cl::desc("Coalesce copies (default=true)"),
cl::init(true));
+static cl::opt<bool> UseTerminalRule("terminal-rule",
+ cl::desc("Apply the terminal rule"),
+ cl::init(false), cl::Hidden);
+
/// Temporary flag to test critical edge unsplitting.
static cl::opt<bool>
EnableJoinSplits("join-splitedges",
/// If the source of a copy is defined by a
/// trivial computation, replace the copy by rematerialize the definition.
- bool reMaterializeTrivialDef(CoalescerPair &CP, MachineInstr *CopyMI,
+ bool reMaterializeTrivialDef(const CoalescerPair &CP, MachineInstr *CopyMI,
bool &IsDefCopy);
/// Return true if a copy involving a physreg should be joined.
/// Returns true if @p CopyMI was a copy of an undef value and eliminated.
bool eliminateUndefCopy(MachineInstr *CopyMI);
+ /// Check whether or not we should apply the terminal rule on the
+ /// destination (Dst) of \p Copy.
+ /// When the terminal rule applies, Copy is not profitable to
+ /// coalesce.
+ /// Dst is terminal if it has exactly one affinity (Dst, Src) and
+ /// at least one interference (Dst, Dst2). If Dst is terminal, the
+ /// terminal rule consists in checking that at least one of
+ /// interfering node, say Dst2, has an affinity of equal or greater
+ /// weight with Src.
+ /// In that case, Dst2 and Dst will not be able to be both coalesced
+ /// with Src. Since Dst2 exposes more coalescing opportunities than
+ /// Dst, we can drop \p Copy.
+ bool applyTerminalRule(const MachineInstr &Copy) const;
+
public:
static char ID; ///< Class identification, replacement for typeinfo
RegisterCoalescer() : MachineFunctionPass(ID) {
return false;
}
-bool RegisterCoalescer::reMaterializeTrivialDef(CoalescerPair &CP,
+bool RegisterCoalescer::reMaterializeTrivialDef(const CoalescerPair &CP,
MachineInstr *CopyMI,
bool &IsDefCopy) {
IsDefCopy = false;
TII->reMaterialize(*MBB, MII, DstReg, SrcIdx, DefMI, *TRI);
MachineInstr *NewMI = std::prev(MII);
+ // A situation like the following:
+ // %vreg0:subX = instr ; DefMI
+ // %vregY = copy %vreg:subX ; CopyMI
+ // does not need subregisters/regclass widening after rematerialization, just
+ // do:
+ // %vregY = instr
+ const TargetRegisterClass *NewRC = CP.getNewRC();
+ if (DstIdx != 0) {
+ MachineOperand &DefMO = NewMI->getOperand(0);
+ if (DefMO.getSubReg() == DstIdx) {
+ assert(SrcIdx == 0 && CP.isFlipped()
+ && "Shouldn't have SrcIdx+DstIdx at this point");
+ const TargetRegisterClass *DstRC = MRI->getRegClass(DstReg);
+ const TargetRegisterClass *CommonRC =
+ TRI->getCommonSubClass(DefRC, DstRC);
+ if (CommonRC != nullptr) {
+ NewRC = CommonRC;
+ DstIdx = 0;
+ DefMO.setSubReg(0);
+ }
+ }
+ }
+
LIS->ReplaceMachineInstrInMaps(CopyMI, NewMI);
CopyMI->eraseFromParent();
ErasedInstrs.insert(CopyMI);
for (unsigned i = NewMI->getDesc().getNumOperands(),
e = NewMI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = NewMI->getOperand(i);
- if (MO.isReg()) {
- assert(MO.isDef() && MO.isImplicit() && MO.isDead() &&
+ if (MO.isReg() && MO.isDef()) {
+ assert(MO.isImplicit() && MO.isDead() &&
TargetRegisterInfo::isPhysicalRegister(MO.getReg()));
NewMIImplDefs.push_back(MO.getReg());
}
}
if (TargetRegisterInfo::isVirtualRegister(DstReg)) {
- const TargetRegisterClass *NewRC = CP.getNewRC();
unsigned NewIdx = NewMI->getOperand(0).getSubReg();
if (DefRC != nullptr) {
return Progress;
}
+/// Check if DstReg is a terminal node.
+/// I.e., it does not have any affinity other than \p Copy.
+static bool isTerminalReg(unsigned DstReg, const MachineInstr &Copy,
+ const MachineRegisterInfo *MRI) {
+ assert(Copy.isCopyLike());
+ // Check if the destination of this copy as any other affinity.
+ for (const MachineInstr &MI : MRI->reg_nodbg_instructions(DstReg))
+ if (&MI != &Copy && MI.isCopyLike())
+ return false;
+ return true;
+}
+
+bool RegisterCoalescer::applyTerminalRule(const MachineInstr &Copy) const {
+ assert(Copy.isCopyLike());
+ if (!UseTerminalRule)
+ return false;
+ unsigned DstReg, DstSubReg, SrcReg, SrcSubReg;
+ isMoveInstr(*TRI, &Copy, SrcReg, DstReg, SrcSubReg, DstSubReg);
+ // Check if the destination of this copy has any other affinity.
+ if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
+ // If SrcReg is a physical register, the copy won't be coalesced.
+ // Ignoring it may have other side effect (like missing
+ // rematerialization). So keep it.
+ TargetRegisterInfo::isPhysicalRegister(SrcReg) ||
+ !isTerminalReg(DstReg, Copy, MRI))
+ return false;
+
+ // DstReg is a terminal node. Check if it inteferes with any other
+ // copy involving SrcReg.
+ const MachineBasicBlock *OrigBB = Copy.getParent();
+ const LiveInterval &DstLI = LIS->getInterval(DstReg);
+ for (const MachineInstr &MI : MRI->reg_nodbg_instructions(SrcReg)) {
+ // Technically we should check if the weight of the new copy is
+ // interesting compared to the other one and update the weight
+ // of the copies accordingly. However, this would only work if
+ // we would gather all the copies first then coalesce, whereas
+ // right now we interleave both actions.
+ // For now, just consider the copies that are in the same block.
+ if (&MI == &Copy || !MI.isCopyLike() || MI.getParent() != OrigBB)
+ continue;
+ unsigned OtherReg, OtherSubReg, OtherSrcReg, OtherSrcSubReg;
+ isMoveInstr(*TRI, &Copy, OtherSrcReg, OtherReg, OtherSrcSubReg,
+ OtherSubReg);
+ if (OtherReg == SrcReg)
+ OtherReg = OtherSrcReg;
+ // Check if OtherReg is a non-terminal.
+ if (TargetRegisterInfo::isPhysicalRegister(OtherReg) ||
+ isTerminalReg(OtherReg, MI, MRI))
+ continue;
+ // Check that OtherReg interfere with DstReg.
+ if (LIS->getInterval(OtherReg).overlaps(DstLI)) {
+ DEBUG(dbgs() << "Apply terminal rule for: " << PrintReg(DstReg) << '\n');
+ return true;
+ }
+ }
+ return false;
+}
+
void
RegisterCoalescer::copyCoalesceInMBB(MachineBasicBlock *MBB) {
DEBUG(dbgs() << MBB->getName() << ":\n");
// yet, it might invalidate the iterator.
const unsigned PrevSize = WorkList.size();
if (JoinGlobalCopies) {
+ SmallVector<MachineInstr*, 2> LocalTerminals;
+ SmallVector<MachineInstr*, 2> GlobalTerminals;
// Coalesce copies bottom-up to coalesce local defs before local uses. They
// are not inherently easier to resolve, but slightly preferable until we
// have local live range splitting. In particular this is required by
MII != E; ++MII) {
if (!MII->isCopyLike())
continue;
- if (isLocalCopy(&(*MII), LIS))
- LocalWorkList.push_back(&(*MII));
- else
- WorkList.push_back(&(*MII));
+ bool ApplyTerminalRule = applyTerminalRule(*MII);
+ if (isLocalCopy(&(*MII), LIS)) {
+ if (ApplyTerminalRule)
+ LocalTerminals.push_back(&(*MII));
+ else
+ LocalWorkList.push_back(&(*MII));
+ } else {
+ if (ApplyTerminalRule)
+ GlobalTerminals.push_back(&(*MII));
+ else
+ WorkList.push_back(&(*MII));
+ }
}
+ // Append the copies evicted by the terminal rule at the end of the list.
+ LocalWorkList.append(LocalTerminals.begin(), LocalTerminals.end());
+ WorkList.append(GlobalTerminals.begin(), GlobalTerminals.end());
}
else {
+ SmallVector<MachineInstr*, 2> Terminals;
for (MachineBasicBlock::iterator MII = MBB->begin(), E = MBB->end();
MII != E; ++MII)
- if (MII->isCopyLike())
- WorkList.push_back(MII);
+ if (MII->isCopyLike()) {
+ if (applyTerminalRule(*MII))
+ Terminals.push_back(&(*MII));
+ else
+ WorkList.push_back(MII);
+ }
+ // Append the copies evicted by the terminal rule at the end of the list.
+ WorkList.append(Terminals.begin(), Terminals.end());
}
// Try coalescing the collected copies immediately, and remove the nulls.
// This prevents the WorkList from getting too large since most copies are
projects / oota-llvm.git / blobdiff