`InternedString::intern(x)` is preferable to
`Symbol::intern(x).as_interned_str()`, because the former involves one
call to `with_interner` while the latter involves two.
The case within InternedString::decode() is particularly hot, and this
change reduces the number of `with_interner` calls by up to 13%.
Place related refactors
Meanwhile I was working on Place 2 I'm finding some little things that I had on my branch but preferred to land a separate PR for things that are simpler to merge.
r? @oli-obk
Multi-variant layouts for generators
This allows generators to overlap fields using variants, but doesn't do any such overlapping yet. It creates one variant for every state of the generator (unresumed, returned, panicked, plus one for every yield), and puts every stored local in each of the yield-point variants.
Required for optimizing generator layouts (#52924).
There was quite a lot of refactoring needed for this change. I've done my best in later commits to eliminate assumptions in the code that only certain kinds of types are multi-variant, and to centralize knowledge of the inner mechanics of generators in as few places as possible.
This change also emits debuginfo about the fields contained in each variant, as well as preserving debuginfo about stored locals while running in the generator.
Also, fixes#59972.
Future work:
- Use this change for an optimization pass that actually overlaps locals within the generator struct (#52924)
- In the type layout fields, don't include locals that are uninitialized for a particular variant, so miri and UB sanitizers can check our memory (see https://github.com/rust-lang/rust/issues/59972#issuecomment-483058172)
- Preserve debuginfo scopes across generator yield points
Cleanup the MIR visitor
* Remove useless `BasicBlock` parameters on methods with `Location`s.
* Prefer `visit_terminator_kind` to `visit_terminator`.
* Remove `Region` from PlaceContexts. `visit_rvalue` should be used when the region is important.
* Remove unused visitor methods.
Add a tidy check for files with over 3,000 lines
Files with a large number of lines can cause issues in GitHub (e.g. https://github.com/rust-lang/rust/issues/60015) and also tend to be indicative of opportunities to refactor into less monolithic structures.
This adds a new check to tidy to warn against files that have more than 3,000 lines, as suggested in https://github.com/rust-lang/rust/issues/60015#issuecomment-483868594. (This number was chosen fairly arbitrarily as a reasonable indicator of size.) This check can be ignored with `// ignore-tidy-filelength`.
Existing files with greater than 3,000 lines currently ignore the check, but this helps us spot when files are getting too large. (We might try to split up all files larger than this in the future, as in https://github.com/rust-lang/rust/issues/60015).
Miri: refactor new allocation tagging
Tagging and initializing `AllocExtra` now go hand-in-hand so one cannot forget to do one when doing the other. In particular, `memory.allocate` is now much easier to use correctly (because it will already return a tagged pointer).
r? @oli-obk
Increase `Span` from 4 bytes to 8 bytes.
This increases the size of some important types, such as `ast::Expr` and
`mir::Statement`. However, it drastically reduces how much the interner
is used, and the fields are more natural sizes that don't require bit
operations to extract.
As a result, instruction counts drop across a range of workloads, by as
much as 10% for `script-servo` incremental builds.
Peak memory usage goes up a little for some cases, but down by more for
some other cases -- as much as 18% for non-incremental builds of
`packed-simd`.
The commit also:
- removes the `repr(packed)`, because it has negligible effect, but can
cause undefined behaviour;
- replaces explicit impls of common traits (`Copy`, `PartialEq`, etc.)
with derived ones.
r? @petrochenkov
This increases the size of some important types, such as `ast::Expr` and
`mir::Statement`. However, it drastically reduces how much the interner
is used, and the fields are more natural sizes that don't require bit
operations to extract.
As a result, instruction counts drop across a range of workloads, by as
much as 12% for incremental "check" builds of `script-servo`.
Peak memory usage goes up a little for some cases, but down by more for
some other cases -- as much as 18% for non-incremental builds of
`packed-simd`.
The commit also:
- removes the `repr(packed)`, because it has negligible effect, but can
cause undefined behaviour;
- replaces explicit impls of common traits (`Copy`, `PartialEq`, etc.)
with derived ones.
Remove adt_def from projections and downcasts in MIR
As part of optimizing generator layouts in MIR, we'd like to allow downcasting generators to variants which do not have a corresponding `def_id`, since they are created by the compiler.
This refactor hopes to allow that, without regressing perf.
r? @eddyb
