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For targets that have instruction itineraries this means no change. Targets that move over to the new schedule model will use be able the new schedule module for instruction latencies in the if-converter (the logic is such that if there is no itineary we will use the new sched model for the latencies). Before, we queried "TTI->getInstructionLatency()" for the instruction latency and the extra prediction cost. Now, we query the TargetSchedule abstraction for the instruction latency and TargetInstrInfo for the extra predictation cost. The TargetSchedule abstraction will internally call "TTI->getInstructionLatency" if an itinerary exists, otherwise it will use the new schedule model. ATTENTION: Out of tree targets! (I will also send out an email later to LLVMDev) This means, if your target implements unsigned getInstrLatency(const InstrItineraryData *ItinData, const MachineInstr *MI, unsigned *PredCost); and returns a value for "PredCost", you now also need to implement unsigned getPredictationCost(const MachineInstr *MI); (if your target uses the IfConversion.cpp pass) radar://15077010 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191671 91177308-0d34-0410-b5e6-96231b3b80d8
289 lines
11 KiB
C++
289 lines
11 KiB
C++
//===-- llvm/Target/TargetSchedule.cpp - Sched Machine Model ----*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements a wrapper around MCSchedModel that allows the interface
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// to benefit from information currently only available in TargetInstrInfo.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/TargetSchedule.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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#include "llvm/Target/TargetSubtargetInfo.h"
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using namespace llvm;
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static cl::opt<bool> EnableSchedModel("schedmodel", cl::Hidden, cl::init(true),
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cl::desc("Use TargetSchedModel for latency lookup"));
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static cl::opt<bool> EnableSchedItins("scheditins", cl::Hidden, cl::init(true),
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cl::desc("Use InstrItineraryData for latency lookup"));
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bool TargetSchedModel::hasInstrSchedModel() const {
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return EnableSchedModel && SchedModel.hasInstrSchedModel();
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}
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bool TargetSchedModel::hasInstrItineraries() const {
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return EnableSchedItins && !InstrItins.isEmpty();
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}
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static unsigned gcd(unsigned Dividend, unsigned Divisor) {
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// Dividend and Divisor will be naturally swapped as needed.
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while(Divisor) {
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unsigned Rem = Dividend % Divisor;
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Dividend = Divisor;
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Divisor = Rem;
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};
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return Dividend;
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}
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static unsigned lcm(unsigned A, unsigned B) {
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unsigned LCM = (uint64_t(A) * B) / gcd(A, B);
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assert((LCM >= A && LCM >= B) && "LCM overflow");
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return LCM;
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}
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void TargetSchedModel::init(const MCSchedModel &sm,
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const TargetSubtargetInfo *sti,
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const TargetInstrInfo *tii) {
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SchedModel = sm;
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STI = sti;
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TII = tii;
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STI->initInstrItins(InstrItins);
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unsigned NumRes = SchedModel.getNumProcResourceKinds();
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ResourceFactors.resize(NumRes);
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ResourceLCM = SchedModel.IssueWidth;
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for (unsigned Idx = 0; Idx < NumRes; ++Idx) {
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unsigned NumUnits = SchedModel.getProcResource(Idx)->NumUnits;
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if (NumUnits > 0)
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ResourceLCM = lcm(ResourceLCM, NumUnits);
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}
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MicroOpFactor = ResourceLCM / SchedModel.IssueWidth;
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for (unsigned Idx = 0; Idx < NumRes; ++Idx) {
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unsigned NumUnits = SchedModel.getProcResource(Idx)->NumUnits;
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ResourceFactors[Idx] = NumUnits ? (ResourceLCM / NumUnits) : 0;
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}
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}
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unsigned TargetSchedModel::getNumMicroOps(const MachineInstr *MI,
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const MCSchedClassDesc *SC) const {
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if (hasInstrItineraries()) {
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int UOps = InstrItins.getNumMicroOps(MI->getDesc().getSchedClass());
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return (UOps >= 0) ? UOps : TII->getNumMicroOps(&InstrItins, MI);
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}
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if (hasInstrSchedModel()) {
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if (!SC)
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SC = resolveSchedClass(MI);
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if (SC->isValid())
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return SC->NumMicroOps;
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}
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return MI->isTransient() ? 0 : 1;
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}
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// The machine model may explicitly specify an invalid latency, which
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// effectively means infinite latency. Since users of the TargetSchedule API
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// don't know how to handle this, we convert it to a very large latency that is
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// easy to distinguish when debugging the DAG but won't induce overflow.
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static unsigned capLatency(int Cycles) {
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return Cycles >= 0 ? Cycles : 1000;
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}
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/// Return the MCSchedClassDesc for this instruction. Some SchedClasses require
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/// evaluation of predicates that depend on instruction operands or flags.
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const MCSchedClassDesc *TargetSchedModel::
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resolveSchedClass(const MachineInstr *MI) const {
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// Get the definition's scheduling class descriptor from this machine model.
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unsigned SchedClass = MI->getDesc().getSchedClass();
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const MCSchedClassDesc *SCDesc = SchedModel.getSchedClassDesc(SchedClass);
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if (!SCDesc->isValid())
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return SCDesc;
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#ifndef NDEBUG
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unsigned NIter = 0;
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#endif
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while (SCDesc->isVariant()) {
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assert(++NIter < 6 && "Variants are nested deeper than the magic number");
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SchedClass = STI->resolveSchedClass(SchedClass, MI, this);
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SCDesc = SchedModel.getSchedClassDesc(SchedClass);
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}
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return SCDesc;
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}
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/// Find the def index of this operand. This index maps to the machine model and
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/// is independent of use operands. Def operands may be reordered with uses or
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/// merged with uses without affecting the def index (e.g. before/after
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/// regalloc). However, an instruction's def operands must never be reordered
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/// with respect to each other.
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static unsigned findDefIdx(const MachineInstr *MI, unsigned DefOperIdx) {
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unsigned DefIdx = 0;
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for (unsigned i = 0; i != DefOperIdx; ++i) {
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const MachineOperand &MO = MI->getOperand(i);
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if (MO.isReg() && MO.isDef())
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++DefIdx;
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}
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return DefIdx;
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}
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/// Find the use index of this operand. This is independent of the instruction's
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/// def operands.
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///
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/// Note that uses are not determined by the operand's isUse property, which
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/// is simply the inverse of isDef. Here we consider any readsReg operand to be
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/// a "use". The machine model allows an operand to be both a Def and Use.
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static unsigned findUseIdx(const MachineInstr *MI, unsigned UseOperIdx) {
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unsigned UseIdx = 0;
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for (unsigned i = 0; i != UseOperIdx; ++i) {
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const MachineOperand &MO = MI->getOperand(i);
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if (MO.isReg() && MO.readsReg())
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++UseIdx;
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}
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return UseIdx;
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}
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// Top-level API for clients that know the operand indices.
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unsigned TargetSchedModel::computeOperandLatency(
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const MachineInstr *DefMI, unsigned DefOperIdx,
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const MachineInstr *UseMI, unsigned UseOperIdx) const {
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if (!hasInstrSchedModel() && !hasInstrItineraries())
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return TII->defaultDefLatency(&SchedModel, DefMI);
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if (hasInstrItineraries()) {
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int OperLatency = 0;
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if (UseMI) {
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OperLatency = TII->getOperandLatency(&InstrItins, DefMI, DefOperIdx,
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UseMI, UseOperIdx);
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}
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else {
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unsigned DefClass = DefMI->getDesc().getSchedClass();
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OperLatency = InstrItins.getOperandCycle(DefClass, DefOperIdx);
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}
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if (OperLatency >= 0)
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return OperLatency;
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// No operand latency was found.
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unsigned InstrLatency = TII->getInstrLatency(&InstrItins, DefMI);
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// Expected latency is the max of the stage latency and itinerary props.
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// Rather than directly querying InstrItins stage latency, we call a TII
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// hook to allow subtargets to specialize latency. This hook is only
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// applicable to the InstrItins model. InstrSchedModel should model all
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// special cases without TII hooks.
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InstrLatency = std::max(InstrLatency,
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TII->defaultDefLatency(&SchedModel, DefMI));
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return InstrLatency;
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}
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// hasInstrSchedModel()
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const MCSchedClassDesc *SCDesc = resolveSchedClass(DefMI);
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unsigned DefIdx = findDefIdx(DefMI, DefOperIdx);
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if (DefIdx < SCDesc->NumWriteLatencyEntries) {
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// Lookup the definition's write latency in SubtargetInfo.
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const MCWriteLatencyEntry *WLEntry =
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STI->getWriteLatencyEntry(SCDesc, DefIdx);
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unsigned WriteID = WLEntry->WriteResourceID;
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unsigned Latency = capLatency(WLEntry->Cycles);
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if (!UseMI)
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return Latency;
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// Lookup the use's latency adjustment in SubtargetInfo.
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const MCSchedClassDesc *UseDesc = resolveSchedClass(UseMI);
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if (UseDesc->NumReadAdvanceEntries == 0)
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return Latency;
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unsigned UseIdx = findUseIdx(UseMI, UseOperIdx);
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int Advance = STI->getReadAdvanceCycles(UseDesc, UseIdx, WriteID);
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if (Advance > 0 && (unsigned)Advance > Latency) // unsigned wrap
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return 0;
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return Latency - Advance;
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}
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// If DefIdx does not exist in the model (e.g. implicit defs), then return
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// unit latency (defaultDefLatency may be too conservative).
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#ifndef NDEBUG
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if (SCDesc->isValid() && !DefMI->getOperand(DefOperIdx).isImplicit()
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&& !DefMI->getDesc().OpInfo[DefOperIdx].isOptionalDef()
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&& SchedModel.isComplete()) {
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std::string Err;
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raw_string_ostream ss(Err);
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ss << "DefIdx " << DefIdx << " exceeds machine model writes for "
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<< *DefMI;
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report_fatal_error(ss.str());
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}
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#endif
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// FIXME: Automatically giving all implicit defs defaultDefLatency is
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// undesirable. We should only do it for defs that are known to the MC
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// desc like flags. Truly implicit defs should get 1 cycle latency.
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return DefMI->isTransient() ? 0 : TII->defaultDefLatency(&SchedModel, DefMI);
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}
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unsigned
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TargetSchedModel::computeInstrLatency(const MachineInstr *MI,
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bool UseDefaultDefLatency) const {
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// For the itinerary model, fall back to the old subtarget hook.
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// Allow subtargets to compute Bundle latencies outside the machine model.
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if (hasInstrItineraries() || MI->isBundle() ||
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(!hasInstrSchedModel() && !UseDefaultDefLatency))
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return TII->getInstrLatency(&InstrItins, MI);
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if (hasInstrSchedModel()) {
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const MCSchedClassDesc *SCDesc = resolveSchedClass(MI);
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if (SCDesc->isValid()) {
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unsigned Latency = 0;
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for (unsigned DefIdx = 0, DefEnd = SCDesc->NumWriteLatencyEntries;
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DefIdx != DefEnd; ++DefIdx) {
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// Lookup the definition's write latency in SubtargetInfo.
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const MCWriteLatencyEntry *WLEntry =
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STI->getWriteLatencyEntry(SCDesc, DefIdx);
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Latency = std::max(Latency, capLatency(WLEntry->Cycles));
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}
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return Latency;
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}
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}
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return TII->defaultDefLatency(&SchedModel, MI);
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}
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unsigned TargetSchedModel::
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computeOutputLatency(const MachineInstr *DefMI, unsigned DefOperIdx,
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const MachineInstr *DepMI) const {
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if (SchedModel.MicroOpBufferSize <= 1)
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return 1;
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// MicroOpBufferSize > 1 indicates an out-of-order processor that can dispatch
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// WAW dependencies in the same cycle.
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// Treat predication as a data dependency for out-of-order cpus. In-order
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// cpus do not need to treat predicated writes specially.
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//
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// TODO: The following hack exists because predication passes do not
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// correctly append imp-use operands, and readsReg() strangely returns false
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// for predicated defs.
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unsigned Reg = DefMI->getOperand(DefOperIdx).getReg();
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const MachineFunction &MF = *DefMI->getParent()->getParent();
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const TargetRegisterInfo *TRI = MF.getTarget().getRegisterInfo();
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if (!DepMI->readsRegister(Reg, TRI) && TII->isPredicated(DepMI))
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return computeInstrLatency(DefMI);
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// If we have a per operand scheduling model, check if this def is writing
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// an unbuffered resource. If so, it treated like an in-order cpu.
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if (hasInstrSchedModel()) {
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const MCSchedClassDesc *SCDesc = resolveSchedClass(DefMI);
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if (SCDesc->isValid()) {
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for (const MCWriteProcResEntry *PRI = STI->getWriteProcResBegin(SCDesc),
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*PRE = STI->getWriteProcResEnd(SCDesc); PRI != PRE; ++PRI) {
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if (!SchedModel.getProcResource(PRI->ProcResourceIdx)->BufferSize)
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return 1;
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}
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}
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}
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return 0;
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}
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