cmd/compile: recognize reassignments involving receives

Previously, reassigned was failing to detect reassignments due to
channel receives in select statements (OSELRECV, OSELRECV2), or due to
standalone 2-value receive assignments (OAS2RECV). This was reported
as a devirtualization panic, but could have caused mis-inlining as
well.

Fixes #43292.

Change-Id: Ic8079c20c0587aeacff9596697fdeba80a697b12
Reviewed-on: https://go-review.googlesource.com/c/go/+/279352
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>

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

@@ -832,16 +832,20 @@ func (v *reassignVisitor) visit(n *Node) *Node {
 		return nil
 	}
 	switch n.Op {
-	case OAS:
+	case OAS, OSELRECV:
 		if n.Left == v.name && n != v.name.Name.Defn {
 			return n
 		}
-	case OAS2, OAS2FUNC, OAS2MAPR, OAS2DOTTYPE:
+	case OAS2, OAS2FUNC, OAS2MAPR, OAS2DOTTYPE, OAS2RECV:
 		for _, p := range n.List.Slice() {
 			if p == v.name && n != v.name.Name.Defn {
 				return n
 			}
 		}
+	case OSELRECV2:
+		if (n.Left == v.name || n.List.First() == v.name) && n != v.name.Name.Defn {
+			return n
+		}
 	}
 	if a := v.visit(n.Left); a != nil {
 		return a

test/fixedbugs/issue43292.go

@@ -0,0 +1,59 @@
+// run
+
+// Copyright 2020 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() {
+	{
+		i := I(A{})
+
+		b := make(chan I, 1)
+		b <- B{}
+
+		var ok bool
+		i, ok = <-b
+		_ = ok
+
+		i.M()
+	}
+
+	{
+		i := I(A{})
+
+		b := make(chan I, 1)
+		b <- B{}
+
+		select {
+		case i = <-b:
+		}
+
+		i.M()
+	}
+
+	{
+		i := I(A{})
+
+		b := make(chan I, 1)
+		b <- B{}
+
+		var ok bool
+		select {
+		case i, ok = <-b:
+		}
+		_ = ok
+
+		i.M()
+	}
+}
+
+type I interface{ M() int }
+
+type T int
+
+func (T) M() int { return 0 }
+
+type A struct{ T }
+type B struct{ T }