Eric Fiselier 8baf83839e Fix PR27658 - Make ~mutex trivial when possible. ... Currently std::mutex has a constexpr constructor, but a non-trivial destruction. The constexpr constructor is required to ensure the construction of a mutex with static storage duration happens at compile time, during constant initialization, and not during dynamic initialization. This means that static mutex's are always initialized and can be used safely during dynamic initialization without the "static initialization order fiasco". A trivial destructor is important for similar reasons. If a mutex is used during dynamic initialization it might also be used during program termination. If a static mutex has a non-trivial destructor it will be invoked during termination. This can introduce the "static deinitialization order fiasco". Additionally, function-local statics emit a guard variable around non-trivially destructible types. This results in horrible codegen and adds a runtime cost to every call to that function. non-local static's also result in slightly worse codegen but it's not as big of a problem. Example codegen can be found here: https://goo.gl/3CSzbM Note: This optimization is not safe with every pthread implementation. Some implementations allocate on the first call to pthread_mutex_lock and free the allocation in pthread_mutex_destroy. Also, changing the triviality of the destructor is not an ABI break. At least to the best of my knowledge :-) llvm-svn: 365273		2019-07-07 01:20:54 +00:00
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include	Fix PR27658 - Make ~mutex trivial when possible.	2019-07-07 01:20:54 +00:00
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test	Fix PR27658 - Make ~mutex trivial when possible.	2019-07-07 01:20:54 +00:00
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