1//=-- SystemZHazardRecognizer.h - SystemZ Hazard Recognizer -----*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file defines a hazard recognizer for the SystemZ scheduler.
10//
11// This class is used by the SystemZ scheduling strategy to maintain
12// the state during scheduling, and provide cost functions for
13// scheduling candidates. This includes:
14//
15// * Decoder grouping. A decoder group can maximally hold 3 uops, and
16// instructions that always begin a new group should be scheduled when
17// the current decoder group is empty.
18// * Processor resources usage. It is beneficial to balance the use of
19// resources.
20//
21// A goal is to consider all instructions, also those outside of any
22// scheduling region. Such instructions are "advanced" past and include
23// single instructions before a scheduling region, branches etc.
24//
25// A block that has only one predecessor continues scheduling with the state
26// of it (which may be updated by emitting branches).
27//
28// ===---------------------------------------------------------------------===//
29
30#include "SystemZHazardRecognizer.h"
31#include "llvm/ADT/Statistic.h"
32
33using namespace llvm;
34
35#define DEBUG_TYPE "machine-scheduler"
36
37// This is the limit of processor resource usage at which the
38// scheduler should try to look for other instructions (not using the
39// critical resource).
40static cl::opt<int> ProcResCostLim("procres-cost-lim", cl::Hidden,
41                                   cl::desc("The OOO window for processor "
42                                            "resources during scheduling."),
43                                   cl::init(8));
44
45unsigned SystemZHazardRecognizer::
46getNumDecoderSlots(SUnit *SU) const {
47  const MCSchedClassDesc *SC = getSchedClass(SU);
48  if (!SC->isValid())
49    return 0; // IMPLICIT_DEF / KILL -- will not make impact in output.
50
51  assert((SC->NumMicroOps != 2 || (SC->BeginGroup && !SC->EndGroup)) &&
52         "Only cracked instruction can have 2 uops.");
53  assert((SC->NumMicroOps < 3 || (SC->BeginGroup && SC->EndGroup)) &&
54         "Expanded instructions always group alone.");
55  assert((SC->NumMicroOps < 3 || (SC->NumMicroOps % 3 == 0)) &&
56         "Expanded instructions fill the group(s).");
57
58  return SC->NumMicroOps;
59}
60
61unsigned SystemZHazardRecognizer::getCurrCycleIdx(SUnit *SU) const {
62  unsigned Idx = CurrGroupSize;
63  if (GrpCount % 2)
64    Idx += 3;
65
66  if (SU != nullptr && !fitsIntoCurrentGroup(SU)) {
67    if (Idx == 1 || Idx == 2)
68      Idx = 3;
69    else if (Idx == 4 || Idx == 5)
70      Idx = 0;
71  }
72
73  return Idx;
74}
75
76ScheduleHazardRecognizer::HazardType SystemZHazardRecognizer::
77getHazardType(SUnit *SU, int Stalls) {
78  return (fitsIntoCurrentGroup(SU) ? NoHazard : Hazard);
79}
80
81void SystemZHazardRecognizer::Reset() {
82  CurrGroupSize = 0;
83  CurrGroupHas4RegOps = false;
84  clearProcResCounters();
85  GrpCount = 0;
86  LastFPdOpCycleIdx = UINT_MAX;
87  LastEmittedMI = nullptr;
88  LLVM_DEBUG(CurGroupDbg = "";);
89}
90
91bool
92SystemZHazardRecognizer::fitsIntoCurrentGroup(SUnit *SU) const {
93  const MCSchedClassDesc *SC = getSchedClass(SU);
94  if (!SC->isValid())
95    return true;
96
97  // A cracked instruction only fits into schedule if the current
98  // group is empty.
99  if (SC->BeginGroup)
100    return (CurrGroupSize == 0);
101
102  // An instruction with 4 register operands will not fit in last slot.
103  assert ((CurrGroupSize < 2 || !CurrGroupHas4RegOps) &&
104          "Current decoder group is already full!");
105  if (CurrGroupSize == 2 && has4RegOps(SU->getInstr()))
106    return false;
107
108  // Since a full group is handled immediately in EmitInstruction(),
109  // SU should fit into current group. NumSlots should be 1 or 0,
110  // since it is not a cracked or expanded instruction.
111  assert ((getNumDecoderSlots(SU) <= 1) && (CurrGroupSize < 3) &&
112          "Expected normal instruction to fit in non-full group!");
113
114  return true;
115}
116
117bool SystemZHazardRecognizer::has4RegOps(const MachineInstr *MI) const {
118  const MachineFunction &MF = *MI->getParent()->getParent();
119  const TargetRegisterInfo *TRI = &TII->getRegisterInfo();
120  const MCInstrDesc &MID = MI->getDesc();
121  unsigned Count = 0;
122  for (unsigned OpIdx = 0; OpIdx < MID.getNumOperands(); OpIdx++) {
123    const TargetRegisterClass *RC = TII->getRegClass(MID, OpIdx, TRI, MF);
124    if (RC == nullptr)
125      continue;
126    if (OpIdx >= MID.getNumDefs() &&
127        MID.getOperandConstraint(OpIdx, MCOI::TIED_TO) != -1)
128      continue;
129    Count++;
130  }
131  return Count >= 4;
132}
133
134void SystemZHazardRecognizer::nextGroup() {
135  if (CurrGroupSize == 0)
136    return;
137
138  LLVM_DEBUG(dumpCurrGroup("Completed decode group"));
139  LLVM_DEBUG(CurGroupDbg = "";);
140
141  int NumGroups = ((CurrGroupSize > 3) ? (CurrGroupSize / 3) : 1);
142  assert((CurrGroupSize <= 3 || CurrGroupSize % 3 == 0) &&
143         "Current decoder group bad.");
144
145  // Reset counter for next group.
146  CurrGroupSize = 0;
147  CurrGroupHas4RegOps = false;
148
149  GrpCount += ((unsigned) NumGroups);
150
151  // Decrease counters for execution units.
152  for (unsigned i = 0; i < SchedModel->getNumProcResourceKinds(); ++i)
153    ProcResourceCounters[i] = ((ProcResourceCounters[i] > NumGroups)
154                                   ? (ProcResourceCounters[i] - NumGroups)
155                                   : 0);
156
157  // Clear CriticalResourceIdx if it is now below the threshold.
158  if (CriticalResourceIdx != UINT_MAX &&
159      (ProcResourceCounters[CriticalResourceIdx] <=
160       ProcResCostLim))
161    CriticalResourceIdx = UINT_MAX;
162
163  LLVM_DEBUG(dumpState(););
164}
165
166#ifndef NDEBUG // Debug output
167void SystemZHazardRecognizer::dumpSU(SUnit *SU, raw_ostream &OS) const {
168  OS << "SU(" << SU->NodeNum << "):";
169  OS << TII->getName(SU->getInstr()->getOpcode());
170
171  const MCSchedClassDesc *SC = getSchedClass(SU);
172  if (!SC->isValid())
173    return;
174
175  for (TargetSchedModel::ProcResIter
176         PI = SchedModel->getWriteProcResBegin(SC),
177         PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI) {
178    const MCProcResourceDesc &PRD =
179      *SchedModel->getProcResource(PI->ProcResourceIdx);
180    std::string FU(PRD.Name);
181    // trim e.g. Z13_FXaUnit -> FXa
182    FU = FU.substr(FU.find('_') + 1);
183    size_t Pos = FU.find("Unit");
184    if (Pos != std::string::npos)
185      FU.resize(Pos);
186    if (FU == "LS") // LSUnit -> LSU
187      FU = "LSU";
188    OS << "/" << FU;
189
190    if (PI->ReleaseAtCycle> 1)
191      OS << "(" << PI->ReleaseAtCycle << "cyc)";
192  }
193
194  if (SC->NumMicroOps > 1)
195    OS << "/" << SC->NumMicroOps << "uops";
196  if (SC->BeginGroup && SC->EndGroup)
197    OS << "/GroupsAlone";
198  else if (SC->BeginGroup)
199    OS << "/BeginsGroup";
200  else if (SC->EndGroup)
201    OS << "/EndsGroup";
202  if (SU->isUnbuffered)
203    OS << "/Unbuffered";
204  if (has4RegOps(SU->getInstr()))
205    OS << "/4RegOps";
206}
207
208void SystemZHazardRecognizer::dumpCurrGroup(std::string Msg) const {
209  dbgs() << "++ " << Msg;
210  dbgs() << ": ";
211
212  if (CurGroupDbg.empty())
213    dbgs() << " <empty>\n";
214  else {
215    dbgs() << "{ " << CurGroupDbg << " }";
216    dbgs() << " (" << CurrGroupSize << " decoder slot"
217           << (CurrGroupSize > 1 ? "s":"")
218           << (CurrGroupHas4RegOps ? ", 4RegOps" : "")
219           << ")\n";
220  }
221}
222
223void SystemZHazardRecognizer::dumpProcResourceCounters() const {
224  bool any = false;
225
226  for (unsigned i = 0; i < SchedModel->getNumProcResourceKinds(); ++i)
227    if (ProcResourceCounters[i] > 0) {
228      any = true;
229      break;
230    }
231
232  if (!any)
233    return;
234
235  dbgs() << "++ | Resource counters: ";
236  for (unsigned i = 0; i < SchedModel->getNumProcResourceKinds(); ++i)
237    if (ProcResourceCounters[i] > 0)
238      dbgs() << SchedModel->getProcResource(i)->Name
239             << ":" << ProcResourceCounters[i] << " ";
240  dbgs() << "\n";
241
242  if (CriticalResourceIdx != UINT_MAX)
243    dbgs() << "++ | Critical resource: "
244           << SchedModel->getProcResource(CriticalResourceIdx)->Name
245           << "\n";
246}
247
248void SystemZHazardRecognizer::dumpState() const {
249  dumpCurrGroup("| Current decoder group");
250  dbgs() << "++ | Current cycle index: "
251         << getCurrCycleIdx() << "\n";
252  dumpProcResourceCounters();
253  if (LastFPdOpCycleIdx != UINT_MAX)
254    dbgs() << "++ | Last FPd cycle index: " << LastFPdOpCycleIdx << "\n";
255}
256
257#endif //NDEBUG
258
259void SystemZHazardRecognizer::clearProcResCounters() {
260  ProcResourceCounters.assign(SchedModel->getNumProcResourceKinds(), 0);
261  CriticalResourceIdx = UINT_MAX;
262}
263
264static inline bool isBranchRetTrap(MachineInstr *MI) {
265  return (MI->isBranch() || MI->isReturn() ||
266          MI->getOpcode() == SystemZ::CondTrap);
267}
268
269// Update state with SU as the next scheduled unit.
270void SystemZHazardRecognizer::
271EmitInstruction(SUnit *SU) {
272  const MCSchedClassDesc *SC = getSchedClass(SU);
273  LLVM_DEBUG(dbgs() << "++ HazardRecognizer emitting "; dumpSU(SU, dbgs());
274             dbgs() << "\n";);
275  LLVM_DEBUG(dumpCurrGroup("Decode group before emission"););
276
277  // If scheduling an SU that must begin a new decoder group, move on
278  // to next group.
279  if (!fitsIntoCurrentGroup(SU))
280    nextGroup();
281
282  LLVM_DEBUG(raw_string_ostream cgd(CurGroupDbg);
283             if (CurGroupDbg.length()) cgd << ", "; dumpSU(SU, cgd););
284
285  LastEmittedMI = SU->getInstr();
286
287  // After returning from a call, we don't know much about the state.
288  if (SU->isCall) {
289    LLVM_DEBUG(dbgs() << "++ Clearing state after call.\n";);
290    Reset();
291    LastEmittedMI = SU->getInstr();
292    return;
293  }
294
295  // Increase counter for execution unit(s).
296  for (TargetSchedModel::ProcResIter
297         PI = SchedModel->getWriteProcResBegin(SC),
298         PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI) {
299    // Don't handle FPd together with the other resources.
300    if (SchedModel->getProcResource(PI->ProcResourceIdx)->BufferSize == 1)
301      continue;
302    int &CurrCounter =
303      ProcResourceCounters[PI->ProcResourceIdx];
304    CurrCounter += PI->ReleaseAtCycle;
305    // Check if this is now the new critical resource.
306    if ((CurrCounter > ProcResCostLim) &&
307        (CriticalResourceIdx == UINT_MAX ||
308         (PI->ProcResourceIdx != CriticalResourceIdx &&
309          CurrCounter >
310          ProcResourceCounters[CriticalResourceIdx]))) {
311      LLVM_DEBUG(
312          dbgs() << "++ New critical resource: "
313                 << SchedModel->getProcResource(PI->ProcResourceIdx)->Name
314                 << "\n";);
315      CriticalResourceIdx = PI->ProcResourceIdx;
316    }
317  }
318
319  // Make note of an instruction that uses a blocking resource (FPd).
320  if (SU->isUnbuffered) {
321    LastFPdOpCycleIdx = getCurrCycleIdx(SU);
322    LLVM_DEBUG(dbgs() << "++ Last FPd cycle index: " << LastFPdOpCycleIdx
323                      << "\n";);
324  }
325
326  // Insert SU into current group by increasing number of slots used
327  // in current group.
328  CurrGroupSize += getNumDecoderSlots(SU);
329  CurrGroupHas4RegOps |= has4RegOps(SU->getInstr());
330  unsigned GroupLim = (CurrGroupHas4RegOps ? 2 : 3);
331  assert((CurrGroupSize <= GroupLim || CurrGroupSize == getNumDecoderSlots(SU))
332         && "SU does not fit into decoder group!");
333
334  // Check if current group is now full/ended. If so, move on to next
335  // group to be ready to evaluate more candidates.
336  if (CurrGroupSize >= GroupLim || SC->EndGroup)
337    nextGroup();
338}
339
340int SystemZHazardRecognizer::groupingCost(SUnit *SU) const {
341  const MCSchedClassDesc *SC = getSchedClass(SU);
342  if (!SC->isValid())
343    return 0;
344
345  // If SU begins new group, it can either break a current group early
346  // or fit naturally if current group is empty (negative cost).
347  if (SC->BeginGroup) {
348    if (CurrGroupSize)
349      return 3 - CurrGroupSize;
350    return -1;
351  }
352
353  // Similarly, a group-ending SU may either fit well (last in group), or
354  // end the group prematurely.
355  if (SC->EndGroup) {
356    unsigned resultingGroupSize =
357      (CurrGroupSize + getNumDecoderSlots(SU));
358    if (resultingGroupSize < 3)
359      return (3 - resultingGroupSize);
360    return -1;
361  }
362
363  // An instruction with 4 register operands will not fit in last slot.
364  if (CurrGroupSize == 2 && has4RegOps(SU->getInstr()))
365    return 1;
366
367  // Most instructions can be placed in any decoder slot.
368  return 0;
369}
370
371bool SystemZHazardRecognizer::isFPdOpPreferred_distance(SUnit *SU) const {
372  assert (SU->isUnbuffered);
373  // If this is the first FPd op, it should be scheduled high.
374  if (LastFPdOpCycleIdx == UINT_MAX)
375    return true;
376  // If this is not the first PFd op, it should go into the other side
377  // of the processor to use the other FPd unit there. This should
378  // generally happen if two FPd ops are placed with 2 other
379  // instructions between them (modulo 6).
380  unsigned SUCycleIdx = getCurrCycleIdx(SU);
381  if (LastFPdOpCycleIdx > SUCycleIdx)
382    return ((LastFPdOpCycleIdx - SUCycleIdx) == 3);
383  return ((SUCycleIdx - LastFPdOpCycleIdx) == 3);
384}
385
386int SystemZHazardRecognizer::
387resourcesCost(SUnit *SU) {
388  int Cost = 0;
389
390  const MCSchedClassDesc *SC = getSchedClass(SU);
391  if (!SC->isValid())
392    return 0;
393
394  // For a FPd op, either return min or max value as indicated by the
395  // distance to any prior FPd op.
396  if (SU->isUnbuffered)
397    Cost = (isFPdOpPreferred_distance(SU) ? INT_MIN : INT_MAX);
398  // For other instructions, give a cost to the use of the critical resource.
399  else if (CriticalResourceIdx != UINT_MAX) {
400    for (TargetSchedModel::ProcResIter
401           PI = SchedModel->getWriteProcResBegin(SC),
402           PE = SchedModel->getWriteProcResEnd(SC); PI != PE; ++PI)
403      if (PI->ProcResourceIdx == CriticalResourceIdx)
404        Cost = PI->ReleaseAtCycle;
405  }
406
407  return Cost;
408}
409
410void SystemZHazardRecognizer::emitInstruction(MachineInstr *MI,
411                                              bool TakenBranch) {
412  // Make a temporary SUnit.
413  SUnit SU(MI, 0);
414
415  // Set interesting flags.
416  SU.isCall = MI->isCall();
417
418  const MCSchedClassDesc *SC = SchedModel->resolveSchedClass(MI);
419  for (const MCWriteProcResEntry &PRE :
420         make_range(SchedModel->getWriteProcResBegin(SC),
421                    SchedModel->getWriteProcResEnd(SC))) {
422    switch (SchedModel->getProcResource(PRE.ProcResourceIdx)->BufferSize) {
423    case 0:
424      SU.hasReservedResource = true;
425      break;
426    case 1:
427      SU.isUnbuffered = true;
428      break;
429    default:
430      break;
431    }
432  }
433
434  unsigned GroupSizeBeforeEmit = CurrGroupSize;
435  EmitInstruction(&SU);
436
437  if (!TakenBranch && isBranchRetTrap(MI)) {
438    // NT Branch on second slot ends group.
439    if (GroupSizeBeforeEmit == 1)
440      nextGroup();
441  }
442
443  if (TakenBranch && CurrGroupSize > 0)
444    nextGroup();
445
446  assert ((!MI->isTerminator() || isBranchRetTrap(MI)) &&
447          "Scheduler: unhandled terminator!");
448}
449
450void SystemZHazardRecognizer::
451copyState(SystemZHazardRecognizer *Incoming) {
452  // Current decoder group
453  CurrGroupSize = Incoming->CurrGroupSize;
454  LLVM_DEBUG(CurGroupDbg = Incoming->CurGroupDbg;);
455
456  // Processor resources
457  ProcResourceCounters = Incoming->ProcResourceCounters;
458  CriticalResourceIdx = Incoming->CriticalResourceIdx;
459
460  // FPd
461  LastFPdOpCycleIdx = Incoming->LastFPdOpCycleIdx;
462  GrpCount = Incoming->GrpCount;
463}
464