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
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
|
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package gc
// Strongly connected components.
//
// Run analysis on minimal sets of mutually recursive functions
// or single non-recursive functions, bottom up.
//
// Finding these sets is finding strongly connected components
// by reverse topological order in the static call graph.
// The algorithm (known as Tarjan's algorithm) for doing that is taken from
// Sedgewick, Algorithms, Second Edition, p. 482, with two adaptations.
//
// First, a hidden closure function (n.Func.IsHiddenClosure()) cannot be the
// root of a connected component. Refusing to use it as a root
// forces it into the component of the function in which it appears.
// This is more convenient for escape analysis.
//
// Second, each function becomes two virtual nodes in the graph,
// with numbers n and n+1. We record the function's node number as n
// but search from node n+1. If the search tells us that the component
// number (min) is n+1, we know that this is a trivial component: one function
// plus its closures. If the search tells us that the component number is
// n, then there was a path from node n+1 back to node n, meaning that
// the function set is mutually recursive. The escape analysis can be
// more precise when analyzing a single non-recursive function than
// when analyzing a set of mutually recursive functions.
type bottomUpVisitor struct {
analyze func([]*Node, bool)
visitgen uint32
nodeID map[*Node]uint32
stack []*Node
}
// visitBottomUp invokes analyze on the ODCLFUNC nodes listed in list.
// It calls analyze with successive groups of functions, working from
// the bottom of the call graph upward. Each time analyze is called with
// a list of functions, every function on that list only calls other functions
// on the list or functions that have been passed in previous invocations of
// analyze. Closures appear in the same list as their outer functions.
// The lists are as short as possible while preserving those requirements.
// (In a typical program, many invocations of analyze will be passed just
// a single function.) The boolean argument 'recursive' passed to analyze
// specifies whether the functions on the list are mutually recursive.
// If recursive is false, the list consists of only a single function and its closures.
// If recursive is true, the list may still contain only a single function,
// if that function is itself recursive.
func visitBottomUp(list []*Node, analyze func(list []*Node, recursive bool)) {
var v bottomUpVisitor
v.analyze = analyze
v.nodeID = make(map[*Node]uint32)
for _, n := range list {
if n.Op == ODCLFUNC && !n.Func.IsHiddenClosure() {
v.visit(n)
}
}
}
func (v *bottomUpVisitor) visit(n *Node) uint32 {
if id := v.nodeID[n]; id > 0 {
// already visited
return id
}
v.visitgen++
id := v.visitgen
v.nodeID[n] = id
v.visitgen++
min := v.visitgen
v.stack = append(v.stack, n)
inspectList(n.Nbody, func(n *Node) bool {
switch n.Op {
case ONAME:
if n.Class() == PFUNC {
if n.isMethodExpression() {
n = asNode(n.Type.Nname())
}
if n != nil && n.Name.Defn != nil {
if m := v.visit(n.Name.Defn); m < min {
min = m
}
}
}
case ODOTMETH:
fn := asNode(n.Type.Nname())
if fn != nil && fn.Op == ONAME && fn.Class() == PFUNC && fn.Name.Defn != nil {
if m := v.visit(fn.Name.Defn); m < min {
min = m
}
}
case OCALLPART:
fn := asNode(callpartMethod(n).Type.Nname())
if fn != nil && fn.Op == ONAME && fn.Class() == PFUNC && fn.Name.Defn != nil {
if m := v.visit(fn.Name.Defn); m < min {
min = m
}
}
case OCLOSURE:
if m := v.visit(n.Func.Closure); m < min {
min = m
}
}
return true
})
if (min == id || min == id+1) && !n.Func.IsHiddenClosure() {
// This node is the root of a strongly connected component.
// The original min passed to visitcodelist was v.nodeID[n]+1.
// If visitcodelist found its way back to v.nodeID[n], then this
// block is a set of mutually recursive functions.
// Otherwise it's just a lone function that does not recurse.
recursive := min == id
// Remove connected component from stack.
// Mark walkgen so that future visits return a large number
// so as not to affect the caller's min.
var i int
for i = len(v.stack) - 1; i >= 0; i-- {
x := v.stack[i]
if x == n {
break
}
v.nodeID[x] = ^uint32(0)
}
v.nodeID[n] = ^uint32(0)
block := v.stack[i:]
// Run escape analysis on this set of functions.
v.stack = v.stack[:i]
v.analyze(block, recursive)
}
return min
}
|
