cmd/link: check for reflect.Value.MethodByName explicitly

Currently we only check for reflect.Value.Method. And
reflect.Value.MethodByName is covered since it calls
reflect.Value.Method internally. But it is brittle to rely on
implementation detail of the reflect package. Check for
MethodByName explicitly.

Change-Id: Ifa8920e997524003dade03abc4fb3c4e64723643
Reviewed-on: https://go-review.googlesource.com/c/go/+/228881
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/cmd/link/internal/ld/deadcode.go b/src/cmd/link/internal/ld/deadcode.go
index b5bc508356..ae676935fc 100644
--- a/src/cmd/link/internal/ld/deadcode.go
+++ b/src/cmd/link/internal/ld/deadcode.go
@@ -22,7 +22,8 @@ import (
 //
 //	1. direct call
 //	2. through a reachable interface type
-//	3. reflect.Value.Method, or reflect.Type.Method
+//	3. reflect.Value.Method (or MethodByName), or reflect.Type.Method
+//	   (or MethodByName)
 //
 // The first case is handled by the flood fill, a directly called method
 // is marked as reachable.
@@ -33,7 +34,7 @@ import (
 // as reachable. This is extremely conservative, but easy and correct.
 //
 // The third case is handled by looking to see if any of:
-//	- reflect.Value.Method is reachable
+//	- reflect.Value.Method or MethodByName is reachable
 // 	- reflect.Type.Method or MethodByName is called (through the
 // 	  REFLECTMETHOD attribute marked by the compiler).
 // If any of these happen, all bets are off and all exported methods