diff options
Diffstat (limited to 'lib/CodeGen/TailDuplication.cpp')
| -rw-r--r-- | lib/CodeGen/TailDuplication.cpp | 963 |
1 files changed, 20 insertions, 943 deletions
diff --git a/lib/CodeGen/TailDuplication.cpp b/lib/CodeGen/TailDuplication.cpp index d2fbf533a787..2b1fb127497a 100644 --- a/lib/CodeGen/TailDuplication.cpp +++ b/lib/CodeGen/TailDuplication.cpp @@ -8,147 +8,52 @@ //===----------------------------------------------------------------------===// // // This pass duplicates basic blocks ending in unconditional branches into -// the tails of their predecessors. +// the tails of their predecessors, using the TailDuplicator utility class. // //===----------------------------------------------------------------------===// -#include "llvm/CodeGen/Passes.h" -#include "llvm/ADT/DenseSet.h" -#include "llvm/ADT/SetVector.h" -#include "llvm/ADT/SmallSet.h" -#include "llvm/ADT/Statistic.h" -#include "llvm/CodeGen/MachineBranchProbabilityInfo.h" #include "llvm/CodeGen/MachineFunctionPass.h" -#include "llvm/CodeGen/MachineInstrBuilder.h" -#include "llvm/CodeGen/MachineModuleInfo.h" -#include "llvm/CodeGen/MachineRegisterInfo.h" -#include "llvm/CodeGen/MachineSSAUpdater.h" -#include "llvm/CodeGen/RegisterScavenging.h" +#include "llvm/CodeGen/Passes.h" +#include "llvm/CodeGen/TailDuplicator.h" #include "llvm/IR/Function.h" -#include "llvm/Support/CommandLine.h" #include "llvm/Support/Debug.h" -#include "llvm/Support/ErrorHandling.h" -#include "llvm/Support/raw_ostream.h" -#include "llvm/Target/TargetInstrInfo.h" -#include "llvm/Target/TargetRegisterInfo.h" -#include "llvm/Target/TargetSubtargetInfo.h" using namespace llvm; #define DEBUG_TYPE "tailduplication" -STATISTIC(NumTails , "Number of tails duplicated"); -STATISTIC(NumTailDups , "Number of tail duplicated blocks"); -STATISTIC(NumInstrDups , "Additional instructions due to tail duplication"); -STATISTIC(NumDeadBlocks, "Number of dead blocks removed"); -STATISTIC(NumAddedPHIs , "Number of phis added"); - -// Heuristic for tail duplication. -static cl::opt<unsigned> -TailDuplicateSize("tail-dup-size", - cl::desc("Maximum instructions to consider tail duplicating"), - cl::init(2), cl::Hidden); - -static cl::opt<bool> -TailDupVerify("tail-dup-verify", - cl::desc("Verify sanity of PHI instructions during taildup"), - cl::init(false), cl::Hidden); - -static cl::opt<unsigned> -TailDupLimit("tail-dup-limit", cl::init(~0U), cl::Hidden); - -typedef std::vector<std::pair<MachineBasicBlock*,unsigned> > AvailableValsTy; - namespace { - /// Perform tail duplication. - class TailDuplicatePass : public MachineFunctionPass { - const TargetInstrInfo *TII; - const TargetRegisterInfo *TRI; - const MachineBranchProbabilityInfo *MBPI; - MachineModuleInfo *MMI; - MachineRegisterInfo *MRI; - std::unique_ptr<RegScavenger> RS; - bool PreRegAlloc; - - // A list of virtual registers for which to update SSA form. - SmallVector<unsigned, 16> SSAUpdateVRs; - - // For each virtual register in SSAUpdateVals keep a list of source virtual - // registers. - DenseMap<unsigned, AvailableValsTy> SSAUpdateVals; +/// Perform tail duplication. Delegates to TailDuplicator +class TailDuplicatePass : public MachineFunctionPass { + TailDuplicator Duplicator; - public: - static char ID; - explicit TailDuplicatePass() : - MachineFunctionPass(ID), PreRegAlloc(false) {} +public: + static char ID; + explicit TailDuplicatePass() : MachineFunctionPass(ID) {} - bool runOnMachineFunction(MachineFunction &MF) override; + bool runOnMachineFunction(MachineFunction &MF) override; - void getAnalysisUsage(AnalysisUsage &AU) const override; + void getAnalysisUsage(AnalysisUsage &AU) const override; +}; - private: - void AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg, - MachineBasicBlock *BB); - void ProcessPHI(MachineInstr *MI, MachineBasicBlock *TailBB, - MachineBasicBlock *PredBB, - DenseMap<unsigned, unsigned> &LocalVRMap, - SmallVectorImpl<std::pair<unsigned,unsigned> > &Copies, - const DenseSet<unsigned> &UsedByPhi, - bool Remove); - void DuplicateInstruction(MachineInstr *MI, - MachineBasicBlock *TailBB, - MachineBasicBlock *PredBB, - MachineFunction &MF, - DenseMap<unsigned, unsigned> &LocalVRMap, - const DenseSet<unsigned> &UsedByPhi); - void UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead, - SmallVectorImpl<MachineBasicBlock *> &TDBBs, - SmallSetVector<MachineBasicBlock*, 8> &Succs); - bool TailDuplicateBlocks(MachineFunction &MF); - bool shouldTailDuplicate(const MachineFunction &MF, - bool IsSimple, MachineBasicBlock &TailBB); - bool isSimpleBB(MachineBasicBlock *TailBB); - bool canCompletelyDuplicateBB(MachineBasicBlock &BB); - bool duplicateSimpleBB(MachineBasicBlock *TailBB, - SmallVectorImpl<MachineBasicBlock *> &TDBBs, - const DenseSet<unsigned> &RegsUsedByPhi, - SmallVectorImpl<MachineInstr *> &Copies); - bool TailDuplicate(MachineBasicBlock *TailBB, - bool IsSimple, - MachineFunction &MF, - SmallVectorImpl<MachineBasicBlock *> &TDBBs, - SmallVectorImpl<MachineInstr *> &Copies); - bool TailDuplicateAndUpdate(MachineBasicBlock *MBB, - bool IsSimple, - MachineFunction &MF); - - void RemoveDeadBlock(MachineBasicBlock *MBB); - }; - - char TailDuplicatePass::ID = 0; +char TailDuplicatePass::ID = 0; } char &llvm::TailDuplicateID = TailDuplicatePass::ID; -INITIALIZE_PASS(TailDuplicatePass, "tailduplication", "Tail Duplication", - false, false) +INITIALIZE_PASS(TailDuplicatePass, "tailduplication", "Tail Duplication", false, + false) bool TailDuplicatePass::runOnMachineFunction(MachineFunction &MF) { - if (skipOptnoneFunction(*MF.getFunction())) + if (skipFunction(*MF.getFunction())) return false; - TII = MF.getSubtarget().getInstrInfo(); - TRI = MF.getSubtarget().getRegisterInfo(); - MRI = &MF.getRegInfo(); - MMI = getAnalysisIfAvailable<MachineModuleInfo>(); - MBPI = &getAnalysis<MachineBranchProbabilityInfo>(); + auto MMI = getAnalysisIfAvailable<MachineModuleInfo>(); + auto MBPI = &getAnalysis<MachineBranchProbabilityInfo>(); - PreRegAlloc = MRI->isSSA(); - RS.reset(); - if (MRI->tracksLiveness() && TRI->trackLivenessAfterRegAlloc(MF)) - RS.reset(new RegScavenger()); + Duplicator.initMF(MF, MMI, MBPI); bool MadeChange = false; - while (TailDuplicateBlocks(MF)) + while (Duplicator.tailDuplicateBlocks(MF)) MadeChange = true; return MadeChange; @@ -158,831 +63,3 @@ void TailDuplicatePass::getAnalysisUsage(AnalysisUsage &AU) const { AU.addRequired<MachineBranchProbabilityInfo>(); MachineFunctionPass::getAnalysisUsage(AU); } - -static void VerifyPHIs(MachineFunction &MF, bool CheckExtra) { - for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ++I) { - MachineBasicBlock *MBB = &*I; - SmallSetVector<MachineBasicBlock*, 8> Preds(MBB->pred_begin(), - MBB->pred_end()); - MachineBasicBlock::iterator MI = MBB->begin(); - while (MI != MBB->end()) { - if (!MI->isPHI()) - break; - for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(), - PE = Preds.end(); PI != PE; ++PI) { - MachineBasicBlock *PredBB = *PI; - bool Found = false; - for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) { - MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB(); - if (PHIBB == PredBB) { - Found = true; - break; - } - } - if (!Found) { - dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI; - dbgs() << " missing input from predecessor BB#" - << PredBB->getNumber() << '\n'; - llvm_unreachable(nullptr); - } - } - - for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) { - MachineBasicBlock *PHIBB = MI->getOperand(i+1).getMBB(); - if (CheckExtra && !Preds.count(PHIBB)) { - dbgs() << "Warning: malformed PHI in BB#" << MBB->getNumber() - << ": " << *MI; - dbgs() << " extra input from predecessor BB#" - << PHIBB->getNumber() << '\n'; - llvm_unreachable(nullptr); - } - if (PHIBB->getNumber() < 0) { - dbgs() << "Malformed PHI in BB#" << MBB->getNumber() << ": " << *MI; - dbgs() << " non-existing BB#" << PHIBB->getNumber() << '\n'; - llvm_unreachable(nullptr); - } - } - ++MI; - } - } -} - -/// Tail duplicate the block and cleanup. -bool -TailDuplicatePass::TailDuplicateAndUpdate(MachineBasicBlock *MBB, - bool IsSimple, - MachineFunction &MF) { - // Save the successors list. - SmallSetVector<MachineBasicBlock*, 8> Succs(MBB->succ_begin(), - MBB->succ_end()); - - SmallVector<MachineBasicBlock*, 8> TDBBs; - SmallVector<MachineInstr*, 16> Copies; - if (!TailDuplicate(MBB, IsSimple, MF, TDBBs, Copies)) - return false; - - ++NumTails; - - SmallVector<MachineInstr*, 8> NewPHIs; - MachineSSAUpdater SSAUpdate(MF, &NewPHIs); - - // TailBB's immediate successors are now successors of those predecessors - // which duplicated TailBB. Add the predecessors as sources to the PHI - // instructions. - bool isDead = MBB->pred_empty() && !MBB->hasAddressTaken(); - if (PreRegAlloc) - UpdateSuccessorsPHIs(MBB, isDead, TDBBs, Succs); - - // If it is dead, remove it. - if (isDead) { - NumInstrDups -= MBB->size(); - RemoveDeadBlock(MBB); - ++NumDeadBlocks; - } - - // Update SSA form. - if (!SSAUpdateVRs.empty()) { - for (unsigned i = 0, e = SSAUpdateVRs.size(); i != e; ++i) { - unsigned VReg = SSAUpdateVRs[i]; - SSAUpdate.Initialize(VReg); - - // If the original definition is still around, add it as an available - // value. - MachineInstr *DefMI = MRI->getVRegDef(VReg); - MachineBasicBlock *DefBB = nullptr; - if (DefMI) { - DefBB = DefMI->getParent(); - SSAUpdate.AddAvailableValue(DefBB, VReg); - } - - // Add the new vregs as available values. - DenseMap<unsigned, AvailableValsTy>::iterator LI = - SSAUpdateVals.find(VReg); - for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) { - MachineBasicBlock *SrcBB = LI->second[j].first; - unsigned SrcReg = LI->second[j].second; - SSAUpdate.AddAvailableValue(SrcBB, SrcReg); - } - - // Rewrite uses that are outside of the original def's block. - MachineRegisterInfo::use_iterator UI = MRI->use_begin(VReg); - while (UI != MRI->use_end()) { - MachineOperand &UseMO = *UI; - MachineInstr *UseMI = UseMO.getParent(); - ++UI; - if (UseMI->isDebugValue()) { - // SSAUpdate can replace the use with an undef. That creates - // a debug instruction that is a kill. - // FIXME: Should it SSAUpdate job to delete debug instructions - // instead of replacing the use with undef? - UseMI->eraseFromParent(); - continue; - } - if (UseMI->getParent() == DefBB && !UseMI->isPHI()) - continue; - SSAUpdate.RewriteUse(UseMO); - } - } - - SSAUpdateVRs.clear(); - SSAUpdateVals.clear(); - } - - // Eliminate some of the copies inserted by tail duplication to maintain - // SSA form. - for (unsigned i = 0, e = Copies.size(); i != e; ++i) { - MachineInstr *Copy = Copies[i]; - if (!Copy->isCopy()) - continue; - unsigned Dst = Copy->getOperand(0).getReg(); - unsigned Src = Copy->getOperand(1).getReg(); - if (MRI->hasOneNonDBGUse(Src) && - MRI->constrainRegClass(Src, MRI->getRegClass(Dst))) { - // Copy is the only use. Do trivial copy propagation here. - MRI->replaceRegWith(Dst, Src); - Copy->eraseFromParent(); - } - } - - if (NewPHIs.size()) - NumAddedPHIs += NewPHIs.size(); - - return true; -} - -/// Look for small blocks that are unconditionally branched to and do not fall -/// through. Tail-duplicate their instructions into their predecessors to -/// eliminate (dynamic) branches. -bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) { - bool MadeChange = false; - - if (PreRegAlloc && TailDupVerify) { - DEBUG(dbgs() << "\n*** Before tail-duplicating\n"); - VerifyPHIs(MF, true); - } - - for (MachineFunction::iterator I = ++MF.begin(), E = MF.end(); I != E; ) { - MachineBasicBlock *MBB = &*I++; - - if (NumTails == TailDupLimit) - break; - - bool IsSimple = isSimpleBB(MBB); - - if (!shouldTailDuplicate(MF, IsSimple, *MBB)) - continue; - - MadeChange |= TailDuplicateAndUpdate(MBB, IsSimple, MF); - } - - if (PreRegAlloc && TailDupVerify) - VerifyPHIs(MF, false); - - return MadeChange; -} - -static bool isDefLiveOut(unsigned Reg, MachineBasicBlock *BB, - const MachineRegisterInfo *MRI) { - for (MachineInstr &UseMI : MRI->use_instructions(Reg)) { - if (UseMI.isDebugValue()) - continue; - if (UseMI.getParent() != BB) - return true; - } - return false; -} - -static unsigned getPHISrcRegOpIdx(MachineInstr *MI, MachineBasicBlock *SrcBB) { - for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) - if (MI->getOperand(i+1).getMBB() == SrcBB) - return i; - return 0; -} - - -// Remember which registers are used by phis in this block. This is -// used to determine which registers are liveout while modifying the -// block (which is why we need to copy the information). -static void getRegsUsedByPHIs(const MachineBasicBlock &BB, - DenseSet<unsigned> *UsedByPhi) { - for (const auto &MI : BB) { - if (!MI.isPHI()) - break; - for (unsigned i = 1, e = MI.getNumOperands(); i != e; i += 2) { - unsigned SrcReg = MI.getOperand(i).getReg(); - UsedByPhi->insert(SrcReg); - } - } -} - -/// Add a definition and source virtual registers pair for SSA update. -void TailDuplicatePass::AddSSAUpdateEntry(unsigned OrigReg, unsigned NewReg, - MachineBasicBlock *BB) { - DenseMap<unsigned, AvailableValsTy>::iterator LI= SSAUpdateVals.find(OrigReg); - if (LI != SSAUpdateVals.end()) - LI->second.push_back(std::make_pair(BB, NewReg)); - else { - AvailableValsTy Vals; - Vals.push_back(std::make_pair(BB, NewReg)); - SSAUpdateVals.insert(std::make_pair(OrigReg, Vals)); - SSAUpdateVRs.push_back(OrigReg); - } -} - -/// Process PHI node in TailBB by turning it into a copy in PredBB. Remember the -/// source register that's contributed by PredBB and update SSA update map. -void TailDuplicatePass::ProcessPHI( - MachineInstr *MI, MachineBasicBlock *TailBB, MachineBasicBlock *PredBB, - DenseMap<unsigned, unsigned> &LocalVRMap, - SmallVectorImpl<std::pair<unsigned, unsigned> > &Copies, - const DenseSet<unsigned> &RegsUsedByPhi, bool Remove) { - unsigned DefReg = MI->getOperand(0).getReg(); - unsigned SrcOpIdx = getPHISrcRegOpIdx(MI, PredBB); - assert(SrcOpIdx && "Unable to find matching PHI source?"); - unsigned SrcReg = MI->getOperand(SrcOpIdx).getReg(); - const TargetRegisterClass *RC = MRI->getRegClass(DefReg); - LocalVRMap.insert(std::make_pair(DefReg, SrcReg)); - - // Insert a copy from source to the end of the block. The def register is the - // available value liveout of the block. - unsigned NewDef = MRI->createVirtualRegister(RC); - Copies.push_back(std::make_pair(NewDef, SrcReg)); - if (isDefLiveOut(DefReg, TailBB, MRI) || RegsUsedByPhi.count(DefReg)) - AddSSAUpdateEntry(DefReg, NewDef, PredBB); - - if (!Remove) - return; - - // Remove PredBB from the PHI node. - MI->RemoveOperand(SrcOpIdx+1); - MI->RemoveOperand(SrcOpIdx); - if (MI->getNumOperands() == 1) - MI->eraseFromParent(); -} - -/// Duplicate a TailBB instruction to PredBB and update -/// the source operands due to earlier PHI translation. -void TailDuplicatePass::DuplicateInstruction(MachineInstr *MI, - MachineBasicBlock *TailBB, - MachineBasicBlock *PredBB, - MachineFunction &MF, - DenseMap<unsigned, unsigned> &LocalVRMap, - const DenseSet<unsigned> &UsedByPhi) { - MachineInstr *NewMI = TII->duplicate(MI, MF); - for (unsigned i = 0, e = NewMI->getNumOperands(); i != e; ++i) { - MachineOperand &MO = NewMI->getOperand(i); - if (!MO.isReg()) - continue; - unsigned Reg = MO.getReg(); - if (!TargetRegisterInfo::isVirtualRegister(Reg)) - continue; - if (MO.isDef()) { - const TargetRegisterClass *RC = MRI->getRegClass(Reg); - unsigned NewReg = MRI->createVirtualRegister(RC); - MO.setReg(NewReg); - LocalVRMap.insert(std::make_pair(Reg, NewReg)); - if (isDefLiveOut(Reg, TailBB, MRI) || UsedByPhi.count(Reg)) - AddSSAUpdateEntry(Reg, NewReg, PredBB); - } else { - DenseMap<unsigned, unsigned>::iterator VI = LocalVRMap.find(Reg); - if (VI != LocalVRMap.end()) { - MO.setReg(VI->second); - // Clear any kill flags from this operand. The new register could have - // uses after this one, so kills are not valid here. - MO.setIsKill(false); - MRI->constrainRegClass(VI->second, MRI->getRegClass(Reg)); - } - } - } - PredBB->insert(PredBB->instr_end(), NewMI); -} - -/// After FromBB is tail duplicated into its predecessor blocks, the successors -/// have gained new predecessors. Update the PHI instructions in them -/// accordingly. -void -TailDuplicatePass::UpdateSuccessorsPHIs(MachineBasicBlock *FromBB, bool isDead, - SmallVectorImpl<MachineBasicBlock *> &TDBBs, - SmallSetVector<MachineBasicBlock*,8> &Succs) { - for (SmallSetVector<MachineBasicBlock*, 8>::iterator SI = Succs.begin(), - SE = Succs.end(); SI != SE; ++SI) { - MachineBasicBlock *SuccBB = *SI; - for (MachineBasicBlock::iterator II = SuccBB->begin(), EE = SuccBB->end(); - II != EE; ++II) { - if (!II->isPHI()) - break; - MachineInstrBuilder MIB(*FromBB->getParent(), II); - unsigned Idx = 0; - for (unsigned i = 1, e = II->getNumOperands(); i != e; i += 2) { - MachineOperand &MO = II->getOperand(i+1); - if (MO.getMBB() == FromBB) { - Idx = i; - break; - } - } - - assert(Idx != 0); - MachineOperand &MO0 = II->getOperand(Idx); - unsigned Reg = MO0.getReg(); - if (isDead) { - // Folded into the previous BB. - // There could be duplicate phi source entries. FIXME: Should sdisel - // or earlier pass fixed this? - for (unsigned i = II->getNumOperands()-2; i != Idx; i -= 2) { - MachineOperand &MO = II->getOperand(i+1); - if (MO.getMBB() == FromBB) { - II->RemoveOperand(i+1); - II->RemoveOperand(i); - } - } - } else - Idx = 0; - - // If Idx is set, the operands at Idx and Idx+1 must be removed. - // We reuse the location to avoid expensive RemoveOperand calls. - - DenseMap<unsigned,AvailableValsTy>::iterator LI=SSAUpdateVals.find(Reg); - if (LI != SSAUpdateVals.end()) { - // This register is defined in the tail block. - for (unsigned j = 0, ee = LI->second.size(); j != ee; ++j) { - MachineBasicBlock *SrcBB = LI->second[j].first; - // If we didn't duplicate a bb into a particular predecessor, we - // might still have added an entry to SSAUpdateVals to correcly - // recompute SSA. If that case, avoid adding a dummy extra argument - // this PHI. - if (!SrcBB->isSuccessor(SuccBB)) - continue; - - unsigned SrcReg = LI->second[j].second; - if (Idx != 0) { - II->getOperand(Idx).setReg(SrcReg); - II->getOperand(Idx+1).setMBB(SrcBB); - Idx = 0; - } else { - MIB.addReg(SrcReg).addMBB(SrcBB); - } - } - } else { - // Live in tail block, must also be live in predecessors. - for (unsigned j = 0, ee = TDBBs.size(); j != ee; ++j) { - MachineBasicBlock *SrcBB = TDBBs[j]; - if (Idx != 0) { - II->getOperand(Idx).setReg(Reg); - II->getOperand(Idx+1).setMBB(SrcBB); - Idx = 0; - } else { - MIB.addReg(Reg).addMBB(SrcBB); - } - } - } - if (Idx != 0) { - II->RemoveOperand(Idx+1); - II->RemoveOperand(Idx); - } - } - } -} - -/// Determine if it is profitable to duplicate this block. -bool -TailDuplicatePass::shouldTailDuplicate(const MachineFunction &MF, - bool IsSimple, - MachineBasicBlock &TailBB) { - // Only duplicate blocks that end with unconditional branches. - if (TailBB.canFallThrough()) - return false; - - // Don't try to tail-duplicate single-block loops. - if (TailBB.isSuccessor(&TailBB)) - return false; - - // Set the limit on the cost to duplicate. When optimizing for size, - // duplicate only one, because one branch instruction can be eliminated to - // compensate for the duplication. - unsigned MaxDuplicateCount; - if (TailDuplicateSize.getNumOccurrences() == 0 && - // FIXME: Use Function::optForSize(). - MF.getFunction()->hasFnAttribute(Attribute::OptimizeForSize)) - MaxDuplicateCount = 1; - else - MaxDuplicateCount = TailDuplicateSize; - - // If the target has hardware branch prediction that can handle indirect - // branches, duplicating them can often make them predictable when there - // are common paths through the code. The limit needs to be high enough - // to allow undoing the effects of tail merging and other optimizations - // that rearrange the predecessors of the indirect branch. - - bool HasIndirectbr = false; - if (!TailBB.empty()) - HasIndirectbr = TailBB.back().isIndirectBranch(); - - if (HasIndirectbr && PreRegAlloc) - MaxDuplicateCount = 20; - - // Check the instructions in the block to determine whether tail-duplication - // is invalid or unlikely to be profitable. - unsigned InstrCount = 0; - for (MachineInstr &MI : TailBB) { - // Non-duplicable things shouldn't be tail-duplicated. - if (MI.isNotDuplicable()) - return false; - - // Do not duplicate 'return' instructions if this is a pre-regalloc run. - // A return may expand into a lot more instructions (e.g. reload of callee - // saved registers) after PEI. - if (PreRegAlloc && MI.isReturn()) - return false; - - // Avoid duplicating calls before register allocation. Calls presents a - // barrier to register allocation so duplicating them may end up increasing - // spills. - if (PreRegAlloc && MI.isCall()) - return false; - - if (!MI.isPHI() && !MI.isDebugValue()) - InstrCount += 1; - - if (InstrCount > MaxDuplicateCount) - return false; - } - - // Check if any of the successors of TailBB has a PHI node in which the - // value corresponding to TailBB uses a subregister. - // If a phi node uses a register paired with a subregister, the actual - // "value type" of the phi may differ from the type of the register without - // any subregisters. Due to a bug, tail duplication may add a new operand - // without a necessary subregister, producing an invalid code. This is - // demonstrated by test/CodeGen/Hexagon/tail-dup-subreg-abort.ll. - // Disable tail duplication for this case for now, until the problem is - // fixed. - for (auto SB : TailBB.successors()) { - for (auto &I : *SB) { - if (!I.isPHI()) - break; - unsigned Idx = getPHISrcRegOpIdx(&I, &TailBB); - assert(Idx != 0); - MachineOperand &PU = I.getOperand(Idx); - if (PU.getSubReg() != 0) - return false; - } - } - - if (HasIndirectbr && PreRegAlloc) - return true; - - if (IsSimple) - return true; - - if (!PreRegAlloc) - return true; - - return canCompletelyDuplicateBB(TailBB); -} - -/// True if this BB has only one unconditional jump. -bool -TailDuplicatePass::isSimpleBB(MachineBasicBlock *TailBB) { - if (TailBB->succ_size() != 1) - return false; - if (TailBB->pred_empty()) - return false; - MachineBasicBlock::iterator I = TailBB->getFirstNonDebugInstr(); - if (I == TailBB->end()) - return true; - return I->isUnconditionalBranch(); -} - -static bool -bothUsedInPHI(const MachineBasicBlock &A, - SmallPtrSet<MachineBasicBlock*, 8> SuccsB) { - for (MachineBasicBlock *BB : A.successors()) - if (SuccsB.count(BB) && !BB->empty() && BB->begin()->isPHI()) - return true; - - return false; -} - -bool -TailDuplicatePass::canCompletelyDuplicateBB(MachineBasicBlock &BB) { - for (MachineBasicBlock *PredBB : BB.predecessors()) { - if (PredBB->succ_size() > 1) - return false; - - MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr; - SmallVector<MachineOperand, 4> PredCond; - if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true)) - return false; - - if (!PredCond.empty()) - return false; - } - return true; -} - -bool -TailDuplicatePass::duplicateSimpleBB(MachineBasicBlock *TailBB, - SmallVectorImpl<MachineBasicBlock *> &TDBBs, - const DenseSet<unsigned> &UsedByPhi, - SmallVectorImpl<MachineInstr *> &Copies) { - SmallPtrSet<MachineBasicBlock*, 8> Succs(TailBB->succ_begin(), - TailBB->succ_end()); - SmallVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(), - TailBB->pred_end()); - bool Changed = false; - for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(), - PE = Preds.end(); PI != PE; ++PI) { - MachineBasicBlock *PredBB = *PI; - - if (PredBB->hasEHPadSuccessor()) - continue; - - if (bothUsedInPHI(*PredBB, Succs)) - continue; - - MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr; - SmallVector<MachineOperand, 4> PredCond; - if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true)) - continue; - - Changed = true; - DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB - << "From simple Succ: " << *TailBB); - - MachineBasicBlock *NewTarget = *TailBB->succ_begin(); - MachineBasicBlock *NextBB = &*std::next(PredBB->getIterator()); - - // Make PredFBB explicit. - if (PredCond.empty()) - PredFBB = PredTBB; - - // Make fall through explicit. - if (!PredTBB) - PredTBB = NextBB; - if (!PredFBB) - PredFBB = NextBB; - - // Redirect - if (PredFBB == TailBB) - PredFBB = NewTarget; - if (PredTBB == TailBB) - PredTBB = NewTarget; - - // Make the branch unconditional if possible - if (PredTBB == PredFBB) { - PredCond.clear(); - PredFBB = nullptr; - } - - // Avoid adding fall through branches. - if (PredFBB == NextBB) - PredFBB = nullptr; - if (PredTBB == NextBB && PredFBB == nullptr) - PredTBB = nullptr; - - TII->RemoveBranch(*PredBB); - - if (PredTBB) - TII->InsertBranch(*PredBB, PredTBB, PredFBB, PredCond, DebugLoc()); - - if (!PredBB->isSuccessor(NewTarget)) - PredBB->replaceSuccessor(TailBB, NewTarget); - else { - PredBB->removeSuccessor(TailBB, true); - assert(PredBB->succ_size() <= 1); - } - - TDBBs.push_back(PredBB); - } - return Changed; -} - -/// If it is profitable, duplicate TailBB's contents in each -/// of its predecessors. -bool -TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, - bool IsSimple, - MachineFunction &MF, - SmallVectorImpl<MachineBasicBlock *> &TDBBs, - SmallVectorImpl<MachineInstr *> &Copies) { - DEBUG(dbgs() << "\n*** Tail-duplicating BB#" << TailBB->getNumber() << '\n'); - - DenseSet<unsigned> UsedByPhi; - getRegsUsedByPHIs(*TailBB, &UsedByPhi); - - if (IsSimple) - return duplicateSimpleBB(TailBB, TDBBs, UsedByPhi, Copies); - - // Iterate through all the unique predecessors and tail-duplicate this - // block into them, if possible. Copying the list ahead of time also - // avoids trouble with the predecessor list reallocating. - bool Changed = false; - SmallSetVector<MachineBasicBlock*, 8> Preds(TailBB->pred_begin(), - TailBB->pred_end()); - for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(), - PE = Preds.end(); PI != PE; ++PI) { - MachineBasicBlock *PredBB = *PI; - - assert(TailBB != PredBB && - "Single-block loop should have been rejected earlier!"); - // EH edges are ignored by AnalyzeBranch. - if (PredBB->succ_size() > 1) - continue; - - MachineBasicBlock *PredTBB, *PredFBB; - SmallVector<MachineOperand, 4> PredCond; - if (TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true)) - continue; - if (!PredCond.empty()) - continue; - // Don't duplicate into a fall-through predecessor (at least for now). - if (PredBB->isLayoutSuccessor(TailBB) && PredBB->canFallThrough()) - continue; - - DEBUG(dbgs() << "\nTail-duplicating into PredBB: " << *PredBB - << "From Succ: " << *TailBB); - - TDBBs.push_back(PredBB); - - // Remove PredBB's unconditional branch. - TII->RemoveBranch(*PredBB); - - if (RS && !TailBB->livein_empty()) { - // Update PredBB livein. - RS->enterBasicBlock(PredBB); - if (!PredBB->empty()) - RS->forward(std::prev(PredBB->end())); - for (const auto &LI : TailBB->liveins()) { - if (!RS->isRegUsed(LI.PhysReg, false)) - // If a register is previously livein to the tail but it's not live - // at the end of predecessor BB, then it should be added to its - // livein list. - PredBB->addLiveIn(LI); - } - } - - // Clone the contents of TailBB into PredBB. - DenseMap<unsigned, unsigned> LocalVRMap; - SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos; - // Use instr_iterator here to properly handle bundles, e.g. - // ARM Thumb2 IT block. - MachineBasicBlock::instr_iterator I = TailBB->instr_begin(); - while (I != TailBB->instr_end()) { - MachineInstr *MI = &*I; - ++I; - if (MI->isPHI()) { - // Replace the uses of the def of the PHI with the register coming - // from PredBB. - ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos, UsedByPhi, true); - } else { - // Replace def of virtual registers with new registers, and update - // uses with PHI source register or the new registers. - DuplicateInstruction(MI, TailBB, PredBB, MF, LocalVRMap, UsedByPhi); - } - } - MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator(); - for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) { - Copies.push_back(BuildMI(*PredBB, Loc, DebugLoc(), - TII->get(TargetOpcode::COPY), - CopyInfos[i].first).addReg(CopyInfos[i].second)); - } - - // Simplify - TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true); - - NumInstrDups += TailBB->size() - 1; // subtract one for removed branch - - // Update the CFG. - PredBB->removeSuccessor(PredBB->succ_begin()); - assert(PredBB->succ_empty() && - "TailDuplicate called on block with multiple successors!"); - for (MachineBasicBlock::succ_iterator I = TailBB->succ_begin(), - E = TailBB->succ_end(); I != E; ++I) - PredBB->addSuccessor(*I, MBPI->getEdgeProbability(TailBB, I)); - - Changed = true; - ++NumTailDups; - } - - // If TailBB was duplicated into all its predecessors except for the prior - // block, which falls through unconditionally, move the contents of this - // block into the prior block. - MachineBasicBlock *PrevBB = &*std::prev(TailBB->getIterator()); - MachineBasicBlock *PriorTBB = nullptr, *PriorFBB = nullptr; - SmallVector<MachineOperand, 4> PriorCond; - // This has to check PrevBB->succ_size() because EH edges are ignored by - // AnalyzeBranch. - if (PrevBB->succ_size() == 1 && - !TII->AnalyzeBranch(*PrevBB, PriorTBB, PriorFBB, PriorCond, true) && - PriorCond.empty() && !PriorTBB && TailBB->pred_size() == 1 && - !TailBB->hasAddressTaken()) { - DEBUG(dbgs() << "\nMerging into block: " << *PrevBB - << "From MBB: " << *TailBB); - if (PreRegAlloc) { - DenseMap<unsigned, unsigned> LocalVRMap; - SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos; - MachineBasicBlock::iterator I = TailBB->begin(); - // Process PHI instructions first. - while (I != TailBB->end() && I->isPHI()) { - // Replace the uses of the def of the PHI with the register coming - // from PredBB. - MachineInstr *MI = &*I++; - ProcessPHI(MI, TailBB, PrevBB, LocalVRMap, CopyInfos, UsedByPhi, true); - if (MI->getParent()) - MI->eraseFromParent(); - } - - // Now copy the non-PHI instructions. - while (I != TailBB->end()) { - // Replace def of virtual registers with new registers, and update - // uses with PHI source register or the new registers. - MachineInstr *MI = &*I++; - assert(!MI->isBundle() && "Not expecting bundles before regalloc!"); - DuplicateInstruction(MI, TailBB, PrevBB, MF, LocalVRMap, UsedByPhi); - MI->eraseFromParent(); - } - MachineBasicBlock::iterator Loc = PrevBB->getFirstTerminator(); - for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) { - Copies.push_back(BuildMI(*PrevBB, Loc, DebugLoc(), - TII->get(TargetOpcode::COPY), - CopyInfos[i].first) - .addReg(CopyInfos[i].second)); - } - } else { - // No PHIs to worry about, just splice the instructions over. - PrevBB->splice(PrevBB->end(), TailBB, TailBB->begin(), TailBB->end()); - } - PrevBB->removeSuccessor(PrevBB->succ_begin()); - assert(PrevBB->succ_empty()); - PrevBB->transferSuccessors(TailBB); - TDBBs.push_back(PrevBB); - Changed = true; - } - - // If this is after register allocation, there are no phis to fix. - if (!PreRegAlloc) - return Changed; - - // If we made no changes so far, we are safe. - if (!Changed) - return Changed; - - - // Handle the nasty case in that we duplicated a block that is part of a loop - // into some but not all of its predecessors. For example: - // 1 -> 2 <-> 3 | - // \ | - // \---> rest | - // if we duplicate 2 into 1 but not into 3, we end up with - // 12 -> 3 <-> 2 -> rest | - // \ / | - // \----->-----/ | - // If there was a "var = phi(1, 3)" in 2, it has to be ultimately replaced - // with a phi in 3 (which now dominates 2). - // What we do here is introduce a copy in 3 of the register defined by the - // phi, just like when we are duplicating 2 into 3, but we don't copy any - // real instructions or remove the 3 -> 2 edge from the phi in 2. - for (SmallSetVector<MachineBasicBlock *, 8>::iterator PI = Preds.begin(), - PE = Preds.end(); PI != PE; ++PI) { - MachineBasicBlock *PredBB = *PI; - if (std::find(TDBBs.begin(), TDBBs.end(), PredBB) != TDBBs.end()) - continue; - - // EH edges - if (PredBB->succ_size() != 1) - continue; - - DenseMap<unsigned, unsigned> LocalVRMap; - SmallVector<std::pair<unsigned,unsigned>, 4> CopyInfos; - MachineBasicBlock::iterator I = TailBB->begin(); - // Process PHI instructions first. - while (I != TailBB->end() && I->isPHI()) { - // Replace the uses of the def of the PHI with the register coming - // from PredBB. - MachineInstr *MI = &*I++; - ProcessPHI(MI, TailBB, PredBB, LocalVRMap, CopyInfos, UsedByPhi, false); - } - MachineBasicBlock::iterator Loc = PredBB->getFirstTerminator(); - for (unsigned i = 0, e = CopyInfos.size(); i != e; ++i) { - Copies.push_back(BuildMI(*PredBB, Loc, DebugLoc(), - TII->get(TargetOpcode::COPY), - CopyInfos[i].first).addReg(CopyInfos[i].second)); - } - } - - return Changed; -} - -/// Remove the specified dead machine basic block from the function, updating -/// the CFG. -void TailDuplicatePass::RemoveDeadBlock(MachineBasicBlock *MBB) { - assert(MBB->pred_empty() && "MBB must be dead!"); - DEBUG(dbgs() << "\nRemoving MBB: " << *MBB); - - // Remove all successors. - while (!MBB->succ_empty()) - MBB->removeSuccessor(MBB->succ_end()-1); - - // Remove the block. - MBB->eraseFromParent(); -} |