On 07/26/2017 02:02 PM, Alexander Monakov wrote: > On Wed, 26 Jul 2017, Alexander Monakov wrote: > >> On Wed, 26 Jul 2017, Jeff Law wrote: >>> I'm not sure what you mean by extraneous compiler barriers -- isn't the >>> worst case scenario here that the target emits them as well? So there >>> would be an extraneous one in that case, but that ought to be a "don't >>> care". >> >> Yes, exactly this. > > I've just realized that we can detect if the backend produced empty RTL > sequence by looking at get_last_insn () before/after gen_mem_thread_fence. > This way we can emit a compiler barrier iff the backend didn't emit a > machine barrier. We could. But I suspect just emitting the barriers in the generic code is the way to go. If we have a redundant barrier, the compile time cost is minimal and I don't think the additional code to avoid creating the exxtra barrier is worth it.
jeff
