cmd/compile: add required CONVIFACE nodes when translating OFUNCINST node

In CL 349614. we removed the early transformation code that
was needed to create the implicit CONVIFACE nodes.

Because the transformCall function is not called when translating OFUNCINST.
So we add in needed CONVIFACE nodes via typecheckaste().

Fixes #48598

Change-Id: If9dc7040cdc38ef2e52fdbb08c840095651426f2
Reviewed-on: https://go-review.googlesource.com/c/go/+/351856
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Dan Scales <danscales@google.com>
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>

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

@@ -1097,6 +1097,10 @@ func (subst *subster) node(n ir.Node) ir.Node {
 				// A call with an OFUNCINST will get transformed
 				// in stencil() once we have created & attached the
 				// instantiation to be called.
+				// We must transform the arguments of the call now, though,
+				// so that any needed CONVIFACE nodes are exposed,
+				// so the dictionary format is correct
+				transformEarlyCall(call)
 
 			case ir.OXDOT, ir.ODOTTYPE, ir.ODOTTYPE2:
 			default:

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

@@ -177,6 +177,12 @@ func transformCall(n *ir.CallExpr) {
 	}
 }
 
+// transformEarlyCall transforms the arguments of a call with an OFUNCINST node.
+func transformEarlyCall(n *ir.CallExpr) {
+	transformArgs(n)
+	typecheckaste(ir.OCALL, n.X, n.IsDDD, n.X.Type().Params(), n.Args)
+}
+
 // transformCompare transforms a compare operation (currently just equals/not
 // equals). Corresponds to the "comparison operators" case in
 // typecheck.typecheck1, including tcArith.

test/typeparam/issue48598.go

@@ -0,0 +1,28 @@
+// run -gcflags=-G=3
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+type Iterator[T any] interface {
+	Iterate()
+}
+
+type IteratorFunc[T any] func(fn func(T) bool)
+
+func (f IteratorFunc[T]) Iterate() {
+}
+
+func FromIterator[T any](it Iterator[T]) {
+	it.Iterate()
+}
+
+func Foo[T, R any]() {
+	FromIterator[R](IteratorFunc[R](nil))
+}
+
+func main() {
+	Foo[int, int]()
+}