cmd/compile: eliminate OASWB

Instead we can just call needwritebarrier when constructing the SSA
representation.

Change-Id: I6fefaad49daada9cdb3050f112889e49dca0047b
Reviewed-on: https://go-review.googlesource.com/34566Reviewed-by: Cherry Zhang <cherryyz@google.com>

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

@@ -1432,7 +1432,7 @@ func (p *exporter) stmt(n *Node) {
 	// case ODCLFIELD:
 	//	unimplemented - handled by default case
 
-	case OAS, OASWB:
+	case OAS:
 		// Don't export "v = <N>" initializing statements, hope they're always
 		// preceded by the DCL which will be re-parsed and typecheck to reproduce
 		// the "v = <N>" again.

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

@@ -761,7 +761,7 @@ func (e *EscState) esc(n *Node, parent *Node) {
 	// This assignment is a no-op for escape analysis,
 	// it does not store any new pointers into b that were not already there.
 	// However, without this special case b will escape, because we assign to OIND/ODOTPTR.
-	case OAS, OASOP, OASWB:
+	case OAS, OASOP:
 		if (n.Left.Op == OIND || n.Left.Op == ODOTPTR) && n.Left.Left.Op == ONAME && // dst is ONAME dereference
 			(n.Right.Op == OSLICE || n.Right.Op == OSLICE3 || n.Right.Op == OSLICESTR) && // src is slice operation
 			(n.Right.Left.Op == OIND || n.Right.Left.Op == ODOTPTR) && n.Right.Left.Left.Op == ONAME && // slice is applied to ONAME dereference

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

@@ -837,7 +837,7 @@ func (n *Node) stmtfmt(s fmt.State) {
 	// Don't export "v = <N>" initializing statements, hope they're always
 	// preceded by the DCL which will be re-parsed and typechecked to reproduce
 	// the "v = <N>" again.
-	case OAS, OASWB:
+	case OAS:
 		if n.Colas && !complexinit {
 			fmt.Fprintf(s, "%v := %v", n.Left, n.Right)
 		} else {

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

@@ -41,7 +41,7 @@ func anyinit(n []*Node) bool {
 		case ODCLFUNC, ODCLCONST, ODCLTYPE, OEMPTY:
 			break
 
-		case OAS, OASWB:
+		case OAS:
 			if isblank(ln.Left) && candiscard(ln.Right) {
 				break
 			}

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

@@ -33,7 +33,6 @@ var opnames = []string{
 	OAS2MAPR:         "AS2MAPR",
 	OAS2DOTTYPE:      "AS2DOTTYPE",
 	OASOP:            "ASOP",
-	OASWB:            "ASWB",
 	OCALL:            "CALL",
 	OCALLFUNC:        "CALLFUNC",
 	OCALLMETH:        "CALLMETH",

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

@@ -136,7 +136,7 @@ func instrumentnode(np **Node, init *Nodes, wr int, skip int) {
 	default:
 		Fatalf("instrument: unknown node type %v", n.Op)
 
-	case OAS, OASWB, OAS2FUNC:
+	case OAS, OAS2FUNC:
 		instrumentnode(&n.Left, init, 1, 0)
 		instrumentnode(&n.Right, init, 0, 0)
 		goto ret

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

@@ -752,11 +752,6 @@ func fixedlit(ctxt initContext, kind initKind, n *Node, var_ *Node, init *Nodes)
 		switch kind {
 		case initKindStatic:
 			a = walkexpr(a, init) // add any assignments in r to top
-			if a.Op == OASWB {
-				// Static initialization never needs
-				// write barriers.
-				a.Op = OAS
-			}
 			if a.Op != OAS {
 				Fatalf("fixedlit: not as, is %v", a)
 			}

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

@@ -641,7 +641,7 @@ func (s *state) stmt(n *Node) {
 		b := s.endBlock()
 		b.AddEdgeTo(lab.target)
 
-	case OAS, OASWB:
+	case OAS:
 		// Generate static data rather than code, if possible.
 		if n.IsStatic {
 			if !genAsInitNoCheck(n) {
@@ -704,7 +704,7 @@ func (s *state) stmt(n *Node) {
 		}
 		var r *ssa.Value
 		var isVolatile bool
-		needwb := n.Op == OASWB
+		needwb := n.Right != nil && needwritebarrier(n.Left, n.Right)
 		deref := !canSSAType(t)
 		if deref {
 			if rhs == nil {
@@ -728,6 +728,9 @@ func (s *state) stmt(n *Node) {
 			// They get similar wb-removal treatment in walk.go:OAS.
 			needwb = true
 		}
+		if needwb && Debug_wb > 1 {
+			Warnl(n.Pos, "marking %v for barrier", n.Left)
+		}
 
 		var skip skipMask
 		if rhs != nil && (rhs.Op == OSLICE || rhs.Op == OSLICE3 || rhs.Op == OSLICESTR) && samesafeexpr(rhs.Left, n.Left) {

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

@@ -1169,7 +1169,12 @@ func ullmancalc(n *Node) {
 		}
 		goto out
 
-	case OCALL, OCALLFUNC, OCALLMETH, OCALLINTER, OASWB:
+	case OAS:
+		if !needwritebarrier(n.Left, n.Right) {
+			break
+		}
+		fallthrough
+	case OCALL, OCALLFUNC, OCALLMETH, OCALLINTER:
 		ul = UINF
 		goto out
 

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

@@ -361,7 +361,6 @@ const (
 	OAS2MAPR         // List = Rlist (x, ok = m["foo"])
 	OAS2DOTTYPE      // List = Rlist (x, ok = I.(int))
 	OASOP            // Left Etype= Right (x += y)
-	OASWB            // Left = Right (with write barrier)
 	OCALL            // Left(List) (function call, method call or type conversion)
 	OCALLFUNC        // Left(List) (function call f(args))
 	OCALLMETH        // Left(List) (direct method call x.Method(args))

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

@@ -338,10 +338,6 @@ func walkstmt(n *Node) *Node {
 
 			ll := ascompatee(n.Op, rl, n.List.Slice(), &n.Ninit)
 			n.List.Set(reorder3(ll))
-			ls := n.List.Slice()
-			for i, n := range ls {
-				ls[i] = applywritebarrier(n)
-			}
 			break
 		}
 
@@ -683,7 +679,7 @@ opswitch:
 			break
 		}
 
-		if !instrumenting && iszero(n.Right) && !needwritebarrier(n.Left, n.Right) {
+		if !instrumenting && iszero(n.Right) {
 			break
 		}
 
@@ -727,7 +723,6 @@ opswitch:
 			static := n.IsStatic
 			n = convas(n, init)
 			n.IsStatic = static
-			n = applywritebarrier(n)
 		}
 
 	case OAS2:
@@ -736,9 +731,6 @@ opswitch:
 		walkexprlistsafe(n.Rlist.Slice(), init)
 		ll := ascompatee(OAS, n.List.Slice(), n.Rlist.Slice(), init)
 		ll = reorder3(ll)
-		for i, n := range ll {
-			ll[i] = applywritebarrier(n)
-		}
 		n = liststmt(ll)
 
 	// a,b,... = fn()
@@ -756,9 +748,6 @@ opswitch:
 		init.Append(r)
 
 		ll := ascompatet(n.Op, n.List, r.Type)
-		for i, n := range ll {
-			ll[i] = applywritebarrier(n)
-		}
 		n = liststmt(ll)
 
 	// x, y = <-c
@@ -2124,19 +2113,6 @@ func needwritebarrier(l *Node, r *Node) bool {
 	return true
 }
 
-// TODO(rsc): Perhaps componentgen should run before this.
-
-func applywritebarrier(n *Node) *Node {
-	if n.Left != nil && n.Right != nil && needwritebarrier(n.Left, n.Right) {
-		if Debug_wb > 1 {
-			Warnl(n.Pos, "marking %v for barrier", n.Left)
-		}
-		n.Op = OASWB
-		return n
-	}
-	return n
-}
-
 func convas(n *Node, init *Nodes) *Node {
 	if n.Op != OAS {
 		Fatalf("convas: not OAS %v", n.Op)