gvn: Invalid dereferences for all non-local mutations
Fixes#132353.
This PR removes the computation value by traversing SSA locals through `for_each_assignment_mut`.
Because the `for_each_assignment_mut` traversal skips statements which have side effects, such as dereference assignments, the computation may be unsound. Instead of `for_each_assignment_mut`, we compute values by traversing in reverse postorder.
Because we compute and use the symbolic representation of values on the fly, I invalidate all old values when encountering a dereference assignment. The current approach does not prevent the optimization of a clone to a copy.
In the future, we may add an alias model, or dominance information for dereference assignments, or SSA form to help GVN.
r? cjgillot
cc `@jieyouxu` #132356
cc `@RalfJung` #133474
Simplify `PartialOrd` on tuples containing primitives
We noticed in https://github.com/rust-lang/rust/pull/133984#issuecomment-2704011800 that currently the tuple comparison code, while it [does optimize down](https://github.com/rust-lang/rust/blob/master/tests/codegen/comparison-operators-2-tuple.rs) today, is kinda huge: <https://rust.godbolt.org/z/xqMoeYbhE>
This PR changes the tuple code to go through an overridable "chaining" version of the comparison functions, so that for simple things like `(i16, u16)` and `(f32, f32)` (as seen in the new MIR pre-codegen test) we just directly get the
```rust
if lhs.0 == rhs.0 { lhs.0 OP rhs.0 }
else { lhs.1 OP rhs.1 }
```
version in MIR, rather than emitting a mess for LLVM to have to clean up.
Test added in the first commit, so you can see the MIR diff in the second one.
This means that things like `<usize as Step>::forward_unchecked` and `<PartialOrd for f32>::le` will inline even if we've already done a bunch of inlining to find the calls to them.
Previously it only did integer-ABI things, but this way it does data pointers too. That gives more information in general to the backend, and allows slightly simplifying one of the helpers in slice iterators.
Reexport likely/unlikely in std::hint
Since `likely`/`unlikely` should be working now, we could reexport them in `std::hint`. I'm not sure if this is already approved or if it requires approval
Tracking issue: #26179
We already did `Transmute`-then-`PtrToPtr`; this adds the nearly-identical `PtrToPtr`-then-`Transmute`.
It also adds `transmute(Foo(x))` → `transmute(x)`, when `Foo` is a single-field transparent type. That's useful for things like `NonNull { pointer: p }.as_ptr()`.
Found these as I was looking at MCP807-related changes.
Bounds-check with PtrMetadata instead of Len in MIR
Rather than emitting `Len(*_n)` in array index bounds checks, emit `PtrMetadata(copy _n)` instead -- with some asterisks for arrays and `&mut` that need it to be done slightly differently.
We're getting pretty close to removing `Len` entirely, actually. I think just one more PR after this (for slice drop shims).
r? mir
Stop pessimizing the use of local variables in core by skipping debug info for MIR temporaries in tiny (single-BB) functions.
For functions as simple as this -- `Pin::new`, etc -- nobody every actually wants debuginfo for them in the first place. They're more like intrinsics than real functions, and stepping over them is good.
Update `NonZero` and `NonNull` to not field-project (per MCP#807)
https://github.com/rust-lang/compiler-team/issues/807#issuecomment-2506098540 was accepted, so this is the first PR towards moving the library to not using field projections into `[rustc_layout_scalar_valid_range_*]` types.
`NonZero` was already using `transmute` nearly everywhere, so there are very few changes to it.
`NonNull` needed more changes, but they're mostly simple, changing `.pointer` to `.as_ptr()`.
r? libs
cc #133324, which will tidy up some of the MIR from this a bit more, but isn't a blocker.
Add `{ignore,needs}-{rustc,std}-debug-assertions` directive support
Add `{ignore,needs}-{rustc,std}-debug-assertions` compiletest directives and retire the old `{ignore,only}-debug` directives. The old `{ignore,only}-debug` directives were ambiguous because you could have std built with debug assertions but rustc not built with debug assertions or vice versa. If we want to support the use case of controlling test run based on if rustc was built with debug assertions, then having `{ignore,only}-debug` will be very confusing.
cc ````@matthiaskrgr````
Closes#123987.
r? bootstrap (or compiler tbh)
Add `from_ref` and `from_mut` constructors to `core::ptr::NonNull`.
Relevant tracking issue: #130823
The `core::ptr::NonNull` type should have the convenience constructors `from_ref` and `from_mut` for parity with `core::ptr::from_ref` and `core::ptr::from_mut`.
Although the type in question already implements `From<&T>` and `From<&mut T>`, these new functions also carry the ability to be used in constant expressions (due to not being behind a trait).
liballoc: introduce String, Vec const-slicing
This change `const`-qualifies many methods on `Vec` and `String`, notably `as_slice`, `as_str`, `len`. These changes are made behind the unstable feature flag `const_vec_string_slice`.
## Motivation
This is to support simultaneous variance over ownership and constness. I have an enum type that may contain either `String` or `&str`, and I want to produce a `&str` from it in a possibly-`const` context.
```rust
enum StrOrString<'s> {
Str(&'s str),
String(String),
}
impl<'s> StrOrString<'s> {
const fn as_str(&self) -> &str {
match self {
// In a const-context, I really only expect to see this variant, but I can't switch the implementation
// in some mode like #[cfg(const)] -- there has to be a single body
Self::Str(s) => s,
// so this is a problem, since it's not `const`
Self::String(s) => s.as_str(),
}
}
}
```
Currently `String` and `Vec` don't support this, but can without functional changes. Similar logic applies for `len`, `capacity`, `is_empty`.
## Changes
The essential thing enabling this change is that `Unique::as_ptr` is `const`. This lets us convert `RawVec::ptr` -> `Vec::as_ptr` -> `Vec::as_slice` -> `String::as_str`.
I had to move the `Deref` implementations into `as_{str,slice}` because `Deref` isn't `#[const_trait]`, but I would expect this change to be invisible up to inlining. I moved the `DerefMut` implementations as well for uniformity.
This change `const`-qualifies many methods on Vec and String, notably
`as_slice`, `as_str`, `len`. These changes are made behind the unstable
feature flag `const_vec_string_slice` with the following tracking issue:
https://github.com/rust-lang/rust/issues/129041
