Re: memory barrier question

[Alan Cox]

> >    LOAD inode = next.dentry->inode
> >    if (inode != NULL)
> >    	LOAD inode->f_op
> > 
> > What is there the compiler can optimize?
> 
> Those two loads depend on each other, I don't think any implementation
> can re-order them. In fact, such data dependency is typically what is
> used to avoid having barriers in some cases. The second load cannot be
> issued until the value from the first one is returned.

Actually I've met several compilers which will optimise them but not gcc
and not in a Linux environment. Some compilers know how to optimise the
== NULL case for pointer dereferences providing their programming
environment has a couple of low pages mapped read only and reading 0.

Alan
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