Use read_unaligned instead of read in transmute_copy
Closes: #55044
This change could result in performance regression on non-x86 platforms. (but it also can fix some of UB which lurks in existing programs) An alternative would be to update `transmute_copy` documentation with alignment requirements.
When reading this I wondered what “some significant optimizations” referred to. As far as I can tell, the specialization of `.fuse()` is the only case where `FusedIterator` has any impact at all. Is this accurate @Stebalien?
Fix emission of niche-filling discriminant values
Bug #55606 points out a regression introduced by #54004; namely that
an assertion can erroneously fire when a niche-filling discriminant
value is emitted.
This fixes the bug by removing the assertion, and furthermore by
arranging for the discriminant value to be masked according to the
size of the niche. This makes handling the discriminant a bit simpler
for debuggers.
The test case is from Jonathan Turner.
Closes#55606
Make `MatcherPos::stack` a `SmallVec`.
This avoids some allocations.
This seems like a trivial change, but the compiler rejects it:
```
Compiling syntax v0.0.0 (/home/njn/moz/rust1/src/libsyntax)
error[E0597]: `initial` does not live long enough=========> ] 89/110: syntax
--> libsyntax/ext/tt/macro_parser.rs:647:57
|
647 | let mut cur_items = smallvec![MatcherPosHandle::Ref(&mut initial)];
| ^^^^^^^^^^^^ borrowed value does not live long enough
...
762 | }
| -
| |
| `initial` dropped here while still borrowed
| borrow later used here, when `initial` is dropped
error: aborting due to previous error
```
This is either a compiler bug, or there's some subtle thing I don't understand. The lifetimes sure seem straightforward: `initial` is declared, and then `cur_items` is declared immediately afterward, and it uses a reference to `initial`. The error message makes it sound like the compiler is dropping the variables in the wrong order.
r? @nikomatsakis, any idea what the problem is?
Remove the `alloc_system` crate
In what's hopefully one of the final nails in the coffin of the "old allocator story of yore" this PR deletes the `alloc_system` crate and all traces of it from the compiler. The compiler no longer needs to inject allocator crates anywhere and the `alloc_system` crate has no real reason to exist outside the standard library.
The unstable `alloc_system` crate is folded directly into the standard library where its stable interface, the `System` type, remains the same. All unstable traces of `alloc_system` are removed, however.
This commit deletes the `alloc_system` crate from the standard
distribution. This unstable crate is no longer needed in the modern
stable global allocator world, but rather its functionality is folded
directly into the standard library. The standard library was already the
only stable location to access this crate, and as a result this should
not affect any stable code.
This commit cleans up allocator injection logic found in the compiler
around selecting the global allocator. It turns out that now that
jemalloc is gone the compiler never actually injects anything! This
means that basically everything around loading crates here and there can
be easily pruned.
This also removes the `exe_allocation_crate` option from custom target
specs as it's no longer used by the compiler anywhere.
NLL Diagnostic Review 3: Unions not reinitialized after assignment into field
Fixes#55651, #55652.
This PR makes two changes:
First, it updates the dataflow builder to add an init for the place
containing a union if there is an assignment into the field of
that union.
Second, it stops a "use of uninitialized" error occuring when there is an
assignment into the field of an uninitialized union that was previously
initialized. Making this assignment would re-initialize the union, as
tested in `src/test/ui/borrowck/borrowck-union-move-assign.nll.stderr`.
The check for previous initialization ensures that we do not start
supporting partial initialization yet (cc #21232, #54499, #54986).
This PR also fixes#55652 which was marked as requiring investigation
as the changes in this PR add an error that was previously missing
(and mentioned in the review comments) and confirms that the error
that was present is correct and a result of earlier partial
initialization changes in NLL.
r? @pnkfelix (due to earlier work with partial initialization)
cc @nikomatsakis
