cmd/compile: fix assert condition in generic method call

Fixes #53406.

Change-Id: If7ae39ec1042a792d82a0a2de96d168c22d8ab71
Reviewed-on: https://go-review.googlesource.com/c/go/+/412614
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Alex Rakoczy <alex@golang.org>
Auto-Submit: Alex Rakoczy <alex@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Wayne Zuo <wdvxdr@golangcn.org>

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

@@ -208,9 +208,15 @@ func (g *genInst) scanForGenCalls(decl ir.Node) {
 
 			st := g.getInstantiation(gf, targs, true).fun
 			dictValue, usingSubdict := g.getDictOrSubdict(declInfo, n, gf, targs, true)
-			// We have to be using a subdictionary, since this is
-			// a generic method call.
-			assert(usingSubdict)
+			if hasShapeTypes(targs) {
+				// We have to be using a subdictionary, since this is
+				// a generic method call.
+				assert(usingSubdict)
+			} else {
+				// We should use main dictionary, because the receiver is
+				// an instantiation already, see issue #53406.
+				assert(!usingSubdict)
+			}
 
 			// Transform to a function call, by appending the
 			// dictionary and the receiver to the args.

test/typeparam/issue53406.go

@@ -0,0 +1,22 @@
+// compile
+
+// Copyright 2022 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
+
+func main() {
+	f[int]()
+}
+
+func f[T1 any]() {
+	var x Outer[T1, int]
+	x.M()
+}
+
+type Outer[T1, T2 any] struct{ Inner[T2] }
+
+type Inner[_ any] int
+
+func (Inner[_]) M() {}