[release-branch.go1.18] cmd/compile/internal/inline: fix latent CalleeEffects issue

ir.ClosureExpr implements ir.InitNode, so ir.InitExpr can prepend init
statements to it. However, CalleeEffects wasn't aware of this and
could cause the init statements to get dropped when inlining a call to
a closure.

This isn't an issue today, because we don't create closures with init
statements. But I ran into this within unified IR.

Easy and robust solution: just take advantage that ir.TakeInit can
handle any node.

Fixes #54918.

Change-Id: Ica05fbf6a8c5be4b11927daf84491a1140da5431
Reviewed-on: https://go-review.googlesource.com/c/go/+/422196
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/429897
Reviewed-by: Michael Knyszek <mknyszek@google.com>

src/cmd/compile/internal/inline/inl.go

@@ -771,18 +771,18 @@ func mkinlcall(n *ir.CallExpr, fn *ir.Func, maxCost int32, inlMap map[*ir.Func]b
 // CalleeEffects appends any side effects from evaluating callee to init.
 func CalleeEffects(init *ir.Nodes, callee ir.Node) {
 	for {
+		init.Append(ir.TakeInit(callee)...)
+
 		switch callee.Op() {
 		case ir.ONAME, ir.OCLOSURE, ir.OMETHEXPR:
 			return // done
 
 		case ir.OCONVNOP:
 			conv := callee.(*ir.ConvExpr)
-			init.Append(ir.TakeInit(conv)...)
 			callee = conv.X
 
 		case ir.OINLCALL:
 			ic := callee.(*ir.InlinedCallExpr)
-			init.Append(ir.TakeInit(ic)...)
 			init.Append(ic.Body.Take()...)
 			callee = ic.SingleResult()
 

test/typeparam/issue54911.go

@@ -0,0 +1,21 @@
+// compile -G=3
+
+// 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
+
+type Set[T comparable] map[T]struct{}
+
+func (s Set[T]) Add() Set[T] {
+	return s
+}
+
+func (s Set[T]) Copy() Set[T] {
+	return Set[T].Add(s)
+}
+
+func main() {
+	_ = Set[int]{42: {}}
+}