[Support] Fix a race initializing a static local in MSVC
static local initialization isn't thread safe with MSVC and a race was reported in PR23817. We can't use std::atomic because it's not trivially constructible, so instead do some lame volatile global integer manipulation. llvm-svn: 239566
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@ -78,7 +78,15 @@ MemoryBlock Memory::allocateMappedMemory(size_t NumBytes,
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// While we'd be happy to allocate single pages, the Windows allocation
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// While we'd be happy to allocate single pages, the Windows allocation
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// granularity may be larger than a single page (in practice, it is 64K)
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// granularity may be larger than a single page (in practice, it is 64K)
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// so mapping less than that will create an unreachable fragment of memory.
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// so mapping less than that will create an unreachable fragment of memory.
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static const size_t Granularity = getAllocationGranularity();
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// Avoid using one-time initialization of static locals here, since they
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// aren't thread safe with MSVC.
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static volatile size_t GranularityCached;
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size_t Granularity = GranularityCached;
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if (Granularity == 0) {
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Granularity = getAllocationGranularity();
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GranularityCached = Granularity;
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}
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const size_t NumBlocks = (NumBytes+Granularity-1)/Granularity;
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const size_t NumBlocks = (NumBytes+Granularity-1)/Granularity;
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uintptr_t Start = NearBlock ? reinterpret_cast<uintptr_t>(NearBlock->base()) +
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uintptr_t Start = NearBlock ? reinterpret_cast<uintptr_t>(NearBlock->base()) +
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