MachineCopyPropagation.cpp [plain text]
#include "llvm/CodeGen/Passes.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;
#define DEBUG_TYPE "codegen-cp"
STATISTIC(NumDeletes, "Number of dead copies deleted");
namespace {
typedef SmallVector<unsigned, 4> RegList;
typedef DenseMap<unsigned, RegList> SourceMap;
typedef DenseMap<unsigned, MachineInstr*> Reg2MIMap;
class MachineCopyPropagation : public MachineFunctionPass {
const TargetRegisterInfo *TRI;
const TargetInstrInfo *TII;
const MachineRegisterInfo *MRI;
public:
static char ID; MachineCopyPropagation() : MachineFunctionPass(ID) {
initializeMachineCopyPropagationPass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &MF) override;
private:
void ClobberRegister(unsigned Reg);
void CopyPropagateBlock(MachineBasicBlock &MBB);
bool eraseIfRedundant(MachineInstr &Copy, unsigned Src, unsigned Def);
SmallSetVector<MachineInstr*, 8> MaybeDeadCopies;
Reg2MIMap AvailCopyMap;
Reg2MIMap CopyMap;
SourceMap SrcMap;
bool Changed;
};
}
char MachineCopyPropagation::ID = 0;
char &llvm::MachineCopyPropagationID = MachineCopyPropagation::ID;
INITIALIZE_PASS(MachineCopyPropagation, "machine-cp",
"Machine Copy Propagation Pass", false, false)
static void removeRegsFromMap(Reg2MIMap &Map, const RegList &Regs,
const TargetRegisterInfo &TRI) {
for (unsigned Reg : Regs) {
for (MCSubRegIterator SR(Reg, &TRI, true); SR.isValid(); ++SR)
Map.erase(*SR);
}
}
static void removeClobberedRegsFromMap(Reg2MIMap &Map,
const MachineOperand &RegMask) {
for (Reg2MIMap::iterator I = Map.begin(), E = Map.end(), Next; I != E;
I = Next) {
Next = std::next(I);
unsigned Reg = I->first;
if (RegMask.clobbersPhysReg(Reg))
Map.erase(I);
}
}
void MachineCopyPropagation::ClobberRegister(unsigned Reg) {
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
CopyMap.erase(*AI);
AvailCopyMap.erase(*AI);
SourceMap::iterator SI = SrcMap.find(*AI);
if (SI != SrcMap.end()) {
removeRegsFromMap(AvailCopyMap, SI->second, *TRI);
SrcMap.erase(SI);
}
}
}
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);
}
bool MachineCopyPropagation::eraseIfRedundant(MachineInstr &Copy, unsigned Src,
unsigned Def) {
if (MRI->isReserved(Src) || MRI->isReserved(Def))
return false;
Reg2MIMap::iterator CI = AvailCopyMap.find(Def);
if (CI == AvailCopyMap.end())
return false;
MachineInstr &PrevCopy = *CI->second;
if (!isNopCopy(PrevCopy, Src, Def, TRI))
return false;
DEBUG(dbgs() << "MCP: copy is a NOP, removing: "; Copy.dump());
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;
}
void MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
DEBUG(dbgs() << "MCP: CopyPropagateBlock " << MBB.getName() << "\n");
for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ) {
MachineInstr *MI = &*I;
++I;
if (MI->isCopy()) {
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!");
if (eraseIfRedundant(*MI, Def, Src) || eraseIfRedundant(*MI, Src, Def))
continue;
for (MCRegAliasIterator AI(Src, TRI, true); AI.isValid(); ++AI) {
Reg2MIMap::iterator CI = CopyMap.find(*AI);
if (CI != CopyMap.end()) {
DEBUG(dbgs() << "MCP: Copy is no longer dead: "; CI->second->dump());
MaybeDeadCopies.remove(CI->second);
}
}
DEBUG(dbgs() << "MCP: Copy is a deletion candidate: "; MI->dump());
if (!MRI->isReserved(Def))
MaybeDeadCopies.insert(MI);
ClobberRegister(Def);
for (MCSubRegIterator SR(Def, TRI, true); SR.isValid();
++SR) {
CopyMap[*SR] = MI;
AvailCopyMap[*SR] = MI;
}
RegList &DestList = SrcMap[Src];
if (std::find(DestList.begin(), DestList.end(), Def) == DestList.end())
DestList.push_back(Def);
continue;
}
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()) {
Defs.push_back(Reg);
continue;
}
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
Reg2MIMap::iterator CI = CopyMap.find(*AI);
if (CI != CopyMap.end()) {
DEBUG(dbgs() << "MCP: Copy is used - not dead: "; CI->second->dump());
MaybeDeadCopies.remove(CI->second);
}
}
if (MO.isUndef())
Defs.push_back(Reg);
}
if (RegMask) {
for (MachineInstr *MaybeDead : MaybeDeadCopies) {
unsigned Reg = MaybeDead->getOperand(0).getReg();
assert(!MRI->isReserved(Reg));
if (!RegMask->clobbersPhysReg(Reg))
continue;
DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
MaybeDead->dump());
MaybeDead->eraseFromParent();
Changed = true;
++NumDeletes;
}
MaybeDeadCopies.clear();
removeClobberedRegsFromMap(AvailCopyMap, *RegMask);
removeClobberedRegsFromMap(CopyMap, *RegMask);
for (SourceMap::iterator I = SrcMap.begin(), E = SrcMap.end(), Next;
I != E; I = Next) {
Next = std::next(I);
if (RegMask->clobbersPhysReg(I->first)) {
removeRegsFromMap(AvailCopyMap, I->second, *TRI);
SrcMap.erase(I);
}
}
}
for (unsigned Reg : Defs)
ClobberRegister(Reg);
}
if (MBB.succ_empty()) {
for (MachineInstr *MaybeDead : MaybeDeadCopies) {
assert(!MRI->isReserved(MaybeDead->getOperand(0).getReg()));
MaybeDead->eraseFromParent();
Changed = true;
++NumDeletes;
}
}
MaybeDeadCopies.clear();
AvailCopyMap.clear();
CopyMap.clear();
SrcMap.clear();
}
bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) {
if (skipOptnoneFunction(*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;
}