Re: [ANNOUNCE] mdb: Merkey's Linux Kernel Debugger 2.6.27-rc4 released

[Avi Kivity]

Peter Zijlstra wrote:
> Not sure - I think all barrier clobber the full register and memory set.
> So if you access a variable after a barrier it will have to issue a
> load.
>   

IIRC a barrier only clobbers memory.  gcc must reload a variable from 
memory unless it can prove the variable's address has not escaped anywhere.

So:

void f()
{
   int v;

   v = g();
   barrier();
   do_domething_with(v);
}

Need not reload v from memory (indeed, v can be in a register for its 
entire lifetime), but

void f()
{
   int v;

   v = g();
   h(&v);
   barrier();
   do_domething_with(v);
}

Will force v into memory, and reload it after the barrier.

--
error compiling committee.c: too many arguments to function

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