cmd/compile: introduce gc.Node.copy method

When making a shallow copy of a node, various methods were used,
including calling nod(OXXX, nil, nil) and then overwriting it, or
"n1 := *n" and then using &n1.

Add a copy method instead, simplifying all of those and making them
consistent.

Passes toolstash -cmp on std cmd.

Change-Id: I3f3fc88bad708edc712bf6d87214cda4ddc43b01
Reviewed-on: https://go-review.googlesource.com/72710
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -223,8 +223,7 @@ func convlit1(n *Node, t *types.Type, explicit bool, reuse canReuseNode) *Node {
 	if n.Op == OLITERAL && !reuse {
 		// Can't always set n.Type directly on OLITERAL nodes.
 		// See discussion on CL 20813.
-		nn := *n
-		n = &nn
+		n = n.copy()
 		reuse = true
 	}
 
@@ -1333,8 +1332,7 @@ func defaultlitreuse(n *Node, t *types.Type, reuse canReuseNode) *Node {
 	}
 
 	if n.Op == OLITERAL && !reuse {
-		nn := *n
-		n = &nn
+		n = n.copy()
 		reuse = true
 	}
 

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

@@ -466,11 +466,11 @@ func funcargs(nt *Node) {
 			// So the two cases must be distinguished.
 			// We do not record a pointer to the original node (n->orig).
 			// Having multiple names causes too much confusion in later passes.
-			nn := *n.Left
-			nn.Orig = &nn
+			nn := n.Left.copy()
+			nn.Orig = nn
 			nn.Sym = lookupN("~b", gen)
 			gen++
-			n.Left = &nn
+			n.Left = nn
 		}
 
 		n.Left.Name.Param.Ntype = n.Right

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

@@ -392,7 +392,7 @@ func inlcopy(n *Node) *Node {
 		return n
 	}
 
-	m := *n
+	m := n.copy()
 	if m.Func != nil {
 		m.Func.Inl.Set(nil)
 	}
@@ -403,7 +403,7 @@ func inlcopy(n *Node) *Node {
 	m.Ninit.Set(inlcopylist(n.Ninit.Slice()))
 	m.Nbody.Set(inlcopylist(n.Nbody.Slice()))
 
-	return &m
+	return m
 }
 
 // Inlcalls/nodelist/node walks fn's statements and expressions and substitutes any
@@ -1192,8 +1192,7 @@ func (subst *inlsubst) node(n *Node) *Node {
 		return m
 
 	case OGOTO, OLABEL:
-		m := nod(OXXX, nil, nil)
-		*m = *n
+		m := n.copy()
 		m.Pos = subst.updatedPos(m.Pos)
 		m.Ninit.Set(nil)
 		p := fmt.Sprintf("%s·%d", n.Left.Sym.Name, inlgen)
@@ -1202,8 +1201,7 @@ func (subst *inlsubst) node(n *Node) *Node {
 		return m
 	}
 
-	m := nod(OXXX, nil, nil)
-	*m = *n
+	m := n.copy()
 	m.Pos = subst.updatedPos(m.Pos)
 	m.Ninit.Set(nil)
 

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

@@ -109,10 +109,10 @@ func (o *Order) cheapExpr(n *Node) *Node {
 		if l == n.Left {
 			return n
 		}
-		a := *n
-		a.Orig = &a
+		a := n.copy()
+		a.Orig = a
 		a.Left = l
-		return typecheck(&a, Erv)
+		return typecheck(a, Erv)
 	}
 
 	return o.copyExpr(n, n.Type, false)
@@ -135,20 +135,20 @@ func (o *Order) safeExpr(n *Node) *Node {
 		if l == n.Left {
 			return n
 		}
-		a := *n
-		a.Orig = &a
+		a := n.copy()
+		a.Orig = a
 		a.Left = l
-		return typecheck(&a, Erv)
+		return typecheck(a, Erv)
 
 	case ODOTPTR, OIND:
 		l := o.cheapExpr(n.Left)
 		if l == n.Left {
 			return n
 		}
-		a := *n
-		a.Orig = &a
+		a := n.copy()
+		a.Orig = a
 		a.Left = l
-		return typecheck(&a, Erv)
+		return typecheck(a, Erv)
 
 	case OINDEX, OINDEXMAP:
 		var l *Node
@@ -161,11 +161,11 @@ func (o *Order) safeExpr(n *Node) *Node {
 		if l == n.Left && r == n.Right {
 			return n
 		}
-		a := *n
-		a.Orig = &a
+		a := n.copy()
+		a.Orig = a
 		a.Left = l
 		a.Right = r
-		return typecheck(&a, Erv)
+		return typecheck(a, Erv)
 
 	default:
 		Fatalf("ordersafeexpr %v", n.Op)

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

@@ -67,17 +67,17 @@ func instrument(fn *Node) {
 		// nodpc is the PC of the caller as extracted by
 		// getcallerpc. We use -widthptr(FP) for x86.
 		// BUG: this will not work on arm.
-		nodpc := *nodfp
+		nodpc := nodfp.copy()
 		nodpc.Type = types.Types[TUINTPTR]
 		nodpc.Xoffset = int64(-Widthptr)
 		savedLineno := lineno
 		lineno = src.NoXPos
-		nd := mkcall("racefuncenter", nil, nil, &nodpc)
+		nd := mkcall("racefuncenter", nil, nil, nodpc)
 
 		fn.Func.Enter.Prepend(nd)
 		nd = mkcall("racefuncexit", nil, nil)
 		fn.Func.Exit.Append(nd)
-		fn.Func.Dcl = append(fn.Func.Dcl, &nodpc)
+		fn.Func.Dcl = append(fn.Func.Dcl, nodpc)
 		lineno = savedLineno
 	}
 

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

@@ -328,35 +328,32 @@ func staticcopy(l *Node, r *Node, out *[]*Node) bool {
 		// copy slice
 		a := inittemps[r]
 
-		n := *l
+		n := l.copy()
 		n.Xoffset = l.Xoffset + int64(array_array)
-		gdata(&n, nod(OADDR, a, nil), Widthptr)
+		gdata(n, nod(OADDR, a, nil), Widthptr)
 		n.Xoffset = l.Xoffset + int64(array_nel)
-		gdata(&n, r.Right, Widthptr)
+		gdata(n, r.Right, Widthptr)
 		n.Xoffset = l.Xoffset + int64(array_cap)
-		gdata(&n, r.Right, Widthptr)
+		gdata(n, r.Right, Widthptr)
 		return true
 
 	case OARRAYLIT, OSTRUCTLIT:
 		p := initplans[r]
 
-		n := *l
+		n := l.copy()
 		for i := range p.E {
 			e := &p.E[i]
 			n.Xoffset = l.Xoffset + e.Xoffset
 			n.Type = e.Expr.Type
 			if e.Expr.Op == OLITERAL {
-				gdata(&n, e.Expr, int(n.Type.Width))
+				gdata(n, e.Expr, int(n.Type.Width))
 			} else {
-				ll := nod(OXXX, nil, nil)
-				*ll = n
+				ll := n.copy()
 				ll.Orig = ll // completely separate copy
 				if !staticassign(ll, e.Expr, out) {
 					// Requires computation, but we're
 					// copying someone else's computation.
-					rr := nod(OXXX, nil, nil)
-
-					*rr = *orig
+					rr := orig.copy()
 					rr.Orig = rr // completely separate copy
 					rr.Type = ll.Type
 					rr.Xoffset += e.Xoffset
@@ -429,13 +426,13 @@ func staticassign(l *Node, r *Node, out *[]*Node) bool {
 		ta := types.NewArray(r.Type.Elem(), bound)
 		a := staticname(ta)
 		inittemps[r] = a
-		n := *l
+		n := l.copy()
 		n.Xoffset = l.Xoffset + int64(array_array)
-		gdata(&n, nod(OADDR, a, nil), Widthptr)
+		gdata(n, nod(OADDR, a, nil), Widthptr)
 		n.Xoffset = l.Xoffset + int64(array_nel)
-		gdata(&n, r.Right, Widthptr)
+		gdata(n, r.Right, Widthptr)
 		n.Xoffset = l.Xoffset + int64(array_cap)
-		gdata(&n, r.Right, Widthptr)
+		gdata(n, r.Right, Widthptr)
 
 		// Fall through to init underlying array.
 		l = a
@@ -445,17 +442,16 @@ func staticassign(l *Node, r *Node, out *[]*Node) bool {
 		initplan(r)
 
 		p := initplans[r]
-		n := *l
+		n := l.copy()
 		for i := range p.E {
 			e := &p.E[i]
 			n.Xoffset = l.Xoffset + e.Xoffset
 			n.Type = e.Expr.Type
 			if e.Expr.Op == OLITERAL {
-				gdata(&n, e.Expr, int(n.Type.Width))
+				gdata(n, e.Expr, int(n.Type.Width))
 			} else {
 				setlineno(e.Expr)
-				a := nod(OXXX, nil, nil)
-				*a = n
+				a := n.copy()
 				a.Orig = a // completely separate copy
 				if !staticassign(a, e.Expr, out) {
 					*out = append(*out, nod(OAS, a, e.Expr))
@@ -522,11 +518,10 @@ func staticassign(l *Node, r *Node, out *[]*Node) bool {
 			// Copy val directly into n.
 			n.Type = val.Type
 			setlineno(val)
-			a := nod(OXXX, nil, nil)
-			*a = n
-			a.Orig = a
-			if !staticassign(a, val, out) {
-				*out = append(*out, nod(OAS, a, val))
+			a := n
+			a.Orig = &a
+			if !staticassign(&a, val, out) {
+				*out = append(*out, nod(OAS, &a, val))
 			}
 		} else {
 			// Construct temp to hold val, write pointer to temp into n.

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

@@ -364,6 +364,11 @@ func nodSym(op Op, left *Node, sym *types.Sym) *Node {
 	return n
 }
 
+func (n *Node) copy() *Node {
+	n2 := *n
+	return &n2
+}
+
 // methcmp sorts methods by name with exported methods first,
 // and then non-exported methods by their package path.
 type methcmp []*types.Field
@@ -439,8 +444,8 @@ func treecopy(n *Node, pos src.XPos) *Node {
 
 	switch n.Op {
 	default:
-		m := *n
-		m.Orig = &m
+		m := n.copy()
+		m.Orig = m
 		m.Left = treecopy(n.Left, pos)
 		m.Right = treecopy(n.Right, pos)
 		m.List.Set(listtreecopy(n.List.Slice(), pos))
@@ -451,7 +456,7 @@ func treecopy(n *Node, pos src.XPos) *Node {
 			Dump("treecopy", n)
 			Fatalf("treecopy Name")
 		}
-		return &m
+		return m
 
 	case OPACK:
 		// OPACK nodes are never valid in const value declarations,
@@ -1252,8 +1257,7 @@ func safeexpr(n *Node, init *Nodes) *Node {
 		if l == n.Left {
 			return n
 		}
-		r := nod(OXXX, nil, nil)
-		*r = *n
+		r := n.copy()
 		r.Left = l
 		r = typecheck(r, Erv)
 		r = walkexpr(r, init)
@@ -1264,8 +1268,7 @@ func safeexpr(n *Node, init *Nodes) *Node {
 		if l == n.Left {
 			return n
 		}
-		a := nod(OXXX, nil, nil)
-		*a = *n
+		a := n.copy()
 		a.Left = l
 		a = walkexpr(a, init)
 		return a
@@ -1276,8 +1279,7 @@ func safeexpr(n *Node, init *Nodes) *Node {
 		if l == n.Left && r == n.Right {
 			return n
 		}
-		a := nod(OXXX, nil, nil)
-		*a = *n
+		a := n.copy()
 		a.Left = l
 		a.Right = r
 		a = walkexpr(a, init)

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

@@ -2873,9 +2873,7 @@ func typecheckcomplit(n *Node) *Node {
 	}
 
 	// Save original node (including n.Right)
-	norig := nod(n.Op, nil, nil)
-
-	*norig = *n
+	norig := n.copy()
 
 	setlineno(n.Right)
 	n.Right = typecheck(n.Right, Etype|Ecomplit)

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

@@ -3894,7 +3894,7 @@ func wrapCall(n *Node, init *Nodes) *Node {
 // The result of substArgTypes MUST be assigned back to old, e.g.
 // 	n.Left = substArgTypes(n.Left, t1, t2)
 func substArgTypes(old *Node, types_ ...*types.Type) *Node {
-	n := *old // make shallow copy
+	n := old.copy() // make shallow copy
 
 	for _, t := range types_ {
 		dowidth(t)
@@ -3903,5 +3903,5 @@ func substArgTypes(old *Node, types_ ...*types.Type) *Node {
 	if len(types_) > 0 {
 		Fatalf("substArgTypes: too many argument types")
 	}
-	return &n
+	return n
 }