Because unification is symmetric, in cases where we have symmetric
code for x and y depending on some property we can swap x and y as
needed and simplify the code.
Also, change u.depth increment/decrement position for slightly
nicer tracing ooutput.
Change-Id: I2e84570d463d1c32f6556108f3cb54062b57c718
Reviewed-on: https://go-review.googlesource.com/c/go/+/464896
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com> Reviewed-by: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com>