cmd/compile: reject not-in-heap types as type arguments
After running the types2 type checker, walk info.Instances to reject
any not-in-heap type arguments. This is feasible to check using the
types2 API now, thanks to #46731.
Fixes #54765.
Change-Id: Idd2acc124d102d5a76f128f13c21a6e593b6790b
Reviewed-on: https://go-review.googlesource.com/c/go/+/427235 Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Keith Randall <khr@google.com>