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dd9dff5d77
Expose the processor resources defined by the machine model to the scheduler and other clients through the TargetSchedule interface. Normalize each resource count with respect to other kinds of resources. This allows scheduling heuristics to balance resources against other kinds of resources and latency. llvm-svn: 167444
307 lines
11 KiB
C++
307 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/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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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/raw_ostream.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 convertLatency(int Cycles) {
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return Cycles >= 0 ? Cycles : 1000;
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}
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/// If we can determine the operand latency from the def only, without machine
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/// model or itinerary lookup, do so. Otherwise return -1.
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int TargetSchedModel::getDefLatency(const MachineInstr *DefMI,
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bool FindMin) const {
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// Return a latency based on the itinerary properties and defining instruction
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// if possible. Some common subtargets don't require per-operand latency,
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// especially for minimum latencies.
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if (FindMin) {
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// If MinLatency is invalid, then use the itinerary for MinLatency. If no
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// itinerary exists either, then use single cycle latency.
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if (SchedModel.MinLatency < 0 && !hasInstrItineraries()) {
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return 1;
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}
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return SchedModel.MinLatency;
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}
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else if (!hasInstrSchedModel() && !hasInstrItineraries()) {
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return TII->defaultDefLatency(&SchedModel, DefMI);
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}
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// ...operand lookup required
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return -1;
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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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#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,
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bool FindMin) const {
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int DefLatency = getDefLatency(DefMI, FindMin);
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if (DefLatency >= 0)
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return DefLatency;
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if (hasInstrItineraries()) {
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int OperLatency = 0;
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if (UseMI) {
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OperLatency =
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TII->getOperandLatency(&InstrItins, DefMI, DefOperIdx, 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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if (!FindMin)
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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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assert(!FindMin && hasInstrSchedModel() &&
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"Expected a SchedModel for this cpu");
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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 = convertLatency(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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return Latency - STI->getReadAdvanceCycles(UseDesc, UseIdx, WriteID);
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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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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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return DefMI->isTransient() ? 0 : 1;
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}
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unsigned TargetSchedModel::computeInstrLatency(const MachineInstr *MI) 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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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, convertLatency(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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// MinLatency == -1 is for in-order processors that always have unit
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// MinLatency. MinLatency > 0 is for in-order processors with varying min
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// latencies, but since this is not a RAW dep, we always use unit latency.
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if (SchedModel.MinLatency != 0)
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return 1;
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// MinLatency == 0 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)->IsBuffered)
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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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