cmd/compile: make sure shapes have proper indexes for sub-instantiation
The computation for determining the shapes to use at the top of
getInstantation was not always creating shapes with the proper indexes.
If an instantiation is being called from another instantiated function,
we cannot just copy the shape types unchanged, because their indexes may
have changed. So, for type args that already shapes, we still call
Shapify() with the correct index.
Fixes #48645
Change-Id: Ibb61c6f9a3c317220fb85135ca87eb5ad4dcff9e
Reviewed-on: https://go-review.googlesource.com/c/go/+/353030
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org>