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This hint allows the compiler to optimize its operation based on this
assumption, in order to compile faster. This is a hint, and does not
guarantee any particular behavior.
This option can substantially speed up compilation if applied to a large
dependency where the majority of the dependency does not get used. This flag
may slow down compilation in other cases.
Currently, this option makes the compiler defer as much code generation as
possible from functions in the crate, until later crates invoke those
functions. Functions that never get invoked will never have code generated for
them. For instance, if a crate provides thousands of functions, but only a few
of them will get called, this flag will result in the compiler only doing code
generation for the called functions. (This uses the same mechanisms as
cross-crate inlining of functions.) This does not affect `extern` functions, or
functions marked as `#[inline(never)]`.
Some performance numbers, based on a crate with many dependencies having
just *one* large dependency set to `-Z hint-mostly-unused` (using
Cargo's `profile-rustflags` option):
A release build went from 4m07s to 2m04s.
A non-release build went from 2m26s to 1m28s.
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Update `InterpCx::project_field` to take `FieldIdx`
As suggested by Ralf in https://github.com/rust-lang/rust/pull/142005#discussion_r2125839015
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As suggested by Ralf in 142005.
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r=oli-obk
Fix for async drop inside async gen fn
Return value (for yield) is corrected for async drop inside async gen function.
In CFG, when internal async drop future is polled and returned `Poll<()>::Pending`, then async gen resume function returns `Poll<(OptRet)>::Pending`.
Fixes rust-lang/rust#140530
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Co-authored-by: Michael Goulet <michael@errs.io>
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azhogin:azhogin/async-drop-unexpected-type-instead-of-drop-fn-fix, r=oli-obk
Async drop - type instead of async drop fn, fixes #140484
Fixes: rust-lang/rust#140484
Fixes: rust-lang/rust#140500
Fixes ICE, when type is provided in AsyncDrop trait instead of `async fn drop()`.
Fixes ICE, when async drop fn has wrong signature.
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don't ICE now
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`slice.get(i)` should use a slice projection in MIR, like `slice[i]` does
`slice[i]` is built-in magic, so ends up being quite different from `slice.get(i)` in MIR, even though they're both doing nearly identical operations -- checking the length of the slice then getting a ref/ptr to the element if it's in-bounds.
This PR adds a `slice_get_unchecked` intrinsic for `impl SliceIndex for usize` to use to fix that, so it no longer needs to do a bunch of lines of pointer math and instead just gets the obvious single statement. (This is *not* used for the range versions, since `slice[i..]` and `slice[..k]` can't use the mir Slice projection as they're using fenceposts, not indices.)
I originally tried to do this with some kind of GVN pattern, but realized that I'm pretty sure it's not legal to optimize `BinOp::Offset` to `PlaceElem::Index` without an extremely complicated condition. Basically, the problem is that the `Index` projection on a dereferenced slice pointer *cares about the metadata*, since it's UB to `PlaceElem::Index` outside the range described by the metadata. But then you cast the fat pointer to a thin pointer then offset it, that *ignores* the slice length metadata, so it's possible to write things that are legal with `Offset` but would be UB if translated in the obvious way to `Index`. Checking (or even determining) the necessary conditions for that would be complicated and error-prone, whereas this intrinsic-based approach is quite straight-forward.
Zero backend changes, because it just lowers to MIR, so it's already supported naturally by CTFE/Miri/cg_llvm/cg_clif.
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mir-opt: Do not transform non-int type in match_branches
Fixes #141378.
r? mir-opt
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Make two transmute-related MIR lints into HIR lint
Make `PTR_TO_INTEGER_TRANSMUTE_IN_CONSTS` (rust-lang/rust#130540) and `UNNECESSARY_TRANSMUTES` (rust-lang/rust#136083) into "normal" HIR-based lints.
Funny enough this came up in the review of the latter (https://github.com/rust-lang/rust/pull/136083#issuecomment-2614301413), but I guess it just was overlooked.
But anywyas, there's no reason for these to be MIR lints; in fact, it makes the suggestions for them a bit more complicated than necessary.
Note that there's probably a few more simplifications and improvements to be done here. Follow-ups can be done in a separate PR, especially if they're about the messaging and suggestions themselves, which I didn't write.
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gvn: bail out unavoidable non-ssa locals in repeat
Fixes #141251.
We cannot transform `*elem` to `array[idx1]` in the following code, as `idx1` has already been modified.
```rust
mir! {
let array;
let elem;
{
array = [*val; 5];
elem = &array[idx1];
idx1 = idx2;
RET = *elem;
Return()
}
}
```
Perhaps I could transform it to `array[0]`, but I prefer the conservative approach.
r? mir-opt
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This reverts commit 3b22c21dd8c30f499051fe7a758ca0e5d81eb638, reversing
changes made to 5f292eea6d63abbd26f1e6e00a0b8cf21d828d7d.
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interpret: add allocation parameters to `AllocBytes`
Necessary for a better implementation of [rust-lang/miri#4343](https://github.com/rust-lang/miri/pull/4343). Also included here is the code from that PR, adapted to this new interface for the sake of example and so that CI can run on them; the Miri changes can be reverted and merged separately, though.
r? `@RalfJung`
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Emit dummy open drop for unsafe binder
Fixes rust-lang/rust#141394
We can't taint the body in wfcheck when we have a `T: Copy` bound failure, so we end up binding MIR here. Emit a dummy open drop so that drop elaboration doesn't fail.
r? oli-obk
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azhogin:azhogin/async-drop-poll-shim-for-error-dropee-fix, r=oli-obk
Async drop poll shim for error dropee generates noop body
Fixes https://github.com/rust-lang/rust/issues/140930.
When dropee type for async drop poll shim is `ty::Error(_)`, the generated poll function will be noop body. To avoid ICE in `elaborate_drop`.
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dont handle bool transmute
removes `transmute(u8) -> bool` suggestion due to ambiguity, leave it for clippy
elaboration on ambiguity in question:
`transmute::<u8, bool>(x)` will codegen to an `assume(u8 < 2)`;
`_ == 1` or `_ != 0` or `_ % 2 == 0` would remove that assumption
`match _ { x @ (0 | 1) => x == 1, _ => std::hint::unreachable_unchecked() }` is very verbose
`@rustbot` label L-unnecessary_transmutes
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r=oli-obk
When AsyncDrop impl is empty, sync drop generated in elaborator
Fixes #140974.
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projection' (#140975)
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We cannot transform `*elem` to `array[idx1]` in the following code,
as `idx1` has already been modified.
```rust
mir! {
let array;
let elem;
{
array = [*val; 5];
elem = &array[idx1];
idx1 = idx2;
RET = *elem;
Return()
}
}
```
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coverage: Detect unused local file IDs to avoid an LLVM assertion
Each function's coverage metadata contains a *local file table* that maps local file IDs (used by the function's mapping regions) to global file IDs (shared by all functions in the same CGU).
LLVM requires all local file IDs to have at least one mapping region, and has an assertion that will fail if it detects a local file ID with no regions. To make sure that assertion doesn't fire, we need to detect and skip functions whose metadata would trigger it.
(This can't actually happen yet, because currently all of a function's spans must belong to the same file and expansion. But this will be an important edge case when adding expansion region support.)
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make `rustc_attr_parsing` less dominant in the rustc crate graph
It has/had a glob re-export of `rustc_attr_data_structures`, which is a crate much lower in the graph, and a lot of crates were using it *just* (or *mostly*) for that re-export, while they can rely on `rustc_attr_data_structures` directly.
Previous graph:
Graph with this PR:
The first commit keeps the re-export, and just changes the dependency if possible. The second commit is the "breaking change" which removes the re-export, and "explicitly" adds the `rustc_attr_data_structures` dependency where needed. It also switches over some src/tools/*.
The second commit is actually a lot more involved than I expected. Please let me know if it's a better idea to back it out and just keep the first commit.
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gvn: avoid creating overlapping assignments
Quick fix #141038, as I couldn't find a way to avoid in-place modification. I'm considering handling all `ravlue` modifications within the `visit_statement` function.
r? mir-opt
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azhogin:azhogin/async-drop-coroutine-layout-returns-layout-error, r=oli-obk
Return value of coroutine_layout fn changed to Result with LayoutError
Continue of https://github.com/rust-lang/rust/pull/140902:
`coroutine_layout` fn is now returns `Result` with `LayoutError` to have consistent error with `layout_of_uncached`.
`async_drop_coroutine_layout` fn is now return `LayoutError::TooGeneric` in case of not-fully-specialized `async_drop_in_place<T>::{closure}` coroutine.
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Remove some unnecessary erases
Some nits I pulled out of https://github.com/rust-lang/rust/pull/140814.
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This allows us to assume that coverage spans will only be discarded during
codegen in very unusual situations.
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Separate dataflow analysis and results
`Analysis` gets put into `Results` with `EntryStates`, by `iterate_to_fixpoint`. This has two problems:
- `Results` is passed various places where only `Analysis` is needed.
- `EntryStates` is passed around mutably everywhere even though it is immutable.
This commit mostly separates `Analysis` from `Results` and fixes these two problems.
r? `@davidtwco`
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Because we no longer merge non-adjacent spans, there is no need to use buckets
to prevent merging across hole spans.
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This also removes some manipulation of the function signature span that only
made sense in the context of merging non-adjacent spans.
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mir-opt: execute MatchBranchSimplification after GVN
This can provide more opportunities for MatchBranchSimplification.
Currently, rustc does not optimize the following code into a single statement at mir-opt, and this PR fixes the first case.
```rust
pub fn match1(c: bool, v1: i32, v2: i32) -> i32 {
if c { v1 - v2 } else { v1 - v2 }
}
pub fn match2(c: bool, v1: i32) -> i32 {
if c { v1 - 1 } else { v1 - 1 }
}
```
https://rust.godbolt.org/z/Y8xPMjrfM
r? mir-opt
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