>             pushl   %ebp
quoted text
>             movl    %esp, %ebp
>             cmpl    __PLACEHOLDER__0_, 8(%ebp)
>             movl    , %eax
>             cmove   v, %eax        ; load (maybe)
>             movl    %eax, v        ; store (always)
>             popl    %ebp
>             ret

How is this even an optimization?  It looks SLOWER to me.  The 
conditional read wastes memory bandwidth sometimes, if the condition is 
true, and v isn't already in the cache.  The unconditional write wastes 
memory bandwidth ALL the time, and dirties/flushes caches, in addition 
to not being thread safe.

This SHOULD be using a conditional write instead of a conditional read 
and an unconditional write.


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