[dev.link] cmd/compile: make read-only static temps content-addressable

For now, we only do this for symbols without relocations.

Mark static temps "local", as they are not referenced across DSO
boundaries. And deduplicating a local symbol and a non-local
symbol can be problematic.

Change-Id: I0a3dc4138aaeea7fd4f326998f32ab6305da8e4b
Reviewed-on: https://go-review.googlesource.com/c/go/+/243141
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

src/cmd/compile/internal/gc/order.go

@@ -206,8 +206,7 @@ func (o *Order) addrTemp(n *Node) *Node {
 		// TODO: expand this to all static composite literal nodes?
 		n = defaultlit(n, nil)
 		dowidth(n.Type)
-		vstat := staticname(n.Type)
-		vstat.MarkReadonly()
+		vstat := readonlystaticname(n.Type)
 		var s InitSchedule
 		s.staticassign(vstat, n)
 		if s.out != nil {

src/cmd/compile/internal/gc/sinit.go

@@ -356,14 +356,22 @@ func (c initContext) String() string {
 
 var statuniqgen int // name generator for static temps
 
-// staticname returns a name backed by a static data symbol.
-// Callers should call n.MarkReadonly on the
-// returned node for readonly nodes.
+// staticname returns a name backed by a (writable) static data symbol.
+// Use readonlystaticname for read-only node.
 func staticname(t *types.Type) *Node {
 	// Don't use lookupN; it interns the resulting string, but these are all unique.
 	n := newname(lookup(fmt.Sprintf("%s%d", obj.StaticNamePref, statuniqgen)))
 	statuniqgen++
 	addvar(n, t, PEXTERN)
+	n.Sym.Linksym().Set(obj.AttrLocal, true)
+	return n
+}
+
+// readonlystaticname returns a name backed by a (writable) static data symbol.
+func readonlystaticname(t *types.Type) *Node {
+	n := staticname(t)
+	n.MarkReadonly()
+	n.Sym.Linksym().Set(obj.AttrContentAddressable, true)
 	return n
 }
 
@@ -627,9 +635,10 @@ func slicelit(ctxt initContext, n *Node, var_ *Node, init *Nodes) {
 
 	mode := getdyn(n, true)
 	if mode&initConst != 0 && !isSmallSliceLit(n) {
-		vstat = staticname(t)
 		if ctxt == inInitFunction {
-			vstat.MarkReadonly()
+			vstat = readonlystaticname(t)
+		} else {
+			vstat = staticname(t)
 		}
 		fixedlit(ctxt, initKindStatic, n, vstat, init)
 	}
@@ -773,10 +782,8 @@ func maplit(n *Node, m *Node, init *Nodes) {
 		dowidth(te)
 
 		// make and initialize static arrays
-		vstatk := staticname(tk)
-		vstatk.MarkReadonly()
-		vstate := staticname(te)
-		vstate.MarkReadonly()
+		vstatk := readonlystaticname(tk)
+		vstate := readonlystaticname(te)
 
 		datak := nod(OARRAYLIT, nil, nil)
 		datae := nod(OARRAYLIT, nil, nil)
@@ -897,8 +904,7 @@ func anylit(n *Node, var_ *Node, init *Nodes) {
 
 		if var_.isSimpleName() && n.List.Len() > 4 {
 			// lay out static data
-			vstat := staticname(t)
-			vstat.MarkReadonly()
+			vstat := readonlystaticname(t)
 
 			ctxt := inInitFunction
 			if n.Op == OARRAYLIT {

src/cmd/compile/internal/gc/walk.go

@@ -1556,8 +1556,7 @@ opswitch:
 		if isStaticCompositeLiteral(n) && !canSSAType(n.Type) {
 			// n can be directly represented in the read-only data section.
 			// Make direct reference to the static data. See issue 12841.
-			vstat := staticname(n.Type)
-			vstat.MarkReadonly()
+			vstat := readonlystaticname(n.Type)
 			fixedlit(inInitFunction, initKindStatic, n, vstat, init)
 			n = vstat
 			n = typecheck(n, ctxExpr)

src/cmd/internal/obj/objfile2.go

@@ -333,7 +333,7 @@ func (w *writer) Sym(s *LSym) {
 }
 
 func (w *writer) Hash64(s *LSym) {
-	if !s.ContentAddressable() {
+	if !s.ContentAddressable() || len(s.R) != 0 {
 		panic("Hash of non-content-addresable symbol")
 	}
 	var b goobj2.Hash64Type
@@ -342,7 +342,7 @@ func (w *writer) Hash64(s *LSym) {
 }
 
 func (w *writer) Hash(s *LSym) {
-	if !s.ContentAddressable() {
+	if !s.ContentAddressable() || len(s.R) != 0 { // TODO: currently we don't support content-addressable symbols with relocations
 		panic("Hash of non-content-addresable symbol")
 	}
 	b := goobj2.HashType(sha1.Sum(s.P))

src/cmd/internal/obj/sym.go

@@ -202,7 +202,7 @@ func (ctxt *Link) NumberSyms() {
 
 	var idx, hashedidx, hashed64idx, nonpkgidx int32
 	ctxt.traverseSyms(traverseDefs, func(s *LSym) {
-		if s.ContentAddressable() {
+		if s.ContentAddressable() && len(s.R) == 0 { // TODO: currently we don't support content-addressable symbols with relocations
 			if len(s.P) <= 8 {
 				s.PkgIdx = goobj2.PkgIdxHashed64
 				s.SymIdx = hashed64idx