rustc_mir: Hide initial block state when defining transfer functions
This PR addresses [this FIXME](2887008e0c/src/librustc_mir/dataflow/mod.rs (L594-L596)).
This makes `sets.on_entry` inaccessible in `{before_,}{statement,terminator}_effect`. This field was meant to allow implementors of `BitDenotation` to access the initial state for each block (optionally with the effect of all previous statements applied via `accumulates_intrablock_state`) while defining transfer functions. However, the ability to set the initial value for the entry set of each basic block (except for START_BLOCK) no longer exists. As a result, this functionality is mostly useless, and when it *was* used it was used erroneously (see #62007).
Since `on_entry` is now useless, we can also remove `BlockSets`, which held the `gen`, `kill`, and `on_entry` bitvectors and replace it with a `GenKill` struct. Variables of this type are called `trans` since they represent a transfer function. `GenKill`s are stored contiguously in `AllSets`, which reduces the number of bounds checks and may improve cache performance: one is almost never accessed without the other.
Replacing `BlockSets` with `GenKill` allows us to define some new helper functions which streamline dataflow iteration and the dataflow-at-location APIs. Notably, `state_for_location` used a subtle side-effect of the `kill`/`kill_all` setters to apply the transfer function, and could be incorrect if a transfer function depended on effects of previous statements in the block on `gen_set`.
Additionally, this PR merges `BitSetOperator` and `InitialFlow` into one trait. Since the value of `InitialFlow` defines the semantics of the `join` operation, there's no reason to have seperate traits for each. We can add a default impl of `join` which branches based on `BOTTOM_VALUE`. This should get optimized away.
Fix meta-variable binding errors in macros
The errors are either:
- The meta-variable used in the right-hand side is not bound (or defined) in the
left-hand side.
- The meta-variable used in the right-hand side does not repeat with the same
kleene operator as its binder in the left-hand side. Either it does not repeat
enough, or it uses a different operator somewhere.
This change should have no semantic impact.
Found by https://github.com/rust-lang/rust/pull/62008
The errors are either:
- The meta-variable used in the right-hand side is not bound (or defined) in the
left-hand side.
- The meta-variable used in the right-hand side does not repeat with the same
kleene operator as its binder in the left-hand side. Either it does not repeat
enough, or it uses a different operator somewhere.
This change should have no semantic impact.
Since the value of `InitialFlow` defines the semantics of the `join`
operation, there's no reason to have seperate traits for each. We can
add a default impl of `join` which branches based on `BOTTOM_VALUE`.
This should get optimized away.
librustc_data_structures: Speedup union of sparse and dense hybrid set
This optimization speeds up the union of a hybrid bitset when that
switches it from a sparse representation to a dense bitset. It now
clones the dense bitset and integrate only the spare elements instead of
densifying the sparse bitset, initializing all elements, and then a
union on two dense bitset, touching all words a second time.
It's not completely certain if the added complexity is worth it but I would
like to hear some feedback in any case. Benchmark results from my machine:
```
Now: bit_set::union_hybrid_sparse_to_dense ... bench: 72 ns/iter (+/- 5)
Previous: bit_set::union_hybrid_sparse_to_dense ... bench: 90 ns/iter (+/- 6)
```
This being the second iteration of trying to improve the speed, since I missed the return value in the first, and forgot to run the relevant tests. Oops.
Allow attributes in formal function parameters
Implements https://github.com/rust-lang/rust/issues/60406.
This is my first contribution to the compiler and since this is a large and complex project, I am not fully aware of the consequences of the changes I have made.
**TODO**
- [x] Forbid some built-in attributes.
- [x] Expand cfg/cfg_attr
This optimization speeds up the union of a hybrid bitset when that
switches it from a sparse representation to a dense bitset. It now
clones the dense bitset and integrate only the spare elements instead of
densifying the sparse bitset, initializing all elements, and then a
union on two dense bitset, touching all words a second time.
rustc: Improve type size assertions
Now they
- Tell what the new size is, when it changes
- Do not require passing an identifier
```
::: src\libsyntax\parse\token.rs:223:1
|
223 | static_assert_size!(Token, 123);
| -------------------------------- in this macro invocation
|
= note: expected type `[(); 123]`
found type `[(); 16]`
```
