[dev.regabi] cmd/compile: use []*CaseStmt in {Select,Switch}Stmt

Select and switch statements only ever contain case statements, so
change their Cases fields from Nodes to []*CaseStmt. This allows
removing a bunch of type assertions throughout the compiler.

CaseStmt should be renamed to CaseClause, and SelectStmt should
probably have its own CommClause type instead (like in go/ast and
cmd/compile/internal/syntax), but this is a good start.

Passes toolstash -cmp.

Change-Id: I2d41d616d44512c2be421e1e2ff13d0ee8b238ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/280442
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>

13 files changed, 73 insertions, 53 deletions

diff --git a/src/cmd/compile/internal/escape/escape.go b/src/cmd/compile/internal/escape/escape.go
index 31d157b165..d8f0111d2d 100644
--- a/src/cmd/compile/internal/escape/escape.go
+++ b/src/cmd/compile/internal/escape/escape.go
@@ -369,7 +369,6 @@ func (e *escape) stmt(n ir.Node) {
 
 		var ks []hole
 		for _, cas := range n.Cases { // cases
-			cas := cas.(*ir.CaseStmt)
 			if typesw && n.Tag.(*ir.TypeSwitchGuard).Tag != nil {
 				cv := cas.Var
 				k := e.dcl(cv) // type switch variables have no ODCL.
@@ -391,7 +390,6 @@ func (e *escape) stmt(n ir.Node) {
 	case ir.OSELECT:
 		n := n.(*ir.SelectStmt)
 		for _, cas := range n.Cases {
-			cas := cas.(*ir.CaseStmt)
 			e.stmt(cas.Comm)
 			e.block(cas.Body)
 		}
diff --git a/src/cmd/compile/internal/ir/mknode.go b/src/cmd/compile/internal/ir/mknode.go
index f5dacee622..edf3ee501c 100644
--- a/src/cmd/compile/internal/ir/mknode.go
+++ b/src/cmd/compile/internal/ir/mknode.go
@@ -37,6 +37,7 @@ func main() {
 	nodeType := lookup("Node")
 	ntypeType := lookup("Ntype")
 	nodesType := lookup("Nodes")
+	slicePtrCaseStmtType := types.NewSlice(types.NewPointer(lookup("CaseStmt")))
 	ptrFieldType := types.NewPointer(lookup("Field"))
 	slicePtrFieldType := types.NewSlice(ptrFieldType)
 	ptrIdentType := types.NewPointer(lookup("Ident"))
@@ -76,6 +77,8 @@ func main() {
 				switch {
 				case is(nodesType):
 					fmt.Fprintf(&buf, "c.%s = c.%s.Copy()\n", name, name)
+				case is(slicePtrCaseStmtType):
+					fmt.Fprintf(&buf, "c.%s = copyCases(c.%s)\n", name, name)
 				case is(ptrFieldType):
 					fmt.Fprintf(&buf, "if c.%s != nil { c.%s = c.%s.copy() }\n", name, name, name)
 				case is(slicePtrFieldType):
@@ -94,6 +97,8 @@ func main() {
 				fmt.Fprintf(&buf, "err = maybeDo(n.%s, err, do)\n", name)
 			case is(nodesType):
 				fmt.Fprintf(&buf, "err = maybeDoList(n.%s, err, do)\n", name)
+			case is(slicePtrCaseStmtType):
+				fmt.Fprintf(&buf, "err = maybeDoCases(n.%s, err, do)\n", name)
 			case is(ptrFieldType):
 				fmt.Fprintf(&buf, "err = maybeDoField(n.%s, err, do)\n", name)
 			case is(slicePtrFieldType):
@@ -113,6 +118,8 @@ func main() {
 				fmt.Fprintf(&buf, "n.%s = toNtype(maybeEdit(n.%s, edit))\n", name, name)
 			case is(nodesType):
 				fmt.Fprintf(&buf, "editList(n.%s, edit)\n", name)
+			case is(slicePtrCaseStmtType):
+				fmt.Fprintf(&buf, "editCases(n.%s, edit)\n", name)
 			case is(ptrFieldType):
 				fmt.Fprintf(&buf, "editField(n.%s, edit)\n", name)
 			case is(slicePtrFieldType):
diff --git a/src/cmd/compile/internal/ir/node_gen.go b/src/cmd/compile/internal/ir/node_gen.go
index ecb39563c4..041855bbe9 100644
--- a/src/cmd/compile/internal/ir/node_gen.go
+++ b/src/cmd/compile/internal/ir/node_gen.go
@@ -781,20 +781,20 @@ func (n *SelectStmt) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }
 func (n *SelectStmt) copy() Node {
 	c := *n
 	c.init = c.init.Copy()
-	c.Cases = c.Cases.Copy()
+	c.Cases = copyCases(c.Cases)
 	c.Compiled = c.Compiled.Copy()
 	return &c
 }
 func (n *SelectStmt) doChildren(do func(Node) error) error {
 	var err error
 	err = maybeDoList(n.init, err, do)
-	err = maybeDoList(n.Cases, err, do)
+	err = maybeDoCases(n.Cases, err, do)
 	err = maybeDoList(n.Compiled, err, do)
 	return err
 }
 func (n *SelectStmt) editChildren(edit func(Node) Node) {
 	editList(n.init, edit)
-	editList(n.Cases, edit)
+	editCases(n.Cases, edit)
 	editList(n.Compiled, edit)
 }
 
@@ -945,7 +945,7 @@ func (n *SwitchStmt) Format(s fmt.State, verb rune) { FmtNode(n, s, verb) }
 func (n *SwitchStmt) copy() Node {
 	c := *n
 	c.init = c.init.Copy()
-	c.Cases = c.Cases.Copy()
+	c.Cases = copyCases(c.Cases)
 	c.Compiled = c.Compiled.Copy()
 	return &c
 }
@@ -953,14 +953,14 @@ func (n *SwitchStmt) doChildren(do func(Node) error) error {
 	var err error
 	err = maybeDoList(n.init, err, do)
 	err = maybeDo(n.Tag, err, do)
-	err = maybeDoList(n.Cases, err, do)
+	err = maybeDoCases(n.Cases, err, do)
 	err = maybeDoList(n.Compiled, err, do)
 	return err
 }
 func (n *SwitchStmt) editChildren(edit func(Node) Node) {
 	editList(n.init, edit)
 	n.Tag = maybeEdit(n.Tag, edit)
-	editList(n.Cases, edit)
+	editCases(n.Cases, edit)
 	editList(n.Compiled, edit)
 }
 
diff --git a/src/cmd/compile/internal/ir/stmt.go b/src/cmd/compile/internal/ir/stmt.go
index cfda6fd234..ce775a8529 100644
--- a/src/cmd/compile/internal/ir/stmt.go
+++ b/src/cmd/compile/internal/ir/stmt.go
@@ -191,6 +191,37 @@ func NewCaseStmt(pos src.XPos, list, body []Node) *CaseStmt {
 	return n
 }
 
+func copyCases(list []*CaseStmt) []*CaseStmt {
+	if list == nil {
+		return nil
+	}
+	c := make([]*CaseStmt, len(list))
+	copy(c, list)
+	return c
+}
+
+func maybeDoCases(list []*CaseStmt, err error, do func(Node) error) error {
+	if err != nil {
+		return err
+	}
+	for _, x := range list {
+		if x != nil {
+			if err := do(x); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func editCases(list []*CaseStmt, edit func(Node) Node) {
+	for i, x := range list {
+		if x != nil {
+			list[i] = edit(x).(*CaseStmt)
+		}
+	}
+}
+
 // A ForStmt is a non-range for loop: for Init; Cond; Post { Body }
 // Op can be OFOR or OFORUNTIL (!Cond).
 type ForStmt struct {
@@ -334,18 +365,18 @@ func (n *ReturnStmt) SetOrig(x Node) { n.orig = x }
 type SelectStmt struct {
 	miniStmt
 	Label    *types.Sym
-	Cases    Nodes
+	Cases    []*CaseStmt
 	HasBreak bool
 
 	// TODO(rsc): Instead of recording here, replace with a block?
 	Compiled Nodes // compiled form, after walkswitch
 }
 
-func NewSelectStmt(pos src.XPos, cases []Node) *SelectStmt {
+func NewSelectStmt(pos src.XPos, cases []*CaseStmt) *SelectStmt {
 	n := &SelectStmt{}
 	n.pos = pos
 	n.op = OSELECT
-	n.Cases.Set(cases)
+	n.Cases = cases
 	return n
 }
 
@@ -367,7 +398,7 @@ func NewSendStmt(pos src.XPos, ch, value Node) *SendStmt {
 type SwitchStmt struct {
 	miniStmt
 	Tag      Node
-	Cases    Nodes // list of *CaseStmt
+	Cases    []*CaseStmt
 	Label    *types.Sym
 	HasBreak bool
 
@@ -375,11 +406,11 @@ type SwitchStmt struct {
 	Compiled Nodes // compiled form, after walkswitch
 }
 
-func NewSwitchStmt(pos src.XPos, tag Node, cases []Node) *SwitchStmt {
+func NewSwitchStmt(pos src.XPos, tag Node, cases []*CaseStmt) *SwitchStmt {
 	n := &SwitchStmt{Tag: tag}
 	n.pos = pos
 	n.op = OSWITCH
-	n.Cases.Set(cases)
+	n.Cases = cases
 	return n
 }
 
diff --git a/src/cmd/compile/internal/ir/visit.go b/src/cmd/compile/internal/ir/visit.go
index a1c345968f..8839e1664d 100644
--- a/src/cmd/compile/internal/ir/visit.go
+++ b/src/cmd/compile/internal/ir/visit.go
@@ -217,10 +217,9 @@ func EditChildren(n Node, edit func(Node) Node) {
 // Note that editList only calls edit on the nodes in the list, not their children.
 // If x's children should be processed, edit(x) must call EditChildren(x, edit) itself.
 func editList(list Nodes, edit func(Node) Node) {
-	s := list
 	for i, x := range list {
 		if x != nil {
-			s[i] = edit(x)
+			list[i] = edit(x)
 		}
 	}
 }
diff --git a/src/cmd/compile/internal/noder/noder.go b/src/cmd/compile/internal/noder/noder.go
index ad66b6c850..b974448338 100644
--- a/src/cmd/compile/internal/noder/noder.go
+++ b/src/cmd/compile/internal/noder/noder.go
@@ -1202,14 +1202,14 @@ func (p *noder) switchStmt(stmt *syntax.SwitchStmt) ir.Node {
 	if l := n.Tag; l != nil && l.Op() == ir.OTYPESW {
 		tswitch = l.(*ir.TypeSwitchGuard)
 	}
-	n.Cases.Set(p.caseClauses(stmt.Body, tswitch, stmt.Rbrace))
+	n.Cases = p.caseClauses(stmt.Body, tswitch, stmt.Rbrace)
 
 	p.closeScope(stmt.Rbrace)
 	return n
 }
 
-func (p *noder) caseClauses(clauses []*syntax.CaseClause, tswitch *ir.TypeSwitchGuard, rbrace syntax.Pos) []ir.Node {
-	nodes := make([]ir.Node, 0, len(clauses))
+func (p *noder) caseClauses(clauses []*syntax.CaseClause, tswitch *ir.TypeSwitchGuard, rbrace syntax.Pos) []*ir.CaseStmt {
+	nodes := make([]*ir.CaseStmt, 0, len(clauses))
 	for i, clause := range clauses {
 		p.setlineno(clause)
 		if i > 0 {
@@ -1266,8 +1266,8 @@ func (p *noder) simpleStmt(stmt syntax.SimpleStmt) []ir.Node {
 	return []ir.Node{p.stmt(stmt)}
 }
 
-func (p *noder) commClauses(clauses []*syntax.CommClause, rbrace syntax.Pos) []ir.Node {
-	nodes := make([]ir.Node, len(clauses))
+func (p *noder) commClauses(clauses []*syntax.CommClause, rbrace syntax.Pos) []*ir.CaseStmt {
+	nodes := make([]*ir.CaseStmt, len(clauses))
 	for i, clause := range clauses {
 		p.setlineno(clause)
 		if i > 0 {
diff --git a/src/cmd/compile/internal/typecheck/iexport.go b/src/cmd/compile/internal/typecheck/iexport.go
index 0c813a71ef..19437a069e 100644
--- a/src/cmd/compile/internal/typecheck/iexport.go
+++ b/src/cmd/compile/internal/typecheck/iexport.go
@@ -1181,10 +1181,9 @@ func isNamedTypeSwitch(x ir.Node) bool {
 	return ok && guard.Tag != nil
 }
 
-func (w *exportWriter) caseList(cases []ir.Node, namedTypeSwitch bool) {
+func (w *exportWriter) caseList(cases []*ir.CaseStmt, namedTypeSwitch bool) {
 	w.uint64(uint64(len(cases)))
 	for _, cas := range cases {
-		cas := cas.(*ir.CaseStmt)
 		w.pos(cas.Pos())
 		w.stmtList(cas.List)
 		if namedTypeSwitch {
diff --git a/src/cmd/compile/internal/typecheck/iimport.go b/src/cmd/compile/internal/typecheck/iimport.go
index 8285c418e9..fd8314b662 100644
--- a/src/cmd/compile/internal/typecheck/iimport.go
+++ b/src/cmd/compile/internal/typecheck/iimport.go
@@ -767,10 +767,10 @@ func (r *importReader) stmtList() []ir.Node {
 	return list
 }
 
-func (r *importReader) caseList(switchExpr ir.Node) []ir.Node {
+func (r *importReader) caseList(switchExpr ir.Node) []*ir.CaseStmt {
 	namedTypeSwitch := isNamedTypeSwitch(switchExpr)
 
-	cases := make([]ir.Node, r.uint64())
+	cases := make([]*ir.CaseStmt, r.uint64())
 	for i := range cases {
 		cas := ir.NewCaseStmt(r.pos(), nil, nil)
 		cas.List.Set(r.stmtList())
diff --git a/src/cmd/compile/internal/typecheck/stmt.go b/src/cmd/compile/internal/typecheck/stmt.go
index 7e74b730bc..03c3e399eb 100644
--- a/src/cmd/compile/internal/typecheck/stmt.go
+++ b/src/cmd/compile/internal/typecheck/stmt.go
@@ -364,8 +364,6 @@ func tcSelect(sel *ir.SelectStmt) {
 	lno := ir.SetPos(sel)
 	Stmts(sel.Init())
 	for _, ncase := range sel.Cases {
-		ncase := ncase.(*ir.CaseStmt)
-
 		if len(ncase.List) == 0 {
 			// default
 			if def != nil {
@@ -508,7 +506,6 @@ func tcSwitchExpr(n *ir.SwitchStmt) {
 	var defCase ir.Node
 	var cs constSet
 	for _, ncase := range n.Cases {
-		ncase := ncase.(*ir.CaseStmt)
 		ls := ncase.List
 		if len(ls) == 0 { // default:
 			if defCase != nil {
@@ -577,7 +574,6 @@ func tcSwitchType(n *ir.SwitchStmt) {
 	var defCase, nilCase ir.Node
 	var ts typeSet
 	for _, ncase := range n.Cases {
-		ncase := ncase.(*ir.CaseStmt)
 		ls := ncase.List
 		if len(ls) == 0 { // default:
 			if defCase != nil {
diff --git a/src/cmd/compile/internal/typecheck/typecheck.go b/src/cmd/compile/internal/typecheck/typecheck.go
index b779f9ceb0..dabfee3bf9 100644
--- a/src/cmd/compile/internal/typecheck/typecheck.go
+++ b/src/cmd/compile/internal/typecheck/typecheck.go
@@ -2103,7 +2103,6 @@ func isTermNode(n ir.Node) bool {
 		}
 		def := false
 		for _, cas := range n.Cases {
-			cas := cas.(*ir.CaseStmt)
 			if !isTermNodes(cas.Body) {
 				return false
 			}
@@ -2119,7 +2118,6 @@ func isTermNode(n ir.Node) bool {
 			return false
 		}
 		for _, cas := range n.Cases {
-			cas := cas.(*ir.CaseStmt)
 			if !isTermNodes(cas.Body) {
 				return false
 			}
@@ -2218,9 +2216,6 @@ func deadcodeslice(nn *ir.Nodes) {
 		case ir.OBLOCK:
 			n := n.(*ir.BlockStmt)
 			deadcodeslice(&n.List)
-		case ir.OCASE:
-			n := n.(*ir.CaseStmt)
-			deadcodeslice(&n.Body)
 		case ir.OFOR:
 			n := n.(*ir.ForStmt)
 			deadcodeslice(&n.Body)
@@ -2233,10 +2228,14 @@ func deadcodeslice(nn *ir.Nodes) {
 			deadcodeslice(&n.Body)
 		case ir.OSELECT:
 			n := n.(*ir.SelectStmt)
-			deadcodeslice(&n.Cases)
+			for _, cas := range n.Cases {
+				deadcodeslice(&cas.Body)
+			}
 		case ir.OSWITCH:
 			n := n.(*ir.SwitchStmt)
-			deadcodeslice(&n.Cases)
+			for _, cas := range n.Cases {
+				deadcodeslice(&cas.Body)
+			}
 		}
 
 		if cut {
diff --git a/src/cmd/compile/internal/walk/order.go b/src/cmd/compile/internal/walk/order.go
index 1e41cfc6aa..ebbd467570 100644
--- a/src/cmd/compile/internal/walk/order.go
+++ b/src/cmd/compile/internal/walk/order.go
@@ -914,7 +914,6 @@ func (o *orderState) stmt(n ir.Node) {
 		n := n.(*ir.SelectStmt)
 		t := o.markTemp()
 		for _, ncas := range n.Cases {
-			ncas := ncas.(*ir.CaseStmt)
 			r := ncas.Comm
 			ir.SetPos(ncas)
 
@@ -996,7 +995,6 @@ func (o *orderState) stmt(n ir.Node) {
 		// Also insert any ninit queued during the previous loop.
 		// (The temporary cleaning must follow that ninit work.)
 		for _, cas := range n.Cases {
-			cas := cas.(*ir.CaseStmt)
 			orderBlock(&cas.Body, o.free)
 			cas.Body.Prepend(o.cleanTempNoPop(t)...)
 
@@ -1036,13 +1034,12 @@ func (o *orderState) stmt(n ir.Node) {
 		n := n.(*ir.SwitchStmt)
 		if base.Debug.Libfuzzer != 0 && !hasDefaultCase(n) {
 			// Add empty "default:" case for instrumentation.
-			n.Cases.Append(ir.NewCaseStmt(base.Pos, nil, nil))
+			n.Cases = append(n.Cases, ir.NewCaseStmt(base.Pos, nil, nil))
 		}
 
 		t := o.markTemp()
 		n.Tag = o.expr(n.Tag, nil)
 		for _, ncas := range n.Cases {
-			ncas := ncas.(*ir.CaseStmt)
 			o.exprListInPlace(ncas.List)
 			orderBlock(&ncas.Body, o.free)
 		}
@@ -1056,7 +1053,6 @@ func (o *orderState) stmt(n ir.Node) {
 
 func hasDefaultCase(n *ir.SwitchStmt) bool {
 	for _, ncas := range n.Cases {
-		ncas := ncas.(*ir.CaseStmt)
 		if len(ncas.List) == 0 {
 			return true
 		}
diff --git a/src/cmd/compile/internal/walk/select.go b/src/cmd/compile/internal/walk/select.go
index 5e03732169..0b7e7e99fb 100644
--- a/src/cmd/compile/internal/walk/select.go
+++ b/src/cmd/compile/internal/walk/select.go
@@ -21,7 +21,7 @@ func walkSelect(sel *ir.SelectStmt) {
 	sel.PtrInit().Set(nil)
 
 	init = append(init, walkSelectCases(sel.Cases)...)
-	sel.Cases = ir.Nodes{}
+	sel.Cases = nil
 
 	sel.Compiled.Set(init)
 	walkStmtList(sel.Compiled)
@@ -29,7 +29,7 @@ func walkSelect(sel *ir.SelectStmt) {
 	base.Pos = lno
 }
 
-func walkSelectCases(cases ir.Nodes) []ir.Node {
+func walkSelectCases(cases []*ir.CaseStmt) []ir.Node {
 	ncas := len(cases)
 	sellineno := base.Pos
 
@@ -40,7 +40,7 @@ func walkSelectCases(cases ir.Nodes) []ir.Node {
 
 	// optimization: one-case select: single op.
 	if ncas == 1 {
-		cas := cases[0].(*ir.CaseStmt)
+		cas := cases[0]
 		ir.SetPos(cas)
 		l := cas.Init()
 		if cas.Comm != nil { // not default:
@@ -75,7 +75,6 @@ func walkSelectCases(cases ir.Nodes) []ir.Node {
 	// this rewrite is used by both the general code and the next optimization.
 	var dflt *ir.CaseStmt
 	for _, cas := range cases {
-		cas := cas.(*ir.CaseStmt)
 		ir.SetPos(cas)
 		n := cas.Comm
 		if n == nil {
@@ -99,9 +98,9 @@ func walkSelectCases(cases ir.Nodes) []ir.Node {
 
 	// optimization: two-case select but one is default: single non-blocking op.
 	if ncas == 2 && dflt != nil {
-		cas := cases[0].(*ir.CaseStmt)
+		cas := cases[0]
 		if cas == dflt {
-			cas = cases[1].(*ir.CaseStmt)
+			cas = cases[1]
 		}
 
 		n := cas.Comm
@@ -170,7 +169,6 @@ func walkSelectCases(cases ir.Nodes) []ir.Node {
 
 	// register cases
 	for _, cas := range cases {
-		cas := cas.(*ir.CaseStmt)
 		ir.SetPos(cas)
 
 		init = append(init, cas.Init()...)
diff --git a/src/cmd/compile/internal/walk/switch.go b/src/cmd/compile/internal/walk/switch.go
index 141d2e5e05..de0b471b34 100644
--- a/src/cmd/compile/internal/walk/switch.go
+++ b/src/cmd/compile/internal/walk/switch.go
@@ -71,7 +71,6 @@ func walkSwitchExpr(sw *ir.SwitchStmt) {
 	var defaultGoto ir.Node
 	var body ir.Nodes
 	for _, ncase := range sw.Cases {
-		ncase := ncase.(*ir.CaseStmt)
 		label := typecheck.AutoLabel(".s")
 		jmp := ir.NewBranchStmt(ncase.Pos(), ir.OGOTO, label)
 
@@ -96,7 +95,7 @@ func walkSwitchExpr(sw *ir.SwitchStmt) {
 			body.Append(br)
 		}
 	}
-	sw.Cases.Set(nil)
+	sw.Cases = nil
 
 	if defaultGoto == nil {
 		br := ir.NewBranchStmt(base.Pos, ir.OBREAK, nil)
@@ -259,7 +258,6 @@ func allCaseExprsAreSideEffectFree(sw *ir.SwitchStmt) bool {
 	// enough.
 
 	for _, ncase := range sw.Cases {
-		ncase := ncase.(*ir.CaseStmt)
 		for _, v := range ncase.List {
 			if v.Op() != ir.OLITERAL {
 				return false
@@ -325,7 +323,6 @@ func walkSwitchType(sw *ir.SwitchStmt) {
 	var defaultGoto, nilGoto ir.Node
 	var body ir.Nodes
 	for _, ncase := range sw.Cases {
-		ncase := ncase.(*ir.CaseStmt)
 		caseVar := ncase.Var
 
 		// For single-type cases with an interface type,
@@ -384,7 +381,7 @@ func walkSwitchType(sw *ir.SwitchStmt) {
 		body.Append(ncase.Body...)
 		body.Append(br)
 	}
-	sw.Cases.Set(nil)
+	sw.Cases = nil
 
 	if defaultGoto == nil {
 		defaultGoto = br