| //===--------------------- RegisterFile.cpp ---------------------*- C++ -*-===// |
| // |
| // 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 defines a register mapping file class. This class is responsible |
| /// for managing hardware register files and the tracking of data dependencies |
| /// between registers. |
| /// |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/MCA/HardwareUnits/RegisterFile.h" |
| #include "llvm/MCA/Instruction.h" |
| #include "llvm/Support/Debug.h" |
| |
| #define DEBUG_TYPE "llvm-mca" |
| |
| namespace llvm { |
| namespace mca { |
| |
| RegisterFile::RegisterFile(const MCSchedModel &SM, const MCRegisterInfo &mri, |
| unsigned NumRegs) |
| : MRI(mri), |
| RegisterMappings(mri.getNumRegs(), {WriteRef(), RegisterRenamingInfo()}), |
| ZeroRegisters(mri.getNumRegs(), false) { |
| initialize(SM, NumRegs); |
| } |
| |
| void RegisterFile::initialize(const MCSchedModel &SM, unsigned NumRegs) { |
| // Create a default register file that "sees" all the machine registers |
| // declared by the target. The number of physical registers in the default |
| // register file is set equal to `NumRegs`. A value of zero for `NumRegs` |
| // means: this register file has an unbounded number of physical registers. |
| RegisterFiles.emplace_back(NumRegs); |
| if (!SM.hasExtraProcessorInfo()) |
| return; |
| |
| // For each user defined register file, allocate a RegisterMappingTracker |
| // object. The size of every register file, as well as the mapping between |
| // register files and register classes is specified via tablegen. |
| const MCExtraProcessorInfo &Info = SM.getExtraProcessorInfo(); |
| |
| // Skip invalid register file at index 0. |
| for (unsigned I = 1, E = Info.NumRegisterFiles; I < E; ++I) { |
| const MCRegisterFileDesc &RF = Info.RegisterFiles[I]; |
| assert(RF.NumPhysRegs && "Invalid PRF with zero physical registers!"); |
| |
| // The cost of a register definition is equivalent to the number of |
| // physical registers that are allocated at register renaming stage. |
| unsigned Length = RF.NumRegisterCostEntries; |
| const MCRegisterCostEntry *FirstElt = |
| &Info.RegisterCostTable[RF.RegisterCostEntryIdx]; |
| addRegisterFile(RF, ArrayRef<MCRegisterCostEntry>(FirstElt, Length)); |
| } |
| } |
| |
| void RegisterFile::cycleStart() { |
| for (RegisterMappingTracker &RMT : RegisterFiles) |
| RMT.NumMoveEliminated = 0; |
| } |
| |
| void RegisterFile::addRegisterFile(const MCRegisterFileDesc &RF, |
| ArrayRef<MCRegisterCostEntry> Entries) { |
| // A default register file is always allocated at index #0. That register file |
| // is mainly used to count the total number of mappings created by all |
| // register files at runtime. Users can limit the number of available physical |
| // registers in register file #0 through the command line flag |
| // `-register-file-size`. |
| unsigned RegisterFileIndex = RegisterFiles.size(); |
| RegisterFiles.emplace_back(RF.NumPhysRegs, RF.MaxMovesEliminatedPerCycle, |
| RF.AllowZeroMoveEliminationOnly); |
| |
| // Special case where there is no register class identifier in the set. |
| // An empty set of register classes means: this register file contains all |
| // the physical registers specified by the target. |
| // We optimistically assume that a register can be renamed at the cost of a |
| // single physical register. The constructor of RegisterFile ensures that |
| // a RegisterMapping exists for each logical register defined by the Target. |
| if (Entries.empty()) |
| return; |
| |
| // Now update the cost of individual registers. |
| for (const MCRegisterCostEntry &RCE : Entries) { |
| const MCRegisterClass &RC = MRI.getRegClass(RCE.RegisterClassID); |
| for (const MCPhysReg Reg : RC) { |
| RegisterRenamingInfo &Entry = RegisterMappings[Reg].second; |
| IndexPlusCostPairTy &IPC = Entry.IndexPlusCost; |
| if (IPC.first && IPC.first != RegisterFileIndex) { |
| // The only register file that is allowed to overlap is the default |
| // register file at index #0. The analysis is inaccurate if register |
| // files overlap. |
| errs() << "warning: register " << MRI.getName(Reg) |
| << " defined in multiple register files."; |
| } |
| IPC = std::make_pair(RegisterFileIndex, RCE.Cost); |
| Entry.RenameAs = Reg; |
| Entry.AllowMoveElimination = RCE.AllowMoveElimination; |
| |
| // Assume the same cost for each sub-register. |
| for (MCSubRegIterator I(Reg, &MRI); I.isValid(); ++I) { |
| RegisterRenamingInfo &OtherEntry = RegisterMappings[*I].second; |
| if (!OtherEntry.IndexPlusCost.first && |
| (!OtherEntry.RenameAs || |
| MRI.isSuperRegister(*I, OtherEntry.RenameAs))) { |
| OtherEntry.IndexPlusCost = IPC; |
| OtherEntry.RenameAs = Reg; |
| } |
| } |
| } |
| } |
| } |
| |
| void RegisterFile::allocatePhysRegs(const RegisterRenamingInfo &Entry, |
| MutableArrayRef<unsigned> UsedPhysRegs) { |
| unsigned RegisterFileIndex = Entry.IndexPlusCost.first; |
| unsigned Cost = Entry.IndexPlusCost.second; |
| if (RegisterFileIndex) { |
| RegisterMappingTracker &RMT = RegisterFiles[RegisterFileIndex]; |
| RMT.NumUsedPhysRegs += Cost; |
| UsedPhysRegs[RegisterFileIndex] += Cost; |
| } |
| |
| // Now update the default register mapping tracker. |
| RegisterFiles[0].NumUsedPhysRegs += Cost; |
| UsedPhysRegs[0] += Cost; |
| } |
| |
| void RegisterFile::freePhysRegs(const RegisterRenamingInfo &Entry, |
| MutableArrayRef<unsigned> FreedPhysRegs) { |
| unsigned RegisterFileIndex = Entry.IndexPlusCost.first; |
| unsigned Cost = Entry.IndexPlusCost.second; |
| if (RegisterFileIndex) { |
| RegisterMappingTracker &RMT = RegisterFiles[RegisterFileIndex]; |
| RMT.NumUsedPhysRegs -= Cost; |
| FreedPhysRegs[RegisterFileIndex] += Cost; |
| } |
| |
| // Now update the default register mapping tracker. |
| RegisterFiles[0].NumUsedPhysRegs -= Cost; |
| FreedPhysRegs[0] += Cost; |
| } |
| |
| void RegisterFile::addRegisterWrite(WriteRef Write, |
| MutableArrayRef<unsigned> UsedPhysRegs) { |
| WriteState &WS = *Write.getWriteState(); |
| MCPhysReg RegID = WS.getRegisterID(); |
| assert(RegID && "Adding an invalid register definition?"); |
| |
| LLVM_DEBUG({ |
| dbgs() << "RegisterFile: addRegisterWrite [ " << Write.getSourceIndex() |
| << ", " << MRI.getName(RegID) << "]\n"; |
| }); |
| |
| // If RenameAs is equal to RegID, then RegID is subject to register renaming |
| // and false dependencies on RegID are all eliminated. |
| |
| // If RenameAs references the invalid register, then we optimistically assume |
| // that it can be renamed. In the absence of tablegen descriptors for register |
| // files, RenameAs is always set to the invalid register ID. In all other |
| // cases, RenameAs must be either equal to RegID, or it must reference a |
| // super-register of RegID. |
| |
| // If RenameAs is a super-register of RegID, then a write to RegID has always |
| // a false dependency on RenameAs. The only exception is for when the write |
| // implicitly clears the upper portion of the underlying register. |
| // If a write clears its super-registers, then it is renamed as `RenameAs`. |
| bool IsWriteZero = WS.isWriteZero(); |
| bool IsEliminated = WS.isEliminated(); |
| bool ShouldAllocatePhysRegs = !IsWriteZero && !IsEliminated; |
| const RegisterRenamingInfo &RRI = RegisterMappings[RegID].second; |
| WS.setPRF(RRI.IndexPlusCost.first); |
| |
| if (RRI.RenameAs && RRI.RenameAs != RegID) { |
| RegID = RRI.RenameAs; |
| WriteRef &OtherWrite = RegisterMappings[RegID].first; |
| |
| if (!WS.clearsSuperRegisters()) { |
| // The processor keeps the definition of `RegID` together with register |
| // `RenameAs`. Since this partial write is not renamed, no physical |
| // register is allocated. |
| ShouldAllocatePhysRegs = false; |
| |
| WriteState *OtherWS = OtherWrite.getWriteState(); |
| if (OtherWS && (OtherWrite.getSourceIndex() != Write.getSourceIndex())) { |
| // This partial write has a false dependency on RenameAs. |
| assert(!IsEliminated && "Unexpected partial update!"); |
| OtherWS->addUser(OtherWrite.getSourceIndex(), &WS); |
| } |
| } |
| } |
| |
| // Update zero registers. |
| MCPhysReg ZeroRegisterID = |
| WS.clearsSuperRegisters() ? RegID : WS.getRegisterID(); |
| if (IsWriteZero) { |
| ZeroRegisters.setBit(ZeroRegisterID); |
| for (MCSubRegIterator I(ZeroRegisterID, &MRI); I.isValid(); ++I) |
| ZeroRegisters.setBit(*I); |
| } else { |
| ZeroRegisters.clearBit(ZeroRegisterID); |
| for (MCSubRegIterator I(ZeroRegisterID, &MRI); I.isValid(); ++I) |
| ZeroRegisters.clearBit(*I); |
| } |
| |
| // If this is move has been eliminated, then the call to tryEliminateMove |
| // should have already updated all the register mappings. |
| if (!IsEliminated) { |
| // Update the mapping for register RegID including its sub-registers. |
| RegisterMappings[RegID].first = Write; |
| RegisterMappings[RegID].second.AliasRegID = 0U; |
| for (MCSubRegIterator I(RegID, &MRI); I.isValid(); ++I) { |
| RegisterMappings[*I].first = Write; |
| RegisterMappings[*I].second.AliasRegID = 0U; |
| } |
| |
| // No physical registers are allocated for instructions that are optimized |
| // in hardware. For example, zero-latency data-dependency breaking |
| // instructions don't consume physical registers. |
| if (ShouldAllocatePhysRegs) |
| allocatePhysRegs(RegisterMappings[RegID].second, UsedPhysRegs); |
| } |
| |
| if (!WS.clearsSuperRegisters()) |
| return; |
| |
| for (MCSuperRegIterator I(RegID, &MRI); I.isValid(); ++I) { |
| if (!IsEliminated) { |
| RegisterMappings[*I].first = Write; |
| RegisterMappings[*I].second.AliasRegID = 0U; |
| } |
| |
| if (IsWriteZero) |
| ZeroRegisters.setBit(*I); |
| else |
| ZeroRegisters.clearBit(*I); |
| } |
| } |
| |
| void RegisterFile::removeRegisterWrite( |
| const WriteState &WS, MutableArrayRef<unsigned> FreedPhysRegs) { |
| // Early exit if this write was eliminated. A write eliminated at register |
| // renaming stage generates an alias, and it is not added to the PRF. |
| if (WS.isEliminated()) |
| return; |
| |
| MCPhysReg RegID = WS.getRegisterID(); |
| |
| assert(RegID != 0 && "Invalidating an already invalid register?"); |
| assert(WS.getCyclesLeft() != UNKNOWN_CYCLES && |
| "Invalidating a write of unknown cycles!"); |
| assert(WS.getCyclesLeft() <= 0 && "Invalid cycles left for this write!"); |
| |
| bool ShouldFreePhysRegs = !WS.isWriteZero(); |
| MCPhysReg RenameAs = RegisterMappings[RegID].second.RenameAs; |
| if (RenameAs && RenameAs != RegID) { |
| RegID = RenameAs; |
| |
| if (!WS.clearsSuperRegisters()) { |
| // Keep the definition of `RegID` together with register `RenameAs`. |
| ShouldFreePhysRegs = false; |
| } |
| } |
| |
| if (ShouldFreePhysRegs) |
| freePhysRegs(RegisterMappings[RegID].second, FreedPhysRegs); |
| |
| WriteRef &WR = RegisterMappings[RegID].first; |
| if (WR.getWriteState() == &WS) |
| WR.invalidate(); |
| |
| for (MCSubRegIterator I(RegID, &MRI); I.isValid(); ++I) { |
| WriteRef &OtherWR = RegisterMappings[*I].first; |
| if (OtherWR.getWriteState() == &WS) |
| OtherWR.invalidate(); |
| } |
| |
| if (!WS.clearsSuperRegisters()) |
| return; |
| |
| for (MCSuperRegIterator I(RegID, &MRI); I.isValid(); ++I) { |
| WriteRef &OtherWR = RegisterMappings[*I].first; |
| if (OtherWR.getWriteState() == &WS) |
| OtherWR.invalidate(); |
| } |
| } |
| |
| bool RegisterFile::tryEliminateMove(WriteState &WS, ReadState &RS) { |
| const RegisterMapping &RMFrom = RegisterMappings[RS.getRegisterID()]; |
| const RegisterMapping &RMTo = RegisterMappings[WS.getRegisterID()]; |
| |
| // From and To must be owned by the same PRF. |
| const RegisterRenamingInfo &RRIFrom = RMFrom.second; |
| const RegisterRenamingInfo &RRITo = RMTo.second; |
| unsigned RegisterFileIndex = RRIFrom.IndexPlusCost.first; |
| if (RegisterFileIndex != RRITo.IndexPlusCost.first) |
| return false; |
| |
| // We only allow move elimination for writes that update a full physical |
| // register. On X86, move elimination is possible with 32-bit general purpose |
| // registers because writes to those registers are not partial writes. If a |
| // register move is a partial write, then we conservatively assume that move |
| // elimination fails, since it would either trigger a partial update, or the |
| // issue of a merge opcode. |
| // |
| // Note that this constraint may be lifted in future. For example, we could |
| // make this model more flexible, and let users customize the set of registers |
| // (i.e. register classes) that allow move elimination. |
| // |
| // For now, we assume that there is a strong correlation between registers |
| // that allow move elimination, and how those same registers are renamed in |
| // hardware. |
| if (RRITo.RenameAs && RRITo.RenameAs != WS.getRegisterID()) { |
| // Early exit if the PRF doesn't support move elimination for this register. |
| if (!RegisterMappings[RRITo.RenameAs].second.AllowMoveElimination) |
| return false; |
| if (!WS.clearsSuperRegisters()) |
| return false; |
| } |
| |
| RegisterMappingTracker &RMT = RegisterFiles[RegisterFileIndex]; |
| if (RMT.MaxMoveEliminatedPerCycle && |
| RMT.NumMoveEliminated == RMT.MaxMoveEliminatedPerCycle) |
| return false; |
| |
| bool IsZeroMove = ZeroRegisters[RS.getRegisterID()]; |
| if (RMT.AllowZeroMoveEliminationOnly && !IsZeroMove) |
| return false; |
| |
| // Construct an alias. |
| MCPhysReg AliasedReg = |
| RRIFrom.RenameAs ? RRIFrom.RenameAs : RS.getRegisterID(); |
| MCPhysReg AliasReg = RRITo.RenameAs ? RRITo.RenameAs : WS.getRegisterID(); |
| |
| const RegisterRenamingInfo &RMAlias = RegisterMappings[AliasedReg].second; |
| if (RMAlias.AliasRegID) |
| AliasedReg = RMAlias.AliasRegID; |
| |
| RegisterMappings[AliasReg].second.AliasRegID = AliasedReg; |
| for (MCSubRegIterator I(AliasReg, &MRI); I.isValid(); ++I) |
| RegisterMappings[*I].second.AliasRegID = AliasedReg; |
| |
| if (IsZeroMove) { |
| WS.setWriteZero(); |
| RS.setReadZero(); |
| } |
| WS.setEliminated(); |
| RMT.NumMoveEliminated++; |
| |
| return true; |
| } |
| |
| void RegisterFile::collectWrites(const ReadState &RS, |
| SmallVectorImpl<WriteRef> &Writes) const { |
| MCPhysReg RegID = RS.getRegisterID(); |
| assert(RegID && RegID < RegisterMappings.size()); |
| LLVM_DEBUG(dbgs() << "RegisterFile: collecting writes for register " |
| << MRI.getName(RegID) << '\n'); |
| |
| // Check if this is an alias. |
| const RegisterRenamingInfo &RRI = RegisterMappings[RegID].second; |
| if (RRI.AliasRegID) |
| RegID = RRI.AliasRegID; |
| |
| const WriteRef &WR = RegisterMappings[RegID].first; |
| if (WR.isValid()) |
| Writes.push_back(WR); |
| |
| // Handle potential partial register updates. |
| for (MCSubRegIterator I(RegID, &MRI); I.isValid(); ++I) { |
| const WriteRef &WR = RegisterMappings[*I].first; |
| if (WR.isValid()) |
| Writes.push_back(WR); |
| } |
| |
| // Remove duplicate entries and resize the input vector. |
| if (Writes.size() > 1) { |
| sort(Writes, [](const WriteRef &Lhs, const WriteRef &Rhs) { |
| return Lhs.getWriteState() < Rhs.getWriteState(); |
| }); |
| auto It = std::unique(Writes.begin(), Writes.end()); |
| Writes.resize(std::distance(Writes.begin(), It)); |
| } |
| |
| LLVM_DEBUG({ |
| for (const WriteRef &WR : Writes) { |
| const WriteState &WS = *WR.getWriteState(); |
| dbgs() << "[PRF] Found a dependent use of Register " |
| << MRI.getName(WS.getRegisterID()) << " (defined by instruction #" |
| << WR.getSourceIndex() << ")\n"; |
| } |
| }); |
| } |
| |
| void RegisterFile::addRegisterRead(ReadState &RS, |
| const MCSubtargetInfo &STI) const { |
| MCPhysReg RegID = RS.getRegisterID(); |
| const RegisterRenamingInfo &RRI = RegisterMappings[RegID].second; |
| RS.setPRF(RRI.IndexPlusCost.first); |
| if (RS.isIndependentFromDef()) |
| return; |
| |
| if (ZeroRegisters[RS.getRegisterID()]) |
| RS.setReadZero(); |
| |
| SmallVector<WriteRef, 4> DependentWrites; |
| collectWrites(RS, DependentWrites); |
| RS.setDependentWrites(DependentWrites.size()); |
| |
| // We know that this read depends on all the writes in DependentWrites. |
| // For each write, check if we have ReadAdvance information, and use it |
| // to figure out in how many cycles this read becomes available. |
| const ReadDescriptor &RD = RS.getDescriptor(); |
| const MCSchedModel &SM = STI.getSchedModel(); |
| const MCSchedClassDesc *SC = SM.getSchedClassDesc(RD.SchedClassID); |
| for (WriteRef &WR : DependentWrites) { |
| WriteState &WS = *WR.getWriteState(); |
| unsigned WriteResID = WS.getWriteResourceID(); |
| int ReadAdvance = STI.getReadAdvanceCycles(SC, RD.UseIndex, WriteResID); |
| WS.addUser(WR.getSourceIndex(), &RS, ReadAdvance); |
| } |
| } |
| |
| unsigned RegisterFile::isAvailable(ArrayRef<MCPhysReg> Regs) const { |
| SmallVector<unsigned, 4> NumPhysRegs(getNumRegisterFiles()); |
| |
| // Find how many new mappings must be created for each register file. |
| for (const MCPhysReg RegID : Regs) { |
| const RegisterRenamingInfo &RRI = RegisterMappings[RegID].second; |
| const IndexPlusCostPairTy &Entry = RRI.IndexPlusCost; |
| if (Entry.first) |
| NumPhysRegs[Entry.first] += Entry.second; |
| NumPhysRegs[0] += Entry.second; |
| } |
| |
| unsigned Response = 0; |
| for (unsigned I = 0, E = getNumRegisterFiles(); I < E; ++I) { |
| unsigned NumRegs = NumPhysRegs[I]; |
| if (!NumRegs) |
| continue; |
| |
| const RegisterMappingTracker &RMT = RegisterFiles[I]; |
| if (!RMT.NumPhysRegs) { |
| // The register file has an unbounded number of microarchitectural |
| // registers. |
| continue; |
| } |
| |
| if (RMT.NumPhysRegs < NumRegs) { |
| // The current register file is too small. This may occur if the number of |
| // microarchitectural registers in register file #0 was changed by the |
| // users via flag -reg-file-size. Alternatively, the scheduling model |
| // specified a too small number of registers for this register file. |
| LLVM_DEBUG(dbgs() << "Not enough registers in the register file.\n"); |
| |
| // FIXME: Normalize the instruction register count to match the |
| // NumPhysRegs value. This is a highly unusual case, and is not expected |
| // to occur. This normalization is hiding an inconsistency in either the |
| // scheduling model or in the value that the user might have specified |
| // for NumPhysRegs. |
| NumRegs = RMT.NumPhysRegs; |
| } |
| |
| if (RMT.NumPhysRegs < (RMT.NumUsedPhysRegs + NumRegs)) |
| Response |= (1U << I); |
| } |
| |
| return Response; |
| } |
| |
| #ifndef NDEBUG |
| void RegisterFile::dump() const { |
| for (unsigned I = 0, E = MRI.getNumRegs(); I < E; ++I) { |
| const RegisterMapping &RM = RegisterMappings[I]; |
| const RegisterRenamingInfo &RRI = RM.second; |
| if (ZeroRegisters[I]) { |
| dbgs() << MRI.getName(I) << ", " << I |
| << ", PRF=" << RRI.IndexPlusCost.first |
| << ", Cost=" << RRI.IndexPlusCost.second |
| << ", RenameAs=" << RRI.RenameAs << ", IsZero=" << ZeroRegisters[I] |
| << ","; |
| RM.first.dump(); |
| dbgs() << '\n'; |
| } |
| } |
| |
| for (unsigned I = 0, E = getNumRegisterFiles(); I < E; ++I) { |
| dbgs() << "Register File #" << I; |
| const RegisterMappingTracker &RMT = RegisterFiles[I]; |
| dbgs() << "\n TotalMappings: " << RMT.NumPhysRegs |
| << "\n NumUsedMappings: " << RMT.NumUsedPhysRegs << '\n'; |
| } |
| } |
| #endif |
| |
| } // namespace mca |
| } // namespace llvm |