1//===-- llvm/Target/TargetSchedule.cpp - Sched Machine Model ----*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements a wrapper around MCSchedModel that allows the interface
11// to benefit from information currently only available in TargetInstrInfo.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/CodeGen/TargetSchedule.h"
16#include "llvm/Support/CommandLine.h"
17#include "llvm/Support/raw_ostream.h"
18#include "llvm/Target/TargetInstrInfo.h"
19#include "llvm/Target/TargetRegisterInfo.h"
20#include "llvm/Target/TargetSubtargetInfo.h"
21
22using namespace llvm;
23
24static cl::opt<bool> EnableSchedModel("schedmodel", cl::Hidden, cl::init(true),
25  cl::desc("Use TargetSchedModel for latency lookup"));
26
27static cl::opt<bool> EnableSchedItins("scheditins", cl::Hidden, cl::init(true),
28  cl::desc("Use InstrItineraryData for latency lookup"));
29
30bool TargetSchedModel::hasInstrSchedModel() const {
31  return EnableSchedModel && SchedModel.hasInstrSchedModel();
32}
33
34bool TargetSchedModel::hasInstrItineraries() const {
35  return EnableSchedItins && !InstrItins.isEmpty();
36}
37
38static unsigned gcd(unsigned Dividend, unsigned Divisor) {
39  // Dividend and Divisor will be naturally swapped as needed.
40  while(Divisor) {
41    unsigned Rem = Dividend % Divisor;
42    Dividend = Divisor;
43    Divisor = Rem;
44  };
45  return Dividend;
46}
47static unsigned lcm(unsigned A, unsigned B) {
48  unsigned LCM = (uint64_t(A) * B) / gcd(A, B);
49  assert((LCM >= A && LCM >= B) && "LCM overflow");
50  return LCM;
51}
52
53void TargetSchedModel::init(const MCSchedModel &sm,
54                            const TargetSubtargetInfo *sti,
55                            const TargetInstrInfo *tii) {
56  SchedModel = sm;
57  STI = sti;
58  TII = tii;
59  STI->initInstrItins(InstrItins);
60
61  unsigned NumRes = SchedModel.getNumProcResourceKinds();
62  ResourceFactors.resize(NumRes);
63  ResourceLCM = SchedModel.IssueWidth;
64  for (unsigned Idx = 0; Idx < NumRes; ++Idx) {
65    unsigned NumUnits = SchedModel.getProcResource(Idx)->NumUnits;
66    if (NumUnits > 0)
67      ResourceLCM = lcm(ResourceLCM, NumUnits);
68  }
69  MicroOpFactor = ResourceLCM / SchedModel.IssueWidth;
70  for (unsigned Idx = 0; Idx < NumRes; ++Idx) {
71    unsigned NumUnits = SchedModel.getProcResource(Idx)->NumUnits;
72    ResourceFactors[Idx] = NumUnits ? (ResourceLCM / NumUnits) : 0;
73  }
74}
75
76unsigned TargetSchedModel::getNumMicroOps(const MachineInstr *MI,
77                                          const MCSchedClassDesc *SC) const {
78  if (hasInstrItineraries()) {
79    int UOps = InstrItins.getNumMicroOps(MI->getDesc().getSchedClass());
80    return (UOps >= 0) ? UOps : TII->getNumMicroOps(&InstrItins, MI);
81  }
82  if (hasInstrSchedModel()) {
83    if (!SC)
84      SC = resolveSchedClass(MI);
85    if (SC->isValid())
86      return SC->NumMicroOps;
87  }
88  return MI->isTransient() ? 0 : 1;
89}
90
91// The machine model may explicitly specify an invalid latency, which
92// effectively means infinite latency. Since users of the TargetSchedule API
93// don't know how to handle this, we convert it to a very large latency that is
94// easy to distinguish when debugging the DAG but won't induce overflow.
95static unsigned capLatency(int Cycles) {
96  return Cycles >= 0 ? Cycles : 1000;
97}
98
99/// Return the MCSchedClassDesc for this instruction. Some SchedClasses require
100/// evaluation of predicates that depend on instruction operands or flags.
101const MCSchedClassDesc *TargetSchedModel::
102resolveSchedClass(const MachineInstr *MI) const {
103
104  // Get the definition's scheduling class descriptor from this machine model.
105  unsigned SchedClass = MI->getDesc().getSchedClass();
106  const MCSchedClassDesc *SCDesc = SchedModel.getSchedClassDesc(SchedClass);
107  if (!SCDesc->isValid())
108    return SCDesc;
109
110#ifndef NDEBUG
111  unsigned NIter = 0;
112#endif
113  while (SCDesc->isVariant()) {
114    assert(++NIter < 6 && "Variants are nested deeper than the magic number");
115
116    SchedClass = STI->resolveSchedClass(SchedClass, MI, this);
117    SCDesc = SchedModel.getSchedClassDesc(SchedClass);
118  }
119  return SCDesc;
120}
121
122/// Find the def index of this operand. This index maps to the machine model and
123/// is independent of use operands. Def operands may be reordered with uses or
124/// merged with uses without affecting the def index (e.g. before/after
125/// regalloc). However, an instruction's def operands must never be reordered
126/// with respect to each other.
127static unsigned findDefIdx(const MachineInstr *MI, unsigned DefOperIdx) {
128  unsigned DefIdx = 0;
129  for (unsigned i = 0; i != DefOperIdx; ++i) {
130    const MachineOperand &MO = MI->getOperand(i);
131    if (MO.isReg() && MO.isDef())
132      ++DefIdx;
133  }
134  return DefIdx;
135}
136
137/// Find the use index of this operand. This is independent of the instruction's
138/// def operands.
139///
140/// Note that uses are not determined by the operand's isUse property, which
141/// is simply the inverse of isDef. Here we consider any readsReg operand to be
142/// a "use". The machine model allows an operand to be both a Def and Use.
143static unsigned findUseIdx(const MachineInstr *MI, unsigned UseOperIdx) {
144  unsigned UseIdx = 0;
145  for (unsigned i = 0; i != UseOperIdx; ++i) {
146    const MachineOperand &MO = MI->getOperand(i);
147    if (MO.isReg() && MO.readsReg())
148      ++UseIdx;
149  }
150  return UseIdx;
151}
152
153// Top-level API for clients that know the operand indices.
154unsigned TargetSchedModel::computeOperandLatency(
155  const MachineInstr *DefMI, unsigned DefOperIdx,
156  const MachineInstr *UseMI, unsigned UseOperIdx) const {
157
158  if (!hasInstrSchedModel() && !hasInstrItineraries())
159    return TII->defaultDefLatency(SchedModel, DefMI);
160
161  if (hasInstrItineraries()) {
162    int OperLatency = 0;
163    if (UseMI) {
164      OperLatency = TII->getOperandLatency(&InstrItins, DefMI, DefOperIdx,
165                                           UseMI, UseOperIdx);
166    }
167    else {
168      unsigned DefClass = DefMI->getDesc().getSchedClass();
169      OperLatency = InstrItins.getOperandCycle(DefClass, DefOperIdx);
170    }
171    if (OperLatency >= 0)
172      return OperLatency;
173
174    // No operand latency was found.
175    unsigned InstrLatency = TII->getInstrLatency(&InstrItins, DefMI);
176
177    // Expected latency is the max of the stage latency and itinerary props.
178    // Rather than directly querying InstrItins stage latency, we call a TII
179    // hook to allow subtargets to specialize latency. This hook is only
180    // applicable to the InstrItins model. InstrSchedModel should model all
181    // special cases without TII hooks.
182    InstrLatency = std::max(InstrLatency,
183                            TII->defaultDefLatency(SchedModel, DefMI));
184    return InstrLatency;
185  }
186  // hasInstrSchedModel()
187  const MCSchedClassDesc *SCDesc = resolveSchedClass(DefMI);
188  unsigned DefIdx = findDefIdx(DefMI, DefOperIdx);
189  if (DefIdx < SCDesc->NumWriteLatencyEntries) {
190    // Lookup the definition's write latency in SubtargetInfo.
191    const MCWriteLatencyEntry *WLEntry =
192      STI->getWriteLatencyEntry(SCDesc, DefIdx);
193    unsigned WriteID = WLEntry->WriteResourceID;
194    unsigned Latency = capLatency(WLEntry->Cycles);
195    if (!UseMI)
196      return Latency;
197
198    // Lookup the use's latency adjustment in SubtargetInfo.
199    const MCSchedClassDesc *UseDesc = resolveSchedClass(UseMI);
200    if (UseDesc->NumReadAdvanceEntries == 0)
201      return Latency;
202    unsigned UseIdx = findUseIdx(UseMI, UseOperIdx);
203    int Advance = STI->getReadAdvanceCycles(UseDesc, UseIdx, WriteID);
204    if (Advance > 0 && (unsigned)Advance > Latency) // unsigned wrap
205      return 0;
206    return Latency - Advance;
207  }
208  // If DefIdx does not exist in the model (e.g. implicit defs), then return
209  // unit latency (defaultDefLatency may be too conservative).
210#ifndef NDEBUG
211  if (SCDesc->isValid() && !DefMI->getOperand(DefOperIdx).isImplicit()
212      && !DefMI->getDesc().OpInfo[DefOperIdx].isOptionalDef()
213      && SchedModel.isComplete()) {
214    errs() << "DefIdx " << DefIdx << " exceeds machine model writes for "
215           << *DefMI;
216    llvm_unreachable("incomplete machine model");
217  }
218#endif
219  // FIXME: Automatically giving all implicit defs defaultDefLatency is
220  // undesirable. We should only do it for defs that are known to the MC
221  // desc like flags. Truly implicit defs should get 1 cycle latency.
222  return DefMI->isTransient() ? 0 : TII->defaultDefLatency(SchedModel, DefMI);
223}
224
225unsigned
226TargetSchedModel::computeInstrLatency(const MCSchedClassDesc &SCDesc) const {
227  unsigned Latency = 0;
228  for (unsigned DefIdx = 0, DefEnd = SCDesc.NumWriteLatencyEntries;
229       DefIdx != DefEnd; ++DefIdx) {
230    // Lookup the definition's write latency in SubtargetInfo.
231    const MCWriteLatencyEntry *WLEntry =
232      STI->getWriteLatencyEntry(&SCDesc, DefIdx);
233    Latency = std::max(Latency, capLatency(WLEntry->Cycles));
234  }
235  return Latency;
236}
237
238unsigned TargetSchedModel::computeInstrLatency(unsigned Opcode) const {
239  assert(hasInstrSchedModel() && "Only call this function with a SchedModel");
240
241  unsigned SCIdx = TII->get(Opcode).getSchedClass();
242  const MCSchedClassDesc *SCDesc = SchedModel.getSchedClassDesc(SCIdx);
243
244  if (SCDesc->isValid() && !SCDesc->isVariant())
245    return computeInstrLatency(*SCDesc);
246
247  llvm_unreachable("No MI sched latency");
248}
249
250unsigned
251TargetSchedModel::computeInstrLatency(const MachineInstr *MI,
252                                      bool UseDefaultDefLatency) const {
253  // For the itinerary model, fall back to the old subtarget hook.
254  // Allow subtargets to compute Bundle latencies outside the machine model.
255  if (hasInstrItineraries() || MI->isBundle() ||
256      (!hasInstrSchedModel() && !UseDefaultDefLatency))
257    return TII->getInstrLatency(&InstrItins, MI);
258
259  if (hasInstrSchedModel()) {
260    const MCSchedClassDesc *SCDesc = resolveSchedClass(MI);
261    if (SCDesc->isValid())
262      return computeInstrLatency(*SCDesc);
263  }
264  return TII->defaultDefLatency(SchedModel, MI);
265}
266
267unsigned TargetSchedModel::
268computeOutputLatency(const MachineInstr *DefMI, unsigned DefOperIdx,
269                     const MachineInstr *DepMI) const {
270  if (SchedModel.MicroOpBufferSize <= 1)
271    return 1;
272
273  // MicroOpBufferSize > 1 indicates an out-of-order processor that can dispatch
274  // WAW dependencies in the same cycle.
275
276  // Treat predication as a data dependency for out-of-order cpus. In-order
277  // cpus do not need to treat predicated writes specially.
278  //
279  // TODO: The following hack exists because predication passes do not
280  // correctly append imp-use operands, and readsReg() strangely returns false
281  // for predicated defs.
282  unsigned Reg = DefMI->getOperand(DefOperIdx).getReg();
283  const MachineFunction &MF = *DefMI->getParent()->getParent();
284  const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
285  if (!DepMI->readsRegister(Reg, TRI) && TII->isPredicated(DepMI))
286    return computeInstrLatency(DefMI);
287
288  // If we have a per operand scheduling model, check if this def is writing
289  // an unbuffered resource. If so, it treated like an in-order cpu.
290  if (hasInstrSchedModel()) {
291    const MCSchedClassDesc *SCDesc = resolveSchedClass(DefMI);
292    if (SCDesc->isValid()) {
293      for (const MCWriteProcResEntry *PRI = STI->getWriteProcResBegin(SCDesc),
294             *PRE = STI->getWriteProcResEnd(SCDesc); PRI != PRE; ++PRI) {
295        if (!SchedModel.getProcResource(PRI->ProcResourceIdx)->BufferSize)
296          return 1;
297      }
298    }
299  }
300  return 0;
301}
302