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As a consistency check in devirtualization, when we determine `i` (of interface type `I`) always has dynamic type `T`, we insert a type assertion `i.(T)`. This emits an itab check for `go:itab.T,I`, but it's always true (and so SSA optimizes it away). However, if `I` is instead the generic interface type `I[T]`, then `go:itab.T,I[int]` and `go:itab.T,I[go.shape.int]` are equivalent but distinct itabs. And notably, we'll have originally created the interface value using the former; but the (non-dynamic) TypeAssertExpr created by devirtualization would ultimately emit a comparison against the latter. This comparison would then evaluate false, leading to a spurious type assertion panic at runtime. The comparison is just meant as an extra safety check, so it should be safe to just disable. But for now, it's simpler/safer to just punt on devirtualization in this case. (The non-unified frontend doesn't devirtualize this either.) Change-Id: I6a8809bcfebc9571f32e289fa4bc6a8b0d21ca46 Reviewed-on: https://go-review.googlesource.com/c/go/+/424774 Reviewed-by: Keith Randall <khr@golang.org> Run-TryBot: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Keith Randall <khr@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com> |
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