cmd/compile: adjust types2 shift check to match go/types (cleanup)
With this change, the shift checking code matches the corresponding
go/types code, but for the differences in the internal error reporting,
and call of check.overflow.
The change leads to the recording of an untyped int value if the RHS
of a non-constant shift is an untyped integer value. Adjust the type
in the compiler's irgen accordingly. Add test/shift3.go to verify
behavior.
Change-Id: I20386fcb1d5c48becffdc2203081fb70c08b282d
Reviewed-on: https://go-review.googlesource.com/c/go/+/398236
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Robert Findley <rfindley@google.com>