On Wed, 2011-08-17 at 11:39 -0400, Andrew MacLeod wrote: > Turns out, C++ will allow you to specify the memory model as a variable > of type enum memory_order... WTF? I would expect that to be pretty > uncommon, and in order to get that right, we'd need a switch statement > and call the appropriate __sync_mem* routine with the appropriate > constant parameter. > > That would be quite ugly, and you get what you deserve if you do that. > I changed the builtins so that if you dont specify a compile time > constant in the memory model parameter, it will simply default to > __SYNC_MEM_SEQ_CST, which will always be safe. That is standard > compliant (verified), and if anyone is really unhappy about it, then the > c++ headers can be really uglified by adding a bunch of switch > statements to handle this twisted case.
IMHO this behavior should be documented so that users will be aware of it, and it would be best if this would raise a warning. Note that I also cannot see any reason why a programmer might want to make barriers runtime-configurable, but silently adding overhead (perhaps the parameter was supposed to be a constant, but wasn't?) can lead to more confusion than necessary. Torvald
