llvm-project/llvm/lib/CodeGen/TargetSchedule.cpp

334 lines
12 KiB
C++

//===- llvm/Target/TargetSchedule.cpp - Sched Machine Model ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements a wrapper around MCSchedModel that allows the interface
// to benefit from information currently only available in TargetInstrInfo.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/TargetSchedule.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/MC/MCInstrItineraries.h"
#include "llvm/MC/MCSchedule.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
using namespace llvm;
static cl::opt<bool> EnableSchedModel("schedmodel", cl::Hidden, cl::init(true),
cl::desc("Use TargetSchedModel for latency lookup"));
static cl::opt<bool> EnableSchedItins("scheditins", cl::Hidden, cl::init(true),
cl::desc("Use InstrItineraryData for latency lookup"));
bool TargetSchedModel::hasInstrSchedModel() const {
return EnableSchedModel && SchedModel.hasInstrSchedModel();
}
bool TargetSchedModel::hasInstrItineraries() const {
return EnableSchedItins && !InstrItins.isEmpty();
}
static unsigned gcd(unsigned Dividend, unsigned Divisor) {
// Dividend and Divisor will be naturally swapped as needed.
while (Divisor) {
unsigned Rem = Dividend % Divisor;
Dividend = Divisor;
Divisor = Rem;
};
return Dividend;
}
static unsigned lcm(unsigned A, unsigned B) {
unsigned LCM = (uint64_t(A) * B) / gcd(A, B);
assert((LCM >= A && LCM >= B) && "LCM overflow");
return LCM;
}
void TargetSchedModel::init(const MCSchedModel &sm,
const TargetSubtargetInfo *sti,
const TargetInstrInfo *tii) {
SchedModel = sm;
STI = sti;
TII = tii;
STI->initInstrItins(InstrItins);
unsigned NumRes = SchedModel.getNumProcResourceKinds();
ResourceFactors.resize(NumRes);
ResourceLCM = SchedModel.IssueWidth;
for (unsigned Idx = 0; Idx < NumRes; ++Idx) {
unsigned NumUnits = SchedModel.getProcResource(Idx)->NumUnits;
if (NumUnits > 0)
ResourceLCM = lcm(ResourceLCM, NumUnits);
}
MicroOpFactor = ResourceLCM / SchedModel.IssueWidth;
for (unsigned Idx = 0; Idx < NumRes; ++Idx) {
unsigned NumUnits = SchedModel.getProcResource(Idx)->NumUnits;
ResourceFactors[Idx] = NumUnits ? (ResourceLCM / NumUnits) : 0;
}
}
/// Returns true only if instruction is specified as single issue.
bool TargetSchedModel::mustBeginGroup(const MachineInstr *MI,
const MCSchedClassDesc *SC) const {
if (hasInstrSchedModel()) {
if (!SC)
SC = resolveSchedClass(MI);
if (SC->isValid())
return SC->BeginGroup;
}
return false;
}
bool TargetSchedModel::mustEndGroup(const MachineInstr *MI,
const MCSchedClassDesc *SC) const {
if (hasInstrSchedModel()) {
if (!SC)
SC = resolveSchedClass(MI);
if (SC->isValid())
return SC->EndGroup;
}
return false;
}
unsigned TargetSchedModel::getNumMicroOps(const MachineInstr *MI,
const MCSchedClassDesc *SC) const {
if (hasInstrItineraries()) {
int UOps = InstrItins.getNumMicroOps(MI->getDesc().getSchedClass());
return (UOps >= 0) ? UOps : TII->getNumMicroOps(&InstrItins, *MI);
}
if (hasInstrSchedModel()) {
if (!SC)
SC = resolveSchedClass(MI);
if (SC->isValid())
return SC->NumMicroOps;
}
return MI->isTransient() ? 0 : 1;
}
// The machine model may explicitly specify an invalid latency, which
// effectively means infinite latency. Since users of the TargetSchedule API
// don't know how to handle this, we convert it to a very large latency that is
// easy to distinguish when debugging the DAG but won't induce overflow.
static unsigned capLatency(int Cycles) {
return Cycles >= 0 ? Cycles : 1000;
}
/// Return the MCSchedClassDesc for this instruction. Some SchedClasses require
/// evaluation of predicates that depend on instruction operands or flags.
const MCSchedClassDesc *TargetSchedModel::
resolveSchedClass(const MachineInstr *MI) const {
// Get the definition's scheduling class descriptor from this machine model.
unsigned SchedClass = MI->getDesc().getSchedClass();
const MCSchedClassDesc *SCDesc = SchedModel.getSchedClassDesc(SchedClass);
if (!SCDesc->isValid())
return SCDesc;
#ifndef NDEBUG
unsigned NIter = 0;
#endif
while (SCDesc->isVariant()) {
assert(++NIter < 6 && "Variants are nested deeper than the magic number");
SchedClass = STI->resolveSchedClass(SchedClass, MI, this);
SCDesc = SchedModel.getSchedClassDesc(SchedClass);
}
return SCDesc;
}
/// Find the def index of this operand. This index maps to the machine model and
/// is independent of use operands. Def operands may be reordered with uses or
/// merged with uses without affecting the def index (e.g. before/after
/// regalloc). However, an instruction's def operands must never be reordered
/// with respect to each other.
static unsigned findDefIdx(const MachineInstr *MI, unsigned DefOperIdx) {
unsigned DefIdx = 0;
for (unsigned i = 0; i != DefOperIdx; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isDef())
++DefIdx;
}
return DefIdx;
}
/// Find the use index of this operand. This is independent of the instruction's
/// def operands.
///
/// Note that uses are not determined by the operand's isUse property, which
/// is simply the inverse of isDef. Here we consider any readsReg operand to be
/// a "use". The machine model allows an operand to be both a Def and Use.
static unsigned findUseIdx(const MachineInstr *MI, unsigned UseOperIdx) {
unsigned UseIdx = 0;
for (unsigned i = 0; i != UseOperIdx; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.readsReg() && !MO.isDef())
++UseIdx;
}
return UseIdx;
}
// Top-level API for clients that know the operand indices.
unsigned TargetSchedModel::computeOperandLatency(
const MachineInstr *DefMI, unsigned DefOperIdx,
const MachineInstr *UseMI, unsigned UseOperIdx) const {
if (!hasInstrSchedModel() && !hasInstrItineraries())
return TII->defaultDefLatency(SchedModel, *DefMI);
if (hasInstrItineraries()) {
int OperLatency = 0;
if (UseMI) {
OperLatency = TII->getOperandLatency(&InstrItins, *DefMI, DefOperIdx,
*UseMI, UseOperIdx);
}
else {
unsigned DefClass = DefMI->getDesc().getSchedClass();
OperLatency = InstrItins.getOperandCycle(DefClass, DefOperIdx);
}
if (OperLatency >= 0)
return OperLatency;
// No operand latency was found.
unsigned InstrLatency = TII->getInstrLatency(&InstrItins, *DefMI);
// Expected latency is the max of the stage latency and itinerary props.
// Rather than directly querying InstrItins stage latency, we call a TII
// hook to allow subtargets to specialize latency. This hook is only
// applicable to the InstrItins model. InstrSchedModel should model all
// special cases without TII hooks.
InstrLatency =
std::max(InstrLatency, TII->defaultDefLatency(SchedModel, *DefMI));
return InstrLatency;
}
// hasInstrSchedModel()
const MCSchedClassDesc *SCDesc = resolveSchedClass(DefMI);
unsigned DefIdx = findDefIdx(DefMI, DefOperIdx);
if (DefIdx < SCDesc->NumWriteLatencyEntries) {
// Lookup the definition's write latency in SubtargetInfo.
const MCWriteLatencyEntry *WLEntry =
STI->getWriteLatencyEntry(SCDesc, DefIdx);
unsigned WriteID = WLEntry->WriteResourceID;
unsigned Latency = capLatency(WLEntry->Cycles);
if (!UseMI)
return Latency;
// Lookup the use's latency adjustment in SubtargetInfo.
const MCSchedClassDesc *UseDesc = resolveSchedClass(UseMI);
if (UseDesc->NumReadAdvanceEntries == 0)
return Latency;
unsigned UseIdx = findUseIdx(UseMI, UseOperIdx);
int Advance = STI->getReadAdvanceCycles(UseDesc, UseIdx, WriteID);
if (Advance > 0 && (unsigned)Advance > Latency) // unsigned wrap
return 0;
return Latency - Advance;
}
// If DefIdx does not exist in the model (e.g. implicit defs), then return
// unit latency (defaultDefLatency may be too conservative).
#ifndef NDEBUG
if (SCDesc->isValid() && !DefMI->getOperand(DefOperIdx).isImplicit()
&& !DefMI->getDesc().OpInfo[DefOperIdx].isOptionalDef()
&& SchedModel.isComplete()) {
errs() << "DefIdx " << DefIdx << " exceeds machine model writes for "
<< *DefMI << " (Try with MCSchedModel.CompleteModel set to false)";
llvm_unreachable("incomplete machine model");
}
#endif
// FIXME: Automatically giving all implicit defs defaultDefLatency is
// undesirable. We should only do it for defs that are known to the MC
// desc like flags. Truly implicit defs should get 1 cycle latency.
return DefMI->isTransient() ? 0 : TII->defaultDefLatency(SchedModel, *DefMI);
}
unsigned
TargetSchedModel::computeInstrLatency(const MCSchedClassDesc &SCDesc) const {
unsigned Latency = 0;
for (unsigned DefIdx = 0, DefEnd = SCDesc.NumWriteLatencyEntries;
DefIdx != DefEnd; ++DefIdx) {
// Lookup the definition's write latency in SubtargetInfo.
const MCWriteLatencyEntry *WLEntry =
STI->getWriteLatencyEntry(&SCDesc, DefIdx);
Latency = std::max(Latency, capLatency(WLEntry->Cycles));
}
return Latency;
}
unsigned TargetSchedModel::computeInstrLatency(unsigned Opcode) const {
assert(hasInstrSchedModel() && "Only call this function with a SchedModel");
unsigned SCIdx = TII->get(Opcode).getSchedClass();
const MCSchedClassDesc *SCDesc = SchedModel.getSchedClassDesc(SCIdx);
if (SCDesc->isValid() && !SCDesc->isVariant())
return computeInstrLatency(*SCDesc);
llvm_unreachable("No MI sched latency");
}
unsigned
TargetSchedModel::computeInstrLatency(const MachineInstr *MI,
bool UseDefaultDefLatency) const {
// For the itinerary model, fall back to the old subtarget hook.
// Allow subtargets to compute Bundle latencies outside the machine model.
if (hasInstrItineraries() || MI->isBundle() ||
(!hasInstrSchedModel() && !UseDefaultDefLatency))
return TII->getInstrLatency(&InstrItins, *MI);
if (hasInstrSchedModel()) {
const MCSchedClassDesc *SCDesc = resolveSchedClass(MI);
if (SCDesc->isValid())
return computeInstrLatency(*SCDesc);
}
return TII->defaultDefLatency(SchedModel, *MI);
}
unsigned TargetSchedModel::
computeOutputLatency(const MachineInstr *DefMI, unsigned DefOperIdx,
const MachineInstr *DepMI) const {
if (!SchedModel.isOutOfOrder())
return 1;
// Out-of-order processor can dispatch WAW dependencies in the same cycle.
// Treat predication as a data dependency for out-of-order cpus. In-order
// cpus do not need to treat predicated writes specially.
//
// TODO: The following hack exists because predication passes do not
// correctly append imp-use operands, and readsReg() strangely returns false
// for predicated defs.
unsigned Reg = DefMI->getOperand(DefOperIdx).getReg();
const MachineFunction &MF = *DefMI->getParent()->getParent();
const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
if (!DepMI->readsRegister(Reg, TRI) && TII->isPredicated(*DepMI))
return computeInstrLatency(DefMI);
// If we have a per operand scheduling model, check if this def is writing
// an unbuffered resource. If so, it treated like an in-order cpu.
if (hasInstrSchedModel()) {
const MCSchedClassDesc *SCDesc = resolveSchedClass(DefMI);
if (SCDesc->isValid()) {
for (const MCWriteProcResEntry *PRI = STI->getWriteProcResBegin(SCDesc),
*PRE = STI->getWriteProcResEnd(SCDesc); PRI != PRE; ++PRI) {
if (!SchedModel.getProcResource(PRI->ProcResourceIdx)->BufferSize)
return 1;
}
}
}
return 0;
}