The compression caches currently don't have any dedicated functionality
that would benefit from being separated. Incorporating caches directly
into the symbol manger also avoids dynamic memory allocation.
The symbol mangler, which is often passed by value, is now slightly
larger. This aspect will be addressed by a follow-up commit.
### Overview
This commit begins the implementation work for RFC 2945. For more
information, see the rendered RFC [1] and tracking issue [2].
A boolean `unwind` payload is added to the `C`, `System`, `Stdcall`,
and `Thiscall` variants, marking whether unwinding across FFI
boundaries is acceptable. The cases where each of these variants'
`unwind` member is true correspond with the `C-unwind`,
`system-unwind`, `stdcall-unwind`, and `thiscall-unwind` ABI strings
introduced in RFC 2945 [3].
### Feature Gate and Unstable Book
This commit adds a `c_unwind` feature gate for the new ABI strings.
Tests for this feature gate are included in `src/test/ui/c-unwind/`,
which ensure that this feature gate works correctly for each of the
new ABIs.
A new language features entry in the unstable book is added as well.
### Further Work To Be Done
This commit does not proceed to implement the new unwinding ABIs,
and is intentionally scoped specifically to *defining* the ABIs and
their feature flag.
### One Note on Test Churn
This will lead to some test churn, in re-blessing hash tests, as the
deleted comment in `src/librustc_target/spec/abi.rs` mentioned,
because we can no longer guarantee the ordering of the `Abi`
variants.
While this is a downside, this decision was made bearing in mind
that RFC 2945 states the following, in the "Other `unwind` Strings"
section [3]:
> More unwind variants of existing ABI strings may be introduced,
> with the same semantics, without an additional RFC.
Adding a new variant for each of these cases, rather than specifying
a payload for a given ABI, would quickly become untenable, and make
working with the `Abi` enum prone to mistakes.
This approach encodes the unwinding information *into* a given ABI,
to account for the future possibility of other `-unwind` ABI
strings.
### Ignore Directives
`ignore-*` directives are used in two of our `*-unwind` ABI test
cases.
Specifically, the `stdcall-unwind` and `thiscall-unwind` test cases
ignore architectures that do not support `stdcall` and
`thiscall`, respectively.
These directives are cribbed from
`src/test/ui/c-variadic/variadic-ffi-1.rs` for `stdcall`, and
`src/test/ui/extern/extern-thiscall.rs` for `thiscall`.
This would otherwise fail on some targets, see:
fcf697f902
### Footnotes
[1]: https://github.com/rust-lang/rfcs/blob/master/text/2945-c-unwind-abi.md
[2]: https://github.com/rust-lang/rust/issues/74990
[3]: https://github.com/rust-lang/rfcs/blob/master/text/2945-c-unwind-abi.md#other-unwind-abi-strings
Stabilize `unsigned_abs`
Resolves#74913.
This PR stabilizes the `i*::unsigned_abs()` method, which returns the absolute value of an integer _as its unsigned equivalent_. This has the advantage that it does not overflow on `i*::MIN`.
I have gone ahead and used this in a couple locations throughout the repository.
This commit modifies v0 symbol mangling to include all generic
parameters from impl blocks (not just those used in the self type).
Signed-off-by: David Wood <david@davidtw.co>
