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//===-- DelaySlotFiller.cpp - MBlaze delay slot filler --------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// A pass that attempts to fill instructions with delay slots. If no
// instructions can be moved into the delay slot then a NOP is placed there.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "delay-slot-filler"
#include "MBlaze.h"
#include "MBlazeTargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
using namespace llvm;
STATISTIC(FilledSlots, "Number of delay slots filled");
static cl::opt<bool> MBDisableDelaySlotFiller(
"disable-mblaze-delay-filler",
cl::init(false),
cl::desc("Disable the MBlaze delay slot filter."),
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 "MBlaze 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;
}
};
char Filler::ID = 0;
} // end of anonymous namespace
static bool hasImmInstruction(MachineBasicBlock::iterator &candidate) {
// Any instruction with an immediate mode operand greater than
// 16-bits requires an implicit IMM instruction.
unsigned numOper = candidate->getNumOperands();
for (unsigned op = 0; op < numOper; ++op) {
MachineOperand &mop = candidate->getOperand(op);
// The operand requires more than 16-bits to represent.
if (mop.isImm() && (mop.getImm() < -0x8000 || mop.getImm() > 0x7fff))
return true;
// We must assume that unknown immediate values require more than
// 16-bits to represent.
if (mop.isGlobal() || mop.isSymbol() || mop.isJTI() || mop.isCPI())
return true;
// FIXME: we could probably check to see if the FP value happens
// to not need an IMM instruction. For now we just always
// assume that FP values do.
if (mop.isFPImm())
return true;
}
return false;
}
static unsigned getLastRealOperand(MachineBasicBlock::iterator &instr) {
switch (instr->getOpcode()) {
default: return instr->getNumOperands();
// These instructions have a variable number of operands but the first two
// are the "real" operands that we care about during hazard detection.
case MBlaze::BRLID:
case MBlaze::BRALID:
case MBlaze::BRLD:
case MBlaze::BRALD:
return 2;
}
}
static bool delayHasHazard(MachineBasicBlock::iterator &candidate,
MachineBasicBlock::iterator &slot) {
// Hazard check
MachineBasicBlock::iterator a = candidate;
MachineBasicBlock::iterator b = slot;
// MBB layout:-
// candidate := a0 = operation(a1, a2)
// ...middle bit...
// slot := b0 = operation(b1, b2)
// Possible hazards:-/
// 1. a1 or a2 was written during the middle bit
// 2. a0 was read or written during the middle bit
// 3. a0 is one or more of {b0, b1, b2}
// 4. b0 is one or more of {a1, a2}
// 5. a accesses memory, and the middle bit
// contains a store operation.
bool a_is_memory = candidate->mayLoad() || candidate->mayStore();
// Determine the number of operands in the slot instruction and in the
// candidate instruction.
const unsigned aend = getLastRealOperand(a);
const unsigned bend = getLastRealOperand(b);
// Check hazards type 1, 2 and 5 by scanning the middle bit
MachineBasicBlock::iterator m = a;
for (++m; m != b; ++m) {
for (unsigned aop = 0; aop<aend; ++aop) {
bool aop_is_reg = a->getOperand(aop).isReg();
if (!aop_is_reg) continue;
bool aop_is_def = a->getOperand(aop).isDef();
unsigned aop_reg = a->getOperand(aop).getReg();
const unsigned mend = getLastRealOperand(m);
for (unsigned mop = 0; mop<mend; ++mop) {
bool mop_is_reg = m->getOperand(mop).isReg();
if (!mop_is_reg) continue;
bool mop_is_def = m->getOperand(mop).isDef();
unsigned mop_reg = m->getOperand(mop).getReg();
if (aop_is_def && (mop_reg == aop_reg))
return true; // Hazard type 2, because aop = a0
else if (mop_is_def && (mop_reg == aop_reg))
return true; // Hazard type 1, because aop in {a1, a2}
}
}
// Check hazard type 5
if (a_is_memory && m->mayStore())
return true;
}
// Check hazard type 3 & 4
for (unsigned aop = 0; aop<aend; ++aop) {
if (a->getOperand(aop).isReg()) {
unsigned aop_reg = a->getOperand(aop).getReg();
for (unsigned bop = 0; bop<bend; ++bop) {
if (b->getOperand(bop).isReg() && !b->getOperand(bop).isImplicit()) {
unsigned bop_reg = b->getOperand(bop).getReg();
if (aop_reg == bop_reg)
return true;
}
}
}
}
return false;
}
static bool isDelayFiller(MachineBasicBlock &MBB,
MachineBasicBlock::iterator candidate) {
if (candidate == MBB.begin())
return false;
--candidate;
return (candidate->hasDelaySlot());
}
static bool hasUnknownSideEffects(MachineBasicBlock::iterator &I) {
if (!I->hasUnmodeledSideEffects())
return false;
unsigned op = I->getOpcode();
if (op == MBlaze::ADDK || op == MBlaze::ADDIK ||
op == MBlaze::ADDC || op == MBlaze::ADDIC ||
op == MBlaze::ADDKC || op == MBlaze::ADDIKC ||
op == MBlaze::RSUBK || op == MBlaze::RSUBIK ||
op == MBlaze::RSUBC || op == MBlaze::RSUBIC ||
op == MBlaze::RSUBKC || op == MBlaze::RSUBIKC)
return false;
return true;
}
static MachineBasicBlock::iterator
findDelayInstr(MachineBasicBlock &MBB,MachineBasicBlock::iterator slot) {
MachineBasicBlock::iterator I = slot;
while (true) {
if (I == MBB.begin())
break;
--I;
if (I->hasDelaySlot() || I->isBranch() || isDelayFiller(MBB,I) ||
I->isCall() || I->isReturn() || I->isBarrier() ||
hasUnknownSideEffects(I))
break;
if (hasImmInstruction(I) || delayHasHazard(I,slot))
continue;
return I;
}
return MBB.end();
}
/// runOnMachineBasicBlock - Fill in delay slots for the given basic block.
/// Currently, we fill delay slots with NOPs. 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->hasDelaySlot()) {
MachineBasicBlock::iterator D = MBB.end();
MachineBasicBlock::iterator J = I;
if (!MBDisableDelaySlotFiller)
D = findDelayInstr(MBB,I);
++FilledSlots;
Changed = true;
if (D == MBB.end())
BuildMI(MBB, ++J, I->getDebugLoc(), TII->get(MBlaze::NOP));
else
MBB.splice(++J, &MBB, D);
}
return Changed;
}
/// createMBlazeDelaySlotFillerPass - Returns a pass that fills in delay
/// slots in MBlaze MachineFunctions
FunctionPass *llvm::createMBlazeDelaySlotFillerPass(MBlazeTargetMachine &tm) {
return new Filler(tm);
}