[dev.regabi] cmd/compile: remove Orig, SetOrig from Node interface

These are only needed for a few opcodes, and we can avoid
wasting storage in every implementation by using the extension
interface pattern with a helper function for access.

Of course, in the current codebase, there is only one Node
implementation (*node) and it has these methods, so there
is no danger of a functional change in this particular CL.

Passes buildall w/ toolstash -cmp.

Change-Id: I440c6c232f1fe7b56b852a00dc530f8f49a6b12d
Reviewed-on: https://go-review.googlesource.com/c/go/+/274089
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -537,7 +537,7 @@ func evalConst(n ir.Node) ir.Node {
 				}
 
 				nl := origConst(s[i], constant.MakeString(strings.Join(strs, "")))
-				nl.SetOrig(nl) // it's bigger than just s[i]
+				nl.(ir.OrigNode).SetOrig(nl) // it's bigger than just s[i]
 				newList = append(newList, nl)
 				i = i2 - 1
 			} else {
@@ -642,7 +642,7 @@ func origConst(n ir.Node, v constant.Value) ir.Node {
 
 	orig := n
 	n = ir.NodAt(orig.Pos(), ir.OLITERAL, nil, nil)
-	n.SetOrig(orig)
+	n.(ir.OrigNode).SetOrig(orig)
 	n.SetType(orig.Type())
 	n.SetVal(v)
 	return n

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

@@ -1871,7 +1871,7 @@ func moveToHeap(n ir.Node) {
 	// temp will add it to the function declaration list automatically.
 	heapaddr := temp(types.NewPtr(n.Type()))
 	heapaddr.SetSym(lookup("&" + n.Sym().Name))
-	heapaddr.Orig().SetSym(heapaddr.Sym())
+	ir.Orig(heapaddr).SetSym(heapaddr.Sym())
 	heapaddr.SetPos(n.Pos())
 
 	// Unset AutoTemp to persist the &foo variable name through SSA to

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

@@ -80,7 +80,7 @@ func tempAt(pos src.XPos, curfn ir.Node, t *types.Type) ir.Node {
 
 	dowidth(t)
 
-	return n.Orig()
+	return ir.Orig(n)
 }
 
 func temp(t *types.Type) ir.Node {

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

@@ -1210,8 +1210,8 @@ func (w *exportWriter) expr(n ir.Node) {
 		if !n.Type().HasNil() {
 			base.Fatalf("unexpected type for nil: %v", n.Type())
 		}
-		if n.Orig() != nil && n.Orig() != n {
-			w.expr(n.Orig())
+		if orig := ir.Orig(n); orig != nil && orig != n {
+			w.expr(orig)
 			break
 		}
 		w.op(ir.OLITERAL)

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

@@ -6675,7 +6675,7 @@ func AddAux2(a *obj.Addr, v *ssa.Value, offset int64) {
 	case ir.Node:
 		if n.Class() == ir.PPARAM || n.Class() == ir.PPARAMOUT {
 			a.Name = obj.NAME_PARAM
-			a.Sym = n.Orig().Sym().Linksym()
+			a.Sym = ir.Orig(n).Sym().Linksym()
 			a.Offset += n.Offset()
 			break
 		}

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

@@ -559,7 +559,7 @@ func assignconvfn(n ir.Node, t *types.Type, context func() string) ir.Node {
 	r.SetType(t)
 	r.SetTypecheck(1)
 	r.SetImplicit(true)
-	r.SetOrig(n.Orig())
+	r.(ir.OrigNode).SetOrig(ir.Orig(n))
 	return r
 }
 

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

@@ -851,7 +851,7 @@ func typecheck1(n ir.Node, top int) (res ir.Node) {
 			checklvalue(n.Left(), "take the address of")
 			r := outervalue(n.Left())
 			if r.Op() == ir.ONAME {
-				if r.Orig() != r {
+				if ir.Orig(r) != r {
 					base.Fatalf("found non-orig name node %v", r) // TODO(mdempsky): What does this mean?
 				}
 				r.Name().SetAddrtaken(true)
@@ -2144,8 +2144,8 @@ func typecheckargs(n ir.Node) {
 	// Rewrite f(g()) into t1, t2, ... = g(); f(t1, t2, ...).
 
 	// Save n as n.Orig for fmt.go.
-	if n.Orig() == n {
-		n.SetOrig(ir.SepCopy(n))
+	if ir.Orig(n) == n {
+		n.(ir.OrigNode).SetOrig(ir.SepCopy(n))
 	}
 
 	as := ir.Nod(ir.OAS2, nil, nil)
@@ -2245,7 +2245,7 @@ func checkdefergo(n ir.Node) {
 		ir.ONEW,
 		ir.OREAL,
 		ir.OLITERAL: // conversion or unsafe.Alignof, Offsetof, Sizeof
-		if n.Left().Orig() != nil && n.Left().Orig().Op() == ir.OCONV {
+		if orig := ir.Orig(n.Left()); orig.Op() == ir.OCONV {
 			break
 		}
 		base.ErrorfAt(n.Pos(), "%s discards result of %v", what, n.Left())
@@ -2814,7 +2814,7 @@ func typecheckcomplit(n ir.Node) (res ir.Node) {
 	}
 
 	// Save original node (including n.Right)
-	n.SetOrig(ir.Copy(n))
+	n.(ir.OrigNode).SetOrig(ir.Copy(n))
 
 	setlineno(n.Right())
 

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

@@ -1223,8 +1223,8 @@ func exprFmt(n Node, s fmt.State, prec int, mode FmtMode) {
 
 	case OLITERAL: // this is a bit of a mess
 		if mode == FErr {
-			if n.Orig() != nil && n.Orig() != n {
-				exprFmt(n.Orig(), s, prec, mode)
+			if orig := Orig(n); orig != nil && orig != n {
+				exprFmt(orig, s, prec, mode)
 				return
 			}
 			if n.Sym() != nil {
@@ -1561,8 +1561,8 @@ func nodeFmt(n Node, s fmt.State, flag FmtFlag, mode FmtMode) {
 
 	// We almost always want the original.
 	// TODO(gri) Why the special case for OLITERAL?
-	if n.Op() != OLITERAL && n.Orig() != nil {
-		n = n.Orig()
+	if n.Op() != OLITERAL && Orig(n) != nil {
+		n = Orig(n)
 	}
 
 	if flag&FmtLong != 0 && t != nil {

src/cmd/compile/internal/ir/node.go

@@ -35,8 +35,6 @@ type Node interface {
 	// Abstract graph structure, for generic traversals.
 	Op() Op
 	SetOp(x Op)
-	Orig() Node
-	SetOrig(x Node)
 	SubOp() Op
 	SetSubOp(x Op)
 	Left() Node
@@ -1616,11 +1614,41 @@ func (n *node) RawCopy() Node {
 	return &copy
 }
 
+// A Node may implement the Orig and SetOrig method to
+// maintain a pointer to the "unrewritten" form of a Node.
+// If a Node does not implement OrigNode, it is its own Orig.
+//
+// Note that both SepCopy and Copy have definitions compatible
+// with a Node that does not implement OrigNode: such a Node
+// is its own Orig, and in that case, that's what both want to return
+// anyway (SepCopy unconditionally, and Copy only when the input
+// is its own Orig as well, but if the output does not implement
+// OrigNode, then neither does the input, making the condition true).
+type OrigNode interface {
+	Node
+	Orig() Node
+	SetOrig(Node)
+}
+
+func Orig(n Node) Node {
+	if n, ok := n.(OrigNode); ok {
+		o := n.Orig()
+		if o == nil {
+			Dump("Orig nil", n)
+			base.Fatalf("Orig returned nil")
+		}
+		return o
+	}
+	return n
+}
+
 // sepcopy returns a separate shallow copy of n, with the copy's
 // Orig pointing to itself.
 func SepCopy(n Node) Node {
 	n = n.RawCopy()
-	n.SetOrig(n)
+	if n, ok := n.(OrigNode); ok {
+		n.SetOrig(n)
+	}
 	return n
 }
 
@@ -1633,8 +1661,8 @@ func SepCopy(n Node) Node {
 // messages; see issues #26855, #27765).
 func Copy(n Node) Node {
 	copy := n.RawCopy()
-	if n.Orig() == n {
-		copy.SetOrig(copy)
+	if n, ok := n.(OrigNode); ok && n.Orig() == n {
+		copy.(OrigNode).SetOrig(copy)
 	}
 	return copy
 }
@@ -1643,7 +1671,7 @@ func Copy(n Node) Node {
 func IsNil(n Node) bool {
 	// Check n.Orig because constant propagation may produce typed nil constants,
 	// which don't exist in the Go spec.
-	return n.Orig().Op() == ONIL
+	return Orig(n).Op() == ONIL
 }
 
 func IsBlank(n Node) bool {
@@ -1664,7 +1692,7 @@ func Nod(op Op, nleft, nright Node) Node {
 }
 
 func NodAt(pos src.XPos, op Op, nleft, nright Node) Node {
-	var n Node
+	var n *node
 	switch op {
 	case ODCLFUNC:
 		var x struct {