[dev.typeparams] cmd/compile: implement generic type switches

Add a new dynamicType node, which is used as a case entry when
the type being switched to is generic.

Change-Id: Ice77c6f224b8fdd3ff574fdf4a8ea5f6c7ddbe75
Reviewed-on: https://go-review.googlesource.com/c/go/+/339429
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/test/typeparam/typeswitch5.go b/test/typeparam/typeswitch5.go
new file mode 100644
index 0000000000..1fc6e0a14e
--- /dev/null
+++ b/test/typeparam/typeswitch5.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 myint int
+func (x myint) foo() int {return int(x)}
+
+type myfloat float64
+func (x myfloat) foo() float64 {return float64(x) }
+
+func f[T any](i interface{}) {
+	switch x := i.(type) {
+	case interface { foo() T }:
+		println("fooer", x.foo())
+	default:
+		println("other")
+	}
+}
+func main() {
+	f[int](myint(6))
+	f[int](myfloat(7))
+	f[float64](myint(8))
+	f[float64](myfloat(9))
+}