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 #define DEBUG_TYPE "codegen-cp"
15 #include "llvm/CodeGen/Passes.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/SetVector.h"
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/ADT/Statistic.h"
20 #include "llvm/CodeGen/MachineFunction.h"
21 #include "llvm/CodeGen/MachineFunctionPass.h"
22 #include "llvm/CodeGen/MachineRegisterInfo.h"
23 #include "llvm/Pass.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Support/ErrorHandling.h"
26 #include "llvm/Support/raw_ostream.h"
27 #include "llvm/Target/TargetInstrInfo.h"
28 #include "llvm/Target/TargetRegisterInfo.h"
31 STATISTIC(NumDeletes, "Number of dead copies deleted");
34 class MachineCopyPropagation : public MachineFunctionPass {
35 const TargetRegisterInfo *TRI;
36 const TargetInstrInfo *TII;
37 MachineRegisterInfo *MRI;
40 static char ID; // Pass identification, replacement for typeid
41 MachineCopyPropagation() : MachineFunctionPass(ID) {
42 initializeMachineCopyPropagationPass(*PassRegistry::getPassRegistry());
45 bool runOnMachineFunction(MachineFunction &MF) override;
48 typedef SmallVector<unsigned, 4> DestList;
49 typedef DenseMap<unsigned, DestList> SourceMap;
51 void SourceNoLongerAvailable(unsigned Reg,
53 DenseMap<unsigned, MachineInstr*> &AvailCopyMap);
54 bool CopyPropagateBlock(MachineBasicBlock &MBB);
55 void removeCopy(MachineInstr *MI);
58 char MachineCopyPropagation::ID = 0;
59 char &llvm::MachineCopyPropagationID = MachineCopyPropagation::ID;
61 INITIALIZE_PASS(MachineCopyPropagation, "machine-cp",
62 "Machine Copy Propagation Pass", false, false)
65 MachineCopyPropagation::SourceNoLongerAvailable(unsigned Reg,
67 DenseMap<unsigned, MachineInstr*> &AvailCopyMap) {
68 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
69 SourceMap::iterator SI = SrcMap.find(*AI);
70 if (SI != SrcMap.end()) {
71 const DestList& Defs = SI->second;
72 for (DestList::const_iterator I = Defs.begin(), E = Defs.end();
74 unsigned MappedDef = *I;
75 // Source of copy is no longer available for propagation.
76 if (AvailCopyMap.erase(MappedDef)) {
77 for (MCSubRegIterator SR(MappedDef, TRI); SR.isValid(); ++SR)
78 AvailCopyMap.erase(*SR);
85 static bool NoInterveningSideEffect(const MachineInstr *CopyMI,
86 const MachineInstr *MI) {
87 const MachineBasicBlock *MBB = CopyMI->getParent();
88 if (MI->getParent() != MBB)
90 MachineBasicBlock::const_iterator I = CopyMI;
91 MachineBasicBlock::const_iterator E = MBB->end();
92 MachineBasicBlock::const_iterator E2 = MI;
95 while (I != E && I != E2) {
96 if (I->hasUnmodeledSideEffects() || I->isCall() ||
104 /// isNopCopy - Return true if the specified copy is really a nop. That is
105 /// if the source of the copy is the same of the definition of the copy that
106 /// supplied the source. If the source of the copy is a sub-register than it
107 /// must check the sub-indices match. e.g.
113 static bool isNopCopy(MachineInstr *CopyMI, unsigned Def, unsigned Src,
114 const TargetRegisterInfo *TRI) {
115 unsigned SrcSrc = CopyMI->getOperand(1).getReg();
118 if (TRI->isSubRegister(SrcSrc, Def)) {
119 unsigned SrcDef = CopyMI->getOperand(0).getReg();
120 unsigned SubIdx = TRI->getSubRegIndex(SrcSrc, Def);
123 return SubIdx == TRI->getSubRegIndex(SrcDef, Src);
129 // Remove MI from the function because it has been determined it is dead.
130 // Turn it into a noop KILL instruction as opposed to removing it to
131 // maintain imp-use/imp-def chains.
132 void MachineCopyPropagation::removeCopy(MachineInstr *MI) {
133 MI->setDesc(TII->get(TargetOpcode::KILL));
136 bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
137 SmallSetVector<MachineInstr*, 8> MaybeDeadCopies; // Candidates for deletion
138 DenseMap<unsigned, MachineInstr*> AvailCopyMap; // Def -> available copies map
139 DenseMap<unsigned, MachineInstr*> CopyMap; // Def -> copies map
140 SourceMap SrcMap; // Src -> Def map
142 DEBUG(dbgs() << "MCP: CopyPropagateBlock " << MBB.getName() << "\n");
144 bool Changed = false;
145 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ) {
146 MachineInstr *MI = &*I;
150 unsigned Def = MI->getOperand(0).getReg();
151 unsigned Src = MI->getOperand(1).getReg();
153 if (TargetRegisterInfo::isVirtualRegister(Def) ||
154 TargetRegisterInfo::isVirtualRegister(Src))
155 report_fatal_error("MachineCopyPropagation should be run after"
156 " register allocation!");
158 DenseMap<unsigned, MachineInstr*>::iterator CI = AvailCopyMap.find(Src);
159 if (CI != AvailCopyMap.end()) {
160 MachineInstr *CopyMI = CI->second;
161 if (!MRI->isReserved(Def) &&
162 (!MRI->isReserved(Src) || NoInterveningSideEffect(CopyMI, MI)) &&
163 isNopCopy(CopyMI, Def, Src, TRI)) {
164 // The two copies cancel out and the source of the first copy
165 // hasn't been overridden, eliminate the second one. e.g.
166 // %ECX<def> = COPY %EAX<kill>
167 // ... nothing clobbered EAX.
168 // %EAX<def> = COPY %ECX
170 // %ECX<def> = COPY %EAX
172 // Also avoid eliminating a copy from reserved registers unless the
173 // definition is proven not clobbered. e.g.
174 // %RSP<def> = COPY %RAX
176 // %RAX<def> = COPY %RSP
178 DEBUG(dbgs() << "MCP: copy is a NOP, removing: "; MI->dump());
180 // Clear any kills of Def between CopyMI and MI. This extends the
182 for (MachineBasicBlock::iterator I = CopyMI, E = MI; I != E; ++I)
183 I->clearRegisterKills(Def, TRI);
192 // If Src is defined by a previous copy, it cannot be eliminated.
193 for (MCRegAliasIterator AI(Src, TRI, true); AI.isValid(); ++AI) {
194 CI = CopyMap.find(*AI);
195 if (CI != CopyMap.end()) {
196 DEBUG(dbgs() << "MCP: Copy is no longer dead: "; CI->second->dump());
197 MaybeDeadCopies.remove(CI->second);
201 DEBUG(dbgs() << "MCP: Copy is a deletion candidate: "; MI->dump());
203 // Copy is now a candidate for deletion.
204 MaybeDeadCopies.insert(MI);
206 // If 'Src' is previously source of another copy, then this earlier copy's
207 // source is no longer available. e.g.
208 // %xmm9<def> = copy %xmm2
210 // %xmm2<def> = copy %xmm0
212 // %xmm2<def> = copy %xmm9
213 SourceNoLongerAvailable(Def, SrcMap, AvailCopyMap);
215 // Remember Def is defined by the copy.
216 // ... Make sure to clear the def maps of aliases first.
217 for (MCRegAliasIterator AI(Def, TRI, false); AI.isValid(); ++AI) {
219 AvailCopyMap.erase(*AI);
221 for (MCSubRegIterator SR(Def, TRI, /*IncludeSelf=*/true); SR.isValid();
224 AvailCopyMap[*SR] = MI;
227 // Remember source that's copied to Def. Once it's clobbered, then
228 // it's no longer available for copy propagation.
229 if (std::find(SrcMap[Src].begin(), SrcMap[Src].end(), Def) ==
231 SrcMap[Src].push_back(Def);
238 SmallVector<unsigned, 2> Defs;
239 int RegMaskOpNum = -1;
240 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
241 MachineOperand &MO = MI->getOperand(i);
246 unsigned Reg = MO.getReg();
250 if (TargetRegisterInfo::isVirtualRegister(Reg))
251 report_fatal_error("MachineCopyPropagation should be run after"
252 " register allocation!");
259 // If 'Reg' is defined by a copy, the copy is no longer a candidate
261 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
262 DenseMap<unsigned, MachineInstr*>::iterator CI = CopyMap.find(*AI);
263 if (CI != CopyMap.end()) {
264 DEBUG(dbgs() << "MCP: Copy is used - not dead: "; CI->second->dump());
265 MaybeDeadCopies.remove(CI->second);
270 // The instruction has a register mask operand which means that it clobbers
271 // a large set of registers. It is possible to use the register mask to
272 // prune the available copies, but treat it like a basic block boundary for
274 if (RegMaskOpNum >= 0) {
275 // Erase any MaybeDeadCopies whose destination register is clobbered.
276 const MachineOperand &MaskMO = MI->getOperand(RegMaskOpNum);
277 for (SmallSetVector<MachineInstr*, 8>::iterator
278 DI = MaybeDeadCopies.begin(), DE = MaybeDeadCopies.end();
280 unsigned Reg = (*DI)->getOperand(0).getReg();
281 if (MRI->isReserved(Reg) || !MaskMO.clobbersPhysReg(Reg))
283 DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
290 // Clear all data structures as if we were beginning a new basic block.
291 MaybeDeadCopies.clear();
292 AvailCopyMap.clear();
298 for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
299 unsigned Reg = Defs[i];
301 // No longer defined by a copy.
302 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
304 AvailCopyMap.erase(*AI);
307 // If 'Reg' is previously source of a copy, it is no longer available for
309 SourceNoLongerAvailable(Reg, SrcMap, AvailCopyMap);
313 // If MBB doesn't have successors, delete the copies whose defs are not used.
314 // If MBB does have successors, then conservative assume the defs are live-out
315 // since we don't want to trust live-in lists.
316 if (MBB.succ_empty()) {
317 for (SmallSetVector<MachineInstr*, 8>::iterator
318 DI = MaybeDeadCopies.begin(), DE = MaybeDeadCopies.end();
320 if (!MRI->isReserved((*DI)->getOperand(0).getReg())) {
331 bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) {
332 bool Changed = false;
334 TRI = MF.getTarget().getRegisterInfo();
335 TII = MF.getTarget().getInstrInfo();
336 MRI = &MF.getRegInfo();
338 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
339 Changed |= CopyPropagateBlock(*I);