Detect when args are always redundant because of another argument

[mvdan]

For example, take this Golang CL: https://go-review.googlesource.com/c/go/+/100455

The func was always called like:

mkinlcall(n, n.Left, n.Isddd())
mkinlcall(n, f, n.Isddd())
etc

Since the func always receives n, receiving n.Method() is redundant.

Other redundant cases that come to mind, when a func receives x:

x.Field
x[i]
x[i:j]
*x

And of course, any combination of the above.

I'm leaving x.PureMethod() and PureFunc(x) out of the list as that's a much more complex one - we'd have to figure out that the func has no side effects. I don't think SSA does this just yet.