//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file implements the machine instruction level if-conversion pass. // //===----------------------------------------------------------------------===// #define DEBUG_TYPE "ifcvt" #include "llvm/Function.h" #include "llvm/CodeGen/Passes.h" #include "llvm/CodeGen/MachineModuleInfo.h" #include "llvm/CodeGen/MachineFunctionPass.h" #include "llvm/Target/TargetInstrInfo.h" #include "llvm/Target/TargetLowering.h" #include "llvm/Target/TargetMachine.h" #include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/raw_ostream.h" #include "llvm/ADT/DepthFirstIterator.h" #include "llvm/ADT/Statistic.h" #include "llvm/ADT/STLExtras.h" using namespace llvm; // Hidden options for help debugging. static cl::opt IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden); static cl::opt IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden); static cl::opt IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden); static cl::opt DisableSimple("disable-ifcvt-simple", cl::init(false), cl::Hidden); static cl::opt DisableSimpleF("disable-ifcvt-simple-false", cl::init(false), cl::Hidden); static cl::opt DisableTriangle("disable-ifcvt-triangle", cl::init(false), cl::Hidden); static cl::opt DisableTriangleR("disable-ifcvt-triangle-rev", cl::init(false), cl::Hidden); static cl::opt DisableTriangleF("disable-ifcvt-triangle-false", cl::init(false), cl::Hidden); static cl::opt DisableTriangleFR("disable-ifcvt-triangle-false-rev", cl::init(false), cl::Hidden); static cl::opt DisableDiamond("disable-ifcvt-diamond", cl::init(false), cl::Hidden); STATISTIC(NumSimple, "Number of simple if-conversions performed"); STATISTIC(NumSimpleFalse, "Number of simple (F) if-conversions performed"); STATISTIC(NumTriangle, "Number of triangle if-conversions performed"); STATISTIC(NumTriangleRev, "Number of triangle (R) if-conversions performed"); STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed"); STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed"); STATISTIC(NumDiamonds, "Number of diamond if-conversions performed"); STATISTIC(NumIfConvBBs, "Number of if-converted blocks"); STATISTIC(NumDupBBs, "Number of duplicated blocks"); namespace { class VISIBILITY_HIDDEN IfConverter : public MachineFunctionPass { enum IfcvtKind { ICNotClassfied, // BB data valid, but not classified. ICSimpleFalse, // Same as ICSimple, but on the false path. ICSimple, // BB is entry of an one split, no rejoin sub-CFG. ICTriangleFRev, // Same as ICTriangleFalse, but false path rev condition. ICTriangleRev, // Same as ICTriangle, but true path rev condition. ICTriangleFalse, // Same as ICTriangle, but on the false path. ICTriangle, // BB is entry of a triangle sub-CFG. ICDiamond // BB is entry of a diamond sub-CFG. }; /// BBInfo - One per MachineBasicBlock, this is used to cache the result /// if-conversion feasibility analysis. This includes results from /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its /// classification, and common tail block of its successors (if it's a /// diamond shape), its size, whether it's predicable, and whether any /// instruction can clobber the 'would-be' predicate. /// /// IsDone - True if BB is not to be considered for ifcvt. /// IsBeingAnalyzed - True if BB is currently being analyzed. /// IsAnalyzed - True if BB has been analyzed (info is still valid). /// IsEnqueued - True if BB has been enqueued to be ifcvt'ed. /// IsBrAnalyzable - True if AnalyzeBranch() returns false. /// HasFallThrough - True if BB may fallthrough to the following BB. /// IsUnpredicable - True if BB is known to be unpredicable. /// ClobbersPred - True if BB could modify predicates (e.g. has /// cmp, call, etc.) /// NonPredSize - Number of non-predicated instructions. /// BB - Corresponding MachineBasicBlock. /// TrueBB / FalseBB- See AnalyzeBranch(). /// BrCond - Conditions for end of block conditional branches. /// Predicate - Predicate used in the BB. struct BBInfo { bool IsDone : 1; bool IsBeingAnalyzed : 1; bool IsAnalyzed : 1; bool IsEnqueued : 1; bool IsBrAnalyzable : 1; bool HasFallThrough : 1; bool IsUnpredicable : 1; bool CannotBeCopied : 1; bool ClobbersPred : 1; unsigned NonPredSize; MachineBasicBlock *BB; MachineBasicBlock *TrueBB; MachineBasicBlock *FalseBB; SmallVector BrCond; SmallVector Predicate; BBInfo() : IsDone(false), IsBeingAnalyzed(false), IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false), HasFallThrough(false), IsUnpredicable(false), CannotBeCopied(false), ClobbersPred(false), NonPredSize(0), BB(0), TrueBB(0), FalseBB(0) {} }; /// IfcvtToken - Record information about pending if-conversions to attemp: /// BBI - Corresponding BBInfo. /// Kind - Type of block. See IfcvtKind. /// NeedSubsumption - True if the to-be-predicated BB has already been /// predicated. /// NumDups - Number of instructions that would be duplicated due /// to this if-conversion. (For diamonds, the number of /// identical instructions at the beginnings of both /// paths). /// NumDups2 - For diamonds, the number of identical instructions /// at the ends of both paths. struct IfcvtToken { BBInfo &BBI; IfcvtKind Kind; bool NeedSubsumption; unsigned NumDups; unsigned NumDups2; IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0) : BBI(b), Kind(k), NeedSubsumption(s), NumDups(d), NumDups2(d2) {} }; /// Roots - Basic blocks that do not have successors. These are the starting /// points of Graph traversal. std::vector Roots; /// BBAnalysis - Results of if-conversion feasibility analysis indexed by /// basic block number. std::vector BBAnalysis; const TargetLowering *TLI; const TargetInstrInfo *TII; bool MadeChange; int FnNum; public: static char ID; IfConverter() : MachineFunctionPass(&ID), FnNum(-1) {} virtual bool runOnMachineFunction(MachineFunction &MF); virtual const char *getPassName() const { return "If Converter"; } private: bool ReverseBranchCondition(BBInfo &BBI); bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const; bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, bool FalseBranch, unsigned &Dups) const; bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI, unsigned &Dups1, unsigned &Dups2) const; void ScanInstructions(BBInfo &BBI); BBInfo &AnalyzeBlock(MachineBasicBlock *BB, std::vector &Tokens); bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl &Cond, bool isTriangle = false, bool RevBranch = false); bool AnalyzeBlocks(MachineFunction &MF, std::vector &Tokens); void InvalidatePreds(MachineBasicBlock *BB); void RemoveExtraEdges(BBInfo &BBI); bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind); bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind); bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, unsigned NumDups1, unsigned NumDups2); void PredicateBlock(BBInfo &BBI, MachineBasicBlock::iterator E, SmallVectorImpl &Cond); void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI, SmallVectorImpl &Cond, bool IgnoreBr = false); void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI); bool MeetIfcvtSizeLimit(unsigned Size) const { return Size > 0 && Size <= TLI->getIfCvtBlockSizeLimit(); } // blockAlwaysFallThrough - Block ends without a terminator. bool blockAlwaysFallThrough(BBInfo &BBI) const { return BBI.IsBrAnalyzable && BBI.TrueBB == NULL; } // IfcvtTokenCmp - Used to sort if-conversion candidates. static bool IfcvtTokenCmp(IfcvtToken *C1, IfcvtToken *C2) { int Incr1 = (C1->Kind == ICDiamond) ? -(int)(C1->NumDups + C1->NumDups2) : (int)C1->NumDups; int Incr2 = (C2->Kind == ICDiamond) ? -(int)(C2->NumDups + C2->NumDups2) : (int)C2->NumDups; if (Incr1 > Incr2) return true; else if (Incr1 == Incr2) { // Favors subsumption. if (C1->NeedSubsumption == false && C2->NeedSubsumption == true) return true; else if (C1->NeedSubsumption == C2->NeedSubsumption) { // Favors diamond over triangle, etc. if ((unsigned)C1->Kind < (unsigned)C2->Kind) return true; else if (C1->Kind == C2->Kind) return C1->BBI.BB->getNumber() < C2->BBI.BB->getNumber(); } } return false; } }; char IfConverter::ID = 0; } static RegisterPass X("if-converter", "If Converter"); FunctionPass *llvm::createIfConverterPass() { return new IfConverter(); } bool IfConverter::runOnMachineFunction(MachineFunction &MF) { TLI = MF.getTarget().getTargetLowering(); TII = MF.getTarget().getInstrInfo(); if (!TII) return false; DEBUG(errs() << "\nIfcvt: function (" << ++FnNum << ") \'" << MF.getFunction()->getName() << "\'"); if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) { DEBUG(errs() << " skipped\n"); return false; } DEBUG(errs() << "\n"); MF.RenumberBlocks(); BBAnalysis.resize(MF.getNumBlockIDs()); // Look for root nodes, i.e. blocks without successors. for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) if (I->succ_empty()) Roots.push_back(I); std::vector Tokens; MadeChange = false; unsigned NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds; while (IfCvtLimit == -1 || (int)NumIfCvts < IfCvtLimit) { // Do an initial analysis for each basic block and find all the potential // candidates to perform if-conversion. bool Change = AnalyzeBlocks(MF, Tokens); while (!Tokens.empty()) { IfcvtToken *Token = Tokens.back(); Tokens.pop_back(); BBInfo &BBI = Token->BBI; IfcvtKind Kind = Token->Kind; unsigned NumDups = Token->NumDups; unsigned NumDups2 = Token->NumDups2; delete Token; // If the block has been evicted out of the queue or it has already been // marked dead (due to it being predicated), then skip it. if (BBI.IsDone) BBI.IsEnqueued = false; if (!BBI.IsEnqueued) continue; BBI.IsEnqueued = false; bool RetVal = false; switch (Kind) { default: assert(false && "Unexpected!"); break; case ICSimple: case ICSimpleFalse: { bool isFalse = Kind == ICSimpleFalse; if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break; DEBUG(errs() << "Ifcvt (Simple" << (Kind == ICSimpleFalse ? " false" :"") << "): BB#" << BBI.BB->getNumber() << " (" << ((Kind == ICSimpleFalse) ? BBI.FalseBB->getNumber() : BBI.TrueBB->getNumber()) << ") "); RetVal = IfConvertSimple(BBI, Kind); DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n"); if (RetVal) { if (isFalse) NumSimpleFalse++; else NumSimple++; } break; } case ICTriangle: case ICTriangleRev: case ICTriangleFalse: case ICTriangleFRev: { bool isFalse = Kind == ICTriangleFalse; bool isRev = (Kind == ICTriangleRev || Kind == ICTriangleFRev); if (DisableTriangle && !isFalse && !isRev) break; if (DisableTriangleR && !isFalse && isRev) break; if (DisableTriangleF && isFalse && !isRev) break; if (DisableTriangleFR && isFalse && isRev) break; DEBUG(errs() << "Ifcvt (Triangle"); if (isFalse) DEBUG(errs() << " false"); if (isRev) DEBUG(errs() << " rev"); DEBUG(errs() << "): BB#" << BBI.BB->getNumber() << " (T:" << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber() << ") "); RetVal = IfConvertTriangle(BBI, Kind); DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n"); if (RetVal) { if (isFalse) { if (isRev) NumTriangleFRev++; else NumTriangleFalse++; } else { if (isRev) NumTriangleRev++; else NumTriangle++; } } break; } case ICDiamond: { if (DisableDiamond) break; DEBUG(errs() << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:" << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber() << ") "); RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2); DEBUG(errs() << (RetVal ? "succeeded!" : "failed!") << "\n"); if (RetVal) NumDiamonds++; break; } } Change |= RetVal; NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev + NumTriangleFalse + NumTriangleFRev + NumDiamonds; if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit) break; } if (!Change) break; MadeChange |= Change; } // Delete tokens in case of early exit. while (!Tokens.empty()) { IfcvtToken *Token = Tokens.back(); Tokens.pop_back(); delete Token; } Tokens.clear(); Roots.clear(); BBAnalysis.clear(); return MadeChange; } /// findFalseBlock - BB has a fallthrough. Find its 'false' successor given /// its 'true' successor. static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB, MachineBasicBlock *TrueBB) { for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(), E = BB->succ_end(); SI != E; ++SI) { MachineBasicBlock *SuccBB = *SI; if (SuccBB != TrueBB) return SuccBB; } return NULL; } /// ReverseBranchCondition - Reverse the condition of the end of the block /// branch. Swap block's 'true' and 'false' successors. bool IfConverter::ReverseBranchCondition(BBInfo &BBI) { if (!TII->ReverseBranchCondition(BBI.BrCond)) { TII->RemoveBranch(*BBI.BB); TII->InsertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond); std::swap(BBI.TrueBB, BBI.FalseBB); return true; } return false; } /// getNextBlock - Returns the next block in the function blocks ordering. If /// it is the end, returns NULL. static inline MachineBasicBlock *getNextBlock(MachineBasicBlock *BB) { MachineFunction::iterator I = BB; MachineFunction::iterator E = BB->getParent()->end(); if (++I == E) return NULL; return I; } /// ValidSimple - Returns true if the 'true' block (along with its /// predecessor) forms a valid simple shape for ifcvt. It also returns the /// number of instructions that the ifcvt would need to duplicate if performed /// in Dups. bool IfConverter::ValidSimple(BBInfo &TrueBBI, unsigned &Dups) const { Dups = 0; if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone) return false; if (TrueBBI.IsBrAnalyzable) return false; if (TrueBBI.BB->pred_size() > 1) { if (TrueBBI.CannotBeCopied || TrueBBI.NonPredSize > TLI->getIfCvtDupBlockSizeLimit()) return false; Dups = TrueBBI.NonPredSize; } return true; } /// ValidTriangle - Returns true if the 'true' and 'false' blocks (along /// with their common predecessor) forms a valid triangle shape for ifcvt. /// If 'FalseBranch' is true, it checks if 'true' block's false branch /// branches to the false branch rather than the other way around. It also /// returns the number of instructions that the ifcvt would need to duplicate /// if performed in 'Dups'. bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, bool FalseBranch, unsigned &Dups) const { Dups = 0; if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone) return false; if (TrueBBI.BB->pred_size() > 1) { if (TrueBBI.CannotBeCopied) return false; unsigned Size = TrueBBI.NonPredSize; if (TrueBBI.IsBrAnalyzable) { if (TrueBBI.TrueBB && TrueBBI.BrCond.empty()) // Ends with an unconditional branch. It will be removed. --Size; else { MachineBasicBlock *FExit = FalseBranch ? TrueBBI.TrueBB : TrueBBI.FalseBB; if (FExit) // Require a conditional branch ++Size; } } if (Size > TLI->getIfCvtDupBlockSizeLimit()) return false; Dups = Size; } MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB; if (!TExit && blockAlwaysFallThrough(TrueBBI)) { MachineFunction::iterator I = TrueBBI.BB; if (++I == TrueBBI.BB->getParent()->end()) return false; TExit = I; } return TExit && TExit == FalseBBI.BB; } static MachineBasicBlock::iterator firstNonBranchInst(MachineBasicBlock *BB, const TargetInstrInfo *TII) { MachineBasicBlock::iterator I = BB->end(); while (I != BB->begin()) { --I; if (!I->getDesc().isBranch()) break; } return I; } /// ValidDiamond - Returns true if the 'true' and 'false' blocks (along /// with their common predecessor) forms a valid diamond shape for ifcvt. bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI, unsigned &Dups1, unsigned &Dups2) const { Dups1 = Dups2 = 0; if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone || FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone) return false; MachineBasicBlock *TT = TrueBBI.TrueBB; MachineBasicBlock *FT = FalseBBI.TrueBB; if (!TT && blockAlwaysFallThrough(TrueBBI)) TT = getNextBlock(TrueBBI.BB); if (!FT && blockAlwaysFallThrough(FalseBBI)) FT = getNextBlock(FalseBBI.BB); if (TT != FT) return false; if (TT == NULL && (TrueBBI.IsBrAnalyzable || FalseBBI.IsBrAnalyzable)) return false; if (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1) return false; // FIXME: Allow true block to have an early exit? if (TrueBBI.FalseBB || FalseBBI.FalseBB || (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred)) return false; MachineBasicBlock::iterator TI = TrueBBI.BB->begin(); MachineBasicBlock::iterator FI = FalseBBI.BB->begin(); while (TI != TrueBBI.BB->end() && FI != FalseBBI.BB->end()) { if (!TI->isIdenticalTo(FI)) break; ++Dups1; ++TI; ++FI; } TI = firstNonBranchInst(TrueBBI.BB, TII); FI = firstNonBranchInst(FalseBBI.BB, TII); while (TI != TrueBBI.BB->begin() && FI != FalseBBI.BB->begin()) { if (!TI->isIdenticalTo(FI)) break; ++Dups2; --TI; --FI; } return true; } /// ScanInstructions - Scan all the instructions in the block to determine if /// the block is predicable. In most cases, that means all the instructions /// in the block are isPredicable(). Also checks if the block contains any /// instruction which can clobber a predicate (e.g. condition code register). /// If so, the block is not predicable unless it's the last instruction. void IfConverter::ScanInstructions(BBInfo &BBI) { if (BBI.IsDone) return; bool AlreadyPredicated = BBI.Predicate.size() > 0; // First analyze the end of BB branches. BBI.TrueBB = BBI.FalseBB = NULL; BBI.BrCond.clear(); BBI.IsBrAnalyzable = !TII->AnalyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond); BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == NULL; if (BBI.BrCond.size()) { // No false branch. This BB must end with a conditional branch and a // fallthrough. if (!BBI.FalseBB) BBI.FalseBB = findFalseBlock(BBI.BB, BBI.TrueBB); if (!BBI.FalseBB) { // Malformed bcc? True and false blocks are the same? BBI.IsUnpredicable = true; return; } } // Then scan all the instructions. BBI.NonPredSize = 0; BBI.ClobbersPred = false; for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end(); I != E; ++I) { const TargetInstrDesc &TID = I->getDesc(); if (TID.isNotDuplicable()) BBI.CannotBeCopied = true; bool isPredicated = TII->isPredicated(I); bool isCondBr = BBI.IsBrAnalyzable && TID.isConditionalBranch(); if (!isCondBr) { if (!isPredicated) BBI.NonPredSize++; else if (!AlreadyPredicated) { // FIXME: This instruction is already predicated before the // if-conversion pass. It's probably something like a conditional move. // Mark this block unpredicable for now. BBI.IsUnpredicable = true; return; } } if (BBI.ClobbersPred && !isPredicated) { // Predicate modification instruction should end the block (except for // already predicated instructions and end of block branches). if (isCondBr) { // A conditional branch is not predicable, but it may be eliminated. continue; } // Predicate may have been modified, the subsequent (currently) // unpredicated instructions cannot be correctly predicated. BBI.IsUnpredicable = true; return; } // FIXME: Make use of PredDefs? e.g. ADDC, SUBC sets predicates but are // still potentially predicable. std::vector PredDefs; if (TII->DefinesPredicate(I, PredDefs)) BBI.ClobbersPred = true; if (!TID.isPredicable()) { BBI.IsUnpredicable = true; return; } } } /// FeasibilityAnalysis - Determine if the block is a suitable candidate to be /// predicated by the specified predicate. bool IfConverter::FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl &Pred, bool isTriangle, bool RevBranch) { // If the block is dead or unpredicable, then it cannot be predicated. if (BBI.IsDone || BBI.IsUnpredicable) return false; // If it is already predicated, check if its predicate subsumes the new // predicate. if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred)) return false; if (BBI.BrCond.size()) { if (!isTriangle) return false; // Test predicate subsumption. SmallVector RevPred(Pred.begin(), Pred.end()); SmallVector Cond(BBI.BrCond.begin(), BBI.BrCond.end()); if (RevBranch) { if (TII->ReverseBranchCondition(Cond)) return false; } if (TII->ReverseBranchCondition(RevPred) || !TII->SubsumesPredicate(Cond, RevPred)) return false; } return true; } /// AnalyzeBlock - Analyze the structure of the sub-CFG starting from /// the specified block. Record its successors and whether it looks like an /// if-conversion candidate. IfConverter::BBInfo &IfConverter::AnalyzeBlock(MachineBasicBlock *BB, std::vector &Tokens) { BBInfo &BBI = BBAnalysis[BB->getNumber()]; if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed) return BBI; BBI.BB = BB; BBI.IsBeingAnalyzed = true; ScanInstructions(BBI); // Unanalyzable or ends with fallthrough or unconditional branch. if (!BBI.IsBrAnalyzable || BBI.BrCond.empty()) { BBI.IsBeingAnalyzed = false; BBI.IsAnalyzed = true; return BBI; } // Do not ifcvt if either path is a back edge to the entry block. if (BBI.TrueBB == BB || BBI.FalseBB == BB) { BBI.IsBeingAnalyzed = false; BBI.IsAnalyzed = true; return BBI; } // Do not ifcvt if true and false fallthrough blocks are the same. if (!BBI.FalseBB) { BBI.IsBeingAnalyzed = false; BBI.IsAnalyzed = true; return BBI; } BBInfo &TrueBBI = AnalyzeBlock(BBI.TrueBB, Tokens); BBInfo &FalseBBI = AnalyzeBlock(BBI.FalseBB, Tokens); if (TrueBBI.IsDone && FalseBBI.IsDone) { BBI.IsBeingAnalyzed = false; BBI.IsAnalyzed = true; return BBI; } SmallVector RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); bool CanRevCond = !TII->ReverseBranchCondition(RevCond); unsigned Dups = 0; unsigned Dups2 = 0; bool TNeedSub = TrueBBI.Predicate.size() > 0; bool FNeedSub = FalseBBI.Predicate.size() > 0; bool Enqueued = false; if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2) && MeetIfcvtSizeLimit(TrueBBI.NonPredSize - (Dups + Dups2)) && MeetIfcvtSizeLimit(FalseBBI.NonPredSize - (Dups + Dups2)) && FeasibilityAnalysis(TrueBBI, BBI.BrCond) && FeasibilityAnalysis(FalseBBI, RevCond)) { // Diamond: // EBB // / \_ // | | // TBB FBB // \ / // TailBB // Note TailBB can be empty. Tokens.push_back(new IfcvtToken(BBI, ICDiamond, TNeedSub|FNeedSub, Dups, Dups2)); Enqueued = true; } if (ValidTriangle(TrueBBI, FalseBBI, false, Dups) && MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) { // Triangle: // EBB // | \_ // | | // | TBB // | / // FBB Tokens.push_back(new IfcvtToken(BBI, ICTriangle, TNeedSub, Dups)); Enqueued = true; } if (ValidTriangle(TrueBBI, FalseBBI, true, Dups) && MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) { Tokens.push_back(new IfcvtToken(BBI, ICTriangleRev, TNeedSub, Dups)); Enqueued = true; } if (ValidSimple(TrueBBI, Dups) && MeetIfcvtSizeLimit(TrueBBI.NonPredSize) && FeasibilityAnalysis(TrueBBI, BBI.BrCond)) { // Simple (split, no rejoin): // EBB // | \_ // | | // | TBB---> exit // | // FBB Tokens.push_back(new IfcvtToken(BBI, ICSimple, TNeedSub, Dups)); Enqueued = true; } if (CanRevCond) { // Try the other path... if (ValidTriangle(FalseBBI, TrueBBI, false, Dups) && MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && FeasibilityAnalysis(FalseBBI, RevCond, true)) { Tokens.push_back(new IfcvtToken(BBI, ICTriangleFalse, FNeedSub, Dups)); Enqueued = true; } if (ValidTriangle(FalseBBI, TrueBBI, true, Dups) && MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && FeasibilityAnalysis(FalseBBI, RevCond, true, true)) { Tokens.push_back(new IfcvtToken(BBI, ICTriangleFRev, FNeedSub, Dups)); Enqueued = true; } if (ValidSimple(FalseBBI, Dups) && MeetIfcvtSizeLimit(FalseBBI.NonPredSize) && FeasibilityAnalysis(FalseBBI, RevCond)) { Tokens.push_back(new IfcvtToken(BBI, ICSimpleFalse, FNeedSub, Dups)); Enqueued = true; } } BBI.IsEnqueued = Enqueued; BBI.IsBeingAnalyzed = false; BBI.IsAnalyzed = true; return BBI; } /// AnalyzeBlocks - Analyze all blocks and find entries for all if-conversion /// candidates. It returns true if any CFG restructuring is done to expose more /// if-conversion opportunities. bool IfConverter::AnalyzeBlocks(MachineFunction &MF, std::vector &Tokens) { bool Change = false; std::set Visited; for (unsigned i = 0, e = Roots.size(); i != e; ++i) { for (idf_ext_iterator I=idf_ext_begin(Roots[i],Visited), E = idf_ext_end(Roots[i], Visited); I != E; ++I) { MachineBasicBlock *BB = *I; AnalyzeBlock(BB, Tokens); } } // Sort to favor more complex ifcvt scheme. std::stable_sort(Tokens.begin(), Tokens.end(), IfcvtTokenCmp); return Change; } /// canFallThroughTo - Returns true either if ToBB is the next block after BB or /// that all the intervening blocks are empty (given BB can fall through to its /// next block). static bool canFallThroughTo(MachineBasicBlock *BB, MachineBasicBlock *ToBB) { MachineFunction::iterator I = BB; MachineFunction::iterator TI = ToBB; MachineFunction::iterator E = BB->getParent()->end(); while (++I != TI) if (I == E || !I->empty()) return false; return true; } /// InvalidatePreds - Invalidate predecessor BB info so it would be re-analyzed /// to determine if it can be if-converted. If predecessor is already enqueued, /// dequeue it! void IfConverter::InvalidatePreds(MachineBasicBlock *BB) { for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(), E = BB->pred_end(); PI != E; ++PI) { BBInfo &PBBI = BBAnalysis[(*PI)->getNumber()]; if (PBBI.IsDone || PBBI.BB == BB) continue; PBBI.IsAnalyzed = false; PBBI.IsEnqueued = false; } } /// InsertUncondBranch - Inserts an unconditional branch from BB to ToBB. /// static void InsertUncondBranch(MachineBasicBlock *BB, MachineBasicBlock *ToBB, const TargetInstrInfo *TII) { SmallVector NoCond; TII->InsertBranch(*BB, ToBB, NULL, NoCond); } /// RemoveExtraEdges - Remove true / false edges if either / both are no longer /// successors. void IfConverter::RemoveExtraEdges(BBInfo &BBI) { MachineBasicBlock *TBB = NULL, *FBB = NULL; SmallVector Cond; if (!TII->AnalyzeBranch(*BBI.BB, TBB, FBB, Cond)) BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty()); } /// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG. /// bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) { BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; BBInfo *CvtBBI = &TrueBBI; BBInfo *NextBBI = &FalseBBI; SmallVector Cond(BBI.BrCond.begin(), BBI.BrCond.end()); if (Kind == ICSimpleFalse) std::swap(CvtBBI, NextBBI); if (CvtBBI->IsDone || (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) { // Something has changed. It's no longer safe to predicate this block. BBI.IsAnalyzed = false; CvtBBI->IsAnalyzed = false; return false; } if (Kind == ICSimpleFalse) if (TII->ReverseBranchCondition(Cond)) assert(false && "Unable to reverse branch condition!"); if (CvtBBI->BB->pred_size() > 1) { BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); // Copy instructions in the true block, predicate them, and add them to // the entry block. CopyAndPredicateBlock(BBI, *CvtBBI, Cond); } else { PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond); // Merge converted block into entry block. BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); MergeBlocks(BBI, *CvtBBI); } bool IterIfcvt = true; if (!canFallThroughTo(BBI.BB, NextBBI->BB)) { InsertUncondBranch(BBI.BB, NextBBI->BB, TII); BBI.HasFallThrough = false; // Now ifcvt'd block will look like this: // BB: // ... // t, f = cmp // if t op // b BBf // // We cannot further ifcvt this block because the unconditional branch // will have to be predicated on the new condition, that will not be // available if cmp executes. IterIfcvt = false; } RemoveExtraEdges(BBI); // Update block info. BB can be iteratively if-converted. if (!IterIfcvt) BBI.IsDone = true; InvalidatePreds(BBI.BB); CvtBBI->IsDone = true; // FIXME: Must maintain LiveIns. return true; } /// IfConvertTriangle - If convert a triangle sub-CFG. /// bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) { BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; BBInfo *CvtBBI = &TrueBBI; BBInfo *NextBBI = &FalseBBI; SmallVector Cond(BBI.BrCond.begin(), BBI.BrCond.end()); if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) std::swap(CvtBBI, NextBBI); if (CvtBBI->IsDone || (CvtBBI->CannotBeCopied && CvtBBI->BB->pred_size() > 1)) { // Something has changed. It's no longer safe to predicate this block. BBI.IsAnalyzed = false; CvtBBI->IsAnalyzed = false; return false; } if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) if (TII->ReverseBranchCondition(Cond)) assert(false && "Unable to reverse branch condition!"); if (Kind == ICTriangleRev || Kind == ICTriangleFRev) { if (ReverseBranchCondition(*CvtBBI)) { // BB has been changed, modify its predecessors (except for this // one) so they don't get ifcvt'ed based on bad intel. for (MachineBasicBlock::pred_iterator PI = CvtBBI->BB->pred_begin(), E = CvtBBI->BB->pred_end(); PI != E; ++PI) { MachineBasicBlock *PBB = *PI; if (PBB == BBI.BB) continue; BBInfo &PBBI = BBAnalysis[PBB->getNumber()]; if (PBBI.IsEnqueued) { PBBI.IsAnalyzed = false; PBBI.IsEnqueued = false; } } } } bool HasEarlyExit = CvtBBI->FalseBB != NULL; bool DupBB = CvtBBI->BB->pred_size() > 1; if (DupBB) { BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); // Copy instructions in the true block, predicate them, and add them to // the entry block. CopyAndPredicateBlock(BBI, *CvtBBI, Cond, true); } else { // Predicate the 'true' block after removing its branch. CvtBBI->NonPredSize -= TII->RemoveBranch(*CvtBBI->BB); PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond); // Now merge the entry of the triangle with the true block. BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); MergeBlocks(BBI, *CvtBBI); } // If 'true' block has a 'false' successor, add an exit branch to it. if (HasEarlyExit) { SmallVector RevCond(CvtBBI->BrCond.begin(), CvtBBI->BrCond.end()); if (TII->ReverseBranchCondition(RevCond)) assert(false && "Unable to reverse branch condition!"); TII->InsertBranch(*BBI.BB, CvtBBI->FalseBB, NULL, RevCond); BBI.BB->addSuccessor(CvtBBI->FalseBB); } // Merge in the 'false' block if the 'false' block has no other // predecessors. Otherwise, add an unconditional branch to 'false'. bool FalseBBDead = false; bool IterIfcvt = true; bool isFallThrough = canFallThroughTo(BBI.BB, NextBBI->BB); if (!isFallThrough) { // Only merge them if the true block does not fallthrough to the false // block. By not merging them, we make it possible to iteratively // ifcvt the blocks. if (!HasEarlyExit && NextBBI->BB->pred_size() == 1 && !NextBBI->HasFallThrough) { MergeBlocks(BBI, *NextBBI); FalseBBDead = true; } else { InsertUncondBranch(BBI.BB, NextBBI->BB, TII); BBI.HasFallThrough = false; } // Mixed predicated and unpredicated code. This cannot be iteratively // predicated. IterIfcvt = false; } RemoveExtraEdges(BBI); // Update block info. BB can be iteratively if-converted. if (!IterIfcvt) BBI.IsDone = true; InvalidatePreds(BBI.BB); CvtBBI->IsDone = true; if (FalseBBDead) NextBBI->IsDone = true; // FIXME: Must maintain LiveIns. return true; } /// IfConvertDiamond - If convert a diamond sub-CFG. /// bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, unsigned NumDups1, unsigned NumDups2) { BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; MachineBasicBlock *TailBB = TrueBBI.TrueBB; // True block must fall through or end with an unanalyzable terminator. if (!TailBB) { if (blockAlwaysFallThrough(TrueBBI)) TailBB = FalseBBI.TrueBB; assert((TailBB || !TrueBBI.IsBrAnalyzable) && "Unexpected!"); } if (TrueBBI.IsDone || FalseBBI.IsDone || TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1) { // Something has changed. It's no longer safe to predicate these blocks. BBI.IsAnalyzed = false; TrueBBI.IsAnalyzed = false; FalseBBI.IsAnalyzed = false; return false; } // Merge the 'true' and 'false' blocks by copying the instructions // from the 'false' block to the 'true' block. That is, unless the true // block would clobber the predicate, in that case, do the opposite. BBInfo *BBI1 = &TrueBBI; BBInfo *BBI2 = &FalseBBI; SmallVector RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); if (TII->ReverseBranchCondition(RevCond)) assert(false && "Unable to reverse branch condition!"); SmallVector *Cond1 = &BBI.BrCond; SmallVector *Cond2 = &RevCond; // Figure out the more profitable ordering. bool DoSwap = false; if (TrueBBI.ClobbersPred && !FalseBBI.ClobbersPred) DoSwap = true; else if (TrueBBI.ClobbersPred == FalseBBI.ClobbersPred) { if (TrueBBI.NonPredSize > FalseBBI.NonPredSize) DoSwap = true; } if (DoSwap) { std::swap(BBI1, BBI2); std::swap(Cond1, Cond2); } // Remove the conditional branch from entry to the blocks. BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); // Remove the duplicated instructions at the beginnings of both paths. MachineBasicBlock::iterator DI1 = BBI1->BB->begin(); MachineBasicBlock::iterator DI2 = BBI2->BB->begin(); BBI1->NonPredSize -= NumDups1; BBI2->NonPredSize -= NumDups1; while (NumDups1 != 0) { ++DI1; ++DI2; --NumDups1; } BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1); BBI2->BB->erase(BBI2->BB->begin(), DI2); // Predicate the 'true' block after removing its branch. BBI1->NonPredSize -= TII->RemoveBranch(*BBI1->BB); DI1 = BBI1->BB->end(); for (unsigned i = 0; i != NumDups2; ++i) --DI1; BBI1->BB->erase(DI1, BBI1->BB->end()); PredicateBlock(*BBI1, BBI1->BB->end(), *Cond1); // Predicate the 'false' block. BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB); DI2 = BBI2->BB->end(); while (NumDups2 != 0) { --DI2; --NumDups2; } PredicateBlock(*BBI2, DI2, *Cond2); // Merge the true block into the entry of the diamond. MergeBlocks(BBI, *BBI1); MergeBlocks(BBI, *BBI2); // If the if-converted block falls through or unconditionally branches into // the tail block, and the tail block does not have other predecessors, then // fold the tail block in as well. Otherwise, unless it falls through to the // tail, add a unconditional branch to it. if (TailBB) { BBInfo TailBBI = BBAnalysis[TailBB->getNumber()]; if (TailBB->pred_size() == 1 && !TailBBI.HasFallThrough) { BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB); MergeBlocks(BBI, TailBBI); TailBBI.IsDone = true; } else { InsertUncondBranch(BBI.BB, TailBB, TII); BBI.HasFallThrough = false; } } RemoveExtraEdges(BBI); // Update block info. BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true; InvalidatePreds(BBI.BB); // FIXME: Must maintain LiveIns. return true; } /// PredicateBlock - Predicate instructions from the start of the block to the /// specified end with the specified condition. void IfConverter::PredicateBlock(BBInfo &BBI, MachineBasicBlock::iterator E, SmallVectorImpl &Cond) { for (MachineBasicBlock::iterator I = BBI.BB->begin(); I != E; ++I) { if (TII->isPredicated(I)) continue; if (!TII->PredicateInstruction(I, Cond)) { #ifndef NDEBUG cerr << "Unable to predicate " << *I << "!\n"; #endif llvm_unreachable(0); } } std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate)); BBI.IsAnalyzed = false; BBI.NonPredSize = 0; NumIfConvBBs++; } /// CopyAndPredicateBlock - Copy and predicate instructions from source BB to /// the destination block. Skip end of block branches if IgnoreBr is true. void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI, SmallVectorImpl &Cond, bool IgnoreBr) { MachineFunction &MF = *ToBBI.BB->getParent(); for (MachineBasicBlock::iterator I = FromBBI.BB->begin(), E = FromBBI.BB->end(); I != E; ++I) { const TargetInstrDesc &TID = I->getDesc(); bool isPredicated = TII->isPredicated(I); // Do not copy the end of the block branches. if (IgnoreBr && !isPredicated && TID.isBranch()) break; MachineInstr *MI = MF.CloneMachineInstr(I); ToBBI.BB->insert(ToBBI.BB->end(), MI); ToBBI.NonPredSize++; if (!isPredicated) if (!TII->PredicateInstruction(MI, Cond)) { #ifndef NDEBUG cerr << "Unable to predicate " << *I << "!\n"; #endif llvm_unreachable(0); } } std::vector Succs(FromBBI.BB->succ_begin(), FromBBI.BB->succ_end()); MachineBasicBlock *NBB = getNextBlock(FromBBI.BB); MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL; for (unsigned i = 0, e = Succs.size(); i != e; ++i) { MachineBasicBlock *Succ = Succs[i]; // Fallthrough edge can't be transferred. if (Succ == FallThrough) continue; ToBBI.BB->addSuccessor(Succ); } std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(), std::back_inserter(ToBBI.Predicate)); std::copy(Cond.begin(), Cond.end(), std::back_inserter(ToBBI.Predicate)); ToBBI.ClobbersPred |= FromBBI.ClobbersPred; ToBBI.IsAnalyzed = false; NumDupBBs++; } /// MergeBlocks - Move all instructions from FromBB to the end of ToBB. /// void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI) { ToBBI.BB->splice(ToBBI.BB->end(), FromBBI.BB, FromBBI.BB->begin(), FromBBI.BB->end()); // Redirect all branches to FromBB to ToBB. std::vector Preds(FromBBI.BB->pred_begin(), FromBBI.BB->pred_end()); for (unsigned i = 0, e = Preds.size(); i != e; ++i) { MachineBasicBlock *Pred = Preds[i]; if (Pred == ToBBI.BB) continue; Pred->ReplaceUsesOfBlockWith(FromBBI.BB, ToBBI.BB); } std::vector Succs(FromBBI.BB->succ_begin(), FromBBI.BB->succ_end()); MachineBasicBlock *NBB = getNextBlock(FromBBI.BB); MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : NULL; for (unsigned i = 0, e = Succs.size(); i != e; ++i) { MachineBasicBlock *Succ = Succs[i]; // Fallthrough edge can't be transferred. if (Succ == FallThrough) continue; FromBBI.BB->removeSuccessor(Succ); ToBBI.BB->addSuccessor(Succ); } // Now FromBBI always falls through to the next block! if (NBB && !FromBBI.BB->isSuccessor(NBB)) FromBBI.BB->addSuccessor(NBB); std::copy(FromBBI.Predicate.begin(), FromBBI.Predicate.end(), std::back_inserter(ToBBI.Predicate)); FromBBI.Predicate.clear(); ToBBI.NonPredSize += FromBBI.NonPredSize; FromBBI.NonPredSize = 0; ToBBI.ClobbersPred |= FromBBI.ClobbersPred; ToBBI.HasFallThrough = FromBBI.HasFallThrough; ToBBI.IsAnalyzed = false; FromBBI.IsAnalyzed = false; }