for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i) + AddPredecessorToBlock(NewSuccessors[i], Pred, BB); + + // Now that the successors are updated, create the new Switch instruction. + SwitchInst *NewSI = new SwitchInst(CV, PredDefault, PredCases.size(),PTI); + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + NewSI->addCase(PredCases[i].first, PredCases[i].second); + + Instruction *DeadCond = 0; + if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) + // If PTI is a branch, remember the condition. + DeadCond = dyn_cast<Instruction>(BI->getCondition()); + Pred->getInstList().erase(PTI); + + // If the condition is dead now, remove the instruction tree. + if (DeadCond) ErasePossiblyDeadInstructionTree(DeadCond); + + // Okay, last check. If BB is still a successor of PSI, then we must + // have an infinite loop case. If so, add an infinitely looping block + // to handle the case to preserve the behavior of the code. + BasicBlock *InfLoopBlock = 0; + for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i) + if (NewSI->getSuccessor(i) == BB) { + if (InfLoopBlock == 0) { + // Insert it at the end of the loop, because it's either code, + // or it won't matter if it's hot. :) + InfLoopBlock = new BasicBlock("infloop", BB->getParent()); + new BranchInst(InfLoopBlock, InfLoopBlock); + } + NewSI->setSuccessor(i, InfLoopBlock); + } + + Changed = true; + } + } + return Changed; +} + +/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and +/// BB2, hoist any common code in the two blocks up into the branch block. The +/// caller of this function guarantees that BI's block dominates BB1 and BB2. +static bool HoistThenElseCodeToIf(BranchInst *BI) { + // This does very trivial matching, with limited scanning, to find identical + // instructions in the two blocks. In particular, we don't want to get into + // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As + // such, we currently just scan for obviously identical instructions in an + // identical order. + BasicBlock *BB1 = BI->getSuccessor(0); // The true destination. + BasicBlock *BB2 = BI->getSuccessor(1); // The false destination + + Instruction *I1 = BB1->begin(), *I2 = BB2->begin(); + if (I1->getOpcode() != I2->getOpcode() || !I1->isIdenticalTo(I2) || + isa<PHINode>(I1)) + return false; + + // If we get here, we can hoist at least one instruction. + BasicBlock *BIParent = BI->getParent(); + + do { + // If we are hoisting the terminator instruction, don't move one (making a + // broken BB), instead clone it, and remove BI. + if (isa<TerminatorInst>(I1)) + goto HoistTerminator; + + // For a normal instruction, we just move one to right before the branch, + // then replace all uses of the other with the first. Finally, we remove + // the now redundant second instruction. + BIParent->getInstList().splice(BI, BB1->getInstList(), I1); + if (!I2->use_empty()) + I2->replaceAllUsesWith(I1); + BB2->getInstList().erase(I2); + + I1 = BB1->begin(); + I2 = BB2->begin(); + } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2)); + + return true; + +HoistTerminator: + // Okay, it is safe to hoist the terminator. + Instruction *NT = I1->clone(); + BIParent->getInstList().insert(BI, NT); + if (NT->getType() != Type::VoidTy) { + I1->replaceAllUsesWith(NT); + I2->replaceAllUsesWith(NT); + NT->setName(I1->getName()); + } + + // Hoisting one of the terminators from our successor is a great thing. + // Unfortunately, the successors of the if/else blocks may have PHI nodes in + // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI + // nodes, so we insert select instruction to compute the final result. + std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects; + for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { + PHINode *PN; + for (BasicBlock::iterator BBI = SI->begin(); + (PN = dyn_cast<PHINode>(BBI)); ++BBI) { + Value *BB1V = PN->getIncomingValueForBlock(BB1); + Value *BB2V = PN->getIncomingValueForBlock(BB2); + if (BB1V != BB2V) { + // These values do not agree. Insert a select instruction before NT + // that determines the right value. + SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)]; + if (SI == 0) + SI = new SelectInst(BI->getCondition(), BB1V, BB2V, + BB1V->getName()+"."+BB2V->getName(), NT); + // Make the PHI node use the select for all incoming values for BB1/BB2 + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) + if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2) + PN->setIncomingValue(i, SI); + } + } + } + + // Update any PHI nodes in our new successors. + for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) + AddPredecessorToBlock(*SI, BIParent, BB1); + + BI->eraseFromParent(); + return true; +} + +/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch +/// across this block. +static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) { + BranchInst *BI = cast<BranchInst>(BB->getTerminator()); + Value *Cond = BI->getCondition(); + + unsigned Size = 0; + + // If this basic block contains anything other than a PHI (which controls the + // branch) and branch itself, bail out. FIXME: improve this in the future. + for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) { + if (Size > 10) return false; // Don't clone large BB's. + + // We can only support instructions that are do not define values that are + // live outside of the current basic block. + for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end(); + UI != E; ++UI) { + Instruction *U = cast<Instruction>(*UI); + if (U->getParent() != BB || isa<PHINode>(U)) return false; + } + + // Looks ok, continue checking. + } + + return true; +} + +/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value +/// that is defined in the same block as the branch and if any PHI entries are +/// constants, thread edges corresponding to that entry to be branches to their +/// ultimate destination. +static bool FoldCondBranchOnPHI(BranchInst *BI) { + BasicBlock *BB = BI->getParent(); + PHINode *PN = dyn_cast<PHINode>(BI->getCondition()); + // NOTE: we currently cannot transform this case if the PHI node is used + // outside of the block. + if (!PN || PN->getParent() != BB || !PN->hasOneUse()) + return false; + + // Degenerate case of a single entry PHI. + if (PN->getNumIncomingValues() == 1) { + if (PN->getIncomingValue(0) != PN) + PN->replaceAllUsesWith(PN->getIncomingValue(0)); + else + PN->replaceAllUsesWith(UndefValue::get(PN->getType())); + PN->eraseFromParent(); + return true; + } + + // Now we know that this block has multiple preds and two succs. + if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false; + + // Okay, this is a simple enough basic block. See if any phi values are + // constants. + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) + if (ConstantBool *CB = dyn_cast<ConstantBool>(PN->getIncomingValue(i))) { + // Okay, we now know that all edges from PredBB should be revectored to + // branch to RealDest. + BasicBlock *PredBB = PN->getIncomingBlock(i); + BasicBlock *RealDest = BI->getSuccessor(!CB->getValue()); + + if (RealDest == BB) continue; // Skip self loops. + + // The dest block might have PHI nodes, other predecessors and other + // difficult cases. Instead of being smart about this, just insert a new + // block that jumps to the destination block, effectively splitting + // the edge we are about to create. + BasicBlock *EdgeBB = new BasicBlock(RealDest->getName()+".critedge", + RealDest->getParent(), RealDest); + new BranchInst(RealDest, EdgeBB); + PHINode *PN; + for (BasicBlock::iterator BBI = RealDest->begin(); + (PN = dyn_cast<PHINode>(BBI)); ++BBI) { + Value *V = PN->getIncomingValueForBlock(BB); + PN->addIncoming(V, EdgeBB); + } + + // BB may have instructions that are being threaded over. Clone these + // instructions into EdgeBB. We know that there will be no uses of the + // cloned instructions outside of EdgeBB. + BasicBlock::iterator InsertPt = EdgeBB->begin(); + std::map<Value*, Value*> TranslateMap; // Track translated values. + for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { + if (PHINode *PN = dyn_cast<PHINode>(BBI)) { + TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB); + } else { + // Clone the instruction. + Instruction *N = BBI->clone(); + if (BBI->hasName()) N->setName(BBI->getName()+".c"); + + // Update operands due to translation. + for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) { + std::map<Value*, Value*>::iterator PI = + TranslateMap.find(N->getOperand(i)); + if (PI != TranslateMap.end()) + N->setOperand(i, PI->second); + } + + // Check for trivial simplification. + if (Constant *C = ConstantFoldInstruction(N)) { + TranslateMap[BBI] = C; + delete N; // Constant folded away, don't need actual inst + } else { + // Insert the new instruction into its new home. + EdgeBB->getInstList().insert(InsertPt, N); + if (!BBI->use_empty()) + TranslateMap[BBI] = N; + } + } + } + + // Loop over all of the edges from PredBB to BB, changing them to branch + // to EdgeBB instead. + TerminatorInst *PredBBTI = PredBB->getTerminator(); + for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i) + if (PredBBTI->getSuccessor(i) == BB) { + BB->removePredecessor(PredBB); + PredBBTI->setSuccessor(i, EdgeBB); + } + + // Recurse, simplifying any other constants. + return FoldCondBranchOnPHI(BI) | true; + } + + return false; +} + +/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry +/// PHI node, see if we can eliminate it. +static bool FoldTwoEntryPHINode(PHINode *PN) { + // Ok, this is a two entry PHI node. Check to see if this is a simple "if + // statement", which has a very simple dominance structure. Basically, we + // are trying to find the condition that is being branched on, which + // subsequently causes this merge to happen. We really want control + // dependence information for this check, but simplifycfg can't keep it up + // to date, and this catches most of the cases we care about anyway. + // + BasicBlock *BB = PN->getParent(); + BasicBlock *IfTrue, *IfFalse; + Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse); + if (!IfCond) return false; + + DEBUG(std::cerr << "FOUND IF CONDITION! " << *IfCond << " T: " + << IfTrue->getName() << " F: " << IfFalse->getName() << "\n"); + + // Loop over the PHI's seeing if we can promote them all to select + // instructions. While we are at it, keep track of the instructions + // that need to be moved to the dominating block. + std::set<Instruction*> AggressiveInsts; + + BasicBlock::iterator AfterPHIIt = BB->begin(); + while (isa<PHINode>(AfterPHIIt)) { + PHINode *PN = cast<PHINode>(AfterPHIIt++); + if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) { + if (PN->getIncomingValue(0) != PN) + PN->replaceAllUsesWith(PN->getIncomingValue(0)); + else + PN->replaceAllUsesWith(UndefValue::get(PN->getType())); + } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB, + &AggressiveInsts) || + !DominatesMergePoint(PN->getIncomingValue(1), BB, + &AggressiveInsts)) { + return false; + } + } + + // If we all PHI nodes are promotable, check to make sure that all + // instructions in the predecessor blocks can be promoted as well. If + // not, we won't be able to get rid of the control flow, so it's not + // worth promoting to select instructions. + BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0; + PN = cast<PHINode>(BB->begin()); + BasicBlock *Pred = PN->getIncomingBlock(0); + if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) { + IfBlock1 = Pred; + DomBlock = *pred_begin(Pred); + for (BasicBlock::iterator I = Pred->begin(); + !isa<TerminatorInst>(I); ++I) + if (!AggressiveInsts.count(I)) { + // This is not an aggressive instruction that we can promote. + // Because of this, we won't be able to get rid of the control + // flow, so the xform is not worth it. + return false; + } + } + + Pred = PN->getIncomingBlock(1); + if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) { + IfBlock2 = Pred; + DomBlock = *pred_begin(Pred); + for (BasicBlock::iterator I = Pred->begin(); + !isa<TerminatorInst>(I); ++I) + if (!AggressiveInsts.count(I)) { + // This is not an aggressive instruction that we can promote. + // Because of this, we won't be able to get rid of the control + // flow, so the xform is not worth it. + return false; + } + } + + // If we can still promote the PHI nodes after this gauntlet of tests, + // do all of the PHI's now. + + // Move all 'aggressive' instructions, which are defined in the + // conditional parts of the if's up to the dominating block. + if (IfBlock1) { + DomBlock->getInstList().splice(DomBlock->getTerminator(), + IfBlock1->getInstList(), + IfBlock1->begin(), + IfBlock1->getTerminator()); + } + if (IfBlock2) { + DomBlock->getInstList().splice(DomBlock->getTerminator(), + IfBlock2->getInstList(), + IfBlock2->begin(), + IfBlock2->getTerminator()); + } + + while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { + // Change the PHI node into a select instruction. + Value *TrueVal = + PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); + Value *FalseVal = + PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); + + std::string Name = PN->getName(); PN->setName(""); + PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal, + Name, AfterPHIIt)); + BB->getInstList().erase(PN); + } + return true; +} + +namespace { + /// ConstantIntOrdering - This class implements a stable ordering of constant + /// integers that does not depend on their address. This is important for + /// applications that sort ConstantInt's to ensure uniqueness. + struct ConstantIntOrdering { + bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const { + return LHS->getRawValue() < RHS->getRawValue(); + } + }; +} + +// SimplifyCFG - This function is used to do simplification of a CFG. For +// example, it adjusts branches to branches to eliminate the extra hop, it +// eliminates unreachable basic blocks, and does other "peephole" optimization +// of the CFG. It returns true if a modification was made. +// +// WARNING: The entry node of a function may not be simplified. +// +bool llvm::SimplifyCFG(BasicBlock *BB) { + bool Changed = false; + Function *M = BB->getParent(); + + assert(BB && BB->getParent() && "Block not embedded in function!"); + assert(BB->getTerminator() && "Degenerate basic block encountered!"); + assert(&BB->getParent()->front() != BB && "Can't Simplify entry block!"); + + // Remove basic blocks that have no predecessors... which are unreachable. + if (pred_begin(BB) == pred_end(BB) || + *pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB)) { + DEBUG(std::cerr << "Removing BB: \n" << *BB); + + // Loop through all of our successors and make sure they know that one + // of their predecessors is going away. + for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) + SI->removePredecessor(BB); + + while (!BB->empty()) { + Instruction &I = BB->back(); + // If this instruction is used, replace uses with an arbitrary + // value. Because control flow can't get here, we don't care + // what we replace the value with. Note that since this block is + // unreachable, and all values contained within it must dominate their + // uses, that all uses will eventually be removed. + if (!I.use_empty()) + // Make all users of this instruction use undef instead + I.replaceAllUsesWith(UndefValue::get(I.getType())); + + // Remove the instruction from the basic block + BB->getInstList().pop_back(); + } + M->getBasicBlockList().erase(BB); + return true; + } + + // Check to see if we can constant propagate this terminator instruction + // away... + Changed |= ConstantFoldTerminator(BB); + + // If this is a returning block with only PHI nodes in it, fold the return + // instruction into any unconditional branch predecessors. + // + // If any predecessor is a conditional branch that just selects among + // different return values, fold the replace the branch/return with a select + // and return. + if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { + BasicBlock::iterator BBI = BB->getTerminator(); + if (BBI == BB->begin() || isa<PHINode>(--BBI)) { + // Find predecessors that end with branches. + std::vector<BasicBlock*> UncondBranchPreds; + std::vector<BranchInst*> CondBranchPreds; + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { + TerminatorInst *PTI = (*PI)->getTerminator(); + if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) + if (BI->isUnconditional()) + UncondBranchPreds.push_back(*PI); + else + CondBranchPreds.push_back(BI); + } + + // If we found some, do the transformation! + if (!UncondBranchPreds.empty()) { + while (!UncondBranchPreds.empty()) { + BasicBlock *Pred = UncondBranchPreds.back(); + DEBUG(std::cerr << "FOLDING: " << *BB + << "INTO UNCOND BRANCH PRED: " << *Pred); + UncondBranchPreds.pop_back(); + Instruction *UncondBranch = Pred->getTerminator(); + // Clone the return and add it to the end of the predecessor. + Instruction *NewRet = RI->clone(); + Pred->getInstList().push_back(NewRet); + + // If the return instruction returns a value, and if the value was a + // PHI node in "BB", propagate the right value into the return. + if (NewRet->getNumOperands() == 1) + if (PHINode *PN = dyn_cast<PHINode>(NewRet->getOperand(0))) + if (PN->getParent() == BB) + NewRet->setOperand(0, PN->getIncomingValueForBlock(Pred)); + // Update any PHI nodes in the returning block to realize that we no + // longer branch to them. + BB->removePredecessor(Pred); + Pred->getInstList().erase(UncondBranch); + } + + // If we eliminated all predecessors of the block, delete the block now. + if (pred_begin(BB) == pred_end(BB)) + // We know there are no successors, so just nuke the block. + M->getBasicBlockList().erase(BB); + + return true; + } + + // Check out all of the conditional branches going to this return + // instruction. If any of them just select between returns, change the + // branch itself into a select/return pair. + while (!CondBranchPreds.empty()) { + BranchInst *BI = CondBranchPreds.back(); + CondBranchPreds.pop_back(); + BasicBlock *TrueSucc = BI->getSuccessor(0); + BasicBlock *FalseSucc = BI->getSuccessor(1); + BasicBlock *OtherSucc = TrueSucc == BB ? FalseSucc : TrueSucc; + + // Check to see if the non-BB successor is also a return block. + if (isa<ReturnInst>(OtherSucc->getTerminator())) { + // Check to see if there are only PHI instructions in this block. + BasicBlock::iterator OSI = OtherSucc->getTerminator(); + if (OSI == OtherSucc->begin() || isa<PHINode>(--OSI)) { + // Okay, we found a branch that is going to two return nodes. If + // there is no return value for this function, just change the + // branch into a return. + if (RI->getNumOperands() == 0) { + TrueSucc->removePredecessor(BI->getParent()); + FalseSucc->removePredecessor(BI->getParent()); + new ReturnInst(0, BI); + BI->getParent()->getInstList().erase(BI); + return true; + } + + // Otherwise, figure out what the true and false return values are + // so we can insert a new select instruction. + Value *TrueValue = TrueSucc->getTerminator()->getOperand(0); + Value *FalseValue = FalseSucc->getTerminator()->getOperand(0); + + // Unwrap any PHI nodes in the return blocks. + if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue)) + if (TVPN->getParent() == TrueSucc) + TrueValue = TVPN->getIncomingValueForBlock(BI->getParent()); + if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue)) + if (FVPN->getParent() == FalseSucc) + FalseValue = FVPN->getIncomingValueForBlock(BI->getParent()); + + TrueSucc->removePredecessor(BI->getParent()); + FalseSucc->removePredecessor(BI->getParent()); + + // Insert a new select instruction. + Value *NewRetVal; + Value *BrCond = BI->getCondition(); + if (TrueValue != FalseValue) + NewRetVal = new SelectInst(BrCond, TrueValue, + FalseValue, "retval", BI); + else + NewRetVal = TrueValue; + + DEBUG(std::cerr << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:" + << "\n " << *BI << "Select = " << *NewRetVal + << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc); + + new ReturnInst(NewRetVal, BI); + BI->eraseFromParent(); + if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond)) + if (isInstructionTriviallyDead(BrCondI)) + BrCondI->eraseFromParent(); + return true; + } + } + } + } + } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->begin())) { + // Check to see if the first instruction in this block is just an unwind. + // If so, replace any invoke instructions which use this as an exception + // destination with call instructions, and any unconditional branch + // predecessor with an unwind. + // + std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB)); + while (!Preds.empty()) { + BasicBlock *Pred = Preds.back(); + if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) { + if (BI->isUnconditional()) { + Pred->getInstList().pop_back(); // nuke uncond branch + new UnwindInst(Pred); // Use unwind. + Changed = true; + } + } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator())) + if (II->getUnwindDest() == BB) { + // Insert a new branch instruction before the invoke, because this + // is now a fall through... + BranchInst *BI = new BranchInst(II->getNormalDest(), II); + Pred->getInstList().remove(II); // Take out of symbol table + + // Insert the call now... + std::vector<Value*> Args(II->op_begin()+3, II->op_end()); + CallInst *CI = new CallInst(II->getCalledValue(), Args, + II->getName(), BI); + CI->setCallingConv(II->getCallingConv()); + // If the invoke produced a value, the Call now does instead + II->replaceAllUsesWith(CI); + delete II; + Changed = true; + } + + Preds.pop_back(); + } + + // If this block is now dead, remove it. + if (pred_begin(BB) == pred_end(BB)) { + // We know there are no successors, so just nuke the block. + M->getBasicBlockList().erase(BB); + return true; + } + + } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { + if (isValueEqualityComparison(SI)) { + // If we only have one predecessor, and if it is a branch on this value, + // see if that predecessor totally determines the outcome of this switch. + if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) + if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred)) + return SimplifyCFG(BB) || 1; + + // If the block only contains the switch, see if we can fold the block + // away into any preds. + if (SI == &BB->front()) + if (FoldValueComparisonIntoPredecessors(SI)) + return SimplifyCFG(BB) || 1; + } + } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { + if (BI->isUnconditional()) { + BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes... + while (isa<PHINode>(*BBI)) ++BBI; + + BasicBlock *Succ = BI->getSuccessor(0); + if (BBI->isTerminator() && // Terminator is the only non-phi instruction! + Succ != BB) // Don't hurt infinite loops! + if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ)) + return 1; + + } else { // Conditional branch + if (Value *CompVal = isValueEqualityComparison(BI)) { + // If we only have one predecessor, and if it is a branch on this value, + // see if that predecessor totally determines the outcome of this + // switch. + if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) + if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred)) + return SimplifyCFG(BB) || 1; + + // This block must be empty, except for the setcond inst, if it exists. + BasicBlock::iterator I = BB->begin(); + if (&*I == BI || + (&*I == cast<Instruction>(BI->getCondition()) && + &*++I == BI)) + if (FoldValueComparisonIntoPredecessors(BI)) + return SimplifyCFG(BB) | true; + } + + // If this is a branch on a phi node in the current block, thread control + // through this block if any PHI node entries are constants. + if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition())) + if (PN->getParent() == BI->getParent()) + if (FoldCondBranchOnPHI(BI)) + return SimplifyCFG(BB) | true; + + // If this basic block is ONLY a setcc and a branch, and if a predecessor + // branches to us and one of our successors, fold the setcc into the + // predecessor and use logical operations to pick the right destination. + BasicBlock *TrueDest = BI->getSuccessor(0); + BasicBlock *FalseDest = BI->getSuccessor(1); + if (BinaryOperator *Cond = dyn_cast<BinaryOperator>(BI->getCondition())) + if (Cond->getParent() == BB && &BB->front() == Cond && + Cond->getNext() == BI && Cond->hasOneUse() && + TrueDest != BB && FalseDest != BB) + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI) + if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) + if (PBI->isConditional() && SafeToMergeTerminators(BI, PBI)) { + BasicBlock *PredBlock = *PI; + if (PBI->getSuccessor(0) == FalseDest || + PBI->getSuccessor(1) == TrueDest) { + // Invert the predecessors condition test (xor it with true), + // which allows us to write this code once. + Value *NewCond = + BinaryOperator::createNot(PBI->getCondition(), + PBI->getCondition()->getName()+".not", PBI); + PBI->setCondition(NewCond); + BasicBlock *OldTrue = PBI->getSuccessor(0); + BasicBlock *OldFalse = PBI->getSuccessor(1); + PBI->setSuccessor(0, OldFalse); + PBI->setSuccessor(1, OldTrue); + } + + if (PBI->getSuccessor(0) == TrueDest || + PBI->getSuccessor(1) == FalseDest) { + // Clone Cond into the predecessor basic block, and or/and the + // two conditions together. + Instruction *New = Cond->clone(); + New->setName(Cond->getName()); + Cond->setName(Cond->getName()+".old"); + PredBlock->getInstList().insert(PBI, New); + Instruction::BinaryOps Opcode = + PBI->getSuccessor(0) == TrueDest ? + Instruction::Or : Instruction::And; + Value *NewCond = + BinaryOperator::create(Opcode, PBI->getCondition(), + New, "bothcond", PBI); + PBI->setCondition(NewCond); + if (PBI->getSuccessor(0) == BB) { + AddPredecessorToBlock(TrueDest, PredBlock, BB); + PBI->setSuccessor(0, TrueDest); + } + if (PBI->getSuccessor(1) == BB) { + AddPredecessorToBlock(FalseDest, PredBlock, BB); + PBI->setSuccessor(1, FalseDest); + } + return SimplifyCFG(BB) | 1; + } + } + + // Scan predessor blocks for conditional branchs. + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) + if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) + if (PBI != BI && PBI->isConditional()) { + + // If this block ends with a branch instruction, and if there is a + // predecessor that ends on a branch of the same condition, make this + // conditional branch redundant. + if (PBI->getCondition() == BI->getCondition() && + PBI->getSuccessor(0) != PBI->getSuccessor(1)) { + // Okay, the outcome of this conditional branch is statically + // knowable. If this block had a single pred, handle specially. + if (BB->getSinglePredecessor()) { + // Turn this into a branch on constant. + bool CondIsTrue = PBI->getSuccessor(0) == BB; + BI->setCondition(ConstantBool::get(CondIsTrue)); + return SimplifyCFG(BB); // Nuke the branch on constant. + } + + // Otherwise, if there are multiple predecessors, insert a PHI that + // merges in the constant and simplify the block result. + if (BlockIsSimpleEnoughToThreadThrough(BB)) { + PHINode *NewPN = new PHINode(Type::BoolTy, + BI->getCondition()->getName()+".pr", + BB->begin()); + for (PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) + if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) && + PBI != BI && PBI->isConditional() && + PBI->getCondition() == BI->getCondition() && + PBI->getSuccessor(0) != PBI->getSuccessor(1)) { + bool CondIsTrue = PBI->getSuccessor(0) == BB; + NewPN->addIncoming(ConstantBool::get(CondIsTrue), *PI); + } else { + NewPN->addIncoming(BI->getCondition(), *PI); + } + + BI->setCondition(NewPN); + // This will thread the branch. + return SimplifyCFG(BB) | true; + } + } + + // If this is a conditional branch in an empty block, and if any + // predecessors is a conditional branch to one of our destinations, + // fold the conditions into logical ops and one cond br. + if (&BB->front() == BI) { + int PBIOp, BIOp; + if (PBI->getSuccessor(0) == BI->getSuccessor(0)) { + PBIOp = BIOp = 0; + } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) { + PBIOp = 0; BIOp = 1; + } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) { + PBIOp = 1; BIOp = 0; + } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) { + PBIOp = BIOp = 1; + } else { + PBIOp = BIOp = -1; + } + + // Finally, if everything is ok, fold the branches to logical ops. + if (PBIOp != -1) { + BasicBlock *CommonDest = PBI->getSuccessor(PBIOp); + BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1); + + DEBUG(std::cerr << "FOLDING BRs:" << *PBI->getParent() + << "AND: " << *BI->getParent()); + + // BI may have other predecessors. Because of this, we leave + // it alone, but modify PBI. + + // Make sure we get to CommonDest on True&True directions. + Value *PBICond = PBI->getCondition(); + if (PBIOp) + PBICond = BinaryOperator::createNot(PBICond, + PBICond->getName()+".not", + PBI); + Value *BICond = BI->getCondition(); + if (BIOp) + BICond = BinaryOperator::createNot(BICond, + BICond->getName()+".not", + PBI); + // Merge the conditions. + Value *Cond = + BinaryOperator::createOr(PBICond, BICond, "brmerge", PBI); + + // Modify PBI to branch on the new condition to the new dests. + PBI->setCondition(Cond); + PBI->setSuccessor(0, CommonDest); + PBI->setSuccessor(1, OtherDest); + + // OtherDest may have phi nodes. If so, add an entry from PBI's + // block that are identical to the entries for BI's block. + PHINode *PN; + for (BasicBlock::iterator II = OtherDest->begin(); + (PN = dyn_cast<PHINode>(II)); ++II) { + Value *V = PN->getIncomingValueForBlock(BB); + PN->addIncoming(V, PBI->getParent()); + } + + // We know that the CommonDest already had an edge from PBI to + // it. If it has PHIs though, the PHIs may have different + // entries for BB and PBI's BB. If so, insert a select to make + // them agree. + for (BasicBlock::iterator II = CommonDest->begin(); + (PN = dyn_cast<PHINode>(II)); ++II) { + Value * BIV = PN->getIncomingValueForBlock(BB); + unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent()); + Value *PBIV = PN->getIncomingValue(PBBIdx); + if (BIV != PBIV) { + // Insert a select in PBI to pick the right value. + Value *NV = new SelectInst(PBICond, PBIV, BIV, + PBIV->getName()+".mux", PBI); + PN->setIncomingValue(PBBIdx, NV); + } + } + + DEBUG(std::cerr << "INTO: " << *PBI->getParent()); + + // This basic block is probably dead. We know it has at least + // one fewer predecessor. + return SimplifyCFG(BB) | true; + } + } + } + } + } else if (isa<UnreachableInst>(BB->getTerminator())) { + // If there are any instructions immediately before the unreachable that can + // be removed, do so. + Instruction *Unreachable = BB->getTerminator(); + while (Unreachable != BB->begin()) { + BasicBlock::iterator BBI = Unreachable; + --BBI; + if (isa<CallInst>(BBI)) break; + // Delete this instruction + BB->getInstList().erase(BBI); + Changed = true; + } + + // If the unreachable instruction is the first in the block, take a gander + // at all of the predecessors of this instruction, and simplify them. + if (&BB->front() == Unreachable) { + std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB)); + for (unsigned i = 0, e = Preds.size(); i != e; ++i) { + TerminatorInst *TI = Preds[i]->getTerminator(); + + if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { + if (BI->isUnconditional()) { + if (BI->getSuccessor(0) == BB) { + new UnreachableInst(TI); + TI->eraseFromParent(); + Changed = true; + } + } else { + if (BI->getSuccessor(0) == BB) { + new BranchInst(BI->getSuccessor(1), BI); + BI->eraseFromParent(); + } else if (BI->getSuccessor(1) == BB) { + new BranchInst(BI->getSuccessor(0), BI); + BI->eraseFromParent(); + Changed = true; + } + } + } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { + for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) + if (SI->getSuccessor(i) == BB) { + BB->removePredecessor(SI->getParent()); + SI->removeCase(i); + --i; --e; + Changed = true; + } + // If the default value is unreachable, figure out the most popular + // destination and make it the default. + if (SI->getSuccessor(0) == BB) { + std::map<BasicBlock*, unsigned> Popularity; + for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) + Popularity[SI->getSuccessor(i)]++; + + // Find the most popular block. + unsigned MaxPop = 0; + BasicBlock *MaxBlock = 0; + for (std::map<BasicBlock*, unsigned>::iterator + I = Popularity.begin(), E = Popularity.end(); I != E; ++I) { + if (I->second > MaxPop) { + MaxPop = I->second; + MaxBlock = I->first; + } + } + if (MaxBlock) { + // Make this the new default, allowing us to delete any explicit + // edges to it. + SI->setSuccessor(0, MaxBlock); + Changed = true; + + // If MaxBlock has phinodes in it, remove MaxPop-1 entries from + // it. + if (isa<PHINode>(MaxBlock->begin())) + for (unsigned i = 0; i != MaxPop-1; ++i) + MaxBlock->removePredecessor(SI->getParent()); + + for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) + if (SI->getSuccessor(i) == MaxBlock) { + SI->removeCase(i); + --i; --e; + } + } + } + } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) { + if (II->getUnwindDest() == BB) { + // Convert the invoke to a call instruction. This would be a good + // place to note that the call does not throw though. + BranchInst *BI = new BranchInst(II->getNormalDest(), II); + II->removeFromParent(); // Take out of symbol table + + // Insert the call now... + std::vector<Value*> Args(II->op_begin()+3, II->op_end()); + CallInst *CI = new CallInst(II->getCalledValue(), Args, + II->getName(), BI); + CI->setCallingConv(II->getCallingConv()); + // If the invoke produced a value, the Call does now instead. + II->replaceAllUsesWith(CI); + delete II; + Changed = true; + } + } + } + + // If this block is now dead, remove it. + if (pred_begin(BB) == pred_end(BB)) { + // We know there are no successors, so just nuke the block. + M->getBasicBlockList().erase(BB); + return true; + } + } + } + + // Merge basic blocks into their predecessor if there is only one distinct + // pred, and if there is only one distinct successor of the predecessor, and + // if there are no PHI nodes. + // + pred_iterator PI(pred_begin(BB)), PE(pred_end(BB)); + BasicBlock *OnlyPred = *PI++; + for (; PI != PE; ++PI) // Search all predecessors, see if they are all same + if (*PI != OnlyPred) { + OnlyPred = 0; // There are multiple different predecessors... + break; + } + + BasicBlock *OnlySucc = 0; + if (OnlyPred && OnlyPred != BB && // Don't break self loops + OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) { + // Check to see if there is only one distinct successor... + succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred)); + OnlySucc = BB; + for (; SI != SE; ++SI) + if (*SI != OnlySucc) { + OnlySucc = 0; // There are multiple distinct successors! + break; + } + } + + if (OnlySucc) { + DEBUG(std::cerr << "Merging: " << *BB << "into: " << *OnlyPred); + TerminatorInst *Term = OnlyPred->getTerminator(); + + // Resolve any PHI nodes at the start of the block. They are all + // guaranteed to have exactly one entry if they exist, unless there are + // multiple duplicate (but guaranteed to be equal) entries for the + // incoming edges. This occurs when there are multiple edges from + // OnlyPred to OnlySucc. + // + while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { + PN->replaceAllUsesWith(PN->getIncomingValue(0)); + BB->getInstList().pop_front(); // Delete the phi node... + } + + // Delete the unconditional branch from the predecessor... + OnlyPred->getInstList().pop_back(); + + // Move all definitions in the successor to the predecessor... + OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList()); + + // Make all PHI nodes that referred to BB now refer to Pred as their + // source... + BB->replaceAllUsesWith(OnlyPred); + + std::string OldName = BB->getName(); + + // Erase basic block from the function... + M->getBasicBlockList().erase(BB); + + // Inherit predecessors name if it exists... + if (!OldName.empty() && !OnlyPred->hasName()) + OnlyPred->setName(OldName); + + return true; + } + + // Otherwise, if this block only has a single predecessor, and if that block + // is a conditional branch, see if we can hoist any code from this block up + // into our predecessor. + if (OnlyPred) + if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator())) + if (BI->isConditional()) { + // Get the other block. + BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB); + PI = pred_begin(OtherBB); + ++PI; + if (PI == pred_end(OtherBB)) { + // We have a conditional branch to two blocks that are only reachable + // from the condbr. We know that the condbr dominates the two blocks, + // so see if there is any identical code in the "then" and "else" + // blocks. If so, we can hoist it up to the branching block. + Changed |= HoistThenElseCodeToIf(BI); + } + } + + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) + if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator())) + // Change br (X == 0 | X == 1), T, F into a switch instruction. + if (BI->isConditional() && isa<Instruction>(BI->getCondition())) { + Instruction *Cond = cast<Instruction>(BI->getCondition()); + // If this is a bunch of seteq's or'd together, or if it's a bunch of + // 'setne's and'ed together, collect them. + Value *CompVal = 0; + std::vector<ConstantInt*> Values; + bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values); + if (CompVal && CompVal->getType()->isInteger()) { + // There might be duplicate constants in the list, which the switch + // instruction can't handle, remove them now. + std::sort(Values.begin(), Values.end(), ConstantIntOrdering()); + Values.erase(std::unique(Values.begin(), Values.end()), Values.end()); + + // Figure out which block is which destination. + BasicBlock *DefaultBB = BI->getSuccessor(1); + BasicBlock *EdgeBB = BI->getSuccessor(0); + if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB); + + // Create the new switch instruction now. + SwitchInst *New = new SwitchInst(CompVal, DefaultBB,Values.size(),BI); + + // Add all of the 'cases' to the switch instruction. + for (unsigned i = 0, e = Values.size(); i != e; ++i) + New->addCase(Values[i], EdgeBB); + + // We added edges from PI to the EdgeBB. As such, if there were any + // PHI nodes in EdgeBB, they need entries to be added corresponding to + // the number of edges added. + for (BasicBlock::iterator BBI = EdgeBB->begin(); + isa<PHINode>(BBI); ++BBI) { + PHINode *PN = cast<PHINode>(BBI); + Value *InVal = PN->getIncomingValueForBlock(*PI); + for (unsigned i = 0, e = Values.size()-1; i != e; ++i) + PN->addIncoming(InVal, *PI); + } + + // Erase the old branch instruction. + (*PI)->getInstList().erase(BI); + + // Erase the potentially condition tree that was used to computed the + // branch condition. + ErasePossiblyDeadInstructionTree(Cond); + return true; + } + } + + // If there is a trivial two-entry PHI node in this basic block, and we can + // eliminate it, do so now. + if (PHINode *PN = dyn_cast<PHINode>(BB->begin())) + if (PN->getNumIncomingValues() == 2) + Changed |= FoldTwoEntryPHINode(PN); + + return Changed; +} |