On Mon, Jun 6, 2016 at 12:14 PM, Sergey Fedorov <serge.f...@gmail.com> wrote: > On 06/06/16 18:58, Pranith Kumar wrote: >> On Mon, Jun 6, 2016 at 11:49 AM, Sergey Fedorov <serge.f...@gmail.com> wrote: >>> On 06/06/16 18:47, Pranith Kumar wrote: >>>> On Mon, Jun 6, 2016 at 11:44 AM, Sergey Fedorov <serge.f...@gmail.com> >>>> wrote: >>>>> On 03/06/16 21:27, Pranith Kumar wrote: >>>>>> On Thu, Jun 2, 2016 at 5:18 PM, Richard Henderson <r...@twiddle.net> >>>>>> wrote: >>>>>>> What if we have tcg_canonicalize_memop (or some such) split off the >>>>>>> barriers >>>>>>> into separate opcodes. E.g. >>>>>>> >>>>>>> MO_BAR_LD_B = 32 // prevent earlier loads from crossing current >>>>>>> op >>>>>>> MO_BAR_ST_B = 64 // prevent earlier stores from crossing current >>>>>>> op >>>>>>> MO_BAR_LD_A = 128 // prevent later loads from crossing current op >>>>>>> MO_BAR_ST_A = 256 // prevent later stores from crossing current op >>>>>>> MO_BAR_LDST_B = MO_BAR_LD_B | MO_BAR_ST_B >>>>>>> MO_BAR_LDST_A = MO_BAR_LD_A | MO_BAR_ST_A >>>>>>> MO_BAR_MASK = MO_BAR_LDST_B | MO_BAR_LDST_A >>>>>>> >>>>>>> // Match Sparc MEMBAR as the most flexible host. >>>>>>> TCG_BAR_LD_LD = 1 // #LoadLoad barrier >>>>>>> TCG_BAR_ST_LD = 2 // #StoreLoad barrier >>>>>>> TCG_BAR_LD_ST = 4 // #LoadStore barrier >>>>>>> TCG_BAR_ST_ST = 8 // #StoreStore barrier >>>>>>> TCG_BAR_SYNC = 64 // SEQ_CST barrier >>>>>> I really like this format. I would also like to add to the frontend: >>>>>> >>>>> Actually, the acquire barrier is a combined load-load + load-store >>>>> barrier; and the release barrier is a combo of load-store + store-store >>>>> barriers. >>>>> >>>> All the above are two-way barriers. Acquire/Release are one-way >>>> barriers. So we cannot combine the above to get acquire/release >>>> semantics without being conservative. >>> Do you mean *barriers* or *memory access* operations implying memory >>> ordering? >> I meant the latter. I know no arch which has acquire/release barriers. >> Sorry for the confusion. > > So I am. By the way, what's the difference between sequential consistent > *barrier* and a combination of all the other barriers?
If I read it correctly TCG_BAR_SYNC is equivalent to OR of all the other four barriers. I am not sure if we can just construct SYNC like this or if we need to define it explicitly though. -- Pranith