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https://github.com/rust-lang/rust
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3aa14e3b2e
In its first step of computing transmutability, `rustc_transmutability` constructs a byte-level representation of type layout (`Tree`). Previously, this representation was computed for ADTs by inspecting the ADT definition and performing our own layout computations. This process was error-prone, verbose, and limited our ability to analyze many types (particularly default-repr types). In this PR, we instead construct `Tree`s from `rustc_target::abi::Layout`s. This helps ensure that layout optimizations are reflected our analyses, and increases the kinds of types we can now analyze, including: - default repr ADTs - transparent unions - `UnsafeCell`-containing types Overall, this PR expands the expressvity of `rustc_transmutability` to be much closer to the transmutability analysis performed by miri. Future PRs will work to close the remaining gaps (e.g., support for `Box`, raw pointers, `NonZero*`, coroutines, etc.).
44 lines
1 KiB
Rust
44 lines
1 KiB
Rust
#![crate_type = "lib"]
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#![feature(transmutability)]
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#![allow(dead_code, incomplete_features, non_camel_case_types)]
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use std::mem::MaybeUninit;
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mod assert {
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use std::mem::{Assume, BikeshedIntrinsicFrom};
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pub fn is_maybe_transmutable<Src, Dst>()
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where
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Dst: BikeshedIntrinsicFrom<Src, { Assume::SAFETY }>
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{}
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}
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fn validity() {
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// An initialized byte is a valid uninitialized byte.
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assert::is_maybe_transmutable::<u8, MaybeUninit<u8>>();
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// An uninitialized byte is never a valid initialized byte.
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assert::is_maybe_transmutable::<MaybeUninit<u8>, u8>(); //~ ERROR: cannot be safely transmuted
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}
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fn padding() {
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#[repr(align(8))]
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struct Align8;
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#[repr(u8)]
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enum ImplicitlyPadded {
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A(Align8),
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}
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#[repr(u8)]
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enum V0 {
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V0 = 0,
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}
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#[repr(C)]
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struct ExplicitlyPadded(V0, MaybeUninit<[u8; 7]>);
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assert::is_maybe_transmutable::<ExplicitlyPadded, ImplicitlyPadded>();
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assert::is_maybe_transmutable::<ImplicitlyPadded, ExplicitlyPadded>();
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}
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