Why does 32-bit ARM use __ldrexd instead of __iso_volatile_load64?
Note that ldrexd is generally useful with strexd, however strexd is not even exposed as intrinsic, so __ldrexd intrinsic is probably exposed specifically for this usage.
(This does not block something, but this is the only two lines of <atomic> I don't understand fully)
Occurrences:
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_NODISCARD _Ty load() const noexcept { // load with sequential consistency
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const auto _Mem = _Atomic_address_as<long long>(_Storage);
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long long _As_bytes;
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#ifdef _M_ARM
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_As_bytes = __ldrexd(_Mem);
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_Memory_barrier();
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#else
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_As_bytes = __iso_volatile_load64(_Mem);
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_Compiler_or_memory_barrier();
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#endif
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return reinterpret_cast<_Ty&>(_As_bytes);
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}
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_NODISCARD _Ty load(const memory_order _Order) const noexcept { // load with given memory order
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const auto _Mem = _Atomic_address_as<long long>(_Storage);
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#ifdef _M_ARM
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long long _As_bytes = __ldrexd(_Mem);
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#else
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long long _As_bytes = __iso_volatile_load64(_Mem);
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#endif
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_Load_barrier(_Order);
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return reinterpret_cast<_Ty&>(_As_bytes);
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}
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