1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
|
//===---- LatencyPriorityQueue.cpp - A latency-oriented priority queue ----===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the LatencyPriorityQueue class, which is a
// SchedulingPriorityQueue that schedules using latency information to
// reduce the length of the critical path through the basic block.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "scheduler"
#include "llvm/CodeGen/LatencyPriorityQueue.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
bool latency_sort::operator()(const SUnit *LHS, const SUnit *RHS) const {
// The isScheduleHigh flag allows nodes with wraparound dependencies that
// cannot easily be modeled as edges with latencies to be scheduled as
// soon as possible in a top-down schedule.
if (LHS->isScheduleHigh && !RHS->isScheduleHigh)
return false;
if (!LHS->isScheduleHigh && RHS->isScheduleHigh)
return true;
unsigned LHSNum = LHS->NodeNum;
unsigned RHSNum = RHS->NodeNum;
// The most important heuristic is scheduling the critical path.
unsigned LHSLatency = PQ->getLatency(LHSNum);
unsigned RHSLatency = PQ->getLatency(RHSNum);
if (LHSLatency < RHSLatency) return true;
if (LHSLatency > RHSLatency) return false;
// After that, if two nodes have identical latencies, look to see if one will
// unblock more other nodes than the other.
unsigned LHSBlocked = PQ->getNumSolelyBlockNodes(LHSNum);
unsigned RHSBlocked = PQ->getNumSolelyBlockNodes(RHSNum);
if (LHSBlocked < RHSBlocked) return true;
if (LHSBlocked > RHSBlocked) return false;
// Finally, just to provide a stable ordering, use the node number as a
// deciding factor.
return LHSNum < RHSNum;
}
/// getSingleUnscheduledPred - If there is exactly one unscheduled predecessor
/// of SU, return it, otherwise return null.
SUnit *LatencyPriorityQueue::getSingleUnscheduledPred(SUnit *SU) {
SUnit *OnlyAvailablePred = 0;
for (SUnit::const_pred_iterator I = SU->Preds.begin(), E = SU->Preds.end();
I != E; ++I) {
SUnit &Pred = *I->getSUnit();
if (!Pred.isScheduled) {
// We found an available, but not scheduled, predecessor. If it's the
// only one we have found, keep track of it... otherwise give up.
if (OnlyAvailablePred && OnlyAvailablePred != &Pred)
return 0;
OnlyAvailablePred = &Pred;
}
}
return OnlyAvailablePred;
}
void LatencyPriorityQueue::push_impl(SUnit *SU) {
// Look at all of the successors of this node. Count the number of nodes that
// this node is the sole unscheduled node for.
unsigned NumNodesBlocking = 0;
for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I) {
if (getSingleUnscheduledPred(I->getSUnit()) == SU)
++NumNodesBlocking;
}
NumNodesSolelyBlocking[SU->NodeNum] = NumNodesBlocking;
Queue.push(SU);
}
// ScheduledNode - As nodes are scheduled, we look to see if there are any
// successor nodes that have a single unscheduled predecessor. If so, that
// single predecessor has a higher priority, since scheduling it will make
// the node available.
void LatencyPriorityQueue::ScheduledNode(SUnit *SU) {
for (SUnit::const_succ_iterator I = SU->Succs.begin(), E = SU->Succs.end();
I != E; ++I) {
AdjustPriorityOfUnscheduledPreds(I->getSUnit());
}
}
/// AdjustPriorityOfUnscheduledPreds - One of the predecessors of SU was just
/// scheduled. If SU is not itself available, then there is at least one
/// predecessor node that has not been scheduled yet. If SU has exactly ONE
/// unscheduled predecessor, we want to increase its priority: it getting
/// scheduled will make this node available, so it is better than some other
/// node of the same priority that will not make a node available.
void LatencyPriorityQueue::AdjustPriorityOfUnscheduledPreds(SUnit *SU) {
if (SU->isAvailable) return; // All preds scheduled.
SUnit *OnlyAvailablePred = getSingleUnscheduledPred(SU);
if (OnlyAvailablePred == 0 || !OnlyAvailablePred->isAvailable) return;
// Okay, we found a single predecessor that is available, but not scheduled.
// Since it is available, it must be in the priority queue. First remove it.
remove(OnlyAvailablePred);
// Reinsert the node into the priority queue, which recomputes its
// NumNodesSolelyBlocking value.
push(OnlyAvailablePred);
}
|
