Alexandre Ganea 4fcb25583c Re-land [Support] On Windows, take the affinity mask into account ...

The number of hardware threads available to a ThreadPool can be limited if setting an affinity mask.
For example:

    > start /B /AFFINITY 0xF lld-link.exe ...

Would let LLD only use 4 hyper-threads.

Previously, there was an outstanding issue on Windows Server 2019 on dual-CPU machines, which was preventing from using both CPU sockets. In normal conditions, when no affinity mask was set, ProcessorGroup::AllThreads was different from ProcessorGroup::UsableThreads. The previous code in llvm/lib/Support/Windows/Threading.inc L201 was improperly assuming those two values to be equal, and consequently was limiting the execution to only one CPU socket.

Differential Revision: https://reviews.llvm.org/D92419

2021-01-14 17:03:22 -05:00

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