go/callgraph: adds benchmarks comparing algorithms

Change-Id: Iff83e5f5790c9d92d6641d98380e1403855c27ab
Reviewed-on: https://go-review.googlesource.com/c/tools/+/460456
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Run-TryBot: Tim King <taking@google.com>
Reviewed-by: Zvonimir Pavlinovic <zpavlinovic@google.com>

1 files changed, 233 insertions, 0 deletions

diff --git a/go/callgraph/callgraph_test.go b/go/callgraph/callgraph_test.go
new file mode 100644
index 000000000..907b317a0
--- /dev/null
+++ b/go/callgraph/callgraph_test.go
@@ -0,0 +1,233 @@
+// Copyright 2023 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 callgraph_test
+
+import (
+	"log"
+	"sync"
+	"testing"
+
+	"golang.org/x/tools/go/callgraph"
+	"golang.org/x/tools/go/callgraph/cha"
+	"golang.org/x/tools/go/callgraph/rta"
+	"golang.org/x/tools/go/callgraph/static"
+	"golang.org/x/tools/go/callgraph/vta"
+	"golang.org/x/tools/go/loader"
+	"golang.org/x/tools/go/pointer"
+	"golang.org/x/tools/go/ssa"
+	"golang.org/x/tools/go/ssa/ssautil"
+)
+
+// Benchmarks comparing different callgraph algorithms implemented in
+// x/tools/go/callgraph. Comparison is on both speed, memory and precision.
+// Fewer edges and fewer reachable nodes implies a more precise result.
+// Comparison is done on a hello world http server using net/http.
+//
+// Current results were on an i7 macbook on go version devel go1.20-2730.
+// Number of nodes, edges, and reachable function are expected to vary between
+// go versions. Timing results are expected to vary between machines.
+//
+// BenchmarkStatic-12	 53 ms/op     6 MB/op	12113 nodes	 37355 edges	1522 reachable
+// BenchmarkCHA-12    	 86 ms/op	 16 MB/op	12113 nodes	131717 edges	7640 reachable
+// BenchmarkRTA-12		110 ms/op	 12 MB/op	 6566 nodes	 42291 edges	5099 reachable
+// BenchmarkPTA-12	   1427 ms/op	600 MB/op	 8714 nodes	 28244 edges	4184 reachable
+// BenchmarkVTA-12		603 ms/op	 87 MB/op	12112 nodes	 44857 edges	4918 reachable
+// BenchmarkVTA2-12		774 ms/op	115 MB/op	 4918 nodes	 20247 edges	3841 reachable
+// BenchmarkVTA3-12		928 ms/op	134 MB/op	 3841 nodes	 16502 edges	3542 reachable
+// BenchmarkVTAAlt-12	395 ms/op	 61 MB/op	 7640 nodes  29629 edges	4257 reachable
+// BenchmarkVTAAlt2-12	556 ms/op	 82 MB/op	 4257 nodes	 18057 edges	3586 reachable
+//
+// Note:
+// * Static is unsound and may miss real edges.
+// * RTA starts from a main function and only includes reachable functions.
+// * CHA starts from all functions.
+// * VTA, VTA2, and VTA3 are starting from all functions and the CHA callgraph.
+//   VTA2 and VTA3 are the result of re-applying VTA to the functions reachable
+//   from main() via the callgraph of the previous stage.
+// * VTAAlt, and VTAAlt2 start from the functions reachable from main via the
+//   CHA callgraph.
+// * All algorithms are unsound w.r.t. reflection.
+
+const httpEx = `package main
+
+import (
+    "fmt"
+    "net/http"
+)
+
+func hello(w http.ResponseWriter, req *http.Request) {
+    fmt.Fprintf(w, "hello world\n")
+}
+
+func main() {
+    http.HandleFunc("/hello", hello)
+    http.ListenAndServe(":8090", nil)
+}
+`
+
+var (
+	once sync.Once
+	prog *ssa.Program
+	main *ssa.Function
+)
+
+func example() (*ssa.Program, *ssa.Function) {
+	once.Do(func() {
+		var conf loader.Config
+		f, err := conf.ParseFile("<input>", httpEx)
+		if err != nil {
+			log.Fatal(err)
+		}
+		conf.CreateFromFiles(f.Name.Name, f)
+
+		lprog, err := conf.Load()
+		if err != nil {
+			log.Fatalf("test 'package %s': Load: %s", f.Name.Name, err)
+		}
+		prog = ssautil.CreateProgram(lprog, ssa.InstantiateGenerics)
+		prog.Build()
+
+		main = prog.Package(lprog.Created[0].Pkg).Members["main"].(*ssa.Function)
+	})
+	return prog, main
+}
+
+var stats bool = false // print stats?
+
+func logStats(b *testing.B, name string, cg *callgraph.Graph, main *ssa.Function) {
+	if stats {
+		e := 0
+		for _, n := range cg.Nodes {
+			e += len(n.Out)
+		}
+		r := len(reaches(cg, main))
+		b.Logf("%s:\t%d nodes\t%d edges\t%d reachable", name, len(cg.Nodes), e, r)
+	}
+}
+
+func BenchmarkStatic(b *testing.B) {
+	b.StopTimer()
+	prog, main := example()
+	b.StartTimer()
+
+	for i := 0; i < b.N; i++ {
+		cg := static.CallGraph(prog)
+		logStats(b, "static", cg, main)
+	}
+}
+
+func BenchmarkCHA(b *testing.B) {
+	b.StopTimer()
+	prog, main := example()
+	b.StartTimer()
+
+	for i := 0; i < b.N; i++ {
+		cg := cha.CallGraph(prog)
+		logStats(b, "cha", cg, main)
+	}
+}
+
+func BenchmarkRTA(b *testing.B) {
+	b.StopTimer()
+	_, main := example()
+	b.StartTimer()
+
+	for i := 0; i < b.N; i++ {
+		res := rta.Analyze([]*ssa.Function{main}, true)
+		cg := res.CallGraph
+		logStats(b, "rta", cg, main)
+	}
+}
+
+func BenchmarkPTA(b *testing.B) {
+	b.StopTimer()
+	_, main := example()
+	b.StartTimer()
+
+	for i := 0; i < b.N; i++ {
+		config := &pointer.Config{Mains: []*ssa.Package{main.Pkg}, BuildCallGraph: true}
+		res, err := pointer.Analyze(config)
+		if err != nil {
+			b.Fatal(err)
+		}
+		logStats(b, "pta", res.CallGraph, main)
+	}
+}
+
+func BenchmarkVTA(b *testing.B) {
+	b.StopTimer()
+	prog, main := example()
+	b.StartTimer()
+
+	for i := 0; i < b.N; i++ {
+		cg := vta.CallGraph(ssautil.AllFunctions(prog), cha.CallGraph(prog))
+		logStats(b, "vta", cg, main)
+	}
+}
+
+func BenchmarkVTA2(b *testing.B) {
+	b.StopTimer()
+	prog, main := example()
+	b.StartTimer()
+
+	for i := 0; i < b.N; i++ {
+		vta1 := vta.CallGraph(ssautil.AllFunctions(prog), cha.CallGraph(prog))
+		cg := vta.CallGraph(reaches(vta1, main), vta1)
+		logStats(b, "vta2", cg, main)
+	}
+}
+
+func BenchmarkVTA3(b *testing.B) {
+	b.StopTimer()
+	prog, main := example()
+	b.StartTimer()
+
+	for i := 0; i < b.N; i++ {
+		vta1 := vta.CallGraph(ssautil.AllFunctions(prog), cha.CallGraph(prog))
+		vta2 := vta.CallGraph(reaches(vta1, main), vta1)
+		cg := vta.CallGraph(reaches(vta2, main), vta2)
+		logStats(b, "vta3", cg, main)
+	}
+}
+
+func BenchmarkVTAAlt(b *testing.B) {
+	b.StopTimer()
+	prog, main := example()
+	b.StartTimer()
+
+	for i := 0; i < b.N; i++ {
+		cha := cha.CallGraph(prog)
+		cg := vta.CallGraph(reaches(cha, main), cha) // start from only functions reachable by CHA.
+		logStats(b, "vta-alt", cg, main)
+	}
+}
+
+func BenchmarkVTAAlt2(b *testing.B) {
+	b.StopTimer()
+	prog, main := example()
+	b.StartTimer()
+
+	for i := 0; i < b.N; i++ {
+		cha := cha.CallGraph(prog)
+		vta1 := vta.CallGraph(reaches(cha, main), cha)
+		cg := vta.CallGraph(reaches(vta1, main), vta1)
+		logStats(b, "vta-alt2", cg, main)
+	}
+}
+
+// reaches returns the set of functions forward reachable from f in g.
+func reaches(g *callgraph.Graph, f *ssa.Function) map[*ssa.Function]bool {
+	seen := make(map[*ssa.Function]bool)
+	var visit func(n *callgraph.Node)
+	visit = func(n *callgraph.Node) {
+		if !seen[n.Func] {
+			seen[n.Func] = true
+			for _, e := range n.Out {
+				visit(e.Callee)
+			}
+		}
+	}
+	visit(g.Nodes[f])
+	return seen
+}