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Convert moves of references to copies in ReferencePropagation
This is a fix for https://github.com/rust-lang/rust/issues/141101.
The root cause of this miscompile is that the SsaLocals analysis that MIR transforms use is supposed to detect locals that are only written to once, in their single assignment. But that analysis is subtly wrong; it does not consider `Operand::Move` to be a write even though the meaning ascribed to `Operand::Move` (at least as a function parameter) by Miri is that the callee may have done arbitrary writes to the caller's Local that the Operand wraps (because `Move` is pass-by-pointer). So Miri conwiders `Operand::Move` to be a write but both the MIR visitor system considers it a read, and so does SsaLocals.
I have tried fixing this by changing the `PlaceContext` that is ascribed to an `Operand::Move` to a `MutatingUseContext` but that seems to have borrow checker implications, and changing SsaLocals seems to have wide-ranging regressions in MIR optimizations.
So instead of doing those, this PR adds a new kludge to ReferencePropagation, which follows the same line of thinking as the kludge in CopyProp that solves this same problem inside that pass: https://github.com/rust-lang/rust/blob/a5584a8fe16037dc01782064fa41424a6dbe9987/compiler/rustc_mir_transform/src/copy_prop.rs#L65-L98
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Consolidate all the panicking functions in `slice/index.rs` to use a single
`slice_index_fail` function, similar to how it is done in `str/traits.rs`.
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Add some pre-codegen MIR tests for debug mode
No functional changes; just some tests.
I made these for rust-lang/rust#144483, but that's going in a different direction, so I wanted to propose we just add them to help see the impact of other related changes in the future.
r? mir
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Because the follow-up commits will affect it, and the goal is to show how.
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Since it's cfg'd instead of type-aliased
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jplatte:matches-allow-non_exhaustive_omitted_patterns, r=Nadrieril
Disable non_exhaustive_omitted_patterns within matches! macro
Closes rust-lang/rust#117304.
I believe I can skip all of the bootstrap stuff mentioned in https://github.com/rust-lang/rust/issues/117304#issuecomment-1784414453 due to https://blog.rust-lang.org/inside-rust/2025/05/29/redesigning-the-initial-bootstrap-sequence/, right?
cc `@Jules-Bertholet`
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Store the type of each GVN value
MIR is fully typed, so type information is an integral part of what defines a value. GVN currently tries to circumvent storing types, which creates all sorts of complexities.
This PR stores the type along with the enum `Value` when defining a value index. This allows to simplify a lot of code.
Fixes rust-lang/rust#128094
Fixes rust-lang/rust#135128
r? ``````@ghost`````` for perf
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Update README.md
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This can provide more opportunities for MatchBranchSimplification.
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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
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This reverts commit 906f66fb4c22daa8a6f97e5c048e9f6ab3fd9051.
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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.
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Uses `__`-named `doc(hidden)` methods instead.
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We have codegen ones, but it looks like we could make those less flakey by just doing something better in the first place...
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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.
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This adds a few more statements to `next`, but optimizes better in the loops (saving 2 blocks in `forward_loop`, for example)
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Probably reasonable anyway since it more obviously drops provenance.
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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.
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r=workingjubilee
Portable SIMD subtree update
r? `@workingjubilee`
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r=davidtwco,RalfJung"
This reverts commit 122a55bb442bd1995df9cf9b36e6f65ed3ef4a1d.
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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
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r=davidtwco,RalfJung"
This reverts commit b57d93d8b9525fa261404b4cd9c0670eeb1264b8, reversing
changes made to 0aeaa5eb22180fdf12a8489e63c4daa18da6f236.
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