a4c5198a3c
Walk desugars switch statements into a bunch of OEQ comparisons, and sometimes (although rarely in practice) this currently requires converting the tag value to the case value's type. And because this conversion is inserted during walk, unified IR can't wire up appropriate RTTI operands for the conversion. As a simple solution, if any of the case values are *not* assignable to the tag value's type, we instead convert them all to `any`. This works because `any(x) == any(y)` yields the same value as `x == y`, as long as neither `x` nor `y` are `nil`. We never have to worry about `x` or `y` being `nil` either, because: 1. `switch nil` is invalid, so `x` can never be `nil`. 2. If the tag type is a channel, map, or function type, they can *only* be compared against `nil`; so the case values will always be assignable to the tag value's type, and so we won't convert to `any`. 3. For other nullable types, the previous commit (adding explicit `nil` handling to unified IR) ensures that `case nil:` is actually treated as `case tagType(nil):`. Change-Id: I3adcb9cf0d42a91a12b1a163c58d4133a24fca5e Reviewed-on: https://go-review.googlesource.com/c/go/+/418101 Reviewed-by: Keith Randall <khr@google.com> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com> Run-TryBot: Matthew Dempsky <mdempsky@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org> |
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