1//===- llvm/Target/TargetSchedule.cpp - Sched Machine Model ---------------===//
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 implements a wrapper around MCSchedModel that allows the interface
10// to benefit from information currently only available in TargetInstrInfo.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/CodeGen/TargetSchedule.h"
15#include "llvm/CodeGen/MachineFunction.h"
16#include "llvm/CodeGen/MachineInstr.h"
17#include "llvm/CodeGen/MachineOperand.h"
18#include "llvm/CodeGen/TargetInstrInfo.h"
19#include "llvm/CodeGen/TargetSubtargetInfo.h"
20#include "llvm/MC/MCInstrDesc.h"
21#include "llvm/MC/MCInstrItineraries.h"
22#include "llvm/MC/MCSchedule.h"
23#include "llvm/Support/CommandLine.h"
24#include "llvm/Support/ErrorHandling.h"
25#include "llvm/Support/raw_ostream.h"
26#include <algorithm>
27#include <cassert>
28#include <cstdint>
29#include <numeric>
30
31using namespace llvm;
32
33static cl::opt<bool> EnableSchedModel("schedmodel", cl::Hidden, cl::init(Val: true),
34 cl::desc("Use TargetSchedModel for latency lookup"));
35
36static cl::opt<bool> EnableSchedItins("scheditins", cl::Hidden, cl::init(Val: true),
37 cl::desc("Use InstrItineraryData for latency lookup"));
38
39static cl::opt<bool> ForceEnableIntervals(
40 "sched-model-force-enable-intervals", cl::Hidden, cl::init(Val: false),
41 cl::desc("Force the use of resource intervals in the schedule model"));
42
43bool TargetSchedModel::hasInstrSchedModel() const {
44 return EnableSchedModel && SchedModel.hasInstrSchedModel();
45}
46
47bool TargetSchedModel::hasInstrItineraries() const {
48 return EnableSchedItins && !InstrItins.isEmpty();
49}
50
51void TargetSchedModel::init(const TargetSubtargetInfo *TSInfo) {
52 STI = TSInfo;
53 SchedModel = TSInfo->getSchedModel();
54 TII = TSInfo->getInstrInfo();
55 STI->initInstrItins(InstrItins);
56
57 unsigned NumRes = SchedModel.getNumProcResourceKinds();
58 ResourceFactors.resize(N: NumRes);
59 ResourceLCM = SchedModel.IssueWidth;
60 for (unsigned Idx = 0; Idx < NumRes; ++Idx) {
61 unsigned NumUnits = SchedModel.getProcResource(ProcResourceIdx: Idx)->NumUnits;
62 if (NumUnits > 0)
63 ResourceLCM = std::lcm(m: ResourceLCM, n: NumUnits);
64 }
65 MicroOpFactor = ResourceLCM / SchedModel.IssueWidth;
66 for (unsigned Idx = 0; Idx < NumRes; ++Idx) {
67 unsigned NumUnits = SchedModel.getProcResource(ProcResourceIdx: Idx)->NumUnits;
68 ResourceFactors[Idx] = NumUnits ? (ResourceLCM / NumUnits) : 0;
69 }
70}
71
72/// Returns true only if instruction is specified as single issue.
73bool TargetSchedModel::mustBeginGroup(const MachineInstr *MI,
74 const MCSchedClassDesc *SC) const {
75 if (hasInstrSchedModel()) {
76 if (!SC)
77 SC = resolveSchedClass(MI);
78 if (SC->isValid())
79 return SC->BeginGroup;
80 }
81 return false;
82}
83
84bool TargetSchedModel::mustEndGroup(const MachineInstr *MI,
85 const MCSchedClassDesc *SC) const {
86 if (hasInstrSchedModel()) {
87 if (!SC)
88 SC = resolveSchedClass(MI);
89 if (SC->isValid())
90 return SC->EndGroup;
91 }
92 return false;
93}
94
95unsigned TargetSchedModel::getNumMicroOps(const MachineInstr *MI,
96 const MCSchedClassDesc *SC) const {
97 if (hasInstrItineraries()) {
98 int UOps = InstrItins.getNumMicroOps(ItinClassIndx: MI->getDesc().getSchedClass());
99 return (UOps >= 0) ? UOps : TII->getNumMicroOps(ItinData: &InstrItins, MI: *MI);
100 }
101 if (hasInstrSchedModel()) {
102 if (!SC)
103 SC = resolveSchedClass(MI);
104 if (SC->isValid())
105 return SC->NumMicroOps;
106 }
107 return MI->isTransient() ? 0 : 1;
108}
109
110// The machine model may explicitly specify an invalid latency, which
111// effectively means infinite latency. Since users of the TargetSchedule API
112// don't know how to handle this, we convert it to a very large latency that is
113// easy to distinguish when debugging the DAG but won't induce overflow.
114static unsigned capLatency(int Cycles) {
115 return Cycles >= 0 ? Cycles : 1000;
116}
117
118/// Return the MCSchedClassDesc for this instruction. Some SchedClasses require
119/// evaluation of predicates that depend on instruction operands or flags.
120const MCSchedClassDesc *TargetSchedModel::
121resolveSchedClass(const MachineInstr *MI) const {
122 // Get the definition's scheduling class descriptor from this machine model.
123 unsigned SchedClass = MI->getDesc().getSchedClass();
124 const MCSchedClassDesc *SCDesc = SchedModel.getSchedClassDesc(SchedClassIdx: SchedClass);
125 if (!SCDesc->isValid())
126 return SCDesc;
127
128#ifndef NDEBUG
129 unsigned NIter = 0;
130#endif
131 while (SCDesc->isVariant()) {
132 assert(++NIter < 6 && "Variants are nested deeper than the magic number");
133
134 SchedClass = STI->resolveSchedClass(SchedClass, MI, SchedModel: this);
135 SCDesc = SchedModel.getSchedClassDesc(SchedClassIdx: SchedClass);
136 }
137 return SCDesc;
138}
139
140/// Find the def index of this operand. This index maps to the machine model and
141/// is independent of use operands. Def operands may be reordered with uses or
142/// merged with uses without affecting the def index (e.g. before/after
143/// regalloc). However, an instruction's def operands must never be reordered
144/// with respect to each other.
145static unsigned findDefIdx(const MachineInstr *MI, unsigned DefOperIdx) {
146 unsigned DefIdx = 0;
147 for (unsigned i = 0; i != DefOperIdx; ++i) {
148 const MachineOperand &MO = MI->getOperand(i);
149 if (MO.isReg() && MO.isDef())
150 ++DefIdx;
151 }
152 return DefIdx;
153}
154
155/// Find the use index of this operand. This is independent of the instruction's
156/// def operands.
157///
158/// Note that uses are not determined by the operand's isUse property, which
159/// is simply the inverse of isDef. Here we consider any readsReg operand to be
160/// a "use". The machine model allows an operand to be both a Def and Use.
161static unsigned findUseIdx(const MachineInstr *MI, unsigned UseOperIdx) {
162 unsigned UseIdx = 0;
163 for (unsigned i = 0; i != UseOperIdx; ++i) {
164 const MachineOperand &MO = MI->getOperand(i);
165 if (MO.isReg() && MO.readsReg() && !MO.isDef())
166 ++UseIdx;
167 }
168 return UseIdx;
169}
170
171// Top-level API for clients that know the operand indices. This doesn't need to
172// return std::optional<unsigned>, as it always returns a valid latency.
173unsigned TargetSchedModel::computeOperandLatency(
174 const MachineInstr *DefMI, unsigned DefOperIdx,
175 const MachineInstr *UseMI, unsigned UseOperIdx) const {
176
177 const unsigned InstrLatency = computeInstrLatency(MI: DefMI);
178 const unsigned DefaultDefLatency = TII->defaultDefLatency(SchedModel, DefMI: *DefMI);
179
180 if (!hasInstrSchedModel() && !hasInstrItineraries())
181 return DefaultDefLatency;
182
183 if (hasInstrItineraries()) {
184 std::optional<unsigned> OperLatency;
185 if (UseMI) {
186 OperLatency = TII->getOperandLatency(ItinData: &InstrItins, DefMI: *DefMI, DefIdx: DefOperIdx,
187 UseMI: *UseMI, UseIdx: UseOperIdx);
188 }
189 else {
190 unsigned DefClass = DefMI->getDesc().getSchedClass();
191 OperLatency = InstrItins.getOperandCycle(ItinClassIndx: DefClass, OperandIdx: DefOperIdx);
192 }
193
194 // Expected latency is the max of InstrLatency and DefaultDefLatency, if we
195 // didn't find an operand latency.
196 return OperLatency ? *OperLatency
197 : std::max(a: InstrLatency, b: DefaultDefLatency);
198 }
199
200 // hasInstrSchedModel()
201 const MCSchedClassDesc *SCDesc = resolveSchedClass(MI: DefMI);
202 unsigned DefIdx = findDefIdx(MI: DefMI, DefOperIdx);
203 if (DefIdx < SCDesc->NumWriteLatencyEntries) {
204 // Lookup the definition's write latency in SubtargetInfo.
205 const MCWriteLatencyEntry *WLEntry =
206 STI->getWriteLatencyEntry(SC: SCDesc, DefIdx);
207 unsigned WriteID = WLEntry->WriteResourceID;
208 unsigned Latency = capLatency(Cycles: WLEntry->Cycles);
209 if (!UseMI)
210 return Latency;
211
212 // Lookup the use's latency adjustment in SubtargetInfo.
213 const MCSchedClassDesc *UseDesc = resolveSchedClass(MI: UseMI);
214 if (UseDesc->NumReadAdvanceEntries == 0)
215 return Latency;
216 unsigned UseIdx = findUseIdx(MI: UseMI, UseOperIdx);
217 int Advance = STI->getReadAdvanceCycles(SC: UseDesc, UseIdx, WriteResID: WriteID);
218 if (Advance > 0 && (unsigned)Advance > Latency) // unsigned wrap
219 return 0;
220 return Latency - Advance;
221 }
222 // If DefIdx does not exist in the model (e.g. implicit defs), then return
223 // unit latency (defaultDefLatency may be too conservative).
224#ifndef NDEBUG
225 if (SCDesc->isValid() && !DefMI->getOperand(i: DefOperIdx).isImplicit() &&
226 !DefMI->getDesc().operands()[DefOperIdx].isOptionalDef() &&
227 SchedModel.isComplete()) {
228 errs() << "DefIdx " << DefIdx << " exceeds machine model writes for "
229 << *DefMI << " (Try with MCSchedModel.CompleteModel set to false)";
230 llvm_unreachable("incomplete machine model");
231 }
232#endif
233 // FIXME: Automatically giving all implicit defs defaultDefLatency is
234 // undesirable. We should only do it for defs that are known to the MC
235 // desc like flags. Truly implicit defs should get 1 cycle latency.
236 return DefMI->isTransient() ? 0 : DefaultDefLatency;
237}
238
239unsigned
240TargetSchedModel::computeInstrLatency(const MCSchedClassDesc &SCDesc) const {
241 return capLatency(Cycles: MCSchedModel::computeInstrLatency(STI: *STI, SCDesc));
242}
243
244unsigned TargetSchedModel::computeInstrLatency(unsigned Opcode) const {
245 assert(hasInstrSchedModel() && "Only call this function with a SchedModel");
246 unsigned SCIdx = TII->get(Opcode).getSchedClass();
247 return capLatency(Cycles: SchedModel.computeInstrLatency(STI: *STI, SClass: SCIdx));
248}
249
250unsigned TargetSchedModel::computeInstrLatency(const MCInst &Inst) const {
251 if (hasInstrSchedModel())
252 return capLatency(Cycles: SchedModel.computeInstrLatency(STI: *STI, MCII: *TII, Inst));
253 return computeInstrLatency(Opcode: Inst.getOpcode());
254}
255
256unsigned
257TargetSchedModel::computeInstrLatency(const MachineInstr *MI,
258 bool UseDefaultDefLatency) const {
259 // For the itinerary model, fall back to the old subtarget hook.
260 // Allow subtargets to compute Bundle latencies outside the machine model.
261 if (hasInstrItineraries() || MI->isBundle() ||
262 (!hasInstrSchedModel() && !UseDefaultDefLatency))
263 return TII->getInstrLatency(ItinData: &InstrItins, MI: *MI);
264
265 if (hasInstrSchedModel()) {
266 const MCSchedClassDesc *SCDesc = resolveSchedClass(MI);
267 if (SCDesc->isValid())
268 return computeInstrLatency(SCDesc: *SCDesc);
269 }
270 return TII->defaultDefLatency(SchedModel, DefMI: *MI);
271}
272
273unsigned TargetSchedModel::
274computeOutputLatency(const MachineInstr *DefMI, unsigned DefOperIdx,
275 const MachineInstr *DepMI) const {
276 if (!SchedModel.isOutOfOrder())
277 return 1;
278
279 // Out-of-order processor can dispatch WAW dependencies in the same cycle.
280
281 // Treat predication as a data dependency for out-of-order cpus. In-order
282 // cpus do not need to treat predicated writes specially.
283 //
284 // TODO: The following hack exists because predication passes do not
285 // correctly append imp-use operands, and readsReg() strangely returns false
286 // for predicated defs.
287 Register Reg = DefMI->getOperand(i: DefOperIdx).getReg();
288 const MachineFunction &MF = *DefMI->getMF();
289 const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
290 if (!DepMI->readsRegister(Reg, TRI) && TII->isPredicated(MI: *DepMI))
291 return computeInstrLatency(MI: DefMI);
292
293 // If we have a per operand scheduling model, check if this def is writing
294 // an unbuffered resource. If so, it treated like an in-order cpu.
295 if (hasInstrSchedModel()) {
296 const MCSchedClassDesc *SCDesc = resolveSchedClass(MI: DefMI);
297 if (SCDesc->isValid()) {
298 for (const MCWriteProcResEntry *PRI = STI->getWriteProcResBegin(SC: SCDesc),
299 *PRE = STI->getWriteProcResEnd(SC: SCDesc); PRI != PRE; ++PRI) {
300 if (!SchedModel.getProcResource(ProcResourceIdx: PRI->ProcResourceIdx)->BufferSize)
301 return 1;
302 }
303 }
304 }
305 return 0;
306}
307
308double
309TargetSchedModel::computeReciprocalThroughput(const MachineInstr *MI) const {
310 if (hasInstrItineraries()) {
311 unsigned SchedClass = MI->getDesc().getSchedClass();
312 return MCSchedModel::getReciprocalThroughput(SchedClass,
313 IID: *getInstrItineraries());
314 }
315
316 if (hasInstrSchedModel())
317 return MCSchedModel::getReciprocalThroughput(STI: *STI, SCDesc: *resolveSchedClass(MI));
318
319 return 0.0;
320}
321
322double
323TargetSchedModel::computeReciprocalThroughput(unsigned Opcode) const {
324 unsigned SchedClass = TII->get(Opcode).getSchedClass();
325 if (hasInstrItineraries())
326 return MCSchedModel::getReciprocalThroughput(SchedClass,
327 IID: *getInstrItineraries());
328 if (hasInstrSchedModel()) {
329 const MCSchedClassDesc &SCDesc = *SchedModel.getSchedClassDesc(SchedClassIdx: SchedClass);
330 if (SCDesc.isValid() && !SCDesc.isVariant())
331 return MCSchedModel::getReciprocalThroughput(STI: *STI, SCDesc);
332 }
333
334 return 0.0;
335}
336
337double
338TargetSchedModel::computeReciprocalThroughput(const MCInst &MI) const {
339 if (hasInstrSchedModel())
340 return SchedModel.getReciprocalThroughput(STI: *STI, MCII: *TII, Inst: MI);
341 return computeReciprocalThroughput(Opcode: MI.getOpcode());
342}
343
344bool TargetSchedModel::enableIntervals() const {
345 if (ForceEnableIntervals)
346 return true;
347
348 return SchedModel.EnableIntervals;
349}
350

source code of llvm/lib/CodeGen/TargetSchedule.cpp