Mmap the incremental data instead of reading it.
Instead of reading the full incremental state using `fs::read_file`, we memmap it using a private read-only file-backed map.
This allows the system to reclaim any memory we are not using, while ensuring we are not polluted by
outside modifications to the file.
Suggested in https://github.com/rust-lang/rust/pull/83036#issuecomment-800458082 by `@bjorn3`
Instead of updating global state to mark attributes as used,
we now explicitly emit a warning when an attribute is used in
an unsupported position. As a side effect, we are to emit more
detailed warning messages (instead of just a generic "unused" message).
`Session.check_name` is removed, since its only purpose was to mark
the attribute as used. All of the callers are modified to use
`Attribute.has_name`
Additionally, `AttributeType::AssumedUsed` is removed - an 'assumed
used' attribute is implemented by simply not performing any checks
in `CheckAttrVisitor` for a particular attribute.
We no longer emit unused attribute warnings for the `#[rustc_dummy]`
attribute - it's an internal attribute used for tests, so it doesn't
mark sense to treat it as 'unused'.
With this commit, a large source of global untracked state is removed.
Avoid creating anonymous nodes with zero or one dependency.
Anonymous nodes are only useful to encode dependencies, and cannot be replayed from one compilation session to another.
As such, anonymous nodes without dependency are always green.
Anonymous nodes with only one dependency are equivalent to this dependency.
cc #45408
cc `@michaelwoerister`
Don't panic when failing to initialize incremental directory.
This removes a panic when rustc fails to initialize the incremental directory. This can commonly happen on various filesystems that don't support locking (often various network filesystems). Panics can be confusing and scary, and there are already plenty of issues reporting this.
This has been panicking since 1.22 due to I think #44502 which was a major rework of how things work. Previously, things were simpler and the [`load_dep_graph`](https://github.com/rust-lang/rust/blob/1.21.0/src/librustc_incremental/persist/load.rs#L43-L65) function would emit an error and then continue on without panicking. With 1.22, [`load_dep_graph`](https://github.com/rust-lang/rust/blob/1.22.0/src/librustc_incremental/persist/load.rs#L44) was changed so that it assumes it can load the data without errors. Today, the problem is that it calls [`prepare_session_directory`](fbf1b1a719/compiler/rustc_interface/src/passes.rs (L175-L179)) and then immediately calls `garbage_collect_session_directories` which will panic since the session is `IncrCompSession::NotInitialized`.
The solution here is to have `prepare_session_directory` return an error that must be handled so that compilation stops if it fails.
Some other options:
* Ignore directory lock failures.
* Print a warning on directory lock failure, but otherwise continue with incremental enabled.
* Print a warning on directory lock failure, and disable incremental.
* Provide a different locking mechanism.
Cargo ignores lock errors if locking is not supported, so that would be a precedent for the first option. These options would require quite a bit more changes, but I'm happy to entertain any of them, as I think they all have valid justifications.
There is more discussion on the many issues where this is reported: #49773, #59224, #66513, #76251. I'm not sure if this can be considered closing any of those, though, since I think there is some value in discussing if there is a way to avoid the error altogether. But I think it would make sense to at least close all but one to consolidate them.
This is necessary for options that should invalidate the incremental
hash but *not* affect the crate hash (e.g. --remap-path-prefix).
This doesn't add `for_crate_hash` to the trait directly because it's not
relevant for *types*, only for *options*, which are fields on a larger
struct. Instead, it adds a new `SUBSTRUCT` directive for options, which
does take a `for_crate_hash` parameter.
- Use TRACKED_NO_CRATE_HASH for --remap-path-prefix
- Add test that `remap_path_prefix` is tracked
- Reduce duplication in the test suite to avoid future churn
Found with https://github.com/est31/warnalyzer.
Dubious changes:
- Is anyone else using rustc_apfloat? I feel weird completely deleting
x87 support.
- Maybe some of the dead code in rustc_data_structures, in case someone
wants to use it in the future?
- Don't change rustc_serialize
I plan to scrap most of the json module in the near future (see
https://github.com/rust-lang/compiler-team/issues/418) and fixing the
tests needed more work than I expected.
TODO: check if any of the comments on the deleted code should be kept.
StructField -> FieldDef ("field definition")
Field -> ExprField ("expression field", not "field expression")
FieldPat -> PatField ("pattern field", not "field pattern")
Also rename visiting and other methods working on them.
Serialize dependency graph directly from DepGraph
Reduce memory usage by serializing dep graph directly from `DepGraph`,
rather than copying it into `SerializedDepGraph` and serializing that.
Remove much of the special-case handling around crate metadata
dependency tracking by replacing `DepKind::CrateMetadata` and the
pre-allocation of corresponding `DepNodes` with on-demand invocation
of the `crate_hash` query.
Reduce a large memory spike that happens during serialization by writing
the incr comp structures to file by way of a fixed-size buffer, rather
than an unbounded vector.
Effort was made to keep the instruction count close to that of the
previous implementation. However, buffered writing to a file inherently
has more overhead than writing to a vector, because each write may
result in a handleable error. To reduce this overhead, arrangements are
made so that each LEB128-encoded integer can be written to the buffer
with only one capacity and error check. Higher-level optimizations in
which entire composite structures can be written with one capacity and
error check are possible, but would require much more work.
The performance is mostly on par with the previous implementation, with
small to moderate instruction count regressions. The memory reduction is
significant, however, so it seems like a worth-while trade-off.
This also eliminates a use of a `Path` convenience function, in support
of #80741, refactoring `std::path` to focus on pure data structures and
algorithms.
