Fixes a performance regression due to CL 418554.
Fixes#56440
Change-Id: I6ff152e9b83084756363f49ee6b0844a7a284880
Reviewed-on: https://go-review.googlesource.com/c/go/+/445875
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>