cmd/compile/internal/pgo: use a slice for locations

Currently locations are stored in a map and looked up by ID from
the map. The IDs are usually small sequential integers (the Go
pprof CPU profiles are so). Using a slice is more efficient (with
a fallback map to handle weirdly large IDs).

Change-Id: I9e20d5cebca3a5239636413e1bf2f0b273038031
Reviewed-on: https://go-review.googlesource.com/c/go/+/447803
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/cmd/compile/internal/pgo/graph.go b/src/cmd/compile/internal/pgo/graph.go
index d422d5b0974a4e2d36034b114ebc8c556e57cb95..203cc618ca17c3b5fbd3208484658a80e88fd988 100644 (file)
--- a/src/cmd/compile/internal/pgo/graph.go
+++ b/src/cmd/compile/internal/pgo/graph.go
@@ -245,10 +245,8 @@ func (e *Edge) WeightValue() int64 {
        return e.Weight / e.WeightDiv
 }
 
-// newGraph computes a graph from a profile. It returns the graph, and
-// a map from the profile location indices to the corresponding graph
-// nodes.
-func newGraph(prof *profile.Profile, o *Options) (*Graph, map[uint64]Nodes) {
+// newGraph computes a graph from a profile.
+func newGraph(prof *profile.Profile, o *Options) *Graph {
        nodes, locationMap := CreateNodes(prof, o)
        seenNode := make(map[*Node]bool)
        seenEdge := make(map[nodePair]bool)
@@ -274,7 +272,7 @@ func newGraph(prof *profile.Profile, o *Options) (*Graph, map[uint64]Nodes) {
                // Group the sample frames, based on a global map.
                for i := len(sample.Location) - 1; i >= 0; i-- {
                        l := sample.Location[i]
-                       locNodes := locationMap[l.ID]
+                       locNodes := locationMap.get(l.ID)
                        for ni := len(locNodes) - 1; ni >= 0; ni-- {
                                n := locNodes[ni]
                                if n == nil {
@@ -303,7 +301,7 @@ func newGraph(prof *profile.Profile, o *Options) (*Graph, map[uint64]Nodes) {
                }
        }
 
-       return selectNodesForGraph(nodes, o.DropNegative), locationMap
+       return selectNodesForGraph(nodes, o.DropNegative)
 }
 
 func selectNodesForGraph(nodes Nodes, dropNegative bool) *Graph {
@@ -389,11 +387,32 @@ func isNegative(n *Node) bool {
        }
 }
 
+type locationMap struct {
+       s []Nodes          // a slice for small sequential IDs
+       m map[uint64]Nodes // fallback for large IDs (unlikely)
+}
+
+func (l *locationMap) add(id uint64, n Nodes) {
+       if id < uint64(len(l.s)) {
+               l.s[id] = n
+       } else {
+               l.m[id] = n
+       }
+}
+
+func (l locationMap) get(id uint64) Nodes {
+       if id < uint64(len(l.s)) {
+               return l.s[id]
+       } else {
+               return l.m[id]
+       }
+}
+
 // CreateNodes creates graph nodes for all locations in a profile. It
 // returns set of all nodes, plus a mapping of each location to the
 // set of corresponding nodes (one per location.Line).
-func CreateNodes(prof *profile.Profile, o *Options) (Nodes, map[uint64]Nodes) {
-       locations := make(map[uint64]Nodes, len(prof.Location))
+func CreateNodes(prof *profile.Profile, o *Options) (Nodes, locationMap) {
+       locations := locationMap{make([]Nodes, len(prof.Location)+1), make(map[uint64]Nodes)}
        nm := make(NodeMap, len(prof.Location))
        for _, l := range prof.Location {
                lines := l.Line
@@ -404,7 +423,7 @@ func CreateNodes(prof *profile.Profile, o *Options) (Nodes, map[uint64]Nodes) {
                for ln := range lines {
                        nodes[ln] = nm.findOrInsertLine(l, lines[ln], o)
                }
-               locations[l.ID] = nodes
+               locations.add(l.ID, nodes)
        }
        return nm.nodes(), locations
 }

diff --git a/src/cmd/compile/internal/pgo/irgraph.go b/src/cmd/compile/internal/pgo/irgraph.go
index 528c27645d0df577fc9cd7859e1d3f2baa6affe5..6ca86e7684230f6efb5d50bd0c2667b47c9786e2 100644 (file)
--- a/src/cmd/compile/internal/pgo/irgraph.go
+++ b/src/cmd/compile/internal/pgo/irgraph.go
@@ -140,7 +140,7 @@ func New(profileFile string) *Profile {
                return nil
        }
 
-       g, _ := newGraph(profile, &Options{
+       g := newGraph(profile, &Options{
                CallTree:    false,
                SampleValue: func(v []int64) int64 { return v[1] },
        })