| //===- RegisterScavenging.cpp - Machine register scavenging ---------------===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| /// \file |
| /// This file implements the machine register scavenger. It can provide |
| /// information, such as unused registers, at any point in a machine basic |
| /// block. It also provides a mechanism to make registers available by evicting |
| /// them to spill slots. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/CodeGen/RegisterScavenging.h" |
| #include "llvm/ADT/ArrayRef.h" |
| #include "llvm/ADT/BitVector.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/CodeGen/LiveRegUnits.h" |
| #include "llvm/CodeGen/MachineBasicBlock.h" |
| #include "llvm/CodeGen/MachineFrameInfo.h" |
| #include "llvm/CodeGen/MachineFunction.h" |
| #include "llvm/CodeGen/MachineFunctionPass.h" |
| #include "llvm/CodeGen/MachineInstr.h" |
| #include "llvm/CodeGen/MachineOperand.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| #include "llvm/CodeGen/TargetFrameLowering.h" |
| #include "llvm/CodeGen/TargetInstrInfo.h" |
| #include "llvm/CodeGen/TargetRegisterInfo.h" |
| #include "llvm/CodeGen/TargetSubtargetInfo.h" |
| #include "llvm/InitializePasses.h" |
| #include "llvm/MC/MCRegisterInfo.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/ErrorHandling.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include <algorithm> |
| #include <cassert> |
| #include <iterator> |
| #include <limits> |
| #include <string> |
| #include <utility> |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "reg-scavenging" |
| |
| STATISTIC(NumScavengedRegs, "Number of frame index regs scavenged"); |
| |
| void RegScavenger::setRegUsed(Register Reg, LaneBitmask LaneMask) { |
| LiveUnits.addRegMasked(Reg, LaneMask); |
| } |
| |
| void RegScavenger::init(MachineBasicBlock &MBB) { |
| MachineFunction &MF = *MBB.getParent(); |
| TII = MF.getSubtarget().getInstrInfo(); |
| TRI = MF.getSubtarget().getRegisterInfo(); |
| MRI = &MF.getRegInfo(); |
| LiveUnits.init(*TRI); |
| |
| assert((NumRegUnits == 0 || NumRegUnits == TRI->getNumRegUnits()) && |
| "Target changed?"); |
| |
| // Self-initialize. |
| if (!this->MBB) { |
| NumRegUnits = TRI->getNumRegUnits(); |
| KillRegUnits.resize(NumRegUnits); |
| DefRegUnits.resize(NumRegUnits); |
| TmpRegUnits.resize(NumRegUnits); |
| } |
| this->MBB = &MBB; |
| |
| for (ScavengedInfo &SI : Scavenged) { |
| SI.Reg = 0; |
| SI.Restore = nullptr; |
| } |
| |
| Tracking = false; |
| } |
| |
| void RegScavenger::enterBasicBlock(MachineBasicBlock &MBB) { |
| init(MBB); |
| LiveUnits.addLiveIns(MBB); |
| } |
| |
| void RegScavenger::enterBasicBlockEnd(MachineBasicBlock &MBB) { |
| init(MBB); |
| LiveUnits.addLiveOuts(MBB); |
| |
| // Move internal iterator at the last instruction of the block. |
| if (MBB.begin() != MBB.end()) { |
| MBBI = std::prev(MBB.end()); |
| Tracking = true; |
| } |
| } |
| |
| void RegScavenger::addRegUnits(BitVector &BV, Register Reg) { |
| for (MCRegUnitIterator RUI(Reg, TRI); RUI.isValid(); ++RUI) |
| BV.set(*RUI); |
| } |
| |
| void RegScavenger::removeRegUnits(BitVector &BV, Register Reg) { |
| for (MCRegUnitIterator RUI(Reg, TRI); RUI.isValid(); ++RUI) |
| BV.reset(*RUI); |
| } |
| |
| void RegScavenger::determineKillsAndDefs() { |
| assert(Tracking && "Must be tracking to determine kills and defs"); |
| |
| MachineInstr &MI = *MBBI; |
| assert(!MI.isDebugInstr() && "Debug values have no kills or defs"); |
| |
| // Find out which registers are early clobbered, killed, defined, and marked |
| // def-dead in this instruction. |
| KillRegUnits.reset(); |
| DefRegUnits.reset(); |
| for (const MachineOperand &MO : MI.operands()) { |
| if (MO.isRegMask()) { |
| TmpRegUnits.clear(); |
| for (unsigned RU = 0, RUEnd = TRI->getNumRegUnits(); RU != RUEnd; ++RU) { |
| for (MCRegUnitRootIterator RURI(RU, TRI); RURI.isValid(); ++RURI) { |
| if (MO.clobbersPhysReg(*RURI)) { |
| TmpRegUnits.set(RU); |
| break; |
| } |
| } |
| } |
| |
| // Apply the mask. |
| KillRegUnits |= TmpRegUnits; |
| } |
| if (!MO.isReg()) |
| continue; |
| Register Reg = MO.getReg(); |
| if (!Register::isPhysicalRegister(Reg) || isReserved(Reg)) |
| continue; |
| |
| if (MO.isUse()) { |
| // Ignore undef uses. |
| if (MO.isUndef()) |
| continue; |
| if (MO.isKill()) |
| addRegUnits(KillRegUnits, Reg); |
| } else { |
| assert(MO.isDef()); |
| if (MO.isDead()) |
| addRegUnits(KillRegUnits, Reg); |
| else |
| addRegUnits(DefRegUnits, Reg); |
| } |
| } |
| } |
| |
| void RegScavenger::unprocess() { |
| assert(Tracking && "Cannot unprocess because we're not tracking"); |
| |
| MachineInstr &MI = *MBBI; |
| if (!MI.isDebugInstr()) { |
| determineKillsAndDefs(); |
| |
| // Commit the changes. |
| setUnused(DefRegUnits); |
| setUsed(KillRegUnits); |
| } |
| |
| if (MBBI == MBB->begin()) { |
| MBBI = MachineBasicBlock::iterator(nullptr); |
| Tracking = false; |
| } else |
| --MBBI; |
| } |
| |
| void RegScavenger::forward() { |
| // Move ptr forward. |
| if (!Tracking) { |
| MBBI = MBB->begin(); |
| Tracking = true; |
| } else { |
| assert(MBBI != MBB->end() && "Already past the end of the basic block!"); |
| MBBI = std::next(MBBI); |
| } |
| assert(MBBI != MBB->end() && "Already at the end of the basic block!"); |
| |
| MachineInstr &MI = *MBBI; |
| |
| for (SmallVectorImpl<ScavengedInfo>::iterator I = Scavenged.begin(), |
| IE = Scavenged.end(); I != IE; ++I) { |
| if (I->Restore != &MI) |
| continue; |
| |
| I->Reg = 0; |
| I->Restore = nullptr; |
| } |
| |
| if (MI.isDebugInstr()) |
| return; |
| |
| determineKillsAndDefs(); |
| |
| // Verify uses and defs. |
| #ifndef NDEBUG |
| for (const MachineOperand &MO : MI.operands()) { |
| if (!MO.isReg()) |
| continue; |
| Register Reg = MO.getReg(); |
| if (!Register::isPhysicalRegister(Reg) || isReserved(Reg)) |
| continue; |
| if (MO.isUse()) { |
| if (MO.isUndef()) |
| continue; |
| if (!isRegUsed(Reg)) { |
| // Check if it's partial live: e.g. |
| // D0 = insert_subreg undef D0, S0 |
| // ... D0 |
| // The problem is the insert_subreg could be eliminated. The use of |
| // D0 is using a partially undef value. This is not *incorrect* since |
| // S1 is can be freely clobbered. |
| // Ideally we would like a way to model this, but leaving the |
| // insert_subreg around causes both correctness and performance issues. |
| bool SubUsed = false; |
| for (const MCPhysReg &SubReg : TRI->subregs(Reg)) |
| if (isRegUsed(SubReg)) { |
| SubUsed = true; |
| break; |
| } |
| bool SuperUsed = false; |
| for (MCSuperRegIterator SR(Reg, TRI); SR.isValid(); ++SR) { |
| if (isRegUsed(*SR)) { |
| SuperUsed = true; |
| break; |
| } |
| } |
| if (!SubUsed && !SuperUsed) { |
| MBB->getParent()->verify(nullptr, "In Register Scavenger"); |
| llvm_unreachable("Using an undefined register!"); |
| } |
| (void)SubUsed; |
| (void)SuperUsed; |
| } |
| } else { |
| assert(MO.isDef()); |
| #if 0 |
| // FIXME: Enable this once we've figured out how to correctly transfer |
| // implicit kills during codegen passes like the coalescer. |
| assert((KillRegs.test(Reg) || isUnused(Reg) || |
| isLiveInButUnusedBefore(Reg, MI, MBB, TRI, MRI)) && |
| "Re-defining a live register!"); |
| #endif |
| } |
| } |
| #endif // NDEBUG |
| |
| // Commit the changes. |
| setUnused(KillRegUnits); |
| setUsed(DefRegUnits); |
| } |
| |
| void RegScavenger::backward() { |
| assert(Tracking && "Must be tracking to determine kills and defs"); |
| |
| const MachineInstr &MI = *MBBI; |
| LiveUnits.stepBackward(MI); |
| |
| // Expire scavenge spill frameindex uses. |
| for (ScavengedInfo &I : Scavenged) { |
| if (I.Restore == &MI) { |
| I.Reg = 0; |
| I.Restore = nullptr; |
| } |
| } |
| |
| if (MBBI == MBB->begin()) { |
| MBBI = MachineBasicBlock::iterator(nullptr); |
| Tracking = false; |
| } else |
| --MBBI; |
| } |
| |
| bool RegScavenger::isRegUsed(Register Reg, bool includeReserved) const { |
| if (isReserved(Reg)) |
| return includeReserved; |
| return !LiveUnits.available(Reg); |
| } |
| |
| Register RegScavenger::FindUnusedReg(const TargetRegisterClass *RC) const { |
| for (Register Reg : *RC) { |
| if (!isRegUsed(Reg)) { |
| LLVM_DEBUG(dbgs() << "Scavenger found unused reg: " << printReg(Reg, TRI) |
| << "\n"); |
| return Reg; |
| } |
| } |
| return 0; |
| } |
| |
| BitVector RegScavenger::getRegsAvailable(const TargetRegisterClass *RC) { |
| BitVector Mask(TRI->getNumRegs()); |
| for (Register Reg : *RC) |
| if (!isRegUsed(Reg)) |
| Mask.set(Reg); |
| return Mask; |
| } |
| |
| Register RegScavenger::findSurvivorReg(MachineBasicBlock::iterator StartMI, |
| BitVector &Candidates, |
| unsigned InstrLimit, |
| MachineBasicBlock::iterator &UseMI) { |
| int Survivor = Candidates.find_first(); |
| assert(Survivor > 0 && "No candidates for scavenging"); |
| |
| MachineBasicBlock::iterator ME = MBB->getFirstTerminator(); |
| assert(StartMI != ME && "MI already at terminator"); |
| MachineBasicBlock::iterator RestorePointMI = StartMI; |
| MachineBasicBlock::iterator MI = StartMI; |
| |
| bool inVirtLiveRange = false; |
| for (++MI; InstrLimit > 0 && MI != ME; ++MI, --InstrLimit) { |
| if (MI->isDebugInstr()) { |
| ++InstrLimit; // Don't count debug instructions |
| continue; |
| } |
| bool isVirtKillInsn = false; |
| bool isVirtDefInsn = false; |
| // Remove any candidates touched by instruction. |
| for (const MachineOperand &MO : MI->operands()) { |
| if (MO.isRegMask()) |
| Candidates.clearBitsNotInMask(MO.getRegMask()); |
| if (!MO.isReg() || MO.isUndef() || !MO.getReg()) |
| continue; |
| if (Register::isVirtualRegister(MO.getReg())) { |
| if (MO.isDef()) |
| isVirtDefInsn = true; |
| else if (MO.isKill()) |
| isVirtKillInsn = true; |
| continue; |
| } |
| for (MCRegAliasIterator AI(MO.getReg(), TRI, true); AI.isValid(); ++AI) |
| Candidates.reset(*AI); |
| } |
| // If we're not in a virtual reg's live range, this is a valid |
| // restore point. |
| if (!inVirtLiveRange) RestorePointMI = MI; |
| |
| // Update whether we're in the live range of a virtual register |
| if (isVirtKillInsn) inVirtLiveRange = false; |
| if (isVirtDefInsn) inVirtLiveRange = true; |
| |
| // Was our survivor untouched by this instruction? |
| if (Candidates.test(Survivor)) |
| continue; |
| |
| // All candidates gone? |
| if (Candidates.none()) |
| break; |
| |
| Survivor = Candidates.find_first(); |
| } |
| // If we ran off the end, that's where we want to restore. |
| if (MI == ME) RestorePointMI = ME; |
| assert(RestorePointMI != StartMI && |
| "No available scavenger restore location!"); |
| |
| // We ran out of candidates, so stop the search. |
| UseMI = RestorePointMI; |
| return Survivor; |
| } |
| |
| /// Given the bitvector \p Available of free register units at position |
| /// \p From. Search backwards to find a register that is part of \p |
| /// Candidates and not used/clobbered until the point \p To. If there is |
| /// multiple candidates continue searching and pick the one that is not used/ |
| /// clobbered for the longest time. |
| /// Returns the register and the earliest position we know it to be free or |
| /// the position MBB.end() if no register is available. |
| static std::pair<MCPhysReg, MachineBasicBlock::iterator> |
| findSurvivorBackwards(const MachineRegisterInfo &MRI, |
| MachineBasicBlock::iterator From, MachineBasicBlock::iterator To, |
| const LiveRegUnits &LiveOut, ArrayRef<MCPhysReg> AllocationOrder, |
| bool RestoreAfter) { |
| bool FoundTo = false; |
| MCPhysReg Survivor = 0; |
| MachineBasicBlock::iterator Pos; |
| MachineBasicBlock &MBB = *From->getParent(); |
| unsigned InstrLimit = 25; |
| unsigned InstrCountDown = InstrLimit; |
| const TargetRegisterInfo &TRI = *MRI.getTargetRegisterInfo(); |
| LiveRegUnits Used(TRI); |
| |
| for (MachineBasicBlock::iterator I = From;; --I) { |
| const MachineInstr &MI = *I; |
| |
| Used.accumulate(MI); |
| |
| if (I == To) { |
| // See if one of the registers in RC wasn't used so far. |
| for (MCPhysReg Reg : AllocationOrder) { |
| if (!MRI.isReserved(Reg) && Used.available(Reg) && |
| LiveOut.available(Reg)) |
| return std::make_pair(Reg, MBB.end()); |
| } |
| // Otherwise we will continue up to InstrLimit instructions to find |
| // the register which is not defined/used for the longest time. |
| FoundTo = true; |
| Pos = To; |
| // Note: It was fine so far to start our search at From, however now that |
| // we have to spill, and can only place the restore after From then |
| // add the regs used/defed by std::next(From) to the set. |
| if (RestoreAfter) |
| Used.accumulate(*std::next(From)); |
| } |
| if (FoundTo) { |
| if (Survivor == 0 || !Used.available(Survivor)) { |
| MCPhysReg AvilableReg = 0; |
| for (MCPhysReg Reg : AllocationOrder) { |
| if (!MRI.isReserved(Reg) && Used.available(Reg)) { |
| AvilableReg = Reg; |
| break; |
| } |
| } |
| if (AvilableReg == 0) |
| break; |
| Survivor = AvilableReg; |
| } |
| if (--InstrCountDown == 0) |
| break; |
| |
| // Keep searching when we find a vreg since the spilled register will |
| // be usefull for this other vreg as well later. |
| bool FoundVReg = false; |
| for (const MachineOperand &MO : MI.operands()) { |
| if (MO.isReg() && Register::isVirtualRegister(MO.getReg())) { |
| FoundVReg = true; |
| break; |
| } |
| } |
| if (FoundVReg) { |
| InstrCountDown = InstrLimit; |
| Pos = I; |
| } |
| if (I == MBB.begin()) |
| break; |
| } |
| } |
| |
| return std::make_pair(Survivor, Pos); |
| } |
| |
| static unsigned getFrameIndexOperandNum(MachineInstr &MI) { |
| unsigned i = 0; |
| while (!MI.getOperand(i).isFI()) { |
| ++i; |
| assert(i < MI.getNumOperands() && "Instr doesn't have FrameIndex operand!"); |
| } |
| return i; |
| } |
| |
| RegScavenger::ScavengedInfo & |
| RegScavenger::spill(Register Reg, const TargetRegisterClass &RC, int SPAdj, |
| MachineBasicBlock::iterator Before, |
| MachineBasicBlock::iterator &UseMI) { |
| // Find an available scavenging slot with size and alignment matching |
| // the requirements of the class RC. |
| const MachineFunction &MF = *Before->getMF(); |
| const MachineFrameInfo &MFI = MF.getFrameInfo(); |
| unsigned NeedSize = TRI->getSpillSize(RC); |
| unsigned NeedAlign = TRI->getSpillAlignment(RC); |
| |
| unsigned SI = Scavenged.size(), Diff = std::numeric_limits<unsigned>::max(); |
| int FIB = MFI.getObjectIndexBegin(), FIE = MFI.getObjectIndexEnd(); |
| for (unsigned I = 0; I < Scavenged.size(); ++I) { |
| if (Scavenged[I].Reg != 0) |
| continue; |
| // Verify that this slot is valid for this register. |
| int FI = Scavenged[I].FrameIndex; |
| if (FI < FIB || FI >= FIE) |
| continue; |
| unsigned S = MFI.getObjectSize(FI); |
| unsigned A = MFI.getObjectAlignment(FI); |
| if (NeedSize > S || NeedAlign > A) |
| continue; |
| // Avoid wasting slots with large size and/or large alignment. Pick one |
| // that is the best fit for this register class (in street metric). |
| // Picking a larger slot than necessary could happen if a slot for a |
| // larger register is reserved before a slot for a smaller one. When |
| // trying to spill a smaller register, the large slot would be found |
| // first, thus making it impossible to spill the larger register later. |
| unsigned D = (S-NeedSize) + (A-NeedAlign); |
| if (D < Diff) { |
| SI = I; |
| Diff = D; |
| } |
| } |
| |
| if (SI == Scavenged.size()) { |
| // We need to scavenge a register but have no spill slot, the target |
| // must know how to do it (if not, we'll assert below). |
| Scavenged.push_back(ScavengedInfo(FIE)); |
| } |
| |
| // Avoid infinite regress |
| Scavenged[SI].Reg = Reg; |
| |
| // If the target knows how to save/restore the register, let it do so; |
| // otherwise, use the emergency stack spill slot. |
| if (!TRI->saveScavengerRegister(*MBB, Before, UseMI, &RC, Reg)) { |
| // Spill the scavenged register before \p Before. |
| int FI = Scavenged[SI].FrameIndex; |
| if (FI < FIB || FI >= FIE) { |
| std::string Msg = std::string("Error while trying to spill ") + |
| TRI->getName(Reg) + " from class " + TRI->getRegClassName(&RC) + |
| ": Cannot scavenge register without an emergency spill slot!"; |
| report_fatal_error(Msg.c_str()); |
| } |
| TII->storeRegToStackSlot(*MBB, Before, Reg, true, Scavenged[SI].FrameIndex, |
| &RC, TRI); |
| MachineBasicBlock::iterator II = std::prev(Before); |
| |
| unsigned FIOperandNum = getFrameIndexOperandNum(*II); |
| TRI->eliminateFrameIndex(II, SPAdj, FIOperandNum, this); |
| |
| // Restore the scavenged register before its use (or first terminator). |
| TII->loadRegFromStackSlot(*MBB, UseMI, Reg, Scavenged[SI].FrameIndex, |
| &RC, TRI); |
| II = std::prev(UseMI); |
| |
| FIOperandNum = getFrameIndexOperandNum(*II); |
| TRI->eliminateFrameIndex(II, SPAdj, FIOperandNum, this); |
| } |
| return Scavenged[SI]; |
| } |
| |
| Register RegScavenger::scavengeRegister(const TargetRegisterClass *RC, |
| MachineBasicBlock::iterator I, |
| int SPAdj, bool AllowSpill) { |
| MachineInstr &MI = *I; |
| const MachineFunction &MF = *MI.getMF(); |
| // Consider all allocatable registers in the register class initially |
| BitVector Candidates = TRI->getAllocatableSet(MF, RC); |
| |
| // Exclude all the registers being used by the instruction. |
| for (const MachineOperand &MO : MI.operands()) { |
| if (MO.isReg() && MO.getReg() != 0 && !(MO.isUse() && MO.isUndef()) && |
| !Register::isVirtualRegister(MO.getReg())) |
| for (MCRegAliasIterator AI(MO.getReg(), TRI, true); AI.isValid(); ++AI) |
| Candidates.reset(*AI); |
| } |
| |
| // Try to find a register that's unused if there is one, as then we won't |
| // have to spill. |
| BitVector Available = getRegsAvailable(RC); |
| Available &= Candidates; |
| if (Available.any()) |
| Candidates = Available; |
| |
| // Find the register whose use is furthest away. |
| MachineBasicBlock::iterator UseMI; |
| Register SReg = findSurvivorReg(I, Candidates, 25, UseMI); |
| |
| // If we found an unused register there is no reason to spill it. |
| if (!isRegUsed(SReg)) { |
| LLVM_DEBUG(dbgs() << "Scavenged register: " << printReg(SReg, TRI) << "\n"); |
| return SReg; |
| } |
| |
| if (!AllowSpill) |
| return 0; |
| |
| ScavengedInfo &Scavenged = spill(SReg, *RC, SPAdj, I, UseMI); |
| Scavenged.Restore = &*std::prev(UseMI); |
| |
| LLVM_DEBUG(dbgs() << "Scavenged register (with spill): " |
| << printReg(SReg, TRI) << "\n"); |
| |
| return SReg; |
| } |
| |
| Register RegScavenger::scavengeRegisterBackwards(const TargetRegisterClass &RC, |
| MachineBasicBlock::iterator To, |
| bool RestoreAfter, int SPAdj, |
| bool AllowSpill) { |
| const MachineBasicBlock &MBB = *To->getParent(); |
| const MachineFunction &MF = *MBB.getParent(); |
| |
| // Find the register whose use is furthest away. |
| MachineBasicBlock::iterator UseMI; |
| ArrayRef<MCPhysReg> AllocationOrder = RC.getRawAllocationOrder(MF); |
| std::pair<MCPhysReg, MachineBasicBlock::iterator> P = |
| findSurvivorBackwards(*MRI, MBBI, To, LiveUnits, AllocationOrder, |
| RestoreAfter); |
| MCPhysReg Reg = P.first; |
| MachineBasicBlock::iterator SpillBefore = P.second; |
| assert(Reg != 0 && "No register left to scavenge!"); |
| // Found an available register? |
| if (SpillBefore == MBB.end()) { |
| LLVM_DEBUG(dbgs() << "Scavenged free register: " << printReg(Reg, TRI) |
| << '\n'); |
| return Reg; |
| } |
| |
| if (!AllowSpill) |
| return 0; |
| |
| MachineBasicBlock::iterator ReloadAfter = |
| RestoreAfter ? std::next(MBBI) : MBBI; |
| MachineBasicBlock::iterator ReloadBefore = std::next(ReloadAfter); |
| if (ReloadBefore != MBB.end()) |
| LLVM_DEBUG(dbgs() << "Reload before: " << *ReloadBefore << '\n'); |
| ScavengedInfo &Scavenged = spill(Reg, RC, SPAdj, SpillBefore, ReloadBefore); |
| Scavenged.Restore = &*std::prev(SpillBefore); |
| LiveUnits.removeReg(Reg); |
| LLVM_DEBUG(dbgs() << "Scavenged register with spill: " << printReg(Reg, TRI) |
| << " until " << *SpillBefore); |
| return Reg; |
| } |
| |
| /// Allocate a register for the virtual register \p VReg. The last use of |
| /// \p VReg is around the current position of the register scavenger \p RS. |
| /// \p ReserveAfter controls whether the scavenged register needs to be reserved |
| /// after the current instruction, otherwise it will only be reserved before the |
| /// current instruction. |
| static Register scavengeVReg(MachineRegisterInfo &MRI, RegScavenger &RS, |
| Register VReg, bool ReserveAfter) { |
| const TargetRegisterInfo &TRI = *MRI.getTargetRegisterInfo(); |
| #ifndef NDEBUG |
| // Verify that all definitions and uses are in the same basic block. |
| const MachineBasicBlock *CommonMBB = nullptr; |
| // Real definition for the reg, re-definitions are not considered. |
| const MachineInstr *RealDef = nullptr; |
| for (MachineOperand &MO : MRI.reg_nodbg_operands(VReg)) { |
| MachineBasicBlock *MBB = MO.getParent()->getParent(); |
| if (CommonMBB == nullptr) |
| CommonMBB = MBB; |
| assert(MBB == CommonMBB && "All defs+uses must be in the same basic block"); |
| if (MO.isDef()) { |
| const MachineInstr &MI = *MO.getParent(); |
| if (!MI.readsRegister(VReg, &TRI)) { |
| assert((!RealDef || RealDef == &MI) && |
| "Can have at most one definition which is not a redefinition"); |
| RealDef = &MI; |
| } |
| } |
| } |
| assert(RealDef != nullptr && "Must have at least 1 Def"); |
| #endif |
| |
| // We should only have one definition of the register. However to accommodate |
| // the requirements of two address code we also allow definitions in |
| // subsequent instructions provided they also read the register. That way |
| // we get a single contiguous lifetime. |
| // |
| // Definitions in MRI.def_begin() are unordered, search for the first. |
| MachineRegisterInfo::def_iterator FirstDef = |
| std::find_if(MRI.def_begin(VReg), MRI.def_end(), |
| [VReg, &TRI](const MachineOperand &MO) { |
| return !MO.getParent()->readsRegister(VReg, &TRI); |
| }); |
| assert(FirstDef != MRI.def_end() && |
| "Must have one definition that does not redefine vreg"); |
| MachineInstr &DefMI = *FirstDef->getParent(); |
| |
| // The register scavenger will report a free register inserting an emergency |
| // spill/reload if necessary. |
| int SPAdj = 0; |
| const TargetRegisterClass &RC = *MRI.getRegClass(VReg); |
| Register SReg = RS.scavengeRegisterBackwards(RC, DefMI.getIterator(), |
| ReserveAfter, SPAdj); |
| MRI.replaceRegWith(VReg, SReg); |
| ++NumScavengedRegs; |
| return SReg; |
| } |
| |
| /// Allocate (scavenge) vregs inside a single basic block. |
| /// Returns true if the target spill callback created new vregs and a 2nd pass |
| /// is necessary. |
| static bool scavengeFrameVirtualRegsInBlock(MachineRegisterInfo &MRI, |
| RegScavenger &RS, |
| MachineBasicBlock &MBB) { |
| const TargetRegisterInfo &TRI = *MRI.getTargetRegisterInfo(); |
| RS.enterBasicBlockEnd(MBB); |
| |
| unsigned InitialNumVirtRegs = MRI.getNumVirtRegs(); |
| bool NextInstructionReadsVReg = false; |
| for (MachineBasicBlock::iterator I = MBB.end(); I != MBB.begin(); ) { |
| --I; |
| // Move RegScavenger to the position between *I and *std::next(I). |
| RS.backward(I); |
| |
| // Look for unassigned vregs in the uses of *std::next(I). |
| if (NextInstructionReadsVReg) { |
| MachineBasicBlock::iterator N = std::next(I); |
| const MachineInstr &NMI = *N; |
| for (const MachineOperand &MO : NMI.operands()) { |
| if (!MO.isReg()) |
| continue; |
| Register Reg = MO.getReg(); |
| // We only care about virtual registers and ignore virtual registers |
| // created by the target callbacks in the process (those will be handled |
| // in a scavenging round). |
| if (!Register::isVirtualRegister(Reg) || |
| Register::virtReg2Index(Reg) >= InitialNumVirtRegs) |
| continue; |
| if (!MO.readsReg()) |
| continue; |
| |
| Register SReg = scavengeVReg(MRI, RS, Reg, true); |
| N->addRegisterKilled(SReg, &TRI, false); |
| RS.setRegUsed(SReg); |
| } |
| } |
| |
| // Look for unassigned vregs in the defs of *I. |
| NextInstructionReadsVReg = false; |
| const MachineInstr &MI = *I; |
| for (const MachineOperand &MO : MI.operands()) { |
| if (!MO.isReg()) |
| continue; |
| Register Reg = MO.getReg(); |
| // Only vregs, no newly created vregs (see above). |
| if (!Register::isVirtualRegister(Reg) || |
| Register::virtReg2Index(Reg) >= InitialNumVirtRegs) |
| continue; |
| // We have to look at all operands anyway so we can precalculate here |
| // whether there is a reading operand. This allows use to skip the use |
| // step in the next iteration if there was none. |
| assert(!MO.isInternalRead() && "Cannot assign inside bundles"); |
| assert((!MO.isUndef() || MO.isDef()) && "Cannot handle undef uses"); |
| if (MO.readsReg()) { |
| NextInstructionReadsVReg = true; |
| } |
| if (MO.isDef()) { |
| Register SReg = scavengeVReg(MRI, RS, Reg, false); |
| I->addRegisterDead(SReg, &TRI, false); |
| } |
| } |
| } |
| #ifndef NDEBUG |
| for (const MachineOperand &MO : MBB.front().operands()) { |
| if (!MO.isReg() || !Register::isVirtualRegister(MO.getReg())) |
| continue; |
| assert(!MO.isInternalRead() && "Cannot assign inside bundles"); |
| assert((!MO.isUndef() || MO.isDef()) && "Cannot handle undef uses"); |
| assert(!MO.readsReg() && "Vreg use in first instruction not allowed"); |
| } |
| #endif |
| |
| return MRI.getNumVirtRegs() != InitialNumVirtRegs; |
| } |
| |
| void llvm::scavengeFrameVirtualRegs(MachineFunction &MF, RegScavenger &RS) { |
| // FIXME: Iterating over the instruction stream is unnecessary. We can simply |
| // iterate over the vreg use list, which at this point only contains machine |
| // operands for which eliminateFrameIndex need a new scratch reg. |
| MachineRegisterInfo &MRI = MF.getRegInfo(); |
| // Shortcut. |
| if (MRI.getNumVirtRegs() == 0) { |
| MF.getProperties().set(MachineFunctionProperties::Property::NoVRegs); |
| return; |
| } |
| |
| // Run through the instructions and find any virtual registers. |
| for (MachineBasicBlock &MBB : MF) { |
| if (MBB.empty()) |
| continue; |
| |
| bool Again = scavengeFrameVirtualRegsInBlock(MRI, RS, MBB); |
| if (Again) { |
| LLVM_DEBUG(dbgs() << "Warning: Required two scavenging passes for block " |
| << MBB.getName() << '\n'); |
| Again = scavengeFrameVirtualRegsInBlock(MRI, RS, MBB); |
| // The target required a 2nd run (because it created new vregs while |
| // spilling). Refuse to do another pass to keep compiletime in check. |
| if (Again) |
| report_fatal_error("Incomplete scavenging after 2nd pass"); |
| } |
| } |
| |
| MRI.clearVirtRegs(); |
| MF.getProperties().set(MachineFunctionProperties::Property::NoVRegs); |
| } |
| |
| namespace { |
| |
| /// This class runs register scavenging independ of the PrologEpilogInserter. |
| /// This is used in for testing. |
| class ScavengerTest : public MachineFunctionPass { |
| public: |
| static char ID; |
| |
| ScavengerTest() : MachineFunctionPass(ID) {} |
| |
| bool runOnMachineFunction(MachineFunction &MF) override { |
| const TargetSubtargetInfo &STI = MF.getSubtarget(); |
| const TargetFrameLowering &TFL = *STI.getFrameLowering(); |
| |
| RegScavenger RS; |
| // Let's hope that calling those outside of PrologEpilogueInserter works |
| // well enough to initialize the scavenger with some emergency spillslots |
| // for the target. |
| BitVector SavedRegs; |
| TFL.determineCalleeSaves(MF, SavedRegs, &RS); |
| TFL.processFunctionBeforeFrameFinalized(MF, &RS); |
| |
| // Let's scavenge the current function |
| scavengeFrameVirtualRegs(MF, RS); |
| return true; |
| } |
| }; |
| |
| } // end anonymous namespace |
| |
| char ScavengerTest::ID; |
| |
| INITIALIZE_PASS(ScavengerTest, "scavenger-test", |
| "Scavenge virtual registers inside basic blocks", false, false) |
