Safe Transmute: Compute transmutability from `rustc_target::abi::Layout` by jswr...
source link: https://github.com/rust-lang/rust/pull/123367
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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 Trees from rustc_target::abi::Layouts. 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.).
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