cmd/compile: redo mknode.go

The current mknode has a few problems:
1) It tends not to run successfully if the tree is in a broken state.
2) It requires that it be run by the go tool in the tree (somewhat related to 1)
3) It requires setting GOROOT
4) It imports code outside the tree (x/packages)

This makes mknode.go very fragile. In particular, I've spent lots of
time fighting mknode when adding or removing code, related to 1.

Rewrite to just use go/ast and friends. No typechecking, no importing,
etc. It can run with any go version, it doesn't need to be the one
corresponding to the code in which it is run. (e.g. you can use go
1.16 to run mknode). It will work as long as the ir package is parseable.

When run, it generates identical output to the old mknode.

Fixes #53959

Change-Id: I5ce0b55572ebcd2fcd11af57a5f29bbf9fa4ed33
Reviewed-on: https://go-review.googlesource.com/c/go/+/418375
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

0 files changed, 0 insertions, 0 deletions