[dev.typeparams] cmd/compile: remove CallExpr.PreserveClosure

This flag is only needed to prevent the directClosureCall optimization
in walkCall, when called for walkGoDefer. But walkGoDefer don't need
to call walkCall: at this point in the compile, the call expression
isn't a real call anymore.

Instead, we just need to walkExpr on the function expression.

Change-Id: I8a5176cfe1bff53700cbd21ed1b479ebd9a839ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/330271
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Matthew Dempsky <mdempsky@google.com>

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

@@ -163,7 +163,6 @@ type CallExpr struct {
 	IsDDD     bool
 	Use       CallUse
 	NoInline  bool
-	PreserveClosure bool // disable directClosureCall for this call
 }
 
 func NewCallExpr(pos src.XPos, op Op, fun Node, args []Node) *CallExpr {

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

@@ -37,14 +37,6 @@ func directClosureCall(n *ir.CallExpr) {
 		return // leave for walkClosure to handle
 	}
 
-	// If wrapGoDefer() in the order phase has flagged this call,
-	// avoid eliminating the closure even if there is a direct call to
-	// (the closure is needed to simplify the register ABI). See
-	// wrapGoDefer for more details.
-	if n.PreserveClosure {
-		return
-	}
-
 	// We are going to insert captured variables before input args.
 	var params []*types.Field
 	var decls []*ir.Name

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

@@ -1564,11 +1564,10 @@ func (o *orderState) wrapGoDefer(n *ir.GoDeferStmt) {
 	// TODO: maybe not wrap if the called function has no arguments and
 	// only in-register results?
 	if len(callArgs) == 0 && call.Op() == ir.OCALLFUNC && callX.Type().NumResults() == 0 {
-		if c, ok := call.(*ir.CallExpr); ok && callX != nil && callX.Op() == ir.OCLOSURE {
+		if callX.Op() == ir.OCLOSURE {
 			clo := callX.(*ir.ClosureExpr)
 			clo.Func.SetClosureCalled(false)
 			clo.IsGoWrap = true
-			c.PreserveClosure = true
 		}
 		return
 	}
@@ -1771,9 +1770,6 @@ func (o *orderState) wrapGoDefer(n *ir.GoDeferStmt) {
 	topcall := ir.NewCallExpr(n.Pos(), ir.OCALL, clo, nil)
 	typecheck.Call(topcall)
 
-	// Tag the call to insure that directClosureCall doesn't undo our work.
-	topcall.PreserveClosure = true
-
 	fn.SetClosureCalled(false)
 
 	// Finally, point the defer statement at the newly generated call.

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

@@ -204,7 +204,9 @@ func walkGoDefer(n *ir.GoDeferStmt) ir.Node {
 	}
 
 	var init ir.Nodes
-	n.Call = walkExpr(n.Call, &init)
+
+	call := n.Call.(*ir.CallExpr)
+	call.X = walkExpr(call.X, &init)
 
 	if len(init) > 0 {
 		init.Append(n)