Don't store locals that have been moved from in generators
This avoids reserving storage in generators for locals that are moved
out of (and not re-initialized) prior to yield points. Fixes#59123.
This adds a new dataflow analysis, `RequiresStorage`, to determine whether the storage of a local can be destroyed without being observed by the program. The rules are:
1. StorageLive(x) => mark x live
2. StorageDead(x) => mark x dead
3. If a local is moved from, _and has never had its address taken_, mark it dead
4. If (any part of) a local is initialized, mark it live'
This is used to determine whether to save a local in the generator object at all, as well as which locals can be overlapped in the generator layout.
Here's the size in bytes of all testcases included in the change, before and after the change:
async fn test |Size before |Size after
-----------------|------------|----------
single | 1028 | 1028
single_with_noop | 2056 | 1032
joined | 5132 | 3084
joined_with_noop | 8208 | 3084
generator test |Size before |Size after
----------------------------|------------|----------
move_before_yield | 1028 | 1028
move_before_yield_with_noop | 2056 | 1032
overlap_move_points | 3080 | 2056
## Future work
Note that there is a possible extension to this optimization, which modifies rule 3 to read: "If a local is moved from, _**and either has never had its address taken, or is Freeze and has never been mutably borrowed**_, mark it dead." This was discussed at length in #59123 and then #61849. Because this would cause some behavior to be UB which was not UB before, it's a step that needs to be taken carefully.
A more immediate priority for me is inlining `std::mem::size_of_val(&x)` so it becomes apparent that the address of `x` is not taken. This way, using `size_of_val` to look at the size of your inner futures does not affect the size of your outer future.
cc @cramertj @eddyb @Matthias247 @nikomatsakis @RalfJung @Zoxc
ci: explicitly disable CRLF conversion on Windows
The Azure image enables CRLF conversion on Windows builders, but that caused regressions both in our test suite (the miri test suite broke) and in the ecosystem, since we started shipping install scripts with CRLF endings instead of the old LF. The [Godbolt Compiler Explorer](https://godbolt.org/) is one such case of breakage.
This adds a step to the build explicitly disabling the conversion before the repository is checked out.
r? @alexcrichton
cc @gnzlbg
The Azure image enables CRLF conversion on Windows builders, but that
caused regressions both in our test suite (the miri test suite broke)
and in the ecosystem, since we started shipping install scripts with
CRLF endings instead of the old LF. The Godbolt Compiler Explorer is one
such case of breakage.
This adds a step to the build explicitly disabling the conversion before
the repository is checked out.
Since switching CI to Azure Pipelines it seems that this test seems
to fail more consistently, so let's disable that for now. It helps
that we have less than a week before release - we disallow PRs that
break the tools to land in this period, so this makes landing critical
PRs smoother now.
r? @alexcrichton
Rollup of 8 pull requests
Successful merges:
- #62062 (Use a more efficient iteration order for forward dataflow)
- #62063 (Use a more efficient iteration order for backward dataflow)
- #62224 (rustdoc: remove unused derives and variants)
- #62228 (Extend the #[must_use] lint to boxed types)
- #62235 (Extend the `#[must_use]` lint to arrays)
- #62239 (Fix a typo)
- #62241 (Always parse 'async unsafe fn' + properly ban in 2015)
- #62248 (before_exec actually will only get deprecated with 1.37)
Failed merges:
r? @ghost
Stabilize `type_alias_enum_variants` in Rust 1.37.0
Stabilize `#![feature(type_alias_enum_variants)]` which allows type-relative resolution with highest priority to `enum` variants in both expression and pattern contexts. For example, you may now write:
```rust
enum Option<T> {
None,
Some(T),
}
type OptAlias<T> = Option<T>;
fn work_on_alias(x: Option<u8>) -> u8 {
match x {
OptAlias::Some(y) => y + 1,
OptAlias::None => 0,
}
}
```
Closes https://github.com/rust-lang/rfcs/issues/2218
Closes https://github.com/rust-lang/rust/issues/52118
r? @petrochenkov
rustdoc: remove unused derives and variants
Though many structs in rustdoc derive `RustcEncodable` and `RustcDecodable`, the impls do not appear to be used by the crate or its dependents. Removing them revealed some enum variants that are never constructed, too.
r? @GuillaumeGomez
Use a more efficient iteration order for backward dataflow
This applies the same basic principle as #62062 to the reverse dataflow analysis used to compute liveness information. It is functionally equivalent, except that post-order is used instead of reverse post-order.
In the long-term, `BitDenotation` should probably be extended to support both forward and backward dataflow, but there's some more work needed to get to that point.
Use a more efficient iteration order for forward dataflow
Currently, dataflow begins by visiting each block in order of ID (`BasicBlock(0)`, `BasicBlock(1)`, etc.). This PR changes that initial iteration to reverse post-order (see [this blog post](https://eli.thegreenplace.net/2015/directed-graph-traversal-orderings-and-applications-to-data-flow-analysis/#data-flow-analysis) for more info). This ensures that the effects of all predecessors will be applied before a basic block is visited if the CFG has no back-edges, and should result in less total iterations even when back-edges exist. This should not change the results of dataflow analysis.
The current ordering for basic blocks may be pretty close to RPO already--`BasicBlock(0)` is already the start block--in which case the cost of doing the traversal up front will outweigh the efficiency gains.
A perf run is needed to check this.
r? @pnkfelix (I think).
