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##### 9.31.3.3 Constants

Several Sparc instructions take an immediate operand field for which mnemonic names exist. Two such examples are membar and prefetch. Another example are the set of V9 memory access instruction that allow specification of an address space identifier.

The membar instruction specifies a memory barrier that is the defined by the operand which is a bitmask. The supported mask mnemonics are:

- #Sync requests that all operations (including nonmemory reference operations) appearing prior to the `membar` must have been performed and the effects of any exceptions become visible before any instructions after the `membar` may be initiated. This corresponds to `membar` cmask field bit 2.
- #MemIssue requests that all memory reference operations appearing prior to the `membar` must have been performed before any memory operation after the `membar` may be initiated. This corresponds to `membar` cmask field bit 1.
- #Lookaside requests that a store appearing prior to the `membar` must complete before any load following the `membar` referencing the same address can be initiated. This corresponds to `membar` cmask field bit 0.
- #StoreStore defines that the effects of all stores appearing prior to the `membar` instruction must be visible to all processors before the effect of any stores following the `membar`. Equivalent to the deprecated `stbar` instruction. This corresponds to `membar` mmask field bit 3.
- #LoadStore defines all loads appearing prior to the `membar` instruction must have been performed before the effect of any stores following the `membar` is visible to any other processor. This corresponds to `membar` mmask field bit 2.
- #StoreLoad defines that the effects of all stores appearing prior to the `membar` instruction must be visible to all processors before loads following the `membar` may be performed. This corresponds to `membar` mmask field bit 1.
- #LoadLoad defines that all loads appearing prior to the `membar` instruction must have been performed before any loads following the `membar` may be performed. This corresponds to `membar` mmask field bit 0.

These values can be ored together, for example:

         membar #Sync
         membar #StoreLoad | #LoadLoad
         membar #StoreLoad | #StoreStore

The `prefetch` and `prefetcha` instructions take a prefetch function code. The following prefetch function code constant mnemonics are available:

- #n_reads requests a prefetch for several reads, and corresponds to a prefetch function code of 0.

  #one_read requests a prefetch for one read, and corresponds to a prefetch function code of 1.

  #n_writes requests a prefetch for several writes (and possibly reads), and corresponds to a prefetch function code of 2.

  #one_write requests a prefetch for one write, and corresponds to a prefetch function code of 3.

  #page requests a prefetch page, and corresponds to a prefetch function code of 4.

  #invalidate requests a prefetch invalidate, and corresponds to a prefetch function code of 16.

  #unified requests a prefetch to the nearest unified cache, and corresponds to a prefetch function code of 17.

  #n_reads_strong requests a strong prefetch for several reads, and corresponds to a prefetch function code of 20.

  #one_read_strong requests a strong prefetch for one read, and corresponds to a prefetch function code of 21.

  #n_writes_strong requests a strong prefetch for several writes, and corresponds to a prefetch function code of 22.

  #one_write_strong requests a strong prefetch for one write, and corresponds to a prefetch function code of 23.

  Onle one prefetch code may be specified. Here are some examples:

                prefetch  [%l0 + %l2], #one_read
                prefetch  [%g2 + 8], #n_writes
                prefetcha [%g1] 0x8, #unified
                prefetcha [%o0 + 0x10] %asi, #n_reads

  The actual behavior of a given prefetch function code is processor specific. If a processor does not implement a given prefetch function code, it will treat the prefetch instruction as a nop.

  For instructions that accept an immediate address space identifier, `as` provides many mnemonics corresponding to V9 defined as well as UltraSPARC and Niagara extended values. For example, #ASI_P and #ASI_BLK_INIT_QUAD_LDD_AIUS. See the V9 and processor specific manuals for details.