1 files changed, 79 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/ssa/sparsemappos.go b/src/cmd/compile/internal/ssa/sparsemappos.go
new file mode 100644
index 0000000..60bad82
--- /dev/null
+++ b/src/cmd/compile/internal/ssa/sparsemappos.go
@@ -0,0 +1,79 @@
+// Copyright 2022 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 ssa
+
+import "cmd/internal/src"
+
+// from https://research.swtch.com/sparse
+// in turn, from Briggs and Torczon
+
+type sparseEntryPos struct {
+	key ID
+	val int32
+	pos src.XPos
+}
+
+type sparseMapPos struct {
+	dense  []sparseEntryPos
+	sparse []int32
+}
+
+// newSparseMapPos returns a sparseMapPos that can map
+// integers between 0 and n-1 to the pair <int32,src.XPos>.
+func newSparseMapPos(n int) *sparseMapPos {
+	return &sparseMapPos{dense: nil, sparse: make([]int32, n)}
+}
+
+func (s *sparseMapPos) cap() int {
+	return len(s.sparse)
+}
+
+func (s *sparseMapPos) size() int {
+	return len(s.dense)
+}
+
+func (s *sparseMapPos) contains(k ID) bool {
+	i := s.sparse[k]
+	return i < int32(len(s.dense)) && s.dense[i].key == k
+}
+
+// get returns the value for key k, or -1 if k does
+// not appear in the map.
+func (s *sparseMapPos) get(k ID) int32 {
+	i := s.sparse[k]
+	if i < int32(len(s.dense)) && s.dense[i].key == k {
+		return s.dense[i].val
+	}
+	return -1
+}
+
+func (s *sparseMapPos) set(k ID, v int32, a src.XPos) {
+	i := s.sparse[k]
+	if i < int32(len(s.dense)) && s.dense[i].key == k {
+		s.dense[i].val = v
+		s.dense[i].pos = a
+		return
+	}
+	s.dense = append(s.dense, sparseEntryPos{k, v, a})
+	s.sparse[k] = int32(len(s.dense)) - 1
+}
+
+func (s *sparseMapPos) remove(k ID) {
+	i := s.sparse[k]
+	if i < int32(len(s.dense)) && s.dense[i].key == k {
+		y := s.dense[len(s.dense)-1]
+		s.dense[i] = y
+		s.sparse[y.key] = i
+		s.dense = s.dense[:len(s.dense)-1]
+	}
+}
+
+func (s *sparseMapPos) clear() {
+	s.dense = s.dense[:0]
+}
+
+func (s *sparseMapPos) contents() []sparseEntryPos {
+	return s.dense
+}