Query Parallelization Tracking Issue (original) (raw)

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Description

This issue is a sub-issue of #48547: it tracks the in-progress effort to parallelize rustc across queries. This work is being spearheaded by @Zoxc.

Goals

Allow rustc to execute queries in parallel with one another. Enable the use of rayon or other tools for intra-query parallelization as well. See this internals thread for more information.

Overview of the plan

Make all types in the compiler send and sync by landing @Zoxc's existing work
- The existing work largely replaces RefCell usage with Mutex
- In many cases, the interior mutability itself can be refactored away. The plan is do this as a second step.
Set up CI so this gets some testing (CI: Make sure that we can bootstrap with cfg(parallel_queries). #48607)
Implement a thread pool that is integrated with Cargo's jobserver (Add support for using a jobserver with Rayon #56946)
Build list of all sources of shared state in the compiler by auditing PR history Audit sources of shared state across rustc #63643
Audit each source of shared state, leading to either refactoring to reduce use of shared state, or persistent documentation covering invariants, atomicity, and lock orderings

Pending refactorings

ParseSess.included_mod_stack might be problematic
Ensure that the err_count() API is not used to discover if errors happen in parallel code (cc [parallel-queries] Refactor error message handling to better integrate with parallel queries #49737)
Find a way to order error messages deterministically so that if a query depends on another query, its error messages appear after the other query (cc [parallel-queries] Refactor error message handling to better integrate with parallel queries #49737)
Make mk_attr_id use a scoped thread local or make it part of ParseSess
See if GlobalCtxt.rcache, OnDiskCache.file_index_to_file and OnDiskCache.synthetic_expansion_infos are faster as thread-locals
Review usages of Session.lint_store and Session.buffered_lints
Fix EvaluationCache overwrites its entries #50507, as it may cause issues with parallel rustc
Find a way to deal with marking attributes as used
Ensure Rayon executes all remaining work when we panic inside the thread pool

Completed refactorings

Remove HIR inlining (Remove HIR inlining (now that we don't need it for constant evaluation anymore) #49690)
Make GlobalCtxt implement Sync
Use scoped thread locals instead of globals, WIP: Less globals #46193
Misc fixes required to use a rayon thread pool, WIP: Parallelize passes using rayon #46564
Ensure metadata loaded by LlvmMetadataLoader does not get freed on the wrong thread
CurrentDepGraph.task_stack has to be made a QueryJob field. (implemented in Make incremental compilation thread-safe #49732)
Check that optimization fuel is not used with parallel queries
Review libproc_macro for issues, Find out which types should be Send, Sync. Deal with Deref impls for Symbol. (Decouple proc_macro from the rest of the compiler. #49219)
Run CI with cfg(parallel_queries)
Refactor away CStore::next_crate_num
Make FileMap.lines, FileMap.multibyte_chars, and FileMap.non_narrow_chars immutable (implemented in Make FileMap::{lines, multibyte_chars, non_narrow_chars} non-mutable. #50997)
When executing queries, instead of keeping around a lock to the query map, create a job object immediately instead (Move query code outside macros and store query jobs separately from query results #50102)
Ensure all diagnostics are emitted before returning from DepGraph.try_mark_green
Refactor DepGraphData.previous_work_products so it becomes immutable ([parallel-queries] DepGraph::previous_work_products could be made immutable to avoid shared mutable state #50501) (implemented in Make DepGraph::previous_work_products immutable #50524)
Remove DepGraphData.work_products by threaded the value through save_trans_partition() -> copy_module_artifacts_into_incr_comp_cache() -> OngoingCrateTranslation::join() ([parallel-queries] Refactor away DepGraph::work_products to avoid shared mutable state #50500) (implemented in Encountered errors [...] resolving bounds after type-checking [rustc 1.28.0-nightly (952f344cd 2018-05-18)] #50885)
The TransitiveRelation doesn't really need to use a RefCell. In the future, it won't even be shared, but regardless the caching scheme could be reworked to avoid RefCell (implemented in get rid of RefCell in TransitiveRelation #99702).
Refactor GlobalCtxt::layout_depth so it does not need global mutable state ([parallel-queries] Refactor layout-depth tracking so it does not need mutable state in the GlobalCtxt #49735) (implemented in add depth_limit in QueryVTable to avoid entering a new tcx in layout_of #100748)