1 files changed, 106 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/escape/leaks.go b/src/cmd/compile/internal/escape/leaks.go
new file mode 100644
index 0000000000..4c848a5ee7
--- /dev/null
+++ b/src/cmd/compile/internal/escape/leaks.go
@@ -0,0 +1,106 @@
+// 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"
+)
+
+const numEscResults = 7
+
+// An leaks represents a set of assignment flows from a parameter
+// to the heap or to any of its function's (first numEscResults)
+// result parameters.
+type leaks [1 + numEscResults]uint8
+
+// Empty reports whether l is an empty set (i.e., no assignment flows).
+func (l leaks) Empty() bool { return l == leaks{} }
+
+// 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(0) }
+
+// 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(1 + i) }
+
+// AddHeap adds an assignment flow from l to the heap.
+func (l *leaks) AddHeap(derefs int) { l.add(0, 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(1+i, derefs) }
+
+func (l *leaks) setResult(i, derefs int) { l.set(1+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 := 0; i < numEscResults; i++ {
+			if l.Result(i) >= x {
+				l.setResult(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
+}