New MIR optimization pass to reduce branches on match of tuples of enums
Fixes#68867 by adding a new pass that turns something like
```rust
let x: Option<()>;
let y: Option<()>;
match (x,y) {
(Some(_), Some(_)) => {0},
_ => {1}
}
```
into something like
```rust
let x: Option<()>;
let y: Option<()>;
let discriminant_x = // get discriminant of x
let discriminant_y = // get discriminant of x
if discriminant_x != discriminant_y {1} else {0}
```
The opt-diffs still have the old basic blocks like
```
bb3: {
_8 = discriminant((*(_4.1: &ViewportPercentageLength))); // scope 0 at $DIR/early-otherwise-branch-68867.rs:21:21: 21:30
switchInt(move _8) -> [1_isize: bb7, otherwise: bb2]; // scope 0 at $DIR/early-otherwise-branch-68867.rs:21:21: 21:30
}
bb4: {
_9 = discriminant((*(_4.1: &ViewportPercentageLength))); // scope 0 at $DIR/early-otherwise-branch-68867.rs:22:23: 22:34
switchInt(move _9) -> [2_isize: bb8, otherwise: bb2]; // scope 0 at $DIR/early-otherwise-branch-68867.rs:22:23: 22:34
}
bb5: {
_10 = discriminant((*(_4.1: &ViewportPercentageLength))); // scope 0 at $DIR/early-otherwise-branch-68867.rs:23:23: 23:34
switchInt(move _10) -> [3_isize: bb9, otherwise: bb2]; // scope 0 at $DIR/early-otherwise-branch-68867.rs:23:23: 23:34
}
```
These do get removed on later passes. I'm not sure if I should include those passes in the test to make it clear?
Rollup of 15 pull requests
Successful merges:
- #76722 (Test and fix Send and Sync traits of BTreeMap artefacts)
- #76766 (Extract some intrinsics out of rustc_codegen_llvm)
- #76800 (Don't generate bootstrap usage unless it's needed)
- #76809 (simplfy condition in ItemLowerer::with_trait_impl_ref())
- #76815 (Fix wording in mir doc)
- #76818 (Don't compile regex at every function call.)
- #76821 (Remove redundant nightly features)
- #76823 (black_box: silence unused_mut warning when building with cfg(miri))
- #76825 (use `array_windows` instead of `windows` in the compiler)
- #76827 (fix array_windows docs)
- #76828 (use strip_prefix over starts_with and manual slicing based on pattern length (clippy::manual_strip))
- #76840 (Move to intra doc links in core/src/future)
- #76845 (Use intra docs links in core::{ascii, option, str, pattern, hash::map})
- #76853 (Use intra-doc links in library/core/src/task/wake.rs)
- #76871 (support panic=abort in Miri)
Failed merges:
r? `@ghost`
use `array_windows` instead of `windows` in the compiler
I do think these changes are beautiful, but do have to admit that using type inference for the window length
can easily be confusing. This seems like a general issue with const generics, where inferring constants adds an additional
complexity which users have to learn and keep in mind.
Remove redundant nightly features
Removes a bunch of redundant/outdated nightly features. The first commit removes a `core_intrinsics` use for which a stable wrapper has been provided since. The second commit replaces the `const_generics` feature with `min_const_generics` which might get stabilized this year. The third commit is the result of a trial/error run of removing every single feature and then adding it back if compile failed. A bunch of unused features are the result that the third commit removes.
Don't compile regex at every function call.
Use `SyncOnceCell` to only compile it once.
I believe this still adds some kind of locking mechanism?
Related issue: https://github.com/rust-lang/rust/issues/76817
Validate constants during `const_eval_raw`
This PR implements the groundwork for https://github.com/rust-lang/rust/issues/72396
* constants are now validated during `const_eval_raw`
* to prevent cycle errors, we do not validate references to statics anymore beyond the fact that they are not dangling
* the `const_eval` query ICEs if used on `static` items
* as a side effect promoteds are now evaluated to `ConstValue::Scalar` again (since they are just a reference to the actual promoted allocation in most cases).
Some promotion cleanup
Based on top of both https://github.com/rust-lang/rust/pull/75502 and https://github.com/rust-lang/rust/pull/75585, this does some cleanup of the promotion code. The last 2 commits are new.
* Remove the remaining cases where `const fn` is treated different from `fn`. This means no longer promoting ptr-to-int casts, raw ptr operations, and union field accesses in `const fn` -- or anywhere, for that matter. These are all unstable in const-context so this should not break any stable code. Fixes https://github.com/rust-lang/rust/issues/75586.
* ~~Promote references to statics even outside statics (i.e., in functions) for consistency.~~
* Promote `&mut []` everywhere, not just in non-`const` functions, for consistency.
* Explain why we do not promote deref's of statics outside statics. ~~(This is the only remaining direct user of `const_kind`.)~~
This can only land once the other two PRs land; I am mostly putting this up already because I couldn't wait ;) and to get some feedback from `@rust-lang/wg-const-eval` .
shim: monomorphic `FnPtrShim`s during construction
Fixes#69925.
This PR adjusts MIR shim construction so that substitutions are applied to function pointer shims during construction, rather than during codegen (as determined by `substs_for_mir_body`).
r? `@eddyb`
Implement a generic Destination Propagation optimization on MIR
This takes the work that was originally started by `@eddyb` in https://github.com/rust-lang/rust/pull/47954, and then explored by me in https://github.com/rust-lang/rust/pull/71003, and implements it in a general (ie. not limited to acyclic CFGs) and dataflow-driven way (so that no additional infrastructure in rustc is needed).
The pass is configured to run at `mir-opt-level=2` and higher only. To enable it by default, some followup work on it is still needed:
* Performance needs to be evaluated. I did some light optimization work and tested against `tuple-stress`, which caused trouble in my last attempt, but didn't go much in depth here.
* We can also enable the pass only at `opt-level=2` and higher, if it is too slow to run in debug mode, but fine when optimizations run anyways.
* Debuginfo needs to be fixed after locals are merged. I did not look into what is required for this.
* Live ranges of locals (aka `StorageLive` and `StorageDead`) are currently deleted. We either need to decide that this is fine, or if not, merge the variable's live ranges (or remove these statements entirely – https://github.com/rust-lang/rust/issues/68622).
Some benchmarks of the pass were done in https://github.com/rust-lang/rust/pull/72635.
As a side effect, we now represent most promoteds as `ConstValue::Scalar` again. This is useful because all implict promoteds are just references anyway and most explicit promoteds are numeric arguments to `asm!` or SIMD instructions.
Some MIR statements and terminators have an (undocumented...) invariant
that some of their input and outputs must not overlap. This records
conflicts between locals used in these positions.
