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/LatencyPriorityQueue.h"
23 #include "llvm/CodeGen/ScheduleDAGSDNodes.h"
24 #include "llvm/CodeGen/ScheduleHazardRecognizer.h"
25 #include "llvm/CodeGen/SchedulerRegistry.h"
26 #include "llvm/CodeGen/SelectionDAGISel.h"
27 #include "llvm/Target/TargetRegisterInfo.h"
28 #include "llvm/Target/TargetData.h"
29 #include "llvm/Target/TargetInstrInfo.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/Support/Compiler.h"
32 #include "llvm/ADT/PriorityQueue.h"
33 #include "llvm/ADT/Statistic.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 ScheduleDAGSDNodes {
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 become available, the instruction is
58 /// added to the AvailableQueue.
59 std::vector<SUnit*> PendingQueue;
61 /// HazardRec - The hazard recognizer to use.
62 ScheduleHazardRecognizer *HazardRec;
65 ScheduleDAGList(MachineFunction &mf,
66 SchedulingPriorityQueue *availqueue,
67 ScheduleHazardRecognizer *HR)
68 : ScheduleDAGSDNodes(mf),
69 AvailableQueue(availqueue), HazardRec(HR) {
74 delete AvailableQueue;
80 void ReleaseSucc(SUnit *SU, const SDep &D);
81 void ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle);
82 void ListScheduleTopDown();
84 } // end anonymous namespace
86 /// Schedule - Schedule the DAG using list scheduling.
87 void ScheduleDAGList::Schedule() {
88 DOUT << "********** List Scheduling **********\n";
90 // Build the scheduling graph.
93 AvailableQueue->initNodes(SUnits);
95 ListScheduleTopDown();
97 AvailableQueue->releaseState();
100 //===----------------------------------------------------------------------===//
101 // Top-Down Scheduling
102 //===----------------------------------------------------------------------===//
104 /// ReleaseSucc - Decrement the NumPredsLeft count of a successor. Add it to
105 /// the PendingQueue if the count reaches zero. Also update its cycle bound.
106 void ScheduleDAGList::ReleaseSucc(SUnit *SU, const SDep &D) {
107 SUnit *SuccSU = D.getSUnit();
108 --SuccSU->NumPredsLeft;
111 if (SuccSU->NumPredsLeft < 0) {
112 cerr << "*** Scheduling failed! ***\n";
114 cerr << " has been released too many times!\n";
119 SuccSU->setDepthToAtLeast(SU->getDepth() + D.getLatency());
121 if (SuccSU->NumPredsLeft == 0) {
122 PendingQueue.push_back(SuccSU);
126 /// ScheduleNodeTopDown - Add the node to the schedule. Decrement the pending
127 /// count of its successors. If a successor pending count is zero, add it to
128 /// the Available queue.
129 void ScheduleDAGList::ScheduleNodeTopDown(SUnit *SU, unsigned CurCycle) {
130 DOUT << "*** Scheduling [" << CurCycle << "]: ";
131 DEBUG(SU->dump(this));
133 Sequence.push_back(SU);
134 assert(CurCycle >= SU->getDepth() && "Node scheduled above its depth!");
135 SU->setDepthToAtLeast(CurCycle);
137 // Top down: release successors.
138 for (SUnit::succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
140 assert(!I->isAssignedRegDep() &&
141 "The list-td scheduler doesn't yet support physreg dependencies!");
146 SU->isScheduled = true;
147 AvailableQueue->ScheduledNode(SU);
150 /// ListScheduleTopDown - The main loop of list scheduling for top-down
152 void ScheduleDAGList::ListScheduleTopDown() {
153 unsigned CurCycle = 0;
155 // All leaves to Available queue.
156 for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
157 // It is available if it has no predecessors.
158 if (SUnits[i].Preds.empty()) {
159 AvailableQueue->push(&SUnits[i]);
160 SUnits[i].isAvailable = true;
164 // While Available queue is not empty, grab the node with the highest
165 // priority. If it is not ready put it back. Schedule the node.
166 std::vector<SUnit*> NotReady;
167 Sequence.reserve(SUnits.size());
168 while (!AvailableQueue->empty() || !PendingQueue.empty()) {
169 // Check to see if any of the pending instructions are ready to issue. If
170 // so, add them to the available queue.
171 for (unsigned i = 0, e = PendingQueue.size(); i != e; ++i) {
172 if (PendingQueue[i]->getDepth() == CurCycle) {
173 AvailableQueue->push(PendingQueue[i]);
174 PendingQueue[i]->isAvailable = true;
175 PendingQueue[i] = PendingQueue.back();
176 PendingQueue.pop_back();
179 assert(PendingQueue[i]->getDepth() > CurCycle && "Negative latency?");
183 // If there are no instructions available, don't try to issue anything, and
184 // don't advance the hazard recognizer.
185 if (AvailableQueue->empty()) {
190 SUnit *FoundSUnit = 0;
192 bool HasNoopHazards = false;
193 while (!AvailableQueue->empty()) {
194 SUnit *CurSUnit = AvailableQueue->pop();
196 ScheduleHazardRecognizer::HazardType HT =
197 HazardRec->getHazardType(CurSUnit);
198 if (HT == ScheduleHazardRecognizer::NoHazard) {
199 FoundSUnit = CurSUnit;
203 // Remember if this is a noop hazard.
204 HasNoopHazards |= HT == ScheduleHazardRecognizer::NoopHazard;
206 NotReady.push_back(CurSUnit);
209 // Add the nodes that aren't ready back onto the available list.
210 if (!NotReady.empty()) {
211 AvailableQueue->push_all(NotReady);
215 // If we found a node to schedule, do it now.
217 ScheduleNodeTopDown(FoundSUnit, CurCycle);
218 HazardRec->EmitInstruction(FoundSUnit);
220 // If this is a pseudo-op node, we don't want to increment the current
222 if (FoundSUnit->Latency) // Don't increment CurCycle for pseudo-ops!
224 } else if (!HasNoopHazards) {
225 // Otherwise, we have a pipeline stall, but no other problem, just advance
226 // the current cycle and try again.
227 DOUT << "*** Advancing cycle, no work to do\n";
228 HazardRec->AdvanceCycle();
232 // Otherwise, we have no instructions to issue and we have instructions
233 // that will fault if we don't do this right. This is the case for
234 // processors without pipeline interlocks and other cases.
235 DOUT << "*** Emitting noop\n";
236 HazardRec->EmitNoop();
237 Sequence.push_back(0); // NULL here means noop
244 VerifySchedule(/*isBottomUp=*/false);
248 //===----------------------------------------------------------------------===//
249 // Public Constructor Functions
250 //===----------------------------------------------------------------------===//
252 /// createTDListDAGScheduler - This creates a top-down list scheduler with a
253 /// new hazard recognizer. This scheduler takes ownership of the hazard
254 /// recognizer and deletes it when done.
255 ScheduleDAG* llvm::createTDListDAGScheduler(SelectionDAGISel *IS,
257 return new ScheduleDAGList(*IS->MF,
258 new LatencyPriorityQueue(),
259 IS->CreateTargetHazardRecognizer());