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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>
27 lines
467 B
Go
27 lines
467 B
Go
// run
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// Copyright 2022 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Test that devirtualization doesn't introduce spurious type
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// assertion failures due to shaped and non-shaped interfaces having
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// distinct itabs.
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package main
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func main() {
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F[int]()
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}
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func F[T any]() {
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var i I[T] = X(0)
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i.M()
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}
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type I[T any] interface{ M() }
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type X int
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func (X) M() {}
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