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llvm-for-llvmta/lib/CodeGen/AggressiveAntiDepBreaker.cpp

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2022-04-25 10:02:23 +02:00
//===- AggressiveAntiDepBreaker.cpp - Anti-dep breaker --------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements the AggressiveAntiDepBreaker class, which
// implements register anti-dependence breaking during post-RA
// scheduling. It attempts to break all anti-dependencies within a
// block.
//
//===----------------------------------------------------------------------===//
#include "AggressiveAntiDepBreaker.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MachineValueType.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <utility>
using namespace llvm;
#define DEBUG_TYPE "post-RA-sched"
// If DebugDiv > 0 then only break antidep with (ID % DebugDiv) == DebugMod
static cl::opt<int>
DebugDiv("agg-antidep-debugdiv",
cl::desc("Debug control for aggressive anti-dep breaker"),
cl::init(0), cl::Hidden);
static cl::opt<int>
DebugMod("agg-antidep-debugmod",
cl::desc("Debug control for aggressive anti-dep breaker"),
cl::init(0), cl::Hidden);
AggressiveAntiDepState::AggressiveAntiDepState(const unsigned TargetRegs,
MachineBasicBlock *BB)
: NumTargetRegs(TargetRegs), GroupNodes(TargetRegs, 0),
GroupNodeIndices(TargetRegs, 0), KillIndices(TargetRegs, 0),
DefIndices(TargetRegs, 0) {
const unsigned BBSize = BB->size();
for (unsigned i = 0; i < NumTargetRegs; ++i) {
// Initialize all registers to be in their own group. Initially we
// assign the register to the same-indexed GroupNode.
GroupNodeIndices[i] = i;
// Initialize the indices to indicate that no registers are live.
KillIndices[i] = ~0u;
DefIndices[i] = BBSize;
}
}
unsigned AggressiveAntiDepState::GetGroup(unsigned Reg) {
unsigned Node = GroupNodeIndices[Reg];
while (GroupNodes[Node] != Node)
Node = GroupNodes[Node];
return Node;
}
void AggressiveAntiDepState::GetGroupRegs(
unsigned Group,
std::vector<unsigned> &Regs,
std::multimap<unsigned, AggressiveAntiDepState::RegisterReference> *RegRefs)
{
for (unsigned Reg = 0; Reg != NumTargetRegs; ++Reg) {
if ((GetGroup(Reg) == Group) && (RegRefs->count(Reg) > 0))
Regs.push_back(Reg);
}
}
unsigned AggressiveAntiDepState::UnionGroups(unsigned Reg1, unsigned Reg2) {
assert(GroupNodes[0] == 0 && "GroupNode 0 not parent!");
assert(GroupNodeIndices[0] == 0 && "Reg 0 not in Group 0!");
// find group for each register
unsigned Group1 = GetGroup(Reg1);
unsigned Group2 = GetGroup(Reg2);
// if either group is 0, then that must become the parent
unsigned Parent = (Group1 == 0) ? Group1 : Group2;
unsigned Other = (Parent == Group1) ? Group2 : Group1;
GroupNodes.at(Other) = Parent;
return Parent;
}
unsigned AggressiveAntiDepState::LeaveGroup(unsigned Reg) {
// Create a new GroupNode for Reg. Reg's existing GroupNode must
// stay as is because there could be other GroupNodes referring to
// it.
unsigned idx = GroupNodes.size();
GroupNodes.push_back(idx);
GroupNodeIndices[Reg] = idx;
return idx;
}
bool AggressiveAntiDepState::IsLive(unsigned Reg) {
// KillIndex must be defined and DefIndex not defined for a register
// to be live.
return((KillIndices[Reg] != ~0u) && (DefIndices[Reg] == ~0u));
}
AggressiveAntiDepBreaker::AggressiveAntiDepBreaker(
MachineFunction &MFi, const RegisterClassInfo &RCI,
TargetSubtargetInfo::RegClassVector &CriticalPathRCs)
: AntiDepBreaker(), MF(MFi), MRI(MF.getRegInfo()),
TII(MF.getSubtarget().getInstrInfo()),
TRI(MF.getSubtarget().getRegisterInfo()), RegClassInfo(RCI) {
/* Collect a bitset of all registers that are only broken if they
are on the critical path. */
for (unsigned i = 0, e = CriticalPathRCs.size(); i < e; ++i) {
BitVector CPSet = TRI->getAllocatableSet(MF, CriticalPathRCs[i]);
if (CriticalPathSet.none())
CriticalPathSet = CPSet;
else
CriticalPathSet |= CPSet;
}
LLVM_DEBUG(dbgs() << "AntiDep Critical-Path Registers:");
LLVM_DEBUG(for (unsigned r
: CriticalPathSet.set_bits()) dbgs()
<< " " << printReg(r, TRI));
LLVM_DEBUG(dbgs() << '\n');
}
AggressiveAntiDepBreaker::~AggressiveAntiDepBreaker() {
delete State;
}
void AggressiveAntiDepBreaker::StartBlock(MachineBasicBlock *BB) {
assert(!State);
State = new AggressiveAntiDepState(TRI->getNumRegs(), BB);
bool IsReturnBlock = BB->isReturnBlock();
std::vector<unsigned> &KillIndices = State->GetKillIndices();
std::vector<unsigned> &DefIndices = State->GetDefIndices();
// Examine the live-in regs of all successors.
for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
SE = BB->succ_end(); SI != SE; ++SI)
for (const auto &LI : (*SI)->liveins()) {
for (MCRegAliasIterator AI(LI.PhysReg, TRI, true); AI.isValid(); ++AI) {
unsigned Reg = *AI;
State->UnionGroups(Reg, 0);
KillIndices[Reg] = BB->size();
DefIndices[Reg] = ~0u;
}
}
// Mark live-out callee-saved registers. In a return block this is
// all callee-saved registers. In non-return this is any
// callee-saved register that is not saved in the prolog.
const MachineFrameInfo &MFI = MF.getFrameInfo();
BitVector Pristine = MFI.getPristineRegs(MF);
for (const MCPhysReg *I = MF.getRegInfo().getCalleeSavedRegs(); *I;
++I) {
unsigned Reg = *I;
if (!IsReturnBlock && !Pristine.test(Reg))
continue;
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
unsigned AliasReg = *AI;
State->UnionGroups(AliasReg, 0);
KillIndices[AliasReg] = BB->size();
DefIndices[AliasReg] = ~0u;
}
}
}
void AggressiveAntiDepBreaker::FinishBlock() {
delete State;
State = nullptr;
}
void AggressiveAntiDepBreaker::Observe(MachineInstr &MI, unsigned Count,
unsigned InsertPosIndex) {
assert(Count < InsertPosIndex && "Instruction index out of expected range!");
std::set<unsigned> PassthruRegs;
GetPassthruRegs(MI, PassthruRegs);
PrescanInstruction(MI, Count, PassthruRegs);
ScanInstruction(MI, Count);
LLVM_DEBUG(dbgs() << "Observe: ");
LLVM_DEBUG(MI.dump());
LLVM_DEBUG(dbgs() << "\tRegs:");
std::vector<unsigned> &DefIndices = State->GetDefIndices();
for (unsigned Reg = 0; Reg != TRI->getNumRegs(); ++Reg) {
// If Reg is current live, then mark that it can't be renamed as
// we don't know the extent of its live-range anymore (now that it
// has been scheduled). If it is not live but was defined in the
// previous schedule region, then set its def index to the most
// conservative location (i.e. the beginning of the previous
// schedule region).
if (State->IsLive(Reg)) {
LLVM_DEBUG(if (State->GetGroup(Reg) != 0) dbgs()
<< " " << printReg(Reg, TRI) << "=g" << State->GetGroup(Reg)
<< "->g0(region live-out)");
State->UnionGroups(Reg, 0);
} else if ((DefIndices[Reg] < InsertPosIndex)
&& (DefIndices[Reg] >= Count)) {
DefIndices[Reg] = Count;
}
}
LLVM_DEBUG(dbgs() << '\n');
}
bool AggressiveAntiDepBreaker::IsImplicitDefUse(MachineInstr &MI,
MachineOperand &MO) {
if (!MO.isReg() || !MO.isImplicit())
return false;
Register Reg = MO.getReg();
if (Reg == 0)
return false;
MachineOperand *Op = nullptr;
if (MO.isDef())
Op = MI.findRegisterUseOperand(Reg, true);
else
Op = MI.findRegisterDefOperand(Reg);
return(Op && Op->isImplicit());
}
void AggressiveAntiDepBreaker::GetPassthruRegs(
MachineInstr &MI, std::set<unsigned> &PassthruRegs) {
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg()) continue;
if ((MO.isDef() && MI.isRegTiedToUseOperand(i)) ||
IsImplicitDefUse(MI, MO)) {
const Register Reg = MO.getReg();
for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
SubRegs.isValid(); ++SubRegs)
PassthruRegs.insert(*SubRegs);
}
}
}
/// AntiDepEdges - Return in Edges the anti- and output- dependencies
/// in SU that we want to consider for breaking.
static void AntiDepEdges(const SUnit *SU, std::vector<const SDep *> &Edges) {
SmallSet<unsigned, 4> RegSet;
for (SUnit::const_pred_iterator P = SU->Preds.begin(), PE = SU->Preds.end();
P != PE; ++P) {
if ((P->getKind() == SDep::Anti) || (P->getKind() == SDep::Output)) {
if (RegSet.insert(P->getReg()).second)
Edges.push_back(&*P);
}
}
}
/// CriticalPathStep - Return the next SUnit after SU on the bottom-up
/// critical path.
static const SUnit *CriticalPathStep(const SUnit *SU) {
const SDep *Next = nullptr;
unsigned NextDepth = 0;
// Find the predecessor edge with the greatest depth.
if (SU) {
for (SUnit::const_pred_iterator P = SU->Preds.begin(), PE = SU->Preds.end();
P != PE; ++P) {
const SUnit *PredSU = P->getSUnit();
unsigned PredLatency = P->getLatency();
unsigned PredTotalLatency = PredSU->getDepth() + PredLatency;
// In the case of a latency tie, prefer an anti-dependency edge over
// other types of edges.
if (NextDepth < PredTotalLatency ||
(NextDepth == PredTotalLatency && P->getKind() == SDep::Anti)) {
NextDepth = PredTotalLatency;
Next = &*P;
}
}
}
return (Next) ? Next->getSUnit() : nullptr;
}
void AggressiveAntiDepBreaker::HandleLastUse(unsigned Reg, unsigned KillIdx,
const char *tag,
const char *header,
const char *footer) {
std::vector<unsigned> &KillIndices = State->GetKillIndices();
std::vector<unsigned> &DefIndices = State->GetDefIndices();
std::multimap<unsigned, AggressiveAntiDepState::RegisterReference>&
RegRefs = State->GetRegRefs();
// FIXME: We must leave subregisters of live super registers as live, so that
// we don't clear out the register tracking information for subregisters of
// super registers we're still tracking (and with which we're unioning
// subregister definitions).
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI)
if (TRI->isSuperRegister(Reg, *AI) && State->IsLive(*AI)) {
LLVM_DEBUG(if (!header && footer) dbgs() << footer);
return;
}
if (!State->IsLive(Reg)) {
KillIndices[Reg] = KillIdx;
DefIndices[Reg] = ~0u;
RegRefs.erase(Reg);
State->LeaveGroup(Reg);
LLVM_DEBUG(if (header) {
dbgs() << header << printReg(Reg, TRI);
header = nullptr;
});
LLVM_DEBUG(dbgs() << "->g" << State->GetGroup(Reg) << tag);
// Repeat for subregisters. Note that we only do this if the superregister
// was not live because otherwise, regardless whether we have an explicit
// use of the subregister, the subregister's contents are needed for the
// uses of the superregister.
for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
unsigned SubregReg = *SubRegs;
if (!State->IsLive(SubregReg)) {
KillIndices[SubregReg] = KillIdx;
DefIndices[SubregReg] = ~0u;
RegRefs.erase(SubregReg);
State->LeaveGroup(SubregReg);
LLVM_DEBUG(if (header) {
dbgs() << header << printReg(Reg, TRI);
header = nullptr;
});
LLVM_DEBUG(dbgs() << " " << printReg(SubregReg, TRI) << "->g"
<< State->GetGroup(SubregReg) << tag);
}
}
}
LLVM_DEBUG(if (!header && footer) dbgs() << footer);
}
void AggressiveAntiDepBreaker::PrescanInstruction(
MachineInstr &MI, unsigned Count, std::set<unsigned> &PassthruRegs) {
std::vector<unsigned> &DefIndices = State->GetDefIndices();
std::multimap<unsigned, AggressiveAntiDepState::RegisterReference>&
RegRefs = State->GetRegRefs();
// Handle dead defs by simulating a last-use of the register just
// after the def. A dead def can occur because the def is truly
// dead, or because only a subregister is live at the def. If we
// don't do this the dead def will be incorrectly merged into the
// previous def.
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || !MO.isDef()) continue;
Register Reg = MO.getReg();
if (Reg == 0) continue;
HandleLastUse(Reg, Count + 1, "", "\tDead Def: ", "\n");
}
LLVM_DEBUG(dbgs() << "\tDef Groups:");
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || !MO.isDef()) continue;
Register Reg = MO.getReg();
if (Reg == 0) continue;
LLVM_DEBUG(dbgs() << " " << printReg(Reg, TRI) << "=g"
<< State->GetGroup(Reg));
// If MI's defs have a special allocation requirement, don't allow
// any def registers to be changed. Also assume all registers
// defined in a call must not be changed (ABI). Inline assembly may
// reference either system calls or the register directly. Skip it until we
// can tell user specified registers from compiler-specified.
if (MI.isCall() || MI.hasExtraDefRegAllocReq() || TII->isPredicated(MI) ||
MI.isInlineAsm()) {
LLVM_DEBUG(if (State->GetGroup(Reg) != 0) dbgs() << "->g0(alloc-req)");
State->UnionGroups(Reg, 0);
}
// Any aliased that are live at this point are completely or
// partially defined here, so group those aliases with Reg.
for (MCRegAliasIterator AI(Reg, TRI, false); AI.isValid(); ++AI) {
unsigned AliasReg = *AI;
if (State->IsLive(AliasReg)) {
State->UnionGroups(Reg, AliasReg);
LLVM_DEBUG(dbgs() << "->g" << State->GetGroup(Reg) << "(via "
<< printReg(AliasReg, TRI) << ")");
}
}
// Note register reference...
const TargetRegisterClass *RC = nullptr;
if (i < MI.getDesc().getNumOperands())
RC = TII->getRegClass(MI.getDesc(), i, TRI, MF);
AggressiveAntiDepState::RegisterReference RR = { &MO, RC };
RegRefs.insert(std::make_pair(Reg, RR));
}
LLVM_DEBUG(dbgs() << '\n');
// Scan the register defs for this instruction and update
// live-ranges.
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || !MO.isDef()) continue;
Register Reg = MO.getReg();
if (Reg == 0) continue;
// Ignore KILLs and passthru registers for liveness...
if (MI.isKill() || (PassthruRegs.count(Reg) != 0))
continue;
// Update def for Reg and aliases.
for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
// We need to be careful here not to define already-live super registers.
// If the super register is already live, then this definition is not
// a definition of the whole super register (just a partial insertion
// into it). Earlier subregister definitions (which we've not yet visited
// because we're iterating bottom-up) need to be linked to the same group
// as this definition.
if (TRI->isSuperRegister(Reg, *AI) && State->IsLive(*AI))
continue;
DefIndices[*AI] = Count;
}
}
}
void AggressiveAntiDepBreaker::ScanInstruction(MachineInstr &MI,
unsigned Count) {
LLVM_DEBUG(dbgs() << "\tUse Groups:");
std::multimap<unsigned, AggressiveAntiDepState::RegisterReference>&
RegRefs = State->GetRegRefs();
// If MI's uses have special allocation requirement, don't allow
// any use registers to be changed. Also assume all registers
// used in a call must not be changed (ABI).
// Inline Assembly register uses also cannot be safely changed.
// FIXME: The issue with predicated instruction is more complex. We are being
// conservatively here because the kill markers cannot be trusted after
// if-conversion:
// %r6 = LDR %sp, %reg0, 92, 14, %reg0; mem:LD4[FixedStack14]
// ...
// STR %r0, killed %r6, %reg0, 0, 0, %cpsr; mem:ST4[%395]
// %r6 = LDR %sp, %reg0, 100, 0, %cpsr; mem:LD4[FixedStack12]
// STR %r0, killed %r6, %reg0, 0, 14, %reg0; mem:ST4[%396](align=8)
//
// The first R6 kill is not really a kill since it's killed by a predicated
// instruction which may not be executed. The second R6 def may or may not
// re-define R6 so it's not safe to change it since the last R6 use cannot be
// changed.
bool Special = MI.isCall() || MI.hasExtraSrcRegAllocReq() ||
TII->isPredicated(MI) || MI.isInlineAsm();
// Scan the register uses for this instruction and update
// live-ranges, groups and RegRefs.
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg() || !MO.isUse()) continue;
Register Reg = MO.getReg();
if (Reg == 0) continue;
LLVM_DEBUG(dbgs() << " " << printReg(Reg, TRI) << "=g"
<< State->GetGroup(Reg));
// It wasn't previously live but now it is, this is a kill. Forget
// the previous live-range information and start a new live-range
// for the register.
HandleLastUse(Reg, Count, "(last-use)");
if (Special) {
LLVM_DEBUG(if (State->GetGroup(Reg) != 0) dbgs() << "->g0(alloc-req)");
State->UnionGroups(Reg, 0);
}
// Note register reference...
const TargetRegisterClass *RC = nullptr;
if (i < MI.getDesc().getNumOperands())
RC = TII->getRegClass(MI.getDesc(), i, TRI, MF);
AggressiveAntiDepState::RegisterReference RR = { &MO, RC };
RegRefs.insert(std::make_pair(Reg, RR));
}
LLVM_DEBUG(dbgs() << '\n');
// Form a group of all defs and uses of a KILL instruction to ensure
// that all registers are renamed as a group.
if (MI.isKill()) {
LLVM_DEBUG(dbgs() << "\tKill Group:");
unsigned FirstReg = 0;
for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI.getOperand(i);
if (!MO.isReg()) continue;
Register Reg = MO.getReg();
if (Reg == 0) continue;
if (FirstReg != 0) {
LLVM_DEBUG(dbgs() << "=" << printReg(Reg, TRI));
State->UnionGroups(FirstReg, Reg);
} else {
LLVM_DEBUG(dbgs() << " " << printReg(Reg, TRI));
FirstReg = Reg;
}
}
LLVM_DEBUG(dbgs() << "->g" << State->GetGroup(FirstReg) << '\n');
}
}
BitVector AggressiveAntiDepBreaker::GetRenameRegisters(unsigned Reg) {
BitVector BV(TRI->getNumRegs(), false);
bool first = true;
// Check all references that need rewriting for Reg. For each, use
// the corresponding register class to narrow the set of registers
// that are appropriate for renaming.
for (const auto &Q : make_range(State->GetRegRefs().equal_range(Reg))) {
const TargetRegisterClass *RC = Q.second.RC;
if (!RC) continue;
BitVector RCBV = TRI->getAllocatableSet(MF, RC);
if (first) {
BV |= RCBV;
first = false;
} else {
BV &= RCBV;
}
LLVM_DEBUG(dbgs() << " " << TRI->getRegClassName(RC));
}
return BV;
}
bool AggressiveAntiDepBreaker::FindSuitableFreeRegisters(
unsigned AntiDepGroupIndex,
RenameOrderType& RenameOrder,
std::map<unsigned, unsigned> &RenameMap) {
std::vector<unsigned> &KillIndices = State->GetKillIndices();
std::vector<unsigned> &DefIndices = State->GetDefIndices();
std::multimap<unsigned, AggressiveAntiDepState::RegisterReference>&
RegRefs = State->GetRegRefs();
// Collect all referenced registers in the same group as
// AntiDepReg. These all need to be renamed together if we are to
// break the anti-dependence.
std::vector<unsigned> Regs;
State->GetGroupRegs(AntiDepGroupIndex, Regs, &RegRefs);
assert(!Regs.empty() && "Empty register group!");
if (Regs.empty())
return false;
// Find the "superest" register in the group. At the same time,
// collect the BitVector of registers that can be used to rename
// each register.
LLVM_DEBUG(dbgs() << "\tRename Candidates for Group g" << AntiDepGroupIndex
<< ":\n");
std::map<unsigned, BitVector> RenameRegisterMap;
unsigned SuperReg = 0;
for (unsigned i = 0, e = Regs.size(); i != e; ++i) {
unsigned Reg = Regs[i];
if ((SuperReg == 0) || TRI->isSuperRegister(SuperReg, Reg))
SuperReg = Reg;
// If Reg has any references, then collect possible rename regs
if (RegRefs.count(Reg) > 0) {
LLVM_DEBUG(dbgs() << "\t\t" << printReg(Reg, TRI) << ":");
BitVector &BV = RenameRegisterMap[Reg];
assert(BV.empty());
BV = GetRenameRegisters(Reg);
LLVM_DEBUG({
dbgs() << " ::";
for (unsigned r : BV.set_bits())
dbgs() << " " << printReg(r, TRI);
dbgs() << "\n";
});
}
}
// All group registers should be a subreg of SuperReg.
for (unsigned i = 0, e = Regs.size(); i != e; ++i) {
unsigned Reg = Regs[i];
if (Reg == SuperReg) continue;
bool IsSub = TRI->isSubRegister(SuperReg, Reg);
// FIXME: remove this once PR18663 has been properly fixed. For now,
// return a conservative answer:
// assert(IsSub && "Expecting group subregister");
if (!IsSub)
return false;
}
#ifndef NDEBUG
// If DebugDiv > 0 then only rename (renamecnt % DebugDiv) == DebugMod
if (DebugDiv > 0) {
static int renamecnt = 0;
if (renamecnt++ % DebugDiv != DebugMod)
return false;
dbgs() << "*** Performing rename " << printReg(SuperReg, TRI)
<< " for debug ***\n";
}
#endif
// Check each possible rename register for SuperReg in round-robin
// order. If that register is available, and the corresponding
// registers are available for the other group subregisters, then we
// can use those registers to rename.
// FIXME: Using getMinimalPhysRegClass is very conservative. We should
// check every use of the register and find the largest register class
// that can be used in all of them.
const TargetRegisterClass *SuperRC =
TRI->getMinimalPhysRegClass(SuperReg, MVT::Other);
ArrayRef<MCPhysReg> Order = RegClassInfo.getOrder(SuperRC);
if (Order.empty()) {
LLVM_DEBUG(dbgs() << "\tEmpty Super Regclass!!\n");
return false;
}
LLVM_DEBUG(dbgs() << "\tFind Registers:");
RenameOrder.insert(RenameOrderType::value_type(SuperRC, Order.size()));
unsigned OrigR = RenameOrder[SuperRC];
unsigned EndR = ((OrigR == Order.size()) ? 0 : OrigR);
unsigned R = OrigR;
do {
if (R == 0) R = Order.size();
--R;
const unsigned NewSuperReg = Order[R];
// Don't consider non-allocatable registers
if (!MRI.isAllocatable(NewSuperReg)) continue;
// Don't replace a register with itself.
if (NewSuperReg == SuperReg) continue;
LLVM_DEBUG(dbgs() << " [" << printReg(NewSuperReg, TRI) << ':');
RenameMap.clear();
// For each referenced group register (which must be a SuperReg or
// a subregister of SuperReg), find the corresponding subregister
// of NewSuperReg and make sure it is free to be renamed.
for (unsigned i = 0, e = Regs.size(); i != e; ++i) {
unsigned Reg = Regs[i];
unsigned NewReg = 0;
if (Reg == SuperReg) {
NewReg = NewSuperReg;
} else {
unsigned NewSubRegIdx = TRI->getSubRegIndex(SuperReg, Reg);
if (NewSubRegIdx != 0)
NewReg = TRI->getSubReg(NewSuperReg, NewSubRegIdx);
}
LLVM_DEBUG(dbgs() << " " << printReg(NewReg, TRI));
// Check if Reg can be renamed to NewReg.
if (!RenameRegisterMap[Reg].test(NewReg)) {
LLVM_DEBUG(dbgs() << "(no rename)");
goto next_super_reg;
}
// If NewReg is dead and NewReg's most recent def is not before
// Regs's kill, it's safe to replace Reg with NewReg. We
// must also check all aliases of NewReg, because we can't define a
// register when any sub or super is already live.
if (State->IsLive(NewReg) || (KillIndices[Reg] > DefIndices[NewReg])) {
LLVM_DEBUG(dbgs() << "(live)");
goto next_super_reg;
} else {
bool found = false;
for (MCRegAliasIterator AI(NewReg, TRI, false); AI.isValid(); ++AI) {
unsigned AliasReg = *AI;
if (State->IsLive(AliasReg) ||
(KillIndices[Reg] > DefIndices[AliasReg])) {
LLVM_DEBUG(dbgs()
<< "(alias " << printReg(AliasReg, TRI) << " live)");
found = true;
break;
}
}
if (found)
goto next_super_reg;
}
// We cannot rename 'Reg' to 'NewReg' if one of the uses of 'Reg' also
// defines 'NewReg' via an early-clobber operand.
for (const auto &Q : make_range(RegRefs.equal_range(Reg))) {
MachineInstr *UseMI = Q.second.Operand->getParent();
int Idx = UseMI->findRegisterDefOperandIdx(NewReg, false, true, TRI);
if (Idx == -1)
continue;
if (UseMI->getOperand(Idx).isEarlyClobber()) {
LLVM_DEBUG(dbgs() << "(ec)");
goto next_super_reg;
}
}
// Also, we cannot rename 'Reg' to 'NewReg' if the instruction defining
// 'Reg' is an early-clobber define and that instruction also uses
// 'NewReg'.
for (const auto &Q : make_range(RegRefs.equal_range(Reg))) {
if (!Q.second.Operand->isDef() || !Q.second.Operand->isEarlyClobber())
continue;
MachineInstr *DefMI = Q.second.Operand->getParent();
if (DefMI->readsRegister(NewReg, TRI)) {
LLVM_DEBUG(dbgs() << "(ec)");
goto next_super_reg;
}
}
// Record that 'Reg' can be renamed to 'NewReg'.
RenameMap.insert(std::pair<unsigned, unsigned>(Reg, NewReg));
}
// If we fall-out here, then every register in the group can be
// renamed, as recorded in RenameMap.
RenameOrder.erase(SuperRC);
RenameOrder.insert(RenameOrderType::value_type(SuperRC, R));
LLVM_DEBUG(dbgs() << "]\n");
return true;
next_super_reg:
LLVM_DEBUG(dbgs() << ']');
} while (R != EndR);
LLVM_DEBUG(dbgs() << '\n');
// No registers are free and available!
return false;
}
/// BreakAntiDependencies - Identifiy anti-dependencies within the
/// ScheduleDAG and break them by renaming registers.
unsigned AggressiveAntiDepBreaker::BreakAntiDependencies(
const std::vector<SUnit> &SUnits,
MachineBasicBlock::iterator Begin,
MachineBasicBlock::iterator End,
unsigned InsertPosIndex,
DbgValueVector &DbgValues) {
std::vector<unsigned> &KillIndices = State->GetKillIndices();
std::vector<unsigned> &DefIndices = State->GetDefIndices();
std::multimap<unsigned, AggressiveAntiDepState::RegisterReference>&
RegRefs = State->GetRegRefs();
// The code below assumes that there is at least one instruction,
// so just duck out immediately if the block is empty.
if (SUnits.empty()) return 0;
// For each regclass the next register to use for renaming.
RenameOrderType RenameOrder;
// ...need a map from MI to SUnit.
std::map<MachineInstr *, const SUnit *> MISUnitMap;
for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
const SUnit *SU = &SUnits[i];
MISUnitMap.insert(std::pair<MachineInstr *, const SUnit *>(SU->getInstr(),
SU));
}
// Track progress along the critical path through the SUnit graph as
// we walk the instructions. This is needed for regclasses that only
// break critical-path anti-dependencies.
const SUnit *CriticalPathSU = nullptr;
MachineInstr *CriticalPathMI = nullptr;
if (CriticalPathSet.any()) {
for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
const SUnit *SU = &SUnits[i];
if (!CriticalPathSU ||
((SU->getDepth() + SU->Latency) >
(CriticalPathSU->getDepth() + CriticalPathSU->Latency))) {
CriticalPathSU = SU;
}
}
assert(CriticalPathSU && "Failed to find SUnit critical path");
CriticalPathMI = CriticalPathSU->getInstr();
}
#ifndef NDEBUG
LLVM_DEBUG(dbgs() << "\n===== Aggressive anti-dependency breaking\n");
LLVM_DEBUG(dbgs() << "Available regs:");
for (unsigned Reg = 0; Reg < TRI->getNumRegs(); ++Reg) {
if (!State->IsLive(Reg))
LLVM_DEBUG(dbgs() << " " << printReg(Reg, TRI));
}
LLVM_DEBUG(dbgs() << '\n');
#endif
BitVector RegAliases(TRI->getNumRegs());
// Attempt to break anti-dependence edges. Walk the instructions
// from the bottom up, tracking information about liveness as we go
// to help determine which registers are available.
unsigned Broken = 0;
unsigned Count = InsertPosIndex - 1;
for (MachineBasicBlock::iterator I = End, E = Begin;
I != E; --Count) {
MachineInstr &MI = *--I;
if (MI.isDebugInstr())
continue;
LLVM_DEBUG(dbgs() << "Anti: ");
LLVM_DEBUG(MI.dump());
std::set<unsigned> PassthruRegs;
GetPassthruRegs(MI, PassthruRegs);
// Process the defs in MI...
PrescanInstruction(MI, Count, PassthruRegs);
// The dependence edges that represent anti- and output-
// dependencies that are candidates for breaking.
std::vector<const SDep *> Edges;
const SUnit *PathSU = MISUnitMap[&MI];
AntiDepEdges(PathSU, Edges);
// If MI is not on the critical path, then we don't rename
// registers in the CriticalPathSet.
BitVector *ExcludeRegs = nullptr;
if (&MI == CriticalPathMI) {
CriticalPathSU = CriticalPathStep(CriticalPathSU);
CriticalPathMI = (CriticalPathSU) ? CriticalPathSU->getInstr() : nullptr;
} else if (CriticalPathSet.any()) {
ExcludeRegs = &CriticalPathSet;
}
// Ignore KILL instructions (they form a group in ScanInstruction
// but don't cause any anti-dependence breaking themselves)
if (!MI.isKill()) {
// Attempt to break each anti-dependency...
for (unsigned i = 0, e = Edges.size(); i != e; ++i) {
const SDep *Edge = Edges[i];
SUnit *NextSU = Edge->getSUnit();
if ((Edge->getKind() != SDep::Anti) &&
(Edge->getKind() != SDep::Output)) continue;
unsigned AntiDepReg = Edge->getReg();
LLVM_DEBUG(dbgs() << "\tAntidep reg: " << printReg(AntiDepReg, TRI));
assert(AntiDepReg != 0 && "Anti-dependence on reg0?");
if (!MRI.isAllocatable(AntiDepReg)) {
// Don't break anti-dependencies on non-allocatable registers.
LLVM_DEBUG(dbgs() << " (non-allocatable)\n");
continue;
} else if (ExcludeRegs && ExcludeRegs->test(AntiDepReg)) {
// Don't break anti-dependencies for critical path registers
// if not on the critical path
LLVM_DEBUG(dbgs() << " (not critical-path)\n");
continue;
} else if (PassthruRegs.count(AntiDepReg) != 0) {
// If the anti-dep register liveness "passes-thru", then
// don't try to change it. It will be changed along with
// the use if required to break an earlier antidep.
LLVM_DEBUG(dbgs() << " (passthru)\n");
continue;
} else {
// No anti-dep breaking for implicit deps
MachineOperand *AntiDepOp = MI.findRegisterDefOperand(AntiDepReg);
assert(AntiDepOp && "Can't find index for defined register operand");
if (!AntiDepOp || AntiDepOp->isImplicit()) {
LLVM_DEBUG(dbgs() << " (implicit)\n");
continue;
}
// If the SUnit has other dependencies on the SUnit that
// it anti-depends on, don't bother breaking the
// anti-dependency since those edges would prevent such
// units from being scheduled past each other
// regardless.
//
// Also, if there are dependencies on other SUnits with the
// same register as the anti-dependency, don't attempt to
// break it.
for (SUnit::const_pred_iterator P = PathSU->Preds.begin(),
PE = PathSU->Preds.end(); P != PE; ++P) {
if (P->getSUnit() == NextSU ?
(P->getKind() != SDep::Anti || P->getReg() != AntiDepReg) :
(P->getKind() == SDep::Data && P->getReg() == AntiDepReg)) {
AntiDepReg = 0;
break;
}
}
for (SUnit::const_pred_iterator P = PathSU->Preds.begin(),
PE = PathSU->Preds.end(); P != PE; ++P) {
if ((P->getSUnit() == NextSU) && (P->getKind() != SDep::Anti) &&
(P->getKind() != SDep::Output)) {
LLVM_DEBUG(dbgs() << " (real dependency)\n");
AntiDepReg = 0;
break;
} else if ((P->getSUnit() != NextSU) &&
(P->getKind() == SDep::Data) &&
(P->getReg() == AntiDepReg)) {
LLVM_DEBUG(dbgs() << " (other dependency)\n");
AntiDepReg = 0;
break;
}
}
if (AntiDepReg == 0) continue;
// If the definition of the anti-dependency register does not start
// a new live range, bail out. This can happen if the anti-dep
// register is a sub-register of another register whose live range
// spans over PathSU. In such case, PathSU defines only a part of
// the larger register.
RegAliases.reset();
for (MCRegAliasIterator AI(AntiDepReg, TRI, true); AI.isValid(); ++AI)
RegAliases.set(*AI);
for (SDep S : PathSU->Succs) {
SDep::Kind K = S.getKind();
if (K != SDep::Data && K != SDep::Output && K != SDep::Anti)
continue;
unsigned R = S.getReg();
if (!RegAliases[R])
continue;
if (R == AntiDepReg || TRI->isSubRegister(AntiDepReg, R))
continue;
AntiDepReg = 0;
break;
}
if (AntiDepReg == 0) continue;
}
assert(AntiDepReg != 0);
if (AntiDepReg == 0) continue;
// Determine AntiDepReg's register group.
const unsigned GroupIndex = State->GetGroup(AntiDepReg);
if (GroupIndex == 0) {
LLVM_DEBUG(dbgs() << " (zero group)\n");
continue;
}
LLVM_DEBUG(dbgs() << '\n');
// Look for a suitable register to use to break the anti-dependence.
std::map<unsigned, unsigned> RenameMap;
if (FindSuitableFreeRegisters(GroupIndex, RenameOrder, RenameMap)) {
LLVM_DEBUG(dbgs() << "\tBreaking anti-dependence edge on "
<< printReg(AntiDepReg, TRI) << ":");
// Handle each group register...
for (std::map<unsigned, unsigned>::iterator
S = RenameMap.begin(), E = RenameMap.end(); S != E; ++S) {
unsigned CurrReg = S->first;
unsigned NewReg = S->second;
LLVM_DEBUG(dbgs() << " " << printReg(CurrReg, TRI) << "->"
<< printReg(NewReg, TRI) << "("
<< RegRefs.count(CurrReg) << " refs)");
// Update the references to the old register CurrReg to
// refer to the new register NewReg.
for (const auto &Q : make_range(RegRefs.equal_range(CurrReg))) {
Q.second.Operand->setReg(NewReg);
// If the SU for the instruction being updated has debug
// information related to the anti-dependency register, make
// sure to update that as well.
const SUnit *SU = MISUnitMap[Q.second.Operand->getParent()];
if (!SU) continue;
UpdateDbgValues(DbgValues, Q.second.Operand->getParent(),
AntiDepReg, NewReg);
}
// We just went back in time and modified history; the
// liveness information for CurrReg is now inconsistent. Set
// the state as if it were dead.
State->UnionGroups(NewReg, 0);
RegRefs.erase(NewReg);
DefIndices[NewReg] = DefIndices[CurrReg];
KillIndices[NewReg] = KillIndices[CurrReg];
State->UnionGroups(CurrReg, 0);
RegRefs.erase(CurrReg);
DefIndices[CurrReg] = KillIndices[CurrReg];
KillIndices[CurrReg] = ~0u;
assert(((KillIndices[CurrReg] == ~0u) !=
(DefIndices[CurrReg] == ~0u)) &&
"Kill and Def maps aren't consistent for AntiDepReg!");
}
++Broken;
LLVM_DEBUG(dbgs() << '\n');
}
}
}
ScanInstruction(MI, Count);
}
return Broken;
}
AntiDepBreaker *llvm::createAggressiveAntiDepBreaker(
MachineFunction &MFi, const RegisterClassInfo &RCI,
TargetSubtargetInfo::RegClassVector &CriticalPathRCs) {
return new AggressiveAntiDepBreaker(MFi, RCI, CriticalPathRCs);
}