gcc-4.5/gcc/config/i386/i386.md: ;; %%% bts, btr, btc, bt. ;; In general these instructions are *slow* when applied to memory, ;; since they enforce atomic operation. When applied to registers,
I haven't found documented confirmation that these instructions are atomic without a lock prefix, having checked Intel and AMD documentation and random web searching. They are mentioned as instructions that can be used with lock prefix. - Jay
