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/Pass.h"
17 #include "llvm/CodeGen/MachineFunction.h"
18 #include "llvm/CodeGen/MachineFunctionPass.h"
19 #include "llvm/Target/TargetRegisterInfo.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/Support/ErrorHandling.h"
22 #include "llvm/Support/raw_ostream.h"
23 #include "llvm/ADT/BitVector.h"
24 #include "llvm/ADT/DenseMap.h"
25 #include "llvm/ADT/SetVector.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/ADT/Statistic.h"
30 STATISTIC(NumDeletes, "Number of dead copies deleted");
33 class MachineCopyPropagation : public MachineFunctionPass {
34 const TargetRegisterInfo *TRI;
35 BitVector ReservedRegs;
38 static char ID; // Pass identification, replacement for typeid
39 MachineCopyPropagation() : MachineFunctionPass(ID) {
40 initializeMachineCopyPropagationPass(*PassRegistry::getPassRegistry());
43 virtual bool runOnMachineFunction(MachineFunction &MF);
46 void SourceNoLongerAvailable(unsigned Reg,
47 DenseMap<unsigned, unsigned> &SrcMap,
48 DenseMap<unsigned, MachineInstr*> &AvailCopyMap);
49 bool CopyPropagateBlock(MachineBasicBlock &MBB);
52 char MachineCopyPropagation::ID = 0;
53 char &llvm::MachineCopyPropagationID = MachineCopyPropagation::ID;
55 INITIALIZE_PASS(MachineCopyPropagation, "machine-cp",
56 "Machine Copy Propagation Pass", false, false)
59 MachineCopyPropagation::SourceNoLongerAvailable(unsigned Reg,
60 DenseMap<unsigned, unsigned> &SrcMap,
61 DenseMap<unsigned, MachineInstr*> &AvailCopyMap) {
62 DenseMap<unsigned, unsigned>::iterator SI = SrcMap.find(Reg);
63 if (SI != SrcMap.end()) {
64 unsigned MappedDef = SI->second;
65 // Source of copy is no longer available for propagation.
66 if (AvailCopyMap.erase(MappedDef)) {
67 for (const unsigned *SR = TRI->getSubRegisters(MappedDef); *SR; ++SR)
68 AvailCopyMap.erase(*SR);
71 for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
72 SI = SrcMap.find(*AS);
73 if (SI != SrcMap.end()) {
74 unsigned MappedDef = SI->second;
75 if (AvailCopyMap.erase(MappedDef)) {
76 for (const unsigned *SR = TRI->getSubRegisters(MappedDef); *SR; ++SR)
77 AvailCopyMap.erase(*SR);
83 static bool NoInterveningSideEffect(const MachineInstr *CopyMI,
84 const MachineInstr *MI) {
85 const MachineBasicBlock *MBB = CopyMI->getParent();
86 if (MI->getParent() != MBB)
88 MachineBasicBlock::const_iterator I = CopyMI;
89 MachineBasicBlock::const_iterator E = MBB->end();
90 MachineBasicBlock::const_iterator E2 = MI;
93 while (I != E && I != E2) {
94 if (I->hasUnmodeledSideEffects() || I->isCall() ||
102 bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
103 SmallSetVector<MachineInstr*, 8> MaybeDeadCopies; // Candidates for deletion
104 DenseMap<unsigned, MachineInstr*> AvailCopyMap; // Def -> available copies map
105 DenseMap<unsigned, MachineInstr*> CopyMap; // Def -> copies map
106 DenseMap<unsigned, unsigned> SrcMap; // Src -> Def map
108 bool Changed = false;
109 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ) {
110 MachineInstr *MI = &*I;
114 unsigned Def = MI->getOperand(0).getReg();
115 unsigned Src = MI->getOperand(1).getReg();
117 if (TargetRegisterInfo::isVirtualRegister(Def) ||
118 TargetRegisterInfo::isVirtualRegister(Src))
119 report_fatal_error("MachineCopyPropagation should be run after"
120 " register allocation!");
122 DenseMap<unsigned, MachineInstr*>::iterator CI = AvailCopyMap.find(Src);
123 if (CI != AvailCopyMap.end()) {
124 MachineInstr *CopyMI = CI->second;
125 unsigned SrcSrc = CopyMI->getOperand(1).getReg();
126 if (!ReservedRegs.test(Def) &&
127 (!ReservedRegs.test(Src) || NoInterveningSideEffect(CopyMI, MI)) &&
128 (SrcSrc == Def || TRI->isSubRegister(SrcSrc, Def))) {
129 // The two copies cancel out and the source of the first copy
130 // hasn't been overridden, eliminate the second one. e.g.
131 // %ECX<def> = COPY %EAX<kill>
132 // ... nothing clobbered EAX.
133 // %EAX<def> = COPY %ECX
135 // %ECX<def> = COPY %EAX
137 // Also avoid eliminating a copy from reserved registers unless the
138 // definition is proven not clobbered. e.g.
139 // %RSP<def> = COPY %RAX
141 // %RAX<def> = COPY %RSP
143 // Clear any kills of Def between CopyMI and MI. This extends the
145 for (MachineBasicBlock::iterator I = CopyMI, E = MI; I != E; ++I)
146 I->clearRegisterKills(Def, TRI);
148 MI->eraseFromParent();
155 // If Src is defined by a previous copy, it cannot be eliminated.
156 CI = CopyMap.find(Src);
157 if (CI != CopyMap.end())
158 MaybeDeadCopies.remove(CI->second);
159 for (const unsigned *AS = TRI->getAliasSet(Src); *AS; ++AS) {
160 CI = CopyMap.find(*AS);
161 if (CI != CopyMap.end())
162 MaybeDeadCopies.remove(CI->second);
165 // Copy is now a candidate for deletion.
166 MaybeDeadCopies.insert(MI);
168 // If 'Src' is previously source of another copy, then this earlier copy's
169 // source is no longer available. e.g.
170 // %xmm9<def> = copy %xmm2
172 // %xmm2<def> = copy %xmm0
174 // %xmm2<def> = copy %xmm9
175 SourceNoLongerAvailable(Def, SrcMap, AvailCopyMap);
177 // Remember Def is defined by the copy.
179 AvailCopyMap[Def] = MI;
180 for (const unsigned *SR = TRI->getSubRegisters(Def); *SR; ++SR) {
182 AvailCopyMap[*SR] = MI;
185 // Remember source that's copied to Def. Once it's clobbered, then
186 // it's no longer available for copy propagation.
193 SmallVector<unsigned, 2> Defs;
194 int RegMaskOpNum = -1;
195 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
196 MachineOperand &MO = MI->getOperand(i);
201 unsigned Reg = MO.getReg();
205 if (TargetRegisterInfo::isVirtualRegister(Reg))
206 report_fatal_error("MachineCopyPropagation should be run after"
207 " register allocation!");
214 // If 'Reg' is defined by a copy, the copy is no longer a candidate
216 DenseMap<unsigned, MachineInstr*>::iterator CI = CopyMap.find(Reg);
217 if (CI != CopyMap.end())
218 MaybeDeadCopies.remove(CI->second);
219 for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
220 CI = CopyMap.find(*AS);
221 if (CI != CopyMap.end())
222 MaybeDeadCopies.remove(CI->second);
226 // The instruction has a register mask operand which means that it clobbers
227 // a large set of registers. It is possible to use the register mask to
228 // prune the available copies, but treat it like a basic block boundary for
230 if (RegMaskOpNum >= 0) {
231 // Erase any MaybeDeadCopies whose destination register is clobbered.
232 const MachineOperand &MaskMO = MI->getOperand(RegMaskOpNum);
233 for (SmallSetVector<MachineInstr*, 8>::iterator
234 DI = MaybeDeadCopies.begin(), DE = MaybeDeadCopies.end();
236 unsigned Reg = (*DI)->getOperand(0).getReg();
237 if (ReservedRegs.test(Reg) || !MaskMO.clobbersPhysReg(Reg))
239 (*DI)->eraseFromParent();
244 // Clear all data structures as if we were beginning a new basic block.
245 MaybeDeadCopies.clear();
246 AvailCopyMap.clear();
252 for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
253 unsigned Reg = Defs[i];
255 // No longer defined by a copy.
257 AvailCopyMap.erase(Reg);
258 for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
260 AvailCopyMap.erase(*AS);
263 // If 'Reg' is previously source of a copy, it is no longer available for
265 SourceNoLongerAvailable(Reg, SrcMap, AvailCopyMap);
269 // If MBB doesn't have successors, delete the copies whose defs are not used.
270 // If MBB does have successors, then conservative assume the defs are live-out
271 // since we don't want to trust live-in lists.
272 if (MBB.succ_empty()) {
273 for (SmallSetVector<MachineInstr*, 8>::iterator
274 DI = MaybeDeadCopies.begin(), DE = MaybeDeadCopies.end();
276 if (!ReservedRegs.test((*DI)->getOperand(0).getReg())) {
277 (*DI)->eraseFromParent();
287 bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) {
288 bool Changed = false;
290 TRI = MF.getTarget().getRegisterInfo();
291 ReservedRegs = TRI->getReservedRegs(MF);
293 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
294 Changed |= CopyPropagateBlock(*I);