[dev.link] cmd/link: reuse slice memory in deadcode pass

cherrymui · cherrymui · commit 78b96db04ec9 · 2020-06-04T19:14:12.000Z
Reuse slice memory in the deadcode pass, reduce allocations. Linking cmd/compile, name old alloc/op new alloc/op delta Deadcode_GC 2.10MB ± 0% 1.41MB ± 0% -32.61% (p=0.008 n=5+5) name old allocs/op new allocs/op delta Deadcode_GC 8.46k ± 0% 5.55k ± 0% -34.45% (p=0.008 n=5+5) Change-Id: Ib9ba0928d68a65879007218697712b53acd3c5c5 Reviewed-on: https://go-review.googlesource.com/c/go/+/236566 Run-TryBot: Cherry Zhang <cherryyz@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Jeremy Faller <jeremy@golang.org> Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/src/cmd/link/internal/ld/deadcode.go b/src/cmd/link/internal/ld/deadcode.go
@@ -24,6 +24,8 @@ type deadcodePass struct {
 	ifaceMethod     map[methodsig]bool // methods declared in reached interfaces
 	markableMethods []methodref        // methods of reached types
 	reflectSeen     bool               // whether we have seen a reflect method call
+
+	methodsigstmp []methodsig // scratch buffer for decoding method signatures
 }
 
 func (d *deadcodePass) init() {
@@ -92,6 +94,7 @@ func (d *deadcodePass) init() {
 }
 
 func (d *deadcodePass) flood() {
+	var methods []methodref
 	for !d.wq.empty() {
 		symIdx := d.wq.pop()
 
@@ -112,7 +115,7 @@ func (d *deadcodePass) flood() {
 			}
 		}
 
-		var methods []methodref
+		methods = methods[:0]
 		for i := 0; i < relocs.Count(); i++ {
 			r := relocs.At2(i)
 			t := r.Type()
@@ -330,7 +333,10 @@ func (m methodref) isExported() bool {
 //
 // Conveniently this is the layout of both runtime.method and runtime.imethod.
 func (d *deadcodePass) decodeMethodSig(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, relocs *loader.Relocs, off, size, count int) []methodsig {
-	var methods = make([]methodsig, count)
+	if cap(d.methodsigstmp) < count {
+		d.methodsigstmp = append(d.methodsigstmp[:0], make([]methodsig, count)...)
+	}
+	var methods = d.methodsigstmp[:count]
 	for i := 0; i < count; i++ {
 		methods[i].name = decodetypeName(ldr, symIdx, relocs, off)
 		methods[i].typ = decodeRelocSym(ldr, symIdx, relocs, int32(off+4))
