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Diffstat (limited to 'contrib/llvm/lib/Transforms/Utils/SimplifyCFG.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 3157 |
1 files changed, 3157 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/contrib/llvm/lib/Transforms/Utils/SimplifyCFG.cpp new file mode 100644 index 0000000..518df7c --- /dev/null +++ b/contrib/llvm/lib/Transforms/Utils/SimplifyCFG.cpp @@ -0,0 +1,3157 @@ +//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===// +// +// The LLVM Compiler Infrastructure +// +// This file 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/DerivedTypes.h" +#include "llvm/GlobalVariable.h" +#include "llvm/IRBuilder.h" +#include "llvm/Instructions.h" +#include "llvm/IntrinsicInst.h" +#include "llvm/LLVMContext.h" +#include "llvm/MDBuilder.h" +#include "llvm/Metadata.h" +#include "llvm/Operator.h" +#include "llvm/Type.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/STLExtras.h" +#include "llvm/ADT/SetVector.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/Support/CFG.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/ConstantRange.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/NoFolder.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Target/TargetData.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include <algorithm> +#include <set> +#include <map> +using namespace llvm; + +static cl::opt<unsigned> +PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1), + cl::desc("Control the amount of phi node folding to perform (default = 1)")); + +static cl::opt<bool> +DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false), + cl::desc("Duplicate return instructions into unconditional branches")); + +STATISTIC(NumSpeculations, "Number of speculative executed instructions"); + +namespace { + /// ValueEqualityComparisonCase - Represents a case of a switch. + struct ValueEqualityComparisonCase { + ConstantInt *Value; + BasicBlock *Dest; + + ValueEqualityComparisonCase(ConstantInt *Value, BasicBlock *Dest) + : Value(Value), Dest(Dest) {} + + bool operator<(ValueEqualityComparisonCase RHS) const { + // Comparing pointers is ok as we only rely on the order for uniquing. + return Value < RHS.Value; + } + }; + +class SimplifyCFGOpt { + const TargetData *const TD; + + Value *isValueEqualityComparison(TerminatorInst *TI); + BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI, + std::vector<ValueEqualityComparisonCase> &Cases); + bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, + BasicBlock *Pred, + IRBuilder<> &Builder); + bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI, + IRBuilder<> &Builder); + + bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder); + bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder); + bool SimplifyUnreachable(UnreachableInst *UI); + bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder); + bool SimplifyIndirectBr(IndirectBrInst *IBI); + bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder); + bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder); + +public: + explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {} + bool run(BasicBlock *BB); +}; +} + +/// 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(); + SmallPtrSet<BasicBlock*, 16> 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; +} + +/// isProfitableToFoldUnconditional - Return true if it is safe and profitable +/// to merge these two terminator instructions together, where SI1 is an +/// unconditional branch. PhiNodes will store all PHI nodes in common +/// successors. +/// +static bool isProfitableToFoldUnconditional(BranchInst *SI1, + BranchInst *SI2, + Instruction *Cond, + SmallVectorImpl<PHINode*> &PhiNodes) { + if (SI1 == SI2) return false; // Can't merge with self! + assert(SI1->isUnconditional() && SI2->isConditional()); + + // We fold the unconditional branch if we can easily update all PHI nodes in + // common successors: + // 1> We have a constant incoming value for the conditional branch; + // 2> We have "Cond" as the incoming value for the unconditional branch; + // 3> SI2->getCondition() and Cond have same operands. + CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition()); + if (!Ci2) return false; + if (!(Cond->getOperand(0) == Ci2->getOperand(0) && + Cond->getOperand(1) == Ci2->getOperand(1)) && + !(Cond->getOperand(0) == Ci2->getOperand(1) && + Cond->getOperand(1) == Ci2->getOperand(0))) + return false; + + BasicBlock *SI1BB = SI1->getParent(); + BasicBlock *SI2BB = SI2->getParent(); + SmallPtrSet<BasicBlock*, 16> 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) != Cond || + !isa<ConstantInt>(PN->getIncomingValueForBlock(SI2BB))) + return false; + PhiNodes.push_back(PN); + } + 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) { + if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do + + PHINode *PN; + for (BasicBlock::iterator I = Succ->begin(); + (PN = dyn_cast<PHINode>(I)); ++I) + PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred); +} + + +/// GetIfCondition - Given a basic block (BB) with two predecessors (and at +/// least one PHI node 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. +/// +/// This does no checking to see if the true/false blocks have large or unsavory +/// instructions in them. +static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, + BasicBlock *&IfFalse) { + PHINode *SomePHI = cast<PHINode>(BB->begin()); + assert(SomePHI->getNumIncomingValues() == 2 && + "Function can only handle blocks with 2 predecessors!"); + BasicBlock *Pred1 = SomePHI->getIncomingBlock(0); + BasicBlock *Pred2 = SomePHI->getIncomingBlock(1); + + // We can only handle branches. Other control flow will be lowered to + // branches if possible anyway. + BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator()); + BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator()); + if (Pred1Br == 0 || Pred2Br == 0) + return 0; + + // 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()) { + // 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 (Pred2->getSinglePredecessor() == 0) + return 0; + + // 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; + } + + 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! + BasicBlock *CommonPred = Pred1->getSinglePredecessor(); + if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor()) + return 0; + + // Otherwise, if this is a conditional branch, then we can use it! + BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator()); + if (BI == 0) return 0; + + 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(); +} + +/// ComputeSpeculuationCost - Compute an abstract "cost" of speculating the +/// given instruction, which is assumed to be safe to speculate. 1 means +/// cheap, 2 means less cheap, and UINT_MAX means prohibitively expensive. +static unsigned ComputeSpeculationCost(const User *I) { + assert(isSafeToSpeculativelyExecute(I) && + "Instruction is not safe to speculatively execute!"); + switch (Operator::getOpcode(I)) { + default: + // In doubt, be conservative. + return UINT_MAX; + case Instruction::GetElementPtr: + // GEPs are cheap if all indices are constant. + if (!cast<GEPOperator>(I)->hasAllConstantIndices()) + return UINT_MAX; + return 1; + case Instruction::Load: + case Instruction::Add: + case Instruction::Sub: + case Instruction::And: + case Instruction::Or: + case Instruction::Xor: + case Instruction::Shl: + case Instruction::LShr: + case Instruction::AShr: + case Instruction::ICmp: + case Instruction::Trunc: + case Instruction::ZExt: + case Instruction::SExt: + return 1; // These are all cheap. + + case Instruction::Call: + case Instruction::Select: + return 2; + } +} + +/// DominatesMergePoint - 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) and its recursive operands +/// that do not dominate BB have a combined cost lower than CostRemaining and +/// are non-trapping. If both are true, the instruction is inserted into the +/// set and true is returned. +/// +/// The cost for most non-trapping instructions is defined as 1 except for +/// Select whose cost is 2. +/// +/// After this function returns, CostRemaining is decreased by the cost of +/// V plus its non-dominating operands. If that cost is greater than +/// CostRemaining, false is returned and CostRemaining is undefined. +static bool DominatesMergePoint(Value *V, BasicBlock *BB, + SmallPtrSet<Instruction*, 4> *AggressiveInsts, + unsigned &CostRemaining) { + Instruction *I = dyn_cast<Instruction>(V); + if (!I) { + // Non-instructions all dominate instructions, but not all constantexprs + // can be executed unconditionally. + if (ConstantExpr *C = dyn_cast<ConstantExpr>(V)) + if (C->canTrap()) + return false; + return true; + } + 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 not, it definitely dominates the region. + BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()); + if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB) + return true; + + // If we aren't allowing aggressive promotion anymore, then don't consider + // instructions in the 'if region'. + if (AggressiveInsts == 0) return false; + + // If we have seen this instruction before, don't count it again. + if (AggressiveInsts->count(I)) return true; + + // Okay, it looks like the instruction IS in the "condition". Check to + // see if it's a cheap instruction to unconditionally compute, and if it + // only uses stuff defined outside of the condition. If so, hoist it out. + if (!isSafeToSpeculativelyExecute(I)) + return false; + + unsigned Cost = ComputeSpeculationCost(I); + + if (Cost > CostRemaining) + return false; + + CostRemaining -= Cost; + + // Okay, we can only really hoist these out if their operands do + // not take us over the cost threshold. + for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) + if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining)) + return false; + // Okay, it's safe to do this! Remember this instruction. + AggressiveInsts->insert(I); + return true; +} + +/// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr +/// and PointerNullValue. Return NULL if value is not a constant int. +static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) { + // Normal constant int. + ConstantInt *CI = dyn_cast<ConstantInt>(V); + if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy()) + return CI; + + // This is some kind of pointer constant. Turn it into a pointer-sized + // ConstantInt if possible. + IntegerType *PtrTy = TD->getIntPtrType(V->getContext()); + + // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*). + if (isa<ConstantPointerNull>(V)) + return ConstantInt::get(PtrTy, 0); + + // IntToPtr const int. + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) + if (CE->getOpcode() == Instruction::IntToPtr) + if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) { + // The constant is very likely to have the right type already. + if (CI->getType() == PtrTy) + return CI; + else + return cast<ConstantInt> + (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false)); + } + return 0; +} + +/// GatherConstantCompares - Given a potentially 'or'd or 'and'd together +/// collection of icmp eq/ne instructions that compare a value against a +/// constant, return the value being compared, and stick the constant into the +/// Values vector. +static Value * +GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra, + const TargetData *TD, bool isEQ, unsigned &UsedICmps) { + Instruction *I = dyn_cast<Instruction>(V); + if (I == 0) return 0; + + // If this is an icmp against a constant, handle this as one of the cases. + if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) { + if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) { + if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) { + UsedICmps++; + Vals.push_back(C); + return I->getOperand(0); + } + + // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to + // the set. + ConstantRange Span = + ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue()); + + // If this is an and/!= check then we want to optimize "x ugt 2" into + // x != 0 && x != 1. + if (!isEQ) + Span = Span.inverse(); + + // If there are a ton of values, we don't want to make a ginormous switch. + if (Span.getSetSize().ugt(8) || Span.isEmptySet()) + return 0; + + for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp) + Vals.push_back(ConstantInt::get(V->getContext(), Tmp)); + UsedICmps++; + return I->getOperand(0); + } + return 0; + } + + // Otherwise, we can only handle an | or &, depending on isEQ. + if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And)) + return 0; + + unsigned NumValsBeforeLHS = Vals.size(); + unsigned UsedICmpsBeforeLHS = UsedICmps; + if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD, + isEQ, UsedICmps)) { + unsigned NumVals = Vals.size(); + unsigned UsedICmpsBeforeRHS = UsedICmps; + if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD, + isEQ, UsedICmps)) { + if (LHS == RHS) + return LHS; + Vals.resize(NumVals); + UsedICmps = UsedICmpsBeforeRHS; + } + + // The RHS of the or/and can't be folded in and we haven't used "Extra" yet, + // set it and return success. + if (Extra == 0 || Extra == I->getOperand(1)) { + Extra = I->getOperand(1); + return LHS; + } + + Vals.resize(NumValsBeforeLHS); + UsedICmps = UsedICmpsBeforeLHS; + return 0; + } + + // If the LHS can't be folded in, but Extra is available and RHS can, try to + // use LHS as Extra. + if (Extra == 0 || Extra == I->getOperand(0)) { + Value *OldExtra = Extra; + Extra = I->getOperand(0); + if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD, + isEQ, UsedICmps)) + return RHS; + assert(Vals.size() == NumValsBeforeLHS); + Extra = OldExtra; + } + + return 0; +} + +static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) { + Instruction *Cond = 0; + if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { + Cond = dyn_cast<Instruction>(SI->getCondition()); + } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { + if (BI->isConditional()) + Cond = dyn_cast<Instruction>(BI->getCondition()); + } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) { + Cond = dyn_cast<Instruction>(IBI->getAddress()); + } + + TI->eraseFromParent(); + if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond); +} + +/// isValueEqualityComparison - Return true if the specified terminator checks +/// to see if a value is equal to constant integer value. +Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) { + Value *CV = 0; + 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) + CV = SI->getCondition(); + } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) + if (BI->isConditional() && BI->getCondition()->hasOneUse()) + if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition())) + if ((ICI->getPredicate() == ICmpInst::ICMP_EQ || + ICI->getPredicate() == ICmpInst::ICMP_NE) && + GetConstantInt(ICI->getOperand(1), TD)) + CV = ICI->getOperand(0); + + // Unwrap any lossless ptrtoint cast. + if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext())) + if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV)) + CV = PTII->getOperand(0); + return CV; +} + +/// GetValueEqualityComparisonCases - Given a value comparison instruction, +/// decode all of the 'cases' that it represents and return the 'default' block. +BasicBlock *SimplifyCFGOpt:: +GetValueEqualityComparisonCases(TerminatorInst *TI, + std::vector<ValueEqualityComparisonCase> + &Cases) { + if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { + Cases.reserve(SI->getNumCases()); + for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); i != e; ++i) + Cases.push_back(ValueEqualityComparisonCase(i.getCaseValue(), + i.getCaseSuccessor())); + return SI->getDefaultDest(); + } + + BranchInst *BI = cast<BranchInst>(TI); + ICmpInst *ICI = cast<ICmpInst>(BI->getCondition()); + BasicBlock *Succ = BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_NE); + Cases.push_back(ValueEqualityComparisonCase(GetConstantInt(ICI->getOperand(1), + TD), + Succ)); + return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ); +} + + +/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries +/// in the list that match the specified block. +static void EliminateBlockCases(BasicBlock *BB, + std::vector<ValueEqualityComparisonCase> &Cases) { + for (unsigned i = 0, e = Cases.size(); i != e; ++i) + if (Cases[i].Dest == 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<ValueEqualityComparisonCase> &C1, + std::vector<ValueEqualityComparisonCase > &C2) { + std::vector<ValueEqualityComparisonCase> *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].Value; + for (unsigned i = 0, e = V2->size(); i != e; ++i) + if (TheVal == (*V2)[i].Value) + return true; + } + + // Otherwise, just sort both lists and compare element by element. + array_pod_sort(V1->begin(), V1->end()); + array_pod_sort(V2->begin(), V2->end()); + unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size(); + while (i1 != e1 && i2 != e2) { + if ((*V1)[i1].Value == (*V2)[i2].Value) + return true; + if ((*V1)[i1].Value < (*V2)[i2].Value) + ++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. +bool SimplifyCFGOpt:: +SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, + BasicBlock *Pred, + IRBuilder<> &Builder) { + 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<ValueEqualityComparisonCase> PredCases; + BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(), + PredCases); + EliminateBlockCases(PredDef, PredCases); // Remove default from cases. + + // Find information about how control leaves this block. + std::vector<ValueEqualityComparisonCase> 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)) + return false; + + if (isa<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!"); + // Insert the new branch. + Instruction *NI = Builder.CreateBr(ThisDef); + (void) NI; + + // Remove PHI node entries for the dead edge. + ThisCases[0].Dest->removePredecessor(TI->getParent()); + + DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() + << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); + + EraseTerminatorInstAndDCECond(TI); + return true; + } + + SwitchInst *SI = cast<SwitchInst>(TI); + // Okay, TI has cases that are statically dead, prune them away. + SmallPtrSet<Constant*, 16> DeadCases; + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + DeadCases.insert(PredCases[i].Value); + + DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() + << "Through successor TI: " << *TI); + + for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) { + --i; + if (DeadCases.count(i.getCaseValue())) { + i.getCaseSuccessor()->removePredecessor(TI->getParent()); + SI->removeCase(i); + } + } + + DEBUG(dbgs() << "Leaving: " << *TI << "\n"); + return true; + } + + // 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].Dest == TIBB) { + if (TIV != 0) + return false; // Cannot handle multiple values coming to this block. + TIV = PredCases[i].Value; + } + 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].Value == TIV) { + TheRealDest = ThisCases[i].Dest; + 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 = Builder.CreateBr(TheRealDest); + (void) NI; + + DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator() + << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); + + EraseTerminatorInstAndDCECond(TI); + 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->getValue().ult(RHS->getValue()); + } + }; +} + +static int ConstantIntSortPredicate(const void *P1, const void *P2) { + const ConstantInt *LHS = *(const ConstantInt**)P1; + const ConstantInt *RHS = *(const ConstantInt**)P2; + if (LHS->getValue().ult(RHS->getValue())) + return 1; + if (LHS->getValue() == RHS->getValue()) + return 0; + return -1; +} + +/// 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. +bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI, + IRBuilder<> &Builder) { + BasicBlock *BB = TI->getParent(); + Value *CV = isValueEqualityComparison(TI); // CondVal + assert(CV && "Not a comparison?"); + bool Changed = false; + + SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB)); + while (!Preds.empty()) { + BasicBlock *Pred = Preds.pop_back_val(); + + // 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<ValueEqualityComparisonCase> BBCases; + BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases); + + std::vector<ValueEqualityComparisonCase> 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. + SmallVector<BasicBlock*, 8> 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*, ConstantIntOrdering> PTIHandled; + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + if (PredCases[i].Dest != BB) + PTIHandled.insert(PredCases[i].Value); + 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].Value) && + BBCases[i].Dest != BBDefault) { + PredCases.push_back(BBCases[i]); + NewSuccessors.push_back(BBCases[i].Dest); + } + + } 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*, ConstantIntOrdering> PTIHandled; + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + if (PredCases[i].Dest == BB) { + PTIHandled.insert(PredCases[i].Value); + 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].Value)) { + // If this is one we are capable of getting... + PredCases.push_back(BBCases[i]); + NewSuccessors.push_back(BBCases[i].Dest); + PTIHandled.erase(BBCases[i].Value);// 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*, ConstantIntOrdering>::iterator I = + PTIHandled.begin(), + E = PTIHandled.end(); I != E; ++I) { + PredCases.push_back(ValueEqualityComparisonCase(*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); + + Builder.SetInsertPoint(PTI); + // Convert pointer to int before we switch. + if (CV->getType()->isPointerTy()) { + assert(TD && "Cannot switch on pointer without TargetData"); + CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()), + "magicptr"); + } + + // Now that the successors are updated, create the new Switch instruction. + SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault, + PredCases.size()); + NewSI->setDebugLoc(PTI->getDebugLoc()); + for (unsigned i = 0, e = PredCases.size(); i != e; ++i) + NewSI->addCase(PredCases[i].Value, PredCases[i].Dest); + + EraseTerminatorInstAndDCECond(PTI); + + // 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 function, because it's either code, + // or it won't matter if it's hot. :) + InfLoopBlock = BasicBlock::Create(BB->getContext(), + "infloop", BB->getParent()); + BranchInst::Create(InfLoopBlock, InfLoopBlock); + } + NewSI->setSuccessor(i, InfLoopBlock); + } + + Changed = true; + } + } + return Changed; +} + +// isSafeToHoistInvoke - If we would need to insert a select that uses the +// value of this invoke (comments in HoistThenElseCodeToIf explain why we +// would need to do this), we can't hoist the invoke, as there is nowhere +// to put the select in this case. +static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2, + Instruction *I1, Instruction *I2) { + 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 && (BB1V==I1 || BB2V==I2)) { + return false; + } + } + } + return true; +} + +/// 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 + + BasicBlock::iterator BB1_Itr = BB1->begin(); + BasicBlock::iterator BB2_Itr = BB2->begin(); + + Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++; + // Skip debug info if it is not identical. + DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1); + DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2); + if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) { + while (isa<DbgInfoIntrinsic>(I1)) + I1 = BB1_Itr++; + while (isa<DbgInfoIntrinsic>(I2)) + I2 = BB2_Itr++; + } + if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) || + (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))) + 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); + I1->intersectOptionalDataWith(I2); + I2->eraseFromParent(); + + I1 = BB1_Itr++; + I2 = BB2_Itr++; + // Skip debug info if it is not identical. + DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1); + DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2); + if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) { + while (isa<DbgInfoIntrinsic>(I1)) + I1 = BB1_Itr++; + while (isa<DbgInfoIntrinsic>(I2)) + I2 = BB2_Itr++; + } + } while (I1->isIdenticalToWhenDefined(I2)); + + return true; + +HoistTerminator: + // It may not be possible to hoist an invoke. + if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) + return true; + + // Okay, it is safe to hoist the terminator. + Instruction *NT = I1->clone(); + BIParent->getInstList().insert(BI, NT); + if (!NT->getType()->isVoidTy()) { + I1->replaceAllUsesWith(NT); + I2->replaceAllUsesWith(NT); + NT->takeName(I1); + } + + IRBuilder<true, NoFolder> Builder(NT); + // 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) continue; + + // 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 = cast<SelectInst> + (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V, + BB1V->getName()+"."+BB2V->getName())); + + // 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); + + EraseTerminatorInstAndDCECond(BI); + return true; +} + +/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1 +/// and an BB2 and the only successor of BB1 is BB2, hoist simple code +/// (for now, restricted to a single instruction that's side effect free) from +/// the BB1 into the branch block to speculatively execute it. +/// +/// Turn +/// BB: +/// %t1 = icmp +/// br i1 %t1, label %BB1, label %BB2 +/// BB1: +/// %t3 = add %t2, c +/// br label BB2 +/// BB2: +/// => +/// BB: +/// %t1 = icmp +/// %t4 = add %t2, c +/// %t3 = select i1 %t1, %t2, %t3 +static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) { + // Only speculatively execution a single instruction (not counting the + // terminator) for now. + Instruction *HInst = NULL; + Instruction *Term = BB1->getTerminator(); + for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end(); + BBI != BBE; ++BBI) { + Instruction *I = BBI; + // Skip debug info. + if (isa<DbgInfoIntrinsic>(I)) continue; + if (I == Term) break; + + if (HInst) + return false; + HInst = I; + } + + BasicBlock *BIParent = BI->getParent(); + + // Check the instruction to be hoisted, if there is one. + if (HInst) { + // Don't hoist the instruction if it's unsafe or expensive. + if (!isSafeToSpeculativelyExecute(HInst)) + return false; + if (ComputeSpeculationCost(HInst) > PHINodeFoldingThreshold) + return false; + + // Do not hoist the instruction if any of its operands are defined but not + // used in this BB. The transformation will prevent the operand from + // being sunk into the use block. + for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end(); + i != e; ++i) { + Instruction *OpI = dyn_cast<Instruction>(*i); + if (OpI && OpI->getParent() == BIParent && + !OpI->mayHaveSideEffects() && + !OpI->isUsedInBasicBlock(BIParent)) + return false; + } + } + + // Be conservative for now. FP select instruction can often be expensive. + Value *BrCond = BI->getCondition(); + if (isa<FCmpInst>(BrCond)) + return false; + + // If BB1 is actually on the false edge of the conditional branch, remember + // to swap the select operands later. + bool Invert = false; + if (BB1 != BI->getSuccessor(0)) { + assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?"); + Invert = true; + } + + // Collect interesting PHIs, and scan for hazards. + SmallSetVector<std::pair<Value *, Value *>, 4> PHIs; + BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0); + for (BasicBlock::iterator I = BB2->begin(); + PHINode *PN = dyn_cast<PHINode>(I); ++I) { + Value *BB1V = PN->getIncomingValueForBlock(BB1); + Value *BIParentV = PN->getIncomingValueForBlock(BIParent); + + // Skip PHIs which are trivial. + if (BB1V == BIParentV) + continue; + + // Check for saftey. + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BB1V)) { + // An unfolded ConstantExpr could end up getting expanded into + // Instructions. Don't speculate this and another instruction at + // the same time. + if (HInst) + return false; + if (!isSafeToSpeculativelyExecute(CE)) + return false; + if (ComputeSpeculationCost(CE) > PHINodeFoldingThreshold) + return false; + } + + // Ok, we may insert a select for this PHI. + PHIs.insert(std::make_pair(BB1V, BIParentV)); + } + + // If there are no PHIs to process, bail early. This helps ensure idempotence + // as well. + if (PHIs.empty()) + return false; + + // If we get here, we can hoist the instruction and if-convert. + DEBUG(dbgs() << "SPECULATIVELY EXECUTING BB" << *BB1 << "\n";); + + // Hoist the instruction. + if (HInst) + BIParent->getInstList().splice(BI, BB1->getInstList(), HInst); + + // Insert selects and rewrite the PHI operands. + IRBuilder<true, NoFolder> Builder(BI); + for (unsigned i = 0, e = PHIs.size(); i != e; ++i) { + Value *TrueV = PHIs[i].first; + Value *FalseV = PHIs[i].second; + + // Create a select whose true value is the speculatively executed value and + // false value is the previously determined FalseV. + SelectInst *SI; + if (Invert) + SI = cast<SelectInst> + (Builder.CreateSelect(BrCond, FalseV, TrueV, + FalseV->getName() + "." + TrueV->getName())); + else + SI = cast<SelectInst> + (Builder.CreateSelect(BrCond, TrueV, FalseV, + TrueV->getName() + "." + FalseV->getName())); + + // Make the PHI node use the select for all incoming values for "then" and + // "if" blocks. + for (BasicBlock::iterator I = BB2->begin(); + PHINode *PN = dyn_cast<PHINode>(I); ++I) { + unsigned BB1I = PN->getBasicBlockIndex(BB1); + unsigned BIParentI = PN->getBasicBlockIndex(BIParent); + Value *BB1V = PN->getIncomingValue(BB1I); + Value *BIParentV = PN->getIncomingValue(BIParentI); + if (TrueV == BB1V && FalseV == BIParentV) { + PN->setIncomingValue(BB1I, SI); + PN->setIncomingValue(BIParentI, SI); + } + } + } + + ++NumSpeculations; + 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()); + unsigned Size = 0; + + for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) { + if (isa<DbgInfoIntrinsic>(BBI)) + continue; + if (Size > 10) return false; // Don't clone large BB's. + ++Size; + + // We can only support instructions that 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, const TargetData *TD) { + 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) { + FoldSingleEntryPHINodes(PN->getParent()); + 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) { + ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i)); + if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue; + + // 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->getZExtValue()); + + if (RealDest == BB) continue; // Skip self loops. + // Skip if the predecessor's terminator is an indirect branch. + if (isa<IndirectBrInst>(PredBB->getTerminator())) continue; + + // 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 = BasicBlock::Create(BB->getContext(), + RealDest->getName()+".critedge", + RealDest->getParent(), RealDest); + BranchInst::Create(RealDest, EdgeBB); + + // Update PHI nodes. + AddPredecessorToBlock(RealDest, EdgeBB, BB); + + // 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(); + DenseMap<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); + continue; + } + // Clone the instruction. + Instruction *N = BBI->clone(); + if (BBI->hasName()) N->setName(BBI->getName()+".c"); + + // Update operands due to translation. + for (User::op_iterator i = N->op_begin(), e = N->op_end(); + i != e; ++i) { + DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i); + if (PI != TranslateMap.end()) + *i = PI->second; + } + + // Check for trivial simplification. + if (Value *V = SimplifyInstruction(N, TD)) { + TranslateMap[BBI] = V; + delete N; // Instruction 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, TD) | 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, const TargetData *TD) { + // 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 || + // Don't bother if the branch will be constant folded trivially. + isa<ConstantInt>(IfCond)) + return false; + + // Okay, we found that we can merge this two-entry phi node into a select. + // Doing so would require us to fold *all* two entry phi nodes in this block. + // At some point this becomes non-profitable (particularly if the target + // doesn't support cmov's). Only do this transformation if there are two or + // fewer PHI nodes in this block. + unsigned NumPhis = 0; + for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I) + if (NumPhis > 2) + return false; + + // 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. + SmallPtrSet<Instruction*, 4> AggressiveInsts; + unsigned MaxCostVal0 = PHINodeFoldingThreshold, + MaxCostVal1 = PHINodeFoldingThreshold; + + for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) { + PHINode *PN = cast<PHINode>(II++); + if (Value *V = SimplifyInstruction(PN, TD)) { + PN->replaceAllUsesWith(V); + PN->eraseFromParent(); + continue; + } + + if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts, + MaxCostVal0) || + !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts, + MaxCostVal1)) + return false; + } + + // If we folded the first phi, PN dangles at this point. Refresh it. If + // we ran out of PHIs then we simplified them all. + PN = dyn_cast<PHINode>(BB->begin()); + if (PN == 0) return true; + + // Don't fold i1 branches on PHIs which contain binary operators. These can + // often be turned into switches and other things. + if (PN->getType()->isIntegerTy(1) && + (isa<BinaryOperator>(PN->getIncomingValue(0)) || + isa<BinaryOperator>(PN->getIncomingValue(1)) || + isa<BinaryOperator>(IfCond))) + 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; + BasicBlock *IfBlock1 = PN->getIncomingBlock(0); + BasicBlock *IfBlock2 = PN->getIncomingBlock(1); + if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) { + IfBlock1 = 0; + } else { + DomBlock = *pred_begin(IfBlock1); + for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I) + if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(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 (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) { + IfBlock2 = 0; + } else { + DomBlock = *pred_begin(IfBlock2); + for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I) + if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(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; + } + } + + DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: " + << IfTrue->getName() << " F: " << IfFalse->getName() << "\n"); + + // If we can still promote the PHI nodes after this gauntlet of tests, + // do all of the PHI's now. + Instruction *InsertPt = DomBlock->getTerminator(); + IRBuilder<true, NoFolder> Builder(InsertPt); + + // 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(InsertPt, + IfBlock1->getInstList(), IfBlock1->begin(), + IfBlock1->getTerminator()); + if (IfBlock2) + DomBlock->getInstList().splice(InsertPt, + 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); + + SelectInst *NV = + cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, "")); + PN->replaceAllUsesWith(NV); + NV->takeName(PN); + PN->eraseFromParent(); + } + + // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement + // has been flattened. Change DomBlock to jump directly to our new block to + // avoid other simplifycfg's kicking in on the diamond. + TerminatorInst *OldTI = DomBlock->getTerminator(); + Builder.SetInsertPoint(OldTI); + Builder.CreateBr(BB); + OldTI->eraseFromParent(); + return true; +} + +/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes +/// to two returning blocks, try to merge them together into one return, +/// introducing a select if the return values disagree. +static bool SimplifyCondBranchToTwoReturns(BranchInst *BI, + IRBuilder<> &Builder) { + assert(BI->isConditional() && "Must be a conditional branch"); + BasicBlock *TrueSucc = BI->getSuccessor(0); + BasicBlock *FalseSucc = BI->getSuccessor(1); + ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator()); + ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator()); + + // Check to ensure both blocks are empty (just a return) or optionally empty + // with PHI nodes. If there are other instructions, merging would cause extra + // computation on one path or the other. + if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator()) + return false; + if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator()) + return false; + + Builder.SetInsertPoint(BI); + // 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 (FalseRet->getNumOperands() == 0) { + TrueSucc->removePredecessor(BI->getParent()); + FalseSucc->removePredecessor(BI->getParent()); + Builder.CreateRetVoid(); + EraseTerminatorInstAndDCECond(BI); + return true; + } + + // Otherwise, figure out what the true and false return values are + // so we can insert a new select instruction. + Value *TrueValue = TrueRet->getReturnValue(); + Value *FalseValue = FalseRet->getReturnValue(); + + // Unwrap any PHI nodes in the return blocks. + if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue)) + if (TVPN->getParent() == TrueSucc) + TrueValue = TVPN->getIncomingValueForBlock(BI->getParent()); + if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue)) + if (FVPN->getParent() == FalseSucc) + FalseValue = FVPN->getIncomingValueForBlock(BI->getParent()); + + // In order for this transformation to be safe, we must be able to + // unconditionally execute both operands to the return. This is + // normally the case, but we could have a potentially-trapping + // constant expression that prevents this transformation from being + // safe. + if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue)) + if (TCV->canTrap()) + return false; + if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue)) + if (FCV->canTrap()) + return false; + + // Okay, we collected all the mapped values and checked them for sanity, and + // defined to really do this transformation. First, update the CFG. + TrueSucc->removePredecessor(BI->getParent()); + FalseSucc->removePredecessor(BI->getParent()); + + // Insert select instructions where needed. + Value *BrCond = BI->getCondition(); + if (TrueValue) { + // Insert a select if the results differ. + if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) { + } else if (isa<UndefValue>(TrueValue)) { + TrueValue = FalseValue; + } else { + TrueValue = Builder.CreateSelect(BrCond, TrueValue, + FalseValue, "retval"); + } + } + + Value *RI = !TrueValue ? + Builder.CreateRetVoid() : Builder.CreateRet(TrueValue); + + (void) RI; + + DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:" + << "\n " << *BI << "NewRet = " << *RI + << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc); + + EraseTerminatorInstAndDCECond(BI); + + return true; +} + +/// ExtractBranchMetadata - Given a conditional BranchInstruction, retrieve the +/// probabilities of the branch taking each edge. Fills in the two APInt +/// parameters and return true, or returns false if no or invalid metadata was +/// found. +static bool ExtractBranchMetadata(BranchInst *BI, + APInt &ProbTrue, APInt &ProbFalse) { + assert(BI->isConditional() && + "Looking for probabilities on unconditional branch?"); + MDNode *ProfileData = BI->getMetadata(LLVMContext::MD_prof); + if (!ProfileData || ProfileData->getNumOperands() != 3) return false; + ConstantInt *CITrue = dyn_cast<ConstantInt>(ProfileData->getOperand(1)); + ConstantInt *CIFalse = dyn_cast<ConstantInt>(ProfileData->getOperand(2)); + if (!CITrue || !CIFalse) return false; + ProbTrue = CITrue->getValue(); + ProbFalse = CIFalse->getValue(); + assert(ProbTrue.getBitWidth() == 32 && ProbFalse.getBitWidth() == 32 && + "Branch probability metadata must be 32-bit integers"); + return true; +} + +/// MultiplyAndLosePrecision - Multiplies A and B, then returns the result. In +/// the event of overflow, logically-shifts all four inputs right until the +/// multiply fits. +static APInt MultiplyAndLosePrecision(APInt &A, APInt &B, APInt &C, APInt &D, + unsigned &BitsLost) { + BitsLost = 0; + bool Overflow = false; + APInt Result = A.umul_ov(B, Overflow); + if (Overflow) { + APInt MaxB = APInt::getMaxValue(A.getBitWidth()).udiv(A); + do { + B = B.lshr(1); + ++BitsLost; + } while (B.ugt(MaxB)); + A = A.lshr(BitsLost); + C = C.lshr(BitsLost); + D = D.lshr(BitsLost); + Result = A * B; + } + return Result; +} + +/// checkCSEInPredecessor - Return true if the given instruction is available +/// in its predecessor block. If yes, the instruction will be removed. +/// +static bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) { + if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst)) + return false; + for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) { + Instruction *PBI = &*I; + // Check whether Inst and PBI generate the same value. + if (Inst->isIdenticalTo(PBI)) { + Inst->replaceAllUsesWith(PBI); + Inst->eraseFromParent(); + return true; + } + } + return false; +} + +/// FoldBranchToCommonDest - If this basic block is simple enough, and if a +/// predecessor branches to us and one of our successors, fold the block into +/// the predecessor and use logical operations to pick the right destination. +bool llvm::FoldBranchToCommonDest(BranchInst *BI) { + BasicBlock *BB = BI->getParent(); + + Instruction *Cond = 0; + if (BI->isConditional()) + Cond = dyn_cast<Instruction>(BI->getCondition()); + else { + // For unconditional branch, check for a simple CFG pattern, where + // BB has a single predecessor and BB's successor is also its predecessor's + // successor. If such pattern exisits, check for CSE between BB and its + // predecessor. + if (BasicBlock *PB = BB->getSinglePredecessor()) + if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator())) + if (PBI->isConditional() && + (BI->getSuccessor(0) == PBI->getSuccessor(0) || + BI->getSuccessor(0) == PBI->getSuccessor(1))) { + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); + I != E; ) { + Instruction *Curr = I++; + if (isa<CmpInst>(Curr)) { + Cond = Curr; + break; + } + // Quit if we can't remove this instruction. + if (!checkCSEInPredecessor(Curr, PB)) + return false; + } + } + + if (Cond == 0) + return false; + } + + if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) || + Cond->getParent() != BB || !Cond->hasOneUse()) + return false; + + // Only allow this if the condition is a simple instruction that can be + // executed unconditionally. It must be in the same block as the branch, and + // must be at the front of the block. + BasicBlock::iterator FrontIt = BB->front(); + + // Ignore dbg intrinsics. + while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt; + + // Allow a single instruction to be hoisted in addition to the compare + // that feeds the branch. We later ensure that any values that _it_ uses + // were also live in the predecessor, so that we don't unnecessarily create + // register pressure or inhibit out-of-order execution. + Instruction *BonusInst = 0; + if (&*FrontIt != Cond && + FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond && + isSafeToSpeculativelyExecute(FrontIt)) { + BonusInst = &*FrontIt; + ++FrontIt; + + // Ignore dbg intrinsics. + while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt; + } + + // Only a single bonus inst is allowed. + if (&*FrontIt != Cond) + return false; + + // Make sure the instruction after the condition is the cond branch. + BasicBlock::iterator CondIt = Cond; ++CondIt; + + // Ingore dbg intrinsics. + while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt; + + if (&*CondIt != BI) + return false; + + // Cond is known to be a compare or binary operator. Check to make sure that + // neither operand is a potentially-trapping constant expression. + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0))) + if (CE->canTrap()) + return false; + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1))) + if (CE->canTrap()) + return false; + + // Finally, don't infinitely unroll conditional loops. + BasicBlock *TrueDest = BI->getSuccessor(0); + BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : 0; + if (TrueDest == BB || FalseDest == BB) + return false; + + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { + BasicBlock *PredBlock = *PI; + BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator()); + + // Check that we have two conditional branches. If there is a PHI node in + // the common successor, verify that the same value flows in from both + // blocks. + SmallVector<PHINode*, 4> PHIs; + if (PBI == 0 || PBI->isUnconditional() || + (BI->isConditional() && + !SafeToMergeTerminators(BI, PBI)) || + (!BI->isConditional() && + !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs))) + continue; + + // Determine if the two branches share a common destination. + Instruction::BinaryOps Opc; + bool InvertPredCond = false; + + if (BI->isConditional()) { + if (PBI->getSuccessor(0) == TrueDest) + Opc = Instruction::Or; + else if (PBI->getSuccessor(1) == FalseDest) + Opc = Instruction::And; + else if (PBI->getSuccessor(0) == FalseDest) + Opc = Instruction::And, InvertPredCond = true; + else if (PBI->getSuccessor(1) == TrueDest) + Opc = Instruction::Or, InvertPredCond = true; + else + continue; + } else { + if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest) + continue; + } + + // Ensure that any values used in the bonus instruction are also used + // by the terminator of the predecessor. This means that those values + // must already have been resolved, so we won't be inhibiting the + // out-of-order core by speculating them earlier. + if (BonusInst) { + // Collect the values used by the bonus inst + SmallPtrSet<Value*, 4> UsedValues; + for (Instruction::op_iterator OI = BonusInst->op_begin(), + OE = BonusInst->op_end(); OI != OE; ++OI) { + Value *V = *OI; + if (!isa<Constant>(V)) + UsedValues.insert(V); + } + + SmallVector<std::pair<Value*, unsigned>, 4> Worklist; + Worklist.push_back(std::make_pair(PBI->getOperand(0), 0)); + + // Walk up to four levels back up the use-def chain of the predecessor's + // terminator to see if all those values were used. The choice of four + // levels is arbitrary, to provide a compile-time-cost bound. + while (!Worklist.empty()) { + std::pair<Value*, unsigned> Pair = Worklist.back(); + Worklist.pop_back(); + + if (Pair.second >= 4) continue; + UsedValues.erase(Pair.first); + if (UsedValues.empty()) break; + + if (Instruction *I = dyn_cast<Instruction>(Pair.first)) { + for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); + OI != OE; ++OI) + Worklist.push_back(std::make_pair(OI->get(), Pair.second+1)); + } + } + + if (!UsedValues.empty()) return false; + } + + DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB); + IRBuilder<> Builder(PBI); + + // If we need to invert the condition in the pred block to match, do so now. + if (InvertPredCond) { + Value *NewCond = PBI->getCondition(); + + if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) { + CmpInst *CI = cast<CmpInst>(NewCond); + CI->setPredicate(CI->getInversePredicate()); + } else { + NewCond = Builder.CreateNot(NewCond, + PBI->getCondition()->getName()+".not"); + } + + PBI->setCondition(NewCond); + PBI->swapSuccessors(); + } + + // If we have a bonus inst, clone it into the predecessor block. + Instruction *NewBonus = 0; + if (BonusInst) { + NewBonus = BonusInst->clone(); + PredBlock->getInstList().insert(PBI, NewBonus); + NewBonus->takeName(BonusInst); + BonusInst->setName(BonusInst->getName()+".old"); + } + + // Clone Cond into the predecessor basic block, and or/and the + // two conditions together. + Instruction *New = Cond->clone(); + if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus); + PredBlock->getInstList().insert(PBI, New); + New->takeName(Cond); + Cond->setName(New->getName()+".old"); + + if (BI->isConditional()) { + Instruction *NewCond = + cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(), + New, "or.cond")); + 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); + } + } else { + // Update PHI nodes in the common successors. + for (unsigned i = 0, e = PHIs.size(); i != e; ++i) { + ConstantInt *PBI_C = cast<ConstantInt>( + PHIs[i]->getIncomingValueForBlock(PBI->getParent())); + assert(PBI_C->getType()->isIntegerTy(1)); + Instruction *MergedCond = 0; + if (PBI->getSuccessor(0) == TrueDest) { + // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value) + // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value) + // is false: !PBI_Cond and BI_Value + Instruction *NotCond = + cast<Instruction>(Builder.CreateNot(PBI->getCondition(), + "not.cond")); + MergedCond = + cast<Instruction>(Builder.CreateBinOp(Instruction::And, + NotCond, New, + "and.cond")); + if (PBI_C->isOne()) + MergedCond = + cast<Instruction>(Builder.CreateBinOp(Instruction::Or, + PBI->getCondition(), MergedCond, + "or.cond")); + } else { + // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C) + // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond) + // is false: PBI_Cond and BI_Value + MergedCond = + cast<Instruction>(Builder.CreateBinOp(Instruction::And, + PBI->getCondition(), New, + "and.cond")); + if (PBI_C->isOne()) { + Instruction *NotCond = + cast<Instruction>(Builder.CreateNot(PBI->getCondition(), + "not.cond")); + MergedCond = + cast<Instruction>(Builder.CreateBinOp(Instruction::Or, + NotCond, MergedCond, + "or.cond")); + } + } + // Update PHI Node. + PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()), + MergedCond); + } + // Change PBI from Conditional to Unconditional. + BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI); + EraseTerminatorInstAndDCECond(PBI); + PBI = New_PBI; + } + + // TODO: If BB is reachable from all paths through PredBlock, then we + // could replace PBI's branch probabilities with BI's. + + // Merge probability data into PredBlock's branch. + APInt A, B, C, D; + if (PBI->isConditional() && BI->isConditional() && + ExtractBranchMetadata(PBI, C, D) && ExtractBranchMetadata(BI, A, B)) { + // Given IR which does: + // bbA: + // br i1 %x, label %bbB, label %bbC + // bbB: + // br i1 %y, label %bbD, label %bbC + // Let's call the probability that we take the edge from %bbA to %bbB + // 'a', from %bbA to %bbC, 'b', from %bbB to %bbD 'c' and from %bbB to + // %bbC probability 'd'. + // + // We transform the IR into: + // bbA: + // br i1 %z, label %bbD, label %bbC + // where the probability of going to %bbD is (a*c) and going to bbC is + // (b+a*d). + // + // Probabilities aren't stored as ratios directly. Using branch weights, + // we get: + // (a*c)% = A*C, (b+(a*d))% = A*D+B*C+B*D. + + // In the event of overflow, we want to drop the LSB of the input + // probabilities. + unsigned BitsLost; + + // Ignore overflow result on ProbTrue. + APInt ProbTrue = MultiplyAndLosePrecision(A, C, B, D, BitsLost); + + APInt Tmp1 = MultiplyAndLosePrecision(B, D, A, C, BitsLost); + if (BitsLost) { + ProbTrue = ProbTrue.lshr(BitsLost*2); + } + + APInt Tmp2 = MultiplyAndLosePrecision(A, D, C, B, BitsLost); + if (BitsLost) { + ProbTrue = ProbTrue.lshr(BitsLost*2); + Tmp1 = Tmp1.lshr(BitsLost*2); + } + + APInt Tmp3 = MultiplyAndLosePrecision(B, C, A, D, BitsLost); + if (BitsLost) { + ProbTrue = ProbTrue.lshr(BitsLost*2); + Tmp1 = Tmp1.lshr(BitsLost*2); + Tmp2 = Tmp2.lshr(BitsLost*2); + } + + bool Overflow1 = false, Overflow2 = false; + APInt Tmp4 = Tmp2.uadd_ov(Tmp3, Overflow1); + APInt ProbFalse = Tmp4.uadd_ov(Tmp1, Overflow2); + + if (Overflow1 || Overflow2) { + ProbTrue = ProbTrue.lshr(1); + Tmp1 = Tmp1.lshr(1); + Tmp2 = Tmp2.lshr(1); + Tmp3 = Tmp3.lshr(1); + Tmp4 = Tmp2 + Tmp3; + ProbFalse = Tmp4 + Tmp1; + } + + // The sum of branch weights must fit in 32-bits. + if (ProbTrue.isNegative() && ProbFalse.isNegative()) { + ProbTrue = ProbTrue.lshr(1); + ProbFalse = ProbFalse.lshr(1); + } + + if (ProbTrue != ProbFalse) { + // Normalize the result. + APInt GCD = APIntOps::GreatestCommonDivisor(ProbTrue, ProbFalse); + ProbTrue = ProbTrue.udiv(GCD); + ProbFalse = ProbFalse.udiv(GCD); + + MDBuilder MDB(BI->getContext()); + MDNode *N = MDB.createBranchWeights(ProbTrue.getZExtValue(), + ProbFalse.getZExtValue()); + PBI->setMetadata(LLVMContext::MD_prof, N); + } else { + PBI->setMetadata(LLVMContext::MD_prof, NULL); + } + } else { + PBI->setMetadata(LLVMContext::MD_prof, NULL); + } + + // Copy any debug value intrinsics into the end of PredBlock. + for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) + if (isa<DbgInfoIntrinsic>(*I)) + I->clone()->insertBefore(PBI); + + return true; + } + return false; +} + +/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a +/// predecessor of another block, this function tries to simplify it. We know +/// that PBI and BI are both conditional branches, and BI is in one of the +/// successor blocks of PBI - PBI branches to BI. +static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) { + assert(PBI->isConditional() && BI->isConditional()); + BasicBlock *BB = BI->getParent(); + + // 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(ConstantInt::get(Type::getInt1Ty(BB->getContext()), + CondIsTrue)); + return true; // Nuke the branch on constant. + } + + // Otherwise, if there are multiple predecessors, insert a PHI that merges + // in the constant and simplify the block result. Subsequent passes of + // simplifycfg will thread the block. + if (BlockIsSimpleEnoughToThreadThrough(BB)) { + pred_iterator PB = pred_begin(BB), PE = pred_end(BB); + PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()), + std::distance(PB, PE), + BI->getCondition()->getName() + ".pr", + BB->begin()); + // Okay, we're going to insert the PHI node. Since PBI is not the only + // predecessor, compute the PHI'd conditional value for all of the preds. + // Any predecessor where the condition is not computable we keep symbolic. + for (pred_iterator PI = PB; PI != PE; ++PI) { + BasicBlock *P = *PI; + if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) && + PBI != BI && PBI->isConditional() && + PBI->getCondition() == BI->getCondition() && + PBI->getSuccessor(0) != PBI->getSuccessor(1)) { + bool CondIsTrue = PBI->getSuccessor(0) == BB; + NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()), + CondIsTrue), P); + } else { + NewPN->addIncoming(BI->getCondition(), P); + } + } + + BI->setCondition(NewPN); + return 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. + BasicBlock::iterator BBI = BB->begin(); + // Ignore dbg intrinsics. + while (isa<DbgInfoIntrinsic>(BBI)) + ++BBI; + if (&*BBI != BI) + return false; + + + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition())) + if (CE->canTrap()) + return false; + + 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 + return false; + + // Check to make sure that the other destination of this branch + // isn't BB itself. If so, this is an infinite loop that will + // keep getting unwound. + if (PBI->getSuccessor(PBIOp) == BB) + return false; + + // Do not perform this transformation if it would require + // insertion of a large number of select instructions. For targets + // without predication/cmovs, this is a big pessimization. + BasicBlock *CommonDest = PBI->getSuccessor(PBIOp); + + unsigned NumPhis = 0; + for (BasicBlock::iterator II = CommonDest->begin(); + isa<PHINode>(II); ++II, ++NumPhis) + if (NumPhis > 2) // Disable this xform. + return false; + + // Finally, if everything is ok, fold the branches to logical ops. + BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1); + + DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent() + << "AND: " << *BI->getParent()); + + + // If OtherDest *is* BB, then BB is a basic block with a single conditional + // branch in it, where one edge (OtherDest) goes back to itself but the other + // exits. We don't *know* that the program avoids the infinite loop + // (even though that seems likely). If we do this xform naively, we'll end up + // recursively unpeeling the loop. Since we know that (after the xform is + // done) that the block *is* infinite if reached, we just make it an obviously + // infinite loop with no cond branch. + if (OtherDest == BB) { + // Insert it at the end of the function, because it's either code, + // or it won't matter if it's hot. :) + BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(), + "infloop", BB->getParent()); + BranchInst::Create(InfLoopBlock, InfLoopBlock); + OtherDest = InfLoopBlock; + } + + DEBUG(dbgs() << *PBI->getParent()->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(); + IRBuilder<true, NoFolder> Builder(PBI); + if (PBIOp) + PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not"); + + Value *BICond = BI->getCondition(); + if (BIOp) + BICond = Builder.CreateNot(BICond, BICond->getName()+".not"); + + // Merge the conditions. + Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge"); + + // 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. + AddPredecessorToBlock(OtherDest, PBI->getParent(), BB); + + // 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. + PHINode *PN; + 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 = cast<SelectInst> + (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux")); + PN->setIncomingValue(PBBIdx, NV); + } + } + + DEBUG(dbgs() << "INTO: " << *PBI->getParent()); + DEBUG(dbgs() << *PBI->getParent()->getParent()); + + // This basic block is probably dead. We know it has at least + // one fewer predecessor. + return true; +} + +// SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a +// branch to TrueBB if Cond is true or to FalseBB if Cond is false. +// Takes care of updating the successors and removing the old terminator. +// Also makes sure not to introduce new successors by assuming that edges to +// non-successor TrueBBs and FalseBBs aren't reachable. +static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond, + BasicBlock *TrueBB, BasicBlock *FalseBB){ + // Remove any superfluous successor edges from the CFG. + // First, figure out which successors to preserve. + // If TrueBB and FalseBB are equal, only try to preserve one copy of that + // successor. + BasicBlock *KeepEdge1 = TrueBB; + BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0; + + // Then remove the rest. + for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) { + BasicBlock *Succ = OldTerm->getSuccessor(I); + // Make sure only to keep exactly one copy of each edge. + if (Succ == KeepEdge1) + KeepEdge1 = 0; + else if (Succ == KeepEdge2) + KeepEdge2 = 0; + else + Succ->removePredecessor(OldTerm->getParent()); + } + + IRBuilder<> Builder(OldTerm); + Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc()); + + // Insert an appropriate new terminator. + if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) { + if (TrueBB == FalseBB) + // We were only looking for one successor, and it was present. + // Create an unconditional branch to it. + Builder.CreateBr(TrueBB); + else + // We found both of the successors we were looking for. + // Create a conditional branch sharing the condition of the select. + Builder.CreateCondBr(Cond, TrueBB, FalseBB); + } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) { + // Neither of the selected blocks were successors, so this + // terminator must be unreachable. + new UnreachableInst(OldTerm->getContext(), OldTerm); + } else { + // One of the selected values was a successor, but the other wasn't. + // Insert an unconditional branch to the one that was found; + // the edge to the one that wasn't must be unreachable. + if (KeepEdge1 == 0) + // Only TrueBB was found. + Builder.CreateBr(TrueBB); + else + // Only FalseBB was found. + Builder.CreateBr(FalseBB); + } + + EraseTerminatorInstAndDCECond(OldTerm); + return true; +} + +// SimplifySwitchOnSelect - Replaces +// (switch (select cond, X, Y)) on constant X, Y +// with a branch - conditional if X and Y lead to distinct BBs, +// unconditional otherwise. +static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) { + // Check for constant integer values in the select. + ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue()); + ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue()); + if (!TrueVal || !FalseVal) + return false; + + // Find the relevant condition and destinations. + Value *Condition = Select->getCondition(); + BasicBlock *TrueBB = SI->findCaseValue(TrueVal).getCaseSuccessor(); + BasicBlock *FalseBB = SI->findCaseValue(FalseVal).getCaseSuccessor(); + + // Perform the actual simplification. + return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB); +} + +// SimplifyIndirectBrOnSelect - Replaces +// (indirectbr (select cond, blockaddress(@fn, BlockA), +// blockaddress(@fn, BlockB))) +// with +// (br cond, BlockA, BlockB). +static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) { + // Check that both operands of the select are block addresses. + BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue()); + BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue()); + if (!TBA || !FBA) + return false; + + // Extract the actual blocks. + BasicBlock *TrueBB = TBA->getBasicBlock(); + BasicBlock *FalseBB = FBA->getBasicBlock(); + + // Perform the actual simplification. + return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB); +} + +/// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp +/// instruction (a seteq/setne with a constant) as the only instruction in a +/// block that ends with an uncond branch. We are looking for a very specific +/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In +/// this case, we merge the first two "or's of icmp" into a switch, but then the +/// default value goes to an uncond block with a seteq in it, we get something +/// like: +/// +/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ] +/// DEFAULT: +/// %tmp = icmp eq i8 %A, 92 +/// br label %end +/// end: +/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ] +/// +/// We prefer to split the edge to 'end' so that there is a true/false entry to +/// the PHI, merging the third icmp into the switch. +static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI, + const TargetData *TD, + IRBuilder<> &Builder) { + BasicBlock *BB = ICI->getParent(); + + // If the block has any PHIs in it or the icmp has multiple uses, it is too + // complex. + if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false; + + Value *V = ICI->getOperand(0); + ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1)); + + // The pattern we're looking for is where our only predecessor is a switch on + // 'V' and this block is the default case for the switch. In this case we can + // fold the compared value into the switch to simplify things. + BasicBlock *Pred = BB->getSinglePredecessor(); + if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false; + + SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator()); + if (SI->getCondition() != V) + return false; + + // If BB is reachable on a non-default case, then we simply know the value of + // V in this block. Substitute it and constant fold the icmp instruction + // away. + if (SI->getDefaultDest() != BB) { + ConstantInt *VVal = SI->findCaseDest(BB); + assert(VVal && "Should have a unique destination value"); + ICI->setOperand(0, VVal); + + if (Value *V = SimplifyInstruction(ICI, TD)) { + ICI->replaceAllUsesWith(V); + ICI->eraseFromParent(); + } + // BB is now empty, so it is likely to simplify away. + return SimplifyCFG(BB) | true; + } + + // Ok, the block is reachable from the default dest. If the constant we're + // comparing exists in one of the other edges, then we can constant fold ICI + // and zap it. + if (SI->findCaseValue(Cst) != SI->case_default()) { + Value *V; + if (ICI->getPredicate() == ICmpInst::ICMP_EQ) + V = ConstantInt::getFalse(BB->getContext()); + else + V = ConstantInt::getTrue(BB->getContext()); + + ICI->replaceAllUsesWith(V); + ICI->eraseFromParent(); + // BB is now empty, so it is likely to simplify away. + return SimplifyCFG(BB) | true; + } + + // The use of the icmp has to be in the 'end' block, by the only PHI node in + // the block. + BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0); + PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back()); + if (PHIUse == 0 || PHIUse != &SuccBlock->front() || + isa<PHINode>(++BasicBlock::iterator(PHIUse))) + return false; + + // If the icmp is a SETEQ, then the default dest gets false, the new edge gets + // true in the PHI. + Constant *DefaultCst = ConstantInt::getTrue(BB->getContext()); + Constant *NewCst = ConstantInt::getFalse(BB->getContext()); + + if (ICI->getPredicate() == ICmpInst::ICMP_EQ) + std::swap(DefaultCst, NewCst); + + // Replace ICI (which is used by the PHI for the default value) with true or + // false depending on if it is EQ or NE. + ICI->replaceAllUsesWith(DefaultCst); + ICI->eraseFromParent(); + + // Okay, the switch goes to this block on a default value. Add an edge from + // the switch to the merge point on the compared value. + BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge", + BB->getParent(), BB); + SI->addCase(Cst, NewBB); + + // NewBB branches to the phi block, add the uncond branch and the phi entry. + Builder.SetInsertPoint(NewBB); + Builder.SetCurrentDebugLocation(SI->getDebugLoc()); + Builder.CreateBr(SuccBlock); + PHIUse->addIncoming(NewCst, NewBB); + return true; +} + +/// SimplifyBranchOnICmpChain - The specified branch is a conditional branch. +/// Check to see if it is branching on an or/and chain of icmp instructions, and +/// fold it into a switch instruction if so. +static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD, + IRBuilder<> &Builder) { + Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); + if (Cond == 0) return false; + + + // Change br (X == 0 | X == 1), T, F into a switch instruction. + // 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 = true; + Value *ExtraCase = 0; + unsigned UsedICmps = 0; + + if (Cond->getOpcode() == Instruction::Or) { + CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true, + UsedICmps); + } else if (Cond->getOpcode() == Instruction::And) { + CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false, + UsedICmps); + TrueWhenEqual = false; + } + + // If we didn't have a multiply compared value, fail. + if (CompVal == 0) return false; + + // Avoid turning single icmps into a switch. + if (UsedICmps <= 1) + return false; + + // There might be duplicate constants in the list, which the switch + // instruction can't handle, remove them now. + array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate); + Values.erase(std::unique(Values.begin(), Values.end()), Values.end()); + + // If Extra was used, we require at least two switch values to do the + // transformation. A switch with one value is just an cond branch. + if (ExtraCase && Values.size() < 2) return false; + + // Figure out which block is which destination. + BasicBlock *DefaultBB = BI->getSuccessor(1); + BasicBlock *EdgeBB = BI->getSuccessor(0); + if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB); + + BasicBlock *BB = BI->getParent(); + + DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size() + << " cases into SWITCH. BB is:\n" << *BB); + + // If there are any extra values that couldn't be folded into the switch + // then we evaluate them with an explicit branch first. Split the block + // right before the condbr to handle it. + if (ExtraCase) { + BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test"); + // Remove the uncond branch added to the old block. + TerminatorInst *OldTI = BB->getTerminator(); + Builder.SetInsertPoint(OldTI); + + if (TrueWhenEqual) + Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB); + else + Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB); + + OldTI->eraseFromParent(); + + // If there are PHI nodes in EdgeBB, then we need to add a new entry to them + // for the edge we just added. + AddPredecessorToBlock(EdgeBB, BB, NewBB); + + DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase + << "\nEXTRABB = " << *BB); + BB = NewBB; + } + + Builder.SetInsertPoint(BI); + // Convert pointer to int before we switch. + if (CompVal->getType()->isPointerTy()) { + assert(TD && "Cannot switch on pointer without TargetData"); + CompVal = Builder.CreatePtrToInt(CompVal, + TD->getIntPtrType(CompVal->getContext()), + "magicptr"); + } + + // Create the new switch instruction now. + SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size()); + + // 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(BB); + for (unsigned i = 0, e = Values.size()-1; i != e; ++i) + PN->addIncoming(InVal, BB); + } + + // Erase the old branch instruction. + EraseTerminatorInstAndDCECond(BI); + + DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n'); + return true; +} + +bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) { + // If this is a trivial landing pad that just continues unwinding the caught + // exception then zap the landing pad, turning its invokes into calls. + BasicBlock *BB = RI->getParent(); + LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI()); + if (RI->getValue() != LPInst) + // Not a landing pad, or the resume is not unwinding the exception that + // caused control to branch here. + return false; + + // Check that there are no other instructions except for debug intrinsics. + BasicBlock::iterator I = LPInst, E = RI; + while (++I != E) + if (!isa<DbgInfoIntrinsic>(I)) + return false; + + // Turn all invokes that unwind here into calls and delete the basic block. + for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) { + InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator()); + SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3); + // Insert a call instruction before the invoke. + CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II); + Call->takeName(II); + Call->setCallingConv(II->getCallingConv()); + Call->setAttributes(II->getAttributes()); + Call->setDebugLoc(II->getDebugLoc()); + + // Anything that used the value produced by the invoke instruction now uses + // the value produced by the call instruction. Note that we do this even + // for void functions and calls with no uses so that the callgraph edge is + // updated. + II->replaceAllUsesWith(Call); + BB->removePredecessor(II->getParent()); + + // Insert a branch to the normal destination right before the invoke. + BranchInst::Create(II->getNormalDest(), II); + + // Finally, delete the invoke instruction! + II->eraseFromParent(); + } + + // The landingpad is now unreachable. Zap it. + BB->eraseFromParent(); + return true; +} + +bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) { + BasicBlock *BB = RI->getParent(); + if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false; + + // Find predecessors that end with branches. + SmallVector<BasicBlock*, 8> UncondBranchPreds; + SmallVector<BranchInst*, 8> CondBranchPreds; + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { + BasicBlock *P = *PI; + TerminatorInst *PTI = P->getTerminator(); + if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) { + if (BI->isUnconditional()) + UncondBranchPreds.push_back(P); + else + CondBranchPreds.push_back(BI); + } + } + + // If we found some, do the transformation! + if (!UncondBranchPreds.empty() && DupRet) { + while (!UncondBranchPreds.empty()) { + BasicBlock *Pred = UncondBranchPreds.pop_back_val(); + DEBUG(dbgs() << "FOLDING: " << *BB + << "INTO UNCOND BRANCH PRED: " << *Pred); + (void)FoldReturnIntoUncondBranch(RI, BB, Pred); + } + + // 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. + BB->eraseFromParent(); + + 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.pop_back_val(); + + // Check to see if the non-BB successor is also a return block. + if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) && + isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) && + SimplifyCondBranchToTwoReturns(BI, Builder)) + return true; + } + return false; +} + +bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) { + BasicBlock *BB = UI->getParent(); + + bool Changed = false; + + // If there are any instructions immediately before the unreachable that can + // be removed, do so. + while (UI != BB->begin()) { + BasicBlock::iterator BBI = UI; + --BBI; + // Do not delete instructions that can have side effects which might cause + // the unreachable to not be reachable; specifically, calls and volatile + // operations may have this effect. + if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break; + + if (BBI->mayHaveSideEffects()) { + if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) { + if (SI->isVolatile()) + break; + } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) { + if (LI->isVolatile()) + break; + } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) { + if (RMWI->isVolatile()) + break; + } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) { + if (CXI->isVolatile()) + break; + } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) && + !isa<LandingPadInst>(BBI)) { + break; + } + // Note that deleting LandingPad's here is in fact okay, although it + // involves a bit of subtle reasoning. If this inst is a LandingPad, + // all the predecessors of this block will be the unwind edges of Invokes, + // and we can therefore guarantee this block will be erased. + } + + // Delete this instruction (any uses are guaranteed to be dead) + if (!BBI->use_empty()) + BBI->replaceAllUsesWith(UndefValue::get(BBI->getType())); + BBI->eraseFromParent(); + 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() != UI) return Changed; + + SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB)); + for (unsigned i = 0, e = Preds.size(); i != e; ++i) { + TerminatorInst *TI = Preds[i]->getTerminator(); + IRBuilder<> Builder(TI); + if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { + if (BI->isUnconditional()) { + if (BI->getSuccessor(0) == BB) { + new UnreachableInst(TI->getContext(), TI); + TI->eraseFromParent(); + Changed = true; + } + } else { + if (BI->getSuccessor(0) == BB) { + Builder.CreateBr(BI->getSuccessor(1)); + EraseTerminatorInstAndDCECond(BI); + } else if (BI->getSuccessor(1) == BB) { + Builder.CreateBr(BI->getSuccessor(0)); + EraseTerminatorInstAndDCECond(BI); + Changed = true; + } + } + } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { + for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); + i != e; ++i) + if (i.getCaseSuccessor() == 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->getDefaultDest() == BB) { + std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity; + for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); + i != e; ++i) { + std::pair<unsigned, unsigned> &entry = + Popularity[i.getCaseSuccessor()]; + if (entry.first == 0) { + entry.first = 1; + entry.second = i.getCaseIndex(); + } else { + entry.first++; + } + } + + // Find the most popular block. + unsigned MaxPop = 0; + unsigned MaxIndex = 0; + BasicBlock *MaxBlock = 0; + for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator + I = Popularity.begin(), E = Popularity.end(); I != E; ++I) { + if (I->second.first > MaxPop || + (I->second.first == MaxPop && MaxIndex > I->second.second)) { + MaxPop = I->second.first; + MaxIndex = I->second.second; + MaxBlock = I->first; + } + } + if (MaxBlock) { + // Make this the new default, allowing us to delete any explicit + // edges to it. + SI->setDefaultDest(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 (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); + i != e; ++i) + if (i.getCaseSuccessor() == 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 = Builder.CreateBr(II->getNormalDest()); + II->removeFromParent(); // Take out of symbol table + + // Insert the call now... + SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3); + Builder.SetInsertPoint(BI); + CallInst *CI = Builder.CreateCall(II->getCalledValue(), + Args, II->getName()); + CI->setCallingConv(II->getCallingConv()); + CI->setAttributes(II->getAttributes()); + // 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) && + BB != &BB->getParent()->getEntryBlock()) { + // We know there are no successors, so just nuke the block. + BB->eraseFromParent(); + return true; + } + + return Changed; +} + +/// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a +/// integer range comparison into a sub, an icmp and a branch. +static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) { + assert(SI->getNumCases() > 1 && "Degenerate switch?"); + + // Make sure all cases point to the same destination and gather the values. + SmallVector<ConstantInt *, 16> Cases; + SwitchInst::CaseIt I = SI->case_begin(); + Cases.push_back(I.getCaseValue()); + SwitchInst::CaseIt PrevI = I++; + for (SwitchInst::CaseIt E = SI->case_end(); I != E; PrevI = I++) { + if (PrevI.getCaseSuccessor() != I.getCaseSuccessor()) + return false; + Cases.push_back(I.getCaseValue()); + } + assert(Cases.size() == SI->getNumCases() && "Not all cases gathered"); + + // Sort the case values, then check if they form a range we can transform. + array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate); + for (unsigned I = 1, E = Cases.size(); I != E; ++I) { + if (Cases[I-1]->getValue() != Cases[I]->getValue()+1) + return false; + } + + Constant *Offset = ConstantExpr::getNeg(Cases.back()); + Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()); + + Value *Sub = SI->getCondition(); + if (!Offset->isNullValue()) + Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off"); + Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch"); + Builder.CreateCondBr( + Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest()); + + // Prune obsolete incoming values off the successor's PHI nodes. + for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin(); + isa<PHINode>(BBI); ++BBI) { + for (unsigned I = 0, E = SI->getNumCases()-1; I != E; ++I) + cast<PHINode>(BBI)->removeIncomingValue(SI->getParent()); + } + SI->eraseFromParent(); + + return true; +} + +/// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch +/// and use it to remove dead cases. +static bool EliminateDeadSwitchCases(SwitchInst *SI) { + Value *Cond = SI->getCondition(); + unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth(); + APInt KnownZero(Bits, 0), KnownOne(Bits, 0); + ComputeMaskedBits(Cond, KnownZero, KnownOne); + + // Gather dead cases. + SmallVector<ConstantInt*, 8> DeadCases; + for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) { + if ((I.getCaseValue()->getValue() & KnownZero) != 0 || + (I.getCaseValue()->getValue() & KnownOne) != KnownOne) { + DeadCases.push_back(I.getCaseValue()); + DEBUG(dbgs() << "SimplifyCFG: switch case '" + << I.getCaseValue() << "' is dead.\n"); + } + } + + // Remove dead cases from the switch. + for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) { + SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]); + assert(Case != SI->case_default() && + "Case was not found. Probably mistake in DeadCases forming."); + // Prune unused values from PHI nodes. + Case.getCaseSuccessor()->removePredecessor(SI->getParent()); + SI->removeCase(Case); + } + + return !DeadCases.empty(); +} + +/// FindPHIForConditionForwarding - If BB would be eligible for simplification +/// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated +/// by an unconditional branch), look at the phi node for BB in the successor +/// block and see if the incoming value is equal to CaseValue. If so, return +/// the phi node, and set PhiIndex to BB's index in the phi node. +static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue, + BasicBlock *BB, + int *PhiIndex) { + if (BB->getFirstNonPHIOrDbg() != BB->getTerminator()) + return NULL; // BB must be empty to be a candidate for simplification. + if (!BB->getSinglePredecessor()) + return NULL; // BB must be dominated by the switch. + + BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator()); + if (!Branch || !Branch->isUnconditional()) + return NULL; // Terminator must be unconditional branch. + + BasicBlock *Succ = Branch->getSuccessor(0); + + BasicBlock::iterator I = Succ->begin(); + while (PHINode *PHI = dyn_cast<PHINode>(I++)) { + int Idx = PHI->getBasicBlockIndex(BB); + assert(Idx >= 0 && "PHI has no entry for predecessor?"); + + Value *InValue = PHI->getIncomingValue(Idx); + if (InValue != CaseValue) continue; + + *PhiIndex = Idx; + return PHI; + } + + return NULL; +} + +/// ForwardSwitchConditionToPHI - Try to forward the condition of a switch +/// instruction to a phi node dominated by the switch, if that would mean that +/// some of the destination blocks of the switch can be folded away. +/// Returns true if a change is made. +static bool ForwardSwitchConditionToPHI(SwitchInst *SI) { + typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap; + ForwardingNodesMap ForwardingNodes; + + for (SwitchInst::CaseIt I = SI->case_begin(), E = SI->case_end(); I != E; ++I) { + ConstantInt *CaseValue = I.getCaseValue(); + BasicBlock *CaseDest = I.getCaseSuccessor(); + + int PhiIndex; + PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest, + &PhiIndex); + if (!PHI) continue; + + ForwardingNodes[PHI].push_back(PhiIndex); + } + + bool Changed = false; + + for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(), + E = ForwardingNodes.end(); I != E; ++I) { + PHINode *Phi = I->first; + SmallVector<int,4> &Indexes = I->second; + + if (Indexes.size() < 2) continue; + + for (size_t I = 0, E = Indexes.size(); I != E; ++I) + Phi->setIncomingValue(Indexes[I], SI->getCondition()); + Changed = true; + } + + return Changed; +} + +bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) { + // If this switch is too complex to want to look at, ignore it. + if (!isValueEqualityComparison(SI)) + return false; + + BasicBlock *BB = SI->getParent(); + + // 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, Builder)) + return SimplifyCFG(BB) | true; + + Value *Cond = SI->getCondition(); + if (SelectInst *Select = dyn_cast<SelectInst>(Cond)) + if (SimplifySwitchOnSelect(SI, Select)) + return SimplifyCFG(BB) | true; + + // If the block only contains the switch, see if we can fold the block + // away into any preds. + BasicBlock::iterator BBI = BB->begin(); + // Ignore dbg intrinsics. + while (isa<DbgInfoIntrinsic>(BBI)) + ++BBI; + if (SI == &*BBI) + if (FoldValueComparisonIntoPredecessors(SI, Builder)) + return SimplifyCFG(BB) | true; + + // Try to transform the switch into an icmp and a branch. + if (TurnSwitchRangeIntoICmp(SI, Builder)) + return SimplifyCFG(BB) | true; + + // Remove unreachable cases. + if (EliminateDeadSwitchCases(SI)) + return SimplifyCFG(BB) | true; + + if (ForwardSwitchConditionToPHI(SI)) + return SimplifyCFG(BB) | true; + + return false; +} + +bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) { + BasicBlock *BB = IBI->getParent(); + bool Changed = false; + + // Eliminate redundant destinations. + SmallPtrSet<Value *, 8> Succs; + for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) { + BasicBlock *Dest = IBI->getDestination(i); + if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) { + Dest->removePredecessor(BB); + IBI->removeDestination(i); + --i; --e; + Changed = true; + } + } + + if (IBI->getNumDestinations() == 0) { + // If the indirectbr has no successors, change it to unreachable. + new UnreachableInst(IBI->getContext(), IBI); + EraseTerminatorInstAndDCECond(IBI); + return true; + } + + if (IBI->getNumDestinations() == 1) { + // If the indirectbr has one successor, change it to a direct branch. + BranchInst::Create(IBI->getDestination(0), IBI); + EraseTerminatorInstAndDCECond(IBI); + return true; + } + + if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) { + if (SimplifyIndirectBrOnSelect(IBI, SI)) + return SimplifyCFG(BB) | true; + } + return Changed; +} + +bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){ + BasicBlock *BB = BI->getParent(); + + // If the Terminator is the only non-phi instruction, simplify the block. + BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime(); + if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() && + TryToSimplifyUncondBranchFromEmptyBlock(BB)) + return true; + + // If the only instruction in the block is a seteq/setne comparison + // against a constant, try to simplify the block. + if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) + if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) { + for (++I; isa<DbgInfoIntrinsic>(I); ++I) + ; + if (I->isTerminator() && + TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder)) + return true; + } + + // If this basic block is ONLY a compare and a branch, and if a predecessor + // branches to us and our successor, fold the comparison into the + // predecessor and use logical operations to update the incoming value + // for PHI nodes in common successor. + if (FoldBranchToCommonDest(BI)) + return SimplifyCFG(BB) | true; + return false; +} + + +bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) { + BasicBlock *BB = BI->getParent(); + + // Conditional branch + if (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, Builder)) + return SimplifyCFG(BB) | true; + + // This block must be empty, except for the setcond inst, if it exists. + // Ignore dbg intrinsics. + BasicBlock::iterator I = BB->begin(); + // Ignore dbg intrinsics. + while (isa<DbgInfoIntrinsic>(I)) + ++I; + if (&*I == BI) { + if (FoldValueComparisonIntoPredecessors(BI, Builder)) + return SimplifyCFG(BB) | true; + } else if (&*I == cast<Instruction>(BI->getCondition())){ + ++I; + // Ignore dbg intrinsics. + while (isa<DbgInfoIntrinsic>(I)) + ++I; + if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder)) + return SimplifyCFG(BB) | true; + } + } + + // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction. + if (SimplifyBranchOnICmpChain(BI, TD, Builder)) + return true; + + // If this basic block is ONLY a compare and a branch, and if a predecessor + // branches to us and one of our successors, fold the comparison into the + // predecessor and use logical operations to pick the right destination. + if (FoldBranchToCommonDest(BI)) + return SimplifyCFG(BB) | true; + + // We have a conditional branch to two blocks that are only reachable + // from BI. 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. + if (BI->getSuccessor(0)->getSinglePredecessor() != 0) { + if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { + if (HoistThenElseCodeToIf(BI)) + return SimplifyCFG(BB) | true; + } else { + // If Successor #1 has multiple preds, we may be able to conditionally + // execute Successor #0 if it branches to successor #1. + TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator(); + if (Succ0TI->getNumSuccessors() == 1 && + Succ0TI->getSuccessor(0) == BI->getSuccessor(1)) + if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0))) + return SimplifyCFG(BB) | true; + } + } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) { + // If Successor #0 has multiple preds, we may be able to conditionally + // execute Successor #1 if it branches to successor #0. + TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator(); + if (Succ1TI->getNumSuccessors() == 1 && + Succ1TI->getSuccessor(0) == BI->getSuccessor(0)) + if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1))) + 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, TD)) + return SimplifyCFG(BB) | true; + + // Scan predecessor blocks for conditional branches. + 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 (SimplifyCondBranchToCondBranch(PBI, BI)) + return SimplifyCFG(BB) | true; + + return false; +} + +/// Check if passing a value to an instruction will cause undefined behavior. +static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) { + Constant *C = dyn_cast<Constant>(V); + if (!C) + return false; + + if (!I->hasOneUse()) // Only look at single-use instructions, for compile time + return false; + + if (C->isNullValue()) { + Instruction *Use = I->use_back(); + + // Now make sure that there are no instructions in between that can alter + // control flow (eg. calls) + for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i) + if (i == I->getParent()->end() || i->mayHaveSideEffects()) + return false; + + // Look through GEPs. A load from a GEP derived from NULL is still undefined + if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use)) + if (GEP->getPointerOperand() == I) + return passingValueIsAlwaysUndefined(V, GEP); + + // Look through bitcasts. + if (BitCastInst *BC = dyn_cast<BitCastInst>(Use)) + return passingValueIsAlwaysUndefined(V, BC); + + // Load from null is undefined. + if (LoadInst *LI = dyn_cast<LoadInst>(Use)) + return LI->getPointerAddressSpace() == 0; + + // Store to null is undefined. + if (StoreInst *SI = dyn_cast<StoreInst>(Use)) + return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I; + } + return false; +} + +/// If BB has an incoming value that will always trigger undefined behavior +/// (eg. null pointer dereference), remove the branch leading here. +static bool removeUndefIntroducingPredecessor(BasicBlock *BB) { + for (BasicBlock::iterator i = BB->begin(); + PHINode *PHI = dyn_cast<PHINode>(i); ++i) + for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) + if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) { + TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator(); + IRBuilder<> Builder(T); + if (BranchInst *BI = dyn_cast<BranchInst>(T)) { + BB->removePredecessor(PHI->getIncomingBlock(i)); + // Turn uncoditional branches into unreachables and remove the dead + // destination from conditional branches. + if (BI->isUnconditional()) + Builder.CreateUnreachable(); + else + Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) : + BI->getSuccessor(0)); + BI->eraseFromParent(); + return true; + } + // TODO: SwitchInst. + } + + return false; +} + +bool SimplifyCFGOpt::run(BasicBlock *BB) { + bool Changed = false; + + assert(BB && BB->getParent() && "Block not embedded in function!"); + assert(BB->getTerminator() && "Degenerate basic block encountered!"); + + // Remove basic blocks that have no predecessors (except the entry block)... + // or that just have themself as a predecessor. These are unreachable. + if ((pred_begin(BB) == pred_end(BB) && + BB != &BB->getParent()->getEntryBlock()) || + BB->getSinglePredecessor() == BB) { + DEBUG(dbgs() << "Removing BB: \n" << *BB); + DeleteDeadBlock(BB); + return true; + } + + // Check to see if we can constant propagate this terminator instruction + // away... + Changed |= ConstantFoldTerminator(BB, true); + + // Check for and eliminate duplicate PHI nodes in this block. + Changed |= EliminateDuplicatePHINodes(BB); + + // Check for and remove branches that will always cause undefined behavior. + Changed |= removeUndefIntroducingPredecessor(BB); + + // 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. + // + if (MergeBlockIntoPredecessor(BB)) + return true; + + IRBuilder<> Builder(BB); + + // 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, TD); + + Builder.SetInsertPoint(BB->getTerminator()); + if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { + if (BI->isUnconditional()) { + if (SimplifyUncondBranch(BI, Builder)) return true; + } else { + if (SimplifyCondBranch(BI, Builder)) return true; + } + } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { + if (SimplifyReturn(RI, Builder)) return true; + } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) { + if (SimplifyResume(RI, Builder)) return true; + } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { + if (SimplifySwitch(SI, Builder)) return true; + } else if (UnreachableInst *UI = + dyn_cast<UnreachableInst>(BB->getTerminator())) { + if (SimplifyUnreachable(UI)) return true; + } else if (IndirectBrInst *IBI = + dyn_cast<IndirectBrInst>(BB->getTerminator())) { + if (SimplifyIndirectBr(IBI)) return true; + } + + return Changed; +} + +/// 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. +/// +bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) { + return SimplifyCFGOpt(TD).run(BB); +} |
