It makes it sound like the `ExprKind` and `Rvalue` are supposed to represent all pointer related
casts, when in reality their just used to share a some enum variants. Make it clear there these
are only coercion to make it clear why only some pointer related "casts" are in the enum.
mir opt + codegen: handle subtyping
fixes#107205
the same issue was caused in multiple places:
- mir opts: both copy and destination propagation
- codegen: assigning operands to locals (which also propagates values)
I changed codegen to always update the type in the operands used for locals which should guard against any new occurrences of this bug going forward. I don't know how to make mir optimizations more resilient here. Hopefully the added tests will be enough to detect any trivially wrong optimizations going forward.
Warn on unused `offset_of!()` result
The usage of `core::hint::must_use()` means that we don't get a specialized message. I figured out that since there are plenty of other methods that just have `#[must_use]` with no message it'll be fine, but it is a bit unfortunate that the error mentions `must_use` and not `offset_of!`.
Fixes#111669.
[libs] Simplify `unchecked_{shl,shr}`
There's no need for the `const_eval_select` dance here. And while I originally wrote the `.try_into().unwrap_unchecked()` implementation here, it's kinda a mess in MIR -- this new one is substantially simpler, as shown by the old one being above the inlining threshold but the new one being below it in the `mir-opt/inline/unchecked_shifts` tests.
We don't need `u32::checked_shl` doing a dance through both `Result` *and* `Option` 🙃
Remove `box_free` lang item
This PR removes the `box_free` lang item, replacing it with `Box`'s `Drop` impl. Box dropping is still slightly magic because the contained value is still dropped by the compiler.
There's no need for the `const_eval_select` dance here. And while I originally wrote the `.try_into().unwrap_unchecked()` implementation here, it's kinda a mess in MIR -- this new one is substantially simpler, as shown by the old one being above the inlining threshold but the new one being below it.
To reproduce the changes in this commit locally:
- Run `./x test tidy` and remove all the output files not associated
with a test file anymore, as reported by tidy.
- Run `./x test tests/mir-opt --bless` to generate the new outputs.
Only check inlining counter after recursing.
This PR aims to reduce the strength of https://github.com/rust-lang/rust/pull/105119 even more.
In the current implementation, we check the inline count before recursing. This means that we never actually reach inlining depth 3.
This PR checks the counter after recursion, to give a chance to inline at depth >= 3.
r? `@scottmcm`
cc `@JakobDegen`
Enable ConstGoto and SeparateConstSwitch passes by default
These 2 passes implement a limited form of jump-threading.
Filing this PR to see if enabling them would be lighter than https://github.com/rust-lang/rust/pull/107009.
Enable ScalarReplacementOfAggregates in optimized builds
Like MatchBranchSimplification, this pass is known to produce significant runtime improvements in Cranelift artifacts, and I believe based on the perf runs here that the primary effect of this pass is to empower MatchBranchSimplification. ScalarReplacementOfAggregates on its own has little effect on anything, but when this was rebased up to include https://github.com/rust-lang/rust/pull/112001 we started seeing significant and majority-positive results.
Based on the fact that we see most of the regressions in debug builds (https://github.com/rust-lang/rust/pull/112002#issuecomment-1566270144) and some rather significant ones in cycles and wall time, I'm only enabling this in optimized builds at the moment.
All the implementations of the trait already are `Copy`, and this seems to be enough to simplify the implementations enough to make the MIR inliner willing to inline basics like `Range::next`.
MIR: opt-in normalization of `BasicBlock` and `Local` numbering
This doesn't matter at all for actual codegen, but after spending some time reading pre-codegen MIR, I was wishing I didn't have to jump around so much in reading post-inlining code.
So this add two passes that are off by default for every mir level, but can be enabled (`-Zmir-enable-passes=+ReorderBasicBlocks,+ReorderLocals`) for humans.
