| //===- MachineCopyPropagation.cpp - Machine Copy Propagation 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 is an extremely simple MachineInstr-level copy propagation pass. |
| // |
| // This pass forwards the source of COPYs to the users of their destinations |
| // when doing so is legal. For example: |
| // |
| // %reg1 = COPY %reg0 |
| // ... |
| // ... = OP %reg1 |
| // |
| // If |
| // - %reg0 has not been clobbered by the time of the use of %reg1 |
| // - the register class constraints are satisfied |
| // - the COPY def is the only value that reaches OP |
| // then this pass replaces the above with: |
| // |
| // %reg1 = COPY %reg0 |
| // ... |
| // ... = OP %reg0 |
| // |
| // This pass also removes some redundant COPYs. For example: |
| // |
| // %R1 = COPY %R0 |
| // ... // No clobber of %R1 |
| // %R0 = COPY %R1 <<< Removed |
| // |
| // or |
| // |
| // %R1 = COPY %R0 |
| // ... // No clobber of %R0 |
| // %R1 = COPY %R0 <<< Removed |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/ADT/SetVector.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/iterator_range.h" |
| #include "llvm/CodeGen/MachineBasicBlock.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/TargetInstrInfo.h" |
| #include "llvm/CodeGen/TargetRegisterInfo.h" |
| #include "llvm/CodeGen/TargetSubtargetInfo.h" |
| #include "llvm/MC/MCRegisterInfo.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/DebugCounter.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include <cassert> |
| #include <iterator> |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "machine-cp" |
| |
| STATISTIC(NumDeletes, "Number of dead copies deleted"); |
| STATISTIC(NumCopyForwards, "Number of copy uses forwarded"); |
| DEBUG_COUNTER(FwdCounter, "machine-cp-fwd", |
| "Controls which register COPYs are forwarded"); |
| |
| namespace { |
| |
| class CopyTracker { |
| struct CopyInfo { |
| MachineInstr *MI; |
| SmallVector<unsigned, 4> DefRegs; |
| bool Avail; |
| }; |
| |
| DenseMap<unsigned, CopyInfo> Copies; |
| |
| public: |
| /// Mark all of the given registers and their subregisters as unavailable for |
| /// copying. |
| void markRegsUnavailable(ArrayRef<unsigned> Regs, |
| const TargetRegisterInfo &TRI) { |
| for (unsigned Reg : Regs) { |
| // Source of copy is no longer available for propagation. |
| for (MCRegUnitIterator RUI(Reg, &TRI); RUI.isValid(); ++RUI) { |
| auto CI = Copies.find(*RUI); |
| if (CI != Copies.end()) |
| CI->second.Avail = false; |
| } |
| } |
| } |
| |
| /// Clobber a single register, removing it from the tracker's copy maps. |
| void clobberRegister(unsigned Reg, const TargetRegisterInfo &TRI) { |
| for (MCRegUnitIterator RUI(Reg, &TRI); RUI.isValid(); ++RUI) { |
| auto I = Copies.find(*RUI); |
| if (I != Copies.end()) { |
| // When we clobber the source of a copy, we need to clobber everything |
| // it defined. |
| markRegsUnavailable(I->second.DefRegs, TRI); |
| // When we clobber the destination of a copy, we need to clobber the |
| // whole register it defined. |
| if (MachineInstr *MI = I->second.MI) |
| markRegsUnavailable({MI->getOperand(0).getReg()}, TRI); |
| // Now we can erase the copy. |
| Copies.erase(I); |
| } |
| } |
| } |
| |
| /// Add this copy's registers into the tracker's copy maps. |
| void trackCopy(MachineInstr *MI, const TargetRegisterInfo &TRI) { |
| assert(MI->isCopy() && "Tracking non-copy?"); |
| |
| unsigned Def = MI->getOperand(0).getReg(); |
| unsigned Src = MI->getOperand(1).getReg(); |
| |
| // Remember Def is defined by the copy. |
| for (MCRegUnitIterator RUI(Def, &TRI); RUI.isValid(); ++RUI) |
| Copies[*RUI] = {MI, {}, true}; |
| |
| // Remember source that's copied to Def. Once it's clobbered, then |
| // it's no longer available for copy propagation. |
| for (MCRegUnitIterator RUI(Src, &TRI); RUI.isValid(); ++RUI) { |
| auto I = Copies.insert({*RUI, {nullptr, {}, false}}); |
| auto &Copy = I.first->second; |
| if (!is_contained(Copy.DefRegs, Def)) |
| Copy.DefRegs.push_back(Def); |
| } |
| } |
| |
| bool hasAnyCopies() { |
| return !Copies.empty(); |
| } |
| |
| MachineInstr *findCopyForUnit(unsigned RegUnit, const TargetRegisterInfo &TRI, |
| bool MustBeAvailable = false) { |
| auto CI = Copies.find(RegUnit); |
| if (CI == Copies.end()) |
| return nullptr; |
| if (MustBeAvailable && !CI->second.Avail) |
| return nullptr; |
| return CI->second.MI; |
| } |
| |
| MachineInstr *findAvailCopy(MachineInstr &DestCopy, unsigned Reg, |
| const TargetRegisterInfo &TRI) { |
| // We check the first RegUnit here, since we'll only be interested in the |
| // copy if it copies the entire register anyway. |
| MCRegUnitIterator RUI(Reg, &TRI); |
| MachineInstr *AvailCopy = |
| findCopyForUnit(*RUI, TRI, /*MustBeAvailable=*/true); |
| if (!AvailCopy || |
| !TRI.isSubRegisterEq(AvailCopy->getOperand(0).getReg(), Reg)) |
| return nullptr; |
| |
| // Check that the available copy isn't clobbered by any regmasks between |
| // itself and the destination. |
| unsigned AvailSrc = AvailCopy->getOperand(1).getReg(); |
| unsigned AvailDef = AvailCopy->getOperand(0).getReg(); |
| for (const MachineInstr &MI : |
| make_range(AvailCopy->getIterator(), DestCopy.getIterator())) |
| for (const MachineOperand &MO : MI.operands()) |
| if (MO.isRegMask()) |
| if (MO.clobbersPhysReg(AvailSrc) || MO.clobbersPhysReg(AvailDef)) |
| return nullptr; |
| |
| return AvailCopy; |
| } |
| |
| void clear() { |
| Copies.clear(); |
| } |
| }; |
| |
| class MachineCopyPropagation : public MachineFunctionPass { |
| const TargetRegisterInfo *TRI; |
| const TargetInstrInfo *TII; |
| const MachineRegisterInfo *MRI; |
| |
| public: |
| static char ID; // Pass identification, replacement for typeid |
| |
| MachineCopyPropagation() : MachineFunctionPass(ID) { |
| initializeMachineCopyPropagationPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.setPreservesCFG(); |
| MachineFunctionPass::getAnalysisUsage(AU); |
| } |
| |
| bool runOnMachineFunction(MachineFunction &MF) override; |
| |
| MachineFunctionProperties getRequiredProperties() const override { |
| return MachineFunctionProperties().set( |
| MachineFunctionProperties::Property::NoVRegs); |
| } |
| |
| private: |
| void ClobberRegister(unsigned Reg); |
| void ReadRegister(unsigned Reg); |
| void CopyPropagateBlock(MachineBasicBlock &MBB); |
| bool eraseIfRedundant(MachineInstr &Copy, unsigned Src, unsigned Def); |
| void forwardUses(MachineInstr &MI); |
| bool isForwardableRegClassCopy(const MachineInstr &Copy, |
| const MachineInstr &UseI, unsigned UseIdx); |
| bool hasImplicitOverlap(const MachineInstr &MI, const MachineOperand &Use); |
| |
| /// Candidates for deletion. |
| SmallSetVector<MachineInstr *, 8> MaybeDeadCopies; |
| |
| CopyTracker Tracker; |
| |
| bool Changed; |
| }; |
| |
| } // end anonymous namespace |
| |
| char MachineCopyPropagation::ID = 0; |
| |
| char &llvm::MachineCopyPropagationID = MachineCopyPropagation::ID; |
| |
| INITIALIZE_PASS(MachineCopyPropagation, DEBUG_TYPE, |
| "Machine Copy Propagation Pass", false, false) |
| |
| void MachineCopyPropagation::ReadRegister(unsigned Reg) { |
| // If 'Reg' is defined by a copy, the copy is no longer a candidate |
| // for elimination. |
| for (MCRegUnitIterator RUI(Reg, TRI); RUI.isValid(); ++RUI) { |
| if (MachineInstr *Copy = Tracker.findCopyForUnit(*RUI, *TRI)) { |
| LLVM_DEBUG(dbgs() << "MCP: Copy is used - not dead: "; Copy->dump()); |
| MaybeDeadCopies.remove(Copy); |
| } |
| } |
| } |
| |
| /// Return true if \p PreviousCopy did copy register \p Src to register \p Def. |
| /// This fact may have been obscured by sub register usage or may not be true at |
| /// all even though Src and Def are subregisters of the registers used in |
| /// PreviousCopy. e.g. |
| /// isNopCopy("ecx = COPY eax", AX, CX) == true |
| /// isNopCopy("ecx = COPY eax", AH, CL) == false |
| static bool isNopCopy(const MachineInstr &PreviousCopy, unsigned Src, |
| unsigned Def, const TargetRegisterInfo *TRI) { |
| unsigned PreviousSrc = PreviousCopy.getOperand(1).getReg(); |
| unsigned PreviousDef = PreviousCopy.getOperand(0).getReg(); |
| if (Src == PreviousSrc) { |
| assert(Def == PreviousDef); |
| return true; |
| } |
| if (!TRI->isSubRegister(PreviousSrc, Src)) |
| return false; |
| unsigned SubIdx = TRI->getSubRegIndex(PreviousSrc, Src); |
| return SubIdx == TRI->getSubRegIndex(PreviousDef, Def); |
| } |
| |
| /// Remove instruction \p Copy if there exists a previous copy that copies the |
| /// register \p Src to the register \p Def; This may happen indirectly by |
| /// copying the super registers. |
| bool MachineCopyPropagation::eraseIfRedundant(MachineInstr &Copy, unsigned Src, |
| unsigned Def) { |
| // Avoid eliminating a copy from/to a reserved registers as we cannot predict |
| // the value (Example: The sparc zero register is writable but stays zero). |
| if (MRI->isReserved(Src) || MRI->isReserved(Def)) |
| return false; |
| |
| // Search for an existing copy. |
| MachineInstr *PrevCopy = Tracker.findAvailCopy(Copy, Def, *TRI); |
| if (!PrevCopy) |
| return false; |
| |
| // Check that the existing copy uses the correct sub registers. |
| if (PrevCopy->getOperand(0).isDead()) |
| return false; |
| if (!isNopCopy(*PrevCopy, Src, Def, TRI)) |
| return false; |
| |
| LLVM_DEBUG(dbgs() << "MCP: copy is a NOP, removing: "; Copy.dump()); |
| |
| // Copy was redundantly redefining either Src or Def. Remove earlier kill |
| // flags between Copy and PrevCopy because the value will be reused now. |
| assert(Copy.isCopy()); |
| unsigned CopyDef = Copy.getOperand(0).getReg(); |
| assert(CopyDef == Src || CopyDef == Def); |
| for (MachineInstr &MI : |
| make_range(PrevCopy->getIterator(), Copy.getIterator())) |
| MI.clearRegisterKills(CopyDef, TRI); |
| |
| Copy.eraseFromParent(); |
| Changed = true; |
| ++NumDeletes; |
| return true; |
| } |
| |
| /// Decide whether we should forward the source of \param Copy to its use in |
| /// \param UseI based on the physical register class constraints of the opcode |
| /// and avoiding introducing more cross-class COPYs. |
| bool MachineCopyPropagation::isForwardableRegClassCopy(const MachineInstr &Copy, |
| const MachineInstr &UseI, |
| unsigned UseIdx) { |
| |
| unsigned CopySrcReg = Copy.getOperand(1).getReg(); |
| |
| // If the new register meets the opcode register constraints, then allow |
| // forwarding. |
| if (const TargetRegisterClass *URC = |
| UseI.getRegClassConstraint(UseIdx, TII, TRI)) |
| return URC->contains(CopySrcReg); |
| |
| if (!UseI.isCopy()) |
| return false; |
| |
| /// COPYs don't have register class constraints, so if the user instruction |
| /// is a COPY, we just try to avoid introducing additional cross-class |
| /// COPYs. For example: |
| /// |
| /// RegClassA = COPY RegClassB // Copy parameter |
| /// ... |
| /// RegClassB = COPY RegClassA // UseI parameter |
| /// |
| /// which after forwarding becomes |
| /// |
| /// RegClassA = COPY RegClassB |
| /// ... |
| /// RegClassB = COPY RegClassB |
| /// |
| /// so we have reduced the number of cross-class COPYs and potentially |
| /// introduced a nop COPY that can be removed. |
| const TargetRegisterClass *UseDstRC = |
| TRI->getMinimalPhysRegClass(UseI.getOperand(0).getReg()); |
| |
| const TargetRegisterClass *SuperRC = UseDstRC; |
| for (TargetRegisterClass::sc_iterator SuperRCI = UseDstRC->getSuperClasses(); |
| SuperRC; SuperRC = *SuperRCI++) |
| if (SuperRC->contains(CopySrcReg)) |
| return true; |
| |
| return false; |
| } |
| |
| /// Check that \p MI does not have implicit uses that overlap with it's \p Use |
| /// operand (the register being replaced), since these can sometimes be |
| /// implicitly tied to other operands. For example, on AMDGPU: |
| /// |
| /// V_MOVRELS_B32_e32 %VGPR2, %M0<imp-use>, %EXEC<imp-use>, %VGPR2_VGPR3_VGPR4_VGPR5<imp-use> |
| /// |
| /// the %VGPR2 is implicitly tied to the larger reg operand, but we have no |
| /// way of knowing we need to update the latter when updating the former. |
| bool MachineCopyPropagation::hasImplicitOverlap(const MachineInstr &MI, |
| const MachineOperand &Use) { |
| for (const MachineOperand &MIUse : MI.uses()) |
| if (&MIUse != &Use && MIUse.isReg() && MIUse.isImplicit() && |
| MIUse.isUse() && TRI->regsOverlap(Use.getReg(), MIUse.getReg())) |
| return true; |
| |
| return false; |
| } |
| |
| /// Look for available copies whose destination register is used by \p MI and |
| /// replace the use in \p MI with the copy's source register. |
| void MachineCopyPropagation::forwardUses(MachineInstr &MI) { |
| if (!Tracker.hasAnyCopies()) |
| return; |
| |
| // Look for non-tied explicit vreg uses that have an active COPY |
| // instruction that defines the physical register allocated to them. |
| // Replace the vreg with the source of the active COPY. |
| for (unsigned OpIdx = 0, OpEnd = MI.getNumOperands(); OpIdx < OpEnd; |
| ++OpIdx) { |
| MachineOperand &MOUse = MI.getOperand(OpIdx); |
| // Don't forward into undef use operands since doing so can cause problems |
| // with the machine verifier, since it doesn't treat undef reads as reads, |
| // so we can end up with a live range that ends on an undef read, leading to |
| // an error that the live range doesn't end on a read of the live range |
| // register. |
| if (!MOUse.isReg() || MOUse.isTied() || MOUse.isUndef() || MOUse.isDef() || |
| MOUse.isImplicit()) |
| continue; |
| |
| if (!MOUse.getReg()) |
| continue; |
| |
| // Check that the register is marked 'renamable' so we know it is safe to |
| // rename it without violating any constraints that aren't expressed in the |
| // IR (e.g. ABI or opcode requirements). |
| if (!MOUse.isRenamable()) |
| continue; |
| |
| MachineInstr *Copy = Tracker.findAvailCopy(MI, MOUse.getReg(), *TRI); |
| if (!Copy) |
| continue; |
| |
| unsigned CopyDstReg = Copy->getOperand(0).getReg(); |
| const MachineOperand &CopySrc = Copy->getOperand(1); |
| unsigned CopySrcReg = CopySrc.getReg(); |
| |
| // FIXME: Don't handle partial uses of wider COPYs yet. |
| if (MOUse.getReg() != CopyDstReg) { |
| LLVM_DEBUG( |
| dbgs() << "MCP: FIXME! Not forwarding COPY to sub-register use:\n " |
| << MI); |
| continue; |
| } |
| |
| // Don't forward COPYs of reserved regs unless they are constant. |
| if (MRI->isReserved(CopySrcReg) && !MRI->isConstantPhysReg(CopySrcReg)) |
| continue; |
| |
| if (!isForwardableRegClassCopy(*Copy, MI, OpIdx)) |
| continue; |
| |
| if (hasImplicitOverlap(MI, MOUse)) |
| continue; |
| |
| if (!DebugCounter::shouldExecute(FwdCounter)) { |
| LLVM_DEBUG(dbgs() << "MCP: Skipping forwarding due to debug counter:\n " |
| << MI); |
| continue; |
| } |
| |
| LLVM_DEBUG(dbgs() << "MCP: Replacing " << printReg(MOUse.getReg(), TRI) |
| << "\n with " << printReg(CopySrcReg, TRI) |
| << "\n in " << MI << " from " << *Copy); |
| |
| MOUse.setReg(CopySrcReg); |
| if (!CopySrc.isRenamable()) |
| MOUse.setIsRenamable(false); |
| |
| LLVM_DEBUG(dbgs() << "MCP: After replacement: " << MI << "\n"); |
| |
| // Clear kill markers that may have been invalidated. |
| for (MachineInstr &KMI : |
| make_range(Copy->getIterator(), std::next(MI.getIterator()))) |
| KMI.clearRegisterKills(CopySrcReg, TRI); |
| |
| ++NumCopyForwards; |
| Changed = true; |
| } |
| } |
| |
| void MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) { |
| LLVM_DEBUG(dbgs() << "MCP: CopyPropagateBlock " << MBB.getName() << "\n"); |
| |
| for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ) { |
| MachineInstr *MI = &*I; |
| ++I; |
| |
| // Analyze copies (which don't overlap themselves). |
| if (MI->isCopy() && !TRI->regsOverlap(MI->getOperand(0).getReg(), |
| MI->getOperand(1).getReg())) { |
| unsigned Def = MI->getOperand(0).getReg(); |
| unsigned Src = MI->getOperand(1).getReg(); |
| |
| assert(!TargetRegisterInfo::isVirtualRegister(Def) && |
| !TargetRegisterInfo::isVirtualRegister(Src) && |
| "MachineCopyPropagation should be run after register allocation!"); |
| |
| // The two copies cancel out and the source of the first copy |
| // hasn't been overridden, eliminate the second one. e.g. |
| // %ecx = COPY %eax |
| // ... nothing clobbered eax. |
| // %eax = COPY %ecx |
| // => |
| // %ecx = COPY %eax |
| // |
| // or |
| // |
| // %ecx = COPY %eax |
| // ... nothing clobbered eax. |
| // %ecx = COPY %eax |
| // => |
| // %ecx = COPY %eax |
| if (eraseIfRedundant(*MI, Def, Src) || eraseIfRedundant(*MI, Src, Def)) |
| continue; |
| |
| forwardUses(*MI); |
| |
| // Src may have been changed by forwardUses() |
| Src = MI->getOperand(1).getReg(); |
| |
| // If Src is defined by a previous copy, the previous copy cannot be |
| // eliminated. |
| ReadRegister(Src); |
| for (const MachineOperand &MO : MI->implicit_operands()) { |
| if (!MO.isReg() || !MO.readsReg()) |
| continue; |
| unsigned Reg = MO.getReg(); |
| if (!Reg) |
| continue; |
| ReadRegister(Reg); |
| } |
| |
| LLVM_DEBUG(dbgs() << "MCP: Copy is a deletion candidate: "; MI->dump()); |
| |
| // Copy is now a candidate for deletion. |
| if (!MRI->isReserved(Def)) |
| MaybeDeadCopies.insert(MI); |
| |
| // If 'Def' is previously source of another copy, then this earlier copy's |
| // source is no longer available. e.g. |
| // %xmm9 = copy %xmm2 |
| // ... |
| // %xmm2 = copy %xmm0 |
| // ... |
| // %xmm2 = copy %xmm9 |
| Tracker.clobberRegister(Def, *TRI); |
| for (const MachineOperand &MO : MI->implicit_operands()) { |
| if (!MO.isReg() || !MO.isDef()) |
| continue; |
| unsigned Reg = MO.getReg(); |
| if (!Reg) |
| continue; |
| Tracker.clobberRegister(Reg, *TRI); |
| } |
| |
| Tracker.trackCopy(MI, *TRI); |
| |
| continue; |
| } |
| |
| // Clobber any earlyclobber regs first. |
| for (const MachineOperand &MO : MI->operands()) |
| if (MO.isReg() && MO.isEarlyClobber()) { |
| unsigned Reg = MO.getReg(); |
| // If we have a tied earlyclobber, that means it is also read by this |
| // instruction, so we need to make sure we don't remove it as dead |
| // later. |
| if (MO.isTied()) |
| ReadRegister(Reg); |
| Tracker.clobberRegister(Reg, *TRI); |
| } |
| |
| forwardUses(*MI); |
| |
| // Not a copy. |
| SmallVector<unsigned, 2> Defs; |
| const MachineOperand *RegMask = nullptr; |
| for (const MachineOperand &MO : MI->operands()) { |
| if (MO.isRegMask()) |
| RegMask = &MO; |
| if (!MO.isReg()) |
| continue; |
| unsigned Reg = MO.getReg(); |
| if (!Reg) |
| continue; |
| |
| assert(!TargetRegisterInfo::isVirtualRegister(Reg) && |
| "MachineCopyPropagation should be run after register allocation!"); |
| |
| if (MO.isDef() && !MO.isEarlyClobber()) { |
| Defs.push_back(Reg); |
| continue; |
| } else if (!MO.isDebug() && MO.readsReg()) |
| ReadRegister(Reg); |
| } |
| |
| // The instruction has a register mask operand which means that it clobbers |
| // a large set of registers. Treat clobbered registers the same way as |
| // defined registers. |
| if (RegMask) { |
| // Erase any MaybeDeadCopies whose destination register is clobbered. |
| for (SmallSetVector<MachineInstr *, 8>::iterator DI = |
| MaybeDeadCopies.begin(); |
| DI != MaybeDeadCopies.end();) { |
| MachineInstr *MaybeDead = *DI; |
| unsigned Reg = MaybeDead->getOperand(0).getReg(); |
| assert(!MRI->isReserved(Reg)); |
| |
| if (!RegMask->clobbersPhysReg(Reg)) { |
| ++DI; |
| continue; |
| } |
| |
| LLVM_DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: "; |
| MaybeDead->dump()); |
| |
| // Make sure we invalidate any entries in the copy maps before erasing |
| // the instruction. |
| Tracker.clobberRegister(Reg, *TRI); |
| |
| // erase() will return the next valid iterator pointing to the next |
| // element after the erased one. |
| DI = MaybeDeadCopies.erase(DI); |
| MaybeDead->eraseFromParent(); |
| Changed = true; |
| ++NumDeletes; |
| } |
| } |
| |
| // Any previous copy definition or reading the Defs is no longer available. |
| for (unsigned Reg : Defs) |
| Tracker.clobberRegister(Reg, *TRI); |
| } |
| |
| // If MBB doesn't have successors, delete the copies whose defs are not used. |
| // If MBB does have successors, then conservative assume the defs are live-out |
| // since we don't want to trust live-in lists. |
| if (MBB.succ_empty()) { |
| for (MachineInstr *MaybeDead : MaybeDeadCopies) { |
| LLVM_DEBUG(dbgs() << "MCP: Removing copy due to no live-out succ: "; |
| MaybeDead->dump()); |
| assert(!MRI->isReserved(MaybeDead->getOperand(0).getReg())); |
| |
| // Update matching debug values. |
| assert(MaybeDead->isCopy()); |
| MaybeDead->changeDebugValuesDefReg(MaybeDead->getOperand(1).getReg()); |
| |
| MaybeDead->eraseFromParent(); |
| Changed = true; |
| ++NumDeletes; |
| } |
| } |
| |
| MaybeDeadCopies.clear(); |
| Tracker.clear(); |
| } |
| |
| bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) { |
| if (skipFunction(MF.getFunction())) |
| return false; |
| |
| Changed = false; |
| |
| TRI = MF.getSubtarget().getRegisterInfo(); |
| TII = MF.getSubtarget().getInstrInfo(); |
| MRI = &MF.getRegInfo(); |
| |
| for (MachineBasicBlock &MBB : MF) |
| CopyPropagateBlock(MBB); |
| |
| return Changed; |
| } |