1 //===-- llvm/MC/MCSchedule.h - Scheduling -----------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the classes used to describe a subtarget's machine model
11 // for scheduling and other instruction cost heuristics.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_MC_MCSCHEDMODEL_H
16 #define LLVM_MC_MCSCHEDMODEL_H
18 #include "llvm/Support/DataTypes.h"
23 struct InstrItinerary;
25 /// Define a kind of processor resource that will be modeled by the scheduler.
26 struct MCProcResourceDesc {
30 unsigned NumUnits; // Number of resource of this kind
31 unsigned SuperIdx; // Index of the resources kind that contains this kind.
33 // Buffered resources may be consumed at some indeterminate cycle after
34 // dispatch (e.g. for instructions that may issue out-of-order). Unbuffered
35 // resources always consume their resource some fixed number of cycles after
36 // dispatch (e.g. for instruction interlocking that may stall the pipeline).
39 bool operator==(const MCProcResourceDesc &Other) const {
40 return NumUnits == Other.NumUnits && SuperIdx == Other.SuperIdx
41 && IsBuffered == Other.IsBuffered;
45 /// Identify one of the processor resource kinds consumed by a particular
46 /// scheduling class for the specified number of cycles.
47 struct MCWriteProcResEntry {
48 unsigned ProcResourceIdx;
51 bool operator==(const MCWriteProcResEntry &Other) const {
52 return ProcResourceIdx == Other.ProcResourceIdx && Cycles == Other.Cycles;
56 /// Specify the latency in cpu cycles for a particular scheduling class and def
57 /// index. Also identify the WriteResources of this def. When the operand
58 /// expands to a sequence of writes, this ID is the last write in the sequence.
59 struct MCWriteLatencyEntry {
61 unsigned WriteResourceID;
63 bool operator==(const MCWriteLatencyEntry &Other) const {
64 return Cycles == Other.Cycles && WriteResourceID == Other.WriteResourceID;
68 /// Specify the number of cycles allowed after instruction issue before a
69 /// particular use operand reads its registers. This effectively reduces the
70 /// write's latency. Here we allow negative cycles for corner cases where
71 /// latency increases. This rule only applies when the entry's WriteResource
72 /// matches the write's WriteResource.
74 /// MCReadAdvanceEntries are sorted first by operand index (UseIdx), then by
76 struct MCReadAdvanceEntry {
78 unsigned WriteResourceID;
81 bool operator==(const MCReadAdvanceEntry &Other) const {
82 return UseIdx == Other.UseIdx && WriteResourceID == Other.WriteResourceID
83 && Cycles == Other.Cycles;
87 /// Summarize the scheduling resources required for an instruction of a
88 /// particular scheduling class.
90 /// Defined as an aggregate struct for creating tables with initializer lists.
91 struct MCSchedClassDesc {
92 static const unsigned short InvalidNumMicroOps = UINT16_MAX;
93 static const unsigned short VariantNumMicroOps = UINT16_MAX - 1;
98 unsigned short NumMicroOps;
101 unsigned WriteProcResIdx; // First index into WriteProcResTable.
102 unsigned NumWriteProcResEntries;
103 unsigned WriteLatencyIdx; // First index into WriteLatencyTable.
104 unsigned NumWriteLatencyEntries;
105 unsigned ReadAdvanceIdx; // First index into ReadAdvanceTable.
106 unsigned NumReadAdvanceEntries;
108 bool isValid() const {
109 return NumMicroOps != InvalidNumMicroOps;
111 bool isVariant() const {
112 return NumMicroOps == VariantNumMicroOps;
116 /// Machine model for scheduling, bundling, and heuristics.
118 /// The machine model directly provides basic information about the
119 /// microarchitecture to the scheduler in the form of properties. It also
120 /// optionally refers to scheduler resource tables and itinerary
121 /// tables. Scheduler resource tables model the latency and cost for each
122 /// instruction type. Itinerary tables are an independant mechanism that
123 /// provides a detailed reservation table describing each cycle of instruction
124 /// execution. Subtargets may define any or all of the above categories of data
125 /// depending on the type of CPU and selected scheduler.
128 static MCSchedModel DefaultSchedModel; // For unknown processors.
130 // IssueWidth is the maximum number of instructions that may be scheduled in
131 // the same per-cycle group.
133 static const unsigned DefaultIssueWidth = 1;
135 // MinLatency is the minimum latency between a register write
136 // followed by a data dependent read. This determines which
137 // instructions may be scheduled in the same per-cycle group. This
138 // is distinct from *expected* latency, which determines the likely
139 // critical path but does not guarantee a pipeline
140 // hazard. MinLatency can always be overridden by the number of
141 // InstrStage cycles.
143 // (-1) Standard in-order processor.
144 // Use InstrItinerary OperandCycles as MinLatency.
145 // If no OperandCycles exist, then use the cycle of the last InstrStage.
147 // (0) Out-of-order processor, or in-order with bundled dependencies.
148 // RAW dependencies may be dispatched in the same cycle.
149 // Optional InstrItinerary OperandCycles provides expected latency.
151 // (>0) In-order processor with variable latencies.
152 // Use the greater of this value or the cycle of the last InstrStage.
153 // Optional InstrItinerary OperandCycles provides expected latency.
154 // TODO: can't yet specify both min and expected latency per operand.
156 static const unsigned DefaultMinLatency = -1;
158 // LoadLatency is the expected latency of load instructions.
160 // If MinLatency >= 0, this may be overriden for individual load opcodes by
161 // InstrItinerary OperandCycles.
162 unsigned LoadLatency;
163 static const unsigned DefaultLoadLatency = 4;
165 // HighLatency is the expected latency of "very high latency" operations.
166 // See TargetInstrInfo::isHighLatencyDef().
167 // By default, this is set to an arbitrarily high number of cycles
168 // likely to have some impact on scheduling heuristics.
169 // If MinLatency >= 0, this may be overriden by InstrItinData OperandCycles.
170 unsigned HighLatency;
171 static const unsigned DefaultHighLatency = 10;
173 // MispredictPenalty is the typical number of extra cycles the processor
174 // takes to recover from a branch misprediction.
175 unsigned MispredictPenalty;
176 static const unsigned DefaultMispredictPenalty = 10;
180 const MCProcResourceDesc *ProcResourceTable;
181 const MCSchedClassDesc *SchedClassTable;
182 unsigned NumProcResourceKinds;
183 unsigned NumSchedClasses;
184 // Instruction itinerary tables used by InstrItineraryData.
185 friend class InstrItineraryData;
186 const InstrItinerary *InstrItineraries;
189 // Default's must be specified as static const literals so that tablegenerated
190 // target code can use it in static initializers. The defaults need to be
191 // initialized in this default ctor because some clients directly instantiate
192 // MCSchedModel instead of using a generated itinerary.
193 MCSchedModel(): IssueWidth(DefaultIssueWidth),
194 MinLatency(DefaultMinLatency),
195 LoadLatency(DefaultLoadLatency),
196 HighLatency(DefaultHighLatency),
197 MispredictPenalty(DefaultMispredictPenalty),
198 ProcID(0), ProcResourceTable(0), SchedClassTable(0),
199 NumProcResourceKinds(0), NumSchedClasses(0),
200 InstrItineraries(0) {
201 (void)NumProcResourceKinds;
202 (void)NumSchedClasses;
205 // Table-gen driven ctor.
206 MCSchedModel(unsigned iw, int ml, unsigned ll, unsigned hl, unsigned mp,
207 unsigned pi, const MCProcResourceDesc *pr,
208 const MCSchedClassDesc *sc, unsigned npr, unsigned nsc,
209 const InstrItinerary *ii):
210 IssueWidth(iw), MinLatency(ml), LoadLatency(ll), HighLatency(hl),
211 MispredictPenalty(mp), ProcID(pi), ProcResourceTable(pr),
212 SchedClassTable(sc), NumProcResourceKinds(npr), NumSchedClasses(nsc),
213 InstrItineraries(ii) {}
215 unsigned getProcessorID() const { return ProcID; }
217 /// Does this machine model include instruction-level scheduling.
218 bool hasInstrSchedModel() const { return SchedClassTable; }
220 const MCProcResourceDesc *getProcResource(unsigned ProcResourceIdx) const {
221 assert(hasInstrSchedModel() && "No scheduling machine model");
223 assert(ProcResourceIdx < NumProcResourceKinds && "bad proc resource idx");
224 return &ProcResourceTable[ProcResourceIdx];
227 const MCSchedClassDesc *getSchedClassDesc(unsigned SchedClassIdx) const {
228 assert(hasInstrSchedModel() && "No scheduling machine model");
230 assert(SchedClassIdx < NumSchedClasses && "bad scheduling class idx");
231 return &SchedClassTable[SchedClassIdx];
235 } // End llvm namespace