Better support for mingw-w64 and GCC-compatible compilers #1212
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The _InterlockedCompareExchange128 intrinsic is missing in mingw-w64, so instead use the __sync_bool_compare_and_swap builtin in GCC-compatible compilers.
The constants _ARM_BARRIER_ISH and _ARM64_BARRIER_ISH are missing in mingw-w64. Use inline assembly to insert the instruction instead.
These intrinsics are missing in mingw-w64 and GCC-compatible compilers. The __iso_volatile_load intrinsics is intended to tell MSVC to use the ISO standard C++ non-atomic volatile load, instead of the MSVC extension which adds other guarantees. For GCC-compatible compilers, the ISO standard volatile load is already the default, so there is no need to use these intrinsics.
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I'm not familiar with the GCC intrinsics. Does someone else want to take a stab at reviewing this? @DefaultRyan @oldnewthing @BenJKuhn |
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I can't speak to the completeness of these changes wrt to making mingw work, but the changes themselves seem correct based on a close reading. The use of __iso_volatile_load64 for the MSVC implementation is to avoid a perf hit due to MS-specific behavior described here: https://learn.microsoft.com/en-us/cpp/build/reference/volatile-volatile-keyword-interpretation?view=msvc-170. It should be unnecessary in MinGW, though if it adds the same memory barriers MS does for volatile reads, it may incur a perf penalty. I couldn't find a quick answer to that. It'll be correct and usable though either way.
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There are still some intrinsics and defines missing in mingw-w64 (see mstorsjo/llvm-mingw#307) which can all be replaced with other compatible constructions. Verified by compiling a sample program locally for i686, x86_64 and aarch64 (aarch64 build is untested because I don't have a compatible system).
(CI checks for mingw-w64 will be coming soon™)
CC: @mstorsjo @cristianadam