[dev.unified] cmd/compile: special case f(g()) calls in Unified IR
For f(g()) calls where g() is multi-valued, we may need to insert
implicit conversions to convert g()'s result values to f()'s parameter
types. This CL refactors code slightly so this will be easier to
handle.
Change-Id: I3a432220dcb62daecf9a66030e8fa1f097e95f95
Reviewed-on: https://go-review.googlesource.com/c/go/+/413362 Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>