debug/gosym: add benchmark

Use a Go 1.15 executable for the benchmark, because it is handy.
Most of the code paths are shared for Go 1.2+.

Change-Id: Id7ddc76a05d76335108c58ff9f1ab2ff837b7227
Reviewed-on: https://go-review.googlesource.com/c/go/+/353131
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Trust: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

src/debug/gosym/pclntab_test.go

@@ -267,7 +267,8 @@ func TestPCLine(t *testing.T) {
 	}
 }
 
-// Test that we can parse a pclntab from 1.15.
+// read115Executable returns a hello world executable compiled by Go 1.15.
+//
 // The file was compiled in /tmp/hello.go:
 // [BEGIN]
 // package main
@@ -276,25 +277,30 @@ func TestPCLine(t *testing.T) {
 //    println("hello")
 // }
 // [END]
-func Test115PclnParsing(t *testing.T) {
+func read115Executable(tb testing.TB) []byte {
 	zippedDat, err := os.ReadFile("testdata/pcln115.gz")
 	if err != nil {
-		t.Fatal(err)
+		tb.Fatal(err)
 	}
 	var gzReader *gzip.Reader
 	gzReader, err = gzip.NewReader(bytes.NewBuffer(zippedDat))
 	if err != nil {
-		t.Fatal(err)
+		tb.Fatal(err)
 	}
 	var dat []byte
 	dat, err = io.ReadAll(gzReader)
 	if err != nil {
-		t.Fatal(err)
+		tb.Fatal(err)
 	}
+	return dat
+}
+
+// Test that we can parse a pclntab from 1.15.
+func Test115PclnParsing(t *testing.T) {
+	dat := read115Executable(t)
 	const textStart = 0x1001000
 	pcln := NewLineTable(dat, textStart)
-	var tab *Table
+	tab, err := NewTable(nil, pcln)
-	tab, err = NewTable(nil, pcln)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -314,3 +320,74 @@ func Test115PclnParsing(t *testing.T) {
 		t.Fatalf("expected to parse name as main.main, got %v", f.Name)
 	}
 }
+
+var (
+	sinkLineTable *LineTable
+	sinkTable     *Table
+)
+
+func Benchmark115(b *testing.B) {
+	dat := read115Executable(b)
+	const textStart = 0x1001000
+
+	b.Run("NewLineTable", func(b *testing.B) {
+		b.ReportAllocs()
+		for i := 0; i < b.N; i++ {
+			sinkLineTable = NewLineTable(dat, textStart)
+		}
+	})
+
+	pcln := NewLineTable(dat, textStart)
+	b.Run("NewTable", func(b *testing.B) {
+		b.ReportAllocs()
+		for i := 0; i < b.N; i++ {
+			var err error
+			sinkTable, err = NewTable(nil, pcln)
+			if err != nil {
+				b.Fatal(err)
+			}
+		}
+	})
+
+	tab, err := NewTable(nil, pcln)
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	b.Run("LineToPC", func(b *testing.B) {
+		b.ReportAllocs()
+		for i := 0; i < b.N; i++ {
+			var f *Func
+			var pc uint64
+			pc, f, err = tab.LineToPC("/tmp/hello.go", 3)
+			if err != nil {
+				b.Fatal(err)
+			}
+			if pcln.version != ver12 {
+				b.Fatalf("want version=%d, got %d", ver12, pcln.version)
+			}
+			if pc != 0x105c280 {
+				b.Fatalf("want pc=0x105c280, got 0x%x", pc)
+			}
+			if f.Name != "main.main" {
+				b.Fatalf("want name=main.main, got %q", f.Name)
+			}
+		}
+	})
+
+	b.Run("PCToLine", func(b *testing.B) {
+		b.ReportAllocs()
+		for i := 0; i < b.N; i++ {
+			file, line, fn := tab.PCToLine(0x105c280)
+			if file != "/tmp/hello.go" {
+				b.Fatalf("want name=/tmp/hello.go, got %q", file)
+			}
+			if line != 3 {
+				b.Fatalf("want line=3, got %d", line)
+			}
+			if fn.Name != "main.main" {
+				b.Fatalf("want name=main.main, got %q", fn.Name)
+			}
+		}
+	})
+}