[dev.regabi] cmd/compile: remove CommStmt.List

Package syntax's parser already ensures that select communication
clauses only have one statement, so there's no need for ir's CommStmt
to need to represent more than one. Instead, noder can just directly
populate Comm in the first place.

Incidentally, this also revealed a latent issue in the inline-body
exporter: we were exporting List (where the case statement is before
type-checking), rather than Comm (where the case statement would be
after type-checking, when export happens).

Passes toolstash -cmp.

Change-Id: Ib4eb711527bed297c7332c79ed6e6562a1db2cfa
Reviewed-on: https://go-review.googlesource.com/c/go/+/280444
Trust: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -297,21 +297,18 @@ func (n *CommStmt) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }
 func (n *CommStmt) copy() Node {
 	c := *n
 	c.init = c.init.Copy()
-	c.List = c.List.Copy()
 	c.Body = c.Body.Copy()
 	return &c
 }
 func (n *CommStmt) doChildren(do func(Node) error) error {
 	var err error
 	err = maybeDoList(n.init, err, do)
-	err = maybeDoList(n.List, err, do)
 	err = maybeDo(n.Comm, err, do)
 	err = maybeDoList(n.Body, err, do)
 	return err
 }
 func (n *CommStmt) editChildren(edit func(Node) Node) {
 	editList(n.init, edit)
-	editList(n.List, edit)
 	n.Comm = maybeEdit(n.Comm, edit)
 	editList(n.Body, edit)
 }

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

@@ -220,13 +220,12 @@ func editCases(list []*CaseStmt, edit func(Node) Node) {
 
 type CommStmt struct {
 	miniStmt
-	List Nodes // list of expressions for switch, early select
+	Comm Node  // communication case
-	Comm Node  // communication case (Exprs[0]) after select is type-checked
 	Body Nodes
 }
 
-func NewCommStmt(pos src.XPos, list, body []Node) *CommStmt {
+func NewCommStmt(pos src.XPos, comm Node, body []Node) *CommStmt {
-	n := &CommStmt{List: list, Body: body}
+	n := &CommStmt{Comm: comm, Body: body}
 	n.pos = pos
 	n.op = OCASE
 	return n
@@ -274,11 +273,13 @@ type ForStmt struct {
 	HasBreak bool
 }
 
-func NewForStmt(pos src.XPos, init []Node, cond, post Node, body []Node) *ForStmt {
+func NewForStmt(pos src.XPos, init Node, cond, post Node, body []Node) *ForStmt {
 	n := &ForStmt{Cond: cond, Post: post}
 	n.pos = pos
 	n.op = OFOR
-	n.init.Set(init)
+	if init != nil {
+		n.init = []Node{init}
+	}
 	n.Body.Set(body)
 	return n
 }

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

@@ -1149,9 +1149,11 @@ func (p *noder) blockStmt(stmt *syntax.BlockStmt) []ir.Node {
 
 func (p *noder) ifStmt(stmt *syntax.IfStmt) ir.Node {
 	p.openScope(stmt.Pos())
-	init := p.simpleStmt(stmt.Init)
+	init := p.stmt(stmt.Init)
 	n := ir.NewIfStmt(p.pos(stmt), p.expr(stmt.Cond), p.blockStmt(stmt.Then), nil)
-	*n.PtrInit() = init
+	if init != nil {
+		*n.PtrInit() = []ir.Node{init}
+	}
 	if stmt.Else != nil {
 		e := p.stmt(stmt.Else)
 		if e.Op() == ir.OBLOCK {
@@ -1186,7 +1188,7 @@ func (p *noder) forStmt(stmt *syntax.ForStmt) ir.Node {
 		return n
 	}
 
-	n := ir.NewForStmt(p.pos(stmt), p.simpleStmt(stmt.Init), p.expr(stmt.Cond), p.stmt(stmt.Post), p.blockStmt(stmt.Body))
+	n := ir.NewForStmt(p.pos(stmt), p.stmt(stmt.Init), p.expr(stmt.Cond), p.stmt(stmt.Post), p.blockStmt(stmt.Body))
 	p.closeAnotherScope()
 	return n
 }
@@ -1194,9 +1196,11 @@ func (p *noder) forStmt(stmt *syntax.ForStmt) ir.Node {
 func (p *noder) switchStmt(stmt *syntax.SwitchStmt) ir.Node {
 	p.openScope(stmt.Pos())
 
-	init := p.simpleStmt(stmt.Init)
+	init := p.stmt(stmt.Init)
 	n := ir.NewSwitchStmt(p.pos(stmt), p.expr(stmt.Tag), nil)
-	*n.PtrInit() = init
+	if init != nil {
+		*n.PtrInit() = []ir.Node{init}
+	}
 
 	var tswitch *ir.TypeSwitchGuard
 	if l := n.Tag; l != nil && l.Op() == ir.OTYPESW {
@@ -1259,13 +1263,6 @@ func (p *noder) selectStmt(stmt *syntax.SelectStmt) ir.Node {
 	return ir.NewSelectStmt(p.pos(stmt), p.commClauses(stmt.Body, stmt.Rbrace))
 }
 
-func (p *noder) simpleStmt(stmt syntax.SimpleStmt) []ir.Node {
-	if stmt == nil {
-		return nil
-	}
-	return []ir.Node{p.stmt(stmt)}
-}
-
 func (p *noder) commClauses(clauses []*syntax.CommClause, rbrace syntax.Pos) []*ir.CommStmt {
 	nodes := make([]*ir.CommStmt, len(clauses))
 	for i, clause := range clauses {
@@ -1275,7 +1272,7 @@ func (p *noder) commClauses(clauses []*syntax.CommClause, rbrace syntax.Pos) []*
 		}
 		p.openScope(clause.Pos())
 
-		nodes[i] = ir.NewCommStmt(p.pos(clause), p.simpleStmt(clause.Comm), p.stmts(clause.Body))
+		nodes[i] = ir.NewCommStmt(p.pos(clause), p.stmt(clause.Comm), p.stmts(clause.Body))
 	}
 	if len(clauses) > 0 {
 		p.closeScope(rbrace)

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

@@ -1197,7 +1197,7 @@ func (w *exportWriter) commList(cases []*ir.CommStmt) {
 	w.uint64(uint64(len(cases)))
 	for _, cas := range cases {
 		w.pos(cas.Pos())
-		w.stmtList(cas.List)
+		w.node(cas.Comm)
 		w.stmtList(cas.Body)
 	}
 }

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

@@ -792,7 +792,7 @@ func (r *importReader) caseList(switchExpr ir.Node) []*ir.CaseStmt {
 func (r *importReader) commList() []*ir.CommStmt {
 	cases := make([]*ir.CommStmt, r.uint64())
 	for i := range cases {
-		cases[i] = ir.NewCommStmt(r.pos(), r.stmtList(), r.stmtList())
+		cases[i] = ir.NewCommStmt(r.pos(), r.node(), r.stmtList())
 	}
 	return cases
 }
@@ -1033,7 +1033,9 @@ func (r *importReader) node() ir.Node {
 	case ir.OFOR:
 		pos, init := r.pos(), r.stmtList()
 		cond, post := r.exprsOrNil()
-		return ir.NewForStmt(pos, init, cond, post, r.stmtList())
+		n := ir.NewForStmt(pos, nil, cond, post, r.stmtList())
+		n.PtrInit().Set(init)
+		return n
 
 	case ir.ORANGE:
 		pos := r.pos()

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

@@ -360,29 +360,23 @@ func tcReturn(n *ir.ReturnStmt) ir.Node {
 
 // select
 func tcSelect(sel *ir.SelectStmt) {
-	var def ir.Node
+	var def *ir.CommStmt
 	lno := ir.SetPos(sel)
 	Stmts(sel.Init())
 	for _, ncase := range sel.Cases {
-		if len(ncase.List) == 0 {
+		if ncase.Comm == nil {
 			// default
 			if def != nil {
 				base.ErrorfAt(ncase.Pos(), "multiple defaults in select (first at %v)", ir.Line(def))
 			} else {
 				def = ncase
 			}
-		} else if len(ncase.List) > 1 {
-			base.ErrorfAt(ncase.Pos(), "select cases cannot be lists")
 		} else {
-			ncase.List[0] = Stmt(ncase.List[0])
+			n := Stmt(ncase.Comm)
-			n := ncase.List[0]
 			ncase.Comm = n
-			ncase.List.Set(nil)
+			oselrecv2 := func(dst, recv ir.Node, def bool) {
-			oselrecv2 := func(dst, recv ir.Node, colas bool) {
+				n := ir.NewAssignListStmt(n.Pos(), ir.OSELRECV2, []ir.Node{dst, ir.BlankNode}, []ir.Node{recv})
-				n := ir.NewAssignListStmt(n.Pos(), ir.OSELRECV2, nil, nil)
+				n.Def = def
-				n.Lhs = []ir.Node{dst, ir.BlankNode}
-				n.Rhs = []ir.Node{recv}
-				n.Def = colas
 				n.SetTypecheck(1)
 				ncase.Comm = n
 			}