[dev.regabi] cmd/compile: change CaseStmt.Vars to Var

There's only ever one variable implicitly declared by a CaseStmt. It's
only a slice because we previous used Rlist for this.

Passes toolstash -cmp.

Change-Id: Idf747f3ec6dfbbe4e94d60546ba04a81754df3fe
Reviewed-on: https://go-review.googlesource.com/c/go/+/280012
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -373,7 +373,7 @@ func (e *escape) stmt(n ir.Node) {
 		for _, cas := range n.Cases { // cases
 			cas := cas.(*ir.CaseStmt)
 			if typesw && n.Tag.(*ir.TypeSwitchGuard).Tag != nil {
-				cv := cas.Vars[0]
+				cv := cas.Var
 				k := e.dcl(cv) // type switch variables have no ODCL.
 				if cv.Type().HasPointers() {
 					ks = append(ks, k.dotType(cv.Type(), cas, "switch case"))

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

@@ -230,7 +230,6 @@ func (n *CaseStmt) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }
 func (n *CaseStmt) copy() Node {
 	c := *n
 	c.init = c.init.Copy()
-	c.Vars = c.Vars.Copy()
 	c.List = c.List.Copy()
 	c.Body = c.Body.Copy()
 	return &c
@@ -238,7 +237,7 @@ func (n *CaseStmt) copy() Node {
 func (n *CaseStmt) doChildren(do func(Node) error) error {
 	var err error
 	err = maybeDoList(n.init, err, do)
-	err = maybeDoList(n.Vars, err, do)
+	err = maybeDo(n.Var, err, do)
 	err = maybeDoList(n.List, err, do)
 	err = maybeDo(n.Comm, err, do)
 	err = maybeDoList(n.Body, err, do)
@@ -246,7 +245,7 @@ func (n *CaseStmt) doChildren(do func(Node) error) error {
 }
 func (n *CaseStmt) editChildren(edit func(Node) Node) {
 	editList(n.init, edit)
-	editList(n.Vars, edit)
+	n.Var = maybeEdit(n.Var, edit)
 	editList(n.List, edit)
 	n.Comm = maybeEdit(n.Comm, edit)
 	editList(n.Body, edit)

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

@@ -176,7 +176,7 @@ func (n *BranchStmt) Sym() *types.Sym { return n.Label }
 // A CaseStmt is a case statement in a switch or select: case List: Body.
 type CaseStmt struct {
 	miniStmt
-	Vars Nodes // declared variable for this case in type switch
+	Var  Node  // declared variable for this case in type switch
 	List Nodes // list of expressions for switch, early select
 	Comm Node  // communication case (Exprs[0]) after select is type-checked
 	Body Nodes

src/cmd/compile/internal/noder/noder.go

@@ -1217,7 +1217,7 @@ func (p *noder) caseClauses(clauses []*syntax.CaseClause, tswitch *ir.TypeSwitch
 		if tswitch != nil && tswitch.Tag != nil {
 			nn := typecheck.NewName(tswitch.Tag.Sym())
 			typecheck.Declare(nn, typecheck.DeclContext)
-			n.Vars = []ir.Node{nn}
+			n.Var = nn
 			// keep track of the instances for reporting unused
 			nn.Defn = tswitch
 		}

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

@@ -1196,7 +1196,7 @@ func (w *exportWriter) caseList(cases []ir.Node, namedTypeSwitch bool) {
 		w.pos(cas.Pos())
 		w.stmtList(cas.List)
 		if namedTypeSwitch {
-			w.localName(cas.Vars[0].(*ir.Name))
+			w.localName(cas.Var.(*ir.Name))
 		}
 		w.stmtList(cas.Body)
 	}

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

@@ -780,7 +780,7 @@ func (r *importReader) caseList(switchExpr ir.Node) []ir.Node {
 			// Sym for diagnostics anyway.
 			caseVar := ir.NewNameAt(cas.Pos(), r.ident())
 			Declare(caseVar, DeclContext)
-			cas.Vars = []ir.Node{caseVar}
+			cas.Var = caseVar
 			caseVar.Defn = switchExpr
 		}
 		cas.Body.Set(r.stmtList())

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

@@ -694,7 +694,7 @@ func tcSwitchType(n *ir.SwitchStmt) {
 			ts.add(ncase.Pos(), n1.Type())
 		}
 
-		if len(ncase.Vars) != 0 {
+		if ncase.Var != nil {
 			// Assign the clause variable's type.
 			vt := t
 			if len(ls) == 1 {
@@ -707,7 +707,7 @@ func tcSwitchType(n *ir.SwitchStmt) {
 				}
 			}
 
-			nvar := ncase.Vars[0]
+			nvar := ncase.Var
 			nvar.SetType(vt)
 			if vt != nil {
 				nvar = AssignExpr(nvar)
@@ -716,7 +716,7 @@ func tcSwitchType(n *ir.SwitchStmt) {
 				nvar.SetTypecheck(1)
 				nvar.SetWalkdef(1)
 			}
-			ncase.Vars[0] = nvar
+			ncase.Var = nvar
 		}
 
 		Stmts(ncase.Body)

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

@@ -334,10 +334,7 @@ func walkSwitchType(sw *ir.SwitchStmt) {
 	var body ir.Nodes
 	for _, ncase := range sw.Cases {
 		ncase := ncase.(*ir.CaseStmt)
-		var caseVar ir.Node
+		caseVar := ncase.Var
-		if len(ncase.Vars) != 0 {
-			caseVar = ncase.Vars[0]
-		}
 
 		// For single-type cases with an interface type,
 		// we initialize the case variable as part of the type assertion.