cmd/compile/internal/devirtualize: use pointer identity for type comparison

Fixes #78404

Change-Id: I6adc1fb42ad6a3acce21333c6819d0796a6a6964
Reviewed-on: https://go-review.googlesource.com/c/go/+/760161
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 15 insertions, 2 deletions

diff --git a/src/cmd/compile/internal/devirtualize/devirtualize.go b/src/cmd/compile/internal/devirtualize/devirtualize.go
index 5f1da23654..59ddc2e536 100644
--- a/src/cmd/compile/internal/devirtualize/devirtualize.go
+++ b/src/cmd/compile/internal/devirtualize/devirtualize.go
@@ -293,9 +293,22 @@ func concreteType1(s *State, n ir.Node, seen map[*ir.Name]struct{}) (outT *types
 				continue
 			}
 		}
-		if t == nil || (typ != nil && !types.Identical(typ, t)) {
-			return nil
+		if t == nil {
+			return nil // unknown concrete type
 		}
+
+		// Methods are only declared on named types, and each named type
+		// is represented by a unique [*types.Type], thus pointer comparison
+		// is fine here.
+		//
+		// The only scenario where [types.IdenticalStrict] could help here is with
+		// unnamed struct types that embed another type (e.g. foo = struct { Impl }{}).
+		// However, such patterns are uncommon and not worth the additional complexity
+		// in the devirtualizer.
+		if typ != nil && typ != t {
+			return nil // assigned with a different type
+		}
+
 		typ = t
 	}