| //===- IfConversion.cpp - Machine code if conversion pass -----------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements the machine instruction level if-conversion pass, which |
| // tries to convert conditional branches into predicated instructions. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "BranchFolding.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/ScopeExit.h" |
| #include "llvm/ADT/SmallSet.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/SparseSet.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/iterator_range.h" |
| #include "llvm/Analysis/ProfileSummaryInfo.h" |
| #include "llvm/CodeGen/LivePhysRegs.h" |
| #include "llvm/CodeGen/MachineBasicBlock.h" |
| #include "llvm/CodeGen/MachineBlockFrequencyInfo.h" |
| #include "llvm/CodeGen/MachineBranchProbabilityInfo.h" |
| #include "llvm/CodeGen/MachineFunction.h" |
| #include "llvm/CodeGen/MachineFunctionPass.h" |
| #include "llvm/CodeGen/MachineInstr.h" |
| #include "llvm/CodeGen/MachineInstrBuilder.h" |
| #include "llvm/CodeGen/MachineModuleInfo.h" |
| #include "llvm/CodeGen/MachineOperand.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| #include "llvm/CodeGen/MBFIWrapper.h" |
| #include "llvm/CodeGen/TargetInstrInfo.h" |
| #include "llvm/CodeGen/TargetLowering.h" |
| #include "llvm/CodeGen/TargetRegisterInfo.h" |
| #include "llvm/CodeGen/TargetSchedule.h" |
| #include "llvm/CodeGen/TargetSubtargetInfo.h" |
| #include "llvm/IR/Attributes.h" |
| #include "llvm/IR/DebugLoc.h" |
| #include "llvm/InitializePasses.h" |
| #include "llvm/MC/MCRegisterInfo.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/BranchProbability.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/ErrorHandling.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include <algorithm> |
| #include <cassert> |
| #include <functional> |
| #include <iterator> |
| #include <memory> |
| #include <utility> |
| #include <vector> |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "if-converter" |
| |
| // Hidden options for help debugging. |
| static cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden); |
| static cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden); |
| static cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden); |
| static cl::opt<bool> DisableSimple("disable-ifcvt-simple", |
| cl::init(false), cl::Hidden); |
| static cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false", |
| cl::init(false), cl::Hidden); |
| static cl::opt<bool> DisableTriangle("disable-ifcvt-triangle", |
| cl::init(false), cl::Hidden); |
| static cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev", |
| cl::init(false), cl::Hidden); |
| static cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false", |
| cl::init(false), cl::Hidden); |
| static cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev", |
| cl::init(false), cl::Hidden); |
| static cl::opt<bool> DisableDiamond("disable-ifcvt-diamond", |
| cl::init(false), cl::Hidden); |
| static cl::opt<bool> DisableForkedDiamond("disable-ifcvt-forked-diamond", |
| cl::init(false), cl::Hidden); |
| static cl::opt<bool> IfCvtBranchFold("ifcvt-branch-fold", |
| cl::init(true), 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(NumForkedDiamonds, "Number of forked-diamond if-conversions performed"); |
| STATISTIC(NumIfConvBBs, "Number of if-converted blocks"); |
| STATISTIC(NumDupBBs, "Number of duplicated blocks"); |
| STATISTIC(NumUnpred, "Number of true blocks of diamonds unpredicated"); |
| |
| namespace { |
| |
| class 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. |
| ICForkedDiamond // BB is entry of an almost diamond sub-CFG, with a |
| // common tail that can be shared. |
| }; |
| |
| /// 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. |
| /// ExtraCost - Extra cost for multi-cycle instructions. |
| /// ExtraCost2 - Some instructions are slower when predicated |
| /// 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 IsBrReversible : 1; |
| bool HasFallThrough : 1; |
| bool IsUnpredicable : 1; |
| bool CannotBeCopied : 1; |
| bool ClobbersPred : 1; |
| unsigned NonPredSize = 0; |
| unsigned ExtraCost = 0; |
| unsigned ExtraCost2 = 0; |
| MachineBasicBlock *BB = nullptr; |
| MachineBasicBlock *TrueBB = nullptr; |
| MachineBasicBlock *FalseBB = nullptr; |
| SmallVector<MachineOperand, 4> BrCond; |
| SmallVector<MachineOperand, 4> Predicate; |
| |
| BBInfo() : IsDone(false), IsBeingAnalyzed(false), |
| IsAnalyzed(false), IsEnqueued(false), IsBrAnalyzable(false), |
| IsBrReversible(false), HasFallThrough(false), |
| IsUnpredicable(false), CannotBeCopied(false), |
| ClobbersPred(false) {} |
| }; |
| |
| /// Record information about pending if-conversions to attempt: |
| /// 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; |
| unsigned NumDups; |
| unsigned NumDups2; |
| bool NeedSubsumption : 1; |
| bool TClobbersPred : 1; |
| bool FClobbersPred : 1; |
| |
| IfcvtToken(BBInfo &b, IfcvtKind k, bool s, unsigned d, unsigned d2 = 0, |
| bool tc = false, bool fc = false) |
| : BBI(b), Kind(k), NumDups(d), NumDups2(d2), NeedSubsumption(s), |
| TClobbersPred(tc), FClobbersPred(fc) {} |
| }; |
| |
| /// Results of if-conversion feasibility analysis indexed by basic block |
| /// number. |
| std::vector<BBInfo> BBAnalysis; |
| TargetSchedModel SchedModel; |
| |
| const TargetLoweringBase *TLI; |
| const TargetInstrInfo *TII; |
| const TargetRegisterInfo *TRI; |
| const MachineBranchProbabilityInfo *MBPI; |
| MachineRegisterInfo *MRI; |
| |
| LivePhysRegs Redefs; |
| |
| bool PreRegAlloc; |
| bool MadeChange; |
| int FnNum = -1; |
| std::function<bool(const MachineFunction &)> PredicateFtor; |
| |
| public: |
| static char ID; |
| |
| IfConverter(std::function<bool(const MachineFunction &)> Ftor = nullptr) |
| : MachineFunctionPass(ID), PredicateFtor(std::move(Ftor)) { |
| initializeIfConverterPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addRequired<MachineBlockFrequencyInfo>(); |
| AU.addRequired<MachineBranchProbabilityInfo>(); |
| AU.addRequired<ProfileSummaryInfoWrapperPass>(); |
| MachineFunctionPass::getAnalysisUsage(AU); |
| } |
| |
| bool runOnMachineFunction(MachineFunction &MF) override; |
| |
| MachineFunctionProperties getRequiredProperties() const override { |
| return MachineFunctionProperties().set( |
| MachineFunctionProperties::Property::NoVRegs); |
| } |
| |
| private: |
| bool reverseBranchCondition(BBInfo &BBI) const; |
| bool ValidSimple(BBInfo &TrueBBI, unsigned &Dups, |
| BranchProbability Prediction) const; |
| bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI, |
| bool FalseBranch, unsigned &Dups, |
| BranchProbability Prediction) const; |
| bool CountDuplicatedInstructions( |
| MachineBasicBlock::iterator &TIB, MachineBasicBlock::iterator &FIB, |
| MachineBasicBlock::iterator &TIE, MachineBasicBlock::iterator &FIE, |
| unsigned &Dups1, unsigned &Dups2, |
| MachineBasicBlock &TBB, MachineBasicBlock &FBB, |
| bool SkipUnconditionalBranches) const; |
| bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI, |
| unsigned &Dups1, unsigned &Dups2, |
| BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const; |
| bool ValidForkedDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI, |
| unsigned &Dups1, unsigned &Dups2, |
| BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const; |
| void AnalyzeBranches(BBInfo &BBI); |
| void ScanInstructions(BBInfo &BBI, |
| MachineBasicBlock::iterator &Begin, |
| MachineBasicBlock::iterator &End, |
| bool BranchUnpredicable = false) const; |
| bool RescanInstructions( |
| MachineBasicBlock::iterator &TIB, MachineBasicBlock::iterator &FIB, |
| MachineBasicBlock::iterator &TIE, MachineBasicBlock::iterator &FIE, |
| BBInfo &TrueBBI, BBInfo &FalseBBI) const; |
| void AnalyzeBlock(MachineBasicBlock &MBB, |
| std::vector<std::unique_ptr<IfcvtToken>> &Tokens); |
| bool FeasibilityAnalysis(BBInfo &BBI, SmallVectorImpl<MachineOperand> &Pred, |
| bool isTriangle = false, bool RevBranch = false, |
| bool hasCommonTail = false); |
| void AnalyzeBlocks(MachineFunction &MF, |
| std::vector<std::unique_ptr<IfcvtToken>> &Tokens); |
| void InvalidatePreds(MachineBasicBlock &MBB); |
| bool IfConvertSimple(BBInfo &BBI, IfcvtKind Kind); |
| bool IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind); |
| bool IfConvertDiamondCommon(BBInfo &BBI, BBInfo &TrueBBI, BBInfo &FalseBBI, |
| unsigned NumDups1, unsigned NumDups2, |
| bool TClobbersPred, bool FClobbersPred, |
| bool RemoveBranch, bool MergeAddEdges); |
| bool IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, |
| unsigned NumDups1, unsigned NumDups2, |
| bool TClobbers, bool FClobbers); |
| bool IfConvertForkedDiamond(BBInfo &BBI, IfcvtKind Kind, |
| unsigned NumDups1, unsigned NumDups2, |
| bool TClobbers, bool FClobbers); |
| void PredicateBlock(BBInfo &BBI, |
| MachineBasicBlock::iterator E, |
| SmallVectorImpl<MachineOperand> &Cond, |
| SmallSet<MCPhysReg, 4> *LaterRedefs = nullptr); |
| void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI, |
| SmallVectorImpl<MachineOperand> &Cond, |
| bool IgnoreBr = false); |
| void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges = true); |
| |
| bool MeetIfcvtSizeLimit(MachineBasicBlock &BB, |
| unsigned Cycle, unsigned Extra, |
| BranchProbability Prediction) const { |
| return Cycle > 0 && TII->isProfitableToIfCvt(BB, Cycle, Extra, |
| Prediction); |
| } |
| |
| bool MeetIfcvtSizeLimit(BBInfo &TBBInfo, BBInfo &FBBInfo, |
| MachineBasicBlock &CommBB, unsigned Dups, |
| BranchProbability Prediction, bool Forked) const { |
| const MachineFunction &MF = *TBBInfo.BB->getParent(); |
| if (MF.getFunction().hasMinSize()) { |
| MachineBasicBlock::iterator TIB = TBBInfo.BB->begin(); |
| MachineBasicBlock::iterator FIB = FBBInfo.BB->begin(); |
| MachineBasicBlock::iterator TIE = TBBInfo.BB->end(); |
| MachineBasicBlock::iterator FIE = FBBInfo.BB->end(); |
| |
| unsigned Dups1 = 0, Dups2 = 0; |
| if (!CountDuplicatedInstructions(TIB, FIB, TIE, FIE, Dups1, Dups2, |
| *TBBInfo.BB, *FBBInfo.BB, |
| /*SkipUnconditionalBranches*/ true)) |
| llvm_unreachable("should already have been checked by ValidDiamond"); |
| |
| unsigned BranchBytes = 0; |
| unsigned CommonBytes = 0; |
| |
| // Count common instructions at the start of the true and false blocks. |
| for (auto &I : make_range(TBBInfo.BB->begin(), TIB)) { |
| LLVM_DEBUG(dbgs() << "Common inst: " << I); |
| CommonBytes += TII->getInstSizeInBytes(I); |
| } |
| for (auto &I : make_range(FBBInfo.BB->begin(), FIB)) { |
| LLVM_DEBUG(dbgs() << "Common inst: " << I); |
| CommonBytes += TII->getInstSizeInBytes(I); |
| } |
| |
| // Count instructions at the end of the true and false blocks, after |
| // the ones we plan to predicate. Analyzable branches will be removed |
| // (unless this is a forked diamond), and all other instructions are |
| // common between the two blocks. |
| for (auto &I : make_range(TIE, TBBInfo.BB->end())) { |
| if (I.isBranch() && TBBInfo.IsBrAnalyzable && !Forked) { |
| LLVM_DEBUG(dbgs() << "Saving branch: " << I); |
| BranchBytes += TII->predictBranchSizeForIfCvt(I); |
| } else { |
| LLVM_DEBUG(dbgs() << "Common inst: " << I); |
| CommonBytes += TII->getInstSizeInBytes(I); |
| } |
| } |
| for (auto &I : make_range(FIE, FBBInfo.BB->end())) { |
| if (I.isBranch() && FBBInfo.IsBrAnalyzable && !Forked) { |
| LLVM_DEBUG(dbgs() << "Saving branch: " << I); |
| BranchBytes += TII->predictBranchSizeForIfCvt(I); |
| } else { |
| LLVM_DEBUG(dbgs() << "Common inst: " << I); |
| CommonBytes += TII->getInstSizeInBytes(I); |
| } |
| } |
| for (auto &I : CommBB.terminators()) { |
| if (I.isBranch()) { |
| LLVM_DEBUG(dbgs() << "Saving branch: " << I); |
| BranchBytes += TII->predictBranchSizeForIfCvt(I); |
| } |
| } |
| |
| // The common instructions in one branch will be eliminated, halving |
| // their code size. |
| CommonBytes /= 2; |
| |
| // Count the instructions which we need to predicate. |
| unsigned NumPredicatedInstructions = 0; |
| for (auto &I : make_range(TIB, TIE)) { |
| if (!I.isDebugInstr()) { |
| LLVM_DEBUG(dbgs() << "Predicating: " << I); |
| NumPredicatedInstructions++; |
| } |
| } |
| for (auto &I : make_range(FIB, FIE)) { |
| if (!I.isDebugInstr()) { |
| LLVM_DEBUG(dbgs() << "Predicating: " << I); |
| NumPredicatedInstructions++; |
| } |
| } |
| |
| // Even though we're optimising for size at the expense of performance, |
| // avoid creating really long predicated blocks. |
| if (NumPredicatedInstructions > 15) |
| return false; |
| |
| // Some targets (e.g. Thumb2) need to insert extra instructions to |
| // start predicated blocks. |
| unsigned ExtraPredicateBytes = TII->extraSizeToPredicateInstructions( |
| MF, NumPredicatedInstructions); |
| |
| LLVM_DEBUG(dbgs() << "MeetIfcvtSizeLimit(BranchBytes=" << BranchBytes |
| << ", CommonBytes=" << CommonBytes |
| << ", NumPredicatedInstructions=" |
| << NumPredicatedInstructions |
| << ", ExtraPredicateBytes=" << ExtraPredicateBytes |
| << ")\n"); |
| return (BranchBytes + CommonBytes) > ExtraPredicateBytes; |
| } else { |
| unsigned TCycle = TBBInfo.NonPredSize + TBBInfo.ExtraCost - Dups; |
| unsigned FCycle = FBBInfo.NonPredSize + FBBInfo.ExtraCost - Dups; |
| bool Res = TCycle > 0 && FCycle > 0 && |
| TII->isProfitableToIfCvt( |
| *TBBInfo.BB, TCycle, TBBInfo.ExtraCost2, *FBBInfo.BB, |
| FCycle, FBBInfo.ExtraCost2, Prediction); |
| LLVM_DEBUG(dbgs() << "MeetIfcvtSizeLimit(TCycle=" << TCycle |
| << ", FCycle=" << FCycle |
| << ", TExtra=" << TBBInfo.ExtraCost2 << ", FExtra=" |
| << FBBInfo.ExtraCost2 << ") = " << Res << "\n"); |
| return Res; |
| } |
| } |
| |
| /// Returns true if Block ends without a terminator. |
| bool blockAlwaysFallThrough(BBInfo &BBI) const { |
| return BBI.IsBrAnalyzable && BBI.TrueBB == nullptr; |
| } |
| |
| /// Used to sort if-conversion candidates. |
| static bool IfcvtTokenCmp(const std::unique_ptr<IfcvtToken> &C1, |
| const std::unique_ptr<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 && C2->NeedSubsumption) |
| 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; |
| } |
| }; |
| |
| } // end anonymous namespace |
| |
| char IfConverter::ID = 0; |
| |
| char &llvm::IfConverterID = IfConverter::ID; |
| |
| INITIALIZE_PASS_BEGIN(IfConverter, DEBUG_TYPE, "If Converter", false, false) |
| INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo) |
| INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass) |
| INITIALIZE_PASS_END(IfConverter, DEBUG_TYPE, "If Converter", false, false) |
| |
| bool IfConverter::runOnMachineFunction(MachineFunction &MF) { |
| if (skipFunction(MF.getFunction()) || (PredicateFtor && !PredicateFtor(MF))) |
| return false; |
| |
| const TargetSubtargetInfo &ST = MF.getSubtarget(); |
| TLI = ST.getTargetLowering(); |
| TII = ST.getInstrInfo(); |
| TRI = ST.getRegisterInfo(); |
| MBFIWrapper MBFI(getAnalysis<MachineBlockFrequencyInfo>()); |
| MBPI = &getAnalysis<MachineBranchProbabilityInfo>(); |
| ProfileSummaryInfo *PSI = |
| &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI(); |
| MRI = &MF.getRegInfo(); |
| SchedModel.init(&ST); |
| |
| if (!TII) return false; |
| |
| PreRegAlloc = MRI->isSSA(); |
| |
| bool BFChange = false; |
| if (!PreRegAlloc) { |
| // Tail merge tend to expose more if-conversion opportunities. |
| BranchFolder BF(true, false, MBFI, *MBPI, PSI); |
| BFChange = BF.OptimizeFunction(MF, TII, ST.getRegisterInfo()); |
| } |
| |
| LLVM_DEBUG(dbgs() << "\nIfcvt: function (" << ++FnNum << ") \'" |
| << MF.getName() << "\'"); |
| |
| if (FnNum < IfCvtFnStart || (IfCvtFnStop != -1 && FnNum > IfCvtFnStop)) { |
| LLVM_DEBUG(dbgs() << " skipped\n"); |
| return false; |
| } |
| LLVM_DEBUG(dbgs() << "\n"); |
| |
| MF.RenumberBlocks(); |
| BBAnalysis.resize(MF.getNumBlockIDs()); |
| |
| std::vector<std::unique_ptr<IfcvtToken>> 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 = false; |
| AnalyzeBlocks(MF, Tokens); |
| while (!Tokens.empty()) { |
| std::unique_ptr<IfcvtToken> Token = std::move(Tokens.back()); |
| Tokens.pop_back(); |
| BBInfo &BBI = Token->BBI; |
| IfcvtKind Kind = Token->Kind; |
| unsigned NumDups = Token->NumDups; |
| unsigned NumDups2 = Token->NumDups2; |
| |
| // 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: llvm_unreachable("Unexpected!"); |
| case ICSimple: |
| case ICSimpleFalse: { |
| bool isFalse = Kind == ICSimpleFalse; |
| if ((isFalse && DisableSimpleF) || (!isFalse && DisableSimple)) break; |
| LLVM_DEBUG(dbgs() << "Ifcvt (Simple" |
| << (Kind == ICSimpleFalse ? " false" : "") |
| << "): " << printMBBReference(*BBI.BB) << " (" |
| << ((Kind == ICSimpleFalse) ? BBI.FalseBB->getNumber() |
| : BBI.TrueBB->getNumber()) |
| << ") "); |
| RetVal = IfConvertSimple(BBI, Kind); |
| LLVM_DEBUG(dbgs() << (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; |
| LLVM_DEBUG(dbgs() << "Ifcvt (Triangle"); |
| if (isFalse) |
| LLVM_DEBUG(dbgs() << " false"); |
| if (isRev) |
| LLVM_DEBUG(dbgs() << " rev"); |
| LLVM_DEBUG(dbgs() << "): " << printMBBReference(*BBI.BB) |
| << " (T:" << BBI.TrueBB->getNumber() |
| << ",F:" << BBI.FalseBB->getNumber() << ") "); |
| RetVal = IfConvertTriangle(BBI, Kind); |
| LLVM_DEBUG(dbgs() << (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; |
| LLVM_DEBUG(dbgs() << "Ifcvt (Diamond): " << printMBBReference(*BBI.BB) |
| << " (T:" << BBI.TrueBB->getNumber() |
| << ",F:" << BBI.FalseBB->getNumber() << ") "); |
| RetVal = IfConvertDiamond(BBI, Kind, NumDups, NumDups2, |
| Token->TClobbersPred, |
| Token->FClobbersPred); |
| LLVM_DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n"); |
| if (RetVal) ++NumDiamonds; |
| break; |
| case ICForkedDiamond: |
| if (DisableForkedDiamond) break; |
| LLVM_DEBUG(dbgs() << "Ifcvt (Forked Diamond): " |
| << printMBBReference(*BBI.BB) |
| << " (T:" << BBI.TrueBB->getNumber() |
| << ",F:" << BBI.FalseBB->getNumber() << ") "); |
| RetVal = IfConvertForkedDiamond(BBI, Kind, NumDups, NumDups2, |
| Token->TClobbersPred, |
| Token->FClobbersPred); |
| LLVM_DEBUG(dbgs() << (RetVal ? "succeeded!" : "failed!") << "\n"); |
| if (RetVal) ++NumForkedDiamonds; |
| break; |
| } |
| |
| if (RetVal && MRI->tracksLiveness()) |
| recomputeLivenessFlags(*BBI.BB); |
| |
| Change |= RetVal; |
| |
| NumIfCvts = NumSimple + NumSimpleFalse + NumTriangle + NumTriangleRev + |
| NumTriangleFalse + NumTriangleFRev + NumDiamonds; |
| if (IfCvtLimit != -1 && (int)NumIfCvts >= IfCvtLimit) |
| break; |
| } |
| |
| if (!Change) |
| break; |
| MadeChange |= Change; |
| } |
| |
| Tokens.clear(); |
| BBAnalysis.clear(); |
| |
| if (MadeChange && IfCvtBranchFold) { |
| BranchFolder BF(false, false, MBFI, *MBPI, PSI); |
| BF.OptimizeFunction(MF, TII, MF.getSubtarget().getRegisterInfo()); |
| } |
| |
| MadeChange |= BFChange; |
| return MadeChange; |
| } |
| |
| /// BB has a fallthrough. Find its 'false' successor given its 'true' successor. |
| static MachineBasicBlock *findFalseBlock(MachineBasicBlock *BB, |
| MachineBasicBlock *TrueBB) { |
| for (MachineBasicBlock *SuccBB : BB->successors()) { |
| if (SuccBB != TrueBB) |
| return SuccBB; |
| } |
| return nullptr; |
| } |
| |
| /// Reverse the condition of the end of the block branch. Swap block's 'true' |
| /// and 'false' successors. |
| bool IfConverter::reverseBranchCondition(BBInfo &BBI) const { |
| DebugLoc dl; // FIXME: this is nowhere |
| if (!TII->reverseBranchCondition(BBI.BrCond)) { |
| TII->removeBranch(*BBI.BB); |
| TII->insertBranch(*BBI.BB, BBI.FalseBB, BBI.TrueBB, BBI.BrCond, dl); |
| std::swap(BBI.TrueBB, BBI.FalseBB); |
| return true; |
| } |
| return false; |
| } |
| |
| /// Returns the next block in the function blocks ordering. If it is the end, |
| /// returns NULL. |
| static inline MachineBasicBlock *getNextBlock(MachineBasicBlock &MBB) { |
| MachineFunction::iterator I = MBB.getIterator(); |
| MachineFunction::iterator E = MBB.getParent()->end(); |
| if (++I == E) |
| return nullptr; |
| return &*I; |
| } |
| |
| /// 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, |
| BranchProbability Prediction) const { |
| Dups = 0; |
| if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone) |
| return false; |
| |
| if (TrueBBI.IsBrAnalyzable) |
| return false; |
| |
| if (TrueBBI.BB->pred_size() > 1) { |
| if (TrueBBI.CannotBeCopied || |
| !TII->isProfitableToDupForIfCvt(*TrueBBI.BB, TrueBBI.NonPredSize, |
| Prediction)) |
| return false; |
| Dups = TrueBBI.NonPredSize; |
| } |
| |
| return true; |
| } |
| |
| /// 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' block |
| /// 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, |
| BranchProbability Prediction) const { |
| Dups = 0; |
| if (TrueBBI.BB == FalseBBI.BB) |
| return false; |
| |
| 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 (!TII->isProfitableToDupForIfCvt(*TrueBBI.BB, Size, Prediction)) |
| return false; |
| Dups = Size; |
| } |
| |
| MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB; |
| if (!TExit && blockAlwaysFallThrough(TrueBBI)) { |
| MachineFunction::iterator I = TrueBBI.BB->getIterator(); |
| if (++I == TrueBBI.BB->getParent()->end()) |
| return false; |
| TExit = &*I; |
| } |
| return TExit && TExit == FalseBBI.BB; |
| } |
| |
| /// Count duplicated instructions and move the iterators to show where they |
| /// are. |
| /// @param TIB True Iterator Begin |
| /// @param FIB False Iterator Begin |
| /// These two iterators initially point to the first instruction of the two |
| /// blocks, and finally point to the first non-shared instruction. |
| /// @param TIE True Iterator End |
| /// @param FIE False Iterator End |
| /// These two iterators initially point to End() for the two blocks() and |
| /// finally point to the first shared instruction in the tail. |
| /// Upon return [TIB, TIE), and [FIB, FIE) mark the un-duplicated portions of |
| /// two blocks. |
| /// @param Dups1 count of duplicated instructions at the beginning of the 2 |
| /// blocks. |
| /// @param Dups2 count of duplicated instructions at the end of the 2 blocks. |
| /// @param SkipUnconditionalBranches if true, Don't make sure that |
| /// unconditional branches at the end of the blocks are the same. True is |
| /// passed when the blocks are analyzable to allow for fallthrough to be |
| /// handled. |
| /// @return false if the shared portion prevents if conversion. |
| bool IfConverter::CountDuplicatedInstructions( |
| MachineBasicBlock::iterator &TIB, |
| MachineBasicBlock::iterator &FIB, |
| MachineBasicBlock::iterator &TIE, |
| MachineBasicBlock::iterator &FIE, |
| unsigned &Dups1, unsigned &Dups2, |
| MachineBasicBlock &TBB, MachineBasicBlock &FBB, |
| bool SkipUnconditionalBranches) const { |
| while (TIB != TIE && FIB != FIE) { |
| // Skip dbg_value instructions. These do not count. |
| TIB = skipDebugInstructionsForward(TIB, TIE, false); |
| FIB = skipDebugInstructionsForward(FIB, FIE, false); |
| if (TIB == TIE || FIB == FIE) |
| break; |
| if (!TIB->isIdenticalTo(*FIB)) |
| break; |
| // A pred-clobbering instruction in the shared portion prevents |
| // if-conversion. |
| std::vector<MachineOperand> PredDefs; |
| if (TII->ClobbersPredicate(*TIB, PredDefs, false)) |
| return false; |
| // If we get all the way to the branch instructions, don't count them. |
| if (!TIB->isBranch()) |
| ++Dups1; |
| ++TIB; |
| ++FIB; |
| } |
| |
| // Check for already containing all of the block. |
| if (TIB == TIE || FIB == FIE) |
| return true; |
| // Now, in preparation for counting duplicate instructions at the ends of the |
| // blocks, switch to reverse_iterators. Note that getReverse() returns an |
| // iterator that points to the same instruction, unlike std::reverse_iterator. |
| // We have to do our own shifting so that we get the same range. |
| MachineBasicBlock::reverse_iterator RTIE = std::next(TIE.getReverse()); |
| MachineBasicBlock::reverse_iterator RFIE = std::next(FIE.getReverse()); |
| const MachineBasicBlock::reverse_iterator RTIB = std::next(TIB.getReverse()); |
| const MachineBasicBlock::reverse_iterator RFIB = std::next(FIB.getReverse()); |
| |
| if (!TBB.succ_empty() || !FBB.succ_empty()) { |
| if (SkipUnconditionalBranches) { |
| while (RTIE != RTIB && RTIE->isUnconditionalBranch()) |
| ++RTIE; |
| while (RFIE != RFIB && RFIE->isUnconditionalBranch()) |
| ++RFIE; |
| } |
| } |
| |
| // Count duplicate instructions at the ends of the blocks. |
| while (RTIE != RTIB && RFIE != RFIB) { |
| // Skip dbg_value instructions. These do not count. |
| // Note that these are reverse iterators going forward. |
| RTIE = skipDebugInstructionsForward(RTIE, RTIB, false); |
| RFIE = skipDebugInstructionsForward(RFIE, RFIB, false); |
| if (RTIE == RTIB || RFIE == RFIB) |
| break; |
| if (!RTIE->isIdenticalTo(*RFIE)) |
| break; |
| // We have to verify that any branch instructions are the same, and then we |
| // don't count them toward the # of duplicate instructions. |
| if (!RTIE->isBranch()) |
| ++Dups2; |
| ++RTIE; |
| ++RFIE; |
| } |
| TIE = std::next(RTIE.getReverse()); |
| FIE = std::next(RFIE.getReverse()); |
| return true; |
| } |
| |
| /// RescanInstructions - Run ScanInstructions on a pair of blocks. |
| /// @param TIB - True Iterator Begin, points to first non-shared instruction |
| /// @param FIB - False Iterator Begin, points to first non-shared instruction |
| /// @param TIE - True Iterator End, points past last non-shared instruction |
| /// @param FIE - False Iterator End, points past last non-shared instruction |
| /// @param TrueBBI - BBInfo to update for the true block. |
| /// @param FalseBBI - BBInfo to update for the false block. |
| /// @returns - false if either block cannot be predicated or if both blocks end |
| /// with a predicate-clobbering instruction. |
| bool IfConverter::RescanInstructions( |
| MachineBasicBlock::iterator &TIB, MachineBasicBlock::iterator &FIB, |
| MachineBasicBlock::iterator &TIE, MachineBasicBlock::iterator &FIE, |
| BBInfo &TrueBBI, BBInfo &FalseBBI) const { |
| bool BranchUnpredicable = true; |
| TrueBBI.IsUnpredicable = FalseBBI.IsUnpredicable = false; |
| ScanInstructions(TrueBBI, TIB, TIE, BranchUnpredicable); |
| if (TrueBBI.IsUnpredicable) |
| return false; |
| ScanInstructions(FalseBBI, FIB, FIE, BranchUnpredicable); |
| if (FalseBBI.IsUnpredicable) |
| return false; |
| if (TrueBBI.ClobbersPred && FalseBBI.ClobbersPred) |
| return false; |
| return true; |
| } |
| |
| #ifndef NDEBUG |
| static void verifySameBranchInstructions( |
| MachineBasicBlock *MBB1, |
| MachineBasicBlock *MBB2) { |
| const MachineBasicBlock::reverse_iterator B1 = MBB1->rend(); |
| const MachineBasicBlock::reverse_iterator B2 = MBB2->rend(); |
| MachineBasicBlock::reverse_iterator E1 = MBB1->rbegin(); |
| MachineBasicBlock::reverse_iterator E2 = MBB2->rbegin(); |
| while (E1 != B1 && E2 != B2) { |
| skipDebugInstructionsForward(E1, B1, false); |
| skipDebugInstructionsForward(E2, B2, false); |
| if (E1 == B1 && E2 == B2) |
| break; |
| |
| if (E1 == B1) { |
| assert(!E2->isBranch() && "Branch mis-match, one block is empty."); |
| break; |
| } |
| if (E2 == B2) { |
| assert(!E1->isBranch() && "Branch mis-match, one block is empty."); |
| break; |
| } |
| |
| if (E1->isBranch() || E2->isBranch()) |
| assert(E1->isIdenticalTo(*E2) && |
| "Branch mis-match, branch instructions don't match."); |
| else |
| break; |
| ++E1; |
| ++E2; |
| } |
| } |
| #endif |
| |
| /// ValidForkedDiamond - Returns true if the 'true' and 'false' blocks (along |
| /// with their common predecessor) form a diamond if a common tail block is |
| /// extracted. |
| /// While not strictly a diamond, this pattern would form a diamond if |
| /// tail-merging had merged the shared tails. |
| /// EBB |
| /// _/ \_ |
| /// | | |
| /// TBB FBB |
| /// / \ / \ |
| /// FalseBB TrueBB FalseBB |
| /// Currently only handles analyzable branches. |
| /// Specifically excludes actual diamonds to avoid overlap. |
| bool IfConverter::ValidForkedDiamond( |
| BBInfo &TrueBBI, BBInfo &FalseBBI, |
| unsigned &Dups1, unsigned &Dups2, |
| BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const { |
| Dups1 = Dups2 = 0; |
| if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone || |
| FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone) |
| return false; |
| |
| if (!TrueBBI.IsBrAnalyzable || !FalseBBI.IsBrAnalyzable) |
| return false; |
| // Don't IfConvert blocks that can't be folded into their predecessor. |
| if (TrueBBI.BB->pred_size() > 1 || FalseBBI.BB->pred_size() > 1) |
| return false; |
| |
| // This function is specifically looking for conditional tails, as |
| // unconditional tails are already handled by the standard diamond case. |
| if (TrueBBI.BrCond.size() == 0 || |
| FalseBBI.BrCond.size() == 0) |
| return false; |
| |
| MachineBasicBlock *TT = TrueBBI.TrueBB; |
| MachineBasicBlock *TF = TrueBBI.FalseBB; |
| MachineBasicBlock *FT = FalseBBI.TrueBB; |
| MachineBasicBlock *FF = FalseBBI.FalseBB; |
| |
| if (!TT) |
| TT = getNextBlock(*TrueBBI.BB); |
| if (!TF) |
| TF = getNextBlock(*TrueBBI.BB); |
| if (!FT) |
| FT = getNextBlock(*FalseBBI.BB); |
| if (!FF) |
| FF = getNextBlock(*FalseBBI.BB); |
| |
| if (!TT || !TF) |
| return false; |
| |
| // Check successors. If they don't match, bail. |
| if (!((TT == FT && TF == FF) || (TF == FT && TT == FF))) |
| return false; |
| |
| bool FalseReversed = false; |
| if (TF == FT && TT == FF) { |
| // If the branches are opposing, but we can't reverse, don't do it. |
| if (!FalseBBI.IsBrReversible) |
| return false; |
| FalseReversed = true; |
| reverseBranchCondition(FalseBBI); |
| } |
| auto UnReverseOnExit = make_scope_exit([&]() { |
| if (FalseReversed) |
| reverseBranchCondition(FalseBBI); |
| }); |
| |
| // Count duplicate instructions at the beginning of the true and false blocks. |
| MachineBasicBlock::iterator TIB = TrueBBI.BB->begin(); |
| MachineBasicBlock::iterator FIB = FalseBBI.BB->begin(); |
| MachineBasicBlock::iterator TIE = TrueBBI.BB->end(); |
| MachineBasicBlock::iterator FIE = FalseBBI.BB->end(); |
| if(!CountDuplicatedInstructions(TIB, FIB, TIE, FIE, Dups1, Dups2, |
| *TrueBBI.BB, *FalseBBI.BB, |
| /* SkipUnconditionalBranches */ true)) |
| return false; |
| |
| TrueBBICalc.BB = TrueBBI.BB; |
| FalseBBICalc.BB = FalseBBI.BB; |
| TrueBBICalc.IsBrAnalyzable = TrueBBI.IsBrAnalyzable; |
| FalseBBICalc.IsBrAnalyzable = FalseBBI.IsBrAnalyzable; |
| if (!RescanInstructions(TIB, FIB, TIE, FIE, TrueBBICalc, FalseBBICalc)) |
| return false; |
| |
| // The size is used to decide whether to if-convert, and the shared portions |
| // are subtracted off. Because of the subtraction, we just use the size that |
| // was calculated by the original ScanInstructions, as it is correct. |
| TrueBBICalc.NonPredSize = TrueBBI.NonPredSize; |
| FalseBBICalc.NonPredSize = FalseBBI.NonPredSize; |
| return true; |
| } |
| |
| /// 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, |
| BBInfo &TrueBBICalc, BBInfo &FalseBBICalc) const { |
| Dups1 = Dups2 = 0; |
| if (TrueBBI.IsBeingAnalyzed || TrueBBI.IsDone || |
| FalseBBI.IsBeingAnalyzed || FalseBBI.IsDone) |
| return false; |
| |
| // If the True and False BBs are equal we're dealing with a degenerate case |
| // that we don't treat as a diamond. |
| if (TrueBBI.BB == FalseBBI.BB) |
| 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 && (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) |
| return false; |
| |
| // Count duplicate instructions at the beginning and end of the true and |
| // false blocks. |
| // Skip unconditional branches only if we are considering an analyzable |
| // diamond. Otherwise the branches must be the same. |
| bool SkipUnconditionalBranches = |
| TrueBBI.IsBrAnalyzable && FalseBBI.IsBrAnalyzable; |
| MachineBasicBlock::iterator TIB = TrueBBI.BB->begin(); |
| MachineBasicBlock::iterator FIB = FalseBBI.BB->begin(); |
| MachineBasicBlock::iterator TIE = TrueBBI.BB->end(); |
| MachineBasicBlock::iterator FIE = FalseBBI.BB->end(); |
| if(!CountDuplicatedInstructions(TIB, FIB, TIE, FIE, Dups1, Dups2, |
| *TrueBBI.BB, *FalseBBI.BB, |
| SkipUnconditionalBranches)) |
| return false; |
| |
| TrueBBICalc.BB = TrueBBI.BB; |
| FalseBBICalc.BB = FalseBBI.BB; |
| TrueBBICalc.IsBrAnalyzable = TrueBBI.IsBrAnalyzable; |
| FalseBBICalc.IsBrAnalyzable = FalseBBI.IsBrAnalyzable; |
| if (!RescanInstructions(TIB, FIB, TIE, FIE, TrueBBICalc, FalseBBICalc)) |
| return false; |
| // The size is used to decide whether to if-convert, and the shared portions |
| // are subtracted off. Because of the subtraction, we just use the size that |
| // was calculated by the original ScanInstructions, as it is correct. |
| TrueBBICalc.NonPredSize = TrueBBI.NonPredSize; |
| FalseBBICalc.NonPredSize = FalseBBI.NonPredSize; |
| return true; |
| } |
| |
| /// AnalyzeBranches - Look at the branches at the end of a block to determine if |
| /// the block is predicable. |
| void IfConverter::AnalyzeBranches(BBInfo &BBI) { |
| if (BBI.IsDone) |
| return; |
| |
| BBI.TrueBB = BBI.FalseBB = nullptr; |
| BBI.BrCond.clear(); |
| BBI.IsBrAnalyzable = |
| !TII->analyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond); |
| if (!BBI.IsBrAnalyzable) { |
| BBI.TrueBB = nullptr; |
| BBI.FalseBB = nullptr; |
| BBI.BrCond.clear(); |
| } |
| |
| SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); |
| BBI.IsBrReversible = (RevCond.size() == 0) || |
| !TII->reverseBranchCondition(RevCond); |
| BBI.HasFallThrough = BBI.IsBrAnalyzable && BBI.FalseBB == nullptr; |
| |
| 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; |
| } |
| } |
| } |
| |
| /// 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, |
| MachineBasicBlock::iterator &Begin, |
| MachineBasicBlock::iterator &End, |
| bool BranchUnpredicable) const { |
| if (BBI.IsDone || BBI.IsUnpredicable) |
| return; |
| |
| bool AlreadyPredicated = !BBI.Predicate.empty(); |
| |
| BBI.NonPredSize = 0; |
| BBI.ExtraCost = 0; |
| BBI.ExtraCost2 = 0; |
| BBI.ClobbersPred = false; |
| for (MachineInstr &MI : make_range(Begin, End)) { |
| if (MI.isDebugInstr()) |
| continue; |
| |
| // It's unsafe to duplicate convergent instructions in this context, so set |
| // BBI.CannotBeCopied to true if MI is convergent. To see why, consider the |
| // following CFG, which is subject to our "simple" transformation. |
| // |
| // BB0 // if (c1) goto BB1; else goto BB2; |
| // / \ |
| // BB1 | |
| // | BB2 // if (c2) goto TBB; else goto FBB; |
| // | / | |
| // | / | |
| // TBB | |
| // | | |
| // | FBB |
| // | |
| // exit |
| // |
| // Suppose we want to move TBB's contents up into BB1 and BB2 (in BB1 they'd |
| // be unconditional, and in BB2, they'd be predicated upon c2), and suppose |
| // TBB contains a convergent instruction. This is safe iff doing so does |
| // not add a control-flow dependency to the convergent instruction -- i.e., |
| // it's safe iff the set of control flows that leads us to the convergent |
| // instruction does not get smaller after the transformation. |
| // |
| // Originally we executed TBB if c1 || c2. After the transformation, there |
| // are two copies of TBB's instructions. We get to the first if c1, and we |
| // get to the second if !c1 && c2. |
| // |
| // There are clearly fewer ways to satisfy the condition "c1" than |
| // "c1 || c2". Since we've shrunk the set of control flows which lead to |
| // our convergent instruction, the transformation is unsafe. |
| if (MI.isNotDuplicable() || MI.isConvergent()) |
| BBI.CannotBeCopied = true; |
| |
| bool isPredicated = TII->isPredicated(MI); |
| bool isCondBr = BBI.IsBrAnalyzable && MI.isConditionalBranch(); |
| |
| if (BranchUnpredicable && MI.isBranch()) { |
| BBI.IsUnpredicable = true; |
| return; |
| } |
| |
| // A conditional branch is not predicable, but it may be eliminated. |
| if (isCondBr) |
| continue; |
| |
| if (!isPredicated) { |
| BBI.NonPredSize++; |
| unsigned ExtraPredCost = TII->getPredicationCost(MI); |
| unsigned NumCycles = SchedModel.computeInstrLatency(&MI, false); |
| if (NumCycles > 1) |
| BBI.ExtraCost += NumCycles-1; |
| BBI.ExtraCost2 += ExtraPredCost; |
| } 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). |
| // 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<MachineOperand> PredDefs; |
| if (TII->ClobbersPredicate(MI, PredDefs, true)) |
| BBI.ClobbersPred = true; |
| |
| if (!TII->isPredicable(MI)) { |
| BBI.IsUnpredicable = true; |
| return; |
| } |
| } |
| } |
| |
| /// Determine if the block is a suitable candidate to be predicated by the |
| /// specified predicate. |
| /// @param BBI BBInfo for the block to check |
| /// @param Pred Predicate array for the branch that leads to BBI |
| /// @param isTriangle true if the Analysis is for a triangle |
| /// @param RevBranch true if Reverse(Pred) leads to BBI (e.g. BBI is the false |
| /// case |
| /// @param hasCommonTail true if BBI shares a tail with a sibling block that |
| /// contains any instruction that would make the block unpredicable. |
| bool IfConverter::FeasibilityAnalysis(BBInfo &BBI, |
| SmallVectorImpl<MachineOperand> &Pred, |
| bool isTriangle, bool RevBranch, |
| bool hasCommonTail) { |
| // If the block is dead or unpredicable, then it cannot be predicated. |
| // Two blocks may share a common unpredicable tail, but this doesn't prevent |
| // them from being if-converted. The non-shared portion is assumed to have |
| // been checked |
| if (BBI.IsDone || (BBI.IsUnpredicable && !hasCommonTail)) |
| return false; |
| |
| // If it is already predicated but we couldn't analyze its terminator, the |
| // latter might fallthrough, but we can't determine where to. |
| // Conservatively avoid if-converting again. |
| if (BBI.Predicate.size() && !BBI.IsBrAnalyzable) |
| return false; |
| |
| // If it is already predicated, check if the new predicate subsumes |
| // its predicate. |
| if (BBI.Predicate.size() && !TII->SubsumesPredicate(Pred, BBI.Predicate)) |
| return false; |
| |
| if (!hasCommonTail && BBI.BrCond.size()) { |
| if (!isTriangle) |
| return false; |
| |
| // Test predicate subsumption. |
| SmallVector<MachineOperand, 4> RevPred(Pred.begin(), Pred.end()); |
| SmallVector<MachineOperand, 4> 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; |
| } |
| |
| /// Analyze the structure of the sub-CFG starting from the specified block. |
| /// Record its successors and whether it looks like an if-conversion candidate. |
| void IfConverter::AnalyzeBlock( |
| MachineBasicBlock &MBB, std::vector<std::unique_ptr<IfcvtToken>> &Tokens) { |
| struct BBState { |
| BBState(MachineBasicBlock &MBB) : MBB(&MBB), SuccsAnalyzed(false) {} |
| MachineBasicBlock *MBB; |
| |
| /// This flag is true if MBB's successors have been analyzed. |
| bool SuccsAnalyzed; |
| }; |
| |
| // Push MBB to the stack. |
| SmallVector<BBState, 16> BBStack(1, MBB); |
| |
| while (!BBStack.empty()) { |
| BBState &State = BBStack.back(); |
| MachineBasicBlock *BB = State.MBB; |
| BBInfo &BBI = BBAnalysis[BB->getNumber()]; |
| |
| if (!State.SuccsAnalyzed) { |
| if (BBI.IsAnalyzed || BBI.IsBeingAnalyzed) { |
| BBStack.pop_back(); |
| continue; |
| } |
| |
| BBI.BB = BB; |
| BBI.IsBeingAnalyzed = true; |
| |
| AnalyzeBranches(BBI); |
| MachineBasicBlock::iterator Begin = BBI.BB->begin(); |
| MachineBasicBlock::iterator End = BBI.BB->end(); |
| ScanInstructions(BBI, Begin, End); |
| |
| // Unanalyzable or ends with fallthrough or unconditional branch, or if is |
| // not considered for ifcvt anymore. |
| if (!BBI.IsBrAnalyzable || BBI.BrCond.empty() || BBI.IsDone) { |
| BBI.IsBeingAnalyzed = false; |
| BBI.IsAnalyzed = true; |
| BBStack.pop_back(); |
| continue; |
| } |
| |
| // 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; |
| BBStack.pop_back(); |
| continue; |
| } |
| |
| // Do not ifcvt if true and false fallthrough blocks are the same. |
| if (!BBI.FalseBB) { |
| BBI.IsBeingAnalyzed = false; |
| BBI.IsAnalyzed = true; |
| BBStack.pop_back(); |
| continue; |
| } |
| |
| // Push the False and True blocks to the stack. |
| State.SuccsAnalyzed = true; |
| BBStack.push_back(*BBI.FalseBB); |
| BBStack.push_back(*BBI.TrueBB); |
| continue; |
| } |
| |
| BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; |
| BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; |
| |
| if (TrueBBI.IsDone && FalseBBI.IsDone) { |
| BBI.IsBeingAnalyzed = false; |
| BBI.IsAnalyzed = true; |
| BBStack.pop_back(); |
| continue; |
| } |
| |
| SmallVector<MachineOperand, 4> |
| RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); |
| bool CanRevCond = !TII->reverseBranchCondition(RevCond); |
| |
| unsigned Dups = 0; |
| unsigned Dups2 = 0; |
| bool TNeedSub = !TrueBBI.Predicate.empty(); |
| bool FNeedSub = !FalseBBI.Predicate.empty(); |
| bool Enqueued = false; |
| |
| BranchProbability Prediction = MBPI->getEdgeProbability(BB, TrueBBI.BB); |
| |
| if (CanRevCond) { |
| BBInfo TrueBBICalc, FalseBBICalc; |
| auto feasibleDiamond = [&](bool Forked) { |
| bool MeetsSize = MeetIfcvtSizeLimit(TrueBBICalc, FalseBBICalc, *BB, |
| Dups + Dups2, Prediction, Forked); |
| bool TrueFeasible = FeasibilityAnalysis(TrueBBI, BBI.BrCond, |
| /* IsTriangle */ false, /* RevCond */ false, |
| /* hasCommonTail */ true); |
| bool FalseFeasible = FeasibilityAnalysis(FalseBBI, RevCond, |
| /* IsTriangle */ false, /* RevCond */ false, |
| /* hasCommonTail */ true); |
| return MeetsSize && TrueFeasible && FalseFeasible; |
| }; |
| |
| if (ValidDiamond(TrueBBI, FalseBBI, Dups, Dups2, |
| TrueBBICalc, FalseBBICalc)) { |
| if (feasibleDiamond(false)) { |
| // Diamond: |
| // EBB |
| // / \_ |
| // | | |
| // TBB FBB |
| // \ / |
| // TailBB |
| // Note TailBB can be empty. |
| Tokens.push_back(std::make_unique<IfcvtToken>( |
| BBI, ICDiamond, TNeedSub | FNeedSub, Dups, Dups2, |
| (bool) TrueBBICalc.ClobbersPred, (bool) FalseBBICalc.ClobbersPred)); |
| Enqueued = true; |
| } |
| } else if (ValidForkedDiamond(TrueBBI, FalseBBI, Dups, Dups2, |
| TrueBBICalc, FalseBBICalc)) { |
| if (feasibleDiamond(true)) { |
| // ForkedDiamond: |
| // if TBB and FBB have a common tail that includes their conditional |
| // branch instructions, then we can If Convert this pattern. |
| // EBB |
| // _/ \_ |
| // | | |
| // TBB FBB |
| // / \ / \ |
| // FalseBB TrueBB FalseBB |
| // |
| Tokens.push_back(std::make_unique<IfcvtToken>( |
| BBI, ICForkedDiamond, TNeedSub | FNeedSub, Dups, Dups2, |
| (bool) TrueBBICalc.ClobbersPred, (bool) FalseBBICalc.ClobbersPred)); |
| Enqueued = true; |
| } |
| } |
| } |
| |
| if (ValidTriangle(TrueBBI, FalseBBI, false, Dups, Prediction) && |
| MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost, |
| TrueBBI.ExtraCost2, Prediction) && |
| FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) { |
| // Triangle: |
| // EBB |
| // | \_ |
| // | | |
| // | TBB |
| // | / |
| // FBB |
| Tokens.push_back( |
| std::make_unique<IfcvtToken>(BBI, ICTriangle, TNeedSub, Dups)); |
| Enqueued = true; |
| } |
| |
| if (ValidTriangle(TrueBBI, FalseBBI, true, Dups, Prediction) && |
| MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost, |
| TrueBBI.ExtraCost2, Prediction) && |
| FeasibilityAnalysis(TrueBBI, BBI.BrCond, true, true)) { |
| Tokens.push_back( |
| std::make_unique<IfcvtToken>(BBI, ICTriangleRev, TNeedSub, Dups)); |
| Enqueued = true; |
| } |
| |
| if (ValidSimple(TrueBBI, Dups, Prediction) && |
| MeetIfcvtSizeLimit(*TrueBBI.BB, TrueBBI.NonPredSize + TrueBBI.ExtraCost, |
| TrueBBI.ExtraCost2, Prediction) && |
| FeasibilityAnalysis(TrueBBI, BBI.BrCond)) { |
| // Simple (split, no rejoin): |
| // EBB |
| // | \_ |
| // | | |
| // | TBB---> exit |
| // | |
| // FBB |
| Tokens.push_back( |
| std::make_unique<IfcvtToken>(BBI, ICSimple, TNeedSub, Dups)); |
| Enqueued = true; |
| } |
| |
| if (CanRevCond) { |
| // Try the other path... |
| if (ValidTriangle(FalseBBI, TrueBBI, false, Dups, |
| Prediction.getCompl()) && |
| MeetIfcvtSizeLimit(*FalseBBI.BB, |
| FalseBBI.NonPredSize + FalseBBI.ExtraCost, |
| FalseBBI.ExtraCost2, Prediction.getCompl()) && |
| FeasibilityAnalysis(FalseBBI, RevCond, true)) { |
| Tokens.push_back(std::make_unique<IfcvtToken>(BBI, ICTriangleFalse, |
| FNeedSub, Dups)); |
| Enqueued = true; |
| } |
| |
| if (ValidTriangle(FalseBBI, TrueBBI, true, Dups, |
| Prediction.getCompl()) && |
| MeetIfcvtSizeLimit(*FalseBBI.BB, |
| FalseBBI.NonPredSize + FalseBBI.ExtraCost, |
| FalseBBI.ExtraCost2, Prediction.getCompl()) && |
| FeasibilityAnalysis(FalseBBI, RevCond, true, true)) { |
| Tokens.push_back( |
| std::make_unique<IfcvtToken>(BBI, ICTriangleFRev, FNeedSub, Dups)); |
| Enqueued = true; |
| } |
| |
| if (ValidSimple(FalseBBI, Dups, Prediction.getCompl()) && |
| MeetIfcvtSizeLimit(*FalseBBI.BB, |
| FalseBBI.NonPredSize + FalseBBI.ExtraCost, |
| FalseBBI.ExtraCost2, Prediction.getCompl()) && |
| FeasibilityAnalysis(FalseBBI, RevCond)) { |
| Tokens.push_back( |
| std::make_unique<IfcvtToken>(BBI, ICSimpleFalse, FNeedSub, Dups)); |
| Enqueued = true; |
| } |
| } |
| |
| BBI.IsEnqueued = Enqueued; |
| BBI.IsBeingAnalyzed = false; |
| BBI.IsAnalyzed = true; |
| BBStack.pop_back(); |
| } |
| } |
| |
| /// Analyze all blocks and find entries for all if-conversion candidates. |
| void IfConverter::AnalyzeBlocks( |
| MachineFunction &MF, std::vector<std::unique_ptr<IfcvtToken>> &Tokens) { |
| for (MachineBasicBlock &MBB : MF) |
| AnalyzeBlock(MBB, Tokens); |
| |
| // Sort to favor more complex ifcvt scheme. |
| llvm::stable_sort(Tokens, IfcvtTokenCmp); |
| } |
| |
| /// Returns true either if ToMBB is the next block after MBB or that all the |
| /// intervening blocks are empty (given MBB can fall through to its next block). |
| static bool canFallThroughTo(MachineBasicBlock &MBB, MachineBasicBlock &ToMBB) { |
| MachineFunction::iterator PI = MBB.getIterator(); |
| MachineFunction::iterator I = std::next(PI); |
| MachineFunction::iterator TI = ToMBB.getIterator(); |
| MachineFunction::iterator E = MBB.getParent()->end(); |
| while (I != TI) { |
| // Check isSuccessor to avoid case where the next block is empty, but |
| // it's not a successor. |
| if (I == E || !I->empty() || !PI->isSuccessor(&*I)) |
| return false; |
| PI = I++; |
| } |
| // Finally see if the last I is indeed a successor to PI. |
| return PI->isSuccessor(&*I); |
| } |
| |
| /// 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 &MBB) { |
| for (const MachineBasicBlock *Predecessor : MBB.predecessors()) { |
| BBInfo &PBBI = BBAnalysis[Predecessor->getNumber()]; |
| if (PBBI.IsDone || PBBI.BB == &MBB) |
| continue; |
| PBBI.IsAnalyzed = false; |
| PBBI.IsEnqueued = false; |
| } |
| } |
| |
| /// Inserts an unconditional branch from \p MBB to \p ToMBB. |
| static void InsertUncondBranch(MachineBasicBlock &MBB, MachineBasicBlock &ToMBB, |
| const TargetInstrInfo *TII) { |
| DebugLoc dl; // FIXME: this is nowhere |
| SmallVector<MachineOperand, 0> NoCond; |
| TII->insertBranch(MBB, &ToMBB, nullptr, NoCond, dl); |
| } |
| |
| /// Behaves like LiveRegUnits::StepForward() but also adds implicit uses to all |
| /// values defined in MI which are also live/used by MI. |
| static void UpdatePredRedefs(MachineInstr &MI, LivePhysRegs &Redefs) { |
| const TargetRegisterInfo *TRI = MI.getMF()->getSubtarget().getRegisterInfo(); |
| |
| // Before stepping forward past MI, remember which regs were live |
| // before MI. This is needed to set the Undef flag only when reg is |
| // dead. |
| SparseSet<MCPhysReg, identity<MCPhysReg>> LiveBeforeMI; |
| LiveBeforeMI.setUniverse(TRI->getNumRegs()); |
| for (unsigned Reg : Redefs) |
| LiveBeforeMI.insert(Reg); |
| |
| SmallVector<std::pair<MCPhysReg, const MachineOperand*>, 4> Clobbers; |
| Redefs.stepForward(MI, Clobbers); |
| |
| // Now add the implicit uses for each of the clobbered values. |
| for (auto Clobber : Clobbers) { |
| // FIXME: Const cast here is nasty, but better than making StepForward |
| // take a mutable instruction instead of const. |
| unsigned Reg = Clobber.first; |
| MachineOperand &Op = const_cast<MachineOperand&>(*Clobber.second); |
| MachineInstr *OpMI = Op.getParent(); |
| MachineInstrBuilder MIB(*OpMI->getMF(), OpMI); |
| if (Op.isRegMask()) { |
| // First handle regmasks. They clobber any entries in the mask which |
| // means that we need a def for those registers. |
| if (LiveBeforeMI.count(Reg)) |
| MIB.addReg(Reg, RegState::Implicit); |
| |
| // We also need to add an implicit def of this register for the later |
| // use to read from. |
| // For the register allocator to have allocated a register clobbered |
| // by the call which is used later, it must be the case that |
| // the call doesn't return. |
| MIB.addReg(Reg, RegState::Implicit | RegState::Define); |
| continue; |
| } |
| if (LiveBeforeMI.count(Reg)) |
| MIB.addReg(Reg, RegState::Implicit); |
| else { |
| bool HasLiveSubReg = false; |
| for (MCSubRegIterator S(Reg, TRI); S.isValid(); ++S) { |
| if (!LiveBeforeMI.count(*S)) |
| continue; |
| HasLiveSubReg = true; |
| break; |
| } |
| if (HasLiveSubReg) |
| MIB.addReg(Reg, RegState::Implicit); |
| } |
| } |
| } |
| |
| /// 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<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); |
| if (Kind == ICSimpleFalse) |
| std::swap(CvtBBI, NextBBI); |
| |
| MachineBasicBlock &CvtMBB = *CvtBBI->BB; |
| MachineBasicBlock &NextMBB = *NextBBI->BB; |
| if (CvtBBI->IsDone || |
| (CvtBBI->CannotBeCopied && CvtMBB.pred_size() > 1)) { |
| // Something has changed. It's no longer safe to predicate this block. |
| BBI.IsAnalyzed = false; |
| CvtBBI->IsAnalyzed = false; |
| return false; |
| } |
| |
| if (CvtMBB.hasAddressTaken()) |
| // Conservatively abort if-conversion if BB's address is taken. |
| return false; |
| |
| if (Kind == ICSimpleFalse) |
| if (TII->reverseBranchCondition(Cond)) |
| llvm_unreachable("Unable to reverse branch condition!"); |
| |
| Redefs.init(*TRI); |
| |
| if (MRI->tracksLiveness()) { |
| // Initialize liveins to the first BB. These are potentially redefined by |
| // predicated instructions. |
| Redefs.addLiveInsNoPristines(CvtMBB); |
| Redefs.addLiveInsNoPristines(NextMBB); |
| } |
| |
| // Remove the branches from the entry so we can add the contents of the true |
| // block to it. |
| BBI.NonPredSize -= TII->removeBranch(*BBI.BB); |
| |
| if (CvtMBB.pred_size() > 1) { |
| // Copy instructions in the true block, predicate them, and add them to |
| // the entry block. |
| CopyAndPredicateBlock(BBI, *CvtBBI, Cond); |
| |
| // Keep the CFG updated. |
| BBI.BB->removeSuccessor(&CvtMBB, true); |
| } else { |
| // Predicate the instructions in the true block. |
| PredicateBlock(*CvtBBI, CvtMBB.end(), Cond); |
| |
| // Merge converted block into entry block. The BB to Cvt edge is removed |
| // by MergeBlocks. |
| MergeBlocks(BBI, *CvtBBI); |
| } |
| |
| bool IterIfcvt = true; |
| if (!canFallThroughTo(*BBI.BB, NextMBB)) { |
| InsertUncondBranch(*BBI.BB, NextMBB, 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; |
| } |
| |
| // 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; |
| } |
| |
| /// 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; |
| DebugLoc dl; // FIXME: this is nowhere |
| |
| SmallVector<MachineOperand, 4> Cond(BBI.BrCond.begin(), BBI.BrCond.end()); |
| if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) |
| std::swap(CvtBBI, NextBBI); |
| |
| MachineBasicBlock &CvtMBB = *CvtBBI->BB; |
| MachineBasicBlock &NextMBB = *NextBBI->BB; |
| if (CvtBBI->IsDone || |
| (CvtBBI->CannotBeCopied && CvtMBB.pred_size() > 1)) { |
| // Something has changed. It's no longer safe to predicate this block. |
| BBI.IsAnalyzed = false; |
| CvtBBI->IsAnalyzed = false; |
| return false; |
| } |
| |
| if (CvtMBB.hasAddressTaken()) |
| // Conservatively abort if-conversion if BB's address is taken. |
| return false; |
| |
| if (Kind == ICTriangleFalse || Kind == ICTriangleFRev) |
| if (TII->reverseBranchCondition(Cond)) |
| llvm_unreachable("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 *PBB : CvtMBB.predecessors()) { |
| if (PBB == BBI.BB) |
| continue; |
| BBInfo &PBBI = BBAnalysis[PBB->getNumber()]; |
| if (PBBI.IsEnqueued) { |
| PBBI.IsAnalyzed = false; |
| PBBI.IsEnqueued = false; |
| } |
| } |
| } |
| } |
| |
| // Initialize liveins to the first BB. These are potentially redefined by |
| // predicated instructions. |
| Redefs.init(*TRI); |
| if (MRI->tracksLiveness()) { |
| Redefs.addLiveInsNoPristines(CvtMBB); |
| Redefs.addLiveInsNoPristines(NextMBB); |
| } |
| |
| bool HasEarlyExit = CvtBBI->FalseBB != nullptr; |
| BranchProbability CvtNext, CvtFalse, BBNext, BBCvt; |
| |
| if (HasEarlyExit) { |
| // Get probabilities before modifying CvtMBB and BBI.BB. |
| CvtNext = MBPI->getEdgeProbability(&CvtMBB, &NextMBB); |
| CvtFalse = MBPI->getEdgeProbability(&CvtMBB, CvtBBI->FalseBB); |
| BBNext = MBPI->getEdgeProbability(BBI.BB, &NextMBB); |
| BBCvt = MBPI->getEdgeProbability(BBI.BB, &CvtMBB); |
| } |
| |
| // Remove the branches from the entry so we can add the contents of the true |
| // block to it. |
| BBI.NonPredSize -= TII->removeBranch(*BBI.BB); |
| |
| if (CvtMBB.pred_size() > 1) { |
| // 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(CvtMBB); |
| PredicateBlock(*CvtBBI, CvtMBB.end(), Cond); |
| |
| // Now merge the entry of the triangle with the true block. |
| MergeBlocks(BBI, *CvtBBI, false); |
| } |
| |
| // Keep the CFG updated. |
| BBI.BB->removeSuccessor(&CvtMBB, true); |
| |
| // If 'true' block has a 'false' successor, add an exit branch to it. |
| if (HasEarlyExit) { |
| SmallVector<MachineOperand, 4> RevCond(CvtBBI->BrCond.begin(), |
| CvtBBI->BrCond.end()); |
| if (TII->reverseBranchCondition(RevCond)) |
| llvm_unreachable("Unable to reverse branch condition!"); |
| |
| // Update the edge probability for both CvtBBI->FalseBB and NextBBI. |
| // NewNext = New_Prob(BBI.BB, NextMBB) = |
| // Prob(BBI.BB, NextMBB) + |
| // Prob(BBI.BB, CvtMBB) * Prob(CvtMBB, NextMBB) |
| // NewFalse = New_Prob(BBI.BB, CvtBBI->FalseBB) = |
| // Prob(BBI.BB, CvtMBB) * Prob(CvtMBB, CvtBBI->FalseBB) |
| auto NewTrueBB = getNextBlock(*BBI.BB); |
| auto NewNext = BBNext + BBCvt * CvtNext; |
| auto NewTrueBBIter = find(BBI.BB->successors(), NewTrueBB); |
| if (NewTrueBBIter != BBI.BB->succ_end()) |
| BBI.BB->setSuccProbability(NewTrueBBIter, NewNext); |
| |
| auto NewFalse = BBCvt * CvtFalse; |
| TII->insertBranch(*BBI.BB, CvtBBI->FalseBB, nullptr, RevCond, dl); |
| BBI.BB->addSuccessor(CvtBBI->FalseBB, NewFalse); |
| } |
| |
| // 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, NextMBB); |
| 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 && |
| NextMBB.pred_size() == 1 && !NextBBI->HasFallThrough && |
| !NextMBB.hasAddressTaken()) { |
| MergeBlocks(BBI, *NextBBI); |
| FalseBBDead = true; |
| } else { |
| InsertUncondBranch(*BBI.BB, NextMBB, TII); |
| BBI.HasFallThrough = false; |
| } |
| // Mixed predicated and unpredicated code. This cannot be iteratively |
| // predicated. |
| IterIfcvt = false; |
| } |
| |
| // 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; |
| } |
| |
| /// Common code shared between diamond conversions. |
| /// \p BBI, \p TrueBBI, and \p FalseBBI form the diamond shape. |
| /// \p NumDups1 - number of shared instructions at the beginning of \p TrueBBI |
| /// and FalseBBI |
| /// \p NumDups2 - number of shared instructions at the end of \p TrueBBI |
| /// and \p FalseBBI |
| /// \p RemoveBranch - Remove the common branch of the two blocks before |
| /// predicating. Only false for unanalyzable fallthrough |
| /// cases. The caller will replace the branch if necessary. |
| /// \p MergeAddEdges - Add successor edges when merging blocks. Only false for |
| /// unanalyzable fallthrough |
| bool IfConverter::IfConvertDiamondCommon( |
| BBInfo &BBI, BBInfo &TrueBBI, BBInfo &FalseBBI, |
| unsigned NumDups1, unsigned NumDups2, |
| bool TClobbersPred, bool FClobbersPred, |
| bool RemoveBranch, bool MergeAddEdges) { |
| |
| 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; |
| } |
| |
| if (TrueBBI.BB->hasAddressTaken() || FalseBBI.BB->hasAddressTaken()) |
| // Conservatively abort if-conversion if either BB has its address taken. |
| return false; |
| |
| // Put the predicated instructions from the 'true' block before the |
| // instructions from the 'false' block, unless the true block would clobber |
| // the predicate, in which case, do the opposite. |
| BBInfo *BBI1 = &TrueBBI; |
| BBInfo *BBI2 = &FalseBBI; |
| SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end()); |
| if (TII->reverseBranchCondition(RevCond)) |
| llvm_unreachable("Unable to reverse branch condition!"); |
| SmallVector<MachineOperand, 4> *Cond1 = &BBI.BrCond; |
| SmallVector<MachineOperand, 4> *Cond2 = &RevCond; |
| |
| // Figure out the more profitable ordering. |
| bool DoSwap = false; |
| if (TClobbersPred && !FClobbersPred) |
| DoSwap = true; |
| else if (!TClobbersPred && !FClobbersPred) { |
| if (TrueBBI.NonPredSize > FalseBBI.NonPredSize) |
| DoSwap = true; |
| } else if (TClobbersPred && FClobbersPred) |
| llvm_unreachable("Predicate info cannot be clobbered by both sides."); |
| 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); |
| |
| MachineBasicBlock &MBB1 = *BBI1->BB; |
| MachineBasicBlock &MBB2 = *BBI2->BB; |
| |
| // Initialize the Redefs: |
| // - BB2 live-in regs need implicit uses before being redefined by BB1 |
| // instructions. |
| // - BB1 live-out regs need implicit uses before being redefined by BB2 |
| // instructions. We start with BB1 live-ins so we have the live-out regs |
| // after tracking the BB1 instructions. |
| Redefs.init(*TRI); |
| if (MRI->tracksLiveness()) { |
| Redefs.addLiveInsNoPristines(MBB1); |
| Redefs.addLiveInsNoPristines(MBB2); |
| } |
| |
| // Remove the duplicated instructions at the beginnings of both paths. |
| // Skip dbg_value instructions. |
| MachineBasicBlock::iterator DI1 = MBB1.getFirstNonDebugInstr(false); |
| MachineBasicBlock::iterator DI2 = MBB2.getFirstNonDebugInstr(false); |
| BBI1->NonPredSize -= NumDups1; |
| BBI2->NonPredSize -= NumDups1; |
| |
| // Skip past the dups on each side separately since there may be |
| // differing dbg_value entries. NumDups1 can include a "return" |
| // instruction, if it's not marked as "branch". |
| for (unsigned i = 0; i < NumDups1; ++DI1) { |
| if (DI1 == MBB1.end()) |
| break; |
| if (!DI1->isDebugInstr()) |
| ++i; |
| } |
| while (NumDups1 != 0) { |
| // Since this instruction is going to be deleted, update call |
| // site info state if the instruction is call instruction. |
| if (DI2->shouldUpdateCallSiteInfo()) |
| MBB2.getParent()->eraseCallSiteInfo(&*DI2); |
| |
| ++DI2; |
| if (DI2 == MBB2.end()) |
| break; |
| if (!DI2->isDebugInstr()) |
| --NumDups1; |
| } |
| |
| if (MRI->tracksLiveness()) { |
| for (const MachineInstr &MI : make_range(MBB1.begin(), DI1)) { |
| SmallVector<std::pair<MCPhysReg, const MachineOperand*>, 4> Dummy; |
| Redefs.stepForward(MI, Dummy); |
| } |
| } |
| |
| BBI.BB->splice(BBI.BB->end(), &MBB1, MBB1.begin(), DI1); |
| MBB2.erase(MBB2.begin(), DI2); |
| |
| // The branches have been checked to match, so it is safe to remove the |
| // branch in BB1 and rely on the copy in BB2. The complication is that |
| // the blocks may end with a return instruction, which may or may not |
| // be marked as "branch". If it's not, then it could be included in |
| // "dups1", leaving the blocks potentially empty after moving the common |
| // duplicates. |
| #ifndef NDEBUG |
| // Unanalyzable branches must match exactly. Check that now. |
| if (!BBI1->IsBrAnalyzable) |
| verifySameBranchInstructions(&MBB1, &MBB2); |
| #endif |
| // Remove duplicated instructions from the tail of MBB1: any branch |
| // instructions, and the common instructions counted by NumDups2. |
| DI1 = MBB1.end(); |
| while (DI1 != MBB1.begin()) { |
| MachineBasicBlock::iterator Prev = std::prev(DI1); |
| if (!Prev->isBranch() && !Prev->isDebugInstr()) |
| break; |
| DI1 = Prev; |
| } |
| for (unsigned i = 0; i != NumDups2; ) { |
| // NumDups2 only counted non-dbg_value instructions, so this won't |
| // run off the head of the list. |
| assert(DI1 != MBB1.begin()); |
| |
| --DI1; |
| |
| // Since this instruction is going to be deleted, update call |
| // site info state if the instruction is call instruction. |
| if (DI1->shouldUpdateCallSiteInfo()) |
| MBB1.getParent()->eraseCallSiteInfo(&*DI1); |
| |
| // skip dbg_value instructions |
| if (!DI1->isDebugInstr()) |
| ++i; |
| } |
| MBB1.erase(DI1, MBB1.end()); |
| |
| DI2 = BBI2->BB->end(); |
| // The branches have been checked to match. Skip over the branch in the false |
| // block so that we don't try to predicate it. |
| if (RemoveBranch) |
| BBI2->NonPredSize -= TII->removeBranch(*BBI2->BB); |
| else { |
| // Make DI2 point to the end of the range where the common "tail" |
| // instructions could be found. |
| while (DI2 != MBB2.begin()) { |
| MachineBasicBlock::iterator Prev = std::prev(DI2); |
| if (!Prev->isBranch() && !Prev->isDebugInstr()) |
| break; |
| DI2 = Prev; |
| } |
| } |
| while (NumDups2 != 0) { |
| // NumDups2 only counted non-dbg_value instructions, so this won't |
| // run off the head of the list. |
| assert(DI2 != MBB2.begin()); |
| --DI2; |
| // skip dbg_value instructions |
| if (!DI2->isDebugInstr()) |
| --NumDups2; |
| } |
| |
| // Remember which registers would later be defined by the false block. |
| // This allows us not to predicate instructions in the true block that would |
| // later be re-defined. That is, rather than |
| // subeq r0, r1, #1 |
| // addne r0, r1, #1 |
| // generate: |
| // sub r0, r1, #1 |
| // addne r0, r1, #1 |
| SmallSet<MCPhysReg, 4> RedefsByFalse; |
| SmallSet<MCPhysReg, 4> ExtUses; |
| if (TII->isProfitableToUnpredicate(MBB1, MBB2)) { |
| for (const MachineInstr &FI : make_range(MBB2.begin(), DI2)) { |
| if (FI.isDebugInstr()) |
| continue; |
| SmallVector<MCPhysReg, 4> Defs; |
| for (const MachineOperand &MO : FI.operands()) { |
| if (!MO.isReg()) |
| continue; |
| Register Reg = MO.getReg(); |
| if (!Reg) |
| continue; |
| if (MO.isDef()) { |
| Defs.push_back(Reg); |
| } else if (!RedefsByFalse.count(Reg)) { |
| // These are defined before ctrl flow reach the 'false' instructions. |
| // They cannot be modified by the 'true' instructions. |
| for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true); |
| SubRegs.isValid(); ++SubRegs) |
| ExtUses.insert(*SubRegs); |
| } |
| } |
| |
| for (MCPhysReg Reg : Defs) { |
| if (!ExtUses.count(Reg)) { |
| for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true); |
| SubRegs.isValid(); ++SubRegs) |
| RedefsByFalse.insert(*SubRegs); |
| } |
| } |
| } |
| } |
| |
| // Predicate the 'true' block. |
| PredicateBlock(*BBI1, MBB1.end(), *Cond1, &RedefsByFalse); |
| |
| // After predicating BBI1, if there is a predicated terminator in BBI1 and |
| // a non-predicated in BBI2, then we don't want to predicate the one from |
| // BBI2. The reason is that if we merged these blocks, we would end up with |
| // two predicated terminators in the same block. |
| // Also, if the branches in MBB1 and MBB2 were non-analyzable, then don't |
| // predicate them either. They were checked to be identical, and so the |
| // same branch would happen regardless of which path was taken. |
| if (!MBB2.empty() && (DI2 == MBB2.end())) { |
| MachineBasicBlock::iterator BBI1T = MBB1.getFirstTerminator(); |
| MachineBasicBlock::iterator BBI2T = MBB2.getFirstTerminator(); |
| bool BB1Predicated = BBI1T != MBB1.end() && TII->isPredicated(*BBI1T); |
| bool BB2NonPredicated = BBI2T != MBB2.end() && !TII->isPredicated(*BBI2T); |
| if (BB2NonPredicated && (BB1Predicated || !BBI2->IsBrAnalyzable)) |
| --DI2; |
| } |
| |
| // Predicate the 'false' block. |
| PredicateBlock(*BBI2, DI2, *Cond2); |
| |
| // Merge the true block into the entry of the diamond. |
| MergeBlocks(BBI, *BBI1, MergeAddEdges); |
| MergeBlocks(BBI, *BBI2, MergeAddEdges); |
| return true; |
| } |
| |
| /// If convert an almost-diamond sub-CFG where the true |
| /// and false blocks share a common tail. |
| bool IfConverter::IfConvertForkedDiamond( |
| BBInfo &BBI, IfcvtKind Kind, |
| unsigned NumDups1, unsigned NumDups2, |
| bool TClobbersPred, bool FClobbersPred) { |
| BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()]; |
| BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()]; |
| |
| // Save the debug location for later. |
| DebugLoc dl; |
| MachineBasicBlock::iterator TIE = TrueBBI.BB->getFirstTerminator(); |
| if (TIE != TrueBBI.BB->end()) |
| dl = TIE->getDebugLoc(); |
| // Removing branches from both blocks is safe, because we have already |
| // determined that both blocks have the same branch instructions. The branch |
| // will be added back at the end, unpredicated. |
| if (!IfConvertDiamondCommon( |
| BBI, TrueBBI, FalseBBI, |
| NumDups1, NumDups2, |
| TClobbersPred, FClobbersPred, |
| /* RemoveBranch */ true, /* MergeAddEdges */ true)) |
| return false; |
| |
| // Add back the branch. |
| // Debug location saved above when removing the branch from BBI2 |
| TII->insertBranch(*BBI.BB, TrueBBI.TrueBB, TrueBBI.FalseBB, |
| TrueBBI.BrCond, dl); |
| |
| // Update block info. |
| BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true; |
| InvalidatePreds(*BBI.BB); |
| |
| // FIXME: Must maintain LiveIns. |
| return true; |
| } |
| |
| /// If convert a diamond sub-CFG. |
| bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind, |
| unsigned NumDups1, unsigned NumDups2, |
| bool TClobbersPred, bool FClobbersPred) { |
| 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 (!IfConvertDiamondCommon( |
| BBI, TrueBBI, FalseBBI, |
| NumDups1, NumDups2, |
| TClobbersPred, FClobbersPred, |
| /* RemoveBranch */ TrueBBI.IsBrAnalyzable, |
| /* MergeAddEdges */ TailBB == nullptr)) |
| return false; |
| |
| // 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) { |
| // We need to remove the edges to the true and false blocks manually since |
| // we didn't let IfConvertDiamondCommon update the CFG. |
| BBI.BB->removeSuccessor(TrueBBI.BB); |
| BBI.BB->removeSuccessor(FalseBBI.BB, true); |
| |
| BBInfo &TailBBI = BBAnalysis[TailBB->getNumber()]; |
| bool CanMergeTail = !TailBBI.HasFallThrough && |
| !TailBBI.BB->hasAddressTaken(); |
| // The if-converted block can still have a predicated terminator |
| // (e.g. a predicated return). If that is the case, we cannot merge |
| // it with the tail block. |
| MachineBasicBlock::const_iterator TI = BBI.BB->getFirstTerminator(); |
| if (TI != BBI.BB->end() && TII->isPredicated(*TI)) |
| CanMergeTail = false; |
| // There may still be a fall-through edge from BBI1 or BBI2 to TailBB; |
| // check if there are any other predecessors besides those. |
| unsigned NumPreds = TailBB->pred_size(); |
| if (NumPreds > 1) |
| CanMergeTail = false; |
| else if (NumPreds == 1 && CanMergeTail) { |
| MachineBasicBlock::pred_iterator PI = TailBB->pred_begin(); |
| if (*PI != TrueBBI.BB && *PI != FalseBBI.BB) |
| CanMergeTail = false; |
| } |
| if (CanMergeTail) { |
| MergeBlocks(BBI, TailBBI); |
| TailBBI.IsDone = true; |
| } else { |
| BBI.BB->addSuccessor(TailBB, BranchProbability::getOne()); |
| InsertUncondBranch(*BBI.BB, *TailBB, TII); |
| BBI.HasFallThrough = false; |
| } |
| } |
| |
| // Update block info. |
| BBI.IsDone = TrueBBI.IsDone = FalseBBI.IsDone = true; |
| InvalidatePreds(*BBI.BB); |
| |
| // FIXME: Must maintain LiveIns. |
| return true; |
| } |
| |
| static bool MaySpeculate(const MachineInstr &MI, |
| SmallSet<MCPhysReg, 4> &LaterRedefs) { |
| bool SawStore = true; |
| if (!MI.isSafeToMove(nullptr, SawStore)) |
| return false; |
| |
| for (const MachineOperand &MO : MI.operands()) { |
| if (!MO.isReg()) |
| continue; |
| Register Reg = MO.getReg(); |
| if (!Reg) |
| continue; |
| if (MO.isDef() && !LaterRedefs.count(Reg)) |
| return false; |
| } |
| |
| return true; |
| } |
| |
| /// 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<MachineOperand> &Cond, |
| SmallSet<MCPhysReg, 4> *LaterRedefs) { |
| bool AnyUnpred = false; |
| bool MaySpec = LaterRedefs != nullptr; |
| for (MachineInstr &I : make_range(BBI.BB->begin(), E)) { |
| if (I.isDebugInstr() || TII->isPredicated(I)) |
| continue; |
| // It may be possible not to predicate an instruction if it's the 'true' |
| // side of a diamond and the 'false' side may re-define the instruction's |
| // defs. |
| if (MaySpec && MaySpeculate(I, *LaterRedefs)) { |
| AnyUnpred = true; |
| continue; |
| } |
| // If any instruction is predicated, then every instruction after it must |
| // be predicated. |
| MaySpec = false; |
| if (!TII->PredicateInstruction(I, Cond)) { |
| #ifndef NDEBUG |
| dbgs() << "Unable to predicate " << I << "!\n"; |
| #endif |
| llvm_unreachable(nullptr); |
| } |
| |
| // If the predicated instruction now redefines a register as the result of |
| // if-conversion, add an implicit kill. |
| UpdatePredRedefs(I, Redefs); |
| } |
| |
| BBI.Predicate.append(Cond.begin(), Cond.end()); |
| |
| BBI.IsAnalyzed = false; |
| BBI.NonPredSize = 0; |
| |
| ++NumIfConvBBs; |
| if (AnyUnpred) |
| ++NumUnpred; |
| } |
| |
| /// 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<MachineOperand> &Cond, |
| bool IgnoreBr) { |
| MachineFunction &MF = *ToBBI.BB->getParent(); |
| |
| MachineBasicBlock &FromMBB = *FromBBI.BB; |
| for (MachineInstr &I : FromMBB) { |
| // Do not copy the end of the block branches. |
| if (IgnoreBr && I.isBranch()) |
| break; |
| |
| MachineInstr *MI = MF.CloneMachineInstr(&I); |
| // Make a copy of the call site info. |
| if (I.isCandidateForCallSiteEntry()) |
| MF.copyCallSiteInfo(&I, MI); |
| |
| ToBBI.BB->insert(ToBBI.BB->end(), MI); |
| ToBBI.NonPredSize++; |
| unsigned ExtraPredCost = TII->getPredicationCost(I); |
| unsigned NumCycles = SchedModel.computeInstrLatency(&I, false); |
| if (NumCycles > 1) |
| ToBBI.ExtraCost += NumCycles-1; |
| ToBBI.ExtraCost2 += ExtraPredCost; |
| |
| if (!TII->isPredicated(I) && !MI->isDebugInstr()) { |
| if (!TII->PredicateInstruction(*MI, Cond)) { |
| #ifndef NDEBUG |
| dbgs() << "Unable to predicate " << I << "!\n"; |
| #endif |
| llvm_unreachable(nullptr); |
| } |
| } |
| |
| // If the predicated instruction now redefines a register as the result of |
| // if-conversion, add an implicit kill. |
| UpdatePredRedefs(*MI, Redefs); |
| } |
| |
| if (!IgnoreBr) { |
| std::vector<MachineBasicBlock *> Succs(FromMBB.succ_begin(), |
| FromMBB.succ_end()); |
| MachineBasicBlock *NBB = getNextBlock(FromMBB); |
| MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : nullptr; |
| |
| for (MachineBasicBlock *Succ : Succs) { |
| // Fallthrough edge can't be transferred. |
| if (Succ == FallThrough) |
| continue; |
| ToBBI.BB->addSuccessor(Succ); |
| } |
| } |
| |
| ToBBI.Predicate.append(FromBBI.Predicate.begin(), FromBBI.Predicate.end()); |
| ToBBI.Predicate.append(Cond.begin(), Cond.end()); |
| |
| ToBBI.ClobbersPred |= FromBBI.ClobbersPred; |
| ToBBI.IsAnalyzed = false; |
| |
| ++NumDupBBs; |
| } |
| |
| /// Move all instructions from FromBB to the end of ToBB. This will leave |
| /// FromBB as an empty block, so remove all of its successor edges and move it |
| /// to the end of the function. If AddEdges is true, i.e., when FromBBI's |
| /// branch is being moved, add those successor edges to ToBBI and remove the old |
| /// edge from ToBBI to FromBBI. |
| void IfConverter::MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges) { |
| MachineBasicBlock &FromMBB = *FromBBI.BB; |
| assert(!FromMBB.hasAddressTaken() && |
| "Removing a BB whose address is taken!"); |
| |
| // In case FromMBB contains terminators (e.g. return instruction), |
| // first move the non-terminator instructions, then the terminators. |
| MachineBasicBlock::iterator FromTI = FromMBB.getFirstTerminator(); |
| MachineBasicBlock::iterator ToTI = ToBBI.BB->getFirstTerminator(); |
| ToBBI.BB->splice(ToTI, &FromMBB, FromMBB.begin(), FromTI); |
| |
| // If FromBB has non-predicated terminator we should copy it at the end. |
| if (FromTI != FromMBB.end() && !TII->isPredicated(*FromTI)) |
| ToTI = ToBBI.BB->end(); |
| ToBBI.BB->splice(ToTI, &FromMBB, FromTI, FromMBB.end()); |
| |
| // Force normalizing the successors' probabilities of ToBBI.BB to convert all |
| // unknown probabilities into known ones. |
| // FIXME: This usage is too tricky and in the future we would like to |
| // eliminate all unknown probabilities in MBB. |
| if (ToBBI.IsBrAnalyzable) |
| ToBBI.BB->normalizeSuccProbs(); |
| |
| SmallVector<MachineBasicBlock *, 4> FromSuccs(FromMBB.successors()); |
| MachineBasicBlock *NBB = getNextBlock(FromMBB); |
| MachineBasicBlock *FallThrough = FromBBI.HasFallThrough ? NBB : nullptr; |
| // The edge probability from ToBBI.BB to FromMBB, which is only needed when |
| // AddEdges is true and FromMBB is a successor of ToBBI.BB. |
| auto To2FromProb = BranchProbability::getZero(); |
| if (AddEdges && ToBBI.BB->isSuccessor(&FromMBB)) { |
| // Remove the old edge but remember the edge probability so we can calculate |
| // the correct weights on the new edges being added further down. |
| To2FromProb = MBPI->getEdgeProbability(ToBBI.BB, &FromMBB); |
| ToBBI.BB->removeSuccessor(&FromMBB); |
| } |
| |
| for (MachineBasicBlock *Succ : FromSuccs) { |
| // Fallthrough edge can't be transferred. |
| if (Succ == FallThrough) { |
| FromMBB.removeSuccessor(Succ); |
| continue; |
| } |
| |
| auto NewProb = BranchProbability::getZero(); |
| if (AddEdges) { |
| // Calculate the edge probability for the edge from ToBBI.BB to Succ, |
| // which is a portion of the edge probability from FromMBB to Succ. The |
| // portion ratio is the edge probability from ToBBI.BB to FromMBB (if |
| // FromBBI is a successor of ToBBI.BB. See comment below for exception). |
| NewProb = MBPI->getEdgeProbability(&FromMBB, Succ); |
| |
| // To2FromProb is 0 when FromMBB is not a successor of ToBBI.BB. This |
| // only happens when if-converting a diamond CFG and FromMBB is the |
| // tail BB. In this case FromMBB post-dominates ToBBI.BB and hence we |
| // could just use the probabilities on FromMBB's out-edges when adding |
| // new successors. |
| if (!To2FromProb.isZero()) |
| NewProb *= To2FromProb; |
| } |
| |
| FromMBB.removeSuccessor(Succ); |
| |
| if (AddEdges) { |
| // If the edge from ToBBI.BB to Succ already exists, update the |
| // probability of this edge by adding NewProb to it. An example is shown |
| // below, in which A is ToBBI.BB and B is FromMBB. In this case we |
| // don't have to set C as A's successor as it already is. We only need to |
| // update the edge probability on A->C. Note that B will not be |
| // immediately removed from A's successors. It is possible that B->D is |
| // not removed either if D is a fallthrough of B. Later the edge A->D |
| // (generated here) and B->D will be combined into one edge. To maintain |
| // correct edge probability of this combined edge, we need to set the edge |
| // probability of A->B to zero, which is already done above. The edge |
| // probability on A->D is calculated by scaling the original probability |
| // on A->B by the probability of B->D. |
| // |
| // Before ifcvt: After ifcvt (assume B->D is kept): |
| // |
| // A A |
| // /| /|\ |
| // / B / B| |
| // | /| | || |
| // |/ | | |/ |
| // C D C D |
| // |
| if (ToBBI.BB->isSuccessor(Succ)) |
| ToBBI.BB->setSuccProbability( |
| find(ToBBI.BB->successors(), Succ), |
| MBPI->getEdgeProbability(ToBBI.BB, Succ) + NewProb); |
| else |
| ToBBI.BB->addSuccessor(Succ, NewProb); |
| } |
| } |
| |
| // Move the now empty FromMBB out of the way to the end of the function so |
| // it doesn't interfere with fallthrough checks done by canFallThroughTo(). |
| MachineBasicBlock *Last = &*FromMBB.getParent()->rbegin(); |
| if (Last != &FromMBB) |
| FromMBB.moveAfter(Last); |
| |
| // Normalize the probabilities of ToBBI.BB's successors with all adjustment |
| // we've done above. |
| if (ToBBI.IsBrAnalyzable && FromBBI.IsBrAnalyzable) |
| ToBBI.BB->normalizeSuccProbs(); |
| |
| ToBBI.Predicate.append(FromBBI.Predicate.begin(), FromBBI.Predicate.end()); |
| FromBBI.Predicate.clear(); |
| |
| ToBBI.NonPredSize += FromBBI.NonPredSize; |
| ToBBI.ExtraCost += FromBBI.ExtraCost; |
| ToBBI.ExtraCost2 += FromBBI.ExtraCost2; |
| FromBBI.NonPredSize = 0; |
| FromBBI.ExtraCost = 0; |
| FromBBI.ExtraCost2 = 0; |
| |
| ToBBI.ClobbersPred |= FromBBI.ClobbersPred; |
| ToBBI.HasFallThrough = FromBBI.HasFallThrough; |
| ToBBI.IsAnalyzed = false; |
| FromBBI.IsAnalyzed = false; |
| } |
| |
| FunctionPass * |
| llvm::createIfConverter(std::function<bool(const MachineFunction &)> Ftor) { |
| return new IfConverter(std::move(Ftor)); |
| } |