llvm-6502/lib/CodeGen/LiveRangeEdit.cpp
Matthias Braun 7d3ec5af28 LiveIntervalAnalysis: Factor out code to update liveness on vreg def removal
This cleans up code and is more in line with the general philosophy of
modifying LiveIntervals through LiveIntervalAnalysis instead of changing
them directly.

This also fixes a case where SplitEditor::removeBackCopies() would miss
the subregister ranges.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226690 91177308-0d34-0410-b5e6-96231b3b80d8
2015-01-21 19:02:30 +00:00

411 lines
14 KiB
C++

//===-- LiveRangeEdit.cpp - Basic tools for editing a register live range -===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// The LiveRangeEdit class represents changes done to a virtual register when it
// is spilled or split.
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/LiveRangeEdit.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
using namespace llvm;
#define DEBUG_TYPE "regalloc"
STATISTIC(NumDCEDeleted, "Number of instructions deleted by DCE");
STATISTIC(NumDCEFoldedLoads, "Number of single use loads folded after DCE");
STATISTIC(NumFracRanges, "Number of live ranges fractured by DCE");
void LiveRangeEdit::Delegate::anchor() { }
LiveInterval &LiveRangeEdit::createEmptyIntervalFrom(unsigned OldReg) {
unsigned VReg = MRI.createVirtualRegister(MRI.getRegClass(OldReg));
if (VRM) {
VRM->setIsSplitFromReg(VReg, VRM->getOriginal(OldReg));
}
LiveInterval &LI = LIS.createEmptyInterval(VReg);
return LI;
}
unsigned LiveRangeEdit::createFrom(unsigned OldReg) {
unsigned VReg = MRI.createVirtualRegister(MRI.getRegClass(OldReg));
if (VRM) {
VRM->setIsSplitFromReg(VReg, VRM->getOriginal(OldReg));
}
return VReg;
}
bool LiveRangeEdit::checkRematerializable(VNInfo *VNI,
const MachineInstr *DefMI,
AliasAnalysis *aa) {
assert(DefMI && "Missing instruction");
ScannedRemattable = true;
if (!TII.isTriviallyReMaterializable(DefMI, aa))
return false;
Remattable.insert(VNI);
return true;
}
void LiveRangeEdit::scanRemattable(AliasAnalysis *aa) {
for (VNInfo *VNI : getParent().valnos) {
if (VNI->isUnused())
continue;
MachineInstr *DefMI = LIS.getInstructionFromIndex(VNI->def);
if (!DefMI)
continue;
checkRematerializable(VNI, DefMI, aa);
}
ScannedRemattable = true;
}
bool LiveRangeEdit::anyRematerializable(AliasAnalysis *aa) {
if (!ScannedRemattable)
scanRemattable(aa);
return !Remattable.empty();
}
/// allUsesAvailableAt - Return true if all registers used by OrigMI at
/// OrigIdx are also available with the same value at UseIdx.
bool LiveRangeEdit::allUsesAvailableAt(const MachineInstr *OrigMI,
SlotIndex OrigIdx,
SlotIndex UseIdx) const {
OrigIdx = OrigIdx.getRegSlot(true);
UseIdx = UseIdx.getRegSlot(true);
for (unsigned i = 0, e = OrigMI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = OrigMI->getOperand(i);
if (!MO.isReg() || !MO.getReg() || !MO.readsReg())
continue;
// We can't remat physreg uses, unless it is a constant.
if (TargetRegisterInfo::isPhysicalRegister(MO.getReg())) {
if (MRI.isConstantPhysReg(MO.getReg(), *OrigMI->getParent()->getParent()))
continue;
return false;
}
LiveInterval &li = LIS.getInterval(MO.getReg());
const VNInfo *OVNI = li.getVNInfoAt(OrigIdx);
if (!OVNI)
continue;
// Don't allow rematerialization immediately after the original def.
// It would be incorrect if OrigMI redefines the register.
// See PR14098.
if (SlotIndex::isSameInstr(OrigIdx, UseIdx))
return false;
if (OVNI != li.getVNInfoAt(UseIdx))
return false;
}
return true;
}
bool LiveRangeEdit::canRematerializeAt(Remat &RM,
SlotIndex UseIdx,
bool cheapAsAMove) {
assert(ScannedRemattable && "Call anyRematerializable first");
// Use scanRemattable info.
if (!Remattable.count(RM.ParentVNI))
return false;
// No defining instruction provided.
SlotIndex DefIdx;
if (RM.OrigMI)
DefIdx = LIS.getInstructionIndex(RM.OrigMI);
else {
DefIdx = RM.ParentVNI->def;
RM.OrigMI = LIS.getInstructionFromIndex(DefIdx);
assert(RM.OrigMI && "No defining instruction for remattable value");
}
// If only cheap remats were requested, bail out early.
if (cheapAsAMove && !TII.isAsCheapAsAMove(RM.OrigMI))
return false;
// Verify that all used registers are available with the same values.
if (!allUsesAvailableAt(RM.OrigMI, DefIdx, UseIdx))
return false;
return true;
}
SlotIndex LiveRangeEdit::rematerializeAt(MachineBasicBlock &MBB,
MachineBasicBlock::iterator MI,
unsigned DestReg,
const Remat &RM,
const TargetRegisterInfo &tri,
bool Late) {
assert(RM.OrigMI && "Invalid remat");
TII.reMaterialize(MBB, MI, DestReg, 0, RM.OrigMI, tri);
Rematted.insert(RM.ParentVNI);
return LIS.getSlotIndexes()->insertMachineInstrInMaps(--MI, Late)
.getRegSlot();
}
void LiveRangeEdit::eraseVirtReg(unsigned Reg) {
if (TheDelegate && TheDelegate->LRE_CanEraseVirtReg(Reg))
LIS.removeInterval(Reg);
}
bool LiveRangeEdit::foldAsLoad(LiveInterval *LI,
SmallVectorImpl<MachineInstr*> &Dead) {
MachineInstr *DefMI = nullptr, *UseMI = nullptr;
// Check that there is a single def and a single use.
for (MachineOperand &MO : MRI.reg_nodbg_operands(LI->reg)) {
MachineInstr *MI = MO.getParent();
if (MO.isDef()) {
if (DefMI && DefMI != MI)
return false;
if (!MI->canFoldAsLoad())
return false;
DefMI = MI;
} else if (!MO.isUndef()) {
if (UseMI && UseMI != MI)
return false;
// FIXME: Targets don't know how to fold subreg uses.
if (MO.getSubReg())
return false;
UseMI = MI;
}
}
if (!DefMI || !UseMI)
return false;
// Since we're moving the DefMI load, make sure we're not extending any live
// ranges.
if (!allUsesAvailableAt(DefMI,
LIS.getInstructionIndex(DefMI),
LIS.getInstructionIndex(UseMI)))
return false;
// We also need to make sure it is safe to move the load.
// Assume there are stores between DefMI and UseMI.
bool SawStore = true;
if (!DefMI->isSafeToMove(&TII, nullptr, SawStore))
return false;
DEBUG(dbgs() << "Try to fold single def: " << *DefMI
<< " into single use: " << *UseMI);
SmallVector<unsigned, 8> Ops;
if (UseMI->readsWritesVirtualRegister(LI->reg, &Ops).second)
return false;
MachineInstr *FoldMI = TII.foldMemoryOperand(UseMI, Ops, DefMI);
if (!FoldMI)
return false;
DEBUG(dbgs() << " folded: " << *FoldMI);
LIS.ReplaceMachineInstrInMaps(UseMI, FoldMI);
UseMI->eraseFromParent();
DefMI->addRegisterDead(LI->reg, nullptr);
Dead.push_back(DefMI);
++NumDCEFoldedLoads;
return true;
}
/// Find all live intervals that need to shrink, then remove the instruction.
void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
assert(MI->allDefsAreDead() && "Def isn't really dead");
SlotIndex Idx = LIS.getInstructionIndex(MI).getRegSlot();
// Never delete a bundled instruction.
if (MI->isBundled()) {
return;
}
// Never delete inline asm.
if (MI->isInlineAsm()) {
DEBUG(dbgs() << "Won't delete: " << Idx << '\t' << *MI);
return;
}
// Use the same criteria as DeadMachineInstructionElim.
bool SawStore = false;
if (!MI->isSafeToMove(&TII, nullptr, SawStore)) {
DEBUG(dbgs() << "Can't delete: " << Idx << '\t' << *MI);
return;
}
DEBUG(dbgs() << "Deleting dead def " << Idx << '\t' << *MI);
// Collect virtual registers to be erased after MI is gone.
SmallVector<unsigned, 8> RegsToErase;
bool ReadsPhysRegs = false;
// Check for live intervals that may shrink
for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
MOE = MI->operands_end(); MOI != MOE; ++MOI) {
if (!MOI->isReg())
continue;
unsigned Reg = MOI->getReg();
if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
// Check if MI reads any unreserved physregs.
if (Reg && MOI->readsReg() && !MRI.isReserved(Reg))
ReadsPhysRegs = true;
else if (MOI->isDef())
LIS.removePhysRegDefAt(Reg, Idx);
continue;
}
LiveInterval &LI = LIS.getInterval(Reg);
// Shrink read registers, unless it is likely to be expensive and
// unlikely to change anything. We typically don't want to shrink the
// PIC base register that has lots of uses everywhere.
// Always shrink COPY uses that probably come from live range splitting.
if (MI->readsVirtualRegister(Reg) &&
(MI->isCopy() || MOI->isDef() || MRI.hasOneNonDBGUse(Reg) ||
LI.Query(Idx).isKill()))
ToShrink.insert(&LI);
// Remove defined value.
if (MOI->isDef()) {
if (TheDelegate && LI.getVNInfoAt(Idx) != nullptr)
TheDelegate->LRE_WillShrinkVirtReg(LI.reg);
LIS.removeVRegDefAt(LI, Idx);
if (LI.empty())
RegsToErase.push_back(Reg);
}
}
// Currently, we don't support DCE of physreg live ranges. If MI reads
// any unreserved physregs, don't erase the instruction, but turn it into
// a KILL instead. This way, the physreg live ranges don't end up
// dangling.
// FIXME: It would be better to have something like shrinkToUses() for
// physregs. That could potentially enable more DCE and it would free up
// the physreg. It would not happen often, though.
if (ReadsPhysRegs) {
MI->setDesc(TII.get(TargetOpcode::KILL));
// Remove all operands that aren't physregs.
for (unsigned i = MI->getNumOperands(); i; --i) {
const MachineOperand &MO = MI->getOperand(i-1);
if (MO.isReg() && TargetRegisterInfo::isPhysicalRegister(MO.getReg()))
continue;
MI->RemoveOperand(i-1);
}
DEBUG(dbgs() << "Converted physregs to:\t" << *MI);
} else {
if (TheDelegate)
TheDelegate->LRE_WillEraseInstruction(MI);
LIS.RemoveMachineInstrFromMaps(MI);
MI->eraseFromParent();
++NumDCEDeleted;
}
// Erase any virtregs that are now empty and unused. There may be <undef>
// uses around. Keep the empty live range in that case.
for (unsigned i = 0, e = RegsToErase.size(); i != e; ++i) {
unsigned Reg = RegsToErase[i];
if (LIS.hasInterval(Reg) && MRI.reg_nodbg_empty(Reg)) {
ToShrink.remove(&LIS.getInterval(Reg));
eraseVirtReg(Reg);
}
}
}
void LiveRangeEdit::eliminateDeadDefs(SmallVectorImpl<MachineInstr*> &Dead,
ArrayRef<unsigned> RegsBeingSpilled) {
ToShrinkSet ToShrink;
for (;;) {
// Erase all dead defs.
while (!Dead.empty())
eliminateDeadDef(Dead.pop_back_val(), ToShrink);
if (ToShrink.empty())
break;
// Shrink just one live interval. Then delete new dead defs.
LiveInterval *LI = ToShrink.back();
ToShrink.pop_back();
if (foldAsLoad(LI, Dead))
continue;
if (TheDelegate)
TheDelegate->LRE_WillShrinkVirtReg(LI->reg);
if (!LIS.shrinkToUses(LI, &Dead))
continue;
// Don't create new intervals for a register being spilled.
// The new intervals would have to be spilled anyway so its not worth it.
// Also they currently aren't spilled so creating them and not spilling
// them results in incorrect code.
bool BeingSpilled = false;
for (unsigned i = 0, e = RegsBeingSpilled.size(); i != e; ++i) {
if (LI->reg == RegsBeingSpilled[i]) {
BeingSpilled = true;
break;
}
}
if (BeingSpilled) continue;
// LI may have been separated, create new intervals.
LI->RenumberValues();
ConnectedVNInfoEqClasses ConEQ(LIS);
unsigned NumComp = ConEQ.Classify(LI);
if (NumComp <= 1)
continue;
++NumFracRanges;
bool IsOriginal = VRM && VRM->getOriginal(LI->reg) == LI->reg;
DEBUG(dbgs() << NumComp << " components: " << *LI << '\n');
SmallVector<LiveInterval*, 8> Dups(1, LI);
for (unsigned i = 1; i != NumComp; ++i) {
Dups.push_back(&createEmptyIntervalFrom(LI->reg));
// If LI is an original interval that hasn't been split yet, make the new
// intervals their own originals instead of referring to LI. The original
// interval must contain all the split products, and LI doesn't.
if (IsOriginal)
VRM->setIsSplitFromReg(Dups.back()->reg, 0);
if (TheDelegate)
TheDelegate->LRE_DidCloneVirtReg(Dups.back()->reg, LI->reg);
}
ConEQ.Distribute(&Dups[0], MRI);
DEBUG({
for (unsigned i = 0; i != NumComp; ++i)
dbgs() << '\t' << *Dups[i] << '\n';
});
}
}
// Keep track of new virtual registers created via
// MachineRegisterInfo::createVirtualRegister.
void
LiveRangeEdit::MRI_NoteNewVirtualRegister(unsigned VReg)
{
if (VRM)
VRM->grow();
NewRegs.push_back(VReg);
}
void
LiveRangeEdit::calculateRegClassAndHint(MachineFunction &MF,
const MachineLoopInfo &Loops,
const MachineBlockFrequencyInfo &MBFI) {
VirtRegAuxInfo VRAI(MF, LIS, Loops, MBFI);
for (unsigned I = 0, Size = size(); I < Size; ++I) {
LiveInterval &LI = LIS.getInterval(get(I));
if (MRI.recomputeRegClass(LI.reg, MF.getTarget()))
DEBUG({
const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
dbgs() << "Inflated " << PrintReg(LI.reg) << " to "
<< TRI->getRegClassName(MRI.getRegClass(LI.reg)) << '\n';
});
VRAI.calculateSpillWeightAndHint(LI);
}
}