[dev.typeparams] cmd/compile: allow typecheck of OCHECKNIL

This CL makes OCHECKNIL typecheckable. Simplifies IR construction code
slightly, and gives one convenient place to check for misuse.

Change-Id: I280b8e47eddcac12947a41d6f911b25bc12a66bf
Reviewed-on: https://go-review.googlesource.com/c/go/+/330194
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/typecheck/stmt.go

@@ -237,6 +237,15 @@ func plural(n int) string {
 	return "s"
 }
 
+// tcCheckNil typechecks an OCHECKNIL node.
+func tcCheckNil(n *ir.UnaryExpr) ir.Node {
+	n.X = Expr(n.X)
+	if !n.X.Type().IsPtrShaped() {
+		base.FatalfAt(n.Pos(), "%L is not pointer shaped", n.X)
+	}
+	return n
+}
+
 // tcFor typechecks an OFOR node.
 func tcFor(n *ir.ForStmt) ir.Node {
 	Stmts(n.Init())

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

@@ -876,6 +876,10 @@ func typecheck1(n ir.Node, top int) ir.Node {
 		n := n.(*ir.TailCallStmt)
 		return n
 
+	case ir.OCHECKNIL:
+		n := n.(*ir.UnaryExpr)
+		return tcCheckNil(n)
+
 	case ir.OSELECT:
 		tcSelect(n.(*ir.SelectStmt))
 		return n

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

@@ -677,9 +677,8 @@ func walkUnsafeSlice(n *ir.BinaryExpr, init *ir.Nodes) ir.Node {
 
 	ptr := walkExpr(n.X, init)
 
-	c := ir.NewUnaryExpr(n.Pos(), ir.OCHECKNIL, ptr)
+	check := ir.NewUnaryExpr(n.Pos(), ir.OCHECKNIL, ptr)
-	c.SetTypecheck(1)
+	init.Append(typecheck.Stmt(check))
-	init.Append(c)
 
 	// TODO(mdempsky): checkptr instrumentation. Maybe merge into length
 	// check above, along with nil check? Need to be careful about

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

@@ -178,11 +178,9 @@ func walkCallPart(n *ir.SelectorExpr, init *ir.Nodes) ir.Node {
 		n.X = cheapExpr(n.X, init)
 		n.X = walkExpr(n.X, nil)
 
-		tab := typecheck.Expr(ir.NewUnaryExpr(base.Pos, ir.OITAB, n.X))
+		tab := ir.NewUnaryExpr(base.Pos, ir.OITAB, n.X)
-
+		check := ir.NewUnaryExpr(base.Pos, ir.OCHECKNIL, tab)
-		c := ir.NewUnaryExpr(base.Pos, ir.OCHECKNIL, tab)
+		init.Append(typecheck.Stmt(check))
-		c.SetTypecheck(1)
-		init.Append(c)
 	}
 
 	typ := typecheck.PartialCallType(n)

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

@@ -762,7 +762,7 @@ func (o *orderState) stmt(n ir.Node) {
 		o.out = append(o.out, n)
 		o.cleanTemp(t)
 
-	case ir.OCLOSE, ir.ORECV:
+	case ir.OCHECKNIL, ir.OCLOSE, ir.OPANIC, ir.ORECV:
 		n := n.(*ir.UnaryExpr)
 		t := o.markTemp()
 		n.X = o.expr(n.X, nil)
@@ -835,16 +835,6 @@ func (o *orderState) stmt(n ir.Node) {
 		orderBlock(&n.Else, o.free)
 		o.out = append(o.out, n)
 
-	case ir.OPANIC:
-		n := n.(*ir.UnaryExpr)
-		t := o.markTemp()
-		n.X = o.expr(n.X, nil)
-		if !n.X.Type().IsEmptyInterface() {
-			base.FatalfAt(n.Pos(), "bad argument to panic: %L", n.X)
-		}
-		o.out = append(o.out, n)
-		o.cleanTemp(t)
-
 	case ir.ORANGE:
 		// n.Right is the expression being ranged over.
 		// order it, and then make a copy if we need one.