86d2e48c22
memory barriers should also ensure that the compiler doesn't reorder paths where they are used. GCC, however, does that aggressively, even in presence of volatile operands. The most reliable way GCC offers for avoid instructions reordering is clobbering "memory" even if that is theoretically an heavy-weight operation, flushing the content of all the registers and forcing reload of them (We could rely, however, on gcc DTRT by just understanding the purpose as this is a well-known pattern for many modern operating-systems). Not all our memory barriers, right now, clobber memory for GCC-like compilers. The most notable cases are IA32 and amd64 where the memory barrier are treacted the same as normal atomic instructions. Fix this by offering the possibility to implement atomic instructions with memory barriers separately from the normal version and implement the GCC-like specific one using memory clobbering. Thanks to Chris Lattner (@apple) for his discussion on llvm specifics. Reported by: jhb Reviewed by: jhb Tested by: rdivacky, Giovanni Trematerra <giovanni dot trematerra at gmail dot com> |
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