MipsDelaySlotFiller.cpp [plain text]
#define DEBUG_TYPE "delay-slot-filler"
#include "Mips.h"
#include "MipsTargetMachine.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(FilledSlots, "Number of delay slots filled");
STATISTIC(UsefulSlots, "Number of delay slots filled with instructions that"
" are not NOP.");
static cl::opt<bool> DisableDelaySlotFiller(
"disable-mips-delay-filler",
cl::init(false),
cl::desc("Disable the delay slot filler, which attempts to fill the Mips"
"delay slots with useful instructions."),
cl::Hidden);
static cl::opt<bool> SkipDelaySlotFiller(
"skip-mips-delay-filler",
cl::init(false),
cl::desc("Skip MIPS' delay slot filling pass."),
cl::Hidden);
namespace {
struct Filler : public MachineFunctionPass {
typedef MachineBasicBlock::instr_iterator InstrIter;
typedef MachineBasicBlock::reverse_instr_iterator ReverseInstrIter;
TargetMachine &TM;
const TargetInstrInfo *TII;
InstrIter LastFiller;
static char ID;
Filler(TargetMachine &tm)
: MachineFunctionPass(ID), TM(tm), TII(tm.getInstrInfo()) { }
virtual const char *getPassName() const {
return "Mips Delay Slot Filler";
}
bool runOnMachineBasicBlock(MachineBasicBlock &MBB);
bool runOnMachineFunction(MachineFunction &F) {
if (SkipDelaySlotFiller)
return false;
bool Changed = false;
for (MachineFunction::iterator FI = F.begin(), FE = F.end();
FI != FE; ++FI)
Changed |= runOnMachineBasicBlock(*FI);
return Changed;
}
bool isDelayFiller(MachineBasicBlock &MBB,
InstrIter candidate);
void insertCallUses(InstrIter MI,
SmallSet<unsigned, 32> &RegDefs,
SmallSet<unsigned, 32> &RegUses);
void insertDefsUses(InstrIter MI,
SmallSet<unsigned, 32> &RegDefs,
SmallSet<unsigned, 32> &RegUses);
bool IsRegInSet(SmallSet<unsigned, 32> &RegSet,
unsigned Reg);
bool delayHasHazard(InstrIter candidate,
bool &sawLoad, bool &sawStore,
SmallSet<unsigned, 32> &RegDefs,
SmallSet<unsigned, 32> &RegUses);
bool
findDelayInstr(MachineBasicBlock &MBB, InstrIter slot,
InstrIter &Filler);
};
char Filler::ID = 0;
}
bool Filler::
runOnMachineBasicBlock(MachineBasicBlock &MBB) {
bool Changed = false;
LastFiller = MBB.instr_end();
for (InstrIter I = MBB.instr_begin(); I != MBB.instr_end(); ++I)
if (I->hasDelaySlot()) {
++FilledSlots;
Changed = true;
InstrIter D;
if (!DisableDelaySlotFiller && (TM.getOptLevel() != CodeGenOpt::None) &&
findDelayInstr(MBB, I, D)) {
MBB.splice(llvm::next(I), &MBB, D);
++UsefulSlots;
} else
BuildMI(MBB, llvm::next(I), I->getDebugLoc(), TII->get(Mips::NOP));
LastFiller = ++I;
LastFiller->setIsInsideBundle();
}
return Changed;
}
FunctionPass *llvm::createMipsDelaySlotFillerPass(MipsTargetMachine &tm) {
return new Filler(tm);
}
bool Filler::findDelayInstr(MachineBasicBlock &MBB,
InstrIter slot,
InstrIter &Filler) {
SmallSet<unsigned, 32> RegDefs;
SmallSet<unsigned, 32> RegUses;
insertDefsUses(slot, RegDefs, RegUses);
bool sawLoad = false;
bool sawStore = false;
for (ReverseInstrIter I(slot); I != MBB.instr_rend(); ++I) {
if (I->isDebugValue())
continue;
InstrIter FI(llvm::next(I).base());
if (I->hasUnmodeledSideEffects()
|| I->isInlineAsm()
|| I->isLabel()
|| FI == LastFiller
|| I->isPseudo()
)
break;
if (delayHasHazard(FI, sawLoad, sawStore, RegDefs, RegUses)) {
insertDefsUses(FI, RegDefs, RegUses);
continue;
}
Filler = FI;
return true;
}
return false;
}
bool Filler::delayHasHazard(InstrIter candidate,
bool &sawLoad, bool &sawStore,
SmallSet<unsigned, 32> &RegDefs,
SmallSet<unsigned, 32> &RegUses) {
if (candidate->isImplicitDef() || candidate->isKill())
return true;
if (candidate->mayLoad()) {
if (sawStore)
return true;
sawLoad = true;
}
if (candidate->mayStore()) {
if (sawStore)
return true;
sawStore = true;
if (sawLoad)
return true;
}
assert((!candidate->isCall() && !candidate->isReturn()) &&
"Cannot put calls or returns in delay slot.");
for (unsigned i = 0, e = candidate->getNumOperands(); i!= e; ++i) {
const MachineOperand &MO = candidate->getOperand(i);
unsigned Reg;
if (!MO.isReg() || !(Reg = MO.getReg()))
continue;
if (MO.isDef()) {
if (IsRegInSet(RegDefs, Reg) || IsRegInSet(RegUses, Reg))
return true;
}
if (MO.isUse()) {
if (IsRegInSet(RegDefs, Reg))
return true;
}
}
return false;
}
void Filler::insertDefsUses(InstrIter MI,
SmallSet<unsigned, 32> &RegDefs,
SmallSet<unsigned, 32> &RegUses) {
MCInstrDesc MCID = MI->getDesc();
unsigned e = MI->isCall() || MI->isReturn() ? MCID.getNumOperands() :
MI->getNumOperands();
if (MI->isCall())
RegDefs.insert(Mips::RA);
for (unsigned i = 0; i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
unsigned Reg;
if (!MO.isReg() || !(Reg = MO.getReg()))
continue;
if (MO.isDef())
RegDefs.insert(Reg);
else if (MO.isUse())
RegUses.insert(Reg);
}
}
bool Filler::IsRegInSet(SmallSet<unsigned, 32> &RegSet, unsigned Reg) {
for (MCRegAliasIterator AI(Reg, TM.getRegisterInfo(), true);
AI.isValid(); ++AI)
if (RegSet.count(*AI))
return true;
return false;
}