cmd/compile: allow loading single field of typed-interface{} OpIData

Same reason as CL 270057, but for OpLoad.

Fixes #42727

Change-Id: Iebb1a8110f29427a0aed3b5e3e84f0540de3d1b7
Reviewed-on: https://go-review.googlesource.com/c/go/+/271906
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

diff --git a/src/cmd/compile/internal/ssa/expand_calls.go b/src/cmd/compile/internal/ssa/expand_calls.go
index 3681af65997cf89aed6694ac56d47bbce8782c07..180afab33b1c72fe17a3c9b1e36d27a5b9ded5c4 100644 (file)
--- a/src/cmd/compile/internal/ssa/expand_calls.go
+++ b/src/cmd/compile/internal/ssa/expand_calls.go
@@ -247,7 +247,7 @@ func expandCalls(f *Func) {
                        // i.e., the struct select is generated and remains in because it is not applied to an actual structure.
                        // The OpLoad was created to load the single field of the IData
                        // This case removes that StructSelect.
-                       if leafType != selector.Type {
+                       if leafType != selector.Type && !selector.Type.IsEmptyInterface() { // empty interface for #42727
                                f.Fatalf("Unexpected Load as selector, leaf=%s, selector=%s\n", leaf.LongString(), selector.LongString())
                        }
                        leaf.copyOf(selector)

diff --git a/test/fixedbugs/issue42727.go b/test/fixedbugs/issue42727.go
new file mode 100644 (file)
index 0000000..4008170
--- /dev/null
+++ b/test/fixedbugs/issue42727.go
@@ -0,0 +1,23 @@
+// compile
+
+// 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.
+
+// Ensure that late expansion correctly handles an OpLoad with type interface{}
+
+package p
+
+type iface interface {
+       m()
+}
+
+type it interface{}
+
+type makeIface func() iface
+
+func f() {
+       var im makeIface
+       e := im().(it)
+       _ = &e
+}