[boost] Re: shared_ptr on ppc?

6 Apr 2005

      Peter Dimov wrote:
...
Alexander Terekhov wrote:
...
and
asm long atomic_decrement_strong( register long * pw ) {
[... loop -> loop1+loop2 ...]
...
but it's either suboptimal (more than one sync) or incorrect (missing sync),
I think. It needs a state machine.
And how is this

 asm long atomic_decrement_strong( register long * pw ) {

      <load-reserved>
      <add -1>
      <branch if zero to acquire>
      {lw}sync

    loop1:

      <store-conditional>
      <branch if !failed to done>

    loop2:

      <load-reserved>
      <add -1>
      <branch if !zero to loop1>

    acquire:

      <store-conditional>
      <branch if failed to loop2>
      isync

    done:

      <...>
  }

incorrrect or suboptimal?
...
loop0:
lwarx
add -1
beq acquire-without-sync
sync
loop1:
stwcx.
beq+ done
loop2:
lwarx
add -1
bne loop1
acquire-with-sync:
stwcx.
bne- loop2
isync
blr
acquire-without-sync:
stwcx.
bne- loop0
isync
done:
blr
I must be missing something, but it looks to me that you have 
way too much branching and isync-ing.

regards,
alexander.