1 //===---- ScheduleDAGList.cpp - Implement a list scheduler for isel DAG ---===//
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 implements a top-down list scheduler, using standard algorithms.
11 // The basic approach uses a priority queue of available nodes to schedule.
12 // One at a time, nodes are taken from the priority queue (thus in priority
13 // order), checked for legality to schedule, and emitted if legal.
15 // Nodes may not be legal to schedule either due to structural hazards (e.g.
16 // pipeline or resource constraints) or because an input to the instruction has
17 // not completed execution.
19 //===----------------------------------------------------------------------===//
21 #define DEBUG_TYPE "pre-RA-sched"
22 #include "llvm/CodeGen/ScheduleDAG.h"
23 #include "llvm/CodeGen/SchedulerRegistry.h"
24 #include "llvm/CodeGen/SelectionDAGISel.h"
25 #include "llvm/Target/TargetRegisterInfo.h"
26 #include "llvm/Target/TargetData.h"
27 #include "llvm/Target/TargetMachine.h"
28 #include "llvm/Target/TargetInstrInfo.h"
29 #include "llvm/Support/Debug.h"
30 #include "llvm/Support/Compiler.h"
31 #include "llvm/ADT/PriorityQueue.h"
32 #include "llvm/ADT/Statistic.h"
33 #include "LatencyPriorityQueue.h"
37 STATISTIC(NumNoops , "Number of noops inserted");
38 STATISTIC(NumStalls, "Number of pipeline stalls");
40 static RegisterScheduler
41 tdListDAGScheduler("list-td", "Top-down list scheduler",
42 createTDListDAGScheduler);
45 //===----------------------------------------------------------------------===//
46 /// ScheduleDAGList - The actual list scheduler implementation. This supports
47 /// top-down scheduling.
49 class VISIBILITY_HIDDEN ScheduleDAGList : public ScheduleDAG {
51 /// AvailableQueue - The priority queue to use for the available SUnits.
53 SchedulingPriorityQueue *AvailableQueue;
55 /// PendingQueue - This contains all of the instructions whose operands have
56 /// been issued, but their results are not ready yet (due to the latency of
57 /// the operation). Once the operands becomes available, the instruction is
58 /// added to the AvailableQueue. This keeps track of each SUnit and the
59 /// number of cycles left to execute before the operation is available.
60 std::vector<std::pair<unsigned, SUnit*> > PendingQueue;
62 /// HazardRec - The hazard recognizer to use.
63 HazardRecognizer *HazardRec;
66 ScheduleDAGList(SelectionDAG *dag, MachineBasicBlock *bb,
67 const TargetMachine &tm,
68 SchedulingPriorityQueue *availqueue,
70 : ScheduleDAG(dag, bb, tm),
71 AvailableQueue(availqueue), HazardRec(HR) {
76 delete AvailableQueue;
82 void ReleaseSucc(SUnit *SuccSU, bool isChain);
83 void ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle);
84 void ListScheduleTopDown();
86 } // end anonymous namespace
88 HazardRecognizer::~HazardRecognizer() {}
91 /// Schedule - Schedule the DAG using list scheduling.
92 void ScheduleDAGList::Schedule() {
93 DOUT << "********** List Scheduling **********\n";
95 // Build scheduling units.
98 AvailableQueue->initNodes(SUnits);
100 ListScheduleTopDown();
102 AvailableQueue->releaseState();
105 //===----------------------------------------------------------------------===//
106 // Top-Down Scheduling
107 //===----------------------------------------------------------------------===//
109 /// ReleaseSucc - Decrement the NumPredsLeft count of a successor. Add it to
110 /// the PendingQueue if the count reaches zero.
111 void ScheduleDAGList::ReleaseSucc(SUnit *SuccSU, bool isChain) {
112 SuccSU->NumPredsLeft--;
114 assert(SuccSU->NumPredsLeft >= 0 &&
115 "List scheduling internal error");
117 if (SuccSU->NumPredsLeft == 0) {
118 // Compute how many cycles it will be before this actually becomes
119 // available. This is the max of the start time of all predecessors plus
121 unsigned AvailableCycle = 0;
122 for (SUnit::pred_iterator I = SuccSU->Preds.begin(),
123 E = SuccSU->Preds.end(); I != E; ++I) {
124 // If this is a token edge, we don't need to wait for the latency of the
125 // preceeding instruction (e.g. a long-latency load) unless there is also
126 // some other data dependence.
127 SUnit &Pred = *I->Dep;
128 unsigned PredDoneCycle = Pred.Cycle;
130 PredDoneCycle += Pred.Latency;
131 else if (Pred.Latency)
134 AvailableCycle = std::max(AvailableCycle, PredDoneCycle);
137 PendingQueue.push_back(std::make_pair(AvailableCycle, SuccSU));
141 /// ScheduleNodeTopDown - Add the node to the schedule. Decrement the pending
142 /// count of its successors. If a successor pending count is zero, add it to
143 /// the Available queue.
144 void ScheduleDAGList::ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle) {
145 DOUT << "*** Scheduling [" << CurCycle << "]: ";
146 DEBUG(SU->dump(DAG));
148 Sequence.push_back(SU);
149 SU->Cycle = CurCycle;
151 // Top down: release successors.
152 for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
154 ReleaseSucc(I->Dep, I->isCtrl);
157 /// ListScheduleTopDown - The main loop of list scheduling for top-down
159 void ScheduleDAGList::ListScheduleTopDown() {
160 unsigned CurCycle = 0;
162 // All leaves to Available queue.
163 for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
164 // It is available if it has no predecessors.
165 if (SUnits[i].Preds.empty()) {
166 AvailableQueue->push(&SUnits[i]);
167 SUnits[i].isAvailable = SUnits[i].isPending = true;
171 // While Available queue is not empty, grab the node with the highest
172 // priority. If it is not ready put it back. Schedule the node.
173 std::vector<SUnit*> NotReady;
174 Sequence.reserve(SUnits.size());
175 while (!AvailableQueue->empty() || !PendingQueue.empty()) {
176 // Check to see if any of the pending instructions are ready to issue. If
177 // so, add them to the available queue.
178 for (unsigned i = 0, e = PendingQueue.size(); i != e; ++i) {
179 if (PendingQueue[i].first == CurCycle) {
180 AvailableQueue->push(PendingQueue[i].second);
181 PendingQueue[i].second->isAvailable = true;
182 PendingQueue[i] = PendingQueue.back();
183 PendingQueue.pop_back();
186 assert(PendingQueue[i].first > CurCycle && "Negative latency?");
190 // If there are no instructions available, don't try to issue anything, and
191 // don't advance the hazard recognizer.
192 if (AvailableQueue->empty()) {
197 SUnit *FoundSUnit = 0;
198 SDNode *FoundNode = 0;
200 bool HasNoopHazards = false;
201 while (!AvailableQueue->empty()) {
202 SUnit *CurSUnit = AvailableQueue->pop();
204 // Get the node represented by this SUnit.
205 FoundNode = CurSUnit->getNode();
207 // If this is a pseudo op, like copyfromreg, look to see if there is a
208 // real target node flagged to it. If so, use the target node.
209 while (!FoundNode->isMachineOpcode()) {
210 SDNode *N = FoundNode->getFlaggedNode();
215 HazardRecognizer::HazardType HT = HazardRec->getHazardType(FoundNode);
216 if (HT == HazardRecognizer::NoHazard) {
217 FoundSUnit = CurSUnit;
221 // Remember if this is a noop hazard.
222 HasNoopHazards |= HT == HazardRecognizer::NoopHazard;
224 NotReady.push_back(CurSUnit);
227 // Add the nodes that aren't ready back onto the available list.
228 if (!NotReady.empty()) {
229 AvailableQueue->push_all(NotReady);
233 // If we found a node to schedule, do it now.
235 ScheduleNodeTopDown(FoundSUnit, CurCycle);
236 HazardRec->EmitInstruction(FoundNode);
237 FoundSUnit->isScheduled = true;
238 AvailableQueue->ScheduledNode(FoundSUnit);
240 // If this is a pseudo-op node, we don't want to increment the current
242 if (FoundSUnit->Latency) // Don't increment CurCycle for pseudo-ops!
244 } else if (!HasNoopHazards) {
245 // Otherwise, we have a pipeline stall, but no other problem, just advance
246 // the current cycle and try again.
247 DOUT << "*** Advancing cycle, no work to do\n";
248 HazardRec->AdvanceCycle();
252 // Otherwise, we have no instructions to issue and we have instructions
253 // that will fault if we don't do this right. This is the case for
254 // processors without pipeline interlocks and other cases.
255 DOUT << "*** Emitting noop\n";
256 HazardRec->EmitNoop();
257 Sequence.push_back(0); // NULL SUnit* -> noop
264 // Verify that all SUnits were scheduled.
265 bool AnyNotSched = false;
266 for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
267 if (SUnits[i].NumPredsLeft != 0) {
269 cerr << "*** List scheduling failed! ***\n";
271 cerr << "has not been scheduled!\n";
275 assert(!AnyNotSched);
279 //===----------------------------------------------------------------------===//
280 // Public Constructor Functions
281 //===----------------------------------------------------------------------===//
283 /// createTDListDAGScheduler - This creates a top-down list scheduler with a
284 /// new hazard recognizer. This scheduler takes ownership of the hazard
285 /// recognizer and deletes it when done.
286 ScheduleDAG* llvm::createTDListDAGScheduler(SelectionDAGISel *IS,
288 const TargetMachine *TM,
289 MachineBasicBlock *BB, bool Fast) {
290 return new ScheduleDAGList(DAG, BB, *TM,
291 new LatencyPriorityQueue(),
292 IS->CreateTargetHazardRecognizer());