cmd/compile: avoid assignment conversion in append(a, b...)
There's no need for a and b to match types. The typechecker already
ensured that a and b are both slices with the same base type, or
a and b are (possibly named) []byte and string.
The optimization to treat append(b, make([], ...)) as a zeroing
slice extension doesn't fire when there's a OCONVNOP wrapping the make.
Fixes #53888
Change-Id: Ied871ed0bbb8e4a4b35d280c71acbab8103691bc
Reviewed-on: https://go-review.googlesource.com/c/go/+/418475
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com> Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Keith Randall <khr@golang.org>