https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59448
--- Comment #17 from torvald at gcc dot gnu.org --- (In reply to Andrew Macleod from comment #15) > So have we concluded that we should promote memory_order_consume to > memory_order_acquire for now? I also think that this is the best way forward. I believe everyone in ISO C++ SG1 agreed that this is basically a defect in the standard. What I haven't thought through is how to deal with with carries_dependency (7.6.4 in C++11): For GCC code generated after we promote consume to acquire, it can safely be ignored; but should GCC code be linked to code generated by another compiler that does not promote and expects the code to preserve dependencies, this won't work. I am not aware of any shipping compiler that would actually try to preserve dependencies, and nobody else mentioned any during the discussion of this topic in ISO C++ SG1. Thus, we could assume that there are no such other compilers, and make it part of the ABI (assumptions) that consume is promoted to acquire in a correct compiler. Alternatively, we could try to be conservative and add an acquire barrier before the function body if any parameter of the function has carries_dependency; and, likewise, add an acquire barrier after every call to a function which has carries_dependency. I don't have more input from the ISO C side, but I would guess that the situation there is similar. Thoughts?
