[dev.regabi] cmd/compile: use names for keep alive variables in function call

Back to pre Russquake, Node.Nbody of OCALL* node is used to attach
variables which must be kept alive during that call.

Now after Russquake, we have CallExpr to represent a function call,
so use a dedicated field for those variables instead.

Passes toolstash -cmp.

Change-Id: I4f40ebefcc7c41cdcc4e29c7a6d8496a083b68f4
Reviewed-on: https://go-review.googlesource.com/c/go/+/280733
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -159,13 +159,13 @@ const (
 type CallExpr struct {
 	miniExpr
 	origNode
-	X        Node
-	Args     Nodes
-	Rargs    Nodes // TODO(rsc): Delete.
-	Body     Nodes // TODO(rsc): Delete.
-	IsDDD    bool
-	Use      CallUse
-	NoInline bool
+	X         Node
+	Args      Nodes
+	Rargs     Nodes   // TODO(rsc): Delete.
+	KeepAlive []*Name // vars to be kept alive until call returns
+	IsDDD     bool
+	Use       CallUse
+	NoInline  bool
 }
 
 func NewCallExpr(pos src.XPos, op Op, fun Node, args []Node) *CallExpr {

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

@@ -251,7 +251,7 @@ func (n *CallExpr) copy() Node {
 	c.init = copyNodes(c.init)
 	c.Args = copyNodes(c.Args)
 	c.Rargs = copyNodes(c.Rargs)
-	c.Body = copyNodes(c.Body)
+	c.KeepAlive = copyNames(c.KeepAlive)
 	return &c
 }
 func (n *CallExpr) doChildren(do func(Node) bool) bool {
@@ -267,7 +267,7 @@ func (n *CallExpr) doChildren(do func(Node) bool) bool {
 	if doNodes(n.Rargs, do) {
 		return true
 	}
-	if doNodes(n.Body, do) {
+	if doNames(n.KeepAlive, do) {
 		return true
 	}
 	return false
@@ -279,7 +279,7 @@ func (n *CallExpr) editChildren(edit func(Node) Node) {
 	}
 	editNodes(n.Args, edit)
 	editNodes(n.Rargs, edit)
-	editNodes(n.Body, edit)
+	editNames(n.KeepAlive, edit)
 }
 
 func (n *CaseClause) Format(s fmt.State, verb rune) { fmtNode(n, s, verb) }
@@ -1381,6 +1381,30 @@ func editCommClauses(list []*CommClause, edit func(Node) Node) {
 	}
 }
 
+func copyNames(list []*Name) []*Name {
+	if list == nil {
+		return nil
+	}
+	c := make([]*Name, len(list))
+	copy(c, list)
+	return c
+}
+func doNames(list []*Name, do func(Node) bool) bool {
+	for _, x := range list {
+		if x != nil && do(x) {
+			return true
+		}
+	}
+	return false
+}
+func editNames(list []*Name, edit func(Node) Node) {
+	for i, x := range list {
+		if x != nil {
+			list[i] = edit(x).(*Name)
+		}
+	}
+}
+
 func copyNodes(list []Node) []Node {
 	if list == nil {
 		return nil

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

@@ -4867,7 +4867,9 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		s.vars[memVar] = call
 	}
 	// Insert OVARLIVE nodes
-	s.stmtList(n.Body)
+	for _, name := range n.KeepAlive {
+		s.stmt(ir.NewUnaryExpr(n.Pos(), ir.OVARLIVE, name))
+	}
 
 	// Finish block for defers
 	if k == callDefer || k == callDeferStack {

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

@@ -518,7 +518,7 @@ func (o *orderState) call(nn ir.Node) {
 				x := o.copyExpr(arg.X)
 				arg.X = x
 				x.Name().SetAddrtaken(true) // ensure SSA keeps the x variable
-				n.Body.Append(typecheck.Stmt(ir.NewUnaryExpr(base.Pos, ir.OVARLIVE, x)))
+				n.KeepAlive = append(n.KeepAlive, x.(*ir.Name))
 			}
 		}
 	}

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

@@ -228,7 +228,7 @@ func walkGoDefer(n *ir.GoDeferStmt) ir.Node {
 
 	case ir.OCALLFUNC, ir.OCALLMETH, ir.OCALLINTER:
 		call := call.(*ir.CallExpr)
-		if len(call.Body) > 0 {
+		if len(call.KeepAlive) > 0 {
 			n.Call = wrapCall(call, &init)
 		} else {
 			n.Call = walkExpr(call, &init)