llvm-project/llvm/lib/Target/Mips/MipsDelaySlotFiller.cpp

270 lines
7.6 KiB
C++

//===-- DelaySlotFiller.cpp - Mips delay slot filler ---------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Simple pass to fills delay slots with useful instructions.
//
//===----------------------------------------------------------------------===//
#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");
static cl::opt<bool> EnableDelaySlotFiller(
"enable-mips-delay-filler",
cl::init(false),
cl::desc("Fill the Mips delay slots with noop."),
cl::Hidden);
namespace {
struct Filler : public MachineFunctionPass {
TargetMachine &TM;
const TargetInstrInfo *TII;
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) {
bool Changed = false;
for (MachineFunction::iterator FI = F.begin(), FE = F.end();
FI != FE; ++FI)
Changed |= runOnMachineBasicBlock(*FI);
return Changed;
}
bool isDelayFiller(MachineBasicBlock &MBB,
MachineBasicBlock::iterator candidate);
void insertCallUses(MachineBasicBlock::iterator MI,
SmallSet<unsigned, 32>& RegDefs,
SmallSet<unsigned, 32>& RegUses);
void insertDefsUses(MachineBasicBlock::iterator MI,
SmallSet<unsigned, 32>& RegDefs,
SmallSet<unsigned, 32>& RegUses);
bool IsRegInSet(SmallSet<unsigned, 32>& RegSet,
unsigned Reg);
bool delayHasHazard(MachineBasicBlock::iterator candidate,
bool &sawLoad, bool &sawStore,
SmallSet<unsigned, 32> &RegDefs,
SmallSet<unsigned, 32> &RegUses);
MachineBasicBlock::iterator
findDelayInstr(MachineBasicBlock &MBB, MachineBasicBlock::iterator slot);
};
char Filler::ID = 0;
} // end of anonymous namespace
/// runOnMachineBasicBlock - Fill in delay slots for the given basic block.
/// We assume there is only one delay slot per delayed instruction.
bool Filler::
runOnMachineBasicBlock(MachineBasicBlock &MBB) {
bool Changed = false;
for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end(); ++I)
if (I->getDesc().hasDelaySlot()) {
MachineBasicBlock::iterator D = MBB.end();
MachineBasicBlock::iterator J = I;
if (EnableDelaySlotFiller)
D = findDelayInstr(MBB, I);
++FilledSlots;
Changed = true;
if (D == MBB.end())
BuildMI(MBB, ++J, I->getDebugLoc(), TII->get(Mips::NOP));
else
MBB.splice(++J, &MBB, D);
}
return Changed;
}
/// createMipsDelaySlotFillerPass - Returns a pass that fills in delay
/// slots in Mips MachineFunctions
FunctionPass *llvm::createMipsDelaySlotFillerPass(MipsTargetMachine &tm) {
return new Filler(tm);
}
MachineBasicBlock::iterator
Filler::findDelayInstr(MachineBasicBlock &MBB,
MachineBasicBlock::iterator slot) {
SmallSet<unsigned, 32> RegDefs;
SmallSet<unsigned, 32> RegUses;
bool sawLoad = false;
bool sawStore = false;
MachineBasicBlock::iterator I = slot;
// Call's delay filler can def some of call's uses.
if (slot->getDesc().isCall())
insertCallUses(slot, RegDefs, RegUses);
else
insertDefsUses(slot, RegDefs, RegUses);
bool done = false;
while (!done) {
done = (I == MBB.begin());
if (!done)
--I;
// skip debug value
if (I->isDebugValue())
continue;
if (I->hasUnmodeledSideEffects()
|| I->isInlineAsm()
|| I->isLabel()
|| I->getDesc().hasDelaySlot()
|| isDelayFiller(MBB, I)
|| I->getDesc().isPseudo()
//
// Should not allow:
// ERET, DERET or WAIT, PAUSE. Need to add these to instruction
// list. TBD.
)
break;
if (delayHasHazard(I, sawLoad, sawStore, RegDefs, RegUses)) {
insertDefsUses(I, RegDefs, RegUses);
continue;
}
return I;
}
return MBB.end();
}
bool Filler::delayHasHazard(MachineBasicBlock::iterator candidate,
bool &sawLoad,
bool &sawStore,
SmallSet<unsigned, 32> &RegDefs,
SmallSet<unsigned, 32> &RegUses) {
if (candidate->isImplicitDef() || candidate->isKill())
return true;
if (candidate->getDesc().mayLoad()) {
sawLoad = true;
if (sawStore)
return true;
}
if (candidate->getDesc().mayStore()) {
if (sawStore)
return true;
sawStore = true;
if (sawLoad)
return true;
}
for (unsigned i = 0, e = candidate->getNumOperands(); i!= e; ++i) {
const MachineOperand &MO = candidate->getOperand(i);
if (!MO.isReg())
continue; // skip
unsigned Reg = MO.getReg();
if (MO.isDef()) {
// check whether Reg is defined or used before delay slot.
if (IsRegInSet(RegDefs, Reg) || IsRegInSet(RegUses, Reg))
return true;
}
if (MO.isUse()) {
// check whether Reg is defined before delay slot.
if (IsRegInSet(RegDefs, Reg))
return true;
}
}
return false;
}
void Filler::insertCallUses(MachineBasicBlock::iterator MI,
SmallSet<unsigned, 32>& RegDefs,
SmallSet<unsigned, 32>& RegUses) {
switch(MI->getOpcode()) {
default: llvm_unreachable("Unknown opcode.");
case Mips::JAL:
RegDefs.insert(31);
break;
case Mips::JALR:
assert(MI->getNumOperands() >= 1);
const MachineOperand &Reg = MI->getOperand(0);
assert(Reg.isReg() && "JALR first operand is not a register.");
RegUses.insert(Reg.getReg());
RegDefs.insert(31);
break;
}
}
// Insert Defs and Uses of MI into the sets RegDefs and RegUses.
void Filler::insertDefsUses(MachineBasicBlock::iterator MI,
SmallSet<unsigned, 32>& RegDefs,
SmallSet<unsigned, 32>& RegUses) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (Reg == 0)
continue;
if (MO.isDef())
RegDefs.insert(Reg);
if (MO.isUse())
RegUses.insert(Reg);
}
}
//returns true if the Reg or its alias is in the RegSet.
bool Filler::IsRegInSet(SmallSet<unsigned, 32>& RegSet, unsigned Reg) {
if (RegSet.count(Reg))
return true;
// check Aliased Registers
for (const unsigned *Alias = TM.getRegisterInfo()->getAliasSet(Reg);
*Alias; ++Alias)
if (RegSet.count(*Alias))
return true;
return false;
}
// return true if the candidate is a delay filler.
bool Filler::isDelayFiller(MachineBasicBlock &MBB,
MachineBasicBlock::iterator candidate) {
if (candidate == MBB.begin())
return false;
const MCInstrDesc &prevdesc = (--candidate)->getDesc();
return prevdesc.hasDelaySlot();
}