Perform `cfg` attribute processing during macro expansion and fix bugs
This PR refactors `cfg` attribute processing and fixes bugs. More specifically:
- It merges gated feature checking for stmt/expr attributes, `cfg_attr` processing, and `cfg` processing into a single fold.
- This allows feature gated `cfg` variables to be used in `cfg_attr` on unconfigured items. All other feature gated attributes can already be used on unconfigured items.
- It performs `cfg` attribute processing during macro expansion instead of after expansion so that macro-expanded items are configured the same as ordinary items. In particular, to match their non-expanded counterparts,
- macro-expanded unconfigured macro invocations are no longer expanded,
- macro-expanded unconfigured macro definitions are no longer usable, and
- feature gated `cfg` variables on macro-expanded macro definitions/invocations are now errors.
This is a [breaking-change]. For example, the following would break:
```rust
macro_rules! m {
() => {
#[cfg(attr)]
macro_rules! foo { () => {} }
foo!(); // This will be an error
macro_rules! bar { () => { fn f() {} } }
#[cfg(attr)] bar!(); // This will no longer be expanded ...
fn g() { f(); } // ... so that `f` will be unresolved.
#[cfg(target_thread_local)] // This will be a gated feature error
macro_rules! baz { () => {} }
}
}
m!();
```
r? @nrc
rustc: Add a new crate type, cdylib
This commit is an implementation of [RFC 1510] which adds a new crate type,
`cdylib`, to the compiler. This new crate type differs from the existing `dylib`
crate type in a few key ways:
* No metadata is present in the final artifact
* Symbol visibility rules are the same as executables, that is only reachable
`extern` functions are visible symbols
* LTO is allowed
* All libraries are always linked statically
This commit is relatively simple by just plubming the compiler with another
crate type which takes different branches here and there. The only major change
is an implementation of the `Linker::export_symbols` function on Unix which now
actually does something. This helps restrict the public symbols from a cdylib on
Unix.
With this PR a "hello world" `cdylib` is 7.2K while the same `dylib` is 2.4MB,
which is some nice size savings!
[RFC 1510]: https://github.com/rust-lang/rfcs/pull/1510Closes#33132
This commit is an implementation of [RFC 1510] which adds a new crate type,
`cdylib`, to the compiler. This new crate type differs from the existing `dylib`
crate type in a few key ways:
* No metadata is present in the final artifact
* Symbol visibility rules are the same as executables, that is only reachable
`extern` functions are visible symbols
* LTO is allowed
* All libraries are always linked statically
This commit is relatively simple by just plubming the compiler with another
crate type which takes different branches here and there. The only major change
is an implementation of the `Linker::export_symbols` function on Unix which now
actually does something. This helps restrict the public symbols from a cdylib on
Unix.
With this PR a "hello world" `cdylib` is 7.2K while the same `dylib` is 2.4MB,
which is some nice size savings!
[RFC 1510]: https://github.com/rust-lang/rfcs/pull/1510Closes#33132
Only break critical edges where actually needed
Currently, to prepare for MIR trans, we break _all_ critical edges,
although we only actually need to do this for edges originating from a
call that gets translated to an invoke instruction in LLVM.
This has the unfortunate effect of undoing a bunch of the things that
SimplifyCfg has done. A particularly bad case arises when you have a
C-like enum with N variants and a derived PartialEq implementation.
In that case, the match on the (&lhs, &rhs) tuple gets translated into
nested matches with N arms each and a basic block each, resulting in N²
basic blocks. SimplifyCfg reduces that to roughly 2*N basic blocks, but
breaking the critical edges means that we go back to N².
In nickel.rs, there is such an enum with roughly N=800. So we get about
640K basic blocks or 2.5M lines of LLVM IR. LLVM takes a while to
reduce that to the final "disr_a == disr_b".
So before this patch, we had 2.5M lines of IR with 640K basic blocks,
which took about about 3.6s in LLVM to get optimized and translated.
After this patch, we get about 650K lines with about 1.6K basic blocks
and spent a little less than 0.2s in LLVM.
cc #33111
r? @Aatch
Clean up `hir::lowering`
Clean up `hir::lowering`:
- give lowering functions mutable access to the lowering context
- refactor the `lower_*` functions and other functions that take a lowering context into methods
- simplify the API that `hir::lowering` exposes to `driver`
- other miscellaneous cleanups
r? @nrc
Make --emit dep-info work correctly with -Z no-analysis again.
Previously, it would attempt to resolve some external crates that weren't necessary for dep-info output.
Fixes#33231.
Currently, to prepare for MIR trans, we break _all_ critical edges,
although we only actually need to do this for edges originating from a
call that gets translated to an invoke instruction in LLVM.
This has the unfortunate effect of undoing a bunch of the things that
SimplifyCfg has done. A particularly bad case arises when you have a
C-like enum with N variants and a derived PartialEq implementation.
In that case, the match on the (&lhs, &rhs) tuple gets translated into
nested matches with N arms each and a basic block each, resulting in N²
basic blocks. SimplifyCfg reduces that to roughly 2*N basic blocks, but
breaking the critical edges means that we go back to N².
In nickel.rs, there is such an enum with roughly N=800. So we get about
640K basic blocks or 2.5M lines of LLVM IR. LLVM takes a while to
reduce that to the final "disr_a == disr_b".
So before this patch, we had 2.5M lines of IR with 640K basic blocks,
which took about about 3.6s in LLVM to get optimized and translated.
After this patch, we get about 650K lines with about 1.6K basic blocks
and spent a little less than 0.2s in LLVM.
cc #33111
Implement constant support in MIR.
All of the intended features in `trans::consts` are now supported by `mir::constant`.
The implementation is considered a temporary measure until `miri` replaces it.
A `-Z orbit` bootstrap build will only translate LLVM IR from AST for `#[rustc_no_mir]` functions.
Furthermore, almost all checks of constant expressions have been moved to MIR.
In non-`const` functions, trees of temporaries are promoted, as per RFC 1414 (rvalue promotion).
Promotion before MIR borrowck would allow reasoning about promoted values' lifetimes.
The improved checking comes at the cost of four `[breaking-change]`s:
* repeat counts must contain a constant expression, e.g.:
`let arr = [0; { println!("foo"); 5 }];` used to be allowed (it behaved like `let arr = [0; 5];`)
* dereference of a reference to a `static` cannot be used in another `static`, e.g.:
`static X: [u8; 1] = [1]; static Y: u8 = (&X)[0];` was unintentionally allowed before
* the type of a `static` *must* be `Sync`, irrespective of the initializer, e.g.
`static FOO: *const T = &BAR;` worked as `&T` is `Sync`, but it shouldn't because `*const T` isn't
* a `static` cannot wrap `UnsafeCell` around a type that *may* need drop, e.g.
`static X: MakeSync<UnsafeCell<Option<String>>> = MakeSync(UnsafeCell::new(None));`
was previously allowed based on the fact `None` alone doesn't need drop, but in `UnsafeCell`
it can be later changed to `Some(String)` which *does* need dropping
The drop restrictions are relaxed by RFC 1440 (#33156), which is implemented, but feature-gated.
However, creating `UnsafeCell` from constants is unstable, so users can just enable the feature gate.
