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comparison lib/CodeGen/LatencyPriorityQueue.cpp @ 0:95c75e76d11b LLVM3.4

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LLVM 3.4
author Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date Thu, 12 Dec 2013 13:56:28 +0900
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children 54457678186b
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-1:000000000000 0:95c75e76d11b
1 //===---- LatencyPriorityQueue.cpp - A latency-oriented priority queue ----===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements the LatencyPriorityQueue class, which is a
11 // SchedulingPriorityQueue that schedules using latency information to
12 // reduce the length of the critical path through the basic block.
13 //
14 //===----------------------------------------------------------------------===//
15
16 #define DEBUG_TYPE "scheduler"
17 #include "llvm/CodeGen/LatencyPriorityQueue.h"
18 #include "llvm/Support/Debug.h"
19 #include "llvm/Support/raw_ostream.h"
20 using namespace llvm;
21
22 bool latency_sort::operator()(const SUnit *LHS, const SUnit *RHS) const {
23 // The isScheduleHigh flag allows nodes with wraparound dependencies that
24 // cannot easily be modeled as edges with latencies to be scheduled as
25 // soon as possible in a top-down schedule.
26 if (LHS->isScheduleHigh && !RHS->isScheduleHigh)
27 return false;
28 if (!LHS->isScheduleHigh && RHS->isScheduleHigh)
29 return true;
30
31 unsigned LHSNum = LHS->NodeNum;
32 unsigned RHSNum = RHS->NodeNum;
33
34 // The most important heuristic is scheduling the critical path.
35 unsigned LHSLatency = PQ->getLatency(LHSNum);
36 unsigned RHSLatency = PQ->getLatency(RHSNum);
37 if (LHSLatency < RHSLatency) return true;
38 if (LHSLatency > RHSLatency) return false;
39
40 // After that, if two nodes have identical latencies, look to see if one will
41 // unblock more other nodes than the other.
42 unsigned LHSBlocked = PQ->getNumSolelyBlockNodes(LHSNum);
43 unsigned RHSBlocked = PQ->getNumSolelyBlockNodes(RHSNum);
44 if (LHSBlocked < RHSBlocked) return true;
45 if (LHSBlocked > RHSBlocked) return false;
46
47 // Finally, just to provide a stable ordering, use the node number as a
48 // deciding factor.
49 return RHSNum < LHSNum;
50 }
51
52
53 /// getSingleUnscheduledPred - If there is exactly one unscheduled predecessor
54 /// of SU, return it, otherwise return null.
55 SUnit *LatencyPriorityQueue::getSingleUnscheduledPred(SUnit *SU) {
56 SUnit *OnlyAvailablePred = 0;
57 for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
58 I != E; ++I) {
59 SUnit &Pred = *I->getSUnit();
60 if (!Pred.isScheduled) {
61 // We found an available, but not scheduled, predecessor. If it's the
62 // only one we have found, keep track of it... otherwise give up.
63 if (OnlyAvailablePred && OnlyAvailablePred != &Pred)
64 return 0;
65 OnlyAvailablePred = &Pred;
66 }
67 }
68
69 return OnlyAvailablePred;
70 }
71
72 void LatencyPriorityQueue::push(SUnit *SU) {
73 // Look at all of the successors of this node. Count the number of nodes that
74 // this node is the sole unscheduled node for.
75 unsigned NumNodesBlocking = 0;
76 for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
77 I != E; ++I) {
78 if (getSingleUnscheduledPred(I->getSUnit()) == SU)
79 ++NumNodesBlocking;
80 }
81 NumNodesSolelyBlocking[SU->NodeNum] = NumNodesBlocking;
82
83 Queue.push_back(SU);
84 }
85
86
87 // scheduledNode - As nodes are scheduled, we look to see if there are any
88 // successor nodes that have a single unscheduled predecessor. If so, that
89 // single predecessor has a higher priority, since scheduling it will make
90 // the node available.
91 void LatencyPriorityQueue::scheduledNode(SUnit *SU) {
92 for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
93 I != E; ++I) {
94 AdjustPriorityOfUnscheduledPreds(I->getSUnit());
95 }
96 }
97
98 /// AdjustPriorityOfUnscheduledPreds - One of the predecessors of SU was just
99 /// scheduled. If SU is not itself available, then there is at least one
100 /// predecessor node that has not been scheduled yet. If SU has exactly ONE
101 /// unscheduled predecessor, we want to increase its priority: it getting
102 /// scheduled will make this node available, so it is better than some other
103 /// node of the same priority that will not make a node available.
104 void LatencyPriorityQueue::AdjustPriorityOfUnscheduledPreds(SUnit *SU) {
105 if (SU->isAvailable) return; // All preds scheduled.
106
107 SUnit *OnlyAvailablePred = getSingleUnscheduledPred(SU);
108 if (OnlyAvailablePred == 0 || !OnlyAvailablePred->isAvailable) return;
109
110 // Okay, we found a single predecessor that is available, but not scheduled.
111 // Since it is available, it must be in the priority queue. First remove it.
112 remove(OnlyAvailablePred);
113
114 // Reinsert the node into the priority queue, which recomputes its
115 // NumNodesSolelyBlocking value.
116 push(OnlyAvailablePred);
117 }
118
119 SUnit *LatencyPriorityQueue::pop() {
120 if (empty()) return NULL;
121 std::vector<SUnit *>::iterator Best = Queue.begin();
122 for (std::vector<SUnit *>::iterator I = llvm::next(Queue.begin()),
123 E = Queue.end(); I != E; ++I)
124 if (Picker(*Best, *I))
125 Best = I;
126 SUnit *V = *Best;
127 if (Best != prior(Queue.end()))
128 std::swap(*Best, Queue.back());
129 Queue.pop_back();
130 return V;
131 }
132
133 void LatencyPriorityQueue::remove(SUnit *SU) {
134 assert(!Queue.empty() && "Queue is empty!");
135 std::vector<SUnit *>::iterator I = std::find(Queue.begin(), Queue.end(), SU);
136 if (I != prior(Queue.end()))
137 std::swap(*I, Queue.back());
138 Queue.pop_back();
139 }
140
141 #ifdef NDEBUG
142 void LatencyPriorityQueue::dump(ScheduleDAG *DAG) const {}
143 #else
144 void LatencyPriorityQueue::dump(ScheduleDAG *DAG) const {
145 LatencyPriorityQueue q = *this;
146 while (!q.empty()) {
147 SUnit *su = q.pop();
148 dbgs() << "Height " << su->getHeight() << ": ";
149 su->dump(DAG);
150 }
151 }
152 #endif