From 75102afce77f1376b0aab3f1d5fee9b881d0f68a Mon Sep 17 00:00:00 2001
From: Keith Randall <khr@golang.org>
Date: Thu, 5 Nov 2015 14:59:47 -0800
Subject: [dev.ssa] cmd/compile: better register allocation

Use a more precise computation of next use.  It properly
detects lifetime holes and deallocates values during those holes.
It also uses a more precise version of distance to next use which
affects which values get spilled.

Change-Id: I49eb3ebe2d2cb64842ecdaa7fb4f3792f8afb90b
Reviewed-on: https://go-review.googlesource.com/16760
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
---
 src/cmd/compile/internal/ssa/sparsemap.go | 69 +++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 src/cmd/compile/internal/ssa/sparsemap.go

(limited to 'src/cmd/compile/internal/ssa/sparsemap.go')

diff --git a/src/cmd/compile/internal/ssa/sparsemap.go b/src/cmd/compile/internal/ssa/sparsemap.go
new file mode 100644
index 0000000000..6c0043b230
--- /dev/null
+++ b/src/cmd/compile/internal/ssa/sparsemap.go
@@ -0,0 +1,69 @@
+// Copyright 2015 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
+
+// from http://research.swtch.com/sparse
+// in turn, from Briggs and Torczon
+
+type sparseEntry struct {
+	key ID
+	val int32
+}
+
+type sparseMap struct {
+	dense  []sparseEntry
+	sparse []int
+}
+
+// newSparseMap returns a sparseMap that can map
+// integers between 0 and n-1 to int32s.
+func newSparseMap(n int) *sparseMap {
+	return &sparseMap{nil, make([]int, n)}
+}
+
+func (s *sparseMap) size() int {
+	return len(s.dense)
+}
+
+func (s *sparseMap) contains(k ID) bool {
+	i := s.sparse[k]
+	return i < len(s.dense) && s.dense[i].key == k
+}
+
+func (s *sparseMap) get(k ID) int32 {
+	i := s.sparse[k]
+	if i < len(s.dense) && s.dense[i].key == k {
+		return s.dense[i].val
+	}
+	return -1
+}
+
+func (s *sparseMap) set(k ID, v int32) {
+	i := s.sparse[k]
+	if i < len(s.dense) && s.dense[i].key == k {
+		s.dense[i].val = v
+		return
+	}
+	s.dense = append(s.dense, sparseEntry{k, v})
+	s.sparse[k] = len(s.dense) - 1
+}
+
+func (s *sparseMap) remove(k ID) {
+	i := s.sparse[k]
+	if i < 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 *sparseMap) clear() {
+	s.dense = s.dense[:0]
+}
+
+func (s *sparseMap) contents() []sparseEntry {
+	return s.dense
+}
-- 
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