1 //===-- llvm/MC/MCInstrItineraries.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 describes the structures used for instruction
11 // itineraries, stages, and operand reads/writes. This is used by
12 // schedulers to determine instruction stages and latencies.
14 //===----------------------------------------------------------------------===//
16 #ifndef LLVM_MC_MCINSTRITINERARIES_H
17 #define LLVM_MC_MCINSTRITINERARIES_H
23 //===----------------------------------------------------------------------===//
24 /// Instruction stage - These values represent a non-pipelined step in
25 /// the execution of an instruction. Cycles represents the number of
26 /// discrete time slots needed to complete the stage. Units represent
27 /// the choice of functional units that can be used to complete the
28 /// stage. Eg. IntUnit1, IntUnit2. NextCycles indicates how many
29 /// cycles should elapse from the start of this stage to the start of
30 /// the next stage in the itinerary. A value of -1 indicates that the
31 /// next stage should start immediately after the current one.
35 /// indicates that the stage occupies FU x for 1 cycle and that
36 /// the next stage starts immediately after this one.
39 /// indicates that the stage occupies either FU x or FU y for 2
40 /// consecuative cycles and that the next stage starts one cycle
41 /// after this stage starts. That is, the stage requirements
45 /// indicates that the stage occupies FU x for 1 cycle and that
46 /// the next stage starts in this same cycle. This can be used to
47 /// indicate that the instruction requires multiple stages at the
50 /// FU reservation can be of two different kinds:
51 /// - FUs which instruction actually requires
52 /// - FUs which instruction just reserves. Reserved unit is not available for
53 /// execution of other instruction. However, several instructions can reserve
54 /// the same unit several times.
55 /// Such two types of units reservation is used to model instruction domain
56 /// change stalls, FUs using the same resource (e.g. same register file), etc.
59 enum ReservationKinds {
64 unsigned Cycles_; ///< Length of stage in machine cycles
65 unsigned Units_; ///< Choice of functional units
66 int NextCycles_; ///< Number of machine cycles to next stage
67 ReservationKinds Kind_; ///< Kind of the FU reservation
69 /// getCycles - returns the number of cycles the stage is occupied
70 unsigned getCycles() const {
74 /// getUnits - returns the choice of FUs
75 unsigned getUnits() const {
79 ReservationKinds getReservationKind() const {
83 /// getNextCycles - returns the number of cycles from the start of
84 /// this stage to the start of the next stage in the itinerary
85 unsigned getNextCycles() const {
86 return (NextCycles_ >= 0) ? (unsigned)NextCycles_ : Cycles_;
91 //===----------------------------------------------------------------------===//
92 /// Instruction itinerary - An itinerary represents the scheduling
93 /// information for an instruction. This includes a set of stages
94 /// occupies by the instruction, and the pipeline cycle in which
95 /// operands are read and written.
97 struct InstrItinerary {
98 int NumMicroOps; ///< # of micro-ops, -1 means it's variable
99 unsigned FirstStage; ///< Index of first stage in itinerary
100 unsigned LastStage; ///< Index of last + 1 stage in itinerary
101 unsigned FirstOperandCycle; ///< Index of first operand rd/wr
102 unsigned LastOperandCycle; ///< Index of last + 1 operand rd/wr
106 //===----------------------------------------------------------------------===//
107 /// Instruction itinerary properties - These properties provide general
108 /// information about the microarchitecture to the scheduler.
110 struct InstrItineraryProps {
111 // IssueWidth is the maximum number of instructions that may be scheduled in
112 // the same per-cycle group.
114 static const unsigned DefaultIssueWidth = 1;
116 // MinLatency is the minimum latency between a register write
117 // followed by a data dependent read. This determines which
118 // instructions may be scheduled in the same per-cycle group. This
119 // is distinct from *expected* latency, which determines the likely
120 // critical path but does not guarantee a pipeline
121 // hazard. MinLatency can always be overridden by the number of
122 // InstrStage cycles.
124 // (-1) Standard in-order processor.
125 // Use InstrItinerary OperandCycles as MinLatency.
126 // If no OperandCycles exist, then use the cycle of the last InstrStage.
128 // (0) Out-of-order processor, or in-order with bundled dependencies.
129 // RAW dependencies may be dispatched in the same cycle.
130 // Optional InstrItinerary OperandCycles provides expected latency.
132 // (>0) In-order processor with variable latencies.
133 // Use the greater of this value or the cycle of the last InstrStage.
134 // Optional InstrItinerary OperandCycles provides expected latency.
135 // TODO: can't yet specify both min and expected latency per operand.
137 static const unsigned DefaultMinLatency = -1;
139 // LoadLatency is the expected latency of load instructions.
141 // If MinLatency >= 0, this may be overriden for individual load opcodes by
142 // InstrItinerary OperandCycles.
143 unsigned LoadLatency;
144 static const unsigned DefaultLoadLatency = 4;
146 // HighLatency is the expected latency of "very high latency" operations.
147 // See TargetInstrInfo::isHighLatencyDef().
148 // By default, this is set to an arbitrarily high number of cycles
149 // likely to have some impact on scheduling heuristics.
150 // If MinLatency >= 0, this may be overriden by InstrItinData OperandCycles.
151 unsigned HighLatency;
152 static const unsigned DefaultHighLatency = 10;
154 // Default's must be specified as static const literals so that tablegenerated
155 // target code can use it in static initializers. The defaults need to be
156 // initialized in this default ctor because some clients directly instantiate
157 // InstrItineraryData instead of using a generated itinerary.
158 InstrItineraryProps(): IssueWidth(DefaultMinLatency),
159 MinLatency(DefaultMinLatency),
160 LoadLatency(DefaultLoadLatency),
161 HighLatency(DefaultHighLatency) {}
163 InstrItineraryProps(unsigned iw, int ml, unsigned ll, unsigned hl):
164 IssueWidth(iw), MinLatency(ml), LoadLatency(ll), HighLatency(hl) {}
167 //===----------------------------------------------------------------------===//
168 /// Encapsulate all subtarget specific information for scheduling for use with
170 struct InstrItinerarySubtargetValue {
171 const InstrItineraryProps *Props;
172 const InstrItinerary *Itineraries;
175 //===----------------------------------------------------------------------===//
176 /// Instruction itinerary Data - Itinerary data supplied by a subtarget to be
177 /// used by a target.
179 class InstrItineraryData {
181 InstrItineraryProps Props;
182 const InstrStage *Stages; ///< Array of stages selected
183 const unsigned *OperandCycles; ///< Array of operand cycles selected
184 const unsigned *Forwardings; ///< Array of pipeline forwarding pathes
185 const InstrItinerary *Itineraries; ///< Array of itineraries selected
189 InstrItineraryData() : Stages(0), OperandCycles(0), Forwardings(0),
192 InstrItineraryData(const InstrItineraryProps *P, const InstrStage *S,
193 const unsigned *OS, const unsigned *F,
194 const InstrItinerary *I)
195 : Props(*P), Stages(S), OperandCycles(OS), Forwardings(F), Itineraries(I) {}
197 /// isEmpty - Returns true if there are no itineraries.
199 bool isEmpty() const { return Itineraries == 0; }
201 /// isEndMarker - Returns true if the index is for the end marker
204 bool isEndMarker(unsigned ItinClassIndx) const {
205 return ((Itineraries[ItinClassIndx].FirstStage == ~0U) &&
206 (Itineraries[ItinClassIndx].LastStage == ~0U));
209 /// beginStage - Return the first stage of the itinerary.
211 const InstrStage *beginStage(unsigned ItinClassIndx) const {
212 unsigned StageIdx = Itineraries[ItinClassIndx].FirstStage;
213 return Stages + StageIdx;
216 /// endStage - Return the last+1 stage of the itinerary.
218 const InstrStage *endStage(unsigned ItinClassIndx) const {
219 unsigned StageIdx = Itineraries[ItinClassIndx].LastStage;
220 return Stages + StageIdx;
223 /// getStageLatency - Return the total stage latency of the given
224 /// class. The latency is the maximum completion time for any stage
225 /// in the itinerary.
227 /// InstrStages override the itinerary's MinLatency property. In fact, if the
228 /// stage latencies, which may be zero, are less than MinLatency,
229 /// getStageLatency returns a value less than MinLatency.
231 /// If no stages exist, MinLatency is used. If MinLatency is invalid (<0),
232 /// then it defaults to one cycle.
233 unsigned getStageLatency(unsigned ItinClassIndx) const {
234 // If the target doesn't provide itinerary information, use a simple
235 // non-zero default value for all instructions. Some target's provide a
236 // dummy (Generic) itinerary which should be handled as if it's itinerary is
237 // empty. We identify this by looking for a reference to stage zero (invalid
238 // stage). This is different from beginStage == endStage != 0, which could
239 // be used for zero-latency pseudo ops.
240 if (isEmpty() || Itineraries[ItinClassIndx].FirstStage == 0)
241 return (Props.MinLatency < 0) ? 1 : Props.MinLatency;
243 // Calculate the maximum completion time for any stage.
244 unsigned Latency = 0, StartCycle = 0;
245 for (const InstrStage *IS = beginStage(ItinClassIndx),
246 *E = endStage(ItinClassIndx); IS != E; ++IS) {
247 Latency = std::max(Latency, StartCycle + IS->getCycles());
248 StartCycle += IS->getNextCycles();
254 /// getOperandCycle - Return the cycle for the given class and
255 /// operand. Return -1 if no cycle is specified for the operand.
257 int getOperandCycle(unsigned ItinClassIndx, unsigned OperandIdx) const {
261 unsigned FirstIdx = Itineraries[ItinClassIndx].FirstOperandCycle;
262 unsigned LastIdx = Itineraries[ItinClassIndx].LastOperandCycle;
263 if ((FirstIdx + OperandIdx) >= LastIdx)
266 return (int)OperandCycles[FirstIdx + OperandIdx];
269 /// hasPipelineForwarding - Return true if there is a pipeline forwarding
270 /// between instructions of itinerary classes DefClass and UseClasses so that
271 /// value produced by an instruction of itinerary class DefClass, operand
272 /// index DefIdx can be bypassed when it's read by an instruction of
273 /// itinerary class UseClass, operand index UseIdx.
274 bool hasPipelineForwarding(unsigned DefClass, unsigned DefIdx,
275 unsigned UseClass, unsigned UseIdx) const {
276 unsigned FirstDefIdx = Itineraries[DefClass].FirstOperandCycle;
277 unsigned LastDefIdx = Itineraries[DefClass].LastOperandCycle;
278 if ((FirstDefIdx + DefIdx) >= LastDefIdx)
280 if (Forwardings[FirstDefIdx + DefIdx] == 0)
283 unsigned FirstUseIdx = Itineraries[UseClass].FirstOperandCycle;
284 unsigned LastUseIdx = Itineraries[UseClass].LastOperandCycle;
285 if ((FirstUseIdx + UseIdx) >= LastUseIdx)
288 return Forwardings[FirstDefIdx + DefIdx] ==
289 Forwardings[FirstUseIdx + UseIdx];
292 /// getOperandLatency - Compute and return the use operand latency of a given
293 /// itinerary class and operand index if the value is produced by an
294 /// instruction of the specified itinerary class and def operand index.
295 int getOperandLatency(unsigned DefClass, unsigned DefIdx,
296 unsigned UseClass, unsigned UseIdx) const {
300 int DefCycle = getOperandCycle(DefClass, DefIdx);
304 int UseCycle = getOperandCycle(UseClass, UseIdx);
308 UseCycle = DefCycle - UseCycle + 1;
310 hasPipelineForwarding(DefClass, DefIdx, UseClass, UseIdx))
311 // FIXME: This assumes one cycle benefit for every pipeline forwarding.
316 /// getNumMicroOps - Return the number of micro-ops that the given class
317 /// decodes to. Return -1 for classes that require dynamic lookup via
319 int getNumMicroOps(unsigned ItinClassIndx) const {
322 return Itineraries[ItinClassIndx].NumMicroOps;
326 } // End llvm namespace