Use undef for uninitialized bytes in constants
Fixes#83657
This generates good code when the const is fully uninit, e.g.
```rust
#[no_mangle]
pub const fn fully_uninit() -> MaybeUninit<[u8; 10]> {
const M: MaybeUninit<[u8; 10]> = MaybeUninit::uninit();
M
}
```
generates
```asm
fully_uninit:
ret
```
as you would expect.
There is no improvement, however, when it's partially uninit, e.g.
```rust
pub struct PartiallyUninit {
x: u64,
y: MaybeUninit<[u8; 10]>
}
#[no_mangle]
pub const fn partially_uninit() -> PartiallyUninit {
const X: PartiallyUninit = PartiallyUninit { x: 0xdeadbeefcafe, y: MaybeUninit::uninit() };
X
}
```
generates
```asm
partially_uninit:
mov rax, rdi
mov rcx, qword ptr [rip + .L__unnamed_1+16]
mov qword ptr [rdi + 16], rcx
movups xmm0, xmmword ptr [rip + .L__unnamed_1]
movups xmmword ptr [rdi], xmm0
ret
.L__unnamed_1:
.asciz "\376\312\357\276\255\336\000"
.zero 16
.size .L__unnamed_1, 24
```
which copies a bunch of zeros in place of the undef bytes, the same as before this change.
Edit: generating partially-undef constants isn't viable at the moment anyways due to #84565, so it's disabled
Use if-let guards in the codebase and various other pattern cleanups
Dogfooding if-let guards as experimentation for the feature.
Tracking issue #51114. Conflicts with #87937.
This can happen when a tag is opened after the length limit is reached;
the tag will not end up being added to `unclosed_tags` because the queue
will never be flushed. So, now, if the `unclosed_tags` stack is empty,
`close_tag()` does nothing.
This change fixes a panic in the `limit_0` unit test.
PGO for LLVM builds on x86_64-unknown-linux-gnu in CI
This shows up to 6% less instruction counts with larger - up to 18% - wins on cycles
on multiple benchmarks, and up to 19% wins on the -j1 wall times for rustc self-compilation.
We can afford to spend the extra cycles building LLVM essentially once more for
the x86_64-unknown-linux-gnu CI build today. The builder finishes in around 50
minutes on average, and this adds just 10 more minutes. Given the sizeable
improvements in compiler performance, this is definitely worth it.
* Highlight the whole pattern if it has no fields
* Highlight the whole definition if it has no fields
* Only highlight the pattern name if the pattern is multi-line
* Determine whether a pattern is multi-line based on distance from name
to last field, rather than first field
This skips bumping Windows sccache because we run into compilation failures when
doing so (-m32 not supported by clang-cl?). Not clear on cause, but seems
easiest to just hold back.
This should avoid PGO-related failures encountered on Linux, and more broadly
seems like a good idea on other platforms as well (though it is likely not
necessary right this moment).
Normalize projections under binders
Fixes#70243Fixes#70120Fixes#62529Fixes#87219
Issues to followup on after (probably fixed, but no test added here):
#76956#56556#79207#85636
r? `@nikomatsakis`
Previously, we would set up the source lines for `match` expressions so
that the code generated to perform the test of the scrutinee was matched
to the line of the arm that required the test and then jump from the arm
block to the "next" block was matched to all of the lines in the `match`
expression.
While that makes sense, it has the side effect of causing strange
stepping behavior in debuggers.
I've changed the source information so that all of the generated tests
are sourced to `match {scrutinee}` and the jumps are sourced to the last
line of the block they are inside. This resolves the weird stepping
behavior in all debuggers and resolves some instances of "ambiguous
symbol" errors in WinDbg preventing the user from setting breakpoints at
`match` expressions.
