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// Copyright 2018 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 escape
import (
"cmd/compile/internal/base"
"math"
"strings"
)
// A leaks represents a set of assignment flows from a parameter to
// the heap, mutator, callee, or to any of its function's (first
// numEscResults) result parameters.
type leaks [8]uint8
const (
leakHeap = iota
leakMutator
leakCallee
leakResult0
)
const numEscResults = len(leaks{}) - leakResult0
// Heap returns the minimum deref count of any assignment flow from l
// to the heap. If no such flows exist, Heap returns -1.
func (l leaks) Heap() int { return l.get(leakHeap) }
// Mutator returns the minimum deref count of any assignment flow from
// l to the pointer operand of an indirect assignment statement. If no
// such flows exist, Mutator returns -1.
func (l leaks) Mutator() int { return l.get(leakMutator) }
// Callee returns the minimum deref count of any assignment flow from
// l to the callee operand of call expression. If no such flows exist,
// Callee returns -1.
func (l leaks) Callee() int { return l.get(leakCallee) }
// Result returns the minimum deref count of any assignment flow from
// l to its function's i'th result parameter. If no such flows exist,
// Result returns -1.
func (l leaks) Result(i int) int { return l.get(leakResult0 + i) }
// AddHeap adds an assignment flow from l to the heap.
func (l *leaks) AddHeap(derefs int) { l.add(leakHeap, derefs) }
// AddMutator adds a flow from l to the mutator (i.e., a pointer
// operand of an indirect assignment statement).
func (l *leaks) AddMutator(derefs int) { l.add(leakMutator, derefs) }
// AddCallee adds an assignment flow from l to the callee operand of a
// call expression.
func (l *leaks) AddCallee(derefs int) { l.add(leakCallee, derefs) }
// AddResult adds an assignment flow from l to its function's i'th
// result parameter.
func (l *leaks) AddResult(i, derefs int) { l.add(leakResult0+i, derefs) }
func (l leaks) get(i int) int { return int(l[i]) - 1 }
func (l *leaks) add(i, derefs int) {
if old := l.get(i); old < 0 || derefs < old {
l.set(i, derefs)
}
}
func (l *leaks) set(i, derefs int) {
v := derefs + 1
if v < 0 {
base.Fatalf("invalid derefs count: %v", derefs)
}
if v > math.MaxUint8 {
v = math.MaxUint8
}
l[i] = uint8(v)
}
// Optimize removes result flow paths that are equal in length or
// longer than the shortest heap flow path.
func (l *leaks) Optimize() {
// If we have a path to the heap, then there's no use in
// keeping equal or longer paths elsewhere.
if x := l.Heap(); x >= 0 {
for i := 1; i < len(*l); i++ {
if l.get(i) >= x {
l.set(i, -1)
}
}
}
}
var leakTagCache = map[leaks]string{}
// Encode converts l into a binary string for export data.
func (l leaks) Encode() string {
if l.Heap() == 0 {
// Space optimization: empty string encodes more
// efficiently in export data.
return ""
}
if s, ok := leakTagCache[l]; ok {
return s
}
n := len(l)
for n > 0 && l[n-1] == 0 {
n--
}
s := "esc:" + string(l[:n])
leakTagCache[l] = s
return s
}
// parseLeaks parses a binary string representing a leaks.
func parseLeaks(s string) leaks {
var l leaks
if !strings.HasPrefix(s, "esc:") {
l.AddHeap(0)
return l
}
copy(l[:], s[4:])
return l
}
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