llvm-project

8daaa26e - [Support] Support nested parallel TaskGroup via work-stealing (#189293)

[Support] Support nested parallel TaskGroup via work-stealing (#189293) Nested TaskGroups run serially to prevent deadlock, as documented by https://reviews.llvm.org/D61115 and refined by https://reviews.llvm.org/D148984 to use threadIndex. Enable nested parallelism by having worker threads actively execute tasks from the work queue while waiting (work-stealing), instead of just blocking. Root-level TaskGroups (main thread) keep the efficient blocking Latch::sync(), so there is no overhead for the common non-nested case. In lld, https://reviews.llvm.org/D131247 worked around the limitation by passing a single root TaskGroup into OutputSection::writeTo and spawning 4MB-chunked tasks into it. However, SyntheticSection::writeTo calls with internal parallelism (e.g. GdbIndexSection, MergeNoTailSection) still ran serially on worker threads. With this change, their internal parallelFor/parallelForEach calls parallelize automatically via helpSync work-stealing. The increased parallelism can reorder error messages from parallel phases (e.g. relocation processing during section writes), so one lld test is updated to use --threads=1 for deterministic output.