[dev.unified] cmd/compile: avoid reflectType in ssagen
This CL adds alternate code paths for the frontend to plumb through
rtypes to package ssagen, so the latter doesn't have to use
reflectType (which in general will only have access to shape types).
Note: This CL doesn't yet plumb through the rtypes for variables that
escape to the heap. However, those rtypes are only used for calling
runtime.newobject, and the status quo as of Go 1.18 is already to use
shape rtypes for most runtime.newobject calls. (Longer term though, I
would like to get rid of shape rtypes altogether.)
Passes toolstash -cmp.
Updates #53276.
Change-Id: I76a281eca8300de2e701fbac89ead32f8568a5f2
Reviewed-on: https://go-review.googlesource.com/c/go/+/413357
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com> Reviewed-by: David Chase <drchase@google.com>