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 uint16_t *SR = TRI->getSubRegisters(MappedDef); *SR; ++SR)
68 AvailCopyMap.erase(*SR);
71 for (const uint16_t *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 uint16_t *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 /// isNopCopy - Return true if the specified copy is really a nop. That is
103 /// if the source of the copy is the same of the definition of the copy that
104 /// supplied the source. If the source of the copy is a sub-register than it
105 /// must check the sub-indices match. e.g.
111 static bool isNopCopy(MachineInstr *CopyMI, unsigned Def, unsigned Src,
112 const TargetRegisterInfo *TRI) {
113 unsigned SrcSrc = CopyMI->getOperand(1).getReg();
116 if (TRI->isSubRegister(SrcSrc, Def)) {
117 unsigned SrcDef = CopyMI->getOperand(0).getReg();
118 unsigned SubIdx = TRI->getSubRegIndex(SrcSrc, Def);
121 return SubIdx == TRI->getSubRegIndex(SrcDef, Src);
127 bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
128 SmallSetVector<MachineInstr*, 8> MaybeDeadCopies; // Candidates for deletion
129 DenseMap<unsigned, MachineInstr*> AvailCopyMap; // Def -> available copies map
130 DenseMap<unsigned, MachineInstr*> CopyMap; // Def -> copies map
131 DenseMap<unsigned, unsigned> SrcMap; // Src -> Def map
133 bool Changed = false;
134 for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ) {
135 MachineInstr *MI = &*I;
139 unsigned Def = MI->getOperand(0).getReg();
140 unsigned Src = MI->getOperand(1).getReg();
142 if (TargetRegisterInfo::isVirtualRegister(Def) ||
143 TargetRegisterInfo::isVirtualRegister(Src))
144 report_fatal_error("MachineCopyPropagation should be run after"
145 " register allocation!");
147 DenseMap<unsigned, MachineInstr*>::iterator CI = AvailCopyMap.find(Src);
148 if (CI != AvailCopyMap.end()) {
149 MachineInstr *CopyMI = CI->second;
150 if (!ReservedRegs.test(Def) &&
151 (!ReservedRegs.test(Src) || NoInterveningSideEffect(CopyMI, MI)) &&
152 isNopCopy(CopyMI, Def, Src, TRI)) {
153 // The two copies cancel out and the source of the first copy
154 // hasn't been overridden, eliminate the second one. e.g.
155 // %ECX<def> = COPY %EAX<kill>
156 // ... nothing clobbered EAX.
157 // %EAX<def> = COPY %ECX
159 // %ECX<def> = COPY %EAX
161 // Also avoid eliminating a copy from reserved registers unless the
162 // definition is proven not clobbered. e.g.
163 // %RSP<def> = COPY %RAX
165 // %RAX<def> = COPY %RSP
167 // Clear any kills of Def between CopyMI and MI. This extends the
169 for (MachineBasicBlock::iterator I = CopyMI, E = MI; I != E; ++I)
170 I->clearRegisterKills(Def, TRI);
172 MI->eraseFromParent();
179 // If Src is defined by a previous copy, it cannot be eliminated.
180 CI = CopyMap.find(Src);
181 if (CI != CopyMap.end())
182 MaybeDeadCopies.remove(CI->second);
183 for (const uint16_t *AS = TRI->getAliasSet(Src); *AS; ++AS) {
184 CI = CopyMap.find(*AS);
185 if (CI != CopyMap.end())
186 MaybeDeadCopies.remove(CI->second);
189 // Copy is now a candidate for deletion.
190 MaybeDeadCopies.insert(MI);
192 // If 'Src' is previously source of another copy, then this earlier copy's
193 // source is no longer available. e.g.
194 // %xmm9<def> = copy %xmm2
196 // %xmm2<def> = copy %xmm0
198 // %xmm2<def> = copy %xmm9
199 SourceNoLongerAvailable(Def, SrcMap, AvailCopyMap);
201 // Remember Def is defined by the copy.
202 // ... Make sure to clear the def maps of aliases first.
203 for (const uint16_t *AS = TRI->getAliasSet(Def); *AS; ++AS) {
205 AvailCopyMap.erase(*AS);
208 AvailCopyMap[Def] = MI;
209 for (const uint16_t *SR = TRI->getSubRegisters(Def); *SR; ++SR) {
211 AvailCopyMap[*SR] = MI;
214 // Remember source that's copied to Def. Once it's clobbered, then
215 // it's no longer available for copy propagation.
222 SmallVector<unsigned, 2> Defs;
223 int RegMaskOpNum = -1;
224 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
225 MachineOperand &MO = MI->getOperand(i);
230 unsigned Reg = MO.getReg();
234 if (TargetRegisterInfo::isVirtualRegister(Reg))
235 report_fatal_error("MachineCopyPropagation should be run after"
236 " register allocation!");
243 // If 'Reg' is defined by a copy, the copy is no longer a candidate
245 DenseMap<unsigned, MachineInstr*>::iterator CI = CopyMap.find(Reg);
246 if (CI != CopyMap.end())
247 MaybeDeadCopies.remove(CI->second);
248 for (const uint16_t *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
249 CI = CopyMap.find(*AS);
250 if (CI != CopyMap.end())
251 MaybeDeadCopies.remove(CI->second);
255 // The instruction has a register mask operand which means that it clobbers
256 // a large set of registers. It is possible to use the register mask to
257 // prune the available copies, but treat it like a basic block boundary for
259 if (RegMaskOpNum >= 0) {
260 // Erase any MaybeDeadCopies whose destination register is clobbered.
261 const MachineOperand &MaskMO = MI->getOperand(RegMaskOpNum);
262 for (SmallSetVector<MachineInstr*, 8>::iterator
263 DI = MaybeDeadCopies.begin(), DE = MaybeDeadCopies.end();
265 unsigned Reg = (*DI)->getOperand(0).getReg();
266 if (ReservedRegs.test(Reg) || !MaskMO.clobbersPhysReg(Reg))
268 (*DI)->eraseFromParent();
273 // Clear all data structures as if we were beginning a new basic block.
274 MaybeDeadCopies.clear();
275 AvailCopyMap.clear();
281 for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
282 unsigned Reg = Defs[i];
284 // No longer defined by a copy.
286 AvailCopyMap.erase(Reg);
287 for (const uint16_t *AS = TRI->getAliasSet(Reg); *AS; ++AS) {
289 AvailCopyMap.erase(*AS);
292 // If 'Reg' is previously source of a copy, it is no longer available for
294 SourceNoLongerAvailable(Reg, SrcMap, AvailCopyMap);
298 // If MBB doesn't have successors, delete the copies whose defs are not used.
299 // If MBB does have successors, then conservative assume the defs are live-out
300 // since we don't want to trust live-in lists.
301 if (MBB.succ_empty()) {
302 for (SmallSetVector<MachineInstr*, 8>::iterator
303 DI = MaybeDeadCopies.begin(), DE = MaybeDeadCopies.end();
305 if (!ReservedRegs.test((*DI)->getOperand(0).getReg())) {
306 (*DI)->eraseFromParent();
316 bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) {
317 bool Changed = false;
319 TRI = MF.getTarget().getRegisterInfo();
320 ReservedRegs = TRI->getReservedRegs(MF);
322 for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
323 Changed |= CopyPropagateBlock(*I);