Skip `Lazy` for some metadata tables
Some metadata tables encode their entries indirectly, through the Lazy construct. This is useful when dealing with variable length encoding, but incurs the extra cost of one u32.
Meanwhile, some fields can be encoded in a single u8, or can use a short fixed-length encoding. This PR proposes to do so, and avoid the overhead.
`impl const Default for Box<[T]>` and `Box<str>`
The unstable `const_default_impls` (#87864) already include empty `Vec<T>` and `String`. Now we extend that concept to `Box<[T]>` and `Box<str>` as well.
This obviates a hack in `rustc_ast`'s `P::<[T]>::new`.
Instead of checking only the user provided sysroot or the default (when
no sysroot is provided), search user provided sysroot and then check
default sysroots for locale requested by the user.
Signed-off-by: David Wood <david.wood@huawei.com>
use `Span::find_ancestor_inside` to get right span in CastCheck
This is a quick fix. This bad suggestion likely lives in other places... but thought it would be useful to fix all of the CastCheck ones first.
Let me know if reviewer would prefer I add more tests for each of the diagnostics in CastCheck, or would like to do a more thorough review of other suggestions that use spans in typeck. I would also be open to further suggestions on how to better expose an API that gives us the "best" span for a diagnostic suggestion.
Fixed#95919
Fix crate_type attribute to not warn on duplicates
In #88681 I accidentally marked the `crate_type` attribute as only allowing a single attribute. However, multiple attributes are allowed (they are joined together [here](027a232755/compiler/rustc_interface/src/util.rs (L530-L542))). This fixes it to not report a warning if duplicates are found.
Closes#95902
Document the current MIR semantics that are clear from existing code
This PR adds documentation to places, operands, rvalues, statementkinds, and terminatorkinds that describes their existing semantics and requirements. In many places the semantics depend on the Rust memory model or other T-Lang decisions - when this is the case, it is just noted as such with links to UCG issues where possible. I'm hopeful that none of the documentation added here can be used to justify optimizations that depend on the memory model. The documentation for places and operands probably comes closest to running afoul of this - if people think that it cannot be merged as is, it can definitely also be taken out.
The goal here is to only document parts of MIR that seem to be decided already, or are at least depended on by existing code. That leaves quite a number of open questions - those are marked as "needs clarification." I'm not sure what to do with those in this PR - we obviously can't decide all these questions here. Should I just leave them in as is? Take them out? Keep them in but as `//` instead of `///` comments?
If this is too big to review at once, I can split this up.
r? rust-lang/mir-opt
Respect -Z verify-llvm-ir and other flags that add extra passes when combined with -C no-prepopulate-passes in the new LLVM Pass Manager.
As part of the switch to the new LLVM Pass Manager the behaviour of flags such as `-Z verify-llvm-ir` (e.g. sanitizer, instrumentation) was modified when combined with `-C no-prepopulate-passes`. With the old PM, rustc was the one manually constructing the pipeline and respected those flags but in the new pass manager, those flags are used to build a list of callbacks that get invoked at certain extension points in the pipeline. Unfortunately, `-C no-prepopulate-passes` would skip building the pipeline altogether meaning we'd never add the corresponding passes. The fix here is to just manually invoke those callbacks as needed.
Fixes#95874
Demonstrating the current vs fixed behaviour using the bug in #95864
```console
$ rustc +nightly asm-miscompile.rs --edition 2021 --emit=llvm-ir -C no-prepopulate-passes -Z verify-llvm-ir
$ echo $?
0
$ rustc +stage1 asm-miscompile.rs --edition 2021 --emit=llvm-ir -C no-prepopulate-passes -Z verify-llvm-ir
Basic Block in function '_ZN14asm_miscompile3foo28_$u7b$$u7b$closure$u7d$$u7d$17h360e2f7eee1275c5E' does not have terminator!
label %bb1
LLVM ERROR: Broken module found, compilation aborted!
```
Fix miscompilation of inline assembly with outputs in cases where we emit an invoke instead of call instruction.
We ran into this bug where rustc would segfault while trying to compile certain uses of inline assembly.
Here is a simple repro that demonstrates the issue:
```rust
#![feature(asm_unwind)]
fn main() {
let _x = String::from("string here just cause we need something with a non-trivial drop");
let foo: u64;
unsafe {
std::arch::asm!(
"mov {}, 1",
out(reg) foo,
options(may_unwind)
);
}
println!("{}", foo);
}
```
([playground link](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=7d6641e83370d2536a07234aca2498ff))
But crucially `feature(asm_unwind)` is not actually needed and this can be triggered on stable as a result of the way async functions/generators are handled in the compiler. e.g.:
```rust
extern crate futures; // 0.3.21
async fn bar() {
let foo: u64;
unsafe {
std::arch::asm!(
"mov {}, 1",
out(reg) foo,
);
}
println!("{}", foo);
}
fn main() {
futures::executor::block_on(bar());
}
```
([playground link](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=1c7781c34dd4a3e80ae4bd936a0c82fc))
An example of the incorrect LLVM generated:
```llvm
bb1: ; preds = %start
%1 = invoke i64 asm sideeffect alignstack inteldialect unwind "mov ${0:q}, 1", "=&r,~{dirflag},~{fpsr},~{flags},~{memory}"()
to label %bb2 unwind label %cleanup, !srcloc !9
store i64 %1, i64* %foo, align 8
bb2:
[...snip...]
```
The store should not be placed after the asm invoke but rather should be in the normal control flow basic block (`bb2` in this case).
[Here](https://gist.github.com/luqmana/be1af5b64d2cda5a533e3e23a7830b44) is a writeup of the investigation that lead to finding this.
[`let_chains`] Forbid `let` inside parentheses
Parenthesizes are mostly a no-op in let chains, in other words, they are mostly ignored.
```rust
let opt = Some(Some(1i32));
if (let Some(a) = opt && (let Some(b) = a)) && b == 1 {
println!("`b` is declared inside but used outside");
}
```
As seen above, such behavior can lead to confusion.
A proper fix or nested encapsulation would probably require research, time and a modified MIR graph so in this PR I simply denied any `let` inside parentheses. Non-let stuff are still allowed.
```rust
fn main() {
let fun = || true;
if let true = (true && fun()) && (true) {
println!("Allowed");
}
}
```
It is worth noting that `let ...` is not an expression and the RFC did not mention this specific situation.
cc `@matthewjasper`
Rollup of 7 pull requests
Successful merges:
- #95743 (Update binary_search example to instead redirect to partition_point)
- #95771 (Update linker-plugin-lto.md to 1.60)
- #95861 (Note that CI tests Windows 10)
- #95875 (bootstrap: show available paths help text for aliased subcommands)
- #95876 (Add a note for unsatisfied `~const Drop` bounds)
- #95907 (address fixme for diagnostic variable name)
- #95917 (thin_box test: import from std, not alloc)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
Only suggest removing semicolon when expression is compatible with `impl Trait`
https://github.com/rust-lang/rust/issues/54771#issuecomment-476423690
> It still needs checking that the last statement's expr can actually conform to the trait, but the naïve behavior is there.
Only suggest removing a semicolon when the type behind the semicolon actually implements the trait in an RPIT `-> impl Trait`. Also upgrade the label that suggests removing the semicolon to a suggestion (should it be verbose?).
cc #54771
