1 //===- MachineCopyPropagation.cpp - Machine Copy Propagation Pass ---------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This is an extremely simple MachineInstr-level copy propagation pass.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/ADT/DenseMap.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SetVector.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/ADT/Statistic.h"
19 #include "llvm/ADT/iterator_range.h"
20 #include "llvm/CodeGen/MachineBasicBlock.h"
21 #include "llvm/CodeGen/MachineFunction.h"
22 #include "llvm/CodeGen/MachineFunctionPass.h"
23 #include "llvm/CodeGen/MachineInstr.h"
24 #include "llvm/CodeGen/MachineOperand.h"
25 #include "llvm/CodeGen/MachineRegisterInfo.h"
26 #include "llvm/CodeGen/TargetRegisterInfo.h"
27 #include "llvm/CodeGen/TargetSubtargetInfo.h"
28 #include "llvm/MC/MCRegisterInfo.h"
29 #include "llvm/Pass.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/Support/raw_ostream.h"
37 #define DEBUG_TYPE "machine-cp"
39 STATISTIC(NumDeletes, "Number of dead copies deleted");
43 using RegList = SmallVector<unsigned, 4>;
44 using SourceMap = DenseMap<unsigned, RegList>;
45 using Reg2MIMap = DenseMap<unsigned, MachineInstr *>;
47 class MachineCopyPropagation : public MachineFunctionPass {
48 const TargetRegisterInfo *TRI;
49 const TargetInstrInfo *TII;
50 const MachineRegisterInfo *MRI;
53 static char ID; // Pass identification, replacement for typeid
55 MachineCopyPropagation() : MachineFunctionPass(ID) {
56 initializeMachineCopyPropagationPass(*PassRegistry::getPassRegistry());
59 void getAnalysisUsage(AnalysisUsage &AU) const override {
61 MachineFunctionPass::getAnalysisUsage(AU);
64 bool runOnMachineFunction(MachineFunction &MF) override;
66 MachineFunctionProperties getRequiredProperties() const override {
67 return MachineFunctionProperties().set(
68 MachineFunctionProperties::Property::NoVRegs);
72 void ClobberRegister(unsigned Reg);
73 void ReadRegister(unsigned Reg);
74 void CopyPropagateBlock(MachineBasicBlock &MBB);
75 bool eraseIfRedundant(MachineInstr &Copy, unsigned Src, unsigned Def);
77 /// Candidates for deletion.
78 SmallSetVector<MachineInstr*, 8> MaybeDeadCopies;
80 /// Def -> available copies map.
81 Reg2MIMap AvailCopyMap;
83 /// Def -> copies map.
92 } // end anonymous namespace
94 char MachineCopyPropagation::ID = 0;
96 char &llvm::MachineCopyPropagationID = MachineCopyPropagation::ID;
98 INITIALIZE_PASS(MachineCopyPropagation, DEBUG_TYPE,
99 "Machine Copy Propagation Pass", false, false)
101 /// Remove any entry in \p Map where the register is a subregister or equal to
102 /// a register contained in \p Regs.
103 static void removeRegsFromMap(Reg2MIMap &Map, const RegList &Regs,
104 const TargetRegisterInfo &TRI) {
105 for (unsigned Reg : Regs) {
106 // Source of copy is no longer available for propagation.
107 for (MCSubRegIterator SR(Reg, &TRI, true); SR.isValid(); ++SR)
112 /// Remove any entry in \p Map that is marked clobbered in \p RegMask.
113 /// The map will typically have a lot fewer entries than the regmask clobbers,
114 /// so this is more efficient than iterating the clobbered registers and calling
115 /// ClobberRegister() on them.
116 static void removeClobberedRegsFromMap(Reg2MIMap &Map,
117 const MachineOperand &RegMask) {
118 for (Reg2MIMap::iterator I = Map.begin(), E = Map.end(), Next; I != E;
121 unsigned Reg = I->first;
122 if (RegMask.clobbersPhysReg(Reg))
127 void MachineCopyPropagation::ClobberRegister(unsigned Reg) {
128 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
130 AvailCopyMap.erase(*AI);
132 SourceMap::iterator SI = SrcMap.find(*AI);
133 if (SI != SrcMap.end()) {
134 removeRegsFromMap(AvailCopyMap, SI->second, *TRI);
140 void MachineCopyPropagation::ReadRegister(unsigned Reg) {
141 // If 'Reg' is defined by a copy, the copy is no longer a candidate
143 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
144 Reg2MIMap::iterator CI = CopyMap.find(*AI);
145 if (CI != CopyMap.end()) {
146 DEBUG(dbgs() << "MCP: Copy is used - not dead: "; CI->second->dump());
147 MaybeDeadCopies.remove(CI->second);
152 /// Return true if \p PreviousCopy did copy register \p Src to register \p Def.
153 /// This fact may have been obscured by sub register usage or may not be true at
154 /// all even though Src and Def are subregisters of the registers used in
155 /// PreviousCopy. e.g.
156 /// isNopCopy("ecx = COPY eax", AX, CX) == true
157 /// isNopCopy("ecx = COPY eax", AH, CL) == false
158 static bool isNopCopy(const MachineInstr &PreviousCopy, unsigned Src,
159 unsigned Def, const TargetRegisterInfo *TRI) {
160 unsigned PreviousSrc = PreviousCopy.getOperand(1).getReg();
161 unsigned PreviousDef = PreviousCopy.getOperand(0).getReg();
162 if (Src == PreviousSrc) {
163 assert(Def == PreviousDef);
166 if (!TRI->isSubRegister(PreviousSrc, Src))
168 unsigned SubIdx = TRI->getSubRegIndex(PreviousSrc, Src);
169 return SubIdx == TRI->getSubRegIndex(PreviousDef, Def);
172 /// Remove instruction \p Copy if there exists a previous copy that copies the
173 /// register \p Src to the register \p Def; This may happen indirectly by
174 /// copying the super registers.
175 bool MachineCopyPropagation::eraseIfRedundant(MachineInstr &Copy, unsigned Src,
177 // Avoid eliminating a copy from/to a reserved registers as we cannot predict
178 // the value (Example: The sparc zero register is writable but stays zero).
179 if (MRI->isReserved(Src) || MRI->isReserved(Def))
182 // Search for an existing copy.
183 Reg2MIMap::iterator CI = AvailCopyMap.find(Def);
184 if (CI == AvailCopyMap.end())
187 // Check that the existing copy uses the correct sub registers.
188 MachineInstr &PrevCopy = *CI->second;
189 if (PrevCopy.getOperand(0).isDead())
191 if (!isNopCopy(PrevCopy, Src, Def, TRI))
194 DEBUG(dbgs() << "MCP: copy is a NOP, removing: "; Copy.dump());
196 // Copy was redundantly redefining either Src or Def. Remove earlier kill
197 // flags between Copy and PrevCopy because the value will be reused now.
198 assert(Copy.isCopy());
199 unsigned CopyDef = Copy.getOperand(0).getReg();
200 assert(CopyDef == Src || CopyDef == Def);
201 for (MachineInstr &MI :
202 make_range(PrevCopy.getIterator(), Copy.getIterator()))
203 MI.clearRegisterKills(CopyDef, TRI);
205 Copy.eraseFromParent();
211 void MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
212 DEBUG(dbgs() << "MCP: CopyPropagateBlock " << MBB.getName() << "\n");
214 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ) {
215 MachineInstr *MI = &*I;
219 unsigned Def = MI->getOperand(0).getReg();
220 unsigned Src = MI->getOperand(1).getReg();
222 assert(!TargetRegisterInfo::isVirtualRegister(Def) &&
223 !TargetRegisterInfo::isVirtualRegister(Src) &&
224 "MachineCopyPropagation should be run after register allocation!");
226 // The two copies cancel out and the source of the first copy
227 // hasn't been overridden, eliminate the second one. e.g.
229 // ... nothing clobbered eax.
237 // ... nothing clobbered eax.
241 if (eraseIfRedundant(*MI, Def, Src) || eraseIfRedundant(*MI, Src, Def))
244 // If Src is defined by a previous copy, the previous copy cannot be
247 for (const MachineOperand &MO : MI->implicit_operands()) {
248 if (!MO.isReg() || !MO.readsReg())
250 unsigned Reg = MO.getReg();
256 DEBUG(dbgs() << "MCP: Copy is a deletion candidate: "; MI->dump());
258 // Copy is now a candidate for deletion.
259 if (!MRI->isReserved(Def))
260 MaybeDeadCopies.insert(MI);
262 // If 'Def' is previously source of another copy, then this earlier copy's
263 // source is no longer available. e.g.
264 // %xmm9 = copy %xmm2
266 // %xmm2 = copy %xmm0
268 // %xmm2 = copy %xmm9
269 ClobberRegister(Def);
270 for (const MachineOperand &MO : MI->implicit_operands()) {
271 if (!MO.isReg() || !MO.isDef())
273 unsigned Reg = MO.getReg();
276 ClobberRegister(Reg);
279 // Remember Def is defined by the copy.
280 for (MCSubRegIterator SR(Def, TRI, /*IncludeSelf=*/true); SR.isValid();
283 AvailCopyMap[*SR] = MI;
286 // Remember source that's copied to Def. Once it's clobbered, then
287 // it's no longer available for copy propagation.
288 RegList &DestList = SrcMap[Src];
289 if (!is_contained(DestList, Def))
290 DestList.push_back(Def);
296 SmallVector<unsigned, 2> Defs;
297 const MachineOperand *RegMask = nullptr;
298 for (const MachineOperand &MO : MI->operands()) {
303 unsigned Reg = MO.getReg();
307 assert(!TargetRegisterInfo::isVirtualRegister(Reg) &&
308 "MachineCopyPropagation should be run after register allocation!");
313 } else if (MO.readsReg())
317 // The instruction has a register mask operand which means that it clobbers
318 // a large set of registers. Treat clobbered registers the same way as
319 // defined registers.
321 // Erase any MaybeDeadCopies whose destination register is clobbered.
322 for (SmallSetVector<MachineInstr *, 8>::iterator DI =
323 MaybeDeadCopies.begin();
324 DI != MaybeDeadCopies.end();) {
325 MachineInstr *MaybeDead = *DI;
326 unsigned Reg = MaybeDead->getOperand(0).getReg();
327 assert(!MRI->isReserved(Reg));
329 if (!RegMask->clobbersPhysReg(Reg)) {
334 DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
337 // erase() will return the next valid iterator pointing to the next
338 // element after the erased one.
339 DI = MaybeDeadCopies.erase(DI);
340 MaybeDead->eraseFromParent();
345 removeClobberedRegsFromMap(AvailCopyMap, *RegMask);
346 removeClobberedRegsFromMap(CopyMap, *RegMask);
347 for (SourceMap::iterator I = SrcMap.begin(), E = SrcMap.end(), Next;
350 if (RegMask->clobbersPhysReg(I->first)) {
351 removeRegsFromMap(AvailCopyMap, I->second, *TRI);
357 // Any previous copy definition or reading the Defs is no longer available.
358 for (unsigned Reg : Defs)
359 ClobberRegister(Reg);
362 // If MBB doesn't have successors, delete the copies whose defs are not used.
363 // If MBB does have successors, then conservative assume the defs are live-out
364 // since we don't want to trust live-in lists.
365 if (MBB.succ_empty()) {
366 for (MachineInstr *MaybeDead : MaybeDeadCopies) {
367 assert(!MRI->isReserved(MaybeDead->getOperand(0).getReg()));
368 MaybeDead->eraseFromParent();
374 MaybeDeadCopies.clear();
375 AvailCopyMap.clear();
380 bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) {
381 if (skipFunction(MF.getFunction()))
386 TRI = MF.getSubtarget().getRegisterInfo();
387 TII = MF.getSubtarget().getInstrInfo();
388 MRI = &MF.getRegInfo();
390 for (MachineBasicBlock &MBB : MF)
391 CopyPropagateBlock(MBB);